Preparation Of Lignin-Containing Cellulose Nanofibers Using Deep Eutectic Solvents And Its Application Of Molecular Imprinting With Composite Membranes

Lignocellulosic nanomaterials have the dual properties of nanocellulose and lignin.The powerful fiber network structure is expected to become the reinforcing agent of composite materials,which has potential application value in emerging fields such as drug separation.The development of traditional preparation methods such as the sulfuric acid process is hindered by the low utilization rate of raw materials and serious pollution.The main research contents and results of this paper are as follows:(1)Bagasse is a widely used industrial and agricultural waste in Guangxi.It is pretreated with a green low-melting solvent(DES)and added with succinic anhydride to introduce charges to promote mechanical micro filamentation.Successfully obtained carboxylated lignocellulose nanofibers(CLCNF)with a well layered network structure and spherical lignin nanoparticles(LNP).The electrostatic force generated by negative charges is beneficial for the better dispersion of CLCNF in water.After DES treatment,the crystallinity of bagasse increased,but the molecular structure did not change significantly.The initial pyrolysis temperature of CLCNF decreases due to the destruction of fiber hydrogen bonds.The maximum thermal degradation temperature of CLCNF is 334.6 ℃,and the LNP is 371.1 ℃,indicating excellent thermal stability.(2)Apply the CLCNF and LNP prepared in the previous chapter to the polyvinyl alcohol(PVA)composite membrane using the tape casting method.We investigated the enhancement effect of PVA membranes and the applicability of composite membrane materials in natural product separation.The results indicate that CLCNF can effectively improve the tensile strength and Young’s modulus of composite films,exhibit good transmittance and excellent UV blocking ability,and improve the heat resistance and surface hydrophobicity of composite membranes.LNP demonstrated the role of lignin in enhancing composite membranes.The CLCNF/PVA composite membrane has a certain separation ability for natural flavonoids,with an adsorption capacity of 31 mg/g.(3)Using baicalin as a template molecule and PVA as a substrate,a functionalized CLCNF was first added using electrospinning technology to successfully prepare a CLCNF-based baicalin molecularly imprinted nanofiber membrane(LMIP)with baicalin recognition ability.LMIP has a dense and uniform structure and excellent mechanical properties.The addition of CLCNF increased the mechanical strength of the molecularly imprinted film by 3.6 times.The optimal spinning conditions are: the content of baicalin is 0.20%,and the mass fractions of PVA and CLCNF are both 8%.The static adsorption capacity of LMIP is as high as 142.1mg/g,which conforms to the quasi-second-order kinetics and Langmuir model.The adsorption process mainly involves chemical adsorption and monolayer adsorption.LMIP exhibits excellent specific selectivity and cyclicity in the adsorption of baicalin.This article innovatively applies high-value-added lignocellulosic nanomaterials to the field of natural drug separation,resulting in a new type of bio-based molecularly imprinted nanofiber membrane.As a promising material for separating baicalin,it provides a new approach for the utilization of lignocellulosic resources and has significant practical significance.