Radiation‐induced crystallinity changes in linear polyethylene

Abstract

Abstract Two kinds of ultrahigh‐molecular‐weight linear polyethylene (UHMW PE), together with conventional high‐density polyethylene (HDPE), were subjected to β irradiation, and changes in their properties were monitored. Elastic modulus increased steadily with dose for all materials, as did the yield stress. A dramatic rise of density with dose was observed in the UHMW PE specimens accompanied by a corresponding increase in heat of fusion, x‐ray crystallinity, and peak melting temperature. The magnitude of such changes in HDPE was much smaller. In UHMW PE specimens, the x‐ray long period simultaneously decreased but crystal thickness remained constant. No changes in long period occurred in HDPE. The effects are attributed to the scission of tie molecules in UHMW PE followed by a growth in the perfection of the crystal lamellae, and suggest a method for assessing the tie‐molecule content of such materials.