Effect of γ-irradiation on the paracrystalline structure of polypropylene film

Thin isotactic polypropylene film (50 μm), irradiated in air, has been investigated by infrared (IR) spectroscopy, wide and small angle X-ray diffraction, and light microscopy. Infrared spectra show that the concentrations of carbonyl, hydroxyl, peroxyl and carboxyl groups increase with irradiation dose as well as the content of molecular chains with helical structure. X-ray experiments and light microscopy studies show that the γ-irradiation does not cause any change in the paracrystalline structure and crystallisation is possible after appropriate thermal treatment or melting. It may be concluded that the paracrystalline structure is not sensitive to γ-irradiation up to doses of 370 kGy (37 Mrad). It is believed that changes at the molecular level such as conformational, destructive, crosslinking, oxidation, post-irradiation effects, etc., do not affect the supermolecular smectic structure of thin film samples of polypropylene.