Polycarbonate/Titania Composites Incorporating TiO2 with Different Nanoscale Morphologies for Enhanced Environmental Stress Cracking Resistance in Dioctyl Phthalate

Polycarbonate (PC) is susceptible to environmental stress cracking (ESC) when the conditions of pre-strain and presence of fluid with a compatible solubility index are both prevalent. One approach to counter this involves using nanoscale fillers to bridge the propagating microcracks, thus, effectively inhibiting impending failure. In this work, we report incorporation of titania (TiO2) with different nanoscale morphologies into polycarbonate matrix to assess its effect on ESC resistance against dioctyl phthalate (DOP). Using a hydrothermal process with a NaOH/Ti molar ratio of 72, TiO2 nanostructures were produced containing nanosheets with large surface area and nanotubes having typical diameter and length values of 15-20 nm and a few hundred nanometers, respectively. PC/TiO2 composites were fabricated with up to 0.5 weight percent of TiO2 nanoparticles (NPs), nanowires (NWs), or hybrid nanostructures (HNs). ESC tests were conducted by exposing test coupons to DOP oil at different temperatures and pre-strain conditions. The results showed that, under identical test conditions, while as-received PC grade exhibited complete fracture in similar to 3.1 h, PC/TiO2-0.05HN composite took similar to 70 h to fail via surface cracking. SEM examination of the fracture surface revealed that homogeneous dispersion and efficient load-bearing capability of TiO2 nanotubes and nanosheets impeded localized crack propagation by bridging the gap between the PC matrix segments. Liquid nitrogen fracture of the PC/TiO2 composite further confirmed the critical role of TiO2 hybrid nanostructures towards improvement in ESC resistance of PC matrix composites.