Vigilancia Tecnológica

Ultrahigh molecular weight polyethylene/high?density polyethylene in?reactor blends (UHMWPE/HDPE IRBs) were synthesized by silyl?chromate/VOx/silica bimetallic catalysts. The catalyst with smaller particle size was less kinetics stable and synthesized UHMWPE/HDPE IRBs with higher Mw and narrower molecular weight distribution. The hot?pressed UHMWPE/HDPE IRBs with smaller particle size had fewer fusion defects, more entanglements, and better mechanical properties.AbstractIn this work, four kinds of silica with similar textural properties but different particle size (PS) from 6 to 60??m were selected as support to prepare silyl?chromate/VOx/silica bimetallic catalysts for ethylene polymerization, thus making it possible to conduct convincing investigation on the effects of catalyst PS over catalytic behaviors and polymer properties. It is found, owing to mass? and heat?transfer limitations, the catalysts with smaller PS showed higher initial activity, while the deactivation in the later stage was more remarkable. Meanwhile, catalysts with smaller PS synthesized bimodal ultrahigh molecular weight polyethylene/high?density polyethylene in?reactor blends (UHMWPE/HDPE IRBs) with higher molecular weight (MW) and narrower molecular weight distribution (MWD). Four PE sample couples with MW increasing from 5?×?105 to 10?×?105?g?mol?1 and PS from 40 to 460??m were selected for tensile and rheological tests. For each couple with similar MW and MWD, the sample with smaller PS always had larger tensile strength and breaking elongation. The cryogenically fractured surface of the samples made by smaller PE particles showed fewer delamination defects and unfused small particles. The rheological results indicate that higher homogeneity was achieved for the sample with smaller PS, which was reflected by the unexpected higher viscosity and storage modulus.