Influence of high doses γ-irradiation on oxygen permeability of linear low-density polyethylene and cast polypropylene films

•High doses γ-irradiation reduces oxygen permeability in PE and PP films.•Increase of crystallinity and decrease of melting point in PP film induced by radiation.•Radiation induced radical formation in PE and PP and their decay monitored by ESR.

Linear low density polyethylene (PE-LLD) and cast polypropylene (PPcast) films were irradiated in a 60Co γ-source. The total irradiation dose varied from 0 kGy (unirradiated samples) to 200 kGy. Oxygen transport was investigated by a manometric method and the structural changes were studied by differential scanning calorimetry (DSC) and Fourier transform infrared spectroscopy (FTIR). Free radicals decay as a function of time was monitored by electron spin resonance (ESR) spectroscopy. The results show that the γ-irradiation reduces oxygen permeability coefficient in both films. The reduction was associated with an increase in crystallinity. DSC thermograms revealed a decrease in PPcast melting point with increasing irradiation dose, indicating higher degradation compared to PE-LLD. The observed peak in FTIR spectra for both samples at 1716 cm−1 corresponds to the stretching of the carbonyl and carboxylic groups which arise from the reaction of oxygen with the free radicals produced in the polymer matrix as a result of irradiation.