PLA/Starch Composite Coating Used for Developing Slow Releasing Fertilizer

Abstract

An eco-friendly coating material based on polylactic acid (PLA) and aged rice starch was developed for slow-release fertilizers (SRFs). In this system, aged starch served as both a cost-effective filler and a channel for facilitating nutrient release during the initial stages. By adjusting the PLA-to-starch ratio, the water channel formation rate within the coating could be precisely controlled, effectively regulating the release behavior of urea. Coated urea particles were prepared using a spraying technique, and their microstructure, morphology, thermal properties, and release rates were systematically evaluated via scanning electron microscopy (SEM), differential scanning calorimetry (DSC), and water release experiments. The results demonstrated that both the morphological and thermal properties of the composites varied with starch content. Notably, the inclusion of starch eliminated the zero-release period, enabling earlier nutrient availability. The release rate of urea increased proportionally with starch content, as starch created diffusion channels in the coating. The optimal composite formulation, PLA85/Starch15, achieved a 77% release rate over 28 days, meeting international standards for SRFs (approximately 75%). This study highlights the potential of PLA/aged rice starch composites as sustainable coating materials for controlled-release fertilizers.