Optimization of Compounding Parameters for Extrusion to Enhance Mechanical Performance of Kenaf-Polypropylene Composites

This work focusses on studying the effects of optimizing compounding parameters (barrel temperature, fiber feeding location, and fiber content) on key mechanical properties of kenaf-polypropylene composites. The evolution of viscosity of the blended compounds as a function of shear rate and temperature was monitored via capillary rheometer. An extruder screw speed chart was developed for the blends at established shear rates based on Couette shear rate theory. Taguchi’s optimization method was used for the design of experiments and analysis of variance (ANOVA) was performed to study the effect of each processing parameter on mechanical properties of the composites. The optimization analysis showed that the mechanical properties of the samples were strongly dependent on fiber content and feeding location within the extruder, complemented by barrel temperature. Average strength and modulus values of 48 MPa and 7 GPa respectively were obtained for compounds consisting of 40 wt% fiber, fed at the melt zone of the extruder, and processed at 190 °C. The viscosity results show relatively lower fluctuations in viscosity at shear rates >1900 s−1, which deemed ideal for processing these compounds. The SEM micrographs show that fibers were uniformly coated with polymer with some amount of seepage through the core, providing double shear action. For the current extruder (Do/Di=1.3 and shear rates 1900 s−1 to 4600 s−1), ideal screw speeds for blends considered in this study were between 75 rpm and 220 rpm.