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.
INFLUENCE OF MOLECULAR STRUCTURE ON PROCESSING BEHAVIOUR OF METALLOCENE AND CONVENTIONAL POLY(ETHYLENE/1-OLEFIN) COPOLYMERS
GAROFALO, EMILIA;DI MAIO, Luciano;INCARNATO, Loredana
2009-01-01
Abstract
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.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.