Solvent spun rayon, modified cellulose fibers and derivatives

Solvent Spun Rayon, Modified Cellulose Fibers and Derivatives In Solvent Spun Rayon, Modified Cellulose Fibers and Deri...

Author: Albin F. Turbak

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Solvent Spun Rayon, Modified Cellulose Fibers and Derivatives

In Solvent Spun Rayon, Modified Cellulose Fibers and Derivatives; Turbak, A.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.


Solvent Spun Rayon, Modified Cellulose Fibers and Derivatives Albin F. Turbak,

EDITOR

ITT Rayonier, Inc.

A symposium sponsored by the Cellulose, Paper, and Textile Division at the 173rd Meeting of the American Chemical Society, New Orleans, La., March 21-23,

1977

58

ACS SYMPOSIUM SERIES

AMERICAN

CHEMICAL

SOCIETY

WASHINGTON, D. C. 1977


Library of CongressCIPData Solvent spun rayon, modified cellulose fibers and derivatives (ACS symposium series; 58) Includes bibliographical references and index. 1. Rayon—Congresses. I. Turbak, Albin F., 1929. II. American Chemical Society. Cellulose, Paper, and Textile Division. III. Series: American Chemical Society. ACS symposium series; 58. TS1688.A1S64 ISBN 0-8412-0388-1

677'.46 ACSMC8

77-12220 58 1-269 (1977)

Copyright © 1977 American Chemical Society All Rights Reserved. No part of this book may be reproduced or transmitted in any form or by any means—graphic, electronic, including photocopying, recording, taping, or information storage and retrieval systems—without written permission from the American Chemical Society. PRINTED IN THE UNITED STATES OF AMERICA


ACS Symposium Series Robert F. Gould, Editor

Advisory Board Donald G. Crosby Jeremiah P. Freeman E. Desmond Goddard Robert A. Hofstader John L. Margrave Nina I. McClelland John B. Pfeiffer Joseph V. Rodricks Alan C. Sartorelli Raymond B. Seymour Roy L. Whistler Aaron Wold


FOREWORD The ACS S Y M P O S I U M SERIES was founded in 1974

to provide

a medium for publishing symposia quickly in book form. The format of the SERIES parallels that of the continuing A D V A N C E S I N C H E M I S T R Y SERIES except that in order to save time the papers are not typeset but are reproduced as they are submitted by the authors in camera-ready form. As a further means of saving time, the papers are not edited or reviewed except by the symposium chairman, who becomes editor of the book. Papers published in the ACS S Y M P O S I U M SERIES are original contributions not published elsewhere in whole or major part and include reports of research as well as reviews since symposia may embrace both types of presentation.


PREFACE "Research and development on new products or improved processes for converting natural based materials such as cellulose are now more important than ever, and shrewd managers are scheduling increasing efforts in the cellulose area. It is indeed ironic that the "miracle" synthetic fibers are operating at record losses while rayon and cotton are enjoying rising sales and improved market status. While this may be upsetting to those 'prophets of doom" who have repeatedly forecast the demise of rayon and cellulosic textiles, it comes as no surprise to wiser, more experienced textile people who cellulosic-based materials have to offer. This symposium, held at the New Orleans American Chemical Society Meeting by the Cellulose, Paper and Textile Division, attempts to highlight some of the current research underway in the following areas: • Solvent Spun Rayon. This is thefirsttime a symposium session was ever devoted solely to this topic, and it deals with diverse efforts to develop a totally recoverable and recyclable solvent spinning system to overcome viscose process deficiencies. • Cellulose Ethers and Esters. This section coversfirst-releaseinformation on Cytrel synthetic tobacco as well as added technology on cellulose acetate and amic acid esters. • Modified Cellulosics. This section includes details on the new Viloft hollow rayonfibers,lignin-modified rayon, microscopic techniques for nonwovens, drying of superabsorbent fibers, ultrasonic fiber treatment, and improved celluloseflameretardants. Undoubtedly, a great deal of additional effort is underway in these areas which will be reported at future meetings. It is hoped that this volume will complement and enhance such research. I would like to thank the various authors for their kind cooperation throughout this effort and also to thank their respective companies for encouraging and supporting participation by their personnel in this undertaking. ITT Rayonier, Inc. Whippany,N.J.07981 July 1977

ALBIN F. TURBAK

ix


1 Rayon—A Fiber with a Future H. L. HERGERT and G. C. DAUL ITT Rayonier, Inc., Eastern Research Div., Whippany, N.J. 07981

The title of this paper could perhaps more a p p r o p r i a t e l y be called "Rayons - the F i b e r S t r i k e s Back! The ter fibers w i t h a wide range o f p r o p e r t i e s . Depending on the manufacturing process used, rayon can be similar to silk, wool, c o t t o n o r even paper. I t can be weak and extremely water-absorbent or as strong as some of the strongest f i b e r s made, including s t e e l . I t can be produced as continuous f i l a m e n t o r as s t a p l e , cut in lengths o f a few m i l l i m e t e r s t o s e v e r a l centimeters, s t r a i g h t o r crimped, lustrous or dull, p r e c o l o r e d , resistant to-water, -flame, o r c a u s t i c soda, c r o s s l i n k e d o r chemically modified. Of most importance, rayon, like c o t t o n , is h y d r o p h i l i c , bio-degradable and d e r i v e d from the most abundant n a t u r a l polymer in the world cellulose. P e r u s a l o f the pages o f the major commercial chemical j o u r n a l s , such as the Chemical and Engineering News, Chemical Week and o t h e r s , during the past s e v e r a l years might lead t o the c o n c l u s i o n that the p u r e l y s y n t h e t i c man-made fibers are the only textile f i b e r s w i t h a significant f u t u r e . Several l a r g e oil companies w i t h a major stake in supplying petro-chemical intermediates, have tried t o f o s t e r that image by suggesting that s u p p l i e r s of wood p u l p , the b a s i c raw m a t e r i a l f o r v i s c o s e rayon, have insurmountable environmental problems and textile producers in the western world should focus t h e i r f u t u r e on p o l y e s t e r . This h a r d l y represents the f a c t s . Rayon is c u r r e n t l y a viable product and has an attractive f u t u r e , especially if sufficient research and development is committed t o r e d u c t i o n o f chemical and energy usage in the v i s c o s e process o r a new r e g e n e r a t i o n process can be p e r f e c t e d along the l i n e s t o be discussed in the subsequent papers. The production o f man-made fibers from c e l l u l o s e can be traced back to Audemar's d i s c o v e r y of nitrocellulose i n 1855, commercialized as f i l a m e n t s by deChardonnet(1) in 1 8 8 9 · Ralph Nader would have had a ball with this product! Because o f its f l a m m a b i l i t y , it had a p r e d i c t a b l e and unpleasant ending i n 1 9 4 0 , 3


4

SOLVENT SPUN RAYON, MODIFIED CELLULOSE FIBERS

w i t h the d e s t r u c t i o n by f i r e of the l a s t producing f a c t o r y i n Brazil. The development of cuprammonium rayon by D e s p a i s s i s ( 2 ) occurred i n time to step i n t o the gap and f l o u r i s h e d as a r t i f i c i a l s i l k . I t s importance as a t e x t i l e f i b e r has g r a d u a l l y diminished u n t i l today i t represents a v e r y s m a l l amount of the t e x t i l e f i b e r s produced. The v i s c o s e p r o c e s s , d i s c o v e r e d by Cross, Bevan, and Beadle i n 1892,(2) was commercialized i n the e a r l y 1900's - f i r s t as continuous f i l a m e n t f o r t e x t i l e s , f o r t i r e yarn and i n d u s t r i a l uses and then i n the 1930 s f o r s t a p l e f i b e r . Rayon p r o d u c t i o n i n the United States peaked i n the 1950's and again i n the 196o's, but i n many cases, p r o f i t s from rayon were used to d i v e r s i f y i n t o s y n t h e t i c f i b e r s . As a r e s u l t , equipment was r e p a i r e d but seldom upgraded and R and D o growth markets have opene nonwovens. Older p l a n t s have been shut down and the s u r v i v i n g North American rayon i n d u s t r y has geared up to meet the t e x t i l e needs of tomorrow. In other p a r t s of the w o r l d , rayon p r o d u c t i o n has had almost steady growth. In R u s s i a f o r example, p r o d u c t i o n of c e l l u l o s i c f i b e r s increased 30$ d u r i n g I 9 7 I - I 9 7 5 , w i t h 6θ# of t h i s growth a t t r i b u t e d to new p l a n t s . Even l a r g e r i n c r e a s e s are p r o j e c t e d f o r the next f i v e - y e a r p l a n . New, more e f f i c i e n t rayon p l a n t s have been b u i l t i n Yugoslavia and Taiwan and other developing countries are s e r i o u s l y c o n s i d e r i n g the p r o d u c t i o n of rayon. Since the I93O's, many v e r s i o n s of rayon have been developed through changes i n the b a s i c v i s c o s e process u s i n g chemical m o d i f i e r s , such as the p o l y - g l y c o l s , amines, and formaldehyde. Other v e r s i o n s , which may or may not r e q u i r e m o d i f i e r s are the p o l y n o s i c s , which because of h i g h D.P. and unique s t r u c t u r e , most c l o s e l y resemble c o t t o n i n end-use p r o p e r t i e s . Some of the p r o p e r t i e s of the v a r i o u s rayons and other major t e x t i l e f i b e r s are shown i n Table I . I t i s seen t h a t many of the p r o p e r t i e s of the rayons o v e r l a p those of the other major t e x t i l e f i b e r s . In F i g u r e 1 t h i s i s f u r t h e r i l l u s t r a t e d by the s t r e s s s t r a i n p r o p e r t i e s of these f i b e r s . At t h i s p o i n t i n our p r e s e n t a t i o n , we had planned a t a b l e showing what might be considered the p r o p e r t i e s of an " i d e a l " rayon f i b e r . A f t e r t h i n k i n g t h i s over, the question kept popping up - i d e a l f o r what? A l i s t of d e s i r a b l e p r o p e r t i e s f o r a t e x t i l e f i b e r might i n c l u d e : 1. Adequate t e n a c i t y (both c o n d i t i o n e d and wet). 2. S u f f i c i e n t l y h i g h wet modulus and r e s i l i e n c e to a f f o r d dimensional s t a b i l i t y i n f a b r i c s . 3. Toughness f o r r e s i s t a n c e to a b r a s i o n . k. Adequate crimp l e v e l to permit ease of p r o c e s s i n g and cover and l o f t i n f a b r i c s . 5 . H y d r o p h i l i c i t y f o r comfort. 6. Resistance to s u n l i g h t , common chemicals, and laundering. f



0.1-0.5 0.9-t.5 3-5 t-10

0.3-0.5 2.7-t.5 o.t

-

0.5-0.7 t.5-6.3 10-it 60-80

0.5-1.0 t.5-9.0 7-9 t5-55

10-it

60-70

Moisture Regain, $

Water R e t e n t i o n , $

30-90 t2-100

3.5-7.2 32-65 2.5-6.1 23-55

0.5-2.0 U.5-18

12-55 12-55

2.t-7-0 22-63 2.t-7-0 22-63

Nylon-6

10-12 12-15

3-0-t.5 27-tl 2.0-3.5 18-32

Polyester

7-9 8-10

1.8-3.2 16-29 1.6-3.2 it-29

HWM Rayon

8-10 10-it

3-5-5.0 32-t5 2.5-t.O 23-36

Cotton

Elongation, # Cond. Wet Wet T e n a c i t y a t 5$ E x t e n s i o n , g/d km

Tenacity Cond. g/d km Wet, g/d km

Polynosic Rayon

PHYSICAL PROPERTIES OF MAJOR TEXTILE FIBERS

TABLE I

90-110

10-it

0.1-0.3 0.9-2.7

15-30 20-ho

0.7-3.2 6-29 0.7-1.8 6-16

Regular Rayon

S

S

ρ


6 8 HT R A Y O N /

6 POLYNOSIC

'NYLON β "POLYESTER

/ HWM RAYON

R

/// f/ /

2

\\v

REGULAR RAYON

wr 2 0

3 0

4

0

Figure 1.

ELONGATION (%)

Fiber stress-strain curves (conditioned)

TABLE I I WORLD FIBER CONSUMPTION* 1972-U

Population ( m i l l

38I7

1985

Change U)

VT59

2k.6

Per C a p i t a l F i b e r Consumption (Kg) F i b e r Consumption (000 t o n s )

6.9 26,978

8Λ 1+0,230

21.7 U9.1

Man-made Rayon and a c e t a t e

3>56^

Non-cellulosic

7,676

k,l90

17.6

18,015

3^.7

15,695

21.0

1,632

5.1

698

-1.8

Natural Cotton

12,970

Wool

1,985

Other

711

* American Dyestuff R e p o r t e r , June, 1976


1.

HERGERT AND DAUL

7. 8. 9· 10.

7

RatfOU

Dyeability. Flame retardancy. U n i f o r m i t y and c l e a n l i n e s s of product, Price s t a b i l i t y .

Obviously, there can be no one f i b e r w i t h a l l these prope r t i e s and f o r the m a j o r i t y of end-uses, not a l l are needed. Therein l i e s the s t r e n g t h of the l a r g e f a m i l y of rayon f i b e r s which can be p r a c t i c a l l y tailor-made or engineered to s u i t spec i f i c end-uses. The t e x t i l e i n d u s t r y of today i s , of n e c e s s i t y a c c e p t i n g t h i s f a c t and i s u s i n g combinations of f i b e r s i n blends chosen to produce the f a b r i c s which are most a e s t h e t i c a l l y a p p e a l i n g , u s e f u l , s e r v i c e a b l e and p r o f i t a b l e . For a p p a r e l , blends of c e l l u l o s i c s and s y n t h e t i c s to provide both comfort and u t i l i t y ar of 50$ or more c e l l u l o s i n e c e s s i t y to prevent d i s c o m f o r t , s o i l e d c l o t h e s , and the embarrassment of wet spots on p l a s t i c seat covers. B u i l d i n g water absorbency i n t o p o l y e s t e r has been a longtime goal of t h i s f i b e r i n d u s t r y but has u s u a l l y been at the s a c r i f i c e of some of the important, d e s i r a b l e a t t r i b u t e s of t h i s f i b e r , and r e s u l t s i n i n c r e a s e d c o s t of p r o d u c t i o n . We b e l i e v e that the most i n t e l l i g e n t and economic approach to the t e x t i l e s of the f u t u r e i s to blend the s y n t h e t i c s w i t h c e l l u l o s e , to get the a p p r o p r i a t e balance of s t r e n g t h , easy c a r e , and moisture absorption. In the June, 1976, American Dyestuff Reporter, p r e d i c t i o n s of world f i b e r consumption r e l a t i v e to world p o p u l a t i o n growth through I985 were g i v e n . (Table I I ) . These f i g u r e s show an i n crease of 17· 6$ i n the p r o d u c t i o n of rayon and a c e t a t e . Rayon, of course, w i l l represent the l a r g e r p r o p o r t i o n of t h i s growth. We b e l i e v e these f i g u r e s are c o n s e r v a t i v e f o r man-made c e l l u l o s i c s r e l a t i v e to s y n t h e t i c s and t h a t the d i v i s i o n s could be more f a v o r a b l e to rayon and acetate provided c o s t - e f f e c t i v e improvements are made to the v i s c o s e process or an a l t e r n a t e lowc a p i t a l approach to forming regenerated c e l l u l o s i c f i b e r s i s found. The growth i n world p o p u l a t i o n w i l l o b v i o u s l y r e s u l t i n a demand f o r food production at the expense of c o t t o n , e s p e c i a l l y i n c o u n t r i e s such as I n d i a and P a k i s t a n , where there i s a burgeoning p o p u l a t i o n w i t h increased t e x t i l e and food needs. Rayon - I t s Problems Considering rayon as a f i b e r w i t h a f u t u r e , i t i s necessary to look at the current problems a s s o c i a t e d w i t h i t s manufacture. Simply put, i n t o d a y s economy and w i t h emphasis on energy cons e r v a t i o n and environmental p r o t e c t i o n , the main problems r e l a t e d to the production of f i b e r s by the v i s c o s e process a r e : 1. Undesirable a i r and water emissions, BOD, H S, z i n c . 1

2



8 2. 3. k. 5.

I n t e n s i v e c a p i t a l requirement. Large energy requirements. R e l a t i v e l y l a r g e l a b o r requirements i n most e x i s t i n g plants. Increasing cost of raw m a t e r i a l s .

Other problems r e l a t e d to the e f f e c t s of meeting environmental p r o t e c t i o n r e g u l a t i o n s can have adverse e f f e c t s on q u a l i t y and a v a i l a b i l i t y of raw m a t e r i a l s . Rayon - I t s

Opportunities

The above problems seem insurmountable, but problems are u s u a l l y followed by o p p o r t u n i t i e s , and such i s the case here. Major advances are bein cose rayon p l a n t s to reduc of z i n c by ion-exchange, c r y s t a l l i z a t i o n , or other techniques; use of more p u r i f i e d c e l l u l o s e s ; r e d u c t i o n of gaseous emissions by a b s o r p t i o n or scrubbing; more e f f i c i e n t f i b e r washing and d r y i n g techniques, and the l i k e . Large s c a l e p l a n t s can be designed t o produce f i b e r s f o r more s p e c i f i c , major end-uses and w i t h fewer product l i n e s which w i l l be more e f f i c i e n t i n use of l a b o r and capital. The major advantages possessed by regenerated c e l l u l o s e f i b e r production of today are: 1. A v a i l a b i l i t y of major raw m a t e r i a l s . a) C e l l u l o s e - n a t u r e s renewable polymer. b) CS - recoverable to the extent of 50$· c) S u l f u r i c a c i d and c a u s t i c soda normally i n l a r g e supply. 2. Non-dependence on o i l . 3. P r i c e s t a b i l i t y r e l a t i v e to c o t t o n . 1

2

These advantages have been recognized i n other c o u n t r i e s w i t h the USSR as a prime example. In the May i s s u e of Khimischeskie Volokna, Shimko(t) describes the t e c h n i c a l progress i n the c e l l u l o s i c f i b e r i n d u s t r y and p r o j e c t i o n s f o r the USSR's 10th f i v e year p l a n . He s t a t e s : "The production of c e l l u l o s i c f i b e r s i s planned to increase f u r t h e r i n the 1 0 t h f i v e - y e a r p l a n , the main reason being: the u s e f u l p r o p e r t i e s , e s p e c i a l l y the p h y s i o l o g i c a l ones, of those f i b e r s and the mass-market a r t i c l e s produced from them. An increase i n the output of c e l l u l o s i c f i b e r s w i l l not o n l y help to overcome the shortage of hygroscopic f i b e r s but w i l l a l s o r e s u l t i n a s u b s t a n t i a l savings of m a t e r i a l and labor r e sources. The f a c t that the USSR possesses a huge self-renewing source of the s t a r t i n g m a t e r i a l ( i . e . , wood) i s a f u r t h e r f a c t o r f a v o r i n g an increase i n the production of c e l l u l o s i c f i b e r s . " He f u r t h e r s t a t e s , "the p r i n c i p a l d i r e c t i o n s of t e c h n i c a l progress i n the production of v i s c o s e rayon s t a p l e f i b e r s are: the production of high-modulus and p o l y n o s i c f i b e r s and higher output


1.

HERGERT AND DAUL

RdtJOn

9

of b e t t e r q u a l i t y v i s c o s e rayon s t a p l e - high-modulus and polyn o s i c f i b e r s - l i k e c o t t o n , possess good s t r e n g t h and a h i g h modulus when wet. Their wet s t r e n g t h i s b e t t e r than t h a t of ( r e g u l a r ) rayon s t a p l e . Although the c o s t - e f f e c t i v e n e s s of the production of high-modulus f i b e r s i s not very f a v o r a b l e , t h e i r use i n the n a t i o n a l economy, i n place of c o t t o n , i s advantageous." In R u s s i a , as i n other c o u n t r i e s , aside from economics and raw m a t e r i a l a v a i l a b i l i t y , there i s a growing awareness that the comfort ( p h y s i o l o g i c a l ) f a c t o r s inherent i n c e l l u l o s i c f i b e r s are e s s e n t i a l i n blends w i t h the s y n t h e t i c s t o overcome t h i s major d e f i c i e n c y i n these f i b e r s . Even assuming o p p o r t u n i t i e s f o r f u r t h e r expansion of v i s c o s e rayon production i n the USSR and elsewhere, and f o r improving the economics of the v i s c o s e process, we, however, b e l i e v e that s i g n i f i c a n t f u t u r e expansio f i b e r s , w i l l result wit designed to overcome the d e f i c i e n c i e s mentioned b e f o r e . One approach to a new process i n v o l v e s the use of a recoverable and r e c y c l a b l e s o l v e n t (or combination of s o l v e n t s ) which w i l l d i s s o l v e c e l l u l o s e by a simple mixing step followed by ext r u s i o n of the s o l u t i o n to form a f i b e r . A closed-loop system, which would emit p r a c t i c a l l y nothing t o the atmosphere or water, would e l i m i n a t e p o l l u t i o n problems. Several leads i n t h i s d i r e c t i o n have been developed at our l a b o r a t o r i e s i n Whippany, New J e r s e y , and w i l l be described i n d e t a i l i n subsequent papers on t h i s program. However, much more needs to be done to reach the ultimate goals. I d e a l l y , such a process should i n v o l v e use of simple c e l l u l o s e s o l u t i o n s of higher concentrations than those p r e s e n t l y used ( 6 - 9 $ ) , use of low b o i l i n g s o l v e n t s to minimize energy r e q u i r e d for recovery, spinning at h i g h speeds s i m i l a r t o those used i n the acetate and s y n t h e t i c f i b e r i n d u s t r i e s , and p u r i f i c a t i o n without the use of excessive amounts of water f o r washing or l a r g e amounts of heat f o r d r y i n g . Such a p l a n t would, t h e r e f o r e , have most of those a t t r i b u t e s r e q u i r e d to overcome the present-day problems a s s o c i a t e d w i t h the rayon i n d u s t r y . This concept should present a r e a l challenge to c e l l u l o s e research f o r the coming years and the rewards would be enormous. Some of the r e q u i r e ments f o r an i d e a l c e l l u l o s e (rayon) f i b e r p r o d u c t i o n process are shown i n Table I I I . Other approaches a r e , of course, p o s s i b l e . One such i s that e n v i s i o n e d by the eminent polymer s c i e n t i s t , Dr. Herman F. Mark, who r e c e n t l y s a i d ( j j ) , "For the f u t u r e , continued research e f f o r t s w i l l be g r e a t l y i n f l u e n c e d by the f a c t that c e l l u l o s e i s the organic substance produced i n g r e a t e s t q u a n t i t y by nature - a r e newable resource that c o n t r a s t s sharply w i t h c o a l , o i l and gas, the reserves of which are being s e r i o u s l y diminished year-by-year. I t would indeed be a wonderful success s t o r y f o r human endeavor, i f , i n the f u t u r e , we can combine our present knowledge of the s t r u c t u r e and r e a c t i v i t y of c e l l u l o s e w i t h a b e t t e r understanding



TABLE I I I REQUIREMENTS FOR IDEAL RAYON FIBER PRODUCTION PROCESS

A.

Renewable/recoverable raw m a t e r i a l s .

B.

Low C a p i t a l and l a b o r c o s t s , low energy r e q u i r e ment.

C.

Minimal e f f e c t on environment.

D.

Simple solution-makin

E.

Dry and/or s o l v e n t s p i n n i n g .

F.

High c o n v e r s i o n r a t e o f spin-dope t o f i b e r high cellulose/solvent r a t i o ) .

G.

A b i l i t y t o produce a uniform product that w i l l r e q u i r e minimal h a n d l i n g from f i b e r t o end product.

(includes


1. HERGERT AND DAUL Rayon

11

of its biosynthesis, in order to produce the cellulose molecule directly from water and CO , with the aid of sunlight, at a rate 5 to 10 times greater than that which occurs in nature." Controlled growth of cellulose in hydroponic factories to produce fibers directly, could be the fulfillment of such a wish or alternately, a means to further extend the capabilities of the world's forest resources to furnish cellulose to produce rayon for the multitude of end-uses required by mankind. Whether it will be made by the viscose process, or spun from solvents, or by some yet to-be-discovered process, or by all three, remains to be seen. To paraphrase a popular automobile commercial — 2

"There Will Be A Rayon In Your Future" Abstract Modern textile blends continue to require the aesthetics and moisture-absorbing properties provided by cellulose in the native state (cotton) or in regenerated form (rayon). Escalating prices and problematical availability of some intermediates for purely synthetic textiles, coupled with gradual conversion of cotton -growing land to food production, suggest a careful re-examination of the future of rayon. Wood cellulose, caustic soda and carbon disulfide, the major raw materials for rayon production by the existing viscose process, are not dependent upon o i l and will continue to be available in ample supply. On the other hand, the viscose process is energy intensive and has emission problems. Significant expansion of the rayon industry w i l l , therefore, require development of a totally new process. The needs of such a process in terms of raw materials, type of spinning, investment costs and fiber properties will be detailed in this paper. Literature Cited 1. Chardonnet, H., French Pat. 165,349 (May 12, 1884). 2. Despaissis, L. H., French Pat. (1890). 3. Cross, et al, British Pat. 8700 (April 8, 1893). 4. I. G. Shimko Khimicheski Volokna, No. 3, pp 8-12, May-June 1976. 5. Mark, H. F., Celluloses - Past Present and Future, 50th Anniversary Lecture, Nov. 26, 1975, Dorval, Que. Can.


2 A Critical Review of Cellulose Solvent Systems A.F.TURBAK, R. B. HAMMER, R. E. DAVIES, andN.A.PORTNOY ITT Rayonier, Inc., Eastern Research Div., Whippany,N.J.07981

C e l l u l o s e is the most abundant renewable, organic raw material a v a i l a b l e in th ability, i t has still no areas of application. One o f the major reasons f o r t h i s is t h a t many end-use a p p l i c a t i o n s r e q u i r e t h a t c e l l u l o s e be in a different form from that found in nature. I n most of these applications, it is necessary first to dissolve cellulose in some manner and then t o re-form it from such s o l u t i o n s i n t o the d e s i r e d products. It is this very important d i s s o l v i n g step which has proved to be either cumbersome o r expensive compared t o alternate m a t e r i a l s which compete for market p o s i t i o n s . In many cases only c e l l u l o s e has the d e s i r a b l e p r o p e r t i e s r e q u i r e d f o r end product use and, in these i n s t a n c e s , the methods r e q u i r e d t o achieve cellulose s o l u t i o n present p o t e n t i a l hazards and pollution control problems. Thus, improved techniques f o r d i s s o l v i n g cellul o s e are u r g e n t l y needed if cellulose is to continue t o occupy a c o m p e t i t i v e market position. This is particularly t r u e o f the v i s c o s e i n d u s t r y where pollution control continues to p l a c e ever i n c r e a s i n g restraints on the process. Scientists have long recognized the need f o r more efficient cellulose s o l v e n t systems and hundreds of p u b l i c a t i o n s have been i s s u e d covering a wide range of approaches. S e v e r a l e x c e l l e n t review articles on s w e l l i n g and dissolving cellulose by Warwicker (1,2) Jayme ( 3 ) , Phillip ( 4 , 5 ) , P o l y o l a (6) and Brandrup (7) have been p u b l i s h e d and we shall not attempt simply t o resubmit t h e i r data. Rather, t h i s paper shall attempt t o consider the v a r i o u s processes from the commercial as well as the scientific viewpoint t o emphasize potential areas f o r c o n t r i b u t i o n which still e x i s t , particularly f o r systems capable of producing cellulosic fibers through the use of organic s o l v e n t s . Fundamentally, a l l o f the known methods f o r d i s s o l v i n g c e l l u l o s e can be summarized under f o u r main c a t e g o r i e s : A. C e l l u l o s e As A Base B. C e l l u l o s e As An A c i d C. C e l l u l o s e Complexes D. C e l l u l o s e D e r i v a t i v e s 12


2.

TURBAK E T A L .

Cellulose Solvent Systems

13

While each of the above areas has r e c e i v e d e x t e n s i v e study and some have been commercialized, s e v e r a l of the approaches are r e a l l y not completely understood. S t i l l others i n v o l v e mixtures of many i n g r e d i e n t s and could never be v a l u a b l e i n d u s t r i a l l y . In t r y i n g to e x p l a i n why c e r t a i n m a t e r i a l s do i n f a c t d i s s o l v e c e l l u l o s e , s e v e r a l authors have s i m p l i s t i c a l l y i n d i c a t e d that what i s r e q u i r e d i s that the s o l u b i l i t y parameter of the s o l v e n t must be the same as t h a t of c e l l u l o s e . While such s t a t e ments are d i r e c t i o n a l l y c o r r e c t , they are incomplete and, perhaps, even a l i t t l e m i s l e a d i n g , s i n c e many s o l v e n t s having the proper s o l u b i l i t y parameter values w i l l not d i s s o l v e c e l l u l o s e . For example, DMF and DMSO both have s o l u b i l i t y parameters i n the range c a l c u l a t e d f o r c e l l u l o s e but n e i t h e r o f these d i s s o l v e c e l l u l o s e under any known c o n d i t i o n s The s o l u b i l i t y paramete (CED) values r e l a t e d i r e c t l which i s e a s i l y o b t a i n a b l e f o r many l i q u i d s , and w i l l apply d i r e c t l y t o the m i s c i b i H t y of l i q u i d s o r amorphous polymers where (&) values w i l l r e l a t e to simple heats of m i x i n g . When d e a l i n g w i t h polymers i n g e n e r a l , other f a c t o r s may be e q u a l l y as important, o r even more important than s i n g l e s o l u b i l i t y parameter v a l u e s . For example, w i t h c r y s t a l l i n e polymers, the heat o f f u s i o n or m e l t i n g energy, must a l s o be considered as an e n t i r e l y separate f a c t o r . Furthermore, superimposed on these f a c t o r s i s the hydrogen bonding c a p a b i l i t y of the polymer i n q u e s t i o n which may not be c o n s e q u e n t i a l f o r polymers such as c r y s t a l l i n e polypropylene, but which i s extremely important w i t h n a t u r a l polymers such as p r o t e i n s and c e l l u l o s e i n p a r t i c u l a r . These f a c t o r s , as w e l l as second order e f f e c t s were recognized many years ago by Spur l i n , B u r r e l l , and Barton and s e v e r a l exc e l l e n t reviews are a v a i l a b l e f o r f u r t h e r reference (8,9,10)· A combination of such f a c t o r s must be considered i n t r y i n g t o f i n d a s o l v e n t f o r c e l l u l o s e and help to g i v e guidance as t o c o n d i t i o n s as w e l l as compounds which must be employed i f usable c e l l u l o s e s o l u t i o n s are to be o b t a i n e d . Even i f a m a t e r i a l i s a s a t i s f a c t o r y s o l v e n t f o r c e l l u l o s e , i t i s necessary to emphasize two other important f a c t o r s which must be s e r i o u s l y evaluated f o r any p o t e n t i a l l y commercial c e l l u l o s e s o l v e n t system, these are "recovery" and " r e c y c l e " . The recovery and r e c y c l e f a c t o r s , perhaps more than any o t h e r s , are the most important ones which, i n the f i n a l a n a l y s i s , decide whether or not any p a r t i c u l a r approach w i l l be economically feasible. One f i n a l f a c t o r must a l s o be kept i n mind r e l a t i v e t o e v a l u a t i n g a l l o f the d a t a t h a t appear i n the l i t e r a t u r e r e garding c e l l u l o s e s o l v e n t s . S p e c i f i c a l l y i t must be emphasized t h a t v a s t d i f f e r e n c e s e x i s t between being able to coagulate o r



14

p r e c i p i t a t e a s o l i d mass, as compared to t r u l y spinning f i b e r s w i t h reasonable p h y s i c a l p r o p e r t i e s . Keeping these f a c t o r s i n mind, l e t us examine the f o u r c a t e g o r i e s l i s t e d above which encompass e s s e n t i a l l y a l l of the c e l l u l o s e s o l v e n t systems reported i n the l i t e r a t u r e . A.

C e l l u l o s e As A Base

A l l a l c o h o l s , whether polymeric or not, can be f o r c e d t o act as acids or bases r e l a t i v e to other reagents, depending upon the s t r e n g t h of the reagent employed. Thus, c e l l u l o s e w i l l act as a base and become protonated by p r o t o n i c a c i d s or w i l l act as a "Lewis" base and supply e l e c t r o n s from i t s oxygens t o e l e c t r o n r e c e p t i v e centers on "Lewis" a c i d s 1. P r o t o n i c Acid a b i l i t y of 78% phosphoric a c i d , 68% n i t r i c a c i d , 42% h y d r o c h l o r i c a c i d or 70% s u l f u r i c a c i d to d i s s o l v e c e l l u l o s e r a p i d l y at room temperature i s w e l l known. While the l i t e r a t u r e i s f u l l of r e p o r t s i n which the r e s u l t i n g s o l u t i o n s are r e f e r r e d to as hyd r a t e s " , they can a l s o be regarded as protonated hydroxyIs where the s p e c i f i c reagent concentrations employed were the ones needed to provide s u f f i c i e n t a c i d s t r e n g t h to protonate the c e l l u l o s e so that the r e s u l t i n g p o s i t i v e l y changed ROHj c e l l u l o s e moiety i s able to d i s s o l v e i n the excess reagent. I n these cases, recovery and r e c y c l e of the concentrated a c i d s i s the l i m i t i n g f a c t o r , economically. For example, e x c e l l e n t c e l l u l o s e s o l u t i o n s can be r a p i d l y prepared a t room temperature using phosphoric a c i d . However, no one has yet suggested a f e a s i b l e approach to c a s t i n g the c e l l u l o s e and recovering the phosphoric a c i d without n e u t r a l i z a t i o n . In our l a b o r a t o r y , we have t r i e d to p r e c i p i t a t e such phosphoric a c i d s o l u t i o n s i n t o g l a c i a l a c e t i c a c i d i n the a n t i c i p a t i o n that the a c e t i c a c i d could be v o l a t i l i z e d , recovered and r e c y c l e d , along w i t h the r e l e a s e d pure phosphoric a c i d . The i n i t i a l r e s u l t s were not too s u c c e s s f u l s i n c e the p r e c i p i t a t i o n was too slow to be u s e f u l under the p a r t i c u l a r c o n d i t i o n s emp l o y e d . However, the concept of using a weaker, v o l a t i l e a c i d i c m a t e r i a l to coagulate strong a c i d c e l l u l o s e s o l u t i o n s does r e present a n o v e l approach to developing a t o t a l r e c y c l a b l e c e l l u l o s e s o l v e n t system. lf

2. Lewis Acids ( z i n c c h l o r i d e , thiocyanates. iodides» b r o ~ mides). The a b i l i t y of c e r t a i n s a l t s o l u t i o n s to s w e l l and d i s s o l v e c e l l u l o s e i s a l s o reported (11). At the high concentrat i o n s normally necessary to achieve s o l u t i o n , these s a l t s not only provide necessary a c i d f u n c t i o n a l i t y but a l s o s i g n i f i c a n t l y a l t e r the i o n i c nature of the aqueous mediums so as to f u r t h e r a s s i s t d i s s o l u t i o n . The need f o r having a c i d s a l t s i s demonstrated i n the case of thiocyanates where the sodium, potassium and ammonium thiocyanates do not d i s s o l v e c e l l u l o s e w h i l e the calcium and


2.

TURBAK E T A L .


15

s t r o n t i u m s a l t s do g i v e c e l l u l o s e s o l u t i o n s up to about the 400 D.P. l e v e l i n d i c a t i n g t h a t i t i s the t h i o c y a n i c a c i d formed i n s o l u t i o n which i s a c t u a l l y i n v o l v e d i n the d i s s o l v i n g a c t i o n . B.

C e l l u l o s e As An A c i d

Perhaps more work has been undertaken on s w e l l i n g c e l l u l o s e w i t h bases than w i t h any other c l a s s of chemical compounds. The hydrogen atoms on the hydroxyIs of c e l l u l o s e , l i k e most a l c o h o l s , have a degree o f a c i d c h a r a c t e r and t h e r e f o r e r e a d i l y i n t e r a c t w i t h reasonably strong i n o r g a n i c and organic bases. 1. Inorganic Bases (sodium z i n c a t e , hydrazine, i n o r g a n i c hydroxides). I t shoul c e n t r a t i o n of base neede ulose by osmotic a c t i o n i s not the same c o n c e n t r a t i o n that i s r e q u i r e d to e f f e c t a c t u a l compound formation. Thus w h i l e 8-10% NaOH e x h i b i t s the maximum s w e l l i n g o f c e l l u l o s e f i b e r s , concent r a t i o n s of about 18% NaOH are a c t u a l l y r e q u i r e d t o form sodium c e l l u l o s a t e s t r u c t u r e s . Other i n o r g a n i c bases l i k e potassium and l i t h i u m hydroxide have a l s o been used s i m i l a r l y f o r t h e i r s w e l l i n g a c t i o n . Various a d d i t i v e s t o the c a u s t i c soda, such as z i n c oxide, have been used to make sodium z i n c a t e s o l u t i o n s which enhance the a c t i o n of c a u s t i c so higher D.P. m a t e r i a l s can be d i s s o l v e d . The temperatures o f these aqueous bases p l a y a f u r t h e r dominant r o l e i n the s w e l l i n g and d i s s o l v i n g phenomenon; w i t h the c o l d e r c o n d i t i o n s g i v i n g more s w e l l i n g and d i s s o l u t i o n . While a c o n s i d e r a b l e amount o f e f f o r t has been devoted t o aqueous a l k a l i systems, they normally do not d i s p l a y s u f f i c i e n t d i s s o l v ing power to completely overcome the c r y s t a l and hydrogen bonding energies of c e l l u l o s e t o g i v e acceptable s o l u t i o n s of h i g h e r D.P. m a t e r i a l s of i n t e r e s t f o r d i r e c t commercial conversion. I n a d d i t i o n , these aqueous a l k a l i n e systems present s e v e r a l r e covery and r e c y c l e problems. The use of the i n o r g a n i c base, h y d r a z i n e , f o r s w e l l i n g c e l l ulose was considered by Hess and Trogus many years ago.(12) However, they were never able to o b t a i n c e l l u l o s e s o l u t i o n s under the c o n d i t i o n s they employed. More r e c e n t l y , L i t t (13) has r e ported c o n d i t i o n s under which he has been able t o o b t a i n comp l e t e s o l u t i o n s of high D.P. c e l l u l o s e i n hot (150°-200°C) hydrazine and 207-345 kPa (30-50 p s i ) p r e s s u r e . These r e s u l t s serve to demonstrate t h a t s e v e r a l f a c t o r s are important f o r a s w e l l i n g reagent t o become a s o l v e n t . The o r i g i n a l i n v e s t i g a t i o n s i n 1931 by Hess employed hydrazine hydrate but d i d not employ the more extreme c o n d i t i o n s of heat and temperature r e c e n t l y employed by L i t t i n 1976 t o o b t a i n s o l u t i o n s . L i t t was able to get s o l u t i o n s of c e l l u l o s e u s i n g e i t h e r pure hydrazine or hydrazine hydrate p r o v i d i n g he employed elevated temperatures and p r e s s u r e s . I t was noted p r e v i o u s l y that c r y s t a l l i n e f o r c e s


16

SOLVENT SPUN RAYON, MODIFIED CELLULOSE FD3ERS

and hydrogen bonding could be important f a c t o r s and t h i s case c l e a r l y demonstrates t h a t even a m a t e r i a l having the proper s o l u b i l i t y parameter had t o be employed under f o r c i n g c o n d i t i o n s t o overcome these f a c t o r s t o achieve s o l u t i o n . I t has y e t t o be demonstrated, however, i f t e x t i l e q u a l i t y yarns o r packaging q u a l i t y f i l m s can be prepared from such hydrazine s o l u t i o n s . C e r t a i n l y , t o our knowledge no data along these l i n e s have y e t been p u b l i s h e d . 2. Organic Bases ( T r i t o n - q u a t e r n a r y h y d r o x i d e s , amines, DMSO/CH^NH?, amine o x i d e s ) . The a b i l i t y of c e l l u l o s e t o a c t as an a c i d towards v a r i o u s o r g a n i c bases has a l s o been e v a l u a t e d . Perhaps the b e s t known organic bases a r e the v a r i o u s " T r i t o n " bases which are quaternar vent of t h i s s e r i e s i d r o x i d e . I t i s i n t e r e s t i n g again t o note here t h a t the b e n z y l grouping i s f a r more e f f e c t i v e than other groups such as m e t h y l , e t h y l o r p r o p y l and t h i s Improvement has been a t t r i b u t e d t o the f a c t t h a t the b u l k i e r b e n z y l group behaves l i k e a "wedge" t o e f f e c t i v e l y separate the c e l l u l o s e chains once i t has entered the c r y s t a l l i n e region. A c o n s i d e r a b l e amount of work has a l s o been r e p o r t e d by S e g a l and others (14) r e l a t i v e t o the use of v a r i o u s amines and diamines f o r s w e l l i n g c e l l u l o s e . None o f these systems were claimed t o cause s u f f i c i e n t s w e l l i n g t o g i v e c e l l u l o s e s o l u t i o n s . More r e c e n t l y , P h i l l i p and h i s co-workers (15,16) have r e p o r t e d t h a t 16.5% methylamine i n DMSO gave b e t t e r c e l l u l o s e s o l u t i o n s than any other amine o r any other c o n c e n t r a t i o n o f methylamine used. The c e l l u l o s e i s claimed t o d i s s o l v e by r e a c t i o n w i t h an equimolar complex of CH3NH2/DMSO and 80% of the i n t r o d u c e d c e l l u l o s e d i s s o l v e d under c o l d anhydrous c o n d i t i o n s . As exc i t i n g as t h i s seems a t f i r s t g l a n c e , d i s s o l u t i o n of only 80% of the c e l l u l o s e may not be o f v a l u e f o r commercial c o n s i d e r a t i o n . Unless the d i s s o l u t i o n of c e l l u l o s e i s a c t u a l l y b e t t e r than 99%, the system would c e r t a i n l y be too expensive t o use r e l a t i v e t o y i e l d and f i l t r a t i o n c o s t s . The s p e c i f i c i t y of CH3NH2 and i n p a r t i c u l a r the 16.5% c o n c e n t r a t i o n i s i n t r i g u i n g and deserves more study. Perhaps, t h i s system might more p r o p e r l y belong under c o n s i d e r a t i o n as an organic complex r a t h e r than as a pure base system, but more data are needed t o f i r m l y decide the exa^t nature of t h e r e a c t i o n . One other organic base system which d i s s o l v e s c e l l u l o s e as an a c i d i n v o l v e s compounds not normally considered as bases, b u t which i n f a c t , are v e r y good "Lewis" bases. I n 1939, Graenacher and Sallman (17) reported t h a t a l i p h a t i c and c y c l o a l i p h a t i c amine oxides such as t r i e t h y l a m i n e oxide o r c y c l o h e x y l d i m e t h y l amine o x i d e gave 7-10% s o l u t i o n s of c e l l u l o s e a t 50-90°C. More r e c e n t l y , Johnson (18) has r e p o r t e d t h a t a l i c y c l i c amine oxides such as N-methylmorpholine oxide g i v e up t o 6% s o l u t i o n s o f c e l l u l o s e a t 110°C. These m a t e r i a l s are most i n t e r e s t i n g and could


TURBAK E T A L .

2.


17

o f f e r commercial p o s s i b i l i t i e s i f adequate recovery and r e c y c l e procedures c o u l d be e s t a b l i s h e d . To our knowledge, no one has yet p u b l i s h e d any a c t u a l f i b e r o r f i l m d a t a on products d e r i v e d from such systems. Thus, a wide range of i n o r g a n i c and organic bases have been examined f o r d i s s o l v i n g and s w e l l i n g c e l l u l o s e . S e v e r a l systems have achieved a s u f f i c i e n t l y good balance of p r o p e r t i e s t o pro v i d e good c e l l u l o s e s o l u t i o n s and i t i s expected t h a t f u r t h e r e f f o r t s w i l l be forthcoming t o achieve a c c e p t a b l e r e c o v e r y / r e c y c l e and p h y s i c a l p r o p e r t i e s which could l e a d t o i n d u s t r i a l acceptance. C.

C e l l u l o s e Complexes

1. I n o r g a n i c Complexe ium). The use of v a r i o u coppe complexe l o s e i s w e l l known. More r e c e n t l y , complexes of cadmium and i r o n have been added t o the l i s t t o reduce the s e n s i t i v i t y of such c e l l u l o s e s o l u t i o n s t o degradation by exposure t o a i r . T h i s work i s reviewed r a t h e r completely by Jayme (3) who, w i t h h i s c o workers, has c o n t r i b u t e d e x t e n s i v e l y t o t h i s a r e a . I n o r g a n i c m e t a l l i c complexes such as cuprammonium have met w i t h o n l y minimal commercial success f o r p r o d u c t i o n f i b e r s and f i l m s f o r two reasons. F i r s t , complete recovery of m e t a l l i c e f f l u e n t contaminants i s d i f f i c u l t a t the extremely low ppm l e v e l s needed t o meet p o l l u t i o n requirements and secondly the o v e r a l l economics and f i b e r p r o p e r t i e s (of the cuprammonium p r o c e s s , a t l e a s t ) were not as good as those of the v i s c o s e p r o c e s s . The second f a c t o r would today be l e s s important than the recovery and p o l l u t i o n aspect and, u n t i l t h i s aspect i s s o l v e d , metal i n o r ganic complexes w i l l continue t o have l i m i t e d u t i l i t y f o r f i l m and f i b e r p r o d u c t i o n . 2 . Organic Complexes (DMSO/CH3NH2, (KOCH2CHOHCH9S) 2. The p o s s i b l e use o f organic complexes t o d i s s o l v e c e l l u l o s e appears to be extremely l i m i t e d . Of a l l the systems r e p o r t e d , o n l y two seem to q u a l i f y as organic complexes. The f i r s t of these uses DMSO/16.5% CH3NH2 and was p r e v i o u s l y d i s c u s s e d under category Β (above) s i n c e i t s a c t i o n may be r e l a t e d more t o i t s b a s i c nature than t o a t r u e complex f o r m a t i o n . The second system was r e p o r t e d by P e t r o v i n 1965 (19) who c l a i m s t h a t c e l l u l o s e d i s s o l v e s d i r e c t l y a t 110°C i n a n e u t r a l s o l v e n t - b i s (φ-Y dihydroxypropyl) d i s u l f i d e - prepared by o x i d a t i o n of t h i o g l y c e r o l . T h i s s o l v e n t works w e l l f o r d i s s o l v i n g cellophane f i l m s a t 300-600 D.P., but i s not good f o r d i r e c t l y d i s s o l v i n g h i g h e r D.P. c o t t o n l i n t e r s o r r e g u l a r p u r i f i e d wood p u l p s . I n any case, i t i s i n t r i g u i n g t o f i n d a n e u t r a l s o l v e n t t h a t appears to be capable o f d i r e c t l y d i s s o l v i n g reason ably h i g h D.P. c e l l u l o s e and f u r t h e r work should be undertaken t o a s c e r t a i n why t h i s p a r t i c u l a r s t r u c t u r e seems t o be e f f e c t i v e .


SOLVENT SPUN RAYON, MODIFIED CELLULOSE FD3ERS

18

D.

Cellulose Derivatives

1. S t a b l e D e r i v a t i v e s ( e s t e r s , e t h e r s ) , A wide v a r i e t y of s t a b l e c e l l u l o s e d e r i v a t i v e s are known and used commercially. The e s t e r s and e t h e r s have found scores of commercial uses but only the acetate and n i t r a t e have ever been u t i l i z e d f o r producing regenerated c e l l u l o s e products; the acetate t o g i v e F o r t i s a n and the n i t r a t e t o make regenerated t u b u l a r c e l l u l o s e f i l m s . 2,

Unstable D e r i v a t i v e s , a.

Sulfur

(xanthates, SC^/amines - s u l f i t e s )

b.

Nitrogen

(DMF/N2O4 DMSO/N

c.

Carbon

(carbonates, formates, DMSO/(CH 0)x me thy l o i ) 2

Unstable c e l l u l o s e d e r i v a t i v e s have been and are being a c t i v e l y i n v e s t i g a t e d i n depth f o r use i n p r e p a r i n g regenerated f i b e r s and f i l m s . This paper w i l l c o n s i d e r such " t r a n s i e n t " d e r i v a t i v e s under three main headings: a) s u l f u r - b) n i t r o g e n and c) carbon-containing i n t e r m e d i a t e s . a) S u l f u r Intermediates: The use of CS to form xanthates some 90 years ago s t i l l forms the backbone of the present day rayon i n d u s t r y . Improved processes are u r g e n t l y needed which can not only overcome the v a r i o u s p o l l u t i o n problems a s s o c i a t e d w i t h the v i s c o s e process, but which might a l s o h o p e f u l l y lower both the i n i t i a l c a p i t a l investment and subsequent o p e r a t i n g c o s t s a s s o c i a t e d w i t h present day rayon p l a n t s . One attempt along these l i n e s i s reported by Kimura et a l (20) who used a m o d i f i e d organic type system f o r x a n t h a t i o n . They used DMSO/CS2/amine to d i s s o l v e c e l l u l o s e and reported f i b e r s having c o n d i t i o n e d and wet t e n a c i t y / e l o n g a t i o n of 3.0 g/d/14% and 1.8 g/d/25% r e s p e c t i v e l y . T h e i r c o a g u l a t i o n and r e g e n e r a t i o n steps d i d not i n v o l v e the use of a c i d s and thus would s i g n i f i c a n t l y reduce part of the p o l l u t i o n l o a d normally a s s o c i ated w i t h rayon p r o d u c t i o n . However, i n i t i a l l a b o r a t o r y attempts to reproduce the r e p o r t e d process gave r i s e to an extremely noxious odor and t h i s could represent s u f f i c i e n t detriment t o o f f s e t other p o s s i b l e advantages. As another p o s s i b l e approach to d i s s o l v i n g c e l l u l o s e , seve r a l i n v e s t i g a t o r s have s t u d i e d the use of S02/amine s o l v e n t s y s tems. E x t e n s i v e work i n t h i s area i s reported by P h i l l i p and h i s coworkers (21) by Yanazaki and Nakao (22) and by Hata and Yokota (23-29). T h e i r e f f o r t s covered a wide range of amines and organic s o l v e n t d i l u e n t s which were both p o l a r and non-polar. 2


2.

TURBAK E T A L .


19

While i n i t i a l l y i t was thought t h a t some type of complex was being formed w i t h the c e l l u l o s e , i t i s now reasonably establ i s h e d that t h i s treatment r e s u l t s i n the formation of amine s a l t s of the r a t h e r unstable c e l l u l o s e s u l f i t e e s t e r . Again f i l a m e n t s r e p o r t e d l y were spun, but no f i b e r p h y s i c a l p r o p e r t i e s were r e p o r t e d . The use of s u l f i t e e s t e r s f o r p r e p a r i n g rayon i n preference t o the v i s c o s e system would c r i t i c a l l y depend on good recovery of a l l s t a r t i n g m a t e r i a l s , and t h i s may be an area worthy of both chemical and engineering e f f o r t . b) Nitrogenous Intermediates: The use o f u n s t a b l e n i t r o genous i n t e r m e d i a t e s f o r a c h i e v i n g c e l l u l o s e s o l u t i o n i n organic s o l v e n t s i s concentrated mainly i n the area of systems i n v o l v i n g n i t r o g e n oxides. I n i t i a l l c e l l u l o s e t o the 6-carbox Kenyon, Y a c k e l , Unruh, Fowler, and McGee i n the 40 s stands as a milestone i n t h i s a r e a . (30-34) More r e c e n t l y , Pavlyuchenko and Ermolenko and coworkers have presented f u r t h e r d e t a i l e d s t u d i e s on the use of N2O4 f o r c e l l u l o s e o x i d a t i o n . (35-39) I n 1947, Fowler e t a l (34) reported t h a t v a r i o u s s o l v e n t s , when used i n c o n j u n c t i o n w i t h N2O4, gave d i f f e r e n t responses t o the a c t i o n of t h i s reagent on c e l l u l o s e and found t h a t many s o l v e n t s a c t u a l l y gave r i s e to s o l u t i o n s o f c e l l u l o s e without h i g h degrees o f o x i d a t i o n o c c u r r i n g . They used over 40 d i f f e r e n t s o l v e n t s where the N2O4 t o s o l v e n t r a t i o s were a t l e a s t 1/1 or h i g h e r and f i n a l l y concluded that the amount of o x i d a t i o n v s . c e l l u l o s e s o l u t i o n was r e l a t e d t o the p o l a r i t y of the s o l v e n t employed. With non-polar s o l v e n t s such as CCI4 e t c . the N2O4 produced mostly o x i d a t i o n w h i l e the more p o l a r s o l v e n t s gave r i s e t o c e l l ulose s o l u t i o n s w i t h g r e a t l y diminished o x i d a t i o n . I f no s o l vents were employed and l a r g e excesses of c o l d l i q u i d N2O4/N2O3 mixtures were used, then c e l l u l o s e d i s s o l v e d w i t h v e r y l i t t l e o x i d a t i o n and could be recovered from such s o l u t i o n s e s s e n t i a l l y c h e m i c a l l y unchanged except f o r a D.P. l o s s . T h i s was f i r s t r e ported by H i a t t and Crane i n 1949 (40) and subsequently s t u d i e d i n great d e t a i l by Chu i n 1970.(41) F o l l o w i n g these c l a s s i c d i s c l o s u r e s by Fowler, other r e searchers began t o examine even more p o l a r s o l v e n t s f o r use w i t h N2O4. Thus, W i l l i a m s (42) s t u d i e d the use o f DMSO/N2O4 as a s o l v e n t system f o r c e l l u l o s e . I t was l a t e r demonstrated r a t h e r c l e a r l y by Hergert and Z o p o l i s (43) t h a t the DMSO/N2O4 system would d i s s o l v e c e l l u l o s e more e f f e c t i v e l y i f t h e r e was a s m a l l amount of water present t o keep the c e l l u l o s e s t r u c t u r e open f o r r e a c t i o n . S u r p r i s i n g l y very l i t t l e more work has been done w i t h the DMSO/N2O4 system up t o the present time. Subsequently, Nakao obtained patent coverage on the use of DMF/N2O4 mixtures t o d i s s o l v e c e l l u l o s e (44,45) and on the a d d i t i o n s o f a wide range o f other polymers i n DMF t o such c e l l u l o s e s o l u t i o n s to produce s p e c i a l types of products. Mahomed (46)


20

S O L V E N T S P U N R A Y O N , MODIFIED C E L L U L O S E FIBERS

d e s c r i b e s the use of cellulose/DMF/N2O4 s o l u t i o n s as c o a t i n g m a t e r i a l s f o r g l a s s f i b e r s t o improve product performance. During t h i s p e r i o d s e v e r a l other workers began to appreciate that very p o l a r s o l v e n t s gave c e l l u l o s e s o l u t i o n s from which c e l l u l o s e could be recovered i n an e s s e n t i a l l y unchanged s t a t e r a t h e r than i n the h i g h l y o x i d i z e d s t a t e p r e v i o u s l y a s s o c i a t e d w i t h N2O4 treatments. A c o n s i d e r a b l e amount of research was p u b l i s h e d t r y i n g to d e f i n e what was o c c u r r i n g when the N2O4 was used w i t h the p o l a r s o l v e n t s . Clermont and Bender and t h e i r a s s o c i a t e s r e p o r t e d s t u d i e s where c e l l u l o s e was d i s s o l v e d i n both c o l d and hot s o l u t i o n s w i t h N2O4/DMF mixtures. (47-49) They found t h a t e s s e n t i a l l y unchanged c e l l u l o s e w i t h no added n i t r o g e n or c a r b o x y l l e v e l s was obtained from c o l d d i s s o l u t i o n , w h i l e waters o l u b l e c e l l u l o s e r e s u l t e d from i n c r e a s e d d i s s o l v i n g temperatures apparently due to the formatio t r a t e s . They subsequentl s o l v e l i g n o c e l l u l o s e removed from wood chips.(50) In a s e r i e s of a r t i c l e s d a t i n g from 1969-1976, Schweiger ha§ been r e p o r t i n g s t u d i e s aimed at t r y i n g to e l u c i d a t e what was happening i n the DMF/N2O4 treatment of c e l l u l o s e and t r i e d to use such s o l u t i o n s f o r forming other d e r i v a t i v e s . (51-56) He was a b l e to i s o l a t e a product from a p y r i d i n e - m o d i f i e d dope which appeared to be an u n s t a b l e c e l l u l o s e n i t r i t e i n t e r m e d i a t e s i n c e i t could produce a l k y l n i t r i t e s when decomposed by lower m o l e c u l a r weight a l c o h o l s . While t h i s i s not a d i r e c t s t r u c t u r a l proof i t c e r t a i n l y i s s u f f i c i e n t t o s u b s t a n t i a t e h i s proposal t h a t c e l l u l o s e r e a c t s w i t h N2O4 to g i v e c e l l u l o s e n i t r i t e and HNO3 r a t h e r than forming some type of N 2 O 4 / c e l l u l o s e a s s o c i a t i o n complex. The c e l l u l o s e n i t r i t e i s subsequently r a p i d l y decom posed by p r o t o n i c s o l v e n t s to regenerate the c e l l u l o s e and g i v e HNO2 along w i t h HNO3 f o r recovery and r e c y c l e . The s t r u c t u r e and r e a c t i o n s of N2O4 i n general have been reviewed by Gray (52) w h i l e the r e a c t i o n s of N 0^ to n i t r a t e and n i t r o s a t e a l c o h o l s and amines are reported by White and Feldman. (58) Pasteka and M i s l o v i c o v a s t u d i e d the e f f e c t s of v a r i o u s d i s s o l v i n g c o n d i t i o n s on the D.P. l o s s of c e l l u l o s e i n the DMF/N2O4 system. (59-61) They noted that the moisture content of the system and even the r a t e of s t i r r i n g caused a drop i n D.P. and t h a t the presence of p y r i d i n e or (ΰ2Η5)βΝ d i d not i n h i b i t such l o s s . W h i l e moisture may w e l l r e l a t e to D.P. l o s s , i t i s d i f f i c u l t to understand how s t i r r i n g r a t e could have such an e f f e c t unless i t was r e f l e c t i n g l o c a l temperature r i s e s t h a t occurred under the c o n d i t i o n s employed f o r s t i r r i n g . I n any case, these i n v e s t i g a t o r s again confirmed no i n c r e a s e i n e i t h e r n i t r o g e n or c a r b o x y l content f o r the regenerated c e l l u l o s e . The N2O4 system has a l s o been i n v e s t i g a t e d by s e v e r a l Russians (62-64) who a c t u a l l y r e p o r t p h y s i c a l p r o p e r t i e s f o r f i b e r s spun from DMF/N2O4 and EtOAc/Ô^ systems. These f i b e r s are about 120 d e n i e r and have t e n a c i t i e s of 1.6 g/d w i t h 5-6% 2


2.

TURBAK E T A L .


21

e l o n g a t i o n s . Obviously more d e f i n i t i o n of the ^ O ^ o r g a n i c s o l vent system i s needed t o determine i t s p o t e n t i a l as a s o l v e n t based rayon process to s u b s t i t u t e f o r v i s c o s e and t h i s work w i l l be r e p o r t e d l a t e r i n t h i s symposium. f

c. Carbon Intermediates: The use of non-hetero atom-cont a i n i n g m o i e t i e s to make c e l l u l o s e i n t e r m e d i a t e s o f t r a n s i e n t s t a b i l i t y has r e c e i v e d r e l a t i v e l y l i t t l e a t t e n t i o n i n s p i t e of the f a c t that such d e r i v a t i v e s might u l t i m a t e l y o f f e r the b e s t prospects f o r n o n - p o l l u t i n g systems. C e l l u l o s e carbonate has been prepared and r e p o r t e d . However, i t e v i d e n t l y i s so uns t a b l e as to have e s s e n t i a l l y no u t i l i t y as an i n t e r m e d i a t e . A l s o , as prepared from phosgene, i t would f a c e other i n d u s t r i a l problems. C e l l u l o s e formate being r a p i d l y prepared y l o s e . The cleavage of c e l l u l o s e formate by hot steam a l s o r e presents an i n t e r e s t i n g approach f o r "dry s p i n n i n g " t h i s d e r i v a t i v e . While f o r m i c a c i d would not be considered a " m a t e r i a l o f c h o i c e " under most circumstances f o r i n d u s t r i a l use, i t i s c e r t a i n l y no worse than "hydrazine" i n most s a f e t y and h e a l t h cons i d e r a t i o n s and t h i s approach, o r one s i m i l a r t o i t , w i l l undoubtedly see f u r t h e r e f f o r t i n the f u t u r e . R e c e n t l y , N i c h o l s o n and D.C. Johnson reported on t h e i r work on d i s s o l v i n g c e l l u l o s e i n mixtures o f DMSO w i t h paraformaldehyde. (65) I n i t i a l i n d i c a t i o n s are that a c e l l u l o s e m e t h y l o l compound i s formed which i s s t a b l e under the e l e v a t e d temperatures of s o l u t i o n p r e p a r a t i o n and i s subsequently s t a b l e f o r days under storage i n open a i r at room temperature. The extreme s p e c i f i c i t y of t h i s combination of reagents i s p a r t i c u l a r l y n o t a b l e . For example, Seymour and E.L. Johnson (66,67) noted t h a t n e i t h e r DMF, DMAc, acetone, HMPA, nitromethane, a c r y l o n i t r i l e , a c e t o n i t r i l e , nor s u l f o l a n e can be s u b s t i t u t e d f o r the DMSO. Thus DMSO and o n l y DMSO has been found to be e f f e c t i v e t o date f o r a c h i e v i n g c e l l u l o s e s o l u t i o n s w i t h formaldehyde. This extreme s p e c i f i c i t y may w e l l r e l a t e i n some way t o the f a c t t h a t DMSO i t s e l f breaks down i n t o DMS and paraformaldehyde on h e a t i n g (68) or may poss i b l y be i n t e r a c t i n g t o s t a b i l i z e the proposed c e l l u l o s e m e t h y l o l i n t e r m e d i a t e whereas no other reagent i s e v i d e n t l y a b l e t o do so. I t should be f u r t h e r noted that w h i l e o n l y one mole of paraformaldehyde i s r e q u i r e d to h o l d one mole of the c e l l u l o s e i n s o l u t i o n , l a r g e molar excesses of 5/1 (CH20)x/cellulose must be employed i n i t i a l l y f o r d i s s o l u t i o n to occur. Thus t h i s system which appears t o i n i t i a l l y o f f e r an easy route t o c e l l u l o s e s o l u t i o n s , may o f f e r c o n s i d e r a b l e d i f f i c u l t y commercially from the aspects o f s p i n n i n g , recovery and r e c y c l e . F u r t h e r data from t h i s work are to be presented l a t e r i n t h i s symposium.


22

S O L V E N T SPUN R A Y O N , MODIFIED C E L L U L O S E

FIBERS

Throughout t h i s review, an attempt has been made t o h i g h l i g h t the need f o r a low investment c o s t , n o n - p o l l u t i n g s o l v e n t system f o r c e l l u l o s e t o s u b s t i t u t e f o r the v i s c o s e process. None o f the systems known t o date meet the necessary requirements f o r commercial e x p l o i t a t i o n . However, as has always been the case, whenever a need l i k e t h i s e x i s t s some outstanding s c i e n t i s t s w i l l develop methods t o produce the d e s i r e d r e s u l t s - and t h i s case w i l l be no e x c e p t i o n . The c e l l u l o s e chemists are equal to the c h a l l e n g e and the rewards f o r success w i l l be l a r g e .

Literature Cited 1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11. 12. 13. 14. 15. 16. 17. 18. 19. 20. 21. 22. 23.

Warwicker, J.O., J e f f r i e s , R . , Colbran, R.L., and Robinson, R . N . , Shirley Inst. Pamphle No 93 (1966) Manchester England. Warwicker, J.O., High Polymers, V o l . V , Part IV, Wiley -Interscience, N . Y . , 1971. Jayme, G . , High Polymers, V o l . V, Part IV, Wiley-Interscience, N . Y . , 1971. Phillip, B . , Schleicher, H., and Wagenknecht, W., Cellulose Chem. Tech., 9, 265-82 (1975). Phillip, B. Schleicher, H., and Wagenknecht, W., C.A. 83 165567s; Chem. Vlakno 25 (10-22) 1975. Polyola, L., and Aarnikowa, P.L., Kem.-Kemi 2, (1) 27-9 (1975). Brandrup, J. and Immergut, E . H . , Polymer Handbook, 2nd ed. V-101, John Wiley & Sons, N . Y . 1975. Spurlin, H.M., High Polymers Vol. V, Part III, Wiley-Inter science, N . Y . (1955). B u r r e l l , H., O f f i c i a l Digest (726-758) 1 9 5 5 . Barton, A.F., Chem. Reviews, 75, No. 6, (731-753) 1975. Williams, H . E . , J. Soc. Chem. Ind., 40, 221T, 1921. Hess, K. and Trogus, C., Z. Phys. Chem., B14, 387 (1931). L i t t , M . , Cell. D i v . Preprints, ACS Mtg., N.Y. 1976. Segal, L., High Polymers, V o l . V, Part IV, Wiley-Intersci ence, N.Y. 1971. P h i l l i p , B . , and Schleicher, H., C . A . , 74, 127361b (1971). Koura, Α., Schleicher, H., and Phillip, B . , Faserforsch. T e x t i l t e c h . 23, (3) 128-33 1972; C . A . , 77, 50396u 1972. Graenacher, C., and Sallmann, U.S. 2,179,181 (1939). Johnson, D . L . , U.S. 3,508,941 (1970); B . P . 1,144,048 (1969). Petrov, V . G . , C.A. 63, 10161g, 1965. Kimura, T . , Yamamura, T . , Kawai, Α., and Nagai, S., Japan Patent 69 02,592. P h i l l i p , B., Schleicher, H., and Laskowski, I., Faserforsch Textiltech., 23, 60-65, (1972). Yamazaki, S., and Nakao, O., C . A . , 81, 154860q (1974). Kata, Κ., and Yokota, K . , C.A. 66, 47464g (1967).


2.

TURBAK

24. 25. 26. 27. 28. 29. 30. 31. 32. 33. 34. 35. 36. 37. 38. 39. 40. 41. 42. 43. 44. 45. 46. 47. 48. 49. 50. 51. 52. 53. 54. 55. 56. 57. 58. 59.

ET

AL.


23

Hata, K. and Yokota, K., C.A. 70, 69191a, (1969). Hata, K. and Yokota, K., C.A. 70, 69192b, (1969). Hata, K. and Yokota, K., U.S. 3,424,702 (1969). Hata, K. and Yokota, K., C.A., 72, 33464u (1970). Hata, K. and Yokota, K., C.A., 74, 14323x (1971). Hata, K. and Yokota, K., C.A., 75, 153094g (1971). Kenyon, W. and Y a c k e l , E., U.S. 2,448,892. Y a c k e l , E.C. and Kenyon, W., J.A.C.S. 64, 121 (1942). Unruh, C.C. and Kenyon, W., J.A.C.S. 64, 127 (1942). McGee, P., Fowler, W.F., et al, J.A.C.S. 69, 355 (1947). Fowler, W., Unruh, C., McGee, P. and Kenyon, W., J.A.C.S. 69, 1636 (1947). Pavlyuchenko, M. and Ermolenko, I., C.A. 1739d (1956) I z v e s t . Akad. Nauk Ermolenko, I. and Zhur. Obshchei Khim., 28, 722-8 (1958). Pavlyuchenko, M. et al C.A. 20187g (1960) Zhur. Priklad. Khim. 33, 1385-91 (1960). Kuznetsova, Z.I. et al, I z v e s t . Akad. Nauk., SSSR, No. 3, 557-59 (1965). Pavlyuchenko, M. et al, C.A. 83, 166024z (1975), Zhur., Priklad. Khim. 48, 1822-5 (1975). H i a t t , G.D. and Crane, C.L. U.S. 2,473,473 (1949). Chü, N.J., Pulp and Paper I n s t . of Canada. Report #42, 1970. W i l l i a m s , H.D., U.S. 3,236,669 (1966). H e r g e r t , H.L. and Z o p o l i s , P., Fr. P a t . 1,469,890, C.A. 68 41234b (1968). Nakao, O., et al, Canadian P a t e n t 876,148 (1971). Nakao, O., et al, U.S. 3,669,916. Mahomed, R.S., B.P. 1,309,234 (1973). Clermont, L.P., Canadian P a t e n t 899,559 (1969). Clermont, L.P. and Bender, F., J. P o l y . Sci., 10 (6), 1665-77 A-1 (1972). Venkateswaran, A. and Clermont, P., J. A p p l . P o l y .Sci.,18, 133-42 (1974). Bender, F., et al, U.S. 3,715,268 (1973). Schweiger, R.G., Chem. & I n d . 296, (1969). Schweiger, R.G., German Patent 2,120,964 (1971). Schweiger, R.G., U.S. 3,702,843 (1972). Schweiger, R.G., TAPPI. 7th D i s s o l v i n g Pulp Conf., A t l a n t a (1973). Schweiger, R.G., TAPPI. 57 #1, 86-90, 1974. Schweiger, R.G., J. Org. Chem., 41, (1) 90-93 (1976). Gray, P., Chemical Reviews, 1069, (1955). White, E.H. and Feldman, W.R., J.A.C.S. 79, 5832-33 (1957). P a s t e k a , M. and M i s l o v i c o v a , D., C e l l u l o s e Chem. & Tech., 8, 107-114 (1974).


24 60. 61. 62. 63. 64. 65. 66. 67. 68.

S O L V E N T SPUN

R A Y O N , MODIFIED C E L L U L O S E

FIBERS

I b i d , 481-486 (1974). ibid, 9, 325-330 (1975). Grinshpan., O., et al, Daklod, Akad. Nauk, B e l l o r o s s , SSSR, 18, (9) 828-31 (1974). Grinshpan, D., K a p u t s k i i , F.N., et al, B e l l o r o s s , Gos. Univ., Minsk., SSSR.; C.A. 194931 (1975). Bashmakov, I.A. et al, Vestsi Akad Nauk, Gos U n i v . B e l l o r o s s SSSR, (4) 29-32 (1973) C.A. 28636u (1973). N i c h o l s o n , M. and Johnson, D.C., TAPPI, 8th D i s s o l v i n g Pulp Conf., Syracuse, N.Y. 1975. Seymour, R.B. and Johnson, E.L., Organic Coatings and Plastics P r e p r i n t s , ACS Mtg. San F r a n c i s c o 665-73 (1976). Seymour, R.B. and Johnson, E.L., Polymer P r e p r i n t s , 17, #2, 382-383 (1976) (ACS Lowe, O.G., J. Org


3 The

Spinning of Unconventional Cellulose Solutions

D. M. MacDONALD International Paper Co., Tuxedo Park,N.Y.10987

About ten years ago it became apparent that the v i s c o s e process was encounterin environmental e f f e c t s . erated c e l l u l o s e was i n d i c a t e d and a p r o j e c t t o screen the v a r i o u s c e l l u l o s e s o l v e n t s was s t a r t e d . In this paper, some o f the r e s u l t s will be d e s c r i b e d . In the first experiments, Table I , the s o l u t i o n s were prepared u s i n g k r a f t hardwood d i s s o l v i n g pulps. C e l l u l o s e , dissolved i n 72% sulfuric a c i d , hydrolyzed t o a DP below 30 in less than 15 minutes a t 0°C. Phosphoric a c i d (85%) gave a very v i s c o u s 2% cellulose s o l u t i o n of practical DP, but the presence of g e l s and fibers made filtration very difficult and H PO could not be washed from f i l m s c a s t on g l a s s p l a t e s . N e u t r a l i z a t i o n w i t h 14% ammonium hydroxide, f o l l o w e d by washing, gave complete removal o f phosphate, but higher concentrations o f ammonium hydroxide gave crystalline ammonium phosphate in the film. 3

4

Table I C r i t i q u e o f C e l l u l o s e Solvents F i r s t Examined Solvent 72%

H

Result Excessive DP l o s s

S 0

2 4 85% H P 0

High g e l and f i b e r , H^PO^ hard t o remove

so

2

-NH

Good s o l u t i o n , i m p r a c t i c a l to

regenerate

so

2

- ( C H ) NH

Good s o l u t i o n , i m p r a c t i c a l to

regenerate

3

4

3

3

2

Good s o l u t i o n , very slow c o a g u l a t i o n

64% ZnCl

The extreme difficulty of filtration along with the poor economics a n t i c i p a t e d in u s i n g a 2% solution prompted an exami n a t i o n o f the newer SO -amine s o l v e n t s reported by Hata and Yokota in Japan (1-3). These s o l v e n t s gave good s o l u t i o n s but, 2

25


26

S O L V E N T SPUN R A Y O N , MODIFIED C E L L U L O S E FIBERS

when regenerated i n water a t 0°C or h i g h e r , S 0 e v o l u t i o n produced a foam. As reported by these Japanese workers Ç3), r e generation at -10 C i n methanol gave a c l e a r f i l m , but the economics of working under pressure at such low temperature seemed d o u b t f u l . The f i n a l s o l v e n t i n Table I , aqueous z i n c c h l o r i d e , gave an e x c e l l e n t s o l u t i o n which, u n f o r t u n a t e l y , could not be coagulated i n a form w i t h s t r e n g t h would permit s p i n n i n g . This was deduced from experiments u t i l i z i n g hand-cast f i l m s which showed l i t t l e or no cohesion. 2

Spinning Experiments Using C e l l u l o s e Dispersed i n Calcium Thiocyanate While examining th i n aqueous c a l c i u m thiocyanat and a c l e a r f i l m was produced. Since f i b e r extruders are used i n p r e p a r i n g s y n t h e t i c f i b e r s , i t seemed p o s s i b l e that t h i s process, i l l u s t r a t e d i n F i g u r e 1, could g i v e a p r a c t i c a l route to regenerated c e l l u l o s e ; t h e r e f o r e , a c l o s e r i n v e s t i g a t i o n of t h i s unusual s o l v e n t system, f i r s t described by Bechtold and Weratz of DuPont (4-6), was commenced. In the a n t i c i p a t e d i n d u s t r i a l process, pulp would be f l o c k e d , mixed w i t h calcium thiocyanate s o l u t i o n , d r a i n e d , and then pressed. These steps are v e r y s i m i l a r to the c a u s t i c s t e e p i n g , p r e s s i n g , and shredding stages of the v i s c o s e process, so v i s c o s e p i l o t p l a n t equipment was used i n our work. The shredded c e l l u l o s e c a l c i u m thiocyanate f i b e r s would be fed i n t o an extruder and extruded through a f i l a m e n t d i e i n t o an aqueous bath c o n t a i n i n g c a l c i u m thiocyanate. A Brabender Model 252 Extruder w i t h four h e a t i n g zones, a H a s t a l l o y b a r r e l , and a chrome-plated, uniform taper screw of 25 f l i t e s w i t h a 3:1 compression r a t i o was used i n the l a b s t u d i e s . Two e i g h t - h o l e c i r c u l a r d i e s (3/4 χ 1/8 i n . ) were used; hole diameters were .013 i n . and .006 i n . ; c a p i l l a r y l e n g t h was .010 i n . ; a 200 χ 1400 Dutch Weave s t a i n l e s s s t e e l f i l t e r was p o s i t i o n e d behind the d i e . The micron r a t i n g of the f i l t e r was 12. The i n i t i a l experiments showed that f i b e r s could be ex truded, but that these f i b e r s could not be s t r e t c h e d i n a i r even when the a i r temperature was r a i s e d as h i g h as 180 C, at which p o i n t decomposition of thiocyanate was o c c u r r i n g . Hole blockage was a r e c u r r i n g problem even though the f i l t e r - h o l e s i z e was f a r s m a l l e r than the d i e - h o l e diameter. D i f f i c u l t y was a l s o experienced w i t h feeding the f l o c k e d d i s p e r s i o n to the extruder screw because of blockage at the hopper neck. T h i s problem was solved by c u t t i n g the pulp i n t o 1/4-inch squares a f t e r sheet s t e e p i n g . A problem w i t h v a r i a b l e e x t r u s i o n behavior was f i n a l l y t r a c e d to v a r i a t i o n s i n c a l c i u m thiocyanate composition. C o n s u l t a t i o n s w i t h the manufacturer, Halby Chemical Co., revealed that ammonium thiocyanate was the


3.

MACDONALD

Unconventional Cellulose Solutions


27

S O L V E N T SPUN R A Y O N , MODIFIED C E L L U L O S E FD3ERS

28

most l i k e l y i m p u r i t y , the a d d i t i o n of ammonium thiocyanate to the c a l c i u m thiocyanate s o l u t i o n was examined. About 1% ammonium t h i o c y a n a t e w i t h 52.5% c a l c i u m thiocyanate i s optimum; l e s s than 0.2% ammonium thiocyanate g i v e s an unextrudable d i s p e r s i o n . Table I I i l l u s t r a t e s what seems to be the optimized process. Calcium thiocyanate c o n c e n t r a t i o n s below 45 or 50% do not g i v e a product which can be extruded, and c o n c e n t r a t i o n s of ammonium thiocyanate above 1% cause f i l a m e n t s to s t i c k to godets and guides. An a l k y l a r y l , n o n - i o n i c s u r f a c t a n t was used to a i d p e n e t r a t i o n d u r i n g steeping.. The long steeping time seems unnecessary i f f l o c k i s used r a t h e r than sheets; however, the f l o c k d i d not feed p r o p e r l y as was mentioned p r e v i o u s l y . Our impression i s that f l o c k would very probably feed i n t o a l a r g e e x t r u d e r . Normally, the sheets press e a s i l y , but e x t r u s i o n temperatures above abou ments, apparently due t Table I I Optimum Conditions f o r E x t r u s i o n of the C e l l u l o s e Ca(SCN) D i s p e r s i o n s 2

Pulp:

low v i s c o s i t y , low r e s i n , d i s s o l v i n g grade

Steeping s o l u t i o n : 52.5% Ca(SCN> , 0.3-1.0% NH SCN, 0.1% n o n - i o n i c s u r f a c t a n t , room temperature, 2 days 2

Pulp:

4

S o l u t i o n ( a f t e r p r e s s i n g ) - 1: 2.2-2.8

D i s p e r s i o n form:

1/4-inch

E x t r u s i o n temperature:

squares

110°C

Bath: Water, 25% Ca(SCN)

2>

( a l l 4 zones).

25% NaCl.

Using m a t e r i a l prepared under these optimum s p e c i f i c a t i o n s w i t h the .013-in. hole diameter d i e , f i l a m e n t s could be necked down to .002 i n . dry diameter by speeding up the f i r s t godet. S t r e t c h between the f i r s t and second godets was poor (normally o n l y about 10%) even w i t h 100 C aqueous calcium thiocyanate i n the s t r e t c h bath. With the .006-in. h o l e diameter d i e , f i l a m e n t diameter d i d not decrease p r o p o r t i o n a l l y as s w e l l i n g at the d i e face became much more pronounced. T h i s was i n t e r p r e t e d as showing the need f o r lower v i s c o s i t y and, consequently, a higher pulp: thiocyanate r a t i o . D i l u t i o n of the d i s p e r s i o n w i t h a d d i t i o n a l thiocyanate gave a homogeneous mixture i f done i n a Banbury-type mixer. However, the extruded f i b e r s refused to coagulate p r o p e r l g unless the extruder temperature was reduced to as low as 60 C. F i b e r s t r e n g t h was extremely poor.


3.

MACDONALD


29

F i n a l l y , a d d i t i o n o f DMSO, methanol, ethylene g l y c o l , b o r i c a c i d , EDTA, hydrazine, and hydroxylamine t o the calcium t h i o cyanate s o l u t i o n was evaluated, but s t r e t c h a b i l i t y was not improved. S y n t h e t i c polymers were a l s o were added without benefit. D i s c u s s i o n t h i s f a r has concerned e x t r u d a b i l i t y o f the v a r i o u s d i s p e r s i o n s . D e l i v e r i e s were low (only 30 g/min a t top extruder speed), and s p i n n i n g speeds above 30 m/min were reached o n l y r a r e l y . Most n o t i c e a b l e was an extreme tendency t o s h r i n k upon d r y i n g . S l a c k - d r i e d yarn s h r i n k s 30% o r more; r e s t r a i n e d d r y i n g on cones gave very f u z z y yarns, due t o f i l a m e n t breakage. T y p i c a l yarn p r o p e r t i e s i l l u s t r a t e d i n Table I I I were v e r y poor, w i t h most runs g i v i n g about 0.3 g/den c o n d i t i o n e d t e n a c i t y (although some yarns have given 0.8 g/den) Elongations were l e s s than 10%, w i t n o t i c e a b l e was the tendenc same s t r e s s , t h e r e f o r e the lowest d e n i e r s always gave the s t r o n g est yarn. Yarn o f s t i l l lower d e n i e r , however, could not be spun w i t h a v a i l a b l e e x t r u s i o n d i e s . Because of s w e l l i n g a t the d i e f a c e , i t i s u n l i k e l y that smaller diameter h o l e s , which a r e very d i f f i c u l t t o d r i l l , would help. **ie a l s o be q u i t e t h i c k as pressures o f 500-4000 l b / i n . have been observed. T h e

m u s t

2

Table I I I T y p i c a l Rayon P r o p e r t i e s from the Thiocyanate C e l l u l o s e D i s p e r s i o n s Cond. Ten., g/den

-

Cond. Elong., %

-

Wet Ten.,

-

0.1-0.3

-

10-20%

g/den

Wet Elong, %

0.1-0.8 4-10%

Spinning Experiments U t i l i z i n g C e l l u l o s e D i s s o l v e d i n NO^-DMF Turning now t o the n i t r o g e n dioxide-DMF s o l v e n t , r e s u l t s i n d i c a t e t h a t i n so f a r as s o l u t i o n p r o p e r t i e s and ease o f s o l u t i o n p r e p a r a t i o n a r e concerned, t h i s i s an e x c e l l e n t comb i n a t i o n that produces yarn p r o p e r t i e s b e t t e r than those o f the thiocyanate c e l l u l o s e - s p u n yarn. Our research was prompted by a paper presented by Schweiger (5) a t the TAPPI D i s s o l v i n g Pulp Conference i n A t l a n t a . I n t h i s paper, Schweiger described both the f a c i l e r e a c t i o n o f c e l l u l o s e w i t h n i t r o g e n d i o x i d e i n dimethylformamide s o l u t i o n (NC^-DMF) t o form a c e l l u l o s e t r i n i t r i t e s o l u t i o n , and the almost i n s t a n t a n eous regeneration o f c e l l u l o s e when t h i s s o l u t i o n i s added t o water.



30

CellOH + NO.

^

m

> CellONO

+

HN0

CellOH + HN0

Q

2

Work was i n i t i a t e d to i n v e s t i g a t e the b e l i e f that p r o d u c t i o n of rayon from c e l l u l o s e spun i n NO^-DMF might be f e a s i b l e i f the p l a n t was adjacent t o an ammonium n i t r a t e p l a n t s u p p l y i n g NO^ and ammonia, and which could process the ammonium n i t r a t e by-product. The tonnage of ammonium n i t r a t e would be h i g h - about 3 times more ammonium n i t r a t e would be produced than c e l l u l o s e , A f l o w diagram f o r a h y p o t h e t i c a With t h i s process t r e a t e d w i t h about 2/3 of the r e q u i r e d q u a n t i t y of DMF and, a f t e r about two hours, t h i s would be t r a n s f e r r e d t o a r e a c t o r t o be combined w i t h s i x moles of N0« ( c o r r e c t e d f o r pulp moisture) and the remaining DMF. The s o l u t i o n forms a t room temperature a f t e r 10-30 minutes and would then be f i l t e r e d , w i t h simultaneous d e a e r a t i o n i f a vacuum f i l t e r i s used. Spinning i s i n t o a bath c o n t a i n i n g water, DMF, and ammonium n i t r a t e a t pH 7 to minimize DMF h y d r o l y s i s . DMF i s recovered from excess s p i n bath, e i t h e r by f r a c t i o n a l d i s t i l l a t i o n o r methylene d i c h l o r i d e e x t r a c t i o n , and i s returned t o the DMF r e s e r v o i r . The r e s i d u a l ammonium n i t r a t e s o l u t i o n would be sent f o r recovery of s o l i d ammonium nitrate. Conventional v i s c o s e p r o c e s s i n g equipment was used i n the experiments. The p u l p , u s u a l l y a low v i s c o s i t y , hardwood k r a f t of d i s s o l v i n g grade, was f i r s t f l o c k e d and placed i n a v i s c o s e mixing can w i t h 2/3 of the d e s i r e d DMF. A f t e r two hours, the r e q u i r e d amount o f N0 was added i n the remaining DMF (2.5 p a r t s N0 per p a r t o f c e l l u l o s e was u s u a l l y used) and mixing, w i t h the can p a r t i a l l y submerged i n a 2 C bath, was s t a r t e d . A f t e r 30 minutes (10 minutes seemed s u f f i c i e n t ) , the can was removed from the bath, a standpipe was i n s e r t e d , and the s o l u t i o n was f o r c e d by a p p l i c a t i o n of 50 p s i a i r pressure t o pass through a 6-micron polypropylene f i l t e r i n t o an adjacent, evacuated can. U s u a l l y the vacuum was a p p l i e d f o r about 2 hours a f t e r the end of f i l t r a t i o n t o complete d e a e r a t i o n ; whether t h i s i s necessary i s doubtful. Every time a can was opened and exposed t o the a i r , a few drops o f l i q u i d N 0 were added. T h i s prevents the s k i n formation which occurs r a p i d l y i n a i r , n i t r o g e n , o r even vacuum. Apparentl y , N0« gas e f f e c t i v e l y suppresses r e v e r s a l o f the n i t r i t e formation r e a c t i o n . C e l l u l o s e DP s l o w l y d r i f t s downward on storage of the s o l u t i o n , the best data on t h i s e f f e c t a r e i n c l u d e d i n a paper by Pasteka ( 8 ) . However, many times we have been a b l e t o s p i n s u c c e s s f u l l y a f t e r s t o r i n g the s o l u t i o n o v e r n i g h t . I t i s im2

2

2


3.


MACDONALD

31

ι

2

Mixer

Activation

Flock

NQ

Pulp

DMF

DMF

DMF

Reservoir

Ammonium

DMF

Nitrate

Recovery

Solution

Regenerated Cellulose Fiber

^

Spinning

Filter,

Machine

ueaer a i e

NH

3

Ammonium Nitrate Plant

N0

2

Figure 2: Flow diagram for NO -DMF spinning t

300

I-

250

200 VISCOSITY, b a l l f a l l sec

159

100

50

% CELLULOSE

Figure 3: Viscosity-% cel lulose relationship for highviscosity Kraft pulp in NOtDMF


32


portant t h a t the s o l u t i o n s be stored a t room temperature, o r lower, and that temperatures above 30 C be avoided d u r i n g d i s s o l u t i o n . F r i c t i o n a l heat o c c u r s , and e f f i c i e n t c o o l i n g d u r i n g s t i r r i n g i s necessary. As Schweiger f i r s t demonstrated, n i t r a t i o n occurs due t o the t r a n s e s t e r i f i c a t i o n w i t h by-product n i t r i c a c i d a t temperatures above room temperature. The data i n Table IV show that l e s s n i t r a t i o n occurs when a pulp o f normal moisture i s used i n p l a c e o f a bone dry pulp. Table IV Cellulose-Bound N i t r o g e n a f t e r Regeneration Compared to S o l u t i o n Age and Pulp M o i s t u r e Pulp M o i s t u r e %

% 1

0 7

0.09 0.03

0.50 0.18

S o l u t i o n v i s c o s i t y was r a t h e r h i g h , as i s i l l u s t r a t e d i n F i g u r e 3, where a h i g h v i s c o s i t y pulp was used. Low v i s c o s i t y pulp w i l l cause the curve to s h i f t about 0.5% t o the l e f t . Spinning was through a 720-hole, .0025-in. hole diameter p l a t i n i u m s p i n n e r e t . Hole blockage was never observed. In the next t a b l e s , some s t r e n g t h r e s u l t s are compared w i t h s p i n bath composition. I n Table V, a few baths which d i d not g i v e s u c c e s s f u l s p i n n i n g are d e s c r i b e d . Included here i s methy l e n e d i c h l o r i d e , which i s a low b o i l i n g solvent capable o f e x t r a c t i n g DMF from water. Methylene d i c h l o r i d e b o i l e d a t the spinneret face thereby i n d i c a t i n g a h i g h heat e v o l u t i o n . A l s o weak o r s t r o n g a c i d s , and s t r o n g bases seem harmful, w h i l e DMFNH^NO^ mixtures do not g i v e s u f f i c i e n t l y f a s t c o a g u l a t i o n . Table V Spinbaths found not S u i t a b l e f o r Spinning the C e l l u l o s e - N 0 - DMF S o l u t i o n s 2

1.

Methylene d i c h l o r i d e

2.

Methylene d i c h l o r i d e - DMF - water

3.

A c e t i c a c i d - DMF - water

4.

50 and 75% methanol i n DMF

5.

Rayon-type s p i n baths

6.

Systems cont. NaOH i n s p i n , o r s t r e t c h , baths

7.

DMF - NH,N0

o


3.

33


MACDONALD

The a d d i t i o n o f water i n t o DMF/ammonium n i t r a t e mixtures a l l o w s s p i n n i n g t o proceed normally and yarn p r o p e r t i e s were unchanged f o r R.0, NH,N0 -H 0 and DMF-NH N0 -H 0 spinbaths. The r e s u l t s i n Table V I a r e t y p i c a l : s t r e n g t h values were a b i t below o r d i n a r y rayon and e l o n g a t i o n was low when 3% s o l u t i o n s were spun a t 10 m/min. Low e l o n g a t i o n i n d i c a t e s a yarn which i s too b r i t t l e f o r easy t e x t i l e p r o c e s s i n g . 3

2

4

3

2

Table V I E f f e c t of DMF and Ammonium N i t r a t e i n Aqueous Spin Baths a t 24°C (3% c e l l u l o s e , 10m/min) Cond. Ten. (g/den.

Bath Comp.

w*

Wet

Cond.

Wet

12

H0

2.0

4.9

0.8

33N

2.1

3.4

0.8

6.3

44D,37N

1.8

2.1

0.6

3.8

2

*D = DMF, Ν = ΝΗ^Ν0

3

Table V I I shows a few experiments where 5% s o l u t i o n s were spun a t 30 m/min i n t o s p i n baths c o n t a i n i n g v a r y i n g q u a n t i t i e s of DMF-NH^NO^ and water. Again, the t e n s i l e p r o p e r t i e s were not good. Table V I I E f f e c t o f DMF and Ammonium N i t r a t e i n Aqueous Spin Baths a t 24°C (5% c e l l u l o s e , 30 m/min) Bath Comp. (%)*

Cond. Ten. (g/den.)

Cond. Elong.

Wet Ten. (g/den.)

Wet Elong. (%)

41D, 29N

1.7

2.9

0.7

7.5

30D, 26N

1.7

2.9

0.6

9.2

28D, 19N

1.7

2.7

0.7

7.8

16D,

1.7

3.0

0.7

9.5

UN

*D = DMF, Ν =» NH,N0 4 3 o



34

Use o f d i v a l e n t c a l c i u m and t r i v a l e n t aluminum was evaluated as an a i d to c o a g u l a t i o n ; yarn p r o p e r t i e s were unchanged. Table V I I I g i v e s r e s u l t s f o r 24° and 50°C s p i n bath temperature. The 50°C yarn s t r e n g t h r e s u l t s were very s l i g h t l y b e t t e r than the 24°C r e s u l t s . Table V I I I E f f e c t of Aluminum and 'Calcium N i t r a t e s on Spinning 6% S o l u t i o n s a t 40 m/min Bath Comp.

w*

Wet. Elong· (%)

0.6

8.6

4.9

0.5

11.0

5.0

0.7

9.8 9.8

1.6

4.0

14A, 17N (24°C)

1.7

4.

14C, 17N (24°C)

1.6

7A, 23N (50°C)

2.0

7A, 23N (24°C)

Wet. Ten. (g/den.)

Cond. Elong. (%)

Cond. Ten. (g/den.)

7C, 23N (24°C)

7C, 23N (50°C)

1.8

4.2

0.6

14A, 17N (50°C)

1.7

4.0

0.6

8.9

14C, 17N (50°C)

2.1

5.3

0.8

10.3

C « Ca ( N 0 ) . 4 H 0 ; Ν = ΝΗ,ΝΟ 4 3 Spinning speed, % c e l l u l o s e i n the N0 /DMF s o l u t i o n , and the presence of g l y c e r o l i n the s t r e t c h bath gave the yarn p r o p e r t i e s i l l u s t r a t e d i n Table IX. Water a t 95°C seemed best f o r the s t r e t c h bath i n previous experiments. Spinning speeds were 10-60 meters/ min and the range of 3% t o 7% c e l l u l o s e was examined. *A = A 1 ( N 0 ) . 9 H 0 ; 3

3

3

2

2

2

2

Table IX E f f e c t o f Spinning Speed, G l y c e r o l i n S t r e t c h Bath and % C e l l u l o s e on Spinning i n t o water a t 25 C Stretch Bath Comp.

Cell

Spinning Speed m/min

Yarn P r o p e r t i e s Wet Wet Cond. Cond. Elong. Elong. Ten. Ten. (g/den) (%) g/den (%)

3

H 0, 95°C

10

1.8

3.1

0.78

7.1

3

50% g l y c e r o l 92°C

10

1.8

2.3

0.81

6.3

5

H 0, 95°C

30

1.8

3.7

0.76

7.1

5

H 0, 95°C

40

1.7

4.5

0.72

8.0

0.60

9.5

0.78

6.0

2

2

2

5

H 0, 95°C

60

1.6

6.0

7

H 0, 95°C

30

1.8

3.3

2

2


3.

MACDONALD

35


A sodium a l k y l s u l f o n a t e w e t t i n g agent i n the s p i n bath d i d not improve the r e s u l t s , shown i n Table X; however, higher s p i n bath temperatures (to 50°C) again gave a very s l i g h t s t r e n g t h improvement without improved e l o n g a t i o n . Table X E f f e c t o f Spin Bath Wetting Agent and Aqueous Spin Bath Temperature on A c e t a k r a f t Spinning a t 30 m/min

Cell.

Spin Bath Comp. and Temp.

Cond. Ten. g/den

Yarn P r o p e r t i e s Cond. Wet Elong. Ten. (%) g/den

Wet Elong.

7

H 0,

7

H O + 1% wett i n g agent, 23 C

2.1

4.2

0.80

6.3

7

H 0 + 1% wett i n g agent, 30 C

2.2

4.0

0.88

7.9

7

H 0 + 1% wett i n g agent, 45 C

2.2

4.1

0.94

15.4

3

H 0,

2.2

4.5

0.73

7.0

2

23°C

2

2

2

50°C

Perhaps the most s t r i k i n g t h i n g about these r e s u l t s i s the l a c k o f response to w i d e l y v a r y i n g s p i n b a t h compositions; i n f a c t , the same yarn p r o p e r t i e s were found f o r s p i n n i n g i n t o methanol. T h i s prompted a b r i e f look at f i b e r e l e c t r o n m i c r o graphs. Gas bubbles, probably from decomposition o f n i t r o u s a c i d to n i t r i c o x i d e , NO, have caused f i b e r damage as shown by the presence o f a h o l l o w core i n F i g u r e 4. A l s o , the f i b e r s have stuck together i n d i c a t i n g that the c o a g u l a t i o n r a t e i s too slow. F i g u r e 5 g i v e s a s i d e view i l l u s t r a t i n g a bundle o f f i b e r s where one f i b e r w a l l has been ruptured by a bubble. As nonaqueous s p i n baths were u n s u c c e s s f u l and c o a g u l a t i o n i n presence of water was i n s u f f i c i e n t l y f a s t t o prevent f i b e r s t i c k i n g and n i t r i c oxide damage, i t was concluded that the N0 -DMF s o l v e n t had l i t t l e chance of i n d u s t r i a l success i n the F i g u r e 2 process. 2

Spinning o f C e l l u l o s e i n DMSO - Paraformaldehyde S o l u t i o n s F i b e r s have a l s o been s u c c e s s f u l l y spun from s o l u t i o n s o f c e l l u l o s e i n DMSO-PF. T h i s i n t e r e s t i n g s o l v e n t system was f i r s t described by D.C. Johnson and coworkers (9, 10). C e l l u l o s e i s suspended i n DMSO and the mixture heated t o about 120°C; s o l i d paraformaldehyde (PF) i s then added. Monomeric formaldehyde smoothly forms and r e a c t s w i t h c e l l u l o s e t o form a m e t h y l o l d e r i v a t i v e . T h i s d e r i v a t i v e i s s t a b l e and s o l u b l e i n DMSO.


36

S O L V E N T SPUN R A Y O N , MODIFIED

CELLULOSE

Figure 4: Electron micrograph of NO -DMFfibersshowing hollow cores and adhering fibers t

Figure 5: Electron micrograph of NO -DMFfibersshowing wall rupture by a gas bubble t


FD3ERS

3.

MACDONALD


>

CH 0 + CellOH 2

37

CellOCH OH 2

DMSO Η or ψθΗ~" CellOH I f the s o l u t i o n i s poured i n t o water, c o a g u l a t i o n occurs. Speed o f c o a g u l a t i o n i s too slow f o r s u c c e s s f u l s p i n n i n g i n t o water. The same i s t r u e f o r acetone, benzene, a c e t i c a c i d , acetone-water and a c e t i c acid-water. As m e t h y l o l decomposition i s c a t a l y s e d by e i t h e r strong a c i d o r strong base, a c i d s and bases were evaluated next f i b e r hav bee s u c c e s s f u l l from both a c i d i c and b a s i MC&B paraformaldehyde and reagent grade DMSO were used. The 6% s o l u t i o n s were prepared i n a 4-1 beaker u s i n g the c o n d i t i o n s d e s c r i b e d by Johnson, and were f i l t e r e d i n the equipment p r e v i o u s l y described f o r N0 -DMF s o l u t i o n s . While f i l t r a t i o n and d e a e r a t i o n d i d not cause problems, the PF must be added v e r y s l o w l y d u r i n g s o l u t i o n p r e p a r a t i o n o r the mixture w i l l c o o l due to the endothermic nature o f the process and the s o l u t i o n w i l l not form. F i b e r s p i n n i n g d i d not take p l a c e i n water, i n 0.5% and 1% H S 0 , o r i n 8% and 20% N a S 0 , as shown i n Table X I . 2

9

A

9

A

Table X I Unsuccessful Spin Baths f o r C e l l u l o s e Regeneration from DMSO - PF S o l u t i o n s

0.5% H S0 2 ' o

1% H S 0 2

A

2

A

20% Na S0 8% H S 0 , F i b e r s were spun w i t h d i f f i c u l t y i n 1% NaOH (Table X I I ) . The yarn was v e r y weak between the spinneret and the f i r s t godet, and frequent breaks o c c u r r e d . Yarn t e s t p r o p e r t i e s were v e r y s i m i l a r t o NO^-DMF yarns and b r i t t l e n e s s i s i l l u s t r a t e d by the low percent e l o n g a t i o n s . Spinning was g r e a t l y improved by use of h i g h NaCl i n presence o f NaOH. The yarn was s t i l l b r i t t l e . 2


38


Table X I I S u c c e s s f u l Spin baths and Yarn P r o p e r t i e s f o r C e l l u l o s e Regenerated f o r DMSO-PF S o l u t i o n s

and temperature

Cond. Ten,g/den 2.2

1%, NaOH, 55°

1.9

1%, NaOH, 24% NaCl, 55° 10% H, 4.2%

Z, 15.2% N, 25°C 2.6

10% H, 4.2%

Z, 15.2% N

10% H, 4.2%

Z, 15.2% N

Yarn P r o p e r t i e s Wet Wet Cond. Ten,g/den Elong,% Elong, % 0.8

7.5

5.4

1.0

8.1

4.4

1.2

5.1

4.8

H = H S 0 , Ζ = ZnS0 , Ν = Na S0, 2 4 2

4

4

o

A h i g h a c i d , rayon-type s p i n bath c o n t a i n i n g z i n c s u l f a t e gave good s p i n n i n g w i t h 30-40% s t r e t c h i n a 95 C aqueous s t r e t c h bath. Spinning speed was only 6 meters/min; t h i s was d i c t a t e d by the volume o f s o l u t i o n a v a i l a b l e and there does not seem t o be any reason why s p i n n i n g would not succeed a t higher speeds. Yarn p r o p e r t i e s were s t i l l below commercial a c c e p t a b i l i t y ; however, yarn p r o p e r t i e s d i d vary w i t h s p i n bath temperature and t h i s was g r a t i f y i n g i n view o f the independence of NO^-DMF yarn p r o p e r t i e s w i t h regard t o s p i n n i n g c o n d i t i o n s . Yarn t e n a c i t y f a l l s as temperature i s i n c r e a s e d , w h i l e e l o n g a t i o n i n c r e a s e s w i t h temperature. At 50 C, r e s u l t s were q u i t e c l o s e t o com mercial acceptability. M i c r o s c o p i c examination o f the yarns showed clumps o f mutually adherent f i b e r s i n a l l yarns, except f o r the sample spun i n 70 C a c i d . Thus, stronger c o a g u l a t i o n c o n d i t i o n s are s t r o n g l y i n d i c a t e d . Higher a c i d and z i n c s u l f a t e , o r replacement of z i n c s u l f a t e w i t h the environmentally more d e s i r a b l e aluminum s u l f a t e , should be t r i e d a t 40 o r 50 C. U n f o r t u n a t e l y , t h i s experiment has not yet been c a r r i e d out. CONCLUSIONS (a)

(b)

(c)

I n d u s t r i a l u t i l i z a t i o n f o r rayon production i s d o u b t f u l f o r c e l l u l o s e d i s p e r s e d i n strong aqueous calcium thiocyanate. Cellulose-N0«-DMF s o l u t i o n s are more promising although use i s d o u b t f u l i n a combined ammonium n i t r a t e - r a y o n process. Cellulose-DMSO-PF s o l u t i o n s are a l s o promising; r e a l d i f f i c u l t y can be foreseen i n d e v i s i n g an e f f i c i e n t recovery system f o r DMSO, formaldehyde, and the s p i n bath components.


3.

MACDONALD


LITERATURE CITED 1. 2. 3. 4. 5. 6. 7. 8. 9.

10.

Hata, K. and Yokota, Κ., Sen-i G a k k a i s k i , (1966) 22 ( 2 ) , 96-102. Hata, K. and Yokota, Κ., Sen-i G a k k a i s k i , (1968) 24 ( 9 ) , 415-419. Hata, K. and Yokota, Κ., Sen-i G a k k a i s k i , (1968) 24 ( 9 ) , 420-424. Bechtold, M.F. and Werntz, J.H., U.S. 2,737,437 dated March 6, 1956. Bechtold, M.F. and Werntz, J.H., U.S. 2,737,459 dated March 6, 1956. Bechtold, M.F. and Werntz, J.H., U.S. 2,810,162 dated October 22, 1957. Schweiger, R.G., TAPPI Pasteka, M. and M i s l o v i c o v , , (1974) 8, 107-114. Johnson, D.C., N i c h o l s o n , M.D. and Haigh, F.C., J . A p p l . Polymer Sci., A p p l . Polymer Symposia, (1976) 28, 931-943. Swenson, H.A., J . A p p l . Polymer Sci., A p p l . Polymer Symposia, (1976) 28, 945-952.


4 Production of Rayon from Solutions of Cellulose in N O -DMF 2

4

R.B.HAMMER andA.F.TURBAK ITT Rayonier Inc., Eastern Research Div., Whippany,N.J.07981

A wide range o f wood pulps in v a r i o u s p h y s i c a l forms were found t o d i s s o l v e readily centration of pulp d i s s o l v e of p o l y m e r i z a t i o n . Dimethylformamide was compared t o dimethyl s u l f o x i d e and acetonitrile and was found t o be p r e f e r a b l e o v e r a l l w i t h respect t o s o l v e n t power, viscosity of solutions, stability and recovery. The temperature o f N O a d d i t i o n and the r e s u l t a n t time f o r dissolution were found to be critically r e l a t e d t o ultimate fiber p h y s i c a l and analytical p r o p e r t i e s . F i b e r s w i t h a h i g h wet modulus and intermediate t e n a c i t y were readily produced from proton donor systems i n v o l v i n g h y d r o x y l i c c o a g u l a t i o n baths such as water, a l c o h o l s and glycols. A wide variety of fiber cross s e c t i o n s could be produced and proved t o be r e l a t e d t o the nature o f the regenerant employed during s p i n n i n g . 2

4

Introduction The most w i d e l y used method f o r c o n v e r t i n g wood pulp i n t o regenerated c e l l u l o s e for films and fiber production is the viscose process. However, there a r e s e v e r a l problems a s s o c i a t e d w i t h the v i s c o s e process which do not appear t o be d i m i n i s h i n g even in view o f c u r r e n t developments. There a r e other processes f o r producing regenerated cellulosic products i n c l u d i n g regeneration from cellulose nitrate which is v e r y hazardous, and cuprammonium hydroxide which forms a s o l u b l e c e l l u l o s e complex. However, the p r o d u c t i o n o f cellulosic articles from these processes is minuscule compared t o the v i s c o s e method. There are entirely different c l a s s e s of chemical systems which are non-aqueous which d i s s o l v e cellulose. D i n i t r o g e n tetr o x i d e , N O , has been used as an agent t o make 6-carboxy cellulose in non-polar s o l v e n t s such as chloroform or carbon t e t r a c h l o r i d e . I n 1947-48 W.F. Fowler e t al(1)evaluated the relative s o l v e n t power o f forty-five organic s o l v e n t s w i t h N O , for 2

4

2

4

40


4.

H A M M E R A N D TURBAK

41

Production of Rayon

d i s s o l v i n g c e l l u l o s e . In separate p a t e n t s , H.D. W i l l i a m s (2) and H.L. Hergert Q ) et a l r e p o r t e d dimethyl s u l f o x i d e as a s p e c i f i c p o l a r s o l v e n t f o r use w i t h N 0 to d i s s o l v e c e l l u l o s e . In l a t e r work, the s o l u t i o n p r o p e r t i e s of c e l l u l o s e / N 0 / D M F s o l u t i o n s or c e l l u l o s e p l u s other polymer/N 0 /DMF s o l u t i o n s were examined. For example, 0. Nakao r e p o r t e d g r a f t copolymers prepared from c e l l u l o s e / N 0 s o l u t i o n s . ^ ) L.P. Clermont(5) and R.G. Schweiger(6) r e p o r t e d t h a t c e r t a i n c e l l u l o s e d e r i v a t i v e s could be prepared through the use of c e l l u l o s e / N 0 / D M F s o l u t i o n s . B a s i c chemical and p h y s i c a l s t u d i e s on t h i s system have been r e ported by N.J. Chu(j) and M. Pasteka and D. M i s l o v i c o v a . ( 8 ) The experiments to be d e s c r i b e d were intended to e x p l o r e the use of c e l l u l o s e s o l u t i o n s i n N 0 /DMF or DMSO f o r the p r o d u c t i o n of regenerated f i b e r s as a p o t e n t i a l replacement f o r the v i s c o s e process. 2

4

2

2

2

4

4

4

2

2

4

4

Experimental Experiments were designed to determine the i n f l u e n c e of the form of the pulp and the degree of p o l y m e r i z a t i o n p r i o r t o d i s s o l u t i o n . Although the m a j o r i t y of the s o l u t i o n s were prepared u s i n g Abbe'cut m a t e r i a l , i . e . a h i g h l y powdered, d e f i b e r e d p u l p , the d i s s o l u t i o n process i s not l i m i t e d w i t h r e s p e c t to the degree of p o l y m e r i z a t i o n or the pulp form. A l l s o l u t i o n compositions are g i v e n as weight percents i n the order p u l p / N 0 / s o l v e n t , eg. 8/15/77 r e p r e s e n t s 8$ c e l l u l o s e , 15$ N 0 and 77$ s o l v e n t . A wide v a r i e t y of c e l l u l o s i c pulps were found to d i s s o l v e i n the Ν 0 s o l v e n t system. Both s u l f a t e and s u l f i t e pulps can r e a d i l y be employed and pulps c u r r e n t l y a v a i l a b l e f o r the v i s c o s e process are among those t h a t may be used. In a d d i t i o n , bleached or non-bleached, barked and non-debarked pulp samples a l s o r e a d i l y d i s s o l v e i n t h i s system. These pulps may c o n s i s t of hardwoods, softwoods or mixtures of the two s p e c i e s . A t y p i c a l example of the s o l u t i o n p r e p a r a t i o n procedure i s d e s c r i b e d below. S i l v a n i e r - J , a prehydrolyzed k r a f t pulp of 1050 D.P., a f t e r c o n v e r t i n g t o a l k a l i c e l l u l o s e by methods w e l l known i n the rayon i n d u s t r y , was a l k a l i n e aged t o a D.P. l e v e l of U 5 0 , n e u t r a l i z e d , washed, d r i e d , then e i t h e r f l u f f e d , d i c e d or d e f i b e r e d . An 8/I5/77 c e l l u l o s e / N 0 / D M F s o l u t i o n was prepared by charging I60 p a r t s of t h i s a l k a l i aged p r e h y d r o l y z e d , k r a f t pulp (D.P. U50) and I5U0 p a r t s of dimethylformamide ( DMF) i n t o a twol i t e r f o u r neck r e s i n r e a c t i o n f l a s k equipped w i t h a s t a i n l e s s s t e e l mechanical s t i r r e r , thermometer, and a 250 ml. e q u a l i z i n g pressure a d d i t i o n f u n n e l . The r e s u l t i n g s l u r r y was s t i r r e d and cooled to below +20°C, p r e f e r a b l y between -5°C and +10°C, w h i l e 300 p a r t s of l i q u i d n i t r o g e n t e t r o x i d e ( N 0 ) was added dropwise over ça. 60 minute time p e r i o d . The temperature of the r e s u l t i n g exothermic r e a c t i o n was maintained below 20°C, p r e f e r a b l y i n the range p r e v i o u s l y s p e c i f i e d d u r i n g N 0 a d d i t i o n and f o r the 2

2

4

4

4

2

4

2

2

4

4



42

d u r a t i o n o f the remaining d i s s o l u t i o n process. C e l l u l o s e / N 0 / C H C N s o l u t i o n s o f 8 / 2 0 / 7 2 composition were prepared i n a s i m i l a r manner. C e l l u l o s e / N 0 / D M S 0 s o l u t i o n s o f 8 / I 5 / 7 7 composition were prepared under s i m i l a r c o n d i t i o n s except that the l i q u i d N 0 was f i r s t added t o the DMSO c o n t a i n i n g 1 . 5 p a r t s o f water. The c e l l u l o s e was then added t o the cooled (20°C) N 0 / D M S 0 mixture. A l l s o l u t i o n s were observed m i c r o s c o p i c a l l y t o be f r e e o f g e l s and unreacted f i b e r s . The s o l u t i o n s were f i l t e r e d through a 9 0 mm. diameter n y l o n , i n - l i n e f i l t e r d u r i n g s p i n n i n g . The s o l u t i o n s were deaerated p r i o r t o s p i n n i n g and v i s c o s i t i e s measured by a B r o o k f i e l d Viscometer and found t o be i n the range 2

2

4

3

4

2

2

of 8 , 0 0 0 - 1 6 , 0 0 0 cps.

4

4

at 2 2 ° C

The m a j o r i t y o f the s p i n n i n g t r i a l s were performed on a bench-scale v e r t i c a l s p i n n i n the a p p r o p r i a t e primar f i b e r s passed v e r t i c a l l y t o a primary godet, then through a sec ondary bath t o a secondary godet, whose speed could be a l t e r e d t o produce d e s i r e d s t r e t c h c o n d i t i o n s . S e v e r a l types o f s p i n n e r e t t e s have been used s u c c e s s f u l l y t o s p i n f i b e r s from these s o l v e n t systems. For example, g o l d - p l a t i num, t y p i c a l f o r the v i s c o s e p r o c e s s , s t a i n l e s s - s t e e l , t y p i c a l f o r c e l l u l o s e acetate s p i n n i n g , and g l a s s . The g l a s s spinner e t t e s have a f f o r d e d the best r e s u l t s and are thus p r e f e r r e d s i n c e they are both inexpensive and o f f e r the advantage o f l a r g e r h o l e length/diameter r a t i o s . R e s u l t s and D i s c u s s i o n The d i s s o l u t i o n o f c e l l u l o s e i n N 0 / s o l v e n t systems i s b e l i e v e d t o r e s u l t from the formation o f a c e l l u l o s e n i t r i t e e s t e r and n i t r i c a c i d . (2) Consequently, the r e g e n e r a t i o n o f c e l l u l o s e d u r i n g s p i n n i n g from a true c e l l u l o s e n i t r i t e e s t e r would r e q u i r e a t r a n s n i t r o s a t i o n r e a c t i o n by some agent t o remove the n i t r i t e and provide a hydrogen i o n t o c e l l u l o s e . These r e quirements are met by p r o t o n i c n u c l e o p h i l i c species such as water, a l c o h o l , and o t h e r s . I f the régénérant-coagulant were water o r a l c o h o l then the spent r e g e n e r a t i o n bath would c o n t a i n n i t r o u s a c i d , H N 0 , and/or the a l k y l n i t r i t e , R0N0, i n a d d i t i o n t o the DMF and HNO3 introduced by the c e l l u l o s e s o l u t i o n . Any unreacted N 0 i n the c e l l u l o s e s o l u t i o n would r e s u l t i n the formation o f a d d i t i o n a l H N 0 (or RONO) and H N 0 . Because o f the r a p i d i t y of c o a g u l a t i o n and r e g e n e r a t i o n o f the c e l l u l o s e from the N 0 s o l u t i o n s , b a s i c f i b e r p r o p e r t i e s a r e determined t o a l a r g e extent by the composition o f the regenerat i o n bath and the s p i n n i n g c o n d i t i o n s employed immediately d u r i n g and a f t e r e x t r u s i o n . Therefore, i n i t i a l j e t s t r e t c h i s important i n determining the o v e r a l l f i b e r p h y s i c a l p r o p e r t i e s . As regene r a t i o n i s r e t a r d e d , godet t o godet s t r e t c h becomes more import a n t and more e f f e c t i v e but i s s t i l l l i m i t e d by the i n i t i a l j e t s t r e t c h . For example, r e g e n e r a t i o n can be r e t a r d e d by the 2

4

2

2

4

2

3

2

4


4.

H A M M E R AND

43

Production of RdyOU

TURBAK

a d d i t i o n of bases such as p y r i d i n e to the c e l l u l o s e s o l u t i o n to n e u t r a l i z e the n i t r i c a c i d present. I n t h i s manner, a c e l l u l o s e n i t r i t e f i b e r can be obtained which i n i t i a l l y was observed to r e d i s s o l v e i n dimethylformamide. A wide range of s o l v e n t s may be used to regenerate the s o l u t i o n emerging from the s p i n n e r e t t e . V i r t u a l l y any l i q u i d which i s compatible w i t h and causes e x t r a c t i o n of the organic s o l v e n t and f u r t h e r d e - e s t e r i f i e s the c e l l u l o s e may be employed. A few of the s o l v e n t s which are a p p l i c a b l e to c o a g u l a t i o n i n c l u d e water, a wide range of a l c o h o l s , ethylene g l y c o l and mixtures of these or other p r o t i c s o l v e n t s w i t h dimethylformamide. In some cases, s p i n n i n g and the r e s u l t i n g f i b e r p h y s i c a l p r o p e r t i e s may be aided or improved by the presence of s o l u b l e s a l t s or bases i n the c o a g u l a t i o n bath. However, f o r such a process t o be commercially f e a s i b l e , such composition f i b e r p r o p e r t i e s and th cess f o r the chemicals i n v o l v e d . By v a r y i n g the composition of the r e g e n e r a t i o n or s p i n b a t h , i t i s p o s s i b l e to o b t a i n a wide v a r i e t y of f i b e r p r o p e r t i e s , from those of r e g u l a r rayon s t a p l e to medium-high performance rayon. For example, use of lower molecular weight a l c o h o l s such as methanol or ethanol a f f o r d s f i b e r s w i t h good t e n s i l e p r o p e r t i e s i n c l u d i n g wet modulus. The a d d i t i o n of s o l u b l e bases to such régénérants appears to improve wet s t r e n g t h w h i l e lowering Sg.^ and water r e t e n t i o n v a l u e s . The S g ^ values are an i n d i c a t i o n of a regenerated c e l l u l o s i c f i b e r ' s s o l u b i l i t y i n 6 . 5 $ sodium hydroxide at 20°C. This i s a u s e f u l t e s t f o r determining the p o t e n t i a l r e s i s t a n c e of such f i b e r s or r e s u l t a n t f a b r i c s to a l k a l i n e t r e a t ment such as a l k a l i n e l a u n d e r i n g or m e r c e r i z a t i o n . A c c o r d i n g l y , r e g u l a r v i s c o s e rayon which cannot be mercerized and i s not r e s i s t a n t to a l k a l i n e washing, unless c r o s s l i n k e d , has a r e l a t i v e l y high of from 2 5 - 3 5 $ . On the other hand, the h i g h p e r f o r mance and p o l y n o s i c rayons have s u p e r i o r r e s i s t a n c e to c a u s t i c soda as evidenced by S g ^ values of from 5 - 1 5 $ . We have r e c e n t l y found that i n a d d i t i o n to u s i n g s o l u b l e bases i n the primary r e g e n e r a t i o n b a t h , that t h i s important f i b e r p r o p e r t y can be obtained by c a r e f u l c o n t r o l of the c o n d i t i o n s employed d u r i n g s o l u t i o n p r e p a r a t i o n j l e , the temperature during N 0 a d d i t i o n and the r e s u l t a n t time and temperature f o r t o t a l d i s s o l u t i o n . Our s t u d i e s have d e f i n i t e l y e s t a b l i s h e d t h a t N0 o x i d a t i o n should be minimized so t h a t low temperatures of N 0 a d d i t i o n (below 10°C f o r example w i t h DMF) and short d i s s o l u t i o n times (k hours at l e s s than 20°C) are mandatory i f S g ^ l e v e l s are to be maintained i n a reasonable range ( 1 0 - 3 0 $ ) f o r commerc i a l u s e f u l n e s s of the r e s u l t i n g rayon f i b e r s . I t should be noted f u r t h e r t h a t i n t h i s s p i n n i n g system i t i s r e a d i l y p o s s i b l e to o b t a i n f i b e r s w i t h h i g h wet modulus w i t h out the use of z i n c or other a d d i t i v e s which are r e q u i r e d i n a v i s c o s e s p i n n i n g o p e r a t i o n . In a d d i t i o n , f i b e r s w i t h v e r y f i n e deniers can be r e a d i l y produced, eg. 0 . 5 d e n i e r , w h i l e m a i n t a i n #

e

2

4

2

2

e


4

44


Figure 1.

Fiber cross sections resulting from various coaguhnts (430X)


4.

H A M M E R AND TURBAK

45

Production of Rayon

i n g reasonable t e n s i l e s t r e n g t h . Although optimum c o n d i t i o n s were not e s t a b l i s h e d , s u c c e s s f u l s p i n n i n g t r i a l s were e a s i l y performed at 115 meters/minute; f a s t e r speeds apparently being l i m i t e d o n l y by equipment and p o s s i b l y by l i q u i d f l o w c h a r a c t e r i s t i c s , but not by k i n e t i c s of r e g e n e r a t i o n . V a r i a t i o n s i n the type of régénérants r e s u l t s i n f i b e r s w i t h d i f f e r e n t c r o s s - s e c t i o n s . Water f o r example gives a s e r r a t e d , gear-shaped c r o s s - s e c t i o n ; methanol y i e l d s a c i r c u l a r c r o s s s e c t i o n ; isopropanol a f f o r d s i r r e g u l a r shapes; isoamyl a l c o h o l g i v e s a t r i l o b a l c r o s s - s e c t i o n ; b e n z y l a l c o h o l gives x-shaped s t r u c t u r e s and o c t a n o l a f f o r d s h o l l o w f i b e r s . S e v e r a l examples of these t y p i c a l c r o s s - s e c t i o n s obtained from c e l l u l o s e / N 0 / D M F s o l u t i o n s are i l l u s t r a t e d i n F i g u r e s 1 and 2 along w i t h those of F i b e r kO and r e g u l a r rayon. S i m i l a r f i b e r c r o s s - s e c t i o n s r e s u l t from c e l l u l o s e / ( N 0 ) / D M S Even the type of h o l l o r e g e n e r a t i o n bath appears to be c o n t r o l l a b l e . Filaments w i t h segments resembling bamboo are o b t a i n a b l e as w e l l as those w i t h v a r i o u s lengths of h o l l o w lumens i n the center of the f i b e r . The frequency of the segmentation appears c o n t r o l l a b l e , w i t h segments occurring 5 P i n c h or 25 per i n c h depending upon the combinat i o n of c o n d i t i o n s employed. In Figure h s t r e s s - s t r a i n curves [^conditioned ( c ) and wet f o r an a l k a l i n e methanol-spun f i b e r are shown f o r comparison w i t h r e g u l a r and high-wet modulus rayon. The shape of the wet curve i s of p a r t i c u l a r importance s i n c e the y i e l d i n g p o r t i o n s i s d i f f e r e n t from that of other rayons. Low e l o n g a t i o n i n the f i b e r r e s u l t s i n the steep slope of the c o n d i t i o n e d s t r e s s - s t r a i n curve f o r these f i b e r s and i s an i n d i c a t i o n of s t i f f n e s s . I f the cond i t i o n e d e l o n g a t i o n could be increased to 1 0 - 1 2 $ or the slope manipulated to f a l l between t h a t of high-wet modulus rayon and c o t t o n f o r example, a s u p e r i o r c e l l u l o s e f i b e r may be o b t a i n a b l e . In f a c t , e l o n g a t i o n s approaching 10$ were observed f o r f i b e r s spun from p y r i d i n e - s t a b i l i z e d c e l l u l o s e / N 0 / D M F s o l u t i o n and from runs employing low j e t s t r e t c h . Some t y p i c a l p h y s i c a l p r o p e r t y data are shown i n Table I emp l o y i n g a v a r i e t y of primary bath coagulants f o r the p r o d u c t i o n of rayon f i b e r s from s p i n n i n g s o l u t i o n s of 8/I5/77 c e l l u l o s e / N 0 / D M F composition. The wide range of p r o p e r t i e s obtained by v a r y i n g the chemical composition of the r e g e n e r a t i o n bath a f f o r d s an a p p r e c i a t i o n of the v e r s a t i l i t y of the system. Some p h y s i c a l property data are shown i n Table I I comparing some commercial rayons w i t h those produced from s p i n n i n g 8/15/77 c e l l u l o s e / N 0 / D M F s o l u t i o n s i n t o an isopropanol primary regenera t i o n bath. 2

2

4

4

e r

2

4

2

2

4


4

46


CELLULOSE

FIBERS

Figure 2. Fiber cross sections resulting from various coagulants compared to viscose rayon (430X)


Production of RdiJOn


Figure S. Segmented hollow fiber IC

j i /

STRESS-STRAIN CURVES

I

N 0 /DMF

1

/ / / // // // //

2

4

R E G . RAYON

r

COM.HWM

t

\\ A If• / «

w 1

Ο

/

/

/

' W

•

f

10

20 30 E L O N G A T I O N (%)

Figure 4. Stress-strain curves of regular rayon, commercial high wet modulus rayon and rayon produced by régénérâting cellulose-N 0 -DMF solutions from alkaline methanol t

4

American Chemical Society Library 1155 16th St. N. W. In Solvent Spun Rayon, Modified Cellulose Fibers and Derivatives; Turbak, A.; Washington, D. C. Society: 20036Washington, DC, 1977. ACS Symposium Series; American Chemical


13.2

9Λ

I.30 I.23 I.51

2.hk 2.29 2Λ8

3.^7 3.29

3.5

1.6

1.25

0.87

1.8

Water

Octanol

Methanol/1.5$ A l k o x i d e

Isopropanol/l.5$ Alkoxide

Methanol/10$ A l k o x i d e

1.90

2.13

11.7

1.U6

3.55

0.81

Methanol

8Λ

6-3

6.7

13.0

11.9

18.9

19.9

15.5

13.5

12.9

6.7

O.80

Isopropanol

2.26

3.58

Denier

Coagulant

Elongation, $ Cond. Wet

4

T e n a c i t y , g/d Cond. Wet

2

PROPERTIES OF FIBERS PREPARED FROM AN 8/I5/77 CELLULOSE/N 0 /DMF SOLUTION

TABLE I

1.19

0.98

0Λ9

0.37

0.51

0.73

0.8U

Wet Modulus,

I

i

Ο


3.5-8.Ο

2.0-3.6

High Wet Modulus Rayon

8/15/77 C e l l u l o s e / N 0 /DMF F i b e r

4

3.5-5.0

Intermediate Wet Modulus Rayon

2

1.5-2.8

1.5-2Λ

2.5-6.0

2.5-3.5

1.0-1.8


Regular Rayon

Staple Type

6-19

6-ik

12-19

lU-25

10-15

9-18

18-2U

18-35


FIBER PHYSICAL PROPERTIES

TABLE I I

0.7-1.7

0.7-3.0

ΟΛ5-Ο.60

0.18-0.28

&M

Wet Modulus

20-80

5-10

15-20

20-35

50


Conclusions A wide range of pulps have been found t o r e a d i l y d i s s o l v e i n the N 0 /DMF system i n c l u d i n g non-debarked experimental samples. However, groundwood f u r n i s h , such as i s employed f o r news p r i n t w i l l not d i s s o l v e i n t h i s system. The pulps may be used i n e i t h e r a f l u f f e d , Abbe^cut, shredded or d i c e d sheet form without encountering d i s s o l u t i o n problems. The c o n c e n t r a t i o n of pulp which can be used depends upon the degree of p o l y m e r i z a t i o n . At 1000 D.P., c o n c e n t r a t i o n s up to 3$ can be spun w h i l e a t U00~500 D.P. up t o 8$ s o l u t i o n s were f e a s i b l e , w h i l e a t 300 D.P. up t o 10$ c e l l u l o s e s o l u t i o n s could be r e a d i l y processed. Dimethyl formamide was found t o be p r e f e r a b l e to d i m e t h y l s u l f o x i d e or a c e t o n i t r i l a l l solution properties e s s e n t i a l l y f r e e from g e l s or f i b e r s t h e r e f o r e r e q u i r i n g o n l y a s i n g l e stage p o l i s h i n g f i l t r a t i o n p r i o r t o s p i n n i n g . The temperature of the N 0 a d d i t i o n and the time of d i s s o l u t i o n were found t o be c r i t i c a l l y r e l a t e d t o the f i n a l Sg c f i b e r l e v e l s . For example, by m a i n t a i n i n g the temperature below 20°C, the S6.5 l e v e l can be h e l d i n the 2 7 - 3 0 $ range which i s s i m i l a r t o t h a t of r e g u l a r rayon. C o a g u l a t i o n and r e g e n e r a t i o n of the c e l l u l o s e / N 0 / D M F s o l u t i o n s i s extremely r a p i d i n the presence of proton donor systems. F i b e r s of e x c e l l e n t h i g h wet modulus eg. up to 1 . 7 g/d can be spun w i t h o u t the need f o r s p i n - b a t h a d d i t i v e s . Spinning speeds of 115 meters per minute were achieved employing o n l y a 3 i n c h primary bath c o a g u l a t i o n t r a v e l l e n g t h . No attempts were made t o o p t i m i z e f i b e r p h y s i c a l p r o p e r t i e s a t t h i s h i g h e r s p i n n i n g speed, which was the maximum speed o b t a i n a b l e and was l i m i t e d by the godet s i z e and motor d r i v e u n i t s . Conditioned f i b e r s t r e t c h g e n e r a l l y was between 7 $ and 10$ which i s n o r m a l l y too low f o r p r o c e s s i n g . However, t h i s l e v e l c o u l d be improved by proper c o n t r o l of j e t s t r e t c h t o godet s t r e t c h r a t i o s . F i b e r cross s e c t i o n a l shapes can be c o n t r o l l e d by the use of v a r i o u s molecular weight a l c o h o l s t o g i v e e i t h e r round, s e r r a t e d , "X" or "Y" shapes or even segmented h o l l o w f i b e r s . These f i b e r s d i s p l a y e x c e l l e n t cover power as compared to r e g u l a r HWM rayon i n k n i t s . 2

4

2

4

2

4

Acknowledgements We are g r a t e f u l t o Dr. A r t h u r C. West* who performed much of the i n i t i a l b a s i c r e s e a r c h and e x p e r i m e n t a t i o n i n v o l v e d i n this investigation. * Present Address - 3-M Company, S t . P a u l , Minnesota


4.


Literature

51

Production of Rayon

Cited

1.

Fowler, W. F. and Kenyon, W. O., J. Amer. Chem. Soc., 69

2. 3.

W i l l i a m s , H. D., U.S. Patent No. 3 , 2 3 6 , 6 6 9 ( 1 9 6 6 ) . H e r g e r t , H. L. and Z o p o l i s , P. N., French Patent No.

4.

a)

5.

6.

1636

(1947).

1,469,890

(1967).

Nakao, O. et. al Canadian Patent No. 8 7 6 , 1 4 8

b ) U.S. Patent No. 3 , 6 6 9 , 9 1 6

(1971),

(1972).

Clermont, L. P., (a) Canadian Patent No. 8 9 9 , 5 5 9 ( 1 9 7 2 ) ; (b) Monthly Research Notes, Dept. o f F i s h e r y and F o r e s t r y , Canada 2 6 , No. 6, 58 (1970); ( c )J.P o l y . Sci., 1 0 , 1669 ( 1 9 7 2 ) ; (d) J. Appl. Poly. Sci., 1 8 , 133 (1974). Schweiger, R. G. (a) Chemistry and Industry 296 ( 1 9 6 9 ) ; (b) U.S. Patent No.

2,120,964 (1971).

7. 8. 9·

Chu, Ν. J., Pulp and Paper Research I n s t i t u t e o f Canada, Report No. 42 ( 1 9 7 0 ) . Pasteka, M. and M i s l o v i c o v a , D., C e l l u l o s e Chemistry and Technology 8 , 107 (1974). Portnoy, Ν. Α., Unpublished R e s u l t s .


5 Chemistry of the

Cellulose-N2O4-DMF

Solution:

Recovery and Recycle of Raw Materials NORMAN A. PORTNOY and DAVID P. ANDERSON ITT Rayonier, Inc., Eastern Research Div., Whippany,N.J.07981

The purpose of th tablish a foundation f o r a technically viable recovery and recycle system based on spinning rayon fibers from the cellulose/ N O /DMF s o l u t i o n . Other papers in this symposium d i s c u s s e d solution makeup, s p i n n i n g , and fiber p r o p e r t i e s . The paper presented h e r e , which is d i v i d e d into two parts, attempts t o e x p l a i n some o f the chemistry of dissolution and r e g e n e r a t i o n as well as our efforts in developing a technically f e a s i b l e recovery and recycle system. 2

A.

4

The Chemistry o f The

Cellulose/N O /DMF 2

4

Solution

Introduction When t h e i n v e s t i g a t i o n of this system was initiated, t h e importance of d e l i n e a t i n g t h e exact mode of dissolution o f t h e cellulose in DMF/N O was r e c o g n i z e d . To understand t h e dissolution step and t o p r o p e r l y formulate a recovery and r e c y c l e system, a thorough study o f the chemistry of cellulose in DMF/N O had t o be undertaken. From a theoretical viewpoint, s e v e r a l possibilities as t o the mechanism of cellulose d i s s o l u t i o n in DMF/N O a r e e v i d e n t . The s i m p l e s t would be a r e a c t i o n between the h y d r o x y l groups of cellulose and N O t o form a cellulose nitrite e s t e r and HNO as shown in equation 1 (mechanism 1). This c e l l u l o s e nitrite e s t e r may then be s o l u b l e in DMF. DMF DMF 1 . ) CellOH + N 0 OCellONO + HNO3 >solution. The components o f such a s o l u t i o n would be c e l l u l o s e n i t r i t e , n i t r i c a c i d (HNO3), unreacted N2O4, and DMF. T h i s k i n d of r e a c t i o n between a l c o h o l s and N2O4 i s w e l l known and has been ext e n s i v e l y documented i n the l i t e r a t u r e f o r a wide range of 2

4

2

2

2

4

4

3

2

4

52


4

5.

PORTNOY AND ANDERSON

Cellulose-N0 -DMF Solution t

4

53

a l c o h o l s . Since c e l l u l o s e i s an a l c o h o l i t should r e a c t i n t h e same manner, A second p o s s i b i l i t y i s t h a t a complex, probably of the donor-acceptor type, between c e l l u l o s e and N2O4 forms and t h a t DMF acts as a s o l v e n t f o r t h i s complex as i n equation 2 (mechanism 2) · DMF 2 · ) CellOH + N 0 > CellOH : N 0 > solution 2

4

2

4

In t h i s case the s p i n n i n g s o l u t i o n would c o n t a i n t h e c e l l u l o s e : N2O4 complex, uncomplexed N2O4 and DMF. A t h i r d p o s s i b i l i t y i s t h a t DMF and N2O4 form a donor-acceptor complex i n which c e l l u l o s e i s s o l u b l e as i n equations 3 a and 3b (mechanism 3 ) · eq. 3 a . )

DMF + N2O

eq. 3 b . )

DMF : N C>4 2

+

C e l l O H — > solution

This s o l u t i o n would c o n t a i n unchanged c e l l u l o s e , DMF 1 ^ 0 4 complex and uncomplexed DMF as t h e s o l v e n t . An a d d i t i o n a l p o s s i b i l i t y would be t h a t d i s s o l u t i o n may occur v i a some combination of the above mechanisms. I t f o l l o w s t h a t the mechanism of d i s s o l u t i o n and thus the chemistry of the c e l l u l o s e 1^04:DMF i n t e r a c t i o n s i s v e r y important s i n c e t h i s w i l l determine not only the composition of the s p i n n i n g s o l u t i o n , s p i n n i n g procedures, and f i b e r p r o p e r t i e s , but a l s o the recovery and r e c y c l e process. Since some o f the above mechanisms r e q u i r e complexation between the c e l l u l o s e and N2O4 or between the DMF and N2O4, i t appeared t h a t during s p i n n i n g the c e l l u l o s i c f i b e r s (rayon) might not r e q u i r e a chemical regenerat i n g r e a c t i o n but might be p r e c i p i t a t e d o r coagulated by a nons o l v e n t system. T h i s could be e s p e c i a l l y t r u e f o r mechanism 3 s i n c e i t r e q u i r e s t h a t c e l l u l o s e remain unchanged and be simply s o l v a t e d by a DMF 1 ^ 0 4 complex. However, i f mechanism 1 were o p e r a t i v e , then a t r a n s n i t r o s a t i o n r e a c t i o n such as h y d r o l y s i s or a l c o h o l y s i s would be necessary t o o b t a i n regenerated c e l l u l o s e . One c o n c e i v a b l e advantage of such a system i s the poss i b i l i t y o f c o n t r o l of molecular o r i e n t a t i o n d u r i n g r e g e n e r a t i o n and s p i n n i n g by c o n t r o l of t h e removal of the n i t r i t e groups. Such i n c r e a s e d c o n t r o l would r e s u l t from the p l a s t i c i t y of t h e c e l l u l o s e n i t r i t e d e r i v a t i v e p e r m i t t i n g o r i e n t a t i o n and i s r e s p o n s i b l e f o r t h e l a r g e v a r i e t y of s t r o n g rayon f i b e r s a v a i l a b l e from the v i s c o s e process, i n which case the i n t e r m e d i a t e i s c e l l u l o s e xanthate. By c o n t r a s t , i f c e l l u l o s e i s merely p r e c i p i t a ted or coagulated from a s o l v e n t the p o s s i b i l i t y of t h i s c o n t r o l i s severely l i m i t e d . As a f u r t h e r consequence, the nature of the u l t i m a t e s p i n ning system i s r e l a t e d t o t h e d i s s o l u t i o n mechanism by the a c t u a l composition of t h e cellulose/N204/DMF s o l u t i o n . I f t h e s p i n n i n g s o l u t i o n contained unreacted c e l l u l o s e as i n mechanism 3 ,


54


then a dry s p i n n i n g system might be developed i n which the c e l l u lose/N204/DMF s o l u t i o n i s spun i n t o an evacuated chamber t o r e move the s o l v e n t s and p r e c i p i t a t e the f i l a m e n t s . This would be s i m i l a r t o the process f o r s p i n n i n g c e l l u l o s e d i a c e t a t e from acetone s o l u t i o n . Advantages t o t h i s are the h i g h speeds o f s p i n ning which are p o s s i b l e and the r e l a t i v e s i m p l i c i t y of the r e covery system which would have only t o r e c y c l e the DMF : N 2 O 4 complex. However, i f c e l l u l o s e had t o be regenerated from a c e l l u l o s e d e r i v a t i v e , i n t h i s case a n i t r i t e e s t e r , more complexity would be i n v o l v e d i n recovery and r e c y c l e . As p r e v i o u s l y e x p l a i n e d , r e g e n e r a t i n g c e l l u l o s e during s p i n n i n g from a t r u e c e l l u l o s e n i t r i t e e s t e r would r e q u i r e a t r a n s n i t r o s a t i o n r e a c t i o n by some agent t o remove the n i t r i t l o s e . These requirement such as water, a l c o h o l , o r o t h e r s . I f the regenerant-coagulant were water o r a l c o h o l , then the spent s p i n bath would c o n t a i n n i t r o u s a c i d , H N O 2 , o r the a l k y l n i t r i t e , RONO, i n a d d i t i o n t o the DMF and H N O 3 from the s p i n n i n g s o l u t i o n , eq, 4 . Any unreacted N 2 O 4 i n the s p i n n i n g s o l u t i o n would make a d d i t i o n a l H N O 2 (or RONO) and H N O 3 i n the s p i n bath, eq. 5 . 4. )

5.

CellONO + H 0 (or ROH) regeneration

C e l l OH + HONO (or RONO)

2

) HOH (or ROH)

+ excess N 04-*HONO (or RONO) + 2

HNO3

T o t a l recovery and r e c y c l e , i n t h i s case, would i n v o l v e s p l i t t i n g the s p i n bath i n t o a t l e a s t 4 components and r e c y c l i n g DMF and H 0 ( o r ROH) w h i l e changing RONO (or HONO) and H N O 3 i n t o a form from which N 2 O 4 could be r e a d i l y obtained. Thus, one of the f i r s t questions t o be answered was whether the s p i n n i n g s o l u t i o n contained c e l l u l o s e n i t r i t e . 2

R e s u l t s and D i s c u s s i o n T h i s q u e s t i o n was answered by chemical and s p e c t r a l s t u d i e s . Because o f the h i g h l y complex nature of the s o l u t i o n , simple s t u d i e s using reagents to measure n i t r i t e composition were not p o s s i b l e . The accuracy o f any method using d i a z o t i z i n g reagents or o x i d a t i o n - r e d u c t i o n r e a c t i o n s to measure the c o n c e n t r a t i o n o f H N O 3 o r CellONO would be hampered by the strong o x i d i z i n g a b i l i t y of the excess N 2 O 4 . Studies i n which the s p i n n i n g s o l u t i o n was p r e c i p i t a t e d w i t h water i n a Waring Blender and the r e s u l t a n t c e l l u l o s i c m a t e r i a l then analyzed f o r n i t r o g e n and c a r b o x y l r e s i dues showed t h a t there was no i n c r e a s e i n these over s t a r t i n g p u l p , but there was a s l i g h t l o s s i n D.P. Thus any n i t r i t e d e r i v a t i v e which was being formed d u r i n g d i s s o l u t i o n was not s t a b l e t o c o a g u l a t i o n w i t h water. T h i s s u b s t a n t i a t e d the claims


5.

Cellulose-N O -DM F Solution

PORTNOY A N D ANDERSON

55

4

t

of e a r l i e r workers. I n f r a r e d s t u d i e s were not p e r t i n e n t s i n c e the n i t r i t e (N«0) a b s o r p t i o n occurs a t r*u 6 . Ou which i s i n d i r e c t c o n f l i c t w i t h the amide c a r b o n y l a b s o r p t i o n of DMF so any spect r a l i d e n t i f i c a t i o n on an i n f r a r e d b a s i s would be considered tenuous · Schweiger (1) had reported that a t r u e c e l l u l o s e n i t r i t e e s t e r could be i s o l a t e d from the c e l l u l o s e / N 0 / D M F s o l u t i o n by f i r s t s t a b i l i z i n g the s o l u t i o n w i t h an a c i d scavenger such as p y r i d i n e and then p r e c i p i t a t i n g the n i t r i t e e s t e r by water coagu l a t i o n . These experiments were repeated. P y r i d i n e was added t o the 8/15/77 c e l l u l o s e / N 0 / D M F s o l u t i o n a t a l e v e l of 20% by weight o f the s o l u t i o n and t h i s was spread on a g l a s s p l a t e . The p l a t e was then immersed i n 20% p y r i d i n e / 8 0 % water a t 5°C and an opaque f i l m ( c e l l u l o s e always formed a c l e a r f i l m ) was c o a g u l a t e d This f i l m was s o l u b l e i vents so i t was o b v i o u s l The UV-VIS. spectrum i n the 300 - 450 my r e g i o n of a DMF s o l u t i o n of the r e - d i s s o l v e d f i l m was n e a r l y i d e n t i c a l t o t h a t of i s o p r o p y l - , 1-pentyl- o r c y c l o h e x y l - n i t r i t e which were prepared as model compounds by adding N 0 t o a DMF s o l u t i o n of t h e corresponding a l c o h o l . When s e v e r a l drops o f aqueous H S 0 were added t o the UV c e l l and the s p e c t r a were rescanned, a l l of t h e above, the model a l k y l n i t r i t e s and the r e d i s s o l v e d f i l m , gave e x a c t l y the same spectrum. This new spectrum was i d e n t i c a l t o that o f an a c i d i f i e d DMF s o l u t i o n o f sodium n i t r i t e i n d i c a t i n g t h a t a l l of these compounds, the a l k y l n i t r i t e s and " c e l l u l o s e n i t r i t e " , were r e l e a s i n g n i t r o u s a c i d thus confirming t h a t the new m a t e r i a l d i d c o n t a i n the n i t r i t e moiety. Table I shows the UV-VIS. p o s i t i o n s and i n t e n s i t i e s o f v a r i o u s n i t r i t e m o i e t i e s used f o r comparison purposes i n t h i s s t r u c t u r e p r o o f . Figures 1 and 2 show the UV-VIS. s p e c t r a of DMF s o l u t i o n s of amyl n i t r i t e , " c e l l u l o s e n i t r i t e " , sodium n i t r i t e and sodium n i t r a t e b e f o r e and a f t e r a c i d i f i c a t i o n . When the " c e l l u l o s e n i t r i t e " f i l m was d r i e d , brown gas evolved from the f i l m and i t then became i n s o l u b l e i n those s o l v e n t s i n which i t had p r e v i o u s l y d i s s o l v e d . The i n f r a r e d spectrum of t h i s i n s o l u b l e d r i e d f i l m was i d e n t i c a l t o t h a t of c e l l u l o s e . This s p e c t r a l study r e p r e sents the f i r s t d e f i n i t i v e p r o o f t h a t the m a t e r i a l i s o l a t e d by c o a g u l a t i o n of t h e p y r i d i n e - s t a b i l i z e d c e l l u l o s e / N 2 0 / D M F s o l u t i o n was indeed c e l l u l o s e n i t r i t e . I t was d e s i r a b l e t o have chemical as w e l l as s p e c t r a l i d e n t i f i c a t i o n of the s t r u c t u r e of t h i s new m a t e r i a l . I n t h i s r e gard, a method was developed f o r i s o l a t i n g a s o l i d from the p y r i d i n e - s t a b i l i z e d s o l u t i o n s under anhydrous c o n d i t i o n s . This was accomplished by t h e a d d i t i o n of d i e t h y l ether t o the p y r i dine s t a b i l i z e d c e l l u l o s e / N 0 / D M F s o l u t i o n s causing p r e c i p i t a t i o n of a s o l i d . A d d i t i o n of 1-pentyl a l c o h o l t o the DMF s o l u t i o n of t h i s s o l i d caused p r e c i p i t a t i o n of a w h i t e f i b r o u s m a t e r i a l which was l a t e r i d e n t i f i e d as c e l l u l o s e . D i s t i l l a t i o n 2

2

4

4

2

4

2

4

2

4


4


56

TABLE I Positions and Intensities of N i t r i t e Ultraviolet Absorption Peaks Sample No.

Compound

Major Peaks max (my) 370 67.2 357 78.9 345 67.2 333 46.8 a

Minor Peaks or Shoulders max (my) a 385 32.2 323 30.2

1.

Amyl N i t r i t e

2.

Isopropyl N i t r i t e

373

55.4

385

31.2

3.

Cyclohexyl N i t r i t e

372 360

58.4 57.8

390 348 338

32.4 44.5 29.7

4.

"Cellulose N i t r i t e "

366 353 341

380 331 320

5.

Sodium N i t r i t e

359

25.5

6.

Sodium Nitrate

310

44

7.

Sodium Nitrate with acid added

270

69

389 375 361 349 338

49.0 80.8 72.0 47.6 37.5

8.

1, 3, 4 or 5 with acid added b

a.) b.)

€

β

molar extinction coefficient.

The values for € are from the experiment i n which H2SO4 was added to the sodium n i t r i t e solution.


5.


57

Cellulose-N O DMF Solution t

r

a. NaN02, DMF

Figure 2. Uv-vis spectra of aqueous acidified DMF solu tions of cellONO or AmylONO as well as NaNO and NaNO before and after aque' ous acidification t

400

Λου WAVELENGTH

(mp)

450

s

, Ί . Γ

. !



58

of the supernatant gave a 60% y i e l d of 1-pentyl n i t r i t e which was i d e n t i c a l to commercial m a t e r i a l i n p h y s i c a l and s p e c t r a l properties. Therefore i t was a c e r t a i n t y t h a t the p y r i d i n e - m o d i f i e d cellulose/NÔ^/DMF s o l u t i o n contained c e l l u l o s e n i t r i t e . I t could be argued however, t h a t the p y r i d i n e not only s t a b i l i z e d the c e l l u l o s e n i t r i t e but a l s o c a t a l y z e d the f o r m a t i o n of t h i s s p e c i e s as p y r i d i n e i s w i d e l y used i n s y n t h e t i c chemistry f o r c a t a l y s i s i n d e r i v a t i z i n g a l c o h o l s ( c e l l u l o s e i s an a l c o h o l ) w i t h anhydrides (N2O4 i s an a n h y d r i d e ) . S p e c t r o s c o p i c s t u d i e s on the cellulose/N204/DMF s o l u t i o n d i d not show t h a t the n i t r i t e was p r e s e n t , i n f a c t UV-VIS. s p e c t r a of the s o l u t i o n are almost the same as those of n i t r o u s a c i d . T h i s i s the r e s u l t of the excess N2O4 which has b a s i c a l l the same UV-VIS spectrum as n i t r o u s a c i d probably because group. However, s y n t h e t i c o h o l s , such as c y c l o h e x a n o l or i s o p r o p a n o l r e a c t immediately w i t h DMF s o l u t i o n s of N2O4 a t 5°C i n the absence of p y r i d i n e and s i n c e c e l l u l o s e i s an a l c o h o l , i t i s expected t o r e a c t s i m i l a r l y .

B.

Recovery and Recycle of Raw M a t e r i a l s

Introduction The e n t i r e area of research and development a s s o c i a t e d w i t h the recovery and r e c y c l i n g of process chemicals i s c e n t r a l t o the t e c h n i c a l and commercial success of s p i n n i n g f i b e r s from o r ganic s o l v e n t s . With the chemistry background presented e a r l i e r i t appeared necessary to develop the recovery system based on p r o c e s s i n g the f o l l o w i n g : a. ) Dimethylformamide (DMF) b. ) Coagulant ( e i t h e r an a l c o h o l o r water) c. ) N i t r o g e n T e t r o x i d e (N2O4) 1.

When the coagulant i s water, then n i t r o u s a c i d (HNO2) and n i t r i c a c i d (HNO3) are the p r e c u r s o r s to N2O4 recovery.

2.

When the coagulant i s an a l c o h o l , then the a l c o h o l n i t r i t e (RONO) and HNO3 a r e the p r e c u r s o r s to N2O4 recovery.

An i n i t i a l c o n c e p t u a l i z a t i o n of the recovery and r e c y c l e system i s shown i n F i g u r e 3 which served as a p r e l i m i n a r y s k e t c h of the requirements of recovery and r e c y c l e f o r s p i n n i n g rayon f i b e r s from the cellulose/N2O4/DMF system. T h i s f i g u r e shows that the crude spent s p i n bath, c o n t a i n i n g DMF, HNO3, the coagu-



SPIN B A T H DMF i-PrOH HNO3 i-PrONO

i-PrOH

4

2

HN0 ,HN03

HNO3

HN02

HNO2

HYDROLYSIS

μρΓΟΝΟ

HNO3

S Ε Ρ A R A Τ I Ο Ν

2

N 0

RAYON FIBER

NOf NO? SALTS

Η

NEUTRALIZATION H ^ J P Y R O L Y S I S

t

k

Figure 3. Initial conceptualization of the total recycle and recovery system for spinning rayonfibersfrom CeUOH-N O -DMF solutions

N2O4 HNO3

Solu. M A K E U P l CallONO DMF

DMF

60


l e n t ( e i t h e r HOH o r ROH) and the n l t r o s a t e d coagulant ( e i t h e r HONO o r R0N0) must be separated i n t o f r a c t i o n s o f pure DMF, pure coagulant and the HN0 -HN0 (R0N0) f r a c t i o n s . The DMF must be returned t o the s o l u t i o n makeup, the coagulant t o the s p i n b a t h and the H N O 3 - H N O 2 (R0N0) p o r t i o n of the spent bath must be comb i n e d i n some way f o r c o n v e r s i o n t o N 2 O 4 . I f t h i s i s the o v e r a l l p l a n , then two major areas of r e s e a r c h would be necessary t o answer the f o l l o w i n g two q u e s t i o n s : a.) which methods o f separat i o n would be most e f f e c t i v e f o r the i n i t i a l s e p a r a t i o n o f t h e crude s p i n bath and b.) how can the n i t r i c and n i t r o u s a c i d f r a c t i o n s r e s u l t i n g from c e l l u l o s e d i s s o l u t i o n and r e g e n e r a t i o n be recombined t o form N 2 O 4 . I n a d d i t i o n , i f the n i t r o u s p o r t i o n of the o r i g i n a l N 0 ^ i s i n the a l k y l n i t r i t e form, i . e . because o f an a l c o h o l coagulant-régénérant the method f o c o n v e r t i n HNO3 and R0N0 to N 2 O 4 woul 3

2

2

R e s u l t s and D i s c u s s i o n The recovery and r e c y c l e of N2O4 was s t u d i e d f i r s t . An ext e n s i v e l i t e r a t u r e survey on N 2 O 4 - H N O 3 chemistry uncovered seve r a l commercial processes which i n c l u d e d a step f o r p y r o l y z i n g a metal n i t r a t e s a l t to produce N 2 O 4 i n h i g h y i e l d s . Most of these processes i n v o l v e d decomposing c a l c i u m n i t r a t e i n a CO2 atmosphere (2) o r sodium n i t r a t e i n a CO atmosphere.(3) None of these r e p o r t s mentioned the recovery of N2O4 by p y r o l y z i n g a n i t r i t e s a l t o r a potassium s a l t as an i n d u s t r i a l p r o c e s s . S e v e r a l methods were considered r e l a t i v e t o the conversion of the HNO3 and HNO2 p o r t i o n o f the spent s p i n bath t o a s a l t and r e c o v e r y of t h i s s a l t f o r p y r o l y t i c p r o c e s s i n g . These methods i n c l u d e d : a.) P r e c i p i t a t i o n o f the s a l t - i f the coagulant were aqueous, then the spent s p i n bath c o n t a i n i n g HNO2 and HNO3 c o u l d be n e u t r a l i z e d t o form s a l t s . F o l l o w i n g t h i s , a d d i t i o n of a s u i t a b l e non-solvent such as a l c o h o l c o u l d p r e c i p i t a t e the s a l t s . T h i s presented unique problems s i n c e the s o l u b i l i t y of K N O 3 i s r e l a t i v e l y s m a l l (1.5%) i n M F , but t h a t o f Ca(N0 )2 or NaN03 i s /•^15-20%. I f the s p i n bath contained a l c o h o l as the coagulant then a h y d r o l y s i s s t e p , t o convert R0N0 to HONO, would precede the a c i d n e u t r a l i z a t i o n . However, i n such a non-aqueous b a t h , the p o s s i b i l i t i e s o f u s i n g other water i m m i s c i b l e précipitants such as methylene c h l o r i d e o r ether were r e c o g n i z e d . When s t u d i e s were done, e f f e c t i v e methods o f p r e c i p i t a t i n g K N O 3 and NaNOo but not C a ( N 0 o ) were found as can be seen i n Table I I . 3

2


5.


61

Cellulose-NODMF Solution t r

TABLE I I S o l u b i l i t i e s of N i t r a t e S a l t s i n D M F ^ P r e c i p i t a t i n g Solvent Mixtures ' Salt Left Precipitating % P r e c i p i t a t i n g Solvent* / D i s s o l v e d i n M i x t u r e Pb(N0 ) NaN0 KN0 Solvent Ca(N03) 0

1

e

3

3

3

2

0/1.1

0/14.2

0/18.0

0/130

None ( L i t . ) ( 4 ) 0/1.5

0/15.4

N. A.

N. A.

50/18.0

49/3.3

59.7/4.3

N. D.

N. D.

None (Exp·)

N

15.7/

2°4

0.5

47.5/

1

MeOH

63.4/1.

EtOH

N. D.

i-PrOH

61.5/

0.5

60.3/

1

56.5/18.0

64/

Ether

59.4/

0.5

39.7/

1

61.3/18.0

N. D.

N. D.

N. D.

CH2C1 a) b) c)

2

73/

67/1.2

1

N. A. - not a v a i l a b l e N.D. •» no data obtained N 0 ^ « d i n i t r o g e n t e t r o x i d e , MeOH = methyl a l c o h o l , EtOH = e t h y l a l c o h o l , i-PrOH = i s o p r o p y l a l c o h o l , CH C1 » methylene c h l o r i d e , ether = d i e t h y l e t h e r % P r e c i p i t a t i n g s o l v e n t based on t o t a l mixture g. s a l t / 1 0 0 g DMF 2

2

d) e)

0.5

2

2

b.) D i s t i l l a t i o n of a l l l i q u i d t o leave a s a l t r e s i d u e - i f the coagulant were aqueous, then n e u t r a l i z a t i o n of the a c i d s f o l lowed by d i s t i l l a t i o n t o a s o l i d s a l t r e s i d u e (the p o t e n t i a l f o r d e t o n a t i o n a t t h i s p o i n t due t o the nitrate-DMF mixture was recogn i z e d e a r l y i n our work) would appear t o be v i a b l e . I f the coagul a n t were a l c o h o l , then as s t a t e d above, the h y d r o l y s i s step would precede the n e u t r a l i z a t i o n s t e p . A l t e r n a t e l y , the HNO3 port i o n o f the s p i n bath could be n e u t r a l i z e d p r i o r t o d i s t i l l a t i o n , the s p i n bath d i s t i l l e d t o a s a l t r e s i d u e and the a l c o h o l n i t r i t e p o r t i o n recovered from the d i s t i l l a t i o n , h y d r o l y z e d , n e u t r a l i z e d and then the n i t r i t e s a l t recovered a f t e r l i q u i d s t r i p p i n g . L i t e r a t u r e a v a i l a b l e on the recovery of DMF from aqueous systems i n d i c a t e d that acceptable y i e l d s could be obtained by d i s t i l l a t i o n . (5) The d i s t i n c t d i f f e r e n c e between schemes (a) and (b) was t h a t i n scheme (a) , the DMF would n o t r e q u i r e d i s t i l l a t i o n . H o p e f u l l y t h i s would have l e d t o lower economics f o r scheme (a) than scheme (b).


62

S O L V E N T S P U N R A Y O N , MODIFIED C E L L U L O S E FD3ERS

c.) Countercurrent e x t r a c t i o n of the aqueous-DMF spent s p i n bath - t h i s would o n l y a p p l y f o r aqueous s p i n baths. Commercial methods f o r c o u n t e r c u r r e n t e x t r a c t i o n of DMF from aqueous-DMF s o l u t i o n s were d e s c r i b e d i n d e t a i l i n the l i t e r a t u r e . ( 6 ) A v a r i e t y of e x t r a c t a n t s i n c l u d i n g chlorocarbons and hydrocarbons were e v a l u a t e d . The c o n c l u s i o n of t h i s l i t e r a t u r e study was that methylene c h l o r i d e was the most e f f i c i e n t e x t r a c t a n t and t h a t the process was economically f e a s i b l e when the aqueous-DMF contained l e s s than 10% DMF. R e s u l t s i n t h i s l a b o r a t o r y d i d not show p r o mise p r o b a b l y because the aqueous DMF spent s p i n baths contained a c i d or s a l t components which complicated e x t r a c t i o n . Recovery of the coagulant p o r t i o n of the s p i n b a t h , i . e . water or an a l c o h o l would be, i n a s i n s e , a l i m i t i n g f a c t o r s i n c e , depending on the composition of the s p i n b a t h v e r y l a r g e volumes would be i n v o l v e p l a i n e d . Although som 8/25/67 cellulose/NoO^/DMF s o l u t i o n s , a d e c i s i o n was made, based on comparative s t u d i e s between 8/25/67 and 8/15/77 s p i n n i n g s o l u t i o n s , t o make the d e t a i l e d process e v a l u a t i o n on an 8/15/77 c e l l ulose/N204/DMF s o l u t i o n . T h i s r e q u i r e s t h a t 1.88 l b s . of N 04 and 9.63 l b s . of DMF be r e c y c l e d per 1.00 l b . of processed f i b e r i n a d d i t i o n t o the coagulant p o r t i o n of the s p i n b a t h . For example, i f the s p i n bath were at e q u i l i b r i u m and were 58/31/5/6, i s o p r o p y l a l c o h o l (i-PrONO/DMF/HN0 /isopropyl n i t r i t e (i-0r0N0) then a t o t a l of/-' 28.3 l b s . (9.63 l b s . DMF and 18.64 l b s . of i-PrONO) of l i q u i d would have t o be r e c y c l e d per 1.00 l b . of f i b e r processed. I f the s p i n bath were aqueous-DMF at a l e v e l of 20% H2O then a minimum of 12.0 l b s . of l i q u i d would be r e c y c l e d per 1.00 l b . of processed f i b e r . These represent examples of how the s p i n b a t h composition s e t s a lower l i m i t on the amount of chemic a l s which must be processed. Therefore the economics of a comm e r c i a l process depend g r e a t l y on the s p i n b a t h composition. I n i t i a l s p i n n i n g experiments i n d i c a t e d t h a t alcohol-DMF s p i n baths produced b e t t e r f i b e r s than aqueous-DMF s p i n b a t h s . Pure methyl-, e t h y l - or i s o p r o p y l - a l c o h o l as coagulant-regenerants produced f i b e r s w i t h approximately e q u i v a l e n t p h y s i c a l p r o p e r t i e s . Since methyl n i t r i t e i s a t o x i c gas and e t h y l n i t r i t e has a v e r y low b o i l i n g p o i n t , they are d i f f i c u l t t o handle at an e x p e r i mental l e v e l . However, i s o p r o p y l n i t r i t e (i-PrONO) i s reasona b l y easy t o handle and t h e r e f o r e i-PrOH was chosen as the coa g u l a n t - régénérant f o r d e t a i l e d recovery s t u d i e s . The p h y s i c a l p r o p e r t i e s of f i b e r s coagulated i n alcohol-DMF systems decreased as the l e v e l of DMF i n c r e a s e d , the b e s t f i b e r s having been spun from pure a l c o h o l primary s p i n b a t h s . However, i t was apparent t h a t , f o r economic reasons, some l e v e l of a l c o h o l i n DMF would have to be chosen and the f i b e r p r o p e r t i e s maximized f o r t h i s chosen system. An i-PrOH/DMF r a t i o of 2/1 was chosen and thus when r e c o v e r y s t u d i e s were begun, s y n t h e t i c spent s p i n baths of 2

3



b. )

80.5 95.5

165.2 99.5

78.0 96.7

76.9

164.3

75.4

96.8

41.1

79.1

23.4

18.5

39.8

5.1 11.0

0.0

0.0

2.4

2

H0

39.8

0.0

0.0

0.0

0.0

HNO3 g.

76.9

i-PrONO g.

T h i s 67.Ig. of DMF i s composed of DMF which i s a v a i l a b l e f o r r e c y c l e by simply d i s t i l l i n g the l i q u i d (28.6g.) and DMF which i s bound to the HNO3 and can be recovered i f the complex i s broken by n e u t r a l i z a t i o n .

a. ) T h i s 76.9g. represents 52.7g. i-PrOH

93.4

408.7

s t a r t i n g s p i n bath

% accounted f o r

381.6

totals

0.0

67.1

120.6

bottoms

4

62.5

4.9

32-46/1

3

18.9

i-PrOH

76.4

88.7

25-32/1

2

-

g.

82.9

95.9

r.t./10

1

DMF

3.4

T o t a l Wt. g.

Conditions bp. °C/mm. Hg

F r a c t i o n No.

Recovery of Process Chemicals by Vacuum D i s t i l l a t i o n of the Crude S p i n Bath

TABLE I I I

g.


64

CELLULOSE

FD3ERS

2/1 i-PrOH/DMF i n which Ν 0 was added t o b r i n g the HN0 l e v e l near 3, 5 and 10% were e v a l u a t e d . These s o l u t i o n s were vacuum d i s t i l l e d without n e u t r a l i z a t i o n to e s t a b l i s h e x a c t l y how such an a c i d i c s o l u t i o n would behave i n a recovery process. Table I I I shows a synopsis of the d i s t i l l a t i o n of a s p i n bath a t the 10% a c i d l e v e l . The i-PrONO and i-PrOH d i s t i l l e d together as the p r e s s u r e was reduced. The next f r a c t i o n contained i-PrOH/DMF and q u i t e unexpectedly, no HNO3 was found i n t h i s f r a c t i o n . I n f a c t , pure DMF was obtained as d i s t i l l a t e i n the next f r a c t i o n u n t i l the bottom r e s i d u e contained n e a r l y 1.0 mole HNO3/I.O mole DMF. This r e s i d u e was f r a c t i o n a l l y d i s t i l l e d t o g i v e a c l e a r , c o l o r l e s s , o i l y l i q u i d , bp. 94-95°C/8 mm Hg. The l i q u i d had a d e n s i t y of 1.21 g/ml and contained 47.07% HNO3 ( t i t r a t i o n w i t h standard c a u s t i c ) and 48.98% DM t h e o r e t i c a l values ar 53.68% DMF. Thus, t h i s new m a t e r i a l represents a 1:1 molar mix t u r e o f HNO3 and DMF i n which there i s o b v i o u s l y some i n t e r a c t i o n between the two molecular s p e c i e s , i . e . complexation t o some ex t e n t . T h i s i n t e r a c t i o n i s a l s o suggested by n u c l e a r magnetic resonance (NMR) s t u d i e s which showed a d o w n f i e l d s h i f t o f t h e DMF-aldehyde and N-methyl protons i n the mixture as compared t o these protons i n pure DMF. As these s p e c t r a were taken i n the neat l i q u i d s , no s o l v e n t e f f e c t s could i n t e r f e r e w i t h the r e s u l t s . This d o w n f i e l d s h i f t was a l s o present when the s p e c t r a were taken i n CDCI3/TMS. A t a b u l a t i o n of these s h i f t s a r e shown i n Table I V . 2

4

3

TABLE IV NMR S h i f t s i n DMF and DMF/HNO3 Complex a

Sample

/(ppm)( ->

DMF-HNO3

3.09

3.24

8.28

DMF

2.80

2.98

8.03

0.29

0.26

0.25

a.) Chemical s h i f t s i n ^(ppm) d o w n f i e l d from the i n t e r n a l s t a n dard TMS. The DMF-HNO3 b i n a r y mixture i s i n t r i g u i n g s i n c e i t provides a method of s e p a r a t i n g most of the DMF from the HNO3 even though the b o i l i n g p o i n t of DMF (154°C) i s much g r e a t e r than t h a t of HNO3 (83°C). The d o w n f i e l d chemical s h i f t of the aldehyde and N-methyl resonances i n d i c a t e a decrease i n e l e c t r o n d e n s i t y at



5.

Cellulose-N O DMF t

65

Solution

r

the amide carbon atom which i s c o n s i s t e n t w i t h a weak complexing of the amide and HNO3. Attempts t o d i s s o l v e c e l l u l o s e i n t h i s b i n a r y mixture were u n s u c c e s s f u l . Thus vacuum d i s t i l l a t i o n o f a s y n t h e t i c s p i n bath a t concent r a t i o n s expected i n a commercial process gave s e p a r a t i o n of a l l components except that p o r t i o n of the DMF which was i n v o l v e d i n a DMF/HNO3 b i n a r y mixture. This DMF c o u l d be r e l e a s e d by a d d i t i o n of a base and v a r i o u s bases were s t u d i e d f o r t h i s purpose but those d e r i v e d from c a l c i u m were chosen f o r s e v e r a l reasons as e x p l a i n e d below. Calcium carbonate (CaC03>, c a l c i u m hydroxide (Ca(CH)«) or c a l c i u m oxide (CaO) were used t o r e l e a s e the DMF from t h i s DMF/HNO3 mixture. The r e s u l t a n t c l e a r t h i c k s o l u t i o n was vacuum d i s t i l l e d t o recover the DMF l e a v i n g a c a l c i u m n i t r a t e (Ca(N03) ) r e s i d u e . This s o l i d r e s i d u e gave when p y r o l y z e d Thus, t h i s sequence e s t a b l i s h e t o f r a c t i o n a t e the s p i , , from HN0 and o b t a i n N 0 from the HNO3 p o r t i o n of the bath. The choice of c a l c i u m bases f o r n e u t r a l i z a t i o n r e s u l t s from a study which was done on the s t a b i l i t y of DMF under a c i d i c and b a s i c c o n d i t i o n s . The data c l e a r l y showed that DMF i s reasonably s t a b l e i n the presence of a c i d as long as water i s excluded b u t t h a t dimethylamine (DMA) i s formed by h y d r o l y s i s when water i s present. By c o n t r a s t , DMF decomposed r a p i d l y when NaOH o r KOH was added w i t h no a d d i t i o n a l H 0. When C a ( 0 H ) , CaO or CaC03 was added t o DMF, even w i t h a d d i t i o n a l H 0 , no measurable amount of DMA was formed even on prolonged standing a t room temperature. I n a d d i t i o n , the recovery o f N 0 from C a ( N 0 o ) by p y r o l y s i s i s a commercial process r e l a t e d t o the phosphoric a c i d i n d u s t r y and l i t e r a t u r e references were found t o i n d i c a t e t h a t good y i e l d s of N 0 from p y r o l y s i s of C a ( N 0 3 ) were customary.(2) F o l l o w i n g an extensive l i t e r a t u r e search, a p r o j e c t was e s t a b l i s h e d to study the p r o d u c t i o n of N 0 v i a p y r o l y s i s o f v a r i o u s metal n i t r a t e s and n i t r i t e s . A m u f f l e furnace was modif i e d t o h o l d a p y r o l y s i s tube c o n t a i n i n g the s a l t under study. A s t a i n l e s s s t e e l p y r o l y s i s chamber was b u i l t so t h a t d i f f e r e n t sweep gases could be used t o create the d e s i r e d atmosphere i n the p y r o l y s i s tube and t o sweep the product N2O4 gases i n t o a capt u r i n g s o l u t i o n of 1-pentyl a l c o h o l i n IMF. The amount of N 0 c o u l d then be determined by UV-VIS. a n a l y s i s of the amount of 1 - p e n t y l n i t r i t e formed i n the c a p t u r i n g s o l u t i o n . References i n the l i t e r a t u r e i n d i c a t e d good N 0 y i e l d s could be obtained from C a ( N 0 ) a t 600°C i n a C 0 atmosphere (2) or NaN0 i n a CO atmosphere (5) b u t no data were a v a i l a b l e on the p y r o l y s i s o f KNO3 or n i t r i t e s a l t s . I n a d d i t i o n t o o b t a i n i n g the N 0 y i e l d , i t was necessary t o measure the content of unpyrolyzed n i t r a t e and n i t r i t e i n the p y r o l y s i s s a l t r e s i d u e t o determine the s e l e c t i v i t y of the process. Methods f o r these determinations were developed· 2

3

2

4

2

2

2

2

2

2

4

2

4

2

4

2

2

3

2

2

4

3

2

4


4

66


The expected s a l t m i x t u r e which would be obtained from the recovery process would be an equimolar m i x t u r e o f c a l c i u m n i t r a t e / c a l c i u m n i t r i t e . N i t r i t e s a l t s decompose t o produce one mole of NO and one mole of NO2 per mole of n i t r i t e s a l t thus a d d i t i o n a l o x i d a t i o n i s r e q u i r e d t o o b t a i n N2O4 from t h i s system. Equations 6 and 7 are examples of the c h e m i c a l changes accompanying the r e l e a s e of N2O4 d u r i n g the decomposition of Ca(N0 ) . Although the byproducts v a r y w i t h the d i f f e r e n t sweep gases and s a l t s , the decomposition of c a l c i u m n i t r a t e , Ca(NO^) and c a l c i u m n i t r i t e , Ca(N02>2 i n the presence of CO2 should serve as adequate examples. 3

2

2

6.

Ca(N0 )

2

+ C0 —>CaC0

7.

Ca(N0 )

2

+ C0

3

2

2

3

+ 2N0

2

+ 1/2

0

2

When a m i x t u r e o f n i t r a t e and n i t r i t e i s p y r o l y z e d , 1/2 mole of oxygen i s produced, which i s the r e q u i r e d amount t o convert the NO from n i t r i t e decomposition t o N 2 O / . However, i n the l a b o r a t o r y experiments, oxygen was mixed w i t h the e f f l u e n t gases i n o x i d a t i o n chambers which were p l a c e d b e f o r e the c a p t u r i n g cham bers f o r a l l p y r o l y s i s runs which i n c l u d e d n i t r i t e . This assured the b e s t p o s s i b l e y i e l d s . Y i e l d s of N2O4 r e s u l t i n g from p y r o l y s i s experiments are shown i n Table V. The r e s u l t s i n t h i s t a b l e show t h a t 93% N2O4 y i e l d s can be obtained from the p y r o l y s i s of a 1:1 ( C a ( N 0 ) / C a ( N O o ) m i x t u r e a t 800°C i n a C 0 a t mosphere. I f the HONO o r C a ( N 0 ) 2 could be o x i d i z e d t o H N 0 or C a ( N 0 > 2 , then the ^ 0 , recovery would i n v o l v e the p y r o l y s i s of C a ( N 0 o ) which r o u t i n e l y gave 98% y i e l d s of N 0, i n C 0 or N at 800°C. T h i s p a r t of the i n v e s t i g a t i o n e s t a b l i s h e d a route to N 0^ r e c o v e r y , i . e . by p y r o l y s i s of a C a ( N 0 ) / C a ( N 0 2 ) 2 mixture. S i n c e the Ν2Ο4 which i s produced by t h i s p y r o l y s i s i s a c o r r o s i v e , o x i d i z i n g gas, a s p e c i f i c study was made to determine the requirements f o r c o n s t r u c t i o n m a t e r i a l s f o r the p y r o l y s i s furnace. Conferences w i t h f a c u l t y members a t the Engineering School, Rutgers U n i v e r s i t y , New Brunswick, N.J. r e s u l t e d i n the s u g g e s t i o n t h a t a ceramic m a t e r i a l would be r e q u i r e d f o r the i n s i d e of the f u r n a c e . The m a t e r i a l of p r e f e r e n c e was A l 2 0 which i s f r e q u e n t l y used f o r furnace l i n i n g s . P r o t o t y p e l a b o r a t o r y p y r o l y s i s tubes of A 1 0 were designed and obtained from Duramic P r o d u c t s , Inc. P r e l i m i n a r y p y r o l y s i s data from a l i m i t e d number of experiments u s i n g pure c a l c i u m n i t r a t e i n d i c a t e t h a t the y i e l d s of N2O4 are s i m i l a r t o those obtained when s t a i n l e s s s t e e l tubes were used. One of the important remaining steps was c o n v e r s i o n of i s o p r o p y l n i t r i t e i n t o the c a l c i u m n i t r i t e s a l t f o r p y r o l y s i s . Hy d r o l y s i s of i-Pr0N0 to HN0 ( n i t r o u s a c i d ) and n e u t r a l i z a t i o n of 3

2

2

2

2

3

3

2

2

2

2

s

2

3

2

3

2

3

2


a

l

t


g)

f)

c) d) e)

b)

a)

2

2

3

2

2

3

2

3

2

d

e

2

2

e

e

e

2

2

2

75.3/86.5 67.7/84.8 93.3/100.1 97.8/97.8 76.8/84.6 61.9/68.8 57.8/92.8/-

Carbon Dioxide

2

11

-/-/-

53.1/54.1 28.8/33.9

-/-/-

35.0/58.0 11.9/36.6

Carbôn Monoxide

2

2

2

2

-/-

9.6/63.9 6.0/69.2 38.2/95.2 98.1/98.1 20.1/31.7 28.8/38.5 34.0/78.8/-

2

2

13.9/41.0 26.0/84.4/-

-/-

-/-

-/-

-/-

Air

Nitrogen

b

These results are averages of 2-4 pyrolysis experiments. If the salts were not thoroughly dried, lower N 0^ yields resulted. The sweep gas flow rates were 100 ml./min. Stainless steel (310) pyrolysis chambers were used. Results are expressed as % y i e l d of N 04/total % of the starting salt which i s accounted for by the sum of the N 04 yield plus analysis of the pyrolysis residue. Pyrolysis at 600°C resulted i n very low N2O4 yields. Pyrolysis at 800°C resulted i n very low N 04 yields. The pyrolysis of a n i t r i t e salt produces a mole of NO per mole of N0 . Therefore 0 was mixed at 50 ml./min. with the pyrolysis effluent to oxidize any NO to N 04 for capture. Carbon monoxide can reduce N0 to NO by the equation CO + N0 -•NO + C0 therefore 0 was mixed at 50 ml ./min. with these pyrolysis effluent streams. When these measurements were made, no method of residue analysis was available.

3

2

3

C

NaN0 /800/90 KNOJ800/90 Ca(N0 ) /600/120 Ca(N0 ) /800/90 NaN0 :NaN0 /1000/90 KNO3:KNO /1000/90 » Ca(N0 )2 :Ca(N0 ) /600/120 > 8 Ca(N0 )2 :Ca(N0 ) /800/90 » 8

c

Salt/Temp. °C/Time (min.)

3

a

The Effect of Temperature and Sweep Gas on N2O4 Yields from the Pyrolysis of Nitrate Salts or 1:1 Nitrate/Nitrite Salt Mixtures >

TABLE V

3

3

S*

Ο ?

ΐ s:

ο

I

r

Ο

ο

01


Spin Bath

3

I ο η

t i I I a t

8

D i

£ 2

Kiln

—a—

2

C0

2

2

2

H 0

3

CaC0 |

Ca(N03>2 ]Ca(N0 ^ Neutraliz ation DMF ΗΝΟ^,ΗΝΟο,1 i-PrOH, DMF, i - P r O H

H2O

DMF

DMF

CaO

Cellulose Fiber

i-PrOH

->>

H 0 Cycle (alternate) Η NO 3, H N 0 , DMF

{Hydrolysis

i-PrONO

DMF/HNO3

L

i-PrOH

4

trace DMF

2

Ca2

ι

Pyrolysis

t

k

Figure 4. Final technically proven total recycle and recovery system for spinning rayon fibers from CellOH-N O -DMF solutions

i-PrOH,HN0

i-PrONO,DMF

Solu.

DMF

Ν2θ

5.


Cellulose-N0 -DMF Solution t

4

69

t h i s HONO appeared reasonable. Although t h i s approach was f o l lowed, the problem of e f f i c i e n t c o n v e r s i o n of i-PrONO t o HONO remained one of the weak p o i n t s i n the recovery scheme. A f t e r d e t a i l e d study, i t appeared t h a t the c h o i c e medium f o r the hyd r o l y s i s was the HNO3/DMF obtained as the bottoms f r a c t i o n from d i s t i l l a t i o n o f the crude s p i n b a t h . T h i s was expected s i n c e h y d r o l y s i s i s a c i d c a t a l y z e d . I n a d d i t i o n , the DMF caused the i-PrONO t o be m i s c i b l e w i t h the H2O added f o r h y d r o l y s i s whereas normally i-PrONO and H2O are not m i s c i b l e . The progress i n development of t h i s aspect o f the recovery c y c l e was impeded by one p a r t i c u l a r f a c t o r . A method f o r monit o r i n g e i t h e r the c o n c e n t r a t i o n of i-PrONO o r HNO2 i n the DMF/HNO3/H2O h y d r o l y s i s s o l u t i o n s was not known. The UV-VIS. s p e c t r a of i-PrONO and HNO2 are o v e r l a p p i n g so t h a t t h i s was not a u s e f u l method. A metho n i t r i t e s , ( i s o p r o p y l , amyl s i n c e the n i t r i t e apparently decomposes during chromatography. In fact,_under a l l o f the c o n d i t i o n s attempted, a peak f o r the parent a l c o h o l was observed when the n i t r i t e was i n j e c t e d . I n a d d i t i o n , s e v e r a l peaks, a t t r i b u t a b l e t o n i t r o g e n oxide gases were present i n these chromatograms. The temperature o f the i n j e c t i o n p o r t and the column as w e l l as the gas f l o w r a t e were changed as was the column composition but no s u i t a b l e c o n d i t i o n s were found under which pure n i t r i t e d i d not f u l l y decompose t o i t s parent a l c o h o l . One method f o r a n a l y s i s may be NMR s p e c t r o scopybut t h i s was not r e a d i l y a v a i l a b l e . Thus, the amount of hyd r o l y s i s was c r u d e l y measured by aqueous t i t r a t i o n w i t h standard caustic. M i x t u r e s o f n i t r i t e s , i s o p r o p y l as w e l l as model a l k y l n i t r i t e s , were s t u d i e d i n DMF and H2O w i t h or without a c i d . A m i x t u r e of i-Pr0N0/H20/DMF was s l u r r i e d f o r 15 minutes a t room temperature and then n e u t r a l i z e d w i t h Ca(0H)2 o r CaO. I t was not e f f i c i e n t t o use CaC03. T h i s new mixture was vacuum d i s t i l l e d t o g i v e a powdery r e s i d u e which gave N2O4 on p y r o l y s i s . A d d i t i o n a l experimentation i n d i c a t e d t h a t i t was p o s s i b l e t o r e cover unhydrolyzed n i t r i t e by c a r e f u l f r a c t i o n a l d i s t i l l a t i o n of the n e u t r a l i z e d i s o p r o p y l n i t r i t e h y d r o l y s i s m i x t u r e . A t o t a l recovery of HNO2 (by t i t r a t i o n ) p l u s the recovered unchanged i-PrONO (by d i s t i l l a t i o n ) was 94%, suggesting the p o s s i b l e use of m u l t i p l e h y d r o l y s i s u n i t s . The e n t i r e recovery and r e c y c l e scheme based on t h i s work i s shown i n F i g u r e 4. This i s e s s e n t i a l l y s i m i l a r t o t h a t proposed i n F i g u r e 3 except t h a t a l l o f the loops have been c l o s e d . A r e covery and r e c y c l e scheme such as t h i s should not r e l e a s e any e f f l u e n t t o the environment because i t i s t o t a l l y c y c l i c a l w i t h a l l steps i n c l u d e d i n c l o s e d loops. Conclusions I t has been d e f i n i t i v e l y proven t h a t the m a t e r i a l which i s r e c o v e r a b l e by c o a g u l a t i o n o f a p y r i d i n e s t a b i l i z e d c e l l u l o s e /


70


N2O4/DMF s o l u t i o n i s c e l l u l o s e n i t r i t e . However, although i t seems reasonable t h a t c e l l u l o s e n i t r i t e i s formed i n the absence of p y r i d i n e t h i s f a c t o r does not l i m i t the u t i l i t y o f the p r o posed r e c y c l e and recovery scheme because t h a t scheme i s d i c t a t e d by the s p i n n i n g system which i s r e q u i r e d t o make the most com m e r c i a l l y acceptable rayon f i b e r s . In t h i s case, the s p i n n i n g system of c h o i c e was based on i s o p r o p y l a l c o h o l and t h i s a l c o h o l immediately forms i s o p r o p y l n i t r i t e when i t c o n t a c t s the c e l l u lose/N204/DMF s o l u t i o n i r r e g a r d l e s s of whether the c e l l u l o s e i s complexed or d e r i v a t i z e d . A l l chemical steps r e q u i r e d t o recover and r e c y c l e the DMF, coagulant and N2O4 from the spent s p i n bath have been d e l i n e a t e d and proven to be f e a s i b l e from a t e c h n i c a l s t a n d p o i n t . Abstract The d i s s o l u t i o n of cellulose i n DMF/N O is d i s c u s s e d in terms of t h r e e p o s s i b l e mechanisms, one i n v o l v i n g derivatization of the cellulose and two d e s c r i b i n g dissolution in terms of com f o r m a t i o n . Chemical and s p e c t r a l s t u d i e s on the p y r i d i n e stabilized cellulose/N O /DMF s o l u t i o n s t r o n g l y support the mechanism of derivatization of the cellulose by NO. A total recovery and r e c y c l e scheme has been proposed and proven to be t e c h n i c a l l y f e a s i b l e . This scheme i n v o l v e s separa tion of the crude spent s p i n b a t h , which c o n t a i n s DMF, NO, i-PrOH and i-PrONO, into four major fractions. These are a.) pure i-PrONO, b.) pure i-PrOH, c.) pure DMF and d.) a 1:1 molar DMF/HNO complex. The DMF/HNO complex is used to c a t a l y z e hy drolysis of the i-PrONO to i-PrOH and HNO . T h i s HNO /HNO combination is n e u t r a l i z e d w i t h CaO and the r e s u l t a n t Ca(NO ) / Ca(NO ) is p y r o l y z e d in a CO atmosphere t o recover N O f o r r e c y c l e . Calcium carbonate r e s u l t i n g from the p y r o l y s i s of Ca(NO ) /Ca(NO ) i n CO is converted t o CaO and CO t o continue the cyclical p r o c e s s . 2

2

4

4

2

4

2

3

4

3

2

3

2

3

2

2

3

3

2

2

Literature 1. 2.

3. 4. 5. 6.

2

2

2

2

4

2

Cited

Schweiger, R.G., U.S. P a t e n t No. 3,702,843 (1972). D e l a s s u s , M a r c e l ; Copin, Robert; Hofman, Theophile; S i n n , Robert, S. A f r i c a n Patent No. 68 0155809 (Aug. 1968). CA 70 Ρ 89317z. Industrie-Werke K a r l s r u h e A k t . Ges. German Patent No. 1,014,086 August 22, 1957 CA 53P11412C. Monograph-DMF: A Review of Catalytic Effects and S y n t h e t i c A p p l i c a t i o n s , E . I . duPont de Nemours and Co., Inc., page 3. Monograph-DMF: Recovery and Purification, E . I . duPont de Nemours and Co., I n c . , page 10. Monograph-DMF: Recovery and Purification, E . I . duPont de Nemours and Co., I n c . , page 12.


6 Production of Rayon Fibers from Solutions of Cellulose in

(CH2O)x-DMSO

R. B. HAMMER, A. F. TURBAK, R. E. DAVIES, N. A. PORTNOY ITT Rayonier, Inc., Eastern Research Div., Whippany,N.J.07981

A wide range o f cellulosic t o d i s s o l v e readily a t e l e v a t e d temperatures in a combination o f (CH O)x/DMSO. The c o n c e n t r a t i o n o f pulp d i s s o l v e d was a direct f u n c t i o n o f the degree o f p o l y m e r i z a t i o n . In g e n e r a l , 6/6/88 cellulose/(CH O)x/DMSO s o l u t i o n s were prepared u s i n g pulps o f 400 t o 600 D.P. The s o l u t i o n s were m i c r o s c o p i c a l l y f r e e o f g e l s and undissolved cellulosic fibers. This d i s s o l u t i o n process was found to be very specific t o the combination o f (CH O)x/DMSO. Other analogous aldehydes and p o l a r organic s o l v e n t s failed to afford cellulose s o l u t i o n s . Cellulosic articles such as fibers and films are easily regenerated from the cellulosic s o l u t i o n in the presence o f aqueous s o l u t i o n s having a pH g r e a t e r than seven, of water s o l u b l e nucleophilic compounds such as ammonia, ammonium salts, and s a t u r a t e d amines. S a l t s o f sulfur compounds in which the s u l f u r has a valence of l e s s than six may a l s o be used. F i b e r s o f h i g h wet modulus, intermediate t e n a c i t y and low e l o n g a t i o n were readily produced from r e g e n e r a t i n g systems such as aqueous ammonia, ammonium carbonate, t e t r a m e t h y l ammonium hydroxide, methyl amine, diethyl amine, t r i m e t h y l amine, sodium sulfide, sodium sulfite and sodium thiosulfate. F i b e r s have been spun w i t h c o n d i t i o n e d and wet t e n a c i t i e s as h i g h as 2 . 7 and 1 . 5 g/d r e s p e c t i v e l y w i t h wet modulus o f as h i g h as 1 g/d and s o l u b i l i t y i n 6.5% NaOH as low as 3-15%. 2

2

2

Introduction Today, rayon i s almost u n i v e r s a l l y produced by the v i s c o s e process. However, the h i g h investment costs and p o t e n t i a l m i l l e f f l u e n t p o l l u t i o n problems a s s o c i a t e d w i t h v i s c o s e rayon p l a n t s makes t h i s process i n c r e a s i n g l y l e s s competitive from both an economic and environmental s t a n d p o i n t . There are other processes f o r producing regenerated c e l l u l o s i c products i n c l u d i n g regenera71


72


t i o n from c e l l u l o s e n i t r a t e which i s v e r y hazardous o r from cuprammonium hydroxide. However, the p r o d u c t i o n o f c e l l u l o s i c a r t i c l e s from these processes i s minuscule compared t o that from the v i s c o s e process. A number o f h i g h l y p o l a r , a p r o t i c o r g a n i c s o l v e n t s f o r c e l l u l o s e have been d i s c l o s e d i n the l i t e r a t u r e . Two s o l v e n t s which have r e c e i v e d frequent mention are dimethylformamide (DMF)(^), (it)" ( 8 ) and dimethyl s u l f o x i d e , ( l ) , (2), each i n combination w i t h one or more a d d i t i o n a l compounds such as N 0 ( l ) - ( l ) , S 0 ( 8 ) (2) o r an amine.(10) More r e c e n t l y , DMS0-paraformaldehyde has been reported as a solvent f o r c e l l u l o s e . ( 1 1 ) While there has been much d i s c u s s i o n o f these and other s o l vent systems f o r c e l l u l o s e , the l i t e r a t u r e contains l i t t l e i n formation concerning the r e g e n e r a t i o n o f f i b e r s , f i l m s or other regenerated c e l l u l o s i are almost no data i n t i e s o f f i b e r s spun from an o r g a n i c solvent system. I n so f a r as i s known, no economically a c c e p t a b l e commercial solvent-based processes have as yet been d i s c l o s e d f o r producing f i b e r s or f i l m s w i t h acceptable p r o p e r t i e s . 2

4

2

Experimental Experiments were designed t o determine the i n f l u e n c e of the form of the pulp and the degree of p o l y m e r i z a t i o n p r i o r t o d i s s o l u t i o n . Although the m a j o r i t y of the s o l u t i o n s were prepared u s i n g Abbe'cut m a t e r i a l , i . e . a h i g h l y comminuted, d e f i b e r e d p u l p , the d i s s o l u t i o n process i s not l i m i t e d w i t h r e s p e c t t o the degree of p o l y m e r i z a t i o n or the pulp form. A l l s o l u t i o n compositions are g i v e n as weight percents i n the o r d e r , pulp/(CHgOjx/DMSO e£. 6/6/88 represents 6 $ c e l l u l o s e , 6 $ paraformaldehyde and 88$ s o l v e n t . A t y p i c a l example of the s o l u t i o n p r e p a r a t i o n procedure i s d e s c r i b e d below. S i l v a n i e r - J , a prehydrolyzed k r a f t pulp o f 1050 D.P., a f t e r c o n v e r t i n g t o a l k a l i c e l l u l o s e by methods w e l l known i n the rayon i n d u s t r y , was a l k a l i n e aged t o a D.P. l e v e l o f ^ 5 0 , n e u t r a l i z e d , washed, d r i e d , then e i t h e r f l u f f e d , d i c e d o r d e f i b e r e d . A 6/6/88 cellulose/(CH20)x/DMS0 s o l u t i o n was prepared by charging 120 p a r t s o f a l k a l i aged prehydrolyzed k r a f t pulp (D.P. kô), 120 p a r t s of powdered paraformaldehyde and I760 p a r t s o f DMS0 i n t o a t w o - l i t e r four neck r e s i n r e a c t i o n f l a s k equipped w i t h a s t a i n l e s s - s t e e l mechanical s t i r r e r and thermometer. The r e s u l t i n g s l u r r y was s t i r r e d and heated t o 120°C over a p e r i o d o f one hour. Although d i s s o l u t i o n i s almost complete a t 120°C a f t e r about one hour, the h e a t i n g and s t i r r i n g were continued f o r l ) an a d d i t i o n a l hour a t 120°C o r 2) the l e n g t h o f time r e q u i r e d t o r e move excess formaldehyde. The cellulose/(CHgOjx/DMSO s o l u t i o n s described h e r e i n were o f 6/6/88 composition. By employing low D.P. pulps ie i n the range of 200-UOO D.P. i t i s p o s s i b l e t o prepare DMSO/ÎCHgOjx s o l u t i o n s


6.

H A M M E R ET A L .

Rayon Fibers from Cellulose Solutions

73

c o n t a i n i n g 1 0 - 1 2 $ c e l l u l o s e . S o l u t i o n s c o n t a i n i n g 8-10$ cellu l o s e can be prepared by u s i n g pulps with.D.P. l e v e l s between UOO and 6θΟ but the r e s u l t i n g v i s c o s i t i e s exceed 3 0 , 0 0 0 cps at ambient temperature. A l l the cellulose/(CIôJx/DMSO s o l u t i o n s were observed to be m i c r o s c o p i c a l l y f r e e of g e l s and unreacted f i b e r s . The s o l u t i o n s were deaerated p r i o r to s p i n n i n g and v i s c o s i t i e s measured by a B r o o k f i e l d Viscometer. They were i n the range of from 8 , 0 0 0 2 0 , 0 0 0 cps. at ambient temperatures f o r pulps w i t h 1+00-600 D.P. l e v e l s . The s o l u t i o n s were f i l t e r e d through a 90 mm diameter nylon, i n - l i n e f i l t e r during spinning. Several types of s p i n n e r e t t e s have been used s u c c e s s f u l l y to s p i n f i b e r s from t h i s s o l v e n t system. For example, gold-platinum t y p i c a l f o r the v i s c o s e process, s t a i n l e s s s t e e l t y p i c a l f o r c e l l u l o s e acetate s p i n n i n g p r e f e r r e d s i n c e they ar The m a j o r i t y of the s p i n n i n g t r i a l s were performed u s i n g a bench-scale v e r t i c a l s p i n n i n g u n i t . The s o l u t i o n s were spun i n t o the a p p r o p r i a t e primary r e g e n e r a t i o n bath and the r e s u l t i n g f i b e r tow passed v e r t i c a l l y to a primary g l a s s godet then through a secondary bath to a secondary g l a s s godet whose speed could be a l t e r e d to produce the d e s i r e d s t r e t c h c o n d i t i o n s . Spinning speeds g e n e r a l l y ranged between 10 and 70 meters/ minute but no attempt was made to optimize t h i s c o n d i t i o n or the resulting fiber physical properties. The cellulose/(CH 0)x/DMS0 s o l u t i o n s regenerate r a p i d l y i n aqueous s o l u t i o n s of n u c l e o p h i l i c species which a c t as formalde hyde scavengers. This c l a s s of compounds i n c l u d e s ammonia, ammonium s a l t s , s a t u r a t e d amines and s a l t s of s u l f u r compounds. A l l f i b e r s were processed as s t a p l e by treatment w i t h 6o-70°C water, a 0 . 3 $ aqueous s o l u t i o n of a f i n i s h i n g agent at 50°C, then c e n t r i f u g e d and oven d r i e d at 100-110°C. The f i b e r s were t e s t e d f o r p h y s i c a l p r o p e r t i e s according to the American S o c i e t y of T e s t i n g and M a t e r i a l s standards D-1577-73 and D - 2 1 0 1 2

72.

R e s u l t s and

Discussion

The s o l v e n t combination of (CHgOjx/DMSO w i l l d i s s o l v e a wide range of c e l l u l o s i c pulps i n e i t h e r f l u f f e d , d i c e d or Abbe' cut form. The percent c e l l u l o s e i n the r e s u l t i n g s o l u t i o n s i s de pendent upon the pulp D.P. In g e n e r a l , 6/6/88 c e l l u l o s e / ( C I U 0 ) x / DMS0 spinnable s o l u t i o n s can be prepared from pulps w i t h i n the *Κ)0-6θΟ D.P. range. The pulps may be e i t h e r s u l f a t e or s u l f i t e grades and i n c l u d e many of the pulps t h a t are t y p i c a l l y employed i n the v i s c o s e process. Ground wood i n the form of newsprint d i d not d i s s o l v e i n the paraformaldehyde/DMS0 combination under the c o n d i t i o n s employed. The d i s s o l u t i o n of c e l l u l o s e i n the (CHgOjx/DMSO s o l v e n t system i s b e l i e v e d to r e s u l t from the formation of a hemiacetal


74


of c e l l u l o s e i e m e t h y l o l c e l l u l o s e . ( 1 1 ) The d i s s o l u t i o n o f c e l l u l o s e was found t o be v e r y s p e c i f i c to the combination o f DMSO and paraformaldehyde. Organic solvents analogous t o DMSO such as s u l f o l a n e , s u l f o l e n e o r DMF d i d not cause d i s s o l u t i o n i n the presence o f paraformaldehyde. L i k e w i s e , aldehydes s i m i l a r t o formaldehyde o r paraformaldehyde, f o r example c h l o r a l , acetaldehyde, benzaldehyde, and compounds such as t r i o x a n e , methyl formcel and b u t y l formcel i n the presence o f a c i d c a t a l y s t s d i d not y i e l d c e l l u l o s e s o l u t i o n s i n combination w i t h DMSO. Cellulose/(CHgO)x/DMSO s o l u t i o n s can be r a p i d l y coagulated by employing n u c l e o p h i l i c s p e c i e s which a c t as formaldehydescavenging agents. I n g e n e r a l , these régénérants are aqueous s o l u t i o n s o f water s o l u b l e n u c l e o p h i l i c compounds which have a pH g r e a t e r than seven ammonia, ammonium s a l t s pounds i n which the s u l f u r has a valence o f l e s s than s i x . In the case o f the nitrogenous compounds, the coagulant i s a c t u a l l y ammonia o r an amine, the source o f which may be, i n a d d i t i o n t o ammonia o r the amine i t s e l f , an ammonium s a l t , o r , i n some i n s t a n c e s , a b a s i c amine s a l t . Under the a l k a l i n e c o n d i t i o n s of the r e g e n e r a t i o n s o l u t i o n , ammonium o r amine s a l t s w i l l hydrol y z e t o l i b e r a t e the f r e e base i e ammonia o r the amine, respectively. A p a r t i c u l a r l y u s e f u l nitrogenous compound i s ammonium hydroxide. I f the r e g e n e r a t i o n bath i s aqueous ammonium hydroxi d e , then a f t e r r e g e n e r a t i o n o f a f i b r o u s tow, the spent bath would c o n t a i n water, DMSO, ammonia and hexamethylenetetramine. The l a t t e r compound would r e s u l t from the r e a c t i o n o f ammonia and formaldehyde. Other nitrogenous compounds which possess the r e q u i s i t e n u c l e o p h i l i c , s o l u b i l i t y and pH p r o p e r t i e s are s a l t s o f ammonia and a weak a c i d such as ammonium a c e t a t e , ammonium s u l f i d e , ammonium carbonate and ammonium b i s u l f i t e . Amines which are u s e f u l a r e , i n g e n e r a l , s a t u r a t e d a l i p h a t i c , c y c l o a l i p h a t i c and a l i c y c l i c amines. Aromatic amines and amines o f more than s i x carbon atoms are normally i n s o l u b l e o r o f b o r d e r l i n e s o l u b i l i t y i n water. P a r t i c u l a r l y e f f e c t i v e s u l f u r compounds are sodium s u l f i d e , sodium s u l f i t e and sodium t h i o s u l f a t e . The s u l f a t e s , i n which s u l f u r has a valence o f s i x are not u s e f u l . An amount o f the n u c l e o p h i l i c compound as l i t t l e as 0 . 2 5 $ by weight o f the regenera t i o n s o l u t i o n has been found e f f e c t i v e f o r r e g e n e r a t i o n o f the c e l l u l o s e . The maximum c o n c e n t r a t i o n i s l i m i t e d o n l y by the s o l u b i l i t y o f the compounds i n water. Normally the c o n c e n t r a t i o n w i l l range from 3 - 1 5 $ . V a r i a t i o n s i n the composition o f the r e g e n e r a t i o n or s p i n bath d i d not a l t e r the f i b e r c r o s s - s e c t i o n s . Both the n i t r o genous and s u l f u r c o n t a i n i n g régénérants a f f o r d rayon f i b e r s w i t h c i r c u l a r shapes. R e p r e s e n t a t i v e S h i r l e y c r o s s - s e c t i o n s o f f i b e r s spun from cellulose/(CHg0)xAJMS0 s o l u t i o n s are i l l u s t r a t e d i n


6.

HAMMER ET AL.

75


Figure 1. Cross sections of cellulose-(CH O)xDMSO fibers spun from nitrogenous containing régénérants t

Figure 2. Cross sections of cellulose-( CH O)xDMSO fibers spun from nitrogenous and sulfurcontaining régénérants t



76

F i g u r e s 1 and 2 . The regenerated c e l l u l o s i c f i b e r s produced from some of these nitrogenous o r s u l f u r c o n t a i n i n g compounds a r e f u l l y com parable i n p r o p e r t i e s t o c e l l u l o s i c f i b e r s produced by the v i s cose p r o c e s s . They are p a r t i c u l a r l y o u t s t a n d i n g i n having a v e r y low " S g ^ " . The S g 5 v a l u e s are measurements of regenerated c e l l u l o s i c f i b e r s o l u b i l i t y i n 6 . 5 $ sodium hydroxide a t 20°C. This i s a u s e f u l t e s t f o r determining the p o t e n t i a l r e s i s t a n c e of such f i b e r s or r e s u l t a n t f a b r i c s t o a l k a l i n e treatment such as a l k a l i n e l a u n d e r i n g o r mercer.ization. A c c o r d i n g l y , r e g u l a r v i s cose rayon which cannot be mercerized and i s not r e s i s t a n t t o a l k a l i n e washing (unless c r o s s - l i n k e d ) , has a r e l a t i v e l y h i g h S g ^ of from 2 5 - 3 5 $ . On the other hand, the h i g h performance and p o l y n o s i c rayons have s u p e r i o r r e s i s t a n c e t o c a u s t i c soda as evidenced by Sg c v a l u e 5-15$. from cellulose/(cBLo)x/DMS range o f from 3 - 1 5 $ . I t should be noted here t h a t i n t h i s s p i n n i n g system i t i s r e a d i l y p o s s i b l e t o o b t a i n f i b e r s w i t h h i g h wet modulus w i t h o u t the use of z i n c or other a d d i t i v e s which are r e q u i r e d i n a v i s cose s p i n n i n g o p e r a t i o n . In F i g u r e 3 s t r e s s - s t r a i n curves [[conditioned ( c ) and wet (w)] f o r a sodium s u l f i d e spun f i b e r a r e shown f o r comparison w i t h r e g u l a r rayon and h i g h wet modulus rayon. Some t y p i c a l f i b e r p h y s i c a l p r o p e r t y data are shown i n Table I employing a v a r i e t y of primary r e g e n e r a t i o n baths f o r the p r o #

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FIBER PHYSICAL PROPERTIES

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6.

HAMMER ET AL.


79

a u c t i o n of rayon f i b e r s from s p i n n i n g s o l u t i o n s o f 6/6/88 c e l l u l o s e / (CH2o)x/DMSO composition. The wide range o f p r o p e r t i e s obtained by v a r y i n g the chemical composition of the r e g e n e r a t i o n bath a f f o r d s an a p p r e c i a t i o n of the nature o f the system. Some f i b e r p h y s i c a l p r o p e r t y data are shown i n Table I I comp a r i n g some commercial rayons w i t h those produced from s p i n n i n g 6/6/88 cellulose/(CHgC^x/DMSO s o l u t i o n s i n t o an aqueous k sodium s u l f i d e primary r e g e n e r a t i o n bath. Conclusions A wide range of pulps have been found t o r e a d i l y d i s s o l v e i n the (CHgOjx/DMSO system i n c l u d i n g experimental samples. However, groundwood f u r n i s h , such as i s employed f o r newsprint w i l l not d i s s o l v e i n t h i s system f l u f f e d , Abbe' c u t , shredde t e r i n g d i s s o l u t i o n problems. The c o n c e n t r a t i o n of pulp which can be used depends upon the degree of p o l y m e r i z a t i o n . A t 1000 D.P. up t o 2 $ can be spun w h i l e a t IJOO-500 D.P. up t o 6 $ s o l u t i o n s were f e a s i b l e , and a t 300 D.P. up t o about 10$ c e l l u l o s e s o l u t i o n s could be processed. The r e a c t i o n and d i s s o l u t i o n process was found t o be v e r y s p e c i f i c t o DMSO. Analogous s o l v e n t s were not e f f e c t i v e i n the presence o f paraformaldehyde. S i m i l a r l y , other aldehydes d i d not a f f o r d c e l l u l o s e s o l u t i o n s . The cellulose/(CHgO)x/DMS0 s o l u t i o n s were c l e a r and e s s e n t i a l l y f r e e from g e l s or f i b e r s t h e r e f o r e r e q u i r i n g only a s i n g l e stage p o l i s h i n g f i l t r a t i o n d u r i n g s p i n n i n g . One unique f e a t u r e of these f i b e r s i s the f a c t that they e x h i b i t u n u s u a l l y low S g 5 v a l u e s . Sg.^ values i n a range of 3 - 1 5 $ can r e a d i l y and c o n s i s t e n t l y be obtained. This t e s t i s a measure of a f i b e r or f a b r i c ' s r e s i s t a n c e t o a l k a l i n e treatment and can be r e l a t e d t o l a u n d e r a b i l i t y performance. Coagulation and r e g e n e r a t i o n o f the cellulose/(CHgO)x/DMS0 s o l u t i o n s i s f a i r l y r a p i d i n the presence o f proton donor systems. F i b e r s w i t h good wet moduli can be spun without the need f o r s p i n bath a d d i t i v e s . Conditioned f i b e r e l o n g a t i o n g e n e r a l l y was between U$ and 10$ which i s normally too low f o r p r o c e s s i n g . This l e v e l could be improved somewhat by proper c o n t r o l of j e t s t r e t c h t o godet s t r e t c h r a t i o s . F i b e r c r o s s - s e c t i o n a l shapes could not be cont r o l l e d by the use o f v a r i o u s primary bath régénérants and a l l were c i r c u l a r i n appearance. Comparison o f the o v e r a l l p r o c e s s i n g steps i n v o l v e d i n the DMSO/iCHgOjx s o l v e n t system r e v e a l s some d i s t i n c t i v e advantages over the complicated v i s c o s e process. For example, v i s c o s e proc e s s i n g steps such as s t e e p i n g , p r e s s i n g , a g i n g , x a n t h a t i o n , r i p e n i n g and f i l t r a t i o n may be e l i m i n a t e d or s i m p l i f i e d i n a s o l vent s p i n n i n g system. However, i t should be p o i n t e d out t h a t the c o m m e r c i a l i z a t i o n of any s o l v e n t process f o r rayon p r o d u c t i o n w i l l depend t o a #


80


l a r g e extent on the development o f a s u i t a b l e r e c o v e r y system, i e one t h a t i s t o t a l l y r e c y c l a b l e , economic and n o n - p o l l u t i n g . Literature Cited 1.

Fowler, W. F. and Kenyon, W. O., J . Amer. Chem. Soc., 69

2. 3.

W i l l i a m s , H. D., U.S. Patent No. 3 , 2 3 6 , 6 6 9 ( 1 9 6 6 ) . H e r g e r t , H. L. and Z o p o l i s , P. N., French Patent No. 1 , 4 6 9 ,

1636

890

4.

(1947).

(1967).

Clermont, L. P., (a) Canadian Patent No. 8 9 9 , 5 5 9 ( 1 9 7 2 ) ; (b) Monthly Research Notes, Dept. o f F i s h e r y and F o r e s t r y , Canada 26, No. 6, 58 ( 1 7 9 0 ) ;

( c ) J. P o l y . Sci., 10, 1669 ( 1 9 7 2 ) , (d)

J. A p p l . P o l y . Sci., 1 8 , Schweiger, R. G., (a U.S. Patent No. 3,702,

5. 6. 7. 8. 9·

2,120,964

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(1974).

(1971).

Chu, Ν. J., Pulp and Paper Research I n s t i t u t e o f Canada, Report No. 42 (1970). P a s t e k a , M. and M i s l o v i c o v a , D., C e l l u l o s e Chemistry and Technology 8 , 107 (1974). Hata, K., Yokota, K., J. Sci. Fiber Sci. Techn. Japan 24, 420 (1968).

P h i l i p p , B., S c h l e i c h e r , H., L a s k o w s k i , I., F a s e r f o r s c h Textiltech. 23, 60 (1972). Koura, Α., Scheicher, H., Philipp, B., Faserforsch Textil tech. 23, 128 (1972). 11. Johnson, D. C., N i c h o l s o n , M. D., and Haugh, F. C., General Paper No. 67 E i g h t h C e l l u l o s e Conference May 1 9 - 2 3 , 1 9 7 5 .


7 Cytrel® Tobacco Supplement—A New Dimension in Cigarette Design R. W. GODWIN and C. H. KEITH Celanese Fibers Co., Charlotte,N.C.28232

O v e r the p a s t 25 y e a r s t h e r e h a s b e e n a d r a m a t i c d e c r e a s e i n the d e l i v e r y of t a r , f r o m cigarettes. This continuin m a r k e d i n the p a s t f e w y e a r s w i t h the i n t r o d u c t i o n of a l a r g e n u m b e r o f n e w b r a n d s d e l i v e r i n g b e t w e e n 1 a n d 15 m i l l i g r a m s o f tar. T h e s e r e p r e s e n t a l a r g e c h a n g e f r o m t h e 2 5 to 3 0 m i l l i g r a m b r a n d s that w e r e c o m m o n i n the 1940's a n d 5 0 s . T h e tobacco i n d u s t r y h a s b r o u g h t a b o u t t h i s c h a n g e i n r e s p o n s e to c o n s u m e r demand for "lower delivery" cigarettes. n

!

There a r e a variety of existing techniques which a r e used to d e c r e a s e the s m o k e d e l i v e r y o f c i g a r e t t e s . A m o n g these a r e filtration, porous and/or fast-burning papers, filter ventilation, m o d i f i c a t i o n of the tobacco f i l l e r , a n d changes i n cigarette dimensions. Filtration is most commonly used andgenerally achieves u p to a 5 0 - 6 0 % r e d u c t i o n i n t a r a n d n i c o t i n e d e l i v e r y , b u t i t h a s l i t t l e e f f e c t o n g a s p h a s e c o n s t i t u e n t s {1). Selective filter media s u c h a s c h a r c o a l a r e u s e d i n s o m e b r a n d s to a c h i e v e s i z a b l e r e ductions i n some smoke components, while leaving others relatively unchanged. Porous and/or perforated papers a r e widely used to a c h i e v e 1 0 - 3 0 % r e d u c t i o n s i n b o t h g a s a n d p a r t i c u l a t e p h a s e components. M o r e r e c e n t l y , f i l t e r ventilation b y m e a n s of p e r f o r a t e d t i p p i n g p a p e r s h a s b e e n e m p l o y e d to a c h i e v e a n o t h e r 50 o r m o r e p e r c e n t r e d u c t i o n i n a l l s m o k e c o m p o n e n t s (2). F i n a l l y , changes i n the p a p e r b u r n i n g r a t e , c i g a r e t t e d i m e n s i o n s , a n d the i n c o r p o r a t i o n of expanded tobacco leaf a n d reconstituted tobacco s h e e t h a s b e e n u s e d to c r e a t e f a s t e r b u r n i n g a n d l o w e r p u f f count cigarettes, w h i c h d i r e c t l y translates into l o w e r smoke chemistry.

C y t r e l ® i s a r e g i s t e r e d t r a d e m a r k of the C e l a n e s e C o r p o r a t i o n .

83


84


In g e n e r a l , these techniques a r e u s e d i n c o m b i n a t i o n w i t h e a c h o t h e r to a c h i e v e a l o w e r d e l i v e r y c i g a r e t t e w i t h a d e q u a t e c o n s u m e r a p p e a l . H o w e v e r , e a c h of these e x i s t i n g methods has l i m i t a t i o n s . S o m e w h i c h h a v e b e e n m e n t i o n e d i n c l u d e the a c t i o n of f i l t e r s o n the p a r t i c u l a t e p h a s e of t o b a c c o s m o k e o n l y , a n d the a c r o s s - t h e - b o a r d a c t i o n of v e n t i l a t i o n . B e c a u s e of t h e s e , i t i s d e s i r a b l e to h a v e a d d i t i o n a l t e c h n i q u e s f o r c o n t r o l l i n g t h e d e l i v e r y of v a r i o u s s m o k e c o m p o n e n t s . One s u c h technique, w h i c h has been under development i n o u r l a b o r a t o r i e s f o r a n u m b e r of y e a r s , i s the i n c l u s i o n of t o b a c co s u p p l e m e n t i n a c i g a r e t t e . T h i s m a t e r i a l , w h i c h h a s the t r a d e m a r k e d n a m e C y t r e l , i s a m a n u f a c t u r e d sheet m a t e r i a l of controllable composition w h i c h looks, p r o c e s s e s , and burns like tobacco. It h a s a f u r t h e t a s t e u p o n c o m b u s t i o n , so that b l e n d s of C y t r e l w i t h t o b a c c o taste essentially like a m i l d tobacco. I t i s t h e p u r p o s e o f t h i s p a p e r to to d e s c r i b e t h e p h y s i c a l , c h e m i c a l , a n d s o m e o f t h e p e r t i n e n t b i o l o g i c a l p r o p e r t i e s of this m a t e r i a l . T h e effect of C y t r e l i n c l u sion i n tobacco blends is also described. C y t r e l is e s s e n t i a l l y a f i l l e d f i l m m a t e r i a l , f o r m e d by casti n g a n d d r y i n g a s h e e t f r o m a d o u g h - l i k e m i x t u r e of o r g a n i c b i n d e r s a n d a d d i t i v e s w i t h m i n e r a l f i l l e r s (3). A typical compos i t i o n i s g i v e n i n T a b l e I. T h e f i n i s h e d sheet is cut into o n e - i n c h squares w h i c h are subsequently blended with tobacco and m a n u factured into cigarettes by conventional techniques. F o r the p u r p o s e s of t h i s d i s c u s s i o n , c i g a r e t t e s d e s c r i b e d a r e t y p i c a l of the construction commonly utilized in Great Britain. These cigar e t t e s w e r e 7 2 m i l l i m e t e r s l o n g w i t h a c i r c u m f e r e n c e o f 25 m i l l i m e t e r s a n d w e r e e q u i p p e d w i t h a 16 m i l l i m e t e r , d u a l a c e t a t e p a p e r f i l t e r w i t h a t a r r e m o v a l e f f i c i e n c y o f 4 9 % (4). Cigarette w e i g h t s w e r e h e l d c o n s t a n t a t 0 . 98 g r a m , a n d p r e s s u r e d r o p s r a n g e d f r o m 90 m i l l i m e t e r s o f w a t e r a t a n a i r f l o w o f 1 7 . 5 m i l l i l i t e r s p e r s e c o n d f o r t h e a l l - C y t r e l c i g a r e t t e s to 116 m i l l i m e t e r s f o r the a l l - t o b a c c o c i g a r e t t e s . B l e n d e d c i g a r e t t e s c o n t a i n i n g 10, 20, a n d 50% C y t r e l w e r e a l s o p r e p a r e d , a n d puff c o u n t s l i n e a r l y r a n g i n g f r o m 1 0 . 2 to 5 . 8 u n d e r s t a n d a r d s m o k i n g c o n d i t i o n s w e r e o b t a i n e d a s the p e r c e n t a g e of C y t r e l i n c l u s i o n i n c r e a s e d . This c h a n g e i n puff c o u n t o n l y p a r t i a l l y a c c o u n t s f o r the d e c r e a s e s i n deliveries shown later. If i t w e r e t h e o n l y e f f e c t , t h e e x p e c t e d d e l i v e r i e s f r o m a C y t r e l c i g a r e t t e w o u l d be 57% of those of a tobacco cigarette. S i n c e d e l i v e r i e s i n t h e r a n g e o f 0 to 3 8 % a r e f o u n d , i t i s evident that o t h e r f a c t o r s a r e i n v o l v e d . F r o m l o o k i n g at the c o m p o s i t i o n of the m a t e r i a l , i t i s a p p a r e n t that 70% of C y t r e l c o n s i s t s o f i n c o m b u s t i b l e m a t e r i a l , a n d a m a x i m u m o f 30%


7.

GODWIN AND KEITH

T a b l e I:

85

Cytrel Tobacco Supplement

C o m p o s i t i o n of C y t r e l Amount

Material Binder (sodium carboxymethyl Inorganic fillers/combustion Humectant/plasticizer

19% 71%

cellulose)

modifiers

5%

(glycerol)

3% 2%

Colorants F l a v o r additives

can burn during smoking.

T a k i n g 30% of 57% g i v e s

17%,

which

s h o u l d b e the d e l i v e r y of a n y g i v e n c o m p o n e n t i f no c h a n g e i n combustion

occurs.

Before examining ponents f r o m C y t r e l and tobacco,

i t i s n e c e s s a r y to r e f e r t o

methods

e m p l o y e d a n d the g e n e r a l p a t t e r n of d e l i v e r i e s .

methods

u t i l i z e d a n d the d e l i v e r i e s of 250

the

The

c o m p o u n d s a n d 75

ele-

ments f r o m these cigarettes have been reported i n a s e r i e s papers by V i c k r o y , Mauldin, f o r s c h u n g (4, j>,

6).

a n d A l l e n i n the B e i t r a g e

Briefly recapitulating,

zur

the v o l a t i l e

collection trap,

graphic techniques

w e r e m e a s u r e d by either gas

or specific tests for individual

(e. g . , h y d r o g e n c y a n i d e , ponents are

components

The semi volatile

of 1 3 0 ° C .

These were analyzed by a

chromatography and mass spectrometry.

densed phase components

(i. e.,

specific techniques.

mass spectography

except for m e r c u r y , spectroscopy.

M

tar

1,

and

a substantial l i n e a r d e c r e a s e i n d e l i v e r y as M

Figure 1

w h i c h i s defined as total p a r t i c u l a t e

c o l l e c t e d o n the f i l t e r p a d m i n u s w a t e r a n d n i c o t i n e . f r o m 15.8

to 3 . 6

milligrams/cigarette.

is a s i m i l a r graph for another important smoke

shows matter

It i s

tine i s absent f r o m the C y t r e l f o r m u l a t i o n .

evi-

mixture

Figure 2

component,

I n t h i s c a s e t h e l i n e g o e s to z e r o f o r 1 0 0 % C y t r e l ,

characteristic

mea-

2,

almost

dent that t h e r e i s m o r e t h a n a f o u r f o l d d e c r e a s e i n this of m a t e r i a l s

and

spark

which was

Figures

the a m o u n t o f C y t r e l i n the b l e n d i s i n c r e a s e d . the d e c l i n e i n

con-

collection

chromatographic

3 i l l u s t r a t e the g e n e r a l d e l i v e r y p a t t e r n o b s e r v e d f o r every component,

combina-

The elements were measured by

s u r e d by a t o m i c f l o u r e s c e n c e

tine.

com-

The

those r e m a i n i n g o n the

pad) w e r e m e a s u r e d b y a v a r i e t y of gas source

fiber

chromato-

t h o s e w h i c h c a n b e d i s t i l l e d f r o m the c o l l e c t i o n p a d

at a t e m p e r a t u r e t i o n of gas

nitric oxide).

Tabak-

smoke

c o m p o n e n t s , w h i c h a r e t h o s e w h i c h p a s s t h r o u g h the g l a s s smoke

of

This pattern

of a n u m b e r of n i t r o g e n - c o n t a i n i n g

smoke

t u e n t s b e c a u s e of the r a t h e r l o w n i t r o g e n c o n t e n t of

as is

consti-

Cytrel.


niconico-


0 100

50 50

CELLULOSE

100 % C y t r e l 0 % Tobacco

Figure 1. Tar delivery

Φ

Figure 2. Nicotine delivery


FIBERS

7.

GODWIN A N D K E I T H


87

F i g u r e 3 shows a s i m i l a r d e l i v e r y p a t t e r n f o r a n i m p o r t a n t gas phase constituent, carbon monoxide. In F i g u r e 4 w e h a v e a n e x a m p l e of o n e of the r a r e i n s t a n c e s where a different pattern is o b s e r v e d . In this case, g l y c e r o l i n c r e a s e s l i n e a r l y a s the a m o u n t of C y t r e l i n the b l e n d i s i n c r e a s e d , g o i n g f r o m z e r o i n t h e u n c a s e d t o b a c c o c i g a r e t t e to 2 . 1 m i l l i g r a m s i n the 100% C y t r e l c i g a r e t t e . In c a s e d cigarettes (such as those u s e d i n the U n i t e d States) w h e r e g l y c e r o l i s c o m m o n l y a d d e d a s a h u m e c t a n t , t h i s c h a n g e i s n o t n e a r l y s o m a r k e d . It i s k n o w n that g l y c e r o l i s d i s t i l l e d i n t o the s m o k e s t r e a m a s a C y t r e l c i g a r e t t e c o m b u s t s , a n d c o m p r i s e s a b o u t 58% of the t a r c o l l e c t e d . O n l y two o t h e r c o m p o u n d s of the 250 e x a m i n e d s h o w a n i n c r e a s e i n d e l i v e r y a s the C y t r e l content i n the b l e n d i s i n c r e a s e d . These a r e : (1) h y d r o g e n s u l f i d e 55 m i c r o g r a m s / c i g a r e t t e , a n d (2) a m m o n i a , w h i c h r e m a i n s c o n s t a n t a t 2 0 - 2 2 m i c r o g r a m s / c i g a r e t t e u p to a 5 0 % b l e n d i n c l u s i o n o f C y t r e l , b u t t h e n i n c r e a s e s to 50 m i c r o g r a m s / c i g a r e t t e f o r a n a l l - C y t r e l cigarette. T h e s e m a t e r i a l s a r e k n o w n to b e d e r i v e d f r o m r e s i d u a l s u l f u r i n the c o l o r a n t u s e d a n d d e c o m p o s i t i o n of a n i t r o g e n e o u s f l a v o r a d d i t i v e , r e s p e c t i v e l y . A m o n g the e l e m e n t s , a l l b u t s o d i u m m a r k e d l y d e c r e a s e a s the C y t r e l c o n t e n t of the b l e n d i s i n c r e a s e d . S o d i u m , w h i c h c a n be d e r i v e d f r o m the s o d i u m c a r b o x y m e t h y l c e l l u l o s e b i n d e r , shows as e r r a t i c i n c r e a s e w i t h i n c r e a s i n g C y t r e l content; but this i s not n e a r l y as m a r k e d as the d e c r e a s e i n p o t a s s i u m , w h i c h i s a m a j o r e l e m e n t i n t o b a c co. A s i n d i c a t e d i n the p r e v i o u s d i s c u s s i o n , a c o m p a r i s o n o f s m o k e c o m p o n e n t d e l i v e r i e s c a n b e s t be done c o n s i d e r i n g the c o m p o s i t i o n s of C y t r e l a n d t o b a c c o . It t h e r e f o r e i s o f i n t e r e s t to e x a m i n e the r e l a t i v e d e l i v e r i e s of a n u m b e r of s m o k e c o m p o n e n t s to s e e i f t h e o v e r a l l c o m b u s t i o n p r o c e s s c a n b e b e t t e r u n d e r s t o o d . F r o m the d i f f e r e n c e s i n p u f f c o u n t s a n d the i n o r g a n i c c o n t e n t of C y t r e l , i t i s e x p e c t e d that the C y t r e l c i g a r e t t e s h o u l d d e l i v e r 17% of the a m o u n t of a n y c o m p o n e n t i n t o b a c c o s m o k e i f a l l o t h e r f a c t o r s w e r e e q u a l . I n T a b l e II the r e l a t i v e d e l i v e r i e s of g a s e s a n d v a p o r p h a s e c o m p o n e n t s a r e l i s t e d a s c a l c u l a t e d f r o m the V i c k r o y d a t a (4). F o r m o s t of t h e s e c o m p o n e n t s , the d e l i v e r i e s a r e n e a r o r b e l o w the e x p e c t e d 17% d e l i v e r y ( w i t h the e x c e p t i o n s p r e viously noted for a m m o n i a and hydrogen sulfide). The l o w levels of a l k a n e s , a l k e n e s , b e n z e n e , and toluene i n C y t r e l s m o k e r e f l e c t the a b s e n c e o f s a t u r a t e d h y d r o c a r b o n s s u c h a s t o b a c c o waxes in Cytrel. T h e r e l a t i v e l y h i g h e r l e v e l s of a l k y n e s , p r i n c i p a l l y a c e t y l e n e , suggest that f r e e r a d i c a l r e a c t i o n s a r e o c c u r r i n g i n the p y r o l y s i s p r o c e s s . The v e r y l o w l e v e l s of a l c o h o l s , f u r a n s ,


88


Figurée. Glycerol delivery


7.

GODWIN A N D KEITH

Table

89


II: R e l a t i v e D e l i v e r i e s o f V a p o r P h a s e Number

Delivery

Delivery

f r o m Tobacco f r o m C y t r e l

of Material

Components

Compounds

(pg/cig)

(ug/cig)

Relat i v e (%)

Hydrocarbons Cj-C^

alkanes

6

2165

312

C i - C

alkenes

10

1106

alkynes

2

169 18

D

14.4 15.3 37. 5

Benzene

1

48 104

Toluene

1 2

163 560

12 < 4

2

164

48

29.3

5

1219 287

238

19.5 10. 1

C1-C5

Methanol and ethanol Saturated

0.7

aldehydes

(C -C ) Unsaturated 2

12. 5 7.4

13

5

aldehydes

(C3-C4) Ketones Furans

(C3-C5)

3 4

(C4-C6)

Nitroles

(C2-C4)

29 8. 0

7.8

13. 1

W i t h t h i s e x t e n s i v e b a c k g r o u n d of i m p r o v e m e n t s i n the chemic a l and b i o l o g i c a l p r o p e r t i e s of C y t r e l s m o k e , i t i s of i n t e r e s t to e s t i m a t e what C y t r e l i n c l u s i o n c o u l d do f o r e x i s t i n g types of c i g a -


94


rettes. In this country the most popular brands of cigarettes have a tar delivery of around 17 m i l l i g r a m s , a nicotine delivery of about 1. 2 m i l l i g r a m s , and a carbon monoxide delivery of 15 m i l l i g r a m s per cigarette. Replacing 30% of the tobacco with C y t r e l should reduce these deliveries to 13. 1, 0. 8, and 13 m i l l i grams per cigarette, respectively. Thus, a medium tar brand can be changed to a lower tar brand by inclusion of 30% C y t r e l . S i m i l a r l y , a ventilated low tar brand might have tar, nicotine, and CO deliveries of 8. 0, 0. 6, and 9. 9 m i l l i g r a m s per cigarette. Inclusion of 30% C y t r e l i n the blend could further reduce these to 6 . 5 , 0.4, and 8. 6 m i l l i g r a m s per cigarette, respectively. In conclusion, we have shown that C y t r e l tobacco supplement offers a means to reduc deliverie f virtuall a l l smok ponents of a cigarette greater than would be expected on the basis of the burning rate of the m a t e r i a l and its composition. The s i m p l e r smoke composition and the reduced deliveries of Cytrel-containing cigarettes a p p e a r to translate into a reduction i n biological response i n animal test systems. Inclusion of C y t r e l i n cigarettes can be readily utilized with other existing techniques to provide lower delivery cigarettes. Abstract C y t r e l i s a tobacco supplement consisting of m i n e r a l components, combustion modifiers, and organoleptic-active materials bound together by a film-forming cellulose ether. C y t r e l i s being used i n several brands of cigarettes on the European market at a 20-25% level blended with tobacco. The amount of "tar" c o n t r i buted to the "mainstream" smoke by C y t r e l i s one-fourth to one-seventh of that from tobacco. There are s i m i l a r reductions for other non-nitrogeneous smoke constituents relative to tobacco. Neither C y t r e l nor C y t r e l smoke contains nicotine, and the number and amount of nitrogen-containing compounds i n C y t r e l smoke are d r a s t i c a l l y reduced. S i m i l a r l y , the amount and complexity of the combustion products i n C y t r e l "sidestream" smoke are significantly reduced. It has been shown that the delivery of smoke components from blends of C y t r e l and tobacco is reduced in direct proportion to the level of C y t r e l i n the blend with tobacco. This relationship has been demonstrated for virtually all the components of smoke studied to date. C y t r e l can be readily blended with tobacco i n conventional cigarette making equipment. F u r t h e r , Cytrel/tobacco blend technology is fully compatible with other means currently being used to modify cigarette smoke, such as various cigarette filters and high porosity cigarette papers.


7.

GODWIN AND KEITH


95

L i t e r a t u r e Cited 1. Keith, C. Η., P r o c . 3rd W o r l d Conf. Smoking and Health, DHEW Publication No. (NIH) 76-1221 (1976), 1, 49. 2. Norman, V., B e i t r . z. Tabakforsch. (1974), 7, 282. 3. Miano, R. R., and K e i t h , C. H., U . S. Patent 3, 931, 824 (1976). 4. V i c k r o y , D. G., B e i t r . z. Tabakforsch. (1976), 8, 415. 5. Mauldin, R. Κ., B e i t r . z. Tabakforsch. (1976), 8, 422. 6. A l l e n , R. Ε., and V i c k r o y , D. G., B e i t r . z. Tabakforsch. (1976), 8, 430. 7. Buch, S. et a l , Inveresk Research International Report 307, Project 403318 (1975). 8. Bernfeld, P., an tants, Inc. Report 9. Black, A . et al, Inveresk R e s e a r c h International Report 408, P r o j e c t 403365 (1975). 10. G o r i , G. Β., "Towards L e s s Hazardous Cigarettes, Report No. 2, The Second Set of Experimental Cigarettes, " Nation al Cancer Institute, Smoking and Health P r o g r a m , Washing ton, D . C . (1976).


8 Characterization of Insoluble Cellulose Acetate Residues W. B. RUSSO Fiber Industries, Inc., Charlotte, N.C. 28237 G. A. SERAD Celanese Fibers Co., Charlotte, N.C. 28232

C o m m e r c i a l cellulos using a very high purity wood pulp because its applications have very c r i t i c a l processing and product requirements. Cellulose acetate films must be c l e a r and free of imperfections that could be caused by undissolved particles during solvent film castings. The preparation of cellulose acetate fibers requires the polymer solution to flow unobstructed through spinneret c a p i l l a r i e s that have extremely s m a l l diameters. A n y undissolved particulate matter that would cause disruptions i n fiber extrusion cannot be tolerated. Since cellulose derived f r o m wood pulp contains im purities which do not f o r m acetate esters soluble i n c o m m e r c i a l cellulose acetate solvents ( e . g . , acetone), these impurities must be reduced to an acceptable l e v e l . Consequently, wood pulps used to manufacture cellulose acetate contain 94 to 99 per cent alpha-cellulose, the remainder being hemicelluloses. This α - c e l l u l o s e level is higher than that required for the preparation of rayon, cellulose nitrate, or cellulose ethers. Of course, the increased purity results i n an increased cost. Hence, it has long been a goal to develop means to reduce the wood pulp purity requirements for the c o m m e r c i a l preparation of cellulose ace tate. This is desirable for the acetate manufacturer, the pulp manufacturer, and the ecology since the higher purity comes at a sacrifice i n wood y i e l d and increased pulp mill effluent treat ment requirements. It is well known that insoluble residues obtained f r o m the dissolution of cellulose acetate in acetone are enriched i n hemi cellulose acetates (1-4). However, our p r o g r a m to investigate the use of lower purity wood pulps to prepare cellulose acetate by either modifying the pulps or the process required quanti96


8.

RUSSO AND SERAD

tative characterizations. isolate,

quantify,

fractions

Hence,

this study was undertaken

and characterize

to

both soluble and insoluble

of c e l l u l o s e a c e t a t e i n a c e t o n e .

F o u r g e n e r a l c l a s s e s of p u l p ,

representing

nations of w o o d f u r n i s h a n d p u l p i n g p r o c e s s , These included a softwood kraft, kraft,

97

Insoluble Cellulose Acetate Residues

and hardwood sulfite.

various

were

combi-

examined.

softwood sulfite,

hardwood

T h e p u r i t y of the v a r i o u s p u l p s ,

along with typical acetylation grade pulps, are given in Table

T A B L E I:

I.

P u r i t y of A c e t y l a t i o n G r a d e a n d " L o w P u r i t y " W o o d Pulps

Glucose Mannose Xylose

Purity-RjQ%

" L o w Purity" Grades Softwood K r a f t

85. 6

6.1

8.3

84

Softwood Sulfite

91.2 83. 5

6.9 0.6

1.9

85

91.5

2.4

15.9 6.1

89 87

98. 1

1.4

0.5

96

97.5

0.3

1.2

97

Hardwood Kraft Hardwood Sulfite Typical Acetylation Grade Softwood Sulfite Hardwood Prehydrolyzed Kraft

Fractionation Acetone,

Sequence the c o n v e n t i o n a l s o l v e n t u s e d to

manufacture

c e l l u l o s e a c e t a t e f i b e r s a n d f i l m s , w a s u s e d to p r e p a r e starting solutions.

(wt/wt) a c e t o n e / w a t e r .

the s o l v e n t a n d the c e l l u l o s e a c e t a t e f l a k e . i n the f r a c t i o n a t i o n ( F i g u r e

A 6 g/100

c a l l e d the a c e t o n e / w a t e r s o l u b l e s

saved for analysis.

a

The

(AWS),

combined were

The residue was weighed and likewise c c s o l u t i o n i n 91/9

methylene

000

fresh

and u l t r a -

A p o r t i o n of the r e s i d u e w a s s u b s e q u e n t l y

p a r e d a s a 6 g/100

solution

1) w a s u l t r a c e n t r i f u g a t i o n a t 1 5 ,

centrifugation repeated under s i m i l a r conditions.

for analysis.

cc

T h e f i r s t step

A f t e r d e c a n t i n g o f f the s u p e r n a t e ,

a c e t o n e / w a t e r s o l u t i o n w a s a d d e d to t h e r e s i d u e s supernates,

95/5

T h e w a t e r i n c l u d e s that c o n t a i n e d i n both

o f the c e l l u l o s e a c e t a t e (bone d r y b a s i s ) w a s u s e d . r p m for four hours.

the

The exact solvent composition used was

saved

pre-

chloride/



Acetone Water Soluble Acetone/ Water

Acetone Water Insoluble

Methyle Chloride/ Methanol

Methylene Chloride/ Methanol Soluble

Methylene C h l o r i d e / M e t h a n o l Insoluble

D r y residue P r e p a r e 6% (wt/vol) s o l u t i o n in

6 g m s of bone d r y f l a k e " p e r 100 cc U l t r a c e n t r i f u g a t i o n (1 5,000 r p m f o - 4 h r s ) Decant s u p c r n a t e A d d 150 cc of f r e s h a c e t o n e / w a t e Repeat steps 2 and 3 C o l l e c t l i q u i d , weigh s o l i d s

Repeat steps 3 and 4 C o l l e c t l i q u i d , weigh s o l i d s

Figure 1. Fractionation sequence

1.0

1.2

1.4

1.6

Intrinsic V i s c o s i t y

Figure 2. Relationship of cellulose acetate intrinsic viscosity and 6% solution viscosity


8.

RUSSO AND SERAD

methanol.

99


T h e s o l u t i o n w a s u l t r a c e n t r i f u g e d at 15, 000 r p m f o r

two h o u r s .

The supernate was decanted,

fresh methylene

i d e / m e t h a n o l a d d e d , a n d the c e n t r i f u g a t i o n r e p e a t e d . bined supernate, (MCMS),

was saved for analysis.

methylene and

designated methylene

chlor-

The

com-

chloride/methanol

The final residue,

chloride/methanol insolubles (MCMI),

soluble

designated

was weighed

saved.

Analytical

Procedures

A c e t y l V a l u e (defined as percent

combined acetic acid).

A five wt. percent

s o l u t i o n of the c e l l u l o s e a c e t a t e f l a k e

was

p r e p a r e d i n a 91/9

(wt/wt) m e t h y l e n e

solvent.

chloride/methanol

A film approximately 0 a n d a l l o w e d to a i r d r y .

It w a s p l a c e d i n a c u r v e d f i l m h o l d e r ,

h e a t e d to r e m o v e r e s i d u a l w a t e r , spectrophotometer

and scanned i n an infrared

o v e r t h e 2 . 5 to 4 . 5 m i c r o n r a n g e .

The

ratio

of the O H a b s o r b e n c e at 2. 9 m i c r o n s a n d the C - H a b s o r b e n c e 2.4

microns was calculated.

T h i s r a t i o w a s c o r r e l a t e d to

at

acetyl

value by m e a n s of a c a l i b r a t i o n p r o c e d u r e u s i n g a k n o w n standard.

F o r a c e l l u l o s e a c e t a t e of 5 5 . 07 a c e t y l v a l u e ,

the

sample

s t a n d a r d d e v i a t i o n (ten a n a l y s e s ) w a s 0. 0 2 . Filtration Value.

M o i s t u r e c o n t e n t of c e l l u l o s e

samples was determined by oven drying.

A 6 g/100

o f t h e s a m p l e w a s p r e p a r e d u s i n g e i t h e r a 95/5 tone/water vent.

acetate

cc

solution

(wt b a s i s ) a c e -

s o l v e n t o r a 91/9 m e t h y l e n e c h l o r i d e / m e t h a n o l s o l -

T h i s w a s s h a k e n f o r t w o h o u r s to a s s u r e d i s s o l u t i o n .

The

solution was filtered through 30-ply K i m p a k and Canton flannel at 200 p s i g n i t r o g e n p r e s s u r e plugged.

u n t i l the f i l t e r w a s

completely

A f i l t r a t i o n v a l u e w a s d e f i n e d as the g r a m s o f d r y

c e l l u l o s e a c e t a t e p e r c m ^ of f i l t e r a r e a w h i c h c a n be before blockage

filtered

occurs.

Cation Analysis.

Calcium,

magnesium,

and sodium were

determined by atomic absorption using conventional Intrinsic Viscosity.

techniques.

I n t r i n s i c v i s c o s i t y of c e l l u l o s e

acetate

f l a k e s w a s d e t e r m i n e d b y m e a s u r i n g the v i s c o s i t y of a 6 g/100

cc

s o l u t i o n of the f l a k e i n a c e t o n e / w a t e r a n d u s i n g the c o r r e l a t i o n of F i g u r e 2.

Solution viscosity was determined using a

d i r e c t r e a d o u t v i s c o m e t e r ( M o d e l 7-006) at

Nametre

25°C.



100

C a r b o x y l Content. A n i o n exchange procedure was used f o r the d e t e r m i n a t i o n of the c a r b o x y l c o n t e n t . Flake was treated w i t h H C 1 to c o n v e r t t h e c a r b o x y l g r o u p s to t h e i r a c i d f o r m . C a r b o x y l protons w e r e then l i b e r a t e d by exchange w i t h c a l c i u m acetate and subsequently titrated. S u g a r A n a l y s i s . Q u a n t i f i c a t i o n of the c a r b o h y d r a t e c o n tent w a s a c c o m p l i s h e d b y gas c h r o m a t o g r a p h y of the t r i m e t h y l s i l a t e d s u g a r m o n o m e r s w h i c h w e r e o b t a i n e d b y h y d r o l y s i s of t h e c e l l u l o s e a c e t a t e o r w o o d p u l p (_5, 6 ) . S p e c i a l p r o c e d u r e s w e r e d e v e l o p e d to c h a r a c t e r i z e 7 0 - 1 0 0 m g s a m p l e s . A n accurate d r y sample weight and acetyl value w e r e f i r s t obtained and the f o l l o w i n g h y d r o l y s i s p r o c e d u r e u s e d : 1.

The sample

f o r about two h o u r s ,

cooled i n a dessicator

to r o o m

temperature,

then weighed. 2.

O n e m l o f 77 p e r c e n t s u l f u r i c a c i d w a s a d d e d f o r

v a t i o n a n d s h a k e n f o r o n e to t h r e e h o u r s .

sol-

Extremely discolored

samples were discarded. 3.

T h e s o l v a t e d s a m p l e w a s d i l u t e d w i t h 25 m l o f d i s t i l l e d

w a t e r a n d 5 m l of a 2. 0 m g / m l m y o - i n o s i t o l s o l u t i o n ( r e f e r e n c e sugar). 4.

The solution was then r e f l u x e d f o r four h o u r s .

N e x t , a n e u t r a l i z a t i o n step c o n s i s t e d of p l a c i n g . a 5 m l a l i q u o t of the h y d r o l y z e d s a m p l e i n a c e n t r i f u g e t u b e , a d d i n g 0. 7 g of b a r i u m c a r b o n a t e p o w d e r , a n d p l a c i n g the c o n t e n t s i n t o a v a c u u m o v e n at 6 5 ° C . A f t e r n e u t r a l i z a t i o n , c o i n c i d e n t w i t h the c e s s a t i o n of b u b b l e s , the m i x t u r e w a s c e n t r i f u g e d (2, 000 r p m f o r 10-15 m i n u t e s ) . T h e r e s u l t a n t s u p e r n a t e w a s p l a c e d i n t o a 10 m l p e a r - s h a p e d f l a s k a n d e v a p o r a t e d to d r y n e s s u n d e r r e d u c e d p r e s s u r e w i t h a r o t a r y e v a p o r a t o r (bath t e m p e r a t u r e 2 5 - 3 5 ° C ) . Trimethylsilation was accomplished by adding a 1 m l a m p u l e of T R I - S I L ( P i e r c e C h e m i c a l C o m p a n y ) i n t o the f l a s k a n d p e r m i t t i n g i t to r e a c t f o r o n e h o u r a t 5 0 ° C . The reaction vial w a s c e n t r i f u g e d to s e t t l e t h e p r e c i p i t a t e . A 1 - 2 m i c r o n s a m p l e of supernate w a s u s e d f o r gas c h r o m a t o g r a p h i c a n a l y s i s . Gas chromatograph conditions were: 1. A 4 0 - f o o t , 1/8 i n c h O . D . s t a i n l e s s s t e e l t u b e p a c k e d w i t h D e x s i l 3 0 0 G C (5 p e r c e n t ) o n C h r o m a s o r b W . 2.

Injection p o r t t e m p e r a t u r e of 2 5 0 ° C ,

p e r a t u r e of

detector

tem-

280°C.

3. P r o g r a m s e q u e n c e w a s to i n j e c t a t 1 6 0 ° C w i t h a 12 m i n u t e h o l d t i m e , f o l l o w e d b y a 1 ° C / m i n u t e p r o g r a m r a t e to 250°C.


8. RUSSO AND SERAD


R e s p o n s e f a c t o r s w e r e d e t e r m i n e d f o r a v a r i e t y of s u g a r s , shown i n T a b l e II· T A B L E II: R e s p o n s e F a c t o r s f o r G a s

as

Chromatography RF

Sugar α Glucose 3 Glucose Y Glucose

1.23 1. 22 1.22

ot, β X y l o s e
/ Λ = bone-dry; unhammered / A = m o i s t u r e - c o n d i t i o n e d : unhammered

\

MC/NH

A

o|

I 0

I

2.5

5.0 (CH ) 0 Applied 2

2

1 _

7.5

{%)

Figure 10. Effect of hydroxyethylation, moisture conditioning, and hammenng on optical character, Δ Τ / Δ Α , of acetylation products produced from a nitrationgrade pulp (samples collected 40 min into the acetylation reaction) 0

0


RILEY

Hydroxyethylated Wood Pulp

0

2.5

141


2

7.5

(*)

Figure 11. Effect of hydroxyethylation, moisture conditioning, and hammering on optical character of haze, T /A , of acetylation products produced from a nitration-grade pulp (samples collected 40 min into the acetylation reaction) Jdc

Jdc


142


Ο φ

» bone-dry; hammered 8

moisture-conditioned; hammered

/V * bone-dry; unhammered ^

= moisture-conditioned; unhammered

•2

+1

-2

1

7.5

5.0

2.5

(CH ) 0 A p p l i e d 2

2

{%)

Figure 12. Effect of hudroxyethuhtion, moisture conditioning, and hammering on optical character of late haze l(T /A ) — (T /Aidc)l of acetylation prod ucts produced from a nitration-grade pulp (samples collected 40 min into the acetylation reaction) 7dc

7dc

lic


10.

RELEY

143


p a r t i c l e s have a l o w e r T/A v a l u e f o r hammered b o n e - d r y p u l p s and a h i g h e r v a l u e when hammering i s n o t u s e d . As p r e v i o u s l y m e n t i o n e d , a h i g h T/A r a t i o i n d i c a t e s a p a r t i c l e of r e l a t i v e l y high r e f r a c t i v e index. The r e f r a c t i v e index of unacetylated c e l l u l o s e i s 1.54; that of c e l l u l o s e acetate i s 1.47. For t h e medium, w h i c h i s p r e d o m i n a n t l y a c e t i c a c i d , i t i s 1.37. The c e n t r l f u g a b l e p a r t i c l e s , w h i c h have a T/A v a l u e o f 2 t o 4 , a r e h i g h 1n u n a c e t y l a t e d c e l l u l o s e . The s m a l l d i s p e r s e p a r t i c l e s i n t h e s u p e r n a t a n t f l u i d , w h i c h have a T/A v a l u e o f 0 . 5 t o 2 , a r e a c e t y l a t e d and p r o b a b l y p a r t l y s o l v a t e d . The I n c r e a s e 1n t h e T/A v a l u e o f t h e s u p e r n a t a n t f l u i d on s t a n d i n g may be due t o a d e c r e a s e i n s o l v a t i o n ; s u c h a change w o u l d r e s u l t in p a r t i c l e s with a higher o p t i c a l density. B a s e d on t h e h i g h T/A v a l u e o f 6 ( F i g u r e 1 0 ) , t h e c e n t r i f u g a b l e p a r t i c l e s f r o m unhammere t r e a t e d w i t h 7.5% e t h y l e n They a r e p r o b a b l y a g g r e g a t i o n s o f c r y s t a l l i n e c e l l u l o s e m i c r o f i b r i l s w i t h a minimal matrix of e s t e r i f i e d c e l l u l o s e . F i g u r e 13 i s an e l e c t r o n m i c r o g r a p h o f s i m i l a r r e s i d u e s o b t a i n e d f r o m an acetylated dissolving-grade pulp. The l o w A T / A A c f o u n d f o r t h e c e n t r i f u g a b l e p a r t i c l e s f r o m m o i s t u r e - c o n d i t i o n e d unhammered h y d r o x y e t h y l a t e d p u l p t r e a t e d w i t h 7.5% e t h y l e n e o x i d e s u g g e s t s that these p a r t i c l e s are mostly e s t e r i f i e d m a t e r i a l s with s u f f i c i e n t i n t e r c o n n e c t i o n s between e l e m e n t s t o p r o v i d e a s t r u c t u r a l i n t e g r i t y which i s not s u s c e p t i b l e to a c e t i c a c i d . C e l l u l o s e t r i a c e t a t e c r y s t a l l i t e s a r e n o t s o l u b l e i n a c e t i c a c i d and may a c t as t i e p o i n t s . C r o s s - l i n k s i n v o l v i n g the hydroxyethyl group a r e also a p o s s i b i l i t y . The i n t r i n s i c v i s c o s i t y o f t h e a c e t y l a t i o n p r o d u c t 30 m i n u t e s i n t o the r e a c t i o n i s independent of the degree of hydroxyethyl a t i o n f o r m o i s t u r e - c o n d i t i o n e d unhammered p u l p s ( F i g u r e 1 4 ) . Hammering r e d u c e s t h e a p p a r e n t i n t r i n s i c v i s c o s i t y * a s t h e d e g r e e o f h y d r o x y e t h y l a t i o n i n c r e a s e s . The a c e t y l a t i o n o f b o n e - d r y c o n t r o l p u l p and o f b o n e - d r y p u l p t r e a t e d w i t h 2 . 5 % e t h y l e n e o x i d e had n o t p r o g r e s s e d s u f f i c i e n t l y i n 30 m i n u t e s t o p r o v i d e s o l u t i o n s s u i t a b l e f o r i n t r i n s i c v i s c o s i t y measurement. For bone-dry pulps w i t h n o r m a l r e a c t i v i t y , s u c h a s one t r e a t e d w i t h 5% e t h y l e n e o x i d e , the i n t r i n s i c v i s c o s i t y i s comparable to t h a t o f m o i s t u r e - c o n d i t ioned samples. The h i g h e r i n t r i n s i c v i s c o s i t y o f p u l p s t r e a t e d w i t h 7.5% e t h y l e n e o x i d e s u g g e s t s t h a t i n the b o n e - d r y system t h e r e may be an a p p r e c i a b l e amount o f c r o s s - l i n k i n g between t h e h y d r o x y l g r o u p o f t h e h y d r o x y e t h y l s u b s t i t u e n t and u r o n i c a c i d s . In t h e p r e s e n c e o f a c e t i c a n h y d r i d e and a c a t a l y s t , t h e m i x e d u r o n i c - a c e t i c a c i d e s t e r forms r a p i d l y , making t h i s a c h e m i c a l possibility. The y e l l o w n e s s o f a c e t y l a t i o n s o l u t i o n s i s p r i m a r i l y due t o C

• I n t r i n s i c v i s c o s i t i e s w e r e o b t a i n e d by c o n v e r s i o n o f p r o d u c t v i s c o s i t i e s ; i t was n o t d e t e r m i n e d w h e t h e r t h e c o n v e r s i o n f a c t o r d i f f e r e d for hydroxyethylated pulps.


144

S O L V E N T S P U N R A Y O N , MODIFIED C E L L U L O S E FD3ERS

Figure 13. Transmission electron micrograph offilmmade from an acetylation mixt Reference mark is 1μ.


RILEY


Q

= bone-dry; hammered = m o i s t u r e - c o n d i t i o n e d ; hammered

/ \

= bone-dry; unhammered

A

= m o i s t u r e - c o n d i t i o n e d ; unhammered

MC/H

5.0


2

7.5

{%)

Figure 14. Effect of hydroxyethylation, moisture conditioning, and hammering on intrinsic viscosity of acetylation products produced from a nitrationgrade pulp (samples collected 30 min into the acetylation reaction)


146

SOLVENT SPUN RAYON, MODIFIED C E L L U L O S E

FD3ERS

t h e s e l e c t i v e s c a t t e r i n g o f b l u e l i g h t by p a r t i c l e s a p p r o x i m a t e l y h a l f the wavelength of blue l i g h t i n diameter. A measure o f t h e f o r m a t i o n o f such p a r t i c l e s i n the process i s t h e r e f o r e p r o v i d e d by t h e y e l l o w n e s s c o e f f i c i e n t , Cy ( F i g u r e 1 5 ) . The h i g h e s t p o p u l a t i o n o f t h e s e s m a l l p a r t i c l e s was measured i n t h e s u p e r n a t a n t f l u i d of the bone-dry c o n t r o l p u l p . The T/A v a l u e o f t h e s e p a r t i c l e s was h i g h ( a b o u t 6 ) , s u g g e s t i n g t h a t t h e p a r t i c l e s a r e p r o b a b l y f r a g m e n t s o f u n a c e t y l a t e d c e l l u l o s e , most l i k e l y m i c r o f i b r i l b u n d l e s 2 0 0 - 2 5 0 πΐμ i n d i a m e t e r ( F i g u r e 1 3 ) . These f r a g ments s e p a r a t e as a r e s u l t o f t h e a c e t y l a t i o n and s o l v a t i o n o f t h e low-order hemicellulose matrix. The m i c r o f i b r i l b u n d l e s a r e dense and u n r e a c t i v e b e c a u s e t h e f i b r i l l a r e l e m e n t s have n o t been s e p a r a t e d by e i t h e r t h e w a t e r / a c e t i c a c i d p r e t r e a t i n g medium o r the hydroxyethyl wedges. With i n c r e a s i n g l e v e l i m p r o v e s and a c t u a l c o n t a c increases. The more h i g h l y h y d r o x y e t h y l a t e d b o n e - d r y p r o d u c t s approach the m o i s t u r e - c o n d i t i o n e d p r o d u c t s i n terms o f Cy. The g e n e r a l l y l o w e r l e v e l s o f Cy f o r m o i s t u r e - c o n d i t i o n e d s a m p l e s p a r a l l e l t h e i m p r o v e d r e a c t i v i t i e s shown by tioo ( F i g u r e 3 ) . The m o i s t u r e - c o n d i t i o n e d c o n t r o l p u l p , w h i c h has a s i g n i f i c a n t l y h i g h e r Cy v a l u e t h a n do t h e m o i s t u r e - c o n d i t i o n e d h y d r o x y e t h y l a t e d p u l p s , i s an e x c e p t i o n i n h a v i n g h i g h r e a c t i v i t y . The r e a c t i v i t y r e t a i n e d i n m i c r o f i b r i l l e r bundles of hydroxyethylated pulps i s h i g h e r than t h a t which m o i s t u r e c o n d i t i o n i n g a l o n e can i n d u c e . The b a s e l e v e l o f C y , a b o u t 0 . 0 7 , i n d i c a t e s t h e c o n t r i b u t i o n t o y e l l o w n e s s o f e x t r a c t a b l e components w h i c h have a m o l e c u l a r absorption function. As c a n be s e e n i n F i g u r e 1 6 , Cy changed between t h e 3 0 - and 40-minute a c e t y l a t i o n samples. With the e x c e p t i o n o f the bone-dry, unhammered p u l p s , t h i s change i n v o l v e d s u b s t a n t i a l i n c r e a s e s , s u g g e s t i n g t h a t t h e p a r t i c l e s s c a t t e r i n g b l u e l i g h t a t 30 m i n u t e s r e m a i n i n s o l u t i o n and t h a t a d d i t i o n a l p a r t i c l e s a r e g e n e r a t e d by f u r t h e r a t t a c k on l a r g e , c e n t r i f u g a b l e p a r t i c l e s . The r e l a t i v e l y s m a l l c h a n g e s o b s e r v e d f o r t h e b o n e - d r y , unhammered p u l p s s u g g e s t s t h a t the l a r g e residues i n those a c e t y l a t i o n s are l e s s vulnerable to attack. The v a l u e s o f A T c were a l s o much h i g h e r f o r t h e b o n e d r y unhammered p u l p s . Discussion Pulp S t r u c t u r e . By what mechanism does p u l p h y d r o x y e t h y 1 a t i o n so p r o f o u n d l y m o d i f y p r e t r e a t m e n t r e q u i r e m e n t s and t h e a c e t y l a t i o n p r o c e s s p r o d u c t ? The f o r m u l a t i o n e v o l v e d f r o m t h e f i n d i n g s o f t h i s i n v e s t i g a t i o n i s b a s e d on t h e a s s u m p t i o n t h a t t h e u l t i m a t e element i n the c e l l u l o s i c s t r u c t u r e i s a m i c r o f i b r i l 35 A i n d i a m e t e r . E l e c t r o n m i c r o g r a p h s o f t h e r e s i d u e s a f t e r peak a c e t y l a t i o n r e g u l a r l v show c o m p o s i t e r o d b u n d l e s whose d i a m e t e r s a r e m u l t i p l e s o f 35 A . A l s o p r e s e n t a r e p a r t i c l e s i n w h i c h an amorphous c e m e n t i n g a g e n t a p p a r e n t l y h o l d s t o g e t h e r d e n s e , r o u g h l y


RILEY


(CH ) 0 A p p l i e d 2

2

147

(*)

Figure 15. Effect of hydroxyethylation, moisture conditioning, and hammering on yellowness coefficient, Cy, of acetylation products produced from a nitration-grade pulp (samples collected 30 min into the acetylation reaction)

American Chemical Society Library 1155 16th St. N. W.

In Solvent Spun Rayon, Modified Cellulose Fibers and Derivatives; Turbak, A.; Washington, D. Society: C. 20036 ACS Symposium Series; American Chemical Washington, DC, 1977.


0

2.5

O*

bone-dry; hammered

0

m o i s t u r e - c o n d i t i o n e d ; hammered

c

5.0

7.5

( C H ) 0 A p p l i e d (X) 2

2

Figure 16. Effect of hydroxyethylation, moisture conditioning, and hammering on the change in the yellowness coefficient, A C y , as the acetylation of a nitration-grade pulp progresses (samples collected 30 and 40 min into the acetylation reaction)


10.

RILEY


149

o v a l - s h a p e d p a r t i c l e s ( F i g u r e s 13 and 1 7 ) , These p a r t i c l e s a r e h e m i c e l l u l o s i c , i n t h a t they are not observed i n a c e t y l ated cotton f i b e r s . Pretreatment The optimum p r e t r e a t i n g l i q u i d i s a w a t e r / a c e t i c a c i d s o l u t i o n a t a 1/1 m o l a r r a t i o . In t h e a b s e n c e o f w a t e r a c e t i c a c i d i s a d i m e r , b u t i n t h e p r e s e n c e o f w a t e r t h e d i m e r decompo ses. The a c t u a l p r e t r e a t i n g a g e n t i s p r o b a b l y t h e m o n o - h y d r a t e of a c e t i c a c i d . I t i s b u l k i e r t h a n H2O and t h e r e f o r e a b e t t e r wedge. I t 1 s , u n l i k e d i m e r i c a c e t i c a c i d , a hydrogen d o n o r . It c a n be p o s t u l a t e d t h a t t h e m o n o h y d r a t e o f a c e t i c a c i d i s e f f e c t i v e i n b r e a k i n g h y d r o g e n bonds i n d e l i g n i f i e d c e l l u l o s i c m a t e r i a l and therefore that i t effect m i c r o f i b r i l l a r u n i t s , thereb f o r the attack of the a c e t y l a t i o n reagent. Mechanical input (hammering) a i d s t h e p e n e t r a t i o n o f t h e a c e t i c a c i d m o n o h y d r a t e . O t h e r s t u d i e s have shown t h a t t h e r e a c t i v i t y o f a p u l p w i t h an e x t r e m e l y l o w h e m i c e l l u l o s e c o n t e n t i s n o t i m p r o v e d by m e c h a n i c a l input during pretreatment. H o w e v e r , where h e m i c e l l u l o s i c cements a r e p r e s e n t , m e c h a n i c a l i n p u t b r e a k s t h e bonds o f t h e s e cements and c r e a t e s b e t t e r a c c e s s f o r t h e a c e t i c a c i d m o n o h y d r a t e . Hydroxyethylation When u n d r i e d p u l p a t a c o n s i s t e n c y o f 100% i s t r e a t e d w i t h e t h y l e n e o x i d e , t h e a c c e s s i b l e s u r f a c e a r e a i s a t l e a s t as g r e a t as t h a t r e s u l t i n g f r o m t h e p r e t r e a t m e n t o f d r i e d p u l p . Ethylene oxide enters the i n t e r f i b r i l l a r s p a c e s , randomly r e a c t s a t a number o f a c c e s s i b l e s i t e s , and p r o v i d e s a s e r i e s o f wedges w h i c h p r e v e n t s t r u c t u r a l c o l l a p s e as d r y i n g t a k e s p l a c e . When t h e degree o f h y d r o x y e t h y l a t i o n i s s u f f i c i e n t , a bone-dry h y d r o x y e t h y l a t e d p u l p , w h i c h has a s open an i n t e r f i b r i l l a r s t r u c t u r e a s a pretreated p u l p , w i l l react at a rate s i m i l a r to that character i s t i c of moisture-conditioned pulps. Supporting evidence f o r t h i s t h e o r y c a n be f o u n d i n t h e s i g n i f i c a n t l y l o w e r number o f l a r g e r e s i d u e s , a s i n d i c a t e d by t h e l o w e r Δ Τ ς v a l u e s , i n h y d r o x y e t h y l a t e d pulps. Hammering a b o n e - d r y h y d r o x y e t h y l a t e d p u l p g e n e r a t e s e v e n more s u r f a c e a r e a and r e s u l t s r e s i d u a l p a r t i c l e s . Moisture conditioning p l a s t i c i z e s hydroxyethylated pulp. Hammering t h e s e p l a s t i c i z e d p u l p s l e a d s to adhesions.where h y d r o g e n bonds d e v e l o p i n r e g i o n s w h i c h were s e p a r a t e d b u t i n w h i c h t h e wedge i n c i d e n c e was s m a l l . The r e s u l t i s an i n c r e a s e i n l a r g e , c e n t r i f u g a b l e p a r t i c l e s , i n d i c a t e d by t h e h i g h i n i t i a l t u r b i d i t y and t h e h i g h A T c v a l u e s o f m o i s t u r e - c o n d i t i o n e d hammered hydroxyethylated pulps. The wedge e f f e c t o f h y d r o x y e t h y l a t i o n i n c o n j u n c t i o n w i t h the a c e t i c a c i d monohydrate p r e t r e a t m e n t a l s o r e s u l t s i n a r e d u c t i o n o f p a r t i c l e s i n t h e s i z e r a n g e o f 0 . 5 t o 1 0 μ . The b a s i s


150


Figure 17. Transmission electron micrograph offilmmade from an acetylation mix Reference mark is Ο.ΐμ.


10.

RILEY


151

f o r t h i s o b s e r v a t i o n i s the low t u r b i d i t i e s o f supernatant f l u i d s from hydroxyethylated p u l p s . T h i s mechanism i s c o m p a t i b l e w i t h the o b s e r v a t i o n o f a h i g h e r c e l l u l o s e c o n t e n t i n p a r t i c l e s formed when b o n e - d r y p u l p s a r e a c e t y l a t e d . Conclusions A l l three l e v e l s of ethylene oxide treatment of a n i t r a t i o n grade p u l p l e a d t o a c e t y l a t i o n products w i t h improved f i l t r a t i o n p e r f o r m a n c e , r e d u c e d f a l s e v i s c o s i t y , and i n c r e a s e d a c e t o n e solution c l a r i t y . Most s t r i k i n g l y , t h e h y d r o x y l a t e d p u l p s c o u l d be a c e t y l a t e d b o n e - d r y w i t h o u t a c t i v a t i o n by m e c h a n i c a l i n p u t (hammering) d u r i n g p r e t r e a t m e n t . The w a t e r s o l u b i l i t y o f t h e h e m i c e l l u l o s e c o n s t i t u e n t s o f t h e h y d r o x y e t h y l a t e d p u l p s wa usually precipitated i of a c i d with water, t h i s increased water s o l u b i l i t y of contamina n t s r e s u l t s i n s e r i o u s y i e l d r e d u c t i o n s i n t h e p r e c i p i t a t i o n and washing s t a g e s . A l t h o u g h improvement i n a c e t y l a t i o n p r o d u c t s p r o d u c e d f r o m a l o w e r q u a l i t y p u l p was a c h i e v e d by h y d r o x y e t h y l a t i o n , t h e e c o n o m i c and t e c h n i c a l l i m i t a t i o n s o f t h i s a p p r o a c h s u g g e s t t h a t t r e a t i n g l e s s p u r i f i e d pulps w i t h e t h y l e n e o x i d e i s not a v i a b l e commercial p r o c e s s and does n o t s o l v e t h e p r o b l e m a t h a n d . In t h e c o n t e x t o f b a s i c s c i e n t i f i c knowledge, however, the f i n d i n g s o f t h i s i n v e s t i gation are considerable. In t e r m s o f a m e c h a n i s m , a s t r u c t u r a l l y m o d i f i e d l o w e r g r a d e p u l p a c e t y l a t e s r a p i d l y and f o r m s a b e t t e r p r o d u c t b e c a u s e much o f t h e i n i t i a l b e f o r e - d r y i n g i n t e r n a l s u r f a c e i s p r e s e r v e d by h y d r o x y e t h y l groups which a c t as m o l e c u l a r wedges, p r e v e n t i n g e x t e n s i v e h y d r o g e n b o n d i n g and a t t e n d a n t r e d u c t i o n i n s u r f a c e . The c u s t o m a r y p r e t r e a t m e n t w i t h a c e t i c a c i d m o n o h y d r a t e and moderate mechanical t r e a t m e n t improve t h e a c e t y l a t i o n response o f t h e p a r e n t p u l p by r e g e n e r a t i n g i n t e r n a l s u r f a c e . In c o n t r a s t , m o d e r a t e m e c h a n i c a l t r e a t m e n t o f an a c e t i c m o n o h y d r a t e p r e t r e a t e d h y d r o x e t h y l a t e d p u l p r e d u c e d i n t e r n a l s u r f a c e by c r u s h i n g t h e s t r u c t u r e and e s t a b l i s h i n g h y d r o g e n b o n d s , t h e r e b y r e d u c i n g i n t e r n a l s u r f a c e and a c c e s s i b i l i t y t o a c e t y l a t i o n r e a g e n t s .


11 Reactions of Cellulose With Amic Acids and Anhydride-Ammonia Part VI: Reaction Stoichiometry B. G. BOWMAN☼and JOHN A. CUCULO Dept. of Textile Chemistry, North Carolina State University, Raleigh, N.C. 27607

The c h e m i c a l an fabrics can be m o d i f i e d i n a pad-bake r e a c t i o n with s o l u t i o n s of c e r t a i n h a l f - a m i d e s of d i c a r b o x y l i c a c i d s (amic a c i d s ) (1, 2, 3). The p r o d u c t s o f the r e a c t i o n are ammonia and cellulose half-acid esters (Equation 1 ) . Woven and nonwoven f a b r i c s composed of

e i t h e r v i s c o s e rayon or c o t t o n (1, 2, 3) and wood p u l p mats (4) have been m o d i f i e d by t h i s p r o c e d u r e . The r e a c t i o n is specific f o r amic a c i d s d e r i v e d from dicarboxylic a c i d s which form i n t e r n a l p e n t a c y c l i c anhydrides (e.g., s u c c i n i c , maleic, p h t h a l i c a c i d s , e t c . ) ( 3 ) . The r e a c t i o n a l s o o c c u r s when s o l u t i o n s of a n h y d r i d e s and aqueous ammonia are r e a c t e d with the cellulosic f a b r i c s ( E q u a t i o n 2) (5). The r e a c t i o n is m o d e r a t e l y c a t a l y z e d by s m a l l amounts of a v a r i e t y of compounds and may be s u c c e s s f u l l y completed when the pad-bath s o l v e n t i s e i t h e r water or formamide (4). The r e a c t i o n does not appear to be s u c c e s s f u l when the pad-bath s o l v e n t i s an a p r o t i c medium such as N,N-dimethylformamide or N-methylpyrrolidone (4). •Present Address: High P o i n t C h e m i s t r y , H i g h P o i n t , Ν. C. 27262

College,Department

152


of

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153

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ο

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c ' Ç

c )

0

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A

+ CellOH

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3(a .) q

C

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0

2

in s i t u Ο

Ο

CellOC-

COH + N H -

The pad-bake p r o c e s s i n v o l v e s the a p p l i c a t i o n o f the amic a c i d and c a t a l y s t i n s o l u t i o n to the f a b r i c , squeezing to a predetermined p i c k - u p , and p l a c i n g i n a hot oven to remove th reaction. The s o l v e n t y p i c a l l y i n about two minutes, l e a v i n g behind a s o l i d or l i q u i d r e s i d u e on the f a b r i c . The r a p i d removal o f the s o l v e n t , water, has been shown to be important (4^) The f a b r i c m o d i f i e d by the pad-bake r e a c t i o n w i t h α , 3 -amic a c i d s has i n c r e a s e d base combining c a p a c i t y and water s e n s i t i v i t y . T h i s i n d i c a t e s t h a t a c i d groups are indeed p r e s e n t on the f a b r i c . The s a p o n i f i c a t i o n e q u i v a l e n t o f the f a b r i c i s g e n e r a l l y twice the n e u t r a l i z a t i o n e q u i v a l e n t i n d i c a t i n g the presence of e q u a l numbers o f a c i d and e s t e r g r o u p s . Longer r e a c t i o n times or h i g h e r temperatures g i v e r i s e to the f o r m a t i o n of d i e s t e r c r o s s l i n k s ( E q u a t i o n 3) U , 4 i ) . Under these c o n d i t i o n s the s a p o n i f i c a t i o n e q u i v a l e n t i s more than twice the n e u t r a l i z a t i o n e q u i v a l e n t . There i s some e v i d e n c e t h a t a s m a l l amount o f h a l f - a m i d e o

o

o

Cell0CCH CH C0H + CellOH 2

2

^

o

CellOCCH CH COCell 2

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e s t e r i s formed (3, 4 ) . S p e c t r o s c o p i c e v i d e n c e f o r the f o r m a t i o n o f the ïïalF-acid e s t e r o f c e l l u l o s e by the pad-bake r e a c t i o n w i t h a , 3 - a m i c a c i d s i s g i v e n i n F i g u r e 1. These i n f r a r e d s p e c t r a were o b t a i n e d from cupraphane f i l m which was m o d i f i e d i n the pad-bake r e a c t i o n with s u c c i n a m i c a c i d . Spectrum A r e p r e s e n t s i n f r a r e d a b s o r p t i o n o f the unmodified c e l l u l o s e i n the c a r b o n y l a b s o r p t i o n r e g i o n . There i s one weak d o u b l e t near 1650 cmwhich i s due to the presence o f water. The c a r b o n y l a b s o r p t i o n r e g i o n of the c e l l u l o s e h e m i s u c c i n a t e i s shown i n spectrum B. The s t r o n g a b s o r p t i o n at 1730 cm" i s due to the o v e r l a p p i n g c a r b o x y l i c a c i d and e s t e r c a r b o n y l a b s o r p t i o n s . The a c i d - e s t e r combination peak i s r e s o l v e d i n spectrum C 1

1



154

œ

l

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1900

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I

I

1400

I

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Figure 1.

I

1

1400

1

1

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1900

1

FIBERS

1

1

1400

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Carbonyl absorption region for (A) unmodified cellulose, (B) cellulose hemisuccinate, and (C) cellulose hemisuccinate, sodium salt


11.

BOWMAN AND

155

Reactions of Cellulose

cucuLO

when the c e l l u l o s e h e m i s u c c i n a t e i s n e u t r a l i z e d w i th sodium b i c a r b o n a t e . The peak a t 1730 cm" d e c r e a s e s i n i n t e n s i t y and i n c r e a s e s i n s h a r p n e s s as a new peak due t o c a r b o x y l a t e appears a t 1570 cm" . These assignments are c o n s i s t e n t with the l i t e r a t u r e (6, 2 ) · The r e a c t i o n between the a, β-amic a c i d s and c e l l u l o s e i s s i g n i f i c a n t because the d e r i v a t i v e , the c e l l u l o s e h a l f - a c i d e s t e r , can be r a p i d l y formed u s i n g r e l a t i v e l y i n e x p e n s i v e s t a r t i n g m a t e r i a l s and aqueous systems. T h i s i s not g e n e r a l l y t r u e f o r t h e other methods o f p r e p a r a t i o n o f c e l l u l o s e h a l f - a c i d e s t e r s which have been r e p o r t e d (8). 1

1

II.

Discussion of R e a c t i o n Betwee

The r e a c t i o n o f c e l l u l o s e w i t h a , 3 - a m i c a c i d s r e p r e s e n t s an apparent d e p a r t u r e from the t r a d i t i o n a l o b s e r v a t i o n s o f amide c h e m i s t r y . The r e a c t i o n i s e s s e n t i a l l y an a l c o h o l y s i s o f the amide group as the o v e r a l l s t o i c h i o m e t r y i n d i c a t e s ( E q u a t i o n 1 ) . The amide group i s a r e l a t i v e l y s e l e c t i v e a c y l moiety and r e q u i r e s a s t r o n g n u c l e o p h i l e f o r a t t a c k a t the t r i g o n a l carbon atom o f the group. The a t t a c k o f an a l c o h o l , a weak n u c l e o p h i l e , on the amide group w i t h subsequent l o s s o f ammonia i s not a v e r y f a v o r a b l e reaction. Indeed, March s t a t e s i n Advanced O r g a n i c Chemistry: R e a c t i o n s , Mechanisms and S t r u c t u r e t h a t " A l c o h o l y s i s o f amides i s p o s s i b l e but i s seldom performed . . ." ( £ ) . The reason f o r t h e i n e r t n e s s o f amides i s the high b a s i c i t y o f the amide i o n which i s the l e a v i n g group expected i n the u n c a t a l y z e d a l c o h o l y s i s (Equation 4 ) .

e ο +

ROH

—>-

ο

R

0

C R

I \

'

+ NH.3

(4)

L

T h i s i s the same r e a s o n i n g used t o e x p l a i n the r e l a t i v e i n e r t n e s s o f amides toward n e u t r a l h y d r o l y s i s ( 9 ) .



156

CELLULOSE

FIBERS

The p r o b a b l e mechanism by which α,β-amic a c i d s r e a c t w i t h c e l l u l o s e can be d i v i d e d i n t o two g e n e r a l classes: 1. D i r e c t a l c o h o l y s i s by a t t a c k o f the c e l l u l o s i c h y d r o x y l s at the amide c a r b o n y l ; and 2. A l c o h o l y s i s o f a r e a c t i v e i n t e r m e d i a t e formed by the i n i t i a l d e c o m p o s i t i o n o f the amic a c i d .

The d i r e c t a l c o h o l y s i s may be e i t h e r c a t a l y z e d by a c i d or u n c a t a l y z e d . The u n c a t a l y z e d r e a c t i o n mechanism i s shown i n E q u a t i o n 4 . The mechanism proposed by Johnson and C u c u l o i n v o l v e s i n t e r m o l e c u l a r acid c a t a l y s i s ( E q u a t i o h y d r o x y l on the amid p r o t o n a t i o n o f the amide and by the f o r m a t i o n o f

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a hydrogen bond between the a l c o h o l i c p r o t o n and the c a r b o x y l c a r b o n y l . The j u s t i f i c a t i o n s g i v e n f o r t h i s r e a c t i o n mechanism were the apparent s p e c i f i c i t y o f the r e a c t i o n f o r a, β-amic a c i d s d e r i v e d from d i c a r b o x y l i c


11. B O W M A N A N D CUCULO


157

a c i d s which form i n t e r n a l p e n t a c y c l i c a n h y d r i d e s and the c a t a l y t i c e f f e c t of a c i d s . Another source of c a t a l y z i n g a c i d i s the a d j a c e n t c a r b o x y l group. This l e a d s to the p o s s i b i l i t y of i n t r a m o l e c u l a r a c i d c a t a l y s i s as shown i n E q u a t i o n 6. The second c l a s s i f i c a t i o n of mechanisms i n v o l v e s the f o r m a t i o n o f r e a c t i v e i n t e r m e d i a t e s which can more e a s i l y undergo a l c o h o l y s i s . S i n c e α , β-amic-acids are c h a r a c t e r i s t i c a l l y easy to h y d r o l y z e (10^ 11_, 12, 13, 14, 15, 1J6, Γ7, 18) t h e r e i s good reason to s u s p e c t t K a t i n an aqueous pad-bath, the amic a c i d c o u l d be hydrolyzed. T h i s h y d r o l y s i s r e a c t i o n would y i e l d both the d i a c i d and ammonia which c o u l d s u b s e q u e n t l y be d e p o s i t e d as the p a r t i a

ammonium s a l t when the water i s removed. E s t e r i f i c a t i o n of c e l l u l o s e by ammonium s a l t s has been r e p o r t e d ( E q u a t i o n 7) (19, 20, 21).



158

r

'OR

+

NH

3

+

(7)

H 0 2

,OH

While t h i s r e a c t i o n c o u l d c o n t r i b u t e to the f o r m a t i o n of the c e l l u l o s e h a l f - a c i d e s t e r , the e x p e r i m e n t a l r e s u l t s of Cuculo and Johnson (2^) have i n d i c a t e d t h a t the ammonium s a l t r e a c t i o n i s not the major c o n t r i b u t o r i n r e a c t i o n s of s u c c i n a m i c a c i d w i t h v i s c o s e rayon. An a l t e r n a t i v e r e a c t i v e i n t e r m e d i a t e i s the a n h y d r i d e which has been proposed as the intermediate i n the h y d r o l y s i s (10, 11, 12, 13, 14, 1£, 16, Γ7, _18) and a m i n o l y s i s (22) r e a c t i o n s oT^ a,~T-amic a c i d s . A n h y d r i d e might "Form i n the r e s i d u e l e f t on the f a b r i c a f t e r the pad-bath s o l v e n t i s removed and s u b s e q u e n t l y r e a c t w i t h the c e l l u l o s e ( E q u a t i o n 8 ) . T h i s mechanism is

attractive 1.

2.

f o r the

following

reasons:

Formation o f a n h y d r i d e from a, 3-amic a c i d s has been d i r e c t l y d e t e c t e d i n s e v e r a l cases (18, 23, 24, 25) and Tïïe anhycfride i n much l e s s s e l e c t i v e than the amide i n s o l v o l y s i s r e a c t i o n s and e a s i l y under goes a l c o h o l y s i s at room tempeature (^6).

T h i s paper d e s c r i b e s a study undertaken to determine the c h e m i c a l changes which occur i n s u c c i n a m i c and p h t h a l a m i c a c i d s d u r i n g the p r e p a r a t i o n of the pad-bath and the pad-bake r e a c t i o n . The


11.

B O W M A N A N D CUCULO


159

pad-bake procedure was s i m u l a t e d under c o n d i t i o n s which a l l o w e d complete r e c o v e r y o f the r e s i d u e o f r e a c t i o n . The r e a c t i o n s were performed i n the absence o f c e l l u l o s i c s u b s t r a t e i n the hope t h a t any s t a b l e i n t e r m e d i a t e which might be the p r e c u r s o r t o the c e l l u l o s e h a l f - a c i d e s t e r might be d i r e c t l y d e t e c t e d . A l s o sought were the p r o d u c t s o f r e a c t i o n s i n c o m p e t i t i o n w i t h the e s t e r i f i c a t i o n . The c o m p o s i t i o n of the r e s i d u e was s t u d i e d as a f u n c t i o n o f bake time and temperature, i n i t i a l c o n c e n t r a t i o n o f the b a t h , presence o f c a t a l y s t , s o l v e n t , and d r y i n g c o n d i t i o n s (removal o f s o l v e n t ) . Experimental P r e p a r a t i o n o f Amic A c i d S o l u t i o n s . Phthalamic a c i d or s u c c i n a m i c a c i d was p r e p a r e d by the methods g i v e n i n r e f e r e n c e s (4^) and (21) . The amic a c i d s o l u t i o n was p r e p a r e d i n a 10 ml v o l u m e t r i c f l a s k m a i n t a i n e d a t 60±3°C i n a water b a t h . The d i s t i l l e d water used t o p r e p a r e the amic a c i d s o l u t i o n was i n c u b a t e d i n the water b a t h . When c a t a l y s t was used i t was added a f t e r the amic a c i d . P e r f o r m i n g the R e a c t i o n . An a l i q u o t o f amic a c i d s o l u t i o n was removed from the f l a s k w i t h a p r e h e a t e d c o n s t a n t d e l i v e r y s y r i n g e and i n j e c t e d through a rubber septum i n t o a p r e h e a t e d 25 ml r e a c t i o n f l a s k . The f l a s k was heated by a l a r g e volume o i l bath h e l d at the r e a c t i o n temperature ±1°C. The i n i t i a l amount o f amic a c i d was determined from the s o l u t i o n c o n c e n t r a t i o n and a l i q u o t volume. The r e a c t i o n f l a s k was f i t t e d w i t h a n i t r o g e n i n l e t and condenser. N i t r o g e n at a s l i g h t p o s i t i v e p r e s s u r e flowed through the r e a c t i o n f l a s k and out through the condenser i n t o a f l a s k c o n t a i n i n g s t a n d a r d a c i d t o t r a p any v o l a t i l e ammonia. In some cases the a c i d t r a p was preceded by a c h l o r o f o r m t r a p . The d u r a t i o n o f the r e a c t i o n was taken as the time from i n j e c t i o n o f the s o l u t i o n u n t i l the removal o f the r e a c t i o n f l a s k from the o i l bath f o r quenching i n a stream o f acetone. The f l a s k was then c l e a n e d , and d r i e d under vacuum at 40°C f o r one hour, and i t s mass determined. R e a c t i o n s from Ν, N-dimethylformamide and formamide r e q u i r e d l o n g e r p e r i o d s o f d r y i n g . The r e s i d u e mass was determined by d i f f e r e n c e . The c o n d i t i o n s under which the r e a c t i o n s were performed are summarized i n T a b l e I . A n a l y s i s o f the P r o d u c t s . The r e a c t i o n p r o d u c t s were a n a l y z e d q u a l i t a t i v e l y by i n f r a r e d s p e c t r o s c o p y . The s p e c t r a were determined as KBr p e l l e t s u s i n g a


In Solvent Spun Rayon, Modified Cellulose Fibers and Derivatives; Turbak, A.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977. 175 200

Ν

" w

tl

M

II

tt tt M M fl tt

175

5 15 10 Ν Ν ft It fl

10 η

Ν

1.5 4.0 1.5 2.5 Μ Ν

ft

s

8

Ρ

8

8

Ρ

14*

15*

16

17

18

tt

Ρ

Μ

2.5

tt

η

M

tt

15

formamide

DMF

formamide

η

tl

II

"

tt

M

η

175 η

8

5

II

M

175 200

Ν

m

It

Ρ

150

η

η

m

η

water

150

10

2.5 M

Bath Solvent

Conditions Reaction Temperature °C

Reaction

I

Duration of Reaction, min.

Concen tration, molar

Ρ η

M

s

Acid

Ρ

Amic

13

12

11

10

9

8

7

6

5

4

3

2

1

Reaction Number

Summary o f

Table

In Solvent Spun Rayon, Modified Cellulose Fibers and Derivatives; Turbak, A.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977. p,

6% ammonium s u l f a m a t e

s o l u t i o n evaporated

**

succinaroic a c i d

*

8,

in a

stream

of

based on the

phthalamic

-

"

of

air

moles of

for

the

-

"

before

acid 12 h r s .

amic

DMF, N , N - d i m e t h y l f o r m a m i d e

compressed

no.

acid

ρ

23

"

melt

8

22

n

"

"

"

e

being

Reaction Temperature C

" -

.

"

—

Duration of Reaction, min.

s

.

Concentration. molar

ρ

ρ

Amic A c i d

1 continued

19 20** 21**

Reaction Number

Table

heated

none

Η

water

DMF

Bath Solvent

r

a

Ο

^

S

»

g

a

Β


igure 2. Infrared spectra of (A) succinamic acid and (B) phthalamic acid in the region 4000-1200 cm' 1


11.

BOWMAN AND

cucuLO

163


P e r k i n - E l m e r I n f r a c o r d 337 R e c o r d i n g Spectrophotometer. The p o s i t i o n o f a b s o r p t i o n maxima r e p o r t e d here were measured from p o l y s t y r e n e r e f e r e n c e f i l m . The p r o d u c t s were a n a l y z e d f o r ammonium i o n by N e s s l e r i z a t i o n (2*8) u s i n g s t a n d a r d s prepared from ammonium s u l f a t e . The n e u t r a l i z a t i o n e q u i v a l e n t o f the r e a c t i o n p r o d u c t was determined by p o t e n t i o m e t r i c t i t r a t i o n w i t h s t a n d a r d ammonium h y d r o x i d e . The e n d p o i n t s were determined a n a l y t i c a l l y from v a l u e s o f the second d e r i v a t i v e curve i n the r e g i o n o f the e n d p o i n t . The a n a l y s i s with the weak base was n e c e s s a r y because a p o r t i o n o f the r e s i d u e was an ammonium s a l t . The determination of fre of the a c i d w i t h a wea (29). The amount o f c h l o r o f o r m s o l u b l e m a t e r i a l i n the r e a c t i o n p r o d u c t was determined by e x t r a c t i o n o f a powdered sample o f p r o d u c t w i t h an a l i q u o t o f c h l o r o f o r m . The e x t r a c t i o n was performed i n a f r i t t e d funnel. The e x t r a c t i o n was c o n s i d e r e d complete when the d e c r e a s e i n mass o f the r e s i d u e on s u c c e s s i v e e x t r a c t i o n s was l e s s than 0.1% o f the i n i t i a l mass. The c h l o r o f o r m e x t r a c t s were r e c o v e r e d by e v a p o r a t i o n and t h e i r i n f r a r e d s p e c t r a and m e l t i n g ranges were determined. T o t a l n i t r o g e n i n the samples was determined by the m i c r o - K j e l d a h l t e c h n i q u e ( 3 0 ) . D e t e r m i n a t i o n o f the S t a b i l i t y o f the Amic A c i d Solutions. The s t a b i l i t y of the s o l u t i o n s prepared as above was determined by f o l l o w i n g the appearance o f ammonium i o n w i t h time and by e x a m i n a t i o n o f the i n f r a r e d spectrum o f the m a t e r i a l i n the s o l u t i o n . In both a n a l y s e s an a l i q u o t o f s o l u t i o n was withdrawn and N e s s l e r i z e d f o r ammonium c o n t e n t or evaporated to d r y n e s s under vacuum f o r e v a l u a t i o n o f the i n f r a r e d spectrum as d e s c r i b e d above. R e s u l t s o f the

Experiments

The i n f r a r e d s p e c t r a o f s u c c i n a m i c and p h t h a l a m i c a c i d s are g i v e n i n F i g u r e 2. The d i s t i n c t i v e f e a t u r e s of the amic a c i d s p e c t r a are the c a r b o n y l d o u b l e t near 1700 cm" and the d o u b l e t i n the r e g i o n 3000 cm" to 3500 cm" due t o the n i t r o g e n - h y d r o g e n s t r e t c h i n g vibrations. The c a r b o n y l peaks i n s u c c i n a m i c a c i d are at 1710 cm" and 1650 cm" . In p h t h a l a m i c a c i d the c a r b o n y l peaks occur a t 1695 cm"^ and 1645 cm' . The h i g h energy peak i s due t o the c a r b o x y l i c a c i d c a r b o n y l s t r e t c h i n g v i b r a t i o n and the low energy peak due t o the 1

1

1

1

1

1


S O L V E N T SPUN

R A Y O N , MODIFIED

CELLULOSE


FD3ERS

11.


165


amide c a r b o n y l s t r e t c h i n g v i b r a t i o n . The n i t r o g e n hydrogen s t r e t c h i n g v i b r a t i o n peaks occur a t 3375 cmand 3215 cmi n s u c c i n a m i c a c i d and a t 3355 cm" and 3155 c m i n phthalamic a c i d . This doublet corresponds to t h e asymmetric and symmetric N-H s t r e t c h i n g vibrations. These assignments a r e c o n s i s t e n t with the l i t e r a t u r e (31, 2, 3 2 ) . The s p e c t r a o f t h e p r o d u c t s o f the r e a c t i o n o f s u c c i n a m i c a c i d f o r t e n minutes a t 1 5 0 ° C 175°C, and 200°C ( r e a c t i o n s 1,2, and 3, T a b l e I ) a r e shown i n F i g u r e 3. Comparison o f these s p e c t r a w i t h t h a t o f s u c c i n a m i c a c i d i n F i g u r e 2 shows t h a t s i g n i f i c a n t changes have o c c u r r e d i n the n i t r o g e n - h y d r o g e n and carbonyl s t r e t c h i n s t r e t c h i n g peaks a r i n the pure amic a c i d t h e h i g h energy peak i s by f a r the most i n t e n s e . In s p e c t r a Β and C (175°C and 200°C, r e s p e c t i v e l y ) t h e i n t e n s i t y o f the low energy N-H s t r e t c h i n g v i b r a t i o n i s the g r e a t e s t . The amide c a r b o n y l a b s o r p t i o n which has begun t o d e c r e a s e i n spectrum A has become a s h o u l d e r i n s p e c t r a Β and C. T h i s i n d i c a t e s a p r o g r e s s i v e d e c r e a s e i n the amount o f amide i n the r e s i d u e as the temperature o f r e a c t i o n increases. In a d d i t i o n the peak which appears near 1575 cm" i n t h e pure amic a c i d ( p r o b a b l y the amide II band (£, p.94,95) has broadened and the p o s i t i o n o f the maximum has s h i f t e d t o 1550 cm' i n s p e c t r a Β and C. T h i s i s an i n d i c a t i o n o f the f o r m a t i o n o f an ammonium s a l t i n the r e s i d u e s i n c e the c a r b o n y l s t r e t c h i n g a b s o r p t i o n o f t h e c a r b o x y l a t e anion o c c u r s near 1550 cm" (j>). T h i s c o n c l u s i o n i s supported by the appearance o f two broad peaks o f medium i n t e n s i t y near 2500 cm" and 2000 cmwhich would be expected i n the s p e c t r a o f ammonium s a l t s ( j 6 , p.94). A f u r t h e r change which o c c u r s i n the c a r b o n y l r e g i o n i s the appearance o f a shoulder a t 1760 cm" i n spectrum Β which i s s h a r p l y r e s o l v e d i n spectrum C. The appearance o f the peak a t 1760 cm' can b e s t be e x p l a i n e d by the presence o f succinimide i n the product. The spectrum o f the pure imide i s shown i n F i g u r e 4 (spectrum A) along w i t h t h a t of s u c c i n a m i c a c i d c o n t a i n i n g 20% s u c c i n i m i d e by weight prepared from t h e pure compounds (spectrum B ) . The s p e c t r a c l e a r l y show t h a t the a b s o r p t i o n peak a t 1760 cm" can be e x p l a i n e d by the presence o f s u c c i n i m i d e . Thus i t can be concluded on the b a s i s o f the i n f r a r e d s p e c t r a t h a t t h e r e l a t i o n p r o d u c t s i n c l u d e unreacted s u c c i n a m i c a c i d , ammonium s a l t which c o u l d be a mixture of ammonium succinamate, monoammonium s u c c i n a t e , and diammonium s u c c i n a t e , and s u c c i n i m i d e . The q u a l i t a t i v e a n a l y s i s o f the r e a c t i o n p r o d u c t s 1

1

1

4

r

1

1

1

1

1

1

1

1


166

S O L V E N T SPUN R A Y O N ,

MODIFIED C E L L U L O S E

FD3ERS

by i n f r a r e d s p e c t r o s c o p y i s supported by the q u a n t i t a t i v e a n a l y t i c a l data presented i n Table I I ( R e a c t i o n s 1,2,3). The presence o f ammonium i o n as determined by N e s s l e r ' s reagent i n d i c a t e s t h a t a s u b s t a n t i a l amount o f h y d r o l y s i s has o c c u r r e d e i t h e r i n the p r e p a r a t i o n o f the s o l u t i o n or i n the bake s t e p . The amount o f ammonium i o n i s markedly lower a t the h i g h e s t temperature, 200°C. The d e c r e a s e i n the amount o f ammonium i o n with temperature i s accompanied by an i n c r e a s e i n the amount of c h l o r o f o r m s o l u b l e m a t e r i a l and n e u t r a l i z a t i o n equivalent. T h i s r e f l e c t s an i n c r e a s i n g amount o f succinimide i n the r e s i d u e . The imide i s c h l o r o f o r m s o l u b l e and i s t o o neutralization equivalen removed from t h e r e s i d u e by e x t r a c t i o n the r e s i d u e c o n t a i n s the a c i d s and s a l t s . The t o t a l amount o f n i t r o g e n (as ammonia) p r e s e n t i n t h i s r e s i d u e was determined by m i c r o - K j e l d a h l a n a l y s i s . T h i s v a l u e r e p r e s e n t s the t o t a l amide and ammonium n i t r o g e n on an i m i d e - f r e e b a s i s . When based on the t o t a l mass o f t h e r e s i d u e t h i s v a l u e can be used t o determine the % amide ammonia i n t h e m i x t u r e . These d e r i v e d v a l u e s f o r % amid ammonia a r e g i v e n i n T a b l e I I . The amount o f amide ammonia d e c r e a s e s from 9.19% a t 150°C t o 7.62% a t 200° C. By u s i n g the v a l u e s f o r % c h l o r o f o r m s o l u b l e m a t e r i a l , i t i s p o s s i b l e to c a l c u l a t e the % y i e l d o f imide i n the r e a c t i o n . I t i s a l s o p o s s i b l e t o c a l c u l a t e t h e y i e l d s o f ammonium s a l t (as monoammonium s u c c i n a t e ) and amic a c i d from the % i o n i c ammonia and % amide ammonia v a l u e s r e s p e c t i v e l y . I t i s a l s o p o s s i b l e to c a l c u l a t e the y i e l d o f d i a c i d from t h e v a l u e s o f the n e u t r a l i z a t i o n e q u i v a l e n t and the y i e l d s o f monoammonium s a l t and amic a c i d . T h i s l a s t c a l c u l a t i o n i s based on the assumption t h a t the a c i d s p r e s e n t i n the m i x t u r e a r e the amic a c i d , t h e monoammonium s a l t and t h e d i a c i d . The r e s u l t s o f such c a l c u l a t i o n s are shown i n T a b l e III. The d a t a f o r r e a c t i o n s 1, 2 and 3 show t h a t the amide content d e c r e a s e s w h i l e the y i e l d s o f imide and d i a c i d i n c r e a s e (as the temperature i s i n c r e a s e d ) . The ammonium s a l t c o n t e n t d e c r e a s e s . These d a t a a r e c o n s i s t e n t with the c o n c l u s i o n t h a t h y d r o l y s i s o c c u r s i n the p r e p a r a t i o n o f the amic a c i d s o l u t i o n and d u r i n g the v o l a t i l i z a t i o n o f the s o l v e n t . The d e h y d r o c y c l i z a t i o n r e a c t i o n which y i e l d s imide i s a competing r e a c t i o n which y i e l d s an i n e r t product (_3) · The s p e c t r a o f the p r o d u c t s o f the pad-bake r e a c t i o n o f p h t h a l a m i c a c i d f o r 10 minutes a t 150 ( A ) , 175 ( B ) , and 200°C (C) ( r e a c t i o n 4 , 5, and 6, T a b l e I)


102.3 100.8 92.4 107.5 104.9 94.9 99.6 97.6 110.7 103.8 96.7 99.3 99.3 99.1 99.5 71.5 84.1 80.1 83.2 98.9 97.6 90.4 88.1

% Mass Recovered

4.09 5.27 0.99 8.36 8.08 5.16 3.63 2.78 8.25 7.58 2.92 3.69 7.87 5.04 7.97 1.32 0.07 0.74 0.13 3.41 6.57 1.65 1.02

0.43 5.84 41.11 6.95 12.41 45.70 0.62 21.42 2.05 11.27 14.88 11.27 3.16 6.36 6.71 1.27 33.87 90.05 100.00 14.73 18.64 24.40 87.20

Ionic NH 3

%

% CHCI3 Extracts

13.31 9.35 13.96 9.41

129.52 223.36 140.51 183.20***

•*

9.19 7.35 7.62 0.31 0.00 0.00 9.61 6.35 0.95 0.00 7.55 7.65 0.83 7.44 1.08 15.80 9.,26 0.51 0.00 7.84 1.06 8.48 0.23 13.33 13.38 14.63 9.32 9.34 9.32 13.33 11.63 9.40 9.39 12.30 12.79 8.98 13.33 9.70 17.34 14.08 12.51

115.40 123.13 173.11 196.67 204.41 331.85 117.53 134.67 185.62 205.14 124.93 122.72 165.55 122.98 202.69 121.92 171.10

* *

% Amide NH-

% NH 3 1n Extract Residue

Study

Neutral 1zation Equivalent

Data f o r R e a c t i o n S t o l c h l o m e t r y

II

* not determined * * no r e s i d u e *** neutralization equivalent of the extraction residue

12 13 14 15 16 17 18 19 20 21 22 23

11

2 3 4 5 6 7 8 9 10

1

Reaction Number

Analytical

Table

£a

0

d

Ο

tions 3

ulos


168


are shown i n F i g u r e 5. Comparison of these s p e c t r a with t h a t of p h t h a l a m i c a c i d (B i n F i g u r e 2) show t h a t a v e r y s i g n i f i c a n t change has o c c u r r e d d u r i n g the r e a c t i o n . A f t e r r e a t i o n at 150°C (spectrum A ) , the N-H s t r e t c h i n g d o u b l e t has been r e p l a c e d by a s t r o n g a b s o r p t i o n , a t 3125 cm"" and a weak a b s o r p t i o n at 3480 cm' . The c a r b o x y l s t r e t c h i n g r e g i o n has a l s o changed. The amide and c a r b o x y l absorbances at 1695 cm" and 1645 cm" have been r e p l a c e d by two peaks at 1675 cnrând 1550 cm" . The l a t t e r peak i s q u i t e i n t e n s e . A d d i t i o n a l l y , two broad, m o d e r a t e l y i n t e n s e peaks have appeared at 2450 crif and 1950 cm" . The absorbances are c o n s i s t e n t with those o f an ammoniu a c i d as noted b e f o r o f s u c c i n a m i c a c i d . In t h i s c a s e however, the spectrum i n d i c a t e s the h y d r o l y s i s r e a c t i o n i s v i r t u a l l y complete. With i n c r e a s i n g temperature, the s p e c t r a change, p a r t i c u l a r l y i n the c a r b o n y l a b s o r p t i o n r e g i o n ( s p e c t r a B, C ) . The peak which appears at 1675 cnr in spectrum A has s h i f t e d to 1705 cm*" i n spectrum Β and has i n c r e a s e d i n i n t e n s i t y r e l a t i v e to the maximum at 1550 cm" . In a d d i t i o n a s m a l l shoulder has appeared at 1780 c m ' i n spectrum B. In spectrum C, the h i g h energy maximum now i s the most i n t e n s e and i s l o c a t e d at 1745 cm" . The s h o u l d e r at 1780 cm" i n Β i s now a sharp peak at 1780 cm' . In a d d i t i o n the broad peaks at 2450 cm' and 1950 cm' noted i n A have s u b s t a n t i a l l y d i s a p p e a r e d i n C. The N-H s t r e t c h i n g r e g i o n i s v i r t u a l l y the same i n each spectrum but, as noted b e f o r e , d i f f e r s r a d i c a l l y from t h a t o f p h t h a l a m i c acid. These s p e c t r a are c o n s i s t e n t with the c o n c l u s i o n t h a t p h t h a l a m i c a c i d i s almost c o m p l e t e l y h y d r o l y z e d i n the pad-bake r e a c t i o n or d u r i n g the p r e p a r a t i o n o f the pad s o l u t i o n . The m a t e r i a l d e p o s i t e d i s e s s e n t i a l l y the monoammonium s a l t o f p h t h a l i c a c i d . T h i s s a l t i s i n c r e a s i n g l y c o n v e r t e d to the i n a c t i v e p r o d u c t , p h t h a l i m i d e as the temperature i s i n c r e a s e d . These c o n c l u s i o n s are supported by the a n a l y t i c a l d a t a i n T a b l e I I . The % amide ammonia i s o n l y 0.31% i n the p r o d u c t s o f r e a c t i o n 4 and zero i n r e a c t i o n s 5 and 6. The i o n i c ammonia v a l u e s are r e l a t i v e l y high but d e c r e a s e from 8.36% a t 150°C ( r e a c t i o n 4) t o 5.16% a t 200°C ( r e a c t i o n 6 ) . The n e u t r a l i z a t i o n e q u i v a l e n t and % c h l o r o f o r m s o l u b l e m a t e r i a l i n c r e a s e from 196.67 g r a m s / e q u i v a l e n t and 6.95% a t 150°C ( r e a c t i o n 4) t o 331.85 g r a m s / e q u i v a l e n t and 45.70% a t 200°C ( r e a c t i o n 6). These o b s e r v a t i o n s can be e x p l a i n e d by the p r o g r e s s i v e c o n v e r s i o n o f the monoammonium s a l t i n t o phthalimide. By u s i n g the methods d i s c u s s e d p r e v i o u s l y 1

1

1

1

1

}

f

-1

1

1

1

1

1

1

1

1


B O W M A N AND CUCULO


Figure 5. Infrared spectra of the products of the reaction of phthalamic acid for 10 min at 150°C (A), 175°C (B), and 200°C (C)



170

CELLULOSE

FIBERS

the y i e l d s o f the v a r i o u s p r o d u c t s pan be c a l c u l a t e d . The r e s u l t s o f t h e c a l c u l a t i o n s a r e shown i n T a b l e I I I . The y i e l d o f ammonium s a l t d e c r e a s e s with i n c r e a s i n g temperature from an i n i t i a l v a l u e o f 87.5% a t 150°C. The amic a c i d was almost e n t i r e l y h y d r o l y z e d i n these r e a c t i o n s and the h y d r o l y z a t e , monoammonium p h t h a l a t e , i s c o n v e r t e d t o p h t h a l i m i d e . The y i e l d o f the imide i n c r e a s e s r a p i d l y w i t h temperature from 8.4% a f t e r 10 minutes a t 150°C t o 48.7% a f t e r 10 minutes a t 200°C. Small amounts o f the amic a c i d and d i a c i d were a l s o indicated. The s p e c t r a o f the p r o d u c t s o f the r e a c t i o n o f s u c c i n a m i c a c i d a t 175°C f o r 5, 10, and 15 minutes ( r e a c t i o n s 7, 2, and 8 r e s p e c t i v e l y ) show i F i g u r e 6. With i n c r e a s i n i n the s p e c t r a a r e v e r y n e a r l y the same as the changes caused by i n c r e a s i n g temperature ( F i g u r e 3 ) . The amide c a r b o n y l s t r e t c h i n g a b s o r p t i o n which appears a t l 6 5 0 cm" i n t h e p a r e n t compound, s u c c i n a m i c a c i d (spectrum A, F i g u r e 2) d e c r e a s e s i n i n t e n s i t y w i t h time as the peak at 1575 cm- broadens and a s h o u l d e r appears a t 1760 cm" . A g a i n the n i t r o g e n - h y d r o g e n s t r e t c h i n g v i b r a t i o n s have r e v e r s e d i n r e l a t i v e i n t e n s i t y . These changes i n the s p e c t r a o f the p r o d u c t s o f the bake r e a c t i o n are c o n s i s t e n t w i t h the c o n c l u s i o n t h a t the succinamic acid i s deposited during v o l a t i l i z a t i o n of the s o l v e n t as a mixture o f s u c c i n a m i c a c i d and monoammonium s u c c i n a t e . T h i s m a t e r i a l i s p r o g r e s s i v e l y c o n v e r t e d i n t o s u c c i n i m i d e as the h e a t i n g i s c o n t i n u e d . A g a i n t h e a n a l y t i c a l d a t a support this conclusion. F i v e minutes i n t o the r e a c t i o n ( r e a c t i o n 7) t h e r e a c t i o n p r o d u c t s c o n t a i n 3.63% ammonia as ammonium i o n . The % amide ammonia i s 9.61% which c o r r e s p o n d s t o a y i e l d o f 65.9% s u c c i n a m i c a c i d . Thus, a f t e r f i v e minutes, t h e amount o f amic a c i d has d e c r e a s e d 34.1%. The y i e l d v a l u e s a r e g i v e n i n T a b l e III. The y i e l d o f s u c c i n a m i c a c i d d e c r e a s e s w i t h time from 65.9% a f t e r 5 minutes t o 39.8% a f t e r 15 minutes as the amic a c i d i s p r o g r e s s i v e l y c o n v e r t e d i n t o s u c c i n i m i d e and ammonium s a l t . The y i e l d o f imide i n c r e a s e s from 0.6% a t 5 minutes t o 23.1% a t 15 minutes. The y i e l d o f ammonium s a l t i s maximum a t 10 minutes a t 34.0% and d e c r e a s e s a f t e r 15 minutes t o 23.1% i n d i c a t i n g the p o s s i b i l i t y o f i t s c o n v e r s i o n t o d i a c i d or i m i d e . The y i e l d o f d i a c i d i n c r e a s e d from 4% a f t e r 5 minutes t o 13% a t 15 minutes. The s p e c t r a o f t h e p r o d u c t s o f the r e a c t i o n o f p h t h a l a m i c a c i d a t 175°C f o r 5 10, and 15 minutes ( r e a c t i o n s 9, 5, and 10 r e s p e c t i v e l y ) a r e shown i n F i g u r e 7. The s p e c t r a a g a i n d i f f e r g r e a t l y from the

:

1

1

f


11.

B O W M A N AND

3500

3000

cucuLo

2500

FREQUENCY, CM"'


2000

1500

171

Figure 6. Infrared spectra of the products of the reaction of succinamic acid at 175°C for 5 min (A), 10 min (B), and 15min(C)



CELLULOSE

Table I I I Product Y i e l d Data, Time, Temp., Cone, and C a t a l y s t % Yield

Reaction Number

Unreacted Amic Acid

Monoammonium «ait

Imide

Diacid

1

64.6

28.6

0.5

6.

2

53.

3

41.5

7.7

41.1

11

4

3.3

87.5

8.4

0

5

0

81.5

14.9

1

6

0

47.6

48.7

1

24.7

0.6

4

7

65.9

8

39.8

23.1

23.1

9

10.2

88.6

2.5

0

10

1.4

82.1

17.2

0

11

50.2

19.3

17.0

8

12

52.1

25.0

13.1

9

13

7.8

74.6

3.6

10

14

51.3

34.6

7.6

7

15

10.9

80.3

6.7

1

13


FD3ERS

11.

B O W M A N A N D cucuLO

173


spectrum o f p h t h a l a m i c a c i d ( F i g u r e 2, spectrum B) and i n d i c a t e by the absence o f any s i g n i f i c a n t a b s o r p t i o n at 1645 cm"" due t o t h e amide c a r b o n y l s t r e t c h i n g a b s o r p t i o n and by the p r e s e n c e o f the s t r o n g a b s o r p t i o n at 1550 cm" and 3200 cm" t h a t t h e p h t h a l a m i c a c i d i s extensively hydrolyzed. Dehydrocyclization to y i e l d imide a l s o o c c u r s as i n d i c a t e d by the appearance o f the s h o u l d e r a t 1780 cm"i i n s p e c t r a Β ( r e a c t i o n 5) and C ( r e a c t i o n 10). These o b s e r v a t i o n s i n d i c a t e t h a t the p h t h a l a m i c a c i d i s almost c o m p l e t e l y h y d r o l y z e d a t the o u t s e t o f the bake s t e p and i s d e p o s i t e d d u r i n g t h e v o l a t i l i z a t i o n o f t h e s o l v e n t as the p a r t i a l ammonium salt. The a n a l y t i c a l d a t a i n T a b l e I I support t h i s c o n c l u s i o n with th 8.25% a f t e r 5 minute 7.58% a f t e r 15 minutes ( r e a c t i o n 10). T h i s decrease i s accompanied by an i n c r e a s e i n the % c h l o r o f o r m e x t r a c t a b l e s from 2.05% t o 11.27% and the n e u t r a l i z a t i o n e q u i v a l e n t from 185.62 g r a m / e q u i v a l e n t to 205.14 g r a m / e q u i v a l e n t i n t h e same r e a c t i o n s . These d a t a were used t o c a l c u l a t e the % y i e l d v a l u e s shown i n T a b l e I I I . Here the y i e l d o f ammonium s a l t i s q u i t e high a t 88.6% a f t e r f i v e minutes and d e c r e a s e s t o a n e a r l y c o n s t a n t v a l u e o f 81.5% a f t e r 10 m i n u t e s . The y i e l d o f p h t h a l i m i d e i n c r e a s e s c o n t i n u o u s l y throughout the r e a c t i o n from a v a l u e o f 2.5% a f t e r 5 minutes t o 17.2% a f t e r 15 m i n u t e s . The r e s i d u a l p h t h a l a m i c a c i d y i e l d which i s 10.2% a f t e r 5 minutes has d e c r e a s e d t o 1.4% a f t e r 15 m i n u t e s . P h t h a l i c a c i d was d e t e c t e d a t 10 minutes i n a 1% y i e l d . These d a t a i n d i c a t e t h a t the ammonium s a l t i s formed i n h i g h y i e l d d u r i n g t h e p r e p a r a t i o n o f the amic a c i d s o l u t i o n and d u r i n g the v o l a t i l i z a t i o n o f the s o l v e n t by the h y d r o l y s i s o f a s u b s t a n t i a l amount (88.6% a t 5 minutes) o f the i n i t i a l phthalamic a c i d . The r e s i d u a l p h t h a l a m i c a c i d d i s appears g r a d u a l l y as does the ammonium s a l t . This d i s a p p e a r a n c e i s accompanied by t h e appearance o f p h t h a l i m i d e which c o u l d r e s u l t from the d e c o m p o s i t i o n of the p h t h a l a m i c a c i d and the p a r t i a l ammonium s a l t . 1

1

1

I t i s o f i n t e r e s t t o determine the e f f e c t o f the pad bath c o n c e n t r a t i o n on the r e s i d u e c o m p o s i t i o n . The s p e c t r a o f the p r o d u c t s o f the r e a c t i o n o f s u c c i n a m i c a c i d a t 175°C f o r 10 minutes a t i n i t i a l c o n c e n t r a t i o n s of 4.00, 2.50, and 1.50 molar ( r e a c t i o n s 12, 2, and 11, r e s p e c t i v e l y ) a r e shown i n F i g u r e 8. In comparison w i t h t h e spectrum o f s u c c i n a m i c a c i d (spectrum A i n F i g u r e 2) a l l t h e s p e c t r a show a d e c r e a s e i n the amide c a r b o n y l s t r e t c h i n g a b s o r p t i o n a t 1650 cm" accompanied by broadening and i n c r e a s e i n absorbance a t 1575 cm" , the c a r b o x y l a t e c a r b o n y l s t r e t c h i n g a b s o r p t i o n , a 1

1


S O L V E N T S P U N R A Y O N , MODIFIED C E L L U L O S E FD3ERS OOi

.50

IJO •

ool

' 3500

• 3000

' 2500

FREQUENCY, CM*

' 2000

1500 1

1

Figure 8. Infrared spectra of the products of the reaction of succinamic acid at 175°C for 10 min at an initial solution con centration of 4.00M (A), 2.5M (B), and 1.50M (C)

3500

3000

I 2500

ι ι ι ι I I 2000 1500

FREQUENCY, CM"'

Figure 9. Infrared spectra of the products of the reaction of phthalamic acid at 175°C for 10 min at an initial solution concen tration of 1.50M (A) and 2.50M (B)


11.


175


change i n the r e l a t i v e i n t e n s i t y of the d o u b l e t i n the n i t r o g e n - h y d r o g e n s t r e t c h i n g r e g i o n (3000 cm" to 3500 c m " ) , and the appearance of a shoulder at 1760 cm"" . These changes i n d i c a t e t h a t the amic a c i d has undergone both h y d r o l y s i s and d e h y d r o c y c l i z a t i o n . From the s p e c t r a i t can be seen t h a t the e x t e n t o f r e a c t i o n i s g r e a t e s t f o r r e a c t i o n 2 (spectrum B) s i n c e the spectrum o f the r e s i d u e of t h i s r e a c t i o n shows the g r e a t e s t change. The a n a l y t i c a l d a t a i n T a b l e I I show q u a n t i t a t i v e l y the changes which occur i n the s u c c i n amic a c i d d u r i n g the pad-bake r e a c t i o n . The amount of h y d r o l y s i s which has o c c u r r e d i s the g r e a t e s t at the i n t e r m e d i a t e c o n c e n t r a t i o n as i n d i c a t e d by the % i o n i c ammonia v a l u e s . In for the % i o n i c ammoni r e s p e c t i v e l y w h i l e i n r e a c t i o n 2, the v a l u e i s 5.27%. The % c h l o r o f o r m e x t r a c t a b l e s i s lower at the i n t e r m e d i a t e c o n c e n t r a t i o n s where the v a l u e i s 5.84% for an i n i t i a l c o n c e n t r a t i o n of 2.50 molar ( r e a c t i o n 2) and 14.88% and 11.27% a t i n i t i a l c o n c e n t r a t i o n s o f 1.50 ( r e a c t i o n 11) and 4.00 molar ( r e a c t i o n 12), respectively. These r e s u l t s i n d i c a t e t h a t the e x t e n t of d e h y d r o c y c l i z a t i o n r e a c t i o n i s l e s s than t h a t at the other c o n c e n t r a t i o n s . The n e u t r a l i z a t i o n e q u i v a l e n t s of the r e s i d u e s are n e a r l y the same as are the % amide ammonia v a l u e s f o r a l l the i n i t i a l c o n c e n t r a t i o n s . The y i e l d d a t a c a l c u l a t e d as b e f o r e are shown i n T a b l e I I I . The d a t a show l i t t l e e f f e c t of the i n i t i a l c o n c e n t r a t r a t i o n on the y i e l d o f s u c c i n a m i c a c i d i n the range o f 1.50 t o 4.00 molar a f t e r 10 minutes bake time at 175°C. The y i e l d o f imide g e n e r a l l y d e c r e a s e s with the s o l u t i o n c o n c e n t r a t i o n w h i l e the y i e l d o f ammonium s a l t increases. The y i e l d o f s u c c i n i c a c i d v a r i e s between 6% and 9%. The s p e c t r a of the p r o d u c t s of the r e a c t i o n o f p h t h a l a m i c a c i d at 175°C f o r 10 minutes at an i n i t i a l c o n c e n t r a t i o n o f 1.50 molar ( r e a c t i o n 13) and 2.50 molar ( r e a c t i o n 5) are shown i n F i g u r e 9. (Solutions of p h t h a l a m i c a c i d o f a c o n c e n t r a t i o n o f 4.00 molar c o u l d not be p r e p a r e d ) . The s p e c t r a show t h a t the p h t h a l a m i c a c i d has been e x t e n s i v e l y h y d r o l y z e d and t h a t d e h y d r o c y c l i z a t i o n has taken p l a c e to a s l i g h t e x t e n t as might be expected from the p r e v i o u s r e s u l t s . In T a b l e I I the d a t a show t h a t the % i o n i c ammonia v a l u e s f o r r e a c t i o n s 5 and 13 are 8.08% and 7.87% r e s p e c t i v e l y i n d i c a t i n g the e x t e n t o f h y d r o l y s i s i s about the same i n each c a s e . At the lower i n i t i a l (1.50 molar) c o n c e n t r a t i o n the % c h l o r o f o r m e x t r a c t a b l e s i s 3.16% compared w i t h 12.41% a t an i n i t i a l c o n c e n t r a t i o n o f 2.50 m o l a r . The n e u t r a l i 1

1

1



FIBERS

350 FREQUENCY, CM"

1

Figure 10. Infrared spectra of the products of the reaction of succinamic ana phthahmic acids at 175°C for 10 min at an initial concentration of 2.50M and 0.171M ammonium sulfamate as catalyst

col

1

,

•

3500

3000

2500

,

2000

FREQUENCY, CM"

•

1500

1

Figure 11. Infrared spectra of the products of the reaction of succinamic acid at 175°C for 10 min at an initial concentration of 2.50M in N,N-dimethylformamide (A), formamide (B), and water (C)


11.

B O W M A N AND cucuLO


177

z a t i o n e q u i v a l e n t o f the r e s i d u e i n r e a c t i o n 5 i s 204.41 g r a m s / e q u i v a l e n t w h i l e t h a t o f the r e s i d u e i n r e a c t i o n 13 i s 165.55 g r a m s / e q u i v a l e n t . The % amide ammonia v a l u e s a r e 0.00 and 0.83% f o r r e a c t i o n s 5 and 13 r e s p e c t i v e l y . These d a t a were used t o c a l c u l a t e the y i e l d v a l u e s g i v e n i n T a b l e I I I which show by the y i e l d of ammonium p h t h a l a t e t h a t the amount o f h y d r o l y s i s i s about the same i n each r e a c t i o n . The y i e l d o f d i a c i d d e c r e a s e s with i n i t i a l c o n c e n t r a t i o n w h i l e the y i e l d o f imide i n c r e a s e s . The y i e l d o f r e s i d u a l p h t h a l a m i c a c i d remains about the same. The s p e c t r a o f the p r o d u c t s o f the r e a c t i o n s o f s u c c i n a m i c a c i d (spectrum A, r e a c t i o n 14) and p h t h a l a m i c a c i d (spectru 10 minutes a t an i n i t i a amic a c i d and 0.171 molar i n ammonium s u l f a m a t e c a t a l y s t are shown i n F i g u r e 10. The s p e c t r a d i f f e r i n the same manner from the s p e c t r a o f the p a r e n t compounds, s u c c i n a m i c a c i d ( F i g u r e 2, spectrum A) and p h t h a l a m i c a c i d ( F i g u r e 2, spectrum B) as do the p r o d u c t s o f r e a c t i o n 2 ( F i g u r e 3, Spectrum B) and r e a c t i o n 5 ( F i g u r e 6, spectrum B) which were performed under i d e n t i c a l c o n d i t i o n s as r e a c t i o n s 14 and 15 except f o r the p r e s e n c e o f the c a t a l y s t . The a n a l y t i c a l d a t a i n T a l e I I r e f l e c t the s i m i l a r i t i e s . The % i o n i c ammonia i n r e a c t i o n 2 i s 5.27% compared with 5.04% i n r e a c t i o n 14. In r e a c t i o n 5 t h e % i o n i c ammonia i s 8.08% whereas i n r e a c t i o n 15 the v a l u e i s 7.97%. In r e a c t i o n 2 the" v a l u e s f o r % c h l o r o f o r m e x t r a c t a b l e s , n e u t r a l i z a t i o n e q u i v a l e n t , and % amide ammonia were 5.84%, 123.13 g r a m s / e q u i v a l e n t , and 7.35%, r e s p e c t i v e l y , w h i l e i n r e a c t i o n 14 w i t h c a t a l y s t p r e s e n t the v a l u e s were 6.36%, 122.98 g r a m s / e q u i v a l e n t , and 7.44%, r e s p e c t i v e l y . In r e a c t i o n 5 the v a l u e s f o r % chloroform extractables, n e u t r a l i z a t i o n equivalent, and % amide ammonia were 12.41%, 204.41 g r a m s / e q u i v a l e n t , and 0.00% r e s p e c t i v e l y w h i l e i n r e a c t i o n 15 the v a l u e s were 6.71%, 202.69 g r a m s / e q u i v a l e n t , and 1.08%. The a n a l y t i c a l d a t a are t r a n s l a t e d i n t o product y i e l d s i n Table I I I . Clearly the presence o f ammonium s u l f a m a t e c a t a l y s t has no g r e a t e f f e c t on t h e y i e l d s o f the p r o d u c t s i n the residue. The s p e c t r a o f the p r o d u c t s o f r e a c t i o n o f s u c c i n a m i c a c i d i n v a r i o u s s o l v e n t s are shown i n F i g u r e 11. The s o l u t i o n s were 2.50 molar i n Ν,Ν-dimethylformamide ( r e a c t i o n 17, spectrum A ) , formamide ( r e a c t i o n 16, spectrum B ) , and water ( r e a c t i o n 2, spectrum C ) . Comparison o f the s p e c t r a i n F i g u r e 11 w i t h t h a t o f the pure s u c c i n a m i c a c i d i n


178


F i g u r e 2 (spectrum A) r e v e a l s a g r e a t e r d i f f e r e n c e i n r e a c t i o n 2 w i t h water as s o l v e n t than i n r e a c t i o n s 16 and 17 w i t h nonaqueous s o l v e n t s . The spectrum o f the p r o d u c t s of r e a c t i o n 16 (B) i s v e r y s i m i l a r to t h a t o f the pure s u c c i n a m i c a c i d w i t h o n l y a s l i g h t d e c r e a s e i n the amide c a r b o n y l a b s o r p t i o n . In spectrum A t h i s d i f f e r e n c e i s more pronounced. A p p a r e n t l y , the changes t a k i n g p l a c e i n DMF and formamide are q u i t e d i f f e r e n t from those o c c u r r i n g i n water. The a n a l y t i c a l d a t a i n T a b l e I I r e f l e c t t h e s e d i f f e r e n c e s . The % i o n i c ammonia v a l u e s f o r the p r o d u c t s from formamide ( r e a c t i o n 16) and DMF ( r e a c t i o n 17) are 1.32% and 0.07%, r e s p e c t i v e l y , whereas the v a l u e i s 5.27% f o r water ( r e a c t i o n 2 ) g r e a t e r amount o f h y d r o l y s i i n the other s o l v e n t s , as e x p e c t e d . The % c h l o r o f o r m e x t r a c t a b l e s i s 5.84% f o r r e a c t i o n 2 (water), 1.27% for r e a c t i o n 16 (formamide), and 33.87% f o r r e a c t i o n 17 (DMF). T h i s i n d i c a t e s t h a t imide i s formed more e a s i l y i n the a p r o t i c s o l v e n t , DMF, than i n the p r o t i c s o l v e n t s , water and formamide. The n e u t r a l i z a t i o n e q u i v a l e n t and the % amide ammonia v a l u e s o f the p r o d u c t s of the r e a c t i o n s are 123.13 g r a m s / e q u i v a l e n t , 7.35%; 121.92 grams e q u i v a l e n t , 15.80% and 171.10 g r a m s / e q u i v a l e n t , 9.26% f o r r e a c t i o n s 2, 16, and 17, respectively. The d a t a were used to c a l c u l a t e the p r o d u c t y i e l d s i n T a b l e IV. The amount o f the o r i g i n a l s u c c i n a m i c a c i d s t i l l p r e s e n t a f t e r the pad-bake p r o c e d u r e i s much g r e a t e r f o r formamide (76.6%) than f o r DMF (59.3%) and water (53.2%). The h y d r o l y s i s r e a c t i o n t a k e s p l a c e to a much g r e a t e r e x t e n t i n water than i n DMF or formamide as i n d i c a t e d by the y i e l d s o f monoammonium s u c c i n a t e . These y i e l d v a l u e s are 34.0%, 7.4% and 0.4% f o r water, formamide, and DMF, respectively. The d e h y d r o c y c l i z a t i o n r e a c t i o n t o y i e l d s u c c i n i m i d e o c c u r r e d to a much g r e a t e r e x t e n t i n DMF (37.3% y i e l d ) than i n water (5.7%) or i n formamide (1.0%). S u c c i n i c a c i d was d e t e c t e d i n low y i e l d i n r e a c t i o n s 2 and 17. The y i e l d o f s u c c i n i c a c i d was 6%, 0%, and 2% f o r r e a c t i o n s 2, 16, and 17, r e s p e c t i v e l y . The s p e c t r a of the p r o d u c t s of the r e a c t i o n o f p h t h a l a m i c a c i d i n DMF ( r e a c t i o n 19), formamide ( r e a c t i o n 18), and water ( r e a c t i o n 5) are shown i n F i g u r e 12. The r e a c t i o n c o n d i t i o n s employed were 10 minutes bake time at 175°C and a s o l u t i o n c o n c e n t r a t i o n o f 2.50 m o l a r . The s p e c t r a o f the r e a c t i o n p r o d u c t s d i f f e r g r e a t l y from t h a t of the pure p h t h a l a m i c a c i d ( F i g u r e 2, spectrum B ) . The s p e c t r a i n d i c a t e t h a t with formamide ( r e a c t i o n 18, spectrum B) and DMF (reaction 19, spectrum A) the r e s i d u e s p e c t r a are q u i t e s i m i l a r


B O W M A N AND cucuLO

°°

3500


3000

2500 FREQUENCY, C M

2000

1500

H

Figure 12. Infrared spectra of the products of the reaction of phthafomic acid at 175°C for 10 min at an initial concentration of 2.50M in N,N-dimethylformamide (A), formamide (B), and water (C)


180


and i n d i c a t e t h a t the major p r o d u c t i s p h t h a l i m i d e . In water (spectrum C) the major p r o d u c t i s the ammonium salt. The d a t a i n T a b l e I I show t h a t the % i o n i c ammonia v l u e s f o r the p r o d u c t s of r e a c t i o n s 18 and 19 are o n l y 0.74% and 0.13%, r e s p e c t i v e l y , w h i l e t h a t o f r e a c t i o n 5 i s 8·08%. The % c h l o r o f o r m e x t r a c t a b l e s i s q u i t e high at 90.05% i n r e a c t i o n 18 and 100.00% i n r e a c t i o n 19. The v a l u e s would be expected to be l a r g e due to the l a r g e amount o f imide i n the r e s i d u e . The % amide v a l u e s are 0.51% f o r r e a c t i o n 18 and zero f o r r e a c t i o n 19. The p r o d u c t y i e l d v a l u e s are g i v e n i n T a b l e IV. The d a t a show t h a t i n a l l t h r e e s o l v e n t s the i n i t i a l p h t h a l a m i c a c i d i s almost c o m p l e t e l y c o n v e r t e d to one major p r o d u c t (reactio 5) t h i p r o d u c t i s the monoammoniu (81.5% y i e l d ) w h i l e i n formamide ( r e a c t i o n 18) and DMF ( r e a c t i o n 19) t h i s p r o d u c t i s p h t h a l i m i d e (74.7% and 92.5% y i e l d , r e s p e c t i v e l y ) . A l l e n has shown t h a t the manner i n which the s o l v e n t i s removed i n the pad-bake r e a c t i o n of aqueous s u c c i n a m i c a c i d s o l u t i o n s w i t h v i s c o s e rayon g r e a t l y a f f e c t s the e x t e n t of the e s t e r i f i c a t i o n r e a c t i o n (4^). F a b r i c which was padded, d r i e d at room temperature and baked was e s t e r i f i e d to a much l e s s e r e x t e n t than f a b r i c which was d r i e d and baked at an e l e v a t e d temperature i n the same s t e p . A l l e n a l s o found t h a t l i t t l e r e a c t i o n o c c u r r e d between molten s u c c i n a m i c a c i d and v i s c o s e rayon f a b r i c , i n e s s e n c e , a r e a c t i o n i n which the amic a c i d i s the s o l v e n t . To determine the e f f e c t of the s o l v e n t removal c o n d i t i o n s on the c o m p o s i t i o n of the r e s i d u e - d e p o s i t e d on the f a b r i c , amic a c i d was r e a c t e d under t h r e e s e t s of c o n d i t i o n s : normal pad-bake, pad, p r e d r y at room temperature f o r 24 hours under a stream of a i r and bake, and f u s i o n w i t h o u t added s o l v e n t . The s p e c t r a of the p r o d u c t s of the r e a c t i o n of s u c c i n a m i c a c i d under normal ( r e a c t i o n 2) p r e d r y ( r e a c t i o n 20) and f u s i o n c o n d i t i o n s ( r e a c t i o n 22) are shown i n F i g u r e 13. In each r e a c t i o n , the spectrum of the p r o d u c t d i f f e r s s i g n i f i c a n t l y from t h a t o f the pure s u c c i n a m i c a c i d ( F i g u r e 2, spectrum A ) . In a l l the s p e c t r a the amide c a r b o n y l s t r e t c h i n g a b s o r p t i o n has decreased s i g n i f i c a n t l y , i n d i c a t i n g p a r t i a l conversion of the o r i g i n a l s u c c i n a m i c a c i d i n t o s u c c i n i m i d e and monoammonium s u c c i n a t e . The a n a l y t i c a l d a t a i n T a b l e I I r e v e a l t h a t the % i o n i c ammonia i s 5.27%, 3.41%, and 1.65% i n r e a c t i o n s 2, 20, and 22, r e s p e c t i v e l y . The amount o f h y d r o l y s i s which has taken p l a c e i s g r e a t e s t i n the pad-bake p r o c e d u r e and l e a s t i n the f u s i o n p r o c e d u r e . The % c h l o r o f o r m e x t r a c t a b l e v a l u e s f o r


B O W M A N AND

cucuLO

Reactions of Cellulose Table

Product

Reaction Number

Unreacted Amic Acid

Yield

IV

Data,

Solvents

Monoammonium salt

Imide

Diacid

16

76.7

7.4

1.0

0

17

59.3

0.4

37.3

2

18

3.9

5.7

74,7

0

19

0

1.1

92.5

0

20

53.1

23.1

17.3

9

21

10.0

22

52,7

13.6

30.8

2

23

2.0

8.7

85.8

0

3500

3000

2500

2000

1500

FREQUENCY, CM*'

Figure 13. Infrared spectra of the products of the reaction of succinamic acid at 175°C for 10 min under normal (A), predry (B), and fusion (C) conditions



αο

Γ

°°

3500

3000

2500

2000

FREQUENCY, CM"

1500

1

Figure 14. Infrared spectra of the products of the reaction of phthalamic acid at 175°C for 10 rain under normal (A), predry (B), and fusion (C) condition


11.


183


r e a c t i o n s 2, 20, and 22 a r e 5.84%, 14.73% and 24.40%, r e s p e c t i v e l y , i n d i c a t i n g t h a t imide f o r m a t i o n i s the most important i n t h e f u s i o n r e a c t i o n (22). This i s a l s o r e f l e c t e d i n the v a l u e s o f the n e u t r a l i z a t i o n e q u i v a l e n t s , 123.1, 129.5, and 140.5 g r a m s / e q u i v a l e n t f o r r e a c t i o n s 2, 20, and 22, r e s p e c t i v e l y . The a n a l y t i c a l d a t a were used t o c a l c u l a t e the % y i e l d v a l u e s i n T a b l e IV. The % y i e l d o f s u c c i n a m i c a c i d i s about the same i n each experiment. The y i e l d o f monoammonium s a l t i s g r e a t e s t i n the normal pad-bake procedure (34.0%) a t l e a s t i n the f u s i o n procedure (13.6%). T h i s r e l a t i o n s h i p i s r e v e r s e d i n the % y i e l d of s u c c i n i m i d e w i t h t h e normal p r o c e d u r e y i e l d 5.7% and the f u s i o n procedur c o n d i t i o n s the y i e l d s u c c i n i m i d e a r e i n t e r m e d i a t e i n v a l u e a t 23.1% and 17.3%, r e s p e c t i v e l y . These r e s u l t s i n d i c a t e t h a t h y d r o l y s i s o f t h e amic a c i d i s most complete i n t h e r e a c t i o n with water as s o l v e n t and t h a t the h i g h e r the temperature o f removal o f the water the g r e a t e r the hydrolysis. Dehydrocyclization t o form imide i s most f a v o r e d i n the absence o f water as the r e s u l t s o f the fusion reaction indicate. The y i e l d o f s u c c i n i c a c i d was 6%, 9%, and 2% i n t h e normal, p r e d r y , and f u s i o n reactions respectively. The t r e n d s noted i n the s u c c i n a m i c a c i d r e a c t i o n above were even more apparent i n the r e a c t i o n s o f p h t h a l a m i c a c i d under normal, p r e d r y , and f u s i o n conditions. The s p e c t r a o f the p r o d u c t s o f the r e a c t i o n s o f p h t h a l a m i c a c i d under normal ( r e a c t i o n 5), p r e d r y ( r e a c t i o n 21), and f u s i o n c o n d i t i o n s ( r e a c t i o n 23) a r e g i v e n i n F i g u r e 14 ( s p e c t r a A, B, and C, r e s p e c t i v e l y ) . S p e c t r a A and Β show t h a t h y d r o l y s i s i s the predominant r e a c t i o n by the absence o f the amide c a r b o n y l s t r e t c h a t 1645 cm"" and t h e presence o f the s t r o n g c a r b o x y l a t e c a r b o n y l s t r e t c h a t 1550 cm" . Spectrum C i n d i c a t e s t h a t the predominant p r o d u c t i n the f u s i o n r e a c t i o n i s p h t h a l i m i d e . These c o n l u s i o n s are r e f l e c t e d i n the a n a l y t i c a l d a t a i n T a b l e I I . In r e a c t i o n s 5 and 21 t h e % i o n i c ammonia i n the p r o d u c t i s 8.08% and 6.57%, r e s p e c t i v e l y , w h i l e i n r e a c t i o n 23 the v a l u e i s 1.02%. The % c h l o r o f o r m e x t r a c t a b l e v a l u e s a r e 12.41% and 18.64% i n r e a c t i o n s 5 and 21, r e s p e c t i v e l y , and 87.20% i n r e a c t i o n 22. The n e u t r a l i z a t i o n e q u i v a l e n t v a l u e s f o r r e a c t i o n s 5 and 21 were 204.4 and 223.4 g r a m s / e q u i v a l e n t , r e s p e c t i v e l y . The n e u t r a l i z a t i o n e q u i v a l e n t o f the p r o d u c t s o f r e a c t i o n 23 was not d i r e c t l y d e t e r m i n e d . The r e s i d u e of the c h l o r o f o r m e x t r a c t i o n was found t o have a n e u t r a l i z a t i o n e q u i v a l e n t o f 183.2 g r a m s / e q u i v a l e n t . 1

1


184

SOLVENT SPUN R A Y O N , MODIFIED C E L L U L O S E

FIBERS

Table Y Mass B a l a n c e and V o l a t i l e P r o d u c t Y i e l d D a t a

Reaction Number

% Yield of A d d Derivatives

% Yield of Nitrogen C o n t . Cmpds.

% Yield of V o l a t i l e Ammonia

1

99.7

93.7

0.0

2

98.9

92.9

0.8

3

97.1

4

99.2

5

98.0

97.0

0.2

6

97.3

96.3

0.3

% Yield of Sublimate

7

95.2

91.0

0.0

8

99.0

86.0

0.6

0.8*

9

100.5

100.5

0.1

0.5**

10

100.8

97.0

0.0

0.8**

11

94.5

86.5

4.0

12

99.4

90.4

2.3

13

96.0

86.0

0.8

14

100.4

94.4

1.7

15

100.0

99.0

0.0 0.6

16

86.1

85.1

17

99.0

97.0

1.7

18

84.4

84.4

3.9

19

93.6

93.6

5.9

20

98.0

89.0

2.2

21

92.7

93.3

0.0

22

98.6

94.6

0.6

23

96.5

96.5

0.1

0.2

* As s u c c i n a m i c a c i d * * As p h t h a l i m i d e


11.



185

The % amide ammonia was g r e a t e s t i n r e a c t i o n 21 at 1.06% and l e a s t i n r e a c t i o n 5 at 0.10%. The product y i e l d v a l u e s are g i v e n i n T a b l e IV. The p h t h a l a m i c a c i d i s almost t o t a l l y c o n v e r t e d i n t o p r o d u c t s under a l l t h r e e s e t s o f c o n d i t i o n s . The r e a c t i o n s under normal and p r e d r y c o n d i t i o n s g i v e the most h y d r o l y s i s as i n d i c a t e d by the % y i e l d o f monoammonium s a l t , 81.5% and 56.3%, r e s p e c t i v e l y . In the f u s i o n r e a c t i o n , 23, the imide y i e l d i s 85.8% w h i l e i n the normal ( r e a c t i o n 5) and p r e d r y r e a c t i o n s the y i e l d s are 14.9% and 28.2%, respectively. L i t t l e p h t h a l i c a c i d was d e t e c t e d . Volatile

Products

During the pad-bak other than the s o l v e n t are e v o l v e d . T h i s becomes apparent when the m a t e r i a l b a l a n c e f o r the r e a c t i o n s i s computed. The m a t e r i a l b a l a n c e on the a c i d d e r i v a t i v e s and n i t r o g e n c o n t a i n i n g p r o d u c t s i s g i v e n i n T a b l e V along w i t h the e x p e r i m e n t a l l y determined v a l u e s of the y i e l d s of v o l a t i l e p r o d u c t s . The m a t e r i a l b a l a n c e v a l u e s vary from 100.5% i n r e a c t i o n 9 t o 84.4% i n r e a c t i o n 18. In the r e a c t i o n s i n formamide (16 and 18) the s o l v e n t was not c o m p l e t e l y removed i n the bake s t e p due t o the low v o l a t i l i t y of the s o l v e n t . The s o l v e n t was removed by e v a p o r a t i o n at room temperature under h i g h vacuum f o r s e v e r a l h o u r s . It i s p o s s i b l e that under these c o n d i t i o n s a p o r t i o n of the p r o d u c t s sublimed from the mixture and was l o s t . In both r e a c t i o n s 16 and 18 the m a t e r i a l balance v a l u e s are c o m p a r a t i v e l y low at 86.1% and 84.4%, r e s p e c t i v e l y , f o r the a c i d d e r i v a t i v e s , and 85.1% and 84.4% f o r the nitrogen containing products. The mass b a l a n c e v a l u e s d e c r e a s e with both the d u r a t i o n and temperature of reaction. The % y i e l d o f s u c c i n i c a c i d d e r i v a t i v e s and n i t r o g e n c o n t a i n i n g compounds i s 99.7% and 93.7%, r e s p e c t i v e l y i n r e a c t i o n 1 (150°C bake temperature) w h i l e i n r e a c t i o n 3 (200°C bake temperature) the v a l u e s are 97.1% and 87.1%, r e s p e c t i v e l y . The y i e l d o f p h t h a l a m i c a c i d d e r i v a t i v e s and n i t r o g e n c o n t a i n i n g compounds was 99.2%, and 99.2%, r e s p e c t i v e l y , i n r e a c t i o n 4 (150°C bake t e m p e r a t u r e ) , and 97.3% and 96.3%, r e s p e c t i v e l y , i n r e a c t i o n 6 (200° C bake temperaure). The e x p e r i m e n t a l l y determined y i e l d s o f s u b l i m a t e and v o l a t i l e ammonia are a l s o g i v e n i n T a b l e V. The s u b l i m a t e was o b t a i n e d by e v a p o r a t i o n of the t r a p of c h l o r o f o r m i n r e a c t i o n s 8, 9, and 10. On e v a p o r a t i o n of the c h l o r o f o r m a s m a l l amount of r e s i d u e was obtained. The i n f r a r e d s p e c t r a o f the r e s i d u e s are



FREQUENCY, CM"

1

Figure 15. Infrared spectra of the volitile products in reactions 8 (A) and 9(B)

60

80

100

120

140

MO

MO

TIME, MMUTES

Figure 16. Variation of the percent yield of ammonium ion in the padbath with time for 2.50M solutions of succinamic and phthafomic acid at 65° ± 1°C


11.


187


g i v e n i n F i g u r e 15. Spectrum A, t h a t o f the s u b l i m a t e from r e a c t i o n 8, when compared w i t h t h a t o f the pure compound i n F i g u r e 2 (spectrum A) appears t o be the spectrum o f a p a r t i a l l y h y d r o l y z e d or n e u t r a l i z e d sample o f s u c c i n a m i c a c i d . Spectrum B, o b t a i n e d from the p r o d u c t o f r e a c t i o n 9 i s i d e n t i c a l t o the spectrum of p h t h a l i m i d e . The same i s t r u e f o r the spectrum o f the v o l a t i l e p r o d u c t o f r e a c t i o n 10 (not shown). Thus, the m a t e r i a l which s u b l i m e s from the r e a c t i o n i s s u c c i n a m i c a c i d i n the r e a c t i o n s o f s u c c i n a m i c a c i d and p h t h a l i m i d e i n the r e a c t i o n o f p h t h a l a m i c a c i d . The % y i e l d o f v o l a t i l e ammonia i n the r e a c t i o n s of s u c c i n a m i c a c i d i s p r o b a b l y too low s i n c e the succinamic acid i t s e l s t a n d a r d a c i d as i p h t h a l a m i c a c i d i n water the y i e l d o f v o l a t i l e ammonia i s g e n e r a l l y lower than the y i e l d o f v o l a t i l e ammonia i n the c o r r e s p o n d i n g s u c c i n a m i c a c i d r e a c t i o n . The e x c e p t i o n t o t h i s i s i n the r e a c t i o n s i n formamide and DMF. Succinamic a c i d i n formamide ( r e a c t i o n 16) and DMF ( r e a c t i o n 17) y i e l d s 0.6% and 1.7% respectively, of v o l a t i l e ammonia, and p h t h a l a m i c a c i d i n formamide ( r e a c t i o n 18) and DMF ( r e a c t i o n 19) y i e l d s 3.9% and 5.9% i o n i c ammonia, r e s p e c t i v e l y . f

Pad

Bath

Stability

I t i s o f i n t e r e s t t o determine the changes which occur i n the pad-bath b e f o r e the bake s t e p . The main change expected i n the pad bath i s h y d r o l y s i s o f the amic a c i d . T h i s r e a c t i o n was f o l l o w e d by d e t e r m i n a t i o n of the i o n i c ammonia c o n t e n t o f a 2.50 molar aqueous pad-bath h e l d a t 65°C and by f o l l o w i n g the changes i n the c a r b o n y l s t r e t c h i n g r e g i o n o f the i n f r a r e d spectrum of the m a t e r i a l i n the b a t h . The % y i e l d o f the ammonium i o n p r e s e n t i n the pad bath i s shown as a f u n c t i o n o f time i n F i g u r e 16. The time o f i n t r o d u c t i o n o f the amic a c i d i n t o the water was the b e g i n n i n g o f the r e a c t i o n . Complete d i s s o l u t i o n o f the amic a c i d o c c u r r e d w i t h i n f i v e minutes i n the procedure. P h t h a l a m i c a c i d i s almost e n t i r e l y h y d r o l y z e d d u r i n g the d i s s o l u t i o n p e r i o d as h y d r o l y s i s rapidly occurs. Pad-bake r e a c t i o n s with aqueous s o l u t i o n s o f p h t h a l a m i c a c i d c e r t a i n l y i n v o l v e the monoammonium s a l t . S u c c i n a m i c a c i d i s more r e s i s t a n t to h y d r o l y s i s w i t h a y i e l d o f monoammonium s u c c i n a t e o f o n l y 34.0% a f t e r 3 h o u r s . These changes a r e a l s o r e f l e c t e d i n the changes which occur i n the c a r b o n y l s t r e t c h i n g r e g i o n o f the s p e c t r a o f the m a t e r i a l i n the bath which a r e shown i n F i g u r e 17. The s p e c t r a show


188

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t h a t the amide c a r b o n y l s t r e t c h i n g . a b s o r p t i o n at 1650 cm*" g r a d u a l l y d i s a p p e a r s as the c a r b o x y l a t e c a r b o n y l s t r e t c h i n g a b s o r p t i o n g r a d u a l l y appears at 1550 cm" The changes i n the s p e c t r a of the p h t h a l a m i c a c i d r e s i d u e s are more d r a m a t i c than those i n the succinamic a c i d experiment. The amide c a r b o n y l a b s o r p t i o n a t 1645 cm^ i s c o m p l e t e l y absent at 15 minutes w h i l e the c a r b o x y l a t e c a r b o n y l s t r e t c h i n g a b s o r p t i o n i s f u l l y developed i n 15 minutes. There i s l i t t l e f u r t h e r change i n the s p e c t r a with time. 1

1

1

Conclusions During the pad-bak d i s s o l v e d i n the s o l v e n The r e s u l t i n g s o l u t i o n i s a p p l i e d to the s u b s t r a t e , the s o l v e n t i s r a p i d l y v o l a t i l i z e d , and a r e s i d u e i s d e p o s i t e d on the s u b s t r a t e . The r e s i d u e i s then f u r t h e r heated i n the c o m p l e t i o n of the bake s t e p . The p r o c e s s can f o r the sake o f d i s c u s s i o n be d i v i d e d i n t o three steps: s o l u t i o n p r e p a r a t i o n and padding, v o l a t i l i z a t i o n of s o l v e n t , and bake of the r e a c t a n t s . During the p r e p a r a t i o n of the s o l u t i o n the predominant c h e m i c a l change which o c c u r s i n the amic a c i d i s h y d r o l y s i s . T h i s was g r a p h i c a l l y i l l u s t r a t e d i n the experiments t o determine the pad-bath s t a b i l i t y . P h t h a l a m i c a c i d i s almost e n t i r e l y h y d r o l y z e d d u r i n g the p r e p a r a t i o n of the s o l u t i o n w h i l e s u c c i n a m i c a c i d i s h y d r o l y z e d a t a somewhat slower r a t e . T h i s r e s u l t i s not s u r p r i s i n g i n l i g h t of the s t u d i e s o f the h y d r o l y s i s of ,α 3-amic a c i d s which have been r e p o r t e d (1^), 11,12,12,L4,JU5,lj>r_17,jj*). α, 3 -amic a c i d s which are derîvecPfrom d i c a r b o x y l i c a c i d s forming i n t e r n a l p e n t a c y c l i c a n h y d r i d e s are h y d r o l y z e d at r a t e s which are u n c h a r a c t e r i s t i c a l l y h i g h f o r amides. The mechanism f i r s t proposed t o e x p l a i n t h i s unusual b e h a v i o r i n v o l v e s the f o r m a t i o n of the i n t e r n a l anhydride i n a r a t e d e t e r m i n i n g s t e p f o l l o w e d by r a p i d hydrolysis (10,LI). T h i s mechanism was i n f e r r e d from the r e s u l t s 0 7 an i s o t o p i c l a b e l i n g experiment ( 1 1 ) . The f a c i l e h y d r o l y s i s o f many a , 3 - a m i c a c i d s has s i n c e been r e p o r t e d (1^,12,14^,15,1^,17,1^8), and the a n h y d r i d e was d i r e c t l y d e t e c t e c P a s tïïê r e a c t i v e i n t e r m e d i a t e i n the r e a c t i o n i n one r e c e n t study ( 1 8 ) . The r a t e c o n s t a n t s f o r the pseudo f i r s t order h y d r o l y s i s of s u c c i n a m i c and p h t h a l a m i c a c i d s at 65°C are 3.3 χ 1 0 " sec" and 1.3 χ 1 0 ~ sec" , r e s p e c t i v e l y (12^). By use of these f i r s t order r a t e c o n s t a n t s , the c o n c e n t r a t i o n of amic a c i d i n the pad bath at v a r i o u s times can be e s t i m a t e d . These v a l u e s 5

1

3

1



189

Reactions of Cellulose T a b l e VI

Comparison o f t h e o r e t i c a l and experimental v a l u e s o f % y i e l d o f ammonium s a l t d u r i n g h y d r o y l s i s o f t h e amic a c i d s i n t h e pad bath

% Y i e l d o f Ammonium S a l t i n Pad Bath

Age o f the Pad Bath (minutes a t 65 C)

Succinamic A c i d Calculated

Ρhtha1amic A c i d Calculated Pound

Found

e

15

1.5

3.0

92,2

87.8

20

3.0

3.9

95.0

94.0

30

6.5

5.8

97.5

98.5

45

12.6 11.3

98.5

99.9

99.0

100.0

60 120

23.2

21.3

180

33.8

30.2 51.3

360

* Ρ Γ Ο Π Ι t h e f i r s t order r a t e c o n s t a n t i n r e f e r e n c e (12).

1900

1600 1900 16001900

16001900

16001900

16001900 1600

FREQUENCY, CM"*

Figure 17. Variation in the carbonyl stretching absorption re gion of the infrared spectra of the pad-bath residues with time for 2.50M solutions of succinamic and phthalamic acid at 65° ± 1°C


190

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are shown i n T a l e VI a l o n g w i t h e x p e r i m e n t a l v a l u e s from the d e t e r m i n a t i o n o f the pad-bath s t a b i l i t y . The d a t a from t h i s study p a r a l l e l c l o s e l y the c a l c u l a t e d data. A l s o , the r a t e c o n s t a n t f o r the pseudo f i r s t o r d e r h y d r o l y s i s o f s u c c i n a m i c a c i d was c a l c u l a t e d t o be 2.6 χ 10"" s e c - which i s i n good agreement with the v a l u e of Kezdy and B r u y l a n t s (12^) g i v e n above. The v a l u e o f the r a t e c o n s t a n t f o r the p h t h a l a m i c a c i d c o u l d not be e s t i m a t e d from the e x p e r i m e n t a l d a t a . The c l o s e p a r l l e l between the d a t a o b t a i n e d i n t h i s study to t h a t p r e d i c t e d by the l i t e r a t u r e i n d i c a t e a s i m i l a r i t y i n the paths by which the amic a c i d i s hydrolyzed. N o t a b l y , the tw their s t a b i l i t i e s a d i f f e r e n c e i n the r e a c i v i t y o f the two amic a c i d s can be r e a d i l y e x p l a i n e d i n terms o f t h e i r s t r u c t u r e s . The c o n f o r m a t i o n a l l y mobile s u c c i n a m i c a c i d can e x i s t as extended c h a i n conformers which do not f a v o r the carboxyl-amide i n t e r a c t i o n demanded by the Bender mechanism f o r f a c i l e h y d r o l y s i s ( 1 1 ) . The p h t h a l a m i c a c i d molecule i s s t u c t u r a l l y r i g i c P a n d the c a r b o x y l and amide groups are c o n s t r a i n e d to i n t e r a c t . The r e l a t i v e r a t e s o f h y d r o l y s i s of the two compounds at 65°C i s g i v e n by the r a t i o of the above r a t e c o n s t a n t s ( 1 1 ) , thus p h t h a l a m i c a c i d i s h y d r o l y z e d 39 times f a s t e r than s u c c i n a m i c a c i d . Other s t r u c t u r a l l y r i g i d α , β -amic a c i d such as maleamic a c i d would be expected to behave i n the same manner as p h t h a l a m i c a c i d and be s u b s t a n t i a l l y h y d r o l y z e d d u r i n g the p r e p a r a t i o n o f the pad-bath at 65°C. The r a t e c o n s t a n t f o r the h y d r o l y s i s of maleamic a c i d at 65°C i s 2.4 χ 10 " s e c " or r o u g h l y t w i c e t h a t of p h t h a l a m i c a c i d (1_1 ). C a l c u l a t i o n s using t h i s c o n s t a n t p r e d i c t t h a t maleamic a c i d would be 88% h y d r o l y z e d i n 15 minutes i n an aqueous pad-bath at 65°C In the second s t e p i n the pad-bake procedure the solvent i s v o l a t i l i z e d . In the experiments with water, the v o l a t i l i z a t i o n of the bulk of the s o l v e n t o c c u r r e d i n a p p r o x i m a t e l y two minutes f o r the 2.50 molar solutions. Formamide and DMF, l e s s v o l a t i l e s o l v e n t s than water were p r e s e n t throughout the r e a c t i o n . Bake temperature made l i t t l e apparent d i f f e r e n c e i n the time r e q u i r e d f o r the removal o f the bulk o f the water. The r e s u l t s o f the experiments with a bake time of 5 minutes at 175°C , r e a c t i o n 7 f o r s u c c i n a m i c a c i d and r e a c t i o n 9 f o r p h t h a l a m i c a c i d , g i v e some i n s i g h t i n t o the changes which occur i n the amic a c i d d u r i n g v o l a t i l i z a t i o n o f the s o l v e n t . In r e a c t i o n 7 o n l y 65.9% o f the i n i t i a l l y p r e s e n t amide was accounted f o r by the amide ammonia a n a l y s i s . 1

3

1


11.

BOWMAN AND

cucuLO


191

S i n c e s u c c i n a m i c a c i d i s r e l a t i v e l y unchanged i n the bath a f t e r 10 m i n u t e s , the maximum bath age at the time of withdrawal o f the a l i q u o t of s o l u t i o n f o r r e a c t i o n , the extent of h y d r o l y s i s of s u c c i n a m i c a c i d would be r e l a t i v e l y s m a l l as p r e d i c t e d by the d a t a i n T a b l e IV and F i g u r e 16. C o n s e q u e n t l y , a s u b s t a n t i a l amount o f h y d r o l y s i s must occur d u r i n g the v o l a t i l i z a t i o n s t e p . By using the a c t i v a t i o n parameters r e p o r t e d i n r e f erence 12 the r a t e c o n s t a n t f o r the h y d r o l y s i s of s u c c i n a m i c a c i d i n water at 100°C can be shown to be 6.9 χ 10 * sec ~ . I f h y d r o l y s i s proceeds f o r two minutes at t h i s r a t e the y i e l d o f i o n i c ammonia expected would be at most about 8-10%, depending on the amount o f hydrolysis occurrin The y i e l d o f i o n i c ammoni be 24.7%, more than t w i c e the maximum amount p r e d i c t e d by the f i r s t order h y d r o l y s i s c o n s t a n t . This d i s c r e p a n c y c o u l d a r i s e f o r a number o f r e a s o n s . The temperature i n the r e a c t i o n mass p r o b a b l y d e v i a t e s c o n s i d e r a b l y from t h a t o f b o i l i n g water, p a r t i c u l a r l y d u r i n g the l a t t e r s t a g e s of the v o l a t i l i z a t i o n when the s o l u t i o n i s concentrated. A l s o , as water i s removed the r e a c t i o n medium undergoes a d r a s t i c change from aqueous s o l u t i o n to a s o l u t i o n of the p r o d u c t s of the r e a c t i o n s i n l i q u i d s u c c i n a m i c a c i d . Under these c o n d i t i o n s the pseudo f i r s t order r a t e c o n s t a n t s p r o b a b l y are not v a l i d . I n f r a r e d s t u d i e s of s o l u t i o n s of N - s u b s t i t u t e d s u c c i n a m i c a c i d s i n non-polar or a p r o t i c s o l v e n t s and i n the s o l i d s t a t e i n d i c a t e the f o r m a t i o n of hydrogen bonded dimers (33,32^). In one study the d i m e r i c form o f the amic a c i d was postulated to be more r e a c t i v e i n s o l v o l y s i s r e a c t i o n s {22). The r e a c t i o n r a t e i n c r e a s e d w i t h an i n c r e a s e i n the c o n c e n t r a t i o n o f s u c c i n a m i c a c i d or on the a d d i t i o n o f acetic acid. Sauers, e t . a l . (25), a l s o noted an e f f e c t of added a c i d i n the attempted d e h y d r o c y c l i z a t i o n s of N - s u b s t i t u t e d p h t h a l a m i c a c i d s in a c e t i c anhydride. In t h e i r study the competition between d e h y d r o c y c l i z a t i o n to form imides or i s o i m i d e s and the i n t e r n a l t r a n s a c y l a t i o n to form p h t h a l i c a n h y d r i d e f a v o r e d a n h y d r i d e f o r m a t i o n i n the presence of added a c i d or l a r g e i n i t i a l c o n c e n t r a t i o n s o f amic acid. The mechanism proposed to e x p l a i n these o b s e r v a t i o n s i n v o l v e d i n t e r m e d i a t e f o r m a t i o n of a mixed p h t h a l i c a c i d - a c e t i c a c i d a n h y d r i d e or d i r e c t f o r m a t i o n of p h t h a l i c a n h y d r i d e by a pathway s i m i l a r to the Bender mechanism (11). Thus, the o b s e r v a t i o n s noted i n the l i t e r a t u r e l e n d support to the c o n c l u s i o n t h a t the r a t e of h y d r o l y s i s of s u c c i n a m i c a c i d c o u l d be enhanced d u r i n g v o l a t i l i z a t i o n of the water due to the change el

l


192

S O L V E N T SPUN R A Y O N ,


FD3ERS

i n r e a c t i o n medium. With p h t h a l a m i c a c i d , l i t t l e change o c c u r s d u r i n g the v o l a t i l i z a t i o n o f the s o l v e n t s i n c e the compound i s s u b s t a n t i a l l y h y d r o l y z e d d u r i n g the p r e p a r a t i o n o f the pad-bath. In r e a c t i o n 9, the y i e l d o f i o n i c ammonia was 88.6%, w h i l e i n the pad bath a f t e r 15 minutes the y i e l d o f i o n i c ammonia was 92.2%. The r e s i d u e d e p o s i t e d by v o l a t i l i z a t i o n o f the s o l v e n t i s s o l i d and c o n s i s t s p r i n c i p a l l y o f monoammonium p h t h a l a t e . R e a c t i o n s o f aqueous s o l u t i o n s o f p h t h a l a m i c a c i d w i t h v i s c o s e rayon g e n e r a l l y l e a d t o lower D.S. v a l u e s than does the same r e a c t i o n w i t h s u c c i n a m i c a c i d ( 3 2 ) . Our r e s u l t s i n d i c a t e t h a t such r e a c t i o n s proceed tïïrough the p a r t i a l ammoniu s a l t which i d e p o s i t e d solid and c o n s e q u e n t l y ha reaction. This probably par r e a c t i v i t y o f p h t h a l a m i c a c i d i n i t s r e a c t i o n s with c e l l u l o s i c substrates. In t h e bake s t e p the r e s i d u e d e p o s i t e d by v o l a t i l i z a t i o n o f the s o l v e n t undergoes f u r t h e r c h e m i c a l change. The predominant r e a c t i o n d u r i n g t h i s phase o f the r e a c t i o n with both s u c c i n a m i c and p h t h a l a m i c a c i d i s d e h y d r o c y c l i z a t i o n t o y i e l d imide. S i n c e n e i t h e r s u c c i n i m i d e nor p h t h a l i m i d e (_3) undergoes any s i g n i f i c a n t r e a c t i o n with c e l l u l o s i c s u b s t r a t e s i n pad-bake r e a c t i o n s , the d e h y d r o c y c l i z a t i o n r e a c t i o n r e p r e s e n t s a s e r i o u s c o m p e t i t i o n i n the f o r m a t i o n o f c e l l u l o s e e s t e r s by r e a c t i o n w i t h a β -amic a c i d s . A f t e r 5 minutes a t 175°C ( r e a c t i o n 7) o n l y 65.9% of the o r i g i n a l s u c c i n a m i c a c i d remained i n the r e s i d u e as measured by the amide ammonia d e t e r m i n a t i o n . The m a j o r i t y o f the s u c c i n a m i c a c i d which has r e a c t e d has undergone h y d r o l y s i s as i n d i c a t e d by the h i g h y i e l d o f i o n i c ammonia (24.7%) i n the r e s i d u e . At t e n minutes bake time ( r e a c t i o n 2) t h e s u c c i n a m i c a c i d c o n t e n t has f u r t h e r d e c r e a s e d t o 53.2% w h i l e the y i e l d o f both imide and i o n i c ammonia have i n c r e a s e d t o 5.7% and 34.0%, r e s p e c t i v e l y . T h i s i n d i c a t e s t h a t s u c c i n a m i c a c i d i s f u r t h e r h y d r o l y z e d i n the melt d e p o s i t e d even a f t e r t h e m a j o r i t y o f the water has been v o l a t i l i z e d . Water i s produced by the d e h y d r o c y c l i z a t i o n r e a c t i o n and c o n s e q u e n t l y i s always p r e s e n t t o some e x t e n t i n the m e l t . The imide which has formed by t h i s time i s p r o b a b l y the r e s u l t o f d e h y d r o c y c l i z a t i o n o f the s u c c i n a m i c a c i d and the s a l t formed by the h y d r o l y s i s reaction. A f t e r 15 minutes at 175°C ( r e a c t i o n 8) o n l y 39.5% o f the i n i t i a l l y p r e s e n t s u c c i n a m i c a c i d i s accounted f o r i n the r e s i d u e w h i l e the y i e l d o f the d e h y d r o c y c l i z a t i o n p r o d u c t , s u c c i n i m i d e , i s 23.1%. The y i e l d o f i o n i c ammonia has d e c r e a s e d t o 23.1%. Thus, f


11.



193

at l o n g e r bake times both the r e s i d u a l s u c c i n a m i c a c i d and the h y d r o l y s i s p r o d u c t are c o n v e r t e d t o the i m i d e . In r e a c t i o n s o f s u c c i n a m i c a c i d the d e h y d r o c y c l i z a t i o n r e a c t i o n i s much f a s t e r a t h i g h e r temperatures. The y i e l d o f imide i n r e a c t i o n 3 a t 200° C i s over s i x times g r e a t e r than the y i e l d o f imide i n reaction 6 a t 175°C. The g r e a t e r c o m p e t i t i o n o f the d e h y d r o c y c l i z a t i o n r e a c t i o n a t h i g h e r tempertures accounts q u i t e w e l l f o r the o b s e r v a t i o n s o f both Johnson and C u c u l o t h a t the f r e e a c i d D.S. o f rayon f a b r i c m o d i f i e d i n t h e pad-bake r e a c t i o n with s u c c i n a m i c a c i d d e c r e a s e d a t bake temperatures h i g h e r than 170°C. The f o r m a t i o n o e x c l u s i o n o f water fro which i s heated i n the absence o f water ( r e a c t i o n 22, melt r e a c t i o n ) y i e l d s over f i v e times the s u c c i n i m i d e as does the r e a c t i o n under normal pad-bake r e a c t i o n c o n d i t i o n s ( r e a c t i o n 2 ) . The ease o f f o r m a t i o n o f s u c c i n i m i d e i n molten s u c c i n a m i c c o u l d account f o r the low y i e l d s i n the r e a c t i o n s o f s u c c i n a m i c a c i d melts with c e l l u l o s i c s u b s t r a t e s ( 4 ) . Succinamic a c i d under the p r e d r y c o n d i t i o n s ( r e a c t i o n 20) a l s o gave a g r e a t e r y i e l d o f imide than d i d the r e a c t i o n under normal pad-bake c o n d i t i o n s ( r e a c t i o n 2 ) . Acknowledgements We wish t o thank The Sherwin W i l l i a m s Co., Tennessee Eastman Co., and N o r t h C a r o l i n a S t a t e u n i v e r s i t y f o r t h e i r support o f p a r t s o f t h i s work. List 1. 2. 3. 4. 5. 6.

7.

8.

of

References

C u c u l o , J. A., Textile Res. J., 41, 321 (1971). C u c u l o , J. Α., U. S. P a t e n t 3,555,585 (1971). Johnson, Ε . H. and C u c u l o , J. Α., Textile Res. J . 43, 283 (1973). A l l e n , T. C. and C u c u l o , J. Α., ACS Symposium S e r i e s 10, 51, (1975). C u c u l o , J. Α., Textile Res. J., 41, 375 (1971). Silverstein, R. M. and B a s s l e r , C. D., S p e c t r o m e t r i c Identification o f O r g a n i c Compounds, John W. W i l e y and Sons, New York, 1967, pp. 89-92. O'Connor, R. T., " A n a l y s i s o f C h e m i c a l l y M o d i f i e d C o t t o n " , Chapter X I I I . 4.3. in Cellulose and C e l l u l o s e D e r i v a t i v e s , Vol. V, Bikales, Ν. M. and S e g a l , Leon, eds., John W. W i l e y and Sons, New York, 1970, pp. 55-57. A l l e n , T. C. and C u c u l o , J. Α., J o u r n a l o f Polymer S c i e n c e : Macromolecular Reviews 7, 187-262 (1973). In Solvent Spun Rayon, Modified Cellulose Fibers and Derivatives; Turbak, A.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

194 9.


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FIBERS

March, J. Advanced O r g a n i c C h e m i s t r y : R e a c t i o n s , Mechanisms, and S t r u c t u r e , McGraw Hill, New York,

1968, p. 323.

10. Bender, M. L., J. Amer. Chem. Soc. 79, 1258 (1957). 11. Bender, M. L., Chow Υ., and Chloupek, F., J. Am. Chem. Soc. 80, 5380 (1958). 12. B r u y l a n t s , A. and Kezdy, F., Rec. Chem. P r o g . 21, 213 (1960). 13. B r u y l a n t s , Α., Voortman, Β. V., and Crooy, P., Bull. Soc. Chim. B e l g . 73, 241 (1964). 14. H i g u c h i , T., E b e r s o n , L., and Herd, A. K., J. Am. Chem. Soc. 88, 3805 (1966). 15. Brown, J., Su, S. C. Κ., and S h a f e r , J. Α., J. Am. Chem. Soc. 88, 4468 (1966). 16. K i r b y , A. J. an 51P (1970). 17. K i r b y , A. J., L a n c a s t e r , P. W., and A l d e r s l e y , M. F., Chem. Comm. 1972, 570. 18. K i r b y , A. J. and L a n c a s t e r , P. W., J. Chem. Soc. Perk. 2, 1972, 1206. 19. Rowland, S P., Welch, C. M., Brannon, M. A. F., and G a l l a g h e r , D. M., Textile Res. J., 37, 933-41 (1967). 20. Rowland, S. P., Welch, C. Μ., and Brannon, M. A. F., U. S. P a t e n t 3,526,048 (1970). 21. B u l l o c k , A. L., Vail, S. L., and Mach, C. H., U. S. P a t e n t 3,294,779 (1966). 22. Gregory, M. J., J. Chem. Soc. P e r k i n 2, 1972, 1390. 23. Ritter, W., German P a t e n t 526,881 (1928). (C.A. 25 4893 (1928)). 24. Sauers, C. K., J. O r g . Chem., 34, 2275 (1969). 25. S a u e r s , C. Κ., Gould, C. L., and Ionannou, E . S., J. Am. Chem. Soc. 94, 8156 (1972). 26. S i e g e l , E. F. and Moran, M. K., J. Am. Chem. Soc. 69, 1457-59 (1947). 27. Bowman, B. G., u n p u b l i s h e d d a t a . 28. B o l t z , D. F., ed., C o l o r i m e t r i c D e t e r m i n a t i o n o f Nonmetals, I n t e r s c i e n c e , New York, 1958, pp. 84-95. 29. K o l t h o f f , I . M. and Steizer, V. Α., V o l u m e t r i c A n a l y s i s II, I n t e r s c i e n c e , New York 1947, pp. 12930. 30. N i e d e r l , J. B. and Niederl V., Micromethods o f Q u a n t i t a t i v e A n a l y s i s , John W i l e y and Sons, New York, 1938. 31. Hargreaves, M. K. and S t e v i n s o n , Ε . Α., Spectro chemica A c t a 21, 1681-9 (1965). 32. Gregory, M. J. and Loadman, M. J. R., J. Chem. Soc. B, 1971, 1862. 33. Antonenko, N. G., J. Gen. Chem. USSR 35, 425-9(1965).


12 Courtaulds Challenge the Cotton Legend M. LANE and J. A. McCOMBES Courtaulds Ltd., Coventry, England

In August 1905, Courtaulds Limited began production of viscose rayon i n Coventry, England. Six years later, their U.S. subsidiar Hook, Pennsylvania. Those two events mark the beginning of over 70 years of Courtaulds' involvement i n viscose both in Europe and North America. 70 years i n which Courtaulds have remained committed to viscose fibres whilst increasing their involvement i n every aspect of the textile trade. Courtaulds Involvement in Viscose 1905 1911 1926 1934 1935 1957 1964 1965 1967 1968 1976

Production of viscose filament begins i n Coventry. Courtauld's U.S. subsidiary - American Viscose Corporation begins production in Pennsylvania. Introduction of Courtaulds matt filament v i s c o s e . Courtaulds pioneer the introduction of viscose staple fibre. Courtaulds introduce Tenasco, high strength viscose tyre yarn. Introduction of Sarille, chemically crimped v i s c o s e . Courtaulds introduce Evlan, a crimped coarse denier carpet fibre. Vincel 28, polynosic type v i s c o s e . Vincel 64, Courtaulds modal fibre is introduced. Darelle, Courtaulds flame retardant v i s c o s e . Viloft.

70 years of viscose innovation and development: of crimped fibres, high tenacity and high wet modulus fibres,

197



CELLULOSE

lure 1. Fabric cover in sheeting


FIBERS

L A N E AND MCCOMBES

Courtaulds Challenge Cotton Legend

199

flame retardants and dye variants, modal fibres, and now Viloft, a new generation of viscose aimed at a new and an increasingly aware consumer market. Viloft Development Background The development of Viloft begins in the late 'sixties and early 'seventies, with the growing success of polyester/cotton, and to a lesser extent polyester/Viscose, in traditional cotton markets. The benefits of polyester are well known: it brought durability, wash stability and the easy care concept to the consumer, and much of our efforts during this period were aimed at producin blends in a wide variety of apparel and household textiles. In the early 1970's, however, we became conscious of a growing consumer reaction against polyester blends, with complaints of a synthetic handle and of leanness. (Figure 1) Some of these faults were implicit in the use of a synthetic fibre like polyester, but many were exacerbated by the use of lower cloth constructions which took advantage of polyester's durability; and by the even higher proportions of polyester, in blends that moved from 50/50 to 67/33 and onward in order to minimise the influence of rising cotton prices. We saw in this situation an opportunity to expand viscose business if we could produce a high bulk fibre for blending with polyester. Our aim was to create a blend which married the wear and care qualities of polyester with the bulk and cover contributed by a new viscose fibre. To produce a modern high performance fabric, but with aesthetics more akin to a traditional, natural cotton cloth. The R & D team to which this challenge was posed faced only two restrictions. 1. The new fibre must be produced on existing viscose machinery and plant. 2. The new fibre must be processed on conventional textile machinery, like an existing viscose fibre. The team's answer was Viloft, a hollow viscose fibre produced by the inflation process. A fibre which was not only to meet the bulk requirement of the original project specification, but which has been found to enhance handle and comfort in a much wider range of fabrics and blends


200


CELLULOSE

Figure 2. FM type fiber

Figure 3. SI type fiber


FIBERS



than originally anticipated. What is an Inflated Viscose Fibre? The concept of an inflated viscose fibre is essentially a simple one. Sodium carbonate is added to the viscose prior to spinning. When this carbonated viscose comes into contact with the acid of the spin bath, carbon dioxide gas is evolved. " The art of manufacturing an inflated fibre is to balance the rates of viscose coagulation and regeneration with the evolution of gas, and so contain within the forming fibre that bubble of carbon dioxide. Inflated viscos proposed for fifty years, but until now.no manufacturer has been able to produce commercially a consistent fibre of predetermined cross-section. It is this problem of manufacturing control which Courtaulds, with their long experience of viscose developments, have now overcome. This ability to control the inflation process opens the way for a whole range of viscose fibres, and the development of this new generation is clearly a major interest in our current viscose research. There are three fibres of immediate interest. The first, known as PM (Figure 2) is a flat sectioned, self bonding fibre produced by inflating and collapsing the fibre in the spin bath. PM was initially designed for paper making, and in particular for security papers. Developed from the PM principle is SI fibre - super inflated (Figure 3). Like PM, it is highly inflated, but the spinning conditions are so arranged that its collapse is irregular, forming not a flat, but a multilimbed fibre. SI, a high water imbibition fibre, was produced for surgical and tampon evaluation. The third fibre is Viloft (Figures 4a, 4b) the first true textile fibre to take advantage of the bulk offered by the inflation process. Viloft is produced by inflating the fibre and fixing it in a hollow tubular configuration. The cross-sections of polyester and cotton are shown for comparison with Viloft (Figure 5 ) . The similarity of cotton and Viloft is apparent; the dissimilarity of polyester equally clear.


201

202


Figures 4a b. Viloft y

Figure 5. Cross sections of polyester and cotton compared with Viloft


LANE AND M c c o M B E s


203

Viloft Manufacture Viloft is manufactured on standard viscose machinery using process conditions which individually are not unusual, but which in combination give a successful new process. The parameters which are additional to those of the average viscose staple process are the inclusion of sodium carbonate and modifier in the viscose. The successful manufacture of Viloft depends on two main areas: chemical control of viscose and spin bath conditions to produce a fibre of consistent properties and cross-section, and engineering control to deal with the problems of handling, washing and drying a bulky fibre. Table I Courtaulds Viloft Process U . S . Pat 3, 626,045 Spin Bath Conditions Viscose Conditions % Sulphuric Acid 8. 0-10. 0 % Cellulose 6.5-9.5 % Zinc Sulphate 1. 0- 3. 0 % Caustic Soda 5.0-7. 0 % Sodium Sulphate 20. 0-26.0 % Sodium Carbonate 3.0-4.0 Temperature C 25-45 % Modifier 0.75-2.0 Hot stretch 2% acid at 95°C % Carbon Disulphide 33-50 Salt Figure 12-18 Ball Fall (18°C) 30-180 sees. Table I shows the chemical conditions required for Courtaulds Viloft. There are six major control areas: salt figure, modifier, and of course carbonate in the viscose making; acid, temperature and sodium sulphate level in the spin bath. Figures 6 and 7 show how these six parameters separately affect fibre inflation. Each parameter is related to the degree of inflation; each also affects viscose quality, fibre quality and properties. A change in any one of these conditions alters the balance of the other five, causing the product to alter, in some instances, almost immediately; sometimes over a matter of hours. It is in this context that the achievement of Courtaulds in producing a consistent inflated product must be measured. On the engineering front some detailed modifications


204


CELLULOSE

FIBERS

Figure 7. Inflatedfibercontrol parameters affecting spin bath control




205

have proved necessary. Improved ventilation at the spin bath is required because of the effects consequent on C O 2 release at this stage in the process. Tows of hollow fibre float on the spin bath, being less dense than normal cellulose, and must be controlled, to prevent interaction with other tows causing end breaks. Cutters require modification to cope with a much thicker, bulkier product, and the bed of fibre produced must be washed and dried more efficiently because of its loft and bulk. Even baling is a problem, and multiple pressings are required to compress the lofty Viloft into a standard weight despatch bale. The end result of this effort is, we believe, worthwhile. Fibre Properties Our original aim in producing Viloft was to make a bulky fibre with similar properties to standard viscose. Table II shows the fibre's physical properties and illustrates that this latter aim was achieved. Table II Viloft Tensile Properties Viloft Fibre decitex Air Dry Tenacity (cN/tex) Air Dry Extension (%) Wet Tenacity (cN/tex) Wet Extension (%) Loop tenacity (cN/tex) Knot tenacity (cN/tex) Initial wet modulus : 2% (cN/tex at 100% extension) : 5% Yield point (cN/tex) Yield extension (%)

1.7 22.0 14.0 11.0 18.0 9.0 13.0 36 50 7.7 1.2

Courtaulds Viscose 1.7 22.0 19.0 10.0 28.0 8.0 15.0 30 40 7.3 2.2

The table shows that in tensile properties Viloft is a close match for standard viscose, though, due to hot stretching, it does have marginally better tenacity and modulus. The true worth of Viloft is however demonstrated in Table III, which shows the characteristics which make it special.


206

S O L V E N T S P U N R A Y O N , MODIFIED

CELLULOSE

FD3ERS

Figure 8. Viloft—worlds first tubular vicose staple fiber in commercial production

Figure 9. Measurement of Viloft fiber density


L A N E A N D MCCOMBES

207


Its high torsional rigidity - a factor contributing to handle. Its low micronair value - illustrating clearly Viloft's greater bulk. Its high water imbibition - related to the fibre's absorbency and comfort. Its low effective density - illustrating how much more cover can be achieved for a given weight of cellulose. TABLE III Viloft Special Characteristics American Viscose Torsional rigidity (χ 10" ) (Nm tex" ) Micronair (cu. ft/hour) Water Imbibition (%) Effective Density 9

2

2

3.7

1.52

Cotton 3.2

4.7

13.7

8.5

130

100

47

1.15*

1.5

1.5

* This is dependent on method of measurement This last feature - the way in which a hollow fibre re duces apparent density - is shown clearly in Figure 9, in which fibre densities are being measured, using a flotation technique. Processing of Viloft The processing of Viloft on conventional equipment was regarded as a cruicial requirement at the inception of the Viloft project. That we can produce a list of successful developments in Viloft blends, the majority produced under commercial con ditions, is a measure of our success, and a tribute not just to our ability to make a workable textile fibre, but also to the textile trade's flexibility and its willingness to take and exploit any new and worthwhile fibre development. Our initial concern about the bulk of Viloft causing


S O L V E N T S P U N R A Y O N , M O D I F I E D C E L L U L O S E FIBERS

problems in yarn spinning has proved groundless. Opener blends with 50/50 polyester mixtures have been spun on a commercial scale in counts ranging from 1/14's to 1/40's. In a 50/50 cotton mixutre yarns from 1/10's to 1/28's have been produced without difficulty, and open end cotton blend yarns in coarser counts are now established in the U.K. tufting trade. The situation upstream in the textile sequence is equally encouraging, with good reports on both weaving and knitting conversion. In dyeing and finishing, Viloft behaves like a standard viscose, but with the unexpected bonus that with reactive dyestuffs it dyes closer to cotton. This reduces partitioning problems in Viloft/cotton mixtures, and extends the range of dyestuff Viloft in Fabrics The Viloft project specification required a bulky fibre for polyester blends, and as the fibre properties showed, this has been achieved. Table IV shows what this additional fibre bulk offers in fabric. The table compares the air permeability and light transmission of knitted fabrics produced from 100% Viloft, Fibro and Vincel, and clearly shows Viloft's advantage over other rayon types. TABLE IV Fabric Cover 1 A comparison of Viloft and other viscose fibres Courtaulds ... Viscose

... . Vincel

15.3

19.4

25.3

4.9

8.1

11.2

w.i Viloft Air Permeability (expressed as air flow in cu.ft/hr) Light transmission (% light from standard source transmitted through fabric)

Perhaps, however, the most crucial test is shown in Table V, which compares two dress fabrics - one in 100% Viloft, the other in 100% cotton - both in identical constructions. Here again Viloft is shown to be superior, its greater bulk providing a serious challenge to cotton in fabric cover.




209

TABLE V Fabric Cover 2 A comparison of fabric cover offered by Viloft and cotton 100% Viloft

100% Cotton

10.8 1.9

15.1 3.7

Air Permeability (cu.ft/hour) Light transmission (%)

Even in 67/33, majority polyester blends, where Viloft represents only a minority component, it still contributes significantly to cover. Figure 10 shows three fabrics in equivalent construction cotton and viscose. The advantage clearly offered by Viloft is, we believe, significant in consumer terms. Viloft has not, however, only contributed bulk. It has made an undoubted contribution to the handle and comfort of polyester/Viloft blends, which unfortunately cannot easily be shown in tables or diagrams. Aesthetics are a matter of critical personal judgment, and we can only ask you to handle and compare Viloft blends for yourself. We are confident, however, that you will agree with so many other textile people that Viloft offers something special. Certainly, that seems to be the view of more and more cotton users. Viloft, designed to improve the aesthetics of polyester blends, is being used to improve the aesthetics of cotton'. Traditionally viscose was used as a cheapener with cotton: it added little, and could take away much of the attractiveness of the cotton cloth. Viloft reverses that trend. It does not detract from the cover and handle - it complements them - and it brings an improved absorbency, which has proved immediately attractive in diapers and towellings. The U.K. diaper market is highly conservative and demanding - nothing is too good for baby. Traditionally diapers are white cotton terry squares of full and soft handle, and perhaps the best compliment to Viloft s aesthetics is that 50/50 Viloft/cotton terry warp diapers have been an immediate commercial success. But Viloft does not just feel good: it absorbs more, faster - an important benefit at this end of the market (and that end of the baby). Figure 11 shows that Viloft takes up more moisture than cotton, at a faster rate. We can 1


210


Figure 10. Comparison of three fabrics in equivalent constructions with minonty c ponents of vicose, cotton, and Viloft


LANE AND MCCOMBES

Courtciulds Challenge Cotton Legend

211

40

TIME

SEC'S

Figure 11. Comparison of moisture uptake on Viloft and standard diapers

also demonstrate that this advantage is preserved in use. Viloft also offers improved absorbency in towels, but without the drawback of a slimey, sleezy handle, the major limitation which has always prevented the use of viscose in towels. Many laboratory evaluations and user trials have been carried out, with exceedingly promising results, and undoubtedly 50/50 Viloft/cotton terry warp towels will make their debut in the market place in 1977. Viloft was made as a bulky viscose fibre designed to enhance the aesthetics of polyester/viscose blends. We believe it has become much more than that. The cover and bulk of Viloft fabrics, their attractive handle and absorbency, add a new dimension to viscose. We have opened up a vast number of possibilities for Viloft, not all of which have been evaluated at this stage in development. Already alternative inflated fibres are being considered, and are competing for a place in the development queue. Prospects look bright indeed.


13 Viscose Rayon Fibers Containing Lignin Derivatives NEAL E. FRANKS American Enka Co., Enka, N.C. 28728

The c o m p a t i b i l i t y throughout the p l a n t world. This c o m p a t i b i l i t y is not necessarily shown as an i n t i m a t e mixture of the two polymers, but r a t h e r as a m a t r i x s t r u c t u r e o f cellulose f i b e r s in lignin. Although chemical p u l p i n g systems have been developed t o p r o v i d e d i s s o l v i n g pulps f r e e o f lignin, it is s u r p r i s i n g that t h e r e appear t o be no r e p o r t e d attempts t o recombine these two polymers in fibrous form. The v i s c o s e system could be the ideal technique by which t o achieve such fibers, since in the alkaline milieu of the c e l l u l o s e xanthate s o l u t i o n both polymers will demonstrate similar charge effects. The experiments d e s c r i b e d here will outline c o n d i t i o n s necessary t o prepare such fibers and t o d e s c r i b e some o f the p r o p e r t i e s o f the resulting f i b e r s . M a t e r i a l s and Methods The sodium l i g n a t e and sodium l i g n o s u l f o n a t e used were commercially a v a i l a b l e m a t e r i a l s o f h i g h e s t purity. This degree of p u r i t y was deemed necessary due t o the p o s s i b l e c o m p l i c a t i o n s which could a r i s e from the i n t r o d u c t i o n o f f o r e i g n i n o r g a n i c m a t e r i a l s i n t o the v i s c o s e process. T y p i c a l analytical v a l u e s f o r the sodium l i g n a t e and sodium l i g n o s u l f o n a t e used a r e provided in Table 1. It was necessary to purge the alkaline s o l u t i o n s o f t h e sodium lignate with nitrogen prior to use to remove amounts o f ammonia added d u r i n g the p r o c e s s i n g of this m a t e r i a l . The cross-linking trials of either sodium lignate or sodium l i g n o s u l f o n a t e were performed u s i n g a 20-25% polymer l o a d i n g in s o l u t i o n . Spinning trials were performed by adding alkaline s o l u t i o n s of the lignin derivatives to a standard textile viscose stream j u s t before the last filtration stage. T h i s mixture was spun through a 750 h o l e s p i n n e r e t i n t o a rayon s p i n b a t h and s t r e t c h was a p p l i e d in a second bath c o n t a i n i n g hot dilute sulfuric

212


FRANKS

213

Vicose Rayon Fibers

acid. The wet y a r n was c o l l e c t e d i n a c e n t r i f u g a l p o t , and t h e wet y a r n c a k e was p u r i f i e d and d r i e d i n n o r m a l f a s h i o n . The t a r g e t d e n i e r i n t h e s e t r i a l s was 1 1 0 0 f o r t h e d r i e d y a r n bundle. Table 1 .

A n a l y t i c a l Data f o r Sodium L i g n a t e Lignosulfonate. Sodium Lignate ( I n d u l i n AT)

Total sulfur, % S u l f a t e s u l f u r as S, S u l f i t e s u l f u r a s S, CaO, % MgO, % Reducing sugars pH i n w a t e r R e s u l t s and

% %

1.6 0 0

(as

and

Sodium

Sodium Lignosulfonate ( M a r a s p e r s e CB) 2.6 0.1 0

ether)

0 8.5-9.

Nil 6

Discussion

U n m o d i f i e d L i g n a t e and L i g n o s u l f o n a t e . The f i b e r d e n i e r v a l u e s o b t a i n e d by a d d i n g an amount o f u n m o d i f i e d s o d i u m l i g n a t e o r sodium l i g n o s u l f o n a t e t o t h e v i s c o s e stream i n amounts t o a c h i e v e 2 0 t o k0% l o a d i n g s , b a s e d on t h e amount o f c e l l u l o s e present, are provided i n Table 2. The d e n i e r v a l u e s shown a r e a v e r a g e v a l u e s o b t a i n e d u s i n g t h e i n s i d e and o u t s i d e v a l u e s o f the y a r n package. Table 2.

R e l a t i v e D e n i e r V a l u e s o f Rayon F i b e r s Spun U s i n g U n m o d i f i e d S o d i u m l i g n a t e and L i g n o s u l f o n a t e .

Sample Control 20% S o d i u m l i g n a t e k0% Sodium l i g n a t e Control 20$ Lignosulfonate

Corrected

denier

1110 1035 965 1105 93*+

I t c a n be s e e n t h a t t h e r e t e n t i o n o f u n m o d i f i e d s o d i u m l i g n a t e was b e t t e r t h a n t h a t o b s e r v e d f o r s o d i u m l i g n o s u l f o n a t e T h i s d i f f e r e n c e i s b e s t e x p l a i n e d by t h e f a c t t h a t t h e s u l f o n i c a c i d r e s i d u e s present i n the sodium l i g n o s u l f o n a t e cause t h i s p o l y m e r t o be more s o l u b l e i n t h e s u b s e q u e n t p u r i f i c a t i o n stages of the v i s c o s e rayon process a l l o w i n g a greater l o s s of lignosulfonate. I t was f e l t t h a t some t e c h n i q u e was n e e d e d t o i m p r o v e t h e r e t e n t i o n o f b o t h s o d i u m l i g n a t e and l i g n o s u l f o n a t e a method o f c r o s s - l i n k i n g was j u d g e d t h e b e s t p o s s i b i l i t y o f a c h i e v i n g t h i s end.


S O L V E N T SPUN R A Y O N , M O D I F I E D C E L L U L O S E

214

FIBERS

C r o s s - l i n k i n g M e t h o d s . The c h o i c e o f t h e p r o p e r c r o s s l i n k i n g m e t h o d was b a s e d on t h e e a s e a n d r e p r o d u c i b i l i t y o f the technique a v a i l a b l e . O x i d a t i v e c r o s s - l i n k i n g , such as t h a t r e p o r t e d b y N i m z , was e l i m i n a t e d on t h e b a s i s t h a t i t could exascerbate the problem o f color i n the r e s u l t i n g f i b e r . A s e c o n d c r o s s - l i n k i n g method c o n s i d e r e d was t h a t o f e t h e r i f y ing the reactive phenolic hydroxyl residues with multifunction a l c r o s s - l i n k i n g agents such as e p i c h l o r o h y d r o n o r c y a n u r i c chloride . Small scale experiments demonstrated that t h i s method was n o t e a s y t o c o n t r o l . Further, a significant reduction of the phenolic hydroxyl population could adversely affect the s o l u b i l i t y of the l i g n i n derivatives, p a r t i c u l a r l y sodium l i g n a t e , i n t h e v i s c o s e system. The m e t h o d f i n a l l y a d o p t e d f o r c r o s s - l i n k i n g b o t h t h e sodium l i g n a t e and l i g n o s u l f o n a t under a l k a l i n e c o n d i t i o n s by c r o s s - l i n k i n g a t pH 1 0 . 5 - 1 1 ; a c r u d e m e a s u r e o f s u c c e s s was o b t a i n e d by p o u r i n g t h e s e c r o s s - l i n k e d m a t e r i a l s i n t o s p i n bath t o observe the y i e l d o f c r o s s - l i n k e d m a t e r i a l . Optimum f o r m a l d e h y d e l e v e l s w e r e f o u n d t o be 5 $ w/w f o r s o d i u m l i g n a t e and 1 0 $ w/w f o r s o d i u m l i g n o s u l f o n a t e . This difference i s a f u r t h e r r e f l e c t i o n o f t h e s o l u b i l i t y d i f f e r e n c e due t o t h e s u l f o n i c a c i d r e s i d u e s p r e s e n t i n sodium l i g n o s u l f o n a t e . S p i n n i n g t r i a l s were a g a i n p e r f o r m e d , b u t u s i n g t h e c r o s s linked derivatives. The r e s u l t s o b t a i n e d w i t h t h e a d d i t i o n o f 20% a n d k0% l e v e l s o f f o r m a l d e h y d e c r o s s - l i n k e d s o d i u m l i g n a t e are provided i n Table 3. I t i s l i k e l y t h a t some e r r o r occurred i n the determination o f the s o l i d s content o f the c r o s s - l i n k e d s o d i u m l i g n a t e , w h i c h was r e f l e c t e d i n t h e l o w e r f i b e r denier determination. As e x p e c t e d , a d d i t i o n o f a d i l u e n t t o t h e c e l l u l o s i c f i b e r r e d u c e d b o t h t h e c o n d i t i o n e d and wet t e n a c i t i e s a s w e l l a s r e d u c i n g t h e e l o n g a t i o n a t b r e a k . A d e n i e r e r r o r i n t h e o p p o s i t e d i r e c t i o n was o b s e r v e d f o r t h e f i b e r c o n t a i n i n g 20% f o r m a l d e h y d e c r o s s - l i n k e d s o d i u m l i g n o s u l f o n a t e (Table k). 1

2

Table 3.

P h y s i c a l P r o p e r t i e s o f Rayon F i b e r s C o n t a i n i n g Formaldehyde C r o s s - L i n k e d Sodium L i g n a t e . ko% 20% Control

Denier Cond. t e n . (gpd) Cond. e l o n g . (%) Wet t e n . ( g p d ) Wet e l o n g . (%)

1110 2.6

2k.k 1.3 37.0

1075 2.16 21.8

1.03 3U.9

1018

1.9^ 19.6 0.82 30 Λ

This difference i s again attributed t o the d i f f i c u l t y of o b t a i n i n g an a c c u r a t e t o t a l s o l i d s c o n t e n t o f t h e c r o s s l i n k e d mixture. The d e c r e a s e i n t h e o t h e r p h y s i c a l properties c l o s e l y matches t h o s e o b s e r v e d f o r t h e c r o s s - l i n k e d sodium l i g n a t e system.


FRANKS

T a b l e k.

215

Vicose Rayon Fibers P h y s i c a l P r o p e r t i e s o f Rayon F i b e r C o n t a i n i n g Formaldehyde C r o s s - L i n k e d Sodium L i g n o s u l f o n a t e .

Denier Cond. t e n . (gpd) Cond. e l o n g . {%) Wet t e n . (gpd) Wet e l o n g . {%)

Control

20%

1105 2.67 26.2

ll80 2.22 19-9

1.35

37-0

Ο.96

28.5

D e m o n s t r a t i o n o f I n c l u d e d L i g n i n D e r i v a t i v e s . I t was d e s i r a b l e t o have a method d e m o n s t r a t i n g t h e p r e s e n c e o f t h e c r o s s - l i n k e d l i g n i n d e r i v a t i v e s i n a d d i t i o n to the denier determinations used i A t t e m p t s w e r e made t o p o l y m e r s c h e m i c a l l y ; i o d i n a t i o n and measurement o f t h e l e v e l o f i o d i n a t i o n o f t h e p h e n o l i c r e s i d u e s was inconclusive. S e l e c t i v e e x t r a c t i o n of the c e l l u l o s e p o r t i o n of the f i b e r w i t h c u p r i e t h y l e n e d i a m i n e d i s s o l v e d b o t h t h e c e l l u l o s i c and l i g n i n portions of the f i b e r . An e x a m i n a t i o n o f some a d d i t i o n a l p h y s i c a l p r o p e r t i e s ( T a b l e 5 ) showed some s l i g h t d i f f e r e n c e s , b u t n o t h i n g o f s u f f i c i e n t magnitude t o c o n v i n c i n g l y demonstrate the presence o f t h e a d d e d p o l y m e r s . The s l i g h t d e c r e a s e i n w a t e r i m b i b i t i o n o f t h e c r o s s - l i n k e d s o d i u m l i g n a t e f i b e r was i n t h e e x p e c t e d d i r e c t i o n s i n c e t h e l i g n a t e w o u l d be e x p e c t e d t o h a v e some hydrophobic character. L i k e w i s e , t h e c r o s s - l i n k e d sodium l i g n o s u l f o n a t e had an i m p r o v e d w a t e r i m b i b i t i o n . N e i t h e r o f t h e s e v a l u e s w e r e f a r enough f r o m c o n t r o l v a l u e s t o be c o n vincing. The same comments c a n be made f o r t h e X - r a y o r d e r and k n o t t e n a c i t y r e t e n t i o n v a l u e s . Table 5.

Sample

W a t e r I m b i b i t i o n , X-Ray O r d e r , and K n o t T e n a c i t y R e t e n t i o n V a l u e s o f Rayon F i b e r s C o n t a i n i n g Cross-Linked Lignins. Knot T e n a c i t y Water X-Ray Retention, % Imbibition,^ Order

Control

80-90

0.87

79

20% C r o s s - l i n k e d lignate 20$ C r o s s - l i n k e d lignosulfonate

72

0.85

77

96

0.85

71

C o n s i d e r a b l y more s u c c e s s was e x p e r i e n c e d u s i n g i n f r a r e d d i f f e r e n c e spectroscopy i n the 5 . 7 5 - 6 . 2 5 micron region. These s p e c t r a l s t u d i e s w e r e p e r f o r m e d u s i n g b o t h c o n t r o l f i b e r s and s a m p l e f i b e r s i n KBr p e l l e t s . C a l i b r a t i o n c u r v e s were o b t a i n e d by m i x i n g known amounts o f t h e c r o s s - l i n k e d l i g n i n d e r i v a t i v e and c o n t r o l r a y o n f i b e r . By t h i s m e a s u r e , t h e r a y o n f i b e r


216

SOLVENT SPUN R A Y O N , MODIFIED C E L L U L O S E

FD3ERS

t h o u g h t t o c o n t a i n 20% c r o s s - l i n k e d s o d i u m l i g n a t e was shown t o c o n t a i n b u t 18% o f t h e i n c l u d e d p o l y m e r . T h i s e x p l a i n s t h e l o w e r t h a n e x p e c t e d ( T a b l e 3) d e n i e r v a l u e s f o r t h i s f i b e r . Color. I t w i l l be a p p r e c i a t e d by t h o s e f a m i l a r w i t h t h e pulp and paper i n d u s t r y t h a t a d d i t i o n o f l i g n i n d e r i v a t i e s t o rayon f i b e r s c r e a t e s a f i b e r t h a t has a d i s t i n c t r e d d i s h b r o w n hue. Q u a n t i t a t i o n o f t h i s c o l o r u s i n g t h e Hunter L A B method i s shown i n T a b l e 6 . I n t h i s system, t h e L value i s a measure o f l i g h n e s s , t h e A v a l u e i n d i c a t e s a r e d hue i f p o s i t i v e a n d a g r e e n hue i f n e g a t i v e , a n d t h e Β v a l u e i n d i c a t e s yellowness i f p o s i t i v e and a blue t i n t i f negative. By t h i s measure, t h e f i b e r c o n t a i n i n g t h e formaldehyde c r o s s - l i n k e d sodium l i g n a t e i s darker t h a n t h e c o r r e s p o n d i n g f i b e r c o n t a i n ing cross-linked lignosulfonate value. The v a l u e s o b s e r v e d f i b e r , would imply that t h e f i b e r s c o n t a i n i n g the c r o s s - l i n k e d l i g n i n d e r i v a t i v e s a r e unacceptable f o r normal t e x t i l e uses. T a b l e 6.

H u n t e r L A B V a l u e s f o r Rayon F i b e r s Cross-Linked L i g n i n Derivatives.

Sample

L

Control 85.0 20% C r o s s - l i n k e d l i g n a t e 3U.0 20% C r o s s - l i n k e d l i g n o s u l f o n a t e U 7 . 5

A -3 +6.8 +6.U

Containing

Β +5 +15.1 +19.8

Conclusion I t i s possible t o spin regenerated c e l l u l o s i c f i b e r s c o n t a i n i n g up t o k0% f o r m a l d e h y d e c r o s s - l i n k e d s o d i u m l i g n a t e or l i g n o s u l f o n a t e using t h eviscose process. There i s a corresponding decrease i n t e n a c i t i e s and elongation a t break f o r such f i b e r s . The p r e s e n c e o f t h e a d d e d p o l y m e r s was b e s t shown u s i n g i n f r a r e d d i f f e r e n c e s p e c t r o s c o p y . There i s a considerable increase i n the c o l o r o f the rayon f i b e r s c o n t a i n i n g t h e s e d e r i v a t i v e s due t o t h e c h r o m o p o r i c r e s i d u e s present i n t h e included polymers. Literature Cited 1. 2.

N i m z , H., German P a t e n t 2 , 2 2 1 , 3 5 3 . Allan, G. G., U. S. P a t e n t 3 , 6 0 0 , 3 0 8 .


14 A Process for Drying a Superabsorbent Pulp P. LEPOUTRE Pulp and Paper Research Institute of Canada

The market for bleached pulp in absorbent sanitary products is rapidly expanding. Pulp, generally in fluffed form, is quite efficient for absorbing quickly fairly large quantities of liquid. Conventional pulp has, however, serious drawbacks. One is the bulk of the products, which require large storage space. Another is the relative ease with which a large proportion of the absorbed liquid is released under light pressure. There is a need for an absorbent material, preferably in fibrous form, capable of absorbing larger volumes of liquid per gram of absorbent and to hold this liquid under moderate pressure. Several such "superabsorbent" products, some in powder form, some in fibrous form, have been developed in the last few years (1,2). A superabsorbent in fibrous form has been developed at the Pulp and Paper Research Institute of Canada to the completion of the laboratory stage; its preparation and properties have been the subject of several publications (3,4,5). Essentially, it consists of wood pulp modified by graft-polymerization of polyacrylonitrile which is subsequently hydrolyzed into a copolymer of sodium polyacrylate and polyacrylamide which confers on the pulp an outstanding affinity for water. In addition to its water absorption properties, this product, or variants of it, may have considerable interest in wet and dry forming of specialty papers. Commercialization of such a material hinges upon the technical and economic feasibility of producing it in dry form. Conventional thermal drying is slow, causes the fibers to lose some of their absorptive capacity and furthermore produces a stiff and brittle sheet which is impossible to fluff. Freezedrying or solvent exchange drying prove much too costly because of the huge quantity of water to be removed. An unconventional drying method had to be developed? this report deals with the development of this novel drying process. 217


218

SOLVENT

SPUN

RAYON,

MODIFIED

CELLULOSE

FD3ERS

I. Requirements t o be met The requirements that had t o be met a r e l i s t e d below: 1. The d r y i n g process should not impair t h e absorption p r o p e r t i e s and should leave the product i n f i b r o u s form. 2. The d r y product should be f l u f f a b l e by o r d i n a r y means. 3. The product should be economical as judged by i t s c o s t / performance r a t i o when compared t o r e g u l a r pulp. II.

F i r s t Attempts

The f i r s t attempts t o produce a product meeting these r e quirements w i l l be d e s c r i b e d as they p o i n t t o a step c r i t i c a l f o r success. 1. H y d r o l y s i s unde non-swellin conditions Unde l c o n d i t i o n s the g r a f t e b o i l i n g aqueous NaOH. pulp remove excess NaOH. T y p i c a l l y , the q u a n t i t y o f l i q u i d a s s o c i a t e d w i t h the f i b e r s was o f the order o f 8-10 g/g f i b e r a f t e r h y d r o l y s i s and o f 30-40 g/g a f t e r washing, as compared t o approximately 1 g/g f o r the untreated f i b e r s . To avoid the l a r g e q u a n t i t y o f water taken up during h y d r o l y s i s i n aqueous NaOH, i t was l o g i c a l t o attempt t h e h y d r o l y s i s under low-swelling c o n d i t i o n s . H y d r o l y s i s experiments c a r r i e d out i n the presence o f a l c o h o l s showed t h a t t h i s could be achieved. In t h i s f a s h i o n t h e amount o f l i q u i d r e t a i n e d by the f i b e r s a t the end o f h y d r o l y s i s was c o n s i d e r a b l y decreased, and f u r t h e r solvent exchange d r y i n g was easy. However, t h i s route had disadvantages: a) h y d r o l y s i s a t r e f l u x temperature was q u i t e long and sometimes incomplete unless s u b s t a n t i a l amounts o f water were present, depending on the a l c o h o l used. b) w h i l e the water absorption c h a r a c t e r i s t i c s o f the d r i e d f i b e r s were u s u a l l y c l o s e t o normal, t h e absorption o f 1% aqueous NaCl (simulating p h y s i o l o g i c a l f l u i d s ) was q u i t e low and p r o p o r t i o n a l t o the amount o f water present i n t h e h y d r o l y s i s l i q u o r . 2. H y d r o l y s i s a t high pulp c o n c e n t r a t i o n . Another way t o reduce the amount o f l i q u i d taken up i s t o reduce the amount o f a v a i l a b l e l i q u i d . H y d r o l y s i s experiments w i t h aqueous NaOH at. high f i b e r c o n c e n t r a t i o n followed by solvent-exchange d r y i n g , produced f i b e r s which swelled normally i n water but not i n NaCl. S w e l l i n g i n aqueous NaCl was i n v e r s e l y p r o p o r t i o n a l t o the f i b e r concentration used, i . e . , p r o p o r t i o n a l t o the amount o f water present during h y d r o l y s i s . 3. Normal aqueous h y d r o l y s i s followed by solvent-exchange drying. The preceding experiments seemed t o i n d i c a t e t h a t the s w e l l i n g t a k i n g p l a c e during normal, low consistency, aqueous h y d r o l y s i s was necessary. Since most o f the t o t a l s w e l l i n g takes p l a c e i n the washing stage ( l i q u i d a s s o c i a t e d w i t h the f i b e r s


14.

LEPOUTRE

Drying a Superabsorbent Pulp

219

increases from 8-10 g/g to 30-40 g/g), solvent exchange d r y i n g was done immediately a f t e r h y d r o l y s i s . Again, while the water absorbency was normal, the s a l t absorbency, while higher than i n the previous experiments, was s t i l l low (7-10 g/g), but became normal a f t e r the f i b e r s had been soaked i n water p r i o r t o cont a c t i n g them w i t h the s a l t s o l u t i o n s . III.

Stage of f u l l s w e l l i n g p r i o r t o d r y i n g ; a r e q u i s i t e

During the course o f t h i s work i t became evident t h a t whenever f i b e r s were d r i e d without having undergone f u l l s w e l l i n g i n water at pH 6-9 i n the absence of a s i g n i f i c a n t concentration of s a l t , they would r e s w e l l i n water more or l e s s to t h e i r normal extent but not i n a s a l t s o l u t i o n . Many experiments the through t h e i r s t a t e of q u i s i t e f o r s a l t s o l u t i o n absorption. In a previous a r t i c l e (3) i t was explained t h a t s w e l l i n g was due to osmotic pressure e f f e c t s and that e q u i l i b r i u m was reached when a balance was achieved between these s w e l l i n g f o r c e s and the f i b e r cohesion f o r c e s . While a l k a l i n e aqueous h y d r o l y s i s c o n t r i b u t e s to a s u b s t a n t i a l reduction i n the f i b e r cohesion, cons i d e r a b l y more weakening takes place during the s w e l l i n g t h a t occurs during the washing operation and the transformation i s i r r e v e r s i b l e , as seen on F i g . 1, l i n e ABC. T h i s requirement o f a f u l l s w e l l i n g stage during the manu f a c t u r i n g process meant t h a t a new approach had to be thought of. IV.

The

d r y i n g process

1. P r i n c i p l e . The process makes use of the s o l u t i o n prop e r t i e s of the g r a f t e d polymer. T h i s polymer i s s o l u b l e i n water a t pHs above 4 but i n s o l u b l e at lower pHs and i n a l c o h o l s . As seen i n F i g . 2, s w e l l i n g as measured by the amount of water r e t a i n e d a f t e r high speed c e n t r i f u g a t i o n (water r e t e n t i o n value, WRV) decreases from 30 at pH 6-9 to 2.5 g/g when the pH i s r e duced t o 3. At t h i s pH, the g r a f t e d polymer i s i n i t s noni o n i z e d p o l y a c r y l i c a c i d form. I f the f i b e r s are d r i e d a t t h a t p o i n t , they w i l l not r e s w e l l i n water t o any extent. However i f the deswollen f i b e r s are converted back i n t o t h e i r sodium s a l t form with NaOH under non-swelling solvent c o n d i t i o n s before d r y i n g them, normal r e s w e l l i n g i n water and i n s a l t s o l u t i o n w i l l take p l a c e . The process then c o n s i s t s of three steps. a. The hydrolyzed f i b e r s are taken through t h e i r maximum s w e l l i n g s t a t e a t pH 6-9 i n the absence o f any s i g n i f i c a n t s a l t concentration.


SOLVENT

SPUN

RAYON,

MODIFIED

CELLULOSE

FIBERS

30 28 26 24

LIQUID RETAINED PER g FIBRES 9/9

22 20 18 16 14 12 10 8 6 4 2 10

11

12

13

14

pH Figure 1.

Liquid retained by the fibers as a function of the pH

2

3

4

5

6

7

8

pH Figure 2.

Rehtive water retention value as a function of the pH


14.

LEPOUTRE


221

b. The pH i s brought down to approximately 3 where the f i b e r s are i n t h e i r minimum s w e l l i n g s t a t e . c. The a c i d groups are converted i n t o sodium carboxylate groups w i t h NaOH i n a l c o h o l (a non-solvent f o r the polymer) and the a l c o h o l i s evaporated. 2. Laboratory procedure. At the end of h y d r o l y s i s the f i b e r s are f i l t e r e d , washed with one volume of water while on the f i l t e r . The pH a t t h a t p o i n t i s 9.5 - 10. The f i b e r s are then s l u r r i e d i n water a t 1% consistency and s u l f u r i c a c i d i s added w i t h good a g i t a t i o n t o a v o i d any l o c a l high c o n c e n t r a t i o n . During the a c i d i f i c a t i o n , the f i b e r s undergo f u l l s w e l l i n g i n the pH range 8-6 i n the absence o f any s i g n i f i c a n t s a l t concent r a t i o n . As the pH continues t o drop, the f i b e r s s t a r t t o des w e l l as evidenced by a r a p i d decrease i n s l u r r y v i s c o s i t y At pH 4 f l o c c u l a t i o n s t a r t 3. At that p o i n t , th and are f l o c c u l a t e d i n l a r g e aggregates. They are s o f t and s t i c k y and w i l l form strong wet bonds when pressed together. The s l u r r y i s then d r a i n e d f r e e l y o r f i l t e r e d w i t h g e n t l e s u c t i o n u n t i l water s t a r t s to recede from the f i b r o u s pad s u r f a c e . S u c t i o n i s r e l e a s e d . T h i s o p e r a t i o n i s c r i t i c a l when a f l u f f a b l e pulp i s d e s i r e d . E x c e s s i v e compaction o f the pad must be avoided because of the tendency o f the s o f t f i b e r s t o form strong i n t e r f i b e r bonds which slows down f u r t h e r p r o c e s s i n g , and makes f l u f f i n g very d i f f i c u l t . While the f i b r o u s pad i s s t i l l on the f i l t e r , a s o l u t i o n of NaOH i n aqueous methanol (e.g., NaOH/HÔ/MeOH - 1/9/90) i s poured on the pad t o d i s p l a c e the i n t e r f i b e r c a p i l l a r y water which i s allowed t o d r a i n f r e e l y or under g e n t l e s u c t i o n . NaOH converts the c a r b o x y l i c a c i d groups i n t o sodium carboxylate while MeOH prevents s w e l l i n g t a k i n g p l a c e . Once a l l the i n t e r f i b e r c a p i l l a r y water has been r e p l a c e d by the methanolic s o l u t i o n the f i b r o u s mat becomes s t i f f because the polymer, which i s i n s o l u b l e i n methanol, " p r e c i p i t a t e s " . From there on, strong s u c t i o n can be a p p l i e d . A s o l u t i o n of aqueous methanol (e.g. H 0/MeOH-8/92) i s poured t o wash out the excess r e s i d u a l NaOH, followed by pure methanol t o remove the l a s t t r a c e s of water. The methanol i s then evaporated to y i e l d a bulky mat of l o o s e l y held f i b e r s . 3. Suggested i n d u s t r i a l d r y i n g process. Two a l t e r n a t i v e d r y i n g process schemes are o f f e r e d f o r c o n s i d e r a t i o n . The f i r s t one i s continuous; the second i s a batch progress. a* As shown s c h e m a t i c a l l y i n F i g . 3, the a c i d i f i e d f i b e r s l u r r y i s d e l i v e r e d through a headbox on an endless screen. Water d r a i n s f r e e l y i n the f i r s t s e c t i o n . T h i s stream i s d i s carded. A l k a l i n e aqueous methanol i s sprayed on top o f the web while g e n t l e s u c t i o n i s a p p l i e d . Once thé s o l u t i o n has d i s ^ p l a c e d the water, strong s u c t i o n i s a p p l i e d t o remove most o f the excess l i q u i d , from which methanol and NaOH may be recovered i n a separate recovery c y c l e . The web i s then sprayed w i t h NaOH2


222

SOLVENT

SPUN

RAYON,

MODIFIED

CELLULOSE

FD3ERS

CONDENSER | « - |

OVEN

ι

1

c

S: SUCTION DEVICE

Figure

NaOH J

ΜβΟΗ-Η2θ-Ν ΟΗ"|4φη 3

MeOH - H 0 2

HYDROLYZED FIBERS

MeOH

>2>-

CONDENSER H S0 2

4

J MeOH J METHANOL RECOVERY

db SCREEN

VACUUM HOT AIR BLOWER DRAIN

Figure 4.

C"

Batch drying process


14.

LEPOUTRE

223


f r e e , aqueous methanol t o remove excess NaOH and continue the dehydration process. I t passes over another strong s u c t i o n dev i c e t o remove the excess l i q u i d which i s sent t o the f i r s t treatment zone a f t e r NaOH make-up. The web then r e c e i v e s a spray of pure methanol, passes over another s u c t i o n device and goes t o an oven where methanol i s evaporated and r e c y c l e d . I t should be understood that dehydration o f the f i b e r s takes p l a c e continuously throughout the sequence. The s o l v e n t s o l u t i o n runs counter-current t o the web and i t s c o n c e n t r a t i o n i s adjusted at each treatment zone so t h a t , a t no p o i n t , do the f i b e r s p i c k up water from the s o l v e n t s o l u t i o n . In the f i r s t s e c t i o n , deh y d r a t i o n i s favored when both the c o n c e n t r a t i o n s o f NaOH and MeOH a r e i n c r e a s e d . However, increased NaOH c o n c e n t r a t i o n means a longer washing zone In the second s e c t i o n , dehydration i s favored by higher MeO i s slowed down. (The of water i n the s o l v e n t and absorbed water i n the f i b e r , though not a v a i l a b l e now, w i l l be r e q u i r e d f o r t h i s c o n t r o l ) . bt The a l t e r n a t i v e process i s a batch o p e r a t i o n . I t i s r e a l l y a scaled-up v e r s i o n o f the l a b o r a t o r y procedure and i s shown i n F i g . 4. I t has the disadvantage o f being discontinuous but would seem t o be much e a s i e r to c o n t r o l and be lower i n c a p i t a l c o s t . The a c i d i f i c a t i o n tank i s equipped with a r o t a t i n g bottom f i t t e d with a screen. The washed hydrolyzed f i b e r s are fed t o the a c i d i f i c a t i o n tank and ° 4

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