Mechanism Of The Formation And Degradation Of LCC During Kraft Pulping

In order to investigate the formation and degradation of lignin-carbohydrate complexes (LCC) during kraft cooking, guaiacylglycerol-β-guaiacyl ether-[α-13C] was first synthesized as a phenolic type lignin model compound in this paper. After both guaiacylglycerol-β-guaiacyl ether and guaiacylglycerol-β-guaiacyl ether-[α-13C] were synthesized with a modified method, the phenolic type lignin model compounds were cooked by kraft method in existence of xylan, glucomannan or xylose. The products from kraft cooking were classified into four compositions by acidfying precipitation and ethyl acetate extractive. And the four compositions were alkali insoluble residue, acid insoluble residue, ethyl acetate extractive and acid soluble residue. The techniques of infrared spectra analysis, 13C-NMR,1H-NMR or HMQC were used to identify the newly formed LCC structure so that the formation and degradation of LCC during kraft cooking could be discovered. In order to investigate the newly formed LCC structure under more close to lignin molecule level condition, milled wood lignin (MWL) from Jacaranda copaia was cooked by kraft method in existence of xylan or xylose. And milled wood lignin (MWL) from Pinus massoniana Lamb was cooked by kraft method in existence of glucomannan. While lignin-carbohydrate complexes (LCC) from Jacaranda copaia and Pinus massoniana Lamb were also cooked with kraft method. The results showed that there were newly formed LCC structures during kraft cooking.The research showed that 4-(α-bromoacetyl)-guaiacol could be obtained when ethanol was applied as solvent in place of the mixture of ethyl acetate/chloroform (1/1,V/V)during the synthesis of guaiacylglycerol-β-guaiacyl ether. The reseason was that ethanol could change this bromination from non-homophase to homophase. As a result, the yield of bromide was enhanced at the same time. The reaction time had little effect on the final yield. The recrystallization by benzene could not separate the final products and 4-(α-bromoacetyl)-guaiacol could be obatained by column chromatography using the mixture of n-hexane and ethyl acetate (2/1,V/V) as mobile phase. The melting point and the techniques of infrared spectra analysis, 13C-NMR or 1H-NMR were used to identify the intermediates during the synthesis.When the phenolic type lignin model compounds- guaiacylglycerol-β- guaiacyl ether and guaiacylglycerol-β-guaiacyl ether-[α-13C] were cooked by kraft method in existence of xylan (or glucomannan). The analysis of the classified products showed that there was no newly formed LCC structure in alkali insoluble residue, acid soluble residue and ethyl acetate extractive. There were new formatuon LCC structures in acid insoluble residue and they were formed by intermediate produced from phenolic type lignin model compounds and xylan (or glucomannan) during kraft cooking. It was found that they were connected with benzyl ether linkage. When the phenolic type lignin model compounds were cooked by kraft method in existence of xylose, it was found that there were few newly formed LCC structures in ethyl acetate extractive and the intermediate from phenolic type lignin model compounds was linked to the alditols from xylose with benzyl ether bond during kraft cooking. There was no newly formed LCC structure in alkali insoluble residue, acid insoluble residue and acid soluble residue.In order to research the change of the structures, MWL was cooked with kraft method in existence of hemicelluloses. The results showed that the lignin linkages were easy to be cleaved by kraft cooking, especiallyα-aryl ether linkages andβ-aryl ether linkages. There were new LCC structures formed during the cleaving of lignin linkages. It was found that the newly formed LCC were stable in alkali solution and they existed with the type of benzyl ether linkage. When MWL from Jacaranda copaia was cooked by kraft method in existence of xylan (or xylose), the newly formed LCC come from lignin structures and xylan (or xylose), such asβ-O-4 lignin structure and 5-5 lignin structure.When MWL from Pinus massoniana Lamb was cooked with kraft method in existence of glucomannan, the newly formed LCC come fromβ-O-4 lignin structure and glucomannan or 5-5 lignin structure and xylose.When Lignin-carbohydrate complexes (LCC) from Jacaranda copaia and Pinus massoniana Lamb were cooked by kraft method, the research indicated that the carbohydrates in LCC were unstable and most of them were cleaved by kraft cooking. While there were some undegraded LCC structures after kraft cooking, which were stable in alkali solution.There were newly formed LCC structures after kraft cooking and they were connected with benzyl ether linkage. When LCC from Jacaranda copaia was cooked by kraft method, the newly formed LCC structure come from 5-5 lignin structure and xylan.When LCC from Pinus massoniana Lamb was cooked by kraft method, the newly formed LCC structure come from 5-5 lignin structure and xylose.