The Structure Characteristics Of Salix Psammophila Lignin And Its Changingmechanism In The Enzyme-assisted High Yield Pulping Process

Salix Psammophila is a desert shrub. It is playing an important role in Windbreakand sand fixation, soil and water conservation, and improvement of the ecologicalbalance. Salix Psammophilahave higer cellulose and hemicellulose contents and can beused as a kind of new raw materials for the pulping and papermaking. In this study, thelignin structure of salix Psammophila, the optimal process conditions of high yieldpulping and the effects of enzyme treatment on the pulp properties and lignin structurewere investigated.The process conditions of chemical pretreatment in the one-stage P-RC APMPprocess were investigated with the orthogonal experimental design method. The effectsof NaOH dosage, H2O2dosage, temperature and time on the pulp properties, and theoptimal chemical pretreatment conditions were obtained. The optimized chemicalpretreatment process in the two-stages P-RC APMP process was studied by usingvariable analysis method on the basis of treatment conditions of the one-stage P-RCAPMP. The optimized process parameters as follows: the dosages of NaOH were3%and5%, and the dosages of H2O2were4%and6%corresponding to the one-stagepulping and two-stages processes, respectively.The P-RC APMP pulps of salix psammophila obtained from the one-stage andtwo-stages P-RC APMP processes were treated by xylanase, laccase-mediator system(LMS) and laccase-xylanase system (LXS). The brightness of the P-RC APMP pulptreated by xylanase improved, and meanwhile, the breaking length and burst indexdecreased. In addition, the crystallinity of the pulp from the one-stage P-RC APMPprocess reduced by6.01%and that from two-stages P-RC APMP process increased by5.61%. The brightness, breaking length, burst index and cellulose crystallinity of thepulp from the one-stage P-RC APMP process treated by laccase-mediator systemdecreased For the two-stages P-RC APMP process, the brightness, tear index andcrystallinity of the pulp treated by laccase-mediator system improved, but thebreaking length and burst index decreased. Almost all the parameters includingbrightness, breaking length, burst index and cellulose crystallinity of the pulp from theone-stage P-RC APMP and two-stages P-RC APMP processes reduced after treating bylaccase-xylanase system in.Compared to the raw material of salix psammophila, the lignin contents of the kraftpulp and the pulps obtained in the one-stage and two-stages P-RC APMP processes decreased after treating by xylanase, LMS and LXS.The total phenolic hydroxyl contents inthe lignin samples of the pulp obtainedfrom the one-stage and two-stages P-RC APMP processes were lower than that in rawmaterial, and the aliphatic hydroxyl contents changed slightly. The carboxyl content inthe lignin samples reduced in the one-stage pulping process, while carboxyl of ligninincreased in the two-stages pulping process. The aliphatic hydroxyl content in the kraftpulp lignin reduced obviously. The number-average molecular weight and theweight-average molecular weight of the lignin samples from raw material, kraft pulp,one-stage and two-stages P-RC APMP process reduced gradually, and the dispersivityof lignin increased.Compared to theP-RC APMP pulp untreated by xylanase, the aliphatic hydroxyland carboxyl of lignin increased, and the total phenolic hydroxyl of the treated pulpfrom the one-stage P-RC APMP process reduced. Different pulps from the one-stagepulping process, the aliphatic hydroxyl decreased, the total phenolic hydroxyl andcarboxyl in the lignin of the treated pulps from the the two-stages P-RC APMP processincreased. For the one-stage P-RC APMP process, the changing trends of aliphatichydroxyl, carboxyl and total phenolic hydroxyl inthe lignin of the pulp treated by LMSwere similar to that of the pulp treated by xylanase. For the two-stages P-RC APMPprocess, the aliphatic hydroxyl and total phenolic hydroxyl reduced, and carboxyl inlignin increased after treatment by LMS.After treatment by LXS, the carboxylincreased, and the aliphatic and total phenolic content in the lignins of thepulps fromtheone-stage and two-stage P-RC APMP processes reduced. In addition, the analysis resultsalso indicated that the dispersivity of the lignin in pulp improved after enzymetreatment.