Cellulosic graft polymers

This chapter reports successful initial efforts to bond wood in the presence of hydrophobic plastic material [polystyrene (PS)] using well-defined and tailored cellulose-polystyrene graft polymers as compatibilizers or interfacial agents. The synthesis of these tailored cellulose graft polymers is also presented. 

The potential use of cellulose graft polymers to compatibilize the linking of a natural polymer (wood) with a synthetic polymer (polystyrene) is based on... 

Results from the initial resin studied are also being employed in the development of additional experimental procedures. Plans are currently being drafted to prepare three-ply test specimens that are similar to the specimens used in the initial study, with the middle ply consisting of solid polystyrene. Comparing specimens with and without the graft polymers introduced to the ply interfaces should provide additional information on the ability of the cellulosic graft polymers to facilitate bonding between wood and plastic materials. If this approach proves successful, additional procedures will then be developed for the production of simple composite specimens. 

Most of the important syntheses of cellulosic graft polymers involve irradiation with high-energy beams. Ultraviolet and x-ray sources are sometimes used, but Co radiation is used most often (Chapiro, 1962). In an oversimplified manner, the synthesis can be described as follows (Chapiro, 1962, p. 600) ... 

Emulsion polymerizations of vinyl acetate in the presence of ethylene oxide- or propylene oxide-based surfactants and protective coUoids also are characterized by the formation of graft copolymers of vinyl acetate on these materials. This was also observed in mixed systems of hydroxyethyl cellulose and nonylphenol ethoxylates. The oxyethylene chain groups supply the specific site of transfer (111). The concentration of insoluble (grafted) polymer decreases with increase in surfactant ratio, and (max) is observed at an ethoxylation degree of 8 (112). 

Following the findings of Mino and Kaizerman [51] that ceric ion can form a redox system with cellulose, grafting onto various natural polymers has been carried out by the ceric ion method. In the case of cellulose, the reaction between ceric ion and cellulose occurs to produce active sites on cellulose in the following manner ... 

An effective method of NVF chemical modification is graft copolymerization [34,35]. This reaction is initiated by free radicals of the cellulose molecule. The cellulose is treated with an aqueous solution with selected ions and is exposed to a high-energy radiation. Then, the cellulose molecule cracks and radicals are formed. Afterwards, the radical sites of the cellulose are treated with a suitable solution (compatible with the polymer matrix), for example vinyl monomer [35] acrylonitrile [34], methyl methacrylate [47], polystyrene [41]. The resulting copolymer possesses properties characteristic of both fibrous cellulose and grafted polymer. 

The hydroxyl radicals formed may abstract hydrogen from the cellulose fiber substrate which gives grafting sites and subsequently grafted polymer with monomer present. The HO- radicals may also initiate homopolymerization. This means that reaction (17) is not specific for initiation of grafting. Another disadvantage is that the Fe + ions formed - if not carefully removed -may cause discoloration of the resulting product. 

The Ce + initiation of grafting and the products obtained from polysaccharides has been reviewed repeatedly5>6. Only some studies of the optimal grafting conditions for grafting of cellulose substrates will be treated here2°>29 30> The reactants should be added to the cellulose suspension in the order CeI,+ initiator and then vinyl monomer to increase the yield of grafted polymer. The optimum conditions are not only related to the pH of the reaction medium but to the relations between the Ce + concentra-... 

We have seen that lignin is a highly branched amorphous pol3rmer containing an extremely complex array of structures and that when in situ in the wood, it is a graft polymer with cellulose and hemicellulose to boot. Characterization of lignins thus becomes a problem. 

GOX (glucose oxidase), 631, 636, 637 GPC (unsaturated glycerophosphocholine), 737 GPO (l-glycerol-3-phosphate oxidase), 633 Graft polymers cellulose, 698 cross-linking initiators, 706 ozonized polymers, 622 Griesbaum co-ozonolysis, 1,2,4-tiioxane antimalarials, 1331... 

Condensation of an acrylic acid-cellulose graft copolymer with 5-amino-l,10-phe-nanthroline (233) has been utilized to provide polymer (234 Scheme 113) with the phenanthroline ligand oriented optimally for complexation (77MI11110). The polymer was described as exhibiting a strong sorption capacity for Co2+ and Cu2+ ions. 

The chemical methods for grafting polymer side chains onto cellulose backbone molecules make use of the following chemical mechanisms or techniques involving radicals ... 

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