Probing the Nature of Strain-Induced Crystallization in Polyisoprene Rubber by Combined Thermomechanical and In Situ X-ray Diffraction Techniques

The nature of strain-induced crystallization in vulcanized polyisoprene rubbers was investigated by in situ synchrotron wide-angle X-ray diffraction under varying thermomechanical conditions. In particular, the methods of constrained cooling and constrained heating under constant strain were used to explore the relationships between the strain-induced crystalline network and corresponding stress. It was found that constrained cooling resulted in a large reduction of stress and a notable increase in the amount of strain-induced crystallites, while constrained heating led to an initial increase in stress and subsequent melting of strain-induced crystallites. Results indicate that strain-induced crystallization induces a new network structure, which reinforces the chemical network points. However, the sulfur bridges in the chemical network points would break down at high temperatures under high strains, despite the existence of strain-induced crystalline network.