Introduction of bio-based hard segment as an alternative strategy to environmentally friendly polyurethane coated urea

Improved degradation performance of bio-based polyurethane coatings has become a significant challenge for agricultural applications of controlled-release fertilizers. In this work, petroleum-based isocyanate components were innovatively replaced with lysine diisocyanate (LDI) ingredients in various ratios by the in-situ reaction with castor oil to synthesize high bio-based content polyurethane coating materials. The chemical structure and properties of the coatings were also investigated to propose the mechanism of LDI-mediated coatings controlled release and degradation performance. The experiment results indicate that as the LDI content increased, the coatings’ thermodynamic stability, cross-linking density, and controlled release performance decreased while their hydrophilicity and degradation performance increased. Compared to other coated ureas, the coated urea with the 1:1 replacement ratio of petroleum-based isocyanate performed well and had adjustable controlled release performance. Its release period was regulated by adjusting the coating rate and reached 60 days with the 3 % coating rate. With the increase of the lysine component, the degradation performance of the coating materials was improved till the replacing ratio of petroleum-based isocyanate was higher than 1:1. In all, the introduction of bio-based isocyanate is an alternative way further to enhance the degradation performance of the coating materials, and the coatings were non-toxic to rice seeds. The coordination of the controlled release and degradation performance of the coatings can be achieved by adjusting the content of LDI. This research designed a novel strategy to solve the bottleneck problem of bio-based polyurethane coating degradation in coated fertilizers.