High density polyethylene composites containing alumina-toughened zirconia particles: mechanical and tribological behavior

Alumina-toughened Zirconia (ATZ) was used as filler with the purpose to endow High Density Polyethylene (HDPE) with enhanced mechanical and wear properties, hence widening the application field of the polyolefin as biomaterial. Composites with ATZ percentages ranging between 2 and 12 wt% were produced by melt extrusion followed by compression molding. A good filler dispersion was obtained for all the materials, despite the presence of few voids and agglomerates observed at increasing ATZ loadings. The polymer crystallinity was enhanced by filler incorporation, particularly at high percentages. The combination of high crystallinity and, mainly, lack of voids and agglomerates, appeared responsible for the improvement of Young modulus and mechanical strength. The filler positively affected the wear resistance of the composites under lubricated conditions. Indeed, under dry condition, the filler debris formation, arising from the poor interaction with the polymer matrix, resulted in an increase of the wear volume. Conversely, in the presence of water and fetal bovine serum, the layer adsorbed at the surface promoted an easy removal of the filler debris, hence highlighting the positive effect of ATZ.