The Structural Changes Of Fast-growing Aspen APMP Pulp And The Change Rules Of Condensed Structure In Lignin Treated By Laccase Mediator System

The production of high-yield pulp is expanding very fast, because of the resourcesand environmental problems. Compared with chemical pulp, high-yield pulp has manyadvantages, such as, high yield, environmental friendly, good optical properties andprinting adaptability. But it also has many shortcomings, such as, low physical strength,low brightness, and easy to return to yellow, which are limit its application scope.Therefore, we need to modify its properties to expand its applications. This this paper,we use laccase mediator system to modify triploid populus tomentosa alkaline hydrogenperoxide pulp, discussed the technological conditions of modification treated bylaccase/HBT and studied the structure changes of lignin with laccase/HBT treatment.After using the laccase/HBT system to modify the unbleached triploid populustomentosa alkaline hydrogen peroxide pulp, we measured physical properties andbrightness of pulp and determination the modification effect on the subsequenthydrogen peroxide bleaching. The main impacting factors were investigated,optimizing its process conductions: dosage of laccase is4IU/g, dosage of HBT is0.5%,pulp concentration is4%, for60min time, temperature of50℃, the initial pH of5.0.Experiments showed that after modification by laccase/HBT system, the brightness ofpulp is reduced, but after modified by LMS, again after treated by hydrogen peroxidebleaching, pulp brightness can be increased by3%ISO. The physical strength of papermodified by LMS is also increased.We used FQA and ESEM to analyze the fiber morphology modified by laccse/HBT,and then found LMS has obvious effect to pulp. At the same time, analyzing thechemical composition of the pulp, we found that the LMS has little effect on cellulose,has no effect on hemicellulose, and mainly effect on lignin.In order to explore the role of LMS to lignin, we isolated the lignin from APMPpulp and fast growing poplar raw material respectively. The separation of ligninextraction process should be as far as possible the high yield, high purity, little structuralchanges. We adopted two-stage method of enzyme-mild acidic hydrolysis.After the isolated lignin was treated with a laccase-mediator system (LMS), thephosphor magnetic resonance spectrum (31P-NMR) measurements and Infrared spectralanalysis technology were chosen to analyze the structural changes of LMS-treatedAPMP residual lignin and LMS-treated fast growing poplar raw material lignin. We found lignin phenol hydroxyl, aliphatic hydroxyl (A-OH), carboxyl content is lower.The content of condensation phenolic hydroxyl(C-OH), syringyl phenolic hydroxyl(S-OH), guaiac phenolic hydroxyl (G-OH) and the p-hydroxyl-phenyl (p-OH) are alldecreased. The processing of the LMS may result in lignin macromolecule side chainfracture; Alpha hydroxyl oxidation occurred generation of alpha carbonyl; cause thelignin removal of methyl group. After modification of LMS, the content of syringylphenolic decreased significantly, the ratio of guaiacyl unit increased, that’s theuncondensation type lignin proportion reduced, condensation type lignin proportionincreased.Using GPC to characterize the molecular weight of LMS-treated APMPresidual lignin and LMS-treated fast growing poplar raw material lignin, we found thatafter the treatment of LMS, the molecular weight of lignin is lower, lignin degradationhave taken place.Compared the raw material lignin and residual lignin in the pulp, we can inferredin APMP pulping process,the content of guaiac structure lignin dissolved more thansyringyl structure lignin and the degradation of lignin is mainly small molecules.