THE

SWELLING

OF C E L L U L O S E

G. N. M u s a t o v a , M. A. Ginzberg,

XANTHATE

IN C A U S T I C

D. N. A r k h a n g e l s k i i , and E. M. M o g i l e v s k i i

SODA S O L U T I O N S UDC 6 7 7 . 4 6 3 . 0 2 1 . 1 2 2 . 2 2 5 . O 1 4 . 3 3 2 . 1

The d i s s o l u t i o n of c e l l u l o s e x a n t h a t e is preceded, like that of any other polymer, by s w e l l i n g the rate and degree of which g o v e r n the p r o c e s s as a whole and also i n f l u e n c e the q u a l i t y of the viscose. C e l l u l o s e x a n t h a t e (CX) dissolves r e a d i l y in water and alkali so that a study of its s w e l l i n g s t a g e s i n v o l v e s c o n s i d e r a b l e e x p e r i m e n t a l difficulties. The l i t e r a t u r e cont a i n s no q u a n t i t a t i v e data on the swelling of CX in alkali solutions. The only r e l e v a n t p u b l i c a t i o n s are a paper by A v i s i e r s and Hess / I / who i n v e s t i g a t e d CX s w e l l i n g in a system of p r o p a n o l a n d water, and a paper by P h i l i p p / 2 / who by the same m e t h o d and by the v i s u a l m o n i t o r i n g of the s w e l l i n g of single fibres o b t a i n e d a certain amount of data on the effect of the c o n d i t i o n s of d e g r a d a t i o n of the soda cellulose on the swelling of the cellulose xanthate. The p r o c e s s of s w e l l i n g of the CX can be a n a l y s e d only by c r e a t i n g c o n d i t i o n s in w h i c h the p o l y m e r swells but does not dissolve. The s o l u b i l i t y of h i g h - p o l y m e r i c comp o u n d s d e c r e a s e s with an i n c r e a s e in the m o l e c u l a r weight. The e x p e r i m e n t s were therefore c a r r i e d out w i t h s p e c i m e n s of a h i g h - m o l e c u l a r CX from cotton with a degree of p o l y m e r i z a t i o n of about 2200. The cotton was m e r c e r i z e d in a 17.5% solution of caustic soda, p r e s s e d out to three times its weight and t r e a t e d with c a r b o n disulphide. The b y - p r o d u c t s and a l k a l i were e l i m i n a t e d by w a s h i n g the CX in a s a t u r a t e d sodium chloride s o l u t i o n and e t h a n o l f o l l o w e d by drying. The degree of e s t e r i f i c a t i o n was v a r i e d by v a r y i n g the amount of c a r b o n disulphide. After x a n t h a t i o n the CX u s u a l l y had too high a degree of e s t e r i f i c a tion y. It was t h e r e f o r e s t o r e d for at least 24 h until y had d e c r e a s e d to the r e q u i r e d level and the c h e m i c a l c o m p o s i t i o n of the CX had become homogeneous. The CX was perm i t t e d to swell in the chosen m e d i u m for two hours, the time r e q u i r e d for a c h i e v i n g the e q u i l i b r i u m state. T h e degree of s w e l l i n g of the CX was d e t e r m i n e d / 3 / by c e n t r i f u g i n g the s p e c i m e n at g = 670 approx.

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Fig.1. The d e g r e e of s w e l l i n g of CX as a f u n c t i o n of the c o n c e n t r a t i o n of the N a O H solution: I) for YCX = 30, 2) for YCX = 20, 3) for YCX = 10, 4) cotton.

The degree of s w e l l i n g is c a l c u l a t e d as the ratio (expressed in percent) of the weight of the c e n t r i f u g e d fibre to that of o v e n - d r y fibre. However, the s w e l l i n g CX a b s o r b s N a O H m o l e c u l e s from the alkali solution at a rate which v a r i e s with the N a O H c o n c e n t r a t i o n in the solution. This fact is r e f l e c t e d in the a b s o l u t e degree of s w e l l i n g so that the N s O H content of a w e i g h e d CX p o r t i o n was d e t e r m i n e d in each e x p e r i m e n t by t i t r a t i o n with an acid and a l l o w e d for Jn the c a l c u l a t i o n of the degree of s w e l l i n g (%) from the e x p r e s s i o n P c Cs = Pd - g N a O H

"100

K i e v B r a n c h of the A l l - U n i o n S c i e n t i f i c R e s e a r c h I n s t i t u t e for M a n - M a d e Fibre; A l l - U n i o n S c i e n t i f i c R e s e a r c h I n s t i t u t e for M a n - M a d e Fibre. T r a n s l a t e d from K h i m i c h e s k i e V o l o k n a , No.4, pp. 47 - ~9, J u l y - August, 1972. O r i g i n a l a r t i c l e s u b m i t t e d June 8,1971.

C) 1973 Comultants Bureau, a division of Plenum Publishing Company Limited, Davis House (4th Floor), 8, Scrul~ Lane, Harletden, London NW10 6SE, England. All rights reserved. This article cannot be tepixKluced for any propose whatsoever without permission of the publisher. A copy of this article is available from the publisher for $15.00.

406

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Degree of esterification of the

N aOH, % CX Fig.2 Fig.3 Fig.2. The effect of the concentration of the N a 0 H solution on the fibre diameter iu the swelling process (the ratio between the diameters of the swollen and original fibres): I) for YCX = 20, 2) for YCX = 10.

Fig.3. The influence of YCX on the swelling of the CX: a 4% solution of NaOH, 2) in an 8% solution of NaOH.

~o

I) in

In the foregoing expression Pc is the weight of the c e n t r i f u g e d fibre, P d is the weight of the oven-dry fibre portion, and gNaOH is the weight of caustic soda a b s o r b e d by the CX.

I

t,°C Fig.4. The t e m p e r a t u r e dependence of the log of the degree of swelling (YCX = 30, concentration of the Na0H solution 4%).

The results of parallel d e t e r m i n a t i o n s of the degree of swelling of the CX agreed satisfactorily. In some cases the degree of swelling was determined in an optical microscope at 10 x 40 from the increase in the fibre section.

An analysis was carried out of the effect of the concentration of the caustic soda solution and of the temperature of the medium on the swelling of CX with varied degrees of esterification. The effect of the caustic soda concentration is shown in Fig.1. It is interesting that the variation of the degree of swelling with the degree of esterification of the CX is similar to that of the swelling of cellulose in alkali /4/. The initial increase and subsequent decrease in the degree of swelling with an increase in the caustic soda concentration is a t t r i b u t a b l e to two factors acting in opposite directions, viz. the increase in the quantity of alkali a b s o r b e d by the fibre and the decrease in the volume of water combined with the sodium ion /5/. The results of the gravimetric determination of the degree of swelling were confirmed by those of the microscope observations of the swelling process (Fig.2). The diagrams in Figs. I and 2 show that the absolute degree of swelling decreases evenly with the degree of compacting of the structure of the cellulosic substance at the various N a O H c o n c e n t r a t i o n s in the descending order from a CX with a relatively high degree of esterifica~ion (y = 30) the structure of which is loosened to a c o n s i d e r a b l e extent by t h i o c a r b o x y l groups,to cotton cellulose, i.e. natural cellulose with a high degree of m a c r o m o l e c u l a r order It is a c o n s p i c u o u s fact that the peak degree of swelling of the denser structures lies in the region of high caustic soda concentrations. This is clearly i l l u s t r a t e d by the results obtained with solutions containing alkali 4 and 8% (Fig.3). The CX u s e d for production purposes is polydisperse with respect to molecular weight and degree of e s t e r i f i c a t i o n /6/. It can be rendered homogeneous only by producing conditions in which the not readily soluble CX fractions are dissolved. The results obatined in this investigation appear to indicate that a solution containing caustic soda 4% would be the best solvent for technical CX of y = 50 - 60. The CX may, however, contain m a c r o m o l e c u l e s of a low degree of esterification /7/. The filterability of the

407

viscose can be improved, therefore, by using a high-concentration caustic soda solution for the first dissolving stage. This has been demonstrated in practice at several producing establishments, among them the Krasnoyarsk rayon plant where the filterability of the viscose has been improved by using a 9 - 9.5% concentration of caustic soda in the first stage of the dissolving process. The temperature dependence of the degree of swelling of a CX with y = 30 in a 4% solution of NaOH is plotted in semilogarithmic co-ordinates in Fig.4. The degree of swelling decreases steadily with an increase in the temperature. The results obtained with other caustic soda concentrations and with CX specimens of other degrees of esterification were similar. The decrease in the degree of swelling of the CX with an increase in the temperature is evidently the result of a decrease in the thickness of the hydrate shell of the sodium ions. The decrease in the degree of swelling is not large. For example, for a CX with y = 30 the decrease in the degree of swelling is only 10% with an increase in the temperature by I0°C. Like the results of earlier research /9/ these findings encourage further experiments aimed at increasing the process rate of cellulose xanthate dissolution by increasing the process temperature.

I. An investigation was carried out of the concentration of the caustic soda solution as a factor in the degree of swelling of cellulose xanthates of various degrees of esterification. It was shown that the swelling of a CX with a low degree of esterification increases With the concentration of the caustic soda solution. 2. It is suggested that in the first stage of the dissolution process the concentration o£ the caustic soda solution should be 8% so that the degree of swelling is at a peak for the xanthate fractions with the lowest degree of esterification. 3. It was shown that the degree of swelling decreases only slightly with an increase in the temperature and that it may be possible to accelerate dissolution by increasing the process temperature. LITERATURE 1. 2. 3. 4. 5.

6.

78. 9.

CITED

J.Avisiers and K.Hess, Eolzforschung, 10, No.1 (1956). B.Philipp, Svesnk Papperstidn., 65, No.-~ (1962). E.Hubert, A.Mattes, and K.Weisbrod, Koll. Z., 98, 173 (1942) N.I.Nikitin, Chemistry of Wood and Cellulose ~'~n Russian), AN SSSR (1962), p.201. Z.A.Rogovin and N.A.Shorygina, Chemistry of Cellulose and its Accessories (in Russian), Goskhimizdat (1953), p.186; R.Bartunek, Das Papier, ~, No.9-10 (1953); K.P.Mishchenko, Zh.Fiz.Khim., 26, No.12 (1952). S.N.Danilov and S.M.Rizov, Isk~ssstvennoe Volokno, No.2 (1934); P.Scherer and R.Phillips, Rayon and Synthetic Textiles, 30, No.5 (1949); A.A.Konkin, Yu.A.Rymashevskaya, and N.V.Shulyatikova, Khim.Volokna, No.4 (1960). R.Stahn, Das Papier, 18, No.12 (1964). G.A.Molochnaya, M.E.Shor, E.P.Efremova, V.I.Prikhodko, N.L.Zubakhina, and L.S.Parashchuk, Fibre Chemistry, No.1 (1969), Plenum Publ.Co.,Ltd.,London. G.N.Musatova, E.M.Mogilevskii, M.A.Ginzberg, and D.N.Arkhangelskii, Fibre Chemistry, No.5 (1970), Plenum Publ. Co.,Ltd.,London.

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