Fertilizers are essential materials that provide nutrients for plant growth and help to increase agriculture productivity. According to worldwide usage of fertilizer, urea is the most commonly used synthetic nitrogen fertilizer with a nitrogen content of 46%. However, to ensure the plants get enough nitrogen, the overuse of urea fertilizer is practiced, which resulted in the loss of nitrogen. So, to overcome these disadvantages, controlled-release fertilizer (CRF) has been practiced. The CRFs are commonly produced with petroleum-derived polymers, including polyethylene, polystyrene and polyurethanes. However, the use of petroleum-derived polymers for fertilizer coatings is in the process of being discouraged and sometimes forbidden due to rising environmental concerns, as they contain non-degradable materials. The objective of this study is to develop a biobased controlled-release fertilizer coating using kraft biorefinery lignin. In this process, we applied user design of response surface methodology in the Design-Expert® Version 12 software to optimize the equivalent ratio of polyols formulations of the biobased polyurethane to coat urea fertilizer. Fourier transform infrared (FTIR) spectroscopy analysis was used to confirm the formation of polyurethane linkages. These spectra revealed the formation of the polyurethane, as there is a considerable reduction in the intensity of the absorption peak of the –NCO group at 2270 cm<sup>-1</sup>. Further, urea release in water showed a controlled release behavior. Findings from this work showed that biobased polyurethane was successfully synthesized using kraft lignin as one of the polyols in the PU system which was used as a coating material for controlled release fertilizer (CRF).

Biobased polyurethane developed from lignin as a coating material for urea fertilizer to achieve sustained nutrient release

ACS Fall 2021

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