Preparation And Application Of The Biorefinery Lignin-based Phenolic Resin

About300million tons of forestry residues and700million tons of straw are producedannually in China. The utilization of agricultural and forestry residues as raw material toprepare cellulose ethanol and butanol through a biorefinery process, has become an importantdirection for the second generation biomass energy. In biorefinery process, a large number ofhigh-activity lignins are produced. As the most abundant renewable phenolic compounds innature, lignins can partially substitute phenol to prepare phenolic resin, because of their similarmolecular structure to phenol. Currently, large quantities of biorefinery lignins have been usedas fuel for energy recovery. Previous researches have mostly focused on preparation andapplication of lignin-based phenolic resin and rarely involved in their theory. Because ofcomplex composites and uncertain molecular structure, lignin sources have a significant impacton the performance of resins, limiting the lignin-based phenolic resin utilization. Therefore,investigation of the preparation of biorefinery lignin-based phenolic resin and its fundamentalmechanism, such as molecular controllable synthesis, copolymerization mechanism, curingreaction kinetics etc, is of great significance for promoting high-value utilization of biomassresources, reducing the overall cost of the biorefinery industry and promoting the developmentof bioenergy and biomaterial industry.In this thesis, the high-performance biorefinery lignin-based phenolic resins wereprepared to relieve the problems of over-reliance on petroleum resources in Chinese phenolicresin industry and low utilization level of biorefinery lignin. Firstly, this thesis focuses on theresearch of lignin purification, lignin molecular structure and chemical activity. Based on thecharacteristics of the hydroxymethyl lignin, copolymer molecules structure was specificallydesigned. Secondly, taking lignin model compounds as raw materials, the copolymerizationmechanism of lignin-phenol-formaldehyde copolymer was studied. Based on the above modelstudy, with full utilization method, biorefinery lignin-based phenolic resin was prepared andused for wood adhesives and construction insulation foams. Meanwhile the growth mechanism of lignin-based phenolic foam and curing kinetics of the lignin-based foamable resin were alsoinvestigated.Biobutanol lignin was used as a raw material to study the purification process. Aftercomparison, it was found that the purity of lignin was increased from81%to93.4%by theLundquist lignin purified method, which was suitable for the study of lignin molecularstructure. In lignin hydroxymethylation reaction, the reaction rate was higher in the initial stageand gradually the rate slowed down until termination after4h. Combined the results ofquantitative1H-NMR and Mannich reaction, it can be calculated that the ratio of new aliphatichydroxyl group on the benzene ring to new aliphatic hydroxyl group on the side chain is7.02,in the process of lignin hydroxymethylation. The content of lignin functional groups wasgenerally consistent with UV differential spectrometry, quantitative1H-NMR method,31P-NMR methods.LM-P-F resin samples of different reaction stages were analysed by methylation, FT-IR,GPC, HPLC, Py-GC-MS and2D-NMR methods. The results showed that in the early stage ofsynthesis, phenol and lignin model compounds appeared rapidly in hydroxymethyl reaction. Atthe same time, hydroxymethyl phenol condensed with the unsubstituted active sites on thebenzene ring to generate a simple dimers, trimers, etc. In the later stage of the reaction, thepolycondensation reaction took place between the hydroxymethyl groups on the various typesof prepolymers. As a result, hydroxymethyl phenol, hydroxymethyl lignin model compoundsand their various types of prepolymer, connected to each other through methylene bond andmethylene ether linkages to form complex crosslinked structure tricopolymer.Four kinds of biorefinery lignin (ethanol lignin, butanol lignin, xylitol lignin, lactic acidlignin) were used as raw material to prepare lignin-based phenolic resins for wood bonded. Itwas found that ELPF resin prepared with bioethanol lignin had better overall performance,when the lignin replacement rate was fixed at50%, performance of the ELPF resin wassuperior to other lignin phenolic resin. The content of free formaldehyde was only0.32%, freephenol content was only0.24%, plywood bonding strength was0.98MPa and formaldehydeemission was0.23mg/L. What is more, the ELPF resin had carried out industrial production and had been used to produce plywoods, whose bonding strength reached grade I andformaldehyde emission reached grade E0.Based on biobutanol lignin, the performance of foamable lignin-based phenolic resin canbe optimized by the three factors in orthogonal experiments. The study found that more amountof alkali catalyst was better, amount of formaldehyde should be moderate, lower lignin phenolreplacement rate was appropriate. Biorefinery lignin phenolic foam had good insulation andflame retardant properties, but the introduction of lignin negatively affect the activity of thefoamable resin. In early stage, bubbles grew fast. It was the period of bubbles nucleating andcells growing. In middle stage, bubbles’ volume expanded larger. Latter stage was post-curingperiod in which resin was cured and foam was molded. Via microscope, it is found that duringthe foaming process the diameter of cells increased gradually with the growth of the foamingtime and the result was consistent with the theoretical derivation model. The cells numberobtained by calculating was not consistent with the theoretical derivation model, but the foamquantity first increased and then decreased significantly. This was mainly due to the mergerbetween adjacent cells, thereby causing the number of cells reduced. Apparent activationenergy and pre-exponential factor of the lignin-based phenolic resin were higher than thephenolic resin, which was consistent with the lower activity of lignin-based phenolic resin.Conclusion of the research of lignin-based phenolic resin curing kinetics by usingnon-isothermal DSC method and isothermal DSC method is consistent.This thesis contributes to the realization of effective replacement of biomass materials topetroleum feedstocks in the field of polymer materials, and provides technical support forfurther research and industrial development of the lignin-based phenolic resin.