A slow-release urea prepared via sandwich with degradable chitosan: Formulation and release mechanisms

Abstract

To reduce environmental pollution due to excessive use of urea fertilizer, a new fertilizer formulation has been created, made from urea combined with sulfosuccinate crosslinked chitosan (CS), polyvinyl pyrrolidone (PVP), and Ca²⁺, for application as slow-release urea. The formulation is made by coating urea using Chitosan-sulfosuccinate-PVP (CSP) and Ca²⁺ to form a mesh material. Based on functional group test data, it is indicated that the interaction between urea and CSP occurs through the formation of hydrogen bonds, where urea is trapped in the middle of the net structure covered by CSP and Ca²⁺ acts as an outer coating. The layer will act to protect water contact with the urea so that dissolution is controlled, and the urea does not decompose quickly into the environment. This system facilitates the regulated solubilization of urea over a duration of 30 days, employing a slow-release mechanism that around 30 ppm/day under conditions of pH 7 at ambient temperature. Based on the SEM morphological traces, urea is released through a small tunnel created by the slow penetration of water from the outside to the inside of the membrane.