古建木构件化学组分近红外光谱分析

在材种鉴定的基础上,通过近红外光谱(NIRS)定性分析了建成约600 a的木造古建筑木构件的化学组分,结合木构件化学组分定量分析,与现代木材相比较,探讨了近红外光谱技术评价木构件老化的可行性。结果表明:近红外二阶导数特征性谱带反映了木材纤维素以及半纤维素和木质素的基团信息,而其差谱反映出木构件与对照样化学组分变化。这些光谱特征与传统的化学组分定量分析的结果非常一致:纤维素和半纤维素相对含量减少而木质素相对含量增加,与各种组分谱带差谱的增减相对应。此外,在5 882,5 587和5 464 cm-1等谱带处反映的纤维素结晶和半结晶区的光谱信息,差谱观察到木构件与现代材落叶松之间化学组分的不变或减少,其结果与X射线衍射(XRD)方法获得的木材结晶度分析结果相一致。通过NIRS定性分析木构件化学组分及结晶度变化,接近于现场检测方法,使用便携式NIRS,在古建筑木构件端头裸露部位获取光谱信息,能够实现现场对木材化学组分的无损定性评价。本实验结果也表明,除了常规的红外光谱(FT-IR)、XRD分析技术,NIRS技术对于木构件老化状况的评价是一种有潜力的无损检测方法。     

Use of near infrared spectroscopy to measure the chemical and mechanical properties of solid wood

Near infrared (NIR) spectroscopy (500 nm–2400 nm), coupled with multivariate analytic (MVA) statistical techniques, have been used to predict the chemical and mechanical properties of solid loblolly pine wood. The samples were selected from different radial locations and heights of three loblolly pine trees grown in Arkansas. The chemical composition and mechanical properties were measured with traditional wet chemical techniques and three point bending tests, respectively. The microfibril angle was measured with x-ray scattering. These chemical and mechanical properties were correlated with the NIR spectra using projection to latent structures (PLS) models. The correlations were very strong, with the correlation coefficients generally above 0.80. The mechanical properties could also be predicted using a reduced spectral range (650 nm–1150 nm) that should allow for field measurements of these properties using handheld NIR spectrometers.     

Prediction of mechanical properties of Chinese fir wood by near infrared spectroscopy

Mechanical properties and the visible and near infrared (NIR) (350–2500 nm) spectra obtained from longitudinal and transverse face of 155 small clear wood samples of Chinese fir (Cunninghamia lanceolata) were measured, and 103 of them were used to establish calibration models. Calibrations were tested on an independent set (52 samples). Differences between calibrations developed by using the longitudinal and transverse face were small. The calibrations developed by using NIR spectra (350–2500 nm) collected from transverse face were slightly inferior to those developed by using NIR spectra collected from longitudinal face. When reducing the spectral range to between 780 and 1050 nm, the calibrations developed by using NIR spectra collected from longitudinal face were slightly inferior to those developed by using NIR spectra collected from transverse face, and reducing the spectral range causes no decrease in the quality of the models developed using NIR spectra collected from transverse face. Partial lease square (PLS) modeling and test showed that calibrations developed using the visible and NIR spectra from transverse and longitudinal faces and calibrations developed by using the reducing spectral range (780–1050 nm) from the transverse face were moderate, and have a RPD range from 1.51 to 1.90. It is concluded that NIR spectroscopy can be used as an initial screening. __________ Translated from Journal of Northwest Forestry University, 2007, 22(5): 149–154 [译自: 西北林学院学报]     

基于近红外光谱技术的热处理竹材物理力学性能

探讨了近红外光谱(NIRs)技术对实现热处理毛竹分选和性能在线检测的可能性。采集了3种不同温度(150,180和210℃)热处理及未处理毛竹的径切面近红外光谱信息,应用主成分分析方法与偏最小二乘法对竹材进行分类,并建立了热处理竹材的材色、密度以及力学性能预测模型。结果表明:1)近红外光谱二阶导数谱图在7 004和6 452 cm-1等吸收带处很好地反映了竹材热处理对应化学成分的变化,表明了近红外光谱变化与化学成分变化的一致性,也说明了NIRs用于快速分析热处理竹材材性的可能性; 2)热处理竹材在主成分得分图中呈明显的聚类分布特征,说明了NIRs技术对于热处理竹材良好的分类能力; 3)材色预测模型的模型参数R2≥0.93、RPD均大于3.90,表现出了非常好的材色预测性能。气干密度、绝干密度以及抗弯强度预测模型的R2分别为0.83,0.85和0.82,RPD分别为2.42,2.59和2.34,能够满足竹材性能的评估精度要求。     

Rapid assessment of wood chemical properties and pulp yield of Eucalyptus camaldulensis in Thailand tree plantations by near infrared spectroscopy for improving wood selection for high quality pulp

Near-infrared (NIR) spectroscopy has been demonstrated as a means for rapid nondestructive determination of the chemical composition and final pulp yield of Eucalyptus camaldulensis in Thailand tree plantations. Multiple linear regression (MLR) analysis and partial least squares (PLS) analysis were introduced to develop statistical models in terms of calibration equations for total pulp yield, screened pulp yield, and contents of -cellulose, pentosans, and lignin in wood. In MLR analysis, a reasonably good calibration equation was found only for pentosans (standard error of prediction (SEP): 0.98%). The PLS analysis improved the accuracy of prediction for every criterion variable, especially for pentosans (SEP: 0.91%) and lignin (SEP: 0.52%). Also, in the case of screened pulp yield, we were able to use such a statistical result as an indicator of the characteristics of the pulp and paper. Thus, NIR spectroscopy could be satisfactorily used as an effective assessment technique for Eucalyptus camaldulensis plantation trees.     

Rapid assessment of physical properties and chemical composition of thermally modified wood by mid-infrared spectroscopy

Characterisation, quality assessment and property prediction are several of the major industrial challenges for widespread acceptance of thermally modified wood (TMW). This study shows the potential of the multivariate analysis of mid-infrared (MIR) spectral data for the prediction of impact strength, five mechanical parameters in bending, moisture content, weight loss, density and chemical composition of small specimens of thermally modified beech, Norway spruce and Scots pine woods. Anti-swelling efficiency was also studied using DRIFT spectroscopy for spruce wood only. Calibrations were successfully accomplished by partial least-squares regression, with R _Y ² and Q _CUM² values >0.96 for 64 out of 67 models. Predictions were also successful, with relative prediction values >0 and RMSEP:SD ratios <1 in most cases. Changes in the MIR spectra of TMW show that bands arising from the lignin environment and new bands appearing due to the degradation of carbohydrates, giving negative loadings, were related to strength loss, while those bands arising from the polysaccharides were associated with property retention. It is concluded that this approach is a powerful tool to characterise a number of properties of TMW with a single after-treatment measurement.     

Kernel regression methods for the prediction of wood properties of Pinus taeda using near infrared spectroscopy

Near infrared diffuse reflectance spectra collected in 10-mm sections were used for the estimation of air-dry density (AD), microfibril angle (MFA), stiffness (MOE), tracheid coarseness (COARS), and tracheid wall thickness (WTHICK) in wood radial strip samples obtained at breast height (1.4 m) from 60 Pinus taeda trees. Calibration models were developed using traditional partial least squares (PLS) and kernel regression. The kernel methods included radial basis functions-partial least squares (RBF-PLS) and least-squares support vector machines (LS-SVM). RBF-PLS and LS-SVM models outperformed PLS-CV calibrations in terms of fit statistics. MFA and MOE, two properties that exhibited nonlinearity, showed the most significant improvements compared to PLS. In terms of predictive ability RBF-PLS performed better than PLS for the prediction of MFA, MOE, and COARS. LS-SVM showed better prediction statistics in all cases, except for WTHICK that gave similar statistics compared to PLS and was superior to RBF-PLS. By adding statistically significant factors to the PLS regressions, it was possible to capture some of the nonlinear features of the data and improve the predictive ability of the PLS models.     

桦木顺纹抗压强度的SEPA-VISSA-RVM近红外光谱预测

木材顺纹抗压强度是评价木材力学性能的重要指标,而传统测量方法操作复杂、精确度低。以桦木为例,提出基于近红外光谱技术(NIR)的SEPA-VISSA-RVM木材顺纹抗压强度模型,实现对其更加精确的预测。试验选取100个木材试件,在900~1700 nm近红外光谱波段上采集数据并测量抗压强度真值;然后采用卷积平滑(SG)方法进行光谱预处理;使用采样误差分布分析(SEPA)作为变量空间迭代收缩算法(VISSA)的改进策略进行特征波长优选;最后通过粒子群优化算法(PSO)优化核函数参数并建立相关向量机(RVM)的预测模型。试验表明:在特征波长优选方面,以偏最小二乘法(PLS)建模为基础的SEPA-VISSA方法,其预测决定系数为0.9593,预测均方根误差为2.8995,相对分析误差为3.0256,光谱变量数由512减小到111个,占总波长的22%,均优于VCPA、CARS和VISSA算法;在建模预测方面,以SEPA-VISSA所选波长为基础的RVM模型,PSO优化的拉普拉斯(Laplacian)核函数的核宽度为10.4043,决定系数为0.9449,预测均方根误差为2.0432,相对分析误差为4.2936,预测效果优于PLS和SVR。因此,基于近红外光谱的SEPA-VISSA-RVM建模能够实现对桦木顺纹抗压强度更准确和稳定的无损检测。     

Rapid estimation of kraft pulp yield and lignin in Eucalyptus camaldulensis and Leucaena leucocephala by diffuse reflectance near-infrared spectroscopy (NIRS)

Near-infrared spectroscopy has been used to develop calibration models for the rapid determination of kraft pulp yield (KPY) and lignin in Eucalyptus camaldulensis and Leucaena leucocephala. The correlation coefficient for cross-validation is 0.90 for KPY and 0.95 for lignin prediction, while the root mean square error for cross-validation for KPY and lignin prediction are 1.46 and 0.77, respectively. The method has been validated with 37 samples of E. camaldulensis and 18 samples of L. leucocephala. The root mean square error of prediction for KPY (1.53) is higher than for lignin (0.77). The method is rapid and can be used for screening a large number of samples.     

Analysis of chemical structure of wood charcoal by X-ray photoelectron spectroscopy

Wood charcoal carbonized at various temperatures was analyzed by X-ray photoelectron spectroscopy (XPS), Fourier-transform infrared spectroscopy (FTIR), and X-ray diffractometry to investigate the changes of chemical structures during the carbonization process. From the infrared spectra, the carbon double bonds and aromatic rings were seen to form at a carbonization temperature of about 600°C. From the XPS spectra, the ratio of aromatic carbons increased in the temperature range 800–1000°C and over 1800°C. The condensation of aromatic rings proceeded as carbonization progressed. The drastic reduction of electrical resistivity of charcoals was observed in almost the same temperature range. It was found that the condensation of aromatic rings had some relation to the decline in electrical resistivity. Wood charcoal carbonized at 1800°C was partly graphitized, a finding supported by the results of X-ray diffraction and XPS. The functional groups containing oxygen diminished with the increase in carbonization temperature.This paper was presented at the 45th Annual Meeting of the Japan Wood Research Society in Tokyo, April 1995 and at the 47th Annual Meeting of the Japan Wood Research Society in Kochi, April 1997     

Comparative analysis of modern and ancient buried Phoebe zhennan wood: surface color,chemical components,infrared spectroscopy,and essential oil composition

We compared the chemical components and essential oils of ancient buried Zhennan(Phoebe zhennan)wood with those in samples from living trees.After removal of the carbon layer the recovered Zhennan exhibited a dark green color,which differed from the yellow color of the living samples.Low molecular weight components(including hot-water and toluene-alcohol extractives),hemicellulose,and 1 % Na OH solubility in the recovered wood were greatly degraded.Degradation of cellulose was minor.Moreover,the ancient wood had somewhat more klason lignin than the modern wood.Fourier transform infrared(FTIR) analysis gave further evidence on the differences in chemical components.According to the GC–MS results,naphthalene derivatives were detected in the essential oils from both the modern and recovered wood.The delicate fragrance of the modern and recovered wood may be attributed to the aromatic constituents as identified by GC–MS.     

Nondestructive evaluation of drying stress level on wood surface using near-infrared spectroscopy

A nondestructive technique for swiftly measuring the stress level of the surface of wood is proposed, which is important for process control in timber drying. Partial least squares (PLS) regression models for predicting surface-released strain (ε) were developed using NIR spectra obtained from Sugi (Cryptomeria japonica D. Don) samples during drying. The predictive ability of the models was evaluated by PLS analysis and by comparing NIR-predicted ε with laboratory-measured values. The PLS regression model using the NIR spectra pre-processed by MSC and second derivatives with a wavelength range of 2,000–2,220 nm showed good agreement with the measurement (R ² = 0.72). PLS analysis identified the wavelengths around 2,035 nm as making significant contributions to the prediction of ε. Orthogonal signal correction (OSC) was an effective pre-processing technique to reduce the number of factors required for the model using the wavelength range 1,300–2,500 nm. However, the predictive ability of the OSC-corrected model was not improved. Elapsed times to reach the maximum tensile stress (T _max) and the stress reversal point (T _rev) at the wood surface during drying were detected correctly for 75 % of the samples. The results show that NIR spectroscopy has potential to predict the drying stress level of the timber surface and to detect critical periods in drying, such as T _max and T _rev.     

Comparison of <Emphasis Type="Italic">Pinus taeda</Emphasis> L. whole-tree wood property calibrations using diffuse reflectance near infrared spectra obtained using a variety of sampling options

A necessary objective for tree-breeding programs, with a focus on wood quality, is the measurement of wood properties on a whole-tree basis, however, the time and cost involved limits the numbers of trees sampled. Near infrared (NIR) spectroscopy provides an alternative and recently, it has been demonstrated that calibrations based on milled increment cores and whole-tree data can provide good estimates of whole-tree properties. Several options exist for sampling standing trees and the aim of this study was to compare wood property calibrations based on NIR spectra collected from samples obtained using different sampling methods. Calibrations for whole-tree lignin and basic specific gravity based on NIR spectra from whole-tree chips (milled or intact) had the strongest statistics, calibrations based on NIR spectra from milled increment cores were similar. Other options for sampling the tree (drill shavings, etc.) gave errors that were too large for practical applications. If an increment core is going to be used to estimate whole-tree properties, it is recommended that it be dried and milled prior to analysis.     

Depth profiling of weathered tropical wood using Fourier transform infrared photoacoustic spectroscopy

Depth profiling analysis of wood samples using Fourier transform infrared photoacoustic spectroscopy (FTIR-PAS) was carried out to obtain information on the chemical changes caused by weathering. The test samples used for PAS measurements were tropical wood species, puspa (Schima wallichii Korth) and kapur (Dryobalanop lanceolata Burck), that were exposed outdoors for periods of 2–32 weeks. FTIR-PAS spectra of the weathered surfaces were recorded at various moving-mirror velocities in the range from 0.081 to 0.56cm/s (linear-scan method) to provide the depth profiling analysis. The band intensity of vibrations attributed to phenyl groups clearly decreased as weathering proceeded and demonstrated a tendency to be reduced with a decrease in the photoacoustic probing depth during relatively short weathering periods. The bands of C=O groups also exhibited remarkable spectral changes. The PAS spectra of the tropical wood changed considerably during the 32 weeks of weathering, and their spectral contours gradually approached that of pure cellulose (microcrystalline). It was noted that FTIR-PAS is very useful for depth profiling analysis of the wood surface in the early stages of deterioration.     

红外光谱技术在我国木材科学领域的应用研究进展

红外光谱法是分析化合物结构与化学组成的重要手段,该文综述了中红外与近红外光谱技术在木材物理与化学性质测试、木材种属分类与鉴定、木材加工领域、林木病虫害预测等木材科学相关方向的国内最新研究进展。今后应在推广红外光谱技术实践应用、方法标准提升、多技术联用等方面开展深入研究。     

杨木应拉木微区结构可视化及化学成分分析

木材微区结构与木材宏观性质密切相关,杨木应拉木与对应木宏观性质存在较大差别,探究杨木应拉木和对应木微区结构和化学成分,可为了解杨木应力木的宏观性质提供理论根据。借助光学显微镜、荧光显微镜、显微拉曼成像光谱仪、透射电镜对杨木应拉木微区结构进行可视化研究,并借助X射线衍射技术和美国可再生能源实验室方法,分析杨木应拉木的微晶尺寸、结晶度以及化学成分。结果表明:杨木应拉木中应拉区和对应区纤维细胞微区结构差异显著。光学显微镜下显示应拉区木纤维中胶质层清晰可见,荧光显微镜和拉曼显微镜下显示胶质层的木质素浓度比对应区低。透射电镜下显示应拉区木纤维细胞壁结构由初生壁、次生壁和胶质层组成,未见次生壁外层,各层的平均厚度分别为0.61,1.22和2.53μm。对应区木纤维为典型的初生壁和次生壁结构,次生壁各层平均厚度分别为0.33,2.28和0.14μm。杨木应拉区纤维素含量(58.91%)比对应区(41.53%)高,木质素含量和半纤维素含量均比对应区的低,应拉区木质素和半纤维素含量分别为21.99%和12.01%,对应区分别为28.10%和17.08%。杨木应拉区结晶度(48.06%)比对应区(41.01%)高,应拉区晶区宽度为2.66 nm,长度为8.84 nm;对应区晶区宽度为2.65 nm,长度为9.87 nm。     

Surface quality sensing of trembling aspen (Populus tremuloides Michx.) veneer products by near infrared spectroscopy

Abstract

The potential of near infrared spectroscopy (NIRS) to estimate wood moisture content (MC), surface energy characteristics and adhesive bond strength were evaluated on aspen (Populus tremuloides Michx.) veneer subjected to different drying times. For samples dried progressively at 103°C, the best MC prediction model was for the total MC range (0–100%) with an R² value of 0.68. However, exposure at 180°C produced surface colour changes, and the CIE L*a*b* colour parameters measuring colour changes were better estimated using the 400–900 nm spectral data than the 1100–2400 nm spectral data. Increased exposure time at 180°C resulted in lower wettability and, hence, larger contact angles, especially when ethylene glycol was used as probe solvent. Lap shear strength tests on veneers showed that adhesion by phenol formaldehyde resins was impaired by the high temperature exposure; however, the lap shear strength test had high variability so there was not always a clear relationship between contact angle and lap shear strength test.     

Predicting oven-dry density of Sugi (Cryptomeria japonica) using near infrared (NIR) spectroscopy and its effect on performance of wood moisture meter

We propose a non-destructive method to predict the oven-dry density of Sugi (Cryptomeria japonica D. Don) using near infrared (NIR) spectroscopy so as to calibrate a commercial moisture meter. A prediction model for oven-dry density was developed using NIR spectra obtained from Sugi samples with a known density. The density of air-dried Sugi boards was predicted with the developed model. Then, the moisture content (MC) of the boards was measured by a hand-held capacitance-type and an in-line microwave moisture meters. For each board, the moisture meters were calibrated by the predicted density. The predicted density was correlated with the measured one with an R ² of 0.81 and a standard error of prediction (SEP) of 15.3 kg/m³ within the measured density of 279.2–436.4 kg/m³, indicating that the developed model was applicable for predicting oven-dry density of Sugi. The MC readings of both moisture meters showed a good correlation with the oven-dry MC that ranged from 12.1 to 28.9 %. For both moisture meters, the density calibration with the NIR-predicted density gave a higher R ² and a lower SEP than with the conventional calibration with the mean density. These results demonstrate that the present density calibration using NIR spectroscopy could improve the performance of the moisture meters for the air-dried Sugi boards with varying densities.     

Rapid and non-destructive evaluation of seed quality of Chinese fir by near infrared spectroscopy and multivariate discriminant analysis

New Forests - Chinese fir (Cunninghamia lanceolata (Lamb) Hook) is a promising timber species for planting in the sub-tropical ecosystem. However, the germination rate of Chinese fir seed lots is...