International Journal of Polymer Science and Engineering
Walnut Shells’ Potential Use as Biofillers in Natural Rubber Composites
1Research Scholar, Department of Chemistry, School of Basic and Applied Sciences, Lingaya’s Vidyapeeth, Faridabad, Hariyana, India.
Abstract
The study assessed the potential of walnut shells as a filler in natural rubber composites. Walnut shells were finely ground, sieved through a 75 μm mesh, and incorporated into natural rubber at different filler loadings: unfilled, 20 parts per hundred rubber (phr), 30 phr, 40 phr, and 50 phr. The physicochemical properties of the walnut shell powder were analyzed, yielding results of 5.30 for pH, 10.10% for moisture content, 2.50% for ash content, 43.70% for loss on ignition, and an iodine adsorption number of 49.70 mg/g. In comparison, carbon black exhibited a pH of 6.30, moisture content of 2.89%, ash content of 6.35%, loss on ignition of 92.90%, and an iodine adsorption number of 79.88 mg/g. The performance of the composites was evaluated based on tensile strength, hardness, abrasion resistance, and compression set. The findings indicated that the walnut shell-filled composites demonstrated significant reinforcement, particularly at filler loadings of 30–40 phr. However, at higher levels, the walnut shell acted primarily as a diluent rather than a reinforcing agent. Overall, walnut shells were categorized as semi-reinforcing fillers, exhibiting an iodine absorption number of 49.70 mg/g, which is approximately half that of carbon black. This suggests that while walnut shells can enhance certain properties of natural rubber composites, their reinforcing effectiveness diminishes beyond a certain filler loading
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