Efficient Separation And Functional Utilization Of Lignocellulose Based On Deep Eutectic Solvent

In the context of global petrochemical energy shortage and double carbon policy,the development of degradable bio-based materials using non-grain lignocellulosic resources is a current international research hotspot.However,due to the multilayer structure of lignocellulose and the complex bonding between its components that form a natural anti-depolymerization barrier,it poses great challenges for efficient separation and conversion utilization of lignocellulose.Currently,the separation and conversion of lignocellulosic components mainly include acid and alkali treatment,organic solvent treatment,ionic liquid treatment,etc.However,these methods have many shortcomings,such as poor regulation and selectivity,complex composition and poor reaction activity of separated products,harsh reaction conditions and serious pollution.Therefore,exploring green and efficient depolymerization systems is an effective way to develop the high-value utilization of lignocellulose.Herein,this study proposed a new strategy for efficient depolymerization and molecular reconstruction of lignocellulose.By exploring the process of treating lignocellulose with deep eutectic solvents（DES）,efficient separation of waste lignocellulose into highly active lignin and cellulose were achieved.Furthermore,the extracted lignin and cellulose were molecularly reconstructed to prepare lignin/cellulose composite film,and the effects of lignin content on the structure,morphology and physicochemical properties of the composite film were systematically investigated.The specific research content and results are as follows:（1）Efficient separation of lignocellulose with deep eutectic solvents:A ternary DES system was constructed using choline chloride/lactic acid/Fe Cl₃ to deconstruct bamboo powder,and the effects of the DES composition ratio,reaction temperature,and time on the yield,purity,chemical structure,and microscopic morphology of the separated lignin and cellulose were investigated.Through process control and optimization,the efficient separation of lignin and cellulose from bamboo powder was achieved.The yield and relative purity of the lignin obtained were 85.57%and 90.42%,respectively,with weight average molecular weight of 1398 Da and phenolic hydroxyl content of 12.86 wt%.The lignin had excellent antibacterial activity and free radical scavenging ability.The maximum yield of cellulose reached to 75.3%,and its surface was esterified,which makes it easier for lignin to be compounded.Lignocellulosic board was prepared by reconstituting the separated bicomponent used simple thermal pressing.As a natural adhesive with hydrophobicity,lignin effectively improved the mechanical properties and water stability of lignocellulosic board.Water contact angle of 58.6°and tensile strength of 53.1 MPa.In addition,the extraction rate of lignin from DES still reached to 68%after five cycles of recycling,which presented excellent recyclability and reusability.（2）Study on preparation and properties of lignocellulosic blend film:Regenerated cellulose film was prepared by phase separation method,and lignocellulosic blend film（LCF）were obtained by reconstituting with the resulting high-phenolic hydroxy lignin impregnation.The effects of lignin content on the chemical structure,microscopic morphology,optical properties,thermal stability,water resistance,antioxidant properties and mechanical properties of LCF were investigated.It was shown that high phenolic hydroxy lignin could be well dispersed in the cellulose matrix and formed interfacial bonding with cellulose through hydrogen bonding,which effectively improved the mechanical properties of LCF.When the lignin addition was 5 wt%,LCF possessed tensile strength of 73.37 MPa,elongation at break of 5.38%,and toughness of 2.93 MJ/m³.In addition,due to the unique functional characteristics of lignin,LCF had excellent UV resistance and antioxidant properties.UVA-blocking efficiency and UVB-blocking efficiency of LCF-3 were 88.94%and 97.60%,respectively,and the free radical scavenging rate was 90.27%.The water contact angle test and moisture absorption test showed that the introduction of hydrophobic lignin significantly improved water resistance of LCF,with water contact angle of 84.3°and 24 h water absorption rate of only 35.85%.（3）Study on preparation and properties of physico-chemical double crosslinked lignocellulosic film:In order to further improve interfacial binding force of lignin/cellulose and avoid lignin migration on the surface of film,a double crosslinked lignocellulose film（ELCF）with dynamic hydrogen bonds and stable covalent bonds was prepared by dissolving cellulose/lignin in Na OH/urea solution and chemical crosslinking with epichlorohydrin.The effects of crosslinker and lignin content on the chemical structure,microscopic morphology,thermal stability,water resistance,UV resistance,antioxidant properties,barrier properties,mechanical properties,and biodegradability of ELCF were systematically investigated.The synergistic effect of dynamic hydrogen bonding and stable covalent bonding significantly improved water resistance and mechanical properties of ELCF.Compared to LCF,tensile strength increased from 73.37MPa to 132.48 MPa,elongation at break increased from 5.38%to 9.77%,and water contact angle increased from 84.3°to 101.2°of ELCF.In particular,ELCF maintained tensile strength of 70.38 MPa and tensile strain of 7.70%after 30 days of water impregnation.ELCF had excellent visible light transmittance,UV resistance,antioxidant properties,and air and water vapor barrier properties.Soil degradation experiments showed that although introduction of lignin and crosslinker reduced the biodegradability of ELCF to a certain extent,the degradation rate was still reached to 64.57%after 90 days of soil degradation.In this paper,the efficient separation and conversion of lignin and cellulose from lignocellulose into lignocellulosic composites was achieved by designing and optimizing the DES system.The excellent dispersion and interfacial binding between highly active lignin and cellulose endowed lignocellulosic film with excellent mechanical properties,water resistance,antioxidant properties,UV resistance,barrier properties,and biodegradability.This work is of great significance to the high-value utilization of waste bamboo powder and the development of biomass derived materials,and provides a new way to promote the replacement of petroleum-based plastics.