| The chemical composition of the cell wall and the contents of the cell cavity will c hange during the lignification process,which will affect the properties of bamboo and its processing and utilization.The research on the structure of lignin in the growth process of bamboo can provide reference data for the adaptability of bamboo mechanical proper ties,bamboo processing technology and high value-added utilization.Therefore,the clean and efficient separation of bamboo components is conducive to the analysis of lignin str ucture,and the advanced nature of various separation methods can lay a foundation for t he industrialization of biomass chemical conversion of bamboo residues.In this study,ba mboo with different growth stages was used as raw material for lignocellulose,and a ne w type of original lignin was obtained based on ball milling and enzymatic hydrolysis.I n addition,lignin was separated by a novel green solvent pretreatment method.The obtai ned samples were combined with infrared spectroscopy(IR)and nuclear magnetic resona nce(NMR)to study the structural changes of lignin.The conclusions are as follows:(1)In order to better clarify the accumulation and structural changes of lignin duri ng the growth of bamboo,the enzymatic hydrolysis residue lignin(DEL)was obtained fr om different ages of bamboo with the method of ball mill and enzymatic hydrolysis in t his chapter.Compared with the traditional original lignin preparation method,the lignin h as the advantages of high yield and representativeness.The results of two-dimensional hy drocarbon correlation spectroscopy(2D-HSQC)indicated that phyllostachys bamboo lignin belongs to the typical GSH-type of gramineous lignin,and its side chain ?-position has a certain degree of acylation,which is mainly from the esterification of the fragrant Soy acid.The semi-quantitative results of 2D-HSQC NMR showed that the main linkages co ntained in lignin of different bamboo ages were ?-O-4 linkages.With the increase of ba mboo age,the S/G value of lignin macromolecules increased,and the content of H-type lignin tended to be stable in bamboo.Moreover,the content of ?-O-4 was positively corr elated with the S/G value.(2)Based on the concept of biorefinery,hydrothermal treatment(180?,30 minutes)was used to selectively break the bond between lignin and hemicellulose in bamboo in this chapter,and the hemicellulose was dissolved in the form of oligosaccharides,as well as to obtain a certain yield of xylooligosaccharides,and can also promote the extractionof subsequent lignin.The bamboo powder after heat treatment was pretreated with p-tol uenesulfonic acid,and it was found that the yield of lignin increased with the concentrat ion of p-toluenesulfonic acid.When the concentration of p-toluene sulfonic acid reached80%,the two-dimensional NMR results showed that the lignin side chain structure had b een destroyed.Excessive concentration of p-toluenesulfonic acid will result in the destruct ion of lignin structure.In addition,in the recovery experiment with a concentration of 40%,the yield of lignin decreased slightly,but since the acidity of the solution increased,the signal of the linkage was strengthened,and therefore,p-toluenesulfonic acid had a c ertain recyclability.The two-dimensional nuclear magnetic semi-quantitative results showed that the content of ?-5 increased gradually and the content of ?-O-4 and ?-? decreased with the increase of bamboo age under the same treatment conditions.(3)In this chapter,the lignin in the hydrothermal treatment of bamboo raw materia ls was separated and extracted by the DES system formed by lactic acid and choline chl oride.As the DES treatment temperature increased(20 minutes,110?,120?,130?),th e lignin yield gradually increased(59%-72%),and the molecular weight became larger.In addition,the recovery performance of DES solvent was also evaluated in this chapter.It was found that the DES cycle remained basically unchanged after three cycles,indica ting that the recovery cycle performance of DES was good.The semi-quantitative results of 2D-HSQC NMR showed that the content of ?-O-4 decreased gradually with the incr ease of temperature.Analogously,the content of ?-O-4 decreased gradually with the incre ase of the number of recovery cycles,which may be related to the acid enhancement of the recovered DES system(acid enhancement will lead to the fracture of lignin ether b ond).The S/G ratio increased gradually with the temperature and then decreased again,i ndicating that demethylation reaction may occur in the process of DES treatment.G-type lignin was preferentially removed at low temperature,and the demethylation reaction oc curred in both S-type and G-type lignin as the temperature increased.The DES three-cyc le experiment also showed this.As the number of cycles increased,the acidity of the sy stem became stronger and stronger,resulting in a decrease in the S/G ratio. |
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