Wood Liquefaction With Microwave Heating And Preparation Of Rigid Polyurethane Foam

Aiming to effectively use wood (renewable biomass resource) and waste plastic, liquefacient was prepared by alcoholysis of polyethylene terephthalate (PET); microwave radiation was used as heating source in this paper. Liquefaction product was modified by propylene epoxide under the condition of double metal cyanide (MMC) as catalyst to prepare stable biomass polyether polyol. Rosin polyester polyols, catalysts, and blowing agents were mixed with biomass polyether polyols as premixed polyether polyol which was applied to prepare rigid polyurethane foam.1. Microwave radiation was used as the sole heating source; liquefacient was prepared from alcoholysis of PET, glycerol as the ancillary reagent; the amount of 2.5% H2SO4 (based on liquefaction solvent) was used as acid catalyst to achieve liquefaction of wood. Wood liquefaction rate (WLR) was over 99% in a short time and above 135℃. The experiment plan of wood liquefaction was designed and its result was analyzed and optimized using Design-Expert 7.1 software. The order of single factors on wood liquefaction was that: temperature> liquid-solid ratio> time. In interaction factors, the order of the factors on wood liquefaction was that: temperature×liquid-solid ratio> time×temperature> time×liquid-solid ratio. Comprehensive factors, the mathematical model between the WLR and variable operation factors could be expressed: WLR% =-514.5044+ 0.8852×A(time)+6.6359×B (temperature) +4.7565×C (microwave radiation power)+ 43.2323×D(liquid-solid rate)+ 0.0076×A+0.0025×AC-0.1000×AD-0.01583×BC-0.09083×BD-0.3000×CD-0.07628×A²-0.02195×B²-0.2199×C²-3.3858×D². The kinetic model for wood liquefaction was built on some assumed conditions. Wood liquefaction obeyed second-order kinetics coming from a linear relationship between 1/R and the rate of liquefaction, activition energy: Ea=1.76×10⁵ J/mol, pre-exponetial factor: A=0.891e50.28 (s·mol)·L^-2.2. Percentage content of water-soluble and ethyl acetate-soluble in products of liquefaction was obtained by extraction. These curves including liquefacient, the products of different liquefaction time and the products of different extraction at the same liquefaction time of GPC and HPLC-MS/MS analysis, were comparative analysed. Effect of time on the molecular mass of product, the molecular mass distribution of each extract and pyrolysis products, the molecule fragments of lignin and cellulose was studied. The relative molecular mass of lignin pyrolysis products was 200⁴00. The molecular mass of cellulose pyrolysis products was more than 10 000. The relative molecular mass of products, which came from some PET debris and liquefied products of wood re-polymerizing and did not dissolve in water, was more than 10 000. The amount of water extraction part decreased with the increasing of liquefaction rate; on the contrary, the amount of ethyl acetate extraction and ethyl acetate insoluble part increased in the liquefaction product. The hydroxyl value, acid value and viscosity of the products increased with the increasing of liquefaction rate.3. The different biomass polyether polyols were prepared by changing the amount of propylene oxide with product of 99.16% liquefaction rate as the starting agent and MMC as catalys. The hydroxyl value, acid value and viscosity of biomass polyether polyol decreased with the increasing of the amount of propylene oxide. Especially the acid value and viscosity of polyether polyol had a sharp decline; the molecular weight distributions changed narrowly, but the thermal stability decreased slightly. IR spectra showed hydroxyl absorption peak intensity reduced with propylene oxide adding. The premixed polyether polyol were prepared by mixing biomass polyether polyols and rosin polyester polyols to synthesis rigid polyurethane foam with one-step. The mechanical properties of foam test results showed that foam compressive strength decreased from 0.07Mpa to 0.03Mpa with the increasing amount of wood polyether from 30% to 70%, but good toughness. The foams were analyzed by using FT-IR, SEM, and TGA. The results showed that the foam diameter changed largely and the hole wall thinner, which led to decrease compression strength. All of foam systems contained six-isocyanate rigid ring structure increasing rigidity and thermal foam stability.