Lactic acid oligomer grafted gum acacia encapsulated controlled release nitrogen fertilizer for crops improvements and greener soil sustainability

• Bio-adhesive synthesized by poly-condensation of lactic acid and gum acacia. • Urea was encapsulated in hydrophobic bio-adhesive to slow down its release. • Grafting efficiency and the urea release rate were inversely proportional. • Slow-release urea fertilizer helps effective use of nitrogen in agriculture. Nitrogen (N) is an essential nutrient for plant growth and productivity. Urea contains 46 % N, the highest content of solid nitrogenous fertilizers, but it is limited in its delivery system. In this research work, urea was encapsulated in a hydrophobic bio-adhesive, which was synthesized through a poly-condensation reaction of lactic acid (LA) and gum acacia (GA) to control its dissolution rate in water. Box-Behnken method of design expert software was used to investigate the effect of process parameters on the grafting efficiency and urea release rate. The grafting efficiency and the urea release rate were inversely proportional. The grafting of lactic acid oligomer (LAO) chains at the O H and N H functional groups of the GA backbone was confirmed by FTIR and NMR analyses. The solubility and hydrophobicity tests of LAO-g-GA exhibit that both increase with grafting efficiency. The study found that the urea release rate increases with the temperature of the medium and urea concentration but decreases with the increase in pH of the medium. The results observed from the study could help commercialize slow-release urea fertilizer for the effective use of nitrogen and maintain a pollution-free environment.