Graft Copolymerization of Lignocellulosic Fibers - American Chemical

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Grafting of Some Vinyl Monomers onto Lignocellulose and Cellulose in the Presence of Lignin O L F A T Y. MANSOUR and A H M E D N A G A T Y Cellulose and Paper Laboratory, National Research Centre, Sh. El Tahrir, Dokki, Cairo, Egypt AL-FOUNS BESHAY Monoufya University, Faculty of Science, A.R. of Egypt

Sodium bisulfite-china clay proved to be an efficient i n i t i a t o r for homopolymerization and graft polymeriza tion of methyl methacrylate onto cellulose. Grafting reactions using ceric ammonium sulfate, sodium b i s u l fite-soda lime glass or -china clay are inhibited or retarded on adding soda lignin to the grafting medium. This may relate to the inhibiting effect of the quinonoid groups present in lignin; also to the consumption of the ceric i n i t i a t o r in oxidizing of the lignin. The extent of inhibition and retardation depends on the amount of added lignin, the i n i t i a t o r used and the grafting temperature. Lignin in-situ of the lignocellulosic substrate effects inhibition or retarda tion only on using ceric ammonium sulfate as i n i t i a t o r . This may relate to the presence of the in-situ lignin in the form of polyhydric alcohols which on oxidation are transformed into quinones. Ceric consumed in oxi dation and the quinone groups subsequently formed may both contribute for the inhibition or retardation of the grafting process. In analogy to soda lime glass and china clay, lignin of the lignocellulosic substrate acts with sodium b i s u l f i t e as an i n i t i a t o r system for grafting of polymethyl methacrylate onto lignocellu lose. In this case, on subjecting the lignocellulosic substrates to the same chemical treatment, the lignin content of the treated samples being the governing factor for the rate and yield of grafting, while the structure of lignin i s the governing factor on subject ing to different chemical treatments. T i r z i n a (1) found that a l k a l i l i g n i n r e t a r d e d the polymerizat i o n of styrene in dimethyl s u l f o x i d e and s t r o n g l y i n h i b i t e d p o l y m e r i z a t i o n in the presence of oxygen and benzoyl peroxide. S t r a f o r e l l i (2) i n v e s t i g a t e d the e f f e c t of l i g n i n on the g r a f t c o p o l y m e r i z a t i o n of methyl methacrylate i n i t i a t e d by azo-

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0097-6156/82/0187-0253$6.00/0 1982 American Chemical Society

Hon; Graft Copolymerization of Lignocellulosic Fibers ACS Symposium Series; American Chemical Society: Washington, DC, 1982.

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b i s i s o b u t y r o n i t r i l e . Kubota and Ogiwara (3) examined the e f f e c t of l i g n i n in a c e r i c i o n - i n i t i a t e d g r a f t c o p o l y m e r i z a t i o n of methyl methacrylate on h i g h - y i e l d pulp d e l i g n i f i e d to d i f f e r e n t l i g n i n l e v e l s . E r d e l y i (4) prepared a s e r i e s of pulps by the s u l f a t e cooking process and subsequent h y p o c h l o r i t e b l e a c h i n g , and determined t h e i r g r a f t a b i l i t y in a system u s i n g c e r i c ammonium s u l f a t e as i n i t i a t o r and a c r y l o n i t r i l e as monomer. From the l a t t e r three s t u d i e s , i t was a r r i v e d at that a higher c o n c e n t r a t i o n of c a t a l y s t i s r e q u i r e d if c o p o l y m e r i z a t i o n i s to be c a r r i e d out in the presence of l i g n i n . A l s o , the presence of l i g n i n generally reduces p o l y m e r i z a t i o n r a t e and gives r i s e to prolonged i n h i b i t i o n periods at higher l i g n i n l e v e l s (5). Given the f a c t that l i g n i n i s e a s i l y o x i d i z e d by most conv e n t i o n a l oxidants which are in t u r n o f t e n used to i n i t i a t e copol y m e r i z a t i o n , one expects that i t s presence w i l l r e t a r d , if not i n h i b i t , the r e a c t i o n as the i n i t i a t o r w i l l be used up p r e f e r e n t i a l l y in the r e a c t i o n w i t h l i g n i n . Moreover, the r e a c t i o n of l i g n i n w i t h oxidants gives r i s e to the formation of quinonoid s t r u c t u r e s which have pronounced r e t a r d i n g and/or i n h i b i t i n g prop e r t i e s (5). However, there are some i n d i c a t i o n s that higher l i g n i n content may not always be to the detriment of pulp g r a f t a b i l i t y (6). Hornof et a l . (7) showed that in the case of s u l f i t e pulp copolym e r i z a t i o n w i t h a c r y l o n i t r i l e by the xanthate method, the g r a f t i n g e f f i c i e n c y increased w i t h r i s i n g l i g n i n content w h i l e the t o t a l conversion remained almost constant. K r a f t pulp, on the other hand, gave a higher t o t a l conversion to polymer w i t h r i s i n g l i g n i n content, w i t h a simultaneous i n c r e a s e in the amount of homopolymer. The same authors (5) showed a l s o in another work that the presence of l a r g e r amounts of l i g n i n in b i s u l f i t e pulps may have a favourable e f f e c t on g r a f t i n g p o l y a c r y l o n i t r i l e u s i n g the c e l l u l o s e xanthate-hydrogen peroxide redox system to i n i t i a t e the c o p o l y m e r i z a t i o n r e a c t i o n . The p l o t s of the t o t a l conversion as w e l l as of polymer l o a d i n g show a minimum centered around a p p r o x i mately 15% of l i g n i n . In the present work, the e f f e c t of adding l i g n i n and the presence of in-situ l i g n i n on the g r a f t a b i l i t y onto c e l l u l o s e has been i n v e s t i g a t e d . Experimental Cotton l i n t e r and bagasse ground to 40 mesh and e x t r a c t e d w i t h methanol-benzene 1:1, a l s o a l k a l i n e t r e a t e d bagasse and bagasse semichemical pulp were g r a f t e d w i t h a c r y l o n i t r i l e , e t h y l a c r y l a t e or methyl methacrylate. G r a f t i n g was c a r r i e d out under p u r i f i e d n i t r o g e n w i t h o c c a s i o n a l l i g h t - h a n d shaking. C e r i c ammonium s u l f a t e was used as i n i t i a t o r f o r g r a f t i n g the two former monomers ( 8 ) , w h i l e sodium b i s u l f i t e - s o d a lime g l a s s (9) or sodium b i s u l f i t e - c h i n a c l a y f o r g r a f t i n g the l a t t e r . C e r i c


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ammonium s u l f a t e c o n c e n t r a t i o n was O.08 or O.1 g% in 1% s u l f u r i c a c i d (pH about 1.0) and sodium b i s u l f i t e c o n c e n t r a t i o n was O.1 g%. L i q u o r , monomer and soda lime g l a s s or china c l a y t o c e l l u l o s e r a t i o s were 30:1, 3:1 and 1:1, r e s p e c t i v e l y . Homopolymerization r e a c t i o n s were a l s o c a r r i e d out w i t h the use of methyl methacrylate monomer. A f t e r the r e a c t i o n p e r i o d , the r e a c t i o n mixture was f i l t e r e d through a d r i e d and weighed s i n t e r e d glass c r u c i b l e G3, washed thoroughly u n t i l f r e e from r e s i d u a l monomer and other reagents, d r i e d , and then weighed. The crude g r a f t e d c e l l u l o s e s were ex t r a c t e d w i t h a s u i t a b l e solvent f o r the removal of the homopoly mer; dimethylformamide (DMF) f o r p o l y a c r y l o n i t r i l e , tetrahydrofuran (THF) f o r p o l y ( e t h y l a c r y l a t e ) , and acetone f o r poly(methyl m e t h a c r y l a t e ) . E x t r a c t i o n was c a r r i e d out u n t i l no f u r t h e r homopolymer was removed. An e x t r a c t i o n p e r i o d of 48 h r s was s u f f i c i e n t to b r i n g about t h i s . Thorough washing w i t h d i s t i l l e d water followed. F i n a l l y , the samples were d r i e d and weighed. The percentage conversion of monomer to polymer f o r homop o l y m e r i z a t i o n r e a c t i o n s and the g r a f t i n g y i e l d s f o r the g r a f t i n g ones were c a l c u l a t e d according t o the f o l l o w i n g equations: Conversion % = (B-S)/M Crude g r a f t i n g y i e l d C % = [(F-S)-Z]/Z True g r a f t i n g y i e l d A % = [(G-S)-Z]/Z where Β i s the weight o f polymer; S i s the weight of glass or china c l a y ; M i s the weight of monomer; Ζ i s the weight of c e l l u l o s e ; F i s the weight o f crude g r a f t e d c e l l u l o s e (before e x t r a c t i o n ) ; and G i s the weight of g r a f t e d c e l l u l o s e ( a f t e r extraction). The c e r i c consumption was determined according t o the method of Mino and Kaizerman (10) as nanomole c e r i c ammonium s u l f a t e per 100 g c e l l u l o s e . P r e p a r a t i o n of M a t e r i a l s . Soda l i g n i n was prepared from bagasse by s u b j e c t i n g t o soda cooking c o n d i t i o n s (11), namely, 20% sodium hydroxide based on d r y raw m a t e r i a l , l i q u o r to c e l l u l o s e r a t i o 5:1, a t 150°C., f o r one hour. L i g n i n was p r e c i p i t a t e d and separated through c e n t r i f u g a t i o n from the cooking l i q u o r , washed w i t h h y d r o c h l o r i c a c i d (1%) and then w i t h water to n e u t r a l i t y ; a f t e r washing, the l i g n i n was obtained by c e n t r i f u g i n g . The washed l i g n i n p r e p a r a t i o n was found t o contain l e s s than 1% ash. Soda lime g l a s s (SLG) was made by El-Nasr Company, Egypt, from the r e a c t i o n of Maadi sand (900 p a r t s ) , sodium carbonate (300 p a r t s ) , dolmite (CaC0 , MgC0 ) (190 p a r t s ) , limestone (63 p a r t s ) and sodium s u l f i t e (12 p a r t s ) . The f i n a l composition of the soda lime glass i s : S i 0 , 71.65%; R 0 , 1.82%; CaO, 8.63%; MgO, 3.27%; Na 0, 14.63%. 3

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Cotton l i n t e r was p u r i f i e d by K i e r b o i l i n g and then bleached w i t h the 4-stage b l e a c h i n g method, namely, c h l o r i n a t i o n , hot a l k a l i - r e f i n i n g , h y p o c h l o r i t e and c h l o r i n e d i o x i d e steps. Bagasse ground to 40 mesh, hot e x t r a c t e d w i t h methanol-benzene mixture (1:1) in a s o x h l e t apparatus and then d e l i g n i f i e d w i t h a c i d i f i e d sodium c h l o r i t e at pH 4.5. Bagasse of 40 mesh was a l s o subjected to a l k a l i n e treatments w i t h sodium hydroxide of 2 and 4% c o n c e n t r a t i o n and ammonium hydroxide of c o n c e n t r a t i o n 12.5 and 25% at a l i q u o r r a t i o 20:1, at room temperature, f o r 24 h r s . The samples were washed t h o r oughly w i t h d i s t i l l e d water and then t r e a t e d w i t h 10% a c e t i c a c i d , rewashed w i t h d i s t i l l e d water t i l l a c i d f r e e and f i n a l l y l e f t to dry at room temperature. Semichemical pulp of bagasse prepared by the a c i d s u l f i t e cooking was obtained from Edfuo Company of Egypt. R e s u l t s and D i s c u s s i o n Dudzik et a l . (12) found that i t i s p o s s i b l e to introduce and trap d i f f e r e n t amounts of s u l f u r - c o n t a i n i n g f r e e r a d i c a l s i n s i d e the framework of the s y n t h e t i c z e o l i t e s . Soda lime g l a s s of the composition: S1O2, 71.65%; R2O3, 1.82%; CaO, 8.63%; MgO, 3.27%; Na 0, 14.63%, when used w i t h sodium b i s u l f i t e proved to be a good i n i t i a t o r system f o r p o l y m e r i z a t i o n and g r a f t p o l y m e r i z a t i o n of methyl methacrylate onto c e l l u l o s e ( 9 ) . A scheme d e a l i n g w i t h the mechanism of i n i t i a t i o n has been proposed assuming t r a p p i n g of the b i s u l f i t e r a d i c a l i n s i d e the g l a s s framework to form a s o - c a l l e d sulfur-impregnated solid. Such a s o l i d has paramagnetic p r o p e r t i e s and a c t s on the methyl methacrylate monomer and c e l l u l o s e as any f r e e - r a d i c a l producing source, i . e . , i n i t i a t o r , thus l e a d i n g to p o l y m e r i z a t i o n and g r a f t p o l y m e r i z a t i o n onto c e l l u l o s e . China c l a y having very n e a r l y the e m p i r i c a l composition: A l 2 O 3 . 2 S i O 2 . 2 H 2 O (13) was used as soda lime g l a s s w i t h sodium b i s u l f i t e as an i n i t i a t o r system f o r g r a f t i n g polymethyl methacryl a t e onto c e l l u l o s e . Figure 1 shows a s l i g h t i n c r e a s e in the r a t e of g r a f t i n g when u s i n g sodium b i s u l f i t e - c h i n a c l a y i n i t i a t o r system compared w i t h sodium b i s u l f i t e - s o d a lime g l a s s , w h i l e the i n c r e a s e in the r a t e of homopolymerization and the conversion % was d i s t i n c t (Figure 2). When used w i t h china c l a y as an i n i t i a t o r , sodium b i s u l f i t e prepared one day before gave higher r a t e of p o l y m e r i z a t i o n and conversion %, compared w i t h the one f r e s h l y prepared (Figure 2). A s i m i l a r r e s u l t was achieved on u s i n g sodium b i s u l f i t e - s o d a lime g l a s s as an i n i t i a t o r system ( 9 ) . 2

G r a f t i n g in Presence of Added L i g n i n . C e r i c ammonium s u l f a t e i s an e f f e c t i v e i n i t i a t o r f o r g r a f t i n g p o l y e t h y l a c r y l a t e and p o l y a c r y l o n i t r i l e onto pure c e l l u l o s e s (8), w h i l e sodium


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Figure 1. Grafting rate using two sodium bisulfate initiator systems. Lignin (g%) using china clay for crude grafting yield (C): Ο — Ο ,O.0;.—.,O.0005;# ., 1.33; and for true grafting yield (Α): χ — χ ,O.0;Ο Ο,O.0005.Lignin (g%) using glass for crude grafting yield (C): . — Φ ,O.0;Η h O.0005; χ - - - χ , 1.33.



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Figure 2. Homopolymediation of methyl methacrylateinpresence of china clay or glass. Key (china clay): χ — X , sodium bisulfite freshly prepared; Ο — Ο , sodium bisulfite prepared one day before. Key (glass): -\ Κ sodium bisulfite prepared one day before.


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b i s u l f i t e - s o d a lime g l a s s (9) and sodium b i s u l f i t e - c h i n a c l a y are e f f e c t i v e f o r g r a f t i n g polymethyl methacrylate. High g r a f t i n g y i e l d s are thus achieved. A d d i t i o n of 1.33% of soda l i g n i n t o the g r a f t i n g systems i n h i b i t e d the g r a f t i n g r e a c t i o n s completely (zero g r a f t i n g y i e l d s ) (Figures 1, 3, 4 and 5 ) . M i n i m i z i n g the percent of added l i g n i n to O.27 r e s u l t e d in g r a f t i n g of the monomers onto c e l l u l o s e , however, the r a t e and y i e l d of g r a f t i n g s were s h a r p l y decreased compared w i t h those achieved in absence of l i g n i n (Figures 3, 4 and 5 ) . I t was observed that there are c e r t a i n s o l u b i l i t i e s of l i g n i n in monomers. Experiments were conducted u s i n g o n l y monomer d i s s o l v e d l i g n i n . The percent of l i g n i n d i s s o l v e d in each monomer was determined and was found O.002% in both a c r y l o n i t r i l e and e t h y l a c r y l a t e and O.005% f o r methyl methacrylate. I n the g r a f t i n g systems, the percentages reach O.0002 and O.0005, r e s p e c t i v e l y . F i g u r e s 1, 3, 4 and 5 show that the presence of such t r a c e s of l i g n i n in the g r a f t i n g media still r e s u l t in sharp decrease in the r a t e and y i e l d of g r a f t i n g compared w i t h those due t o absence of l i g n i n . The decrease may be as h i g h as that due to the presence of O.27% l i g n i n (Figures 3 and 4 ) . Again, from Figures 1, 3, 4 and 5 i t i s c l e a r that the presence of traces of l i g n i n in the g r a f t p o l y m e r i z a t i o n system p a r t i a l l y r e t a r d s the g r a f t i n g r e a c t i o n when sodium b i s u l f i t e soda lime glass or - c h i n a c l a y are used as i n i t i a t o r s . Here, r e t a r d a t i o n i s a t t r i b u t e d to the quinonoid groups present in soda l i g n i n . Strong r e t a r d a t i o n i s achieved when the i n i t i a t o r i s e e r i e ammonium s u l f a t e . The l a t t e r r e s u l t r e l a t e s to the p r e f e r e n t i a l consumption of the i n i t i a t o r in o x i d i z i n g l i g n i n (5). I t was a l s o observed that a t the same percent of the l i g n i n added, the decrease in the r a t e and y i e l d of g r a f t i n g i s higher on lowering the g r a f t i n g temperature (Figures 3, 4 and 5). This may r e l a t e to a higher e f f i c i e n c y f o r the r e t a r d i n g or i n h i b i t i n g p r o p e r t i e s of l i g n i n a t the lower temperature. G r a f t i n g in the Presence of I n - s i t u L i g n i n . Extracted ground and semi chemical pulp of bagasse of the l i g n i n contents 19.6 and 1.89%, r e s p e c t i v e l y , were subjected t o g r a f t i n g w i t h e t h y l a c r y l a t e and a c r y l o n i t r i l e u s i n g O.08 g e e r i e ammonium s u l fate/100 ml as i n i t i a t o r . The r e s u l t s as i l l u s t r a t e d in F i g u r e 6, show absence of g r a f t i n g as i n d i c a t e d by the zero g r a f t i n g y i e l d s achieved. I n s u f f i c i e n t r a t e and y i e l d of g r a f t i n g s were only observed on g r a f t i n g the semichemical pulp w i t h a c r y l o n i t r i l e at 30°C. For the extracted bagasse w i t h high l i g n i n content, i n h i b i t i o n (zero g r a f t i n g y i e l d ) took p l a c e a l s o even on i n c r e a s i n g the c o n c e n t r a t i o n of e e r i e ammonium s u l f a t e t o O.1 g/100 ml. I n h i b i t e d g r a f t i n g was a l s o a f f e c t e d on using a l k a l i n e t r e a t e d ground bagasse. I n h i b i t i o n of the g r a f t i n g process has been r e l a t e d to the p r e f e r e n t i a l consumption of the i n i t i a t o r in o x i d i z i n g l i g n i n . This i s revealed by comparing the e e r i e consumed by


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Figure 3. Rate of grafting. Conditions: initiator, eerie ammonium sulfate (O.08 g/100 mL, 1% H SO ); monomer, ethyl acrylate; 30°C. Lignin (g%): O—O, O.0; X-X, O.0002; .—.,O.27;Χ — X , 1.33. 2

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Figure 4. Rate of grafting. Conditions: initiator, eerie ammonium sulfate (O.08 g/100 mL, 1% HgSOt); monomer, acrylonitrile; 30°C. Lignin (g%) for crude grafting yield (C): O—O, O.0; Ο Ο,O.0002;χ — χ , O.27; Χ Χ, 1.33. Lignin (g%) for true grafting yield (A): .—., O.0; Φ . , O.0002.


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Figure 5. Grafting rate of two monomers. Conditions: initiator, eerie ammonium sulfate (O.08 g/100 mL, 1% H SO^). Lignin (g%) using ethyl acrylate (40°C): O—O, O.0; . .,O.0002;-\ h 1-33. Lignin (g%) using acrylonitrile (40°C): Ο Ô, O.0; χ χ,O.0002;.—., 1.33. Lignin (g%) using ethyl acrylate (60°C): .—., O.0; Χ — X , O.27. 2

Figure 6. Grafting rate of semichemical pulp. Conditions: initiator, eerie am monium sulfate (O.08 g/100 mL, 1% H SO^; 30°C. Key (monomer): O—O, acrylonitrile; .—., ethyl acrylate. Grafting rate of extracted bagasse. Condi tions: monomer, ethyl acrylate; 60°C. Key (initiator, eerie ammonium sulfate): X—X, O.08 g/100 mL, 1 % H S0 ; Η b O.10 g/100 mL, 1 % H SO . 2

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the l i g n o c e l l u l o s i c s u b s t r a t e bagasse semichemical pulp and the pure c e l l u l o s e c o t t o n l i n t e r , where the former s u b s t r a t e showed a sharp i n c r e a s e in the e e r i e consumed at the e a r l y stages (Figure 7). On u s i n g sodium b i s u l f i t e - s o d a lime g l a s s as i n i t i a t o r f o r g r a f t i n g polymethyl methacrylate onto ground bagasse of the l i g n i n content of 19.6%, low r a t e and y i e l d of g r a f t i n g were achieved. The same was a l s o obtained when g r a f t i n g was c a r r i e d out in presence of sodium b i s u l f i t e alone, i . e . , in the absence of soda lime g l a s s . The r a t e and y i e l d of g r a f t i n g s were as low as in the presence of soda lime g l a s s ( F i g u r e 8 ) . Reducing the l i g n i n content to 4%, then to 2.62% through d e l i g n i f i c a t i o n w i t h a c i d i f i e d sodium c h l o r i t e , increased the r a t e and y i e l d of g r a f t i n g p r o g r e s s i v e l y in the absence of soda lime g l a s s . Semichemical pulp of lower l i g n i n content (1.89%) showed higher r a t e and y i e l d of g r a f t i n g (Figure 8 ) . The r e s u l t s achieved above r e v e a l the f o l l o w i n g : (1) For g r a f t i n g polymethyl methacrylate onto l i g n o c e l l u l o s i c s u b s t r a t e s , sodium b i s u l f i t e may be used alone, i . e . , in the absence of soda lime g l a s s or c h i n a c l a y . I t i s worthy to ment i o n that g r a f t i n g onto pure c e l l u l o s e s f a i l e d to take p l a c e in absence of soda lime g l a s s ( 9 ) ; (2) l i g n i n a l r e a d y present in the c e l l u l o s i c s u b s t r a t e , i . e . , in-situ, does not possess r e t a r d ing or i n h i b i t i n g p r o p e r t i e s on the process of g r a f t i n g of p o l y methyl methacrylate in the presence of sodium b i s u l f i t e . This r e l a t e s to that l i g n i n i s present in p l a n t as p o l y h y d r i c a l c o h o l s and not as quinones. I t a c q u i r e s the quinonoid s t r u c t u r e respons i b l e f o r the i n h i b i t i n g p r o p e r t i e s only on i s o l a t i o n (14). G r a f t i n g polymethyl methacrylate s u c c e s s f u l l y onto p a r t i a l l y d e l i g n i f i e d bagasse or semichemical pulp on u s i n g sodium b i s u l f i t e alone, i . e . , in the absence of soda lime g l a s s or china c l a y may not be c o n t r i b u t e d to the i n o r g a n i c matter, p a r t i c u l a r l y s i l i c a , present in bagasse, s i n c e : 1. S i l i c a i s l e s s e f f i c i e n t than soda lime g l a s s in i n i t i a t i n g the g r a f t i n g of polymethyl methacrylate in presence of sodium b i s u l f i t e ( 9 ) . The r e s u l t s achieved w i t h semichemical pulp show v e r y h i g h r a t e and y i e l d of g r a f t i n g s (Figure 8 ) . 2. Crude g r a f t i n g y i e l d s higher than 100% could be only achieved at soda lime g l a s s to c e l l u l o s e r a t i o O.5:1 and f u r t h e r increased at 1:1. A maximum y i e l d higher than 200% was achieved at 2:1 r a t i o (15). In the present work, the amount of i n o r g a n i c matter determined as ash content i s 4.029% f o r bagasse and 1.115% f o r semichemical pulp. In other words, the r a t i o of i n o r g a n i c matter ( i n which s i l i c a forms one of i t s c o n s t i t u e n t s ) to c e l l u l o s e i s O.04:1 f o r the former and O.01:1 f o r the l a t t e r and hence these r a t i o s are i n s u f f i c i e n t to produce the h i g h g r a f t i n g y i e l d s achieved w i t h the p a r t i a l l y d e l i g n i f i e d bagasse and the semichemic a l pulp.


264


30P ,0 0

1

60

1

•

'

1

•

•

'

1

120 180 Time minutes

24 0

Figure 7. Ceric ammonium sulfate consumption for cotton linter: Ο — Ο , 30° C.; .—., 60°C.; and for semichemical pulp: H h 30°C.; χ — X , 60°C.


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Figure 8. Graft polymerization of methyl methacrylate. Onto bagasse: Φ ., in absence of glass; Ο Ο,inpresence of glass. Onto semichemical pulp: Ο — Ο ,inabsence of glass; Φ—., in presence of glass. Onto delignifted bagasse: Χ — X , 4.00% lignin; Η f-, 2.60% lignin.


266


From the above, i t may be concluded that in analogy t o the mechanism of g r a f t i n g i n i t i a t e d by sodium b i s u l f i t e - s o d a lime g l a s s system (9), l i g n i n w i t h i t s network s t r u c t u r e c o n f i g u r a t i o n may p l a y the r o l e of soda lime g l a s s in t r a p p i n g the b i s u l f i t e r a d i c a l i n s i d e i t s framework forming a sulfur-impregnated s o l i d of paramagnetic p r o p e r t i e s which a c t on the methyl methacrylate monomer and c e l l u l o s e as any f r e e - r a d i c a l - p r o d u c i n g source, thus l e a d i n g t o p o l y m e r i z a t i o n and g r a f t p o l y m e r i z a t i o n onto c e l l u l o s e . Again, i t i s noteworthy t h a t the y i e l d of g r a f t i n g was pract i c a l l y the same a t e q u i l i b r i u m on c a r r y i n g out the g r a f t i n g process on semichemical pulp in presence and absence of soda lime g l a s s (Figure 8 ) . S u b j e c t i n g the ground bagasse to t r e a t i n g w i t h 2 and 4% sodium hydroxide decreased the l i g n i n content to 11.19 and 7.36%, r e s p e c t i v e l y ; w h i l e t r e a t i n g w i t h 25% ammonium hydroxide a t l i q u o r to c e l l u l o s e r a t i o s 10:1 and 20:1, decreased i t to 18.85 and 11.61%, r e s p e c t i v e l y . Figure 9 shows that f o r the same a l k a l i n e treatment (sodium or ammonium h y d r o x i d e ) , the sample of the lower l i g n i n content showed again h i g h e r r a t e and y i e l d of g r a f t i n g s . For d i f f e r e n t a l k a l i n e treatments, samples t r e a t e d w i t h ammonium hydroxide were of higher g r a f t i n g r a t e s and y i e l d s than those t r e a t e d w i t h sodium hydroxide, in s p i t e of the higher l i g n i n content of those of the former treatment. A l s o , the r a t e and y i e l d of g r a f t i n g s were higher f o r the bagasse subjected to a l k a l i n e treatments than that t r e a t e d w i t h a c i d c h l o r i t e (Figures 8 and 9 ) , in s p i t e again of the higher l i g n i n content of the former samples. This may r e l a t e to d i f f e r e n c e s in the s t r u c t u r e of the r e s i d u a l l i g n i n due t o p r e f e r e n t i a l removal of d i f f e r e n t l i g n i n f r a c t i o n s and combined h e m i c e l l u l o s e s , accompanying d i f f e r e n t chemical t r e a t ments. In c o n c l u s i o n , the l i p n i n content i s the governing f a c t o r f o r the r a t e and y i e l d of g r a f t i n g of polymethyl methacrylate in the presence of sodium b i s u l f i t e onto l i g n o c e l l u l o s i c substrate when the l a t t e r i s subjected to the same chemical treatment. For d i f f e r e n t chemical treatments, the s t r u c t u r e of the r e s i d u a l l i g n i n i s the governing f a c t o r . I n other words, the extent to which l i g n i n i n t e r f e r e s w i t h the g r a f t i n g r e a c t i o n v a r i e s from one type of c e l l u l o s i c s u b s t r a t e to another, depending l a r g e l y on i t s chemical h i s t o r y . A s i m i l a r achievement was a r r i v e d a t by Hornof et a l . ( 5 ) , although t h e i r s t u d i e s were d i f f e r e n t from those of ours.


16.


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0

1

2

267

3 Time

hrs.

Figure 9. Grafting rate onto bagasse treated with ammonium hydroxide: Ο Ο, 10:1; .—., 20:1; and with sodium hydroxide: Χ — X , 2%; O—O, 4%.


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Literature Cited 1.

2. 3. 4. 5. 6.

7. 8. 9. 10. 11. 12.

13.

14. 15.

Tirzina, J.; Issled, Obl.; Khim, Drev. Tezisy Dokl. Konf. Moledykh Uch. 1975, 151, 41 (Russ.); Chem. Abstr. 1976, 84, 180747q. S t r a f o r e l l i , J. B., Ph.d. Thesis, University of British Columbia, Vancouver, B.C., 1973. Kubota, H.; Ogiwara, Y. J. Appl. Polym. Sci. 1969,13,1569. Erdélyi, J. Zellstoff und Papier. 1970, 243. Hornof, V.; Kokta, Β. V.; Valade, J. L. J. Appl. Polym. Sci. 1976, 20, 1543. P h i l l i p s , R. B.; Kobayashi, A. J.; Brown, W.; Stannett, V.T. "Pollution Abatement by More Effective Lignin U t i l i z a t i o n : Grafting to Lignin and Lignin-Containing Pulps"; North Carolina State University, 1970. Hornof, V.; Kokta, Β. V.; Valade, J. L. J. Appl. Polym. Sci. 1975, 19, 1573. Mansour, O. Y.; Schurz, J. Svensk Papperstidn. 1973, 76, 258. Mansour, O. Y.; Nagaty, A. J. Polym. Sci., Polym. Chem. Ed. 1975, 13, 2785. Mino, G.; Kaizerman, S.; Rasmussen, E. J. Polym. Sci. 1959, 38, 393. Mansour, O. Y.; Seif El-Dien, M. Paperi j a Puu 1972, 54, 189. Dudzik, Z.; Cvetanovîé. Proceedings of the Fourth Interna tional Congress on Catalysis, Moscow, 1968, Adadémiai Kiadó, Budapest, 1971, p 175. Parkes, G. D. "Mellor's Modern Inorganic Chemistry"; Long mans, Green and Co.: London, New York and Toronto, 1951, p 721. Mansour, O. Y.; Nagaty, Α.; Salama, Μ. Α.; Abdel Mouty, F. Paperi j a Puu (in press). Mansour, O. Y.; Moustafa, A. B. J. Polym. Sci., Polym. Chem. Ed. 1975, 23, 2795.

RECEIVED January 22, 1982.


Graft Copolymerization of Lignocellulosic Fibers - American Chemical

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