EFFECT OF GAMMA IRRADIATION UPON CELLULOSE

The purified cotton linter and purified wood pulp were irradiated by gamma radiation at various doses, and the number-average degree of polymerization (DP) of each sample was determined according to the method worked out by Immergut et al. by the measurements of intrinsic viscosity. The log-log plots of the difference between the reciprocal of DP of the irradiated cellulose and that of the original cellulose against the radiation dose ranging from 5.2 x 10/sup 5/ to 1.1 x 10/sup 8/ roentgens gave a straight line, which indicated that the chain cleavage took place in proportion to R/sup 0.85/, R being the radiation dose. The rapid decrease in the leveling off DP with increasing dose suggested that the cleavage took place equally likely both in amorphous domains and in crystalline domains. The reduction in size of crystallites was shown by electron microscopic observation. The analysis by a mass-spectrometer of the gas evolved from deuterated cellulose during the irradiation revealed that it was composed mostly of H/sub 2/ and HD, being accompanied by only a small amount of CO, CO/sub 2/, and CH/sub 4/. The primary reactions induced by gamma radiation were discussed. The carbonyl group and the carboxyl group were identifiedmore » in the irradiated samples, which, however, showed enormously large copper numbers in comparison with the carbonyl content. Therefore, the measurements of copper number results in greatly overestimated values of carbonyl content. The high ratio of oxidant to carbonyl content would be due to the formation of various alkali-sensitive groups by irradiation. The formation of carbonyl group and carboxyl group were estimated to be proportional to R/sup 0.35/ similar to the case of chain rapture. A considerable amount of formic acid ester was found in the irradiated samples, which also would be an origin of producing very high copper numbers. The paper chromatographic analysis showed the hydrolyzate of strongly irradiated cellulose to contain an appreciable amount of xylose, arabinose and glucuronic acid besides glucose, which suggested the transformation of carbohydrate components by irradiation. Hypothetic formulas are given. (auth)« less