Study On The Preparation And Application Of Phenolic Lignin By The Synergism Of Deep Eutectic Solvents With Subcritical Ethanol

In this thesis,choline chloride was used as hydrogen bond acceptor,xylitol,glycerol and oxalic acid was used as three hydrogen bond donors to prepare deep eutectic solvents,and AlCl3·6H2O was used to improve the hydrogen bond acceptance of the deep eutectic solvent.Then the lignin from pubescens biomass was separated by deep eutectic solvent and subcritical ethanol system,and high phenolic structure lignin was prepared.The effects of reaction system and reaction conditions on the separation and structure of lignin were studied.Then the UV resistant composite films were prepared by mixing lignin and cellulose nanofibril.The properties of the composite films were characterized,which provided a new idea for the preparation and application of phenolic lignin.Firstly,the formation of deep eutectic solvent prepared by choline chloride,three hydrogen bond donors and AICl3·6H2O and the feasibility of synergistic reaction at subcritical temperature of ethanol were studied.the results showed that the deep eutectic solvent could maintain liquid stability at room temperature.Thermogravimetric analysis showed that the deep eutectic solvent had good thermal stability at subcritical temperature of ethanol,in which the weight loss rate of glycerol-deep eutectic solvent was only 5%.The synergistic reaction was feasibleThen the effect of deep eutectic solvent combined with subcritical ethanol system on lignin separation process was studied.It turns out that the yield of lignin was related to the type of hydrogen bond donor,reaction time and reaction temperature.When the hydrogen bond donor was oxalic acid,the reaction time was 120 min,the reaction temperature was 160?.The yield of lignin was 62.2%.The detection of phenolic hydroxyl content showed that the phenolic hydroxyl group in the prepared lignin was 1.871 mmol·g-1,which was much higher than that alkali lignin and sodium lignosulfonate.It was proved that the lignin was mainly composed of phenolic structure.Two-dimensional nuclear magnetic resonance showed that the main unit structure of lignin was guaiacylphenylalanine structure,and there was no condensation between lignin molecules.The results of high performance gel osmotic chromatography showed that the average molecular weight of lignin was 1158 and the weight average molecular weight was 1515,which was lower than that of ethanol lignin.UV resistance analysis showed that the lignin had blocking effect on UV light,and the transmittance of UV light was only 1%.The results of antioxidant analysis showed that the inhibition rate of lignin free radical was 94%,and the antioxidant activity was better than that of alkali lignin and sodium lignosulfonateFinally,lignin/cellulose nanofibril anti-ultraviolet films were prepared by mixing lignin and cellulose nanofibril,and the effect of lignin addition on the properties of the films was studied.The experimental results show that the addition of lignin can effectively improve the purple resistance of the films,and the UV transmittance wss only 0.5%.The addition of lignin also endowed the hydrophobic properties of the films.Thermogravimetric analysis showed that the increase of lignin addition can reduce the thermal stability of the films.It was found by video microscope that when the lignin content was 10%,the lignin agglomeration around the cellulose whisker were occurred,and the dispersion of lignin was poor,which affected the visible light transmittance of the films,and the optimum lignin content in the composite film was 5%.