Influence of Particle Size and Surface Treatment on Mechanical Properties of Bambara Nut Shell and Cowpea Husk-Polyester Composites

Bambara nut (Vigna subterranea) is a grain legume native to sub-Saharan Africa, with its shell remaining an underutilised agricultural waste. Similarly, cowpea (Vigna unguiculata L. Walp), a widely cultivated legume crop in Africa, has husks with untapped potential for composite applications. Despite their availability, using Bambara nutshell and cowpea husk as fillers in polyester resin composites has been minimally explored. This study aims to develop natural particulate-based composites using Bambara nutshell and cowpea husk fillers of varying particle sizes and loadings within an unsaturated polyester resin matrix. The physical, mechanical, structural, and morphological properties of these composites were investigated. The study revealed that optimal composite properties were achieved at a filler loading of 10 wt% for both Bambara nutshell and cowpea husk. Treatment of the fillers with a 5% alkaline solution significantly enhanced the composite performance. Bambara nutshell-filled composites exhibited superior hardness, whereas cowpea husk-filled composites demonstrated better tensile and flexural properties, higher crystallinity index, lower density, and more pronounced peak intensities. These results suggest that the developed composites are suitable for nonload- bearing applications, particularly in packaging and indoor partition board systems