Study On The Manufacturing Of Binderless Fiberboard Made From Wood Fibers Catalyzed By Immobilized Laccase/Mediator System

In order to solve the problems of releasing free formaldehyde from traditional man-made board, the defects of instable activity, high cost and cannot be reused, which restrict the industrial application of laccase. The paper put forward the research plan that using the wood fiber consisted of Pinus koraiensis, Larix gmelinii, Populus as raw materials, and catalytic oxidize wood fiber by the magnetic immobilized laccase/mediator system to manufacture the binderless fiberboard under the hot pressing condition. The paper aims to study the optimal process parameters of binderless fiberboard which treated by magnetic immobilized laccase/mediator system and further reveal the self-bonding mechanism of binderless fiberboard. Moreover, the environmental effect evaluation of the binderless fiberboard manufacturing process within the laboratory boundary was also investigated. The conclusions of this research were as follows:(1) Study on the synthesis and properties of embedded structure of magnetic immobilized laccase.A novel magnetically separable laccase immobilized system was constructed by immobilizing an Aspergillus laccase on the embedded structure of amino-functionalised magnetic silica nanoparticles (AF-MSNPs) via a chemical crosslinking method. The synthesis mechanism of magnetic immobilization laccase was also put forward. The results showed that the saturation magnetization of the magnetic immobilization laccase was 13.327emu/g and its coercive force is almost zero, presenting the superparamagnetism property. The average activity of immobilized laccase was 650±20 U/g of settled carrier particles. The activity recovery obtained from immobilized laccase was around 53.4±3.1% and the immobilized amount of laccase was 613.5±10.5 mg/g of settled carrier particles. Compared to the free laccase, the optimal reaction temperature and pH was 50℃ and 3.5, moreover, the magnetic immobilization laccase not only exhibited better resistance to a broader pH and temperature value, but also exhibited significantly higher thermal stability, storage stability and operational stability of the biocatalysts.(2) The surface properties of wood fibers treated by magnetic immobilized laccase/mediator system.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 due to the laccase oxidation is limited to lignins located on the surface of the fibers 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 played a positive effect on de-polymerization of surface lignin. The surface hydrophilicity enhancement of the ILMS-treated fiber was confirmed according to the increasing of water-holding capacity (WHC).(3) Study on the optimal manufacture process parameters of binderless fiberboard made from wood fibers treated by magnetic immobilized laccase/mediator system.The average thickness of 2.7mm and average density of 0.78g/cm3 binderless fiberboard was made according to the Response surface optimization method testing scheme. Four groups of response surface regression models regarding modulus of rupture, modulus of elasticity, internal bonding and 24h thickness swell, respectively, as objective function has been built by Response Surface Methodology (RSM). Variance analysis showed that four groups of mathematical regression model both were accurate and reliable, which can be used to analyze and forecast the response values. The optimal process parameters of binderless fiberboard were as follow:the catalytic reaction time was 64min, the enzyme dosage was 21U/g and the catalytic reaction temperature was 52 ℃. The catalytic reaction time, enzyme dosage and catalytic reaction temperature as well as their interaction had a significant effect on the physical and chemical properties of binderless fiberboard. Verification test showed that the binderless fiberboard of modulus of rupture was 33.4 MPa, modulus of elasticity was 3328 MPa, internal bonding was 0.83 MPa and 24h thickness swell was 13.7%. The four deviation rates between the test values and model prediction are all below 7%. The physicochemical properties of binderless fiberboard fulfilled the requirements for ordinary medium density fiberboard being used in damp conditions defined in the standard of GB/T 11718-2009 MDF of China. The correlation coefficient (R2) of the nonlinear fitting equations between the immobilized laccase recycle time and physical and chemical performance index of fiberboard were all above 0.97. The good correlation plays an important role on the efficient utilization of the immobilized enzyme and the prediction of physical and chemical performance.(4) Study on the self-bonding mechanism of binderless fiberboards made from wood fibers treated by magnetic immobilized laccase/mediator system.During the preparation process of fiberboards made from wood fibers treated by magnetic immobilized laccase/mediator system, the self-bonding way inside wood fiber is very complex. The main possible chemical reactions can be summarized as follows:1) the radical polymerization (coupling termination) between the phenoxy radical (Phe-O·) produced from the lignin catalyzed by laccase; 2) the hydrogen bonding between the hydroxyl groups among various components of wood; 3) the condensation reaction between the hydroxyl and aldehyde group produced from lignin and the thermal degradation products of hemicellulose; 4) the esterification reaction between the hydroxyl and carboxyl among various components of wood; 5) the polycondensation crosslinking reaction between furfural class materials and lignin components and synthesis the compounds similar to phenolic compounds. The important order of chemical reactions mentioned above in the process of laccase activation treatment and hot pressing was depended on two factors. On the one hand, it depends on the quantity of each kind of active groups in wood fiber components. On the other hand, it depends on the contact probability of active groups during the hot-pressing process.(5) The environmental effect evaluation of binderless fiberboards made from wood fibers treated by magnetic immobilized laccase/mediator system.In this study, 1m3 binderless fiberboard products and the manufacturing scope of laboratory was defined as a functional unit and system boundary of LCA, respectively. The production process was divided into four subsystems, and eight major manufacturing processes. Through the characteristic and the normalized processing, Gabi 6.0 LCA software was used to evaluate the environmental effect in each subsystem and production process of binderless fiberboard. Finally, the interpretation of LCA was put forward involving in four high environmental load manufacturing process of the synthesis of magnetic carrier, the synthesis of immobilized enzyme, the fiber drying and the hot pressing. Some corresponding energy saving measures in the future industrialization process has been put forward. For example, to optimize the immobilized enzyme synthesis process paremeters, to improve immobilized enzyme synthesis equipment, to regulate fiber drying technology, to recycle the heat enzrgy during the drying and hot pressing process, to preheat the slab and to select energy-saving equipment and so on.