Effect Of The Lignin Content And Structure Changes On High Yield Pulp Properties

At present, the shortage of energy and the pollution of environmental problems have become increasingly serious, the research of biotechnology will to be a hot spot. The main content of this research is to use laccase and hydrogen peroxide process with pulp, so as to reduce environmental pollution, conserve natural resources, improve pulp properties and expand the application range of pulp, etc.The fiber surface properties of pulp which were modified and processed by enzyme and bleaching were analyzed by FQA, ESEM and other testing methods. The analysis results show that the curl index, kink index of fiber have increased, indicating that the laccase modification and bleaching had a great influence on the pulp fibers.The beating, refining and other operations on the impact of lignin content were analyzed. Compared with the control pulp, bleached pulp after refining, pulp after beating the Klason Lignin content decreased after laccase or laccase mediator system modification, suggesting that the laccase or laccase mediator system had a certain extent influence on the Klason Lignin content in the pulp.The Alkalin Peroxide Mechanical Pulps (APMP) of fast-growing poplar were modified by Laccase-Mediator-System (LMS), and then were bleached with hydrogen peroxide. The main impacting factors were investigated, optimizing its bleaching processes. The optimum conditions of laccase/mediator system process were: pulp consistency 4%, pH 5, at temperature 50℃for 60min and the optimum charge of laccase was 2U·g^-1 with 0.5% mediator (HBT). It was found that the optimum bleaching conditions were: 4% NaOH, 5% H₂O₂, 5% Na₂SiO₃, 0.1% MgSO₄, 0.5% EDTA, 10% pulp consistency at 70℃for 1.5 hours. The effects on pulp physical properties were analysed by testing the hand-made sheets. During the modification with laccase/ mediator system process under the optimum conditions, the brightness of APMP reached 72.2% ISO, with an increase of 18.7% compared to the control pulp.The tensile index increased from 8.30 N·m·g^-1 to 32.80 N·m·g^-1, which increased 2.95 times. The tear index increased from 1.48 mN·m²Â·g^-1 to 3.61 mN·m²Â·g^-1, an increased of 1.44 times. These results showed that the strength properties of APMP treated with laccase/mediator followed by hydrogen peroxide bleaching increased significantly compared to control pulp.Lignin samples were isolated from the unbleached and bleached pulp before or after the modified with laccase through a two-stage method: enzymatic and mild acidic hydrolysis. Then the contents of Aliphatic OH, total Phenolic OH, COOH and different phenolic function groups in the lignin structures were analyzed and compared qualitatively and quantitatively using infrared spectroscopy FTIR, 13C-NMR, 31P-NMR techniques.The analysis results show that: during the Unbleached pulp of the APMP modified process with the laccase, the content of aliphatic OH (A-OH) increased, but the contents of the total phenolic OH (T-OH),the COOH decreased. In the lignin the contents of the syringyl phenolic (S-OH),the p-hydroxyl-phenyl OH (p-OH),the condensed phenolic OH (C-OH),the guaiacyl and dementhylated OH (G-OH) decreased. During the Unbleached pulp of the APMP modified process with Laccase-Mediator-System, the contents of the aliphatic OH (A-OH),the total phenolic OH (T-OH),the COOH decreased. In the lignin the contents of the syringyl phenolic (S-OH),the p-hydroxyl-phenyl OH (p-OH),the guaiacyl and the dementhylated OH (G-OH),the condensed phenolic OH (C-OH) decreased.After APMP bleached pulp modified with the laccase, the contents of aliphatic OH (A-OH) and total phenolic OH (T-OH) decreased, while the contents of the COOH increased. In the lignin the contents of the guaiacyl and dementhylated OH (G-OH),the syringyl phenolic (S-OH),the condensed phenolic OH (C-OH) decreased, but the contents of the p-hydroxyl-phenyl OH (p-OH) increased. After APMP bleached pulp modified with LMS, the content of aliphatic OH (A-OH),the COOH,the total phenolic OH (T-OH) decreased. In the lignin the contents of the guaiacyl and dementhylated OH (G-OH),the syringyl phenolic (S-OH),the condensed phenolic OH (C-OH) decreased, but the contents of p-hydroxyl-phenyl OH (p-OH) increased in the lignin.