Preparation and Properties of Dehydroabietic Acid-Grafted Chitosan-Modified Castor Oil-Based Polyurethane-Coated Controlled-Release Fertilizer

In this work, a castor oil-based polyurethane-based controlled-release urea modified with dehydroabietic acid-grafted chitosan was prepared, overcoming the poor hydrophobicity of traditional coatings. Dehydroabietic acid-grafted chitosan (HNCSDA) was synthesized and incorporated into castor oil-based polyurethane to fabricate modified coated fertilizers. The chemical structure, micromorphology, thermal stability, hydrophobicity, nitrogen release, phytotoxicity and antifungal performance of the coatings were systematically characterized. HNCSDA improved coating compactness and continuity, reduced structural defects and formed an effective diffusion barrier. Increasing the HNCSDA dosage from 0% to 20% increased the hydrophobicity and thermal stability of the coating; the water contact angle increased from 80.6° to 116.7°, and the release longevity increased by 15.54%. In the absence of maize phytotoxicity and effectiveness against Botrytis cinerea and Rhizoctonia solani, the modified coatings increase seedling growth, offering a feasible route to eco-friendly biobased slow-release antifungal fertilizers for sustainable agriculture.