Modern Tendencies in Organic and Bioorganic Chemistry - Today and Tomorrow

MODERN TENDENCIES IN ORGANIC AND BIOORGANIC CHEMISTRY: TODAY AND TOMORROW MODERN TENDENCIES IN ORGANIC AND BIOORGANIC...

Author: Abdulakh K. Mikitaev | Mukhed Kh Ligidov | Gennady E. Zaikov

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MODERN TENDENCIES IN ORGANIC AND BIOORGANIC CHEMISTRY: TODAY AND TOMORROW

MODERN TENDENCIES IN ORGANIC AND BIOORGANIC CHEMISTRY: TODAY AND TOMORROW

ABDULAKH MIKITAEV MUKHED KH. LIGIDOV AND

GENNADY E. ZAIKOV EDITORS

Nova Science Publishers, Inc. New York

Copyright © 2008 by Nova Science Publishers, Inc.

All rights reserved. No part of this book may be reproduced, stored in a retrieval system or transmitted in any form or by any means: electronic, electrostatic, magnetic, tape, mechanical photocopying, recording or otherwise without the written permission of the Publisher. For permission to use material from this book please contact us: Telephone 631-231-7269; Fax 631-231-8175 Web Site: http://www.novapublishers.com NOTICE TO THE READER The Publisher has taken reasonable care in the preparation of this book, but makes no expressed or implied warranty of any kind and assumes no responsibility for any errors or omissions. No liability is assumed for incidental or consequential damages in connection with or arising out of information contained in this book. The Publisher shall not be liable for any special, consequential, or exemplary damages resulting, in whole or in part, from the readers’ use of, or reliance upon, this material. Any parts of this book based on government reports are so indicated and copyright is claimed for those parts to the extent applicable to compilations of such works. Independent verification should be sought for any data, advice or recommendations contained in this book. In addition, no responsibility is assumed by the publisher for any injury and/or damage to persons or property arising from any methods, products, instructions, ideas or otherwise contained in this publication. This publication is designed to provide accurate and authoritative information with regard to the subject matter covered herein. It is sold with the clear understanding that the Publisher is not engaged in rendering legal or any other professional services. If legal or any other expert assistance is required, the services of a competent person should be sought. FROM A DECLARATION OF PARTICIPANTS JOINTLY ADOPTED BY A COMMITTEE OF THE AMERICAN BAR ASSOCIATION AND A COMMITTEE OF PUBLISHERS. LIBRARY OF CONGRESS CATALOGING-IN-PUBLICATION DATA Modern tendencies in organic and bioorganic chemistry : today and tomorrow / Abdulakh Mikitaev, Mukhed Kh. Ligidov, Gennady E. Zaikov (editor). p. cm. ISBN 978-1-60692-454-9 1. Chemistry, Organic. 2. Bioorganic chemistry. I. Mikitaev, Abdulakh K. II. Ligidov, Mikhail Kh. III. Zaikov, Gennadii Efremovich. QD251.3.M636 2008 547--dc22 2007051490

Published by Nova Science Publishers, Inc.

New York

CONTENTS Preface Chapter 1

Chapter 2

Chapter 3

Chapter 4

ix Thermal and Thermal-oxidative Degradation of Polyethylene Nanocomposite Prepared by Intercalation Polymerization S. M. Lomakin, L. A. Novokshonova, P. N. Brevnov, A. N. Shchegolikhin and G. E. Zaikov Modification of Catalytic Activity of Complexes of Acetylacetonates Fe(II,III) with Quaternary Ammonium Salts in the Ethylbenzene Oxidation with Molecular O2 in the Presence of Small Amounts of H2O L. I. Matienko and L. A. Mosolova

1

33

Modeling the Kinetics of Moisture Adsorption by Wood during the Drying Process A. Farjad, S. H.Rahrovan and A. K. Haghi

51

New Trends, Achievements and Developments on the Effects of Beam Radiation on Different Materials K. Mohammadi and A. K. Haghi

65

Chapter 5

Structural Behavior of Composite Materials О. А. Legonkova, J. L. Gordeeva and E. S. Obolonkova

Chapter 6

Comparative Evaluation of Antioxidant Properties of Spice-aromatic Plant Essential oils A. L. Samusenko

103

The Polymeric Compositions Stabilized Nanodimensions Phosphor Organically by Compounds A. Kh. Shaov, A. N. Teuvazhukova and A. A. Akezheva

113

Composite Materials for Ortopedical Stomatology on the Basis of Utilized Glassy Organically A. Kh. Shaov, E. M. Kushhov and K. A. Sohrokova

117

Chapter 7

Chapter 8

89

vi Chapter 9

Chapter 10

Chapter 11

Chapter 12

Chapter 13

Contents A Preliminary Study on Antimicrobial Edible Films from Pectin and Other Food Hydrocolloids by Extrusion Method LinShu Liu, Tony Jin, Cheng-Kung Liu, Kevin Hicks, Amar K. Mohanty, Rahul Bhardwaj and Manjusri Misra

121

Controlled Release of the Antiseptic from Poly(3-hydroxybutyrate) Films. Combination of Diffusion and Zero-order Kinetics R. Yu. Kosenko, Yu. N. Pankova, A. L. Iordanskii and G. E. Zaikov

139

Photo Composites on the Base of Polymer-monomer Combined System, Modified by Oligomers N. V. Sidorenko, I. M. Gres, N. G. Bulycheva, M. A. Vaniev and I. A. Novakov Stabilization of Cell Membranes by Hybrid Antioxidants in Therapy of Neurodegenerative Diseases L. D. Fatkullina, O. M. Vekshina, E. B. Burlakova, A. N. Goloshchapov and Yu. A. Kim Wear Resistant Composite Polymeric Materials Based on Polyurethanes and Polyisocyanurates L. V. Luchkina, A. A. Askadsky and V. V. Kazantseva

Chapter 14

Photodestruction of Chlorophyll in Non-biological Systems A. V. Lobanov, O. V. Nevrova, Yu. A. Vedeneeva, G. V. Golovina and G. G. Komissarov

Chapter 15

Some Microkinetic Particularities of Deep Hydrolysis Pet Calcium Gidrokside in Bead Mill A. S. Harichkin and A. M. Ivanov

147

151

161 165

171

Chapter 16

Transport Phenomena within Porous Media Sh. Rahrovan and A. K. Haghi

175

Chapter 17

Block-copolysulfonarilates of Polycondensational Type E. B. Barokova, A. M. Kharaev, R. Ch. Bazheva and T. R. Umerova

211

Chapter 18

Liguid-crystalline Polyesthers on the Basis of Terephtaloyl-di(n-oxibenzoat) and Aromatic Polyethers L. A. Asueva, M. A. Nasurova, G. B. Shustov, A. M. Kharaev, A. K. Mikitaev

Chapter 19

Fireproof Aromatic Block Copolymer Resin on the Basis of 1,1- Dichlor-2,2 DI(N-oxyphenyl)ethylene A. M. Kharaev, R. C. Bazheva, E. B. Barokova, O. L. Istepanova, R. A. Kharaeva and A. A.Chaika

215

219

Contents Chapter 20

Chapter 21

Chapter 22

Chapter 23

Chapter 24

Chapter 25

Chapter 26

Chapter 27

Chapter 28

Chapter 29

Increase in Selectivity of Molecular Complex Formation of Metalloporphyrins due to π-π-interactions Nataliya A. Pavlycheva, Nataliya Sh. Lebedeva, Anatoliy I. Vyugin and Elena V. Parfenyuk

vii

223

Influence of Individual Components of Essential Oils and Flavorings on Citral Oxidation А. L. Samusenko

231

Some Aspects of Dynamic Water Vapour and Heat Transport through Fabrics A. K. Haghi

239

A Novel Approach for Measurement of NanoFiber Diameter of Electrospun Webs M. Ziabari, V. Mottaghitalab and A. K. Haghi

271

Lasers Application Boundaries to Stimulate Photochemical Processes R. H. Chaltykian and N. M. Beylerian

295

Quantum-chemical Analysis of the Mechanism of Nucleophilic Substitution of Bromine in Methyl(benzyl)bromide by s-, o-anions Generated from 2-thiouracil A. V. Babkin, A. I. Rakhimov, E. S. Titova, R. G. Fedunov, R. A. Reshetnikov, V. S. Belousova and G. E. Zaikov

311

Conformational Behavior of Propagating Chains of Polyacrylate- and Polymethacrylate Guanidines in Water Solutions N. A. Sivov, A. I. Martynenko, Yu. A. Malkanduev, M. H. Baidaeva, A. A. Zhansitov, O. A. Taov and A. I. Sarbasheva Biocide and Toxicological Properties of Synthesized Guanidine Containing Polymer and their Structure N. A. Sivov, Yu. A. Malkanduev, S. Yu. Khashirova, M. H. Baidaeva, A. I. Sarbasheva, A. A. Zhansitov and O. A. Taov Co-polymerization of Diallyldimethylammonium Chloride and Diallylguanidine Acetates on High Conversion for Creation of New Biocide Materials N. A. Sivov, Yu. A. Malkanduev, A. I. Sarbasheva, M. H. Baidaeva and S. Yu. Khashirova The Approach to Calculation of Different Co-polymers Composition by NMR1H Spectroscopy Method N. A. Sivov, M. Yu. Zaremsky, A. N. Sivov, E. V. Chernikova, D. N. Sivov, A. A. Zhansitov and O. A. Taov

325

335

341

345

viii Chapter 30

Chapter 31

Chapter 32

Chapter 33

Chapter 34

Chapter 35

Chapter 36

Index

Contents Structure Peculiarities of Guanidine Containing Monomers on NMR Spectroscopy Data N. A. Sivov, M. P. Filatova, A. N. Sivov, A. I. Rebrov, D. N. Sivov and E. B. Pomakhina Peculiarities of Radical Polymerization Reactions of Acrylate- and Methacrylate Guanidines N. A. Sivov, A. I. Martynenko, Yu. A. Malkanduev, E. Yu. Kabanova, N. I. Popova, A. A. Zhansitov, O. A. Taov and S. Yu. Khashirova The Strategy of Ionizing Monomers Synthesis and Investigation of their Radical Polymerization for Preparation of New Polyelectrolytes with Useful Properties N. A. Sivov Effect of Vibration on Structure and Properties of Polymeric Membranes V. N. Fomin, A. P. Bobylev, E. B. Malyukova, V. V. Smolyaninov, I. A. Arutyunov and N. A. Bulychev

349

353

361

367

One-stage Synthesis of Polymer Flocculant on the Acrylonitrile Basis N. V. Kozhevnikov, M. D. Goldfein and N. I. Kozhevnikova

379

Ultrasonic Treatment Assisted Surface Modification of Inorganic and Organic Pigments in Aqueous Dispersions N. A. Bulychev, E. V. Kisterev, I. A. Arutunov, and V. P. Zubov

385

Investigation of Antioxidant Activity of Essential Oils from Lemon, Pink Grapefruit, Coriander, Clove and its Mixtures by Capillary Gas Chromatography A. L. Samusenko

397 407

PREFACE “Heroes are born after their death” Sigmund Freid Austria We hope that scientific popularity of those who has taken part in a preparation of the given compilation book, will come earlier, than it declared Sigmund Freid (see an epigraph). The present collection of articles is made of reports which have been reported on four international conferences: •

• • •

The first All-Russia Scientific and Technical Conference “Nanostructures in polymers and polymeric nanocomposites” (the Kabardino-Balkarian State University, Nalchik, Russia, June, 2 - 5 2007); The Thirds All-Russia Scientific conference “New polymeric composite materials” (the Kabardino-Balkarian State University, June, 6 - 9 2007). XIIIth International Conference for Renewable Resources and Plant Biotechnology (Institute of Natural Fibres, Poznan, Poland, June, 18 – 19 2007); IXth International Conference on Frontiers of Polymers and Advanced Materials (Cracow University of Technology, Cracow, Poland, July, 8 – 12 2007).

This volume is including information about thermal and thermooxidative degradation of polyolefine nanocomposites, modeling of catalytic complexes in the oxidation reactions, modeling the kinetics of moisture adsorption by natural and synthetic polymers, new trends, achievements and developments on the effects of beam radiation, structural behaviour of composite materials, comparative evaluation of antioxidants properties, synthesis, properties and application of polymeric composites and nanocomposites, photodegradation and light stabilization of polymers, wear resistant composite polymeric materials, some macrokinetic phenomena, transport phenomena in polymer matrix, liquid crystals, flammability of polymeric materials and new flame retardants. We expect that this information will be useful for students, scientists and engineers who are working in the field of organic and bioorganic chemistry (including monomers, oligomers, polymers, composites and filled polymers as well as in agriculture and biotechnology).

In: Modern Tendencies in Organic and Bioorganic Chemistry ISBN: 978-1-60456-295-8 Editors: A. Mikitaev, M. K. Ligidov, pp. 1-32 © 2008 Nova Science Publishers, Inc.

Chapter 1

THERMAL AND THERMAL-OXIDATIVE DEGRADATION OF POLYETHYLENE NANOCOMPOSITE PREPARED BY INTERCALATION POLYMERIZATION S. M. Lomakin1, L. A. Novokshonova2, P. N. Brevnov2, A. N. Shchegolikhin1 and G. E. Zaikov1 1

N.M. Emanuel Institute of Biochemical Physics of Russian Academy of Sciences, 119991 Kosygin 4, Moscow, Russia, 2 N.N. Semenov Institute of Chemical Physics of Russian Academy of Sciences, 119991 Kosygin 4, Moscow, Russia

ABSTRACT A comparative study of thermal and thermal-oxidative degradation processes for polyethylene/organically modified montmorillonite (PE-MMT) nanocomposites, prepared by the ethylene intercalative polymerization in situ with or without subsequent addition of an antioxidant, is reported. The results of TGA and time/temperature dependent FTIR spectroscopy experiments have provided evidence for an accelerated formation and decomposition of hydroperoxides during the thermal oxidative degradation tests of PE-MMT nanocomposites in the range of 170-200oC as compared to the unfilled PE, thus indicating to a catalytic action of MMT. It has been shown that effective formation of intermolecular chemical cross-links in the PE-MMT nanocomposite has ensued above 200oC as the result of recombination reactions involving the radical products of hydroperoxides decomposition. Apparently, this process is induced by the oxygen deficiency in PE-MMT nanocomposite due to its lowered oxygen permeability. It is shown that the intermolecular cross-linking and dehydrogenation reactions followed by the shear carbonization lead to appreciable increase of thermal-oxidative stability of PE nanocomposite as compared to that of pristine PE. Notably, the TGA traces for the antioxidant-stabilized PE-MMT nanocomposites recorded in air were quite similar to those obtainable for the non-stabilized PE-MMT nanocomposites in argon. The results of treatment of the experimentally acquired TGA data in frames of an advanced model kinetic analysis are reported and discussed.

2

S. M. Lomakin, L. A. Novokshonova, P. N. Brevnov et al.

Keywords: Catalysis; intercalation polymerization; kinetics; layered clay; nanocomposite; oxidation; polyethylene; thermal degradation

1. INTRODUCTION Polyethylene (PE), being the most commercially important thermoplastic commodity, is heavily used for consumer products in many applications, but in a number of cases general applicability of PE turns out to be undermined by its relatively low thermal stability and flame resistance. The concept of compounding polymer matrices with nanoscale fillers (in particular, clays or layered silicates) has already been proved to be an effective method of preparing nanocomposites with excellent physicochemical properties [1 – 11]. It is believed that, in the course of high temperature pyrolysis and/or combustion, clay nanoparticles are capable of promoting formation of protective clay-reinforced carbonaceous char which is responsible for the reduced mass loss rates, and hence the lower flammability. Accordingly, considerable attention has been paid also to polyolefin/layered silicate nanocomposites. Reportedly, the latter have exhibited improved mechanical properties, gas impermeability, thermal stability, and flame retardancy as compared with corresponding pristine polymers [4,5,9,10]. This study deals with polyethylene/layered silicate nanocomposites that can be prepared by intercalative polymerization route. In accordance with the latter [12], the polymer chains growing within the interlayer spacing of montmorillonite (MMT) should be able to exfoliate the original MMT particles down to the nanoscale inorganic monolayers. Here, an experimental study of the universal intercalative approach, involving in the particular case (1) intercalation of a metallorganic catalyst system into the interlayer spacing of organically modified MMT and (2) subsequent polymerization of ethylene on thus intercalated catalyst, will be reported as well as the properties of the correspondingly produced PE/MMT nanocomposites will be discussed. To clarify the mechanisms of the clay-reinforced carbonaceous char formation, which may be responsible for the reduced mass loss rates, and hence the lower flammability of the polymer matrices, a number of thermo-physical characteristics of the PE/MMT nanocomposites have been measured in comparison with those of the pristine PE (which, by itself is not a char former) in both inert and oxidizing atmospheres. The evolution of the thermal and thermal-oxidative degradation processes in these systems was followed dynamically with the aid of TGA and FTIR methods. Proper attention was paid also to the effect of oxygen on the thermal-oxidative stability of PE nanocomposites in their solid state, in both the absence as well as in the presence of an antioxidant. Several sets of experimentally acquired TGA data have provided a basis for accomplishing thorough model-based kinetic analyses of thermal and thermal-oxidative degradation of both pristine PE and PE/MMT nanocomposites prepared in this work.

Thermal and Thermal-oxidative Degradation of Polyethylene Nanocomposite …

3

2. EXPERIMENTAL 2.1. Materials A Cloisite 20A (purchased from Southern Clay Products, Inc.) has been used as the organically modified montmorillonite (MMT) to prepare PE/MMT nanocomposites throughout this study. The content of an organic cation-exchange modifier, N+2CH32HT (HT=hydrogenated tallow, C18≈65%; C16≈30%; C14≈5%; anion: Cl-), in the MMT was of 38 % by weight. VCl4 (vacuum distilled at 40°С before use, TU 48-05-50-71) and Al(i-Bu)3 (Aldrich) have been used for catalytic activation of MMT. Ethylene monomer was of a standard polymerization grade.

2.2. Procedure of Polyethylene Nanocomposite Synthesis Intercalation of the catalyst has been accomplished by treating the freshly dehydrated MMT with Al(i-Bu)3 and then with VCl4. The polymerization reaction was started by admitting ethylene into the reactor and then was carried out until desired amount of PE nanocomposite (PE-n-MMT) was obtained. The polymerization reaction was stopped by adding ethanolic HCl solution (5 wt % HCl) to the reactor. The polymer composite product was filtered off, washed with ethanol and dried under vacuum at 60°C. The weight loads of MMT in the resulting composites were calculated by neglecting the contribution of the organic modifier in MMT. The sample of unfilled polyethylene (PE) was prepared by ethylene polymerization on VCl3 activated with Al(i-Bu)3 at the same conditions as applied to the nanocomposite synthesis. Stabilized samples of both the nanocomposites (st-PE-n-MMT) and pristine PE (st-PE) were prepared by treating them with synergetic composition of Topanol CA and di-lauryl3,3’-thiodipropionate (DLTDP) solutions in heptane [Voigt J., Die Stabilisierung der Kunstoffe Gegen Licht und Wärme, Springer-Verlag, Berlin-Heidelberg-New York, 1966, p.542] at 70°C, followed by drying in vacuum. The concentrations of Topanol and DLTDP in (st-PE-n-MMT) and (st-PE) comprised 0.3 and 0.5 wt.%, respectively. For further testing, the prepared materials were hot-pressed into films at applied pressure of 20 MPa and 160°С.

2.3. Characterization of Materials Small-angle X-ray Scattering (SAXS) The structure of the composites was studied by SAXS using a KRM-1 camera (Cu Kα radiation, λ = 0.154 nm, Ni filter). The test samples were powders or films. The data collected were normalized with due regard to the concentration of MMT and the coefficients of attenuation.

4


Transmission Electron Microscopy (TEM). Micrograph of PE nanocomposite sample was obtained on a JEM-100B transmission electron microscope at an accelerating voltage of 80 kV. The sample of 70 nm thickness was cut with the aid of LKV-III ultramicrotome from the composite plate prepared by hot pressing. Thermogravimetric Analysis (TGA) A Perkin-Elmer TGA-7 instrument calibrated by Curie points of several metal standards has been employed for non-isothermal thermogravimetric analysis. The measurements were carried out at a desired heating rate (in the range of 3 – 40 K/min) in both inert (argon) and oxidizing (oxygen) atmospheres, as appropriate. Fourier Transform Infrared (FTIR) Spectroscopy Infrared spectra of the investigated materials in their nascent form were acquired with the aid of a Perkin-Elmer 1725X FTIR instrument by using a Spectra-Tech "Collector" DRIFT accessory furnished with a heated sample post, embedded thermo couple and the corresponding external heater/controller providing temperature reading precision of ±1.0C. The series of FTIR spectra for the polymer samples have been recorded at systematically varied temperatures or over predetermined time intervals (in isothermal regimes) by employing a modified diffuse reflectance-absorbance Fourier Transform (DRAFT) spectroscopy technique published elsewhere [13]. All measurements were performed using the instrument DTGS detector and a 4cm-1 resolution. Kinetic analysis of PE compositions thermal degradation was carried out using Thermokinetics software by NETZSCH-Gerätebau GmbH.

3. RESULTS AND DISCUSSION 3.1. Morphology (Structure Evaluation) Small-angle X-ray scattering (SAXS) has been used to evaluate the degree of exfoliation of the organoclay particles in the polymer matrix [12]. SAXS diffractograms of pristine C20A MMT and those of PE nanocomposites prepared by the intercalation polymerization route for MMT contents of 2.0 vol. % (2) and 6.5 vol. % (3) are shown in Figure 1. The SAXS curve for C20A MMT shows a reflection at around of 3.6o corresponding to the interlayer mean distance of 2.46 nm (Figure 1, 1). As can be seen from the same Figure 1 (2, 3), for the PE/clay nanocomposites having different MMT contents, the 3.6o reflection is absent. This result infers that PE chains, while growing in the course of polymerization in the interlayer spacing of the layered filler particles, are able to commit full exfoliation of the MMT particles down to the monolayers.

Intensity, cps


5

3 2 1

0

2

4

6

8

2θ, degrees Figure 1. SAXS patterns for the original C20A MMT (1) and PE nanocomposites with MMT content of 2.0 vol. % (2) and 6.5 vol. % (3)

Figure 2 shows TEM image of the PE nanocomposite containing 1 vol. % of MMT. The dark features in the micrograph correspond to the exfoliated monolayers and nanostacks of MMT distributed throughout the PE matrix. It can be seen that the nanoscale MMT layers lack any sort of orientation in the matrix of the pressed composite. Moreover, the exfoliated MMT particles exhibit a very high aspect ratio (longitudinal size: thickness).

Figure 2. TEM micrograph of the PE nanocomposite containing 1% by volume of MMT.


Intensity, cps

6

1 2

0

2

4

6

8

2θ, degrees Figure 3. SAXS patterns for the original C20A MMT (1) and C20A MMT treated with HCl solution in ethanol (5 wt % HCl) (2).

It is worth noting here that the organic ammonium cations present in pristine C20A MMT are susceptible to washing out from the interlayer spacing of MMT under acidic treatment of the latter with ethanolic HCl (5% by wt.). The ammonium cations are substituted for protons, and this leads to a prominent decrease of the interlayer distances in the MMT structure (Figure 3). If the intercalative polymerization of ethylene would not accomplish exfoliation of the MMT particles in the composite to the full extent, the diffractogram should contain a wide reflection positioned somewhere at greater angles than in the pristine C20A MMT. It is obvious also that the acidic after-treatment of the synthesized exfoliated nanocomposites should lead to removal of the major part of the original organic MMT modifier.

3.2. Thermal Degradation of PE Nanocomposite It is generally accepted that thermal stability of polymer nanocomposites is higher than that of pristine polymers, and that this gain is explained by the presence of anisotropic clay layers hindering diffusion of volatile products through the nanocomposite material. It is important to note that the exfoliated nanocomposites, prepared and investigated in this work, had much lower gas permeability in comparison with that of pristine unfilled PE [12]. Thus, the study of purely thermal degradation process of PE nanocomposite seemed to be of interest in terms of estimation of the nanoclay barrier effects on thermal stability of polyolefin/clay nanocomposites. The radical mechanism of thermal degradation of pristine PE has been widely discussed in a framework of random scission type reactions [14-22]. It is known that PE decomposition products comprise a wide range of alkanes, alkenes and dienes. Branching of PE chains causes enhanced intermolecular hydrogen transfer and results in lowering thermal stability. The polymer matrix transformations, usually observed at lower temperatures and involving


7

molecular weight alteration without formation of volatile products, are principally due to the scission of weak links, e. g. oxygen bridges, incorporated into the main chain as impurities. The kinetics of thermal degradation of PE is frequently described by a first-order model of mass conversion of the sample [21]. A broad variation in Arrhenius parameters can be found in literature, i. e., activation energy (E) ranging from 160 to 320 kJ/mol and pre-exponential factor (A) variations in the range of 1011 and 1021 s-1 [20-22] are not unusual. It is believed that the broad range of E values reported may be explained by the polymers molecular mass variations, by use of various additives, and by different experimental conditions [22] employed by different authors. Previously Bockhorn et al. have reported that thermal degradation of PE leads to a large number of paraffins, dienes and olefins without a residue formation [20]. Analysis of the pyrolysis products with GC-MS revealed high yields of linear n-alkanes and n-alkenes. Neither branched aliphatics, alicyclics or aromatic compounds nor Diels-Alder derivatives of butadiene have been detected [20]. In order to formulate a simple kinetic model adequately explaining the isothermic global kinetic data of the authors, a mechanism embracing only the main reactions has been proposed [20]. The latter is based on a radical chain mechanism (Scheme 1) initiated by random scission of the polymer chains into primary radicals Rp (1). βScission of these radicals leads to ethylene (2). At higher temperatures, the unzip reaction leading to ethylene becomes more evident [15]. At low temperatures, intramolecular hydrogen transfer followed by β-scission occurs (3). This reaction leads to the more stable secondary radicals Rs. The 1,5 rearrangement reaction (3) in Scheme 1 stands for all preferred rearrangement reactions via cyclic intermediates such as 1,9, 1,13, 1,17, etc. Subsequent βscission of the secondary radicals contributes to the radical chain mechanism because the primary radical is produced in each step (propagation). Two β-scission reactions (4, 4’) are possible. Reaction (4) leads to alkenes, whereas reaction (4’) leads to a short primary radical and a polymer with a terminal double bond. It is important that the change in the reaction order is dependent on the intermolecular hydrogen transfer in reaction (5) leading to the alkanes. In this case only the intermolecular hydrogen transfer of the primary radicals is considered because the latter are less stable than the secondary radicals. At high temperatures and at a high degrees of conversion, the alkanes formation via reaction 5 becomes favored and, therefore, the reaction order alters from 0.5 to 1.5 [20]. In the present work, the processes of thermal degradation of both unstabilized PE and PE-n-MMT nanocomposite with MMT content of 4.3 wt.% have been investigated by TGA in an inert (argon) atmosphere at the heating rates of 3, 5, 10 and 20 K/min. According to the dynamic TGA data, the polymer degradation starts at about 300°C and then, through a complex radical chain process (Scheme 1), the material totally destructs and completely volatilizes in the range of 500-550oC (Figure 4). It is obvious that, taken at the same heating rates in argon, the thermograms for pristine PE and PE-n-MMT are practically identical, except that the solid silicate residue amounting to 4-5 % wt. can be seen on the curves for the nanocomposites (Figure 4). This result suggests that the mechanisms of thermal degradation of PE and PE-n-MMT nanocomposites, and hence the global kinetic parameters of their thermal degradation processes are rather similar.

8

S. M. Lomakin, L. A. Novokshonova, P. N. Brevnov et al. Initiation H2 C

H2 C

C H2

C H2

C H2

H2 C

H2 C

k1

+

C H2

C H2

H2 C C H2

C H2

(1)

H 2C

CH2

(2)

2RP

P Propagation H2 C

H2 C

C H2

C H2

H2 C

k2

C H2

C H2

C H2

RP

+

RP Hydrogen transfer (intramolecular)

H2 C

H2 C

H2 C

C H2

C H2

C H2

H2 C

k3

H2 C

C H2

C H2

C H2

C H2

CH3

β-scission H2 C

k4 C H

H2 C

(3)

Rs

RP

H2 C

C H

C H2

CH3

C H2

C H2

H 2C

RP

H2 C C H2

+

H2 C

H C

(4) 3)

alkene/diene

k 4' H2 C

Rs

CH3

C H

C H2

+

CH2

C H2

P

H2 C

(4')

CH3

RP

Hydrogen transfer (intermolecular) H2 C H 3C

n C

H2 C

+

H2

H2 C

RP

n C

H 3C

C H2

C H2

H2 C

k5

H2

alkane

P

CH3

+

H C C H2

C H2

(5) )

Rs

Termination -2nd order (recombination)

H2 C

RP

+

H2 C

k6

RP

Scheme 1. Mechanism of PE thermal degradation [20].

C C H2 H2

P

(6) )


9

100

Weight, %

80

3

60

1 40

2 4

20

0 200

300

400

500

600

o

Temperature, C Figure 4. TGA thermograms for PE (firm lines) and PE-n-MMT (dotted lines) taken in Ar at the heating rates of: 3K/min - 1, 2 and 10K/min. - 3, 4.

3.3. Kinetic Analysis of PE Nanocomposite Thermal Degradation Based on TGA Data Kinetic studies of materials degradation have long history, and there exists a long list of data analysis techniques employed for the purpose. Often, TGA is the method of choice for acquiring experimental data for subsequent kinetic calculations, and namely this technique was employed here. It is commonly accepted that the degradation of materials follows the base equation (1) [15]. dc/dt = - F(t,T co cf)

(1)

where: t - time, T - temperature, co - initial concentration of the reactant, and cf concentration of the final product. The right-hand part of the equation F(t,T,co,cf) can be represented by the two separable functions, k(T) and f(co,cf): F(t,T,co,cf) = k[T(t)·f(co,cf)]

(2)

Arrhenius equation (4) will be assumed to be valid for the following: k(T) = A·exp(-E/RT)

(3)

10

S. M. Lomakin, L. A. Novokshonova, P. N. Brevnov et al. Therefore, dc/dt= - A·exp(-E/RT)·f(co,cf )

(4)

All feasible reactions can be subdivided onto classic homogeneous reactions and typical solid state reactions, which are listed in Table 1 [23]. The analytical output must provide good fit to measurements with different temperature profiles by means of a common kinetic model. Kinetic analysis of PE and PE-n-MMT thermal degradation at heating rates of 3, 5, 10 and 20K/min was accomplished by using a NETZSCH Thermokinetics software in accordance with a formalism we proposed earlier [7]. In order to assess the activation energy for development of a reasonable model for kinetic analysis of pristine PE and PE-n-MMT thermal degradation processes, a few evaluations by model-free methods have been done as the starting point. As an example, the results of a model-free Friedman analysis for thermal degradation of PE, where the activation energy is a function of partial mass loss change [24], are shown in Figure 5. Table 1. Reaction types and corresponding reaction equations, dc/dt= - A·exp(E/RT)·f(co,cf ) Name F1 F2 Fn

f(co,cf ) c c2 cn

Reaction type first-order reaction second-order reaction nth-order reaction

R2 R3

2 · c1/2 3 · c2/3

two-dimensional phase boundary reaction three-dimensional phase boundary reaction

D1 D2 D3 D4

0.5/(1 - c) -1/ln(c) 1.5 · e1/3(c-1/3 - 1) 1.5/(c-1/3 - 1)

one-dimensional diffusion two-dimensional diffusion three-dimensional diffusion (Jander's type) three-dimensional diffusion (Ginstling-Brounstein type)

B1 Bna

co · cf con · cfa

simple Prout-Tompkins equation expanded Prout-Tompkins equation (na)

C1-X

c · (1+Kcat · X)

first-order reaction with autocatalysis through the reactants, X. X = cf.

Cn-X

cn · (1+Kcat · X)

nth-order reaction with autocatalysis through the reactants, X

A2 A3 An

2 · c · (-ln(c))1/2 3 · c · (-ln(c))2/3 N · c · (-ln(c))(n-

two-dimensional nucleation three-dimensional nucleation n-dimensional nucleation/nucleus growth according to Avrami/Erofeev

1)/n


E, kJ/ mol

11

log (A,s-1) 2

35

1 25 1 15

5

0

5 0

0. 0. Conversion degree

0.

0.

1.

Figure 5. The graphs for activation energy and pre-exponential factor as the functions of the conversion degree (partial mass loss) for thermal degradation of PE in argon, obtained with the aid of Friedman analysis.

Further, nonlinear model fitting procedure for PE and PE-n-MMT TGA-curves has led to the following triple-stage model scheme of successive reactions (Figure 6 a, b):

Dn

A

Fn

B

C

Fn

D

(5)

Taking this as a reasonable approximation for PE and PE-n-MMT, the fits with the aid of nonlinear regression were attempted by the model (5), where an one-dimensional diffusion type reaction was used for the first step and the nth-order (Fn) reaction - for the two subsequent steps of the overall thermal degradation process (Figure 6, Table 1). Assuming a radical chain mechanism is operative in the process of PE and PE-n-MMT thermal degradation (Scheme 1), the apparent activation energy and the pre-exponential factor values calculated in this work turned out to be in perfect match with the data from isothermal analysis and dynamic TGA published earlier (Ea = 268 ± 3 kJ/mol, log A = 17.7 ± 0.01 min-1 and Ea = 262.1 kJ/mol, log A = 18.09± 0.14 min-1 [25].)

12


a

100

80 3

Weight, %

2

4 1

60

40

20

0

200

300

400

500

600

o

Temperature, C

b

100

80 3

2

Weight, %

4 1

60

40

20

0

200

300

400

500

600

o

Temperature, C

(b)

Figure 6. Outcome of multiple models-based nonlinear fitting for pristine PE (a) and PE-n-MMT (b). The experimental TGA-data (dots) in comparison with the model calculations results (firm lines) are shown for different heating rates: 3K/min – (1), 5K/min – (2), 10K/min – (3) and 20K/min – (4).


13

Table 2. The kinetic parameters for the three-step thermal degradation of PE and PE-nMMT as obtained by the multiple-curve analysis of the experimental TGA-data (heating rates 3, 5, 10 and 20 K/min) in frames of the reaction model Fn Dn Fn

A Material

PE

PE-n-MMT

B

C

Parameter

Value

logA1, s-1 E1, kJ/mol

11.7 197.7

logA2, s-1 E2, kJ/mol n2

15.5 253.1 0.50


16.6 268.1 1.50

logA1, s-1 E1, kJ/mol

10.3 186.3


14.5 237.5 0.50


17.6 274.3 1.50

D

Corr. Coeff.

0.9994

0.9992

The TGA data acquired for PE and PE-n-MMT in argon has not provided any evidence in favour of the hypothesis that the barrier effect, being clearly manifested in the gas permeability experiments with the same PE-n-MMT at room temperature [12], is operative also during thermally stimulated degradation of PE-n-MMT. It should be noted that, in an inert atmosphere, degradation/volatilization of both PE and PE-n-MMT starts at about 350°C and is totally completed upto 500-550oC, not taking into account a solid silicate residue amounting to 4-5 % wt. which remains in the case of the nanocomposites (Figure 4, 6). Based on TGA data, the first stage of the degradation process (1D-diffusion limiting stage) develops in the range of 350-410oC corresponding to the overall mass loss of 5-7%. The subsequent steps of the thermal degradation processes (410 - 500oC) for PE and PE-n-MMT proceed in the liquid melt of high molecular weight degradation products (Scheme 1). In the light of the above findings, we believe that during the high-temperature degradation stages (above, e. g., 410oC) in an inert atmosphere, the barrier diffusion restrictions can become insignificant since the viscosity of the pyrolyzed polymer melt at these temperatures is rather low and, because of the intensified mobility of the clay layers in such melt, the overall ‘labyrinth effect’ normally provided by the clay particles in more viscous matrices may be considerably diminished.

14


Scheme 2. A flow-chart of elementary steps constituting PE thermal-oxidative degradation process.

3.4. Thermal-oxidative Degradation of PE Nanocomposite Thermal oxidative degradation of PE and PE nanocomposites has been extensively studied over the past decades [26-30]. It has been reported that the main oxidation products of PE are aldehydes, ketons, carboxylic acids, esters and lactones [26, 27]. According to Lacoste and Carlsson [28], β-scission plays an important role in thermal oxidation of UHMWPE. Notably, the feasibility of intra-molecular hydrogen abstraction by the peroxy radicals for polyethylene has been questioned in frames of a thermal oxidation mechanism proposed by Gugumus [29, 30]. It is usually supposed that the reaction of hydrogen abstraction from an alkane molecule, R-H, may lead to either hydroperoxide or alkyl radicals according to the overall reaction scheme (Scheme 2). A mechanism describing oxidation of organic molecules by virtue of complex chain reactions has been proposed earlier by Benson [31]. At temperature below 190oC, oxidation of organic compounds involves free-radical chain initiation and the main products are hydroperoxides and oxygenated species indicated in the routes A1 and A2 of Scheme 2. At temperatures below 200oC, the abstraction of H from R· resulting to HO2· + olefin (routes B1 and B2) proceeds at least 200 times slower than the addition of O2 to R· to give RO2·. Above 250oC, the route A2 becomes reversible and the very slow step B2 becomes rate determining. As a consequence, at temperatures above 300oC, there is some retardation of the rate of oxidation of the polymer. The H2O2 can play the same role as ROOH in providing a secondary radical source just above 480oC where the rate of oxidation picks up again.


15

It is worth noting that simple digital photo camera was of help for qualitative assessment of differences in the processes of thermal oxidation of neat PE as compared to PE-n-MMT. Figure 7 shows color photographs of the neat PE (1) and PE-n-MMT (2) taken after both samples having been heated during 2 minutes at 180oC in air. It can be seen that coloration of the PE-n-MMT sample (2) is much darker than that of the neat PE (1), thus evidencing that MMT is able to induce an oxidative dehydrogenation of PE, resulting in emergence of unsaturated bonds, which subsequently lead to crosslinking, aromatization and carbonization of the polymer. Figure 8 compares the TGA thermograms for neat PE and PE-n-MMT which has been acquired at a 10K/min heating rate in air. Obviously, under the thermal oxidative degradation conditions, these two materials demonstrate strikingly different behavior.

1

2 Figure 7. Differences in coloration of neat PE (1) and PE-n-MMT (2) samples - both heated for two minutes at 180oC in air.

16

S. M. Lomakin, L. A. Novokshonova, P. N. Brevnov et al. 100

Weight, %

80

2

1

60

40

20

0

100

200

300

400

500

600

o

Temperature, C Figure 8. TGA curves for PE (1) and PE-n-MMT (2) recorded in air at the heating rates of 10K/min.

The earliest stage of thermal oxidative degradation of unstabilized samples of PE-nMMT and PE manifests itself as a clear weight gain feature emerging on the TGA curves well below 200oC and is attributed to the oxygen absorption followed by the hydroperoxides formation (Figure 8, 9). Of importance, however, is the fact that for PE-n-MMT this process seems to be accelerated due to the presence of nanosilicate additive as compared with the pristine PE. Dependences of the hydroperoxides formation onset temperatures versus the heating rate, which have been derived from the TGA data for unstabilized PE-n-MMT and PE samples, are presented in Figure 10. O2 H2C

H2C MMT

OO*

+

CH2 H2C

CH2

Δ MMT

OO

H

CH

H2C

Δ MMT

OOH

+

CH2

CH2 H2C

CH2

H C H2C

H2C

CH2

Δ MMT

Scheme 3. The earliest stages of the process of PE thermal oxidative degradation in the presence of exfoliated MMT nanoparticles.


104 179

o

190

o

204

o

223

o

Weight, %

102

100

98

o

20 /min

o

96

10 /min

o

o

3 /min

5 /min

94 100

150

200

250

300

350

o

Temperature, C Figure 9. Exploded view of TGA traces characterizing the primary stage of PE-n-MMT thermal oxidative degradation at different heating rates.

2

200

1

o

Temperature (Ton), C

190 180 170 160 150 140 0

10

20

30

40

Heating Rate, K/min Figure 10. The onset temperatures of hydroperoxides formation vs. heating rate for: 1 – PE, 2 - PE-nMMT.

17

18


We believe that O2 molecules, being adsorbed on the defect centers of MMT represented by the traces of transitional metals, transform into more active species which are able to react with PE at lower temperatures, thus inducing formation of active centers on the hydrocarbons chains (Scheme 3). Apparently, this chain of events should result to accelerated formation of PE hydroperoxides. Notably, while the hydroperoxides accumulation starts at lower temperatures in PE-nMMT than in the unfilled PE (cf. e. g., Figure 8), the clearly visible mass loss of the nanocomposite (attributable solely to decomposition of the accumulated hydroperoxides) ensues at lower temperatures as well. It is reasonable to suggest that this effect is caused by a catalytic action of exfoliated MMT nanoparticles on the hydroperoxides decomposition. As it has been mentioned above, the treatment of PE-n-MMT with alcoholic HCl solution led to substitution of the major part of the organic modifier by acidic protonic centers. Moreover, it is widely accepted that MMT-type clay minerals always comprise a plenty of different catalytically capable sites, which may be represented by weakly acidic Brønsted-like Si-OH sites, by strongly acidic -OH groups localized at the edges of the silicate layers, by transition metal cations captured in the galleries, and by crystallographic defect sites within the layers [32,33]. All these sites are able to trigger decomposition of hydroperoxides within the bulk of the PE-n-MMT. It has been shown that acid-catalyzed rearrangements of hydroperoxides can proceed in both polar and non-polar solvents. Hence, such rearrangements can be expected to occur also in PE-n-MMT. Acids can decompose primary and secondary hydroperoxides according to two different pathways [34]. Both these routes are depicted in Scheme 4 for the secondary hydroperoxides most probably present in PE. Since mobility of the methylene units in the PE backbone is rather limited, it is reasonable to assume that reaction (2) in Scheme 4 should be of minor importance. Then the main reaction [reaction (1) in Scheme 4] must lead to transformation of the hydroperoxide into the ketone group with elimination of water. The reaction might proceed according to the general mechanism or be simply dehydration [35]. At the same time, the acidic sites of MMT may turn out to be sufficiently active to abstract single electrons from donor molecules with formation of free radicals, the latter being capable of further accelerating the thermal oxidation of PE chains e. g. by virtue of branching reactions. H2 H C C O

H2 H C C

C H2

AH

H2 C

C O

C H2

+

H2O

(1)

C C H2

(2)

OH

C H2

O

H

AH C OH H2

+ O

OH Scheme 4. Acid-catalyzed decomposition of PE hydroperoxides.


19

In addition to the accumulation and subsequent decomposition of the hydroperoxides on the earlier stage resulting to emergence of the oxygen-containing groupings, the ensued process of thermal oxidative degradation of the nanocomposite involves the reactions of oxidative dehydrogenation and intermolecular cross-linking. The latter two reactions have been revealed with the aid of the DRAFT FTIR spectra presented below. It seems reasonable to suggest that namely at this step the thermally stable carbonized charred layer on the nanocomposite surface is formed and starts to hinder the diffusion transport of both the volatile degradation products (out of the polymer melt into the gas phase) and the oxygen (from the gas phase into the polymer). The above set of events results in actual increase of the nanocomposite thermal stability in the temperature range of 350-500°C, where normally a shear degradation of the main part of PE takes place. This point is illustrated by TGA and DTG plots presented in Figs. 11 and 12. 100

Weight, %

80

3

60

2

1

40 20 0 200

300

400

500

600

0.0

dm/dT

-0.7

1

-1.4 -2.1

2

-2.8 200

300

3

400

500

600

o

Temperature, C Figure 11. Acquired at 10 K/min heating rate in air or argon TGA and DTG curves for: 1 - PE (air), 2 – st-PE (air), 3 - PE (Ar).

20

S. M. Lomakin, L. A. Novokshonova, P. N. Brevnov et al. 100

3

Weight, %

80

2 60

1

40 20 0 200

300

400

500

600

0.0

dm/dT

-0.7

2

-1.4

1

-2.1

3

-2.8 200

300

400

500

600

o

Temperature, C Figure 12. Acquired at 10 K/min heating rate in air or argon TGA and DTG curves for: 1 - PE-n-MMT (air), 2 – st-PE-n-MMT (air), 3 - PE-n-MMT (Ar).

The diverse behavior of stabilized and unstabilized samples (Figure 11 and 12, curves 1,2 TG and DTG) shows that the addition of antioxidants has resulted to higher thermal-oxidative stability. It can be seen also that the overall thermal oxidative stability of PE-n-MMT irrelevantly of the antioxidant presence was higher that that of the pristine PE. Moreover, incorporation of the antioxidants in PE-n-MMT has led to a notable change in the character of the mass loss process (Figure 12, curves 2,3 of TG and DTG). It is quite probable that the antioxidant is able to “deactivate” the sites of MMT that have been occupied earlier with absorbed oxygen. In the result, the MMT nanolayers could become chemically inert in respect to the hydroperoxides formation and hence to further accelerated PE oxidation. It may be seen as well that, with the exception of the first thermal oxidation step, the TGA and DTG curves for st-PE-n-MMT taken in air become closely resembling those characteristic for PE-n-MMT run in argon. Having taken into account the above findings, it seems reasonable to explain the observed retardation of thermal oxidative degradation of st-PE-n-MMT by the capability of exfoliated MMT nanolayers to hinder the diffusion of oxygen throughout the partly cross-linked and carbonized nanocomposite matrix.


21

3.5. Kinetic Analysis of PE-n-MMT thermal Oxidative Degradation Kinetic analysis of thermal oxidative degradation of unstabilized PE and PE-n-MMT at the heating rates of 3, 5, 10 and 20K/min. (Figure 13 a, b) (as well as of the same samples stabilized with antioxidants) has been accomplished by using the aforesaid interactive model based nonlinear fitting approach. With best fidelity, the undertaken nonlinear model fitting for the stabilized samples of PE and PE-n-MMT has provided a triple-stage model scheme of successive reactions, wherein an nth-order autocatalysis reaction (Cn) was used at the first step, while a general nthorder (Fn) reaction was used for both the second and the third steps of the overall process of thermal oxidative degradation (Table 1):

Cn

A

Fn

B

C

Fn

D

(8)

For unstabilized PE and PE-n-MMT at the beginning stage of degradation, the degree of conversion depends on the heating rate (Figure 13a), such dependence being a strong evidence in favor of a branched reaction path. For this case, the same approach has provided a dissimilar triple-stage model scheme comprising two competitive reactions: an n-th order autocatalytic reaction (Cn), for the first competing path, and two nth-order (Fn) successive reactions, for the second competing path (9). Cn

A

Fn

B B

Fn

C

(9)

As data in Table 3 for the first stage of thermal oxidative degradation reaction show, the activation energies values for st-PE and st-PE-n-MMT amount to 74 and 96 kJ/mol, while for unstabilized materials those values are of 65 and 51 kJ/mol, correspondingly, thus indicating that the degradation of these samples is initiated by the similar oxygen induced reactions. At this stage, the lower activation energy of PE-n-MMT compared to that of PE may be related to the catalysis exerted by the ММТ during formation and decomposition of hydroperoxides. At the same time, the values of activation energy found at the second and the third stages of thermal-oxidative degradation for PE-n-MMT are higher than those for PE (Table 3, Figure 14). This difference may be attributed to a shift of the PE-n-MMT degradation process to a diffusion-limited mode owing to emergence in the system of a carbonized cross-linked material. The activation energy values of st-PE-n-MMT at the first and the last stages are higher than those of st-PE (Table 3, Figure 14). Actually, at the last stage, the activation energy of stPE-n-MMT rises up to 274.8 kJ/mol, almost reaching the activation energy value found for degradation of PE-n-MMT in inert atmosphere (274.3 kJ/mol) (Table 2). This fact infers that the last stage of the st-PE-n-MMT degradation process is governed mainly by random scission of C-C bonds, rather than by an oxygen catalyzed reactions. On the other hand, these results are also consistent with the barrier model mechanism, which suggests that inorganic

22


clay layers can play a role of barriers retarding the diffusion of oxygen from gas phase into the nanocomposite. a

3

100

2

Weight, %

80

1

60

40

20

0

100

200

300

400

500

600

o

Tem perature, C

b

100

Weight, %

80

60 2

1

3

40

20

0

100

200

300

400

500

600

700

o

Temperature, C Figure 13. Nonlinear kinetic modelling of PE-n-MMT (a) and st-PE-n-MMT (b) in air. Comparison between experimental TGA data (dots) and the model results (firm lines) at several heating rates: 3K/min – (1), 5K/min – (2) and 10K/min.

Thermal and Thermal-oxidative Degradation of Polyethylene Nanocomposite … Table 3. Results of the multiple-curve kinetic analyses for thermal-oxidative degradation of PE and PE-n-MMT in accordance with the reaction models 8 and 9 Material

St-PE

PE

St-PE-n-MMT

PE-n-MMT

Parameter

Value

logA1, s-1 E1, kJ/mol n1 log Kcat 1

3.6 74.9 0.79 0.59


14.9 225.9 0.51


16.1 254.4 1.79

logA1, s-1 E1, kJ/mol n1 log Kcat 1

3.6 65.3 1.62 0.14

logA2, s-1 E2, kJ/mol n2 logA3, s-1 E3, kJ/mol n3 logA1, s-1 E1, kJ/mol n1 log Kcat 1

5.1 120.2 0.55 13.7 219.7 1.37 6.3 96.3 2.4 0.15


13.8 230.2 0.64

logA3, s-1 E3, kJ/mol n3 logA1, s-1 E1, kJ/mol n1 log Kcat 1

16.8 274.8 1.66 2.2 51.5 2.81 0.12


6.8 146.2 0.53

logA3 s-1 E3 kJ/mol n3

14.7 238.2 1.69

Corr. Coeff.

0.9987

0.9953

0.9993

0.9993

23

24


250

0

PE-n-MMT

PE

3 stage 2 stage 1 stage

1 stage

2 stage

1 stage

50

1 stage

2 stage

100

3 stage

2 stage

3 stage

150

3 stage

En, kJ/mol

200

st-PE

st-PE-n-MMT

Figure 14. Comparative diagram of activation energies for PE and PE-n-MMT thermal-oxidative degradation processes.

Thus, from the results of the kinetic analyses of TGA data for both antioxidant-stabilized and unstabilized PE and PE-MMT nanocomposite it follows that the organoclay nanoparticles can exert two counteracting effects influencing the thermal-oxidative stability of the PEMMT nanocomposite: 1. the barrier effect in partly carbonized cross-linked polymer matrix tending to improve the thermal-oxidative stability of the nanocomposite; 2. observed at the earlier stages the catalytic effect inducing the accumulation and decomposition of hydroperoxides, thus in fact promoting degradation of the polymer matrix and hence impairing the thermal stability of PE-n-MMT.

3.6. Dynamic FTIR Analysis of PE-n-MMT Thermal Oxidative Degradation Simultaneously to TGA measurements, thermal oxidative degradation of non stabilized samples of PE and PE-n-MMT has been monitored in this work with the aid of a dynamic FTIR spectroscopy in a temperature range of 25 – 240oС. The overall evolution of the dynamic FTIR spectra in the course of thermal-oxidative degradation of PE and PE-n-MMT in the condensed phase is shown in Figure 15 (a, b).


25

a

o

240 C o

230 C o

220 C o

210 C o

200 C o

Absorbance, %

190 C o

180 C o

170 C o

160 C o

150 C o

140 C o

130 C o

120 C o

110 C o

100 C o

90 C o

80 C o

70 C o

60 C o

50 C o

25 C

3500

3000

2500

2000

W avenumber, cm

1500

1000

-1

b

o

240 C o

240 C o

230 C o

220 C o

Absorbance, %

210 C o

200 C o

190 C o

180 C o

170 C o

160 C o

150 C o

140 C o

130 C o

120 C o

110 C o

100 C o

50 C o

25 C

3500

3000

2500

2000

1500

Wavenumber, cm

-1

Figure 15. Dynamic FTIR analysis of PE – (a) and PE-n-MMT – (b).

1000

500

26

S. M. Lomakin, L. A. Novokshonova, P. N. Brevnov et al. Table 4. Assignments of the dynamic FTIR spectra

Wavenumber (cm-1)

Assignment

Reference

3630-3690 3552

-OH hydroxyl groups -OH hydroxyl groups of MMT free hydroperoxide groups (-OOH)

[46] [S] [45]

3410

associated hydroperoxide groups (-OOH)

[45]

3400

ν (-OH) hydroxyl groups of MMT

[S]

2930

ν (CH2)a

[44]

2852

ν (CH2)s

[44]

1790 1746

-lactone C=O stretching ν (C=O) in ester

[43] [45,46]

1734

ν (C=O) in aldehyde

[48]

1717

ν (C=O) in ketone

[45,46]

1700

ν (C=O) in

[45]

1600-1590 1458

ν (C=C) δ (CH2)a

[45] [44]

1363

δ (CH2)s

[44]

1163

ν (C–O-C) in ester

[44,45]

1072

ν (Si–O)

[45,]

1010

ν (Si–O)

[45,]

719

γ (CH2)

[45]

–β unsaturated ketone

Table 4 shows peak positions of the absorption bands monitored during the heating experiment along with the corresponding assignments of the vibrations. At room temperature (25oC), the FTIR spectra of both materials are typical for PE. The absorption bands at 2845-2960 cm-1 are assigned to -CH-, -CH2-, or -CH3 stretching vibration [36]. The absorption at 1472 cm-1 is due to the deformation vibration of -CH2- or -CH3 groups, while that at about 720 cm-1 is due to (CH2)n rock when n ≥ 4 [36, 37]. Beside these, the FTIR spectra of PE-n-MMT revealed the absorptions belonging to MMT (ν (Si–O) 1047 cm-1) [37]. Another MMT absorption band at 3630 cm-1 has been assigned to the structural hydroxyl groups, directed toward the vacant positions in the inner octahedral layer of montmorillonite. Else, a broad absorption band of hydroxyl groups was observed at 3400 cm-1 [38]. During the dynamic recording of the PE and PE-n-MMT spectra under the step-wise heating a sharp growth of the absorption in the range of 1700 - 1800 cm-1 was noted at temperatures above 200oC indicating the emergence and accumulation of carbonyl-containing products resulting from the thermal-oxidative degradation process (Figure 16).

Thermal and Thermal-oxidative Degradation of Polyethylene Nanocomposite … 88

3500

2500

2000

719

1072

1363 1311

1590

920 1041

719

1363 1311 1163

1734 1746 1717

1790

2678

3000

1458

2853 2856

66 64 62 60 58 56

2

1604

2922 2934

1458

2678

1746 1717

3550

1

3550

Transmitance

86 84 82 80 78 76 74 72 70 68

27

1500

1000

Wavenumber, cm

500

-1

Figure 16. FTIR spectra of PE – (1) and of PE-n-MMT – (2) taken at 220oC in the course of the heating runs (Excerpted from the corresponding dynamic FTIR spectra sets).

Obviously, the complex band in the range of 1700-1800 cm-1 comprises (1) a carbonyl absorption (shoulder at 1717 cm-1) belonging to ketone groups embedded into the polymer chain [37, 39], which are known to be the main oxidation products for the neat PE [3], (2) a shoulder peaking close to 1734 cm-1 (Figure 17, Table 3) which is attributed to aldehyde groups [40], (3) another shoulder with maxima in the vicinity of 1746 cm-1 (Figures 17 Table 3) which is normally assigned to ester groups vibrations [37, 39], and (4) an absorption at 1790 cm-1 belonging to the carbonyl in -lactone moiety [41]. Gradual growth of concentration of the vinylene groups absorbing close to 1600 cm-1 has also been noted [37]. The dynamic FTIR spectra show that, while the fractional ratio of different carbonyl absorptions was almost the same for both PE and PE-n-MMT, the apparent concentration of the carbonyl-containing products (overall intensity of the complex absorption band) in PE-nMMT was considerably higher than in pristine PE (Figure 17), other conditions being the same. For non stabilized samples of both PE and PE-n-MMT, temperature dependences of the Carbonyl Index (CI) have been estimated which are shown in Figure 18. The carbonyl index (CI) was defined to illustrate the formation of non-volatile carbonyl containing oxidation products:

CI =

SC=O − CIo S2019

28

S. M. Lomakin, L. A. Novokshonova, P. N. Brevnov et al. 0.025

Absorbance

1717

0.020

1790

1746

0.010

1734

0.015

0.005

0.000

1800

1750

1700

1650

-1

Wavenumbers, cm

Figure 17. An exploded view of the 1700 - 1800 cm-1 infrared region showing the separated modes belonging to different carbonyl-containing groups formed in the course of thermal-oxidative degradation of PE and PE-n-MMT. 14

2

10 8

i

CI = S[C=O] /S2019- CIo

12

6 4

1

2 0 50

100

150

200

250

o

Temperature, C Figure 18. The Carbonyl Index (CI) vs. temperature dependences for: (1) PE; (2) PE-n-MMT.


29

where SC=O is peaks area of carbonyl containing groups at 1800-1700 cm-1, S2019 is internal reference at 2019 cm-1, which was attributed to the combination of 1300 cm-1 and 720 cm-1 , CIo is initial carbonyl index. Along with the carbonyl absorptions growth, the FTIR spectra have revealed a clear decay of intensities of the bands belonging to -СН2- vibrations as the result of the PE chain scission. Both investigated materials experienced the chain scission during pyrolysis, but with drastically different rates. The relative rates of the decay are illustrated by the overlaid spectra in Figure 19 showing evolution of the symmetrical and asymmetrical –CH2- stretch absorption bands with the pyrolysis temperature for pristine PE as compared to PE-n-MMT. At any given temperature above 200oC, PE-n-MMT has higher content of intact CH2 units than the pristine PE sample, and the apparent rate of disappearance of the aliphatic units in the pyrolysis temperature range of 220-260oC is much higher for pristine PE than for the corresponding nanocomposite. Thus, the observed evolution of the spectra is an extra proof of the fact that, at temperatures above 220oC, PE-n-MMT nanocomposite undergoes thermaloxidative degradation with a considerably slower rate than the neat PE does. The same conclusion has been derived in the preceding section based on the analysis of corresponding TGA data (Figure 10). We explained this fact by the formation of chemical crosslinking between the polyethylene macromolecules in the nanocomposite. Figures 15b and 16 show the medium absorption band at 1162 cm-1 which can be attributed to intermolecular esters groups (>С-ОСC-C< and >С-О-С< bonds [26]. The difference lies in the subsequent reactions of alkyl macro-radicals after depletion of oxygen which is both dissolved in the polymer and trapped between the clay particles. Increasing the concentration of oxygen leads to the predominance of chain scission in PE (Scheme 6, reactions c, d), whereas at low concentration of oxygen the intermolecular crosslinking followed by carbonization takes place (Scheme 6, reactions e, f). When a silicate is dispersed into a polymer matrix giving a nanocomposite an improvement of the barrier properties of the material is obtained, due to the labyrinth effect of the silicate layers towards the diffusing gas or liquids.

CONCLUSION Performed study of the thermal and thermal-oxidative degradation of PE and its nanocomposites revealed distinguishing features for nanocomposites thermal-oxidative degradation. It is shown that thermal degradation of PE in the inert environment proceeds identical with PE nanocomposite, which is the evidence against the MMT influence on this process. On the other hand, the thermal-oxidative degradation of these materials in the presence of oxygen proceeds in different ways:

Thermal and Thermal-oxidative Degradation of Polyethylene Nanocomposite … •

•

•

• •

31

During the thermal oxidation at 170-200oC for inhibitor-free PE-MMT nanocomposites it was observed the accelerated formation and decomposition of hydroperoxides as compared with unfilled PE which is caused by catalytic action of montmorillonite (at the presence of oxygen). It was registered above 200oC the effective formation of intermolecular chemical cross-links in the PE-MMT nanocomposite, as a result of recombination reactions of the products of radical decomposition of hydroperoxides, caused by deficiency of oxygen in a polymeric matrix due to the lowered oxygen permeability. Cumulative action of chemical cross-linking and catalytic dehydration presents arise a necessary and sufficient condition of carbonization, which is observed in the process of thermal-oxidative degradation of PE-MMT nanocomposites. Carbonized layer formation leads to appreciable increase of thermal stability of PE nanocomposite, owing to a hindrance of the mass transfer in the nanocomposite. An incorporation of the antioxidant in PE and its nanocomposite suppresses the formation and decomposition of hydroperoxides and reduces the catalytic action of MMT on these processes. These facts lead to an increase of thermal-oxidative stability in both materials, at that the nanocomposite thermal stability exceeds PE and approaches the values obtained in inert atmosphere.

REFERENCES [1] [2] [3] [4] [5]

Messersmith PB, Giannelis EP. Chem Mater 1993;5:1064. Zanetti M, Lomakin S, Camino G. Macromol Mater Eng 2000; 279:1-9. M. Alexandre, P. Dubois, Mater. Sci. Eng. R 28 (2000) 1–63. Giannelis EP. Adv Mater. 1996; 8:29-35. Oya A. Polypropylene clay nanocomposites. In: Pinnavaia TJ, Beall GW, editors. Polymer clay nanocomposites. London:Wiley; 2000. [6] J.W. Gilman, T. Kashiwagi, M. Nyden, J.E.T. Brown, C.L. Jackson, S.M. Lomakin, E.P. Gianellis, E. Manias, in: S. Al-Maliaka, A. Golovoy, C.A. Wilkie (Eds.), Chemistry and Technology of Polymer Additives, Blackwell Scientific, London, 1998, pp. 249–265. [7] S.M. Lomakin, I.L. Dubnikova, S.M. Berezina, G.E Zaikov, Polymer International, v.54, 7, (2005), 999-1006. [8] Lomakin SM, Zaikov GE, Modern Polymer Flame Retardancy, VSP Int. Sci. Publ. Utrecht, Boston, 2003, 272. [9] Gilman JW. Applied Clay Sci. 1999. V.15. P.31. [10] Gilman GW, Jackson C L., Morgan A B, Harris R H, Manias E, Giannelis E P, Wuthenow M, Hilton D, Phillips S. Chem. Mater. 2000. V.12. P.1866. [11] T. Kashiwagi, R.H. Harris Jr, Xin Zhang, R.M. Briber, B.H. Cipriano, S. R. Raghavan, W. H. Awad, J. R. Shields. Polymer. 2004. V. 45. P.881. [12] N.Yu. Kovaleva, P.N. Brevnov, V.G. Grinev, S.P. Kuznetsov, I.V. Pozdnyakova, S.N. Chvalun, E.A. Sinevich, L.A. Novokshonova, Polymer Science, Series A, 2004, V. 46, 6, p.651.

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[13] A.N. Shchegolikhin and O.L. Lazareva Int. J. Vib. Spect., [www.ijvs.com] 1, 4, 95-116 (1997). [14] D.J. Lacey, V. Dudler, Polym. Degrad. Stab. 51 (1996) 1011. [15] M. Paabo, B.C. Levin, Fire Mater. 11 (1987) 55. [16] R.P. Lattimer, J. Anal. Appl. Pyrolysis 31 (1995) 203–226. [17] T. Kuroki, T. Sawaguchi, S. Niikuni, T. Ikemura, Macromolecules 15 (1982) 1460– 1462. [18] E. Kiran, J.K. Gillham, J. Anal. Appl. Pyrolysis 20 (1976) 2045–2068. [19] M. Blazso, J. Anal. Appl. Pyrolysis 25 (1993) 25–35. [20] U. Hornung, A. Hornung, H. Bockhorn, Chem. Ing. Tech. 70 (1998) 145–148. [21] U. Hornung, A. Hornung, H. Bockhorn, Chem. Eng. Technol. 21 (1998) 332–337. [22] H. Bockhorn, A. Hornung, U. Horung, J. Anal. Appl. Pyrolysis 46 (1998) 1–13. [23] Opfermann J. J Thermal Anal Cal. 2000. V.60. № 3. P. 641. [24] Friedman H.L. J Polym. Sci. C. 1965. V.6. № 1. P.175. [25] Bockhorn H, A. Hornung A, Hornung U, Schawaller D. Journal of Analytical and Applied Pyrolysis. 1999. V.48. No.2. P.93. [26] N. Grassie, Gerald S. Polymer Degradation and Stabilization, Cambridge University Press, Cambridge - New York – Melbourne – Sydney, 1988, 222 p. [27] Gugumus F. Polym Degrad Stab 2000; 69:23–34. [28] Lacoste L, Carlsson DJ. Gamma-, photo-, and thermally-initiated oxidation of linear low density polyethyleneda quantitative comparison of oxidation products. J Polym Sci Part A Polym Chem 1992;30:493e500. [29] Gugumus F. Re-examination of the thermal oxidation reactions of polymers 2. Thermal oxidation of polyethylene. Polym Degrad Stab 2002;76(2):329-40. [30] Gugumus F. Re-examination of the thermal oxidation reactions of polymers 3. Various reactions in polyethylene and polypropylene. Polym Degrad Stab 2002;77(1):147-55. [31] S.W. Benson, Thermochemical Kinetics, S. 114, Wiley, New York, 1976. [32] Zaragoza D.F. Organic Synthesis on Solid Phase, Wiley, New York, 2000. [33] Xie W, Gao ZM, Pan WP, Hunter D, Singh A, Vaia R., Chem Mater 2001;13:2980. [34] Yablokov VA. Russ Chem Rev 1980;49:833–42. [35] Plesnicar B. In: Patai S, editor. The chemistry of functional groups, peroxides. New York: John Wiley; 1983. p. 521–84. [36] Bugajny M, Bourbigot S, Bras ML, Delobel R. Polym Int 1999; 48:264. [37] Xie RC, Qu BJ, Hu KL. Polym Degrad Stab 2001;72:313. [38] Serratosa J.M., Bradlay W.F., J. Phys. Chem. 62, 1164, 1958 [39] Zanetti M, Bracco P, Costa L. Polym Degrad Stab 2004;85:657. [40] Morlat S, Mailhot B, Gonzalez D, Gardette J. Chem Mater 2004;16:377. [41] S.M .Desai, J.K. Pandey and R.P.Singh, Macromol Symp, 169 (2001), p.121.


Chapter 2

MODIFICATION OF CATALYTIC ACTIVITY OF COMPLEXES OF ACETYLACETONATES FE(II,III) WITH QUATERNARY AMMONIUM SALTS IN THE ETHYLBENZENE OXIDATION WITH MOLECULAR O2 IN THE PRESENCE OF SMALL AMOUNTS OF H2O L. I. Matienko*, L. A. Mosolova Emanuel Institute of Biochemical Physics, Russian Academy of Sciences, 4 Kosygin str., Moscow, 119991 Russia

ABSTRACT The catalytic effects of small amounts of H2O (~10-3 mol/l), introduced in the ethylbenzene oxidation with molecular O2, catalyzed with {Fe(III)(acac)3 + R4NBr} systems, where R4NBr = exo ligands-modifiers, quaternary ammonium salts CTAB, (С2H5)4NBr, Me4NBr, were discovered by us. The synergetic effects of increase in the selectivity (SPEH) and the conversion degree (C) (parameter S·C) of ethylbenzene oxidation with molecular O2 into α-phenylethylhydroperoxide (PEH) were obtained in the case of the ethylbenzene oxidation, catalyzed with {Fe(III)(acac)3 + CTAB+ H2O} system. The proposed “dioxygenase-like” mechanism of the iron catalyst transformation into new catalytic particles in the course of oxidation process in the presence {Fe(III)(acac)3 + R4NBr} and activating additives of the water is discussed. The method of evaluation of the activity of formed complexes (Fe(II)(acac)2)x·(R4NBr)y (H2O)n in the micro stages of the catalytic chain-radical ethylbenzene oxidations is offered.

Keywords: oxidation, ethylbenzene, α-phenylethylhydroperoxide, homogeneous catalysis, dioxygen, iron (III) tris(acetylacetonate), quaternary ammonium salts, trace amount of H2O. *

E-mail:[email protected]

34

L. I. Matienko and L. A. Mosolova

1. INTRODUCTION The selective oxidation of hydrocarbons into hydroperoxides, primary products of oxidation is the most difficult problem because of the high catalytic activity of the majority of applied catalysts in ROOH decomposition. At the same time, the problem of selective oxidation of alkylarens (ethylbenzene and cumene) with molecular O2 in ROOH, is of current importance from the practical point of view in connection with ROOH use in large-tonnage productions such as production of propylene oxide and styrene (α-phenylethylhydroperoxide, PEH), or phenol and acetone (cumyl hydroperoxide) [1]. In recent decades the interest to fermentative catalysis and investigation of possibility of modeling of biological systems able to carry out selective introduction of oxygen atoms by C−H bond of organic molecules (mono- and dioxygenase) is grown [2,3]. Unfortunately, dioxygenase capable of to realize chemical reactions of alkanes dioxygenation are unknown [2]. The method of modifying of homogeneous catalysts by additives of different electrondonor ligands for increase in the rate, selectivity and conversion degree of alkylarens (ethylbenzene and cumene) oxidations with molecular O2 in corresponding ROOH was proposed by us [4]. The mechanism of control of Ni(II)(L1)2 (L1=(acac)-) complexes catalytic activity by additives of electron-donor monodentate ligands L2 (L2=HMPA, DMF, MP (Nmethyl pyrrolidone-2), MSt (M=Li, Na, K)) was established on the example of ethylbenzene oxidation. The probable mechanisms of catalysis with iron complexes Fe(II,III)(acac)n, activated with L2 (L2= DMF, R4NBr) were offered. On the basis of the established (Ni) and probable (Fe) mechanisms of the catalysis the methods of control of catalytic ethylbenzene oxidation into PEH including of the use of additives of crown-ethers and ammonium quaternary salts as ligands-modifiers were proposed by us. As result the more active catalytic systems were constructed and so the mechanism of the selective catalysis was confirmed. The values of selectivity, conversion degree and ROOH yield reached at the catalysis by {Ni(II)(L1)2+L2} (L2= Me4NBr, 18C6 (18-crown-6)) exceed analogous parameters in the presence of {Ni(II)(L1)2+L2 (L2=monodentate ligand HMPA, DMF, MP (N-methyl pyrrolidone-2), MSt (M=Li, Na, K))} and known catalysts of ethylbenzene oxidation into PEH (homogenous and heterogonous) [5-7]. The relatively low efficiency of Fe(III)(acac)3 and {Fe(III)(acac)3+L2} systems (as a selective catalysts for ethylbenzene oxidation to PEH) as compared to the efficiency of Ni(II) complexes is due to the simultaneous formation of PEH, methylphenylcarbinol (MPC), acetophenone (AP) and the high rates of accumulation of MPC and AP as the principle products. We established that mechanism of the formation of the selective nickel(II) catalyst responsible for the rise in the selectivity SREH in the process of the ethylbenzene oxidation, consisted in the oxygenation of Ni(II)(L1)2·(L2)n complexes with molecular O2. Coordination of electron-donor extra-ligand L2 by nickel complex Ni(L1)2 (L1=acac-) promoting stabilization of intermediate zwitter-ion L2(L1M(L1)+O2⎯ leads to increase of possibility of regio-selective connection of O2 to the γ-C atom of acetylacetonate ligand, activated in complex with nickel (II) ion. Further introduction of O2 into chelate cycle accompanying by proton transfer and bonds redistribution in formed transition complex (Griegee rearrangement) leads to break of cycle configuration with formation of (OAc)⎯ ion, acetaldehyde, elimination of CO, completing by the formation of catalytic particles with

Modification of Catalytic Activity of Complexes of Acetylacetonates Fe(II,III) ...

35

mixed ligands of general formula Ni(II)x(acac)y(OAc)z(L2) (L1ox= MeCOO--) (“A”) [4,7]. Similar change in complexes' ligand environment was observed in reactions, catalyzed with the only known to date a Ni(II)-containing dioxygenase – acireductone dioxygenase, ARD [8], and in reactions of oxygenation simulating the action of quercetin 2,3-dioxygenase (Cu, Fe) [9, 10]. The proposed mechanism of transformation of (Fe(II)(acac)2)x (L2)y complexes formed in the initial stages of the ethylbenzene oxidation catalyzed with {Fe(III)(acac)3 + L2(DMF, R4NBr)} into active selective catalytic species consists in dioxygenation of acetylacetonate ligand. By analogy to the dioxygenation of nickel (II) complexes a regioselective addition of O2 to the γ-C atom of acetylacetonate ligand (controlled by L2 ligand) with the intermediate formation of zwitterions L2(L1ML1+O2⎯) takes place obviously also in this case [11]. However due to the favorable combination of the electronic and steric factors appeared at inner and outer sphere coordination (hydrogen bonding) of R4NBr or DMF with Fe(II)(acac)2 the oxidative degradation of the acetylacetonate ligand may follow another mechanism. Insertion of O2 into C−C bond (not the C=C bond as takes place for nickel(II) complexes) via 1,2dioxetane intermediate can lead to the formation of methylglyoxal as the second destruction product in addition to the (OAc)⎯ ion (by analogy with the action of Fe(II) containing acetylacetone dioxygenase (Dke 1) (Scheme 1) [12]. As in the case of catalysis by Ni(II) complexes an increase in the selectivity of (Fe(II)(acac)2)m (L2)n (L2=R4NBr, DMF) – catalyzed ethylbenzene oxidation to hydroperoxide is presumably due to the formation of a mixed-ligand complex as a dioxygenation intermediate M(II)x(acac)y(OAc)z(L2)n (M = Fe(II), complex “B”), and the final oxygenation product, Fe(II) acetate, is responsible for the decrease in selectivity [11,13]. We considered the possibility of the positive effect of small amounts of water on the rate of the transformation of iron complexes with R4NBr and probably on the parameters SPEH and C in the ethylbenzene oxidation, catalyzed {Fe(III)(acac)3 + R4NBr}. Outer sphere coordination of H2O molecules may promote the stabilization of intermediate zwitterions L2(L1ML1+O2⎯) and as a consequence the increase in the probability of the regioselective addition of O2 to nucleophilic γ-C аtom of (acac)⎯ ligand can be expected [14]. It is wellknown that the stability of zwitterions increases in the presence of the polar solvents [14]. The H – bond formation between H2O molecule and zwitterion may also promote the proton transfer inside of the zwitterion followed by the zwitterion conversion into the products via Scheme 1 [15]. It is known the cases of the increase in the ratio of alkylation’s products on γC atom of the R4N(acac) in the presence of insignificant additives of water (∼10-3 моль/л) as compared to the alkylation’s reaction in the non proton solvents [16]. Few examples are known to date about the influence of small additives of H2O (~10-3 mol/l) on the homogeneous catalysis by transition metal complexes in the hydrocarbon oxidation with molecular O2. The role of H2O as a ligand in metal complex-catalyzed oxidation has not been practically investigated [15,17,18]. And it is unknown examples of catalytic reactions, when addition of water in small amounts enhances the reaction rate and the product yield. Some of known facts are concerned of the use of onium salts QX together with metal catalyst. So the decrease in the rate of the tetralin oxidation, catalyzed with oniumdecavanadate(V) ion-pair complexes in the presense of ~10-3 mol/l H2O was observed[19]. The oxidations are dependent on structural changes in the inverse micelles, in response to concentration changes of ion-pair complexes existing only in the presence of small amounts


36

of H2O [20]. The most known facts are connected with the influence of small concentrations of H2O on the catalysis of the ROOH homolysis by onium salts (including quaternary ammonium salts). The acceleration of ROOH homolysis may be the consequence of H – bond formation between ROOH, H2O and QX [21]. Also it is important to understand the role of small amounts of water because some water is always formed during the catalytic oxidation of the hydrocarbon. The homogeneity of the hydrocarbon solution remains upon addition of small amounts H2O ([H2O] ∼ 10-3 моль/л) [20].

2. EXPERIMENTAL Ethylbenzene (RH) oxidation was studied at 80°C in glass bubbling-type reactor in the presence of Fe(III)(acac)3(5·10--3 mol/l) and additives of R4NBr(5·10-4 mol/l) (R4NBr = (С2H5)4NBr, Me4NBr, CTAB). The selectivity SPEH and RH conversion degree C of ethylbenzene into PEH oxidation were determined using the formulas: SPEH = [PEH] / Δ[RH]·100% and C = Δ[RH] / [RH]0·100%. H

3

C H

C O

3

O

Fe O H

3

+

H

O

O

O

C

C H H

3

3

H

C

3

C O

O

O O Fe

O H

3

C

C H

3

H

O C H

3

O O

O

H

+

3

C

Fe H

3

O

O

C

O

+

O

O

C H

O O

O

+

Fe H

3

C

3

O

O

C H

3

H

3

C O

Scheme 1. The principle scheme of dioxygen-dependent conversion of 2,4-pentandione catalyzed by acetyl acetone dioxygenase Fe(II).


37

Analysis of Oxidation Products α-Phenylethylhydroperoxide was analyzed by iodometry. By-products, including methylphenylcarbinol (MPC) acetophenone (AP), and phenol (PhOH), as well as the RH content in the process were examined by GLC [11,22]. The overall rate of the process was determined from the rate of accumulation of all oxidation products. A correlation between RH consumption and product accumulation was established: Δ[RH] = [PEH] + [P] + [PhOH], where P = AP + MPC. The reaction rates were determined with accuracy of ± 0.5 - 5% [11,22]. The catalytic ethylbenzene oxidation with dioxygen was carried out in the O2 – solution two phase systems under kinetic control. The order in which PEH, AP, and MPC formed was determined from the time dependence of product accumulation rate rations at t → 0. The variation of these rations with time was evaluated by graphic differentiation [11,22].

3. RESULTS AND DISCUSSION Previously we established the interesting fact – the catalytic effect of small concentrations of quaternary ammonium salts, [R4NBr] = 5·10-4 mol/l, which in 10 times less than initial catalyst concentration [Fe(III)(acac)3] (synergetic effects of the grow in the parameters – the rate w0, selectivity SPEHmax, conversion degree C (parameter S·C) in the ethylbenzene oxidation, catalyzed with {Fe(III)(acac)3 + R4NBr} [13]. It was established also that the small amounts of CTAB (5·10-4 mol/l) did not form micelles in the ethylbenzene oxidation, catalyzed with {Fe(III)(acac)3 + CTAB} (800 C) [13]. But there are known the facts of the increase in the rate of the ROOH decomposition in the hydrocarbon solvents, catalyzed by the transition metal compounds, in the presence of CTAB due to including of the metal compound and ROOH in micelles of CTAB [23]. So in this article kinetic studies were carried with additives of H2O into the ethylbenzene oxidation, catalyzed with {Fe(III)(acac)3(5·10-4 mol/l)+ R4NBr(5·10-4 mol/l)} (R4NBr = CTAB, and also R4NBr = (С2H5)4NBr, Me4NBr, 800 C). On the addition of 3,7·10-3 mol/l H2O into the ethylbenzene oxidation, catalyzed with Fe(III)(acac)3 and R4NBr (R4NBr = (С2H5)4NBr, Me4NBr) the effectivity of catalytic systems, estimated by the values of parameters SPEHmax (and S·C) decreases (Figure 1, a-c). In the case of catalysis by system {Fe(III)(acac)3 + (С2H5)4NBr + H2O} the decrease in SPEH took place due to the decrease in the PEH concentration. The contents of PhOH, MPC and AP are changing insignificantly (Figure 1, a,b). At the admixed H2O to the ethylbenzene oxidation, catalyzed with {Fe(III)(acac)3 + Me4NBr} the PEH kinetic unchanged in fact. At the same time the increase in concentrations of [AP] and [MPC] was observed (Figure 1, c). The all reactions to investigate proceed in autocatalytic mode due to the transition Fe(III) to Fe(II) [11,22]. The products were formed with auto acceleration period longer than in the case of the H2O additives – free process (Figure 1, a-c). The reaction rates (as well as in the absence of the H2O additives [22]) rapidly becomes equal to w = wlim = wmax (w0). Under these steady – state reaction conditions the changes in oxidation rates in the both


38

cases were due to the changes in PEH or P (AC+MPC) accumulations [11,22] (Figure 1, a-c; Table 1). The increase in w0 at catalysis by complexes (Fe(II)(acac)2)n(Me4NBr)m in the presence of the H2O is observed (as compared with catalysis by Fe(II)(acac)2, and catalysis by complexes (Fe(II)(acac)2)n(Me4NBr)m without H2O [13]). The rate w0 decreases insignificantly in the case of catalysis by (Fe(II)(acac)2)n((С2H5)4NBr)m and H2O additives (as compared with catalysis by complexes (Fe(II)(acac)2)n((С2H5)4NBr)m without H2O additives [13].

(a)

35 30

mol/l

2

3

[PEH].10 , [PhOH].10 ,

40

25 20 15 10 5 0 0

10

20

30

40

50

t, h

2

[АP], [МPC].10 , mol/l

(b) 45 40 35 30 25 20 15 10 5 0 0

10

20

30

t, h Figure 1. Continued on next page.

40

50


39

(c)

2

[АP], [МPC].10 , mol/l

100 90 80 70 60 50 40 30 20 10 0 0

20

40

t, h

(d) 70

SPEH, %

60 50 40 30 20 10 0

5

10

15

20

C, % Figure 1. a. Kinetic of PEH (◊-1,-2) and PhOH (∆-3,c-4) communication in the course of the ethylbenzene oxidation, catalyzed with of {Fe(III)(acac)3 + (C2H5)4NBr(5·10-4 mol/l)} (◊-1,∆-2) or {Fe(III)(acac)3 + (C2H5)4NBr(5·10-4 mol/l) + H2O} (-2,c-4). [H2O]=3,7·10-3 mol/l, 800C. b. Kinetic of AP (◊-1,-2) and MPC (∆-3,c-4) communication in the course of the ethylbenzene oxidation, catalyzed with of {Fe(III)(acac)3 + (C2H5)4NBr(5·10-4 mol/l)} (◊-1,∆-2) or {Fe(III)(acac)3 + (C2H5)4NBr(5·10-4 mol/l) + H2O} (-2,c-4). [H2O]=3.7·10-3 mol/l. 800C. c. Kinetic of AP (◊-1,-2) and MPC (∆-3,c-4) communication in the course of the ethylbenzene oxidation, catalyzed with of {Fe(III)(acac)3+Me4NBr (5·10-4 mol/l)} (◊-1,∆-3) or {Fe(III)(acac)3 + Me4NBr (5·10-4 mol/l) + H2O} (-2,c-4). [H2O]=3.7·10-3 mol/l. 800C. d Dependences SPEH от C in the reactions of the ethylbenzene oxidation in the presence systems {Fe(III)(acac)3 + R4NBr} (◊-1,∆-2) or { Fe(III)(acac)3 + R4NBr + H2O} (-3,c-4). R4NBr = Me4NBr (◊-1,-3), (C2H5)4NBr (∆-2,c-4). [Fe(III)(acac)3]=5·10-3 mol/l. [R4NBr (Me4NBr, (C2H5)4NBr)]=5·10-4 mol/l [H2O] = 3.7·10-3mol/l. 800C.


40

Table 1. The rates (mol·l-1·s-1) of PEH and P accumulations (P = {AC+MPC}) in the presence of systems {Fe(III)(acac)3 + R4NBr(L2)} without admixed H2O (L3) and at the addition of small amounts of H2O (3,7·10-3.mol/l) L2, L3 ⎯ (C2H5)4NBr (C2H5)4NBr + H2O Me4NBr Me4NBr + H2O CTAB CTAB + H2O

wPEH0· ·106 ⎯

wp0· ·106 ⎯

5.9 4.9

8.3 7.7

wPEH· ·106 2.90 (wPEH0=wPEH) 3.3 3.03

wp· ·106 3.40 (wP0=wP) 4.3 4.1

4.2 5.0

3.4 5.87

2.5 2.5

1.87 4.8

4.35 3.75

3.3 1.1

2.5 3.19

1.2 0.85

w0 – The initial rate of the products accumulation. w – The rate of the products accumulation in the course of the ethylbenzene oxidation. [Fe(III)(acac)3]=5·10-3 mol/l. [R4NBr (Me4NBr, (C2H5)4NBr, CTAB )]=5·10-4 mol/l. 800C.

S·C·10-2 (%,%) 8

6,91

7 6

5,46

4,97

5

3,43

4

2,9

3 2

1,14

1

TA

B

+

H

2O

C TA B C

N

Br +

H 2O

Br M e4

M e4 N

(C

2H

(C

5) 4N

2H

Br

+

H

5) 4N

2O

Br

0

Figure 2. Parameter S·C·10-2 (%,%) in the ethylbenzene oxidation at catalysis by Fe(III)(acac)3 and catalytic systems {Fe(III)(acac)3+R4NBr} and {Fe(III)(acac)3+R4NBr+H2O}. [Fe(III)(acac)3]=5·10-3 mol/l, [R4NBr]=0.5·10-3 mol/l, 80°C.


41

These are unusual results as compared with known facts of inhibiting effects of water, formed in the oxidation process in the absence of Cat, on the hydrocarbon oxidation rates owing to solvatation of RO2• radicals by H2O molecules [24], deactivation of Cat with water in the processes of chain-radical hydrocarbon oxidation by O2 in no polar medium [25]. The dependence of SPEH on the C in the discussed ethylbenzene oxidation, catalyzed with iron complexes in the presence of small amounts of H2O has extremum as well in the absence of H2O additives. The decrease in values of SPEHmax was observed. Thus, SPEHmax ≈ 43% ({Fe(III)(acac)3 + (C2H5)4NBr + H2O}) < SPEHmax = 48% (at the catalysis with {Fe(III)(acac)3 + (C2H5)4NBr (5·10-4 М)} in the absence of H2O) and SPEHmax ≈ 43% ({Fe(III)(acac)3 + Me4NBr + H2O}) < SPEHmax = 64% ({Fe(III)(acac)3 + Me4NBr}) (Figure 4). The growth in SPEH from SPEH0 to SPEHmax was parallel to decrease in wPEH and wP as in the case of catalysis with systems in the absence of H2O additives (Figure 1 a-d, Table 1). The decreases in values of parameter S·C in the ethylbenzene oxidation, catalyzed with catalytic systems {Fe(III)(acac)3 + (C2H5)4NBr(Me4NBr)} (◊, ∆) or {Fe(III)(acac)3 + (C2H5)4NBr(Me4NBr) + H2O}, the most significant at R4NBr = Me4NBr, are presented on the Figure 5. At the catalysis by Fe(III)(acac)3 without L2, L3, the value of S·C = 2.1(·10-2 (%,%) (Figure 3) [22]. The performance of catalysis with iron complexes was compared in terms of the parameter S·C. In this case we assumed: S was averaged selectivity characterizing change of S in the course of oxidation from S0 at the beginning of the reaction to some Slim, selected as a standard for the series of catalyst systems to be matched in efficiency, C was the conversion degree for which SPEH ≤ Slim (80°С). Slim was assumed to be 40%. This value of S approximately corresponds to the selectivity of the ethylbenzene oxidation in the presence of exo ligand – free Fe(III)(acac)3 (5·10-3 mol/l, 800C) under the steady – state reaction conditions (at the catalysis with Fe(II)(acac)2, formed in the process) [11,13,22]. The changes in parameters SPEH, C (S·C), and w0 and w observed in the reactions catalyzed by Fe(III)(acac)3 in the presence of R4NBr and H2O additives, and also obtained kinetics of catalytic ethylbenzene oxidation are evidently caused with the formation of catalytic active complexes of (Fe(II)(acac)2)x(R4NBr)y(H2O)n and products of their transformation in the course of ethylbenzene oxidation. [11,13]. The decrease in SPEHmax (S·C) is assumed due to the increase in the rates of the oxygenation of intermediate products of the (Fe(II)(acac)2)x(R4NBr)y(H2O)n transformation to the end products as a consequence of coordination of H2O molecules with iron complexes. As result, the decrease in steady-state concentrations of selective catalysts Fe(II)x(acac)y(OAc)z(L2)n(H2O)m, took place. Unlike the catalytic ethylbenzene oxidation, presented above, addition of 3.7·10-3 mol/l H2O into the ethylbenzene oxidation, catalyzed with {Fe(III)(acac)3 + CTAB}, results in the increase in parameters SPEHmax and S·C (Figure 2, 3). At the beginning of the reaction (C < 1%) SPEH = 85.4%. Then with the grow in C the selectivity falls to SPEH =70.3% (the catalysis with Fe(II) complexes, formed in the process [22]). After that at C > 1% the dependences SPEH от C has extremum as in the absence of H2O additives (probably as a consequence of the catalysis with products of Fe(II) complexes dioxygenation). At that SPEHmax = 78.2%, and this value is significantly higher than SPEHmax = 65% in the case of the H2O additives – free process. The increase in C (∆C) is observed. ∆C ≈ 8% as compared to catalysis by Fe(II)(acac)2 or is ∆C ≈ 4% as compared to catalysis by complexes (Fe(II)(acac)2)p·(CTAB)q (Figure 3).


42

95 85

SPEH, %

75 65 55 45 35 25 0

5

10

C, % * The value of Clim at SPEH=40% was estimated by the extrapolation. Figure 3. Dependences SPEH от C in the ethylbenzene oxidation in the presence Fe(III)(acac)3 (∆-1) and systems {Fe(III)(acac)3 + CTAB} (◊-2) and {Fe(III)(acac)3 + CTAB + H2O} (-3)*. 800C.

In this case the increase in SPEHmax at the H2O additives is due to the increase in PEH concentration (from [PEH]max= 0,33 mol/l to [PEH]max = 0,4 mol/l, the rate of PEH accumulation wPEH in the process (in the presence of H2O) > wPEH in the process (in the absence of H2O)). The Decreases in AP and MPC concentration and in the (AP + MPC) accumulation rate wАP+МPC in the course of the ethylbenzene oxidation as compared with the H2O additives – free process took place (Figure 4, Table 1). Unlike the catalysis by {Fe(III)(acac)3+R4NBr} (R4NBr=Me4NBr, (C2H5)4NBr) the significant fall in initial rate of principal products {P=AP+MPC} formation, w0АP+МPC, (in ∼ 3 times) was observed (compare Figure 4 and Figure 1,a-b, and also data in Tables 1, 2). The initial rate of PEH accumulation wPEH0 decreased insignificantly. In the ethylbenzene oxidation in the presence of {Fe(III)(acac)3+CTAB(5·10-4 mol/l)} system without H2O the grow in the rate of PEH accumulation wPEH0 took place (in ∼ 1.5 times) as compared to catalysis with Fe(II)(acac)2, but the rate of P accumulation w0АP+МPC is unchanged in fact (Table 1). In the oxidation in the presence of {Fe(III)(acac)3 + CTAB(5·10-4 mol/l) + H2O (3.7·10-3 mol/l)} system the PhOH as oxidation product was not found right up to 50 hours of the ethylbenzene oxidation. This fact may be explained by the significant decrease in the activity of formed catalyst in the heterolytic decomposition of PEH with formation of phenol (PhOH) and acetaldehyde and by the inhibition of the rate of particles formation (Fe(OAc)2), responsible for PEH heterolysis [4,11,13,22].


43

(a)

[PEH].10 , [PhOH].10 , mol/l

50

3

40 30

2

20 10 0 0

10 20 30 40 50 60

t, ч

10 8

2

[АP], [MPC].10 , mol/l

(b)

6 4 2 0 0 10 20 30 40 50

t, h Figure 4. a. Kinetics of PEH (◊-1,-2) and PhOH (∆-1) communication in the course of the ethylbenzene oxidation, catalyzed with {Fe(III)(acac)3 + CTAB(5·10-4 mol/l)} (◊,∆) or {Fe(III)(acac)3 + CTAB(5·10-4 mol/l) + H2O} (). [H2O]=3.7·10-3 mol/l. 800C. b. Kinetics of AP (◊-1,-2) and MPC (∆-3,c-4) accumulation in the course of the ethylbenzene oxidation, catalyzed in the presence of {Fe(III)(acac)3+ CTAB (5·10-4 mol/l)} (◊,∆) or {Fe(III)(acac)3 + CTAB (5·10-4 mol/l) + H2O} (,c). [H2O]=3.7·10-3 mol/l. 800C.

The rise in SPEHmax in the course of ethylbenzene oxidation in the presence of {Fe(III)(acac)3 + CTAB(5·10-4 mol/l) + H2O (3.7·10-3 mol/l)} is accompanied by the decrease in the value w of oxidation rate as compared with the value w0 in the initial stage of oxidation process mainly due to decrease in wАP+МPC (Table1,2). These changes in kinetics of {AP + MPC} accumulations and hindering of the heterolytic of PEH decomposition point to the


44

transformation of complexes (Fe(II)(acac)2)x·(CTAB)y·(H2O)n, into new active selective catalysts (Scheme 1). We established that at the addition of 3.7·10-3 mol/l H2O into the ethylbenzene oxidation, catalyzed with {Fe(III)(acac)3+ CTAB} (and {Fe(III)(acac)3+ R4NBr(Me4NBr, (C2H5)4NBr)} also) the mechanism of products formation is obviously unchanged. As in the absence of H2O the products AP and MPC formed parallel to PEH formation, at parallel stages of chain propagation and chain quadratic termination, AP and MPC formed in parallel stages also (wP/wPEH ≠ 0 at t → 0, wAP/wMPC ≠ 0 at t → 0 (here P= AP or MPC)) [11,22]. The heterolysis of PEH was not observed. These data differed from known facts of catalysis with CTAB and systems, including CTAB and transition metal complexes, consisting in the acceleration of PEH decomposition in the micelles of CTAB [23]. Thus the significant rise in the of value of SPEHmax from 40% (the catalysis with {Fe(III)(acac)3) to SPEHmax ≈ 78.2% at the catalysis with {Fe(III)(acac)3+ CTAB+ H2O (~ 10-3 mol/l)} in the ethylbenzene oxidation may be achieved. The significant increase in SPEHmax, in C, (parameter S·C) (unlike the catalysis with {Fe(III)(acac)3+R4NBr(Me4NBr, (C2H5)4NBr)+H2O} systems) may be connected in this case with the increase in the life time of active selective heteroligand complexes of probable structure Fe(II)x(acac)y(OAc)z(R4NBr)n(H2O)m (“B”), formed perhaps according to Scheme 1. The outspherical coordination of CTAB, may create sterical hindrances from H2O coordination and regio-selective oxidation of (acac)- − ligand by the described earlier mechanism, and the rate of intermediate complex “B” oxygenation to inactive final product Fe(OAc)2 reduced. Besides that the part of H2O molecules may be absorbed by hydrophilic cation nC16H33Me3N+, and as a result the lowering of the rate of the intermediate heteroligand complex “B” conversion to the end products was realized.

4. PARTICIPATION OF CATALYSTS ACTIVE FORMS IN ELEMENTARY

STAGES OF RADICAL-CHAIN ETHYLBENZENE OXIDATION CATALYZED BY {FE(II,III)(ACAC)N+R4NBR} Previously we suggested the method for estimation of catalytic activity of complexes (Fe(II)(acac)2)x(R4NBr)y at the micro stages of radical-chain ethylbenzene oxidation by simplified scheme assuming quadratic termination of chain and equality to zero of rate of homolytic decomposition of ROOH [4,7,11,13,22]. We found that at the catalysis Fe(II,III)(acac)n ([Cat]=(0.5-5)·10-3 mol/l)) products MPC and AP were formed parallel to PEH, at stages of chain propagation Cat + RO2•→ and quadratic termination of chain 2RO2•→, and Cat was inactive in the reaction of PEH homolysis [22]. In the framework of radical-chain mechanism the chain termination rate in this case will be (1):

wterm=k6[RO2•]2=k6

⎧ w PEH ⎫ ⎨ ⎬ ⎩k 2 [RH]⎭

2

(1)


45

where wPEH − rate of PEH accumulation, k6 − constant of reaction rate of quadratic chain termination (k6=1.9 107 mol-1 s-1); k2 − constant of rate of chain propagation reaction (RO2• + RH) → (k2=5.72 l mol-1 s-1 (800C) [22]). The hydrocarbon consumption was taken into account in the calculations (the initial concentration of the ethylbenzene [RH]0 = 8.2 mol/l) Actually, we found that w0 (wlim, iron(II) complexes) ~ [Cat]1/2, and wi0 ~ [Cat], and linear radicals termination on catalyst may be not taken into account [22]. With allowance for quasisteady-state conditions for RO2• radicals the calculated by formula (1) wterm.= wi can be considered a measure of activation of molecular oxygen with iron(II) complexes. Discrepancy between wAP+MPC and wterm in the case of absence of linear termination of chain is connected with additional formation of alcohol and ketone at the stage of chain propagation Cat + RO2•→ (2): wpr.= wAP+MPC – wterm

(2)

The direct proportional dependence of wpr0 on [Cat] testifies in favor of iron(II) complexes participation at stage of chain propagation Cat + RO2•→. The conditions w0~[Cat]1/2 and wi0~[Cat] are supposed to be fulfill also in the presence of R4NBr additives. The values of wi0 (O2 activation) and wpr0 (Cat + RO2•→) were estimated [22]. The chain initiation in the ethylbenzene oxidation with dioxygen in the presence of Fe(III)(acac)3 or {Fe(III)(acac)3+ R4NBr} can be represented by the following reaction [13,22]: Fe(III)(acac)3 ((Fe(III)(acac)2)m·(R4NBr)n)+ RH → → Fe(II)(acac)2 ((Fe(II)(acac)2)x·(R4NBr)y) … Hacac + R•

(I)

The reaction (I) and interaction of the resulting Fe(II) complex with dioxygen appear to be responsible for chain initiation in the ethylbenzene oxidation, catalyzed by Fe(III)(acac)3 or {Fe(III)(acac)3+ + R4NBr}. The schemes of radical-chain oxidation including reaction of Cat with RO2•-radicals with intermediate formation peroxo-complexes [LM-OOR] [26-29] and further homolytic decomposition of peroxo-complexes ([LM-OOR]→R′C=O (ROH) + R•) (cage “latent radical” mechanism) may explain parallel formation of alcohol and ketone under ethylbenzene oxidation in the presence of M(L1)n (L1 = acac-) and their complexes with R4NBr (wpr0 (Cat + RO2•→)). As mentioned above the mechanism of the ethylbenzene oxidation catalyzed with {Fe(III)(acac)3+ R4NBr} is obviously unchanged at the addition of 3.7·10-3 mol/l H2O. So we proposed that catalysis by complexes (Fe(II)(acac)2)x·(R4NBr)y (H2O)n satisfied the conditions w0~[Cat]1/2 and wi0~[Cat] that allowed wi0 and wpr0 to be calculated by Eqs. (1) and (2) and the catalytic activity of complexes (Fe(II)(acac)2)x·(R4NBr)y (H2O)n at the micro stages of chain initiation (activation of O2, wi0) and chain propagation (Cat + RO2•→, wpr0) can be evaluated. Calculated rates of chain initiation (wi0), chain propagation (wpr0) and (wi0/wpr0)·100%. [Fe(III)(acac)3]=5·10-3 mol/l. [L2] = 0.5·10-3 mol/l). 800 C.


46

As follows from the data in Table 2 the growth in SPEH0 at the catalysis by complexes Fe(II)(acac)2)x·(CTAB)y (H2O)n is connected mainly with the considerable fall in the value of wpr0 ~ 3.2 times. The value of wi0 decreases by a factor of ~ 1.3. At that the rate of {AP+MPC} accumulation wp0 decreases ~ 3 times, and wPEH0 decreases only by a factor of ~ 1.26. The decrease in the rate of chain propagation wpr0 at the catalysis by complexes Fe(II)(acac)2)x·(CTAB)y (H2O)n seems to be caused by unfavorable steric factors for the RO2• coordination with metal centre appeared in this case. The value of SPEHmax ≈ 78.2% in the process is caused with the transformation of (Fe(II)(acac)2)x·(CTAB)y nH2O in the course of the ethylbenzene oxidation. At the catalysis with complexes Fe(II)(acac)2)x·(CTAB)y (H2O)n the growth in ratio wi0/ wpr0 to a grate extent (by a factor of ~ 2.35 as compared with Fe(II)(acac)2)x·(CTAB)y) was received. In the case of the use of the other R4NBr as ligand-modifier L2 the decrease in parameter wi0/ wpr0 was observed at the H2O addition :~ 1.4 times (L2 = (C2H5)4NBr (mainly in consequence of the decrease in wi0~ 1.5 times)); ~ 1.22 times (L2 = Me4NBr (mainly in consequence of the increase in wpr0~ 1.7 times (wi0 increases ~ 1.4 times))) as compared with catalysis by systems without admixed H2O. The observed insignificant decrease in wi0 (CTAB or (C2H5)4NBr) was assumed to be caused with the outer sphere H2O coordination with acetylacetonate ligand and the structure of the formed complex Fe(II)(acac)2)x·(R4NBr)y nH2O, the steric factors created the hindrance from the O2 coordination with metal centre. At that the possibility of formation of O2-complexes, active in chain-radical oxidation would decrease [30-32]. The rise in wi0 (Me4NBr) may be explained by more stable coordination of Me4NBr with acetylacetonate ligand of Fe(II)(acac)2 as compared with CTAB or (C2H5)4NBr [6]. The role of H2O may be consist in the stabilization of active (L2)δ+Fe(II)(L1)2·O2δ⎯ in consequence of H – bonding [32]. Table 2. The initial rates (mol l-1 s-1) of PEH (wPEH0) and P(AC+MPC) (wp0) accumulations at the catalysis with Fe(III)(acac)3, with systems {Fe(III)(acac)3 + R4NBr(L2)} without admixed H2O (L3) and at the addition of small amounts of H2O (3,7·10-3.mol/l). w0 – The initial rate of {PEH+P} accumulation L2, L3 ⎯ (C2H5)4NBr (C2H5)4NBr +H2O Me4NBr Me4NBr +H2O CTAB CTAB +H2O

wPEH0· ·106 2,90 5,90 4,90

wp0 · ·106 3,40 8,30 7,70

w0 · ·106 6,30 14,20 12,60

wi0· ·107 0,79 3,00 2,07

wpr0· ·106 3,32 8,00 7,50

(wi0/ wpr0) 100% 2,38 3,75 2,66

4,20

3,40

7,60

1,52

3,25

4,67

5,00

5,87

10,87

2,16

5,65

3,82

4,35 3,75

3,30 1,10

7,65 4,85

1.63 1,21

3,14 0,98

5,19 12,24


47

As seen from the data presented in Table 2, the reaction of the chain propagation (Cat + RO2•→) is evidently the principal reaction of the AP and MPC formation in the ethylbenzene oxidation in the presence of systems {Fe(III)(acac)3 + L2 + H2O}. It took place also in the cases of use of composition of {Fe(III)(acac)3 + L2} or only Fe(III)(acac)3. The contribution of the reaction of chain quadratic termination in the mechanism of AP and MPC formation is inessential.

5. CONCLUSION Thus we first established the increase in catalytic activity of system on basis of transition metal complex and donor ligand-modifier, namely, system {Fe(III)(acac)3 + CTAB}, as catalyst of the ethylbenzene oxidation to PEH at the addition of small amounts of H2O (~10-3 mol/l). It was found that the admixtures of H2O caused a no additive (synergistic) effects of growth in selectivity SPEHmax, conversion degree C (SPEHmax ≈ 78.2%, C ≈ 12%) (parameter S·C), changes that were due to the formation of more active selective (Fe(II)(acac)2)x·(CTAB)y (H2O)n complexes, and products of (Fe(II)(acac)2)x·(CTAB)y (H2O)n transformation [33]. ∆SPEHmax ≈ 14% and ∆C ≈ 4%, as compared with catalysis by {Fe(III)(acac)3 + CTAB} and ∆SPEHmax ≈ 40% and ∆C ≈ 8% as compared with catalysis by Fe(III)(acac)3. The additives of ~10-3 mol/l H2O decreased the activity of systems {Fe(III)(acac)3 + R4NBr} (R = Me или C2H5) as catalysts of the ethylbenzene oxidation to PEH that was expressed in the fall in the parameters SPEHmax and S·C. But the rise in w0 (wi0, wpr0) at the catalysis by complexes (Fe(II)(acac)2)x·(Me4NBr)y (H2O)n formed at the initial stages of the ethylbenzene oxidation was observed. The probable “dioxygenase-like” mechanism of the iron catalyst transformation in the presence H2O is offered. The discovered fact of increase in parameters SPEHmax, C (and S·C) at catalysts of the ethylbenzene oxidation by {Fe(III)(acac)3 + CTAB + H2O(~10-3 mol/l)} system may be result of the increase in stationary concentration of active selective heteroligand complexes of probable structure Fe(II)x(acac)y(OAc)z(CTAB)n(H2O)m, intermediate products of transformation of complexes (Fe(II)(acac)2)x·(CTAB)y (H2O)n in the course of the ethylbenzene oxidation. Upon the addition of 3.7·10-3 mol/l H2O into the ethylbenzene oxidation, catalyzed with {Fe(III)(acac)3 + R4NBr} (R4NBr = CTAB, Me4NBr, C2H5)4NBr) systems the mechanism of principal products acetophenone (AP) and methylphenylcarbinol (MPC) formation is unchanged. As in the absence of H2O, AP and MPC formed parallel to PEH formation, at parallel stages of chain propagation and chain quadratic termination, AP formed parallel to MPC also (wP/wPEH ≠ 0 at t → 0, wAP/wMPC ≠ 0 at t→ 0) in the course of all oxidation process. The system {Fe(III)(acac)3 + CTAB + H2O(~10-3 mol/l)} is inactive in heterolysis of PEH. It was found that the oxidation rate w0 and the hydroperoxide selectivity SPEH0 at the catalysis by complexes (Fe(II)(acac)2)x·(R4NBr)y (H2O)n formed at the initial stages of the ethylbenzene oxidation depend on the catalyst activity in micro stages of chain initiation (activation of O2) and chain propagation mediated by the catalyst (Cat + RO2•→). The growth in PEH selectivity at the catalysis by (Fe(II)(acac)2)x·(CTAB)y (H2O)n is connected mainly with the considerable fall in the rate of chain propagation wpr0 (Cat + RO2•→).

48


The ratio wi0/ wpr0 ≈ 2.66 – 12.24%, estimated for catalysis by (Fe(II) (acac)2)x·(R4NBr)y (H2O)n, indicates a significant role of the chain propagation (Cat + RO2•→) in the mechanism of catalysis by these complexes pertaining to the ethylbenzene oxidation with molecular oxygen. At the same time the rate of chain initiation at catalysis by (Fe(II)(acac)2)x·(R4NBr)y (H2O)n is higher than in the reaction catalyzed by Fe(II)(acac)2 and much higher than in the no catalytic reaction (wi0 ≈ 10-9 mol l-1 s-1 [7]).

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[20] Csanyi L.J., Jaky K., Dombi G., e.a. // J. Mol. Catal. A: Chem., V.195, P.109-124, 2003. [21] Csanyi L.J., Jaky K., Palinko I., e.a. // Phys. Chem. Chem. Phys., N 2, P.3801-3805, 2000. [22] Matienko L.I., Mosolova L.A. // Kinetika i kataliz.. V.46, N 3, PP.354–359, 2005. [23] Maksiмоvа Т.V., Sirota Т.V., Koverzanova Е.V., Kasaikina O.T. // Neftekhimiya. V. 41. N 5. PP. 289-293, 2001. [24] Emanuel N.M., Zaikov G.E., Maizus Z.K. The role of medium in radical-chain reactions of organic compounds oxidation. // M: Nauka, 1973, 279 P. [25] Partenheimer W. // Catalysis Today, V.23, PP.69–158, 1991. [26] Semenchenko A.E., Solyanikov V.M., Denisov E.T. // Zh. Phiz. Khimii, V. 47, N 5, PP. 1148-1151, 1973. [27] Chavez F.A., Rowland J.M., Olmstead M.M., Mascharak P.K. // J. Am. Chem. Soc., V.120. N 35, PP.9015–9027, 1998. [28] Solomon-Rapaport E., Masarwa A., Cohen H., Meyerstein D. // Inorg. Chim. Acta, N 299, PP.41–46, 2000 [29] Krishnamurthy D., Kasper G.D., Namuswe F., Kerber W.D., e.a. // J. Am. Chem. Soc, V.128, N 44, PP.14222–14223, 2006. [30] Carter M.J., Rillema D.P., Basolo F. // J. Am. Chem. Soc., V. 96, N 2, PP. 392-400, 1974. [31] Martell A.E.. // Acc. Chem. Res, V.15, N 5, PP.155-162, 1982. [32] Stynes D.V., Stynes H.C., Ibers J.A, James B.R. // J. Am. Chem. Soc., V.95, N 4, PP.1142-1149, 1973. [33] Golodov V.A. // Ross. Khim. Zh., V. 44, N 3, PP. 45-57, 2000.


Chapter 3

MODELING THE KINETICS OF MOISTURE ADSORPTION BY WOOD DURING DRYING PROCESS A. Farjad, S. H.Rahrovan, and A. K. Haghi* Faculty of engineering, The University of Guilan Rasht 41635, P. O. Box 3756, Iran

ABSTRACT A mathematical model was developed for optimization of heat and mass transfer in capillary porous media during drying process to predict the drying constants. The modeling equations verified the experimental results and proved to be an important tool in predicting the drying rate under different drying conditions.

Keywords: Heat transfer, mass transfer, drying time, diffusion, moisture content, mathematical model

INTRODUCTION The importance of heat and mass transfer in capillary porous materials like wood has increased in the last few decades due to its wide industrial as well as research applications. In order to reduce moisture content in woods to a level low enough, to prevent undesirable biochemical reactions and microbiological growth, prolonged drying time and high temperature must often be used. In practice, several different techniques are used; natural drying, vacuum drying, convectional convective drying, high temperature convective drying, and more recently microwave drying [1]. Several physical mechanisms contribute to moisture migration during the process. For a porous solid matrix, with free water, bound water, vapor, and air, moisture transport through the matrix can be in the form of either diffusion or capillary flow driven by individual or

52

A. Farjad, S. H.Rahrovan and A. K. Haghi

combined effects of moisture, temperature and pressure gradients. The predominant mechanisms that control moisture transfer depend on the hygroscopic nature and properties of the materials, as well as the heating conditions and the way heat is supplied. In this regard, there is a need to assess the effects of the heat and mass transfer within the wood on the transfer in the fluid adjacent to it. There are three stages of drying: In the first stage when both surface and core MC are greater than the FSP. Moisture movement is by capillary flow. Drying rate is evaporation controlled. In the second stage when surface MC is less than the FSP and core MC is greater than the FSP. Drying is by capillary flow in the core and by bound water diffusion near the surface as fiber saturation line recedes into wood, resistance to drying increases. Drying rate is controlled by bound water diffusion and finally in the third stage when both surface and core MC is less than the FSP. Drying is entirely by diffusion. As the MC gradient between surface and core becomes less, resistance to drying increases and drying rate decreases. For wood, model developments have been based on either a mechanistic approach with the transfer phenomena derived from Fick’s and Fourier’s laws, or on the principles of thermodynamics and entropy production. These models may be divided into three categories: (a) diffusion models [2], (b) models based on transport properties [3,4] and (c) models based on both the transport properties and the physiological properties of wood related to drying [5,6]. Drying adds value to timber but also costs money. Working out the complete cost of drying is a complex process. Timber drying is a critical and costly part of timber processing. Comparing the cost and effectiveness of drying systems and technology is an important exercise, before drying systems are commissioned or are upgraded. Reduction in drying time and energy consumption offers the wood industries a great potential for economic benefit. But the reduction in drying time often results in an increase in drying related defects such as checks, splits and warp. In previous work drying curves were fitted to four drying models and the goodness of fit of each model (Correlation Coefficient and Standard Error) was evaluated [7]. The main aim of this work is to find out a model for drying time and to predict the required time for drying samples to desired moisture content. In the second part the forecast time is compared with the theoretical approach. The predicted values by the theoretical model are compared with experimental data taken under actual drying conditions to demonstrate the efficiency of the predictive model.

2. ANALYTICAL APPROACHES A software tool “Trend Analysis” for analysis the time series was applied. Trend analysis fits a general trend model to time series data and provides forecasts. S-curve is best fitted to our drying case. The S-curve model fits the Pearl-Reed logistic trend model. This accounts for the case where the series follows an S-shaped curve. The model is:

**

[email protected], http://www.guilan.ac.ir

Modeling the Kinetics of Moisture Adsorption

MC =

10 a b0 + b1b2t

53

(1)

This tool is useful when we have dried the wood to moisture content not near to 30% and then predict the time needed to dry it completely. Minitab computes three measures of accuracy of the fitted model: MAPE, MAD, and MSD for each of the simple forecasting and smoothing methods. For all three measures, the smaller the value, the better the fit of the model. These statistics are used to compare the fits of the different methods. Mean Absolute Deviation (MAD) measures the accuracy of fitted time series values. It expresses accuracy in the same units as the data, which helps conceptualize the amount of error: n

MAD =

∑y t =1

t

− yˆ t (2)

n

Where yt equals the actual value at time yˆ t equals the fitted value, and n equals the number of observations. Mean Absolute Percentage Error (MAPE) measures the accuracy of fitted time series values. It expresses accuracy as a percentage.

MAPE =

∑

( yt − yˆ t ) yt

× 100 ( yt ≠ 0)

n

(3)

Where yt equals the actual value at time yˆ t equals the fitted value, and n equals the number of observations. MSD stands for Mean Squared Deviation. MSD is always computed using the same denominator, n, regardless of the model, so we can compare MSD values across models. MSD is a more sensitive measure of an unusually large forecast error than MAD. n

MSD =

∑ t =1

2

yt − yˆ t n

(4)

Where yt equals the actual value, t equals the forecast value, and n equals the number of forecasts.


54

3. GOVERNING EQUATIONS Heat and mass transfer in a body take place simultaneously during the drying process. The time required to go from an initial moisture content, U 0 , to a certain value U is given in[8]: t=

(μ

1.6 × 10 −4 S x2 S y2 2 x1

D x S y2 + μ y21 D y S x2

)

⎛ ⎛ U 0 − U eq Log ⎜ Γx1 Γ y1 ⎜ ⎜ U −U ⎜ eq ⎝ ⎝

⎞⎞ ⎟⎟ ⎟⎟ ⎠⎠

(5)

μ l21 can be defined as: μ l21 =

1

(6)

4

1 + π 2 Bl

Where Bl is the dimensionless constant called the "bio-criterion "of the sample: Bl =

α l Rl

(7)

Dl

Where Rl is half of the length of the rod, l is any of the two coordinates x,y, S x × S y is the width and thickness of sample,

α l is the coefficient of moisture exchange(m/s), Dl is the

2

moisture diffusion coefficient( m /s) which can vary in each of the different directions for the wood sample. The value Γl1 is determined as:

2 Bl2 Γl1 = 2 2 μ l1 Bl + Bl + μ l21

(

)

(8)

and an average dimensionless moisture content E Σ is: EΣ =

U − U eq U 0 − U eq

U eq is the equilibrium moisture content of the wood. Another theoretical approach is presented by [9]:

(9)


t=

65S 2 ⎛ π 2 D ⎞ U 0 − U eq ⎟ log ⎜1 + 2αs ⎟⎠ U − U eq D10 6 ⎜⎝

55

(10)

Where D is the average diffusion coefficient and S is the average length of the dimensions of specimens.

4. EXPERIMENTAL DATA Experimental material was obtained from two types of wood species, Guilan spruce and pine. The wood specimens were selected from Guilan region which is located in the north of Iran. The experiments were performed in a programmable domestic microwave drying system (Deawoo, KOC-1B4k) with a maximum power output of 1000 W at 2450MHz. Samples were dried in four methods: convection drying (150°C), microwave drying (270 W), infrared drying (100% power) and combination of microwave and convection drying. The dryer was run without the sample placed in, for about 30 min to set the desired drying conditions before each drying experiment. Throughout the experimental run the sample weights were continuously recorded at predetermined time intervals until wood reached to 30% of its moisture content.

5. RESULTS AND DISCUSSION Figures 1-8 show the graphs moisture content variation against drying time, the model and the forecasted time for the four methods of drying on pine and Guilan spruce. Drying time is estimated to a moisture content of 14%. Results are relatively in a good agreement with drying curves. Just in some cases in heating up period this model didn’t fit the experimental data closely. Heat is transferred by convection from heated air to the product to raise the temperatures of both the solid and moisture that is present. Moisture transfer occurs as the moisture travels to the evaporative surface of the product and then into the circulating air as water vapor. The heat and moisture transfer rates are therefore related to the velocity and temperature of the circulating drying air. Moreover, the momentum transfer may take place simultaneously coupled with heat and moisture transfer. Convective drying at intermediate temperatures has proved to be very effective from the economical point of view, thanks to the short drying time, the reduced sizes of the kilns, and the better control of the energy consumption and the possibility of a good integration in the production line. Infrared energy is transferred from the heating element to the product surface without heating the surrounding air. When infrared radiation is used to heat or dry moist materials, the radiation impinges the exposed material, penetrates it and the energy of radiation converts into heat. Since the material is heated intensely, the temperature gradient in the material reduces within a short period the depth of penetration of radiation depends upon the property of the material and wavelength of radiation. Further by application of intermittent radiation, wherein the period of heating the material is followed by cooling, intense displacement of moisture from core towards surface can be achieved.


56

Moisture content(%)

120 100

Actual

80

Fits

60

Forecasts

40 20 0 0

20

40

60

80

100

Time(min)

Figure 1. Moisture content vs. time for pine, (Convection drying).

Microwave drying generate heat from within the grains by rapid movement of polar molecules causing molecular friction and help in faster and more uniform heating than does conventional heating. It should be pointed out that by variation of drying conditions (i.e. air temperature, humidity and air velocity) within a lumber stack, it is expected that the drying rate and the moisture content distribution varies as well [10].

Moisture content(%)

120 100

Actual

80

Fits

60

Forecasts

40 20 0 0

10

20

30 Time(min)

Figure 2. Moisture content vs. time for pine, (Infrared drying).

40

50

60


57

Moisture content(%)

120 100

Actual

80

Fits

60

Forecasts

40 20 0 0

100

200

300

400

500

600

Time(s)

Figure 3. Moisture content vs. time for pine (Microwave drying).

Moisture content(%)

120 100

Actual

80

Fits

60

Forecasts

40 20 0 0

50

100 Time(sec)

Figure 4. Moisture content vs. time for pine (Combined dryer).

150

200


58

Moisture content(%)

120 100

Actual

80

Fits

60

Forecasts

40 20 0 0

50

100

150

200

Time(min)

Figure 5. Moisture content vs. time for spruce (Convection drying).

Moisture content(%)

140 120

Actual

100

Fits 80

Forecasts

60 40 20 0 0

200

400

600

800

1000

Time(s)

Figure 6. Moisture content vs. time for spruce (Microwave drying).

The method of drying, type of samples, Mean Absolute Deviation, Mean Absolute Percentage Error, Mean Squared Deviation of these models used for moisture content change with time are presented in Table1.


59

Moisture content(%)

120 100

Actual

80

Fits

60

Forecasts

40 20 0 0

20

40

60

80

Time(min)

Figure 7. Moisture content vs. time for Spruce (Infrared drying).

Moisture content(%)

120 100

Actual

80

Fits

60

Forecasts

40 20 0 0

100

200

300

400

Time(sec)

Figure 8. Moisture content vs. time for spruce (Combined dryer).

It is clear that the MAPE, MAD, MSD values of this model were changed between 0.344.8, 0.22-1.63 and 0.08-33.22 respectively. As it can be seen for pine samples the convection method has a better fitness to the model and for spruce infrared drying model fitted the experimental data properly. The estimated values are based on data from [11] and can be conveniently used for theoretical approach are shown in table 2.


60

Table 1. Results of fitness Type of Samples

pine

spruce

Drying methods

MAPE

MAD

MSD

Convection Microwave Infrared Combined

0.341876 1.08315 1.07610 1.26813

0.221418 0.86600 0.83372 1.00335

0.080966 2.08191 2.51506 3.72067

Convection Microwave Infrared Combined

1.61692 4.8156 0.638023 2.46335

1.16996 3.3411 0.420579 1.63377

4.21973 33.2286 0.342695 9.40387

Table 2. Set of data selected for this study Specifications Sx

value 2.9cm

Reference [11

Sy

10.2cm

[11]

u0

82.5%

[11]

u eq

16.2%

[11]

u

19% 316.15K

α

0.787 × 10 −5 cm / s

[11] [11] [11]

D

8.711× 10 −6 cm / s

Equation(11)

βx

1.3099

Equation(7)

βy

4.6072

Equation(7)

μx

0.925

Equation(6)

μy

1.2676

Equation(6)

Γx

0.99

Equation(8)

Γy

0.985

Equation(8)

A

[11]

B

11.7cm 2 / s 3.14cm 2 / s

[11]

t t t t (real time)

213hr 557.32hr 420hr 550hr

Equation(5) Equation(10) Trend analysis [11]

T


61

It was assumed that the diffusion coefficient bellow FSP can be represented by [11]:

D = A.e

−5280 T

.e

Bu 100

(11)

Where T is the temperature in Kelvin, u is percent moisture content, A and B are experimentally determined. Drying time is calculated from theoretical approach and evaluated model. Results show that real time had best agreement with which was obtained from equation (10) while there was a significant difference between real time and the one obtained from equation (5). Some authors have assumed that the diffusion coefficient depends strongly on moisture content [1214] while others have taken the diffusion coefficient as constant [15-18]. Also, different boundary conditions have been assumed by different authors [19-22]. But Liu. et al concluded that the diffusion coefficient is a function of time, position, moisture content, and moisture gradient, which is at variance with assumptions in the literature that the diffusion coefficient is either a constant or a function of moisture content only [23].The difference in drying time may be due to the fact that diffusion coefficient was assumed to be the same in tangential and radial direction. So this assumption can’t be used for equation (5). The same calculation can be done for other drying methods to predict the drying time.

6. CONCLUSION Selection of the optimum operating conditions to obtain good quality dried products requires knowledge of the effect of the process parameters on the rate of internal-external mass transfer. High temperature heat treatment of wood is a complex process involving simultaneous heat, mass and momentum transfer phenomena and the effective models are necessary for process design, optimization, energy integration, and control. Infrared heating offers many advantages over conventional drying under similar drying conditions. These results in high rate of heat transfer compared to conventional drying and the product is more uniformly heated rendering better quality characteristics. Microwave drying offers a number of advantages such as rapid heating, selective heating and self-limiting reactions which in turn can lead to improved quality and product properties, reduced processing time, and energy consumption and labor savings. For pine samples the convection method has accurate result to the model and for spruce infrared drying model fitted the experimental data properly, thus their model was found to be adequate in predicting drying time of wood samples under different drying methods. The principle reason for drying wood at higher temperatures is because the rate of diffusion increases with the temperature. Water molecules generally diffuse from a region of high moisture content to a region of low moisture content, which reduces the moisture gradient and equalizes the moisture content. Diffusion plays an important role in the drying of lumber, at all moisture content with impermeable timbers and in permeable timber wherever the moisture content is too low for hydrodynamic flow of water through the lumens. Diffusion coefficient is influenced by the drying temperature, density and moisture content of timber.

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Other factors affecting the diffusion coefficient that are yet to be quantified are the species (specific gravity) and the growth ring orientation.

REFERENCES [1]

[2] [3] [4] [5] [6] [7]

[8] [9] [10]

[11]

[12] [13]

[14] [15]

[16]

Perre. P., Turner. I.W., The use of numerical simulation as a cognitive tool for studying the microwave drying of softwood in an over-sized waveguide, Wood Science and Technology 33, 1999, 445–446. Rosen H.N., Drying of wood and wood products. In: Mujumdaar A.S. (ed.): Handbook of Industrial Drying. Marcel Dekker Inc., New York: 1987, 683-709. Plumb O.A., Spolek G.A., Olmstead B.A., Heat and mass transfer in wood during drying. Intern. J. Heat Mass Transfer 28(9), 1985: 1669-1678. Stanish M.A., Schajer G.S., Kayihan F. A mathematical model of drying for porous hygroscopic media. AIChE J. 32(8): 1986, 1301-1311. Pang S. Moisture content gradient in softwood board during drying: simulation from a 2-D model and measurement. Wood Science and Technology 30, 1996, 165-178. Pang S., Relationship between a diffusion model and a transport model for softwood drying. Wood and Fiber Science 29(1), 1997, 58-67. Naghashzadegan. M., Haghi. A.K., Amanifard. N., Rahrovan. Sh., Microwave drying of wood: Prductivity improvement, Wseas Trans. on Heat and Mass Transfer, Issue 4, Vol.1, 2006, pp. 391-397. Pavlo Bekhta, Igor Ozarkiv , Saman Alavi, Salim Hiziroglu, A theoretical expression for drying time of thin lumber, Bioresource Technology 97, 2006, 1572–1577. Sergovskii, P.S., Heat Treatment and Preservation of Timber, unpublished report, Moscow, Russia, 1975, p 400. Pang, S. "Airflow reversals for kiln drying of softwood lumber: Application of a kilnwide drying model and a stress model", Proceedings of the 14th International Drying Symposium, vol. B, 2004, pp. 1369-1376. Baronas,F. Ivanauskas,M. Sapagovas, R., Modelling of wood drying and an influence of lumber geometry on drying dynamics, Nonlinear Analysis: Modelling and Control, Vilnius, IMI, No 4, 1999, pp.11-22. Meroney, R.N., The State of Moisture Transport Rate Calculations in Wood Drying, Wood Fiber, 1(1), 1969, pp. 64–74. Simpson, W.T., Determination and Use of Moisture Diffusion Coefficient to Characterize Drying of Northern Red Oak, Wood Science and Technology, 27(6), 1993, pp. 409–420. Skaar, C., Analysis of Methods for Determining the Coefficient of Moisture Diffusion in Wood, Journal of Forest Products Research Society, 4(6), 1954, pp. 403–410. Avramidis, S. and Siau, J.F., An Investigation of the External and Internal Resistance to Moisture Diffusion in Wood, Wood Science and Technology, 21(3), 1987, pp. 249– 256. Droin, A., Taverdet, J.L. and Vergnaud, J.M., Modeling the Kinetics of Moisture Adsorption by Wood, Wood Science and Technology, 22(1), 1988, pp. 11–20.


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[17] Mounji, H., Bouzon, J. and Vergnaud, J.M., Modeling the Process of Absorption and Desorption of Water in Two Dimension (Transverse) ina Square Wood Beam, Wood Science and Technology, 26(1), 1991, pp. 23–37. [18] Soderstro¨ m, O. and Salin, J.G., On Determination of Surface Emission Factors in Wood Drying, Holzforschung, 47(5), 1993, pp. 391–397. [19] Crank, J., The Mathematics of Diffusion, Chap. 9, 2nd ed., ClarendonPress, Oxford. 1975. [20] Plumb, O.A., Spolek, G.A. and Olmstead, B.A., Heat and Mass Transfer in Wood during Drying, International Journal of Heat and Mass Transfer, 28(9), 1985, pp. 1669–1678. [21] Salin, J.-G., Mass Transfer from Wooden Surface and Internal Moisture Nonequilibrium, Drying Technology, 14(10), 1996, pp. 2213–2224. [22] Hukka, A., The Effective Diffusion Coefficient and Mass Transfer Coefficient of Nordic Softwoods as Calculated from Direct Drying Experiments, Holzforschung, 53(5), 1999, pp. 534–540. [23] Jen Y. Liu, William T. Simpson, and Steve P. Verrill, An inverse moisture diffusion algorithm for the determination of diffusion coefficient, Drying Technology, 19(8), 2001, 1555–1568.


Chapter 4

NEW TRENDS, ACHIEVEMENTS AND DEVELOPMENTS ON THE EFFECTS OF BEAM RADIATION ON DIFFERENT MATERIALS K. Mohammadi, and A. K. Haghi* The University of Guilan, P. O. Box 3756, Rasht, Iran

ABSTRACT To get around the secondary electron generation, it will be imperative to use lowenergy electrons as the primary radiation to expose photoresist. Ideally, these electrons should have energies on the order of not much more than several ev in order to expose the photoresist without generating any secondary electrons, since they will not have sufficient excess energy. Such exposure has been demonstrated using a scanning tunneling microscope as the electron beam source. This article contains the theory relevant to the technique and the practical aspects of the work. We reported the effects of beam radiation on different form of materials such as microwave dried fibers or materials used for lithography.

1. INTRODUCTION After more than 40 years of commercial availability of SEM (Scanning Electron Microscope), it is still largely being known as a “look-see” microscope for many users. Scanning electron microscope is one of the most complete tools for engineers and scientists in order to investigate the materials characteristics. The high magnification ranges of this instrument as well as its X-ray spectrometry can easily provide resolutions of defects on nano-scale ranges. The SEM can focuses at high magnification and play a key role in a *

Corresponding author e-mai: [email protected]

66

K. Mohammadi and A. K. Haghi

variety of materials science studies [1]. Research with the scanning electron microscope (SEM) consists of the study of a wide range of problems in instrumentation, theory, and applications. According to previous investigations by Gao Yu and his colleagues [2] the electron irradiation causes an increase in the tear resistance of the some polymers. However, the electron energy can changes adhesion properties [3] and strength and elongation in the some other polymers as well [4,5]. In essence this is due to the similarity between internal atmosphere an electron microscope (SEM) and space environment in the section of vacuumed and charged particles (i.e. electrons). Meanwhile, the effect of SEM electron beam on fiber is similar to the effect of irradiation of an accelerator on the polymer film

1-2. Electron Beam Technology Electron beam accelerators (or linear accelerators) produce a stream of electrons (negatively charged particles) moving at very high speeds. The electrons are generated when a current is passed through a tungsten wire filament in a vacuum. The wires heat up due to the electrical resistance and emit a cloud of electrons. These electrons are then accelerated by an electric field to over half the speed of light and pass out of the vacuum chamber through a thin titanium window into the atmosphere. Once outside the vacuum chamber, the electron beam can be used for a number of applications including polymerization, sterilization, air treatment and plasma generation, amongst others.

1-3. Commercial Use of Electron Beam Technology Commercial applications for Electron beam technology are based broadly on the electron beam as a source of ionizing energy to initiate chemical reactions (e.g., polymerization) or to break down more complex chemical structures. The commercial potential of electron beams was first recognized in the 1970s. Since then, electron beams have been used in many industrial processes such as for drying or curing inks, adhesives, paints and coatings. Electron beams are also used for liquid, gas and surface sterilization as well as to clean up hazardous waste. These (and other) applications are discussed in more detail below. There are presently around 1,000 electron beam systems in commercial operation worldwide. Of these about 700 are high voltage systems, although the number of low voltage installations is now growing at a much faster rate of acceptance. Conventional electron beam applications for industrial purposes include an electron beam accelerator that directs an electron beam onto the material to be processed. The accelerator has a large lead encased vacuum chamber containing an electron generating filament or filaments powered by a filament power supply. During operation, the vacuum chamber is continuously evacuated by vacuum pumps.Although Electron beams have a number of advantages over possible alternatives, they have historically suffered from the major commercial disadvantage that the systems were large, expensive, and complex to maintain. In particular, Electron beam systems have, until now, required vacuum pumping equipment, large high voltage power supplies and complex shielding, as well as inplant engineering and maintenance expertise. As a result, it has not been easy or sometimes possible at all to integrate the systems into manufacturing equipment.

New Trends, Achievements and Developments on the Effects …

67

1-4. Theory In light microscopy, a specimen is viewed through a series of lenses that magnify the visible-light image. However, the scanning electron microscope (SEM) does not actually view a true image of the specimen, but rather produces an electronic map of the specimen that is displayed on a cathode ray tube (CRT). The electron radiation in the SEM is produced by a thermoyonic effect, which is induced by a tungsten filament.[6] The electron waves have an extra acceleration and the electron wave length is calculated by the equation (1)

λ=

150 V + 10 −6 V 2

(1)

where;

λ = Electron radiation wave length V = The voltage of SEM

The amount of the energy of electron beam is being calculated by Plank equation: E=ν h

(2)

Where; E = Electron wave energy h= Plank coefficient

ν =C λ C = Light speed From (1) and (2) one can observe that an increase in SEM voltage may cause a decrease in electron radiation wave length. In view of the above, the diffusion depth is expected to increase as well.[7] It should be noted that the irradiation of electron beam causes elastic and inelastic diffraction in the sample. On the other hand, the energy of primary electrons are dispersed or transferred to sample electrons. Nearly all of the kinetic energy is changed to heat and just a little of it is transferred to the former Cathodoluminescence and secondary electron. These are based on the images of SEM displayed on a cathode ray tube (CRT) and spots on the CRT mimic and the motion of electron beam on the sample. Hence

P=

10 × 10 M

(3)

where; M= Magnification Based on this relation, with increasing the magnification, the beam scanned area will be decrease.

68


When an electron enters the specimen surface it will “see” the atoms of the specimen. If by coincidence the electron travels close to an atom the presence of the atomic and nuclear potential will result in a force affecting the velocity of the electron. This implies that the initial velocity of the electron is disturbed or in other words the electron is scattered. It is important to realize that such a scattering process is a statistical event. moreover the velocity change may be directional only (elastic scattering) or both the direction and the size of the velocity may be changed (inelastic scattering). If an electron penetrates into the atom so that it reaches the nucleus the coulomb potential of this positively charged nucleus has a large influence on its velocity. Classically this interaction mechanism is known as Rutherford scattering and the deviation of the electron from its original track can be calculated with a good accuracy. The force on the electron approaching the nucleus is the classical coulomb force, so it is linearly proportional to the charge of the nucleus. on the atomic number z. it should be noted that the nucleus itself is hardly affected by the movement of the electron as a result of its large mass, compared to that of the electron: for hydrogen the nuclear mass is already 1830 times the electron mass. At the interaction between electron and nucleus there is a conservation of energy and momentum so this is an elastic scattering process. However, for a proper interpretation the screening of the nucleus by the Surrounding atomic electrons has to be taken into account the single scattering models which are available in literature are used as elementary models to describe the successive scattering of an electron as it travels from one atom to the other. This results in the so called multiple scattering model which can be used to calculate elastic electron scattering at a loose energy and this phenomenon has to be dealt with as well. An electron entering the material will also interact with the electron cloud around the nucleus, mainly resulting in inelastic scattering of the electron and a transfer of to the atom. As a result of the interaction electrons in the atomic shell will be released and/or excited. Mostly the outer shell electrons are involved, because of the relatively low energy required to remove them from the shell. These electrons start to drift through the material and are subjected to the inelastic scattering process as well. Moreover, the remaining ionized atom may pick up a drifting electron again. The specimen itself is connected to earth, so electrons may also be added to the sample. The drifting electrons have a low average energy and they can only escape form the material if they are in neighborhood of the surface and have sufficient energy to overcome the work function.The penetration depth of the electrons depends on the material composition which influences both the elastic and the inelastic scattering processes. In particular the inelastic scattering, resulting in slowing down of the electrons (also known as the stopping power) is far better for high z materials than for low z materials. This means that although the elastic scattering increases for high z materials the penetration is smaller than for low z materials. Using both inelastic and elastic multiple scattering models probabilities for scattering angles and energy transfer can be defined and used in Monte-Carlo simulations. In such a simulation many stochastic electron tracks within the specimen are calculated and with the statistics of the tracks a good impression of the interaction volume.


69

Figure 1.1. and 1.2. Monte-Carlo simulations of the scattering of 20 Ke v electrons in carbon and iron.

A few of those types of simulations are shown in the figures 2.1-2.4 for C, Fe, Ag and Au from the 0.5 micron bars shown in these figures we see that there is a strong influence of the z value of the material on the interaction volume. For instance, the range of the 20 Kev electrons in carbon is about 3 micron, whereas the corresponding range in silver is about 0.7 micron. The influence of the initial energy of the electron beam is shown in the figures 2.5-2.7 for iron. As shown in these figures the penetration depth increases with increasing electron beam energy Epe For many materials the range of the electrons as a function of the energy has been determined and generally the range r be described by: R= a(Epe)b

Figure 1.3. and 1.4. Monte-Carlo simulations of the scattering of 20 Kev electrons in silver and uranium.

70


Where the constants a and b are material constants. From this general relationship again we find that there is an increase of the range, as the energy Epe increases. A good knowledge about the range of the electron beam is important if one is interested in non-homogeneous materials such as layers on an integrated circuit or inclusions in a metal. The range will then provide information about the origin of the signal. Furthermore it is possible to obtain depth information of the specimen for instance for EBIC, using the accelerating voltage as a parameter.

Figure 1.5. –1.7. Monte-Carlo simulations of the scattering of electrons in iron, using Epe as a parameter.


71

The shape of the interaction volume is also affected by the internal structure of the sample. In a material such as a crystal the electrons are allowed to pass through certain channels, without a strong energy loss per unit of length. This means that locally the interaction volume changes and that in the scattering models this channeling phenomenon has to be included, thus resulting in a scattering pattern which is strongly peaked into the direction of a channel. If the channels are in the direction of the primary electron beam an increase of the penetration depth will be the result.

1-5. The Origin of the Signals As discussed in the preceding section the electron looses energy on its way through the material. This energy is then released from the specimen in many different forms, depending on the type of interaction between the primary electron and the atoms of the specimen. As a result of the elastic and inelastic interaction the electron may become a back scattered electron with a maximum energy equal to the primary electron energy (in this case there is a single head-on collision). Ionization occurs as well, so electrons are produced throughout the total interaction volume; the electrons escape from the material and have an average energy of 2 to 5 eV. These electrons are called secondary electrons and they come from a small exit depth of about 1 nm for metals, and of the order of 10 nm for carbon. It should be noted that a backscattered electron generated deep in the material is energetic enough to produce a secondary electron on its way back to the surface this means that secondary electrons are also generated outside the actual interaction volume of the primary electron beam. This may even be outside the specimen it self, for instance if a back scattered electron hits the chamber or the pole piece of the electron microscope. These effects are schematically shown in Figure 1.8.

Figure 1.8. The production of secondary electrons by backscattered electrons.

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When the primary electron interaction results in ionization of an atom, the atom is left with a vacancy in one of its shells. One of the ways for the atom to loose the excess of energy is to transfer it to an electron in another shell, thus resulting in the generation of an electron with a energy characteristic for the material of the sample. These electrons have an energy up to about 2 Kev and are called Auger electrons. The spectrum of all electrons coming out of a specimen when it is irradiated with an electron beam of energy Epe is shown in figure 2.9. by convention the electrons with an energy below 50 eV are called secondary electrons (SE) and those remaining are the back scatter electrons (BSE). The large peak around the primary beam energy results from Rutherford scattering and this process increases with increasing atomic number z. therefore the number of BSE coming out of the specimen reflects the average z value of the material: this is the important contrast mechanism for the backscattered electrons (see also section 3.2). A second way an atom can fill the vacancy in one of its shells, is to catch one of the electrons of a higher shell. This electron jumps from one shell to a lower one and the difference in energy is emitted as an x-ray quantum. Since the electronic energy levels of the atom are fixed, and since the allowed jumps from one shell to another are subjected to strong quantum mechanical selection rules, the energy of the emitted x – ray quantum is characteristic for the atom itself. The x-ray quanta are generated everywhere the primary electron has sufficient energy to remove an inner shell electron from the atom on their way to the surface the generated x-ray quanta can be captured by an atom, which in turn may emit an x-ray quantum, usually with a different (lower) energy. This phenomenon is known as fluorescence, and it influences the position at which the x-rays come out of the specimen and it decreases the number of quanta that are originally produced.

Figure 1.9. The spectrum of the electrons leaving the specimen.


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2. SECONDARY ELECTRONS Of all signals that can be used for specimen investigation with a SEM the secondary electron signal are most frequently used. The most important characteristics of the SE signal are discussed below.

a) Energy Range Electrons that are emitted from the specimen with an energy less than 50 eV are defined as secondary electrons. Within this energy range there will always be a small number of backscattered electrons that have lost most of their energy but since their, contribution is small they contribution is small they can effectively be ignored. The maximum number of secondary electrons has an energy of between 2 and 5 eV with the exact peak position and energy spread varying for different materials. With the standard secondary electron detector the position and width of the peak do not effect the collected signal.

b) Angular Distribution When the primary electron beam strikes a specimen set at 0 degrees tilt the yield of secondary electrons for different exit trajectories follows a so called cosine rule [I (a) = I0 cos (a)] as shown in figure 3.1.The maximum yield is for electrons with an exit angle normal to the specimen surface with the intensity decreasing as the cosine of the angle the trajectory path makes with the incident beam.

Figure 1.10. The angular dependence of the secondary electron yield.

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The total yield of secondary electrons will increase as the specimen is tilted but the angular distribution remains the same. This is a consequence of the isotropic nature of secondary electron generation where the path direction of the secondary electrons is independent of the direction of the initiating high energy electrons.

c) Information Depth Electron beam specimen interactions give rise to secondary electrons throughout the total interaction volume but only those that are generated close to the surface will leave the sample and contribute to the signal. The depth is about 1 nm for metals and 10 nm for most insulating (low z) materials. Secondary electrons are generated by the primary beam as it enters the sample and also by backscattered electrons as they leave the sample material (see Figure 1.8). thus although the secondary electrons themselves come from a depth of a few nanometers there is also a contribution to the SE signal as a result of backscattered electrons emerging from several hundred nanometers beneath the specimen surface. When the primary beam impinges on such an area, backscatter electrons are emitted from the specimen surface in the usual way. The backscatter electrons are not influenced significantly by the leakage fields because of their energy is relatively high. However, as a result of their low energy, the secondary electrons will be influenced by the magnetic fields above the specimen. when the secondary electrons emerge from the specimen in a region where there are leakage fields they will experience a force which in some regions will deflect them towards the secondary electron collector and in others, with different fields, will deflect them away from it.

Figure 1.11. The interaction volume and the origin of some signals.


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A reduction in the field strength of the secondary electron detector (by reduction of the grid bias) may help to enhance the contrast since the secondaries deflected away from it are less likely to be collected. as with the crystal orientation, described in the previous section, this contrast mechanism is only normally visible when the stronger effects such as those due to topography are reduced.

3. BACKSCATTERED ELECTRONS This signal is the result of electrons from the primary beam undergoing a sequence of elastic and inelastic scattering events, in which the net change in direction is sufficient to carry them out of the specimen. The most important characteristics of the BSE signal are discussed below.

a) Energy Range As a result of the definition of the SE energy as discussed in previous sections the electrons in the remaining energy interval i.e. 50 eV to the energy Epe of the primary electrons, are referred to as backscattered electrons. The BSE with an energy close to E are the ones that are subject to elastic scattering and they form a substantial part of the total BSE signal.

b)Angular Distribution Normalized angular distributions of the BSE are shown in figure 1.12 for a normal incident beam on Al and on Ag For a given z the BSE yield follows more or less a cosine relationship, so most of the electrons are reflected back in the direction of the primary beam. The shape of the curve does not strongly depend on the primary beam energy for an angle of incidence of 60° the angular distributions of Al and Ag are shown in Figure 1.13 in this case there is a maximum in the direction opposite to the primary beam direction and a” deformed cosine relation” describes the distribution. Moreover, the same normalization is used as in figure 3.6 and as shown in the figures the ratio of the maximum yields of Ag and Al is larger for normal incidence than for 60 o incidence. So tilting the specimen results in a stronger peaked signal, but also in a decrease of the signal difference i.e. the signal contrast.

c) Information Depth As stated, the high energetic backscattered electrons result from a single interaction and are therefore most likely to come from the upper layer of the specimen. So if only the high energetic BSE are detected the information depth is smaller than the penetration depth. If a non-dispersive detector is used all BSE are detected simultaneously, so the information depth becomes a substantial part of the penetration depth of the primary electron beam.

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Figure 1-12. the angular distribution of the backscattered electrons for a normal incident beam on Al and on Ag.

Figure 1.13. The angular distribution of the backscattered electrons for an electron beam on Al and on Ag with an angle of incidence of 60.

4. CATHODOLUMINESCENCE As a result of electron bombardment of the specimen, light may be generated inside the specimen, and if the specimen is transparent for emitted and detectable wavelengths, this Cathodoluminescence signal can be used for imaging as a result of the way excited states of the specimen can decay to lower levels there might be a considerable amount of time between the moment of excitation by the electron beam and the moment the energy is released again by photon emission. The emitted radiation may even cause fluorescence in the specimen and the effective decay time is strongly increased his time between excitation and total decay is the reason why a Cathodoluminescence image might not be clearly visible at the TV scan speed. The total image will then appear blurred, and selection of a slower scan speed is the only remedy for this.


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a) Energy The energy of the emitted radiation is strongly dependant on the material composition and may be somewhere in the total spectrum from the very ultra violet to the far infra-rad. Not all these wavelengths are suited for imaging, since low noise detection with a photomultiplier has to be possible as well; therefore imaging is restricted to those wavelengths which are in the detectable range of the photomultiplier.

b) Angular Distribution As a result of the nature of the photon emission there is no preference for a certain angle. However, the presence of local obstructions and absorption variations of the sample will have an influence on the distribution. Moreover the local variation of the specimen surface (topography)may result in variation of the internal reflection coefficient, and this reduces the efficiency for the light to get out of the specimen (analogous to light in an optical fiber)and induces local polarization of the light.

c) Information Depth The information depth is very large, since as long as the electrons have sufficient energy for the excitation of atoms or molecules of the specimen, Cathodoluminescence may occur. Thus the volume where the photons come from is larger than for instance for backscatter electrons, since these electrons are subject to the same scattering mechanisms as the incoming electrons. For Cathodoluminescence the signal is carried by other elementary particles (photons) than the particles that generated the signal, so the absorption of the signal on its way back will be principally different.

5. THE X–RAY SIGNAL a) Energy Range In the case of characteristic x-rays the energy range depends on the nature of the sample. assuming that many elements are present characteristic x-rays have a theoretical upper energy limit equal to E pe . The probability of emission of that radiation is however very low. The lower limit of the x-ray radiation is less then 0.1 kev and in fact enters the transition region for Cathodoluminescence. In the case of the continuum radiation (bremsstrahlung) the spectrumranges from zero to E pe and here there is also a strong decrease of the emission probability for high energetic xrays. The spectrum is schematically shown in figure 1.14.

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Figure 1.14. The x-ray continuum spectrum obtained with an electron beam of energy E pe .

b) Angular Distribution Principally the characteristic emission is randomly emitted, but as a result of internal absorption (i.e. absorption of the x-rays in the sample on their way from the interaction volume to the surface) the x-ray signal is peaked into the direction of the electron beam; the lower the energy, the stronger the peak. The direction of the continuum radiation is related to the velocity of the decelerated electron, so principally it is related to the initial beam direction, but as a result of the multiple scattering this direction preference is lose. A peak of the signal in the direction of the electron beam comes from absorption phenomena inside the specimen as is the case for the characteristic radiation.

c) Information Depth Assuming that all generated x-rays can escape from the sample, the information depth is related to the primary beam energy, reflecting the interaction volume of the primary and the backscattered electrons. The information depth is also related to the characteristic radiation of interest. By decreasing E pe the interaction volume is decreased as well (thus the information comes from a region that is closer to the surface) but the obtained x-ray spectrum is also different since the maximum energy of the x-rays has decreased. So the reduction of E pe to obtain a decrease of the information depth is accompanied by a reduction of the maximum energy that is emitted, and thus of the number of detectable elements.


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6. TRANSMITTED ELECTRONS Transmission of electrons only takes place if the specimen is very thin The thickness must certainly be less than about 1 micron. Usually the transmission of electrons through the specimen is investigated in a TEM. With this special instrument it is possible to visualize diffraction patterns that contain valuable specimen information such as crystallographic constants and orientation. Since extra lenses below the specimen are required for this, a SEM is not suited to detect diffraction patterns. The most important information for a SEM in transmission mode comes from the locally variable transmission coefficient (the thickness) of the specimen. The various characteristics of the transmission signal will be discussed below.

a) Energy Range Depending on the specimen thickness and/or density the energy of the transmitted electrons ranges from zero to the primary electron energy E pe .The greater the specimen thickness (density),the smaller the averaged energy of the transmitted electrons.

b) Angular Distribution When the specimen is sufficiently thin the signal will be strongly peaked in the direction of the optical axis. As a result of many interactions in a thick sample, this angular spread will become larger. The mentioned diffraction phenomenon is beyond the scope of this basic course. Because of the detection method normally employed in a SEM the angular distribution is of minor importance.

c) Information Depth In fact the transmission signal itself reflects the absorption of electrons in specimen. The information depth thus depends on the combination of specimen thickness (and composition) and applied high voltage.

7. CONVENTIONAL ELECTRON-BEAM LITHOGRAPHY The practice of using a beam of electrons to generate patterns on a surface is known as electron beam lithography. The primary advantage of this technique is that it is one of the ways to beat the diffraction limit of light and make features in the sub-micrometer regime. Beam widths may be on the order of nanometer as of the year 2005. This form of lithography

80


has found wide usage in research, but has yet to become a standard technique in industry. The main reason for this is speed. The beam must be scanned across the surface to be patterned -pattern generation is serial. This makes for very slow pattern generation compared with a parallel technique like photolithography (the current standard) in which the entire surface is patterned at once. As an example, to pattern a single layer of semiconductor containing 60 devices (each device consists of many layers) it would take an electron beam system approximately two hours; compared with less than two minutes for an optical system. One caveat: While electron beam lithography is used directly in industry for writing features, the process is used mainly to generate exposure masks to be used with conventional photolithography. However, when it is more cost-effective to avoid the use of masks, low volume production or prototyping, electron-beam direct writing is also used. For commercial applications, electron beam lithography is usually produced using dedicated beam writing systems that are very expensive (>$2M USD). For research applications, it is very common to produce electron beam lithography using an electron microscope with a home-made or relatively low cost lithography accessory. Such systems have produced line widths of ~20 nm since at least 1990, while current systems have produced line widths on the order of 10 nm or smaller. These smallest features have generally been isolated features, as nested features exacerbate the proximity effect, whereby electrons from exposure of an adjacent feature spill over into the exposure of the currently written feature, effectively enlarging its image, and reducing its contrast, i.e., difference between maximum and minimum intensity. Hence, nested feature resolution is harder to control. For most resists, it is difficult to go below 25 nm lines and spaces, and a limit of 20 nm lines and spaces has been cited here[9]. With today's electron optics, electron beam widths can routinely go down to a few nm. This is limited mainly by aberrations and space charge. However, the practical resolution limit is determined not by the beam size but by forward scattering in the photo resist and secondary electron travel in the photoresist [10]. The forward scattering can be decreased by using higher energy electrons or thinner photoresist, but the generation of secondary electron is inevitable. The travel distance of secondary electron is not a fundamentally derived physical value, but a statistical parameter often determined from many experiments or Monte Carlo simulations down to < 1 eV. This is necessary since the energy distribution of secondary electrons peaks well below 10 eV[11]. Hence, the resolution limit is not usually cited as a well-fixed number as with an optical diffraction-limited system[12]. Repeatability and control at the practical resolution limit often require considerations not related to image formation, e.g., photoresist development and intermolecular forces. In addition to secondary electrons, primary electrons from the incident beam with sufficient energy to penetrate the photoresist can be multiply scattered over large distances from underlying films and/or the substrate. This leads to exposure of areas at a significant distance from the desired exposure location. These electrons are called secondary electron and have the same effect as long-range flare in optical projection systems. A large enough dose of backscattered electrons can lead to complete removal of photoresist in the desired pattern area.


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8. NEW FRONTIERS IN ELECTRON-BEAM LITHOGRAPHY To get around the secondary electron generation, it will be imperative to use low-energy electrons as the primary radiation to expose photoresist. Ideally, these electrons should have energies on the order of not much more than several ev in order to expose the photoresist without generating any secondary electrons, since they will not have sufficient excess energy. Such exposure has been demonstrated using a scanning tunneling microscope as the electron beam source[13]. The data suggest that electrons with energies as low as 12 eV can penetrate 50 nm thick polymer photoresist. The drawback to using low energy electrons is that it is hard to prevent spreading of the electron beam in the photoresist[10]. Low energy electron optical systems are also hard to design for high resolution [14,15]. Coulomb inter-electron repulsion always becomes more severe for lower electron energy. Another alternative in electron-beam lithography is to use extremely high electron energies (at least 100 keV) to essentially "drill" or sputter the material. This phenomenon has been observed frequently in transmission electron microscope[16]. However, this is a very inefficient process, due to the inefficient transfer of momentum from the electron beam to the material. As a result it is a slow process, requiring much longer exposure times than conventional electron beam lithography. Also high energy beams always bring up the concern of substrate damage. Interference lithography using electron beams is another possible path for patterning arrays with nanometer-scale periods. A key advantage of using electrons over photons in interferometry is the much shorter wavelength for the same energy. Despite the various intricacies and subtleties of electron beam lithography at different energies, it remains the most practical way to concentrate the most energy into the smallest area.

9. EXPERIMENTAL STUDIES In this experiment, a commercial electron microscope Philips armored to (EDXE) detector. The characteristic of this microscope is presented in the Table 2.1. In order to compare the effect of irradiation on the fibers, four types of fibers are kindly provided by industrial sectors (i.e., acrylic, polyester, cotton and viscose rayon). Table 2.1. The Characteristic of Electron Microscope Model

XL30

The Size Of Chamber

20.×20

Filament

W-gun

Kind of pump

Oil Diffusion Pump

MAX Voltage

30KeV


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At the end of drying process each fiber sample is glued to ample holder with carbon stick and then they are placed in the SME vacuum chamber and the electron gun is switched on. At the first stage each sample is observed by 12800 x magnification with various voltage namely; 12,15, 20,25,30 KV, alter to get to a steady state condition. The photographs are then taken from each sample and the size variations are measured. At the second stage the samples size variations are measured after irradiation with respect to time.

10. RESULTS AND DISCUSSIONS Diagram1 shows the inflation or deflation of different fibers versus different voltages. According to Diagram2.1, increase of beam voltage causes some changes in the fibers diameter, but this change is different for each fiber. The most variation belongs to viscose and the least variation belongs to acrylic. The diameter variation is most likely for inflation of viscose, cotton and polyester, whilst this is shown as deflation for acrylic. Diagram 2.2 to2.5 show diameter changes for polyester, acrylic, cotton and viscose rayon. It can be seen that with increasing the time of irradiation, the destruction of fibers increased significantly. For polyester, cotton and viscose fibers this destruction appears in the form of increase in the fiber diameter whilst for the acrylic fiber, this deformation appears as decrease of the fiber diameter. Series1

Series2

Series3

Series4

Percent of fiber change

60 50 40 30 20 10 0 -10 0

10

20

30

-20 voltage(KeV)

Diagram 2.1. Fiber diameter change verses different voltage at 13000 x.

40

percent of inflation in polyester


30 25 20 15 10 5 0 0

200

400

600

time (s)

perenct of deflation in acrylic

Diagram 2.2. Polyester fiber diameter change verses time after irradiation at13000 x.

20 15 10 5 0 0

200

400

600

800

time (s)

percent of inflation in cotton

Diagram 2.3. Acrylic fiber diameter change verses time after irradiation at13000 x.

50 40 30 20 10 0 0

50

100

150

200

time(s)

Diagram 2.4. Cotton fiber diameter change verses time after irradiation at13000 x.

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percent of inflation in viscose rayon

84

60 50 40 30 20 10 0 0

10

20

30

40

time(s)

Diagram 2.5. Viscose fiber diameter change verses time after irradiation at13000 x.

The destruction depends electron radiation in vacuumed atmosphere and the formation on the surface of fibers is shown in the Figures 2.1 to 2. 4. Distraction of the polyester fiber is showed in the Figure 2.1 where some sorts of fractures are seen on the surface of fiber. On contrast, in Figure 2.2 the diameter decreased and the necking of fiber is obvious. In Figure 2.3, it is clearly observed that the transverse bonding of cotton has broken.[2,8] In Figure 2.4 the variation of viscose rayon is shown as bulging of fiber cross section.

Figure 2.1. Electron micrograph of polyester.


Figure 2.2. Electronmicrograph of acrylic.

Figure 2.3. Electron micrograph of cotton.

Figure 2.4. Electron micrograph of viscose rayon.

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86

K. Mohammadi and A. K. Haghi Table 2.2. The Characteristic of Fiber Changing

Kind of fiber polyester acrylic cotton viscose

Maximum change in fiber diameter 25 -14.5 42 48.7

Minimum time for maximum change 450 S 640S 120S 30S

11. CONCLUSION The radiation modification of fibers by means of the SEM electron beam was studied in this paper. From the pictures captured, it is observed that the proper selection of SEM radiation wavelength and time can have significant effects on the appearance of fibers studied. The effect of time on this variation is summarized in Table 2. For the case of acrylic fiber it takes 640s to get to a maximum deflation whilst this time for viscose rayon is as short as 30s. It is also concluded that electron irradiation has much faster effects on the viscose comparing to the other samples. Nevertheless, the rate and amount of changes for acrylic is least. In essence, it is expected that the irradiation of electrons break the chemical bonds with lower binding energies in the fibers surface layer. (i.e. the C-C, C-H, C-N and C-O bonds)[8]. Hence the tendency and range of changes in the materials depend on the amount of energy absorbed by materials. Meanwhile, as irradiation time increases, the amount of energy absorbed by the fiber will increase as well. This is due to the increase in the duration of surface scanning by electron probe. However, increase of voltage of beam causes decrease in the wavelength and for each case the fibers may absorb more energy. The electron energy may produce some defects and abrupt crosslink bonds. The effect of electron on the different fibers could depend on the length and the type of fiber bonds charges. The deformation of observed in the samples is similar to deformation in the wool and silk fiber which were investigated and reported earlier in

Figure 2.5. Electron micrograph of silk.


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Figure 2.6. Electron micrograph of wool.

REFERENCES [1] [2] [3] [4] [5] [6] [7] [8] [9] [10] [11] [12] [13] [14] [15] [16]

A. K. Haghi, K. Mahfouzi, K. Mohammadi, J. Univ. Ch. Tech. Metallur. (Sofia), 138, 85 (2002). Y. Gao, S. L. Jiang, M. Sun, D. Yang, S. He &Z. Li, Radiat. Phys. Chem, 73, 384(2005). M. Zenkiewicz, Int. J. Adhesion Adhesive, 25, 61(2005). M. Zenkiewicz, Int. J. Adhesion Adhesive, 24, 256(2004). M. Zenkiewicz, Radiat. Phys. Chem, 69, 373(2004). P. G. Fuochi, M. Lavalle, A. Martelli, U. Corda, A. Kovacs, P. Hargittai&K. Mehta, Radiat. Phys. Chem, 67, 593(2003). B. D. Cullity, Elements of X-Ray diffraction, Addision-Wesley Company, Inc, edn. 2(1978). S. B. Warner, Fiber Science, Prentice hall Inc(1995). J. A. Liddle et. al., Mat. Res. Soc. Symp. Proc. vol. 739, pp. 19-30 (2003). A. N. Broers et. al., Microelectronic Engineering 32, pp. 131-142 (1996). H. Seiler, J. Appl. Phys. 54, R1-R18 (1983). L. Feldman and J. Mayer, Fundamentals of Surface and Thin Film Analysis, pp. 130133 (North-Holland, 1986). C. R. K. Marrian et. al., J. Vac. Sci. Tech. B 10, pp. 2877-2881 (1992). T. M. Mayer et. al., J. Vac. Sci. Tech. B 14, pp. 2438-2444 (1996). L. S. Hordon et. al., J. Vac. Sci. Tech. B 11, pp. 2299-2303 (1993). R. F. Egerton et. al., Micron 35, pp. 399-409 (2004).


Chapter 5

STRUCTURAL BEHAVIOR OF COMPOSITE MATERIALS О. А. Legonkova1,*, J. L. Gordeeva 1, E. S. Obolonkova2 1

Moscow State University of Applied Biotechnology, Moscow, 109316, Talalikhina str., 33, 2 Institute of synthetic polymer materials RAS named after Enikolopov N.S.

ABSTRACT Physical and mechanical properties of the filled polymer composite materials (PCM) in dependence on the extent of filling, the rate of deformation were investigated. It was found out that structural properties of the filled composite materials are determined with the nature of polymer matrix, filling degree, nature of the fillers, structural organization of FCM, that is being formed in the process of receiving of the composite materials, and conditions of tests.

Keywords: composite materials, physical and mechanical properties, strength Today the overwhelming majority of polymers are applied as composite materials (PCM). Properties PCM, as a rule, are not a sum of properties of the components, and are defined by the variety of chemical and physical processes as the result of interaction of components on the borders of phases. Introduction of fillers into polymers brings essential changes in the mobility of macromolecules on boundary layers, arises various kinds of interaction between polymers and the surface of fillers, influences on chemical structure of the fillers and polymers during reception and exploitation of PCM [1-5]. However insufficient attention is given to research of physical and mechanical properties of highly filled materials consisting of polymeric matrix and mixture of fillers of various nature, giving biodegrability of composition as a whole. At present work the following large-capacity polymers were taken as polymeric basis: acrylate-styrene carboxylated latex - Lentex А4 (TU 2241-001-47923137-01); copolymer of *

[email protected]

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О. А. Legonkova, J. L. Gordeeva and E. S. Obolonkova

ethylene and vinyl acetate (cevilen, mark #11306-070; polyamide (PA, which is copolymer of hexamethylene diamine, adipate and sebacic acids with melting temperature 1300С); thermoplastic polyurethane (PU), which is produced by "Agropolymer" firm (Russia, TU 5141-003-17823007), polyvinyl spirit (PVS) with the degree of saponification - 88 %. Waste products of thrashing grains(organic filler) of the third category (size of particles 63-240mcm, bulk density of 350 kg / m3; humidity of 4 %), and water-soluble mineral fertilizer (inorganic filler with the following make-up (in %): (NH4) 2SO4- 35, NH4H2PO4 - 6, KNO3 - 32, MgSO4*7H2O - 27) were taken as fillers. Depending on properties of polymeric matrix various ways of reception of composites were applied. Compositions on basis of watersoluble PVS and industrial Lentex А4 have been received via watering of water solutions consisting of organic and inorganic fillers. Compositions on polyurethane basis were received through hardening on air of the component mixture. For reception of samples of PCM on sevilen basis and PA matching of components were carried out by laminar mixture in melt, pressing, and also by making a mixture of components and pressing. Thus samples received as plates with thickness 500 microns. It was noticed while investigating the physical and mechanical properties of PCM on PA basis and speed of deformation at 100 mm/min for two component systems, that at introduction of inorganic filler into composition up to 10 % the breaking point insignificantly falls. It could be explained by the following: the filler at its small concentration in PCM in absence of aggregation powdered particles, carries out role of concentrator of internal pressure and is a potential source of cracks’ growth [1]. At increase of concentration inorganic filler up to 30 % durability of PCM increases in 2, 5 times and that is explained with the creation of more obstacles for development of cracks. Owing to this the breaking processes of destruction stops [1]. Reduction of durability with increase of contents of filler is typical for highly filled PCM. At concentration of inorganic filler in the quantity of 75 % samples become very fragile, have durability on order below, than the initial samples. Relative lengthening at break for all samples decreases, and finally, becomes in 2 times less, than at initial sample. For two componental PCM with organic filler similar law is traced, relative hardening system is observed at small concentration of filler (up to 10 %) which is not so significant as in two-componental system with inorganic filler (increase of durability in 1,5 times). At creation of two component systems on sevilen basis at monoaxial deformation 100mm/mines the «effect of temporary conversion of reinforcing action of fillers», for the first time described in the work [7], wasn’t found: with increase of content of organic and inorganic fillers durability and relative deformation reduced, Figures 1,2. Samples become more rigid (module grows) in case of filling organic filler. At introduction of inorganic filler even at large concentrations (weights of 60 %) samples keep rather high plasticity (deformation at destruction is appr. 400 %).

Structural Behavior of Composite Materials

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σр, МПа 1

2

σр, МПа

А. εотн, % 3

5

4

B. εотн, % Figure 1. Physical and mechanical properties PCM on basis of sevilen. Content of organic filler, weight in %: 1 - 0 %; 2 - 20 %; 3 - 40 %; 4 - 50 %; 5 - 60 %. Speed of monoaxial deformation is 100 mm / min.

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МПа

1

2

4 3 5

εотн, % Figure 2. Physical and mechanical properties of two componental PCM on basis of sevilen. Content of inorganic of filler, weight in %: 1-0 %; 2 - 20 %; 3 - 40 %; 4 - 50 %; 5 - 60 %. Speed of monoaxial deformations - 100 mm / min.

According to IK-spectroscopy inorganic filler is inert in the relation to polymeric matrix because the identical spectra of absorption of initial unfilled polymer and the polymer filled with inorganic filler are the same. Hence, mechanical behavior of PCM is defined by structural organization of composite materials, its dependence on conditions of formation and test on PCM (in our case, speed of deformation). Electronic- microscopic photos of PCM surface on basis of PA and sevilen are submitted on Figure 3, 4. It is visible, that systems heterogeneous. Introduction of organic filler results in reception of more homogeneous systems, than introduction of inorganic filler. Systems with inorganic filler include as crystallites of salts of filler as their more difficult formations. However distribution of inorganic filler in sevilen environment is distinct from its distribution in PA environment, Figure 3 (1-3). In PCM on basis of PA structure of composite at 20 % filling is more defective on all surface of spalling, creating obstacles for development of cracks. While in PCM systems on basis of sevilen defects "were pressed" in homogeneous structure of composite, therefore decrease in durability PCM occurs due to the reduction of maintenance of polymer in a composition and hardenings PCM is not observed at speed of deformation of 100 mm / min.

Structural Behavior of Composite Materials 1.

4.

10% inorganic filler

10% organic filler

2.

5.


20% organic filler

3.

6.


50% organic filler

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Figure 3. Electronic - microscopic photos of chips of two component systems PCM on basis of PA and inorganic filler (1,2,3), and organic filler (4,5,6.) (Increase 200 microns)


94 1.


4.

tree componental PCM

2.

5.


40% organic filler

3.

6.


60% organic filler

Figure 4. Electronic - microscopic photos of chips of two component systems PCM on basis of sevilen and inorganic filler (1,2,3), and organic filler(5,6), three componental PCM: 50 % organic filler, 35 % inorganic filler. (Increase 200 microns)


95

Physical and mechanical properties of two componental PCM on basis of PU, Lentex А4, PVS are submitted in Tables 1-2, Figure 5. Introduction of organic filler resulting in decrease of elasticity of PCM and introduction of inorganic filler leading to preservation of enough elasticity of composite in comparison with PCM, filled with organic filler are general for all investigated systems. «Effect of temporary conversion of reinforcing action of fillers» was found at filling with organic and inorganic fillers, both in two and three componental systems. Physical and mechanical properties of PCM on basis of PVS with concentration of filling inorganic filler 20 % at various speeds monoxial stretching are presented on Figure 6. While investigating the three component PCM on basis of investigated polymers, Figures 6-7, Tables 3, 4, it should be noted that the basic contribution to durability of three componental PCM brings organic filler. Even in highly filled systems where the general content of fillers reaches 85 %, the given dependence is kept. Inorganic filler, as well as in case with two-component materials gives plasticity of PCM. Table 1. Physical and mechanical properties of two component PCM on the basis of PU at stretching (speed of deformation is 100 mm / min) Maintenance, weight %

durability, МPa

deformation, %

Polimer 90

organic filler 10

inorganic filler -

21,4

480

80

20

-

16,4

360

79

30

-

13,3

270

46

54

-

4,4

6,6

90

-

10

25,0

500

80

-

20

22,6

480

70

-

30

16,3

300

60

-

40

8,6

240

Table 2. Physical and mechanical properties of two componental PCM on basis Lentex А4 at stretching (speed of deformation is 100 mm / min) Maintenance of Lentex А4, %

maintenance organic filler, %

maintenance inorganic filler, %

durability, МPa

100

0

0

3,1

Deformation of destruction, % 600

90 80 60 90 80 60

0 0 0 10 20 40

10 20 40 0 0 0

1,3 1,0 0,8 2,5 1,7 1,6

300 300 180 300 20 12


96

300

Pressure, MPa

250

5 1

200

2 3

150

4 5

100

3

6

50

2

4

1

6

0 0

5

10

15

20

25

30

35

Deformation, % Figure 5. Physical and mechanical properties of PCM on the basis of PVS (monoaxial deformation 100 mm/min). Content of inorganic filler, weight in %: 1-0 %; 2 - 10 %; 3 - 20 %; 4 - 50 %; ratiot of organic filler, weight in %: 5 - 20 %; 6 - a parity of polymer, organic filler and inorganic filler in three component PCM is 1:1:1.

120

Pressure, MPa

100 2 80

1 1

60

2 3

40

3

20 0 0

2

4

5

8

10

15

20

25

30

35

40

Deformation, % Figure 6. Physical and mechanical properties of PCM on the basis of PVS, filled inorganic filler (20 % of weights) at various speeds monoaxial deformation: 1-0,5 mm / min; 2 - 10 mm / min; 3 - 100 mm / min.


97

1

5

3 4

2

εотн, % Figure 7. Physical and mechanical properties three component PCM on the basis of sevilen, weight in mass. %: 1 - sevilen/organic filler - 50/50; 2 - sevilen/ inorganic filler - 50/50; 3 - sevilen/ inorganic filler/ organic filler. - 50/37/13; 4 - sevilen/ inorganic filler/ organic filler.-50/25/25; 5 - sevilen/ inorganic filler/ organic filler.-50/13/37. The rate of stretching is 100 mm/ min.

At research of physical and mechanical properties of PCM received via pressing, all the above described dependences in changes of durability depending on degree of filling and conditions of test are kept. Being based on the above discussed results we can estimate that durability dependence on content of each type of the fillers (organic or inorganic) is linear:

( )

f x j = α 0 j + α1 j ⋅ x j ,

(1)

Table 3. Physical and mechanical properties of three componental PCM on basis PU at test for stretching (speed of deformation of 100 mm / min)

80

Content, % Organic filler 10

72

14

14

7,1

94

60

20

20

6,5

63

50

25

25

6,1

26

polymer

Inorganic filler

Durability, МPa

Deformation, %

10

7,3

110


98

σ, МPа 1 2

3

4 ε, %

Figure 8. Physical and mechanical properties of three component PCM on the basis of PA. Content of polymer/organic filler/inorganic filler, weight in mass. %: 1 - 50/10/40; 2 - 50/20/30; 3 - 50/25/25; 4 50/40/10.

where j – factor number (filler), α0j, α1j – equation coefficient for the j-factor (j = 1, 2). For example, these dependences for samples based on sevilen are given in the Figure 8 (а, б). Brandon’s method was used to describe the behavior of three component PCM [7,8]. According to this method the approximate function has the following appearance:

y = λ ⋅ f1 ( x 1 ) ⋅ f 2 ( x 2 ) ,

(2)

Table 4. Physical and mechanical properties of the high filled PCM on the basis of sevilen (speed of deformation is 100 mm / min) Content, % polymer

durability, МPa

Deformation, %

Inorganic filler

15

Organic filler 35

50

0,72

5,2

15

45

45

1,06

5,0

15

50

35

1,20

6,3

15

60

25

1,31

4,0

10

55

35

0,80

6,3


99

Durability

2,5 2 1,5 1 0,5 0 0

0,2

0,4

0,6

x1 а) 2,5

Durability

2 1,5 1 0,5 0 0

0,2

0,4

0,6

0,8

x2 b) Figure 8. Dependence durability of filler content: а – of inorganic filler (x1); b – of organic filler (x2).

where

y

–

durability

of

f 2 (x 2 ) = α 02 + α12 ⋅ x 2

PCM;

λ

-

constant;

f1 (x1 ) = α 01 + α11 ⋅ x1 ,

– dependence of PCM durability on filler content,

correspondingly, inorganic (x1) and organic (x2) fillers. The meaning of λ constant equals to the medium experimental meaning of the exit parameter

λ=

1 N ∑ y i , i=1, 2, …, N. N i =1

Where yi – durability for PCM. After normalization of experimental data via division yi on λ according to the formula

(3)


100

y*i =

yi λ

(4)

for two pairs of variables

(x

)

* 1i , y i with the help of method of minimum squares, constants

of the first component in the regression equation

f1 (x1 ) = α 01 + α11 ⋅ x1

calculated. Constants of the second component of the function

were

f 2 (x 2 ) = α 02 + α12 ⋅ x 2

for

variable x2 and remaining function yi1 were calculated via excluding the meaning of the first * component of the function f1(x1) out of the normalized meanings of the exit parameter y i according to the formula

y i1 =

y*i f1 ( x1 )

.

(5)

After determination of f1(x1) и f2(x2) the common formula of plural regression was built. As a result, the following regression equations for three component PCM were received: - for PCM based on sevilen

y = 1,82 ⋅ (1,29 − 0,96x1 ) ⋅ (1,36 − 0,95x 2 )

(6)

- for PCM based on PA

y = 8,41 ⋅ (2,07 − 4,08x1 ) ⋅ (0,96 − 0,15x 2 )

(7)

- for PCM based on PU

y = 6,75 ⋅ (1,21 − 1,23x1 ) ⋅ (1,01 − 0,03x 2 )

(8)

- for PCM based on Lentex

y = 1,40 ⋅ (2,01 + 9,64 x1 ) ⋅ (1,27 − 1,01x 2 )

(9)

- for PCM based on PVS

y = 39,63 ⋅ (4,36 − 11,40 x1 ) ⋅ (2,54 − 6,76x 2 )

(10)


101

The quality control of approximation according to Fisher criteria revealed that equations (6-10) sufficiently reflect the behavior of three component PCM at p lemon grass = ginger > fennel = caraway > cardamom = juniper > black pepper As mentioned above biological activity of the essential oils depends on its composition. The changes in the composition of the essential oils during autooxidation may be directly connected with its AO activity. The results presented in the Figures 2 - 9 demonstrate the changes in composition of all essential oils under study during THO of aldehyde in each oil. The main components of essential oil from black pepper are β-caryophyllene, 1,8cineole, limonene and monoterpene hydrocarbons. As seen from Figure 2, we observed significant oxidation of sesquiterpene hydrocarbons, especially β-caryophyllene, and as a result increasing of it’s oxide content. Monoterpene hydrocarbons, except for α-phellandrene, have been oxidized to less extent. However γ-terpinene and α-terpinolene, which are known to be the strong antioxidants, during oil storage time have been completely oxidized. Their initial content in the oil composition was not high; possibly it is a reason for comparatively low AO activity of the essential oil from black pepper (Figure 1).

A. L. Samusenko

106

120 day 100 80 60 40 20 0 1

2

3

4

5

6

7

8

9

Figure 1. Time of half-oxidation (THO) of trans-2-hexenal in various essential oils: 1 – control, 2 – black pepper, 3 – berries of juniper, 4 – cardamom, 5 – seeds of caraway, 6 – fennel, 7 – lemon grass, 8 – ginger, 9 - mace Change of main component content in studied essential oils during autooxidation.

120 % 100 80 60 40 20 0 1

2

3

4

5

6

7

8

Figure 2. Black pepper: 1 - α-pinene, 2 - sabinene, 3 - β-pinene, 4 - limonene + 1,8-cineole, 5 - γterpinene, 6 - α-terpinolene, 7 - β-caryophellene, 8 – myristicine.

The essential oil from ginger is not only food flavoring, but is used in pharmacology. That is why the study of it’s AO properties is of special interest. AO activity of the extracts from ginger has been investigated in Ref. 25, 26. The data obtained by us showed that change of ginger essential oil composition was mainly connected with oxidation of sesquiterpene hydrocarbons (Figure 3). Content of zingiberene, which is the main component of this oil, decreased nearly to 30 times, content of β-sesquiphellandrene and β-besabolene – to 2 times,

Comparative Evaluation of Antioxidant Properties …

107

whereat we observed significant deterioration of oil odor. Degradation of monoterpenes practically did not occur. We suppose that the main antioxidant of ginger essential oil is zingiberene. AO activity of ginger essential oil was lower only than that of the essential oil from mace (Figure 1).

120 % 100 80 60 40 20 0 1

2

3

4

5

6

Figure 3. Ginger: 1 - 1.8-cineole, 2 - α-terpinolene, 3 - zingiberene, 4 - β-bisabolene, 5 - γ-cadinene, 6 β-sesquiterpene.

120 % 100 80 60 40 20 0 1

2

3

4

5

6

7

8

Figure 4. Cardamom: 1 - α- pinene, 2 – sabinene, 3 - β-myrcene, 4 – 1,8-cineole, 5 - γ-terpinene, 6 - αterpinolene, 7 – 4-terpineol, 8 – terpinyl acetate.

A. L. Samusenko

108

120 % 100 80 60 40 20 0 1

2

3

4

5

6

Figure 5. Berries of juniper: 1 - α-pinene, 2 - β-myrcene, 3 – limonene, 4 - γ-terpinene, 5 - αterpinolene, 6 - β-caryophellene.

The results on change of volatile component composition of the essential oils from cardamom and berries of juniper are presented in Figures 4 and 5. The both oils have the same value of aldehyde THO and, therefore, the same AO activity. The content of main components of cardamom essential oil – 1,8-cineole and terpinyl acetate – insignificantly changed during storage time, monoterpene hydrocarbons underwent to oxidative degradation to a lower extent. The content of citrals didn’t practically changed. As it was expected, α-, γterpinenes and α-terpinolene were completely oxidized. These compounds proved to be the antioxidants in cardamom essential oil. The essential oil from berries of juniper had a lot of the same compounds as compared with cardamom oil, but contained much more monoterpene hydrocarbons, the main of which being α-pinene, β-myrcene and limonene. Its oxidation occurred approximately to the same extent, which we observed in cardamom essential oil (Figure 5). Besides that, the oxidation of sesquiterpenes, for instance β-caryophyllene, took a place. It is of interest that total content of α-, γ-terpinenes and α-terpinolene was the same in the both oils. This compounds have the highest AO activity in comparison with other monoterpenes [15]. Considering all these factors it could be explained the same AO activity of the essential oils from cardamom and juniper (Figure 1) by the similar character of its autooxidation during storage. As seen from Figure 6, the main components of fennel essential oil were trans-anethol, fenchone, estragol and limonene. During storage trans-anethol underwent to noticeable oxidation; it partly was oxidized to anise aldehyde and partly transformed in cis-isomer, having toxicity [17]. Because of low content α-, γ-terpinenes and α-terpinolene in fennel essential oil the main antioxidant in this sample was trans-anethol. However, as shown in Ref. 9, it’s AO activity was significantly lower than that of γ-terpinene. It is a possible reason for low value of aldehyde THO in fennel essential oil, which was equal only to 54 days, while in mace essential oil, having a high γ-terpinene content, the value of THO was 2 times as large (Figure 1). As mentioned above, essential oil from mace possessed the highest AO activity as


109

compared with all samples studied in this work. This fact may be explained by mace oil composition: besides a high γ-terpinene content, it also has very high content of other monoterpene hydrocarbons, which is 1 – 2 order as large than that in fennel oil. None from strong antioxidants in essential oil from mace (α-, γ-terpinenes, α-terpinolene) has completely oxidized during storage time, which was longer than 3 months (Figure 7). Except for αphellandrene and some minor components, such as β-caryophyllene, the composition of mace essential oil inconsiderably changed. It is necessary to note that source of mace essential oil is a skin of nutmeg, which is characterized by not only a high AO activity, but used in pharmacology due to antimicrobial properties and improvement of glucose and insulin metabolism [27, 28].

120 % 100 80 60 40 20 0 1

2

3

4

5

6

Figure 6. Fennel: 1 - α-pinene, 2 - β-myrcene, 3 – limonen, 4 – fenchon, 5 – estragol, 6 – trans-anethol.

120 % 100 80 60 40 20 0 1

2

3

4

5

6

7

8

9

Figure 7. Mace: 1 - α-pinene, 2 – sabinene, 3 - β-pinene, 4 - α-terpinene, 5 – limonene + 1,8-cineole, 6 - γ- terpinene, 7 - α-terpinolene, 8 – 4-terpineol, 9 – myristicine.

A. L. Samusenko

110

120 % 100 80 60 40 20 0 1

2

3

4

5

6

7

8

Figure 8. Lemon grass: 1 – camphene, 2 – limonene, 3 - γ-terpinene, 4 - α-terpinolene, 5 – linalool, 6 – neral, 7 – geraniol, 8 – geranial.

120 % 100 80 60 40 20 0 1

2

3

4

5

6

7

8

Figure 9. Seeds of caraway: 1 - α-pinene, 2 – sabinene, 3 - β-myrcene, 4 – limonene, 5 - γ-terpinene, 6 – dihydrocarvon, 7 – dihydrocarveol, 8 – carvone.

Figures 8 – 9 demonstrate the change of composition of the essential oils from lemon grass and seeds of caraway. The main components of lemon grass oil were citrals – neral and geranial, content of which considerably decreased during storage time (Figure 8). Oxidation of limonene and linalool has resulted in increasing of epoxylimonene content and appearance of cis- and trans-linalool oxides correspondingly in the oil composition. The content of γterpinene in lemon grass oil was low and it didn’t change. It could be supposed that citrals were the antioxidants in this sample; oxidation of citrals led to deterioration of oil odor. The


111

other aldehydes and alcohols, being the components of lemon grass oil – citronellal and decanal, citronellol and geraniol, were also oxidized (Figure 8). The composition of lemon grass oil drastically changed, but AO activity was keeping relatively high. The data obtained by us were in concordance with those of Ref. 8, where high AO activity was revealed for the oils, having a high content of citrals. The main components of caraway seed essential oil were limonene and carvone. Caraway seed oil, as well as fennel, had a medium value of AO activity in series of the oils studied (Figure 1). The composition of this oil slightly changed during storage time. Oxidation of carvone, though not very considerable, allowed to suppose that it was the main antioxidant in this sample. We observed a stronger oxidation of monoterpene hydrocarbons, especially βmyrcene (Figure 9), but its initial quantity in the oil composition was not quite high.

CONCLUSION The comparison of AO activity of the essential oils studied with the change of its composition during autooxidative process has showed that cyclic monoterpene hydrocarbons - α-, γ-terpinenes, α-terpinolene and citrals – neral and geranial were the most prominent antioxidants. High AO activity of the essential oils was also caused by the presence of significant quantity of sesquiterpene hydrocarbons – zingiberen and β-caryophyllene. The essential oil from mace was found to have the highest antioxidant activity while the essential oil from black pepper possessed the lowest one.

REFERENCES [1] [2] [3] [4] [5] [6] [7] [8] [9] [10] [11] [12] [13]

D.W. Reishe, D.A Lillard, R.R. Eitenmiller: Chemistry, Nutrition and Biotechnology ( Eds. C.C.Ahoh & D.B.Min). Marcel Dekker, New York, 1998, p.423. R.S. Farag, M.N. Ali, S.H. Taha: J.Amer.Oil Chem.Soc., 67, 188 (1990). K.P Svoboda, S.G. Deans: Flavour Fragrance J., 7 ( 2), 81 (1992). H.L. Madsen , G. Bertelsen: Trends Food Sci. and Technol., 6, 271 (1995). M. Sawamura: Aroma Research., 1 (1), 14 (2000). K. Platel, K. Shrinivasan: Nahrung., 44 (1), 42 (2000). M.A. Murcia, I. Egea, F. Romojaro, P. Parras, A.M. Jimenez, M. Martinez-TOME: J.Agric.Food Chem., 52 (7), 1872 (2004). G. Sacchetti, S. Maietti, M. Muzzoli, M. Scaglianti, S. Manfredini, M. Radice, R. Bruni: Food Chem., 91, 621 (2005). Т, А. Мisharina, A.N. Polshkov: Prikladnaya Biokhimiya i Mikrobiologiya, 41 (6), 693 (2005) (in Russian). I. Popov, G. Lewin G.: Methods in Enzymology, 300, 437 (1999). M.S. Taga, E.E. Miller, D.E. Pratt: J.Amer.Oil Chem.Soc., 61, 928 (1984). H.S. Choi, H.S. Song, H. Ukeda, M. Sawamura: J.Agric.Food Chem., 48 (9), 4156 (2000). K.G. Lee, T. Shibamoto: J.Agric.Food Chem., 50 (15), 4947 (2002).

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[14] K. Yanagimito, H. Ochi, K.G. Lee, T. SHIBAMOTO: J.Agric.Food Chem., 51 (25), 7396 (2003). [15] G. Ruberto, M. Baratta: Food Chem., 69, 167 (2002). [16] F. Gong, Y.-S. Fung, Y.-Z. Liang: J.Agric.Food Chem., 52 (21), 6378 (2004). [17] S.A. Voitkevitch: Ephirniyi masla dlya parfyumerii i aromaterapii. Pischevaya prom., Moscow, 1999. [18] A. Sivropoulou, E. Papanikolaou, C. Nikolaou, S. Kokkini, T. Lanaras, M. Arsenakis: J.Agric.Food Chem., 44 (5), 1202 (1996). [19] T.A. Мisharina, R.V.Golovnya, I.V. Beletskii: Zhurnal analit. khimii, 54 (2), 219 (1999) (in Russian). [20] N. Gopolakrishnan: J.Agric.Food Chem., 42 (3), 796 (1994). [21] T.A. Мisharina, A.N. Polshkov: Prikladnaya Biokhimiya i Mikrobiologiya, 37 (6), 726 (2001) (in Russian). [22] T.A. Мisharina, A.N. Polshkov, Е.L. Ruchkina, I.B. Мedvedeva: Prikladnaya Biokhimiya i Mikrobiologiya, 39 (3), 353 (2003) (in Russian). [23] W. Jennings, T. Shibamoto: Qualitative Analysis of the Flavor and Fragrance Volatiles by Glass Capillary Gas Chromatography. Acad.Press, New York, 1980. [24] K.G. Lee, T. Shibamoto: Food Chem.Toxicol., 39, 1199 (2001). [25] C.Z. Kelly, O.M.M. Marcia, J.P. Ademir, A.M.M. Angela: J.Supercrit.Fluids, 24, 57 (2002). [26] G.B. Alexander, T.W. Gordon, C. Byung-Soo: J.Supercrit.Fluids, 13, 319 (1998). [27] C.L. Broadhurst, M.M. Polansky, R.A. Anderson: J.Agric.Food Chem., 48 (2), 849 (2000). [28] S.W. Choi, T. OSAWA: Food Biotechnol., 5, 156 (1996).


Chapter 7

THE POLYMERIC COMPOSITIONS STABILIZED NANODIMENSIONS PHOSPHOR ORGANICALLY BY COMPOUNDS A. Kh. Shaov*, A. N. Teuvazhukova, and A. A. Akezheva Kabardino-Balkarian state university it. H.M.Berbekov, 173 Chernyshevsky St., 360004, Nalchik, Russia

ABSTRACT Technical progress is impossible without wide use polymeric materials in all areas of human activity. Wide circulation of plastic and synthetic pitches it is impossible without giving of necessary stability by him to ageing, i.e. To deterioration of physical and chemical and physical-mechanical properties in process of processing, operation and storage of polymers. In the present work results of researches are given on to definition of stabilizing and modifying influence cyclohexyl phosphonic acids and her potassium the salts having the size of molecules within the limits of 0,097-0,191 нм3 on polyethylene high density (PEHD), as one of most distributed industrial thermoplastics.

Keywords: polymers, compositions, phosphonates, nanodimensions, polyethylene of high density, potassium, stabilization

Studying of processes of ageing and stabilization of polymers is one of the most important and least developed directions of a modern chemical science. Therefore works of complex research on creation of new stabilizers and modifiers get especially big value. The general tendency in the given area of a science are questions of compatibility of antioxidizers with polymers, their influence on coloring of materials, shock durability and adaptability to manufacture, and also development of target additives for concrete types of *

E-mail: [email protected]

114

A. Kh. Shaov, A. N. Teuvazhukova and A. A. Akezheva

polymeric materials. Mark, that the mechanism of action phosphor organically compounds (FОС) is defined by type of stabilizing substance and conditions of its oxidation. If to consider a problem, in general as stabilizers of polymeric materials against various kinds of ageing use the inorganic and organic connections promoting delay of processes, operational characteristics of polymers resulting in deterioration under action of various factors : light, heat, mechanical loadings, radiation etc. Widely widespread stabilizers of polymeric materials of a various structure and class are connections of phosphorus. The most investigated as stabilizers of polymers among them are connections of trivalent phosphorus. As to stabilizing properties derivative five-valent phosphorus they are investigated not yet full. The majority of polymeric materials at operation contact to oxygen of air i.e. are in the oxidizing environment. Basically all reactions at ageing in natural conditions are characterized oxidizing деструкции and represent radical - chain oxidizing process. This process is activated by various external factors - thermal, radiating, chemical, mechanical. Lately the attention of researchers to acids and salts of five-valent phosphorus that proves to be true sharp increase of number of the publications devoted to synthesis and studying of stabilizing properties of such substances has strongly increased. Modifying and stabilizing influence phosphonate in relation to polymeric materials is investigated to a lesser degree, than others organic derivative the four-co-ordinates phosphorus. In this connection by the purpose of the present work it was put synthesis and research of stabilizing and modifying properties cyclohexyl phosphonic acids and it potassium salts in relation to polythene of high density (PEHD), as to one of the most widespread industrial thermoplastic. More often phosphonates stabilize polyolefins and various copolymers olefins. The results received at research of character of influence organic phosphorus of compounds on physic-mechanical characteristics PEHD in conditions shock test (Table), allow to assert with the big share of reliability, that FOC show plasticization property, that in turn raises values of sizes of mechanical characteristics. It, apparently, is connected by that organic phosphorus of compounds, borrowing free volumes in macro chain and getting in intermolecular "space", the polar groups strengthen intermolecular interaction a little. As confirmation of such assumption that circumstance, that at van-der-waals volume (VW) polyethylene in 20,6 sm3/mol, found on can serve a known technique, the share of free volume (VE) makes 7,6 sm3/mol, and volumes organic phosphorus of compounds – cyclohexyl phosphonic acids, potassium hydrocyclohexyl phosphonate, potassium cyclohexyl phosphonate - are accordingly equal 0,097 нм3, 0,144 нм3, 0,191 нм3. The effect of small additives, probably, is connected by that at such dosages FOC they in the optimum image "find room" in free volume and intermolecular "space" of polymer. Forces of intermolecular interaction "work" on distance about 0,35 нм so our structures are nanosystems typical.

The Polymeric Compositions Stabilized Nanodimensions Phosphor …

115

Physic-mechanical properties of structures on a basis. PEHD and FOC in conditions of shock test No

Structure

1 2 3 4 5 6

PEHD PEHD+ 0,05 % cyclohexyl phosphonic acid - « - + 0,1 % - «- « - + 0,3 % - «- « - + 0,5 % - «PEHD+0,05 % potassium hydrocyclohexyl phosphonate - « - + 0,1 % - «- « - + 0,3 % - «- « - + 0,5 % - «PEHD + 0,05 % potassium hydrocyclohexyl phosphonate - « - + 0,1 % - «- « + 0,3 % - «- « + 0,5 % - «-

7 8 9 10 11 12 13

А, kJ/m2 11,0 19,5 16,3 18,8 20,0 20,0

Е, GPa 1,06 0,82 0,90 0,81 0,87 1,05

21,1 14,1 18,6 17,1 16,5 29,9

ε, % 5,7 9,5 7,6 7,6 8,7 5,1

19,3 15,0 12,1 20,5

0,85 0,82 0,57 0,92

16,0 16,0 18,7 16,0

8,1 7,5 6,9 8,6

19,0 15,5 15,4

0,85 0,91 0,82

18,0 17,3 18,3

7,6 8,4 8,5

σ МPa

REFERENCES [1] [2] [3] [4] [5] [6] [7]

Tager A.A. Fizikohimya of polymers //M.: Chemistry.-1978.-544 p. Kytaigorodsky A.I. The organically of crystal chemistry //M.: USSR of АN. - 1955 558 p. Askadsky A.A. Structure and properties higher termoresystens polymers //M.: Chemistry.-1981.-320 p. Askadsky A.A., Matveev U.I. Chemical a structure and physical properties of polymers.-M.: Chemistry.-1983.-248 p. Barshtein R.S., Kirillovich V.I., Nosovsky U.E. Softener for polymers.-M.: Chtmistry.1982.-200 p. Kozlov P.V., Papkov S.P. Physical and chemical of a basis of plasticization of polymers.-M.: Chemistry.-1982.-224 p. Korbrig D. Phosphorus: Bases of chemistry, biochemistry, technology //M.: Mir-1982.680 p.


Chapter 8

COMPOSITE MATERIALS FOR ORTOPEDICAL STOMATOLOGY ON THE BASIS OF UTILIZED GLASSY ORGANICALLY* A. Kh. Shaov*, E. M. Kushhov, K. A. Sohrokova Kabardino-Balkarian State University it. H. M. Berbekov 173 Chernyshevsky st., 360004, Nalchik, Russia

ABSTRACT Use of polymers and the polymeric compositions having property polymeryzated at room temperature, in practice orthopedic stomatology allows to reduce the price of process manufacturing of various products, in particular bugles skeletons, the dental prosthetics. The polymeric composition prepares on to basis methylmethakrylate, received at recycling waste products polymethylmethakrylate. A way of manufacturing bugles skeletons on the basis of a polymeric composition from utilized PMMA allows to reduce quantity of stages of multiphasic process (necessity of manufacturing of fireresistant model is excluded at traditional way) and to improve quality of a product. In result we receive essential economy material and time resources, that, undoubtedly, reduces the cost price of process manufacturing bugles a skeleton.

Keywords: recycling, polymethylmetacrylate, composition, orthopedic stomatology, bugles a skeleton.

*


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A. Kh.Shaov, E. M. Kushhov and K. A. Sohrokova

Life of a modern civilized society cannot be presented without wide use of polymeric materials in all areas of human activity. The volume and rates of growth of manufacture of high-molecular connections and composite materials on their basis have reached very much a high level. To the beginning of 21 centuries manufacture of synthetic plastic in the world has reached more than 130 million tons per one year. The ecological situation will depend on rates of the decision of a problem of plastic waste products in the world, so both intensity and directions of development of manufacture of synthetic plastic in the come century substantially. Otherwise people will bury themselves plastic dust. Problem of protection of an environment - one of the major problems of the modernity. Emissions of the industrial enterprises, power systems and transport in an atmosphere, reservoirs and bowels at the present stage of development of a science and engineering have reached such sizes, that in a number of areas, is especial in large industrial centre, levels of pollution in some times exceed allowable sanitary norms. The problem of preservation of the environment is a complex problem and has global character. The further development of mankind is impossible without the complex account of social, ecological, technical, economic, legal and international aspects of a problem as applied not only to a concrete production cycle, but also in scales of regions, the countries and all world. Despite of prescription and a plenty of researches in the field of non-polluting manufacture, the problem of recycling and processing of industrial wastes remains actual till now. Therefore, all has appeared economically, technologically and ecologically proved necessity for development and introduction of new progressive and safe methods of the decision of a problem of disposal of biosphere from danger of its pollution by waste products of manufacture and consumption. The preliminary account and estimation of waste products is necessary for a choice of more rational way of the decision of a problem. The polymeric materials found wide application in various branches of a science and engineering, polymers on a basis acrylic acids are. Many of them are known under the technical name "glassy organically". Glassy organically (acryl) represents a synthetic material from acryl pitches with some interest of the various additives giving to a material certain properties. In the international literature glassy organically it is designated as PMMA. Glassy organically it is applied in the most various areas: lighting engineering (plafonds, partitions, obverse screens); the outdoor advertising (obverse glasses for box, light letters, molded volumetric products); the trading equipment (supports, show-windows, price lists); the sanitary technician (the equipment of bathrooms); construction and architecture (glaze ion apertures, a partition, a dome, a dance-floor, volumetric molded products); transport (glaze ion planes, boats); instrument making (dials, observation ports, cases, dielectric details, capacities). Glassy organically completely can be used repeatedly after his processing. We both have taken advantage of last circumstance, i.e. an opportunity of repeated processing, and have tried from utilized PMMA to create polymeric composite materials which can be used in orthopedic stomatology at manufacturing bugles skeletons and attachments to them during prosthetics.

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More and more becoming tougher requirements to materials, industrial necessity to have molding materials with stable properties which are not present at natural waxes, result in creation similar wax the synthetic materials used for modeling bugles of artificial limbs. It is necessary to note, that manufacturing of a dental artificial limb is many studies process at which it is practically impossible to use standard forms. Work of the doctor and dental engineering is under construction on the basis of the account of specific features of the patient, in particular morphological and functional his characteristic dental jawing systems. Clearly, that wax as too plastic materials, not absolutely precisely can transfer forms at modeling. Received at recycling glassy organically MMA forms a basis for reception of a polymeric composition, polymerization room temperature which further can be used at manufacturing bugles skeletons in practice of orthopedic stomatology. In volume of the present work process chemical hardened, taking place is comprehensively investigated at room temperature (19-220 С), polymeric compositions on a basis methylmetakcylate and polymethylmetacrylate (plays a role filling). On their base for the first time are developed about 40 structures of the polymeric compositions, distinguished by a various mass parity of a hardener and the accelerator of process of polymerization for which time initial polymerization makes 8-30 minutes, impact strength is within the limits of 1,2-7,4 kJ/m2. Efficiency developed bugles skeletons from polymeric compositions is defined by that a way of manufacturing bugles skeletons on the basis of a polymeric composition from utilized polymethylmetacrylate will allow to reduce quantity of stages of multiphase process (is excluded necessity of manufacturing of fire-resistant model at a traditional way) and to improve quality of a product. Finally we receive essential economy of material and time resources, that, naturally, reduces the cost price of process of manufacturing of all bugles a skeleton, so cost of orthopedic service for the patient.

ACKNOWLEDGEMENTS Work is executed with the financial help of Federal Fund of assistance to development of small forms of the enterprises in scientific and technical sphere under the innovational program "Start -2005" (Government contract No4037р/5987 from 25.05.2006).

REFERENCES [1]

[2] [3] [4]

Shaov A.Kh., Kushhov M.I., Kushhov E.M. Polymeric composite materials cold hardened for orthopedic stomatology //Abstr. VI Russian scientific forum “Stomatology 2004”.-2004.-P.194-195. Shaov A.Kh., Kushhov M.I., Begretov M.M. Way of manufacturing bugles a skeleton //Pat. 2245116, Russia (2005) (a priority from 21.07.2003). Kuznetsov E.V., Divgun S.M., Budaryna L.А etc. //The practical work in chemistry and physics polymers.-M.: Chemistry. - 1977.-256 p. Nikolaev A.F. //Synthetic polymers and plastics on their basis.- M.,L.-1966.-768 p.

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V.N.Kopejkin, L.M.Demner. //Dental orthopedic technical.-M.:"Success".-1988.-416 p. A.I.Dojnikov, V.D.Sinitsyn. //Dental technical material-keeping. - M.: Medicine. 1986. - 208 p. [7] Кushhov M.I. New a method of manufacturing bugles a skeleton //Dental technical. 2001. - No1. – P.36. [8] Kalmykov K.V., Кushhov M.I. Way of manufacturing bugles an artificial limb and container attachments //Pat. 2000754, Russia (1993). [9] Garner M.M., Napadov M.A. etc. //Materiology in stomatology. M.,1969. [10] Napadov M.A., Shturman A.A. etc. //Increase of durability and biological indifference of orthopedic designs from acrylic plastic //Stomatology.-1976.-No1. [11] Shaov A.Kh. Reception of polymeric compositions for orthopedic stomatology on the basis of utilized glassy organically //Abstr. of XXVI international conf. and exhibitions “Composite materials in the industry”.-Yalta (Crimea) .-2006.-P. 239-241. [12] Kushhov E.M., Shaov A.Kh. Polymeric of a composition for orthopedic stomatology //Abstr. XVI Russian youth scientific conf., devote to an 85-anniversary from birthday prof. V.P.Kochergin. - Ekaterinburg.-2006. – P.255.


Chapter 9

A PRELIMINARY STUDY ON ANTIMICROBIAL EDIBLE FILMS FROM PECTIN AND OTHER FOOD HYDROCOLLOIDS BY EXTRUSION METHOD LinShu Liu1,*, Tony Jin1,†, Cheng-Kung Liu1,‡, Kevin Hicks1,§, Amar K. Mohanty2, Rahul Bhardwaj2, and Manjusri Misra3 1

Eastern Regional Research Center, ARS, U.S. Department of Agriculture, Wyndmoor, PA 19038, USA 2 The School of Packaging, 130 Packaging Building, Michigan State Universities, East Lansing, MI 48824, USA 3 Composite Materials and Structure Center, 2100 Engineering Building, Michigan State University, East Lansing, MI 48824, USA

ABSTRACT Antimicrobial Edible films were prepared from natural fiber of pectin and other food hydrocolloids for food packaging or wrapping by extrusion followed by compression or blown film method. Microscopic analysis revealed a well mixed integrated structure of extruded pellets and an even distribution of the synthetic hydrocolloid in the biopolymers. The resultant composite films possess the mechanical properties that are comparable to films cast from most natural hydrocolloids that consumed as foods or components in processed foods. The inclusion of poly(ethylene oxide) alters the textures of the resultant composite films and therefore, demonstrating a new technique for the modification of film properties. The composite films were produced in mild processing conditions, thus, the films are able to protect the bioactivity of the incorporated nisin, as shown by the inhibition of Listeria monocytogenes bacterial growth by a liquid incubation method. *

E-mail: [email protected] E-mail: [email protected] ‡ E-mail: [email protected] § E-mail: [email protected] †

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LinShu Liu, Tony Jin, Cheng-Kung Liu et al. Keywords: Pectin, antimicrobial, fiber, films, extrusion

INTRODUCTION Pectin is a branched heterogeneous polysaccharide, consisting of 11 monosaccharides and their methyl or acetylated derivatives (Varagen 1996). Pectin is produced by extraction from cell walls of higher plants. The isolated pectin is water soluble. In water solutions or as the commercially available form of powders, pectin macromolecules aggregate each other to form fibers or small particles (Fishman, Jen 1986). Figure 1A shows the AFM imagine of pectin fibers in aqueous solution; the fibers with the size ranging from 100 nm to 400 nm are further associated to form a network. Soluble pectin readily reacts with most natural polymers to form hydrogels. Thus, pectin has a long history in the use as a gelling agent and film forming material (Liu et al. 2003). In the industry, the sources of pectin include citrus peel, sugar beet pulp, apple pomace, sunflower heads, or grape skins, etc. In the U.S., more than 300 thousand tons of pectin are available annually from the byproducts of fruit juice and beet sugar processing. However, only less than 2% of the available pectin is produced and they are mainly consumed as food additives. We have been interested in new utilizations of pectin and other agricultural commodities. In the previous studies, we showed that the blends of pectin with glycerol, and high amylose starch or poly(vinyl alcohol) can be used to produce biodegradable films with a wide range of mechanical properties and excellent oxygen barrier activity (Coffin, Fishman 1993; Coffin et al. 1995; Fishman, Coffin 1995; Fishman et al. 1996; Coffin et al. 1996). We also explored the medical applications of pectin-derived composites by incorporating with bioactive substances (Liu et al. 2003; Liu et al. 2004; Liu et al. 2005a; Liu et al. 2005b; Liu et al. 2006a). Recently, we extended our research to active packaging materials (Liu et al. 2006b; Liu et al. 2007a; Liu et al. 2007b). A series of pectin cast films have been prepared with the inclusion of various food proteins and a bacteriocin and tested for food packaging and wrapping applications, showing improved mechanical properties, water resistant and sustained antimicrobial activity. Extrusion is a cost effective manufacturing process. Extrusion is popularly used in large scale production of food, plastics and composite materials. Most widely used thermoplastics are processed by extrusion method. Many biopolymers and their composite materials with petroleum-based polymers can also be extruded. These include pectin/starch/poly(vinyl alcohol) (Fishman et al. 2004), poly(lactic acid)/sugar beet pulp (Liu et al. 2005c), and starch/poly(hydroxyl ester ether) (Otey et al. 1980), etc. In this study, composite films of pectin, soybean flour protein and an edible synthetic hydrocolloid, poly(ethylene oxide), were extruded using a twin-screw extruder, palletized and then processed into films by compression molding process or blown film extrusion. The films were analyzed for mechanical and structural properties, as well as antimicrobial activity.

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Figure 1. Atomic force microscopic images of pectin (A), soybean flour protein (B) and poly(ethylene oxide) (C). Concentration of solutions: A and B, 100 μg/ml; C 10 μg/ml. Field width: 2.5 μm.

LinShu Liu, Tony Jin, Cheng-Kung Liu et al.

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EXPERIMENTAL Materials Citrus pectin (MexPec 1400) with the molecular weight (M.W.) of 1.8 × 105 dalton and the degree of esterification of 82 and Nisaplin® (2.5% Nisin) were purchased from DaniscoCultor (Kansas City, KS). Soybean flour protein (SFP), poly(ethylene oxide) (PEO, M.W. 900,000), and glycerol (reagent grade, < 99.5%) were obtained from Aldrich Chemical Corp. (Milwaukee, WI).

Preparation Prior to extrusion, dry ingredients of pectin, SFP, glycerol and Nisaplin were blended using a model C-100-T Hobart heavy-duty blender (Hobart Mfg. Co., Troy, OH). The compositions of blends are shown in Table 1. The blends were freeze-dried for 8 h and stored in a plastic bucket covered with lid at 4°C. The premixed pectin, SFP, glycerol were blended with PEO using a Werner & Pfleiderer ZSK-30 twin screw extruder and processed into pellets. This extruder has co-rotating screws (L/D ratio of 30/1) having variable screw profiles throughout its length. The screw speed was 105 rpm, which gave a torque value of 54%. The temperature profile of this extruder from zone 1 to zone 6 was 83, 90, 90, 88, 87, and 86°C. For formulation I, tap water was fed with solids together into the extruder barrel using a series 6300 Digital Feeder at the weight ratio of 19:81, liquid to solid. For formulation II, no water was used. The film blown was processed using a Killion Extruder (Davis Standards Corporation, Troy, OH). The extruder has a bottom fed blown film die. The die has a concentric air opening for film blowing. The air pressure can be controlled with an air valve. The die is also surrounded by an air ring for cooling. The screw rotation was varied between 25-50 rpm. The rotation speed of rollers on the tower was extremely slow to avoid the breaking of the film. The temperature profile of the extruder was also shown in Table 2. Some pellets were ground with the help of Polymer Machinery B.T.P granulator for 5-10 minutes to get powder for film compression processing. A Carver Laboratory press (Fred S. Carver Inc., Summit, NJ) was used for this purpose. The temperatures of upper and lower plates were controlled at 90°C. Composite powders were placed between the 2 metal plates and pressed for 3 minutes under the load of 15000-20000 lbs. Teflon sheet were used between the metal plates to avoid the sticking of the materials to metal plates. Table 1. Compositions of two formulations* Formulations I II

Pectin 50 35

SFP 19 13

* Date expressed as w% of total solid.

PEO 0 30

Glycerol 30 21

Nisaplin® 1 1


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Table 2. Extrusion temperature profiles (°C)

Zone 1 1000

Barrel Zones Zone 2 Zone 3 100 100

Clamp ring 90

Adaptor 85

Die 1 85

Die 2 80

All samples thus obtained were stored in a desiccator over CaCl2 at room temperature for structural and mechanical examinations.

Microscopic Analysis Confocal laser scanning microscopy. A laser scanning confocal microscope system was used to analyze the microstructure of the film components and films. A model IRBE (inverted) microscope (Leica Microsystems, Bannockburn, IL) with a universal stage and 20X objective lens was coupled to a TCS NT/SP scanner head (Leica Microsystems, Exton, PA). Sheets of samples or powders in MatTek dishes (MatTek Corp., Ashland, MA) were illuminated with the 488 nm line of an Argon laser and fluorescence was collected in one channel (520-580 nm) and reflection at 488 nm was collected in another. Fluorescence emission spectra for the sample powders of SFP and Pectin were collected in the range of 500-680 nm. Atomic force microscope (AFM). Sample solutions at 100 ng/ml or less were cemented onto mica and imaged in a model Nanoscope IIIa scanning probe microscope with TESP cantilevers (Veeco/Digital Instruments, Santa Barbara, CA) operated in the intermittent contact mode on an atomic force microscope. Scanning electron microscopy. A Quanta 200 FEG scanning electronic microscope (SEM, FEI, Hillsboro, OR) was used to collect images. Prior to examination, samples were mounted to specimen stubs and sputtered with a thin layer of gold. Samples were examined in the high vacuum/secondary electron imaging model at 5,000X and 50,000X.

Dynamic Mechanical Analysis (DMA) Small deformation dynamic mechanical analysis on compressed or blown films was done using a Rheometrics Scientific RSA II Solids Analyzer. Samples were tested using an initial applied force of 150 grams, an applied strain of 0.1%, and were heated from -100oC to 200oC at 10oC/min. A triplicate set of tests were performed for each samples

Tensile Test and Acoustic Emission (AE) The mechanical property and AE measurements were performed as previously described (Liu et al. 2005). An upgraded Instron mechanical property tester, model 1122, and Testworks 4 data acquisition software (MTS Systems Corp., Minneapolis, MN) were used throughout this investigation. The strain rate was set at 50 mm/min. Date of tensile strength,

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Young’s modulus, and fracture energy was collected. The tensile tester was also programmed to perform a cyclic test. Samples were repeatedly stretched to 2 % strain at 50 mm/min and back to 0% strain. A total of 5 cycles were tested and the peak stress was recorded for each cycle. AE measurement was performed simultaneously with the stress-strain tests. A small piezoelectric transducer (Model R15, Physical Acoustics Corp., Princeton, NJ) was clipped against the samples. AE signals emanating from this transducer when the Instron stretched samples were processed with an upgraded LOCAN-AT acoustic emission analyzer (Physical Acoustics Corp.), which connected to a PC base with enhanced graphing and data acquisition software with all features and options of the SPARTAN 2000.

Bacterial Inhibition Test Pathogenic bacteria Listeria monocytogenes Scott A 724 was obtained from the in house culture collection. Stock cultures of L. monocytogenes were maintained at -80ºC in BHI medium (Difco Laboratory, Detroit, MI). Working Cultures of L. monocytogenes were maintained on BHI agar at 4 ºC and were sub-cultured bi-weekly and grown aerobically at 37ºC in BHI broth. Prior to inoculation of product the organism was cultured in BHI broth at 37ºC for 16-18 h. Bacterial inhibition by the antimicrobial films was evaluated using a liquid incubation method, 4 pieces of films (1 cm2 each) were placed in a glass test tube with 9 ml BHI broth inoculated with 1 ml L.monocucytogenes overnight culture. The test tubes then placed in a shaker (Innovas 3100, New Brunswick Sci. Inc., Edison, NJ) at room temperature and shaken at 200 rpm. One ml of inoculated sample was taken at 0, 8, 24, and 48 h. The samples were serially diluted by sterile phosphate buffer (Hardy Diagnostics, Santa Maria, CA), then pour plated onto BHI agar. Plates were incubated at 37ºC for 24 h. A film-free inoculated BHI broth served as a control. Plates with 30-300 colonies were enumerated using a manual colony counter (Bantex Colony Counter 920; Bantex, Burlingame, CA).

RESULTS AND DISCUSSION Characterization of raw materials for films was firstly conducted on the three ingredients and their blends. Figure 1 shows the AFM images of pectin, SFP and PEO in diluted solutions. The three macromolecules were in the form of fibers in the size ranging from 100 nm to 10 μm. The fibers associated each other. Both the pectin and SFP have intrinsic fluorescence emission (Figure 2A, B) and show a similar profile in their fluorescence spectra (Figure 2C), except that the protein has a narrow maximal intensive peak at around 530 nm, the pectin has a broad peak extended from 530 to 550 nm. Furthermore, the autofluorescence of protein is stronger than that from pectin. PEO doesn’t emit fluorescently, PEO can be detected by reflection (Figure 2D). The differences of the ingredients in photoemission were used to probe the microstructure of resultant composite films. Figure 3 reveals the homogeneity of extruded pellets. After processing, we are still able to identify specific regions that consist of pectin or SFP alone. Each of these regions stretched


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about 10 μm in width; between the two regions of interest there was a well mixing area, which also sized at about 10 μm. The florescent emission from the mixed area reflects the profiles of each spectrum of the two single biopolymers. Figure 4 shows the microscopic images of one of the final products, compression film of formulation II, obtained by confocal reflection and confocal fluorescence in stereo projection. The red area correlated with PEO reflection; the green area correlated with the pectin and protein. The image indicates a well mixed integrated structure, showing an even distribution of the synthetic hydrocolloid in the biopolymers.

Figure 2. Confocal laser scanning microscopic image: (A) fluorescence of pectin, (B) fluorescence of soybean flour protein, (C) fluorescence spectra of pectin and soybean flour protein, and (D) reflection of poly(ethylene oxide). Field width: A, B and D, 480 μm.

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Figure 3. Structure analysis of extruded pellets: Region I (X) colored with green, indicating more pectin component in the area; regions II (∆) colored with yellow, indicating there is more soybean flour protein; regions III (○) colored with brown, indicating the well mixing areas. Field width, 550 μm.

Small deformation dynamic mechanical analysis is a well known method used as a complement for microscopic examination in material structure study. Figure 5 comprises of DMA curves for samples prepared by compression method from formulations I (PEO-free, Figure 5A), formulation II (PEO included, Figure 5B) and PEO alone (Figure 5C). Two significant differences were seen between the samples. One is the location of the sub-ambient glass transition temperature. This is seen at -55oC in sample of formulation I and at -69oC in sample of formulation II. The other is that samples with PEO shows a melting behavior at about 64oC, while a melting behavior is not seen in the PEO-free samples until about 145oC. These differences are certainly due to the presence of the PEO which has a melting point of 57oC. The PEO-free samples also have a transition at 34oC which is probably related to the protein in the sample.


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Figure 4. Confocal laser scanning microimages of compression film from formulation II. The organization of the biopolymers were resolved by confocal fluorescence (excitation 484 nm, emission 520-580 nm), the PEO was defined by confocal reflection (633 nm). The micrograph was collected in stereo projection in extended focus images of 20-30 micrometer-thick slabs of the film. Field width, 470 μm.

Mechanical properties of tensile strength, Young’s modulus, elongation at break and toughness are important for packaging and wrapping materials. In a variety of end uses, packaging and wrapping materials are often subjected to a force during tensile strain. The materials must be able to resist considerable stress without failing to a fracture at a designed stress. Furthermore, as an edible food wrapping materials, the materials may be taken with foods together either for convenient purpose or to enhance or alter the food texture. In these cases, their mechanical properties directly related to the mouth feeling of accepters, which is an important measurement of food quality. Table 3 shows the mechanical properties of selected samples of compression and blown films. In general, the composite films have mechanical properties that are similar to cast films from most natural hydrocolloids, which consumed in our ordinary life (Liu et al. 2006a). For compression films, the addition of PEO almost doubled the Young’s modulus, which is an indication of stiffness; but only had a minor impact on the tensile strength, maximal elongation, and toughness. In comparison of blown film with compression films with same composition, the blown films seemed to be stiffer, but they were not as strong as the films prepared by compression method. Moreover,

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the replacement of SFP with PSG dramatically enhanced the mechanical properties of the composite films (Table 3). The results of the stress-strain cyclic tests are shown in Figure 6. For the PEO-free samples, the loop created by the first cycle is bigger than those created by following cycles. Among the following cycles, the different in loop size is not significant. For samples containing PEO, the size of loop decreased gradually as cycled, then, became constant in the last two cycles. At the end of the cyclic test, the PEO containing sample expressed a much higher stress than the PEO-free sample. Although the PEO free samples are more resistant to mechanical force and less permanent deformation occurred than the PEOincluded sample; the inclusion of PEO strengthens the composite films.

Figure 5. Continued on next page.


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Figure 5. Dynamic Mechanical Analysis of composites containing with PEO (A) or without PEO (B) and PEO alone (C). The PEO-free samples show a melting point at about 145 °C; while, both the PEO alone samples and PEO-included samples a melting behavior at about 64 °C.

Figure 6. Continued on next page.

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Figure 6. Stress-strain curves obtained from cyclic tensile tests. Samples of soybean flour protein and pectin containing without PEO (A) and with PEO (B). For the PEO free films, the loop created in the first cycle is larger than following cycles. For the PEO included films, the size of loops gradually decreased as cycled, then became constant in the last two cycles.

The addition of PEO has an influence on film destruction caused by an external destructive force (Figure 7). Without PEO, the external force created a clear-cut fracture surface, indicating the good adhesion between the two biopolymers. With the inclusion of PEO, the deformation created a fibrous surface. This can be seen more clearly from SEM and fluorescent microscopy. As shown in Figure 8 A and B, fibers were pulled out, extended, and then, broken, but still embedded in the matrix phase. We examine the fibers with confocal reflection and confocal fluorescence in two channels. It confirms that the main component of the fibers is PEO; however, the biopolymers were either inserted or encapsulated within the fibers (Figure 8C). Table 3. Mechanical properties Samples, processing method I, compression I-b, compression* II, compression II, blown

Tensile strength (MPa) 2.35 ± 0.09 8.8 ± 0.3 3.1 ± 0.8 2.3 ± 0.3

Elongation at break (%) 6.14 ± 0.6 13.1 ± 2.0 7.3 ± 1.5 2.8 ± 0.3

* I-b, PSG was used to replace SFP in this composite film.

Young’s modulus (MPa) 77.2 ± 4.49 353.4 ± 26.9 125.2 ± 25.3 151.2 ± 20.8

Toughness (J/cm3) 0.16 ± 0.08 0.90 ± 0.12 0.20 ± 0.07 0.03 ± 0.01


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Figure 7. Photographs of fractural surfaces of samples of PEO-Free (a and b) and PEO-included composite films (c and d).

To probe the structural changes of a composite film that subjected to a destructive force, we measured the AE event simultaneously with the tensile test. Figure 9 shows the correlation between the stress-strain curve and the AE hit pattern. For the PEO-free samples, AE activity detected only at the peak stress, when the samples were completely destructed. This confirms the homogeneity of the composite films. Since the two biopolymers are compatible, they are able to transfer stress evenly. For the samples containing with PEO, the phenomena are similar, the samples emitted sound at the peak stress; however, signals were continually collected as the PEO fiber were pulled and broken, being consistent with the results shown in Figures 7 and 8.

Figure 8. Microscopic images of the fractural surfaces of PEO-included composite samples obtained by scanning electron microscope (left), laser microscope (middle), and confocal laser scanning microscope in confocal fluorescence and confocal reflection two channels (right). Field width: 520 μm (left) and 480 μm (middle and right).

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Figure 9. Correlation between Stress-strain curves and AE patterns of PEO-free samples (A) and the samples containing with PEO (B).

In the colorful family of food packaging and wrapping materials, antimicrobial film is a new member. Besides providing a physical barrel, the films function in prohibition, protection and suppression of microbial migration to or growth in the packages by creating antimicrobial surfaces or releasing antimicrobial substances. The use of antimicrobial materials in food packaging improves food safety and is more convenient to the consumers; therefore, the


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market for antimicrobial food packaging has a fast growth (Cutter 2006; Ozdemir, Floros 2004). In the present study, we incorporated an antimicrobial polypeptide, nisin, into the film formulation. The antimicrobial activity of resultant films is shown in Figure 10. Nisin alone was firstly tested for stability and the results were compared to that treated in the conditions as same as film compression. No statistically significant differences could be detected. Then, we compared the activity of nisin incorporated in blown films and compression films with that of non-treated nisin. As shown in Figure 9, the non-treated nisin was little more active than that formulated in pectin films at the fist 24 hours; however, the difference disappeared in 48 hours incubation. This result indicates that the extrusion conditions applied in the current experiments are mild and not harmful to nisin. Thus, the resultant composite films are able to retain nisin activity.

CONCLUSION The current study provides a new type of edible, antimicrobial food packaging or wrapping films from food-grade natural fibers or hydrocolloid. Besides film casting, the films can also be produced by compression, extrusion blown methods. The inclusion of PEO hydrocolloid in natural fiber formulations makes films tougher and caused less permanent deformation when the films were subjected to an external force. Since the extrusion and compression were performed in mild conditions, nisin can be incorporated into films without diminishing its antimicrobial activity.

Figure 10. Growth of Listeria monocytogenes in BHI broth at 24 °C. Control (diamond), nisaplin prior to extrusion (square), nisaplin post extrusion (circle), nisaplin in compress film (up triangle), and nisaplin in blown film (down triangle).

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ACKNOWLEDGMENTS Authors acknowledge Dr. Peter H. Cooke, Mr. Nicholas Latona, Ms. Guo-ping Bao, Dr. David R. Coffin and Dr. Vitoria L. Finkensdadt for their technical assistant.

REFERENCES Coffin, D. R., Fishman, M. L. 1993. Viscoelastic Properties of Pectin/Starch Blends. Journal of Agricultural and Food Chemistry, Vol. 41, pp. 1192-1197. Coffin, D. R., Fishman, M. L. Cooke, P. H. 1995. Mechanical and Microstructural Properties of pectin/Starch Films. Journal of Agricultural and Food Chemistry, Vol. 57, pp. 663670. Coffin, D. R., Fishman, M. L., Ly, T.V. 1996. Thermomechanical Properties of Blends of Pectin and Poly(vinyl alcohol). Journal of Applied Polymer Science, Vol. 61, 663-670. Cutter, C. N. 2006. Opportunities for Bio-Based Packaging Technologies to Improve the Quality and Safety of Fresh and Further Processed Muscle Foods. Meat Science, Vol. 74, 131-142. Fishman, M. L., Coffin, D. R. 1995. Films Fabricated form Mixtures of Pectin and Starch. US Patent 5,451,673. Fishman, M. L., Jen, J. J. 1986. Chemistry and Function of Pectins. ACS Series 310, American Chemical Society press, Washington D.C. Fishman, M. L., Coffin, D. R., Unruh, J. J., Ly, T. 1996. Pectin/Starch/Glycerol Films: Blends or Composites. Journal of Macromolecular Science: Pure and Applied Chemistry, Vol. A33, pp. 639-654. Fishman, M. L., Coffin, D. R., Onwulata, C. I., Konstance, R. P. 2004. Extrusion of Pectin and Glycerol with Various Combinations of Orange Albedo and Starch. Carbohydrate Polymers, Vol. 57, pp. 401-413. Liu, L. S., Fishman, M. L., Kost, J., Hicks, K. B. 2003. Pectin-Based Systems for ColonSpecific Drug Delivery via Oral Route. Biomaterials, Vol. 24, 3333-3343.doi: Liu, L. S.; Won, Y.-J.; Cooke, P. H., Coffin, D. R., Fishman, M. L., Hicks, B. K., Ma, P. X. 2004. Pectin/Poly(lactide-co-glycolide) Composite Matrices for Biomedical Applications. Biomaterials, Vol. 25, pp. 3201-3210. Liu, L. S., Chen, G., Fishman, M. L., Hicks, K. B. 2005a. Pectin Gel Vehicles for Controlled Fragrance Delivery. Drug Delivery, Vol. 12, pp. 149-157. Liu, L. S., Fishman, M. L., Hicks, K. B., Kende, M. 2005b. Interaction of Various pectin Formulations with Porcine Colonic Tissues. Biomaterials, Vol. 26, pp. 5907-5916. Liu, L. S., Fishman, M. L., Hicks, K. B., Liu, C.-K. 2005c. Biodegradable Composites from Sugar Beet Pulp and Poly(lactic acid). Journal of Agricultural and Food Chemistry, Vol. 53, No. 23, pp. 9017-9022.doi:10.1021/jf058083w. Liu, L. S., Fishman, M. L., Hicks, K. B., Kende, M., Ruthel, G. 2006a. Pectin/Zein Beads for Potential Colon-Specific Drug Delivery: Synthesis and in vitro Evaluation 13:417-423. Liu, L. S., Liu, C.-K., Finkenstadt, V. L., Jin, T. Z., Fishman, M. L., Hicks, K. B. 2006b. Pectin Films for Various Applications. Proceedings of the 35th United States – Japan Cooperative Program in Natural Resources PR31-34.


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Liu, L. S., Finkenstadt, V. L., Liu, C.-K., Jin, T. Z., Fishman, M. L., Hicks, K. B. 2007a. Preparation of Poly(Lactic acid) and Pectin Composite Films for Application in Antimicrobial Packaging. Journal of Applied Polymer Science, in press. Liu, L. S., Liu, C.-K., Fishman, M. L., Hicks, K. B. 2007b. Composite Films from Pectin and Fish Skin Gelatin or Soybean Flour Protein. Journal of Agricultural and Food Chemistry, 55(6), 2349-2355. doi: 10.1021/jf062612u. Otey, F. H., Westhoff, R. P., Doane, W. M. 1980. Starch-Based Blown Films. Industrial Engineering Chemical Products Research and Development, Vol. 19, pp. 592-595. Ozdemir, M., Floros, J. H. 2004. Active Food Packaging Technologies Critical Reviews in Food and Nutrition, Vol. 44, pp. 185-193. Voragen, A. G. J. 1996. Pectin and Pectinases. Elsevier Science Publisher, New York, NY.


Chapter 10

CONTROLLED RELEASE OF THE ANTISEPTIC FROM POLY(3-HYDROXYBUTYRATE) FILMS. COMBINATION OF DIFFUSION AND ZERO-ORDER KINETICS R. Yu. Kosenko1, Yu. N. Pankova1, A. L. Iordanskii1,*, and G. E. Zaikov2 1

Semenov’s Institute of Chemical Physics. 4 Kosygin str., B-334, Moscow 119991, Russia 2 Emanuel’s Institute of Biochemical Physics. 4 Kosygin str., B-334, Moscow 119991, Russia

ABSTRACT The modeling polymer system based on biocompatible and biodegradable poly (3hydroxybutyrate) [PHB] and antiseptic (5- nitrofurfuryliden semicarbazone) [Fr] has been devised. The system PHB - Fr is potentially destined for study of drug controlled release from degradable matrices. Release kinetics from membranes of PHB loaded by 0, 5 – 5, 0 wt % Fr into aqueous media have been investigated by UV spectroscopy technique at 25oC. Profiles of the release comprise diffusion and kinetic impacts. Diffusion component of the release has been analyzed and diffusivity dependence on the drug concentrations has been determined. Kinetics constants of release are directly related with hydrolytic destruction of PHB and dependence on initial concentration of the drug. The destruction of PHB is clearly demonstrated at long-term experiments (after first week of release). These results are required for further elaboration of novel drug delivery systems including a combination of several drugs that will give combined action on tissues and organs in biological systems.

*


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R. Yu. Kosenko, Yu. N. Pankova, A. L. Iordanskii et al.

INTRODUCTION A dramatic rise of the cost for liquid and gaseous hydrocarbons stimulates development of novel biopolymers which production is not depended on fossil fuels. Fermentative biosynthesis of poly(3-hydroxybutyrate) [PHB] and its homologues – poly(3hydroxyalkonoates) [PHAs] bases on using renewable organic substrates. Hydrocarbons’ wastes of food- and wine/juice industries (sugars, melissa, starch et al.) present the basic “structural material” for bacterial PHB (and PHA). Utilization of hydrocarbons during biosynthesis of PHA is favorable to eco-efficiency. In the last decade, PHB and its copolymers begin productively to use in medicine. For example, the composites of PHB are master of high biocompatibility with bone tissues that allows using such composites as bioresorbable osteo implants [1]. The modified PHB works as high effective scaffold in tissue engineering and promotes proliferation, adhesion, and production of cells [2,3]. The PHB materials [4] have good hemocompatibility. Authors [5] have reported that, under blood contact, surfaces of PHB and PHBcoHV films do not activate hemostatic changes on the cell-level. The great progress for poly(4-hydroxybutyrate) [P4HB] is observed in cardio implantation [6]. The artificial heart valves are produced by stereolithography [7] with P4HB and controlled by x-ray tomography. They have demonstrated a relevant combination of mechanical properties and hemocompatibility [8]. In [9] the stent fabrication based on PHB is described. By this means, PHB and its derivatives can be considered as a novel perspective medical materials for tissue engineering [10], design of osteoprostheses with progressive replacement of biodegradable material by germinated bone tissues [11], and hemocompatible coatings for cardiovascular surgery [12]. In framework of this paper it should be emphasize especially that there is a further area of PHB application : design of matrices, reservoirs, and micro/nanoparticles for controlled drug release [13 – 15]. In this case, information on biocompatibility, rate of resorption and diffusion characteristics of the polymer systems is required. On this basis the object of this paper is design and study of therapeutical PHB system loaded by the antiseptic (furacelin), and destined for drug release into modeling aqueous media. Recently [16] we have shown that water diffusion in the PHB films with 100 µm thick was completed in several tens of minutes, whereupon the films absorbed the limiting equilibrium concentration of water (ca. 1 wt %). Structural relaxation in PHB under humid conditions is finished in longer period of time (nearly 1000 minutes). We have investigated kinetics of release for several tens of days, therefore, to a first approximation, a water transport phenomenon in PHB is not essential. However, long-term kinetics of drug release from PHB films has an intricate form and demands special analysis for both diffusion modeling and drug delivery application.

EXPERIMENTAL PART We used PHB supplied by the company “Biomer” (Krailing Germany) : Lot F16. Initial powder of PHB was solved in chloroform under long-term boiling. Hot polymer solution was filtered and after filtration, molecular weight of PHB was determined by viscosimetry technique in accordance with procedure desribed in [17]. Averaged value of Mw is 183.5×103

Controlled Release of the Antiseptic from Poly(3-hydroxybutyrate) Films

141

g/mol. As aseptic drug we used furacilin (Fr) (MW = 198 g/mol) qualified as Medical grade and with general formula of 5- nitrofurfuryliden semicarbazone:

Basic characteristics of the polymer include density = 1,25 g/cm3; Tm = 178oC; Tg = 9 o C; crystallinity degree = 70% (determined by WAXS data). Films of PHB containing Fr were prepared by two different methods: 1-stage procedure. 1g of the polymer powder was mixed with 50 ml of chloroform and boiled in retort with reverse glass refrigerator. After heating, saturated solution of Fr was added. The mixture was allowed to cool down till room temperature and then cast on glass surface for slow removal of solvent. 2-stage procedure. 1g of powder was mixed with 50 ml of 1,4-dioxane and boiled in retort with reverse glass refrigerator as well. Then after cooling and the removal of 1,4dioxane by the vacuum pump, the PHB and Fr were solved in chloroform and procedure looked like 1st stage operation. Thickness of cast PHB films varied from 120±10 µm to 180±15 µm and concentration of loaded Fr changed in the set 0,5; 1,0; 1,5; 1,75; 2,0; 3,0 и 5,0 wt % . The drug release profiles of PHB were registered in water and phosphate buffer (pH = 7.4) by UV technique with UV spectrophotometer Beckman DU65 at 25 oC.

RESULTS AND DISCUSSION The typical kinetic profiles of Fr release from PHB films are illustrated in Figure 1. As is clear from the graph, for PHB release systems loaded by the drug at the concentrations exceeding 1% there are no constant limiting values of equilibrium concentration that would be typical for Fick-law diffusion picture. These kinetic curves are characterized by initial nonlinear range and final range where the drug release profile is linear relative to time (zero-order kinetics). Analyze of data in Figure 1. gives ground to expect that the superposition of the proper diffusion and a linear kinetic process defines the complicated character of release. Most clearly the linear ranges are manifested after completion of drug diffusion and observed for last 8 – 10 days. Based on aforesaid, the release profile is described by the following equation ∂Ct/∂t = D[∂2Ct/∂x2] + k ,

(1)

where D is drug diffusion coefficient, cm2/sec; k is kinetic constant of hydrolytic destruction, sec-1; Ct is drug concentration in the polymer; wt %, x (cm) and t (sec) are coordinate and time of diffusion respectively. After subtraction of linear impact on the profile of release (k·t) from the integral values of concentration Сt Сt – kt ≡ Gt ,

(2)


142 0,45

5

0,40 0,35 0,30

3

Dt

0,25 0,20 0,15

1

0,10 0,05 0,00 0

5

10

15

20

25

30

time, days Figure 1. Kinetic profiles of aseptic release. The figures show the initial concentrations of the drug (% wt) ; Dt is optical density of the dug in liquid medium at 373 nm.

the equation 1 takes a traditional diffusion form ∂Gt/∂t = D[∂2Gt/∂x2]

(3)

Numerical subtraction of linear contribution in release kinetics from total concentration of the drug (shown in Figure 1) has been performed for separation of the diffusion and kinetic impacts. The solution of Eq 3 for plane sheet diffusion and small times (i.e. under condition 0 < Gt/Goo < 0.60) has the classical form Gt/Goo ≈ 4/π2(D·t/L2)0,5,

(4)

where L is the film thickness, cm; Gt and Goo are concentrations of the drug being available for diffusion and determined by eq.2 at any time t or t → ∞ respectively. Finding the slop of linear part of the curves on Figure 2 in coordinates Gt/Goo - t0,5 and solving this equation graphically, we can calculate the diffusion coefficients of Fr in the PHB films. We emphasize two features of drug release profiles : 1) the linear character of data in the above diffusion coordinates holds within limits 0 < Gt/Goo < 0.65 that attests a predominance of diffusion in initial stage of release; 2) the slope of lines in the same coordinates depends on the initial concentration of the drug that demonstrates the dependence of diffusivity on drug concentration. Limiting (equilibrium) values of the drug (Goo) dissolved in the PHB films are needed for construction of the curves in Figure 3. Additionally, these values show the portion of the drug taking part in molecular diffusion.


143

1

1,0

2

3

0,8

Gt/Goo

3 0,6

5 0,4

0,2

0,0 0

5

10

15

20

25 1/2

30

35

40

1/2

(Time) , (h)

Figure 2. Impact of diffusion in total drug release kinetics for PHB films (thickness = 180 mkm). Initial concentration of the aseptic are 1 : 1,75%; 2 : 2,5%; 3 : 3%; 5 : 5 wt. %.

Mobile fraction of furaciline, % wt

3,0

2,5

2,0

1,5

1,0

0,5

0,0 0

1

2

3

4

5

Total furaciline concentration, % Figure 3. Relation between loaded (total) and mobile (Goo) concentrations of the drug in films of PHB.


144

2

Drug diffusion coefficient*10 , cm /s

1,6

10

1,2

0,8

0,4

0,0 0,0

0,5

1,0

1,5

2,0

2,5

3,0

Aseptic concentration, % wt. Figure 4. Diffusivity dependence on mobile fraction of antiseptic concentration in drug release process.

The impact of initially loaded concentration of Fr sorption on equilibrium drug sorption is shown in the Figure 3. From this Figure it follows that till 3 wt % both concentrations are related by the linear function. The deviation from the linearity is observed at maximal concentration (5 wt %) of the loaded Fr. At this point the drug forms its proper phase in the polymer that looks as yellow crystals, while the effect of phase formation does not distort the general manner of kinetic curve (compare in Figure 2, curve3 for 3% and curve 5 for 5%). Summarizing results presented in Figures 1 and 2 we can estimate effective diffusion coefficients for all initial concentrations of the drug. Figure 4 shows the concentration dependence of diffusivities (D) on mobile fraction of the drug (Goo) which has maximum defined clearly in the drug concentration area 1.0 – 1.5 wt %. The rising branch of the curve D(C) results likely from disordering of the PHB structure after drug loading. In contrast, the dropping branch is related with the drug crystal formation in the PHB matrix that bring to the decrease of low-molecular-weight component mobility. The formation of Fr crystals in PHB has been observed recently in our work by Krivandin with WAXS technique [18]. Above we have mentioned that simultaneously with diffusion kinetics the linear kinetic process of Fr release is observed. In this case, the greater initial concentration of loaded drug, the higher is the constant rate of drug release. More informatively this effect is shown in Figure 5, where the exponential dependence of degradation constant (k) on drug concentration is observed. Simultaneously with measurement of the concentration in the drug desorbing from films PHB we have determined the loss of weight for the polymer samples. Gravimetric measurements shown that the polymer sample loses its weight in accordance with the linear low as well. Initial polymer with no content of the drug has the stable weight


145

for all time of release. Preliminary experiments show that, in contrast to enzymatic biodegradation of PHB going on the polymer surface [19], hydrolytic destruction involves all accessible volume of PHB that supported by the increase in brittleness and the decrease in the strength of PHB films.

CONCLUSION We suggested a polymer system for aseptic controlled release that includes films of PHB and furaciline. The release goes on simultaneously in accordance with kinetic (polymer degradation) and diffusion mechanism. The rates of kinetic mode for release obey a zero degree curves relative to time. The diffusion mode which determines the profiles of release in the initial range of time (about a first week) were analyzed in more detail. The dependences of both diffusion coefficients (D) and kinetic constant (k) of release on the drug concentrations were demonstrated. These results are requisite for further development of the drug release systems with multicomponent action when several drugs simultaneously have a local action on biological tissues and cells.

3

Destruction constant of PHB film x10 , g/cm /h

7

2

6 5 4 3 2 1 0 1

2

3

4

5

Initial drug concentration, wt % Figure 5. Dependence of release destruction constant (k) on loaded drug concentration for PHB films.

146


REFERENCES [1] [2] [3] [4] [5] [6] [7] [8] [9] [10] [11] [12] [13] [14] [15] [16] [17]

[18]

[19]

C. Doyle, E.T. Tanner, and W. Bonfield. Biomaterials. 12, 841 – 847 (1991). S.G. Hu, C.H. Jou, and M.C. Yang. Carbohydr.Polym. 58, 173 – 179 (2004). S.G. Hu, C.H. Jou, and M.C. Yang. Biomaterials .24, 2685 – 2693 (2003). G.X. Cheng, Z.J. Cai, and L.Wang. J. Mater. Sci. 14, 1073 – 1078 (2003). V.I.Sevastianov, N.V.Perova, E.I. Shishatskaya, G.S.Kalacheva, T.G. Volova. J.Biomater Sci. Polymer Ed. 14, 1029 – 1042 (2003). D.P.Martin and S.F. Williams. Biochem Eng. J. 16, 97 – 105 (2003). R. Sodian, M.Loebe, A.Hein, D.P.Martin, S.P. Hoerstrup, E.V.Potapov et al. ASAIO J. 48, 12 – 16 (2002). R.Sodian, S.P. Hoerstrup, J.S. Sperling, et al. Ann. Thorac. Surg. 70, 140 – 144 (2000). M.Unverdorben, A.Spielberger, A. Schywalsky et al. Cardiovasc. Intervent. Radiol. 25, 127 – 132, (2002). G.T. Köse, S.Ber, F.Korkusuz, et al. Biomaterials .24, 4998 – 5007 (2003). L.J.Chen and M.Wang. Biomaterials .23, 2631 – 2639 (2002). G.-Q. Chen and Q.Wu. Biomaterials .26, №33, 6565 – 6578 (2005). D.P.Martin, F.Skraly, and S.F. Williams. US Patent 403242 2003. C.W.Pouton and S. Akhtar. Adv.Drug.Deliver. Rev. .18, 133 – 162 (1996). D.Sendil, I.Gürsel, D.L.Wise, and V.Hasirci. J.Controlled Release 59, 207 – 217 (1999). A.L.Iordanskii, P.P.Kamaev J.Macrom.Chem. (Rus) V.41, Ser.B. #1-2, 39-43 (1999). R. H Marchessault, K. Okamura,., C.J Su. Physical properties of poly(βhydroxybutyrate). II. Conformational Aspects in Solution. // Macromolecules. 1970. V.3. №6. 735-740. Shatalova, A.V.Krivandin, and A.L. Iordanskii. 6th European Symposium on Polymer Blends. Program and Abstracts. May 16-19, 1999 Max-Planck-Institut fur Polymerforschung. Mainz, PC90, p.69. Germany. X-ray diffraction study of films prepared from polyethylene-poly(3-hydroxybutyrate) blends. Tamao Hisano, Ken-ichi Kasuya , Yoko Tezuka , Nariaki Ishii , Teruyuki Kobayash , Mari Shiraki , Emin Oroudjev , Helen Hansma , Tadahisa Iwata , Yoshiharu Doi , Terumi Saito and Kunio Miki . Journal of Molecular Biology V356, #4 , 993-1004 (2006).


Chapter 11

PHOTO COMPOSITES ON THE BASE OF POLYMERMONOMER COMBINED SYSTEM, MODIFIED BY OLIGOMERS N. V. Sidorenko, I. M. Gres, N. G. Bulycheva, M. A. Vaniev*, I. A. Novakov Volgorad State Technical University, 28 Lenin Av., Volgograd, 400131, Russia

ABSTRACT Composite materials based on monomer-polymeric systems have been obtained by UV-initiated polymerization method. The flow characteristics of these compositions and their effect on further polymerization have been studied. The polymerization of monomers in the presence of dissolved polymers and properties of the materials have been investigated.

Keywords: photopolymerization, monomer-polymeric systems, polymer solutions, gel-effect, polymeric composite materials.

Perspective course in the case of creation new polymeric composite materials is combining of two or more various high-molecular compounds. This principle may be realized by dissolution or swelling of polymer component in monomer and further polymerization of the last. The diversity of possible polymer-monomer combinations permits to vary a wide range of compounds structure and properties. The employment of such systems makes it possible to design materials with a new complex of characteristics [1, 2, 3].

*

e-mail: [email protected]

N. V. Sidorenko, I. M. Gres, N. G. Bulycheva et al.

148

The subjects of inquiry of this research have been methacrylic and styrene solutions of polyurethane- and fluoroelastomers and polysulphone accordingly in combination with diand three- methacrylic comonomers. The reological properties of investigated solutions have been studied. It has been shown that such compositions have non-Newtonian flow mode, structural nature of flow becomes more expressed with decrease of temperature and increase of solution concentration. It has been shown that viscosity of the composition may be varied in wide range (1.6 – 500 mPa·s). It makes possible to apply different production techniques. Influence of dimethacrylic comonomer concentration on dynamic viscosity and flow activation parameters of compositions has been analyzed. The polymerization of monomer in the presence of dissolved polymers has been studied. It has been shown that the rate of polymerization of monomer-polymer solutions is higher compared to that of pure monomer (Figure 1). The influence of the content of dissolved polymers on the conversion of monomers corresponding to the onset of the gel effect has been estimated. In the presence of the polymer being added, this phenomenon manifests itself at a lower fractional conversion of the monomer. The greater the content of the polymer and the higher the viscosity of the reaction system, the sooner the rise in the rate of polymerization. The effect of the photoinitiator type and amount on the reaction rate, degree of polymerization and structural characteristics of the material has been considered. By using UV-spectroscopy method, it has been shown that initiation efficiency depends on polymeric influence on initiator absorption spectrum. 100

1

3 2

G,%

75

50

25

0 250

2000

3750

5500

7250

9000

10750

12500 Time,s

Figure 1. Effect of the amount of fluoroelastomer on degree of methyl methacrylate polymerization: 1- without polymer, 2- 5% , 3 – 15% of polymer.

Photo Composites on the Base of Polymer-monomer Combined System …

149

It has been determined that polymerization rate may be increased by application of oligomer. Influence of backbone chain and finite groups nature of methacrylic additives on polymerization process and properties of the derivable materials has been studied. Variation of oligomer chemical structure allows improving heat stability, chemical resistance, wear resistant by three-dimensional structure formation. For example in the case of polysulphonestyrene systems, we can vary these characteristics in wide range by using oligomer that illustrated in the Figure 2 (a, b). 40 35

Tensile strength, MPa

30 25 20 15 10 5 0 0

10

20

30

40

50

60

Сontents of comonomer, %

(a)

200 190 180 170

VST, ºС

160 150 140 130 120 110 100 0

5

10

15

20

25

30

35

40

45

Сontents of comonomer, %

(b) Figure 2. Effect of the amount of methacrylic olygomer on the properties of polysulphone-styrene composite materials: (a) tensile strength, (b) heat stability (VST).

150

N. V. Sidorenko, I. M. Gres, N. G. Bulycheva et al. Application of phosphoprous-containing dimethacrylic comonomer FOM-II H2 C H 3C O

O

CH

Cl CH2

O

CH2

O

O

CH3

C

C

CH2

C

C

CH2

O

CH3

P O

CH H2 C

Cl

enables to produce materials with high incombustibility. Thus, new materials on the base of polymer-monomer system have been produced. The results of researches have allowed to develop methods of creating shock-resistant, heatresistant, abrasion-resistant and aggression resistant compounds.


Vaniev M. A., Candidate’s Dissertation in Technical Sciences (Volgograd, 1996). Polymer Science Series A. Volume 48, Number 7 / July, 2006. - p. 707-711. Polymer Science Series A. Volume 49, Number 4 / April, 2007. - p. 388-394.


Chapter 12

STABILIZATION OF CELL MEMBRANES BY HYBRID ANTIOXIDANTS IN THERAPY OF NEURODEGENERATIVE DISEASES L. D. Fatkullinaa,*, O. M. Vekshinaa, E. B. Burlakovaa, A. N. Goloshchapova, and Yu. A. Kimb a

Emanuel Institute of Biochemical Physics, Russian Academy of Sciences, Moscow, Russia b Institute of Biophysics of Cell, Russian Academy of Sciences ,Pushchino, Russia

ABSTRACT A hybrid antioxidant of new generation – ichfan is suggested for the therapy of membrane-pathologies associated with neurodegenerative diseases. It was shown that the compound applied in a wide range of concentrations modifies the properties of erythrocyte membranes and cells of Ehrlich ascitic carcinoma and changes the functional state of cells. Incorporated in the lipid phase and near-protein lipids of membranes, the antioxidant affects the structural state of the lipid bilayer, the structure and functional activity of proteins, in particular, the functions of ionic channels. Recommendations were made as to the compound doses responsible for the pronounced antioxidant and stabilizing effects and the absence of unfavorable side-effects.

Keywords: antioxidants, Alzheimer's disease, membranes, microviscosity, 2+ neurodegeneration, light scattering, thermodenaturation, Ca -dependent K+-channels

*

4, Kosygin Str., Moscow, 119334, Russia. Fax: (495) 137 41 01; E-mail: [email protected]

152

L. D. Fatkullina, O. M. Vekshina, E. B. Burlakova et al.

INTRODUCTION As is known, the Alzheimer's disease (AD) is associated with membrane pathologies that are characterized by the oxidative stress and drastic changes in the structural state, lipid composition, and functions of membranes. The Alzheimer's disease is often characterized by increasing nonsaturation and fluidity of the membrane lipid phase and promotion of oxidation [1,2]. The microviscosity of the membrane lipid bilayer controls the functions of membranebound proteins responsible for the general cellular response and, particularly, the work of ionic channels of plasmalemma, activated by increased intracellular concentration of Ca2+, which is characteristic of many pathologies [3, 4]. Hybrid antioxidants (HA) ichfans [β-4oxy- (3.5-ditertbutyl-4-oxyphenyl) potassium propionate] derivatives of antioxidant phenozan) were synthesized at the Emanuel Institute of Biochemical Physics, Russian Academy of Sciences. These are potential agents in the therapy of neurodegenerative diseases. Ichfan is a combined antioxidant aimed at several targets of a pathological process. Its protective effect is enhanced due to addition of the saturated fatty-acid tail into the phenozan molecule; the incorporation of the tail in the membrane increases the rigidity of the corresponding sites of the membrane and increases the probability for the compound to pass through the hematoencephalic barrier. The choline residue imparts the hybrid antioxidant the anticholine activity [5, 6]. Ichfan exhibits a high antioxidizing activity and inhibits the cholinesterase activity in human erythrocytes and in cytosol and membrane fractions of animal brain [7]. The task was to determine the contribution of membrane modification to the mechanisms of AD occurrence and development and to the drugs efficiency for AD. The aim of this work was to study the effect of ichfan on the structure and functions of membranes in model experiments. We tested the lipid bilayer microviscosity, thermo stability of protein domains of membranes, and K+ - release through Ca2+-dependent K+-channels (CaK channels) in the presence of HA in concentrations from 10-4 M to 10-17 M and determined the ranges of applicability of the compound. We used erythrocytes and cells of Ehrlich ascitic carcinoma (EAC). Erythrocytes are the primary targets for drugs getting into blood vessels. The structural elements of erythrocyte membranes are similar to those of other cells of organism. However, erythrocytes are devoid of the whole system of signal transduction that is characteristic of other less specialized cells. Therefore, experiments were performed in EAC cells that give a typical cellular response to a signal and possess the system of transduction of signal from the cell surface to inside.

MATERIALS AND METHODS The structural state of membranes was studied by EPR-spectroscopy using paramagnetic spin probes [8]. Rat and mice blood erythrocytes and mice EAC cells were incubated in the presence of ichfan for 45 min; then, probes were inserted. The microviscosity of various membrane sites was measured on an ER 200D-SRC spectrometer (Bruker, Germany). Probe I (2.2.6.6-tetramethyl-4-capryloyl-oxypiperidine-1-oxyl) is localized mainly in the surface lipid bilayer of membrane; probe II (5.6-benzo-2.2.6.6-tetramethyl-1.2.3.4-tetrahydro-γ-carboline3-oxyl) permeates into deep-located near-protein sites of the lipid bilayer. From the EPR spectra obtained, using the formula for rapidly rotating probes, the rotation correlation time

Stabilization of Cell Membranes by Hybrid Antioxidants…

153

that has the meaning of the period of the radical reorientation by the angle π/2 was calculated (τc x 10-10 s) [9]. The results were expressed in arbitrary units (samples without the compound were used as the control). Isolation of erythrocytes and erythrocyte ghosts of mongrel white rats and determining the cell stability degree with regard to the level of hemolysis of erythrocytes were performed by the methods described in [10,11]. The releasing activity of Ca-K channels was measured potentiometrically using the K+ -selecting electrode [12]. The thermograms of erythrocyte ghosts were recorded with the aid of a DASM-4 differential adiabatic scanning microcalorimeter [13]. Isolation of EAC cells and recording of right angle light scattering of dilute suspension of EAC cells were performed on a Perkin–Elmer-44B spectrofluorometer at a wavelength of 510 nm by the method described in [14].

RESULTS AND DISCUSSION

1,2

1,2 microviscozity of AKE (rel.un.)

microviscozity of erythrocites (rel.un.)

The EPR-spectroscopy data obtained showed that ichfan applied in various concentrations modifies the microviscosity of both layers (probes I and II) of erythrocyte membranes and EAC cells (Figure 1). We discovered a complex nonlinear character of the dose–effect dependence. In all cases, the membrane microviscosity increased by 18% relative to the control at the HA concentrations 10-16–10-14 M and 10-6–10-4 M. For EAC cells, under the action of the compound, the microviscosity of both layers of the membrane lipid bilayer decreased on the average by 20% with the exception of the extreme concentrations. Consequently, in vitro experiments showed that ichfan modifies the structural state of biomembranes; the effect depends on the compound dose and type of membranes.

1,15 1,1 1,05 1 0,95 0,9

1,1 1 0,9 0,8 0,7 0,6

-16 -14 -12 -10

-8

lg[ichfan-10] М

-6

-4

-16

-14

-12

-10

-8

-6

-4

lg[ichfan-10] M

Figure 1. Dose-response diagram for the effect of ichfan on microviscosity of the erythrocyte (A), and of the cell of Ehrlich ascitic carcinoma (B). Probe I (light) (2,2,6,6-tetramethyl-4-capryloyloxypiperidin-1-oxyl) is localized in the surface layer of the membrane lipid bilayer; Probe II (dark) (5,6-benzo-2,2,6,6-tetramethyl-1,2.3,4-tetrahydro-γ-carbolin-3-oxyl) in the deep near-protein sites of lipids.

154


4,1

K+-release (rel.un.)

4,05 4 3,95 3,9 3,85

-4

-6

-8

-1 0

-1 2

-1 4

-1 6

0

3,8

lg[ichfan-10] M

A hemolysis of erythrocytes (rel.un.)

4 3,5 3 2,5 2 1,5 1 0,5

-4

-6

-8

-1 0

-1 2

-1 4

0 -1 6

0

lg[ichfan-10] M

B Figure 2. a. Dose-response curve for the effect of ichfan on the erythrocyte Ca-K-channels. Before the potentiometric assays of the dependence of intensity of K+ releasing from erythrocytes on the concentration of ichfan the red blood cells were preincubated in the absence or presence of ichfan at 37o C for 45 minutes. Than cells were precipitated by centrifugation and were resuspended. Ca-K-channels are activated by the A23187 adding .b. Dose- response curve for the effect of ichfan on the hemolysis of erythrocytes. Before spectrophotometric assays of the dependence of intensity of haemoglobin releasing from erythrocytes on the concentration of ichfan the red blood cells were preincubated in the absence or presence of ichfan at 37o C for 45 minutes. Than cells were precipitated by centrifugation and supernatant was tested. Axis of ordinates – optical density upon the λ of haemoglobin absorbency (575 nm).


155

The effect of HA on the Ca-K channels (Figure 2a) and the cells stability (Figure 2b) was studied in erythrocytes. The Ca2+-activated release of K+ was initiated by adding a calcium ionophore A23187 (from 2 to 4 μM) under condition of a low content of K+ (up to 1 μM) [12]. At the ichfan concentration 10-4 M, we observed a complete hemolysis of erythrocytes and the maximum release of K+ to the incubation medium. At low concentrations of the compound, the dose–effect curves of release of K+ ions and the curves of the hemolysis degree differed. The curve of dependence of the K+ release is of the S-shape: about 20% of K+ is released at the HA concentrations 10-10–10-6 M; at 10-15–10-11 M, the K+ release decreases; at 10-17–10-16 M, a slight increase is observed. The values of hemolysis do not differ from the control over the range from 10-17 M to 10-6 M. Thus the membrane stability is disrupted at high concentrations of ichfan (10-5–10-4 M). At the doses of 10-17–10-6 M, we observed no effect but discovered two maxima of activation of the Ca-K channels. The effect of the compound on the system of signal transduction in cell was studied by recording the light scattering in a dilute suspension of EAC cells; the light scattering correlated with a change in the cell volume. The cell volume is controlled considerably by functioning of the Ca2+-dependent - K+- and -Cl--channels of the plasmalemma. The regulation of these channels proceeds by several transduction pathways. We used the ATPdependent pathway of enhancement of intracellular Ca2+ concentration by activating EAC cells purinoreceptors by means of ATP additives [14]. The ichfan concentrations 10-5 M modify the light scattering considerably; the effect points to changes in the cell form and, correspondingly in the Ca-K and Ca-Cl channels (Figure 3). The Ca2+ - signal transduction initiated by the ATP effect on plasmalemma purinoreceptors is inhibited by HA applied in the dose 10-5 M; the ichfan concentrations 10-8 M and lower produce no effect. Thus, we observed no side effects at the cellular level produced by ichfan in the concentration 10-8 M. The effect of the compound on the structural organization of membrane proteins was studied by means of the differential scanning microcalorimetry of erythrocyte ghosts. The thermograms exhibited five identified thermo induced transitions depending on the denaturation of certain domains of the membrane framework: A (a complex of α- and βspectrine and actine), B1 (anchirine, proteins of bands 4.1 and 4.2, and dematine), B2 (a cytoplasmic fragment of protein of band 3), C (a membrane fragment of 55 kDa of protein of band 3 – ionic channels), and D (unidentified proteins and vesiculation of membrane [15, 16]. The preincubation of erythrocyte ghosts with ichfan for 45 min results in a slight shift in the temperature of the transitions (Figure 4a). A is shifted to the region of higher temperatures, B1 is retained, B2, C and D are shifted to the region of lower temperatures The treatment of ghosts with ethanol (Figure 4b) results in lowering of the peaks of the B1, B2, and D transitions. After treatment of membranes with HA at a dose of 10-6 M results in returning of the thermograms to their almost initial form with the exception of the D transition. A conclusion was drawn about the stabilizing effect of ichfan applied in the dose 10-6 M on the structure of isolated membranes.

156


Figure 3. Effect of ichfan on the ATP-depended Ca2+- transduction system of cells of Ehrlich ascitic carcinoma. The kinetic curves of light – scattering of a dilute suspension of cells. The succession of adding: the medium of incubation, (1) – AKE; (2) – ATP; (3) – ichfan(10-5 M); (4) – Triton –X100.

The effect of a biologically active substance on an isolated membrane and an intact cell membrane may differ considerably as to the concentration dependence and qualitatively. Therefore, we performed a preliminary treatment of whole cells of erythrocytes with ichfan; then, we isolated ghosts. The thermogram of erythrocyte ghosts (Figure 4c) varies considerably upon the preincubation of erythrocytes with HA at doses of 10-6–10-5 M. The thermogram of erythrocyte ghosts preincubated with ethanol (this additive is equivalent to


157

that of HA dissolved in ethanol) exhibits a decrease in the peak of the A transition as compared with untreated ghosts. In fact, the A transition disappearing is associated with a loss of deformation of erythrocytes and ghost membranes [17,18]. The treatment of erythrocytes with ichfan results in restoration of the A transition peak, i.e., restoration of the cytoskeleton. In a similar way, the temperature maxima are shifted to the region of lower temperatures; the peaks amplitudes vary. At a higher HA concentration of 10-5 M, the peaks of the B1 and B2 transitions converge into one junctional B transition; normally, this effect is observed on an ionic strength decreasing [15,16]. Hence, ichfan (at doses of 10-6–10-5 M) causes significant changes in the protein structure of the whole erythrocyte membrane and protects from damages. Thus, the maximum changes in the viscosity of the lipid bilayer of erythrocyte membranes are observed for the HA concentrations 10-16–10-14 M and 10-6–10-4 M, which correlate with two peaks of K+ releasing from erythrocytes. At higher ichfan concentrations, along with enhancement of the membrane viscosity, the organization of cytoskeletal proteins and functioning of the Ca-K channels are modified. At very high HA doses (10-4 M), the integrity of erythrocytes cells is disrupted. At low ichfan concentrations, the microviscosity increases and the K+ channels are activated, although no significant structural changes are observed (according to testing of hemolysis of erythrocytes). For EAC cells membranes, the compound (almost over the entire concentration range) decreases significantly the microviscosity of surface lipids and near-protein domains of the lipid bilayer; only at the HA concentrations 10-16 and 10-4 M, the viscosity increases. In particular, the compound dose 10-5 M affects the Ca2+ signal system of EAC cells. At lower ichfan concentrations (10-8 M), the membrane microviscosity decreases and the compound produces no effect on the cell volume. Evidently, over this concentration range, the compound produces no effect on the membrane and Ca2+ signal system. The studies on the effect of HA on EAC cells made it possible to determine the concentration range, within which the compound produces no side effects. On the basis of data obtained, we suggest using ichfan in concentrations no higher than 10-8 M that causes no side effects. Using the compound at higher doses (10-5 M) cause considerable changes in the characteristics of the Ca2+ signal system. Also, we detected changes in the structural organization of ghost membranes of erythrocytes after a preliminary incubation of them with HA at concentrations 10-5–10-6 M, which correlate with changes in the degree of hemolysis and activity of the Ca-K channels. A similar dependence of changes in the erythrocyte cell form and hemolysis degree was shown previously in [19]. Over the range of lower concentrations, the compound effect decreases and disappears completely, although the cytoskeletal structure and functions of cell ionic channels do not experience significant changes. A certain increase in the activity of the K+ channels is observed over the range of ultra-low concentrations (10-15–10-17 M). At these concentrations of ichfan, the integrity of cell is retained and the viscosity of the upper leaf of the bilayer increases significantly; the viscosity of deep proteins-permeated layers of the lipid bilayer increases insignificantly.

158

L. D. Fatkullina, O. M. Vekshina, E. B. Burlakova et al. a

b

c

Figure 4. a. Differential scanning calorimetric thermogram of red blood cells ghosts: (1) - ghosts of erythrocytes preincubated with phenozan before the preparation of red blood cells membranes; (2) – with ichfan; (3) – control, intact ghosts. b. Differential scanning calorimetric thermogram of red blood cells ghosts: (1) – control, intact ghosts; (2) - ghosts of erythrocytes preincubated with ethanol, before the preparation of red blood cells membranes; (3) – ghosts of erythrocytes preincubated with ichfan, before the preparation of red blood cells membranes. c. Differential scanning calorimetric thermogram of ghosts, preincubated with ichfan, before the preparation of red blood cells membranes. (1) – with ichfan (10-5 M); (2) - with ichfan (10-6 M); (3) – control, ghosts of erythrocytes preincubated with ethanol. Axis of ordinates - ΔCp – the change of relative thermal capacity (J g-1 k-1).


159

Consequently, at high concentrations, ichfan may form its own phase and drastically digitizes the membrane; indirectly (through lipids) it modifies the activity of membranebound proteins, which leads to destruction, i.e., the integrity of cells is disrupted as a result of the lipid bilayer disordering. It is possible that the compound in low concentrations is distributed in the bilayer in the proximity to proteins as a raft-forming substance. The HAinduced changes detected in the structure of membranes of erythrocytes are possible to occur in membranes of other cells, because the families of structural proteins studied are characteristic of many other cells of organism. Thus, the discovered stabilizing efficiency of hybrid antioxidant ichfan on cell membranes with regard to its pronounced antioxidizing effect and feasibility of permeation through the hematoencephalic barrier may be of primary importance for the membrane therapy of neurodegenerative diseases.

REFERENCES [1] [2] [3] [4] [5] [6] [7] [8] [9] [10] [11] [12] [13] [14] [15] [16] [17] [18] [19]

M.R. Prasad, M.A. Lovell, M. Yatin et al.: Neurochem. Res., 23 (1), 81 (1998). L. Ginsberg, J.H. Xuereb, N.L. Gershfield: J. Neurochem., 70 (3), 2533 (1998). L. Bolis, D.F. Hofmann, A. LIF: Membranes and diseases, Мedicine, Мoscow, 1980. 341 p. (in Russian). Yu.V. Postnov, S.N. Orlov: Primary hypertension as pathology of cell membranes, Мedicine, Moscow, 1987. 237 p. (in Russian). E.M. Molochkina, I.B. Ozerova, E.B. Burlakova: Free Rad. Biol. Med.,33, 229 (2002). E.M. Molochkina, I.B. Ozerova: Radiation Biol./Radioecol., 43 (3), 294 (2003) (in Russian). E.M. Molochkina, N.Yu. Gerasimov, L.D. Fatkullina et al.: Chem. and Phys. of Lipids, 143, 94 (2006). A.N. Kuznetsov: Method of spine probes, Nauka, Moscow, 1976. 209 p.(in Russian). A.N. Goloshchapov, E.B. Burlakova: Biofizica, 20 (5), 816 (1975)(in Russian). A.K. Gulevskiy, V.V. Ryazantsev, A.M. Belous: Scientific Proceedings Higher Schools, Biol. Scien., 29 (1990) (in Russian). E. Beutler, C. West: J.Lab.Clin.Med., 88 (2), 328 (1976). N.V. Maksimova, S.Yu. Tchizhevskaya, Yu. A. Karpov et al.: Kardiologiya, 5, 45 (1999)(in Russian). P. L. Privalov, V.V. Plotnikov: Therm. Acta, 139, 257 (1989). V.P. Zintchenko, V.A. Kasimov, V.V. LI et. al.: Biofizica, 50 (5), 1055 (2005)(in Russian). W.M. Jackson, J. Kostyla, J.H. Nordin et al.: Biochemistry, 12, 3662 (1973). J.F. Brandts, K.A Lysko, A.T. Schwartz et al.: Colloques internationaux. C. R. S., 246, 169 (1976). N. Mohandas, A.C. Greenquist, S.B. Shohet: The Red Cell, Alan R. Liss, Inc., New York,1978. 453 p. B.P. Heath, N. Mohandas, J.L. Wyatt et al.: Biochim. Biophys. Acta, 691, 211 (1982). E.Yu. Parshina, L.Ya. Gendel, A.B. Rubin: Biofizica, 49 (6), 1094 (2004) (in Russian).


Chapter 13

WEAR RESISTANT COMPOSITE POLYMERIC MATERIALS BASED ON POLYURETHANES AND POLYISOCYANURATES L. V. Luchkina, A. A. Askadsky, and V. V. Kazantseva A.N. Nesmeyanov Institute of Organoelement Compounds, Russian Academy of Sciences, 28 Vavilov street, 119991 Moscow, Russia

ABSTRACT Reaction molding method has given composite impact and wear resistant reinforced gradient polymeric materials, based on polyisocyanurates (PIC) and polyurethanes (PU). The materials are good for mechanical processing that allowed production of wear resistant gears, working practically noiselessly.

Keywords: polyurethanes, polyisocyanurates, gradient materials, impact resistance, wear resistance, gears At the present time, the traditional methods of property control for polymeric materials is their level-to-level alignment using expensive welding or adhesion processes that represents a labor-intensive and multistage process, which also may lead to obtaining materials with defective interlayer adhesion. To our opinion, there is possible and perspective method for production of materials with controllable properties in the given directions, which is synthesis of gradient polymeric materials based on PU and PIC composites. Their technology includes the use of a “solution” method for combining a binder and a carrier, and their processing to articles using the reaction molding method. These are materials without interfaces, having elastic rather than viscoelastic properties typical of all known polymers present in the transition zone from the glassy-like to the rubbery state. This work is targeted at the study of impact resistance and wearability in gradient polymeric materials based on PU and PIC composites, produced by reaction molding method, with respect to the composition. Two types of composite gradient polymeric materials: the

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L. V. Luchkina, A. A. Askadsky and V. V. Kazantseva

ones reinforced by strengthening fillers and composite ones with a carrier which does not change the polymer properties. In this work, the polymeric binders are network polyurethane isocyanurates of the controlled composition based on polypropylene glycol (PPG) having MM = 2200, polyester urethane diisocyanate (PEUD) having MM = 3800, 2,4-toluylene diisocyanate (TDI), and diamine (di(3-chlor-4-aminophenyl)methane) [1, 2]. The reinforcement fillers in this case fibrous carbon material based on hydrated cellulose fibers (carbon tissue of UVIS-T, UVIS-TM/4 trademarks); the carriers causing no changes in properties of produced materials which are highly porous systems, such as elastic polyurethane foam of PPU-EM-1 trademark (PUF), have been used. The use of one or another type of carrier or filler has predetermined the ranges for application of gradient polyurethane isocyanurate polymeric materials. Based on the composite polyurethane isocyanurate gradient materials, shock absorbing layings and supports for household appliances (refrigerators, laundry washers, ventilators and so on), which perceive high vibration, have been developed under laboratory conditions. In this case, the rigid polyisocyanurate part of the material provides the ability of strong connection between parts of the article, and the rubber-like part acts as a shock absorber. A possibility of production of comfortable, including the orthopedic one, footwear based on composite materials, in which tensile loads are perceived by the rubber-like material, and compressing loads are perceived by the rigid material to which rubber-like material is gradually transferred. However, if materials with strengthened properties have been required than, as mentioned above, carbon fabric was used to create reinforced materials. The reinforced gradient materials obtained are well mechanically processed; as a result, gears are obtained which teeth have much lower modulus of elasticity than the core. For 350 h of operation the wear of such gears equaled 0.25% only. It is found that as polyurethane component content in the elastic part of gradient composite materials increases to 50-60 wt.%, impact strength obtain the highest values (16.9 and 13.7 kg⋅cm/cm2, respectively). Hence, flexural strength at the same ratio of polyisocyanurate and polyurethane is maximal in the rigid part of the material rather than in the elastic one. Mechanical tests of reinforced gradient materials have shown that impact strength of such materials, measured at the elastic side, is several time higher than for composite materials with a carrier. In the second series of experiments, the impact strength measured at the elastic side of the reinforced material specimen is higher than for the rigid part irrespective of PU content. It is found that impact strength of the samples tested at impacting the elastic side affects concentration of the PU component, because isocyanurate network crosslink points in these samples are linked by PU fragments containing propylene oxide group. It is noted that the impact strength, determined at impacting the rigid side of the samples, changes in the concentration of TDI and PU had a low effect: it has changed in the range of 11.1 to 17.6 kg⋅cm/cm2. The bending strength of reinforced gradient materials remains practically equal for rigid and elastic sides. Only in some cases its value is higher for the elastic side rather than for the rigid side. The abrasion value of gradient composite and reinforced polymeric materials has been estimated on a Schopper-Schloban type device (Table 1). Samples 1-7 shown in the Table contain polyurethane foam as the carrier of polymeric composite, and the sample 8 contains

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163

carbon tissue UVIS-T. The sample 5 contains 2 wt.% of K 354 trademark technical carbon, and the sample 6 2 wt.% of P803. It is found that the abrasion value is minimal at a side of the gradient sample contained from PU only or its content is greater in relation to the PIC component, and obtains the values typical of standard rubbers [3]. As PIC concentration in the rigid part increases, the abrasion value also increases to significant values (6-7⋅10−3 cm3/m). It is found that the abrasion value also is affected the technical carbon trademark. As the trademark P803 is used, the abrasion index is insignificantly lower compared with K354 trademark use. For a gradient reinforced material, the following regularity is observed: abrasion is maximal for the rigid side consisting of PIC only. As the PU component in the material increases, the abrasion index becomes minimal exceeding insignificantly abrasion indices typical of standard rubbers. This indicates that PU component addition to polyisocyanurate materials increases wearability of the materials obtained. Thus, reinforced impact resistant and wear resistant gradient polymeric materials based on PU and PIC. Specific impact strength and flexural strength of such samples depend on the quantity of PU component in the gradient materials, and the articles produced (gears) work almost noiselessly and do not show any wear. Table 1. Abrasion values for gradient polymeric materials No.

TDI concentration in PIC

Sample side composition PIC:PU

1 2 3 4 5

50 50 50 60 60

Elastic PU PU PU PU PU

6

60

PU

7 8

60 50

50:50 20:80

rigid 80:20 60:40 20:80 PIC 80:20 K354 80:20 P803 60:40 PIC

Side abrasion index I·103, cm3/m elastic rigid 1.0 5.4 2.3 4.9 3.4 3.4 1.5 5.6 1.7 6.4 1.2

5.9

4.7 4.7

7.2 7.4


Luchkina L.V., Askadsky A.A., Bychko K.A., and Kazantseva V.V. // Plastich. Massy. 2005. No. 9. P. 21. (Rus). Luchkina L.V., Bychko K.A., Kovriga O.V. et al. // Plastich. Massy. 2005. No. 10. P. 19. (Rus). Reznikovsky M.M. and Lukomskaya A.I. // Mechanical tests of natural and artificial rubbers. M.: Khimia. 1968. 359 p. (Rus).


Chapter 14

PHOTODESTRUCTION OF CHLOROPHYLL IN NON-BIOLOGICAL SYSTEMS A. V. Lobanov1,2, O. V. Nevrova1, Yu. A. Vedeneeva1, G. V. Golovina3, and G. G. Komissarov1 1

Semenov Institute of Chemical Physics RAS, Kosygina st. 4, Moscow 119991, Russia; 2 Lomonosov Moscow State University, Chemistry Department, Leninskie Gory 1-3, Moscow 119899, Russia; 3 Emanuel Institute of Biochemical Physics RAS, Kosygina st. 4, Moscow 119991, Russia

1. INTRODUCTION The structure of plant photosynthetic systems is interrogated by numerous methods [1-3], but there are not comprehensive information about factors influencing on stability of chlorophyll (Chl). Furthermore the data of photodestruction of Chl are important for development of structure functional models of photosynthesis. The study of effect of hydrogen peroxide on Chl photodestruction intensity is of particular interest because the active role of H2О2 in photosynthesis mechanism was shown [4] and Н2О2 was used in several artificial photosynthetic systems [5, 6]. Transformations of Chl under the visible light irradiation include in opening of chlorine macrocycle (Figure 1) which results to formation of colourless oxygen-containig compounds (λabs ≤ 350 nm) [7] and/or elimination of Mg2+ ion that leads to production of pheophytin (Pheo) with another absorption spectrum. This work is concerned with the investigation of photodestruction of Chl in a number of non-biological systems.

2. EXPERIMENTAL Extraction of Chl from dry nettle leaves and its purification were carried out by methods [4]. Ethanol (50 or 100 vol.%), micelles of cetyltrimethylammonium bromide (CTAB), liposomes of 1,2-diacyl-sn-glycero-3-phosphocholine (PC), complexes based on bovine

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serum albumin (BSA) and poli-N-vinylpyrrolidone (PVP), adsorption layers on silica gel as well as Photosystem I (PSI) extracted from spinach chloroplasts were used as the systems for the study of Chl photodestruction. To elucidate the effect of hydrogen peroxide on Chl photodestruction kinetics H2O2 (0.1 M) was added to the samples. The samples (solutions or suspensions), 10 ml, were agitated by a stirrer at visible light irradiation. The lighter consisted of halogen tube (150 W), lens and condenser. The concentration of Chl was measured by spectrophotometer Beckman DU-8. X X = CH3 N

N

Chl a

X = CH=O Chl b

Mg N

N

H3C H H H3COOC O

H

O

O CH3 H CH3 H

Figure 1. The structure of Chl molecules.

3. RESULTS AND DISCUSSION During studying of Chl photodestruction its concentration varied in the systems. General peculiarity of photodestruction is its acceleration at Chl aggregation, e.g. at [Chl] > 10-4 М in ethanol, at ≥20 molecules of Chl on one micelle in CTAB micelles, at monolayer exceeding on silica gel. Consequently, in Chl aggregates photodestruction occurs as Chl* + Chl. It is quite possible that singlet oxygen participates in photodestruction because 1O2 can be produced by triplet excited chlorophyll molecules 3Chl*. The photodestruction of smaller quantity of Chl depends on concentration of solved oxygen or other oxidant. As it turned out the type of Chl photodestruction is affected by polarity of the systems. The formation of Pheo takes place at high degree of Chl photodestruction in only polar systems (ethanol, water/ethanol, PSI, BSA, PVP), when bindig of Mg2+ and medium ligands

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(Figure 2). But producing of Pheo does not happen at non-polar environment (PC, CTAB), in which Chl molecules are in hydrophobic region. Individual Pheo is stable at experimental conditions. However Pheo formed by Chl photodestruction is subjected to photodestruction. The reason of this fact is possibility of Mg-containing Chl as well as complexes of porphyrines and nontransition metals to generate long-living triplet excited states 3Chl* (1 ms) with high quantum yield (≥60%) in contrast to free Pheo. 3.5 3.0

1

2.5

D

2.0 1.5 1.0

2 0.5 0.0 400

500

600

700

800

nm Figure 2. Adsorption spectra of Chl in BSA (10-6 M) before (1) and after 180 min of irradiation (2). 1,1

1.01,0 0.90,9

D / D0

0.80,8 0.70,7 0.60,6

1

0.50,5 0.40,4

2

0.30,3 0.2 0 0

20

40

20

40

60

60

80

100

80

120

100

140

120

140

160

180

t, min Figure 3. Kinetics of Chl photodestruction in 1.2 · 10-3 M CTAB (1) and in 1.2 · 10-3 M CTAB with 0.1 M H2O2(2).

A. V. Lobanov, O. V. Nevrova and Yu. A. Vedeneeva

168 1.0 0.9

D / D0

0.8

5

0.7 0.6 0.5

12 3

0.4 0

20

40

4 60

80

100

t, min Figure 4. Kinetics of Chl photodestruction in ethanol (1), ethanol-PVP (2), ethanol-PVP-H2O2 (3), water-PVP (4), water-PVP-H2O2 (5). Content of PVP is 10 weight %.

Addition of Н2О2 to the Chl systems accelerates Chl photodestruction in all cases except PVP system (Figure 3). It unexpectedly proved that of Chl associated with PVP is more stable in presence of Н2О2 (Figure 4). Obviously this effect are explained by high affinity between PVP and Н2О2 [8], when Н2О2 molecules bind polymer chain by hydrogen bond and steric factor protecting Chl appears. In artificial systems Chl is more stable than one in PSI. Adsorbed Chl molecules are the most stable.

ACKNOWLEDGEMENTS The research was supported by grant NSh-5236.2006.3.

REFERENCES [1] [2] [3] [4]

S. Iwata, J. Barber. Current Opinion in Structure Biology. 2004. V. 14. № 4. P. 447453. W. Hillier, T. Wydrzynski. Biochim. Biophys. Acta. 2001. V. 1503. P. 197-209. R.D. Britt, K.A. Campbell, J.M. Peloquin et al. Biochim. Biophys. Acta. 2004. V. 1655. P. 158-171. G.G. Komissarov. Fotosintez: fiziko-khimicheskiy podkhod. Мoscow: Editorial URSS, 2003. 224 p. (in Russian).

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A.V. Lobanov, S.N. Kholuiskaya, G.G. Komissarov. Doklady Akademii Nauk. 2004. V. 399. № 1. P. 73-75 (in Russian). A.V. Lobanov, S.N. Kholuiskaya, G.G. Komissarov. Khim. Fizika. 2004. V. 23. № 5. P. 44-47 (in Russian). B.D. Berezin. Koordinatsionnye soedineniya porfirinov i ftalotsianina. Мoscow: Nauka, 1978. 280 p. (in Russian). E.F. Panarin, K.K. Kalninsh, D.V. Pestov. Doklady Akademii Nauk. 1998. V. 363. № 2. P. 208-210 (in Russian).


Chapter 15

SOME MAKROKINETICHESKIE PARTICULARITIES OF DEEP HYDROLYSIS PET CALCIUM GIDROKSIDE IN BEAD MILL A. S. Harichkin*and A. M. Ivanov Kursk State Technical University, 94, 50 years October Str., 305040, Kursk, Russia

ABSTRACT The variant of hydrolysis PET calcium hydroxide interesting in that plan that both components in reactionary mixture are present in the manner of independent hard phases, but fluid phase needs for ensuring the mobilities reactionary mixture, as well as for carrying alkali on surface PET way to adsorptions from solution. Chemical reaction occurs on surfaces PET itself.

Keywords: Hydrolysis, polyethyleneterephthalate (PET), calcium hydroxide, bead mill, salvaging, ethyleneglycol

One method of a polymer utilization is its decomposition into monomers. Considering that PET is ester the easiest way of its decomposition will be a deep alkali hydrolysis. The cheapest and most available alkali is calcium hydroxide. However, it is slightly soluble in water. That makes significant difficulties for its using for the mentioned purpose. An attempt has been made to overcome this problem by carring out the process in the beaded mill in accordance with the following scheme:

*

[email protected], [email protected]

A. S. Harichkin and A. M. Ivanov

172

PET (granules) Ca(OH)2 (CaO) distilled water

beaded mill

samples of the reaction mixture for analyses

powder

screening

heating of finedispersed suspension being stirred up to working temperature proceeding the process in thebeaded-mill up to self-stopping

fraction of fixed sizes dosage mixing initial reaction mixture

addition of distilled water or another liquid phase or

Ca(OH)2 Ca(OH)2 stirring and heating up to working temperature distilled water final reaction mixture

PET fraction of fixed sizes

water

hydrolysis Ca(OH)2

Ca(OH)2

distilled water

The process was controlled by taking samples for analysis and determining amount of alkali in them (total amount in all phases and alkali concentration in liquid phase of the reaction mixture (using a conductometric method)). Samples were taken without stopping stirring the reaction mixture that excluded significant phase division of the system into layers and change of the phase ratio in samples to be taken because of the stated reason. As a whole such an attempt was successful. PET was decomposed into ethylene glycol and calcium salt of terephthalic acid astheproducts. However, the process was found to be not simple. Considerable growth in viscosity of the reaction mixture and progressing self-braking that may be followed by untimely self-stopping in case of untaking effective actions could be observed (Figure 1). Under model conditions ethyleneglycol as a hydrolysis product increases solubility of Ca (OH)2. However, its accumulation or introduction into the beaded mill as a component of the liquid phase does not lead to hydrolysis intensification. Probably it occurs because presence of ethyleneglycol promotes the growth of liquid phase viscosity that may be connected with increase in solubility of calcium salt of terephthalic acid in liquid phase of the reaction mixture. In consequence of this significant drop in efficiency of the beaded mill work is observed.

Some Makrokineticheskie Particularities …

173

Simultaneos reduction of PET and Ca(OH)2 dosage was found to be unproductive. The process being considered is heterogenous and the place of its proceeding is a polymer surface. Reduction of the latter undoubtedly leads to decrease of the process. Farther investigations were directed to understanding what prevents the process from fast proceeding at deep stages. For this purpose the following results were estimated: • use of fractional introduction of stechiometric amount of calcium hydroxide or its excess instead of introduction for one time; • various programmes of dillution the reaction mixture becoming thick during the course of the process with distilled water, ethyleneglycol, aqueous solutions of ethyleneglycol etc.; • use of calcium oxide that could interact with water giving finer-dispersed Ca(OH)2 instead of calcium hydroxide; • substitution distilled water or aqueous solution of calcium hydroxide for a part of liquid phase of the reaction mixture during the course of the process; • variation of initial content of PET and Ca(OH)2; • variation of temperature of carrying out the process; • variation of operations succession while introducing the reagents; As mentioned above the process being considered is heterogenous and the place of its proceeding is a polymer surface from liquid phase by means of adsorbtion in the form of both Ca(OH)2 molecules and Ca(OH)+ and OH- ions. In other words the following displacement of the alkali reagent takes place:

Ca(OH)2

Ca(OH)2sol

PET surface

adsorption +

-

Ca(OH) + OH

Various chemical reactions occur on the surface of PET, for instance

~C6H4C(O)O- + Ca(OH)+

~ C6H4C(O)OCaOH

~CH2CH2OC(O)C6H4C(O)OCa+ + OH-

~C6H4C(O)OCH2CH2OH + OHetc.

~C6H4C(O)OCa+ + OH-

~CH2CH2OH- + OC(O)C6H4C(O)OCa+ Ca(OC(O))2C6H4

~C6H4C(O)O- + OHCH2CH2OH

174

A. S. Harichkin and A. M. Ivanov

Calcium salt of terephthalic acid that is slightly soluble in water remains on the surface of the solid part of the polymer and ethylene glycol that is soluble in water mainly goes into the liquid phase. Finally surface sediments of the products arise on particles of PET. Under conditions of intensive mechanical stirring and interaction of the particles with each other the sediments can move from particles of PET to ones of Ca(OH)2. It will lead to blocking of both particles of PET and ones of Ca(OH)2.In consequence of this the concentration of Ca(OH)2 in solution decreases that may be a reason of self-stopping to be met practice.

Drawing 1. Kinetic curves of the spending calcium hydroxide on hydrolysis PET in bead mill of the vertical type; the fluid phase: 1 - water; 2,3 - water-whine solution ethyleneglycol; 4 - ethyleneglycol.

Drawing 2. Influence of the contents ethyleneglycol (EG) in fluid phase on soluble calcium hydroxide.


Chapter 16

TRANSPORT PHENOMENA WITHIN POROUS MEDIA Sh. Rahrovan and A. K. Haghi* Faculty of engineering, The University of Guilan Rasht 41635, P. O. Box 3756, Iran

ABSTRACT Wood is a hygroscopic, porous, anisotropic and non-homogenous material. Microwave drying generate heat from within the grains by rapid movement of polar molecules causing molecular friction and help in faster and more uniform heating than does conventional heating. In this paper, a comprehensive review is presented on the researches and developments related to drying processes of wood. Other issues regarding the technology limitation, research challenges, and future trends are also discussed.

NOMENCLATURE

**

A= a= e a* = b* = CP =

area; xposed area per unit volume of the stack; color parameters; color parameters; specific heat;

D=

Da =

diffusion coefficient; inter diffusion coefficient of vapor in air;

Dbt =

transverse bound water diffusion coefficient of wood;

Eb =

activation energy;

f= G=

relative drying rate; dry air mass flow rate;

[email protected]

Sh. Rahrovan and A. K. Haghi

176 h=

heat transfer coefficient;

hD =

mass transfer coefficient;

Jb =

bound water diffusion flux;

Jf =

liquid free water flow flux;

J vf =

water vapor flow flux;

j0 =

constant drying rate;

K=

thermal conductivity;

KL =

longitudinal thermal conductivity;

KT =

transverse conductivity;

k= k0 =

permeability; mass transfer coefficient;

kr =

relative permeability;

L= L* = Le = MC =

M cr1 =

length of specimen parallel to the direction of flow; lightness; Lewis number; moisture content; first critical moisture content;

M cr 2 =

second critical moisture content;

Me =

equilibrium moisture content;

Mw= m& = m& ij =

molecular weight of water; mass flow rate per unit surface area;

Nν =

moisture flux;

P=

Pressure;

P = pc = Q& =

Average pressure across the specimen; capillary pressure;

q= R=

Ra =

heat flux; gas constant; average roughness;

Rq =

root mean square (RMS) roughness;

Rz =

average maximum height of the profile;

r= SG =

SGd =

latent heat of vaporization of water; specific gravity of wood; nominal specific gravity of wood substance;

T=

temperature;

transition from phases i and j;

heat flow rate;

Transport Phenomena within Porous Media t= u= V= v= X= x= Y=

177

time; moisture content; volume; fluid velocity; Distance in x coordinate axis; water transfer distance; air humidity;

Greek Symbols

αR = α LS = β= ν= ΔE * = ΔΗ wv = ε = μ= ρ= ρ0 =

coefficients to reflect effects of heat radiation; coefficients to reflect effects of heat loss; mass transfer coefficient when vapor partial pressure difference is taken as driving force; porosity of wood; total color change; Latent heat of vaporization; void fraction in the lumber stack; viscosity; density; density of oven-dry wood;

ρs =

wood basic density;

ρ Gν =

vapor partial pressure in the air stream;

ρ νs = ϕ= φ = φi = χ=

vapor partial pressure at the wood surface; humidity coefficient relative humidity; volumetric fraction; water transfer distance;

Subscripts a _ air; b _ bound water; c_ capillary; C _ Celsius; conv _ convection; cs _cross sectional; cw _ cell wall;

178

Sh. Rahrovan and A. K. Haghi DB _ dry Bulb; evap _ evaporation; ex _ exit; f_after drying; f.s.p._fiber saturation point; G _main stream; i_before drying; in _ initial; k _ kelvin; L _ longitudinal; l _liquid phase; m _ mean value; mt _ moisture or wet; r _ relative; s _ solid skeleton of wood; sat _ Wood, at saturation; surf _ surface of wood board; so _ wood segment o; T_ transverse; v _ vapor; ν _gas phase; w _ free water; wood _ wood; wv _ water vapor;

1. WOOD AS A POROUS MEDIA Wood is a hygroscopic, porous, anisotropic and non-homogeneous material. After log sawing, the lumber contains liquid water in fiber cavities (capillary water) and bound water inside the fiber wall (hygroscopic water). Porosity refers to volume fraction of void space. This void space can be actual space filled with air or space filled with both water and air. Capillary-porous materials are sometimes defined as those having pore diameter less than

10 −7 m. Capillary porous materials were defined as those having a clearly recognizable pore space. In capillary porous material, transport of water is a more complex phenomena. In addition to molecular diffusion, water transport can be due to vapor diffusion, surface diffusion, Knudsen diffusion, capillary flow, and purely hydrodynamic flow. In hygroscopic materials, there is large amount of physically bound water and the material often shrinks during heating. In hygroscopic materials there is a level of moisture saturation below which the internal vapor pressure is a function of saturation and temperature. These relationships are called equilibrium moisture isotherms. Above this moisture saturation, the vapor pressure is a function of temperature only (as expressed by the Clapeyron equation) and is independent of the moisture level. Thus, above certain moisture level, all materials behave non-hygroscopic. Green wood contains a lot of water. In the outer parts of the stem, in the sapwood, spruce and pine have average moisture content of about 130%, and in the inner parts, in the

Transport Phenomena within Porous Media

179

heartwood, the average moisture content is about 35%. Wood drying is the art of getting rid of that surplus water under controlled forms. It will dry to an equilibrium moisture content of 8–16% fluid content when left in air which improves its stability, reduces its weight for transport, prepares it for chemical treatment or painting and improves its mechanical strength. Water in wood is found in the cell cavities and cell walls. All void spaces in wood can be filled with liquid water called free water. Free water is held by adhesion and surface tension forces. Water in the cell walls is called bound water. Bound water is held by forces at the molecular level. Water molecules attach themselves to sites on the cellulose chain molecules. It is an intimate part of the cell wall but does not alter the chemical properties of wood. Hydrogen bonding is the predominant fixing mechanism. If wood is allowed to dry, the first water to be removed is free water. No bound water is evaporated until all free water has been removed. During removal of water, molecular energy is expended. Energy requirement for vaporization of bound water is higher than free water. Moisture content at which only the cell walls are completely saturated (all bound water) but no free water exists in all lumens is called the fiber saturation point (F.S.P). Typically the F.S.P of wood is within the range of 2040 % moisture content depending on temperature and wood species. Water in wood normally moves from high to low zones of moisture content. The surface of the wood must be drier than the interior if moisture is to be removed. Drying can be divided into two phases: movement of water from the interior to the surface of the wood, and removal of water from the surface. Water moves through the interior of the wood as a liquid or water vapor through various air passageways in the cellular structure of wood and through the cell walls. Drying is a process of simultaneous heat and moisture transfer with a transient nature. The evolution process of the temperature and moisture with time must be predicted and actively controlled in order to ensure an effective and efficient drying operation. Lumber drying can de understood as the balance between heat transfer from air flow to wood surface and water transport from the wood surface to the air flow. Reduction in drying time and energy consumption offers the wood industries a great potential for economic benefit. In hygroscopic porous material like wood, mathematical models describing moisture and heat movements may be used to facilitate experimental testing and to explain the physical mechanisms underlying such mass transfer processes. The process of wood drying can be interpreted as simultaneous heat and moisture transfer with local thermodynamic equilibrium at each point within the timber. Drying of wood is in its nature an unsteady-state nonisothermal diffusion of heat and moisture, where temperature gradients may counteract with the moisture gradient.

2. SOME ASPECTS OF HEAT FLOW DURING DRYING PROCESS 2.1. Stages of Drying First stage: When both surface and core MC are greater than the F.S.P. Moisture movement is by capillary flow. Drying rate is evaporation controlled. Second stage: When surface MC is less than the FSP and core MC is greater than the F.S.P. Drying is by capillary flow in the core and by bound water diffusion near the surface as

180


fiber saturation line recedes into wood, resistance to drying increases. Drying rate is controlled by bound water diffusion. Third stage: When both surface and core MC are less than the F.S.P. Drying is entirely by diffusion. As the MC gradient between surface and core becomes less, resistance to drying increases and drying rate decreases.

2.2. Capillary Capillary pressure is a driving force in convective wood drying at mild conditions [1]. The temperature is higher outside than inside. The moisture profile during convective drying is in the opposite direction, namely, the drier part is toward the exposed surface of wood. This opposite pattern of moisture and temperature profiles lead to the concept of the wet front that separates the outer area, where the water is bound to the cell wall, from the inner area, where free water exists in liquid and vapor form. A wet front that moves slowly from the surface toward the center of a board during convective drying leads to subsequent enhancement of the capillary transportation. Capillary transportation can then be justified due to the moisture gradients developed around that area. When the drying conditions are mild, the drying period is longer so the relative portion of the total moisture removal, due to the capillary phenomena, is high, and it seems that this is the most important mass transfer mechanism [2].

2.3. Bound Water Diffusion Credible data on the bound water diffusion coefficient in wood and the boundary condition for the interface between moist air and wood surface are very important for accurate description of timber drying as well as for the proper design and use of products, structures and buildings made of wood already dried below the fiber saturation point. During the last century, two groups of methods for measuring the bound water diffusion coefficient in wood were developed. The first one, traditionally called the cup method, uses data from the steadystate experiments of bound water transfer and is based on Fick’s first law of diffusion. Unfortunately, the method is not valid for the bound water diffusion coefficient determination in wood because it cannot satisfy the requirements of the boundary condition of the first kind and the constant value of the diffusion coefficient [3]. The second group of methods is based on the unsteady-state experiments and Fick’s second law of diffusion. The common name of this group is the sorption method and it was developed to overcome the disadvantages of the cup technique [4].

2.4. Diffusion In solving the diffusion equation for moisture variations in wood, some authors have assumed that the diffusion coefficient depends strongly on moisture content [5-9] while others have taken the diffusion coefficient as constant [10-14]. It has been reported [15-19] that the diffusion coefficient is influenced by the drying temperature, density and moisture content of timber. The diffusion coefficient of water in cellophane and wood substance was shown by


181

[20] to increase with temperature in proportion to the increase in vapor pressure of water. Stamm and Nelson also observed that the diffusion coefficient decreased with increasing wood density [21]. Simpson recorded an exponential relationship for the diffusion coefficient in the moisture content range of 5 to 30 % [17]. Other factors affecting the diffusion coefficient that are yet to be quantified are the species (specific gravity) and the growth ring orientation. Literature has suggested that the ratios of radial and tangential diffusion coefficients vary for different tree species [16]. The radial diffusion coefficient of New Zealand Pinus radiate has been estimated to be approximately 1.4 times the tangential diffusion coefficient [22]. Jen Y. Liu et al observed that for northern red oak, the diffusion coefficient is a function of moisture content only. It increases dramatically at low moisture content and tends to level off as the fiber saturation point is approached [23]. Also, different boundary conditions have been assumed by different authors [24-27]. In a one-dimensional formulation with moisture moving in the direction normal to a specimen of a slice of wood of thickness 2a, the diffusion equation can be written as:

∂ ( MC ) ∂ ⎛ ∂ ( MC ) ⎞ = ⎜D ⎟ (0 < X < a, t > 0) ∂t ∂X ⎝ ∂X ⎠

(1)

Where MC is moisture content, t is time, D is diffusion coefficient, and X is space coordinate measured from the center of the specimen. The moisture content influences on the coefficient D only if the moisture content is below the fiber saturation point (F.S.P.) (typically 20%-30% for softwoods) [28]:

⎧ f D (u ) , u < u fsp ⎪ D(u ) = ⎨ ⎪ f (u ) , u ≥ u fsp ⎩ D fsp

(2)

Where u fsp denotes the F.S.P. and f D (u ) is a function which expresses diffusion coefficient in moisture content, temperature and may be some other parameters of ambient air climate [7], [29]. The expression of f D (u ) depends on variety of wood.

It was assumed that the diffusion coefficient bellow F.S.P. can be represented by:

f D (u ) = A.e

−

5280 T

.e

B .u 100

(3)

Where T is the temperature in Kelvin, u is percent moisture content, A and B are experimentally determined [30]. The regression equation of diffusion coefficient of Pinus radiata timber using the dry bulb temperature and the density is [31]:

(

)

D 10 −9 = 1.89 + 0127 × TDB − 0.00213 × ρ S ( R 2 =0. 499)

(4)


182

The regression equations of diffusion coefficients below of Masson’s pine during high temperature drying are [32]:

D = 0.0046 MC 2 + 0.1753MC + 4.2850 (R 2 = 0.9391)

(5)

Tangential diffusion

D = 0.0092MC 2 + 0.3065MC + 4.9243 (R 2 = 0.9284 )

(6)

Radial diffusion The transverse diffusion coefficient D can be expressed by the porosity of wood ν , the transverse bound water diffusion coefficient Dbt of wood and the vapor diffusion coefficient

Dν in the lumens [33]: D=

ν Dbt Dν

(1 −ν )( ν Dbt + (1 − ν )Dν )

(7)

The vapor diffusion coefficient Dν in the lumens can be expressed as:

M w Da Ps dφ . SGd ρ w RTk du

Dν =

(8)

Where M w (kg/kmol) is the molecular weight of water.

Da =

9.2.10 −9 Tk2.5 (Tk + 245.18)

(9)

is the inter diffusion coefficient of vapor in air [34].

SGd =

1.54 (1 + 1.54u )

(10)

is the nominal specific gravity of wood substance at the given bound water content [35].

ρw

3

= 103 kg / m is the density of water, R = 8314.3 kmol, K is the gas constant, Tk is the Kelvin temperature,

φ is the relative humidity (%/100), and Psat is saturated vapor pressure

given by [36, 37]:

(

p sat = 3390 exp − 1.74 + 0.0759TC − 0.000424 TC2 + 2.44 .10 −6 TC3

)

(11)

Transport Phenomena within Porous Media The derivative of air relative humidity

183

φ with respect to moisture content u is calculated

from the Hailwood-Horrobin equation adopted for wood by Simpson [37] and given as:

u=

k Φ ⎞ 18 ⎛ k1k 2 Φ ⎜⎜ ⎟ + 2 w ⎝ 1 + k1k 2 Φ 1 − k 2 Φ ⎟⎠

(12)

Where:

k1 = 4.737 + 0.04773TC − 0.00050012TC2

(13)

k 2 = 0.7059 + 0.001695TC + −0.000005638TC2

(14)

W = 223.4 + .6942TC + 0.01853TC2

(15)

The diffusion coefficient Dbt of bound water in cell walls is defined according to the Arrhenius equation as:

Dbt = 7.10 −6 exp(− Eb / RTk )

(16)

Where:

(

)

Eb = 40.195 − 71.179u + 291u 2 − 669.92u 3 .10 6

(17)

is the activation energy [38]. The porosity of wood is expressed as:

ν = 1 − SG(0.667 + u )

(18)

Where specific gravity of wood SG at the given moisture content u is defined as:

SG =

Where

ρS

ρW (1 + u )

=

ρ0

(19)

ρW + 0.883 ρ 0 u

ρ s is density of wood, ρ 0 is density of oven-dry wood (density of wood that has 0

been dried in a ventilated oven at approximately 104 C until there is no additional loss in weight) [35].


184

Table 1. Thermal conductivity of selected hardwoods and softwoods Species Hardwoods Ash Black White Aspen Big tooth Quaking Basswood, American Beech, American Birch Sweet Yellow Cherry, black Chestnut, American

Cottonwood Black Eastern Elm American Rock Slippery Hackberry Hickory, pecan Hickory, true Mockernut Shagbark Magnolia, Southern Maple Black Red Silver Sugar Oak, red Black Northern red Southern red Oak, white Bur White Sweetgum Sycamore, American Tupelo Black

Specific gravity

Conductivity(W/m·K) Oven dry

Conductivity(W/m·K) 12% MC

0.53 0.63

0.12 0.14

0.15 0.17

0.41 0.40 0.38 0.68

0.10 0.10 0.092 0.15

0.12 0.12 0.11 0.18

0.71 0.66 0.53 0.45

0.16 0.15 0.12 0.11

0.19 0.18 0.15 0.13

0.35 0.43

0.087 0.10

0.10 0.12

0.54 0.67 0.56 0.57 0.69

0.12 0.15 0.13 0.13 0.15

0.15 0.18 0.15 0.16 0.19

0.78 0.77 0.52

0.17 0.17 0.12

0.21 0.21 0.14

0.60 0.56 0.50 0.66

0.14 0.13 0.12 0.15

0.16 0.15 0.14 0.18

0.66 0.65 0.62

0.15 0.14 0.14

0.18 0.18 0.17

0.66 0.72 0.55 0.54

0.15 0.16 0.13 0.12

0.18 0.19 0.15 0.15

0.54

0.12

0.15


185

Table 1. Continued Species

Specific gravity 0.53 0.46

Conductivity(W/m·K) Oven dry 0.12 0.11

Conductivity(W/m·K) 12% MC 0.15 0.13

Water Yellow-poplar Softwoods Baldcypress Cedar Atlantic white Eastern red Northern white Port-Orford Western red Yellow Douglas-fir Coast Interior north Interior west Fir Balsam White Hemlock Eastern Western Larch, western Pine Eastern white Jack Loblolly Lodgepole Longleaf Pitch Ponderosa Red Shortleaf Slash Sugar Western white Redwood Old growth Young growth Spruce Black Engelmann Red Sitka White

0.47

0.11

0.13

0.34 0.48 0.31 0.43 0.33 0.46

0.085 0.11 0.079 0.10 0.083 0.11

0.10 0.14 0.094 0.12 0.10 0.13

0.51 0.50 0.52

0.12 0.12 0.12

0.14 0.14 0.14

0.37 0.41

0.090 0.10

0.11 0.12

0.42 0.48 0.56

0.10 0.11 0.13

0.12 0.14 0.15

0.37 0.45 0.54 0.43 0.62 0.53 0.42 0.46 0.54 0.61 0.37 0.40

0.090 0.11 0.12 0.10 0.14 0.12 0.10 0.11 0.12 0.14 0.09 0.10

0.11 0.13 0.15 0.12 0.17 0.15 0.12 0.13 0.15 0.17 0.11 0.12

0.41 0.37

0.10 0.090

0.12 0.11

0.43 0.37 0.42 0.42 0.37

0.10 0.090 0.10 0.10 0.090

0.12 0.11 0.12 0.12 0.11


186

2.5. Thermal Conductivity Wood thermal conductivity ( K wood ) is the ratio of the heat flux to the temperature gradient through a wood sample [39]. Wood has a relatively low thermal conductivity due to its porous structure, and cell wall properties. The density, moisture content, and temperature dependence of thermal conductivity of wood and wood-based composites were demonstrated by several researchers [40-44]. MacLean [40] measured the thermal conductivities of various woods with a large range of MC and specific gravities (SG). He presented two empirical equations which gave the best agreement with his experimental data. The transverse thermal conductivity can be expressed as:

K wood = [SG × (4.8 + 0.09 × MC ) + 0.57]× 10 −4

cal cm * Cs

(20)

cal cm * Cs

(21)

When moisture content of wood is below 40%.

K wood = [SG × (4.8 + 0.125 × MC ) + 0.57]× 10 −4 When moisture content of wood is above 40%.

The specific gravity and moisture content dependence of the solid wood thermal conductivity in the transverse (radial and tangential) direction is given by Siau [45] as:

K T = SG (K cw + K w .M ) + K aν

(22)

Where: SG= specific gravity of wood, K cw = Conductivity of cell wall substance (0.217 J /m/s/K),

K w = conductivity of water (0.4 J / m/s /K), K a = conductivity of air (0.024 J /m/s /K), M = moisture content of wood (fraction),

ν = porosity of wood.

The thermal conductivity of wood is affected by a number of basic factors: density, moisture content, extractive content, grain direction, structural irregularities such as checks and knots, fibril angle, and temperature. Thermal conductivity increases as density, moisture content, temperature, or extractive content of the wood increases. Thermal conductivity is nearly the same in the radial and tangential directions with respect to the growth rings. The longitudinal thermal conductivity of solid wood is approximately 2.5 times higher than the transverse conductivity [45]:


K L = 2.5K T

187 (23)

For moisture content levels below 25%, approximate thermal conductivity K across the grain can be calculated with a linear equation of the form [46]:

K wood = G (B + CM ) + A

(24)

Where SG is specific gravity based on oven dry weight and volume at a given moisture content MC (%) and A, B, and C are constants. For specific gravity >0.3, temperatures around 24°C, and moisture content values M Cr1 dt

(25)


188

Figure1. Drying characteristic of porous media: (A) constant rate region; (B) first falling rate region; (C) second falling rate region.

−

d ( MC ) = A + B * MC For M cr1 > MC > M cr 2 dt

(26)

−

d ( MC ) A + B * M cr 2 = * (MC − M e ) For MC< M cr 2 dt M cr 2 − M e

(27)

Where: j 0 is constant drying rate, M Cr1 is the first critical moisture content, M cr 2 is the second critical moisture content, constants A and B also vary with wood thickness, wood density, and drying conditions.

4. MOISTURE CONTENT AND PERMEABILITY Moisture content of wood is defined as the weight of water in wood expressed as a fraction, usually a percentage, of the weight of oven dry wood. Moisture exists in wood as bound water within the cell wall, capillary water in liquid form and water vapor in gas form in the voids of wood. Capillary water bulk flow refers to the flow of liquid through the interconnected voids and over the surface of a solid due to molecular attraction between the liquid and the solid [57]. Moisture content varies widely between species and within species of wood [57-59]. It varies particularly between heartwood and sapwood. The amount of moisture in the cell wall may decrease as a result of extractive deposition when a tree undergoes change from sapwood to heartwood. The butt logs of trees may contain more water than the top logs. Variability of moisture content exists even within individual boards cut


189

from the same tree. Green wood is often defined as freshly sawn wood in which the cell walls are completely saturated with water. Usually green wood contains additional water in the lumens. Moisture content at which both the cell lumens and cell walls are completely saturated with water is the maximum moisture content. An average green moisture content value taken from the Wood Handbook [59] and Dry Kiln Operator’s Manual [58] of southern yellow pine (loblolly) is 33 and 110% for heartwood and sapwood, respectively. Sweetgum is 79 and 137% while yellow-poplar is 83 and 106% for heartwood and sapwood, respectively [58, 59]. Permeability refers to the capability of a solid substance to allow the passage of gases or liquids under pressure [60]. Permeability assumes the mass movement of molecules in which the pressure or driving force may be supplied by such sources as mechanically applied pressure, vacuum, thermal expansion, gravity, or surface tension [61]. Under this condition, the permeability of wood is the dominant factor controlling moisture movement. Fluid movement in wood is a very important process in wood products industries [62]. An understanding of wood permeability is essential for determining lumber drying schedules for treating lumber and for producing high-quality wood products. The flow of gas inside the wood particle is limited due to the fact that wood consists of a large number of clustered small pores. The pore walls act as barriers largely preventing convective flow between adjacent pores. The wood annular rings also act as barriers for flow in the radial direction which makes flow in the axial direction more favorable and giving a lower permeability in the radial direction than in the axial direction where the axial flow is regarded as flow parallel to the wood fiber grains and the radial flow as flow perpendicular to the wood grains. The permeability in the wood cylinder is therefore an important parameter for the velocity field in the wood. From [63] the dry wood radial permeability is 10000 times lower than the dry wood axial permeability. The chemical composition of the wood/ char structure also affects the permeability, where the permeability in char is in order of 1000 times larger than for wood [64]. Longitudinal flow becomes important, particularly in specimens having a low ratio of length to diameter, because of the high ratio of longitudinal to transverse permeability [65]. Longitudinal permeability was found to be dependent upon specimen length in the flow direction [66], i.e. the decrease of specimen length appears result in greater permeability in less permeable species. For example, Sebastian et al. [67] found that the permeability of white spruce decreased with increasing specimen length. Bramhall [68] observed a negative relationship between the gas permeability and the lengths of Douglas fir specimens ranging from 0.5-3.5 cm. Siau [69] also reported similar results for Douglas fir and loblolly pine specimens of 2-30 cm in length. Banks [70] described that (due to decreased permeability with increases in specimen length) some flow paths may remain unchanged as length is increased while others may totally be blocked with a wide variation in pore diameter. Liquid, therefore, penetrates into some flow paths more rapidly than others, giving rise to the occurrence of surface forces resisting penetration with both wetting and non wetting liquids [71]. The effect of drying conditions on gas permeability and preservative treatability was assessed on western hemlock lumber. Although there were no differences in gas permeability between lumber dried at conventional and high temperatures, there were differences in preservative penetration. High temperature drying significantly reduced drying time, but did not appear to affect permeability or shell-to-core MC differences compared with drying at conventional temperature [72]. Pits have a major influence on softwood permeability [73].


190

Across pits can be impeded by aspiration or occlusion by deposition extractives on the membrane. Drying conditions can significantly affect pit condition, sometimes inducing aspiration that blocks both air and fluid flow [74]. Pressure treatment is presumed to enhance preservative uptake and flow across pits, but the exact impact of pit condition (i.e., open or aspirated) is unknown. Drying conditions may also alter the state of materials deposited on pits, thereby altering the effects of pressure and perhaps the nature of preservative wood interactions [75]. The latter effect may be especially important, since changes in wood chemistry could affect the rates of preservative fixation, which could produce more rapid preservative deposition on pit membranes that would slow further fluid ingress. Peter Y.S et al measured vessel lumen area and the longitudinal and radial permeabilities of the sapwood of each species to evaluate the effect of diameter growth rate on vessel lumen area percentage and on the intrinsic permeability. The longitudinal permeability of the outer heartwood of each species also was determined to evaluate the effect of growth rate on the decrease in longitudinal permeability following sapwood conversion to heartwood. Faster diameter growth produced higher longitudinal permeability in the sapwood of yellow-poplar, but not in the sapwood of northern red oak or black walnut. Growth rate had no effect on either vessel lumen area percentage or decrease in longitudinal permeability in newly formed heartwood for all three species [76]. Table 2 represents typical values for gas permeability. Values are given in orders of magnitude [77]. Darcy’s law for liquid flow:

V flux (t × A) = V × L k= = ΔP t × A × ΔP gradient L

(28)

Table 2. Typical values for gas permeability Type of sample

Longitudinal gas permeability 3

Red oak (R = 150 micrometers)

[ cm (gas)/(cm at sec)] 10,000

Basswood (R = 20 micrometers)

1,000

Maple, Pine sapwood, Coast Douglas-fir sapwood

100

Yellow-poplar sapwood, Spruce sapwood, Cedar sapwood

10

Coast Douglas-fir heartwood

1

White oak heartwood, Beech heartwood

0.1

Yellow-poplar heartwood, Cedar heartwood, Inland Douglasfir heartwood Transverse Permeabilities(In approx. same species order as longitudinal)

0.01 0.001 - 0.0001


191

Where: 3

k = Permeability [ cm (liquid)/ (cm atm sec)] 3

V = Volume of liquid flowing through the specimen ( cm ) t = Time of flow (sec) A = Cross-sectional area of the specimen perpendicular to the direction of flow 2

( cm ) ΔP = Pressure difference between ends of the specimen (atm) L = Length of specimen parallel to the direction of flow (cm) Darcy’s law for gaseous flow:

kg =

V × L× P t × A × ΔP × P

(29)

Where:

k g = Superficial gas permeability [ cm 3 (gas)/ (cm atm sec)] 3

V = Volume of gas flowing through the specimen ( cm (gas)) P = Pressure at which V is measured (atm) t = Time of flow (sec) A = Cross-sectional area of the specimen perpendicular to the direction of flow 2

( cm ) ΔP = Pressure difference between ends of the specimen (atm) L = Length of specimen parallel to the direction of flow (cm)

P = Average pressure across the specimen (atm)

5. BASIC THEORETICAL CONCEPTS 5.1. Mass Conservation Equations To simulate the heat and mass transport in drying, conservation equations for general non-hygroscopic porous media have been developed in Whitaker [78] based on averaging procedures of all of the variables. These equations were further employed and modified for wood drying by Perre´ et al. [79] Mass conservation equations for the three phases of moisture in local form are summarized in equations (30-32). Water vapor:

∂ (φ g ρV ) = −div ρV VV + m& WV + m& bV ∂t

(

)

(30)


192 Bound water:

∂ (φ s ρ b ) = −div(ρ bVb ) + m& bV + m& wb ∂t

(31)

Free water:

∂ (φ w ρ w ) = −div(ρ wVw ) − m& wv − m& wb ∂t Where the velocity of the transported quantity is denoted by Vi ,

(32)

ρ i is the density, and

m& ij denotes the transition from phases i and j. From here on, the subscripts w, b, v, and s refer, respectively, to free water, bound water, water vapor, and the solid skeleton of wood. Denoting the total volume by V and the volume of the phase i by Vi , the volumetric fraction of this phase is:

φi =

Vi V

(33)

with the geometrical constraint:

φ g + φs + φw = 1

(34)

5.2. The Generalized Darcy’s Law Darcy’s law, by using relative permeabilities, provides expressions for the free liquid and gas phase velocities as follows: vl = −

K l K rl

∇Pl

(35)

vv= −

K v K rv

∇Pv

(36)

μl

and

μv

Where K is the intrinsic permeability ( m 2 ), k r is the relative permeability, P is the

pressure (Pa), and μ is the viscosity (Pa .s).


193

5.3. External heat and Mass Transfer Coefficients The heat flux (q) and the moisture flux ( Nν

(

q = h TG − Tsurf

) are estimated by:

)

(37)

(

Nν = ϕK 0 (Ysurf − YG ) = β pνG − pνats

)

(38)

In which Tsurf , Υsurf andpνs are respectively, the wood temperature, the air humidity and the vapor partial pressure at the wood surface and, TG , ΥG andp νG are the corresponding parameters in the air stream. The heat-transfer coefficient is represented by h. The masstransfer coefficient is β when vapor partial pressure difference is taken as driving force and is k 0 when humidity difference is taken as the driving force with ϕ being the humidity factor. The mass-transfer coefficient related to humidity difference is a function of distance along the airflow direction from the inlet side [80]. The heat-transfer coefficient is correlated to the mass-transfer coefficient, as shown by and can be calculated from it [81]. The humidity coefficient ϕ has been found to vary from 0.70 to 0.76, depending on the drying schedules and board thickness [82].

5.4. Moisture and Heat Balance Equations For the moisture mass transfer and balance, the moisture loss from wood equals the moisture gain by the hot air, and the moisture transfer rate from the board is described by mass transfer coefficient multiplied by driving force (humidity difference, for example). These considerations yield:

−

⎧− ϕK .a.(Υ − Υ )(condensation) ∂ [MC.ρ s .(1 − ε )] = G. ∂Υ = ⎨ 0 surf G ∂τ ∂X ⎩ϕK 0 .a. f .(Υsat − ΥG )(evaporation)

Where MC is the wood moisture content,

(39)

ρ s is the wood basic density, ε is the void

fraction in the lumber stack, a is the exposed area per unit volume of the stack and G is the dry air mass flow rate. In order to solve the above equations, the relative drying rate (f) needs to be defined which is a function of moisture content [83, 84]. For the heat transfer and balance, the energy loss from the hot air equals the heat gain by the moist wood. The convective heat transfer is described by product of heat transfer coefficient and the temperature difference between the hot air and the wood surface. The resultant relationships are as follows:


194

(1 + α R − α LS ) ∂Twood = ∂τ ρ s .(1 − ε ).C Pwood

∂Υ ⎤ ⎡ .⎢h.a.(TG − Twood ) − G.ΔH wv . G ⎥ ∂X ⎦ ⎣

∂ΥG ⎞ ⎛ ⎟.(TG − Twood ) ⎜ h.a + G.C Pν ∂TG ⎝ ∂Ζ ⎠ = G.(C Pν + ΥG .C Pν ) ∂X In the above equations, Twood is the wood temperature,

(40)

α R and α LS are coefficients to

reflect effects of heat radiation and heat loss, C Pwood is the specific heat of wood, and ΔΗ wv is the of water evaporation. These equations have been solved to determine the changes of air temperature and wood temperature along the airflow direction and with time [85].

5.5. Energy rate Balance on Drying Air and Wood The energy rate balance (kW) of a drying air adjacent to the wood throughout the wood board can be represented as follows [86]:

dT 1 1 Va ρ a ,mt cp a ,mt a = νAcs cp a ,mt (Ta ,in −Ta ,ex ) + Q& evap − Q& conv dt 2 2

(41)

Where Q& evap and Q& conv (kW) are the evaporation and convection heat transfer rates between the drying air and wood, which can be calculated as follows:

Q& evap = rm& wv ,s Asurf

(42)

Q& conv = hA(Ta − TSO )

(43) 2

& wv ,surf ) (kg/ m s) to the drying air can be The specific water vapor mass flow rate ( m calculated as follows:

m& wv ,surf =

hD (Pwv,surf − Pwv,a ) RwvTSO

(44)

The vapor pressure on the wood surface can be determined from the sorption isotherms of wood [87]. The mass transfer coefficient ( hD ) (m/s) can be calculated from the convection 2

heat transfer coefficient (h) (kW/ m K) as follows [88]:


hD = h

1

ρ a ,mt cpa ,mt Le

0.58

⎛ ρ wv ,m / ⎜⎜1 − P ⎝

⎞ ⎟⎟ ⎠

195

(45)

5.6. Water Transfer model above F.S.P. Water transfer in wood involves liquid free water and water vapor flow while MC of lumber is above the F.S.P. According to Darcy’s law the liquid free water flux is in proportion to pressure gradient and permeability. So Darcy’s law for liquid free water may be written as:

Jf =

k l ρ l ∂Pc . μ l ∂χ

(46)

Where:

J f =liquid free water flow flux, kg/ m 2 ·s,

k l =specific permeability of liquid water, m 3 (liquid ) / m ,

ρ l = density of liquid water, kg / m 3 , μ l = viscosity of liquid water, pa .s , pc = capillary pressure, pa , χ = water transfer distance, m, ∂pc / ∂χ = capillary pressure gradient, pa / m . The water vapor flow flux is also proportional to pressure gradient and permeability as follows:

J vf =

kV ρ v ∂PV . μV ∂χ

Where:

J vf = water vapor flow flux, kg/ m 2 ·s,

kV = specific permeability of water vapor, m 3 (vapor ) / m ,

ρ v , μ v = density and viscosity of water vapor respectively, kg / m 3 and pa .s , ∂pV / ∂χ =vapor partial pressure gradient, pa / m .

(47)


196

Therefore the water transfer equation above F.S.P. during high temperature drying can be written as:

ρs

∂ ( MC ) ∂ = (J f + J vf ∂t ∂x

)

(48)

Where:

ρ S = basic density of wood, kg / m 3 , MC = moisture content of wood, %, t = time, s, ∂ ( MC ) / ∂t = the rate of moisture content change, %/s, x = water transfer distance, m.

5.7. Water Transfer Model below F.S.P. Water transfer in wood below F.S.P. involves bound water diffusion and water vapor diffusion. The bound water diffusion in lumber usually is unsteady diffusion; the diffusion equation follows Fick’s second law as follows:

∂ ( MC ) ∂ ⎛ ∂ ( MC ) ⎞ = ⎜ Db ⎟ ∂t ∂x ⎝ ∂x ⎠

(49)

Where Db is bound water diffusion coefficient, m 2 /s, ∂ (MC)/ ∂x is MC gradient of lumber, %/m. The bound water diffusion flux J b can be expressed as:

J b = Db ρ s

∂ ( MC ) ∂x

(50)

Where:

ρ S is basic density of wood, kg/ m 3 . The water vapor diffusion equation is similar to bound water diffusion equation as follows

∂ ( MC ) ∂ ⎛ ∂ ( MC ) ⎞ = ⎜ DV ⎟ ∂t ∂ ( MC ) ⎝ ∂x ⎠ Where DV is water vapor diffusion coefficient, m 2 /s.

(51)


197

The water vapor diffusion flux can be expressed as:

J V = DV ρ s

∂ ( MC ) ∂x

(52)

Therefore the water transfer equation below F.S.P. during high temperature drying can be expressed as:

ρs

∂ ( MC ) ∂ = (J b + J V ) ∂t ∂x

(53)

6. EXPERIMENTAL APPROACHES Two types of wood samples (namely; Guilan spruce and pine) were selected for drying investigation. Natural defects such as knots, checks, splits, etc which would reduce strength of wood are avoided. All wood samples were dried to a moisture content of approximately 30%. The effect of drying temperature and drying modes on the surface roughness, hardness and color development of wood samples are evaluated.

6.1. Surface Roughness The average roughness is the area between the roughness profile and its mean line, or the integral of the absolute value of the roughness profile height over the evaluation length: L

1 Ra = ∫ r ( x)dx L0

(54)

When evaluated from digital data, the integral is normally approximated by a trapezoidal rule:

Ra =

1 N

N

∑r n =1

n

(55)

The root-mean-square (rms) average roughness of a surface is calculated from another integral of the roughness profile: L

Rq =

1 2 r ( x)dx L ∫0

The digital equivalent normally used is:

(56)


198

Rq =

1 N 2 ∑ rn N n=1

(57)

Rz (ISO) is a parameter that averages the height of the five highest peaks plus the depth of the five deepest valleys over the evaluation length. These parameters which are characterized by ISO 4287 were employed to evaluate influence of drying methods on the surface roughness of the samples. [89]. ÜNSAL, Ö. et al investigated the influence of drying temperatures on the surface roughness characteristics of veneer samples. The results showed that the effect of drying temperatures used in practice is not remarkable on surface roughness of the sliced veneer and maximum drying temperature (130°C) applied to sliced veneers did not affect significantly surface roughness of the veneers [90]. Results obtained from previous similar studies supported the findings of this study [91, 92]. Ismail Aydin and Gursel Colakoglu conducted a study on veneer. Veneer sheets were classified into four groups and dried at 20, 110, 150, and 180°C. According to the results, the smoothest surfaces were obtained for 20°C drying temperature while the highest values of surface roughness were obtained for 180°C [93]. Because some surface checks may develop in the oven-drying process [94]. It was also found in a study that the surface roughness values of beech veneers dried at 110°C was higher than that of dried at 20°C [95]. Ismail Aydin et al. performed an experimental study on Alder and beech. Veneer sheets were oven-dried in a veneer dryer at 110°C (normal drying temperature) and 180° C (high drying temperature) after peeling process. The surfaces of some veneers were then exposed at indoor laboratory conditions to obtain inactive wood surfaces for glue bonds, and some veneers were treated with borax, boric acid and ammonium acetate solutions. After these treatments, surface roughness measurements were made on veneer surfaces. Alder veneers were found to be smoother than beech veneers. They concluded that the values mean roughness profile ( Ra ) decreased slightly or no clear changes were obtained in Ra values after the natural inactivation process. However, little increases were obtained for surface roughness parameters, no clear changes were found especially for beech veneers. It was concluded in a study that the surface of CCAtreated wood was rougher than that of untreated and water-treated wood [96, 97]. Ali Temiz et al. investigated the changes created by weathering on impregnated wood with several different wood preservatives. The study was performed on the accelerated weathering test cycle, using UV irradiation and water spray in order to simulate natural weathering. Wood samples were treated with ammonium copper quat (ACQ 1900 and ACQ 2200), chromated copper arsenate (CCA), Tanalith E 3491 and Wolmanit CX-8 in accelerated weathering experiment. The changes on the surface of the weathered samples were characterized by roughness measurements on the samples with 0, 200, 400 and 600 h of total weathering. Generally the surface values of alder wood treated with copper-containing preservatives decreased with over the irradiation time except for treated Wolmanit CX-82% when comparing unweathered values. Surface values of pine treated samples generally increased with increasing irradiation time except for ACQ-1900 groups [98]. Because the stylus of detector was so sensitive first each sample was smoothened with emery paper then measurement test was performed before and after drying. The Mitutoyo


199

Surface roughness tester SJ-201P instrument was employed for surface roughness measurements. Cut-off length was 2.5 mm, sampling length was 12.5 mm and detector tip radius was 5 μm in the surface roughness measurements. Table 3 and Table 4 displays the changes in surface roughness parameters ( Ra , R z and Rq ) of the Pine and Guilan spruce at varying drying methods. In both cases the surface roughness becomes higher during microwave and infrared heating while surface smoothness of both pine and Guilan spruce increased during convection and combined drying [99]. However, the roughness of wood is a complex phenomenon because wood is an anisotropic and heterogeneous material. Several factors such as anatomical differences, growing characteristics, machining properties of wood, pre-treatments (e.g. steaming, drying, etc.) applied to wood before machining should be considered for the evaluation of the surface roughness of wood [100]. Table 3. Surface roughness (μm) for pine Drying methods

Drying conditions

Microwave

Before drying After drying Before drying After drying

4.525.46

24.6830.21

5.396.62

4.42 4.87

25.52 26.55

5.43 5.69

Convection

Before drying After drying

4.66 4.08

26.87 24.64

5.86 5.12

Combined

Before drying After drying

5.23 3.41

32.59 21.7

6.42 4.27

Infrared

Ra

Rz

Rq

Table 4. Surface roughness (μm) for Guilan spruce Drying methods

Drying conditions

Microwave

Before drying After drying Before drying After drying Before drying After drying Before drying After drying

Infrared Convection Combined

Ra

Rz

Rq

6.44 7.77 4.92 6.42 4.97 4.78 10.41 9.11

34.18 44.3 30.61 38.93 32.41 32.27 59.5 54.31

7.85 9.82 6.30 8.17 6.5 6.34 13.37 11.5

6.2. Hardness Hardness represents the resistance of wood to indentation and marring. In order to measure the hardness of wood samples, the Brinell hardness method was applied. In this


200

method a steel hemisphere of diameter 10 mm was forced into the surface under test. The Brinell method measures the diameter of the mark caused by the steel ball in the specimens. The specimens were loaded parallel and perpendicular to the direction of wood grains. After applying the force the steel ball was kept on the surface for about 30 seconds. The values of hardness are shown in figures 2, 3 respectively. In both type of samples the hardness measured in longitudinal direction is reported to be higher than tangential. The amount of fibers and its stiffness carrying the load are expected to be lower when the load direction is angled to the grain. Results showed that hardness of wood increased in combined drying. The hardness of wood is proportional to its density [101]. The hardness of wood varies, depending on the position of the measurement. Latewood is harder than early wood and the lower part of a stem is harder than the upper part. Increase in moisture content decreases the hardness of wood [102]. Selhlstedt_Persson has observed the effect of different drying temperatures during air circulation drying. The result indicates no significant influence of temperature on hardness; still the specimens dried at higher temperature gave a hard and brittle impression [103]. L.Hansson and A.L.Antti investigated whether wood hardness is affected by temperature level during microwave drying and whether the response is different from that of conventionally dried wood. They concluded that there is a significant difference in wood hardness parallel to the grain between methods when drying progresses to relatively lower level of moisture content, i.e. wood hardness becomes higher during microwave drying. Variables such as density and moisture content have a greater influence on wood hardness than does the drying method or the drying temperature [104].

perpendicular to the grain

C

In fra re d C om bi ne d

parallel to the grain

on ve ct io n M icr ow av e

Hardness(Mpa)

30 25 20 15 10 5 0

DIFFERENT DRYING METHODS Figure 2. Brinell hardness for Guilan spruce.


Hardness(Mpa)

25

201

perpendicular to the grain

20 15

parallel to the grain

10 5

bi ne d om

C

In fra re d

C

on ve ct io n M icr ow av e

0

DIFFERENT DRYING METHODS Figure 3. Brinell hardness for pine.

6.3. Color Development Measurement Color development of wood surfaces can be measured by using optical devices such as spectrophotometers. With optical measurement methods, the uniformity of color can be objectively evaluated and presented as L*, a* and b* coordinates named by CIEL*a*b* color space values [105]. Measurements were made both on fresh and dried boards and always from the freshly planed surface. Three measurements in each sample board were made avoiding knots and other defects and averaged to one recording. The spectrum of reflected light in the visible region (400-750 nm) was measured and transformed to the CIEL*a*b* color scale using a 10º standard observer and D65 standard illuminant. These color space values were used to calculate the total color change ( ΔE ) applied to samples according to the following equations: *

ΔL* = L*f − L*i Δa * = a *f − ai* Δb * = b *f − bi*

(58)

ΔE * = (ΔL* ) 2 + (Δa * ) 2 + (Δb * ) 2 f and i are subscripts after and before drying respectively. In this three dimensional coordinates, L* axis represents non-chromatic changes in lightness from an L* value of 0 (black) to an L* value of 100 (white), +a* represents red, -a* represents green, +b* represents yellow and -b* represents blue [106]. As can be seen from figure4 and figure5 color space values of both pine and Guilan spruce changed after drying.


Surface color

202 7 6 5 4 3 2 1 0 -1 -2 -3

o i cr M

ΔL* Δa* Δb* d n tio ine c b e m In nv o Co C Different drying methods

ve wa

ΔE*

d re a r f

Surface color

Figure 4. Surface color of Pine. 6 5 4 3 2 1 0 -1 -2 -3 -4

o i cr M

ΔL* Δa* Δb* d n ne tio i c b e In nv om o C C Different drying methods

ve a w

re fra

d

ΔE*

Figure 5. Surface color of Guilan spruce.

Results shows that Δa ∗ generally decreased but Δb ∗ increased for both pine and Guilan spruce wood samples except for Guilan spruce during combined heating. The lightness values ΔL increased during drying. The L of wood species such as tropical woods which originally have dark color increases by exposure to light [107, 108]. This is due to the special species and climate condition of Guilan spruce and pines wood. Positive values of Δb* indicate an increment of yellow color and negative values an increase of blue color. Negative values of Δa* indicate a tendency of wood surface to greenish. A low ΔE* corresponds to a *

*

low color change or a stable color. The biggest changes in color appeared in ΔE values of pine samples during infrared drying while for Guilan spruce it was reversed. Due to differences in composition of wood components, the color of fresh, untreated wood varies between different species, between different trees of the same species and even within a tree. *


203

Within a species wood color can vary due to the genetic factors [109, 110] and environmental conditions [111, 112]. In discoloration, chemical reactions take place in wood, changing the number and type of chromophores. Discolorations caused by the drying process are those which actually occur during drying and are mainly caused by non-microbial factors [113]. Many environmental factors such as solar radiation, moisture and temperature cause weathering or oxidative degradation of wooden products during their normal use; these ambient phenomena can eventually change the chemical, physical, optical and mechanical properties of wood surfaces [114]. A number of studies have been conducted that have attempted to find a solution to kiln brown stain, the majority of them being pre-treatment processes. Biological treatment [115], compression rolling [116], sap displacement [117, 118] and chemical inhibitors [119] have all been used as pre-treatments. In all cases these processes were successful in reducing or eliminating stain but were not considered economically viable. Vacuum drying [120] and modified schedules [121] have been tried as modified drying processes with only limited success. Within industry various schedules have been developed, though these are generally kept secret and it is difficult to gauge their success. Generally it seems that industry has adopted a post-drying process involving the mechanical removal of the kiln brown stain layer as recommended by Kreber and Haslett [121].

7. CONCLUDING REMARKS Microwave processing of materials is a relatively new technology that provides new approaches to improve the physical properties of materials. Microwave drying generate heat from within the grains by rapid movement of polar molecules causing molecular friction and help in faster and more uniform heating than does conventional heating. If wood is exposed to an electromagnetic field with such high frequency as is characteristic for microwaves, the water molecules, which are dipoles, begin to turn at the same frequency as the electromagnetic field. Wood is a complex composite material, which consists mainly of cellulose (40–45%), hemicelluloses (20–30%) and lignin (20–30%). These polymers are also polar molecules, and therefore even they are likely to be affected by the electromagnetic field. This could possibly cause degradation in terms wood hardness. For Guilan spruce the average of hardness is shown to be much higher than pine. From the experimental results it can be observed that in combined microwave dryer, the hardness was relatively improved in comparison to the other drying methods. Microwave and infrared drying can increase wood surface roughness while the smoothness of wood increases during convection and combined drying. The effect varies with the wood species. Thus this work suggests keeping the core temperature below the critical value until the wood has dried below fiber saturation as one way of ensuring that the dried wood is acceptably bright and light in color.

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Chapter 17

BLOCK-COPOLYSULFONARILATES OF POLYCONDENSATIONAL TYPE E. B. Barokova, A. M. Kharaev, R. Ch. Bazheva, T. R. Umerova Kabardino-Balkarian State University, Nalchik, 173 Chernishevskaye street, KBR, Russia

ABSTRACT The review on the ways of receiving, properties and the use of some blockcopolysulfonarilates on the basis of bisphenols of different kinds of construction is represented here.

Keywords: block-copolysulfonarilates, bisphenols, dichloranhydride, sulphonoxide, 1,1-dichloro-2,2-di(n-oxyphenyl)ethylene.

oligoarilen-

The production of polymers of prefabricated construction – one of the ways of creation of high-molecular compounds with a beforehand given complex of properties. The perspective in this direction is the synthesis of chemically active bifunctional oligomers, able to react with polycondensations. Polycondensational pokymers, as a rule, have valuable operational characteristics, as a high heat-, fire-, thermo-, chemicalstability in combination with good strengthening indices. Polysulfonarilates belong to such ones. Block-copolysulfonarilates may be received in several ways, for instance, by the interaction of separately received macrodychlorinehydride on the basis of oligoarylate of needed molecular weight and oligoarylensulfoxide (OASO) with terminal hydroxyl groups. It is obvious that this way may be realised by the method of acceptor- catalytic polycondensation. Oligomers of both types of the given molecular weight with terminal hydroxyl groups may be also received and their transformation into block-copolymers may be realised by interaction with dichloranhydride of dicarboxylic acid – the extender of the chain. There is also a possibility of introducing one of the beforehand received olygomers, for instance,

E. B. Barokova, A. M. Kharaev, R. Ch. Bazheva et al.

212

oligoarylensulfoxide as a macrobisphenol into the reactionary compound, containing lowmolecular bisphenol and dichloranhydride of dicarboxylic acid. At the same time there is a formation of olygoarialate blocks of an indeterminate molecular weight which are chemically connected with blocks of oligoarylensulfoxide of the given molecular weight, and also the lengthening of oligoarylensulfoxide blocks through dichloranhydride of dicarboxylic acid, that is the block-copolymers are noticeably of less well-ordered structure. These two ways of receiving block-copolymers may be realised by acceptor- catalytic, emulsive and high-temperature polycondensation. For receiving different block-copolysulfonarilates the initial monomers are, as a rule, such widespread monomers as diphenylolpropane, phenolphtalein, dichloranhydrides of phthalic acid, and also OASO of different degree of condensation on the basis of these bisphenols and 4,4'-dichlorodiphenilsulfon. As the investigations of properties of block-copolymers datas, received by different ways, show that if having OASO – blocks till 10-15% the thermic properties of samples remain on the level of polyarilates, and the mechanical properties noticeably improve. Simultaneously the viscosity of fluxes of block-copolymers greatly decrease, and that has a great practical significance as it leads to a considerable simplification of heat-resistant polymers. With the aim of getting block-copolysulfonarilates with a smaller degree of fusion, and with good physio-mechanical properties the block-copolymers are synthesized on the basis of dian or phenolphtalein oligoarilensulphonoxides and dichloranhydrides of different structure [1-6]. The received block-copolysulfonarilates, on the basis of dian OASO and dichloranhydride 1,1-dichlor-2,2-di(n-oxyphenyl)ethylene, have the following structure:

C CH3

CH3

O

CH3 O

O

S O

O

C CH3

O n

C

C

C

O

CCI2

O m

where n = 1,5,7,10 and 20 The use of 1,1-dichloro-2,2-di(n-oxyphenyl)ethylene as an acid agent leads to an improvement of a number of mechanical datas. The block-copolymers are soluble in chlorinated hydrocarbons and are not soluble in alcohol and in aliphatic hydrocarbon, have stability in deluted and concentrated solutions of alkali, in strong mineral acids, but resolve in a concetrated sulphuric acid. The films received by the method of watering in chloroform, are transparent and have good physio-mechanical properties. If compared the mechanical properties of the given layer of block-copolysulfonarilates it is evident that with a increase of the length of initial oligoether the significance of the breaking-down voltage doesn’t change greatly, while the percent elongation increases greatly. The block-copolysulfonarilates o the basis of OASO –20D have good plasticity. High datas of deformation- strengthening properties of given block-copolysulfonarilates are explained that the last ones combine inflexibility of polyarilates as well as elasticity of polysulfones. In this case the elasticity is gained by OASO of different degree of polycondensation, which makes the system in the hole more plastic.

Block-copolysulfonarilates of Polycondensational Type

213

Commparatively low datas of temperatures of glass transition and the flow of this level of block-copolysulfonarilates are explained by the content of a big number of flexible simple ether bonds. The size of permittivity of all investigated samples of block-copolymers~3 – 3,6 and is stable in the interval of temperatures 20-200 °C. The characteristics of inflammation and combustibility of polymer materials are connected closely with the existance of macromolecules haloidcontaining groupings in the chain. The introduction of a macromolecule >C=CCl2 groupings into the chain and the increase of their percentage in block-copolymers promote the increase of the index of the oxygen index (OI). The ramp OI of block-copolymers with the increase of the content of chlorinated components, is apparently connected with the changes of the amount of combustible products, exuded from unit of volume of block-copolymers when burning. The other group of block-copolysulfonarilates – are block-copolymers on the basis of phenophthalein oligoarilensulphonoxides (OASO) of different length and dichloranhydride 1,1-dichlor-2,2-di(n-oxyphenyl)ethylene, having the following structure: O O

C

O

O

O C

S

O

O

O

C

C O

O C

O

n

R

C O m

The use of phenolphtalein oligoethers, intruduction of volumetric carded classifications as a bridge group into the structure of oligoethers noticeably increases the temperature of glass transition and the flow of block-copolysulfonarilates in comparison with blockcopolysulfonarilates on the basis of OASO. The investigation of the temperature dependence of dielectric characteristics of these block-copolysulfonarilates showed that the permittivity in the interval 20-250°C is stable. When higher than this temperature its increase is seen, which is explained by the transition to a hyperelastic state. These block-copolysulfonarilates are steady in diluted solutions of acids and alkalies. A big degree of turgescence of polyethers on the basis of phenolphtalein oligoethers is connected with a lesser density of the packaging materials of these block-copolysulfonarilates in comparison with block-copolysulfonarilates on the basis of OASO. A high chemical stability, refractoriness, good dielectric characteristics in a wide interval of temperatures receivings of linear and structural polymers make them suitable as insulating, chemicaly stable, fire-resistant coverages, and high physio-mechanical characteristics – as constructive materials. An important characteristic for polyarilatesulfones and their derivatives is their incombustibility, refractoriness and thermal stability. In the work [7] with the aim to receive incombustible polymeric materials some polyarilatsulfon block-sopolymers on the basis of halogen containing bisphenols are synthesized and their properties are investigated. The BSP datas have a high refractoriness, rising with an increase of the halogen content in BSP. When the initial halogen containing

214

E. B. Barokova, A. M. Kharaev, R. Ch. Bazheva et al.

bisphenol is changed for bromide the refractoriness of received block-sopolymers increase greately. The datas of oxygen index for given block-sopolymers are in the interval 30-55%. In last three decades prof. Mikitaev and his pupils in the Kabardino-Balkarian State university hundreds of different block-copolysulfonarilates with high exploitation characteristics. Olygoarilensulfonoxides of different construction and structure are used in them, making a high heat resistance in combination with a high explosive solidity and plasticity. In the scientific works of these scientists it is shown that the introduction of some elements of olygosulfons into the macrochain of blok-sopolyethers influence positively some properties of the last ones. Different polyarilates and block-copolysulfonarilates based on the different unsaturated halogen containing monomers are also created - chloral derivatives, characterised by a complex of important properties, including an especially high fire- and chemicalstability. The use of such monomers helps to enlarge greatly the assortment of constructive and insulating polyesters. Besides, the egsistense of an unsaturated bond in these monomers makes it possible to thermoset block-copolysulfonarilates, thus improoving a number of operational characteristics. Taking into consideration the above-stated, we synthesized a number of blockcopolysulfonarilates on the basis of different bisphenols, the results of which will be presented in the subsequent works.

REFERENCES [1] [2]

[3]

[4] [5]

[6] [7] [8] [9]

Mikitaev A.K., Shustov G.B., Kharaev A.M. Synthesis and properties of blockcopolysulfonarilates. // Vysokomolek. Soed., 1984, 26A, №1, - P. 75-78. Kharaev A.M., Mikitaev A.K., Shustov G.B. and others. Synthesis and properties of block-copolysulfonarilates on the basis of oligoarilensulfophenolphthalein. // Vysokomolek. Soed., 1984, V.26B №14. – P. 271-274. Mikitaev A.K., Kharaev A.M., Shustov G.B. Unsaturated aromatic compound polyesters on the basis of chloral’s derivatives as constructive and membraneous materials. // Vysokomolek. Soed.,. 1998, v.39 №15, P.228-236. Kharaev A.M. Aromatic polyesters as thermostable constructive and membraneous materials: thesis for a Doctor's degree in chemistry, - Nalchik, 1993. 297 p. Mikitaev A.K., Korshak V.V., Shustov G.B. and others. Synthesis and investigations of some properties of halogen containing block-copolymers on the basis of oligomeric sulfone. Thes. Rep. of rep. conf. “Polymeric materials and the use in national economy”. Nalchik, 1976, publication 3, P. 49-50. Ozden S, Charaev A.M., Shaov A.H. High impact thermally stable blok- copolyethers. J. Mater. Sci. – 2001.-36.-P. 4479-4484. Mikitaev A. K., Shustov G. B, Charaev A. M., Korshak V. V., Kunizhev B. I. and. Dorofeev V. T. Vysokomolek. Soed. 1984.A, V.26, 75. Ozden S., Charaev A. M., Shaov A. H. and Shustov G.B., J. Appl. Polym. Sci.,1998, V.68, 1013. Shustov G.B., Mikitaev A. K., Charaev A. M., Dorofeev V. T. Patent 1485642, МКИ4 С08G 75/20.


Chapter 18

LIGUID-CRYSTALLINE POLYESTHERS ON THE BASIS OF TEREPHTALOYL-DI(N-OXIBENZOAT) AND AROMATIC POLYETHERS L. A. Asueva*, M. A. Nasurova, G. B. Shustov, A. M. Kharaev, and A. K. Mikitaev Khasbulatova Z. S.-Chechen State Pedagogical Institute, Grozny, 33 Kievskaya Str., Russia Kabardino-Balkar State University, Nalchic, 173 Chernishevskogo Str, Russia

ABSTRACT The briet review of coming out of liguid-grystalline poyethers, containing terephtaloyl-di(n-oxybenzoat) links and description of oligoethers, oligoketons, oligosulphoneketons which are used by the authors to get liguid-crystalline blokcopolymers is given.

Keywords: Liguid-crystalline, polycondensation, termotropic, terefhtaloyl-di(n-oxibenzoat) links, mesohenic groups, spacers, nematic, smectic, cholesteric structures, oligoethers, blockcopolymers

Nowadays we know several types of polymers, which are capable of liguid-crystalline solutions and m elts formation. Termotropic liguid-crystalline polymers with meso-henic rigid and flexible parts in the bacic chain is a comparatively new class of hing-molecular compounds. Changes in the chemical nature and length of flexible parts spacers, and structures of mesohenic groups allow to get polymers exhibiting liguid-crystalline properties in the wide temperature interval. Polyethers are examples of such compounds. Low temperatures of transformation into liguid-crystalline state in comparison to polyarylats and *


L. A. Asueva, M. A. Nasurova, G. B. Shustov et al.

216

conseguently low temperatures of processing, high solubility in available solvenst on the one hand, and subbiciently. Ligh resistance on the other hand let to use them as necessary material and takes these systems guite attractive. Liguid-crystalline polymers can have nematic, smectic and cholesteric structure, theu are called termotropic liguid-crystalles. Scientists all over the world work on making liguid-grystalline polymers. So blockcopolymers containing terephtaloyl-di(n-oxybenzoat) and polyarylat has been got by polycondensation of corresponding oligomers [1]. Thermal properties and structure of blockcopolymers have been studied by means of IRS and DSK. Termotropic liguid-crystalline nematic phase of these block-copolymers was identified by means of DSK. It was found out that biphase olivision is seen at the temperature ligher than 2800C. Description of termotropic liguid-crystalline copolyether polyethyleneterephtalat and terephtaloyl-di(n-oxybenzoat) is given in this work [2]. Microstructure of given blockcopolymer is characterized by means of IR-spectroscopy with fourie-transformation. Pictures of polarization microscopy show, that copolyether is nematic liguid-crystalline polymer. Molecular properties and structure of termotropic liguid-crystalline polymers containing terephtaloyl-di(n-oxybenzoat) are studied in the works [3, 4, 5]:

C O

O

C

C

O

O

O

C O

n

So, is has been found out that poly(terephtaloyl-di-n-oxybenzoat) polymer with flexible methylene and siloxane spacers takes smectic structures with folded molcule dispositoon in the loyers in the melt. Polymer was got by heating chlorophorme in the atmosphere of agon 1,1,3,3-tetramethyle-1,3-bis-(3-hydroxypropyl)disiloloxane [6], chloranhydrite terephtaloyldi(n-oxybenzoic acid) [7] triethylamin in the ratio 1:1:2 correspondingly. X-ray studies were done for poly(terephtaloyl-di-n-ozybenzoat) with decamethilene flexible spacers [8]. Atter several heating-cooling cycles it was found that polymer transforms into melt at T=1100C. Disorder of layer structures and transformation of system into isotropic state from liguid-crystalline occurs at temperature rise up to 1900C. When polymer is cooled at 1800C melt transforms from isotropic state into liguid-crystalline-state with the structure of smectic type. Description of liguid-crystalline polyethers properties researches containing mesohenic links of terephtaloyl-di(n-oxybenzoat) in the basic chain and methylene spacers of different length is giver in the work [9]. It is found that share of more movable cycles for oxybenzol groups in polyethers with terephtaloyl-di(n-oxibenzoat) mesogen is higher than in terephtaloyl ones. Share of more movable terephtaloyl groups is higher in polyethers with nonamethylene spacer, than in polyether with decamethylene spacer (exhibition of even effect). In decamethylene spacer flexibility of CH2-groups grows with removal from mesohen. Polyethers have smectic type structures. Polymers containing mesohenic groups of terephtaloyl-di(n-oxybenzoat) are synthesized in the work [10]. 1,6-hexanediol, 1,10-decandiol, oligomers of ethylene oxide and propylene oxide of different molecular weight, playing the role of spacers in the macromolecule has

Liguid-crystalline Polyesthers …

217

been used in the polycondensation. Segmenteo liguid-crystalline polyethers, containing seven or nine para-phenylene parts in the mesohenic link were got. It was shown that part of synthesized polyethers was processed into products by means of fiber formation and melting under pressure we synthesized oligoformals, oligoketons, oligosulphones, oligosulphoneketons, terephtaloyl-di-n-oxybenzoic acid and dichloranhydrite of terephtaloyl-di-n-oxibenzoic acid to get termotropic liguid-crystalline polyethers [11]. Oligoformals of different level of condensation were synthesized by excess of bisphenole with digaloidmethylene of common formula interaction: HO-Ar-[-CH2-O-Ar-O-]-H, С(ССl2)=; n=5, 10, 20.

where

Ar=n-C6H4-R-C6H4-;

m-C6H4-;

R=-C(CH3)2-;

Oligoketons, oligosulphoneketons, oligosulphones of different level of condensation were synthesized by method of high temperature polycondensation in the aprotonic dipolar solvent medium in the atmosphere of inert gase. 4,4/- dioxydiphenylpropans, phenolphthalein, 4,4/dichlordiphenylsulphon, 4,4/-dichlorbenzophenon were used as initial materials. Dichloranhydrite terephtaloyl-di(n-oxybenzoat) was synthesized by effect of thionyl chloride on terephtaloyl-di-n-oxybenzoic acid. Composition of polyethers whick were got on the basis of different aromatic oligoethers and dichloranhydrites of terephtaloyl-di-n-oxybenzoic acid were confirmed by IRspectroscopy data, the properties were studied by different physico-chemical methods.

BIBLIOGRAPHY [1]

He Xiao-hua, Wang Xia-yu // Xiangtan daxue ziran kexue xuebau-Netur. Sci. J. Xiangtan Univ., 2001, 23, №1, p. 49-52. [2] Wang Jiu-fen, Zhu Long-xin, Huo Hong-xing // Ctongneng gaofensi xuebao=J. Funct. Polym., 2003, 16, №2, p. 233-237. [3] Grigoryev A. P., Andreeva N. A., Bylibyn A. J., Skorohodov S. S., Eskin V. E. // Highmolecular compounds, B 1985, V. 27, №1, p. 4. [4] Grigoryev A. P., Andreeva N. A., Bylibyn A. J., Skorohodov S. S., Eskin V. E. // Highmolecular compounds, B 1985, V. 27, №10, p. 758. [5] Grigoryev A. P., Andreeva N. A., Volkov A. J., Smirnova G. S., Skorohodov S. S., Eskin V. E. // High-molecular compounds, A 1987, №6, p. 1158-1161. [6] Knath W. H., jr., Lindsey R. V.,jr., // J. Amer. Chem. Soc. 1985, V. 80, №15, p. 4106. [7] Bylibyn A. J., Tenkovtsev A. V., Pyraner O. N., Skorohodov S. S. // High-molecular compounds, A 1984, V. 26, №12, p. 2570. [8] Grigoryev A. P., Andreeva N. A., Skorohodov S. S., Eskin V. E. // High-molecular compounds, B 1984, V. 26, №8, p. 591. [9] Kapralova V. M. Dynamics of liguid-crystalline alkylnonaromatic polyethers and its development in NMR // Abstract of Physico-Chemestry Masters. Thesis. St. Peterburg, 1992. [10] Stepanova A. R. Liguid-crystalline polyethers synthesis on the basis of biphenyl derivatives. // Abstract of Chemistry Masters. Thesis. St. Peterburg 1992.

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[11] Bylibyn A. J., Shepelevski A. A., Savinova T. E., Skorohodov S. S. // Patent № 792834 USSR Published V.1, 1982, №12, p. 284.


Chapter 19

FIREPROOF AROMATIC BLOCK COPOLYMER RESIN ON THE BASIS OF 1,1- DICHLOR-2,2 DI(NOXYPHENYL)ETHYLENE A. M. Kharaev*, R. C. Bazheva, E. B. Barokova, O. L. Istepanova, R. A. Kharaeva, and A. A.Chaika Kabardino-Balkar State University, 360004, Nalchik, Chernishevsky st. 173, KBR, Russia

ABSTRACT By the method of p-type-catalytic polycondensation the blockcopolysulfonearylates on the basis of 1,1- dichlor-2,2 di(n-oxyphenyl) ethylene were received. The physicalchemical properties of block copolymer resins are investigated.

Keywords: Polycondensation, monomers, oligomers, blockcopolysulfonearylates, physicalchemical properties.

At present time the limited flammable, heat- and thermostable polymers with a high mechanical and dielectric properties are widely adopted in different spheres of science and technics [1]. The lowering of inflammability with a simultaneous improvement of other operational characteristics of polymeric materials remains to be an actual problem today. This task is also actual for such perspective highheatproof thermoplastics and reactive layers, as polyarylates, polysulphones, blockcopolysulfonearylates and polyesterketone. The acquisition of such polymeric materials may be realized in two ways – by the creation of new ones or by the modification of the existent polymers, which are released in production quantities. The both ways are effective depending on the concrete current task [2]. *

[email protected]

A. M. Kharaev, R. C. Bazheva, E. B. Barokova et al.

220

The usage of halogen containing monomers for making fireproof polymeric materials is a traditional way for solving the problems of improovement of the flame retarded constructive and membranous materials. One of the ways of solving this actual and important scientific problem is the utilization of the chloral and the usage of monomers on its basis, such as 1,1- dichlor-2,2 di(noxyphenyl)ethylene and the dichloranhydride of the 1,1- dichlor-2,2 di(n-oxyphenyl)ethylene [3]. The supplies of this raw material are big and have no any practical application. Thus, we have a number of blockcopolysulfonearylates (BSN–7D) according to the following scheme: C H3 n HO

C

OH

m HO

C

C H3 (n m k ) C l

OH

k HO

R

OH

C C l2

C

C

O

O

Cl

2 (n m k )E t 3 N - 2 (n m k ) E t 3 N HC l

C H3 O

C

O

C H3

C

C

O

O n

O

C

O

C C l2

C

C

O

O

O m

R

O

C

C

O

O

k

z

there O

C H3 R =

C C H3

O

S O

C H3 O

C 10

CH 3

For that we used a highly perspective, in terms of small expenses of time and energy, ptype-catalytic method of polycondensation. The mechanism of synthesis of these unsaturated polyesters was investigated. The influence of some parameters on the given viscosity and the outlet of polyesters was studied. The main parameters, which define the properties of polymers, received in conditions of ptype-catalytic polycondensation, are the nature of vehicle, the temperature and the duration of the metathesis, and also the concentration of initial substances. As a result of the conducted investigation the following conditions of synthesis of block-copoly sulfone on the basis of 1,1dichlor-2,2 di(n-oxyphenyl)ethylene and 4,4΄-dioxidephenylpropane, oligoarylensulfoneoxide OASO – 10D and mixture (50:50) dichloranhydride izo- and teraphthalic acids: vehicle – 1,2-dichlorethane; synthesis temperature is 20 ˚C; synthesis duration is 1 hour, triethylamine’s quantity - double spillover relative to bisphenols; solution’s concentration is 0,6 mole/l. Selecting the correlation of initial monomers, using first of all oligosulfone OASO – 10D in in the small (10 weight %) quantity, the compounding of polyesters, characterised by high deformation-strengthening properties (74 – 102 Mfa and relative lengthening 13,5 – 60,0 %). The initial bisphenols are taken in equimol correlations. The particular dignity of polymeric materials, derived in such a way, is that these polyesters in heat treatment make a spatial structure, because of the existance of unsaturated bond in the macrochain, and the last ones,

Fireproof Aromatic Block Copolymer Resin …

221

as a rule, differ from linear structures in several properties. In heat treatment of these polymers a partial structuring is observed, which helps to raise their disconnected strength till 150 Mfa and more. The investigations showed that the given block- copolymers are characterised by a sufficiently low polydispersity. It is shown that the threshold of the coagulation BSN–7D increases with the increase of the content of the chloride-bearing bisphenol, which is apparently connected with the polarity >C=CCl2 – group, and thus, a better solubility of these polymers. Polyesters are soluble in such organic vehicles as chloroform, dichlorethane, tetrachloroethane, tetrahydrofuran and others. Synthesized copolysulfonarilats have stable indices of inductive capacity in the interval of temperatures 20-200 ˚C and sufficiently persistent in deluted and concentrated solutions H2SO4, HCl, NaOH. The characteristics of these indexes considerably improve for heat-treated blockcopolymers, which is of no small importance for membranous materials. The thermomechanical tests of synthesized BSN showed, that the temperature magnitudes of glass transition and fluidity greatly depend on the composition and construction of the initial substances and are in in the interval 207-217 ˚C and 250-350 ˚C correspondingly. Such low indices of Ttr. May be explained by a presence of the remains of dichloranhydride of isophthalic acid and oligoarylensulfonoxidation OASO-10D in the structure of macrochain. Besides, it should be mentioned that the polyarylates on the basis of dian and DHDOFA, having in their structure isopropyliden and >C=CCl2 groups, are characterised not by high indices of glass transition. Things go differently with fluidity temperature. In the BSN–7D layer with the increase of the bisphenol DHDOFA part the fluidity temperature changes from 250 ˚C to 350˚C. Probably, the reason of such increase is a saturation of the macrochain by a >C=CCl2 group, which contains a dangling bond and polymers are inclined to structuring. All the received block-copolymers relate to the class of thermostable polymers. It is ascertained that the introduction of some quantity of oligoarylensulfonoxidation OASO-10D into the structure positively influence the heat resistance of polyesters, rising it for 10-20 ˚C in comparison with polyarylates on the basis of dian and 1,1- dichlor-2,2 di(noxyphenyl)ethylene [4]. For some BSN the noticeable destructive process begins at 400˚C and more, which correspond to good thermostable polymeric materials. Observing the regimen of optimal heat treatment, the heat resistance of the materials may be raisen for 3050˚C. Table 1. The results of thermomechanical analysis of block-copolysulfonarilats BSN BSN–7D

BSN on the basis of bisphenols, mol % Dian DHDOFA 0 100 25 75 50 50 75 25 100 0

Ttr. ˚C 207 210 210 215 217

Tfl. ˚C 250 255 270 310 350

A. M. Kharaev, R. C. Bazheva, E. B. Barokova et al.

222

Table 2. Refractoriness of block-copolysulfonarilats BSN BSN–7D

BSN on the basis of bisphenols, mol % Dian DHDOFA 0 100 25 75 50 50 75 25 100 0

Chlorine content, % 4,79 9,24 13,39 17,27

Oxygen index, % 27,0 30,0 35,0 37,5 43,5

The refractoriness of polymer samples were evaluated by amount of oxygen index. From the acquired results it follows that the presented block-copolysulfonarilats possess an increased refractoriness (Table 2). As it seen from Table 2 the greatest significance of the oxygen index has BSN, where as an acid component only 1,1- dichlor-2,2 di(n-oxyphenyl)ethylene was used, each molecule of which has two atoms of chlorine as an residue. In this layer because of the inconstancy of content of halogen value of the oxygen index change fundamentally. For a layer of block-copolysulfonarilats, containing remains of a monomer 1,1- dichlor2,2 di(n-oxyphenyl)ethylene, it is determined, that with the increase of the chlorinated content the oxygen index rises for 50% and more, that is a sufficiently considerable result and makes this approach attractive and perspective for solving the problem. The acquired polymers do not form inflammation drops, that is they are not the secondary source of inflammation, they are self-extinguishing and nonflammable materials. The complex of physical-chemical properties enable to hold out the unsaturated halogen containing block-copolysulfonarilats as warm-, thermo- and fire-proof constructive and membranous materials. The accessibility of the feedstock for receiving monomers on the basis of chloral, and also the manufacturability acceptor-catalytic polycondensation mekes it possible to refer the new halogen containing unsaturated block-copolysulfonarilats to industrialy-perspective polymeric materials.


[4]

Korshak V.V., Kzireva N.M. The progresses of synthetic chemistry of high-molecular compounds. The progresses of chemistry. 1979, T.48, №1, c.5-29. Korshak V.V., Vinogradova S.V. Nonequilibrium polycondensation. M., Science, 1972. Kharaev A.M., Kekharsaeva E.R., Mikitaev A.K. The properties of aromatic unsaturated polyesters on the basis of 1,1- dichlor-2,2 di(n-oxyphenyl)ethylene. Plast. Masses. 1985, №7, c.22. Kharaev A.M. Aromatic polyesters as thermostable constructive and membranous materials. Thesis for a Doctor of Chemistry Science, 1993, 297c.


Chapter 20

INCREASE IN SELECTIVITY OF MOLECULAR COMPLEX FORMATION OF METALLOPORPHYRINS DUE TO π-π-INTERACTIONS Nataliya A. Pavlycheva, Nataliya Sh. Lebedeva*, Anatoliy I. Vyugin, and Elena V. Parfenyuk Institute of Solution Chemistry, Russian Academy of Sciences, 1, Akademicheskaya St., Ivanovo, 153045, Russia

ABSTRACT Peculiarities of desolvation of crystallosovates of zinc(II)porphyrins with benzene, npropylamine and their mixtures have been studied by method of thermogravimetric analysis. It has been found that in two component systems zinc(II)porphyrin-ligand coordination properties of the metalloporphyrins increase in the following order: ZnTPhPZnTPhP and are inversely proportional to an ability of the macrocycle to π-π-interactions with benzene. Thus, the new approach to molecular recognition based on specific salvation π-πinteractions is demonstrated on example of znc(II)porphyrins.

Keywords: Thermogravimetric analysis; Molecular complexes; Metalloporphyrins

*


224

Nataliya A. Pavlycheva, Nataliya Sh. Lebedeva, Anatoliy I. Vyugin et al.

1. INTRODUCTION The metalloporphyrins as macrocyclic compounds have a few sites for specific and universal solvation and are able to axial coordination of some ligands. At the present time chemical modification of macrocycle is a main way of increasing of selectivity of molecular complex formation. The data obtained earlier [1,2] show that the selectivity may be increased due to specific π-π interactions of the metalloporphyrins with aromatic molecules. Aromatic molecules coplanar to the macrocycle will rise geometrical requirements to axial coordinating ligands. In particular, the results of the thermodynamic study of the axial coordination of npropylamine by zinc(II) porphyrins in benzene have demonstrated the formation of the complexes of the metalloporphyrin containing both n-propylamine and benzene [2]. The aim of this work is to study the molecular complexes of zinc(II) porphyrins prepared by slow crystallization from saturated solutions in benzene, n-propylamine and mixed solvent benzene - n-propylamine.

2. EXPERIMENTAL The objects of this study are the synthetic symmetrically substituted zinc(II)tetraphenylporphyrin (I) – ZnTPhP and the porphyrins of heme blood: zinc(II) hematoporphyrin t.m.e.(II) - ZnHP, zinc(II)deuteroporphyrin IX d.m.e.(III) - ZnDP, zinc(II)protoporphyrin IX d.m.e. (IV) - ZnPP having different peripheral substitutes.

II. ZnHP M=Zn, R=CH(OCH3)CH3 III. ZnDP M=Zn, R=H IV. ZnPP M=Zn, R=CH=CH2

I. ZnTPhP M=Zn

Benzene (analytical grade) was dried by molecular sieves of 4Å size and distillated. NPolyamine (Aldrich, 98%) was double distillated under vacuum. Purity of the reagents was checked chromatographically. It was 99.95 % for CH3(CH2)2NH2 and 99.98% for C6H6. The content of water was determined by Karl Fisher method It was not greater than 0.01%. Thermogravimetric measurements were made with thermoanalytical set. The detail description of the equipment, procedures of the measurements and software for treatment of the experimental data and calculations of uncertainties were reported earlier [3]. The chemical analysis of content of C,N,H was performed with CHNS-O Analyzer Flash TF 1112 Series.

Increase in Selectivity of Molecular Complex Formation …

225

Table 1. Physicochemical properties of molecular complexes of ZnP with benzene and n-propylamine

ZnP

ZnHP ZnDP ZnPP ZnTPhP

Benzene Compos. of ZnP:L 1:2 1:1 1:1 1:1 1:2

Тdestr, 0С 60 122 72 49 60

Solvent n-propylamine * ΔevpН , kJ Compos.of mol-1 ZnP:L 39 1:2 96 1:1 62 1:2 1:1 38 1:1 150 1:1

Тdestr, 0С 70 113 67 81 82 114

ΔevpH*, kJ mol-1 58 199 53 171 168 113

*

Uncertainty in ΔevpН is ±(3÷8) kJ mol-1.

3. RESULTS AND DISCUSSION The results of the thermogravimetric analysis of crystallosolvates of the porphyrins with benzene and n-propylamine are presented in Table 1. As an example, typical thermograms of the crystallosolvates of ZnTPhP and ZnPP are shown in Fig.1 and 2. For all zinc(II)porphyrins studied, the process of removing of n-propylamine from the crystallosolvates has several steps. In the first step, the ΔevpH value of the organic solvent for the crystallosolvates giffers slightly from that for pure solvent. This may be explained by destruction of the solvates formed due to universal interactions. The peaks at higher temperatures are characterized by a significantly greater ΔevpH values than for pure npropylamine. This may be due to destruction of the specific molecular complexes in these steps. ΔevpH consists of two contributions: (i) the energy losses associated with breaking of macrocycle-ligand bonds and (ii) the work of expansion at transition of the substance to the gas phase [4]. The last contribution is negligible (2-3 kJ mol-1). Thus, in the first approach the ΔevpH value reflects energetic strength of the macrocycle – ligand bonds. Clear stoichiometry and high repeatability of the results testifies about destruction of the specific molecular complexes but not inclusion complexes. As can be seen from Table 1, the energetic strength of the metalloporphyrin complexes with n-propylamine increases in the following order: ZnTPhP

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