Effect of Molecular Weight, Particle Size and Ringer’s Solution on Mechanical Properties of Surface-treated Polypropylene-Hydroxyapatite Biocomposites

Abstract

Bovine bone is burned at 400°C and the resulting ash is heat treated at 900°C for 90 min in order to obtain a white powder. Chemical analysis shows that this white powder is mainly hydroxyapatite (HA). Three different average particle sizes of this powder are produced by milling at three different times. The produced HA is surface treated with a silane coupling agent. Composite samples with 40% (by volume) of HA are produced by hot press molding, followed by mechanical testing in air and in Ringer’s solution. The results show that by increasing the molecular weight of polypropylene (PP), the creep strain of composites decreases proportionally, and the ultimate tensile strength (UTS) and impact resistance increase dramatically. In addition, the effect of testing in Ringer’s solution is to decrease UTS, creep, and impact properties of PP-HA composites. Furthermore, by decreasing the HA particle size, the creep strain decreases, while the UTS and impact resistance increase for the composites tested in air. Vice versa, in a wet condition decreasing of HA particle size causes UTS, creep, and impact resistance to fall. Fracture surfaces of the samples after impact tests are analyzed by a scanning electron microscope.