Lignin-based polyols were synthesized through microwave-assisted liquefaction under different microwave heating time (5–30 min). Liquefaction reactions were carried out using polyethylene glycol (PEG-400)/glycerol as liquefying solvents and 97wt% sulfur acid as a catalyst at 140 °C. The polyols obtained were analyzed for their yield, composition, and structural characteristics using gel permeation chromatography (GPC), Fourier transform infrared (FT-IR) and NMR spectra. FT-IR and NMR spectra results showed that the liquefying solvents reacted with the phenol hydroxyl groups of the lignin in the liquefied product. With increasing microwave heating time, polyols’ viscosity became slightly increased and their corresponding molecular weight (MW) was gradually reduced. The optimal condition at microwave heating time (5 min) ensured a high liquefaction yield (97.47%) and polyol with suitable hydroxyl number (8.628 mmol/g) to be used as a precursor in polyurethane (PU) foam synthesis. PU foams were then prepared from the polyols obtained with methylene diphenylene diisocyanate (MDI) by one-shot method. With the isocyanate/hydroxyl group ([NCO]/[OH]) ratio increased from 0.6 to 1.0, their compressive strength were gradually increased. Mechanical properties of the liquefied lignin based PU foams could be adjusted for various end uses by changing the [NCO]/[OH] ratio. This study provided some insight into the liquefied lignin polyols for the production of rigid PU foam.

Producing lignin-based polyols through microwave-assisted liquefaction for rigid polyurethane foam production

249th National Meeting (2015)

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