RADIATION CROSS-LINKING OF POLYETHYLENE WITH ELECTRON-BEAM AT DIFFERENT TEMPERATURES

The effect of temperature over the range -196 to 150 degrees C on the crosslinking of polyethylenes irradiated by electron beam has been inv estigated on the basis of gel content determination and Fourier transf orm infra-red (FTIR) spectroscopy. The crosslinking efficiency increas es significantly with increasing irradiation dose and at elevated irra diation temperature. The crosslinking rates of high density polyethyle ne (HDPE) and low density polyethylene (LDPE) samples above the meltin g point (T-m) are much higher than those below T-m. The FTIR data give positive evidence: (i) that trans-vinylene double bonds in crosslinke d HDPE and LDPE samples increase with increasing irradiation dose and irradiation temperature, (ii) that vinyl double bonds in HDPE decrease rapidly with increasing irradiation dose and temperature, and (iii) t hat vinylidene groups in LDPE decrease slowly with increasing temperat ure at the lower dose and are almost independent of the irradiation te mperature at above room temperature and the higher dose of more than 1 00 kGy. Gas bubbles are observed in LDPE samples irradiated at 100 and 150 degrees C with high dose (200 to 250 kGy). The size of the bubble s increases gradually at high temperatures.