Biodegradable hydrogels of cassava starch-g-polyacrylic acid/natural rubber/polyvinyl alcohol as environmentally friendly and highly efficient coating material for slow-release urea fertilizers

[Display omitted] •A novel CSt-g-PAA/NR/PVA semi-IPN hydrogel was developed for slow-release nitrogen fertilizer.•The properties of coating hydrogels were strongly depended on the NR/PVA ratios.•The BHWCU/9:1 formulation showed the excellent performance of slow-release property.•The developed BHWCU fertilizer could be applicable in sustainable agriculture and horticulture. Biodegradable semi-IPN hydrogels of cassava starch (CSt)-g-polyacrylic acid (PAA)/natural rubber (NR)/polyvinyl alcohol (PVA) at different NR/PVA ratios were developed as low-cost coating membrane for improving slow-released fertilizer with low negative impact on environments. The effect of NR/PVA ratios on mechanical properties, swelling behavior, water retention and biodegradation of the semi-IPN hydrogels was evaluated. The biodegradable hydrogel wax coated urea (BHWCU) was produced by coating urea particles with semi-IPN hydrogel and wax as inner and outer layers, respectively. Results revealed that the higher NR/PVA ratios caused the significant decrease in water swelling, modulus, water-retention and biodegradation of the hydrogels. The BHWCU/9:1 formulation exhibited an excellent slow-release N nutrient in both water (47.5% at 168 h) and soil (38.5% at 30 day), relating well with the lowest surface area (1.95 m2/g) and pore volume (3.75 × 10−3 cm3/g). The release kinetics of BHWCUs in both water and soil followed the Korsmeyer-Peppas model. The released nutrient from the BHWCU/9:1 was strongly depended on the pH, temperature and ionic strength. The growth of chili plant was effectively facilitated by the BHWCU/9:1 having 4–5 times lower production cost (80.36 Baht/kg) than commercial slow-release fertilizer. Thus, the BHWCU formulations could be extensively applicable in sustainable agriculture.