INFLUENCE OF MOLECULAR STRUCTURE ON PROCESSING BEHAVIOUR OF METALLOCENE AND CONVENTIONAL POLY(ETHYLENE/1-OLEFIN) COPOLYMERS

The influence of branching on the properties of polyethylenes has gained great interest during the last years. In particular, a controlled amount of short-chain branches (SCBs) can be incorporated by polymerizing ethylene with a comonomer, such as -olefins, in order to primarily improve the mechanical properties of the materials in the solid state [2]. More recently, the development of metallocene catalysts has led to a new class of polyethylenes with narrow molecular weight distribution (MWD). Although linear metallocene catalysed resins exhibit better physical and mechanical properties, they also suffer from poor melt processability [3]. In this work the influence of sparse short-chain branching and molecular weight distribution on the melt fracture behaviour of poly(ethylene/1-olefin) copolymers was investigated. Rheological measurements were performed both in shear and extensional flow, and melt extrusion experiments were carried out using a controlled rate capillary rheometer. A single capillary geometry was used to focus on the effects of materials properties on flow instability rather than geometric factors