The influence of molecular orientation on the crosslinking/oxidative behaviour of iPP exposed to gamma radiation

Abstract

This paper presents a study of the influence of structural peculiarities, uniaxial orientation and fibrillar structure on the radiation-induced changes in iPP. For the purposes of this study, iPP was oriented via solid-state stretching at elevated temperature to various draw ratios and, later on, gamma irradiated in air. In order to investigate orientation- and/or radiation-induced structural changes, optical microscopy (OM), scanning electron microscopy (SEM), wide angle X-ray scattering (WAXS), differential scanning calorimetry (DSC), infrared spectroscopy (IR) and gel measurements were employed. To quantify the degree of molecular orientation, Herman’s orientation function ( f c ), was used. IR spectroscopy and gel measurements were used to determine the changes in the oxidative degradation and degree of network formation, respectively. Sol–gel analysis was studied in detail using the Charlesby–Pinner (C–P) equation. The radiation-induced changes in the structure and evolution of oxygen-containing species were also studied through dielectric loss (tan δ) analysis in a wide frequency range; the polar groups that were introduced by irradiation in apolar iPP were considered as tracer groups. Conclusions derived according to different methods were compared. Presented results reveal two different radiation-induced dynamics; gamma irradiation of initial and fully developed fibrillar iPP structures leads to significantly different crosslinking and/or oxidation response.