天然ゴムの伸長結晶化における新概念

Abstract

Despite the long history of studies, a quantitative theory on strain-induced crystallization of natural rubber has not been fully established. All the theories so far have considered the entropy change due to extension as the only factor to enhance crystallization. We obtained experimental data about the dependence of crystallization rate on stretch ratio. The results were compared with theoretical calculations based on the previous concept regarding the entropy change as the only factor. However, the theoretical calculations were totally inconsistent with the experimental results. The origin of this discrepancy was found to be the calculated high activation energy of nucleation even after the entropy change due to extension was considered. This quantitative comparison indicated that the reduced surface free energy due to the formation of bundle-like nuclei is the additional factor to enhance crystallization. Furthermore, it was revealed that surface energies have a greater effect on the decrease of the activation energy than the entropy change by extension.