Kinetics of Strain-Induced Crystallization in Natural Rubber Studied by WAXD: Dynamic and Impact Tensile Experiments

The time-dependence of strain-induced crystallization in cross-linked natural rubber was studied using synchrotron wide-angle X-ray diffraction (WAXD) with an less than 10 ms, it was found that roughly half of the unprecedented time resolution in the ms range. In-situ dynamic mechanical tests and tensile impact tests were carried out. In tensile impact tests, consisting of a strain step within crystallization process was complete within less than 5 ms, provided the strain is large enough. Afterward, crystallization proceeded on a time scale of a few seconds. This implies that under dynamic loading at frequencies which are typically encountered in the application of rubbers, the degree of crystallinity is considerably lower than under equilibrium conditions. This was directly confirmed by in situ dynamic cyclic experiments at a frequency of approximately 1 Hz. Since crystallization is a major factor contributing to the outstanding mechanical properties of natural rubber, these findings can aid in the interpretation and prediction of the frequency-dependence of mechanical properties.