Glass transition of polyethylene: Volume relaxation

Data are presented to show that when linear polyethylene is quenched from room temperature to temperatures below 273 K, it exhibits a volume decrease for times long compared with that required to establish temperature equilibrium. The time, temperature, and density dependence of this decrease is shown to be consistent with a relaxation occurring in the amorphous portion (lamella boundary layers) of the samples. The data can be superposed and the shift factors follow the WLF formalism. Analysis by this method yields a Tg of 231 ± 9 K but the uncertainties preclude any correlation with specific volume over the range 1.01–1.05 cm3 g−1. The data indicate the absence of any comparably strong time dependence of the volume near 150 K. This method of detecting a glass transition in partially crystalline polymers is relatively freer of subjective judgment than most.