Effect of surface modification on the mechanical, thermal, and water absorption properties of waste citrus grandis pectin and Chrysopogon zizanioides fiber-reinforced vinyl ester composites

This study investigates the development of sustainable hybrid biocomposites reinforced with silane-treated Chrysopogon zizanioides root fibers and pomelo peel-derived pectin filler in a vinyl ester matrix. The composites were fabricated using the conventional hand lay-up technique with a constant fiber loading of 40 vol.% and varying pectin filler contents of 1–5 vol.%. Fourier transform infrared spectroscopy (FTIR) confirmed the effectiveness of silane treatment through the presence of characteristic functional groups associated with improved interfacial interaction. The fabricated composites were evaluated for mechanical, thermal conductivity, water absorption, and morphological behaviour. The incorporation of silane-treated reinforcements significantly enhanced the composite performance compared to sample V. Among all formulations, the VNP2 composite containing 3 vol.% pectin filler exhibited the best mechanical properties, achieving a tensile strength of 149 MPa, flexural strength of 162 MPa, impact strength of 4.5 J, and hardness of 82 Shore-D, corresponding to improvements of 161.4%, 134.8%, 1306.3%, and 7.9%, respectively, over the sample V. Thermal Conductivity increased progressively from 0.23 W/mK for the unreinforced matrix to 0.45 W/mK for VNP3, representing a 95.7% enhancement. Water absorption decreased from 1.84% to 1.23%, corresponding to a 33.2% reduction due to improved interfacial adhesion and restricted moisture diffusion pathways. Scanning Electron Microscopy (SEM) analysis revealed improved matrix–reinforcement interaction and reduced crack propagation in the treated composites. Overall, the results demonstrate that silane-treated Chrysopogon zizanioides fibers and pomelo-derived pectin filler effectively improve the mechanical, thermal, and moisture resistance characteristics of vinyl ester composites, highlighting their potential for lightweight and sustainable structural applications.