Characterisation of Palm Kernel Shell Ash as a Reinforcing Filler in Natural Rubber Compounds for Tyre Tread Applications

The rubber goods manufacturing sector in Nigeria depends heavily on imported carbon black as the primary reinforcing filler for natural rubber compounds, creating cost pressures and supply chain vulnerabilities. This study characterises palm kernel shell ash as a potential alternative or supplementary reinforcing filler in natural rubber compounds formulated for tyre tread applications, using ash produced from palm kernel processing facilities in Cross River State, South South Nigeria. Palm kernel shell ash was prepared by controlled combustion at 500 and 700 degrees Celsius, and characterised for particle size, surface area by BET analysis, silica content by X-ray fluorescence, and pore structure. Rubber compounds were prepared at filler loadings of 20, 40, and 60 parts per hundred rubber, cured by sulphur vulcanisation, and tested for tensile strength, elongation at break, tear strength, abrasion resistance, and hardness following ISO test methods. Results demonstrate that ash calcined at 500 degrees Celsius contained 38 percent silica and achieved BET surface area of 42 m2/g, higher than ash calcined at 700 degrees Celsius. Rubber compounds filled with 40 parts per hundred of 500-degree ash achieved tensile strength of 18.2 MPa, elongation at break of 520 percent, and abrasion resistance index of 112 relative to unfilled control. Performance was significantly below carbon black-filled controls at equivalent loading but represents substantial cost savings at 15 percent of carbon black pricing. The study recommends palm kernel shell ash as a partial carbon black replacement in cost-sensitive rubber compound formulations in South South Nigeria. Keywords: palm kernel shell ash, natural rubber, reinforcing filler, tyre tread, Cross River State