Estimation of Chain Fracture and Cross-Linking of Rubber by High-energy Radiation

Abstract

Lightly masticated pale crepe rubber, which had been freshly extracted with acetone, was evacuated and sealed in glass tubes. After gamma irradiation from a cobalt-60 source or a linear electron accelerator, the soluble fraction was measured by extraction of the samples with benzene. In each case the mean intensity of the radiation was estimated by ferrous sulfate dosimetry. Solubility data for the gamma irradiation of rubber at two dose rates at 25 deg C were quantitatively analyzed by the method of Charlesby and Dinner. Results show that the rate of cross-linking is directly propertional to the intensity of radiation. Results indicate that the initial distribution of molecular weights is not perfectly random and some dislinking is necessary to obtain the results. The ratio of the rate of dislinking to cross-linking was calculated. Infrared spectroscopic analysis revealed a marked increase in the absorption near 1,639 cm/ sup -1/, identified as terminal unsaturation, which was presumed to arise from the dislinking reaction. There was also evidence of transvinylene unsaturation during irradiation. (C.H.)