| Abstract: | Two very different high-modulus polyethylene fiber samples, a low molecular weight melt-spun and drawn fiber, and a high molecular weight gel-spun and drawn fiber, have been subjected to electron beam irradiation to various doses in vacuum and in the presence of acetylene. The gel content after irradiation in acetylene was found to be much greater than for an equivalent dose in vacuum. The gel content–dose relationship could not be described by either Charlesby–Pinner analysis or the Inokuti equation. This is attributed to the polydispersity and the complications introduced by the unique morphologies of highly drawn fibers. Following previous studies, the tensile creep behavior was interpreted in terms of a model comprising two thermally activated processes in parallel, a low stress process relating to the amorphous network, and a high stress process relating to the continuous crystal fraction. Analysis of the creep behavior of the melt-spun, low molecular weight fiber irradiated in vacuum revealed crosslinking in the amorphous regions and chain scission in the crystal. Chain scission was found to be much reduced when irradiating in acetylene, for which a mechanism has been proposed. The creep rates and activation volumes of the high molecular weight, gel-spun fiber were found to be significantly lower, probably due to the unique morphology. In this case the dominant effect of irradiation on the mechanical properties can be attributed to chain scission rather than crosslinking. |
