Non-aqueous Solvents of Cellulose - ACS Symposium Series (ACS

20 Non-aqueous Solvents of Cellulose BURKART PHILIPP, HARRY SCHLEICHER, and WOLFGANG WAGENKNECHT

Downloaded by UNIV OF PITTSBURGH on May 4, 2015 | http://pubs.acs.org Publication Date: June 1, 1977 | doi: 10.1021/bk-1977-0048.ch020

Akademie der Wissenschaften der DDR, Institut für Polymerenchemie in Teltow-Seehof, German Democratic Republic

Non-aqueous s o l v e n t s f o r c e l l u l o s e r e c e i v e d a g r e a t d e a l o f i n t e r e s t d u r i n g t.he l a s t d e c a d e , a s t h e y p r o mised a deeper i n s i g h t i n t o d i s s o l u t i o n processes of c e l l u l o s e i n r e l a t i o n t o c e l l u l o s e s t r u c t u r e , as w e l l as a l t e r n a t i v e p r o c e d u r e s f o r r e g e n e r a t e c e l l u l o s e f i b e r s p i n n i n g . Thus, t h e r e i s r a t h e r ample e x p e r i m e n t a l e v i d e n c e on a v a r i e t y o f b i n a r y and t e r n a r y s o l v e n t s y s t e m s f o r c e l l u l o s e , a s w e l l a s on t h e p e r manent s u b s t i t u t i o n r e a c t i o n s p r o c e e d i n g d u r i n g d i s s o l u t i o n i n some o f t h e s e s y s t e m s . R e a c t i o n m e d i a * • nisms have been p r o p o s e d f o r s e v e r a l o f these p r o c e s s e s , b u t m o s t l y a r e n o t p r o v e n , and we a r e s t i l l a t the b e g i n n i n g o f a s y s t e m a t i z a t i o n and g e n e r a l i z a t i o n i n u n d e r s t a n d i n g t h e a c t i o n o f non-aqueous s o l v e n t s y s t e m s on c e l l u l o s e . F u r t h e r m o r e , e x p e r i m e n t a l f a c t s are r a t h e r s c a r c e w i t h r e g a r d t o the i n f l u e n c e o f c e l l u l o s e s t r u c t u r e on e x t e n d and r a t e o f d i s s o l u t i o n and w i t h r e g a r d t o c h a i n d e g r a d a t i o n d u r i n g d i s s o l u tion. W i t h t h i s p a p e r , we summarize and interprète r e s u l t s o f o u r own and o f o t h e r s c e n t e r i n g on t h e f o l lowing problems: - I s t h e r e a g e n e r a l i z a b l e " f i r s t s t e p " o f the d i s s o l u t i o n p r o c e s s t o be c o n s i d e r e d on t h e c o n c e p t o f e l e c t r o n p a i r donator-aeceptor (EDA) i n t e r a c t i o n ? - What a r e t h e p r e m i s e s f o r a permanent s u b s t i t u t i o n during dissolution? - What i s t h e r o l e o f c e l l u l o s e p h y s i c a l s t r u c t u r e i n c o n n e c t i o n w i t h non-aqueous s o l v e n t s y s t e m s ? F i n a l l y , some g e n e r a l c o n c l u s i o n s a r e drawn, c o v e r i n g non-aqueous and aqueous s o l v e n t s y s t e m s as well. A s u r v e y o f non-aqueous s o l v e n t s y s t e m s f o r c e l l u l o s e i s presented i n Table I , systems found i n our 278

In Cellulose Chemistry and Technology; Arthur, J.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.


Systems

Two-component

4

Tbreeôomponent

4

Systems

Q

NOHSO.-polar o r g a n i c , \ liquid ^

2

-polar organic liquid (3-9) NOCl-polar organic liquid (4,8)

Systems

One-component

Hon-aqueous

SOpClp-amine-polar organic liquid

SOClp-amine-polar organic liquid

p

( V O

(10)

CD

SO -amine-polar(£JL organic liquid 16,17)

3

( S 0 - D M F o r DMSO)

2

S0 -amine 2

- D14S0

(12J

(2)

CD

3

CIS)

EH^-Ua-salt-polar organic l i q u i d l i k e DMSO, ethanolamine (18)

3

HH^-inorganic salt l i k e NaSCN

chlorale-polar organic liquid (8,1?) paraformaldehyde-DMSO ( H )

3

CH MH

trifluoracetic acid ethylpyridinium chloride

TABLE I Solvent Systems f o r C e l l u l o s e



280

CELLULOSE CHEMISTRY A N D TECHNOLOGY

work b e i n g marked by f r a m i n g . O b v i o u s l y , one-component s y s t e m s a r e r a t h e r a n e x c e p t i o n , a s o n l y v e r y few s i n g l e l i q u i d s comply w i t h b o t h the demands on a c e l l u l o s e s o l v e n t , i . e . the s p l i t t i n g o f H-bonds com b i n e d w i t h a d d u c t f o r m a t i o n and the s o l v a t i o n o f the adduc t s . U s i n g a c o m m e r c i a l s u l p h i t e d i s s o l v i n g p u l p , and i n some c a s e s a l s o l i n t e r s o r r a y o n a s a s t a r t i n g ma t e r i a l , our e x p e r i m e n t a l work has been c e n t e r e d on - the c o m p a r i s o n o f the " n i t r o s y l i c " compounds ϋρΟ-, NOC1, 3TOHS0, i n b i n a r y systems w i t h a p o l a r o r g a n i c liquid - the s y s t e m a t i z a t i o n o f 3-component-systems c o n s i s t i n g o f S 0 , a n amine and a p o l a r l i q u i d , e x t e n d i n g t h i s p r i n c i p l e t o the whole s e r i e s o f o x i d e s and o x y c h l o r i d e s o f s u l f u r , i . e . SOp, SOClp, SO^ClpjSOo - the i n v e s t i g a t i o n of amine o r ammonia c o n t a i n i n g systems w i t h o u t an a c i d anhydride or c h l o r i d e , l i k e DMSO - CH.WHp. F o r a d i s c u s s i o n o f our e x p e r i m e n t a l r e s u l t s o b t a i n e d w i t h these s o l v e n t s y s t e m s , we c e n t e r e d on the three questions o f - s o l v e n t a c t i o n and s o l v e n t s t a b i l i t y i n r e l a t i o n t o solvent composition - permanent s u b s t i t u t i o n at the c e l l u l o s e c h a i n d u r ing d i s s o l u t i o n - r o l e o f c e l l u l o s e p h y s i c a l s t r u c t u r e i n the p r o c e s ses o f d i s s o l u t i o n and r e p r e c i p i t a t i o n . a

S o l v e n t A c t i o n and S o l v e n t Solvent Composition

S t a b i l i t y i n Relation to

F i r s t o f a l l , two f a c t s may be s t a t e d , v a l i d f o r a l l s o l v e n t systems d i s c u s s e d here: - A r a t h e r b i g e x c e s s o f the " a c t i v e a g e n t " i n t e r a c t i n g w i t h the c e l l u l o s e c h a i n , a t l e a s t a r a t i o o f 3 moles p e r mol g l u c o s e - u n i t i s n e c e s s a r y f o r complete d i s s o l u t i o n . - O r g a n i c l i q u i d s b e i n g used a s a component o f the " a c t i v e agent" and/or as a s o l v e n t f o r t h i s " a c t i v e a g e n t " can be p r o t i c a s w e l l a s a p r o t i c ones, but have to be o f r a t h e r h i g h p o l a r i t y . T h i s h i g h po l a r i t y may promote d i s s o l u t i o n due to c h a r g e s e p a r a t i o n at the p r i m a r y a d d u c t formed o r due t o s w e l l i n g the c e l l u l o s e s t r u c t u r e . L i q u i d s m a i n l y to be c o n s i d e r e d here a r e f o r m a m i d e , d i m e t h y l f o r m a m i d e (DMF), e t h a n o l a m i n e and d i m e t h y i s u l f o x i d e (DM30), most o f them r e p r e s e n t i n g r a t h e r s t r o n g s w e l l i n g a g e n t s f o r c e l l u l o s e by t h e m s e l v e s . I n some c a s e s


20.

PHiLipp ET AL.

Nonaqueous Solvents

the c h o i c e among these l i q u i d s i s f u r t h e r l i m i t e d . by r e a c t i o n w i t h t h e " a c t i v e a g e n t " a f f e c t i n g t h e s t a b i l i t y o f the s o l v e n t system. The v a r i a b i l i t y o f t h e components w i t h i n one c l a s s o f s o v e n t s i s d e p e n d i n g on t h e k i n d o f " a c t i v e a g e n t " . The r a n g e o f c o n c e n t r a t i o n s u i t a b l e f o r d i s s o l u t i o n o f c e l l u l o s e i s d e t e r m i n e d by t h e c l a s s o f s o l v e n t , i . e . t h e kind, o f " a c t i v e a g e n t " a s w e l l a s by t h e s p e c i a l components c h o s e n , and sometimes by cellulose physical structure, too. Thus, t h e b i n a r y s y s t e m G H M / D M S 0 r e p r e s e n t s a r a t h e r s p e c i a l one, q u i t e on îhe b o r d e r l i n e o f s o l v e n t s y s t e m s a t a l l : There i s no v a r i a b i l i t y o f comp o n e n t s w i t h r e g a r d t o amine o r p o l a r l i q u i d , a m i x t u r e o f DMSO and ΟρΗ,-ΕΗρ s h o w i n g no s o l v e n t a c t i o n . C e l l u l o s e c a n be d i s s o l v e d c o m p l e t e l y o n l y i n a s m a l l c o n c e n t r a t i o n range between 10 and 20 % 0H.JJH , d e p e n d i n g on i t s p h y s i c a l s t r u c t u r e , and h i g n Bf n a t i v e c e l l u l o s e was n o t c o m p l e t e l y d i s s o l v e d a t a l l . With b i n a r y systems c o n s i s t i n g o f a n i t r o s y l c a t i o n - f o r m i n g compound l i k e i i ^ O ^ , 1Ï0C1 o r M)HS0, a s an " a c t i v e a g e n t " and a p o l a r o r g a n i c l i q u i d , t h i s second, component may be v a r i e d r a t h e r w i d e l y , a s w e l l as t h e c o n c e n t r a t i o n o f t h e n i t r o s y l i c compound, w i t h o u t l o s s o f s o l v e n t power. A c c o r d i n g t o p u b l i s h e d d a t a (ο), i n some s o l v e n t s , i . e . DMF, a h i g h e r e x c e s s o f " a c t i v e a g e n t " i s needed i n s y s t e m s w i t h 3£0 CI t h a n i n l\i 0>,-containing o n e s , and t h e v a r i a b i l i t y o f t h e polaf- l i q u i d i s somewhat s m a l l e r i n t h e f o r m e r c a s e . W i t h NOHSO^ t h e c h o i c e o f t h e p o l a r l i q u i d i s r a t h e r l i m i t e d due t o the l i m i t e d s o l u b i l i t y o f t h i s s a l t l i k e compound, b\it s e v e r a l l i q u i d s a l r e a d y m e n t i o n e d i . e . DMSO, DMF, d i me t h y l a c e t a m i d e p r o v e d t o be s u i t a b l e , t h e r a t e o f d i s s o l u t i o n s being h i g h e r than i n comparable systems with Πρθ I n C o n t r a s t t o these " n i t r o s y l i c s y s t e m s " , a n a l o g o u s b i n a r y m i x t u r e s o f a p o l a r o r g a n i c l i q u i d and an o x i d e o r o x y c h l o r i d e o f s u l f u r c a n n o t be c l a s s i f i e d a s " s o l v e n t s o f c e l l u l o s e " , SOp and SOClp show i n g no s o l v e n t a c t i v i t y s a t a l l , SOpClp i n formamide o r DMF d i s s o l v i n g c e l l u l o s e a f t e r a l o n g time w i t h s e v e r e d e g r a d a t i o n , and S 0 ^ i n DMF s u l f a t i n g c e l l u l o s e t o a h i g h Do u n d e r d i s s o l u t i o n and e x c e s s i v e chain degradation. On t h e o t h e r hand, b i n a r y s y s t e m s o f S 0 and. a s e c o n d a r y o r t e r t i a r y a l i p h a t i c amine a r e a b l e t o d i s s o l v e c e l l u l o s e as shown b y Ha t a ( j [ 0 ) , w h i l e HH ana p r i m a r y amines f o r m s o l i d a d d u c t s w i t h SOp, w h i c h Q


281

2

o

o

Δ #

o

Q



0,2-

0,1-17

0,1-1,9*

1-7,5*

Propylamine

Diethylamine

Triethylamine

Ethylenediamine

6

4

9

6

3

3

5

investigated

not

Ethylamine

6

0,4-

i - i r

o

2

Formamide Molar Ratio Amine :S0 | A m i n e / S 0 : Glucose Unit

b

b

amine

no d i s s o l u ti o n

0,1-7

0,1-7

0,2-4

0,5-1,4

0,5-2

1-5

o

3

3

3

5

6

3

DMSO Molar Ratio Amine:S0 Amine/SOpt Glucose Unit

TABLE I I o f P o l a r L i q u i d Component on the Composition

Methylamine

Ammonia

Amine

Influence

Solvent

2

no d i s s o l u t i o n

0,25-0,78

no d i s s o l u t i o n

14

Acetonitrile Molar Ratio Amine:SO Amine/S0 : Glucose Unit

of Cellulose


PHiLipp ET AL.

20.

Non-aqueous Solvents

283

are i n s o l u b l e i n an e x c e s s of one of the components. The same happens i n s y s t e m s of SOClp o r SQ,,Ci and any k i n d of a l i p h a t i c amine, t h u s r e n d e r i n g ^ a l i t h e s e m i x t u r e s i n e f f e c t i v e as p o t e n t i a l s o l v e n t s f o r c e l l u l o s e . A d d i t i o n of a p o l a r o r g a n i c l i q u i d as a t h i r d , component o f t e n e f f e c t s a d i s s o l u t i o n of t h e s e s o l i d , a d d u c t s and t h u s l e a d s to the r a t h e r ample s p e c t r u m of three-component s o l v e n t s y s t e m s i n v e s t i g a t e d m a i n l y by Uakao ( 8 , Vf) and by us ( j j , 1 6 ) . W i t h r e g a r d t o type of amine and t o p o l a r l i q u i d , v a r i a b i l i t y i s by f a r the b r o a d e s t w i t h SOp as an a c c e p t o r component i n complex f o r m a t i o n . As shown by the d a t a i n T a b l e I I formamide p r o v e d to be most s u i t a b l e as a p o l a r l i q u i d component, c l o s e l y f o l l o w ed by DMSO. I n c o m b i n a t i o n w i t h these two l i q u i d s , a l l k i n d s of amines and even 1\IH^ can be a p p l i e d i n composing c e l l u l o s e s o l v e n t s , and the e f f e c t i v e range of component c o n c e n t r a t i o n s i s r a t h e r ample, w i t h s e v e r a l amines an e x c e s s of e i t h e r SOp o r amine b e i n g e q u a l l y s u i t a b l e . With other l i q u i d s t i k e a c e t o n i t r i l e the c h o i c e of amine as w e l l as the s u i t a b l e c o n c e n t r a t i o n r a n g e i s r a t h e r l i m i t e d . C o n s i d e r i n g the o r d e r of amines s e c o n d a r y amines are o b v i o u s l y most g e n e r a l a p p l i c a b l e , f o l l o w e d by t e r t i a r y and p r i m a r y amines and a t l a s t by 1ŒU# The same o r d e r h o l d s t r u e w i t h r e s p e c t s of the s t a b i l i t y of the s o l v e n t systems, men w i t h the most f a v o r a b l e c o m p o s i t i o n s , the m o l a r r a t i o o f the amine-SOp-complex to g l u c o s e u n i t has to exceed, v a l u e of 3, the l i m i t a r y r a t i o v a r y i n g w i d e l y w i t h type of amine and. p o l a r l i q u i d , and a l s o w i t h the l i q u i d to c e l l u l o s e r a t i o ( T a b l e I I I ) . O b v i o u s l y , an e q u i l i b r i u m e x i s t s i n b i n d i n g of the " a c t i v e comp l e x " to the c e l l u l o s e and to the l i q u i d m i x t u r e , t h i s e q u i l i b r i u m of c o u r s e b e i n g d e t e r m i n e d not o n l y by the c o m p l e x : c e l l u l o s e r a t i o but a l s o by the comp l e x c o n c e n t r a t i o n i n the s o l v e n t s y s t e m .


0

TABLE I I I I n f l u e n c e of L i q u i d : C e l l u l o s e R a t i o on L i m i t i n g M o l a r R a t i o of SO /Amine : G l u c o s e U n i t i n the System S 0 - D i e thylamine-DMSO p

2

Liquid Ratio

to C e l l u l o s e 100 25

Molar Ratio SOp/Amine:Glucose U n i t 5 3


284

CELLULOSE CHEMISTRY AND TECHNOLOGY

I n s o l v e n t s y s t e m s c o n t a i n i n g S 0 C l o r S O p C i ^ as an a c c e p t o r i n c o m p l e x f o r m a t i o n , f o r m a & i d e o r DMSO p r o v e d t o be o u t s t a n d i n g as a p o l a r l i q u i d component, too. But i n c o n t r a s t to S 0 - c o b t a i n i n g systems, the l i m i t e d s o l u b i l i t y o f t h e âmine-acceptor-adducts l e d to r a t h e r s m a l l u s a b l e c o n c e n t r a t i o n r a n g e s o f t h e components. Systems o f s a t i s f a c t o r y s o l v e n t a c t i o n and s t a b i l i t y c o u l d be o b t a i n e d h e r e o n l y by u s i n g a s e c o n d a r y o r t e r t i a r y amine i n e x c e s s t o the o x y c h l o r i d e , and, a s show η i n T a b l e I V f o r aGpClp c o n t a i n i n g systems, a r a t h e r l a r g e molar r a t i o or acceptor-aminecomplex t o g l u c o s e u n i t i s r e q u i r e d , f o r c o m p l e t e d i s s o l u t i o n o f c e l l u l o s e . I n s y s t e m s c o n t a i n i n g SO*-,, t h e r o l e o f amines i s d i f f e r e n t , as t h e a d d i t i o n o f an amine t o a s o l u t i o n o f SO,, i n DMF o r DMSO i n h i b i t s s u l f a t i o n as w e l l as d i s s o l u t i o n of the c e l l u l o s e s a m p l e , i f the m o l a r r a t i o o f amine t o S u e x c e e d s a v a l u e o f i , i n d i c a t i n g an i n a c t i v a t i o n of^SO., by b i n a i n g t o t h e amine. o


o

Q

J

TABLE I V L i m i t i n g M o l a r R a t i o s o f S 0 C 1 t o G l u c o s e u n i t and Amine t o S 0 C I f o r D i s s o l v i n g ^ o f C e l l u l o s e 9

o

C

o

Molar Ratio S0 Cl to Glucose * * U n i.t

System

o

o

Molar Ratio Amine t o so ci 2

2

Propylamine/SOpClp/Formamide

ό

7

Diethylamine/S0 Clp/Formamide

ο

A

T r i e thylamine/SOpClp/Formamide Diethylamine/S0 Cl /DMSQ

4 ο

4 4

Τ r i e t hy 1 a m i η e / S 0 C 1 / DMS 0

b

3,5

0

o

o

2

2

Permanent S u b s t i t u t i o n a t t h eC e l l u l o s e C h a i n and C h a i n D e g r a d a t i o n i n R e l a t i o n to S o l v e n t C o m p o s i t i o n I n t h e b i n a r y s y s t e m CHÊHp/DMSO d i s s o l u t i o n was accompanied b y o n l y r a t h e r s m a l l c h a i n d e g r a d a t i o n and no permanent s u b s t i t u t i o n was o b s e r v e d , o f c o u r s e , a f t e r r e g e n e r a t i o n of the c e l l u l o s e by p r e c i p i t a t i o n i n water. I n s o l v e n t s y s t e m s c o n t a i n i n g an a c i d a n h y d r i d e , a c i d c h l o r i d e , o r E'OHSO., r e s p e c t i v e l y , a n e s t e r i f i c a t i o n o f c e l l u l o s e OH-groups i s p r i n c i p i a l i y p o s s i -


PHiLipp ET AL.

20.


285

b l e , and i n m o s t c a s e s c a n be r e a l i z e d e x p e r i m e n t a l l y , the degree of s u b s t i t u t i o n d i f f e r i n g w i d e l y i n d e p e n d ence of the " a c t i v e agent and the p o l a r o r g a n i c liqu i d of the s o l v e n t systems* S u b s t i t u t i o n to a r a t h e r h i g h DS i s g e n e r a l l y c o m b i n e d w i t h s e v e r e c h a i n d e g r a d a t i o n , thus e x c l u d i n g the action, of these solvent s y s t e m s a s a r o u t e t o h i g h DP c e l l u l o s e e s t e r s . Some analytic data of c e l l u l o s e regenerated from systems c o n t a i n i n g S 0 , SOClp, S C U C l p , o r S 0 r e s p . are summar i z e d i n T a b l e V. W i x h S O p - c o n t a i n i n g s y s t e m s , n o s u b s t i t u t i o n a t a l l was o b s e r v e d . W i t h S 0 C 1 and S 0 C 1 i n c o m b i n a t i o n w i t h an amine and a p o l a r l i q u i d s m a l l amounts of s u l f u r as w e l l as c h l o r i n e were f i x e d a t the c e l l u l o s e c h a i n . As a l r e a d y known by w o r k o f Schweiger (11), a mixture of S0 a n d DMF c a n b e u s e d to prepare ETgh-DS c e l l u l o s e s u l f a t e s * 1 1

2

3


2

2

2

3

TABLE V Permanent S u b s t i t u t i o n of C e l l u l o s e a f t e r D i s s o l u t i o n i n 3-Component Systems C o n t a i n i n g S0 , S 0 C 1 , S 0 C 1 a n d SOo r e s p , ( P r e c i p i t a t i o n i n t o Waxer a ) , D i e t n y l ether D)) 2

System

2

2

DS Sulfur

S 0 / D i e t h y l a m i n e / F o r m a m i d e a)

no

2

S0G1 /Diethylamine/Formamide 2

S0 Cl /Diethylamine/Formamide 2

2

2

a) a)

Substitution

0,073 o;03

S O o / D i m e t h y l f o r m a m i d e b)

Chlorine

0,056 0,015

1,26

W i t h n i t r o s y l i c compounds (N 0,, N0HS0-) i n b i nary systems with a polar l i q u i d , s u b s t i t u t i o n react i o n s are r a t h e r complex. With a l l of these compounds, p r i m a r i l y a n i t r i t e e s t e r of c e l l u l o s e i s formed acc o r d i n g to C e l l - 0 H + N0 >Cell~0-N0 + H 2

+

+

T h e DS o f n i t r i t e e s t e r g r o u p s i n t h e s a m p l e m a i n l y d e p e n d s on the n i t r o s y l i c compound and the mode of prec i p i t a t i o n of the sample ( T a b l e V I ) . P a r a l l e l to n i t r i t e e s t e r f o r m a t i o n , the a n i o n i c p a r t of the n i t r o s y l i c compound, r e s p . the c o r r e s p o n d i n g m i n e r a l a c i d , may r e a c t w i t h t h e c e l l u l o s e , t o o , f o r m i n g t h e a p p r o p r i a t e e s t e r . T h u s , by the a c t i o n o f NOHSO, i n DMF, o r D M S O r e s p . , we f i n a l l y a r r i v e d a t a m i x e d n i t r i t e -


CELLULOSE CHEMISTRY AND


286

TECHNOLOGY

sulphate-ester o f cellulose with a n equimolar s u b s t i t u t i o n o f Ν a n dS b e i n g a c h i e v e d i na w i d e range o f m o l a r r a t i o NOHSO, : g l u c o s e u n i t . A s s h o w n i n F i g u r e 1, the DS s t e a d y ^ i n c r e a s e s a f t e r e x c e e d i n g a mo l a r r a t i o o f 1:1, a n d t e n d s t o r e a c h a l i m i t i n g v a l u e o f 1,5 f o r e a c h k i n d o f t h e e s t e r g r o u p s complying with a total s u b s t i t u t i o n o f a l l hydroxy! groups. The i n f l u e n c e o f p o l a r l i q u i d component o n the DS r e a c h e d at f i x e d conditions o f r e a c t i o n i s demonstrated i n Table νΐζ showing a rather loose c o r r e l a t i o n with d o nor number (19) a n d s w e l l i n g v a l u e (20) o f t h e l i q uids. Chain ïïegradation v a r i e d t o a Targe extend with the n i t r o s y l i c compound used, b e i n g r a t h e r s m a l l w i t h N0C1 a n dN 0 i n t h e a b s e n c e o f w a t e r ( c o m p a r e 4 ) , b u t a r r i v i i l g ^ a t D P - v a l u e s o f 1 0 0 t o 2 0 0 w i t h NOHSO,, s t a r t i n g from a commercial s u l p h i t e d i s s o l v i n g pulp. P

A

TABLE

VI

Permanent S u b s t i t u t i o n o f C e l l u l o s e a f t e r D i s s o l u t i o n i n 2-Component S y s t e m s C o n t a i n i n g N 0., N0C1, a n d NOHSO, r e s p . ( P r e c i p i t a t i o n i n t o Acetone a ) , D i e t h y l e t h e rb ) ) o

d

System

4

DS Nitrogen Chlorine Sulfur

NOCl/Dimethylformamide a)

0,11

NgO^/Dimethylformamide a)

0,23

-

NOHSO^/Dime t h y l f o r m a m i d e

1,07

1,10

b)

0,06

Role o f C e l l u l o s e Structure i n Connection with aqueous Solvent Systems ~"

Non-

The i n f l u e n c e o f c e l l u l o s e s t r u c t u r e o n t h e course o f d i s s o l u t i o n i n aqueous a n d non-aqueous s o l v e n t s h a sb e e n t r e a t e d i no u r p r e v i o u s p u b l i c a t i o n (£)· Thus, o n l y a s h o r t summary w i l l b e g i v e n h e r e , s u p p l e m e n t e d b y some r e m a r k s o n c e l l u l o s e s t r u c t u r e s regenerated from non-aqueous s o l v e n t s . Within t h e s u i t a b l e range o f composition a l l s o l v e n t systems c o n t a i n i n g a n i t r o s y l i c compound o r a n oxide o r oxyc h l o r i d e o f s u l f u r d i s s o l v e native c e l l u l o s e even o f h i g h DP r a t h e r q u i c k l y , w i t h i n m i n u t e s a t room temp e r a t u r e , a n dw i t h o u t r e s i d u e , comparable to the act i o n o f cadoxene, f o r example. B u ti n comparison t o this a n dother aqueous solvent systems, three p o i n t s of difference are remarkable:


PHiLipp ET AL.

20.


287

TABLE V I I I n f l u e n c e o f P o l a r L i q u i d Component on t h e S u b s t i t u t i o n o f C e l l u l o s e b y N0HS0. ( M o l a r R a t i o UOHSO^ t o G l u f f o s e U n i t « 1) Polar Liquid

D N

s

w

l

LRV

b

DS-Sulfur

Dime t h y l s u l f o x i d e

29,8

72

0,71

Dime

26,6

25 20

0,71 0,42

15 8

0,08

-

5 6

0,05

17,0

5

thyIformamide

Dimethylacetamide Downloaded by UNIV OF PITTSBURGH on May 4, 2015 | http://pubs.acs.org Publication Date: June 1, 1977 | doi: 10.1021/bk-1977-0048.ch020

a

Dioxane

0

28,2

Acetonitrile

0

Diethylether

c

Chloroform Acetone

0

0

a)

D

N

27,8

=

sbCl

D o l : l o r

14,1 19,2

Number w i t h

0,06 0,04 0,02

SbCl^

5 b) LRV = L i q u i d R e t e n t i o n V a l u e = S w e l l i n g v a l u e i n t h e p o l a r l i q u i d c o n c e r n e d (%) c ) NOHSO^ n o t d i s s o l v e d c o m p l e t e l y 1· T h e r a n g e o f c o m p o s i t i o n s u i t a b l e f o r c o m p l e t e d i s s o l u t i o n i s g e n e r a l l y smaller w i t h non-aqueous solvents. 2. I n s t e a d o f t h e " K u g e l b a u c h " - s w e l l i n g u s u a l l y o b served as an intermediate stage i n aqueous s o l v e n t s , we f i n d a c o u r s e o f d i s s o l u t i o n p r o c e e d i n g from the fibre surface, leading to spindle-like fragments as intermediate structures Figure[2, ^ 3· D i s s o l u t i o n o f c e l l u l o s e I I , i . e . o f r a y o n o r a l k a l i c e l l u l o s e regenerated by acid washing and drying, proceeded r a t h e r s l o w l y i n s e v e r a l nonaqueous systems as compared t o native c e l l u l o s e s a m p l e s o f m u c h h i g h e r DP, a n d i n some c a s e s n o dissolution a t a l l has been observed with regenerated samples even a f t e r s e v e r a l days. A s a p r o p a b l e c a u s e we a s s u m e a h i n d r a n c e o f reagent transport i n t o the c e l l u l o s e f i b r e due t o the large volume o f the " a c t i v e agent" i n connection w i t h the l i m i t e d p e n e t r a b i l i t y o f t h e pore system o f regenerated c e l l u l o s e . The enhanced d i s s o l u t i o nrate w i t h




288

1

2

3

4

5

6

7

8

9

MOLAR RATIO NOSO^H CELLULOSE Figure

1.

Substitution of cellulose by NOHSO DMF

/f

in

Figure 2. "Kugelbauch"—swelling of cellulose in cuen



20.

PHiLipp ET AL.


289

c e l l u l o s e I I s a m p l e s p r e - s w o l l e n i n DMSO s e e m s t o c o n f i r m t h i s s t a t e m e n t . H o w e v e r , some c o n t r a d i c t i o n arises here with respect to the morphological changes observed during dissolution, and possibly also the different lattice structure of cellulose I and I Ii s o f some i m p o r t a n c e h e r e . Quite a d i f f e r e n t response to c e l l u l o s e struct u r e i s s h o w n b y t h e b i n a r y s y s t e m DMSO-CH^MEL, t h i s "borderline solvent system" d i s s o l v i n g only c e l l u l o s e s a m p l e s o f r a t h e r l o w s t a t e o f o r d e r a n d / o r l o w DP, i r r e s p e c t i v e o f l a t t i c e type. Thus, rayon staple and h y d r o l y i i c a l l y degraded wood pulp a r e d i s s o l v e d w i t h out r e s i d u e , while l i n t e r must be r e p r e c i p i t a t e d t o achieve a d i s s o l u t i o n . With regard to cellulose physical structure obtained by p r e c i p i t a t i o n from non-aqueous s o l u t i o n i n to a n aqueous medium, a r a t h e r p e c u l i a r b e h a v i o r o f the DMSO-CHoUHp-system was c o n f i r m e d a g a i n : The p r e cipitate consisted only partially of cellulose I I , showing simultaneously an other l a t t i c e type c l a s s i f i e d by us as c e l l u l o s e I , while a l l the other prec i p i t a t e s obtained f r o m non-aqueous and aqueous s o l u t i o n s u n d e r t h e same c o n d i t i o n s w e r e c o m p o s e d o f c e l l u l o s e I I o n l y . W i t h n o n - a q u e o u s s o l v e n t s y s t e m s we arrived a t p r e c i p i t a t e s generally showing a trend to a somewhat l o w e r s t a t e o f o r d e r - a s measured b y Xr a y - d i f f r a c t i o n - as compared t o samples regenerated f r o m aqueous s o l u t i o n * w h i l e no s i g n i f i c a n t a n d g e n e r a l i z a b l e d i f f e r e n c e s c o u l d be s t a t e d w i t h r e g a r d t o several a c c e s s i b i l i t y c r i t e r i a o f samples p r e c i p i tated from aqueous and non-aqueous s o l u t i o n s (21). Obviously, a c c e s s i b i l i t y i s determined here predominantly by the procedure o f p r e c i p i t a t i o n and not by the type o f s o l v e n t . Discussion o f the Mechanism o f Interaction C e l l u l o s e and Non-aqueous Solvents

between

Previous c o n s i d e r a t i o n s on the d i s s o l u t i o n mechanism o f c e l l u l o s e i n non-aqueous solvents u s u a l l y were centered on the p e c u l i a r solvent system i n v e s tigated. Starting from the assumption o f electrondona tor-accept or (EDA) complex formation i n these s y s t e m s f i r s t m e n t i o n e d b y N a k a o ( 8 ) , we a r r i v e d a t a generalizable q u a l i t a t i v e model T o r the f i r s t step of i n t e r a c t i o n between c e l l u l o s e and solvent, which permits a n i n t e r p r e t a t i o n o f most o f the experimental data acquired f o rthe d i f f e r e n t solvent systems and which i s not i n contradiction with the remaining onea




290

Figure 3. Spindle-like structures of cellulose during dissolution in N Oj,DMF 2

C T ; < ( T

CELLULOSE / H ΙΟΙ

l 0 1

ΙΟΙ

,

Α

H.

ιοί

Η

( Γ (Γ

Α

D 1

S0LV.

A

*η'

C

IOI

D

SOLV. Figure 4. Scheme of EDA-interaction as a first step of dissolution



20. PHiLipp ET AL.


291

P r i n c i p a l assumptions o f t h i s model a r e - t h e p a r t i c i p a t i o n o f the 0-atom and the Η-atom o f a c e l l u l o s i c OH-group i n E D A - i n t e r a c t i o n , w i t h t h e 0-atom a c t i n g a s a n n - e l e c t r o n - p a i r donator and the Η-atom as an -electron-pair acceptor - the presence o f a donor and an acceptor centre i n the " a c t i v e agent" o f t h e s o l v e n t system, b o t h cen tres being i n a steric position suitable f o r inter action with 0 and H o f the hydroxyl group - t h e e x i s t e n c e o f a d e f i n i t e optimal range o f EDAinteraction strength, leading - i n connection with the s t e r i c p o s i t i o n o f t h e donor a n d a c c e p t o r cen tre and the action of the polar organic liquid - to t h e o p t i m a l a m o u n t o f c h a r g e s e p a r a t i o n o f t h e OHgroup s f o r d i s s o l v i n g the complexed c e l l u l o s e chain. Figure 4 demonstrates i n a strongly schematized form these c o n s i d e r a t i o n s . T h i s f i r s t step o f i n t e r action, decisive for getting the cellulose into solu t i o n , may be f o l l o w e d b y a permanent e s t e r i f i c a t i o n o f O H - g r o u p s , a s s h o w n w i t h UT0HS0. f o r e x a m p l e , b u t t h i s e s t e r i f i c a t i o n i s n o p r e r e q u i s i t e fper d i s s o l u t i o n , a s shown by t h e v e r y good s o l v e n t a c t i o n o f S 0 - c o n t a i n i n g systems. By means o f t h i s EDA-concept w i f h the premises given above, a reasonable mechanism of i n t e r a c t i o n w i t h c e l l u l o s e may be p l o t t e d down f o r a l l non-aqueous s o l v e n t systems known today. B e t w e e n t h e b i n a r y s y s t e m DMSO-CH^MHp a n d c e l l u l o s i c OH-groups s e v e r a l modes o f E D A - i n t e r a c t i o n a r e t o b e c o n s i d e r e d , a s s h o w n i n F i g u r e 5· I n a l l p o s s i b l e cases t h e i n t e r a c t i o n i s r a t h e r weak, thus l i m i t i n g the solvent action o f this system and explain i n g the s p e c i f i t y o f components b y the n e c e s s i t y o f a s p e c i a l s t e r i c arrangement o f the d i f f e r e n t charge c e n t r e s . A s a m o s t p r o b a b l e m e c h a n i s m we d i s c u s s a primary i n t e r a c t i o n between t h e h y d r o x y l i e 0-atoms a s a d o n o r a n d t h e a c c e p t o r c e n t r e o f DMSO, w h i c h i t s e l f i s complexed b y t h e amine, t h e amine a d d i t i o n a l l y binding the Η-atom o f the c e l l u l o s i c hydroxyl group. Common f e a t u r e o f a l l " n i t r o s y l i c s y s t e m s " i s t h e i n t e r a c t i o n o f t h e s t r o n g a c c e p t o r NO , p r e s e n t as a f r e e i o no r a s an i o n d i p o l e , w i t h the hydrox y l i c 0 - a t o m a s a d o n o r / F i g u r e 6J, f o l l o w e d b y c o m p l e t e c h a r g e s e p a r a t i o n i n t h e NO Z ~ - d i p o l a n d t h e formation o f the n i t r i t e e s t e r o f c e l l u l o s e . Depend ing on the anionic part o f the ΝΟΣ-molecule resp. on the a c i d formed b y i t c a p t u r i n g t h e Η-atom o f t h e c e l l u l o s i c hydroxyl, a second kind o f e s t e r groups can be introduced i n t o the c e l l u l o s e c h a i n e i t h e r b y d i r e c t e s t e r i f i c a t i o n o f free OH-groups· o r by transe s t e r i f i c a t i o n v i a n i t r i t e e s t e r g r o u p s / P i g u r e IjL E x 2


CELLULOSE CHEMISTRY AND TECHNOLOGY CELLULOSE

CH

3

10 — r

X

\_/CH N

A CH

H

3

/ \

/ Η---Ι0 = S

01 — Η

3

C

X

H

C H

3 3

CELLULOSE

r H

01

IÔ

S

/SI

Figure 5. EDA-interaction cellulose with CH NH -DMSO


3

CELL—0— Η

N0

6.

3

CELL—0—Η

| CH

H _ / C H

| H-IO = S CH

3

X

3

3

X

CH

3

CELL ~ 0 — Η - —EPD-LIQUID

OW EPD-LIQUID

N

EPD-LIQUID Figure

C H

2

χΗ

W

of

Κ

I N '

N0 X " W

l

J

X^

EDA-interaction

of cellulose with nitrosylic compounds in strong polar liquids

CELLULOSE

ι

Γ

I0 -H 0 = NI

Γ

ΙΟΙ

W

Χ

I

Ô ==Ν Ι η

_/, Χ

*H

W

N0

2

W

- W χΗ H

. 1_ I0 -H W

g-i

IQ-H ~ ~

χ""

ΙΟΙ

X

3-NI

• H 0 7. Substitution of cellulose by reaction with nitrosylic compounds 2

Figure


PHiLipp ET AL.

20.

Nonaqueous Solvents

CELL— Ô

Η

τ ι ι

CELL—δ — Η

τ

ι

ι 1 R NI—I S — Ο

1

Τ

ΙΟΙ 8.

— I N R

3

1

I

IS =

3

Figure

293

'

g

ΙΟΙ EDA-interaction of cellulose with ternary system SO —amine—polar liquid


%

périmental evidence i s i n favor o fthe f i r s t r e a c t i o n p a t h w i t h B O H S O , , w h i l e w i t h NOC1 a t r a n s e s t e r i f i c a t i o n i smore p r o b a b l e . I n systems c o n t a i n i n g S 0 , S0C1 o rSO^Clp, t h e a c c e p t o r s t r e n g t h o f t h e S - a t o m i s a l o n e no τ s u f f i cient f o r a i n t e r a c t i o n leading t od i s s o l u t i o n , but must b esupported a n d i n c r e a s e d b y t h e complexing a c t i o n o f a n amine, t h e amine a d d i t o n a l l y b i n d i n g t h e Η-atom o f t h e OH-groups. A sshown i n F i g u r e 8 f o r SOp as a n acceptor, t h i s complex d i s s o l v e s i n the p o l a r l i q u i d present a sa t h i r d component, the i n t e r a c t i o n with this l i q u i d f u r t h e r promoting p o l a r i z a t i o n o f the S-O-bonds o fS 0 a n d t h e subsequent interaction w i t h the c e l l u l o s i c OH-groups. A p p l y i n g S0C1 o rS0 C1 a s a n a c c e p t o r compo nent, f u l l complexation r e q u i r e s a n excess o f amine, i . e . a minimum molar r a t i o o famine t oSOCl^ o r S 0 C 1 , resp., o f 3:1, probably due t oa s t r o n g e r i n t r i n s i c d i s s o c i a t i o n o fthe acceptor molecule /Figurefl General conclusions covering nitrosylic systems as w e l l a s oxides o ro x y c h l o r i d e s o fs u l f u r c o n t a i n i n g o n e s , m u s t b e d r a w n w i t h c a u t i o n , o f c o u r s e . How ever, the f o l l o w i n g statements maybe summarized from our experiments and from data published b y others: 2

2

2

2

2

2

2

2

1. I f " s o l v e n t p o w e r " i s d e f i n e d a s t h e n u m b e r o f moles o f" a c t i v e agent" ( a c t i v e component o r a c tive complex)per mole glucose u n i t needed f o r d i s s o l v i n g h i g h D P - c e l l u l o s e , a n d i f D M F a n d DMSO

CELL—0—H—NR

CELL —

3

0 — H — NR

ClH R N 3

'

I CI

N

NR

Cl

R N '

3

3

I NR Ct

3

(.)

N

3

Figure 9. EDA-interaction of cellulose with ternary sys tem SOCl or SO Cl -amine—polar liquid 2

%

%


CELLULOSE CHEMISTRY AND

294

TECHNOLOGY

( w i t h N O X - s y s t e m s ) o r f o r m a m i d e a n d DMSO ( w i t h oxides andoxychlorides o f sulfur) are considered as p o l a r l i q u i d component, a n order o f a c c e p t o r components w i t h r e s p e c t t o s o l v e n t power c a nbe given according to N 0 2

4

^ S 0

2

^N O H S O ^ S 0 C 1 * N0C1 > S 0 C 1 . 2

2

2

2. T h e p o l a r l i q u i d c o m p o n e n t s h o u l d c o m p l y w i t h t h e rather different requirements o f d i s s o l v i n g the NOX-compound o r t h e a m i n e - S 0 ( S 0 G 1 , S 0 C 1 ^ c o m p l e x , o f f u r t h e r p o l a r i z i n g i h e s e compounds v i a E D A - i n t e r a c t i o n , b u tn o t r e a c t i n g w i t h them i n a permanent, i r r e v e r s i b l e way, a n d o f s o l v a t i n g t h e EDA-adduct formed w i t h c e l l u l o s e . F o r m a m i d e a n d DMSO p r o v e d t o b e o u t s t a n d i n g i n coming u p t o these demands. 3· I f a n amine i s t o be added t o t h esystem, i t should have a r a t h e r h i g h donor s t r e n g t h combined with a minimal r e a c t i v i t y with regard t o the other components o f t h esystem, thus t e r t i a r y a n d s e c o n d a r y amines g e n e r a l l y b e i n g more s u i t a b l e than primary ones o r Β Η ^ ·


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F i n a l Remarks a n d Conclusions G e n e r a l l y s p e a k i n g , we a r e s t i l l a t t h e b e g i n ning o f a mechanistic understanding o f cellulose dis s o l u t i o n p r o c e s s e s i nnonaqueous a n d aqueous systems as w e l l . T h e EDA-concept used here may be a g u i d e l i n e i n t h i s s y s t e m a t i z a t i o n a n d i n s e a r c h i n g f o r new n o n - a q u e o u s s o l v e n t s y s t e m s i f we a r e awarer o f i t s l i m i t a t i o n s , too. L i m i t a t i o n s t o be kept i nmind a r e - t h es t i l l r a t h e r q u a l i t a t i v e c h a r a c t e r o f t h e mod els used here, due t o l a c k o f r e l i a b l e q u a n t i t a t i v e d a t a e s p e c i a l l y o r a c c e p t o r s t r e n g t h o f t h e com pounds concerned. Recent work p u b l i s h e d b y Gutmann (19) might be h e l p f u l here, b u t much e x p e r i m e n t a l work h a ss t i l l t o be done, b y spectroscopy o r c o n ductometry, f o r example, t o q u a n t i f y these i n t e r a c t i o n s i no u r s p e c i a l two- o r three-component sys tems; - t h ei m p o s s i b i l i t y t o g i v e a n yr e g a r d t o c e l l u l o s e morphology i n connection w i t h molar volume o f s o l vent components; - t h ea p p l i c a b i l i t y o f t h e c o n c e p t j u s t t o t h e f i r s t step o f cellulose-solvent-interaction. On t h e o t h e r h a n d , t h i s E D A - c o n c e p t m a y b e e x tended t o aqueous s o l v e n t systems, too, a n d thus s e r -


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Ή on-aqueous Solvents

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ve a synoptic d i s c u s s i o n of c e l l u l o s e s o l u t i o n pro cesses i n g e n e r a l . As demonstrated by the s e r i e s of s o l v e n t systems S0 -KH2""P organic s o l v e n t HELj-inorganic s a l t - p o l a r organic l i q u i d l i q u i d MH^-inorganic s a l t HÔ-inorganic s a l t olar

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there i s no d e f i n i t e gap between aqueous and non-a queous s o l v e n t s f o r c e l l u l o s e . A p p l y i n g the EDA-con cept to the f i r s t step of p o l y m e r - s o l v e n t - i n t e r a c t i o n , we can c o n s i d e r as an n-ele s NR CH -S N-H /\ !\ 1 y 11 CH ΙΟΙ H CH I Cl ΙΟΙ 2NR

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Non-aqueous Solvents of Cellulose - ACS Symposium Series (ACS

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