Formulating the effects of applied temperature and pressure of hot pressing process on the mechanical properties of polypropylene–hydroxyapatite bio-composites by response surface methodology

Mechanical properties of polypropylene–hydroxyapatite (PP–HA) bio-composites produced by hot press molding depend on different parameters, particularly the pressure and temperature of the hot pressing process. In this study, a mathematical models for the effects of the pressure and temperature of the hot pressing process on the mechanical properties of the polypropylene–hydroxyapatite composites is developed using a response surface methodology. Ultimate tensile strength, Young’s modulus and impact absorbed energy were target parameters of the formulas and the temperature and pressure of the hot pressing process were independent input parameters. Formulas were derived by a nonlinear regression analysis and then were refined at the end. The validity of the formulas was also verified by experimental data. It was found that the obtained results by the formulas are matched closely to the experimental results; and the formulas have adequate precision in the ranges of the experimental data. The maximum error that occurs for the calculated results by the formulas is about 7%. The effectiveness of the pressure and temperature of hot pressing process on the mechanical properties of the composites was investigated using sensitivity analyses of the formulas. It was found that the sensitivity of the mechanical properties with respect to pressure of hot pressing process is more than temperature. Furthermore, the ultimate tensile strength of the composites has most sensitivity respect to the pressure and temperature of the hot pressing process than other mechanical properties.