Bimodal Polyethylene: Synthesis and Study of Shear Induced Oriented Structures Generated from High Molecular Weight Polyethylene Chains

摘要

Flow induced crystallization in polymer melts is an important phenomenon, which influences the industrial processing techniques such as extrusion, injection and blow molding and consequently the product properties [1]. It is well known that external flow causes orientation and extension of polymer chains in the melt and thus affects the crystallization kinetics and morphology. Crystallization from melts produces spherulites and oriented structures known as shish and kebab morphology [2-5]. To establish fundamental concepts on the influence of molar mass on crystallization and the resultant morphology during shear flow a study on the polymer having two different molar masses with distinct differences in the relaxation times, mixed at the molecular length scale is a requisite. In this paper we report, flow induced orientation of high molecular weight polyethylene from the bimodal reactor blend. In this study we developed a synthesis route to obtain intimately mixed bimodal polyethylene generated using a supported dual catalyst system. This synthesis route provides a precise control in the composition of PE having distinctly different molar masses. The polymer produced is an intimate blend of PE having high and low molar mass, due to the synthesis carried out using a co-immobilized catalyst combination.