The Potential Application of Walnut Shells as Biofillers for Natural Rubber Composites

Abstract

It was evaluated whether walnut shells should be used as filler in composites made of natural rubber. Samples of walnut shells were ground to fine powders, sieved through a 75 μm mesh, and were used in compounding natural rubber using varying filler loading of unfilled, 20 hpr, 30 hpr, 40 hpr, and 50 hpr. The physicochemical analysis results of the walnut shell powder were 5.30, 10.10%, 2.50%, 43.70%, 49.70 mg/g, and 50.75 g/100 g for pH, moisture content, ash content loss of ignition and iodine adsorption number respectively. While the values obtained for the carbon black were 6.30, 2.89%, 6.35%, 92.90%, 79.88 mg/g, and 54.0 g/100 g for pH, moisture content, ash content loss of ignition and iodine adsorption number respectively. These properties include tensile strength, hardness, abrasion resistance, and compression set. The result shows that walnut shell-filled composite has a high reinforcement at filler loading of 30-40 phr and at a certain higher level it only acts as a diluent. In addition, the walnut shell is grouped as a semi-reinforcing filler having an absorption number of 49.70 mg/g which is about half the value of carbon black.