Hydrolytic depolymerization of corncob lignin in the view of a bio-based rigid polyurethane foam synthesis

Corncob lignin was efficiently depolymerized in an isopropanol-water mixture with NaOH as catalyst into bio-polyols with low molecular weight and suitable hydroxyl number in view of the preparation of a biobased rigid polyurethane foam. The effects of process parameters including the reaction temperature, NaOH concentration, isopropanol-water ratio and reaction time on the product yields were investigated. The depolymerized lignin (DL) products obtained were further analyzed by GPC, FT-IR, 2D-HSQC NMR, P-31-NMR, GC-MS and thermogravimetric analysis. The results showed that 22.1% DL with a low molecular weight (860 g mol(-1)) and a suitable hydroxyl number (5.10 mmol g(-1)) together with 5.1% solid residue was obtained under an optimum condition (at 280 degrees C, 5% NaOH in 25% isopropanol-water ratio for 15 min). In short, this depolymerization process would effectively produce the bio-polyols, which would have great potential as a polyol substitution for partial incorporation into rigid polyurethane foams.