Effects of high energy irradiation on polypropylene

Abstract

AbstractIsotactic polypropylene (Profax) film samples irradiated in the Pennsylvania State University (PSU) reactor at ambient temperatures were examined by solvent extraction and infrared absorption techniques. At low irradiation doses, samples annealed (density = 0.909 g./cc. at 24°C.) prior to irradiation were found to have a lower gel content and a higher concentration of oxidation products than quenched samples (density = 0.899 g./cc. at 24°C.) irradiated under identical conditions. Similar gel fraction results were obtained for electron irradiated samples of polypropylene. These effects are believed to arise from the accumulation of a greater concentration of free macroradicals in the higher density samples. At higher reactor dosages the irradiation effects in the annealed and quenched films appear to be about the same. The gel content as a function of dose was found to be independent of the irradiation intensity level over a twofold range. Irradiations in the PSU reactor were also carried out on high density polyethylene (Marlex 50) pellets at two temperatures, viz., 40 ± 10°C. and 150°C. Irradiation at 150°C. led to a greater gel content at any given dose, a result in agreement with that reported by Lawton, Balwit, and Powell for electron‐irradiated specimens. Nuclear magnetic resonance spectra were obtained for molded annealed samples of partially isotactic polypropylene, irradiated in the Brookhaven reactor, at temperatures of 90–330°K. The observed shifts in the line narrowing process that occur in the 270–330°K. region are explained in terms of the decrease in crystallinity and the increasing density of crosslinks that accompany irradiation.