Micro structure analysis of the coating of polyurethane coated urea during nitrogen release process.

The performance of polyurethane coating was the key factor affecting the nitrogen release characteristics of polyurethane coated urea(PCU). This paper took castor oil based PCU(PCU_L and PCU_H) as the research object, nitrogen release characteristics in different application environments (water and soil) and the damage of soil to the structure of polyurethane coating were discussed, when nitrogen was released from PCU, the microstructure of polyurethane coating(coating_L and coating_H) was analyzed. The results showed that the number and size of damaged holes caused by the solidification and coating-forming process of polyurethane resin solution were key factors affecting the nitrogen release rate of PCU in soil. Although wax could fill the holes as a lubricant, its degradation rate in the soil environment was faster, the swelling process of PCU caused the stretching of the coating, leading to the failure of the wax filling effect, the stretching of the coating could also cause further amplification of damaged holes.Therefore, adjusting the formula, reducing the number of damaged holes in the coating, increasing the cross-linking density of the coating, reducing the introduction of degradable components, could improve the coating performance and stabilize the nitrogen release rate. [ABSTRACT FROM AUTHOR]