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 1-olefins, in order to primarily improve the mechanical properties of the materials in the solid state [1-2]. 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 behavior of poly(ethylene/1-olefin) copolymers was investigated. Four commercial linear low density polyethylenes (LLDPE) were employed for this study: three conventional LLDPE/1-olefin copolymers (with butene, hexene and octene) and a metallocene LLDPE/1-hexene. 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 rather than geometric factors on flow instability. Correlations between the molecular characteristics of the resins and their processing behavior (melt fracture performance) were established. In particular, it was found improved processability with increasing SCB length for conventional LLDPE, which have similar molecular weight (Mw) and MWD. Comparing the metallocene and conventional LLDPE samples, polymerized using the same comonomer (hexene), the metallocene catalysed resin exhibited early onset and more severe melt fracture, that can be reasonably attributed to its narrow MWD.

Study of melt fracture behavior of metallocene and conventional poly(ethylene/1-olefin) copolymers

GAROFALO, EMILIA;INCARNATO, Loredana;DI MAIO, Luciano
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 1-olefins, in order to primarily improve the mechanical properties of the materials in the solid state [1-2]. 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 behavior of poly(ethylene/1-olefin) copolymers was investigated. Four commercial linear low density polyethylenes (LLDPE) were employed for this study: three conventional LLDPE/1-olefin copolymers (with butene, hexene and octene) and a metallocene LLDPE/1-hexene. 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 rather than geometric factors on flow instability. Correlations between the molecular characteristics of the resins and their processing behavior (melt fracture performance) were established. In particular, it was found improved processability with increasing SCB length for conventional LLDPE, which have similar molecular weight (Mw) and MWD. Comparing the metallocene and conventional LLDPE samples, polymerized using the same comonomer (hexene), the metallocene catalysed resin exhibited early onset and more severe melt fracture, that can be reasonably attributed to its narrow MWD.
File in questo prodotto:
Non ci sono file associati a questo prodotto.

I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.

Utilizza questo identificativo per citare o creare un link a questo documento: https://hdl.handle.net/11386/3093955
 Attenzione

Attenzione! I dati visualizzati non sono stati sottoposti a validazione da parte dell'ateneo

Citazioni
  • ???jsp.display-item.citation.pmc??? ND
  • Scopus ND
  • ???jsp.display-item.citation.isi??? ND
social impact