Photoinduced Grafting Reactions in Cellulose and Cellulose Derivatives

8 Photoinduced Grafting Reactions in Cellulose and Cellulose Derivatives DAVID N.-S. HON Virginia Polytechnic Institute and State University, Department of Forest Products, Blacksburg, V A 24061-0299

Downloaded by CORNELL UNIV on July 22, 2016 | http://pubs.acs.org Publication Date: June 18, 1982 | doi: 10.1021/bk-1982-0187.ch008

HOW-CHING C H A N Mount Sinai School of Medicine, The City University of New York, New York, N Y 10029 Photoinduced free radicals generated i n cellulose and cellulose derivatives, namely, methyl cellulose, ethyl cellulose, acetyl cellulose, hydroxyethyl cellulose and carboxymethyl cellulose, were examined by electron spin resonance (ESR) spectroscopy, and their capability of i n i t i a t i n g graft copolymerization was studied. ESR findings revealed that a high concentration of free radicals was generated i n all samples irradiated with ultraviolet light of λ > 254 nm and λ > 280 nm. Free radicals generated i n cellulose were due to chain scission, dehydrogenation, and dehydroxymethylation reactions, whereas free radicals generated in cellulose derivatives were due to cleavage of substituted side chains. Grafting reactions of cellulose took place at the main back bone, whereas grafting reactions of cellulose derivatives took place at the substituted side chains. High degrees of grafting and grafting efficiency were inevitably obtained from samples treated with ultraviolet light of λ > 280 nm in homo geneous media. C e l l u l o s e , the most abundant renewable a g r i c u l t u r a l raw m a t e r i a l , i s transformed i n t o m u l t i f a r i o u s products a f f e c t i n g every phase of our d a i l y l i f e . The presence of a c t i v e h y d r o x y l groups i n c e l l u l o s e has been u t i l i z e d i n a v a r i e t y of chemical r e a c t i o n s to produce commercially important c e l l u l o s e d e r i v a t i v e s , such as c e l l u l o s e ethers and c e l l u l o s e e s t e r s . Although the p r a c t i c a l purpose o f c e l l u l o s e d e r i v a t i z a t i o n i s by and l a r g e to improve v a r i o u s p r o p e r t i e s of the o r i g i n a l c e l l u l o s e , these c e l l u l o s e d e r i v a t i v e s are o f t e n not c o m p e t i t i v e w i t h most of the p e t r o c h e m i c a l l y d e r i v e d s y n t h e t i c polymers. In order to provide a b e t t e r market p o s i t i o n f o r c e l l u l o s e d e r i v a t i v e s , there i s l i t t l e doubt that f u r t h e r chemical m o d i f i c a t i o n i s r e q u i r e d . G r a f t i n g of v i n y l monomers onto c e l l u l o s e and

©

0097-6156/82/0187-0101$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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GRAFT COPOLYMERIZATION OF LIGNOCELLULOSIC FIBERS

c e l l u l o s e d e r i v a t i v e s may improve the i n t r i n s i c p r o p e r t i e s of these polymers. Several papers d e a l i n g with g r a f t i n g r e a c t i o n s i n c e l l u l o s e d e r i v a t i v e s have been reported r e c e n t l y . Bardhan et a l . (1) and Mukhopadhyay et a l . (2) g r a f t e d acrylamide and a c r y l i c a c i d , r e s p e c t i v e l y , onto methyl c e l l u l o s e using potassium p e r s u l f a t e as the i n i t i a t o r . Hebeish et a l . (3, 4) grafted a c r y l o n i t r i l e and methyl a c r y l a t e onto a c e t y l a t e d cotton and p a r t i a l l y carboxymethylated cotton. G r a f t i n g of methyl methacrylate to c e l l u l o s e n i t r a t e by e e r i e i o n i n i t i a t i o n has been developed by Santappa and h i s co-workers (5, 6 ) . The r a d i a t i o n induced g r a f t i n g of a c r y l o n i t r i l e onto cyanoethylated cotton and c e l l u l o s e acetate have been i n v e s t i g a t e d by Arthur et a l . (7) and by Stannett e t a l . (8), r e s p e c t i v e l y . Grafting of styrene to c a r b o n i l a t e d c e l l u l o s e s by γ-irradiation was done by Guthrie et a l . ( 9 ) . In s p i t e of the common use of u l t r a v i o l e t l i g h t f o r g r a f t i n g v i n y l monomers onto c e l l u l o s e , there i s as y e t no l i t e r a t u r e a v a i l a b l e on photoinduced g r a f t i n g r e a c t i o n s i n c e l l u l o s e d e r i v a t i v e s . Research on g r a f t i n g v i n y l monomers onto c e l l u l o s e d e r i v a t i v e s by u l t r a v i o l e t l i g h t i s i n progress i n our l a b o r a t o r y . This paper w i l l report the d e t e c t i o n of photoinduced f r e e r a d i c a l s i n c e l l u l o s e and various c e l l u l o s e d e r i v a t i v e s , namely, methyl c e l l u l o s e , e t h y l c e l l u l o s e , a c e t y l c e l l u l o s e , hydroxyethyl c e l l u l o s e and carboxymethyl c e l l u l o s e , and t h e i r c a p a b i l i t y of i n i t i a t i n g g r a f t copolymerization. The e l e c t r o n s p i n resonance (ESR) studies r e v e a l that most of the f r e e r a d i c a l s were generated at the s u b s t i t u t e d s i d e chains of c e l l u l o s e d e r i v a t i v e s by u l t r a v i o l e t l i g h t and these f r e e r a d i c a l s are r e s p o n s i b l e f o r g r a f t i n g and homopolymerization r e a c t i o n s . Experimental Materials. C e l l u l o s e and c e l l u l o s e d e r i v a t i v e s used f o r t h i s study are summarized i n Table 1. Commercial products were used as received without f u r t h e r p u r i f i c a t i o n s . Methyl methacrylate was used as the monomer, which was p u r i f i e d by sodium hydroxide/sodium c h l o r i d e e x t r a c t i o n followed by d i s t i l l a t i o n under reduced pressure (10). Methods P h o t o i r r a d i a t i o n and ESR Measurements. The samples of c e l l u l o s e and c e l l u l o s e d e r i v a t i v e s were packed uniformly i n t o c l e a r fused S u p r a s i l quartz tubes (O.D. 4 mm), which d i d not produce any ESR s i g n a l during the i r r a d i a t e d sequences. The quartz tubes containing the samples were evacuated to a constant pressure (10 ~6 mm Hg) and sealed. The source of u l t r a v i o l e t i r r a d i a t i o n was a high pressure mercury-xenon compact a r c lamp (Conrad Hanovia type 901 B0011, 200 W) which


Hon; Graft Copolymerization of Lignocellulosic Fibers ACS Symposium Series; American Chemical Society: Washington, DC, 1982. 3

Hercules, I n c .

Hercules, I n c .

3

35% CH CO

250GR

12M8

D.S. = 2.2

N-4

95.8% α-cellulose from y e l l o w poplar

Type

^Preparation i n laboratory. (Methods i n Carbohydrate Chemistry, R. C. W h i s t l e r , ed., V o l . I I I . Academic P r e s s , New York, 1963, p. 193.)

P r e p a r a t i o n i n laboratory. (Methods i n Carbohydrate Chemistry, R. L. W h i s t l e r , ed., V o l . I I I . Academic P r e s s , New York, 1963, p. 322.

A c e t y l c e l l u l o s e (Fibrous)*

5

(Powder)

Carboxylmethylcellulose

Hydroxyethylcellulose

(Fibrous)

Hercules, I n c .

Ethyl Cellulose

Carboxylmethylcellulose

Buckeye C e l l u l o s e

Manufacturer

Cellulose

Specimen

TABLE I . C e l l u l o s e D e r i v a t i v e s C h a r a c t e r i s t i c s



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emitted wavelengths ranging from 254 nm to 2000 nm, w i t h the s t r o n g e s t wavelength a t 365 nm. For c e r t a i n s t u d i e s , a Corning g l a s s f i l t e r ( c o l o r s p e c i f i c a t i o n number, 0-53; g l a s s code number, 7440) was used to e l i m i n a t e wavelengths s h o r t e r than 280 nm. I n all cases of u l t r a v i o l e t i r r a d i a t i o n , the d i s t a n c e between l i g h t source and sample was about 30 cm, and the sample was kept i n l i q u i d n i t r o g e n i n a Dewar f l a s k . ESR s p e c t r a of i r r a d i a t e d samples i n the Dewar f l a s k were recorded using a spectrometer ( V a r i a n Ε-12) operated at X-band w i t h 100 KHz modulation. The s p e c t r a were recorded at 9.3 GHz at 3300 gauss. The g values were measured by comparison w i t h the p i t c h sample provided by V a r i a n A s s o c i a t e s . G r a f t Copolymerization. G r a f t copolymers of c e l l u l o s e and c e l l u l o s e d e r i v a t i v e s were prepared i n a quartz r e a c t o r c o n t a i n i n g O.5 g oven d r i e d sample, 10 ml monomer and 100 ml water a t 45°C. The g r a f t i n g mixtures or s o l u t i o n s were photoi r r a d i a t e d w i t h the u l t r a v i o l e t l i g h t of λ 254 nm and λ 280 nm. Grafted products of c e l l u l o s e were washed w i t h d i s t i l l e d water and e x t r a c t e d w i t h acetone f o r 72 hours to remove homopolymers; g r a f t e d products of c e l l u l o s e d e r i v a t i v e s were washed and e x t r a c t e d w i t h benzene repeatedly, the f i n a l products were then f r e e z e - d r i e d . Degree of g r a f t i n g and g r a f t i n g e f f i c i e n c y were c a l c u l t e d according to the f o l l o w i n g formula: Degree of g r a f t i n g (%) = G r a f t i n g e f f i c i e n c y (%) =

A-B —- χ Β

100

A-B (A-B) + C

X

1 0 0

Where A i s weight of g r a f t e d sample a f t e r e x t r a c t i o n , Β i s weight of o r i g i n a l sample (oven-dry), and C i s weight of homopolymer. R e s u l t s and D i s c u s s i o n Photoinduced Free R a d i c a l s i n C e l l u l o s e and C e l l u l o s e D e r i v a t i v e s . Most c e l l u l o s e and c e l l u l o s e d e r i v a t i v e s are s u s c e p t i b l e to photochemical r e a c t i o n i n the presence of u l t r a v i o l e t l i g h t below the wavelength of 340 nm (11) v i a a f r e e r a d i c a l process. These f r e e r a d i c a l intermediates may be capable of i n i t i a t i n g g r a f t c o p o l y m e r i z a t i o n r e a c t i o n i f they are not decayed r a p i d l y or undergo secondary t e r m i n a t i o n r e a c t i o n s . The d e t e c t i o n of f r e e r a d i c a l s generated i n c e l l u l o s e and c e l l u l o s e d e r i v a t i v e s by u l t r a v i o l e t l i g h t was s t u d i e d . ESR s p e c t r a of c e l l u l o s e and c e l l u l o s e d e r i v a t i v e s used f o r t h i s study are shown i n Figures 1 and 2 f o r samples t r e a t e d w i t h u l t r a v i o l e t l i g h t of λ 280 nm and λ 254 nm r e s p e c t i v e l y . I t i s obvious t h a t f r e e r a d i c a l s were generated i n all samples i r r a d i a t e d w i t h both l i g h t sources. The ESR


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Photoinduced Grafting Reactions

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8.

Figure 1. ESR spectra of cellulose and cellulose derivatives irradiated with UV light of λ 280 nm for 60 min at 77 K. Spectra were recorded at 77 K. Key: a, cellulose; b, methylcellulose; c, ethylcellulose; d, acetylcellulose; e, hydroxyethylcellulose; f, carboxymethylcellulose.




106



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s i g n a l s derived from samples i r r a d i a t e d with l i g h t of λ 280 nm e x h i b i t e d i l l - d e f i n e d m u l t i p l e t h y p e r f i n e s p l i t t i n g while prominent s i g n a l s with b e t t e r r e s o l u t i o n were observed from those with l i g h t of λ 254 nm because of higher energy i n v o l v e d . From the l a t t e r l i g h t source, an e l e v e n - l i n e s i g n a l with a g value of 2.003 was detected i n c e l l u l o s e , and s e v e n - l i n e s i g n a l s with i d e n t i c a l g values were detected from methyl c e l l u l o s e , e t h y l c e l l u l o s e , a c e t y l c e l l u l o s e , hydroxyethyl c e l l u l o s e (weak) and carboxymethyl c e l l u l o s e (weak). I n t e r p r e t a t i o n of the e l e v e n - l i n e s i g n a l of c e l l u l o s e has been published elsewhere (12), I t was the r e s u l t of superimposing s i g n a l s generated from s i x kinds of r a d i c a l s p e c i e s , as a consequence of chain s c i s s i o n , dehydrogenation and dehydroxymethylation r e a c t i o n s i n p h o t o i r r a d i a t e d c e l l u l o s e . Details of the mechanism of f r e e r a d i c a l formation were a l s o discussed elsewhere (13, 14). A s e v e n - l i n e s i g n a l was observed from p h o t o i r r a d i a t e d methyl c e l l u l o s e (Figure 3). When t h i s photoi r r a d i a t e d sample was warmed g r a d u a l l y from 77°K to ambient temperature f o r 1 minute and kept again a t 77°K, a poorly r e s o l v e d f i v e - l i n e spectrum was observed (Figure 3b). When i t was warmed f o r 5 minutes, the s i g n a l was f u r t h e r decayed to a s i n g l e t s i g n a l with a l i n e - w i d t h of 21 gauss (Figure 3c). By s u b t r a c t i n g b from a i n F i g u r e 3, a quartet spectrum with i n t e n s i t y r a t i o 1:3:3:1 i s obtained (Figure 3d). Since t h i s f o u r - l i n e s i g n a l has a s p l i t t i n g constant of 22.8 gauss, we assigned t h i s s i g n a l to methyl r a d i c a l s . Consequently, i t i s obvious that demethylation took place i n methyl c e l l u l o s e , as shown i n equation 1. C e l l u l o s e — 0CH

h 3

v

ψ

Cellulose — (singlet)

O.

+

. CH (quartet) 3

(1)

The s i n g l e t s i g n a l i s hence due to the alkoxy r a d i c a l , which has a longer l i f e time than carbon r a d i c a l s a t ambient temperature. When e t h y l c e l l u l o s e was i r r a d i a t e d with l i g h t of λ 254 nm f o r 60 minutes a t 77°K, a complicated e l e v e n - l i n e s i g n a l was observed (Figure 4). When t h i s sample was warmed to ambient temperature f o r 5 minutes, only a s i n g l e t s i g n a l w i t h a l i n e - w i d t h of 26 gauss was observed. Analyzing the s p l i t t i n g constants of the m u l t i - i n t e n s i t y resonance peaks, i t r e v e a l s that, i n a d d i t i o n to the s i n g l e t component, the spectrum was superimposed with two s i g n a l s : a strong s i x - l i n e component with a h y p e r f i n e s p l i t t i n g constant of 25 gauss (V i n F i g u r e 4), and a weak f i n e - l i n e component with a h y p e r f i n e s p l i t t i n g constant of 25 gauss (ο i n F i g u r e 4 ) . This implies that d e e t h y l a t i o n took place p r e f e r e n t i a l l y during p h o t o i r r a d i a t i o n to c r e a t e a r a d i c a l p a i r of s i x - l i n e and s i n g l e t components. A hydrogen a b s t r a c t i o n r e a c t i o n a l s o l i k e l y occurred generating the f i v e - l i n e component. A c c o r d i n g l y , the mechanisms are i l l u s t r a t e d i n equations 2, 3 and 4.



108


20G

Figure 3. Changes in ESR spectra of methylcellulose. Key: a, initial spectrum observed at 77 Κ immediately after irra diation with light of λ 254 nm at 77 Κ for 60 min; b, after sample was warmed to ambient temperature for 1 min; c, after sample was warmed to ambient tempera ture for 5 min; d, a quartet component which was obtained by subtracting b from a.

Figure 4. ESR spectra of ethylcellulose irradiated with UV light of λ 254 nm at 77 Κ for 60 min. Spectra were recorded at 77 K. Dotted line signal was ob tained after sample was warmed to ambient temperature for 5 min.


8.

HON AND


CHAN

C e l l u l o s e - 0 - CH CH Ζ

— •

109

Cellulose -

O.

+-CH CH L J (2) (6-line)

J

(singlet) C e l l u l o s e - 0 - CH CH 2

C e l l u l o s e - 0 - CH "CH * (3)

3

2

2

(5-line) C e l l u l o s e - 0 - CH CH 2

C e l l u l o s e - 0 - CH - CH

3

(4)

3


(5-line) The h y p e r f i n e s p l i t t i n g constant of the s i x - l i n e component i s closed to the e t h y l r a d i c a l s of e t h y l i o d i d e (15). A prominent seven-line s i g n a l was observed from a c e t y l c e l l u l o s e when i r r a d i a t e d with l i g h t of λ 254 nm f o r 60 minutes a t 77°K (Figure 5). The warm-up treatment, as f o r methyl c e l l u l o s e , revealed that a f o u r - l i n e s i g n a l with a h y p e r f i n e s p l i t t i n g constant of 22.8 gauss was generated, i n d i c a t i n g d e a c e t y l a t i o n and demethylation took place, as i l l u s t r a t e d i n equations 5 and 6.

8 Cellulose—OC—CH

0 +-8—CH

Cellulose—O.

Q

(5)

3

CO +-CH

3

Cellulose-0 —C—CH

• •

3

Cellulose — 0

C. +.CH

3

(6)

D e t a i l s of the f r e e r a d i c a l formation mechanism were d i s cussed elsewhere (16). When hydroxyethyl c e l l u l o s e was i r r a d i a t e d with the same l i g h t , a seven-line s i g n a l was a l s o observed (Figure 6). When t h i s sample was warmed to ambient temperature, a f i v e - l i n e s i g n a l with a hyperfine s p l i t t i n g constant of 29 gauss disappeared, only a s i n g l e t s i g n a l with a l i n e - w i d t h of 24 gauss was observed. I t i s c l e a r that dehydroxyethylation took p l a c e f o r t h i s sample. Reaction i s shown i n equation 7. Cellulose —0—CH —CH 0H — 2

2

^

Cellulose-O.

+

(Singlet)

(7)

•CH CH 0H 2

2

(5-line) A seven-line l i k e s i g n a l was detected from carboxymethyl c e l l u l o s e i r r a d i a t e d with u l t r a v i o l e t l i g h t of 254 nm (Figure 7). When t h i s sample was warmed to ambient temperature f o r 60 seconds, t h i s m u l t i p l e t spectrum was transformed r a p i d l y i n t o a prominent doublet s i g n a l w i t h a h y p e r f i n e s p l i t t i n g constant of 20 gauss. This i n d i c a t e d that the primary f r e e r a d i c a l s




110

Figure 5. Changes in ESR spectra of acetylcellulose. Key: a, initial spectrum observed at 77 Κ immediately after irradiation with UV light of λ 254 nm at 77 Κ for 60 min; b, after sample was warmed to ambient temperature for 1 min; c, after sample was warmed to ambient temperature for 5 min; d, a quartet com ponent which was obtained by subtracting b from a.


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8.

Figure 7. ESR spectra of carboxymethylcellulose irradiated with UV light of λ 254 nm at 77 Κ for 60 min. Spectra were recorded at 77 K. Dotted line signal was obtained when sample was warmed to ambient temperature for 1 min.


112


generated were transformed i n t o a r a d i c a l s i t e a t t r i b u t i n g the doublet s i g n a l . Based on the chemical s t r u c t u r e of carboxymethyl c e l l u l o s e , i t i s l i k e l y that the f o l l o w i n g r e a c t i o n took p l a c e (equation 8 ) : primary r a d i c a l s

heat (8)


Cell—0—CH—COOH (doublet) From t h i s ESR i n f o r m a t i o n , i t i s obvious that more f r e e r a d i c a l s were generated when samples were i r r a d i a t e d w i t h u l t r a v i o l e t l i g h t of λ 254 nm than those w i t h l i g h t of λ 280 nm. S e v e r a l types of f r e e r a d i c a l s were generated i n c e l l u l o s e due t o c h a i n s c i s s i o n , dehydrogenation and dehydroxym e t h y l a t i o n , whereas f r e e r a d i c a l s generated i n c e l l u l o s e d e r i v a t i v e s were by and l a r g e due t o the cleavage o f the substituted side chains. G r a f t a b i l i t y of Photoinduced C e l l u l o s i c Free R a d i c a l s . Various f r e e r a d i c a l s a r e generated i n c e l l u l o s e and c e l l u l o s e d e r i v a t i v e s by u l t r a v i o l e t l i g h t , which may be capable of i n i t i a t i n g g r a f t c o p o l y m e r i z a t i o n r e a c t i o n s w i t h v i n y l monomers. The g r a f t a b i l i t y of these photoinduced f r e e r a d i c a l s i n homogeneous and heterogeneous media was s t u d i e d . The degree of g r a f t i n g and g r a f t i n g e f f i c i e n c y of g r a f t i n g r e a c t i o n s induced w i t h u l t r a v i o l e t l i g h t of λ 280 nm and λ 254 nm were s c r u t i n i z e d . The r e s u l t s obtained by using u l t r a v i o l e t l i g h t of λ 280 nm a r e shown i n F i g u r e s 8 and 9 f o r degree of g r a f t i n g and grafting efficiency respectively. I t appears that the degree of g r a f t i n g increased as the f u n c t i o n o f i r r a d i a t i o n time. A f t e r f o u r hours, the degree o f g r a f t i n g f o r v a r i o u s samples are i n the order of f i b r o u s carboxymethyl c e l l u l o s e cellulose hydroxyethyl c e l l u l o s e ethyl cellulose methyl c e l l u l o s e powdered carboyxmethyl c e l l u l o s e acetyl cellulose. Powdered carboxymethyl c e l l u l o s e and a c e t y l c e l l u l o s e showed a r a t h e r low degree of g r a f t i n g . However, the g r a f t i n g e f f i c i e n c y f o r these samples v a r i e d . A f t e r four hours of r e a c t i o n , they are i n the order of f i b r o u s carboxymethyl c e l l u l o s e hydroxy ethyl cellulose methyl c e l l u l o s e powdered carboxymethyl cellulose ethyl cellulose cellulose acetyl cellulose. When carboxymethyl c e l l u l o s e and hydroxyethyl c e l l u l o s e were used as the s u b s t r a t e s , the g r a f t i n g e f f i c i e n c y was over 90%, i n d i c a t i n g that fewer homopolymers were produced. I t i s of great i n t e r e s t t o observe that e t h y l c e l l u l o s e , c e l l u l o s e and a c e t y l c e l l u l o s e , which were all d i s p e r s e d i n the g r a f t i n g m i x t u r e , e x h i b i t e d low g r a f t i n g e f f i c i e n c y , whereas carboxy methyl c e l l u l o s e , h y d r o x y e t h y l c e l l u l o s e and methyl c e l l u l o s e , which were d i s s o l v e d i n the g r a f t i n g s o l u t i o n , e x h i b i t e d h i g h g r a f t i n g e f f i c i e n c y . These f i n d i n g s suggest that g r a f t i n g


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1


300

Irradiation Time (h)

Figure 8. Degree of grafting for cellulose and cellulose derivatives initiated by UV light of λ y 280 nm. Key: a, fibrous carboxymethylcellulose; b, cellulose; c, hydroxyethylcellulose; d, ethylcellulose; e, methylcellulose; f, powdered carboxy methylcellulose; g, acetylcellulose.




114


Figure 9. Grafting efficiency for cellulose and cellulose derivatives initiated by UV light of λ 280 nm. Key: a,fibrouscarboxymethylcellulose; b, hydroxyethylcellulose; c, methylcellulose; d, powdered carboxymethylcellulose; e, ethylcellulose; f, cellulose; g, acetylcellulose.



8.

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r e a c t i o n c a r r y i n g out i n a homogeneous system achieves a high degree of g r a f t i n g w i t h l e s s homopolymer formation. The g r a f t i n g r e a c t i o n s are not favored i n a heterogeneous system and a h i g h degree of homopolymer formation i s l i k e l y to occur. However, when the g r a f t i n g r e a c t i o n s were c a r r i e d out u s i n g u l t r a v i o l e t l i g h t of λ 254 nm, the degree of g r a f t i n g (Figure 10) and g r a f t i n g e f f i c i e n c y (Figure 11) were r a t h e r low f o rallsamples, i m p l y i n g that a l a r g e amount of homopolymer was formed. This may be a s c r i b e d to the shorter wavelengths and higher energy i n v o l v e d , which created g r e a t e r amounts of f r e e r a d i c a l s i n c e l l u l o s e and c e l l u l o s e d e r i v a t i v e s . Most of the low molecular f r e e r a d i c a l s generated from the samples are l i k e l y t o undergo a homopolymerization r e a c t i o n . As a r e s u l t , the g r a f t i n g e f f i c i e n c y i s decreased. Conclusions Based on the ESR and g r a f t c o p o l y m e r i z a t i o n r e a c t i o n s studied on c e l l u l o s e and p a r t i c u l a r l y on c e l l u l o s e d e r i v a t i v e s , the f o l l o w i n g conclusions may be drawn: 1. Free r a d i c a l s were generated i n c e l l u l o s e and c e l l u l o s e d e r i v a t i v e s i r r a d i a t e d w i t h u l t r a v i o l e t l i g h t of λ 254 nm and λ 280 nm. More f r e e r a d i c a l s were generated by u s i n g the former l i g h t due to the shorter wavelength, i . e . , stronger energy of the l i g h t . S e v e r a l types of f r e e r a d i c a l s were generated i n c e l l u l o s e due to chain s c i s s i o n , dehydrogenation and dehydroxymethylation r e a c t i o n s ; whereas f r e e r a d i c a l s generated i n c e l l u l o s e d e r i v a t i v e s , namely, c a r b o x y m e t h y l c e l l u l o s e , methyl c e l l u l o s e , e t h y l c e l l u l o s e , hydroxymethyl c e l l u l o s e and a c e t y l c e l l u l o s e , were by and l a r g e due to the cleavage of the s u b s t i t u t e d s i d e chains. G r a f t i n g r e a c t i o n s of c e l l u l o s e took p l a c e a t the main backbone, whereas g r a f t i n g r e a c t i o n s of c e l l u l o s e d e r i v a t i v e s took p l a c e a t the s u b s t i t u t e d s i d e chains. 2. Free r a d i c a l s i n c e l l u l o s e and c e l l u l o s e d e r i v a t i v e s by u l t r a v i o l e t l i g h t of λ 254 nm and λ 280 nm were capable of i n i t i a t i n g g r a f t i n g r e a c t i o n s . A h i g h degree of g r a f t i n g e f f i c i e n c y , that i s , low degree of homopolymer formation, was observed from samples u s i n g u l t r a v i o l e t l i g h t of λ 280 nm. Due to the shorter wavelength, h i g h energy i n v o l v e d from the l i g h t of λ 254 nm, although more f r e e r a d i c a l s were generated from the s u b s t r a t e s , they were unfavorably p a r t i c i p a t i n g i n the homopolymer formation r e a c t i o n . 3. G r a f t i n g r e a c t i o n s c a r r i e d out i n the homogeneous medium f o r carboxymethyl c e l l u l o s e , methyl c e l l u l o s e , and h y d r o x y e t h y l c e l l u l o s e , always achieved higher degree of g r a f t i n g e f f i c i e n c y than those samples such as c e l l u l o s e , e t h y l c e l l u l o s e and a c e t y l c e l l o s e , i r r a d i a t e d i n the heterogeneus medium.



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Figure 10. Degree of grafting for cellulose and cellulose derivatives initiated by UV light of λ y 254 nm. key: a, fibrous carboxymethylcellulose; b, ethylcellulose; c, methylcellulose; d, cellulose; e, powdered carboxymethylcellulose; f, hydroxyethylcellulose; g, acetylcellulose.


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100

0

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Figure 11. Grafting efficiency for cellulose and cellulose derivatives initiated by UV light of λ 254 nm. Key: a, fibrous carboxymethylcellulose; b, cellulose; c, powdered carboxymethylcellulose; d, methylcellulose; e, ethylcellulose; f, hydroxyethylcellulose; g, acetylcellulose.


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Literature Cited 1. 2. 3. 4. 5. Downloaded by CORNELL UNIV on July 22, 2016 | http://pubs.acs.org Publication Date: June 18, 1982 | doi: 10.1021/bk-1982-0187.ch008

6. 7. 8. 9. 10. 11. 12. 13.

14. 15. 16.

Bardhan, K.; Mukhopadhyay, S.; Chatterjee, S. R. J. Polym. Sci. Polym. Chem. Ed. 1977, 15, 141. Mukhopadhyay S.; Prasad J.; Chatterjee, S. R. Makromol Chem. 1975, 176, 1. Hebeish, Α.; Kantouch Α.; El-Rafie, M. H. J . Appl. Polym. Sci. 1977, 15, 11. Kantouch, Α.; Hebeish, Α.; El-Rafie, M. H. Europ. Polym. J. 1970, 6, 1575. Sadhakar, D.; Srinivasan, K.S.V.; Joseph, R. T.; Santappa, M. J. Appl. Polym. Sci. 1979, 23, 2923. Srinivasan, K.S.V.; Hon, D.N.-S.; Santappa, M. This volume, p.155. Demint, R. J.; Arthur, J. C., Jr.; McSherry, F. Textile Res. J. 1961, 31, 821. Wellons, J. D.; Williams, J . L.; Stannett, V. J. Polym. Sci. Part A, 1967, 5, 1341. Guthrie, J. T.; Huglin, M. B.; P h i l l i p s , G. O. Europ. Polym. J . 1972, 8, 747. Hon, D.N.-S. J. Appl. Polym. Sci. 1979, 23, 3591. Hon, N.-S. J. Polym. Sci. Polym. Chem. Ed. 1975, 13, 1347. Hon, N.-S. J. Polym. Sci. Polym. Chem. Ed. 1975, 13, 2653. Hon, D.N.-S. Photochemical Degradation of Lignocellulosic Materials i n Development i n Polymer Degradation - 3 (N. grassie, ed.), Applied Science Publishers, Essex, England, 1981, pp. 229-281. Hon, N.-S. J. Polym. Sci. Polym. Chem. Ed. 1976, 14, 2497. Fenrick, H. W.; Willard, J . E. J. Amer. Chem. Soc. 1963, 85, 3731. Hon, N.-S. J. Polym. Sci. Polym. Chem. Ed. 1977, 15, 725.

RECEIVED December 24,

1981.


Photoinduced Grafting Reactions in Cellulose and Cellulose Derivatives

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