Crystallization and Phase Separation of Branched Low Molecular Weight Polyethylene/Ultrahigh Molecular Weight Polyethylene Blend under a Controlled Temperature Gradient

Abstract

Crystallization and phase separation of polyethylene blend were first studied under a controlled temperature gradient (T-gradient) condition. Branched low molecular weight polyethylene (B-LMWPE) and ultrahigh molecular weight polyethylene (UHMWPE) blend films were prepared by casting the blend solutions on the T-gradient stage and then evaporating the solvent. The morphological evolution of blend films was investigated in detail. The blend films showed a continuous gradients surface. With increasing temperature, the degrees of crystallinity for both of the B-LMWPE and UHMWPE decreased in the blend films. The results indicated that phase separation behavior of B-LMWPE and UHMWPE blend with composition 10/1 or 5/1 occurred in both of solution and gel, and the phase separation was prior to crystallization. It is suggested that phase separation should induce molecular ordering and crystallization in the B-LMWPE/UHMWPE blend in the initial stage, and the phase separation and crystallization compete with each other in the later period. Another fact is that high viscosity of blend solution plays a more important role in phase separation rather than in crystallization, and it will be the main disincentive in inhibiting the Marangoni phenomenon when the composition of UHMWPE increases in the blend.