Effect of Hydroxyl Value and Compatibilizing Additives on Green Polyurethane Composite Films Based‐On Rubber Seed Oil for Slow‐Release Fertilizer Applications

The hydroxyl value of the polyol plays a pivotal role in the formation of the polyurethane network, significantly influencing the properties of the resulting composites, especially in coating applications. Despite its importance, this factor has not been systematically investigated in previous literature. In this study, the P230 GPUC film (utilizing a bio‐polyol with a hydroxyl value of 230 mg KOH/g) exhibited superior tensile properties and enhanced hydrophobicity. While bentonite modified with PEG is a common approach in existing studies, this work introduces a novel combination of additives TRITON CF‐10 (CF10), Dynoadd F‐100 (F100), and BYK‐333 (BYK333) to further improve compatibility and surface tension. Among the various formulations proposed, experiments demonstrate that the BYK‐0.4 GPUC film (containing 0.5 wt.% F100, 0.2 wt.% CF10, and 0.4 wt.% BYK333) achieved the best overall performance. It not only displays excellent mechanical strength but also yields the highest hydrophobicity, alongside the lowest water absorption, vapor permeability, and nitrogen permeation. These synergistic properties render the film highly suitable for slow‐release fertilizers coating with extended‐release cycles and making it ideal for long‐term crops.