DSC Evidence for Microstructure and Phase Transitions in Polyethylene Melts at High Temperatures

Abstract

Thermal/microstructural transitions were found at 208 and 227 °C in commercial polyethylenes of types HDPE, LDPE, and LLDPE. DSC data were obtained for a range of heating and cooling rates, over a broad high-temperature regime (30− 280 °C) that spans the melt processing regime. Six samples, from four resin suppliers, were tested; all were of moderate molecular weight (M̄w = (36−85) × 103). Results are discussed in terms of molecular order and transitions between different degrees of ordering. No transitions were detectable in highly branched metallocene samples. The DSC results are in agreement with our previous rheology findings of order and high-temperature transitions in polyethylene melts.