CROSS-LINKING RATE DEPENDENCE ON THE THICKNESS OF HIGH-DENSITY POLYETHYLENE SHEETS AFTER GAMMA-RAY IRRADIATION IN THE PRESENCE OF AIR

Structural changes and dynamic mechanical properties of istotropic hig h-density polyethylene (HDPE) for both virgin and gamma-ray irradiated samples of different thickness, have been studied. The structural cha nges due to irradiation in the presence of air were studied by using i nfra-red spectroscopy. The radiation induced radicals were not post-ir radiation annealed. The effects of these changes on the mechanical beh aviour were investigated by using a modified dynamic resonance techniq ue. It was found that the polymer chain crosslinking rate, as a result of irradiation by gamma-ray doses up to 200 kGy, depends on the sampl e thickness. However, for irradiation doses above 600 kGy, polymer cha in scission is the most dominant phenomenon and is independent of the sample thickness.