Study Of The Mechanism Of Laccase-Induced Transfering Of Phenols In Papermaking White Water To The Fiber Surface

After laccase treatment, the property of the pulp fibers and the strength of paper sheet will be improved because some material can be grafted to the pulp fiber surface. Find easily accessible, ecological and environment-friendly natural small molecules in paper making raw materials and pulp will help to advance the laccase/mediator system application in paper making industrial. Wagberg L found that dissolved and colloidal substances contained30%fragments of lignin phenols. This showed white water contains large amounts of lignin phenols, phenolic compounds has the main compounds of DCS (accumulation of DCS can cause many adverse effects).This paper aims to reduce white water DCS content and improve fiber surface properties by using laccase treatment to remove white water lignin and polyphenols and grafte small molecules phenols onto the surface of pulp fibers. In this study we use APMP white water and OCC white water were used as experimental subjects. Firstly natural phenolic compounds were identified by using GC-MS (gas chromatography-mass spectrometry). And GPC(gel chromatography)was employed to analysis these phenolic compounds. Finally after laccase treatment analysis OCC pulp fiber surface performance and physical properties of paper sheet.GC-MS analysis suggested that APMP white water contained4-methoxy-phenol,syringol and coniferyl alcohol. OCC white water contained syringol and coniferyl alcohol. After laccase treatment phenols in both white water have been removed in certain extent, and phenols may involved in the laccase treatment process, GPC model compound proved that free radical condensation of small molecule phenols occurred. Based on fiber morphology tester, after laccase/white water system treatment the fiber coarseness increased2%compare with control samples.The SEM images of laccase treated fibers and laccase/white water system treated fibers showed:The surfaces of laccase treated fibers appeared rough and vertical packed micro fibers in OCC fiber surface were observed; after laccase/white water system treatment, the surfaces of OCC fibers appeared smooth and a surface adhesion between fibers was observed.Infrared spectroscopy showed that after laccase/white water system treatment benzene and molecular weight increased compared with the control sample. XPS(X-ray photoelectron spectroscopy analysis) indicated that after r laccase/white water system treatment fiber surface lignin content significantly increased (increased31.6%) compared with the control sample, fiber surface was almost covered by lignin and C1increase while C2decreased. In addition28.63%improvement of wet ring crush strength and28.75%improvement of wet tensile strength were observed after laccase/white water treatment.This study exhibited that during laccase treatment process small molecule lignin derived phenols that existing in white water act as natural mediators, after free radical condensation they deposited to the surface of the pulp fiber surface, and chemical bonds generated between phenols and fiber surface, lignin content increased while DCS decreased, laccase/white water system has prorided an efficience way in modifying the fiber surface properties and improved quality of white water.