Polyurethane-coated urea using fully vegetable oil-based polyols: Design, nutrient release and degradation

Abstract

Fully vegetable oil-based polyols with a low hydroxyl value and viscosity were designed and prepared using epoxidized soybean oil (ESO) and oleic acid as raw materials, which were also used to prepare polyurethane films 1-5 with different isocyanate indices. Their structures were characterized by FTIR and 1H NMR. The GPC data indicated that the number-average molecular weight (Mn) of the polyols was 3331 and the distribution index was 1.578. The effects of the isocyanate index on the morphology, DMA, mechanical properties, water absorption, water contact angle, TGA and soil degradation of PU films were investigated. When the isocyanate index increased from 1.13 to 2.65, the glass transition temperature (Tg) and crosslinking density (νe) of polyurethane increased from −4.5 °C to 74.7 °C and from 630 mol/m3 to 2000 mol/m3, respectively. By 180 days, the degradation percentages of the five PU films (1-5) were 10.23%, 20.01%, 21.85%, 26.78% and 29.63%, respectively. Two coated ureas (Oil-PCUs) were successfully prepared containing 70% vegetable oil. The 80% cumulative release of Oil-PCUs-6% (isocyanate index: 1.58) took more than 70 days, indicating that the prepared Oil-PCUs have great potential for use in agriculture, forestry and grasslands.