Enhancing Hydrolytic Stability of Rice Husk‐Polyvinyl Alcohol Biocomposites Through Fertilizer Incorporation for Sustainable Agricultural Mulches

Rice husk-polyvinyl alcohol (RH-PVA) biocomposites offer a biodegradable alternative to synthetic mulches but are prone to moisture-induced degradation under tropical conditions. This study aimed to evaluate the hydrolytic stability of RH-PVA composites enhanced with NPK-Mg fertilizer at 0%, 9%, and 18% (w/w) under simulated field watering levels of 4, 8, and 16 mm/day. Fertilizer incorporation markedly improved dimensional and mechanical stability. At 16 mm/day, unfertilized mats showed a 27.5% thickness reduction and 12% diameter shrinkage, whereas 9%-18% fertilizer mats maintained > 97.5% thickness and > 96% diameter. Biomass loss decreased from 42% (0% fertilizer) to 35% (18% fertilizer), while tensile strength increased from 0.21 to 0.37 MPa (1.8-fold) and stress resistance from 2.6 to 7.6 MPa (2.9-fold). Scanning electron microscopy imaging indicated fertilizer-induced PVA agglomeration forming a continuous protective matrix that reduced fiber-matrix separation. Fourier transform infrared spectroscopy analysis showed selective PVA degradation but preserved Si-O-Si bands, indicating silica network stability and controlled nutrient release. Differential scanning calorimetry analysis revealed progressive melting point depression from 223.6°C for pure PVA to 190.8°C for the composite with 18% fertilizer and reduced crystallinity consistent with ionic interactions restricting polymer chain mobility. Overall, fertilizer integration significantly enhances RH-PVA moisture resistance, supporting its use as a durable, biodegradable mulch for high-rainfall agricultural systems.