Details of Molecular Organization during Strain-Induced Crystallization in Natural Rubber/Clay Systems As Revealed by Real-Time Mechano-Optical Behavior

A real-time spectral birefringence technique was implemented to follow the coupled relationships among birefringence, true stress, and true strain behavior of natural rubber vulcanizates containing a series of clay concentrations. The dynamics of structural evolution was also followed by off-line wide-angle X-ray diffraction to characterize the order and orientation at different extension levels. The results show that at the same true strain level the natural rubber/organomodified clay (NR/OC) nanocomposite with higher OC content exhibits higher true stress and birefringence. While the stress optical relationship shows three different linear stages during stretching, the strain optical relationship is nonlinear and found to always exhibit a positively increasing slope with increasing strain. XRD results show higher OC-content-induced earlier appearance of strain crystallization and higher orientation factor in crystalline domains of rubber, as also evidenced by the real time birefringence results.