Research on the interfacial reaction between amine group in urea and the coating materials of polyurethane coated urea

Abstract

In this work, the polyurethane coated urea (PCU) and PE coated urea (PECU) were prepared by spraying the coating material. The isocyanates coatings on the surface of urea and granule inorganic compound fertilizer (NPK) were prepared and their infrared spectra were compared. The polyurethane coatings of PCU was analyzed by IR. The interface morphology between the PU coating and PE coating PECU and the surface of urea was compared by scanning electron microscope. The inner and outer surfaces morphology of polyurethane coatings was studied. The results showed that the peak of -NCO groups in the infrared spectrum of the coating on urea was weaker than of the coating on NPK, while the peaks of N-H, C-N and C = O were all relatively stronger, which proved that -NH2 in urea reacted with -NCO during the coating formation. SEM images showed that there was an obvious gap between PE coating and its urea core, while PU coating was tightly bonded with the surface of urea core, and the inner surface of PU coating had something undissolved after fully dissolved in water, which further illustrated that urea participate in the reaction of isocyanates with polyols. All of this results demonstrated that the amine group (-NH2) in urea reacted with the -NCO group in isocyanates and urea linkage (-NH-CO-NH-) was formed in the polyurethane coating.