Eco-Friendly Polymer Materials Based on ESO and Citric Acid for Controlled-Release Urea and Improved Nutrient Use

Abstract

Controlled-release fertilizers offer a promising solution to improve nitrogen use efficiency (NUE) in agriculture, reducing environmental losses associated with conventional urea application. In this study, a biodegradable biocomposite matrix based on epoxidized soybean oil and citric acid to encapsulate urea and achieve sustained nutrient release is developed. The resulting biocomposites were characterized by Fourier-transform infrared spectroscopy and scanning electron microscopy to confirm chemical structure and morphology. Biocomposites urea-release studies indicated a controlled-release profile dominated by Fickian diffusion, with a burst zone within the first 2 h (up to 16% of urea release percentage) followed by a slower, sustained release. The biocomposites demonstrated minimal swelling, supporting a diffusion-driven release mechanism, further validated by fitting the release data to Korsmeyer-Peppas and Weibull models. SEM analysis revealed a network of micro and nanopores facilitating gradual nutrient diffusion. Additionally, preliminary greenhouse evaluations on maize demonstrated that biocomposites significantly enhanced plant growth and biomass accumulation compared to free urea, confirming their potential to improve NUE in agricultural settings. These results underscore that biocomposites offer an effective, sustainable alternative for nitrogen fertilization, mitigating environmental impact while bolstering crop performance. Future work will focus on expanding field trials to assess the practical applications of biocomposites under diverse soil and crop conditions.