Strain-Induced Crystallization Behavior of Natural Rubber and Trans-1,4-Polyisoprene Cross linked Blends

The strain-induced crystallization (SIC) behaviors of crosslinked blends based on natural rubber (NR) and trans-1,4-polyisoprene (TPI) with different content of TPI were probed explored by using synchrotron two-dimensional wide angle X-ray diffraction and dynamic mechanical analysis. The results showed that when TPI content is less than 70% no reflection peak of TPI but NR crystallite diffractions can be observed and the diffractions of TPI beta form appear when TPI content is 70 wt % in the cocured blend. SIC of cocured blends started at smaller strain ratio than the pure NR. By calculating Delta S-def, it is found that the drop in entropy upon strain decreased when TPI is incorporated into NR due to the reduction of molecular mobility of NR. The degree of SIC and crystallization rate index in crosslinked blends monotonously decreased with the increase of TPI content. The apparent crystallite size exhibited some surprising variations. L-200 and L-120 decreased with the increase of TPI content in the cocured blends. These observations were usually caused by two factors: (i) Less number of polymer chains could involve in crystal growth due to the lower mobility of polymer chains in the cocured blends which is proved by dynamic mechanical analysis results; (ii) The mean distance between nuclei decreases, which was caused by the fluctuation of crosslink density in NR phase derived from the heterogeneous distribution of curatives in two phases supported by the varying tendency of curing degree and crosslink density. (C) 2010 Wiley Periodicals, Inc. J Appl Polym Sci 120: 1346-1354, 2011