Viscoelastic properties of decrosslinked irradiation-crosslinked polyethylenes in supercritical methanol

The viscoelastic properties of decrosslinked irradia-tion-crosslinked polyethylenes using a supercritical methanol were investigated via oscillatory dynamic shear measurements. Decrosslinked polymers at a low reaction temperature exhibited solid-like rheological properties, as evidenced by a small slope at G and G", a long relaxation time, slow stress relaxation behavior, and considerable yield stress. In contrast, decrosslinked polymers at a high temperature exhibited liquid-like rheological properties that included a large slope in G and G, a short relaxation time, fast stress relaxation behavior, and nonyield stress. The difference. in the viscoelastic properties of the decrosslinked polyethylenes was attributed to the difference in the gel content with the reaction temperature. A higher gel content induced stronger solid-like viscoelastic properties. Hence, the rheological measurements were useful for analyzing the molecular structure of decrosslinked polymers using a supercritical fluid.