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 investigated on the basis of gel content determination and Fourier transform infra-red (FTIR) spectroscopy. The crosslinking efficiency increases significantly with increasing irradiation dose and at elevated irradiation temperature. The crosslinking rates of high density polyethylene (HDPE) and low density polyethylene (LDPE) samples above the melting point (T-m) are much higher than those below T-m. The FTIR data give positive evidence: (i) that trans-vinylene double bonds in crosslinked 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) that vinylidene groups in LDPE decrease slowly with increasing temperature at the lower dose and are almost independent of the irradiation temperature at above room temperature and the higher dose of more than 100 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 bubbles increases gradually at high temperatures.