| Microwave-assisted liquefaction of biomass is a new and excellent biomass utilizationtechnology. It can significantly shorten the liquefaction time that derived from conventionalbiomass liquefaction technology. Microwave-assisted liquefaction of biomass has beenobtaining more and more attention. Microwave-assisted liquefaction product of biomass can beused to produce biobased polymer materials, which have very broad application prospect. Fivebiomass feedstocks were liquefied using phenol and the mixed solvents of PEG400/glycerolcatalyzed by sulfuric acid under microwave heating in order to evaluate the effects of themoisture content, microwave power, liquefaction time, liquefaction solvent/biomass ratio andbiomass powder diameter on the liquefaction reaction, the properties of liquefaction productwere also analysed. Biobased polyurethane foam and phenolic resin were prepared from theliquefaction product respectively. Finally, the liquefaction product and liquefaction residuewere analysed. The main results from this study are as follows:1. Microwave-assisted liquefaction of poplar using polyhydric alcohol showed that exceptthat the hydroxyl number increased with increasing liquefaction solvent/wood ratio, generallyspeaking, with the increase of microwave power, liquefaction time, liquefaction solvent/woodratio and the decrease of wood powder diameter, the liquefaction yield increased and thehydroxyl number decreased gradually. The highest liquefaction yield and hydroxyl number canbe obtained from the liquefaction condition under moisture content of4.7%. The optimalconditions that poplar was liquefied using the mixed solvents of PEG400/glycerol bymicrowave heating are as follows: moisture content of4.7%, microwave power of500W,liquefaction solvent/wood ratio of2, liquefaction time of15min and wood powder diameter(≤0.450mm). Microwave-assisted polyhydric alcohol liquefaction reaction rate is at least eighttimes that of conventional oil heating liquefaction.2. The polyhydric alcohol liquefaction properties of five biomass feedstocks indicated thatwhen the liquefaction solvent/biomass ratio is same, the poplar and chinese fir showed the highest liquefaction yield, followed by bamboo and hemp, the rice straw showed the leastliquefaction yield.3. Microwave-assisted liquefaction of poplar using phenol indicated that the liquefactionyield increased first, and then decreased with the increase of moisture content and the decreaseof wood powder diameter. The continuous increase in liquefaction yield was also observed asmicrowave power, liquefaction solvent/wood and liquefaction time increased. The optimalconditions that poplar was liquefied using phenol by microwave heating are as follows:moisture content of40%, microwave power of400W, liquefaction solvent/wood ratio of2,liquefaction time of15min and wood powder diameter(≤0.450mm). Microwave-assistedphenol liquefaction reaction rate is at least six times that of oil heating liquefaction.4. The phenol liquefaction properties of five biomass feedstocks showed that when theliquefaction solvent/biomass ratio is same, the poplar、fir and bamboo showed the highestliquefaction yield, followed by hemp and the rice straw showed the least liquefaction yield.5. The properties of polyhydric alcohol liquefaction product of poplar and biobasedpolyurethane foam showed that as liquefaction solvent/wood ratio increased from2to2.5, theviscosity and relative molecular weight of liquefaction product decreased and thepolydispersity narrowed, especially the viscosity reduced significantly; both the apparentdensity and compressive strength of polyurethane foam increased. However, as liquefactionsolvent/wood ratio increased from2.5to3, the effect of liquefaction solvent/wood ratio onthese properties weakened.6. The properties of phenol liquefaction product of poplar indicated that as liquefactionsolvent/wood ratio increased from2to3, both the viscosity and relative molecular weight ofthe liquefaction product declined but polydispersity narrowed. The viscosity, pH, solid content,free formaldehy content and bonding strength of liquefied wood-based Phenolic Resinproduced from the liquefaction product of liquefaction solvent wood ratio of2.5were480mPa·s,11.2,48.3,0.26%and1.36MPa.7. On the basis of Gel permeation chromatography（GPC）analyses：Overall, the Mn, Mwand Mw/Mn of polyhydric alcohol liquefaction product decreased first and then increased as the liquefaction time was prolonged; the minimum of Mn, Mw and Mw/Mn of polyhydricalcohol liquefaction product occured at liquefaction time of15min, the Mn, Mw and Mw/Mnwere466,685and1.47respectively. The Mn and Mw of phenol liquefaction product underliquefaction time of2min were significantly higher than these under the liquefaction time5~30min; the Mn, Mw and Mw/Mn of phenol liquefaction product were relatively least underthe liquefaction time of20min, the Mn, Mw and Mw/Mn were610,1122and1.84respectively.The polyhydric alcohol and phenol liquefaction product analysed by FT-IR showed that theintensities of the bands at1601cm-1,1595cm-1and1501cm-1(aromatic skeletal vibrations oflignin),1352cm-1(O-H bending vibration) were strong. The results showed that lignin was theeasiest liquefaction composition, cellulose and hemicellulose were also easiely liquefied.8. The liquefaction residue was characterized in terms of FT-IR, the analysis showed thatthe intensities of the bands at1722cm-1(corresponds to hemicellulose),1616cm-1and1594cm-1(corresponds to lignin) weakened but the intensities of the bands at1152cm-1and1060cm-1(corresponds to cellulose) strengthened as the liquefaction time increased. It issuggested that lignin was the easiest liquefaction composition, followed by hemicellulose, andcellulose was the most difficult liquefaction composition. As evidenced by scanning electronmicroscopy（SEM）measurements, the longer the liquefaction time, the deeper the damagedextent of the wood powder cell wall. When the liquefaction time is short, the residue fibersseemed to be short lump, some holes and cracks appeared on the fiber surface; As theliquefaction time increased, the residue fibers became looser and shorter and more irregular,the fibers consisted of a large number of fragments. X-ray diffractograms（XRD）analysesshowed that the crystallinity indexs of the liquefaction residues from different liquefactiontimes were higher than that of the poplar, the liquefaction time had less impact on thecrystallinity index of the liquefaction residue. |
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