Apparent reversal of physical aging by electron beam irradiation - further investigations

An investigation into the irradiation of physically aged glassy polymers has lead to further refinements of a previous study. Polymers used in this investigation were: polycarbonate, polystyrene, and poly(ethylene terephthalate). In this work we have followed up an earlier study in which it was observed that the characteristic DSC enthalpy relaxation peak associated with physical aging was reduced when the sample was irradiated with an electron beam accelerator below T-g. This reduction was proportional to the dose the sample received. In this work we have investigated the volumetric changes that occur in these samples as well as further enthalpic relaxation studies. It was found through the use of the classical Charlesby-Pinner analysis that there exists a strong correlation between the scission G value, G(s), and little if any for the cross-linking G value, G(x) with the enthalpic relaxation behavior. This leads us to modify our earlier hypothesis and conclude that the phenomenon is primarily caused by internal energy changes manifested in endgroup creation through main chain scission during irradiation and not accompanied by the typical density changes associated with physical aging. (C) 1998 Elsevier Science Ltd. All rights reserved.