Thermo-Oxidative Aging Effect on Charge Transport in Polypropylene/Ultra-High Molecular Weight Polyethylene Nanocomposites

Abstract

This study investigates the impact of magnesium oxide (MgO) nanoparticles on the thermo-oxidative aging behavior of blends of polypropylene (PP) and ultra-high molecular weight polyethylene (UHMWPE). The samples, both unfilled and filled with MgO, were aged at 120 °C for varying durations of up to 672 h. The observed structural changes are not monotonic; recrystallization leads to the increased crystallinity and melting temperature of UHMWPE until 336 h. Beyond this, the consumption of the antioxidant leads to chain scission which, in turn, results in decreased crystallinity. The presence of carbonyl groups indicates chemical changes and, as such, the carbonyl index is used as an indicator of aging, with subsequent changes to charge transport. During thermal aging, the interaction between PP and UHMWPE chains at interfaces is enhanced, leading to improved compatibility and the emergence of a new single crystallization peak in PP/UHMWPE blends. Although MgO does not show evidence of elevating the crystallization temperature, implying the absence of enhanced nucleation, it acts as a compatibilizer, improving interfacial interaction compared with the unfilled blend counterparts. MgO hinders the breakage of molecular structures and impedes the diffusion of oxygen. This, in turn, results in nanocomposites filled with MgO having reduced their charge accumulation and conductivity, thus delaying the aging process compared to PP/UHMWPE blends without nanofiller.