Effects of high energy irradiation on polypropylene

Abstract

SynopsisIsotactic 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. a t 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. a t 24OC.) 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 irradition intensity level over a twofold range. Irradiations in the PSU reactor were also carried out on high density polyethylene (Marlex 50) pellets a t two temperatures, viz., 40 f 10°C. and 150°C. Irradiation at 150°C. led to a greater gel content a t 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.

Effect of γ‐radiation on the thermal conductivity of polypropylene

“…If one uses a conversion factor of about 35 Mrad/lO" nvt," an estimate can be made of the correlation of changes observed by Chappell et al 9 and work presented herein. On this basis their sample which received a radiation dose of 3.2 X 10l8 nvt (reactor radiation) received a radiation dose of about 1100 Mrad.…”

“…DMP studies3 and the work of Chappell et al 9 indicate that high-energy irradiation of polypropylene produces crosslinking into a three-dimensional network accompanied by the destruction of the crystallites and a loss of rigidity. At lower doses where the crystallites were still present, it was reported that heat treatments at temperatures above the crystalline melting points tended to cause a decrease in density, while at higher doses, where the crosslinking density was higher and very few crystallites existed, a similar heat treatment caused an increase in density.…”

Performance of crystallization analysis fractionation and preparative fractionation on the characterization of γ‐irradiated low‐density polyethylene

“…Also, high‐energy radiation can be used to enhance its thermal and chemical resistance. Because of this technological importance, the effects of γ‐radiation on the morphology and composition of polyethylene have been widely studied over the years by many investigators 1–22. However, it is difficult to obtain a full interpretation of the changes that polyethylene undergoes after high‐energy radiation exposure because different aspects take part in this process.…”