Spectroscopic investigation of degradation reaction mechanism in γ-rays irradiation of HDPE

Abstract

Radiation damage and reaction mechanism of product formation due to γ-irradiation in high-density polyethylene (HDPE) have been studied by Fourier transform infrared (FTIR), UV-vis spectroscopic, and x-ray diffraction (XRD) techniques. A Co60 gamma source (with a dose rate of 1.707 kGy/hr) has been used up to the total dose of 570 kGy. There are dose-dependent changes in the polymer. The optical band gap decreases with the increase of the γ-irradiation dose. Formations of unsaturation centers have been observed. FTIR observed that a lower dose of γ-irradiation induces the formation of an unsaturated (-C=C-) group and a ketone carbonyl group. Breaking of the C-H bond is more frequent than the breaking of the C-C bond in irradiated HDPE. Crosslinking dominates over chain scission (breaking of C-C bond of the main chain) at a lower dose (100 kGy). There has been no significant influence of γ-irradiation on the crystalline structure, although crystalline size decreases. Mechanisms of the formation of alkyl, allylic, and polyenyl radicals have been investigated.