Asymmetric functional-coating strategy for biomass fiber-based biodegradable membranes with enhanced hydrophobicity and nutrient release for sustainable agriculture

The development of biodegradable membranes with tunable nutrient release is critical for sustainable agriculture but remains challenging due to insufficient mechanical strength, poor hydrophobicity, and uncontrollable degradation behavior. Given that nutrient release occurs primarily at the soil interface while hydrophobicity is required on the air-facing side, an asymmetric functional-coating strategy is needed to reconcile these competing requirements. We propose an asymmetric functional-coating strategy for a biomass fiber-based membrane. The air-facing side was modified with chitosan (CS) and stearic acid (SA) to enhance hydrophobicity, whereas the soil-facing side was coated with a mixture of gelatin, urea, and seaweed extract to achieve controlled nutrient release. The resulting composite membrane showed a marked increase in water contact angle from 45.8° to 125.1° and a decrease in water absorption from 220.59% to 78.59%. Meanwhile, the burst resistance index and elongation at break increased from 5.66 kPa·m2/g and 14.09% to 8.10 kPa·m2/g and 39.24%, respectively. And at 30 days, the nitrogen slow-release amount of the coating membrane reached 158.17 mg/L. This asymmetric bilayer design overcomes key performance limitations of conventional biodegradable membranes and integrates dual functions of moisture protection and nutrient regulation. The proposed strategy provides new insights into the high-value utilization of biomass-based degradable materials and supports the sustainable development of green agriculture.