The chemistry, morphology, crystal structure and hydrophilicity properties of wood fibers treated by a magnetic immobilized laccase–mediator system

Abstract

The aim of this study was to investigate the surface properties of wood fibers treated by a magnetic immobilized laccase–mediator system (ILMS), which had never previously been examined. ESR results revealed that stable phenoxy radicals were generated in ILMS-treated fibers. No significant chemical structure changes in the fiber surface were observed in FTIR spectra, which was due to the fact that the laccase oxidation reaction is limited to occur in the part of the fiber surface lignin during a short incubation time of 1 h. Increased O/C ratio of the fiber surface, and also a reduction in the surface coverage of lignin were calculated from XPS spectra, which could be ascribed to the ILMS-catalyzed degradation of fiber surface lignin. The ILMS treatment also revealed 9.5% increase in the crystallinity index (CrI) of treated fibers as compared to the control. The SEM observations indicated that the mediator had a positive effect on depolymerization of surface lignin. The surface hydrophilicity enhancement of the ILMS-treated fiber was confirmed according to the increasing of water-holding capacity (WHC). These results have suggested the separable characteristics of the magnetic immobilized laccase, providing a promising approach to control the oxidation degree of fiber surface efficiently.