Grafting cellulose conversion

UV light induced grafting onto wood cellulose is reported for several vinyl monomers. The reaction is initiated by free radical initiators such as phenylace-tophenone and benzophenone derivatives. Percent grafting-time conversion curves are determined as a function of the initiators, monomers, pulps and additives. Additional typical results obtained in IR spectroscopy, GPC and thermal analysis are reported. A discussion about the use of a photochemical procedure in obtaining cellulose graft copolymers is presented. 

The grafting process gives reproducible conversion and grafting efficiency (Table I) both for ethyl cellulose (EC, DS=0.60) and grease-proof pulp (GP). The measured grafting efficiency for the EC samples is lowered by a partial water solubility of the substrate. 

Grafting reactions were also carried out in organic solvents. Fig. 4 shows the polymerization of methyl methacrylate in the fifteen species of organic solvents having various dielectric constants and water systems without cellulose. The numbers in the figure express the dielectric constants of the solvent in the order. As the organic solvent (No. 1-6) with the dielectric constants around 2 was added, the conversion became 0-11% and the value of dioxane (No. 2), which is soluble in water, was the highest. As the solvents with dielectric constants above 8 were used, the conversion increased, except cyclohexane (No. 11). 

The same authors (5) showed also in another work that the presence of larger amounts of lignin in bisulfite pulps may have a favourable effect on grafting polyacrylonitrile using the cellulose xanthate-hydrogen peroxide redox system to initiate the copolymerization reaction. The plots of the total conversion as well as of polymer loading show a minimum centered around approximately 15% of lignin. 

Considering that both grafting efficiency as well as conversion in this study shows optimal values for pH 4 - 7, we have used pH 5 which favors the attachment of ferrous ion on partial cellulose xanthate and other ion exchange groups present. (The term "partial cellulose xanthates" stands for xanthates bound statistically to any component of the pulp (cellulose, hemicellulose, lignin). The importance of the presence of ferrous ions on grafting is shown in Diagrams I-II-III, which show reaction mechanism sug-... 

Dependence of grafting efficiency and monomeric conversion on reaction time are shown in Figures 2 and 3. It is shown that a rapid polymerization takes place during the first 2 hrs of the reaction the rate then decreases, and after about 8 hrs the reaction almost ceases. It is interest to note that grafting efficiency is directly proportional to time during the first 2 hife of the reaction and after that remains constant at about the 85% level. It seems that the homopolymer formation (see diagrams II-III) is remakably suppressed at pH 5 at which there is not very much ferrous ion in solution to form free OH radical and polymerization takes place mostly on partially xanthated cellulose. 

Cellulose constitutes a ubiquitous and renewable natural material that has great potential for chemical conversion into high-quality adhesive products. The resurrection of research and development of cellulose derivatives, such as cellulose esters and ethers, cellulose graft-copolymers, and cellulose polyblends, has instituted new avenues for adhesive applications. There is little doubt that new solvent systems for cellulose have created the potential of developing uniform cellulose products with superior properties for adhesive applications. 

Polymer-analoguous conversion of polymer chains grafted to cellulose. 

This review deals with recent results on the structure and properties of cellulose graft copolymers depending on the structure of cellulose, its pretreatment and the conditions of grafting. Also discussed are polymer-analogous conversions involving grafted chains. 

Fig. 2. Effect of the number of grafted chains on conversion of cellulose. Grafting initiated by Curve 1 Fe2+ -H202 system average grafting rate Vav - 2%/min, curve 2 CC-Fea+ system Vav-40%/min, curve 3 CC-V5+ system Vav - 70%/min...

Polymer-Analogous Conversions of Functional Groups in Polymer Chains Grafted to Cellulose... 

The effect reported in 7,88) was attributed to the higher hydrophilicity of the graft copolymers as compared to the cellulose esters. The authors did not allow for the role played by the grafted polymer structure in these reactions. At the same time, it could be interesting to investigate the conversion of cyano groups in the graft copolymer and in PAN chains isolated from the copolymer so that their supramolecular and molecular structures would remain intact. 

The elucidation of the mechanism which accounts for the nitration behaviour of cellulose-PS graft copolymers, particularly the mutual influence of the copolymer components in polymer-analogous conversions, is a problem of great scientific interest. 

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