Development and characterization of water-resistant thermal insulating composites incorporating modified agricultural waste products including electrochemical aspects

To improve the water resistance of agricultural waste-based composites, this study applied four hydrophobic treatments: polyether-modified silicone oil (PMSO), sodium methylsiliconate (SMS), waterborne polyurethane (APU), and hydrochloric acid (HCl). These modifiers were used to prepare composites incorporating expanded vermiculite/PMSO, moso bamboo fiber/SMS, sugarcane bagasse/APU, and rice husk ash/HCl, each treated with its corresponding hydrophobic agent. The study examined the composites' structural features, morphological characteristics, microstructure, moisture resistance, mechanical behavior, thermal insulating ability, waterproofing capabilities and electrochemical performance. The modified composites transitioned into a highly hydrophobic state with contact angles reaching 117.4° and adhesion forces of 0.12 mN. Random forest regression models validated these results, identifying the sliding angle and chemical composition as primary performance predictors. With a thermal conductivity of 0.19 W/m·K, the developed boards demonstrated competitive thermal performance relative to lightweight masonry materials. Finite element simulations conducted in ANSYS and Cast3M validated these results, showing high correlation with experimental measurements. The high sugarcane bagasse content variant achieved a compressive strength of 1.24 MPa (tested according to ASTM C578), while high microstructural tortuosity (6.97%) and optimized pore distribution effectively mitigated water uptake (ASTM C209-20). This integrated approach shows that hydrophobic treatments and specialized fillers significantly enhance interfacial bonding, thermal efficiency, and long-term durability for bio-based building insulation.