The Structure of High Molecular Weight Linear Polyethylene Injection Moulded at High Pressures

Abstract

Abstract High density polyethylene with a low melt flow index (0.1 g/10 min) was injection moulded at pressures ranging from 100 to 500 MPa. The tensile modulus and strength in the flow direction increased substantially with the injection pressure. Three regions are characteristic of the specimens produced; a thin layer near the surface, a transition layer beneath the skin, and a core. DSC, wide angle X-ray scattering (WAXS), scanning and transmission electron microscopy were used to study the structure of the different layers. It was concluded that the skin was slightly oriented containing primarily chain-folded lamellae; the transition layer had a fibre texture and was oriented in the flow direction; the orientation of the core was similar to that of the transition layer but contained extended chain-morphologies similar to those found by Porter et al. in capillary extruded specimens. The composite structure gives rise to the improvement of mechanical properties and the increase in modulus is due to the ...