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Effect of some chemical treatments on the reactivity of purified Egyptian cotton waste fibres towards xanthation
EFFECT OF SOME CHEMICAL TREATMENTS ON THE REACTIVITY OF PURIFIED EGYPTIAN COTTON WASTE FIBRES TOWARDS XANTHATION
M. AMINE ABOU-STATE and FOUAD F. ABD EL-MEGEID
Department of Chemisto', Faculty oJ Science, University O/Cairo, Giza (Arab Republic of Egypt)
SUMMARY
Egyptian cotton waste fibres were purified by different chemical treatments and the eff'ects of these treatments on certain characteristics of thefibres, in particular their reactivity towards xanthation, were investigated. Pulps produced by the soda process were not reactive towards xanthation. A mild sulphuric acidpre-hydrolysis treatment improved the reactivity and allowed a great reduction in the duration of the alkaline pulping. Higher concentrations of either sulphuric acid or sodium hydroxide during pre-hydrolysis-alkali pulping improved the physical characteristics of the.fibres as well as their reactivity towards xanthation. Lowering the degree of polymerisation (DP) by intensifying the conditions of sulphuric acid pre-hydrolysis improved the reactivity towards xanthation. Hydrochloric acid was more effective than sulphuric acid in reducing the DP, yet it impaired the reactivity. This is due to increased re-erystallisation of cellulose.
INTRODUCTION AND AIM OF THE WORK
Cellulose fibres differ in their specifications according to the object intended for their use. The fibres intended for the preparation of nitrocellulose, cellulose acetate, and similar cellulose derivatives should be free from pentosans, degraded cellulose and other non-cellulosic materials. A wood pulp with an alpha cellulose content of 94-98% and a pentosan content less than 1 . 5 ~ is considered necessary for acetylation. 1 In the case of viscose rayon the pulp should have an alpha cellulose content between 88 and 91%. A high pentosan content is objectionable because it indicates that the morphological structure of the pulp has not been altered sufficiently to obtain the desired reactivity. / However, it has often been noticed that a pulp may meet all the specifications of viscose pulps and is even of a higher degree 273 Fibre Science and Technology(lO) (1977) Printed in Great Britain
~': Applied Science Publishers Ltd, England, 1977
274
M. A M I N E ABOU-STATE, F O U A D F. ABD EL-MEGEID
of chemical purity but is insufficiently reactive towards xanthation. 3 The ability of cotton cellulose to form viscose was found to be lower than that of sulphite cellulose. 4 The reactivity of the pulp depends upon its morphological structure, i.e. the thickness of the different cell walls, the orientation of the fibres, and the magnitude of the interfibrillar and intermiscellar spaces. The morphological structure depends upon the degree of pulping and bleaching, i.e. the maintenance of the original biochemical structure.5 The physical structure of the pulp, such as the degree of polymerisation, plays also an important role. Also, the chemical composition of the pulp, to the extent that it shows how far the native morphological structure is attacked, influences the reactivity. Pulps with a higher degree of whiteness are generally characterised by better reactivity towards xanthation. 6 However, the most important factor governing the reactivity is the assessibility of the cellulose hydroxyls to reactant molecules. 6 The distribution of the non-cellulosiccomponents on the surface of the miscellae and fibres also affects the reactivity. 7 The aim of the present investigation was to purify Egyptian cotton waste fibres by different chemical treatments and to find out the effects of these treatments on the chemical, physical and sub-microscopic characteristics of the fibres, and in particular their reactivity towards xanthation.
EXPERIMENTAL
The Egyptian cotton waste fibres were mechanically purified as before. 8,9 Pulping of the mechanically-purified fibres was carried out in round-bottomed flasks fitted with reflux condensers. The temperature was thermostatically controlled. After pulping, the fibres were subjected to multi-stage bleaching treatment. They were first treated with 0.5 ~o chlorine (based on fibres) in the form of chlorine water at 20 °C for 30 rain at a consistency of 3 o/ Jo. Then they were extracted for 30 min and at 40°C with 4 !~; sodium hydroxide (based on fibres) at a consistency of 7 '~,;. In the third step, sodium hypochlorite with 0"155o active chlorine (based on fibres) was applied. This treatment was carried out for 30 min at 40 °C and a consistency of 3 o;. Finally, the cotton fibres were acidified with 0.5 iJ'o sulphurous acid for 20 min at 20°C. The ash, a-cellulose, degree ofpolymerisation (DP), water retention value (WRV), liquor retention value (LRV), sodium hydroxide retention value (NaOH-RV), crystallinity, and reactivity towards xanthation were determined as before.l°'11
RESULTSAND DISCUSSION
Pulping by the soda process In experiment I (Table 1) pulping was carried out by the action of 17,; sodium
EFFECT OF CHEMICALTREATMENTON REACTIVITYOF COTTON WASTEFIBRES
275
TABLE 1 COMPARISON BETWEEN SODA PULPING AND PRE-HYDROLYSIS-SODA PULPING
Parameter Concentration of H2SO 4 solution (~o) Liquor ratio Maximum temperature (°C) Time at maximum temperature (h) Concentration of NaOH solution (~o) Liquor ratio Maximum temperature (°C) Time at maximum temperature (h) Yield (~o) Ash (o/) a-Cellulose (o~,) DP WRV (%) LRV ('!/o) NaOH-RV (%) Crystallinity (o/,) Reactivity ( ~/,,insoluble cellulose)
I
Experiment No. 11 I11
--
--
--
--
--
- -
20:1
--
--
- -
100
IV 0.05
20:1 100 4
20:1 100 4
1.5 20:1 100 4
20:1 100 2
93.0 0.07 99-7 2002 24.5 196.2 30.8 96 94.0
90.9 0-05 99.8 1968 24.9 200.0 32-7 93 92.9
89.3 0-04 99.7 1870 26.3 203.0 34-2 92 91.4
92.7 0.05 99.7 1662 26-7 206.2 35-3 91 90-0
1
1-25
1
hydroxide solution for 4 h at 100 °C. The bleached pulp was obtained in 93.0 ~ yield and was characterised by high s-cellulose, low ash and high D P . However, itwas not reactive towards xanthation. W h e n the concentration o f sodium hydroxide solution was raised to 1-25 ~o (experiment II) the yield and D P were slightly lowered, the affinity towards water and alkali was slightly improved, the crystallinity was reduced and the reactivity towards xanthation was slightly improved. Further slight improvements in the swelling ability o f the fibres and in the reactivity were attained by increasing the concentration o f the sodium hydroxide solution used in pulping to 1.5 ~o (experiment III).
Comparison between soda pulping and prehydrolysis-soda pulping (Table 1 ) In experiment I, pulping was carried out by the soda process, while in experiment IV the pre-hydrolysis-soda process was used. Pre-hydrolysis was carried out by the action o f 0.05 % H 2 S O 4 solution for 1 h at 100 °C, and the alkaline step was the same as in experiment I with the exception that the duration o f p u l p i n g w a s reduced from 4 to 2 h. It is clear that the pre-hydrolysis-soda process resulted in higher affinities towards water and alkali, lower degree o f crystallinity and better reactivity towards xanthation. Also, by c o m p a r i n g experiment tV with experiments I, II and III, one can conclude that the application o f a mild acid pre-hydrolysis treatment results in more favourable physical and sub-microscopic characteristics as well as better reactivity towards xanthation than the use o f sodium hydroxide alone, even under intensified conditions. F o r this reason, it was tried in the following experiments to find out the effects o f intensifying the conditions o f sulphuric acid pre-hydrolysis.
276
M. A M I N E A B O U - S T A T E , F O U A D F. ABD E L - M E G E I D
Effects of intensifying the conditions of sulphuric acid pre-hydrolysis It is clear from T a b l e 2 that increasing the c o n c e n t r a t i o n o f s u l p h u r i c acid solution f r o m 0.05 to 0.1 ~o a n d the d u r a t i o n o f acid t r e a t m e n t from 1 to 2 h (experiments IV a n d V, respectively) h a d practically no effect on the ash a n d a-cellulose. However, it r e d u c e d the D P from 1662 to 1144. This r e d u c t i o n in the D P was a c c o m p a n i e d by a higher degree of swelling in water a n d sodium hydroxide solution as well as better reactivity t o w a r d s x a n t h a t i o n . Also, further increase in the c o n c e n t r a t i o n o f sulphuric acid (experiments VI a n d VII) did not affect the chemical characteristics, b u t lowered the D P and the crystallinity, increased the swelling ability o f the fibres a n d i m p r o v e d their reactivity t o w a r d s x a n t h a t i o n . TABLE 2 EFFECTS OF INTENSIFYING THE PRE-HYDROLYSIS CONDITIONS
Parameter /V
Experiment No. V VI
Concentration of HzSO 4 solution ("2,) Liquor ratio Maximum temperature (°C) Time at maximum temperature (h)
0"05 20:1 100
0.1 20:1 100
1
2
Concentration of NaOH solution (!~0) Liquor ratio Maximum temperature (°C) Time at maximum temperature (h)
1
I
1
1
20:1 100 2
20:1 100 2
20:1 100 2
20:1 100 2
92.7 0.05 99.7 1662 26.7 206.2 35.3 91 90.0
91.8 0-03 99.6 1144 27.1 209.5 36.4 90 88.1
90.0 0-04 99-6 900 28.4 211.0 37.6 89 85.2
86-0 0.06 99.5 480 29.4 214-1 43-4 88 82.8
Yield ('~o) Ash (~o) a-Cellulose (,~,) DP WRV (~o) LRV (~o) NaOH-RV (~,) Crystallinity (%) Reactivity (°/o insoluble cellulose)
0"175 20:1 100
VII
2
0'25 20:1 100 2
It is clear t h a t increasing the c o n c e n t r a t i o n o f sulphuric acid resulted in favourable effects on the physical p r o p e r t i e s o f c o t t o n fibres and their reactivity t o w a r d s x a n t h a t i o n . In the following section it b e c o m e s o f interest to find o u t the effects o f increasing the c o n c e n t r a t i o n o f alkali in p r e - h y d r o l y s i s - s o d a pulping.
Effect of increasing the concentration hydrolysis-soda pulping
oJ" sodium hydroxide during pre-
It is clear from T a b l e 3 that raising the alkali c o n c e n t r a t i o n d u r i n g preh y d r o l y s i s - s o d a p u l p i n g did not affect the chemical characteristics o f the p u l p s o b t a i n e d . It lowered the yield, D P a n d crystallinity, raised the W R V , L R V a n d N a O H - R V , a n d resulted in better reactivity t o w a r d s x a n t h a t i o n .
EFFECT OF CHEMICALTREATMENT ON REACTIVITYOF COTTON WASTEFIBRES 277 TABLE 3 EFFECTOF ALKALICONCENTRATIONIN PRE-HYDROLYSISSODAPULPING
Parameter IV Concentration of H2SO4 solution (~,,,) Liquor ratio Maximum temperature (°C) Time at maximum temperature (h) Concentration of NaOH solution (%) Liquor ratio Maximum temperature (°C) Time at maximum temperature (h) Yield (~o) Ash (%) =t-Cellulose(~) DP WRV (~o) LRV (%) NaOH-RV (~o) Crystallinity (~) Reactivity ( ~o insoluble cellulose)
Experiment No. VIII
IX
0.05 20:1 100
0-05 20:1 100
0-05 20:1 100
1
1
1
1
20:1 100 2
1.25 20:1 100 2
1.5 20:1 100 2
92.7 0-05 99.7 1662 26-7 206.2 35.3 91 90.0
91.6 0.05 99.6 1620 27.0 206.8 35.9 89 89.7
88-0 0.06 99.7 1593 28.1 209.6 36.7 87 88.6
Pre-hydrolysis with hydrochloric acid In e x p e r i m e n t s X, X I a n d X I I (Table 4) h y d r o c h l o r i c acid was used as preh y d r o l y s i n g agent. Increasing the c o n c e n t r a t i o n o f the h y d r o c h l o r i c acid solution from 0.05 to 0 . 1 % (experiments X a n d XI, respectively) resulted in a slight increase in the a-cellulose content. It also lowered the D P f r o m 1074 to 600 and increased the affinities t o w a r d s water a n d alkali. However, it raised the crystallinity a n d i m p a i r e d the reactivity. W h e n the time o f p r e - h y d r o l y s i s was increased to 2 h (experiment XII), the D P was c o n s i d e r a b l y reduced. The a-cellulose as well as the degree o f crystallinity increased, while the affinities t o w a r d s water a n d alkali as well as the reactivity t o w a r d s x a n t h a t i o n were decreased.
Comparison between sulphuric and hydrochloric acid pre-hydrolysis (Table 5) In e x p e r i m e n t s IV a n d X, 0.05 % sulphuric a n d h y d r o c h l o r i c acid solutions, respectively, were used in pre-hydrolysis. T h e D P was 1662 in the first e x p e r i m e n t a n d 1074 in the second. A l s o in e x p e r i m e n t V, p r e - h y d r o l y s i s was effected with 0.1 s u l p h u r i c acid solution, while in e x p e r i m e n t X I I , 0 . 1 % h y d r o c h l o r i c acid s o l u t i o n was used. T h e D P in the sulphuric acid e x p e r i m e n t was 1144, c o m p a r e d to a value o f 475 in the case o f h y d r o c h l o r i c acid. T h e fact t h a t h y d r o c h l o r i c acid is m o r e effective t h a n sulphuric acid in lowering the D P is further illustrated b y e x p e r i m e n t s VII a n d X I I . Thus, while the use o f 0.25 % sulphuric acid solution in e x p e r i m e n t VII lowered the D P to 480, the D P in e x p e r i m e n t X I I was lowered to the same value when o n l y 0 . 1 % h y d r o c h l o r i c acid solution was used.
278
M. AMINE ABOU-STATE, FOUAD F. ABD EL-MEGEID
TABLE 4 PRE-HYDROLYSISWITH HYDROCHLORICACID Parameter
E?cperiment No. XI
X
Xll
Concentration of HCI solution ('~,,) Liquor ratio Maximum temperature (°C) Time at maximum temperature (h)
0-05 20:1 100 I
0.1 20:1 100 1
0.1 20:1 100 2
Concentration of NaOH solution ( ",3 Liquor ratio Maximum temperature (°C) Time at maximum temperature (h)
l 20:1 100 2
1 20:1 100 2
1 20:1 100 2
90.0 0.06 99.6 1074 27.0 206.2 35.0 89 88-5
85.0 0-04 99-7 600 28.1 210-3 37.4 91 89.2
84.0 0.05 99.8 475 22-0 202.1 34.0 96 93.0
Yield (%1,) Ash (9~) c~-Cellulose (o;,) DP WRV (~,) LRV (%) NaOH-RV (~V,o) Crystallinity (O/o) Reactivity ( o/~ insoluble cellulose)
TABLE 5 COMPARISON BETWEENSULPHURICAND HYDROCHLORICACID PRE-HYDROLYSESa Parameter
Experiment No. VII X
IV
V
VI
Concentration of acid solution ('~.~,) Liquor ratio Maximum temperature (°C) Time at maximum temperature (h)
0-05 20:1 100 1
0.1 20:1 100 2
0-175 20:1 100 2
0.25 20:1 100 2
Concentration of N a O H solution ('~,~,) Liquor ratio Maximum temperature (°C) Time at maximum temperature (h)
1 20:1 100 2
1 20:1 100 2
1 20:1 100 2
1 20:1 100 2
Yield (%) Ash (~o) co-Cellulose (04) DP WRV (°.o) LRV (~o) NaOH-RV (~o) Crystallinity (~o) Reactivity ( ~ insoluble cellulose)
92.7 91.8 90-0 0.05 0.03 0.04 99.7 99.6 99.6 1662 1144 900 26-7 27-1 28.4 206.2 2 0 9 - 5 211-0 35.3 36.4 37-6 91 90 89 90-0 88.1 85.2
° Experiments IV VII, H2SO,; experiments X-XII, HCI.
XI
XII
0.05 20:1 100 I
0-1 20:1 100 1
0.1 20:1 100 2
1 20:1 100 2
1 20:1 100 2
1 20:1 100 2
86.0 90.0 85-0 84.0 0.06 0.06 0.04 0.05 99.5 99.6 99.7 99.8 480 1074 600 475 29-4 27-0 28.1 22-0 2 1 4 . 1 216-2 210-3 202-2 43.4 35.0 37.4 34-0 88 89 91 96 82.8 88-5 81.2 93.0
EFFECT OF CHEMICAL TREATMENT ON REACTIVITY OF COTTON WASTE FIBRES
279
It is clear from experiments IV-VII that intensifying the conditions of sulphuric acid pre-hydrolysis lowered the DP and that this reduction in the DP was accompanied by a higher degree of swelling in water and in aqueous alkali, a lower degree of crystallinity and better reactivity towards xanthati6n. In the case of experiments X-XII, in which hydrochloric acid was used as a pre-hydrolysing agent, intensifying the pre-hydrolysis conditions also reduced the DP. Despite the fact that hydrochloric acid is more effective than sulphuric acid in reducing the DP, it still impaired the reactivity towards xanthation instead of improving it. It was noticed that whilst intensifying the pre-hydrolysis conditions reduced the degree of crystallinity in the case of the sulphuric acid experiments, the reverse occurred when hydrochloric acid was used, i.e. the degree ofcrystallinity was increased by intensifying the pre-hydrolysis conditions. This explains the deterioration in the reactivity towards xanthation which accompanies the reduction in the DP by means of hydrochloric acid pre-hydrolysis and the improvement in the reactivity which results from lowering the DP by sulphuric acid pre-hydrolysis. It was also noticed that lowering the DP was accompanied by an increase in the ~cellulose content in the case of hydrochloric acid pre-hydrolysis (experiments XXII), and a decrease in the s-cellulose in the case of sulphuric acid pre-hydrolysis (experiments IV-VII). CONCLUSIONS
The purification of Egyptian cotton waste fibres by the soda process results in the formation of pulps characterised by a high degree of chemical purity and high D P. However, they are not reactive towards xanthation. Increasing the concentration of the alkaline pulping liquor results in slight improvements in the reactivity towards xanthation. The application of a mild sulphuric acid pre-hydrolysis treatment allows a great reduction in the duration of the alkaline pulping and results in more favourable physical and sub-microscopic characteristics and better reactivity towards xanthation. Increasing the concentration of either the sulphuric acid in the pre-hydrolysis step or the sodium hydroxide in the pulping step does not seem to affect the chemical characteristics, but it reduces the DP and crystallinity, and improves the swelling ability of the fibres and their reactivity towards xanthation. Lowering the DP by intensifying the conditions of sulphuric acid pre-hydrolysis results in a higher degree of swelling in water and aqueous alkali, a lower degree of crystallinity and better reactivity towards xanthation. Hydrochloric acid is much more effective in reducing the DP when used as a pre-hydrolysing agent, yet it impairs the reactivity towards xanthation. This is because it results in increased recrystallisation, and consequently decreased accessibility of cellulose. Another difference between the two acids is that intensifying the pre-hydrolysis conditions lowers the a-cellulose in the case of sulphuric acid and increases it in the case of hydrochloric acid.
280
M. AMINE ABOU-STATE, FOUAD F. ABD EL-MEGEID
REFERENCES I. E. H EUSER , W. SHOKLEY and J. A. VAN D EN AKKER, Tuppi, 32 (1949) p. 251. 2. E. HEUSER, Tappi, 33 (1950) p. 118. 3. Y. A. FAHMY and M. A. A BOU-STATE , Das Papier, 15 (1961) p. 44. 4. V. P. KISELAVA, Naufi.-lssl. Trudy VsesojuZ. ~uu~.-ls~~ed. Inst. iskus. Volokna, 16 (1955) p, 2; Chemical Abstracts 53 (1959) p, 10771. 5. G. JAYME, ZeBstqff‘ 1939-1946, Verein Zellchemung, Darmstadt (1953) p. 105. 6. M. A. ABOU-STATE and S. A. H ELMY. Journal of’ Applied Chemistry and Biotechnology, 22 (1972) p. 1227. 7. G. JAYME, T?q@, 41 (1958) p. 178. 8. M. A. ABOU-STATE and F. F. ABDEL-MEGEID, Fuserjbrschung undTexri/rechnik, 24(1973) p. 340. 9. M. A. A BOL&TATE and F. F. ABD E L-M EGEID, Journul ?~Applied Chemistry and Biotechnology, 22 (1972) p. 993. 10. M. A. ABOU-STATE and S. A. HELMY. Fo.~e~~or.schu~z~ und Te,~I~~iechnik. 25 (1974) p. 54. Il. M. A. AB O U- ST A T E , Zellsro~f’und Papier, 2J (1976) p. 179.
M. AMINE ABOU-STATE and FOUAD F. ABD EL-MEGEID
Department of Chemisto', Faculty oJ Science, University O/Cairo, Giza (Arab Republic of Egypt)
SUMMARY
Egyptian cotton waste fibres were purified by different chemical treatments and the eff'ects of these treatments on certain characteristics of thefibres, in particular their reactivity towards xanthation, were investigated. Pulps produced by the soda process were not reactive towards xanthation. A mild sulphuric acidpre-hydrolysis treatment improved the reactivity and allowed a great reduction in the duration of the alkaline pulping. Higher concentrations of either sulphuric acid or sodium hydroxide during pre-hydrolysis-alkali pulping improved the physical characteristics of the.fibres as well as their reactivity towards xanthation. Lowering the degree of polymerisation (DP) by intensifying the conditions of sulphuric acid pre-hydrolysis improved the reactivity towards xanthation. Hydrochloric acid was more effective than sulphuric acid in reducing the DP, yet it impaired the reactivity. This is due to increased re-erystallisation of cellulose.
INTRODUCTION AND AIM OF THE WORK
Cellulose fibres differ in their specifications according to the object intended for their use. The fibres intended for the preparation of nitrocellulose, cellulose acetate, and similar cellulose derivatives should be free from pentosans, degraded cellulose and other non-cellulosic materials. A wood pulp with an alpha cellulose content of 94-98% and a pentosan content less than 1 . 5 ~ is considered necessary for acetylation. 1 In the case of viscose rayon the pulp should have an alpha cellulose content between 88 and 91%. A high pentosan content is objectionable because it indicates that the morphological structure of the pulp has not been altered sufficiently to obtain the desired reactivity. / However, it has often been noticed that a pulp may meet all the specifications of viscose pulps and is even of a higher degree 273 Fibre Science and Technology(lO) (1977) Printed in Great Britain
~': Applied Science Publishers Ltd, England, 1977
274
M. A M I N E ABOU-STATE, F O U A D F. ABD EL-MEGEID
of chemical purity but is insufficiently reactive towards xanthation. 3 The ability of cotton cellulose to form viscose was found to be lower than that of sulphite cellulose. 4 The reactivity of the pulp depends upon its morphological structure, i.e. the thickness of the different cell walls, the orientation of the fibres, and the magnitude of the interfibrillar and intermiscellar spaces. The morphological structure depends upon the degree of pulping and bleaching, i.e. the maintenance of the original biochemical structure.5 The physical structure of the pulp, such as the degree of polymerisation, plays also an important role. Also, the chemical composition of the pulp, to the extent that it shows how far the native morphological structure is attacked, influences the reactivity. Pulps with a higher degree of whiteness are generally characterised by better reactivity towards xanthation. 6 However, the most important factor governing the reactivity is the assessibility of the cellulose hydroxyls to reactant molecules. 6 The distribution of the non-cellulosiccomponents on the surface of the miscellae and fibres also affects the reactivity. 7 The aim of the present investigation was to purify Egyptian cotton waste fibres by different chemical treatments and to find out the effects of these treatments on the chemical, physical and sub-microscopic characteristics of the fibres, and in particular their reactivity towards xanthation.
EXPERIMENTAL
The Egyptian cotton waste fibres were mechanically purified as before. 8,9 Pulping of the mechanically-purified fibres was carried out in round-bottomed flasks fitted with reflux condensers. The temperature was thermostatically controlled. After pulping, the fibres were subjected to multi-stage bleaching treatment. They were first treated with 0.5 ~o chlorine (based on fibres) in the form of chlorine water at 20 °C for 30 rain at a consistency of 3 o/ Jo. Then they were extracted for 30 min and at 40°C with 4 !~; sodium hydroxide (based on fibres) at a consistency of 7 '~,;. In the third step, sodium hypochlorite with 0"155o active chlorine (based on fibres) was applied. This treatment was carried out for 30 min at 40 °C and a consistency of 3 o;. Finally, the cotton fibres were acidified with 0.5 iJ'o sulphurous acid for 20 min at 20°C. The ash, a-cellulose, degree ofpolymerisation (DP), water retention value (WRV), liquor retention value (LRV), sodium hydroxide retention value (NaOH-RV), crystallinity, and reactivity towards xanthation were determined as before.l°'11
RESULTSAND DISCUSSION
Pulping by the soda process In experiment I (Table 1) pulping was carried out by the action of 17,; sodium
EFFECT OF CHEMICALTREATMENTON REACTIVITYOF COTTON WASTEFIBRES
275
TABLE 1 COMPARISON BETWEEN SODA PULPING AND PRE-HYDROLYSIS-SODA PULPING
Parameter Concentration of H2SO 4 solution (~o) Liquor ratio Maximum temperature (°C) Time at maximum temperature (h) Concentration of NaOH solution (~o) Liquor ratio Maximum temperature (°C) Time at maximum temperature (h) Yield (~o) Ash (o/) a-Cellulose (o~,) DP WRV (%) LRV ('!/o) NaOH-RV (%) Crystallinity (o/,) Reactivity ( ~/,,insoluble cellulose)
I
Experiment No. 11 I11
--
--
--
--
--
- -
20:1
--
--
- -
100
IV 0.05
20:1 100 4
20:1 100 4
1.5 20:1 100 4
20:1 100 2
93.0 0.07 99-7 2002 24.5 196.2 30.8 96 94.0
90.9 0-05 99.8 1968 24.9 200.0 32-7 93 92.9
89.3 0-04 99.7 1870 26.3 203.0 34-2 92 91.4
92.7 0.05 99.7 1662 26-7 206.2 35-3 91 90-0
1
1-25
1
hydroxide solution for 4 h at 100 °C. The bleached pulp was obtained in 93.0 ~ yield and was characterised by high s-cellulose, low ash and high D P . However, itwas not reactive towards xanthation. W h e n the concentration o f sodium hydroxide solution was raised to 1-25 ~o (experiment II) the yield and D P were slightly lowered, the affinity towards water and alkali was slightly improved, the crystallinity was reduced and the reactivity towards xanthation was slightly improved. Further slight improvements in the swelling ability o f the fibres and in the reactivity were attained by increasing the concentration o f the sodium hydroxide solution used in pulping to 1.5 ~o (experiment III).
Comparison between soda pulping and prehydrolysis-soda pulping (Table 1 ) In experiment I, pulping was carried out by the soda process, while in experiment IV the pre-hydrolysis-soda process was used. Pre-hydrolysis was carried out by the action o f 0.05 % H 2 S O 4 solution for 1 h at 100 °C, and the alkaline step was the same as in experiment I with the exception that the duration o f p u l p i n g w a s reduced from 4 to 2 h. It is clear that the pre-hydrolysis-soda process resulted in higher affinities towards water and alkali, lower degree o f crystallinity and better reactivity towards xanthation. Also, by c o m p a r i n g experiment tV with experiments I, II and III, one can conclude that the application o f a mild acid pre-hydrolysis treatment results in more favourable physical and sub-microscopic characteristics as well as better reactivity towards xanthation than the use o f sodium hydroxide alone, even under intensified conditions. F o r this reason, it was tried in the following experiments to find out the effects o f intensifying the conditions o f sulphuric acid pre-hydrolysis.
276
M. A M I N E A B O U - S T A T E , F O U A D F. ABD E L - M E G E I D
Effects of intensifying the conditions of sulphuric acid pre-hydrolysis It is clear from T a b l e 2 that increasing the c o n c e n t r a t i o n o f s u l p h u r i c acid solution f r o m 0.05 to 0.1 ~o a n d the d u r a t i o n o f acid t r e a t m e n t from 1 to 2 h (experiments IV a n d V, respectively) h a d practically no effect on the ash a n d a-cellulose. However, it r e d u c e d the D P from 1662 to 1144. This r e d u c t i o n in the D P was a c c o m p a n i e d by a higher degree of swelling in water a n d sodium hydroxide solution as well as better reactivity t o w a r d s x a n t h a t i o n . Also, further increase in the c o n c e n t r a t i o n o f sulphuric acid (experiments VI a n d VII) did not affect the chemical characteristics, b u t lowered the D P and the crystallinity, increased the swelling ability o f the fibres a n d i m p r o v e d their reactivity t o w a r d s x a n t h a t i o n . TABLE 2 EFFECTS OF INTENSIFYING THE PRE-HYDROLYSIS CONDITIONS
Parameter /V
Experiment No. V VI
Concentration of HzSO 4 solution ("2,) Liquor ratio Maximum temperature (°C) Time at maximum temperature (h)
0"05 20:1 100
0.1 20:1 100
1
2
Concentration of NaOH solution (!~0) Liquor ratio Maximum temperature (°C) Time at maximum temperature (h)
1
I
1
1
20:1 100 2
20:1 100 2
20:1 100 2
20:1 100 2
92.7 0.05 99.7 1662 26.7 206.2 35.3 91 90.0
91.8 0-03 99.6 1144 27.1 209.5 36.4 90 88.1
90.0 0-04 99-6 900 28.4 211.0 37.6 89 85.2
86-0 0.06 99.5 480 29.4 214-1 43-4 88 82.8
Yield ('~o) Ash (~o) a-Cellulose (,~,) DP WRV (~o) LRV (~o) NaOH-RV (~,) Crystallinity (%) Reactivity (°/o insoluble cellulose)
0"175 20:1 100
VII
2
0'25 20:1 100 2
It is clear t h a t increasing the c o n c e n t r a t i o n o f sulphuric acid resulted in favourable effects on the physical p r o p e r t i e s o f c o t t o n fibres and their reactivity t o w a r d s x a n t h a t i o n . In the following section it b e c o m e s o f interest to find o u t the effects o f increasing the c o n c e n t r a t i o n o f alkali in p r e - h y d r o l y s i s - s o d a pulping.
Effect of increasing the concentration hydrolysis-soda pulping
oJ" sodium hydroxide during pre-
It is clear from T a b l e 3 that raising the alkali c o n c e n t r a t i o n d u r i n g preh y d r o l y s i s - s o d a p u l p i n g did not affect the chemical characteristics o f the p u l p s o b t a i n e d . It lowered the yield, D P a n d crystallinity, raised the W R V , L R V a n d N a O H - R V , a n d resulted in better reactivity t o w a r d s x a n t h a t i o n .
EFFECT OF CHEMICALTREATMENT ON REACTIVITYOF COTTON WASTEFIBRES 277 TABLE 3 EFFECTOF ALKALICONCENTRATIONIN PRE-HYDROLYSISSODAPULPING
Parameter IV Concentration of H2SO4 solution (~,,,) Liquor ratio Maximum temperature (°C) Time at maximum temperature (h) Concentration of NaOH solution (%) Liquor ratio Maximum temperature (°C) Time at maximum temperature (h) Yield (~o) Ash (%) =t-Cellulose(~) DP WRV (~o) LRV (%) NaOH-RV (~o) Crystallinity (~) Reactivity ( ~o insoluble cellulose)
Experiment No. VIII
IX
0.05 20:1 100
0-05 20:1 100
0-05 20:1 100
1
1
1
1
20:1 100 2
1.25 20:1 100 2
1.5 20:1 100 2
92.7 0-05 99.7 1662 26-7 206.2 35.3 91 90.0
91.6 0.05 99.6 1620 27.0 206.8 35.9 89 89.7
88-0 0.06 99.7 1593 28.1 209.6 36.7 87 88.6
Pre-hydrolysis with hydrochloric acid In e x p e r i m e n t s X, X I a n d X I I (Table 4) h y d r o c h l o r i c acid was used as preh y d r o l y s i n g agent. Increasing the c o n c e n t r a t i o n o f the h y d r o c h l o r i c acid solution from 0.05 to 0 . 1 % (experiments X a n d XI, respectively) resulted in a slight increase in the a-cellulose content. It also lowered the D P f r o m 1074 to 600 and increased the affinities t o w a r d s water a n d alkali. However, it raised the crystallinity a n d i m p a i r e d the reactivity. W h e n the time o f p r e - h y d r o l y s i s was increased to 2 h (experiment XII), the D P was c o n s i d e r a b l y reduced. The a-cellulose as well as the degree o f crystallinity increased, while the affinities t o w a r d s water a n d alkali as well as the reactivity t o w a r d s x a n t h a t i o n were decreased.
Comparison between sulphuric and hydrochloric acid pre-hydrolysis (Table 5) In e x p e r i m e n t s IV a n d X, 0.05 % sulphuric a n d h y d r o c h l o r i c acid solutions, respectively, were used in pre-hydrolysis. T h e D P was 1662 in the first e x p e r i m e n t a n d 1074 in the second. A l s o in e x p e r i m e n t V, p r e - h y d r o l y s i s was effected with 0.1 s u l p h u r i c acid solution, while in e x p e r i m e n t X I I , 0 . 1 % h y d r o c h l o r i c acid s o l u t i o n was used. T h e D P in the sulphuric acid e x p e r i m e n t was 1144, c o m p a r e d to a value o f 475 in the case o f h y d r o c h l o r i c acid. T h e fact t h a t h y d r o c h l o r i c acid is m o r e effective t h a n sulphuric acid in lowering the D P is further illustrated b y e x p e r i m e n t s VII a n d X I I . Thus, while the use o f 0.25 % sulphuric acid solution in e x p e r i m e n t VII lowered the D P to 480, the D P in e x p e r i m e n t X I I was lowered to the same value when o n l y 0 . 1 % h y d r o c h l o r i c acid solution was used.
278
M. AMINE ABOU-STATE, FOUAD F. ABD EL-MEGEID
TABLE 4 PRE-HYDROLYSISWITH HYDROCHLORICACID Parameter
E?cperiment No. XI
X
Xll
Concentration of HCI solution ('~,,) Liquor ratio Maximum temperature (°C) Time at maximum temperature (h)
0-05 20:1 100 I
0.1 20:1 100 1
0.1 20:1 100 2
Concentration of NaOH solution ( ",3 Liquor ratio Maximum temperature (°C) Time at maximum temperature (h)
l 20:1 100 2
1 20:1 100 2
1 20:1 100 2
90.0 0.06 99.6 1074 27.0 206.2 35.0 89 88-5
85.0 0-04 99-7 600 28.1 210-3 37.4 91 89.2
84.0 0.05 99.8 475 22-0 202.1 34.0 96 93.0
Yield (%1,) Ash (9~) c~-Cellulose (o;,) DP WRV (~,) LRV (%) NaOH-RV (~V,o) Crystallinity (O/o) Reactivity ( o/~ insoluble cellulose)
TABLE 5 COMPARISON BETWEENSULPHURICAND HYDROCHLORICACID PRE-HYDROLYSESa Parameter
Experiment No. VII X
IV
V
VI
Concentration of acid solution ('~.~,) Liquor ratio Maximum temperature (°C) Time at maximum temperature (h)
0-05 20:1 100 1
0.1 20:1 100 2
0-175 20:1 100 2
0.25 20:1 100 2
Concentration of N a O H solution ('~,~,) Liquor ratio Maximum temperature (°C) Time at maximum temperature (h)
1 20:1 100 2
1 20:1 100 2
1 20:1 100 2
1 20:1 100 2
Yield (%) Ash (~o) co-Cellulose (04) DP WRV (°.o) LRV (~o) NaOH-RV (~o) Crystallinity (~o) Reactivity ( ~ insoluble cellulose)
92.7 91.8 90-0 0.05 0.03 0.04 99.7 99.6 99.6 1662 1144 900 26-7 27-1 28.4 206.2 2 0 9 - 5 211-0 35.3 36.4 37-6 91 90 89 90-0 88.1 85.2
° Experiments IV VII, H2SO,; experiments X-XII, HCI.
XI
XII
0.05 20:1 100 I
0-1 20:1 100 1
0.1 20:1 100 2
1 20:1 100 2
1 20:1 100 2
1 20:1 100 2
86.0 90.0 85-0 84.0 0.06 0.06 0.04 0.05 99.5 99.6 99.7 99.8 480 1074 600 475 29-4 27-0 28.1 22-0 2 1 4 . 1 216-2 210-3 202-2 43.4 35.0 37.4 34-0 88 89 91 96 82.8 88-5 81.2 93.0
EFFECT OF CHEMICAL TREATMENT ON REACTIVITY OF COTTON WASTE FIBRES
279
It is clear from experiments IV-VII that intensifying the conditions of sulphuric acid pre-hydrolysis lowered the DP and that this reduction in the DP was accompanied by a higher degree of swelling in water and in aqueous alkali, a lower degree of crystallinity and better reactivity towards xanthati6n. In the case of experiments X-XII, in which hydrochloric acid was used as a pre-hydrolysing agent, intensifying the pre-hydrolysis conditions also reduced the DP. Despite the fact that hydrochloric acid is more effective than sulphuric acid in reducing the DP, it still impaired the reactivity towards xanthation instead of improving it. It was noticed that whilst intensifying the pre-hydrolysis conditions reduced the degree of crystallinity in the case of the sulphuric acid experiments, the reverse occurred when hydrochloric acid was used, i.e. the degree ofcrystallinity was increased by intensifying the pre-hydrolysis conditions. This explains the deterioration in the reactivity towards xanthation which accompanies the reduction in the DP by means of hydrochloric acid pre-hydrolysis and the improvement in the reactivity which results from lowering the DP by sulphuric acid pre-hydrolysis. It was also noticed that lowering the DP was accompanied by an increase in the ~cellulose content in the case of hydrochloric acid pre-hydrolysis (experiments XXII), and a decrease in the s-cellulose in the case of sulphuric acid pre-hydrolysis (experiments IV-VII). CONCLUSIONS
The purification of Egyptian cotton waste fibres by the soda process results in the formation of pulps characterised by a high degree of chemical purity and high D P. However, they are not reactive towards xanthation. Increasing the concentration of the alkaline pulping liquor results in slight improvements in the reactivity towards xanthation. The application of a mild sulphuric acid pre-hydrolysis treatment allows a great reduction in the duration of the alkaline pulping and results in more favourable physical and sub-microscopic characteristics and better reactivity towards xanthation. Increasing the concentration of either the sulphuric acid in the pre-hydrolysis step or the sodium hydroxide in the pulping step does not seem to affect the chemical characteristics, but it reduces the DP and crystallinity, and improves the swelling ability of the fibres and their reactivity towards xanthation. Lowering the DP by intensifying the conditions of sulphuric acid pre-hydrolysis results in a higher degree of swelling in water and aqueous alkali, a lower degree of crystallinity and better reactivity towards xanthation. Hydrochloric acid is much more effective in reducing the DP when used as a pre-hydrolysing agent, yet it impairs the reactivity towards xanthation. This is because it results in increased recrystallisation, and consequently decreased accessibility of cellulose. Another difference between the two acids is that intensifying the pre-hydrolysis conditions lowers the a-cellulose in the case of sulphuric acid and increases it in the case of hydrochloric acid.
280
M. AMINE ABOU-STATE, FOUAD F. ABD EL-MEGEID
REFERENCES I. E. H EUSER , W. SHOKLEY and J. A. VAN D EN AKKER, Tuppi, 32 (1949) p. 251. 2. E. HEUSER, Tappi, 33 (1950) p. 118. 3. Y. A. FAHMY and M. A. A BOU-STATE , Das Papier, 15 (1961) p. 44. 4. V. P. KISELAVA, Naufi.-lssl. Trudy VsesojuZ. ~uu~.-ls~~ed. Inst. iskus. Volokna, 16 (1955) p, 2; Chemical Abstracts 53 (1959) p, 10771. 5. G. JAYME, ZeBstqff‘ 1939-1946, Verein Zellchemung, Darmstadt (1953) p. 105. 6. M. A. ABOU-STATE and S. A. H ELMY. Journal of’ Applied Chemistry and Biotechnology, 22 (1972) p. 1227. 7. G. JAYME, T?q@, 41 (1958) p. 178. 8. M. A. ABOU-STATE and F. F. ABDEL-MEGEID, Fuserjbrschung undTexri/rechnik, 24(1973) p. 340. 9. M. A. A BOL&TATE and F. F. ABD E L-M EGEID, Journul ?~Applied Chemistry and Biotechnology, 22 (1972) p. 993. 10. M. A. ABOU-STATE and S. A. HELMY. Fo.~e~~or.schu~z~ und Te,~I~~iechnik. 25 (1974) p. 54. Il. M. A. AB O U- ST A T E , Zellsro~f’und Papier, 2J (1976) p. 179.