Fractionation and oxypropylation of corn-stover lignin for the production of biobased rigid polyurethane foam

Bio-based rigid polyurethane foams (B-RPF) were synthesized from fractionated lignin with high functionality and low molar mass. In this process, ethanol organosolv fractionation was conducted using corn stover as the raw material followed by simple precipitation of the dissolved lignin. The high homogeneity lignin fractions were fully characterized by P-31-NMR, 2D-HSQC NMR and TGA. Then, the surface group of lignin fractions was oxypropylated by chemical cross-linking for B-RPF production. B-RPFs containing 50 % and 100 % oxypropylation lignin fractions were tested by SEM, TGA, tensile test and thermal conductivity. Results indicate B-RPF based on different lignin fractions showed significant differences in thermomechanical properties. Specifically, lignin fractions precipitated in low ethanol concentrations (30 % and 15 %) has relatively lower molecular weights, higher active hydroxyl content and higher thermal stability than other fractions, which leaded to higher compressive strength (0.78 +/- 0.02 MPa), lower thermal conductivity (0.037 +/- 0.01 W m(-1) K-1) and better thermal stability in corresponding B-RPF product. This study indicated that ethanol fractionated lignin may be used as a sustainable core material substitute for the synthesis of high-quality B-RPF.