Strain-Induced Crystallization of Pre- and Post-Vulcanized Natural Rubber Latex During Uniaxial Deformation by In-Situ Synchrotron X-Ray Diffraction

The structural development and morphology in vulcanized and un-vulcanized natural rubber latex was studied under deformation by in-situ synchrotron X-ray scattering and Multiple-Quantum (MQ) NMR. MQ NMR experiments provided a quantitative determination of cross-linking density. Pre- and post-vulcanized latex with various concentrations of dipentamethylenethiuram tetrasulfide (DPTT), were studied using wide-angle X-ray diffraction (WAXD) and small-angle X-ray scattering (SAXS). Molecular orientation and strain-induced crystallization was analyzed by both stress-strain relations and WAXD. It was found that an increase in the DPTT concentration led to an increase in modulus and crystalline fraction, which is consistent with the increase in cross-linking density from MQ NMR results. By comparing the pre- and post-vulcanized latex samples, it was found that the high temperature of post-vulcanized latex at 130C caused the degradation of proteins and phospholipids, causing the further interactions between rubber particles and additional reaction of DPTT. SAXS results provided new insights on the morphology of the latex rubber particle during deformation.