New Concept of Strain-Induced Crystallization in Cross-Linked Natural Rubber

When elongation is given to supercooled polymer, crystallization is greatly accelerated. Theoretically, this acceleration has been thought to come from the entropy reduction of amorphous polymer chains that elevates melting temperature. However, no theory that can quantitatively explain general crystallization behavior of elongated polymers has been established so far. We experimentally obtained the relation between the draw ratio and the crystallization rate about strain-induced crystallization of cross-linked natural rubber, and compared them with the theoretically expected relation. As a result, we found that the entropy change of elongated polymer chains, which has been conventionally considered as the only driving force of strain-induced crystallization, is insufficient to explain the experimental results. Accordingly, we concluded that formation of bundle nuclei which have low surface free energy is the main cause of accelerated crystallization.