Uniaxial Extensional Behavior of Ziegler- atta High Density Polyethylenes

The aim of this paper is investigation of elongational behavior of polydisperse linear polyethylenes. This type of deformation makes an important role in many processing operations. For this purpose, the transient uniaxial extensional viscosities of two commercial Ziegler-Natta synthesized HDPE, one with monomodal distribution and the other with bimodal distribution, were measured using SER (Sentmanat Extensional Rheometer) fixture at different strain rates. Since, this behavior is very sensitive to long chain branches; the molecular structure of these materials was surveyed using measured linear viscoelastic data atdifferent temperatures. The measured activation energies, Ea, were compared with those have been reported for linear polyethylene. Also Van Gurp-Palmen plot, as a powerful tool for study the rheological behavior of these materials, was employed. Finally relation between observed extensional properties and molecular structure of these materials was investigated. In this regard, the molecular theories based on tube model of Doi & Edwards were utilized. According to these theories, the extensional behavior of polymeric melts is a direct function of chain stretching which is appeared as strain hardening behavior in transient uniaxial tests

کلیدواژه ها:

High Density Polyethylene ، Uniaxial Extensional Viscosity ، DE Theory