METHOD

OF

DETERMINING

CAUSTIC

SODA IN VISCOSE

T. B. Filicheva, Z. and A. B. Pakshver

THE

FREE

UDC 677.463.021.123.014.2

S. L a p k i n a ,

The p r o p e r t i e s of v i s c o s e a r e influenced by its content of f r e e caustic soda, i.e. the v i s c o s i t y d e c r e a s e s , filterability i m p r o v e s , and ripening b e c o m e s slower with an i n c r e a s e in the content of caustic soda not c o m bined with the cellulose or with the i m p u r i t i e s [1]. The existing methods of d e t e r m i n i n g the content C Oof f r e e caustic soda lack p r e c i s i o n and depend on the conditions in which the a n a l y s i s is c a r r i e d out [2, p. 134; 3]; i.e., during the dilution of the v i s c o s e with w a t e r p r i o r to the a n a l y s i s , the dithiocarbonyl groups of the cellulose split off so that the t r i t h i o c a r b o n a t e content i n c r e a s e s . T h e s e r e a c t i o n s d e v e l o p a s a r e s u l t of some of the NaOH being combined and C Od e c r e a s i n g as a consequence. In a NaOH solution the f r e e carboxyl g r o u p s of cellulose a r e solvated in the r e a c t i o n Cell. OH + NaOH ~

CelL OH-HONa

(1)

w h e r e the d e g r e e of solvation, i . e . TNaOH' depends on the NaOH content of the solution. In cellulose m e r c e r izing with an 18% NaOH solution ~/NaOH is approximately 100 [4, p. 130]. The dilution of the v i s c o s e p r i o r to the a n a l y s i s should r e s u l t in a lower ~/NaOH and l a r g e r C 0. The l i t e r a t u r e contains no d e s c r i p t i o n of methods of analyzing undiluted v i s c o s e sq that the p r e s e n t w r i t e r s attempted to calculate COf r o m analytical data relating to the content of cellulose xanthate and s u l f u r containing i m p u r i t i e s , m o r e p a r t i c u l a r l y t r i t h i o c a r b o n a t e , in the v i s c o s e . It is known that some of the caustic soda in the v i s c o s e helps to f o r m thiocarbonyl groups: CelL OH + CSz + NaOH ~

Cell. OCSSNa + H20

(2)

while s o m e of it c o m b i n e s with the CS2 3CSl -]- 6NaOH = 2NazCSs + NasCOs.

(3)

Finally, some of the caustic soda solvates the hydroxyl g r o u p s of the cellulose in a c c o r d a n c e with Eq. (1). Equations (1)-(3) make it possible to calculate the amount (%) of caustic soda combined with the thioc a r b o n a t e g r o u p s in the cellulose xanthate: C1 ~

a'40'YCSt 162.100

(4) '

and in the t r i t h i o c a r b o n a t e : C~ ~ aCNajCS*'6'40 2.154. 100

'

<5)

T r a n s l a t e d f r o m Khimicheskie Volokna, No. 5, pp. 69-70, S e p t e m b e r - O c t o b e r , 1976. Original a r t i c l e submitted August 1, 1975.

I This material is protected by copyright registered in the name o f Plenum Publishing Corporation, 227 West 17th Street, New York, N.Y. 10011. No part o f this publication may be reproduced, stored in a retrieval system, or transmitted, in any form or by any means, electronic, mechanical, photocopying, microfilming, recording or otherwise, without written permission o f the publisher. A copy o f this article is available from the publisher for $ Z 50.

553

T A B L E 1. T h e Content of F r e e C a u s t i c Soda i n the Viscose Determined by Various Methods Calculated results

Analysisresults o m

C,, % C,, %! Cs, % Co, % ~=

L)

L) Viscose after solution

0,70 0,70 0,69 0,76 0,78 0,78 0,79

8,48 8,56 9,16 8,57 8,22 8,16 8,48

5,95 3,19 1,06 0,75 5,97 3,26 1,10 0,77 6,30 3,36 1,14 0,77 6,51 4,02 1,16 0,63 6,45 4,04 1,03 0,56 6,41 4,08 1,09 0,64 6,69 4,40 1,03 0,74 Viscose after ageing

0,42 0,42 0,47 0,48 0,48 0.45 0,49

3,72 t 3,68 ] 3,92 [ 4,24 I 4,38 [ 4,23 [4,43

0,53 0,42 0,56 0,22 0,34 0,15 0,03

0,70 0,71 0,70 0,74 0,77 0,78 0,79

8,53 8,53 9,02 8,57 8,17 8,19 8,52

5,95 6,09 6,37 6,36 6,28 6,36 6,74

0,41 0,41 0,47 0,44 0,42 0,44 O,47

3,59 3,59 3,77 3,96 3,89 4,03 4,21

0,59 0,59 0,54 0,60 o, 49 0,55 0,53

3,00 0,85 3,00 0,87 3,13 0,94 3,36 0,84 3,40 0,79 3,48 0,85 3,68 0,88

,I0 ,22 ,19 ,12 ,18 ,03 ,18

Note. C t o t a 1 i s t h e t o t a l NaOH c o n t e n t of t h e v i s c o s e ; C f r e e a n d C o t h e f r e e NaOH in the v i s c o s e d e t e r m i n e d b y a n a l y s i s and c a l c u l a t e d , r e s p e c t i v e l y ; C i t h e NaOH in the c e l l u l o s e x a n t h a t e , C 2 t h e NaOH i n the t r i t h i o c a r b o n a t e , and C 3 the NaOH in t h e s o d a c e l l u l o s e .

SO

.2

2

4,

G

8

fg

f2

l~,

C,%

F i g . 1. T h e c o n t e n t of NaOH c o m b i n e d w i t h t h e c e l l u l o s e (TNaOH) a s a f u n c t i o n o f the NaOH c o n t e n t in t h e s o l u t i o n (C, %). a n d w i t h t h e OH g r o u p s o f t h e c e l l u l o s e : Cs=

aVNaOH'40 100.162

(6)

w h e r e a i s t h e c e l l u l o s e c o n t e n t o f the v i s c o s e , %; VCS2 i s t h e d e g r e e o f c e l l u l o s e e s t e r i f i c a t i o n p e r 100 g l u c o s e r a d i c a l s ; 7NaO H i s t h e d e g r e e o f s o l v a t i o n o f OH g r i p s o f t h e c e l l u l o s e p e r 100 g l u c o s e r e s i d u e s ; CNa2CS3 i s t h e c o n t e n t of t r i t h i o c a r b o n a t e in t h e v i s c o s e (%) c a l c u l a t e d f r o m t h e s u l f u r c o n t e n t o f t h e i m p u r i t i e s ; 40, 154, a n d 162 a r e t h e m o l e c u l a r w e i g h t s o f t h e c a u s t i c s o d a , t r i t h i o c a r b o n a t e , and g l u c o s e r e s i d u e , r e s p e c t i v e l y . T h e c o n t e n t o f f r e e c a u s t i c s o d a C o c a n b e c a l c u l a t e d b y a d d i n g t o g e t h e r the a m o u n t s of c o m b i n e d c a u s t i c s o d a a c c o r d i n g to E q s . (4)-(6) a n d d e d u c t i n g t h e a n a l y t i c a l l y d e t e r m i n e d t o t a l c o n t e n t Ctota I o f c a u s t i c s o d a in t h e v i s c o s e : co = Ctotal- (c, + c, + c~)

554

(7)

F o r this calculation it is n e c e s s a r y to d e t e r m i n e 7CS° and CNa2CS3 [2, p. 134] as well as ~/NaOH a n a lyticaUy. The p r e s e n t w r i t e r s d e t e r m i n e d ~/NaOH for a bro~ad r a n g e of the NaOH content in the solution by a method d e s c r i b e d e l s e w h e r e [4, p. 129] (using isobutyl alcohol f o r rinsing) and obtained the function shown in Fig. 1. The S-shape of the c u r v e in the d i a g r a m is evidently attributable to the fact that the a c c e s s i b i l i t y of the OH g r o u p s of the m a c r o m o l e c u l e s in the fibre body i n c r e a s e with an i n c r e a s e in the NaOH content of the s o lution to 8-10%, whilewith its i n c r e a s e to o v e r 12%, the swelling of the cellulosic f i b r e s d e c r e a s e s owing to a deficiency in the alkaline solution of w a t e r m o l e c u l e s not combined in the h y d r a t e envelope of the Na+ and OH-. To d e t e r m i n e Cs the amount of NaOH combined with the cellulose xanthate and t r i t h i o c a r b o n a t e was calculated f r o m Eqs. (4) and (5) after which this amount was deducted f r o m the total NaOH in the v i s c o s e and the a p p r o x i m a t e content of f r e e caustic soda was calculated f r o m the equation C0' = Ctota 1 - C t - C 2. The u n c o r r e c t e d ~/NaOH was d e t e r m i n e d f r o m the g r a p h and C 3' was calculated f r o m Eq. (6), a f t e r which a c o r r e c t i o n was m a d e taldrLg C3' into account (the p r i m e s denote the i n t e r m e d i a t e calculated values). Determining the content of f r e e caustic soda by titrating the v i s c o s e gives Understated r e s u l t s (Table 1), m o r e p a r t i c u l a r l y for a v i s c o s e with a low NaOH content. The different is g r e a t e r for ripened v i s c o s e . The fact that the calculated content of f r e e caustic soda is g r e a t e r than that d e t e r m i n e d by analysis is explained as follows: 1. The amount of caustic soda combined with the cellulose by r e a c t i o n (1) is in fact l a r g e r than c a l culated b e c a u s e the data given in Fig. 1 and u s e d for calculating C 3 r e l a t e to caustic soda combined with c e l lulose in the solid phase so that in the solutions ~/NaOH m u s t be g r e a t e r . 2. In the calculations all sulfur-containing i m p u r i t i e s of the v i s c o s e w e r e t r e a t e d as sodium t r t t h i o c a r b o n a t e and the caustic soda consumption was calculated f r o m Eq. (3),whereas it is well known that v i s c o s e contains sodium sulfides and polysulfides, p e r t h i o c a r b o n a t e s , c a r b o n a t e s , and other compounds. The NaOH consumption in the f o r m a t i o n of these compounds was not taken into account. It follows that the method b a s e d on Eqs. (4)-(6) can be r e c o m m e n d e d f o r a sufficiently p r e c i s e d e t e r m i nation of the f r e e caustic soda in v i s c o s e . LITERATURE

lo 2. 3. 4.

CITED

T. B. Filicheva, E. M. Mogilevstdi, and S. P. Papkov, Khim. Volokna, No. 2, 18-20 (1974). A. B. P a k s h v e r and A. A. Konkin (editors), Man-Made F i b r e Production Control [in Russian], Khtmiya, Moscow (1967), 606 pp. V. Ahlqvist, E. Gruber, and E. T r e i b e r , Svensk Papperstidn., 23, No. 15, 842 (1965). Z. A. Rogovin, The C h e m i s t r y of Cellulose [in Russian], Khimiya, Moscow (1972), 518 pp.

555