A Study Of Fiberboard Based On Laccase Mediator System Activation On Lignin

With the reduction of wood resources and the enhancement of people’s awareness of environmental protection, people pay more and more attention to the environmental friendly wood fiber board. In the premise of efficient utilization of wood resources, it is of great significance for improving people’s living conditions and protecting environment to produce the formaldehyde free wood-based panel.In this study, wood fibers and ammonium lignosulfonate activated by white rot fungi laccase and mediators(2,2’-azinobis(3-ehtylbenzothiazolin-6-sulfnic acid)diammonium salt(ABTS), 1-hydroxybenzotriazole(HBT), syringaldehyde and vanillin) were used as raw materials to prepare fiberboard by hot pressing. The following conclusions were drawn after analysis:(1) The absorbance of laccase solution with ABTS as substrate was detected at 420 nm by UV visible spectrophotometer at 40℃ and pH=5 and the maximum enzyme activity of laccase was 1583U/g, which was calculated by the formula of enzyme activity.(2) The conditions of laccase mediator system activating ammonium lignosulfonate were optimized through single factor experiments and the results showed that physical and mechanical properties of Lac+HBT/MLF were optimal when the dosage of laccase was 20U/g, the dosage of HBT was 0.2% and the activation time was 120 minutes. The changes of ammonium lignosulfonate components before and after the activation of laccase and laccase mediator system were analyzed and the results showed that the hydroxyl and syringyl content was decreased and phenolic hydroxyl group content was increased after activation. It indicated that ammonium lignosulfonate could be degraded after the laccase activation and may polymerize after the laccase mediator system activation at the same time.(3) The conditions of preparing fiberboard by ammonium lignosulfonate activated by laccase-HBT mediator system were optimized through the orthogonal test and the optimum conditions were:the dosage of lignin 20%, hot pressing time 8 minutes, hot pressing temperature 170℃ and moisture content of mat 25%, the mechanical properties of the board could meet the requirements of GB/T11718-2009 for medium-density fiberboard. According to the properties analysis of fiberboard, compared with the OLF, the thermal stabilities of Lac/MLF and Lac+HBT/MLF were poorer, but the relative crystallinity and hydrophobicity were better. Besides, the wood fiber of Lac/MLF and Lac+HBT/MLF combined more closely and the physical and mechanical properties of Lac/MLF and Lac+HBT/MLF were relatively higher.(4) The environmental impact of preparing fiberboard by laccase mediator system activated ammonium lignosulfonate was analyzed with GaBi6.0. The results showed that the largest environmental impact types were global warming potential, acidification potential and photochem and ozone creation potential and the proportion were 40%,33.07% and 20.60%, respectively. In the process of preparing fiberboard, the largest impact on the environment was hot pressing. Therefore, adding insulation board in hot pressing process would be an efficient way to avoid energy loss and reduce environmental impact of fiberboard preparation.