Preparation of multimodal high and ultra-high molecular weight polyethylene

Abstract

The multimodal molecular weight distribution of high molecular weight polyethylene combines enhanced mechanical properties and good processing properties. The conventional slurry process produces a high-density polyethylene with mono or bimodal molecular weight distribution, using the classical Ziegler type catalysts supported on inorganic materials. The production of multimodal molecular weight distribution high molecular weight polyethylene is very intricate and requires parallel reactor cascades with different residence times or the use of a supported catalyst with different active sites. This study shows that ethylene polymerization reactions using an unsupported Ziegler type catalyst, in a batch reactor, can produce polymers with a density higher than 0.93 g mL−1, a melting temperature of about 140 °C, and a degree of crystallization of about 79%. The molecular weight distributions of the produced polymer have a broad dispersion of molecular weight (log M) 2 to 7.2 and there are four peaks, showing multimodal distribution and large molar weight. The polyethylene produced using this single-step method is a blend of high and very high molecular weight polyethylene.