A statistical model was developed in this study to describe cure characteristic, rebound resilience and tensile strength of natural rubber/starch composites which was prepared by using a Haake internal mixer. Response surface methodology (RSM) based on central composite centered design (CCD) was employed to statistically evaluate and optimize the conditions for maximum cure characteristic, rebound resilience and tensile strength and study the significance and interaction of carbon black and glycerol on rebound resilience and tensile strength yield. The experimental runs were carried out according to a 22 full factorial design for the two identified design independent variables, namely, carbon black (X1) and glycerol (X2). With the use of the developed quadratic model equation, a maximum rebound resilience 71% was obtained to be a carbon black loading of 50 phr and glycerol loading of 7 %.

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The effect of substrate cleaning using ultrasonic cleaner on tungsten carbide was investigated. The surface energy of the substrate was measured using two liquids with dominant polar and dominant dispersion components which were distilled water (DI) and methylene iodide. Owens-Wendt method was carried out to calculate the surface energy of the substrate. The result showed that the cleaning process using solvent B (alkaline, DI, acid, DI, DI, alcohol) for 20 minutes without the wiping process led to the highest surface energy of 126.3399 dyne/cm with the polar component of 80.538 dyne/cm. Findings from this research suggested that type of solvent, cleaning time, and interactions among solvent type, cleaning time, and wiping process significantly influenced surface energy of the substrate.