Synthesis And Characteristic Of Lignin-based Polyisocyanurate Foam

As the most abundant and renewable aromatic compound in nature,lignin has attracted much attention as feedstock to produce bio-based chemicals,materials,and fuels.However,no rapid progress has been made on the lignin conversion due to its poor quality,low copolymerization,and low catalytic conversion rate.In order to improve the properties of lignin and enhance its utilization efficiency,the present study was carried out on the following aspects:（1）Tetrahydrofurfuryl alcohol was used to extract high-quality lignin from walnut shells,which was then phenolized under acidic conditions to obtain phenolic lignin.The results showed that the phenolic hydroxyl content of phenolic lignin reached3.77%,with the content of methoxyl group reduced to 1.82%under 140℃,3 h,5%（v/w）H₂SO₄,the lignin-phenol ratio of 25%.Compared with the lignin without phenolic modification,the weight average molecular weight and PDI of the modified lignin were reduced from 4183 to 2666,2.45 to 2.20.This would enhance the lignin reactivity in polyurethane foams preparation.（2）The response surface design was used to optimize the treatment of the tetrahydrofurfuryl alcohol lignin with alkaline hydrogen peroxide.The optimal condition was obtained:40℃,2 h,2%H₂O₂,the solid-liquid ratio of 1%.The average molecular weight and PDI of the pretreated lignin were reduced from 2413 to 1222,and1.85 to 1.38,respectively.Subsequently,propylene carbonate/DBU was used to alkylate tetrahydrofurfuryl alcohol lignin/pre-treated lignin to obtain different lignin-based bio-polyols.The structure of alkylated lignin and the changes of various hydroxyl content in the two bio-polyols were compared based on infrared and phosphorus spectra characterization.The results showed that the aliphatic hydroxyl content of the alkylated lignin obtained by the two-step process changed from 0.80 mmol/g to 1.87 mmol/g with an increase of 130%.（3）Based on the obtained PIR foam formula,the above two lignin-based bio-polyols with different mass parts were added to investigate the effect of different bio-polyols on the PIR foam performance.It was found that the lignin bio-polyol synthesized by the two-step method was more suitable to be added into the polyurethane composition A.When the mass part reaches 30 parts,the synthesized foam had the same density as the control foam,indicating the reduction of the use of petrochemical polyols.It was also characterized with the better flame retardant properties and lower thermal conductivity.