Synthesis and Application of Modified Lignin Polyurea Binder for Manufacturing a Controlled-Release Potassium Fertilizer

Conventional potassium chloride granules have inefficient applications in agricultural production due to particle irregularity and low fluidity. The application of controlled-release potassium chloride could increase the potassium-use efficiency and alleviate the shortage of potassium ore resources. In this study, a well-rounded potassium chloride fertilizer core was prepared, using the graft modification of polyurea to enhance the coating rate and release performance. The adhesive and tensile characteristics of the modified polyurea binder, as well as the granule properties of modified polyurea binder potassium chloride, were studied to determine the ideal lignin-grafted ratio. The effect of the modified polyurea binder with potassium chloride on the properties of coated fertilizer was investigated. The findings, shown by radar maps of the binder's properties, demonstrated that the ideal mass ratio of the modified lignin polyurea binder to urea is 1:2. The Fourier-transform infrared spectroscopy results demonstrated that the amino functional groups of lignin were enhanced, improving the product's interfacial compatibility with the polyurea matrix. Compared to humic acid (HA; 12%) and bentonite (Ben; 30%) treatments, the granule intensity of the 9.9%-1:2 treatment considerably increased by 139.10% and 38.86%, respectively, while the static angle of the granules reduced by 16.67% and 3.81%. The 28-day cumulative release rate of the modified polyurea (9.9%-2:1) with a 5% coating thickness was the lowest (28%), 42% lower than that of the lowest conventional treatment. In summary, the creation of a bio-lignin polyurea binder under the optimum conditions reduced the need for petrochemical-based materials, allowed the preparation of fertilizer with granules of increased fluidity, and enabled the successful coating of a high-salt potassium fertilizer, offering a novel technique for the high-value application of potash fertilizer coating.