Mechanical and Thermal Characterisation of Coconut Shell Particle-Filled Polypropylene Composites Produced in Rivers State

Coconut shell is an abundant agricultural waste material in coastal regions of South South Nigeria, offering a low-cost filler option for thermoplastic composite production. This study characterises polypropylene composites filled with varying weight fractions of coconut shell particles prepared from shells collected in Rivers State. Shell particles were processed by drying, milling, and sieving to particle sizes of 150 and 300 micrometres. Composites were prepared by melt compounding using a twin-screw extruder at filler loadings of 10, 20, and 30 percent by weight, with and without silane coupling agent treatment of filler surfaces. Tensile strength, flexural strength, hardness, and notched impact strength were determined following ASTM standard procedures. Thermogravimetric analysis and differential scanning calorimetry characterised thermal stability and crystallinity modifications. Results demonstrate that 20 percent filler loading with silane-treated particles produced the most favourable mechanical response, with tensile strength of 29.8 MPa and flexural modulus of 1.84 GPa. Impact strength declined progressively with filler loading, a trend attributed to stress concentration effects at filler-matrix interfaces. Thermal analysis confirmed that coconut shell particles slightly elevated the onset of thermal degradation by approximately 8 degrees Celsius relative to neat polypropylene, suggesting marginal thermal stabilisation. Crystallinity measurements showed a nucleating effect of shell particles, increasing crystallinity fraction from 43 to 51 percent. The study recommends optimised silane coupling agent concentrations and compatibiliser addition for further enhancement of interfacial properties in coconut shell-polypropylene composites for industrial application in South South Nigeria. Keywords: coconut shell, polypropylene composite, filler, mechanical properties, Rivers State