The optimization of tensile strength property of polypropylene/clay composite prepared in a twin screw extruder

The addition of clay to polypropylene (PP) has been known to improve the mechanical properties of PP/clay composites. There are several important variables that affect the increase in tensile strength properties of PP/clay composites. However, the optimum conditions for these variables are not known. The important variables are material composition and processing conditions. The purpose of this study was to find the optimum conditions to obtain the best tensile strength properties of the polypropylene (PP)/clay composite. The optimum conditions are clay:compatibilizer ratio, screw speed, and process temperature. PP/clay composites were processed via melt mixing using twin screw extruder. The Box-behnken response surface method was selected to obtain optimum conditions of PP/clay composite prepared by twin screw extruder. The ratio of clay:compatibilizer with variations of 1:1;1:2;1:3, screw speeds of 30, 40, and 50 rpm, and process temperatures of 180, 200, and 220 °C were analyzed to determine the effect of these variables. Polypropylene-grafted-maleic anhydride (PP-g-MA) 6 wt% was used as a compatibilizer to facilitate PP-clay bonding. The experimental results showed an increase in tensile strength from 27.895 N/mm2 for pure PP and around 30.359 to 32.353 N/mm2 for PP/clay composites. As a result, the optimum tensile strength value of the composite was predicted at a clay:compatibilizer ratio of 1:1.25, screw speed 50 rpm, and a process temperature of 220 °C. An experiment at the optimum conditions were carried out to verify the tensile strength value predicted by the software. At the optimum conditions, the tensile strength was 32.84 N/mm2 or an increase of 17.7%. The clay structure on PP was investigated using XRD analysis and showed the peak shifting to lower angle.