Polycarbonate/Titania Composites Incorporating TiO₂ with Different Nanoscale Morphologies for Enhanced Environmental...

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 ~3.1 h, PC/TiO₂-0.05HN composite took ~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.