Study On Extraction,Structure Characterization And Chemical Modification Of Lignin Extracted From Pine Wood By Formic

In nature,lignin is the second largest biomass resource.It is abundant,environmental friendly and renewable.However,due to its complex structure and uneven distribution of molecular weight,the utilization of lignin has not been fully explored.Therefore,how to better use of lignin also is of critical importance for reducing the consumption of non renewable resources such as oil,and the sustainable development of human society.In this paper,a lignin-based concrete water-reducer was prepared through organic solvent fractionation and chemical modification of lignin extracted from pine wood with formic acid.FAL was prepared under the optimum conditions for extraction（140℃,the mass ratio of formic acid and pine was 6:1;H₂O₂ solution dosage was 5%（dry pine quality as the base）;40min）.Soluble lignin（S-FAL）and insoluble lignin（I-FAL）can be obtained by using organic solvent to dissolve FAL.The structure changes of lignin samples（FAL;S-FAL;I-FAL）were characterized by elemental analyzer,high performance liquid chromatography（HPLC）,gel permeation chromatography（GPC）,FT-IR and ¹H-NMR.Results showed: 1.The highest delignification rate was 87.2%,the purity of cellulose was about 89.3%,the yield of cellulose was about 88.7%,and the yield of hemicellulose was about 76.6%.2.The fractionated lignin with more reactive points（e.g.more methylene and phenolic hydroxyl,and less methoxyl groups）could be easier to be modified（like sulfonation or sulfomethylation）,thus enhancing its workability as water reducer.Fractionation and modification of lignin（MS-FAL;MI-FAL）was prepared under the optimum conditions for oxidation reaction（50% H₂O₂ solution（with dry FAL quality as the base）;100℃;1 h）and the optimum conditions for sulfonation reaction（100%HCHO solution and 50% Na₂SO₃（with dry FAL quality as the base）;150℃;2 h）.The structure changes of lignin samples（MS-FAL;MI-FAL）were characterized by elemental analyzer,HPLC,GPC,FT-IR and ¹H-NMR,respectively.Performance of water reducer was characterized by the test of fluidity of cement paste,sulfonation and water reducing rate of cement paste.Results showed that the fluidity of cement paste with the fractionated lignin（by pure acetone）after oxidation-sulfonation modification was 21% higher than the sulfonated FAL（M-FAL）without fractionation.The whole fractionation process was sustainable,because the solvents used could be easily recovered the reused.