Damage formation during fracture of polystyrene/clay and polystyrene/nanoporous silica nanocomposites

Although clay-based polymer nanocomposites provide enhanced chemical properties, the mechanical properties and in particular, the effects of the nanoscale particles on mechanical properties, are not yet well understood. For this study, two types of raw polystyrene specimens, three polystyrene/clay nanocomposites, and one polystyrene/nanoporous silica nanocomposite were investigated. The nanocomposites differed in that one was produced through mechanical mixing, one through in situ polymerization, and one through exfoliation of the clay. All the clay composites had 5% particulate loading and tensile properties were similar. Standard three-point-bend fracture tests were performed to determine the fracture toughnesses of the different polystyrene nanocomposites and to investigate crack resistance curves. The process zone during crack propagation was observed in situ with an optical stereo microscope and with an optical profilometer. Post-test analysis of the microstructure and fracture surfaces was performed with electron microscopy. For the 5% particle loadings all composite polystyrene systems have lower toughnesses than the raw polystyrene.