Crystallization Behavior of Linear Low Density Polyethylene in its Blend with a Rubber Polymer as Revealed by Synchrotron SAXS/WAXS/Hv-SALS Simultaneous Measurements

Abstract

This study concerns crystallization behavior of crystalline polymers in a phase-separated polymer blend. It might be generally considered that spherulites cannot grow bigger than phase-separated domains. However, it has been confirmed experimentally that it is possible. We found that the same phenomena for blends of LLDPE (linear low density polyethylene) with a rubber polymer. In this study, effects of phase-separated domains on the spherulite growth and the crystallization behavior of LLDPE were studied. For quantitative discussion, we employed a simultaneous measurement technique of synchrotron SAXS/WAXS/Hv-SALS. It was found that the spherulites were 10~20 times lager than the phase-separated domains. It was also found that the long period of crystalline lamellae was smaller than phase-separated domains. Therefore, we suppose that the phase-separated structure has no influence on the fibril growth, which is the fundamental step of spherulites growth. Namely, the fibril growth through a channel of phase-separated crystalline domains enables the overall growth of spherulites. In the meantime, it was found that the index of degree of crystallinity in the LLDPE phase decreased slightly with the blend composition and induction periods of SAXS, WAXS, Hv-SALS in the phase-sepatared blend of LLDPE with a rubbery polymer were longer than those in a neat LLDPE. It was also suggested that nuclear growth was obstructed to some extent by the phase-separated domains. We suppose that nuclei which were not obstructed grew so that spherulites in the phase-sepatared blend sample became bigger than in a neat LLDPE sample.