Study On The Technology Parameters And Bonding Mechanism Of Board Made From Laccase-treated Bamboo Particle

Using the bamboo processing surplus and small diameter bamboo as raw material, the technology parameters and bonding mechanism of board made from laccase-treaeted bamboo particle was researched, which can provide the technical support and the theoretical basis for the production of binderless bamboo particleboard.By the orthogonal test and the single factor experimental, the laccase treatment condition and the thermo-compression technological parameter of boards made from laccase-treaeted bamboo particle was researched. Using ESR (electron spin resonance) detection technology, association with single factor analysis of variance, the category of free radicals produced by laccase activation of moso bamboo powder is analyzed. The effects of laccase treatment conditions of moso bamboo on the relative concentration of reactive oxygen species (ROS) free radicals are discussed. Bamboo flour treated with ROS free radicals produced by laccase activation was used to produce panels, and the resulting panels were assessed for internal bond strength (IB), modulus of rupture (MOR), and thickness swelling (TS). After comparison the chemical composition change of laccase-treated and control-treated bamboo power, by analysis the ROS free radical content of laccase-treated different age bamboo, combined with the recative of pure laccase enzyme and three principal constituent such as lignin, the cellulose, the hemicellulose, effects of bamboo chemical composition on the ROS free radical is studied. Setting the untreated bamboo powder, laccase treated bamboo powder and bamboo particleboard as the samples, by XRD, the cellulose crystallinity of raw material in the processing was researched, and by FTIR the functional group of raw material in the processing was discussed.The results shows that:(1) The best laccase treatment conditions are as follows: enzyme dosage of 30u/g bamboo powder, pH=4, 2 hours of incubation, 60℃of incubation temperature; and that for 0.70g.cm-3 of the bamboo particleboard density and 10mm of panel thickness, the best hot-pressing parameters are as follows: 4.0MPa of pressure, 200℃of temperature, 140℃of mat core temperature, 17.5min of hot pressing time. Under this condition the avereage IB of bamboo particleboard is 0.60Mpa and the maximum value even can reach 0.71Mpa.(2) Several factors are very significant for the relative concentration of ROS free radicals including dosage of laccase, pH value of the reaction system, time of incubation, incubation temperature and the concentration of Cu2+. The relative concentration of ROS free radicals is highest when the bamboo powder was treated under the following conditions: enzyme dosage of 30u/g, pH=4, incubation of 2 hours, incubation temperature of 60℃and the Cu2+ concentration of 30 mmol/L.(3) Board properties were highly correlated with concentration of ROS free radicals.The IB and the ROS free radical relative concentration assumes the logarithmic function relations, and its regression equation is: y=0.15ln(x)-0.38, correlation coefficient r=0.967; the MOR and the ROS free radical relative concentration assumes the logarithmic function relations, its regression equation is: y=2.60ln(x)-6.90, correlation coefficient r=0.935. The 2h TS and the ROS free radical relative concentration assumes the hyperbolic curve functional relations, its regression equation is: y=709.17/x +20.17, correlation coefficient r=0.955.(4) The laccase only when affects with the lignin produces the ROS free radicals, but in with cellulose, hemicellulose does not produce the ROS free radicals Confirmed through the ESR examination with free radical signal evidence, the laccase activation on bamboo is mainly a course of the laccase catalyzed oxidation of the lignin ingredient to produce the ROS free radicals.(5) Laccase treatment and the thermo-compression process enhance the cellulose crystallinity of bamboo powder. The cellulose and the hemicellulose may degrade to produce a series of carbonyl monosaccharide, the lignin degradation will form including carbonyl resolvent, the two kinds of material can affect with the hydroxyl functional group in the thermo-compression process, just like the phenol aldehyde polycondensation, which is advantageous for the bonding of the board made from laccase-treated bamboo particle.