Investigating The Effect Of Lignin On Enzymatic Hydrolysis Of Lignocellulosic Biomass By Quartz Crystal Microbalance

In the process of enzymatic hydrolysis of lignocellulosic biomass,lignins in substrates produce non-productive adsorption of cellulase,which decrease the efficiency of enzymatic hydrolysis.However,the addition of sulfonated lignin(SL)could effectively improve the yield of enzymatic hydrolysis.But,the mechanism is not elucidated clearly.In this work,poplar and green-liquor pretreated poplar were used to prepare novel ultrathin lignocellulosic films,investigating the effect of lignin on enzymatic hydrolysis monitored by quartz crystal microbalance(QCM).Meanwhile,QCM analysis was used to investigate the mechanism of promoting enzymatic hydrolysis yield by adding SL.And the interactions between SL and cellulase were analyzed using chemical and spectra methods.The main research and results are as follows:The preparation and characterization of ultrathin lignocellulosic films.After milling,ball-milling and vacuum-drying,lignocellulose was directly dissolved in LiCl/DMSO solvent system at the concentration of 0.5-1%.Lignocellulose-LiCl/DMSO solutions were deposited on QCM gold sensors by spin-coating to prepare ultrathin lignocellulosic films with nanometer thickness.The obtained films were characterized by atomic force microscope(AFM)and X-ray photoelectron spectroscopy(XPS).The results indicate that an even-textured lignocellulosic film could be formed on QCM gold sensors.These lignocellulosic films were prepared from the cell walls of all components,avoiding components isolation and derivatization.What's more important,in molecular level,the structure of the cell wall was kept.The effect of lignins in substrates on enzymatic hydrolysis.Milled and ball-milled poplar and GL-poplar were dissolved in LiCl/DMSO to prepare ultrathin films with different components by spin-coating.The enzymatic hydrolysis process was monitored by QCM at 40?C,fitted with Lagergren and Boltzmann-sigmoidal kinetic models to reveal the effect of lignin on enzymatic hydrolysis.The enzymatic hydrolysis of lignocellulosic materials could be divided into three stages,including cellulase adsorption,fast substrate hydrolysis,and slow substrate hydrolysis.In the cellulase adsorption stage,cellulase adsorption on lignin and cellulose are competitive,the non-productive adsorption on lignin reduced the speed of cellulase adsorption on cellulose.In enzymatic hydrolysis,a high content of lignin in poplar leaded to the yield of enzymatic hydrolysis lower.In the last stage,enzymatic hydrolysis rate of cellulose was slow,and even inhibited completely by lignin.The mechanism of promoting enzymatic hydrolysis by adding SL monitored by QCM.It has been proved that the addition of SL can effectively improve the enzymatic hydrolysis of pretreated lignocellulose.However,the mechanism is not elucidated clearly.In this work,QCM analysis was used to monitor cellulase adsorption on lignin and enzymatic hydrolysis of cellulose after adding SL.When the addition amount of SL is 10 and 20 times of cellulase(w/w),the non-productive adsorption of cellulase on lignin decreased obviously.The addition of SL has no promoting effect on enzymatic hydrolysis of cellulose,even reduce the hydrolysis rate.So,it is inferred that the promoted hydrolysis yield by adding SL is mainly due to the reduced non-productive adsorption on lignin.The interaction between SL and cellulase.In this work,the interactions between SL and cellulase were investigated by QCM,chemical and spectra analysis.SL could combine with cellulase rapidly through electrostatic interaction,to form SL-cellulase complexes.The structure of SL-cellulase complexes depends on the SL content,mainly including “necklace model” and “spheres model”.