Development of bio polyurethane coated-urea for controlled release fertilizer

Traditional fertilizers have been known to improve crop yield significantly, but they also have glaring disadvantages, such as excessive nutrient release, low utilization rate, waste of resources, and environmental pollution. Petroleum-based polymer-coated fertilizers are not environmentally friendly and can cause secondary pollution. In our study, palm kernel oil-based polyurethane (PU) was successfully used as a renewable coating material for controlled nutrient release for the first time. The bio-PU coating at varying NCO/OH ratios (0.8:1, 1:1, 1.2:1) was investigated by physical and chemical testing methods. The PU coating with a higher NCO/OH ratio (1.2:1) showed poor thermal stability, lower water absorption (2.02%), lower surface free energy (40.85 γSV), higher shore hardness (92.83), and higher degree of crosslinking (90.55%). The effect of the NCO/OH ratio on bio-PU-coated urea properties was then explored. The bio-PU was coated on the surface of the urea, effectively controlling urea release in water, while a higher NCO/OH ratio did not necessarily give better results. When the coating amount was 9%, the release longevity of bio-PU-coated urea was delayed to 56 (1:1 NCO/OH ratio) and 42 days (1.2:1 NCO/OH ratio), respectively. Without the modification of PU and treatment of urea surface, the controlled release performance of the bio-PU by adjusting the NCO/OH ratio alone has exceeded that of some modified bio-based PU. Palm kernel oil-based PU is a potential coating to produce controlled-release fertilizers (CRFs) to support the green and sustainable agriculture applications.