Mechanism And Application Of Acidic DES Pretreatment Of Biomass

Deep eutectic solvents(DES)are excellent solvents for lignocellulosic biomass pretreatment due to their specific solubility and adjustable physical and chemical properties,which are the focus of green chemistry research.However,the mechanism of lignocellulosic biomass separation and related applications need further research and development.In this paper,the mechanism of lignin degradation by multi-acidic DES under microwave conditions and its application in biomass high-value utilization were explored.The main research contents and achievements of this paper are as follows:Firstly,three kinds of acid DES(LC,FLC,FC)were prepared with acetic acid(LA),formic acid(FA)and choline chloride(Ch Cl)in a certain ratio,and their properties were characterized;To explore the degradation mechanism of lignin by acid DES composed of FA and LA,the structure and properties of regenerated lignin were analyzed by using double enzymatic lignin(DEL)as raw material and pretreatment with DES under microwave condition.The results showed that the more DES containing FA,the more serious the damage to β–O–4 bond,the more stable the regenerated lignin,the higher the content of phenolic hydroxyl,the better the antioxidant.At the same time,the prepared acidic DES all lead to condensation of lignin at the β-β site,the DES containing FA will lead to the condensation of G structural units,while the DES containing LA will lead to the condensation of S and G structural units at the same time,and also lead to the acetylation of lignin at the γ site.So,the structure of lignin can be regulated by the content of FA,LA and Ch Cl.In addition,lignin nanoparticles with different morphology and particle size can be obtained by adjusting reaction conditions and reverse precipitation conditions.Then,the prepared triple DES(FLC)was used for biomass pretreatment,and its pretreatment effect was evaluated;lignin-containing cellulose nanofibrils(LCNF)was obtained by high pressure homogenization with the FLC treated residue,and the related properties of LCNF were characterized.The results showed that 76.82% hemicellulose and43.22% lignin could be removed by FLC under microwave condition,and the cellulose loss rate was only 14.06%.Meanwhile,it had good recycling performance.The average particle size of LCNF prepared by FLC is 23.75 nm,the crystallinity index is 49.67%,the surface lignin content is 32.42%,and it also has high thermal stability and fluorescence characteristics.Finally,LCNF and polyvinyl alcohol(PVA)were blended to prepare bio-nanocomposite membrane(LCNF/PVA-AT),and its formation mechanism,mechanical properties,optical properties,salt concentration stimulus responsiveness performance and application in flexible strain sensor were analyzed.The results show that the LCNF/PVA-AT film has high stretchability,mechanical stability,water resistance,shape memory,and excellent UV resistance and optical haze in water environment.Compared with pure PVA film,the tensile stress and Young ’s modulus of LCNF/PVA-AT film in dry state is increased up to 227% and206%,respectively.The tensile strain of LCNF/PVA-AT film in aqueous environments is increased up to 92%.The soft robot prepared by LCNF/PVA-AT film can grasp and release the target well with the change of salt concentration in the environment.The underwater flexible strain sensor prepared based on LCNF/PVA-AT with a gauge factor of 7.1,which can generate a good real-time response to specific motion underwater.