The Effect Of Treatment With Laccase On Wood Composites Properties And Their Bonding Mechanism

In order to eliminate the pollution problem of formaldehyde, to developa new way for producing the wood composites without dissociative formaldehyde using laccase-treatment. Fibers of Liquidambar formasana, sapwood and heartwood of Pinus khasya var. langbianensis, veneers of Poplus tomentosa, laccases, lignin and salts of lignosulphonate were selected as materials, fiberboards were manufactured by laccase-treated on density, thickness expansion rate of water absorbing and internal bonding strength (IB) of fiberboard were measured; Plywood were manufactured using adhesive made by lignin and salts of lignosulphonate with laccase-treated, the effect of parameters of laccase-treated on the shearing strength of plywood was studied. The changes and stability of reactive oxygen species (ROS) and their bonding mechanisms of laccase-treated wood fibers, lignin and salts of lignosulphonate respectively were determined by ESR.The results shows that :1) The correlation between the conditions of laccase-treated to three kinds of wood and the physio-mechanics properties of fiberboard was analyzed. Result shows that the optimum parameters of laccase-treated wood fibers were at pH3.0, times 2h, temperature 50 ℃, laccase dosages 20u/g during the process of fiberboard manufacture. Under the hot-press parameters including temperature 200 ℃, press 5-7MPa and time 15 minutes, the IB of fiberboard at 0.88g/cm~3 density which was made of Liquidambar formasana wood is higher than that of Pinus khasya var. langbianensis, it reaches 1.26MPa.2) The correlation between the parameters of laccase-treated lignin and salts of lignosulphonate and the shearing strength of plywood was analyzed. Result shows that the optimum parameters of laccase-treated lignin and salts of lignosulphonate were different respectively. Ammonium lignin sulphonate was treated by laccase which be used as adhesive for plywood manufacture at pH5.5, time 60 minutes, temperature 25℃, the shearing strength of plywood of Poplus tomentosa wood reaches 0.76MPa under the hot-press parameters at temperature 150℃, time 30 minutes, press 4.5-5.0MPa.3) The changes and stability of ROS of three kinds of laccase-treated wood, the correlation between the change of ROS concentration and IB of fiberboard were measured and discussed. The optimum parameters of laccase-treated wood fibers were pH3.0, temperature 50 °C, time 2h and laccase dosages 20u/g, ROS concentration was highest in this condition; ROS concentration decreased slowly in 48h, then declined rapidly after 48h and disappeared in 7 days later. The correlation between ROS concentration and IB of fiberboard was in positive.