Soybean-Oil-Modified Petrochemical-Source Polyester Polyurethane Improves the Nutrient Release Performance of Coated Urea

Abstract

Due to the difficult degradation and high cost of polyester polyols (PPs), their further development in controlled-release fertilizers (CRFs) has been limited. It was of great significance to partially substitute PPs with soybean oil polyols (SOPs) in the preparation of CRFs, which can adjust the proportion of substitution to balance the nutrient release period and membrane degradability. And it is possible to adjust the nitrogen release curve and prepare coated urea with different release days without changing the coating thickness. In this study, a two-factor five-level interaction experiment was designed with different SOP addition ratios (70%, 60%, 50%, 40%, and 30%) and mass ratios of polyols to PAPI (1:1.2; 1:1; 1.2:1; 1.4:1; and 1.6:1). In 25 groups of soybean-oil-modified polyester polyurethane-coated urea (SMPCU) treatments, with the increase in SOP, the thermal decomposition performance of the coated urea was improved, and the residual ash contents of the coating material was reduced. The coating surface was made smoother and denser with a reasonable ratio of polyols to PAPI, preventing the release of non-film-forming substances. When the proportion of soybean oil was 60% and the ratio of polyols to PAPI was 1.2:1, the N release days of the prepared SMPCU reached 137 days. Compared to soybean-oil polyol-coated urea (SOPCU) and polyester polyol-coated urea (PPCU), the nitrogen release days increased by 73.42% (79 days) and 234.15% (41 days), respectively. The ratio of polyols to polyaryl polymethylene isocyanate (PAPI) was explored, as well as the effect of polyol composition on coatings, and prepared SMPCUs with different nitrogen release days. According to the growth needs of crops and soil environmental characteristics, adjusting the proportion of coating materials, prolonging or shortening the nitrogen fertilizer release time, meets the nutritional needs of crops under different planting systems and provides conditions for farmers to plant different crops.