Effect of solvents on de-cross-linking of cross-linked polyethylene under subcritical and supercritical conditions

The effect of various solvents on the de-cross-linking reaction of cross-linked polyethylene under subcritical and supercritical conditions was studied. The gel content of the de-cross-linked polyethylene decreased from 60 to 0.8-2.5% at 380 °C within 5 min in all of the solvents tested in this study. When water, ethanol, and 2-propanol were used, the M_w of the de-cross-linked polyethylenes decreased from 349,000 to 200,000-227,000 g/mol, and much lower M_w values of 70,000-90,000 g/mol were observed when acetone and diisopropyl ether were used. The de-cross-linked polyethylenes treated in the different solvents had a very similar chemical structure to raw polyethylene. According to a kinetic study using a first-order reaction model, the de-cross-linking rate in each solvent increased in the order 2-propanol < ethanol < n-hexane < water < methanol ≪ diisopropyl ether ≪ acetone at 350 °C.