Influence of injection process parameters on mechanical properties of isotactic polypropylene: A design of experiments approach

This study optimizes the effect of injection parameters such as melting temperature, injection pressure, injection speed, holding pressure, mold temperature, and cooling time on isotactic polypropylene (iPP) moldings. The 2k factorial design is used to employ for planning the experiment to study the tensile properties of iPP specimens, such as ultimate tensile strength, and strain at yield. The effect of the parameters on the mechanical properties is determined by using the variance analysis. The four factors as melting temperature, holding pressure, mold temperature, and cooling time were the results obtained by screening with a full factorial design, which is a significant parameter. The optimum condition for the highest tensile properties of iPP was obtained when setting injection molding conditions with melting temperature, mold temperature, holding pressure, and cooling time remained at 230 °C, 60 °C, 80 bar, and 20 sec. Base on ANOVA, empirical equations are proposed to relationship for predicting the ultimate tensile strength and strain at yield. The changes in the microstructure of the injection molding specimens are discussed in terms of crystallinity degree. All of this was supported by a polarized optical microscopy (POM) and one-dimension wide-angle X-ray diffraction (1D-WAXD) measurements.