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 delta values, it can be seen that the beta transition affects the way in which the polymer behaves under impact. A method for predicting impact performance over a wide temperature range is proposed.