An investigation of the relationship between thermal relaxations and the impact performance of rotationally moulded linear low density polyethylenes

The objective of this paper is to provide a better understanding of how thermal relaxations in linear low density polyethylenes are related to the crack initiation energy of rotomoulded parts. Trials were carried out on two Ziegler-Natta catalysed linear low density polyethylenes (LLDPE) and two metallocene catalysed linear low-density polyethylenes (mLLDPE). Instrumented impact tests and dynamic mechanical thermal analysis (DMTA) were carried out on each material at a wide range of temperatures. The frequency of impact at each test temperature was determined, and the DMTA results were shifted to a corresponding frequency. A correlation can be seen between changes in loss modulus and crack initiation energy with temperature. When comparing the crack initiation energy of the samples and the tan δ values, it can be seen that the β transition affects the way in which the polymer behaves under impact. A method for predicting impact performance over a wide temperature range is proposed.