Photochemical Grafting on Wood Cellulose - American Chemical Society

7 Photochemical Grafting on Wood Cellulose

Downloaded by CALIFORNIA INST OF TECHNOLOGY on November 16, 2017 | http://pubs.acs.org Publication Date: June 18, 1982 | doi: 10.1021/bk-1982-0187.ch007

J. P. FOUASSIER Laboratoire de Photochimie Générale, Equipe de Recherche Associée au CNRS, Ecole Nationale Supérieure de Chimie, 68093 Mulhouse Cedex, France

UV light induced grafting onto wood cellulose i s re ported for several vinyl monomers. The reaction i s i n i tiated by free radical initiators such as phenylacetophenone and benzophenone derivatives. Percent graf ting-time conversion curves are determined as a func tion of the i n i t i a t o r s , monomers, pulps and additives. Additional typical results obtained i n IR spectros copy, GPC and thermal analysis are reported. A discus sion about the use of a photochemical procedure i n ob taining cellulose graft copolymers i s presented. 1. INTRODUCTION Photochemical and photophysical processes i n c e l l u l o s e and r e l a t e d compounds have r e c e i v e d considerable a t t e n t i o n during the l a s t decades, r e s u l t i n g i n research work concerned w i t h the improvement o f c e l l u l o s i c m a t e r i a l s v i a p h y s i c a l and chemical m o d i f i c a t i o n s . One method was t o apply a copolymer between the c e l l u l o s e and a s y n t h e t i c polymer which are g e n e r a l l y g r a f t e d by f r e e radical reactions. Two routes can be explored w i t h a view t o modify the surface p r o p e r t i e s of c e l l u l o s i c s . The f i r s t one i n v o l v e s chemical react i o n s i n v o l v i n g the f u n c t i o n a l groups o f c e l l u l o s e . The second route can be achieved through i r r a d i a t i o n o r thermal g r a f t i n g of monomers onto c e l l u l o s e . Several r a d i c a l r e a c t i o n s have been e x t e n s i v e l y s t u d i e d as a f u n c t i o n o f the e x c i t a t i o n e.g. γ i r r a d i a t i o n , U.V. i r r a d i a t i o n , redox chemical i n i t i a t o r s , h e a t i n g , d y e - s e n s i t i z e d r e a c t i o n . Some of these i n v e s t i g a t i o n s are reported i n t h i s volume. U n t i l r e c e n t l y , few s t u d i e s o f UV l i g h t induced g r a f t i n g o f c e l l u l o s i c s have been reported (e.g.1-7 and references t h e r e i n ) . I t f u r t h e r appears that s e n s i t i z e d p h o t o g r a f t i n g r e a c t i o n s are more a t t r a c t i v e , since longer wavelengths o f e x c i t a t i o n may be used, thus i n c r e a s i n g the p o s s i b i l i t y o f a p o t e n t i a l l y v a l u a b l e ©

0097-6156/82/0187-0083$6.00/0 1982 American Chemical Society

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

84

GRAFT COPOLYMERIZATION OF LIGNOCELLULOSIC FIBERS


commercial e x p l o i t a t i o n . Moreover, l e s s degradation of c e l l u l o s e i s obtained. However, t h i s k i n d of r e a c t i o n r e q u i r e s a knowledge of the p h o t o r e a c t i v i t y of the i n i t i a t o r w i t h respect to the che m i c a l nature of the monomer and the macromolecule. Our previous papers i n t h i s f i e l d d e a l t w i t h p h o t o s e n s i t i z e d f r e e r a d i c a l generation on c e l l u l o s e (8) and photochemical g r a f t i n g of v a r i o u s monomers i n presence of a l a r g e v a r i e t y of i n i t i a t o r s onto c o t t o n (9) and s t a r c h (10). Several parameters of the g r a f t i n g r e a c t i o n have been i n v e s t i g a t e d : i n c i d e n t l i g h t i n t e n s i t y , i r r a d i a t i o n wavelength, temperature, oxygen e f f e c t , i r r a d i a t i o n time, p h o t o - i n i t i a t o r c o n c e n t r a t i o n , monomer c o n c e n t r a t i o n and presence of a d d i t i v e s . The r e s u l t s obtained make i t p o s s i b l e to determine the most s u i t a b l e c o n d i t i o n s f o r g r a f t i n g and to d i s c u s s the mechanism of r e a c t i o n . The present r e p o r t extends our work to the p h o t o g r a f t i n g of v a r i o u s monomers, using s e v e r a l p h o t o - i n i t i a t o r s , onto wood c e l l u l o s i c m a t e r i a l s . Moreover, i t gives the p o s s i b i l i t y to d i s c u s s some problems r e l a t e d to the photochemical g r a f t i n g . 2. EXPERIMENTAL a) M a t e r i a l s Several samples of commercial d i s s o l v i n g pulp from softwood were used : bleached pulp (whiteness 92 % ) , almost e n t i r e l y f r e e of l i g n i n , c o n t a i n i n g about 94 % α c e l l u l o s e (I) y paper pulp ( I I ) (whiteness : 91,5 %) ; mechanical y e l l o w pulp ( I I I ) ( c o n t a i n i n g l i g n i n ) , K r a f t Laponia pulp ( I V ) , whiteness : 92 % ) . Benzoin d e r i v a t i v e s and benzophenone d e r i v a t i v e s were commer c i a l products o f the highest p u r i t y grade. They a r e 2,2 - dimethoxy-2-phenyl acetophenone (DMPA), benzophenone (BP), 4-benzoylbenzoic a c i d (BBA), 3,3',4,4'-benzophenone and t e t r a c a r b o x y l i c dianhydride (BTCD). Methyl methacrylate (MMA) was washed w i t h a s o l u t i o n of so dium carbonate, d r i e d over calcium c h l o r i d e and d i s t i l l e d under reduced pressure and n i t r o g e n . A c r y l o n i t r i l e was washed w i t h s u l f u r i c a c i d (5 % ) , sodium carbonate (5 %) and w a t e r ; a f t e r d r y i n g , the monomer was d i s t i l l e d under reduced pressure and n i t r o g e n . Styrene was washed w i t h sodium hydroxyde (10 %) and water, d r i e d and d i s t i l l e d . THF was p u r i f i e d by washing and distillation. - Graft

copolymerization

The c e l l u l o s e sample was g e n e r a l l y t r e a t e d according to the procedure described p r e v i o u s l y ( 9 ) . I n some experiments, the c e l l u l o s e sample was t r e a t e d w i t h an aqueous s o l u t i o n of sodium hydroxide (17,6 %) f o r 2 h a t room temperature and washed w i t h water to n e u t r a l i t y f o r 24 h. The swollen sample was obtained after f i l t r a t i o n .


7.

FOUASSIER

85

Photochemical Grafting on Wood


In the p h o t o s e n s i t i z e d experiments, the c e l l u l o s e sample was t r e a t e d w i t h a s o l u t i o n of the i n i t i a t o r i n acetone f o r 1 h at room temperature and the solvent evaporated i n a i r . When t h i s k i n d of adsorption was not p o s s i b l e , the i n i t i a t o r was d i s s o l v e d i n THF and added to the reactant medium. G r a f t copolymerization was c a r r i e d out at a chosen temperatur r e , f o r a given time i n n i t r o g e n , by i r r a d i a t i n g r e a c t i o n c e l l s c o n t a i n i n g 80 ml of d i s t i l l e d water, O.5g of t r e a t e d or untreated c e l l u l o s e sample and a v a r i a b l e amount of monomer. The U.V. l i g h t source was a high pressure mercury lamp (HPK 125 W). For the s e n s i t i z e d experiments, s u i t a b l e wavelengths were chosen through a pass band f i l t e r centered around 366 nm. The i n c i d e n t l i g h t i n t e n s i t y was determined through actinometry measurements. T y p i c a l values were i n the range of 2 x l 0 p h o t o n s cm^s"* on the sample. The i r r a d i a t e d samples were e x t r a c t e d by r e f l u x i n g f o r 24 hours (we v e r i f i e d that subsequent e x t r a c t i o n d i d not modify the r e s u l t s ) w i t h the f o l l o w i n g s o l v e n t s , according to the monomer : acetone (methyl m e t h a c r y l a t e ) ; benzene ( s t y r e n e ) ; N,N-dimethylformamide ( a c r y l o n i t r i l e ) . 16

1

The percent g r a f t i n g i s considered (see d i s c u s s i o n ) as the weight i n c r e a s e of the d r i e d c e l l u l o s e sample a f t e r e x t r a c t i o n . The percent homopolymer i s c a l c u l a t e d as the r a t i o weight of homopolymer over the weight of o r i g i n a l monomer. 3. RESULTS AND

DISCUSSION

3.1. G r a f t i n g experiments a) Investîgation^of^the^general^ËEâïïÉÊËEË The r e s u l t s of the g r a f t copolymerization on c e l l u l o s e i n v a r i o u s c o n d i t i o n s are shown as a f u n c t i o n of the i r r a d i a t i o n time, i n i t i a t o r c o n c e n t r a t i o n , monomer c o n c e n t r a t i o n , presence of a d d i t i v e . Table I shows the e v o l u t i o n of the percent g r a f t i n g and percent homopolymer as a f u n c t i o n of the i r r a d i a t i o n time. A f a s t increase i n g r a f t i n g was observed f o r short i r r a d i a t i o n times whereas longer ones r e s u l t e d i n a decreased percent g r a f t i n g . Table I I shows an optimum value of the i n i t i a t o r c o n c e n t r a t i o n . The percent g r a f t i n g may be expected to increase as a f u n c t i o n of the amount of i n i t i a t o r up to a c r i t i c a l c o n c e n t r a t i o n . At higher c o n c e n t r a t i o n s , the percent g r a f t i n g decreases presumably i n connection w i t h secondary r e a c t i o n s induced by the i n i t i a t o r radicals. The percent g r a f t i n g and the percent homopolymer are a funct i o n of the monomer c o n c e n t r a t i o n (Table I I I ) . An optimum value i s obtained. The maximum of the percent g r a f t i n g i s s t r o n g l y dependent on the comparative values of the MMA and i n i t i a t o r concentrations.


86


Table I : Percent g r a f t i n g and percent homopolymer as a ~" f u n c t i o n of time. MMA : 5 g ; THF : 5 c m ; sample ( I ) : 0 , 5 g ; water : 8 0 g ; λ = 365 n m ; Τ = 20°C.


3

Initiator

BP

DMPA

BBA

BBA

BTCD

Initiator

Irradiation

amount (mg)

time (h)

% grafting

% homopolymer

-

50

1

13,4

50

2

28,2

50

3

12

50

1

14,4

-

50

2

30,2

10,2

50

3

10,4

13,6

50

1

7,4

50

2

23

-

50

3

16

-

25

1

21,6

-

25

lh30

29,2

2,2

25

2

30,8

8,9

25

3

36,4

9,7

25

4

52,2

20,8

25

5hl5

30

54

25

6

38

61,5

50

1

47,4

-

50

2

57,2

30,6

50

3

26

57,5

1,5


7.

FOUASSIER


87

Table I I : Percent g r a f t i n g versus i n i t i a t o r amount; sample ( I ) ; monomer : MMA; i n i t i a t o r : BTCD; water (80 cm ) + THF (5 cm ) 3


Initiator amount (mg) 5 10 25 50

% grafting 12 40 81 57

3

Irradiation time (h)

% homopolymer

2 2 2 2

-

25,3 30,6

Table I I I : Percent g r a f t i n g versus t i m e ; monomer : MMA;

Initiator amount (mg)

Time (h)

initiator

: BTCD

Monomer amount (g)

%

grafting

25

1

1

0

25

1

2,5

0

25

1

5

4 2

25

2

1

25

2

2,5

19,2

25

2

5

40

25

3

1

17,4

25

3

2,5

30

25

3

5

55,4

25

4

5

34

50

1

1

2

50

1

2,5

36,4

50

1

5

47,4

50

2

5

57,2

50

3

5

26



88


When u s i n g p h o t o i n i t i a t o r s such as phenyl acetophenone d e r i v a t i v e s , a d d i t i o n of an hydrogen donating s o l v e n t (Table IV) to the system improved u l t i m a t e l y the percent g r a f t i n g and, i n a d d i t i o n , the c o n c e n t r a t i o n s of i n i t i a t o r r e q u i r e d were lower. Moreover, the presence of THF i s necessary w i t h benzophenone d e r i v a t i v e s . These r e s u l t s are i n agreement w i t h s i m i l a r observations w i t h respect to MMA p o l y m e r i z a t i o n i n s o l u t i o n ; i n f a c t , the r a t e of p o l y m e r i z a t i o n was enhanced i n the presence of THF. However, a d d i t i o n of amine molecules ( t r i e t h y l a m i n e TEA) not i n c r e a s e the percent g r a f t i n g .

did

b) G r a f t i n g i £ t h e D r e s e n c e o f v a r i o u s i n i t i a t o r s The r e s u l t s of the g r a f t c o p o l y m e r i z a t i o n of MMA onto c e l l u l o s e i n the presence of v a r i o u s water i n s o l u b l e i n i t i a t o r s are shown i n F i g u r e 1 which d i s p l a y the time dependence on the percent g r a f t i n g . In a general way, one observes a r a p i d i n c r e a s e of the percent g r a f t i n g w i t h i n two hours of i r r a d i a t i o n w i t h wavelength of 365 nm. For longer i r r a d i a t i o n times, the percent g r a f t i n g curves l e v e l o f f ; i n some cases the percent g r a f t i n g decreases. This was a l s o reported i n the previous paper ( 9 ) . At f i r s t s i g h t , benzophenone compounds appear to be the most e f f i c i e n t p h o t o - i n i t i a t o r f o r 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 , whereas phenylacetophenone d e r i v a t i v e s do not rank among the b e s t . In comparison, 2,2-dimethoxy-2-phenylacetophenone seems even p o o r l y e f f i c i e n t , although t h i s compound i s g e n e r a l l y considered as very r e a c t i v e i n UV c u r i n g (11) or i n s o l u t i o n photopolymeriz a t i o n of v i n y l monomers (12).

Table i y ; T y p i c a l e f f e c t s ot the amount of THF on the percent g r a f t i n g . Sample I ; monomer : MMA; water : 80 cm . 3

Initiator

Initiator amount (mg)

THF amount (cm )

max

% grafting

3

DMPA

50 50 25 25

0 5 0 5

25 30 18 25

BBA

25 25

0 5

0 52



7.

FOUASSIER


89

Figure 1. Percent grafting vs. time. The monomer was MM A; the initiators were BP {!), DMPA (2), BBA (3), and BTCD (4).


GRAFT COPOLYMERIZATION

OF LIGNOCELLULOSIC FIBERS


A d d i t i o n of THF i s necessary w i t h benzophenone d e r i v a t i v e s and enhances the e f f i c i e n c y of phenyl acetophenone d e r i v a t i v e s as shown by the f o l l o w i n g r e a c t i o n s (the photochemistry of these compounds a r e very w e l l known i n homogeneous s o l u t i o n s ) :

Benzophenone d e r i v a t i v e s : hv

R

-

S

^ Τ

(1)

1

[- c - \ + Cell*

ketyl radical

(2)

Cell-H \ ' OH o J

ketyl radical

+

(3)

THF*

THF DMPA

0 R = R

f

= OCH

α-cleavage

3

°+THF

R

^THF*

+

(4)

0

(S)


7.

FOUASSIER


91

A b e t t e r s o l u b i l i z a t i o n of the i n i t i a t o r i n the mixture waterTHF may a l s o p l a y a part i n the improved e f f i c i e n c y .


c ) Graf t i n g o f various2°-S2îSÈI£

2DË2£ËIIHI2ËÈ

The experiments were c a r r i e d out w i t h three monomers. Some t y p i c a l r e s u l t s are reported i n Table V. I n a general way, v a r i ous percent g r a f t i n g s were obtained depending on the monomeri n i t i a t o r couple. The percent g r a f t i n g may be adjusted to a given value by m o d i f i c a t i o n of the experimental c o n d i t i o n s . Table V : T y p i c a l maximum percent g r a f t i n g as a f u n c t i o n of the nature of the i n i t i a t o r , monomer and pulp. % grafting

Initiator

Monomer

(I)

BTCD (25 mg)

MMA (5g)

40 %

(I)

BTCD (50 mg)

MMA (5g)

57

(I)

BTCD (25 mg)

AN (3g)

13

(ID

BTCD (25 mg)

MMA (5g)

60

(III)

BTCD (25 mg)

MMA (3g)

20

(IV)

DMPA (25 mg)

Styrene(2g)

46

Sample

The d i f f e r e n c e s i n r e a c t i v i t y are due presumably to s p e c i f i c quenching of the r e a c t i v e species by the monomer and to the s p e c i f i c r e a c t i v i t y between the monomer and the r a d i c a l s created upon the c e l l u l o s i c backbone. As reported i n l i t e r a t u r e (13) the i r r a d i a t i o n of a c e l l u l o s e sample a t 254 nm r e s u l t s i n g l u c o s i d i c bond s c i s s i o n and C - H bond s c i s s i o n . Recent r e s u l t s i n p h o t o s e n s i t i z e d experiments (15) show that the same behaviour can be obtained : h

Initiator

v

.

•

.

.

.

excited i n i t i a t o r £ C e l l u l o s e sample

Energy t r a n s f e r or H a b s t r a c t i o n



92

thus, g r a f t copolymer should occur through : - recombination β

THF

Μ +

reaction

'Cell


- glucosidic scission propagation, eg :

Cell*

+ M

- occlusion

•

• THF

M - Cell

or C-H bond scission,

C e l l - M*

initiation,

•Cell

of homopolymer in the cellulosic

* chain

d) Graftingontovarious£ul£S Recent t y p i c a l r e s u l t s are represented i n F i g u r e 2 and Table V. They show a strong i n f l u e n c e o f the nature o f the p u l p ; s p e c i a l l y i n the r a t e of the r e a c t i o n (Figure 2 ) . More r e s u l t s are needed f o r a d e t a i l e d d i s c u s s i o n of these e f f e c t s . 3.2.

A n a l y s i s of the g r a f t e d samples a)

Thermalanal^sis

The r e s u l t s are reported i n F i g u r e 3 and show the t y p i c a l behaviour of the g r a f t e d sample compared t o that o f PMMA and c e l l u l o s e . From the experimental curves, i t i s concluded that the polymer c h a i n i s c h e m i c a l l y l i n k e d onto the c e l l u l o s i c backbone. In curve B, the f i r s t and second peaks correspond t o the unsatu r a t e d c h a i n end and t o the saturated c h a i n end of the polymer r e s p e c t i v e l y . I n curve C., one observes that the peak corresponding to polymer chains terminated through d i s p r o p o r t i o n have d i s a p p e a r e d ; t h i s p o i n t s out the f a c t that the c e l l u l o s i c macromolecules could be c r o s s l i n k e d by PMMA c h a i n s . b) InfraredS£ectrosco££ A t y p i c a l IR spectrum i s shown by F i g u r e 4. One can see the d i f f e r e n c i a l spectrum between c e l l u l o s e and a blend homopolymer c e l l u l o s e . The IR spectrum of the g r a f t e d sample e x h i b i t s the c h a r a c t e r i s t i c bands o f c e l l u l o s e and PMMA. Moreover, a p l o t o f the IR absorbance shows that the e x t i n c t i o n c o e f f i c i e n t o f the blends are higher than that o f the g r a f t e d copolymer (Figure 5 ) . These two arguments are i n favour of the presence o f c h e m i c a l l y l i n k e d PMMA c h a i n s . c) A n a l y j i s o f t h e g r a f t s The g r a f t e d polymer was separated from the c e l l u l o s e by h y d r o l y z i n g w i t h 72 % H^SO^. The molecular weights were determined by GPC a f t e r n e u t r a l i z a t i o n , washing and d r y i n g . The molecular weights are g e n e r a l l y high ( T y p i c a l l y 900 000) and the p o l y d i s -



FOUASSIER


93

Figure 2. Percent grafting vs. time. The initiator was BTCD (25 mg); the monomer was MMA (3 g); and the three pulps 1, II, III (1-3).




94

Temperature

300

350

400 °C

Figure 3. Typical DTG thermogram obtained in thermal analysis. Key: A, cellulose; B, PMMA;C.,graft copolymer.



Figure 4.

A: IR spectrum of the graft copolymer; B: differential IR spectrum of PMMA. Continued.



F/gwre 4.

Continued. C: IR spectrum of cellulose. D: IR spectrum of VMMA.


w

03

Β

•Π

ο

I

1

Η cj r

ο ο

r S

hd

ο

δ

>

Ν

2

M

κ!

r

hi Ο

8

H

>

Ο

ON

FOUASSIER


97


7.

%PMMA

Figure 5.

1

IR absorbances (v = 1730 cm' ) as a function of PMMA content in a graft sample (O) and in a blend copolymer (A).


98


p e r s i t y has the usual value obtained i n r a d i c a l homopolymerizat i o n . I t seems that there are few l i n k a g e s between the polymer and the c e l l u l o s i c c h a i n . Complete r e s u l t s on the a n a l y s i s of the g r a f t s w i l l be published l a t e r (14).


4. DISCUSSION AND

CONCLUSION

The aim of t h i s work was to o b t a i n g r a f t copolymers of c e l l u l o s e w i t h monomers and to study the d i f f e r e n t p o s s i b i l i t i e s of a photo-induced r a d i c a l r e a c t i o n . The use of UV l i g h t seems very promising, due to the l a r g e p o s s i b l e v a r i e t y of experimental g r a f t i n g c o n d i t i o n s . The r e s u l t s presented i n t h i s paper appeared i n the p e r s p e c t i v e of a s e r i e s d e a l i n g w i t h an i n v e s t i g a t i o n of the g r a f t i n g r e a c t i o n s onto n a t u r a l s u b s t r a t e s . The f o l l o w i n g p o i n t s have been demonstrated (a more d e t a i l e d i n v e s t i g a t i o n w i l l be published l a t e r ( 14)): a) The photochemical g r a f t i n g of monomers onto commercial paper pulps can be developed as a l a b o r a t o r y process. In t h i s case, the t r e a t e d pulp corresponds to O.5g dry weight. The expe r i m e n t a l procedure i n v o l v e s the i r r a d i a t i o n of a heterogeneous suspension of pulp and monomer i n water. b) As shown i n previous experiments (9) conducted w i t h other s u b s t r a t e s , the g r a f t i n g r e a c t i o n i s dependent on a l o t of f a c t o r s : experimental c o n d i t i o n s (wavelength of i r r a d i a t i o n , i n c i dent l i g h t i n t e n s i t y , temperature, oxygen, p H . . . ) , monomer, i n i t i a t o r , pulp, a d d i t i v e . . . c) In such experiments, the r a t e s of g r a f t i n g (% g r a f t i n g mn" ) can reach values about 1 % mn" f o r a power d e n s i t y of i l l u m i n a t i o n i n the range of 15 mW cm"" at λ = 366 nm. 1

1

2

d) P r e l i m i n a r y r e s u l t s i n thermal a n a l y s i s and i n f r a red spectroscopy suggest that the g r a f t e d sample contains polymer chains which are c h e m i c a l l y l i n k e d onto the c e l l u l o s i c backbone. Extensive works (14) are now i n progress to o b t a i n complete informations upon the number of g r a f t s , the number of s c i s s i o n s and the DP of the g r a f t s as a f u n c t i o n of the v a r i o u s c o n d i t i o n s of g r a f t i n g . A d d i t i o n n a i data w i l l be a l s o provided by i n f r a red and Raman spectroscopy, E.S.C.A. and thermal a n a l y s i s . Other works are a l s o c a r r i e d out upon the a n a l y s i s of the p h y s i c a l p r o p e r t i e s of the g r a f t e d samples. Last but not the l e a s t , we would l i k e to d i s c u s s some of important p o i n t s which can be pointed out i n the use of a photo chemical procedure i n o b t a i n i n g g r a f t copolymers of l i g n o cellulosic materials. a) The f i r s t problem i s r e l a t e d to the d i s c u s s i o n concerning



7.

FOUASSIER


99

the problem between a g r a f t copolymer sample and a sample c o n t a i ning o c c l u s i o n of homopolymer i n the s u b s t r a t e without chemical bonding. I t seems that homopolymerization predominates i n a presence of a p h o t o - i n i t i a t o r i n c o n t r a s t o f a d i r e c t UV e x c i t a t i o n o f the s u b s t r a t e . (However, the p h o t o s e n s i t i z e d g r a f t i n g i s more a t t r a c t i v e since i t gives the p o s s i b i l i t y to s e l e c t the c h a r a c t e r i s t i c s of the samples (9). I n our case, we show that the polymer, remaining even a f t e r a d r a s t i c solvent e x t r a c t i o n , i s s t r o n g l y f i x e d on the c e l l u l o s e . In many experiments, i t appears that such d r a s t i c solvent e x t r a c t i o n can remove the major part of the s y n t h e t i c polymer, showing that the g r a f t e d polymer presents, i n p o i n t of f a c t , a good "adhesive b o n d a b i l i t y . However, i n the case of surface m o d i f i c a t i o n , a heavy g r a f t i n g i s not necessary and the degre of permanence i s a f u n c t i o n o f the i n s o l u b i l i t y of the homopolymer i n the s o l v e n t s used i n the common course of subsequent treatments. So i t can be i n f e r r e d that t h i s n o t i o n of g r a f t i n g may be dependent on the e f f i c i e n c y of the solvent e x t r a c t i o n . 11

b) The second problem i s r e l a t e d to the improved p h y s i c a l p r o p e r t i e s of the g r a f t e d pulp as a f u n c t i o n of the % g r a f t i n g and the c h a r a c t e r i s t i c s of the g r a f t s (DP, molecular weight, number of g r a f t s , number o f bonds between the c e l l u l o s e and the g r a f t e d polymer. In a general way, i t i s known that a r a d i c a l type p o l y m e r i z a t i o n y i e l d s very long growing chains and consequent l y , the DP a r e high and the number o f g r a f t s (G) i s low. The question i s to have a s u b s t a n t i a l amount of g r a f t e d samples i n order to ( i ) o b t a i n the DP and G dependence on the experimental c o n d i t i o n s , t o ( i i ) determine the p h y s i c a l p r o p e r t i e s of the samples and to ( i i i ) t r y t o e s t a b l i s h a s t r u c t u r e property r e l a t i o n s h i p . This type of work i s important s i n c e i t could d e f i n e a d d i t i o n a l experiments i n which the DP of the g r a f t s would be adjusted. However, many experimental r e s u l t s (e.g.2) support the f a c t that an improvment o f the p h y s i c a l p r o p e r t i e s can be a c h i e ved through g r a f t c e l l u l o s e even w i t h long chain polymers. c) The t h i r d problem concerns the t r a n s p o s i t i o n of these experiments to a p i l o t s c a l e or an i n d u s t r i a l process. We are t r y i n g t o develop a photo chemical r e a c t o r i n which pulp sample of about 50g can be t r e a t e d . Our f i r s t attempts do not always y i e l d to s u c c e s s f u l l r e s u l t s and up to now, the reasons of that are not very c l e a r (even i f we take i n t o account the problem of l i g h t penetration). In c o n c l u s i o n , we would l i k e to dwell on the f a c t that the present study demonstrates the f e a s a b i l i t y of a photochemical treatment, through a g r a f t i n g r e a c t i o n , o f a c e l l u l o s i c s u b s t r a t e . I t i s obvious that the r e s u l t s cannot be e a s i l y e x t r a p o l a t e d to the case o f an i n d u s t r i a l process of surface m o d i f i c a t i o n of the pulps. In f a c t , due to i t s low p e n e t r a t i o n , UV l i g h t can be



100


reserved i n s u r f a c e treatment, d u r i n g o r a f t e r the making o f paper. However, we are convinced that such a study i s o f i n t e r e s t f o r the understanding of processes such those o c c u r i n g i n the photopolymerization o f d i o r t r i f u n c t i o n n a l monomers i n order to get c o a t i n g s f o r paper o r wood (14). Aknowledgments - The work i s supported i n p a r t by the Centre N a t i o n a l de l a Recherche S c i e n t i f i q u e and the Centre Technique du P a p i e r o f Grenoble. C o l l a b o r a t o r s who a r e a c t i v e l y c o n t r i b u t i n g t o t h i s program a r e : R. SALVIN and L. TRAN THAN.

Literature

cited

1. GARNETT, J.L., ACS symposium series 1977, 48, 334 2. REINHARDT, R.M. ; HARRIS, J.Α., Text. Res.J 1980, 1, 139 3. OGIWARA, Y; HAYASE, Κ; KUBOTA, Η; J . Appl. Polym. S c i . 1979, 23, 1 4. GUTHRIE, J.T., Prog. Polym. Sci., 1978, 6, 31 5. TAKAHASHI, A; TAKAHASHI, S; Kobunshi Ronbunshu 1980, 37, 151 6. HEBEISH, A; GUTHRIE, J.T. "The chemistry and technology of cellulosic copolymers" Springer Verlag N.Y. 1981 7. STANNET, V.T. ; MEMETEAT, Τ J . Polym. Sci. Polym. Symposia 1978, 64, 57 8. MERLIN, A; FOUASSIER, J.P. Angew. Makromol. Chem. 1980, 86, 109 9. HEROLD, R; FOUASSIER, J.P. Angew. Makromol. Chem. 1980, 86, 123 10. HEROLD, R; FOUASSIER, J.P. Starch 1981,3,90 11. HEINE, H.G. ; RUDOLPH, Η ; ROSENKRANZ, H.J. J . Polym. S c i . Appl. Polym. Symp. 1975, 26, 157 12. MERLIN, A ; FOUASSIER, J.P. J . Chim. Phys. 1981, 78, 3 13. HON, N.S. J . Polym. Sci., Polym. Chem. Ed. 1976,14,14 14. LONG, T.T. ; SALVIN, R; FOUASSIER, J.P. to be published 15. HEROLD, R. ; BENDAIKHA, Τ; FOUASSIER, J.P. ; DECKER, C unpublished results. RECEIVED December 17,

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Photochemical Grafting on Wood Cellulose - American Chemical Society

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