Production of Rayon Fibers from Solutions of Cellulose in (CH2O)x

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

Downloaded by UNIV LAVAL on October 19, 2015 | http://pubs.acs.org Publication Date: June 1, 1977 | doi: 10.1021/bk-1977-0058.ch006

ITT Rayonier, Inc., Eastern Research Div., Whippany,N.J.07981

A wide range o f cellulosic pulps in v a r i o u s forms were found 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

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

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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 c a r t i c l e s from such solvent systems. There are almost no data i n the l i t e r a t u r e , f o r example, on the propert 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

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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. k^o), 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



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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/(CI^oJx/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 , and g l a s s . Glass s p i n n e r e t t e s are p r e f e r r e d s i n c e they are inexpensive. 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



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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. Examples o f u s e f u l régénérants i n c l u d e ammonia, ammonium s a l t s , s a t u r a t e d amines and s a l t s o f s u l f u r compounds 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



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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


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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 s of from 5 - 1 5 $ . C e l l u l o s i c f i b e r s spun from cellulose/(cBLo)x/DMSO s o l u t i o n s have S g 5 v a l u e s i n the 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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STRESS-STRAIN CURVES

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Figure 3. Stress-strain curves of regularI rayon, commercial high wet modulus rayon and rayon produced by regenerating cettu-ψ/ lose-(CH O) x-DMSO solutions from aque ous sodium sulfide t

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Production of Rayon Fibers from Solutions of Cellulose in (CH2O)x

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