MECHANICAL PROPERTIES AND FRACTURE MECHANISMS OF Al_2O_3/POLYPROPYLENE NANOCOMPOSITES

摘要

The key objectives of this investigation are to study the fracture characteristics and identify the fracture mechanisms of spherical alumina (Al_2O_3) nanoparticle filled polypropylene (PP) composites. Nanocomposites containing 1.5, 3.0 and 5.0 wt% of Al_2O_3 particles (average diameter ～ 47 nm) were prepared for investigation. The Al_2O_3 nanoparticles were pre-treated with silane coupling agent before melt blending with PP matrix. Tensile test shows that both Young's modulus and tensile yield strength increase with the particle content. This suggests that the interaction between the nanoparticles and the PP matrix is strong enough so as to restrict inter-molecular sliding and subsequent yielding in the localized scale. Under quasi-static loading rate, the fracture toughness (G_C) was found to be insensitive to filler content. Using the SEDN-4PB specimens, numerous microcracks were observed to form around the sub-critical crack tip. Under impact loading rate, fracture toughness of the nanocomposites were evaluated by the Izod impact test and the impact G_C value. Both techniques indicate the impact fracture toughness increased initially with the addition of 1.5 wt% of Al_2O_3 nanofillers into the PP matrix. However, with the further addition of up to 3.0 and 5.0 wt% nano-Al_2O_3, both Izod impact strength and impact GC decreased slightly. Considering the small size of Al_2O_3 nanoparticles, their roles in the fracture mechanisms need to be studied by means of transmission electron microscopy (TEM). This part of work is currently in progress and will be presented in due course.