Increasing Charpy Impact Value of Polycarbonate (PC) Sheets Irradiated by Electron Beam

Abstract

Applying low-potential electron beam irradiation (EBI) dose of 0.13 MGy to polycarbonate (PC) sheet on both side surfaces apparently improved the impact value (a uc ) over the untreated samples at all accumulative probabilities of fracture (P f ). Based on 3-parameter Weibull equation, the 0.13 MGy-EBI also raised the lowest limit of a uc (25.5 kJ m ¹2 ) estimated at P f = 0 (a s ) 14% over the untreated samples (22.0 kJ m ¹2 ), indicating improved reliability and safety. EBI generates dangling bonds where repulsive forces are generated between the outer shell electrons at terminated atoms in the PC polymer irradiated near the sample surface, probably inducing relaxation of heterogeneous stress concentration, as well as compressive stress (high molecular density) by micro-expansion around terminated atoms increasing the a uc . Increasing EBI dose increased ductility by decreasing the fractured split ratio, R s a characterization of separated portion of total cross-section of fractured PC. The 0.13 MGy dose (R s = 0.30) appears to be at or near the optimal EBI dose obtaining the highest a uc . Above 0.22 MGy the a uc reduces with increasing dose. Excessive dangling bonds generation appeared to increase ductility in the form of lowering the R s but weakens the molecular structure allowing chains to slide past each other easier decreasing impact values with less crack propagation. Therefore, when applying EBI to polycarbonate parts in industrial applications carefulness is highly recommended to adjust dose to optimal level for maximum strength and safety.