Swift Appraisal Of Lignin Content In Poplar Timber And Probe Into Fabrication Of Fiberboard Via Acgivation Of Lignin By Laccase

Poplars(Populus spp.) with various traits including rapid growth, easy propagation, adaptability, stress resistance and wide use of wood are distributed in a wide range of geographical locations. The processing and utilization of poplar wood are closely associated with the plantation wood properties and lignin content. Fourier transform infrared spectroscopy has great potential and prospects as a non-destructive evaluation and forecasting technique. The evaluation of the physical and chemical properties of wood by means of infrared spectroscopy has lured attention from researchers around the world. Rapid prediction of poplar lignin content by Infrared Spectroscopy is not only a crucial chain in the development of technology for the green enzyme-bonded wood composites, but also essential screening analysis in the cultivation of timber tree species in bio-energy and paper-making. The pollution of volatile organic compounds including free formaldehyde has been paid more attention, environment-friendly wood-based panels has become a worldwide problem, therefore there is the urgent need to reduce environmental load and the development of renewable resources, preparation of new technology wood-based panels. The site conditions, genetic characteristics, growth climatic conditions, forest management methods and other factors of wood species have different effects on the physical and chemical properties of wood, in order to achieve high efficiency and optimal use of materials it is required to use Fourier transform infrared-attenuated total reflection spectroscopy combined with multivariate data analysis method to build the prediction model calibration for the overall chemical nature of wood by making fast and accurate forecasts, and thus fully understand the nature of wood. This work is of great significance to address free formaldehyde pollution from wood-based panels and improve the living conditions of people's lives, protect the natural environment of human life.In this thesis, Fourier Transform Infrared Spectroscopy with Multivariate Data Analysis algorithm makes fast prediction of poplar lignin content. Optimized calibration model is used to establish factors affecting the qualitative evaluation of wood properties through infrared spectroscopy. The establishment of poplar tree-laccase direct detection of intermediate fibers and quantitative analysis is fulfilled through electron spin resonance spectroscopy to study the catalytic oxidation of laccase and role of free radicals, to explore the manufacture of fiberboards made of laccase catalyzed oxidation of wood fibers, which eliminates the use of synthetic resin and excludes the source of formaldehyde contamination.The main findings of this paper are as follows:1. The lignin content of Extractive-free wood samples from hybrid poplar (P. trichocarpa×deltoides) ranges from 23.45% to 32.07%(w/w), showing a normal distribution with a mean value of 27.02%. Modifications to the traditional wet chemical analysis - acetyl bromide lignin assay consist of:The weighing range during the period of weighing wood powder sample strictly centered on 0.99 and 1.01 mg, and wood flour together with polypropylene weighing paper was transferred into micro-tube. Prior to the addition of acetyl bromide/acetic acid mixture, the micro-tubes filled with wood flour was placed into the icy water bath, and acetyl bromide/acetic acid mixture was stored at room temperature before use. Within 10 min immediately after the final dilution by acetic acid, the UV absorbance measurement was supposed to complete. By means of the modified acetyl bromide lignin analysis the standard deviation for the current batch of samples was 0.18%, and combined standard deviation was as low as 0.042%, which proves suitable for analysis of lignin content of samples used for secondary calibration. As for preparation flour of for Fourier transform infrared-ATR spectra, we recommend the following steps:finely ground flour as possible, preferably less than 20 microns particle size; to avoid overheating in the course of grinding, milling under liquid nitrogen environment if possible. Wood flour should be placed for at least 3 days in the laboratory for infrared spectrometer before recording IR spectrum for the purpose of equilibrating moisture content in the wood powder.2. The intra-specific natural variability of chemical composition in extractive-free wood samples of hybrid poplar (P. trichocarpa×deltoides) is sufficient for building lignin content prediction model. Fourier transform infrared spectroscopy combined with partial least squares regression modelling technique yielded optimized calibration model which went through external validation. The resultant optimized calibration model was of high quality, with high coefficients of determination (R2 (calibration)=0.906 and R2 (cross-validation)=0.806) and low root mean square error of cross validation (RMSECV=0.77%) respectively. Verification of the best model through independent data sets of wood samples resulted in R2=0.88. These results showed that FTIR-ATR spectroscopy is suitable as a high-throughput method for poplar lignin estimations in large-scale breeding or genetic engineering projects. Poplar lignin content and energy content within the species variability is unrelated. By means of principal component analysis to identify the key wavenumbers influencing the above-mentioned two traits,14 most divergent wavenumbers in the first four factor loading spectra of lignin containing 32 maximum difference in wavenumbers mainly attributes to aromatic compounds, whereas only 7 most divergent wavenumbers in the first four factor loading spectra of the energy content attributes to aromatic compounds, and is generally hydrocarbon ring vibration.3. The lignin content in genetically modified non-Isoprene releasing grey poplar (Populus×canescens) and wild-type poplar cultivated in Gottingen wood ranges from 24.06% to 26.59%, and a-cellulose content from 42.95% to 47.73%. The dendrogram obtained from Cluster analysis showed that the lignin content, cellulose content, soluble extractive content between genetically modified non-Isoprene releasing grey poplar wood and wild-type poplar wood displayed no significant difference. The semi-quantitative analysis of the fingerprint region of IR spectra collected from poplar wood four showed that absorption peak height ratio of the characteristic absorption peak of cellulose and hemicelluloses to lignin ranges from 2.18 to 2.23, whereas the corresponding ratio for wild-type poplar wood was 2.16; therefore the major chemical components including lignin and cellulose in the two categories of wood showed no significant difference. The determination of the traditional wet chemical methods with soluble extractives (0.96 to 1.83%), holocellulose (70.17% to 74.47%), a-cellulose, lignin content, and energy content (17690 J/g to 18280 J/g) verified the results of cluster analysis. The projection of three-dimensional data of genetically modified grey poplar wood, wild-type poplar wood and hybrid poplar (P. trichocarpa×deltoides) wood as a result of principal component analysis showed that there was slightly better degree of differentiation between genetically modified grey poplar wood and wild-type poplar wood, which corroborated the results of wet chemistry analysis:The soluble extractives content with an average of 1.11% of one progeny in genetically modified grey poplar wood was significantly lower than that of wild-type poplar grown in Gottingen (mean 1.50%). Through tentative assignment of the characteristic functional groups in the highest seven peaks of the factor loading spectra, it was found that 12 out of 21 most divergent absorption bands corresponds to ring vibration with hydrocarbon origin, but also contains a small number of lignin functional groups with only 7 significantly different wavenumbers.4. In reference to MDF dry process hot-press curve, slab core temperature was measured by thermocouples to determine the dry process technology of laccase-bonded fiberboard. The specific parameters of hot pressing are:pressing temperature 190℃, the maximum pressure to maintain the pressure at 5 MPa, time 1.5 min; low pressure plastics section 3.5 MPa, time of 3 min. The enzyme binding strength within the fiberboard was significantly higher than the control board in the same process conditions, control the internal bond strength of fiberboard 0.19 MPa, enzyme dosage of 5.58 U/g oven-dry wood fiber laccase the internal bond strength of fiberboard 0.53 MPa. Fiber density is less than 0.9 g/cm3, the enzyme is very low internal bond strength cf fiberboard, is only 0.17 MPa, fiber density reached a certain level to get a higher bond strength within the enzymatic fiberboard. Copper ions can significantly improve the internal bond strength fiber enzymatic, within the control enzyme binding strength of fiberboard 0.38 MPa, adding copper ions within the enzyme binding strength of fiberboard increased to 0.59 MPa.5. To investigate the radical reaction intermediates during the laccase-catalyzed oxidation of poplar wood fibers, electron spin resonance spin trapping technique using N-tert-butyl-a-phenylnitrone as a spin trap followed by ethyl acetate extraction were empioyed to identify and quantify the reaction intermediates. The electron spin resonance spectrum of free radicals trapped by N-tert-butyl-a-phenylnitrone had a triplet at g value=2.005 and an= 15.0 G, showing reactive oxygen species is the major products of laccase oxidation of wood fibers. The Fenton system produced a standard curve for hydroxyl radical with a determination coefficient of 0.9799. Using reactive oxygen species standard curve, the reactive oxygen species detected via N-tert-butyl-a-phenylnitrone spin trap method was quantified as 3.74±0.05×1018 spins/g wood fiber dry substances. Based on the findings of the presence of reactive oxygen species during the activation of wood fiber with laccase and previous studies on related free radical reactions, we propose the possible reaction mechanism for laccase oxidation of wood fibers:the laccase-mediated reaction cannot directly reach the majority of the lignin domain, the low molecular weight soluble lignin may function as reactive compounds like adhesives, clinging back to the fiber surface.