Bio-Based High Functionality Polyols and Their Use in 1K Polyurethane Coatings

Bio-based polyols with high functionality were successfully synthesized by ring-opening epoxidized sucrose esters of soybean oil with methanol under acidic conditions, and were subsequently formulated with blocked isocyanates to form one package polyurethanes (1KPU). The bio-based polyols were characterized by gel permeation chromatography (GPC), Fourier transform infrared (FTIR) spectroscopy, proton nuclear magnetic resonance (¹H-NMR) spectroscopy, and Brookfield viscosity. Bio-based coatings were prepared by formulating the polyols with blocked polyisocyanates based on isophorone diisocyanate (IPDI) and hexamethylene diisocyanate (HDI). Two types of bio-based polyols were synthesized and the ratio of NCO:OH functional groups was varied to explore the effect of stoichiometry. The crosslinked PU coatings were characterized by differential scanning calorimetry (DSC), dynamic mechanical analysis (DMA), tensile testing, and thermogravametric analysis (TGA). The coatings applied to steel substrates were also characterized using ASTM methods which measured hardness, adhesion, flexibility, and solvent resistance. As a control, a commercial soybean oil polyol was used and was found to have a lower modulus and a lower crosslink density and glass transition temperature (T_g) compared to coatings formulated with sucrose soyate polyols.