Siloxane and polyether dual modification improves hydrophobicity and interpenetrating polymer network of bio-polymer for coated fertilizers with enhanced slow release characteristics

Sustainable bio-based coated fertilizers not only reduce nonpoint-source pollution, but also shift dependence away from petroleum-based materials. In this paper, a bio-based polyurethane (BPU) was derived from liquefied cotton straw (LCS) and was used to coat urea prills for a BPU-coated fertilizer (BPCF). Siloxane was incorporated into the BPU for the synthesis of a siloxane modified BPCF (SBPCF). In addition, both siloxane and polyether were used to modify the BPU to prepare a dual-modified BPCF (DBPCF). Various analytical and characterization tools were used to determine the properties (e.g., composition, structure, and morphology) of the BPU and the coating shells. Nutrient release experiments were also conducted to evaluate the nitrogen (N) release characteristics of the coated fertilizers. Structure and morphology analyses and measurements of the water contact angle and water adsorption revealed that the siloxane modification enhanced the hydrophobicity of the coatings of SBPCF and DBPCF to repel water entrance and thus improved the N release characteristics. As evidenced by the composition, structure and morphology analyses, further polyether modification created an interpenetrating polymer network (IPN) with the DBPCF coating to fix some of the inactive components that mitigated the rising of micropore number and size in the coating during nutrient release. As a result, the DBPCF showed the best properties and release characteristics. Findings of this work suggest that BPU-coated fertilizers, particularly DBPCF, present promising opportunities to the sustainable development of modern agriculture.