Development of Agro-Residue Polymer Composites With Enhanced Mechanical Strength and Extended Service Life

Abstract The increasing demand for sustainable construction materials has motivated the exploration of agro-residue-based polymer composites as an alternative to conventional synthetic materials. This study investigates the mechanical behavior and environmental durability of agro-residue fiber-reinforced epoxy composites as sustainable alternatives for grain storage structures. Eleven composite formulations were fabricated using paddy straw, bagasse, mustard stalk, and wood sawdust as reinforcements with epoxy resin, silica filler, and hardener (HY-951) at varying residue-to-epoxy ratios (RERs). Mechanical testing—including tensile, compressive, flexural strength, toughness, and Brinell hardness—was performed according to ASTM standards, with the paddy straw–bagasse hybrid showing optimal performance (tensile strength: 40.5 MPa, compressive strength: 42.8 MPa, and flexural strength: 52.3 MPa). Statistical analysis revealed a strong linear correlation (R2 = 0.98) between RER and density, validating formulation stability. Durability assessments under moisture, ultraviolet (UV), and microbial exposure indicated uncoated composites degraded within 2.5–3 years due to hydrolytic, photochemical, and fungal activity. To extend service life, protective strategies—UV-stable polyurethane coatings, silane-based hydrophobic barriers, and antifungal additives (ZnO nanoparticles, quaternary ammonium compounds)—were employed, and accelerated testing confirmed resistance improvements projecting 7–10 years of durability. These findings provide a mechanics-based understanding of reinforcement effects and protective treatments on structural performance, demonstrating that agro-residue composites not only enable value-added waste utilization but also offer eco-efficient, durable materials aligned with sustainable polymer development and materials science goals.