Effect of Temperature on Environmental Stress Cracking Resistance and Crystal Structure of Polyethylene

Abstract

Studies were conducted on the crystalline properties of different polyethylene resins to identify their influence on phase interconnectivity between amorphous and crystalline regions. This work offers a thorough investigation on the potential correlation between environmental stress cracking resistance (ESCR) and crystalline structure characteristics, namely, crystallinity, mean lamella thickness and its distribution, and lamella surface area (LSA). The initial objective of this work was to investigate an existing ambiguity in the literature with respect to the effect of the crystalline phase on ESCR. In addition, research was conducted to evaluate the degree of variability in the lamella surface area, as a measure of phase interconnectivity and ESCR, with processing temperature and post-process annealing. Annealing at various conditions, along with cooling at different rates, were employed to investigate the effect of temperature on LSA. It was observed that a clear correlation exists between crystalline phase properties and ESCR, given that the comparison is made between polymers with similar molecular weights. Annealing temperature and time were found to cause a general reduction in LSA, however, to varying degrees, according to the type of PE molecular structure (significant interactions exist between annealing conditions and polymer type). LSA showed a significant dependence on cooling rate, however, no interaction was found between cooling rate and type of PE molecular structure. Additionally, lamella surface areas obtained from quenching and air cooling were found to be almost the same.