The Preparation And Study Of Peanut Shell Nanofibers And Freshness-preserving Composite Films By Deep Eutectic Solvents Of Ultrasonic Synergistic Lignin-derived Phenol

Peanut shells have the advantages of high yield and renewable energy,and their chemical conversion and production of bio-based materials are of great significance for maximizing the utilization of agricultural waste resources.However,the complex structure of cellulose,hemicellulose and lignin in peanut shell closely interweaves with each other,which limits its efficient utilization,and requires effective pretreatment to destroy its complex structure and improve its utilization rate.Deep eutectic solvent（DES）has been developed and utilized as a new green and biodegradable pre-treatment solvent.The commonly used DES is mainly prepared using acids,alcohols,and amines,while the DES synthesized using lignin derived phenols is relatively rare.Lignin is abundant in biomass,and its valuation is crucial for future bio refining,requiring further utilization and research.This article uses peanut shells as raw materials and first constructs binary and ternary DES pretreatment systems based on lignin-derived phenols to deconstruct peanut shell biomass.Then ultrasonic was applied to nanosized it to prepare lignin-containing cellulose nanocrystal（LCNC）,and the effects of pretreatment on the conversion of cellulose and hemicellulose,as well as the preparation of LCNC were investigated.Finally,the prepared LCNC was blended with chitosan（CS）to obtain a CS-LCNC composite film,and its effect on cherry tomato preservation was investigated.The main research content and results are as follows（1）The effect of ternary DES pretreatment based on lignin-derived phenols on the chemical composition,structure,and enzymatic hydrolysis of peanut shell biomass was studied.A ternary DES was prepared using choline chloride（Ch Cl）as a hydrogen bond acceptor and guaiacol（GG）and p-hydroxybenzoic acid（PB）as double hydrogen bond donors to pretreat peanut shell biomass.The effects of molar ratio,temperature,and time on the pretreatment performance were compared with binary DES（Ch Cl-GG,Ch Cl-PB）.The results showed that Ch Cl-GG-PB had the best pretreatment performance.The lignin removal rate reached 69.54%,and it also had the highest cellulose recovery rate,which increased by 20.93%compared to the untreated peanut shell sample（160℃,6 h）.In addition,the maximum enzymatic hydrolysis yield was achieved,with a xylose content 5.50 times that of the untreated sample.Through further characterization analysis,it was found that the cellulose in peanut shell biomass was enriched,and the crystallinity significantly increased after Ch Cl-GG-PB pretreatment.Scanning electron microscopy observed that the surface morphology of peanut shell biomass was destroyed,exposing a fibrous bundle like structure.（2）The effect of ternary DES pretreatment based on ultrasonic lignin-derived phenols on the preparation of peanut shell nano lignocellulose was studied.In the first part of the study,DES using wood-derived phenols as hydrogen bonding donors was effectively pre-treated for peanut shell biomass,but the pre-treatment performance of Ch Cl-GG DES was poor.Therefore,this chapter aims to improve the quality and efficiency of the harmful solvent Ch Cl-GG by adding different molar ratios of aluminum chloride hexahydrate（Al Cl₃·6H₂O）to the DES based on the first chapter.The results showed that the removal rates of lignin and hemicellulose were 73.31%and93.10%,respectively,and the recovery rate of cellulose was 59.52%after the addition of 0.07 molar ratio of Al Cl₃·6H₂O（120℃,3 h）.Chemical structure analysis further confirmed the effective dissociation of lignin,which has the highest crystallinity（58.94%）compared to other samples,and its microscopic morphology has been destroyed,exposing a fibrous bundle like structure.After ultrasonic treatment,the yield of LCNC prepared was 55.97%,with an average diameter of 2.60±0.53 nm,and had good anti-aggregation ability（Zeta potential is-37.87 m V）and thermal stability(T_max=337℃).In addition,lignin particles can be observed on LCNC through transmission electron microscopy,indicating the presence of lignin in LCNC.This can also be confirmed through analysis such as UV-visible spectroscopy,Fourier transform infrared spectroscopy,and X-ray photoelectron spectroscopy.（3）The effect of peanut shell nano lignocellulose on the preparation of composite film and the preservation of cherry tomato coating was studied.The CS-LCNC composite film was obtained by blending the LCNC prepared in the previous chapter with CS.The optimal amount of LCNC addition was explored to obtain the best-performance composite film for the preservation of cherry tomatoes.The influence of the composite film on the preservation effect of cherry tomatoes was also investigated.The results showed that when the amount of LCNC added was 40%,the tensile strength and elongation at the break of the composite film reached the maximum,40.14 MPa,and 31.12%,respectively.At the same time,it had the lowest water vapor and oxygen permeability,which decreased by 31.01%and 36.21%compared to the pure CS film,respectively.Further characterization revealed an interaction between LCNC and CS molecules,but the addition of LCNC did not alter the original structure of CS.After coating cherry tomatoes for freshness preservation,it was found that the CS-LCNC coating treatment significantly reduced the quality loss and softening rate of cherry tomatoes in the later stage of storage compared to other treatments and had the lowest decay rate.On the 15 d,the decay rate of the CS-LCNC coating group was 55.57%and33.35%lower than that of the uncoated and CS coating groups,respectively.In addition,the observation of appearance color also indicates that CS-LCNC coating has the best preservation effect,with the smallest changes in L value,a value,and color difference（?E）of cherry tomatoes coated with it.The above research results indicate that the DES pretreatment system based on ultrasound assisted lignin derived phenols can effectively depolymerize agricultural product waste peanut shells and improve the utilization efficiency of each component.The prepared LCNC composite membrane is expected to extend the shelf life of cherry tomatoes and further promote the green resource utilization of peanut shell biomass.