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

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 m(2)/g) and pore volume (3.75 x 10(-3) cm(3)/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. (C) 2021 The Korean Society of Industrial and Engineering Chemistry. Published by Elsevier B.V. All rights reserved.

Automated summary

The biodegradable semi-IPN hydrogels of cassava starch (CSt)-g-polyacrylic acid (PAA)/natural rubber (NR)/ polyvinyl alcohol (PVA) developed at different NR/PVA ratios showed varying mechanical properties, swelling behavior, water retention, and biodegradation. The BHWCU/9:1 formulation demonstrated excellent slow-release nitrogen nutrient release both in water and soil, with lower production cost than commercial slow-release fertilizers, making it a promising option for sustainable agriculture.