Crystal and Crystallites Structure of Natural Rubber and Peroxide-Vulcanized Natural Rubber by a Two-Dimensional Wide-Angle X-ray Diffraction Simulation Method. II. Strain-Induced Crystallization versus Temperature-Induced Crystallization

Abstract

New insights into the strain-induced crystallization (SIC) and temperature-induced crystallization (TIC) of unvulcanized natural rubber (NR) and peroxide-vulcanized natural rubber (PVNR) have been obtained by wide-angle X-ray diffraction (WAXD) and small-angle X-ray scattering (SAXS). The SIC samples were deformed at various temperatures (from −50 to 50 °C) to determine the effect of temperature on the crystallite structure. In the WAXD patterns, highly oriented sharp crystal reflections were observed for the SIC samples, whereas sharp rings without preferred orientation were observed for the TIC samples. A novel 2D method to calculate WAXD patterns was used to obtain information on the crystallite structure. For the SIC samples, the crystallite sizes, volume, number of chains per crystallite, crystallite orientation, and crystal displacement disorder increased with increasing temperature but with a decrease in the number of crystals. The crystallite sizes and volume were much larger for the TIC samples as compared to the SIC samples. In the SAXS patterns, the presence of a lamellar peak was observed only for the SIC samples at low temperatures, whereas diffuse scattering was observed for the SIC samples at high temperatures and for the TIC samples. A two-phase stacking model was applied to the 1D integrated intensities of the TIC samples to determine the thicknesses of the crystalline and amorphous phases and the long-period spacing. The long period increased with increasing temperature, which was attributed to the reduction in the number of crystallites and the translation of chains from the crystalline regions to an amorphous state.