Microwave-assisted liquefaction of wood with polyhydric alcohols and its application in preparation of polyurethane (PU) foams
Microwave radiation was used as the heating source in southern pine wood liquefaction with PEG/ glycerin binary solvent. It was found that microwave heating was more efficient than conventional oil bath heating for wood liquefaction. The wood residue content of the H2SO4 catalyzed liquefied wood dropped to zero within 5 min with microwave heating. The resulting liquefied wood polyols have suitable hydroxyl values for the preparation of rigid PU foams. Both the compressive strength and apparent modulus of the liquefied-wood-based PU foams increased as the isocyanate index increased from 80 to 120. The foams from H3PO4 catalyzed polyols had lower densities than those from H2SO4 and the petroleum-based controls. They also showed lower strength and modulus than those from H2SO4. Liquefied-wood-based PU foams generally have lower compressive strength and apparent modulus than the petroleumbased controls. However, they showed better restorability from deformation than the petroleum-based controls.