Rapid Liquefaction of Wood in Polyhydric Alcohols Under Microwave Heating and its Liquefied Products for Preparation of Rigid Polyurethane Foam

Abstract

Comparing to the conventional bath heating, the effects of liquefaction parameters on the degree of liquefaction of wood in polyhydric alcohols by using microwave as an energy source were evaluated. Polyurethane foams were successfully prepared from the liquefied biomass-based polyols. The effects of heating methods (conventional bath heating and microwave) and liquefaction reaction time on the properties of liquefied biomass-based polyols were investigated. The influences of isocyanate index on the properties of rigid polyurethane foams were also discussed, and feasible formulations for preparing liquefied biomass-based polyurethane foams were proposed. The results indicated that rapid liquefaction of wood in polyhydric alcohols under microwave heating could be achieved. The foams prepared from liquefied biomass-based polyols obtained by microwave-assistant liquefaction exhibited excellent mechanical properties. Polyurethane foams (PU Foams) are used widely in many fields as heat-insulating, packaging, structural, flotation and load bearing materials, due to their ease of processing and unique combination of excellent thermal insulation and mechanical properties. Traditional PU foams are prepared by the polymerization of polyol with isocyanate simultaneously occurring with gas generation resulting from the chemical reaction of water of blowing agent evaporation by the exothermic reaction itself. However, the raw materials for preparing PU foams, based on polyol (polyether of polyester polyols) and isocyanate, are obtained mainly from fossil resources. With increasing concern of the shortages of fossil resources and the impetus for reducing costs of polyurethane, preparation of polyols from renewable biomass resources has been an interesting subject in the polyurethane industry. Biomass as natural polymer contains more than one hydroxyl group in the molecular chains, and can be used as polyol for preparing polyurethane materials. By the hydroxyalkylation reaction, polyols with desirable hydroxyl values and viscosities have been prepared from many hydroxyl-containing biomass substances such as sorbitol (1), sucrose (2), methyl glucoside (3), lignins (4, 5), and so forth. These polyols have become important ingredients for rigid polyurethane foams because of the great functionalities of the starting materials.