Influence of temperature on molecular regroupings and chain rupture under stretching deformation of high-oriented linear polyethylene

Abstract

Conformational regrouping and rupture of macromolecular chains at different stretching deformation temperatures of highly oriented linear polyethylene samples (monofilaments) were studied. Measurements of the relative concentration of rotational isomers and chain rupture were determined by IR spectroscopy. Regroupings occur in the highly oriented polymer when elastic stretching of the sample exceeds a threshold value, irrespective of deformation temperature; this is assumed to be due to steric conditions that influence the cooperative transition of coiled-chain isomers in the extended isomeric conformational state. Polymer stretching at elevated temperatures, in comparison with room temperature, occurred at considerably lower loads and showed increases in elastic deformation, extent of conformational regroupings of molecular segments and reduction in the number of macromolecular ruptures. Deformation at identical values was accompanied by a smaller decrease in concentration of coiled-chain rotational isomers. The number of molecular chain ruptures, which is proportional to stress load, appeared to be unaffected by temperature. It is proposed that the small decreases observed in the content of coiled-chain isomers and of chain rupture with deformation are facilitated by macromolecular slippage processes that occur through polymer crystallites.