Update on Troubleshooting the PVC Extrusion Process

Update on Troubleshooting the PVC Extrusion Process Natami Subramanian Muralisrinivasan iSmithers – A Smithers Group C...

Author: Natamai Subramanian Muralisrinivasan

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Update on Troubleshooting the PVC Extrusion Process

Natami Subramanian Muralisrinivasan

iSmithers – A Smithers Group Company Shawbury, Shrewsbury, Shropshire, SY4 4NR, United Kingdom Telephone: +44 (0)1939 250383 Fax: +44 (0)1939 251118 http://www.ismithers.net

First Published in 2011 by

iSmithers Shawbury, Shrewsbury, Shropshire, SY4 4NR, UK

©2010, Smithers Rapra

All rights reserved. Except as permitted under current legislation no part of this publication may be photocopied, reproduced or distributed in any form or by any means or stored in a database or retrieval system, without the prior permission from the copyright holder.

A catalogue record for this book is available from the British Library.

Every effort has been made to contact copyright holders of any material reproduced within the text and the authors and publishers apologise if any have been overlooked.

ISBN: 978-184735-550-8 (Hardback) 978-184735-551-5 (ebook)

Typeset by Argil Services Printed and bound by Lightning Source Inc.

P

reface

The basic work for ‘Update on Troubleshooting in PVC Extrusion’ was laid out during my industrial visits to pipe, profile, film, and sheet industries. An obvious strength of this book is that its nine chapters capture most of the literature citations in this arena. The coverage is intentionally contemporary. Chapters 1–5 serve as starting points for PVC extrusion processing. Chapter 6 covers PVC composites and discusses progress in environmental protection. Recently, considerable pressure for more effective substitutes for wood has come from the interest garnered from applying PVC–wood composites in environmentally friendly products. Chapter 7 deals with problems and defects during processing. Chapter 8 is dedicated to the analysis of troubleshooting (particularly in processing and end products). This book addresses problems specific to extrusion such as PVC pipe, profile, sheet and film extrusion. It guides the user through the methods in a user-friendly manner. The solutions mentioned in this book are easy to incorporate. In summary, this book is a valuable addition to the repertoire of PVC processing as well as an excellent source of information for engineers, academics, processors, and students interested in processing methods and troubleshooting. Knowledge of the content will also provide the reader with a communication tool for discussing the subject with a PVC specialist. I would like to thank God for his support in helping me to write this book. In particular I also express appreciation to my wife and sons

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for their continuing support, and to my professors from the beginning of my career for their encouragement. Final thanks go to Frances Powers- Gardiner, Cal Parkinson, Eleanor Garmson and others at iSmithers Publishing for their help in my endeavour.

Muralisrinivasan Natamai Subramanian February 2011

iv

C

ontents

1

Introduction ............................................................. 1

2

Poly (Vinyl Chloride) ................................................ 5 2.1 Characteristics ................................................. 5 2.2 Poly (Vinyl Chloride) Structure ....................... 6 2.2.1 Crystallinity .......................................... 8 2.2.2 Thermal Stability of Poly (Vinyl Chloride) .................................... 8 2.3 Manufacture of Poly (Vinyl Chloride) Resin .. 10 2.3.1 Raw Material ..................................... 11 2.3.2 Energy Requirement ........................... 11 2.3.3 Process ................................................ 11 2.3.4 K-Value .............................................. 12 2.4 Modification of Poly (Vinyl Chloride) ............ 12 2.4.1 By the Addition of Metal Compounds 12 2.4.2 Structural Modification....................... 14 2.5 Regrind Poly (Vinyl Chloride) Material ........ 14 2.6 Advantages of Poly (Vinyl Chloride) .............. 15 2.7 Disadvantages ................................................ 16

3

Additives and Compounding .................................. 23 3.1 Poly (Vinyl Chloride) Formulation ................. 23


3.2 Role of Additives ........................................... 24 3.3 Classification of Poly(Vinyl Chloride) Additives ........................................................ 26 3.3.1 Heat Stabilisers ................................... 27 3.3.1.1 Lead Stabilisers .................... 29 3.3.1.2 Secondary Heat Stabilisers ... 29 3.3.1.3 Tin Stabilisers ...................... 30 3.3.1.4 Calcium–zinc Stabilisers ....... 31 3.3.1.5 Other Heat Stabilisers .......... 32 3.3.1.6 One-pack Stabilisers ............ 32 3.3.2 Lubricants........................................... 33 3.3.3 Impact Modifiers ................................ 34 3.3.4 Plasticisers .......................................... 34 3.3.5 Fillers .................................................. 36 3.3.6 Flame Retardants ................................ 37 3.3.7 Blowing Agents ................................... 37 3.3.8 Pigments ............................................ 38 3.3.9 Coupling Agents ................................. 39 3.3.10 Smoke Suppressants ............................ 39 3.4 Migration of Additives ................................... 39 3.5 Compounding ................................................ 40 3.5.1 Technology ......................................... 41 4

Poly(Vinyl Chloride) Extrusion .............................. 49 4.1 Basic Requirement of Poly (Vinyl Chloride) Compounds ................................................... 49 4.1.1 Machine.............................................. 50

vi

Contents

4.3

4.4

4.4 4.5

4.6

4.7 4.8 4.9 5

4.1.2 Processing .......................................... 50 Extrusion ....................................................... 50 4.3.1 Extruder: Operating Conditions ......... 51 4.3.2 Screw .................................................. 52 4.3.3 Processing Technology ........................ 53 4.3.4 Processing Temperature ...................... 54 4.3.5 Power Consumption ........................... 54 Extrusion ....................................................... 55 4.4.1 Single-screw Extruder ......................... 56 4.4.1.1 Advantages/Disadvantages ... 57 4.4.2 Twin-screw Extrusion ......................... 57 4.4.2.1 Advantages .......................... 58 4.4.3 Die Design .......................................... 59 Calibration System ......................................... 60 Poly (Vinyl Chloride) Pipe Extrusion ............. 60 4.5.1 Pipe Dies ............................................. 62 4.5.2 Cooling System ................................... 62 Poly (Vinyl Chloride) Profile Extrusion .......... 63 4.6.1 Calibrator ........................................... 63 4.6.2 Cooling System ................................... 65 Poly (Vinyl Chloride) Sheet Extrusion ............ 65 Poly (Vinyl Chloride) Films ............................ 67 Regrind .......................................................... 68

Degradation and Stabilisation of Poly(Vinyl Chloride) ............................................... 71 5.1 Degradation of Poly (Vinyl Chloride)............. 71

vii


5.2 5.3 5.4 5.5 5.6 5.7 5.8 5.9 6

Structural Defects .......................................... 72 Tacticity ......................................................... 73 Dehydrochlorination ...................................... 73 Stabilisers ....................................................... 74 Impurities ..................................................... 75 Photochemical Degradation ........................... 75 Mechanism of Degradation ............................ 76 Poly(Vinyl Chloride) Stabilisation .................. 78

Poly(Vinyl Chloride)–Wood Composites ................ 93 6.1 Additives ........................................................ 94 6.2 Properties of Wood-Poly(vinyl Chloride) Composites .................................................... 96 6.3 Processing ...................................................... 96 6.4 Advantages of Wood-Poly(Vinyl Chloride) Composites ................................................... 98

7

Poly(Vinyl Chloride) Extrusion: Problems and Defects ........................................... 103

8

Troubleshooting Problems in Poly(Vinyl Chloride) Extrusion ............................................................. 107 8.1 Problems and Troubleshooting in Pipe/Profile Extrusion .................................. 108 8.1.1 Production Problems in the Extruder 108 8.1.1.1 Problem: Difficult to String-up Melt during Startup ............................... 109

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Contents

8.1.1.2

Problem: Powder Pulled into a Vacuum.................... 109 8.1.1.3 Problem: High Bearing Throat at Back Pressure ..... 109 8.1.1.4 Problem: Motor Load is too High ............................ 110 8.1.1.5 Problem: Low Output ........ 113 8.1.2 Product Problems.............................. 114 8.1.2 Production Problems in Downstream Areas ................................................ 115 8.1.2.1 Problem: A Longitudinal Scratch in Pipe or Profile is Found While Sizing ............ 115 8.1.2.2 Problem: Folding of Material in the Calibrator .. 115 8.1.2.3 Problem: Blowouts in the Cooling Zone ..................... 116 8.1.2.4 Problem: Uncontrolled Wall Thickness .................. 118 8.1.2.5 Problem: Poor Inner Surface .............................. 119 8.1.2.6 Problem: Regular Wavy Lumps ................................ 120 8.1.2.7 Problem: Irregular Lumps (Random With No Regular Pattern) ............................. 121 8.1.2.8 Problem: Dimples on the Product ............................. 122 8.1.2.9 Problem: Burning or Yellowing of the Extrudate 122

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8.1.2.10 Problem: Poor Overall Appearance ....................... 124 8.1.2.11 Problem: Dull Surface Appearance ....................... 125 8.1.2.12 Problem: Low Results in the Drop Weight Impact Test .. 125 8.1.2.13 Problem: Gauge Variation . 126 8.1.2.14 Problem: Degassing is Difficult ............................ 128 8.1.2.15 Problem: Frictional Heat: Zone-4 Overheating .......... 129 8.1.2.16 Problem: Melt Fracture and Surface Roughness ..... 130 8.1.2.17 Problem: Lumpy, Cold or Oval (egg-shaped) mark Surfaces ............................ 131 8.1.2.18 Problem: Over-lubrication 132 8.1.2.19 Problem: Impact Failure .... 133 8.1.2.20 Problem: Black Specks ...... 134 8.1.2.21 Problem: Variation in Load or Amperage from Batch-to-Batch or Between Batches ............................. 135 8.1.3 Quality Problems in the End Product 136 8.1.3.1 Problem: Failure in the Methylene Chloride Test .... 136 8.1.3.1.1 Problem - Inside Portion Granular ............................ 136 8.1.3.1.2 Problem: Middle Portion is Mealy ................................ 138 x

Contents

8.1.3.1.3 Problem: Outside Portion is Mealy ................................ 139 8.1.3.2 Problem: Bubbles at the Oil Reversion Test at the Inner Surface ............................... 139 8.1.4 Quality Problems in Pipes ................. 141 8.2 Troubleshooting for Poly (Vinyl Chloride) Blown Film .................................................. 143 8.3 Troubleshooting for Poly (Vinyl Chloride) Sheets ........................................................... 145 9

Future Requirements: Developments in Poly(Vinyl Chloride) ............................................. 149 9.1 9.2 9.3 9.4 9.5

Poly(Vinyl Chloride) Formulation ................ 149 Wood – Poly(Vinyl Chloride) Composites .... 150 Medical Applications ................................... 150 Construction ................................................ 150 Biodegradation ............................................ 150

xi

1

Introduction

Poly(vinylchloride) (PVC) has a broad range of application. It has substituted many conventional materials (especially metals) in various applications. PVC has advantages over conventional materials due to its toughness and flexibility. PVC is also an easily processable and lowcost material. During processing, PVC requires comparatively less energy compared with the manufacture of, for example, paper and metal. Its physical and resistance properties make PVC a substitute for many applications. For some PVC products, mechanical properties such as strength and toughness are inadequate [1–6]. PVC can be made softer and more flexible by the addition of plasticizers. In applications such as building materials, pipes and plumbing products, PVC, as a hard thermoplastic, offers more strength and rigidity than most other plastics. It has outstanding response to functional additives, which permit its use in designed engineering applications [7, 8]. In the last four decades, PVC has become a major building material and leading synthetic polymer. Global vinyl production is >30 million tons per year [9–12], and has significant cost as well as processing advantages. A large part of the PVC produced worldwide is used for outdoor applications (e.g., house siding panels, waste-water tubes, window profiles) [13]. PVC can incorporate with additives to suit many applications. Although additives are required to meet various technical requirements, most PVC resin is used for building, furnishing, electronic and medical applications. Besides the cost of the raw materials, PVC has outstanding chemical resistance to a wide range of corrosive liquids, and it can last for a long time.

1


In general, PVC is an important commercial plastic with many rigid and flexible applications. It is used in building and construction, packaging, electrical applications, electronic applications, automotive applications, furniture, office equipment, healthcare and, to some extent, in clothing and footwear. The only continuous production of PVC is extrusion, and it is used to manufacture pipe, profile, sheet and film. PVC is an engineering polymer for the ‘average man’. Toughness is the key parameter that determines if PVC products can be used as engineering materials [14]. It delivers excellent durability, chemical resistance and other value-added properties.

References 1.

J. Fang and P. Fowler, Journal of the Science of Food and Agriculture, 2003, 1, 3/4, 82.

2.

D.N. Saheb and J. Jog, Advanced Polymer Technology, 1999, 18, 4, 351.

3.

B. Seymour Raymond, Polymer Chemistry: An Introduction, Marcel Dekker Inc., New York, NY, USA, 1971, p.268.

4.

Y. Orhan, J. Hrenovic and H. Buyukgungor, Acta Chimica Slovenica, 2004, 51, 3, 579.

5.

A.L. Andrady, S.H. Hamid, X. Hu and A. Torikai, Journal of Photochemistry and Photobiology B: Biology, 1998, 46, 1-3, 96.

6.

P. Meenakshi, S.E. Noorjahan, R. Rajini, U. Venkateswarlu, C. Rose and T.P. Sastry, Bulletin of Material Science, 2002, 25, 1, 25.

7.

L. Nass in Encyclopedia of PVC, 2nd Edition, Eds., L. Nass and C.A. Heiberger, Marcel Dekker, New York, NY, USA, 1985.

2

Introduction

8.

Plastic Piping Handbook, Eds., D. Willoughby, R. Dodge Woodson and R. Sutherland, McGraw-Hill, New York, NY, USA, 2002.

9.

M. Engelmann, Angewandte Makromolekulare Chemie, 1997, 244, 1, 1.

10. A. Bos and S.R. Tan in Proceedings of an Institute of Materials Conference - PVC 96, Brighton, UK, 1996, p.77. 11. Y. Saeki and T. Emura, Progress in Polymer Science, 2002, 27, 10, 2055. 12. D. Braun, Journal of Polymer Science: Polymer Chemistry Edition, 2004, 42, 3, 578. 13. A. Andreas in Plastics Additives Handbook, 3rd Edition, Eds., R. Gächter, H. Müller and P.P. Klemchuk, Hanser, Munich, Germany, 1990, p.271. 14. W. Jiang, L-J. An and B-Z. Jiang, Chinese Journal of Polymer Science, 2003, 21, 2, 129.

3

2

Poly (Vinyl Chloride)

Poly(vinylchloride) (PVC) is a polar polymer. It is interesting because of its backbone constructed from repeating chlorine atoms. PVC is one of the world’s leading synthetic polymers [1]. It is basically an amorphous material [2, 3] and also a vinyl polymer. It has the vinyl group (CH2=CH-). PVC is manufactured from vinyl chloride (VC) monomer (CH2=CHCl). It is a colourless gas possessing a faintly sweet odour which can cause anaesthesia at high concentrations. Through common usage, the word ‘vinyl’ generally refers to PVC and its copolymers, even though other examples of group members of the vinyl ‘family’ (e.g., polyethylene, polypropylene, polystyrene, polyvinylacetae, polymethylmethacrylate) are available [4]. Its amorphous characteristics confer application advantages [2, 3]. PVC has the ability to be compounded with many additives to produce a wide range of flexible and rigid products represents the major factor responsible for the success and versatility of PVC processing [5]. In the last four decades, PVC has become a major building material. Most of the global production of vinyl is directed to building applications, furnishings, and electronics. PVC enjoys significant cost as well as processing advantages. However, several additives are required to meet the various technical requirements.

2.1 Characteristics PVC has outstanding chemical resistance to wide range of corrosive

5


fluids. It offers more strength and rigidity than most other thermoplastics. Chlorine in PVC accounts for 56.8% of the total weight. Hence, PVC is less affected by the cost of petroleum and natural gas than other polymers. The price of petroleum and natural gas is volatile, and PVC is less expensive compared with other polymers [6]. Some of the important characteristics of PVC are shown in Table 2.1.

Table 2.1 Characteristics of PVC Properties Density Tensile stress Modulus of elasticity Decomposition temperature

Value

Unit

Reference

1380–1410

kg/m

[7]

40–60

MPa

[7]

2–7

GPa

[7]

210–360

°C

[8]

3

PVC is considered to be ~55% syndiotactic [2, 9, 10]. Since a growth of species with conversion destroy all memory and may only be regenerated and observed after subsequent processing, hence domain is not feature of PVC morphology in high conversion samples [10]. Decomposition occurs with release of 58% HCl in an auto-catalytic dehydrochlorination step through a degenerate branched chain freeradical reaction mechanism [12].

2.2 Poly (Vinyl Chloride) Structure The structure of PVC (Figure 2.1) is described as the SEM structure cryogenically fractured porous PVC particle and it’s interior [11].

6

Poly (Vinyl Chloride)

• The grain has an approximate size of 50–250 μm (average size, 130 μm). It originates from a visible constituent of free-flowing powder comprising more than one monomer droplet • Sub-grain agglomerates have an approximate size of 10–150 μm (average, 40 μm) made from polymerised monomer droplets. However, particles of approximate size 1–10 μm (average, 5 μm) are formed during the early stage with polymerisation by coalescence or of primary particles (1–2 μm) that grow upon conversion (Figure 2.1) • Primary particles grow from the domain with a particle size of 0.6–0.8 μm (average, 0.7 μm). They are formed at low conversion (i.e., 47% • The median on the top cut should be C=O at 1720 cm–1. Ultraviolet–visible (UV–VIS) spectroscopy shows polyenes resulting from elimination reactions absorbing below a wavelength of 600–700 nm [57].

5.5 Stabilisers Processing without stabilisers and lubricants leads to PVC degradation. The degradation occurs with liberation of HCl due to the cracking of PVC. Even processing PVC with an insufficient quantity of stabiliser in the formulation leads to degradation. This

74

Degradation and Stabilisation of Poly(Vinyl Chloride)

results in colour changes from white to yellow, from yellow to brown, and finally to black, which leads to disaster. Not only an insufficient quantity of stabiliser but also an insufficient quantity of lubricant results in flow hindrance in the processing equipment, and leads to colour changes. However, irrespective of the heat stabilising capacity of the heat stabiliser, the efficiencies suffer from the deleterious effect of the byproducts produced mostly from many metal chlorides accumulated during the reaction of the heat stabilisers with PVC material. These metal chlorides are considered to be strong catalysts for the subsequent dehydrochlorination process. They are also responsible for the sudden blackening of certain formulations, and may present a serious environmental problem [37–39]. This has recently, led to the extensive use of organic stabilisers for the thermal stabilisation of PVC [57–59].

5.6 Impurities Various aspects of degradation in relation to PVC stabilisation must be understood. Contaminants present in the PVC material and in the additives act as powerful promoters of degradation and cause considerable distortion. Hence, the effectiveness of the stabiliser system is significantly decreased due to such unknown contamination [37].

5.7 Photochemical Degradation External factors such as solar UV radiation, moisture, temperature, and pollutants promote the degradation of properties [60, 61]. These factors affect the structure of PVC and the quantities of the additives present within it. Products are slowly degraded under the influence of the environment. This is indicated by yellowing (or other discoloration) or the loss of brightness with filler or pigments in PVC, progressive destruction of the surface layer with gloss deterioration,

75


and loss of mechanical strength. PVC in outdoor uses requires protection from mechanical deterioration, as well as attack by heat and light (normal and UV). Out of the variety of PVC compounds, transparent rigid material is the best for long service [62]. PVC weathering causes a photochemical degradation that produces chain rupture, formation of oxidised structures, and HCl generation [15, 63, 64]. These chemical changes subsequently produce a loss in mechanical properties and formation of a yellow colour due to polyene propagation. UV stabilisers only slow down these reactions and do not stop degradation. However, these products degrade slowly under environmental influences as indicated by yellowing (or other discoloration or loss of brightness with fillers and colour pigments in PVC) and progressive destruction of surface layers (deteriorating gloss and eventually decrease in mechanical strength). Hence, much work has been devoted to developing an understanding of and to control PVC degradation. Accordingly, PVC may degrade thermally as well as by photochemical means. Solar irradiation (UV light and heating effect) and oxygen from the atmosphere may trigger both mechanisms. In contrast to other polymeric materials, moisture is not an important factor. The underlying chemical reactions are the formation of carotinoid polyenes from intrinsic defects by the elimination of HCl, and their oxidation (via allyl peroxy radicals), leading to the breaking of residual C-C bonds [46–49].

5.8 Mechanism of Degradation Defects at high temperature that occur in free-radical polymerisation are backbiting, chain transfer to monomer and polymers, and self-initiated chain reactions; relatively high isotactic content is also important. The mechanisms that underlie degradation are incompletely understood. The type of reaction is also dependent upon the conditions (e.g., temperature, presence of oxygen) during the decomposition. The main labile sites for dehydrochlorination

76


are the allylic and tertiary chlorines. Radical, ionic and molecular mechanisms have been proposed [65], including a mechanism consisting of an initiation reaction, cis–trans isomerisations, and 1,3 rearrangements and propagation [66-67]. PVC may degrade by thermal as well as photochemical reactions. The effect of UV light and the heating effect from solar irradiation and oxygen from the atmosphere may trigger both mechanisms. Moisture is not an important factor with PVC. In principle, the chemical reactions are the formation of carotinoid polyenes from intrinsic defects by the elimination of HCl and their oxidation via allyl peroxy radicals to break residual C-C bonds [46–49]. The thermal degradation mechanism is similar to the photochemical degradation mechanism. However, photodegradation generates more HCl molecules [47, 64]. The elimination of HCl at relatively low temperatures (~100 °C) or under the influence of light is one of the fundamental aspects of PVC decomposition. Figure 5.1 illustrates the first stage: this reaction leads to the formation of double bonds followed by a rapid ‘zipper-like’ splitting off of further HCl molecules to give polyene sequences. These sequences (with an average length of 6–14 conjugated double bonds) cause the polymer to turn yellow, brown, and eventually black [2–4].

CI CI CI

CI CI - HCI

CI

CI

- HCI n

Figure 5.1 PVC dehydrochlorination (schematic). Reproduced with permission from D. Braun, Progress in Polymer Science, 2002, 27, 2171. ©2002, Elsevier [57]

77


Elimination reactions can be followed by UV–VIS spectroscopy because the resulting polyenes absorb below a wavelength of 600–700 nm, and oxidation reactions are recognised by the growth of IR absorption bands for >C=O at 1720 cm–1. Due to the slow diffusion of oxygen into PVC, oxidation products develop only in the upper 200 mm of a plate, whereas polyenes are generated up to 400 mm below [58]. These, however, act as intrinsic UV absorbers and shield the polymer bulk.

5.9 Poly(Vinyl Chloride) Stabilisation Stabilisation of PVC against thermal degradation is essential for processing and use at high temperatures. Thermal stabilisers intervene in the dehydrochlorination process and react with the double bonds created on the backbone chains as a result of HCl loss during degradation. Thermal stabilisers are known to function as PVC stabilisers by replacing labile atoms. The inhibitor suppresses the elimination of HCl. It interrupts the formation of a conjugated polyene sequence in the polymer [5]. The main function of heat stabilisers is to prevent degradation during processing. Thermal stabilisers replace labile chlorine atoms to enhance heat stability. Stabilisation of PVC involves substituting the labile chlorine atoms or a reaction with the HCl generated during processing [53, 68, 69]. Thermal stabilisers can block or retard thermal oxidative degradation. Moreover, the stabiliser may disrupt conjugated systems, thereby reducing polymer discoloration. Mercaptans are typical examples of these stabilisers [70]. A part of the stabiliser will be consumed during processing and sometimes during the application period. Hence, the efficiency of the stabiliser system is considerably reduced after compounding PVC with the necessary additives [70]. Thermal stabilisers can react with the evolved HCl gas to retard the deleterious catalytic action of the eliminated HCl [71, 72].

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Under the action of strong nucleophiles (e.g., thiols, thiolates), labile chlorines are replaced and the thermal stability of PVC increased. Another approach is to use a low temperature ‘living’ radical polymerisation technique that enables PVC to be almost free of such structural defects and provides thermal stability [73–76]. Control of the core-shell structure in PVC has been reported to improve thermal stability [75]. Stabilisation mechanisms are controversial because PVC is the plastic with probably the highest variety of stabilizers. Indeed, PVC cannot be used as a plastic material without stabilisers. Thermal stabilisers such as organometallic compounds and inorganic salts are particularly effective. Mercaptans are organic stabilisers [70]. Esters or mercaptides of dialkyltin [76–78] can exchange the labile chlorines in the backbone chains for more stable ester or mercaptide groups derived from the stabiliser. Moreover, quinone–tin polymers act as stabilisers through intervention in the radical process of degradation and through effective absorption of the degradation products [79]. Environmental problems have recently led to the extensive use of organic stabilisers for the thermal stabilisation of PVC [60, 61]. Mixtures of calcium–zinc carboxylates are one of the oldest systems used. They are becoming important again due to their lack of toxicity. Metal carboxylates are considered to be HCl scavengers and involve substitution of allylic chloride through an esterification reaction with PVC [80]. It is well known that the zinc carboxylate is the most active and that the calcium carboxylate acts mainly as an HCl scavenger. Calcium soap [81] reduces the rate of dehydrochlorination by avoiding the 1,3-rearrangements and controlling propagation of the HCl elimination reaction. Formation of a coordinated complex between both carboxylates was proposed in 1967 [81], and has been used regularly to explain certain types of unknown behaviour [80, 81]. The main function of metal soaps is the interaction with growing polyenes by the formation of a coordinated complex between both carboxylates [82–84].

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Using mixtures of zinc and calcium carboxylates reveals that calcium carboxylates act as ester exchangers with zinc chloride. A sufficient quantity of calcium stearate prevents the formation of zinc chloride [85–89]. Zinc carboxylates have are strong Lewis acids and scavenge HCl. They react with the allylic chlorine atom, resulting in the formation of zinc chloride, which promotes PVC dehydrochlorination [90, 91]. Pre-heated stearates have effects on material color during initial processing and after processing. They can be useful for industrial purposes when designing the formulation. They affect the formulation composition with respect to initial mechanical behaviour and release of HCl during post-processing. However, the additional cost of preheating can be justified upon achieving satisfactory movement on the thermal stability of formulations. Pre-heated calcium stearate mixed with zinc stearate leads to a reduction in heat stability. During processing, calcium stearate may have decomposed and further does not participate in the stabilisation and zinc stearate is the only heat stabilizer available for further heat stabilisation. Pre-heated zinc stearate alone shows significant changes in the thermal stability of PVC. However, if calcium and zinc stearates are mixed and pre-heated, a slight improvement in thermal stability occurs. Pre-heated zinc stearate mixed with calcium stearate shows moderate improvement in heat stabilisation. There is controversy in the literature about the effect of pre-heated stearates on the thermal stability of unplasticised PVC formulations, and there are no reports about such effects on industrial-grade plasticised PVC compounds [91]. Common thermal stabilisers in use for the stabilisation of PVC are usually basic lead salts [92], metallic soaps [93–96] and esters or mercaptides of dialkyltin [78, 80, 97]. The most important stabilisers of PVC are different metal soaps such as lead, cadmium, barium, calcium and zinc carboxylates and some di- and mono-alkyltin compounds (e.g., maleates, carboxylates, mercaptides) [80]. Several inorganic lead compounds and organic secondary stabilisers such as epoxides, polyols, phosphites, b-diketones, and

80


dihydropyridine are also used in industrial recipes [94, 98–103]. They act as acceptors for the liberated HCl [99, 104] and retardants for the appearance of discoloration [105–107]. Metal salts of organic acids, organometallic compounds, and inhibitors of radical chain reactions are used in the stabilisation of PVC. PVC stabilisers are usually basic salts [73] which can react with the evolved HCl gas to retard the deleterious catalytic action of the eliminated HCl [75, 93] or metallic soaps [73, 93–95]. Thermo-oxidative degradation of PVC can be blocked or retarded by metal soaps, epoxy compounds, phosphites, aliphatic and aromatic compounds and organotin compounds. Organotin stabilisers are mainly used in the production of sheets, profiles, general purpose and potable water pipes, sidings, films, foils, bottles and articles for paper packaging. Organic thermal stabilisers for the thermal stabilisation of PVC have recently been extensively studied [60, 95]. Improving the thermal stability of PVC requires the use of stabilisers in processing. Additives that have found practical application as thermal stabilisers for PVC include metal salts of organic acids, organometallic compounds, and inhibitors of radical-chain reactions. Copolymerisation of vinyl chloride monomer, grafting, blending, and chemical modifications such as nucleophilic substitution [61, 108–110] and copolymerisation with imide monomers and further chlorination of PVC to increase the heat resistance of PVC has been studied [113–115]. Alternatively, thermal stability can be enhanced by the preparation of PVC/clay nanocomposites [116]. Several studies have been initiated to improve the various properties of PVC for making new materials for specific applications. Research on PVC materials to modify their properties for specific applications is underway [110, 113–115]. This includes copolymerisation of vnyl chloride monomer, grafting, blending and chemical modifications [110, 112, 113, 117]. Using stabilisers with the action of nucleophilic

81


reactions, these defects are replaced and, ultimately, thermal stability is increased.

References 1.

A. Bos and S.R. Tan, PVC Pipes—Current Status and New Developments, Conference Papers PVC’96, Brighton, UK, 1996.

2.

D. Braun in Developments in Polymer Degradation 3, Ed., N. Grassie, Applied Science Publishers, London, UK, 1981.

3.

T. Kelen in Polymer Degradation, Van Nostrand Reinhold Company, New York, NY, USA, 1983.

4.

J. Wypych in Polymer Science Library 3, Ed., A.D. Jenkins, Elsevier, Amsterdam, The Netherlands, 1985.

5.

B. Ivan, T.T. Nagy, T. Kelen, B. Turcsanyi and F. Tudos, Polymer Bulletin, 1980, 2, 83.

6.

F.E. Okieimen and O.C. Eromonsele, European Polymer Journal, 2000, 36, 525.

7.

N.A. Mohamed, M.W. Sabaa, E.H. Oreby and A.A. Yassin, European Polymer Journal, 2002, 76, 367.

8.

Kh.D Khalil and A.A. Yassin, Polymer Degradation and Stability, 2001, 72, 53.

9.

B. Li, Polymer Degradation and Stability, 2000, 68, 197.

10. N.A. Mohamed, W. Mohamed and A. Magrhi, Polymer Degradation and Stability, 2003, 80, 275. 11. R. Bacaloghi and M. Fisch, Polymer Degradation and Stability, 1994, 45, 315.

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12. P. Simon, Polymer Degradation and Stability, 1992, 36, 85. 13. I. McNeill, I. Memetea and W.J. Cole, Polymer Degradation and Stability, 1995, 49, 181. 14. P. Simon, Polymer Degradation and Stability, 1990, 29, 155. 15. V. Percec, E. Ramirez-Castillo, L.A. Hinojosa-Falcon and A.V. Popov, Journal of Polymer Science, Part A: Polymer Chemistry Edition, 2005, 43, 2185. 16. E.D. Owen in Degradation Stabilisation of PVC, Elsevier Applied Publishers, London, UK, 1984. 17. G. Allen and J.C. Bevington in Comprehensive Polymer Science, Volume 6, 1st Edition, Pergamon Press, Oxford, UK, 1989. 18. N.A. Mohamed, M.W. Sabaa, Kh.D. Khalil and A.A. Yassin, Polymer Degradation and Stability, 2001, 72, 53. 19. M.W. Sabaa, N.A. Mohamed, E.H. Oreby and A.A. Yassin, Polymer Degradation and Stability, 2002, 76, 367. 20. V. Percec, A.V. Popov, E. Ramirez-Castillo, J.F.J. Coelho and L.A. Hinojosa-Falcon, Journal of Polymer Science, Part A: Polymer Chemistry Edition, 2004, 42, 6267. 21. V. Percec, A.V. Popov, E. Ramirez-Castillo, J.F.J. Coelho and L.A. Hinojosa-Falcon, Journal of Polymer Science, Part A: Polymer Chemistry Edition, 2005, 43, 779. 22. T. Millan, G. Martineze, J.M. Gomez-Elvira, N. Guarrotxena and P. Tumblo, Polymer, 1996, 37, 219. 23. N.A. Mohamed, W. Mohamed and A. Magrhi, Polymer, 2003, 80, 275.

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24. D. Braun, B. Bohcinger, B. Ivan, T. Kelen and F. Tudos, European Polymer Journal, 1986, 22, 1. 25. T. Hjertburg and E.M. Sorvik, Polymer, 1983, 24, 685. 26. W.H. Starnes, Progress in Polymer Science, 2002, 27, 2133. 27. W. H. Starnes, Journal of Polymer Science: Polymer Chemistry, 2005, 43, 2451. 28. G. Martinez, C. Mijangos and J. Millan, Revista de Plasticos Modernos, 1982, 43, 629. 29. G. Martinez, C. Mijangos and J. Millan, Journal of Macromolecular Science Chemistry A, 1982, 17, 1129. 30. G. Martinez and J.L. Millan, Journal of Polymer Science, Part A: Polymer Chemistry Edition, 2002, 40, 3944. 31. G. Martinez and J.L. Millan, Journal of Polymer Science, Part A: Polymer Chemistry Edition, 2004, 42, 6052. 32. C. Mijangos, G. Martinez, A. Michel, J. Millan and A. Guyot, European Polymer Materials, 1984, 20, 1. 33. T. Hjertburg and E.M. Sorvik, Polymer Degradation and Stability, 1983, 24, 673. 34. T. Hjetberg and E.M. Sorvik, Report IUPAC Working Party on PVC, Cleveland, OH, USA, 1980. 35. N. Bensemra, T.V. Hoang and A. Guyot, Polymer Degradation and Stability, 1990, 28, 173. 36. J. Bauer and A. Sabel, Die Angewandte Makromolekulare Chemie, 1975, 47, 15. 37. Sbarski, E. Kosior and S.N. Bhattacharya, International Polymer Proceedings, 1997, 12, 341.

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38. G. Martineze, J.M. Gomez-Elvira and T. Millan, Polymer Degradation and Stability, 1993, 40, 1. 39. T. Radiotis and G.R. Brown, JMS-Pure Applied Chemistry, 1997, A34, 743. 40. Z. Ahmed and W.J. Mazoor, Thermal Analysis, 1992, 38, 2349. 41. W. Khan and Z. Ahmed, Polymer Degradation and Stability, 1996, 53, 243. 42. M. Asahina and M. Onozuka, Journal of Polymer Science, 1994, A2, 3505. 43. K.B. Abbas and E.M. Sorvik, Journal of Applied Polymer Science, 1975, 19, 2991. 44. Z. Vymazad, E. Czako, K. Volka and J. Stepek, European Polymer Journal, 1985, 16, 149. 45. V.D. Daniels and H.H. Rees, Journal of Polymer Science, Part A: Polymer Chemistry Edition, 1974, 12, 2115. 46. D. Braun and D. Sonderhof, Polymer Bulletin, 1985, 14, 39. 47. Benavides R, Edge M, Allen NS, Tellez MM, Polymer Bulletin, 1999, 42, 273. 48. Skowronski TA, Rabek JF, Ranby B. Polymer Degradation and Stability, 1984, 8, 37. 49. S. Gaumet and J-L. Gardette, Polymer Degradation and Stability, 1991, 33, 17. 50. J-L. Gardette and J. Lemaire, Polymer Degradation and Stability, 1991, 34, 135. 51. J-L. Gardette and J. Lemaire, Journal of Vinyl Additive Technology, 1997, 3, 107. 85


52. M. Veronelli, M. Mauro and S. Bresadola, Polymer Degradation and Stability, 1999, 66, 349. 53. R. Benavides, M. Edge, N.S. Allen, M. Shah and M.M. Tellez, Polymer Degradation and Stability, 1995, 48, 377. 54. I.J. González-Ortiz, M. Arellano, M.J. Sánchez-Peña and E. Mendizábal, Polymer Degradation and Stability, 2006, 91, 2715. 55. R. Bacaloglu and M.H. Fisch in Plastics Additives Handbook, 5th Edition, Ed., H. Zweifel, Hanser, Munich, Germany, 2001, Chapter 3. 56. F. Tudos, T. Kelen, T.T. Nagy and B. Turcsanyi, Pure and Applied Chemistry, 1974, 38, 201. 57. D. Braun, Progress in Polymer Science, 2002, 27, 2171. 58. T. Kelen, Journal of Macromolecular Science Chemistry, 1978, A12, 349. 59. R.P. Lattimer and W.J. Kroenke, Journal of Applied Polymer Science, 1980, 25, 101. 60. K.S. Minsker, S.V. Kolesov and G.E. Zaikov in Degradation and Stabilisation of Vinyl Chloride-Based Polymers, Pergamon, Oxford, UK, 1998, p.76. 61. a) M. Beltrań and A. Marcilla, Polymer Degradation and Stability, 1995, 48, 219. 62. C. Anton-Prinet, G. Mur, M. Gay, L. Audouin and J. Verdu, Polymer Degradation and Stability, 1998, 61, 211. 63. N.A. Mohamed, A.A. Yassin, Kh.D. Khalil and M.W. Sabaa, Polymer Degradation and Stability, 2000, 70, 5.

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64. M.W. Sabaa, N.A. Mohamed, Kh.D. Khalil and A.A. Yassin, Polymer Degradation and Stability, 2000, 70, 121. 65. A. Andreas in Plastics Additives Handbook, 3rd Edition, Eds., R. Gaèchter, H. MuÈ ller and P.P. Klemchuk, Hanser Publishers, Munich, Germany, 1990, p.271. 66. A. Maier, Polymer Engineering & Science, 1996, 36, 1502. 67. V. Chiriac, M. Chiriac, D. Arion, D., Pavel, R. Antonie, E. Grosu, L. Pop, M. Burlacel, M. Gutiu, Materiale Plastice, 2000, 37, 2, 88. 68. L. Jian, Z. Dafei and Z. Deren, Polymer Degradation and Stability, 1991, 31, 1. 69. F. Castillo, G. Martinez, R. Sastre and J. Millan, Revista de Plasticos Modernos, 1987, 367, 86. 70. K. Patel, A. Velazquez, H.S. Calderon and G.R. Brown, Journal of Applied Polymer Science, 1992, 46, 179. 71. R. Bacaloglu and M. Fish, Polymer Degradation and Stability, 1994, 45, 301. 72. E. Ureta and M.E. Cantú, Journal of Applied Polymer Science, 2000, 77, 2603. 73. Encyclopedia of Polymer Science and Technology, Volume 12, Eds., H.F. Mark, N.G. Gaylord and Bikales Wiley, New York, NY, USA, 1970, p.725. 74. D. Braun, Die Makromolekulare Chemie, Macromolecular Symposia, 1992, 57, 265. 75. R.J. Meier and B.J. Kip, Polymer Degradation and Stability, 1992, 38, 69.

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76. P. Simon and L. Valko, Polymer Degradation and Stability, 1992, 35, 249. 77. V. Percec, A.V. Popov, E. Ramirez-Castillo, J.F.J. Coelho and L.A. Hinojosa-Falcon, Journal of Polymer Science, Part A: Polymer Chemistry Edition, 2004, 42, 6267. 78. V. Percec, A.V. Popov, E. Ramirez-Castillo, J.F.J. Coelho and L.A. Hinojosa-Falcon, Journal of Polymer Science, Part A: Polymer Chemistry Edition, 2005, 43, 779. 79. V. Percec, E. Ramirez-Castillo, L.A. Hinojosa-Falcon, A.V. Popov, Journal of Polymer Science, Part A: Polymer Chemistry Edition, 2005, 43, 2185. 80. K. Endo, Progress in Polymer Science, 2002, 27, 2021. 81. V.H. Tran, T.P. Nguyen and P. Molinie, Polymer Degradation and Stability, 1996, 53, 279. 82. X. Ruijian, Polymer Degradation and Stability, 1990, 28, 323. 83. C. Garrigues, A. Guyot and V.H. Tran, Polymer Degradation and Stability, 1994, 43, 299. 84. A.A. Yassin, M.W. Sabaa and N.A. Mohamed, Polymer Degradation and Stability, 1985, 13, 255. 85. A.H. Frye and R.W. Horst, Journal of Polymer Science, 1959, 40, 419. 86. M.H. Fish and R. Bacaloglu, Journal of Vinyl Additive Technology, 1999, 5, 4, 205. 87. G.Y. Levai, G.Y. Ocskay and Z.S. Nyitrai, Polymer Degradation and Stability, 1989, 26, 11.

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88. R. Benavides, M. Edge and N.S. Allen, Polymer Degradation and Stability, 1994, 44, 375. 89. R.F. Grossman, Journal of Vinyl Technology, 1990, 12, 34. 90. B. Ivan, B. Turcsanyi, T. Kelen and F. Tudos, Journal of Vinyl Technology, 1990, 12, 126. 91. D. Balköse, H.I. Gökcel and S.E. Göktepe, European Polymer Journal, 2001, 37, 1191. 92. K.B. Abbas and E. Sorvik, Journal of Vinyl Additive Technology, 1980, 2, 87. 93. M. Onozuka, Journal of Polymer Science, Part A: Polymer Chemistry Edition, 1967, 5, 2229. 94. N.L. Thomas, Plastics and Rubber Processing and Applications, 1993, 19, 263. 95. G. Ayrey, B.C. Head and R.C. Poller, Journal of Polymer Science, Macromolecular Reviews, 1974, 8, 1. 96. H.I. Gökçel and D. Balköse, Advances in Polymer Technology, 1998, 17, 63. 97. L.J. Gonzalez-Ortiz, M. Arellano, C.F. Jasso, E. Mendizabal and J.M. Sanchez- Pena, Polymer Degradation and Stability, 2005, 90, 154. 98. R.D.J. Dworkin, Vinyl Technology, 1989, 11, 15. 99. M. Bartholin, N. Bensemra, T.V. Hoang and A. Guyot, Polymer Bulletin, 1990, 23, 425. 100. G.Y. Levai, G.Y. Oeskey and Z.S. Nyitrai, Polymer Degradation and Stability, 1994, 43, 159. 101. N. Bensemra, T.V. Hoang and A. Guyot, Polymer Degradation and Stability, 1990, 29, 175. 89


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115. E. Beati and M. Pegoraro, Die Angewandte Makromolekulare Chemie, 1978, 73, 35. 116. N.A. Mohamed and Al-Magribi, Polymer Degradation and Stability, 2003, 82, 421. 117. D.D. Sotiropoulou, K.G. Gravalos and N.K. Kalfoglou, Journal of Applied Polymer Science, 1992, 45, 273. 118. J.F. Maggioni, A. Eich, B.A. Wolf and S.P. Nunes, Polymer, 2000, 41, 4743.

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6

Poly(Vinyl Chloride)–Wood Composites

Poly(vinyl chloride) (PVC) has been used as a polymer matrix for wood–plastic composites. The growth in wood–PVC composite (WPC) products has been slowly increasing since 2006. The outdoor durability of WPC products is more like that of PVC made from mixtures of wood filler (typically of 40–80% by weight) and plastics. However, the deployed loading level is >60 wt%. This results in serous disadvantages: the high density and lack of flexibility of the end products, the low mechanical properties, and problematic compounding and processing. Extrusion is one of the techniques used in the manufacture of wood– plastic composites. The manufacture of wood–plastic composites started in the 1980s, but dramatic growth has recently been experienced [1]. The market for WPC has been very active, with growth of 200% from 2002 to 2010 among wood–plastic composites [2]. Composites with UV resistance and dimensional stabilities are better than those of solid wood. Wood–polymer composites and wood–plastic composites are entirely different [3–11]. The main application of wood–polymer composites is flooring. In WPC composites, the advantage of wood includes low density, low equipment abrasiveness, relatively low cost, and good biodegradability; PVC provides good moisture and decay resistance [1, 9, 10]. In addition, various surface optical effects can be obtained by adding different wood species and coloured pigments [12]. WPC composites are used in many applications because they: are easy to process; have high productivity; have low economical cost; and have good versatility. However, for certain specific uses, mechanical

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properties such as strength and toughness of materials are inadequate. Composites have better specific properties and find applications in diverse fields, ranging from domestic appliances to spacecraft [13]. The use of wood in thermoplastics has been plagued by the thermalstability limitation of wood, as well as the difficulties in obtaining good filler dispersion and strong interfacial adhesion [14–20].

6.1 Additives In the composites industry, additives are commonly used to modify behaviour, appearance, mechanical properties and processability [21]. Additives are still needed for manufacturing products with WPC composites to maintain the properties. In addition to the wood component, several classes of PVC additives (i.e., impact modifiers), processing aids and lubricants are used to improve processing. The correct selection and use of these additives can predict an overall formulation designed to produce a composite with optimum properties [22]. The processing of wood-filled wood composite WCP is challenging because of the high temperature increase due to shear heating, high melt viscosity, and low melt strength that leads to poor extrusion quality. To overcome these difficulties, very-high-molecular-weight process aids are beneficial. However, it has been shown that their chemical composition is a critical parameter [23]. The use of antimicrobial agents is dependent upon the type and content of wood fibre, microbe types to the application, environment, and humidity. Aminosilane has been promoted for the interaction between wood fibre and PVC as an adhesion promoter [24]. It has been observed to be a suitable for WPC composites, significantly improving the tensile strength of the composites. Other treatments (dichlorodiethylsilane, phthalic anhydride, maleated polypropylene) were found to be ineffective [25].

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Phosphate esters are often used as flame retardants. However, they have negative effects on the environment and a limited effect on flame retardancy and smoke suppression. Flame retardants such as antimony trioxide and halogenated organic compounds as well as smoke suppressants such as molybdenum trioxide and ammonium octamolybdate have been shown to be effective. Antimony trioxide promotes the dehydrochlorination of PVC. Thus, there are reservations about the general use of this retardant. Recently, inorganic flame retardants and fillers such as alumina trihydrate and magnesium hydroxide have been used for the purpose. The use of layered silicate polymer nanocomposites has been proposed as a totally new and promising approach for the fire retardancy and smoke suppression of polymers. They also produce remarkable improvements in certain material properties (e.g., mechanical strength, optical properties, electric properties, fire retardancy). A low loading of nano-montmorillonite particles (5–10 wt% content) can reduce the maximum rate of heat release by 70% [26–28]. Coupling agents such as copper amine, silanes, maleic anhydride and their grafting polymers improve composite properties [12, 29–31]. However, unlike polyolefin–wood fibre composites, the conversion of the hydrophilic surface of wood to a hydrophobic surface is not sufficiently effective for enhancing the adhesion of PVC to wood fibre. The Lewis acid–base interactions for decomposition are significant for enhancing interfacial adhesion. The other reason is that the induced acid–base reaction favours fire retardancy and smoke suppression [9, 32]. WPC composites must resist fire and suppress smoke. Pure PVC has high chlorine content (56.8%), which gives good flame retardancy. However, the high content of wood fibre and low-molecular-weight additives (as well as subsequent thermal degradation) reduces the flame retardancy of the composites.

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PVC generates a lot of black smoke during forced burning. Flame retardants and smoke suppressants are added to prevent smoke evolution, reduce heat release, and to lower the extent of burning. Flame retardants and smoke suppressants are often incorporated with WPC composites.

6.2 Properties of Wood-Poly(vinyl Chloride) Composites In structural applications, WPC products are viable substitutes for solid woods and PVC. WPC products are strongly influenced by wood content [33]. An increase in wood fraction increases the notched impact energy, flexural strength, and elastic modulus while decreasing the melt index, tensile strength and tensile elongation at break. Moreover, increasing the fibre size causes the melt index, flexural and tensile moduli, as well as tensile elongation at break to increase.

6.3 Processing PVC–wood flour composites have attracted attention due to their combination of good mechanical properties, chemical stability and water resistance. PVC–wood flour composites are used for decking, siding, and indoor building materials [34]. However, the processing of PVC–wood flour composites is associated with poor interfacial compatibility, poor fire resistance and weak impact strength. In addition, these composites burn readily, so the application may be faced with more danger from fire. Among wood–plastic composites, wood–PVC thermoplastic composites are manufactured by incorporating and dispersing wood fibres or wood flour into molten plastics to form composite materials. The advantages of plastics and wood are therefore employed. The poor interfacial attraction between the hydrophilic wood and the hydrophobic plastic matrix results in poor adhesion. Hence, stress is

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transferred from the matrix to the wood flour fibre, thereby reducing mechanical strength and ductility. Extruded PVC–wood flour composites are being developing rapidly thanks to recent developments in formulation technology. Potential modifications with additives may lead to improvements in key properties [35]. Wood filler with moisture content of 6–9% by weight and PVC is compounded into pellets. Wood filler is pelletising at a high aspect ratio to reinforce the structure. Downstream feeding may be the preferred processing configuration [36]. Figure 6.1 shows a conical intermeshed twin-screw extruder. A kneading zone is an important part in screw design where the wood and PVC will be mixed and pumped to the die. Mixing of PVC and wood creates high-viscosity flow. Hence, care must be taken during compounding with appropriate addition of additives such as heat stabilisers and lubricants.

Precompression zone Metering zone

Compression zone

Vent zone

Feed zone

Kneading zone

Figure 6.1 A conical intermeshed twin-screw extruder (schematic). Reproduced with permission from [37]. ©2004, Society of Plastics Engineers

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6.4 Advantages of Wood-Poly(Vinyl Chloride) Composites The major advantages of WPC composites are: 1. WPC composites provide low outdoor maintenance costs. 2. Products can also be extruded without expensive wood-working operations. 3. WPC composites have superior mechanical properties with respect to resistance to weathering and flame-retardancy. 4. WPC made out of PVC can be cut, sawed, nailed, screwed, and processed by conventional wood-working equipment [12, 38]. 5. WPC composites are used in window/door profiles, decking, railing and siding; interior and marine applications are under development.

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10. J.A. Meyer, Forest Products Journal, 1982, 32, 24. 11. J.A. Meyer, Technologist, 1987, 1, 3, 4. 12. A.K. Bledzki, S. Reihmane and J. Gassan, Polymer Plastics Technology and Engineering, 1998, 37, 4, 451. 13. D.N. Saheb and J. Jog, Advanced Polymer Technology, 1999, 18, 4, 351. 14. L.M. Matuana, J.J. Balatineez, and C.B. Park, Polymer Engineering and Science, 1998, 38, 765. 15. D. Maidas and B.V. Kokta, Journal of Vinyl Technology, 1993, 15, 38. 16. L.M. Matuana, C.B. Park, and J.J. Balatineez, Polymer Engineering and Science, 1998, 38, 1862. 17. L.M. Matuana, C.B. Park and J.J. Balatineez, Polymer Engineering and Science, 200, 80, 1943. 18. L.M. Matuana and F. Mengeloglu, Journal of Vinyl Additive Technology, 2001, 7, 67. 19. J.Z. Lu, Q. Wu, and I.I. Negulescu, Wood and Fiber Science, 2002, 34, 434. 20. H. Jiang, D.P.Kamdem, B. Bezubic, and P. Ruede, Journal of Vinyl Additive Technology, 2003, 9, 138. 21. M.R. Snyder, Composites Technology, 2008, 14, 1, 40. 22. F. Sim in Proceedings of an SPE Conference - Vinyltec 2004, Iselin, NJ, 2004, Paper 21.

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23. B. Azimipour and P. Schipper in Proceedings of an SPE Conference - Vinyltec, 2002, p.337. 24. L.M. Matuana and F. Mengeloqlu, Journal of Vinyl Additive Technology, 2002, 8, 4, 264. 25. L.M. Matuana, R.T. Woodhams, J.J. Balatinecz and C.B. Park, Polymer Composites, 1998, 19, 4, 446. 26. G. Beyer, Plastics, Additives and Compounding, 2005, 7, 5, 32. 27. M. Bartholmai and B. Schartel, Polymers for Advanced Technologies, 2004, 15, 355. 28. T.J. Pinnavaia, L. Tie, P.D. Kaviratna and M.S. Wang, Journal of Engineering and Applied Sciences, 1994, 346, 81. 29. B.L. Shah and L.M. Matuana, Journal of Vinyl Additive Technology, 2005, 11, 160. 30. H.H. Jiang and D.P. Kamdem, Journal of Vinyl Additive Technology, 2004, 10, 2, 70. 31. A.K. Bledzki, M. Letman, A. Viksne and L. Rence, Composites Part A: Applied Science and Manufacturing, 2005, 36, 6, 789. 32. S.M. Lai, F.C. Yeh, Y. Wang, H.C. Chan and H.F. Shen, Journal of Applied Polymer Science, 2003, 87, 3, 487. 33. N. Stark and M. Berger in the Proceedings of a Forest Products Society Conference - Functional Fillers for Thermoplastics and Thermosets, Madison, WI, USA, 1997, p.119. 34. H.H. Jiang and D.P. Kamdem, Journal of Vinyl Additive Technology, 2004, 2, 10.

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35. P. Kroushl in Proceedings of an SPE Conference - Vinyltec 2002, Itasca, IL,USA, 2002, Session 4, Paper 4, p.463. 36. R. Cutillo and S. Jackson in Proceedings of an SPE Conference - Vinyltec 2005, Philadelphia, PA, USA, 2005, Paper 13. 37. H. Jiang and D.P. Kamdem, Journal of Vinyl & Additive Technology, 2004, 10, 2, 59. 38. A.K. Bledzki, J. Gassan and S. Theis, Mechanics of Composite Materials, 1998, 34, 563.

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7

Poly(Vinyl Chloride) Extrusion: Problems and Defects

Poly(vinyl chloride) (PVC) is used in the production of hundreds of products that are very important in construction, electronics, healthcare, and other applications. In processing, PVC is used in >90% of all extrusions in Europe [1]. Like other group members such as polyethylene, polypropylene, polystyrene, polyvinylacetate, polymethylmethacrylate and polyvinylidene chloride, PVC has the vinyl group (CH2=CH-). However, ‘vinyl’ generally refers to PVC and its copolymer. Examination of problems and defects is very important in PVC extrusion. PVC extrusion involves blending between resins and additives in high-speed mixtures. The defects are related to PVC compounds and processing. The formulation of PVC decides the processing and product performance. The useful service lifetimes of PVC products is estimated by subjecting the products to constant testing. In PVC extrusion, process variations are one among several problems that have an effect on temperature. The melt temperature is important to ensure constant processing. Thermal degradation is primarily an initiated break in the polymer chain, and does not have a direct bearing on the decrease in molecular weight. It is a function of temperature, rheological parameters and molecular weight. Degradation is a too severe a problem and requires cleaning of the extruder. The effects of degradation are: a reduction in physical properties; surface defects; process instability; wear; and increased quality-control costs [2]. There are many defects and problems that are specific to a particular

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type of extrusion operation. In extrusion, uneven cooling can cause bending or collapse of the product. It is important to know the relative temperature distribution during cooling of an extruded product. Similarly, problems with surging are due to solids conveying or a melting problem, changes must be based on this assumption [3]. Selecting PVC for industrial applications (e.g., automotive, domestic appliances, garden) is strongly dependent upon PVC composition, part design and processing conditions. Fillers, pigments, and other additives may have a greater influence, and there may be a need to characterise material selection for the required application. Extrusion problems must first be diagnosed to determine the solutions. Shortterm implementation of the solution is important in PVC processing. Particularly in a continuous process such as extrusion, it is important to have solutions to solve problems and defects. ‘Visible defects’ due to running a process too fast can result in, for example, shark-skin finishes, melt fracture, failure to hold dimensional tolerances, air occlusion, and visible discoloration of products. ‘Hidden defects’ are often more damaging because a large quantity of off-grade material may have been produced before the realization that a mistake has been made. Such hidden defects include: loss of needed residual heat stability and light stability; subsequent warpage due to built-in strains; low sag temperature; and low heat distortion temperature. Incipient degradation causing loss of residual stability may often be detected by checking parts for fluorescence under ultraviolet (UV) light, which reveals the presence of short sequences of double bonds in degrading PVC molecules [4]. Flow velocity and stress discontinuity is responsible for surface defects. Such discontinuities may induce a high flow stretching rate or cohesive failure of the polymer melt, consequently causing the onset of shark-skin finishes [5–8]. With respect to problems related to extrusion (particularly problems that occur inside the extruder), it is important to have good

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Poly(Vinyl Chloride) Extrusion: Problems and Defects

instrumentation. Melting, mixing and metering of PVC is totally obscured by the extruder and is dependent upon instrumentation to determine the events occurring within the extruder. The seriousness of the problem can be assessed only by instrumentation. Problems and defects are based on the part morphology of PVC. Part morphology is defined by crystal content, morphology and orientation, non-crystalline content and orientation as well as all important interconnections between these morphological units. The levels of these properties are determined by the orientation of the molecular chains as well as chain packaging. The crystallinity and strained chain conformation impact property retention with respect to the glass transition temperature and the melting point. The extruded PVC products are essentially identical chemically. PVC processing in the future will centre on the management of chain entanglements, structural defects, and process control. Several aspects of molecular-structure control will influence solid-phase processing of polymers with respect to the networks, initial morphology in crystalline polymers, and thermally activated processes. PVC extrusion offers several advantages such as continuous processing, easy processability and relatively economical cost. However, differences in the rheology of the PVC compound can lead to the formation of several defects and problems depending on other parameters such as process settings and the die. Defects and problems can be detrimental in terms of the mechanical strength and appearance of the products. Problems regarding diffusion during PVC processing can be neglected because PVC is compounded with other ingredients. Understanding the role of various parameters such as rheology, geometric details, and process parameters are useful for the prediction and prevention of problems and defects.

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6.

B. Tremblay, Journal of Rheology, 1991, 35, 6, 985.

7.

E.R. Howells and J.J. Benbow, Transactions of the Plastics Institute, 1962, 30, 240.

8.

S.J. Kurtz in Advances in Rheology, Eds., B. Mena, A. Garcia-Rejon and C.Rangel-Nafaile, Univerisdad Nacional Autonoma de Mexico, Mexico, 1984, p.197.

106

8

Troubleshooting Problems in Poly(Vinyl Chloride) Extrusion

Studies on poly(vinyl chloride) (PVC) problem-solving have traditionally used deterministic tasks that require execution of a systematic series of steps to reach a rational and optimal solution. Most of the problems are characterised by uncertainty, the need to consider an enormous number of variables (e.g., raw material, processing method, machinery, product) as well as the need to optimise the solution to multiple interacting constraints. It is necessary to have a strategy to identify the problem. It is important to have multiple strategies to solve the problem. Once an action plan is ready, several factors influence the formation and selection of the strategy. Assessment of the problem allows for the development of more efficient problem-solving strategies in PVC processing. Each problem requires more information related to the raw material, formulation, processing technique, machinery, and end product. Problems are likely to fit into a given plan or one needs to select the most appropriate plan. Troubleshooting goes to show: • There is typically more than one way to solve a problem • Ability and experience affect the strategy chosen In troubleshooting of PVC extrusion, solving the problem and optimising the process is paramount. This involves finding the shortest route through a set of points and returning to the raw material used in the processing. Diagnosing problems involves examining the properties and settings of the extrusion process to control the

107


performance of a particular extrusion problem. This is followed by examining the outcome of the change and interpretation of the results [1]. Selecting the optimum solutions to the problems is one of the most crucial challenges in PVC processing. Without troubleshooting methods, many extrusion problems would be unsolved or solved incorrectly, which can lead to huge wastage. The challenges are: • Limitation of human capabilities to compare or to decide. The challenges become more intricate if the comparison is made on the basis of multiple solutions • The possible solution in comparison with the early data may not match due to variable parameters

8.1 Problems and Troubleshooting in Pipe/Profile Extrusion To achieve better extrusion, materials should appear in the vent with a ‘cheesy’ appearance instead of a melted appearance. In the cheesy condition, the powder can be appropriately degassed. The screw flight in the feed section should be properly filled with powder so the open feed throat is effectively sealed off.

8.1.1 Production Problems in the Extruder Problems in pipe and profile extrusion are common. They can be divided into three areas: extrusion, calibration and product. During extrusion processing or troubleshooting, four points must be kept in mind: 1. Do not allow physical damage to the equipment 2. The product must meet the quality requirement 108


3. Increase temperature in steps of 5 °C but, at the same time, too much of an increase in temperature may lead to burning 4. In the adaptor and spider portion of the die, care must be taken to control the temperature because cooling of these zones is very difficult

8.1.1.1 Problem: Difficult to String-up Melt during Startup This problem may be due to a lack of strength. During processing, the extrudate (string-up melt) is hot and breaks easily when leading through the cooling tank to the puller. Figure 8.1 illustrates the troubleshooting process to solve the problem of difficult to stringup melt material during startup. The material after extrusion, at high temperature, (the extrudate) can exhibit reddish or black lines which may lead to charring. This is commonly known as burning in PVC extrusion.

8.1.1.2 Problem: Powder Pulled into a Vacuum This problem may be due to a loss of vacuum of vent or excessive clogging in vacuum traps or filters. Figure 8.2 illustrates the troubleshooting process to solve the problem of a product pulled into a vacuum. Reduce production rate by reducing machine’s screw rotation per minute (RPM) and appropriately adjust take-off or puller RPM.

8.1.1.3 Problem: High Bearing Throat at Back Pressure This problem can be indicated in the thrust indicator of the back pressure gauge. Figure 8.3 illustrates the troubleshooting process to solve a high bearing throat at back pressure.

109


8.1.1.4 Problem: Motor Load is too High This problem may be due to poorly plasticised material in the degassing zone. Screws should be filled and the motor speed must match with the feed dosing. Figure 8.4 illustrates the troubleshooting process to solve the problem of a too-high motor load (i.e., ampere or power reading reaches the maximum to the motor). If the restrictor is wire mesh or filters, the size of the restrictor is increased or it is removed.

Note: Indicates Increase

Reduce temperature Motor

Indicates Decrease Bz 1 Bz 2

Bz 3

Bz 4

Barrel zones Controllers

If “No”

Increase Temperature Aaptor


Spider

Die

Die

Pipe Die

Profile Die

Figure 8.1 Problem: difficult to string-up melt during startup

110


Increase Vaccum Motor

Bz 1 Bz 2 Bz 3 Bz 4 Barrel zones Controllers

Note: Indicates Increase If “No” Indicates Decrease

Motor

Bz 1 Bz 2 Bz 3 Bz 4 Bz 5 Barrel zones Controllers

If “No”

Increase Temperature

Motor

Oil hot-cool unit

Increase Temperature Pump Bz 1 Bz 2 Bz 3 Bz 4

If “No” Barrel zones Controllers

Figure 8.2 Problem: powder pulled into a vacuum

111


Increase Extruder RPM Barrel temperature

Motor

Bz 1

Bz 2

Bz 3

Bz 4

Note: IndicatesIncrease IndicatesDecrease Controllers

If “No’

FeederRPM

Motor

Bz 1

Bz 2

Bz 3

Bz 4 If “No’

Reduce tempeerature Controllers

Oil hot-cool unit If “No’

Aaptor


Spider

Die Pipe Die

(OR)

Pump


Aaptor

Die Profile Die

Figure 8.3 Problem: high bearing throat at back pressure

112

Troubleshooting Problems in Poly(Vinyl Chloride) Extrusion Feeder RPM Note:

Motor

IndicatesIncrease IndicatesDecrease

Bz 1

Bz 2

Bz 3

Bz 4

If “No’

Controllers


Motor

Bz 1

Bz 2

Bz 3

Bz 4 Barrel zones

If “No’

Aaptor Aaptor

Increase Tempature

Spider

Die

Aaptor

(OR)

Pipe Die

Controllers

Increase Tempature

Die Profile Die Try different formutatio n

If “No’

PVC compounding Hot-coolmixr

Figure 8.4 Problem: Motor load is too high

8.1.1.5 Problem: Low Output A machine that is not reaching the expected production may be due to caking of the material in the hopper or due to high temperature. For given product dimensions, the production is below the normal output and RPM of the machine. Figure 8.5 illustrates the troubleshooting process to solve the problem of low output.

113

Update on Troubleshooting the PVC Extrusion Process Note:

Check Extruder RPM

Bz 1

IndicatesIncrease

Bz 4

Bz 3

Bz 2

IndicatesDecrease

Check Extruder RPM

Barrel zones

Controllers

Motor If “No’

Bz 1

DecreaseTemperature

Bz 2

Bz 3

Bz 4

Motor

Bz 1

Bz 4

Bz 3

Bz 2

If “No’

Controllers

Barrel zones Try diftrent Controllers

If “No’

Increase Extruder RPM

Bz 1

If “No’

formulatio n

PVC compounding Hot- coolmixer

Bz 2

Bz 3

Bz 4

Barrel zones

If “No’

CheckWear and tear Controllers

Figure 8.5 Problem: low output

8.1.2 Product Problems During processing in the production process, the product must be checked for appearance, melt fracture, lumpy, and cool or oval (eggshaped) mark surfaces. Lubricants and process aids decrease the melt viscosity and from the sticking of PVC in the extruder. High levels 114


of fillers decrease properties and a higher temperature is required for processing. A sufficient level of stabiliser must be used to ensure appropriate stability during processing. Heat stability can be adversely affected by incompatibility of the additives with PVC. Stabilisers should be highly compatible with PVC. The use of solid barium/cadmium stabilisers could adversely affect post-extrusion processes. The use of high levels of lubricants with high PVC incompatibility may cause surface blooming or exudation after extrusion. This will affect the quality of the product.

8.1.2 Production Problems in Downstream Areas The troubleshooting flowcharts shown below explain the way to solve problems related to downstream areas once the extrudate emerges from the extruder.

8.1.2.1 Problem: A Longitudinal Scratch in Pipe or Profile is Found While Sizing Scratching is a production and quality problem. Figure 8.6 illustrates the troubleshooting process to solve a longitudinal scratch while sizing.

8.1.2.2 Problem: Folding of Material in the Calibrator The folding of material in the calibrator may be due to filler or delustrant build-up or plate-out. In such cases, kerosene or lubrication oil must be placed at periodical intervals to remove the plate. Figure 8.7 illustrates the troubleshooting process to solve the folding of material in the calibrator.

115


8.1.2.3 Problem: Blowouts in the Cooling Zone Blowouts in the cooling zone may be due to lumps or holes present in the material. Figure 8.8 illustrates the troubleshooting process to solve the problem of blowouts in the cooling zone. In the case of pipe products, air pressure must be decreased within the pipe if using a floating pressure plug.

Note:

Change PVC formulation

Indicates Increase Indicates Decrease Mandrel Burr or plate-out

If “No”

may be present

PVC compounding Hot-cool mixer

Pipe Burr or plate-out may be present Profile

Figure 8.6 Problem: a longitudinal scratch in a pipe or profile found while sizing

116

Troubleshooting Problems in Poly(Vinyl Chloride) Extrusion Note: Indicates Increase

plate-out or white deposition

Indicates Decrease

Pipe Calibrator Change PVC formulation

If “No”

Profile calibrator plate-out or white deposition

PVC compounding Hot-cool mixer

Put kerosene or lubricating oil

Mandrel Burr or plate-out If “No” may be present

Pipe Burr or plate-out may be present Profile

Figure 8.7 Problem: folding of material in the calibrator

117

Update on Troubleshooting the PVC Extrusion Process Increase water velocity

Die

Note:

May be lumps or hole

Indicates Increase

Cooling tank

Indicates Decrease plate-out or white deposition

Pipe Calibrator

If “No”

Water Inlet Increase Temperature

Aaptor

Spider Pipe Die

plate-out or white deposition


Aaptor

Profile calibrator

If “No”

Put kerosene or lubricating oil

Die

If “No”

Profile Die

Mandrel Burr or plate-out

Die

may be present

Reduce the water temperature

May be lumps or hole

Cooling tank

If “No” Pipe Burr or plate-out may be present

Water Inlet

Profile

Figure 8.8 Problem: blowouts in the cooling zone

8.1.2.4 Problem: Uncontrolled Wall Thickness Thin and thick spots on the product may be due to uneven viscosity in the melt reaching the die. The variation does not respond to die adjustment. Figure 8.9 illustrates the troubleshooting process to solve the problem of uncontrolled wall thickness.

118


Reduce temperature Motor

Note: Indicates Increase Bz 1 Bz 2 Bz 3 Bz 4

Indicates Decrease Barrel zones Controllers

If “No” Increase Temperature


Aaptor

Aaptor

Spider

Die

(OR)

Pipe Die

Die Profile Die

Figure 8.9 Problem: uncontrolled wall thickness

8.1.2.5 Problem: Poor Inner Surface If small cracks are visible on the inside of the product and can be seen as small swellings on the outside of the product, this may be due to poor fusion of the material. Figure 8.10 illustrates the troubleshooting process to solve the problem of a poor inner surface. Die land length has to be changed or increased, if possible.

119


Note: Motor

Indicates Increase

Reduce temperature

Indicates Decrease

If “No”

Bz 1 Bz 2 Bz 3 Bz 4

Increase Temperature Motor Controllers Bz 1 Bz 2 Bz 3 Bz 4

If “No”

Barrel zones Controllers Spider Aaptor

Decrease Temperature

Die


Aaptor

If “No”

(OR) Die

Pipe Die

Profile Die Increase Temperature Oil hot-cool unit

Pump

Figure 8.10 Problem: poor inner surface

8.1.2.6 Problem: Regular Wavy Lumps For this particular problem, the die system must be changed to increase the land length of the die system and the compression ratio between the spider and annular opening of the die system. Figure 8.11 illustrates the troubleshooting process to solve the problem of regular wavy lumps.

120


Note: Indicates Increase If “No”


Indicates Decrease

Decrease Temperature Motor

Oil hot-cool unit

Bz 1 Bz 2 Bz 3 Bz 4

If “No”

Barrel zones Controllers

Spider Aaptor


Die Pipe Die

Aaptor


If “No”

(OR) Die Profile Die

Reduce extruder RPM Motor Bz 1 Bz 2 Bz 3 Bz 4

Controllers

Figure 8.11 Problem: regular wavy lumps

8.1.2.7 Problem: Irregular Lumps (Random With No Regular Pattern) Figure 8.12 illustrates the troubleshooting process to solve the problem of irregular lumps which are random with no regular pattern. Using an adaptor with a smaller hole in the die system will give better mixing.

121


Barrel temperature

Screw temperature

Bz 1 Bz 2 Bz 3 Bz 4

Note: Indicates Increase Indicates Decrease

Figure 8.12 Problem: irregular lumps (random with no regular pattern)

8.1.2.8 Problem: Dimples on the Product Figure 8.13 illustrates the troubleshooting process to solve the problem of dimples on the product. The pipe should be examined for voids. Collapse of voids in the pipe may give dimples on the surface.

8.1.2.9 Problem: Burning or Yellowing of the Extrudate During extrusion, the problem occurs due to black specks or discoloration such as yellowing or burning of melt string. Any temperature zone that approaches >195 °C should be suspected. Figure 8.14 illustrates the troubleshooting process to solve the problem of burning or yellowing of the extrudate. The adaptor and spider are often the causes of burned material. Check for mismatched metal parts, dechromed surfaces, or other areas where material could stick and burn.

122

Troubleshooting Problems in Poly(Vinyl Chloride) Extrusion Increase water velocity

Die

Note:

Cooling tank

Indicates Increase Indicates Decrease

Check Vaccum

Water Inlet


Figure 8.13 Problem: dimples on the product Reduce temperature

Motor

Note: Indicates Increase

Bz 1 Bz 2 Bz 3 Bz 4

Indicates Decrease

Barrel zones

If “No”

Controllers

Reduce Temperature

Check Burnt material Oil hot-cool unit

Spider Aaptor

Pump


Die

(OR)

Pipe Die

Die Profile Die

Spider Aaptor

Aaptor


Die Pipe Die

Aaptor


(OR) Die Profile Die

Figure 8.14 Problem: burning or yellowing of the extrudate 123


If the die is removed, burning shows in the adaptor area. Remove the barrel or screw, and use a purge compound to clear the material sticking to the screws. Because of the large mass of material in the head area, changes will not be rapid. In some cases, a temperature change may take as long as 1 hour to take effect. Check the vents for burned compounds that may be falling back.

8.1.2.10 Problem: Poor Overall Appearance Figure 8.15 illustrates the troubleshooting process to solve the problem of poor overall appearance. The adaptor and spider are often causes of burned material.

Troubleshooting process – Pipe/Profile extrusion Flow chart – 8.1.2.10 Problem – Overall appearance bad

Check rubber gaskets in cooling tanks to see if they are too tight

Black specks or yellowing or discolored or burning

Suspect any temperature zone approach 195 ºC

Checks sizer for alignment and vibration

Overall appearance bad Check puller for slipping being too tight, uneven pulling or vibration

Check spider and adaptor

Check for mismatched metal parts, dechromed surfaces, or other areas where material could stick and burn

Figure 8.15 Problem: poor overall appearance

124


8.1.2.11 Problem: Dull Surface Appearance Figure 8.16 illustrates the troubleshooting process to solve the problem of dull surface appearance of the products.

Surface appearance dull

Surface dull, increase temperature

Surface glaze, decrease temperature

Figure 8.16 Problem: dull surface appearance

8.1.2.12 Problem: Low Results in the Drop Weight Impact Test Figure 8.17 illustrates the troubleshooting process to solve the problem of low results in the drop weight impact test. Poor impact sometimes results in the die system; the shear must be increased through the use of a large spider.

125


Increase average heat by increasing barrel and screw

Check vent for volatiles removing

Low results in drop Weight impact test

Check for powder has not plugged screen to vacuum pipe or lines

Check material for moisture or volatiles

Figure 8.17 Problem: low results in the drop weight impact test

8.1.2.13 Problem: Gauge Variation Figure 8.18 illustrates the troubleshooting process to solve the problem of gauge variation. The basic extrusion process converts thermoplastic materials into a continuous melt stream. Extrusion dies are then employed for spreading the melt to a given width and establishing a uniform cross-section. Sometime gauge variations occur in wall thickness with time. It may not be a requirement to make any die adjustments.

126


Gauge variation

Yes Gauge variation Yes Check exlruder for surging No Check die melt flow No Check temperature contoller and thermocouple function Yes Finish No Check previous data

Figure 8.18 Problem: gauge variation

127


8.1.2.14 Problem: Degassing is Difficult Figure 8.19 illustrates the troubleshooting process to solve the problem of difficult degassing. In the case of a fully plasticised material in the degassing zone, decrease the temperature in zones 1 and 2.

Degassing difficult

Yes Increase screw as much as screw allows No Increase barrel zone 1 & 2 temperature not beyond 180 ºC No Increase screw core thermo-regulation Yes Finish No Check previous data

Figure 8.19 Problem: degassing is difficult

128


8.1.2.15 Problem: Frictional Heat: Zone-4 Overheating Figure 8.20 illustrates the troubleshooting process to solve the problem of overheating due to the development of frictional heat.

Frictional heat

Yes Check controllers are working

No

Check cooling agent flow

No Decrease thermo-core regulation Yes Finish No Check previous data

Figure 8.20 Problem: frictional heat: zone-4 overheating

129


8.1.2.16 Problem: Melt Fracture and Surface Roughness Figure 8.21 illustrates the troubleshooting process to solve the problem of melt fracture and surface roughness. Melt fracture occurs due to low fusion of the material. In this case, all die surfaces are clean and smooth, and a melt fracture or surface roughness occurs anyway. If surface roughness increases, more calcium stearate or polyethylene wax may be necessary.

Melt fracture and surface roughness

Yes Low temperature profile - increase temperature profile No

Increase lubrication level in formulation

No Material vent out - slow down the screw speed Yes Finish No Check previous data

Figure 8.21 Problem: melt fracture and surface roughness

130


8.1.2.17 Problem: Lumpy, Cold or Oval (egg-shaped) mark Surfaces Figure 8.22 illustrates the troubleshooting process to solve the problem of lumpy, cold or oval surfaces. Over-lubrication or an inappropriate temperature profile can result in lumpy, cold or oval surfaces.

Lump, cold or ovary surfaces

Yes Adjust temperature profile

No

Adjust oil hotcool temperature

No Adjust or reduce lubrication level Yes Finish No Check previous data

Figure 8.22 Problem: lumpy, cold or ovary surfaces

131


8.1.2.18 Problem: Over-lubrication Figure 8.23 illustrates the troubleshooting process to solve the problem of over-lubrication. Worn-out barrels and screws will cause an appearance of over-lubrication due to decreased levels of shear and material transport in the extruder. Slow reduction in load or amperage and output under identical operating conditions is also a sign of worn-out barrels and screws. A decrease in external lubricants will temporarily alleviate this problem, as will the addition of ≤10% of a pelletised form of the formulation. However, these are, at best, temporary solutions, and product properties may suffer.

Over lubrication

Yes Worn out screw and barrel. No Indicates reduction in amperage or output No Feed the material in pellets or granular form Yes Finish No Check previous data

Figure 8.23 Problem: over-lubrication 132


8.1.2.19 Problem: Impact Failure Figure 8.24 illustrates the troubleshooting process to solve the problem of impact failure. Inconsistent impact along the profile can be due to trapped gas. Impact-modified formulations tend to collect moisture. Over-lubrication can reduce shear in the feed and transition to an extent that poor dispersion of the impact modifier and inconsistent impact will result.

Impact failure

Yes Adjust screw and barrel temperature No

Check material flowing properly in feed zone

No Decrease lubrication level Yes Finish No Check previous data

Figure 8.24 Problem: impact failure

133


8.1.2.20 Problem: Black Specks Figure 8.25 illustrates the troubleshooting process to solve the problem of black specks. A prolonged extrusion run can sometimes result in black specks in the extrudate due to plate out. High loading of filler can cause exudation or plate out.

Black specks

Yes Adjust the formulation No

Choose better stabilizer and lubricants

No Check barrel and die temperatures Yes Finish No Check previous data

Figure 8.25 Problem: black specks

134


8.1.2.21 Problem: Variation in Load or Amperage from Batch-to-Batch or Between Batches Figure 8.26 illustrates the troubleshooting process to solve the problem of variation in load or amperage from batch-to-batch or between batches. The quality of the raw material and compounding must be checked. Inherent viscosity (K value) and the particle-size distribution of the PVC resin will affect bulk density, fusion rate, and output. A good quality-control programme for incoming raw materials and blended compound will maintain product consistency and productivity levels.

Variation in load or amperage

Yes Check raw material quality No

Check compounding

No Check feeding in the extruder Yes Finish No Check previous data

Figure 8.26 Problem: variation in load or amperage from batch-tobatch or between batches 135


8.1.3 Quality Problems in the End Product After production, the product may have defects and problems which may be related to the extrusion process. The flowcharts below illustrate the troubleshooting method used to solve the quality-quality problems in the end product using the extrusion process.

8.1.3.1 Problem: Failure in the Methylene Chloride Test Figure 8.27-8.29 illustrates the troubleshooting process to solve the problem of failure in the methylene chloride test. One of the methods to check the quality of the end product is the methylene chloride test.

8.1.3.1.1 Problem - Inside Portion Granular

136


Failure in methylene chloride test

Yes

Increase Temperature Oil hot-cool unit

Pump

Motor

No


Bz 1 Bz 2 Bz 3 Bz 4 Barrel zones Controllers No


Aaptor Spider

Die Pipe Die


Die Profile Die

Figure 8.27 Problem - Inside portion mealy

137


8.1.3.1.2 Problem: Middle Portion is Mealy


Yes

Increase Temperature Oil hot-cool unit

Pump

Motor

No



Figure 8.28 Problem: Middle portion is mealy

138


8.1.3.1.3 Problem: Outside Portion is Mealy


Yes Increase Temperature Aaptor

Aaptor Spider

Die Pipe Die


Die Profile Die

Figure 8.29 Problem: outside portion is mealy

8.1.3.2 Problem: Bubbles at the Oil Reversion Test at the Inner Surface Figure 8.30 illustrates troubleshooting for bubbles at the oil reversion test at the inner surface. It is due to the die, which is not suitable for the size required.

139


Bubble at oil reversion testinner surface Yes

Motor


Bz 1 Bz 2 Bz 3 Bz 4 Barrel zones Controllers No

Increase Vaccum Motor


Figure 8.30 Problem: bubble at the oil reversion test at the inner surface

140


8.1.4 Quality Problems in Pipes Table 8.1 shows the problems related to pipe quality and their probable solution.

Table 8.1 Troubleshooting problems of pipe products with probable extrusion solutions No.

Problem

Probable cause

Troubleshooting method

Mean outer diameter minimum

Insufficient air pressure or vacuum

Increase air pressure or vacuum

Mean outer diameter - over the maximum

Excess air pressure

Reduce air pressure

Outer surface is porous

Surface looks porous due to low temperature

Increase die temperature Also increase other temperatures

Over surface glossy roughness

Excessive temperature leads to a loss of glossy surface

Reduce temperature of the barrel and die

Burned particles on outer surface

Excessive temperature in barrel and die

Decrease barrel temperature in zones 1–3 Possibly increase the speed of the extruder

Burned streaks or streaks on the outer surface

Excessive temperature in the barrel and die

Decrease the die temperature Decrease the overall temperature of the barrel and die

Longitudinal streaks and grooves on the outer surface

Excessive barrel and die temperature

Decrease die temperature Decrease overall temperature of the barrel and die

141


142

Inner surface uneven (rugged) due to use of regrind

Excessive temperature in the barrel zone and mandrel

Increase barrel zone 4 Reduce Mandrel temperature

Inner surface glossy and wavy (overheated)

Excessive temperature in the barrel zone, mandrel and screw

Decrease the temperatures of barrel zones 1–4 Reduce Mandrel temperature Reduce Screw oil cool unit temperature

Longitudinal streaks and grooves on the inner surface

Excessive temperature in the mandrel

Decrease mandrel temperature

Increased porosity in the middle of the wall (thick wall pipes)

Low temperature in the barrel zone and low vacuum

Increase vacuum in the vent zone Increase temperature of barrel zones 1–4

Maximum and minimum tolerances encoded in places located near each other

Excessive temperature in the die and mandrel

Decrease die and mandrel temperatures If not possible to dismantle, clear and reassemble

Thinnest section of the wall located horizontally

Low screw and barrel temperature

Increase screw oil heat cool temperature Increase temperature of barrel zone 4

Vacuum pump drawing raw material

Low temperature in the barrel zone and an excessive vacuum

Decrease vacuum in the vent zone Increase the temperature of barrel zones 1–3


8.2 Troubleshooting for Poly (Vinyl Chloride) Blown Film Table 8.2 illustrates the troubleshooting solution for PVC blown films. Raw material has to be checked thoroughly in blown film to minimize the problems.

Table 8.2 Troubleshooting problems of PVC blown film with probable extrusion solutions No.

Problem

Probable cause


Blocking

Due to poor cooling process Moisture content too high

Reduce resin temperature and increase cooling time Lower humidity of the surrounding air Addition of anti-blocking agents such as silicate powder or slip agent into the air blower

Poor clarity

Mainly due to unsuitable raw material, processing temperature being too low, and a poor cooling process

Change raw materials or adjust formulation Increase the processing temperature Lower the cooling temperature further for better cooling Increase the blown ratio

Sagging

May be due to curtain Slipping of film guide Non-uniformity of blown air

Uneven thickness of film; adjust slit thickness of the die lip Use a longer guide with smaller angle Adjust the direction and rate of blown air Lower the processing temperature

143


144

Scratch mark drawing raw material

May be due to poor surface quality of the guide plate Poor rotation of the guide roll

Polish guide pin Adjustment of the guide roll

Fish eye

May be due to contamination by foreign matter Inferior quality of raw materials Poor dispersion of filler and moisture absorption

Cleaning die, screw/barrel of extruder Switching raw material Substitute with filler of better dispersibility Provide ample drying for raw materials

Spider mark

Mainly due to poor die condition

Cleaning or repairing of die Increase resin temperature

Uneven width of sheet/poor dimensional stability

Due to poor cooling process

Adjustment of cooling conditions

Sticking of melt resin around the die lip

Sticking of resin on the die orifice

Clean the die orifice

Decomposed material

Because of burn-up or hand-up in the die or extruder

Adjust formulation and replace unsuitable materials Clean the die and extruder

Pin hole

Due to processing temperature being too low

Increase setting temperature of the cylinder

Poor fusion

Because of unsuitable raw materials or formulation Poor dispersion of raw materials and low setting temperature

Change raw materials or adjust formulation Replace with raw materials of better dispersion Increase processing temperature


8.3 Troubleshooting for Poly (Vinyl Chloride) Sheets In PVC sheet production, material should appear through a coathanger die. There are a lot of possibilities to have problems due to raw materials, compounding and processing. There may be possibility of using the Table 8.3 on troubleshooting problems of PVC sheet to minimize the wastage of the material.

Table 8.3 Troubleshooting problems of PVC sheets with probable extrusion solutions No.

Problem

Probable cause


Fish eye

Presence of high-molecularweight resin

Check all resins and additives for oversized particles, dust or foreign matter Prevent partial gelation to increase shear rate

Oil stain

Reduce moisture content of compound

Replace with materials of better compatibility Use vacuum-type hoppers and a vent-type pre-mixing machine Remove oil film on the final calender roll Prevent adhesion of volatile matter on the take-up roll; clean off oil materials

(observable only under high humidity)

145


146

Poor ink adhesion and printability

Due to bleeding or oil stains

Use additives which have high compatibility with PVC Pay special attention to the migrating lubricants Reduce the moisture content of the compound Replace with materials of better compatibility Use vacuum-type hoppers and a vent-type pre-mixing machine Remove oil film on the final calender roll Prevent adhesion of volatile matter on the take-up roll; clean off oil materials

Unequal tension on the cooling roll and take-off roll

Increase external lubricant to prevent cohesion

Prevent cohesion of melt on the calender roll Adjust the take-off to give equal tension Gradual cooling instead of shock cooling Do not slack the sheet from the cooling roll to the take-off roll Due to mixing of cold resins in the sheet during processing Ensure appropriate mixing of the compound Maintain stock temperature and constant compound feeding rate Increase temperature of rolls (to soften the resin on the roll bank) Maintain a suitable amount of resin on the bank (smaller bank diameter)

Pin hole

Foreign matter, burnt resin or filler coming off from the sheet at the cooling rate and takeoff rolls

Prevent contamination by foreign matter Check the powder particle size of all solid materials Remove foreign matter on the roll (in this case, pin holes generated in the same cycle)


Blooming (white powder appears on sheet surface)

Poor compatibility among components present in the compound

Migration of additives from the compound to the contacted plastics Wrinkles in transverse direction

Cold mark

Replace with materials of higher compatibility (e.g., changing of fillers in opaque PVC can sometimes prevent blooming and bleeding)

Reduce concentration of additives such as lubricants and plasticisers; avoid unsaturated materials in the formulation Remove volatile matter in the raw materials and compounds Due to the excellent compatibility between the additives and materials of contacted objects, but replace with materials of lower compatibility with the contacted objects

Blocking (sticking of rolled and piled sheets)

Oozing of lowmelting-point materials to the sheet surface

Presence of vacuum cavities between sheets; replace with materials of higher melting point Apply anti-blocking agents or silica in formulations Apply anti-static agent and allow ample cooling Material: increase lubricant to prevent sticking Adjust formulation to prevent plate out Ensure adequate gelation during mixing; ensure adequate dispersion of additives Calendering: remove stain on the calendar roll surface Prevent plate out Improve smoothness of the roll surface by plating or grinding

Electromagnetic charges

147


Bubble

Presence of volatile matter, moisture or air in the sheet

Reduce volatile matter and moisture in raw materials and additives: optimum lubrication Pre-heat the system for the compound (e.g., vacuum hopper, vent-type extruder); supply stock constantly Avoid supplying cold stock; maintain consistent and smooth rolling back (prevent chapped surface of rolls) Prevent sheet from coming up the rolls; try to obtain smooth take off; uneven thickness of sheet or machine direction Examine formulation to reduce peeling; improve heat stability and increase the amount of lubricant Ensure good mixing in the blender kneader Calendering: clean the roll surfaces, equalise the temperature of the rolls; adjust roll clearance by crossing and bending; check for burns at the edge of the sheet and check lubrication on the calender rolls Take off-try to achieve smooth take-off

Troubleshooting results show substantial agreement on several basic aspects of performance. However, there is one fundamental issue on which they diverge: whether or not performance differs reliably across individual problems.

References 1.

148

E.M. Mount, III., in the Proceedings of the 61st Annual SPE Conference - ANTEC 2003, Nashville, TN, USA, 2003, p.251.

9

Future Requirements: Developments in Poly(Vinyl Chloride)

Extruded products such as pipes and profiles are the usual applications of poly(vinyl chloride) (PVC). The requirement of homogeneity of structure and properties along the length of the extruded products is of high importance in technical products. The properties along the length of the extruded PVC products may be determined by the measurement of mechanical properties [1–4]. In PVC, inclusion of nitrile rubber improves the oil and solvent resistance, low-temperature flexibility, abrasion resistance, flex resistance, tear resistance, and ageing characteristics [5].

9.1 Poly(Vinyl Chloride) Formulation In PVC formulation, many areas of rigid PVC have not seen dramatic changes in technology over the past 10–15 years. There are areas where the technology is developing rapidly. Rigid PVC formulations have garnered much interest in three areas, in the extrusion of: • PVC foam • PVC–wood composites The most recent formulation technology in each area indicates enhancement by additives on the processability, appearance and performance of the final product. Potential applications of each formulation lead to improvements in certain key properties [6].

149


9.2 Wood – Poly(Vinyl Chloride) Composites There are environmental reasons for replacing part of the plastic with wood. Challenges for wood–plastic composites include improving the toughness, reducing the weight, and improving long-term properties. There has been a lot of research over the past decades on different types of coupling agents to improve the adhesion between wood and plastic. Wood–plastic composites (particularly PVC–wood composites) are used to replace impregnated wood in many outdoor applications because of recent regulations regarding forest preservation.

9.3 Medical Applications PVC material is very useful for the manufacture of blood bags and other medical applications. PVC is flame-retardant and easy to degrade due to degradation of chlorine present in the polymer, which leads to colour changes. Many flexible products are very useful in medical applications. However, plasticiser leaching in the case of phthalate plasticisers proved to be very harmful. Hence, flexible PVC requires better plasticisers and no oozing.

9.4 Construction PVC is useful in the construction industry. Pipes and profiles are made out of different techniques from other construction products. Flame retardancy is the important property required in the building industry.

9.5 Biodegradation PVC is an unstable polymer. As the chlorine in PVC is freely available, degradation occurs continuously and leads to yellowness or burned material. PVC is cheaper compared with other materials, so mixing of biodegradable materials is not worthwhile.

150

Future Requirements: Developments in Poly(Vinyl Chloride)

In indoor pollution (e.g., chemical, biological, irritants), PVC–wood composites are well-suited and replace traditional materials in building and construction sectors. They require less maintenance and cleaning, which lowers the level of indoor pollution [7]. Furthermore, improvements in long-term properties such as durability during outdoor exposure and long-term load performance, are necessary. Exposure to ultraviolet radiation and moisture during outdoor use is of particular concern for wood–plastic composites [8].

References 1.

B. Terselius, J.F. Jansson and J.J. Bystedt, Journal of Macromolecular Science, Part B: Physics, 1981, 20, 3, 403.

2.

M. Gilbert, Plastics and Rubber International, 1985, 10, 3, 16.

3.

O.P. Obande and M. Gilbert, Plastics and Rubber Processing and Applications, 1988, 10, 4, 231.

4.

K. Bortel and P. Szewczyk, Polimery, 1996, 41, 11/12, 643.

5.

P. Giudici and P.W. Milner in the Proceedings of the 2nd PRI European Conference, Brussels, Belgium, 1976, p.C1.

6.

P. Kroushl in the Proceedings of the SPE Conference Vinyltec 2000, Itasca, IL, USA, p.463.

7.

F.E. Borrelli, Journal of Vinyl and Additive Technology, 2007, 13, 3, 138.

8.

N.M. Stark and L.M. Matuana, Journal of Applied Polymer Science, 2004, 94, 6, 2263.

151

A

bbreviations

ABS

Acrylonitrile-butadiene-styrene

AZO

Azodicarbonamide

DNPT

Dinitrosopentamethylenetetramine

ESO

Epoxidised sunflower oil

HCl

Hydrogen chloride

IR

Infrared

NaCl

Salt

PVC

Poly(vinyl chloride)

RPM

Rotation per minute

RPVC

Rigid poly(vinyl chloride)

TiO2

Titanium dioxide

UPVC

Unplasticised-poly(vinyl chloride)

UV

Ultraviolet

UV-VIS

Ultraviolet–visible

VC

Vinyl chloride

VCM

Vinyl chloride monomer

153


WPC

154

Wood–poly(vinyl chloride)

INDEX

Index Terms

Links

A Acrylonitrile-butadiene-styrene

34

Additives

94

Agglomerates, sub-grain

104

148

7

Aminosilane

94

Antimony trioxide

95

B Backbiting

76

Barium-cadmium stearate system

32

Black specks

134

Blending

14

81

Blocking

143

147

Blooming

147

Blow moulding

41

Blowing agents

27

Azodicarbonamide

37

Dinitrosopentamethylenetetramine

38

Sodium bicarbonate

38

Blowouts

116

37

118

C Calcium-barium-zinc system

32

Calcium carboxylates

80

This page has been reformatted by Knovel to provide easier navigation.

Index Terms Calcium soap

Links 79

Calcium-zinc Carboxylates

79

Stabilisers

24

non-toxic

31

28

Calendering

23

26

Calibration system

55

60

Sizer

60

Calibrator

60

Carotionoid polyenes

76

Charring Chlorine, labile

63

109 14

Cold mark

147

Colorants

40

Compression zone

51

62

Copolymerisation

10

14

Coupling agents

27

γ-Aminopropyltriethoxy-silane

39

Metallic copper complex

39

Organometallic

39

Poly[methylene(polyphenyl isocyanate)]

39

Crammer feed Crystallinity Curling

147

81

56 8 65


Index Terms

Links

D Degassing zone Dehydrochlorination

128 14

16

28

31

71

73

80

95

Degradation, photochemical

71

75

De-volatilisation zone

58

Dialkyltin, mercaptides of

79

Di-(isodecyl)diphthalate

35

Die design

65

28

71

Die lip

144

Die opening

49

Die system

120

Dies, surface roughness

130

Dihexylphthalate Dimples Discoloration

35 122 8

Dissipative mixing

56

Double-batching

42

Drop weight impact test Dry blend compounding Dull surface appearance

59

16

125 53 40 125

E Epoxidised sunflower oil

30

Esters

79

Ethylene dichloride

11

Extrudate

109


Index Terms

Links

Extruded polyvinyl chloride - wood flour composites Extruder

97 52

Parallel-screw

58

Single screw

57

Extrusion

54

23

26

34

40

42

49

51

55

93

104

122

136

141 Bubble

148

Hidden defects

104

High-speed

63

Irregular lumps

121

Over-lubrication in

131

Pin holes

144

Regular wavy lumps

120

Scratching

115

146

Single-screw

50

55

Twin-screw

50

55

57

24

26

36

95

104

F Feed dosing Fillers

110

Calcium carbonate

36

Glass fibre

36

Talc

36

Ultrafine

37

41


Index Terms Film-blowing process Bubble Fish eye Flame retardants

Links 67 68 144 26

Alumina trihydrate

37

Char formation

37

Smoke suppression

37

Floating pressure plug

116

Flow velocity

104

Foaming agents

38

Free-radical polymerisation

10

Frictional heat

37

95

39

95

72

76

150

129

G Gauge variation Grafting

126 14

81

H Heat conduction

55

Heat stabilisers

24

26

40

49

71

75

78

97

Lead

23

28

One-pack

41

Heavy metal stabilisers

29

Hot-cool mixture equipment

41

Hydrogen chloride absorbers

37

scavengers

14

31

79


Index Terms

Links

I Impact failure

133

Impact modifier

26

36

49

Injection moulding

23

26

41

Initiators, self-accelerated decomposition Inorganic salts

11 79

K Kneading zone

97

K-values

12

135

L Lattice basket

62

Lead salts

80

Lewis acid-base interactions

95

Liquid stabilisers

38

Long-chain fatty esters

33

Low or intermediate shear mixers

42

Lubricants

24

26

33

40

72

74

97

114

M Magnesium hydroxide Melt fracture

95 130

Melt string

55

Melt temperature

54

Mercaptans

78

103


Index Terms

Links

Metal carboxylates

31

Metallic soaps

80

Metering zone

51

Methylene chloride test

136

Migration of additives

39

Mixer, high shear

41

Mixer, jacketed low shear

41

79 62

N Neopentyl glycol diesters

35

Nip rollers

68

Nitrile rubber

34

Nucleophiles

14

79

Nucleophilic substitution

14

81

O Oil reversion test Bubble Oil stain Organometallic compounds

139 139 145 29

79

81

P Paraffin wax

33

Particle aggolomeration

42

Pellets

97

Phosphate esters

32

Pigmentation

24

95


Index Terms Pigments Titanium dioxide

Links 27

38

40

38

Pipe die

59

Pipe extrusion, single-layer

62

Pipe/profile extrusion

23

108

124

Plasticisers

24

34

40

Adipates

34

Citrates

34

Leaching of

150

Phosphates

34

Phthalates

34

Bis-(2-ethylhexyl)phthalate

35

Di-(isononyl) phthalate

35

Trimellitates

96

Plate-out reduction

37

Polyene propagation

76

Polyethylene wax

33 7

Living radical

79

Low-temperature living radical

10

Suspension

11

Polymers, synthetic

5

Polyolefin-wood fibre composites

62

49

150

34

Plastic matrix, hydrophobic

Polymerisation

104

11

72

14

95

Polyvinyl chloride Additives Blown films spider mark

25 143 144


Index Terms

Links

Core-shell structure of

14

Extrusion

58

Foam

24

Morphology

6

Pipe extrusion

60

Plasticised compounds

37

Production

11

Regrinds

15

Resin

11

Rigid

36

23 72

135

145

Stabilisers

78

Tacticity of

71

Unmodified and unplasticised

16

Weathering

76

Wood composites

107

149

Formulation

Sheet production

103

149

Wood flour composites

96

Wood powder

38

Powder blend compounds

40

Profile extrusion

63

Short calibrator

63

Quinone tin polymers

32

73

151

Q 79


Index Terms

Links

R Regrind

68

Resins, low K-value

40

Retardants

81

S Sagging Scanning electron microscope

143 7

Screen packs

65

Screw cooling

62

Screw design

52

Screw speed

53

Shear heating

55

Shear stress

54

Sheet extrusion

23

Warping of

65

Silica, precipitated

37

Smoke suppressants

27

Solar irradiation

76

Solid-particle mechanism

68

Spider dies

62

Spiral mandrel

62

Stabilisation, ultraviolet

24

Stabilisers

24

β-diketones

29

Dihydropyridine

29

Epoxides

29

Organic

75

65

96

40

74


Index Terms

Links

β-diketones (Cont.) Organic thermal

81

Organotin

31

Polyols

29

Secondary heat

30

Secondary organic

29

Solid barium/cadmium

81

115

Tin

24

Ultraviolet

76

Stabiliser systems, one-pack

32

Stainless-steel calibrators

63

Stearic acid

33

Stearic acid-based lubricants

23

Stress discontinuity

104

String-up melt

109

Surging

42

Swelling

119

30

T Thermal degradation Thermal instability

8

28

30

71

74

77

95

103

9

Thermal stabilisation

75

81

Thermal stabilisers

27

78

9

12

14

16

28

54

68

80

Thermal stability Thermo-oxidative degradation

81

Thermoplastics

68


Index Terms Toxicity

Links 14

24

31

79

56

118

U Ultraviolet irradiation Ultraviolet radiation Ultraviolet-visible spectroscopy

72 151 74

78

V Vacuum calibrators

60

Vacuum die

60

Venting

58

zone

56

Vinylchloride monomer

11

Viscosity

40

Inherent

135

Melt

114

Visible defects

54

104

W Water spray system

63

Wood filler

93

Wood-filled wood composite

94

Wood flour

39

Wood, hydrophilic

96

Wood - plastic composites

93

Wood - polyvinyl chloride composites

97

150

150

composites

94

products

93

96

98


Index Terms Wood - polymer composites

Links 93

Wood - polyvinyl chloride thermoplastic composites

96

Zinc carboxylates

80

Z Zipper dehydrochlorination Zipper-like splitting

9

74

77


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