Study On The Preparation And Performance Of Lignin-based Polyurethane Foam

Lignin is the second most abundant biomass resource in nature,which is rich in phenolic hydroxyl group,alcohol hydroxyl group and other active groups,and can be used as the potential raw material of polyurethane foam in industrial production.However,due to its complex structure and extremely uneven molecular weight,it is difficult to be used on a large scale.In this paper,by using fractional extraction method to improve the traditional extraction method of lignin,and a lignin component with a smaller molecular weight,a higher uniformity and a higher hydroxyl content can be obtained.The thermal stability and mechanical properties of lignin-based polyurethane rigid foams can be improved by using surface functionalization and oxypropyl modification,and then replacing polyether polyols to prepare lignin-based polyurethane rigid foams,and positive modification effect can be obtained.By adjusting the pH value during the extraction of kraft lignin and the concentration of the organic solvent during the extraction of lignin by the organic solvent,a lignin fraction with higher hydroxyl content,lower molecular weight and higher uniformity can be obtained.The lignin-isocyanate prepolymer was prepared by surface functionalization of the fractionation-extracted kraft lignin,which can improve the shortcomings of poor coMPatibility between lignin and isocyanate,and improve the utilization rate of lignin.The properties of rigid polyurethane foams prepared by using surface functionalization lignin to replace 25 wt%and 50 wt%poly ether polyols have been improved to a certain extent.The kraft lignin extracted at pH 5 has a higher hydroxyl content(8.84 mmol/g)and a more uniform molecular weight(PDI=1.52).The rigid polyurethane foam(SFL5-RPF)has a lower apparent density(42.22 ± 0.76 kg/m3)and a higher compressive strength(0.39 ± 0.01 MPa).The addition of lignin improves the thermal stability of the foam,and all foams are stable at about 240℃ exist.The organic solvent lignin extracted by the ethanol-water system was modified by oxypropylation to prepare lignin-based polyols.The 31P-NMR shows that the oxypropylation promotes the conversion of phenolic hydroxyl groups in lignin to alcoholic hydroxyl groups,and it changes from solid to liquid polyol,which improves the reactivity and coMPatibility of lignin and isocyanate.For the first time,100 wt%of lignin-based polyols replaced commercial polyether polyols to prepare lignin-based polyurethane foam,and the lignin extracted at low ethanol concentration was modified with oxypropyl to prepare lignin-based polyurethane foam that has more uniform Cell structure,higher compressive strength(0.78± 0.02 MPa),lower apparent density and lower thermal conductivity(0.037 ± 0.01 W·m-1·K-1)than the reference foam.The addition of lignin improves the thermal stability of the polyurethane rigid foam.All the lignin-based rigid polyurethane foam can be the potential materials of building insulation and pipeline insulation area.