| The high-value utilization of biomass resources can effectively alleviate the energy crisis and reduce the burdens on the environment.Bagasse,as a common agricultural waste,has the characteristics of low acquisition cost,large annual production,and has a broad prospect of high-value utilization.Additionally,the prerequisite for high value utilization is green and efficient extraction of hemicellulose,lignin and cellulose from bagasse.It has been proved that pToluenesulfonic Acid(p-TsOH)has the unique advantage for the extraction of lignin from biomass and can achieve the efficient removal of lignin at atmospheric pressure and lower temperature(below 100℃).However,the lignin extraction approach can inevitably result in the removal of hemicellulose from bagasse.In addition,the reaction mechanism of hemicellulose and lignin extraction using pTsOH has not been clarified,and the reaction pattern of p-TsOH with lignin and hemicellulose has been rarely reported.Therefore,in this work,the efficiency of bagasse hemicellulose and lignin extraction using p-TsOH at atmospheric pressure was investigated,and the extraction mechanism of hemicellulose and lignin was elucidated by combining the structural changes of each component and the extraction kinetics of hemicellulose and lignin.The lignin-containing nanocellulose films were obtained by high-pressure homogenization and hotpressing treatment using the residual followed by the removal of hemicellulose and lignin.Besides that,the mechanical and moisture-proof properties were investigated.The major research and results of this thesis are presented as follows:The effects of p-TsOH concentration,reaction temperature and reaction time on the extraction rate of hemicellulose using p-TsOH were studied to obtain the optimal extraction conditions for hemicellulose:The p-TsOH concentration was 3.0%,the reaction temperature was 80℃,and the reaction time was 120 min.The composition analysis showed that the extraction yield and the removal yield of hemicellulose were 36.02%and 73.23%,respectively.The content of lignin and cellulose in the obtained hemicellulose samples were 2.85%and 1.35%,respectively.The purity of the hemicellulose samples was 95.60%,and the samples were mainly polysaccharides up to 81.37%,which revealed that the hemicellulose samples extracted by p-TsOH have higher purity and larger molecular weight.FT-IR and 2D-HSQC NMR were conducted for the structural identification of hemicellulose samples.The results showed that hemicellulose was extracted in polymer formation during the fraction process.Furthermore,both the LCCs and the lignin were not found in hemicellulose samples,which demonstrated that selectivity was confirmed in the extraction of hemicellulose by p-TsOH.The hemicellulose extraction process is composed of two parts:hemicellulose solubilization and hemicellulose polysaccharide depolymerization.These two parts are integrated and presented in the modified kinetic model:The reaction rate constant in the hemicellulose solubilization is kE=3.69 s-1 and the reaction rate constant for the hemicellulose polysaccharide depolymerization is kS=1.74×10-6 s-1 through fitting the kinetic model and analysis for the kinetic parameters.Comparing the reaction constants of the two processes,it was showed that the dissolution of hemicellulose was much faster than the depolymerization of hemicellulose polysaccharide.The phenomenon that hemicellulose was existed in the form of glycans was explained in the terms of the kinetics.In the macrokinetic,the activation energy of reaction(Ea)is 29.74 kJ·mol-1.The lower activation energy of reaction indicated the high efficiency of hemicellulose extraction using p-TsOH.The effects of reaction conditions such as the concentration of p-TsOH,reaction temperature and reaction time on the lignin extraction yield were studied in detail,and the optimal reaction conditions were obtained:p-TsOH concentration of 80%,reaction temperature at 80℃ and reaction time lasted 20 min.The composition analysis showed that the lignin extraction yield was up to 85.01%and the purity was 96.87%.The selectivity of p-TsOH for lignin extraction was demonstrated in the optimal conditions.2D-HSQC NMR and PyGC/MS were used to observe the structure of lignin samples,and the results showed that lignin underwent the reaction path of α-methoxylation of β-O-4linked intermediate structures to achieve efficient depolymerization and extraction as the result of autocatalysis by p-TsOH.In the obtained samples,theβ-O-4 bonds were dominated among the lignin phenylpropane units with only a small number of β-β and β-5 linkage bonds,which indicated that lignin extracted with p-TsOH has a relatively small degree of condensation.Laser confocal microscopy imaging techniques were utilized to reveal that collapse happened on lignin from the edge of the cell wall to the center of the cell wall layer by layer during the removal process,which is consistent with the results of the flat plate condensation model.The kinetic model of lignin extraction using p-TsOH was also developed by lignin extraction pattern.The reaction kinetics were as follows.The rapid delignification phase:XL=（kP1MLCP1/LSρL)t The slow delignification phase:The kinetics were fitted to obtain the reaction rate constants of kP2=2.22×10-10 L·mol-1·s-1 for the rapid delignification phase and kP3=1.28×10-13L·mol-1·s-1 for the slow delignification stage.The fitting result of kinetics was showed that the reaction rate of the rapid delignification phase was three orders higher than that of the slow delignification phase,providing fundamental basis for precise regulation of the reaction conditions for the lignin removal.The bagasse after extraction of hemicellulose and lignin using p-TsOH was rich in cellulose fraction with 90.64%,4.15%of hemicellulose,and 4.87%of lignin.2756 cellulose polymerization and 69.67%crystallinity,which suggested that the cellulose was less damaged during the p-TsOH treatment and did not affect the utilization value of cellulose.The residual was processed to lignin-containing nanocellulose membranes by vacuum filtration and hot-pressing treatment.FESEM analysis illustrated that the average diameter of lignin-containing nanocellulose fibrils using high-pressure homogenization method was 17.2 nm and the average particle size of lignin particles was 25 nm.In addition,the lignin endowed the nanocellulose suspension with better dispersibility.The mechanical properties were analyzed using the Electronic Universal Tensile Testing Machine.The results showed a 50%increase in tensile strength and a 200%increase in elongation at break for the obtained membranes,comparing to the pure nanocellulose membrane.Finally,its water stability was conducted by dynamic water absorption and the hygroscopicity was reduced by 48%.It was shown that the lignin after the hot-pressing treatment can effectively enhance the mechanical properties and water stability for nanocellulose films. |
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