| The pressure of petroleum-based products on the environment can be effectively alleviated through the high-value application of lignocellulosic biomass resources.Based on the progress of existing studies,the multiple interaction relationship between lignin and enzymatic saccharification rate was investigated in this work using acidic deep eutectic solvent as the reaction medium.Then,the reaction solvent system was designed and optimized to release the maximum potential of enzymatic saccharification of moso bamboo cellulose.In addition,the deep eutectic solvent（DES）pretreatment was combined with high pressure homogenization action to prepare lignin-containing cellulose nanofibers directly from moso bamboo raw materials,which provides theoretical basis and technical support for high-value conversion and utilization of lignocellulosic fibers and promotes the rapid development of DES-based biomass refining.The pretreatment effect of moso bamboo under different conditions was compared using choline chloride/oxalic acid（Ch Cl/OA）as the pretreatment solvent.The results showed that Ch Cl/OA had a good effect on the removal of hemicellulose and lignin from moso bamboo,but the excessive removal of lignin did not consistently enhance the enzymatic saccharification process of moso bamboo cellulose.The effects of apparent morphological changes and crystal structure changes of pretreatment residues on the enzymatic saccharification rate were investigated using scanning electron microscopy（SEM）and X-ray diffraction analysis（XRD）characterization techniques,respectively.The analysis showed that the enzymatic hydrolysis process of pretreated moso bamboo was facilitated to varying degrees through the changes in microstructure of moso bamboo by Ch Cl/OA,and the correlation between lignin and cellulose enzymatic saccharification rate was greater than that of crystallinity.With the help of XPS characterization technique,the surface chemical structure of moso bamboo residue was deeply resolved.The relationship among surface lignin content,accessibility and esterification and enzymatic saccharification rate in this solvent system was discussed in depth.The results showed that the surface lignin content of the Ch Cl/OA pretreated residue did not directly affect the accessibility of cellulose to the enzyme.The enzymatic saccharification rate was determined by the combination of surface lignin content,accessibility and hydrophobicity of the substrate.In particular,hydrophobic interactions arising from ester bonds were the dominant factor leading to the reduced rate of enzymatic saccharification.Finally,it was demonstrated that bovine serum protein could effectively overcome the non-productive adsorption between cellulose and cellulase and promote enzymatic conversion.Finally,it was demonstrated that non-productive adsorption between cellulose and cellulase could be effectively overcome by the addition of bovine serum albumin to promote enzymatic conversion of cellulose.In order to further enhance the enzymatic saccharification rate of moso bamboo cellulose,four polyol-based DES with different hydroxyl content were redesigned and synthesized for the pretreatment of moso bamboo based on the above findings to achieve the maximum utilization of cellulose.The results showed that the four polyol-based DES exhibited excellent removal effects on hemicellulose and lignin in moso bamboo under the same conditions,and the removal rates were maintained above72%.The influence of viscosity on the pretreatment process was discussed in terms of solvent properties.It was found that the viscosity of the four polyol-based DES decreased significantly at high temperatures and the viscosity and temperature sensitivity of DES were positively correlated with the number of hydroxyl groups in the hydrogen bond donor（HBD）.The effects of surface morphology and crystal structure of pretreatment residues on enzymatic saccharification rate were discussed in combination with SEM and XRD characterization,respectively.The effects of temperature,acid content and time on pretreatment efficiency of the preferred Ch Cl/XL were comprehensively investigated.The optimal pretreatment conditions for this system were determined to be 120°C,1.0 wt%H2SO4,3 h,and the 48 h enzymatic saccharification rate of the pretreated substrate was 96.08%.Meanwhile,the recyclability of Ch Cl/XL was proved by solvent recovery pretreatment.The preferred solvent was determined to be choline chloride/ethylene glycol（Ch Cl/Et G）oriented to facilitate cellulose defibrillation according to the phenomenon of the above polyol-based DES pretreatment comparison experiment and related literature.The lignin-containing cellulose nanofibers（LCNF）were prepared directly from moso bamboo raw materials by combining Ch Cl/Et G pretreatment and high pressure homogenization to achieve the diversified utilization of moso bamboo cellulose.The lignin residues with a gradient distribution of lignin content were obtained by pretreating moso bamboo under different conditions attributed to the high selectivity of Ch Cl/Et G for cellulose.The above residues were prepared as LCNF in combination with high pressure homogenization.The results exhibited that Ch Cl/Et G was effective in removing hemicellulose and lignin from moso bamboo,which established the foundation for the efficient utilization of lignocellulose.LCNF suspensions exhibited excellent aqueous stability,with light transmission up to 85.2%and lignin was evenly distributed in the suspension.XRD analysis illustrated that the combined treatment process had limited effect on the crystal conformation of moso bamboo cellulose and the prepared LCNF still maintained the natural cellulose I crystalline structure.SEM and TEM analysis results proved that the prepared LCNF diameter ranged from 6 nm to 30 nm.In particular,the lower lignin content in LCNF the narrower the width of LCNF and the more uniform width distribution.In addition,the LCNF will swell to about 300 nm in fiber diameter after freeze-drying.The evaluation of the mechanical properties showed that the lower lignin content in LCNF,the greater tensile strength and breaking strain of the LCNF film.However,the tensile strength and breaking strain were significantly reduced when the lignin content was below 6%.The above results indicated that the tensile strength（51.33 MPa）and breaking strain（14.59%）of the LCNF film were reinforced due to the presence of a moderate amount of lignin.In addition,the lower elastic modulus（1755.83 MPa）provided the LCNF film with better flexibility. |
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