A Study Of Wood Fiber Board Based On Laccase Mediator System Activation On Wood Fiber

With the rapid growth of world economy, ecological security, human health and harmonious development became an important evaluation criterion of the international community. Wood based panel as the important ingredient in forestry industry, the free formaldehyde restricted its development all the time. However, laccase was proved to be an effective method to resolve this problem. Meanwhile, laccase had special significance in the insurance of ecological environment security, the development of low carbon economy, the advancement of energy conservation and the construction of a resource-efficient society.According to the activation of laccase mediator system, wood fibers were made binderless medium density fiberboard by hot-press. This research focused on four aspects, which were:(1) based on the models of phenol compound (guaiacol) and non-phenol compound (veratryl alcohol), the proportion and reaction conditions of laccase, artificial mediator (ABTS) and natural mediator (vanillin) were determined primarily;(2) UV pretreatment process was determined in view of FTIR and XRD. The technological parameters of enzymatic reaction and hot-press were optimized based on response surface methods. Dimensional stability process was determined by mechanical analysis, physical and chemical analysis. Then optimized technology of medium density fiberboard based on laccase mediator system activation on wood fiber was achieved by above three sections;(3) the binding mechanism of binderless medium density fiberboard was explored by FTIR, XRD, SEM, XPS and contact angle measuring instrument;(4) carbon storage of medium density fiberboard based on laccase mediator system activation on wood fiber was researched by artificial weathering test.The conclusions of this research were summarized as follows:(1) The process parameters of UV pretreatment were as follows:the UV irradiation time was24h, the UV irradiation distance was50cm and the UV irradiation intensity was150W/m2At the moment, cellulose was degraded which increased the reaction activity sites of laccase. Meanwhile, a little lignin was degraded into alkyl aldehyde which be used for mediator to catalyze non-phenol lignin;(2) Based on the model compounds of lignin, the optimized technologies of laccase mediator system activation on wood fibers were as follows:pH value was5.0, the reaction temperature was50℃, the reaction time was55min, the volume fraction of wood fibers was4.0%, the molarity of ABTS was0.28mmol/L, the molarity of vanillin was1.66mmol/L and the laccase activity was60U/mL. The hot-press optimized technologies of medium density fiberboard were as follows:the hot-press temperature was165℃, the hot-press pressure was10MPa and the hot-press time was512s. The hot-press process consisted of dry process and plastics process. Dry process was three cycles, and each cycle was52s at10MPa firstly, and then52s at4MPa. Plastics process was200s at10MPa.(3) Binderless medium density fiberboard without dimension stability treatment was as control sample. The effects of chitosan and solid paraffin on dimension stability were comparative analysis based on physical properties, mechanical properties, contact angle, functional groups, cellulose crystallinity and morphology. The results showed that solid paraffin closed water-flow path with hydrophobic property which could improve the dimension stability of medium density fiberboard, but the mechanical strength was reduced and the effective time was relatively short. Chitosan decreased or blocked the water-flow path by chemical bonding to improve the dimension stability, while the effective time was relatively long and enhanced the mechanical strength. Therefore, chitosan was chosen to improve the dimension stability, and the suitable mass fraction was1.2%;(4) Based on the optimized technologies, the MOR of medium density fiberboard was34.41MPa, the MOE was2887.9MPa, the IB was0.89MPa and the TS was24.80%. On the basis of Chinese National Standard GB/T11718-2009, the binderless medium density fiberboard reached the performance requirement of MDF-FN MR.(5) By the analysis of FTIR, XRD and XPS, the reactions of binderless medium density fiberboard consisted of esterification, hydrogen bonding, polycondensation, coupling reaction and Schiff base reaction. Polycondensation and coupling reaction were main reactions. These reactions helped to bring about new crystalline regions which enhanced the mechanical strength. During the hot-press, lignin flowed in the interior of medium density fiberboard, and then the carboxyl group increased on the surface of medium density fiberboard, while the aldehyde group increased in the interior of medium density fiberboard. Therefore, the bonding types were different between the surface and the interior of binderless medium density fiberboard;(6) Under the different artificial weathering time, the carbon storage of test sample was most, and then was control2and control1. The carbon storage decreased with the increasing time, but the rate reduced gradually. The loss rate of controll was greater than test sample and control2. The primary cause of decreasing carbon storage was the breakage of C-O/C-C and the degradation of aromatic ring in medium density fiberboard. The efficient cause was the increasing of diffusion-permeability coefficient. In the short time, the increasing of diffusion-permeability coefficient accelerated the medium density fiberboard to decay. The wood rotting fungi (white-rot fungi and brown-rot fungi) damaged the structures of cellulose, hemicelluloses and lignin which decreased the carbon storage. In the long time, the increasing degree of wood rotting reduced the density of fiberboard observably, and enhanced the hygroscopicity and permeability. Therefore, the medium density fiberboard would create destabilizing buckling deformation which reduced the service life. Consequently, the carbon storage time of medium density fiberboard was reduced.