Preparation And Modification Of Liquefied Rice Straw Based Polyurethane Foam

The large use of petrochemical resources has brought increasingly prominent environmental problems, the use of renewable resources to replace petrochemical resources have become an inevitable trend, biomass has become a powerful resource and gotten more and more attentions.Rice straw was selected as raw material to study the heterogeneous liquefaction mechanism. Liquefaction of Rice straw was carried out in the presence of PEG400 and glycerin ?4:1, w/w? as a liquefying reagent, with concentrated sulfuric acid as catalysts.The liquefaction conditions of rice straw were selected as the amount of catalyst 98mg / g?Based on rice straw?, solid - solvent ratio 1: 5, reaction time 90min, reaction temperature 160 ?. The liquefaction number of liquefied rice straw was 55%, the acid number was 3mg/g, and the hydroxyl number was 450mg/g, which could be used directly for the synthesis of polyurethane foam. Fourier Transform Infrared Spectrometer ?FTIR? showed that the liquefied rice straw was rich in hydroxyl groups, and it could be used to prepare rice straw-based polyurethane foams instead of polyether polyol.A water-blown polyurethane form was produced with liquefied rice straw as raw materials, N,N,N,N,N-pentamethyl diethylenetriamine?P5? and N,N-dimethyl cyclohexlemine ?P8? as co-catalyst, which replaced traditional petrochemical polyether polyols and harmful organotin. Physicochemical properties of the prepared polyurethane foam were investigated at different preparation conditions, including water content, the proportion of co-catalyst, isocyanate index and foam stabilizer amount. By which, the optimum synthesis conditions was confirmed. Material Testing Machine,Thermogravimetric Analysis ?TGA?, Fourier Transform Infrared Spectrometer ?FT-IR? and Scanning Electron Microscope ?SEM? were conducted to characterize the mechanical property, the thermal stability, the chemical structures and microstructure of the polyurethane foam. The results showed that the carbamate structure was produced in the foam matrix. Tensile strength and compressive strength of the product with density of 40Kg/m3 were 309KPa and 154KPa, respectively. The liquefied rice straw based polyurethane foam synthesized in this study displayed mechanical property and thermal stability was superior to which derived from organotin and tertiary amine. In addition, the polyurethane foam has good thermal stability.With the increase of the heating rate, the TG and DTG curves move to the high temperature side in turn. The increase of the heating rate has a great effect on the degradation and carbonization of isocyanates and polyols. When the conversion rate is 0.7,the activation energy reaches a maximum of 272kJ/mol, and the energy required for thermal cracking is the largest. The kinetic model of pyrolysis reaction of PUF is D3,which could obtain a good linear fitting result.With the addition of nano-SiO₂, the mechanical property and the thermal stability of liquefied rice straw based polyurethane foam has been enhanced. The nano-SiO₂-enhanced rice straw-based polyurethane foam has good thermal stability. SEM showed that the diameter of cell is reduced, the closure rate is decreased, and the cell became more uniform.