Synthesis And Characterization Of Lignin-epoxy Resin

Lignin is considered to be one of the most promising future biomass resources.However, the utilization of lignin-based materials is limited in practical human life,and the widespread application of lignin has not been achieved. At present, a largenumber of lignins exist in the papermaking black liquor. The composition of blackliquor varies considerably between different mills depending on the cooking processand the wood used. But the pollution caused by black liquor is the same. How totransform the waste of black liquor into useful products is a very meaningful thing.We know that pulping black liquor contains20%-30%of lignin. The complexstructure of lignin is very difficult for biodegradation, so it is one of the world’s majorsources of pollution. It is the best way to reduce the pollution by black liquor if wecan use lignin to synthesize high value products from black liquor. Lignin andbisphenol A are structurally similar for possessing more phenolic hydroxy groupswhich make it possible for lignin to be used as a substitute for the part of bisphenol Ain the synthesis of epoxy resin. However, epoxy resins have poor thermal conductivity(thermal conductivity is about0.2W/m·K) and epoxy resins are very flammable(limiting oxygen index is19.5). Flame retarded epoxy resins are needed greatly by themarket for what we have mentioned.In the present work, lignin/silica hybrid was isolated from black liquor. Selectiveprecipitation was achieved by decreasing black liquor pH from1.00to8.00.Lignin/silica hybrid obtained from black liquor, had been used as reactants to partlyreplace bisphenol A in preparing green epoxy composites. The effect ofepoxy-lignin/silica composites on the mechanical and thermal properties of thecomposites were investigated and compared with the composites cured with anethylenediamine curing agent. We had successfully got good performancelignin/silica-based epoxy resin. Lignin has received wide attention due to the enormous renewable supply andpotential use of this inexpensive organic raw material. We used straw lignin to partlyreplace bisphenol A for preparing epoxy resins. This process not only greatly reducesthe environmental pollution caused by lignin, but also decreases the production costof epoxy resins. The lignin coming from agricultural waste was modified by Mannichreaction. We took a new way of padding. At the beginning, we would get the mixtureafter diethanolamine was reacted with formaldehyde for2hours. Then the modifiedlignin was prepared by adding dropwise the mixture into lignin solution. The contentsof active groups, including phenolic hydroxyl and hydroxymethyl, in modified ligninby Mannich reaction had been improved effectively. In addition, lignin-based epoxyresins which we prepared by modified lignin have good thermal stability.At present, how to synthesize the epoxy resin with the heat-temperature resistanceis the focus of researchers. However, the effective and environmentally friendly epoxyresin with the high-temperature resistance continues to be explored. To resolve thisproblem, we synthesized zinc borate (3ZnO3B2O33.5H2O) and hydrophobic zincborate by the solid-liquid reaction. This method is simple and does not bring pollution.Zinc borate and hydrophobic zinc borate also had the irregular lamellar structure. Thecontact angle of hydrophobic zinc borate was121.49o. Furthermore, we directly addedzinc borate and hydrophobic zinc borate into the epoxy resin. The maximum on-setdecomposition temperature of zinc borate/epoxy resin composite was increased by14oC, and that of hydrophobic zinc borate/epoxy resin composite was increased by26oCcompared to the neat epoxy resin.The significance of this thesis is:First, we developed a new way of feeding of Mannich reaction to modify the ligninand then we compared our method with others.Second, the lignin modified by Mannich can directly be used to prepare epoxyresins. In this way, we can avoid lignin extraction and have no sewage discharge. Upto now, this is the first time to use this method to synthesize lignin-based epoxy resins.By this way, pollution would be reduced and the environment could be protected. Thirdly, bisphenol A is expensive and can cause worse environmental pollution.Meanwhile, lignin is a kind of inexpensive and environmentally friendly resource.Pollutant emissions and production cost will be reduced if we use lignin to replacebisphenolA.Fourthly, lignin/silica hybrid prepared from black liquor. This method not only canmake full use of resources, economize energy, but also can effectively reduceenvironmental pollution and improve environmental quality.Fifthly, three-dimensional network structures of lignin and the thermal stability ofsilica are good for the performance of epoxy resin.Sixthly, we synthesized zinc borate and hydrophobic zinc borate with new structure.These zinc borates have been applied to the epoxy resin, and the thermal stability ofepoxy resin was improved greatly.