Influence of Alkali Treatment and Loading on the Physical, Mechanical, and Morphological Properties of the Composites from Waste Corn Cob Reinforced Polystyrene Foam

This study investigated the influence of alkali (NaOH) treatment and filler loading on the performance of waste corn cob–reinforced polystyrene foam composites. The work was motivated by the need to convert agricultural residues into value-added materials suitable for lightweight structural applications. Composites were produced with corn cob filler contents ranging from 0 to 50 wt.%, and the treated fillers were incorporated into the polymer matrix through conventional processing techniques. To evaluate performance, physical and mechanical tests were conducted, including flexural strength and modulus, tensile strength and modulus, hardness, density, and water absorption. In addition, scanning electron microscopy (SEM) was used to examine the interfacial interaction between the filler and the matrix. Data were collected systematically across all filler loadings to determine the effect of reinforcement level on composite behaviour. The results showed that alkali treatment improved filler–matrix adhesion, particularly at moderate filler contents. Flexural strength was highest in the unreinforced matrix (31.687 MPa) but decreased with increasing filler content, reaching 12.844 MPa at 50 wt.%. However, the flexural modulus peaked at 30 wt.% (2428.646 MPa), indicating improved stiffness at this composition. Tensile modulus increased progressively with filler loading, attaining 1858.215 MPa at 50 wt.%, while tensile strength declined to 1.431 MPa. Hardness values varied across compositions, with the highest value (388) recorded at 20 wt.%. Water absorption increased as filler content rose due to the hydrophilic nature of corn cob, whereas density decreased, reflecting reduced compactness at higher loadings. SEM observations confirmed improved dispersion and interfacial bonding at moderate filler levels but revealed agglomeration at higher contents. Therefore, the study demonstrates that alkali-treated corn cob can serve as a viable and sustainable reinforcing filler in polystyrene foam composites. Optimal performance was achieved between 20 and 30 wt.% filler loading, where a balance between stiffness, strength, and durability was observed. It is recommended that future studies focus on optimizing fiber dispersion and exploring surface modification techniques to further enhance mechanical performance at higher filler loadings.