Abstract

The development of sustainable and high-performance acoustic materials requires replacing petroleum-based polyurethane foams (PUFs) with renewable alternatives. In this work, fully bio-based PUFs were synthesized using castor oil as polyol and reinforced with rice husk-derived silica (RHS) and cellulose (RHC). A series of formulations with varying additive loadings (0–2.0 phr) was fabricated and systematically characterized for chemical structure, morphology, thermal stability, mechanical strength, moisture resistance, and acoustic absorption. Results confirmed successful integration of silica–cellulose fillers within the castor oil-based polyurethane matrix, with Fourier-transform infrared spectroscopy indicating enhanced hydrogen bonding and filler–matrix interactions. The addition of RHS/RHC improved compressive strength and stiffness, with the optimum performance observed at 0.7–1.5 phr. Thermal analysis revealed enhanced degradation resistance at higher filler loadings, while moisture absorption tests showed reduced equilibrium uptake, particularly at ≥0.7 phr. Acoustic evaluation demonstrated that moderate filler contents preserved sound absorption performance comparable to that of neat PUF, while excessive loading reduced broadband absorption. Overall, the findings highlight the dual advantage of sustainable sourcing and functional property enhancement, positioning castor oil-based PUF reinforced with agro-waste fillers as a promising candidate for green acoustic and structural applications. Future work will explore replacing petroleum-based isocyanates with bio-derived or less-toxic alternatives, alongside filler ratio optimization, flammability and durability assessments, scalability, and environmental adaptability under humid conditions.