Exploratory Analysis of the Distribution of Lignin and Cellulose in Woods by Raman Imaging and Chemometrics

The determinations of cellulose and lignin are important in wood analysis from both perspectives: chemistry composition, commercial and industrial application of woods. In this context, Raman image spectroscopy was applied in the determination of cellulose and lignin distribution in wood surfaces of Swietenia macrophylla King (Mahogany) and Eucalyptus hybrid (E. urophylla × E. camaldulensis). The relative concentration maps were obtained by applying a multivariate curve resolution procedure. The estimated Raman spectra for cellulose and lignin agrees with the ones available in the literature. The cellulose concentration maps showed similar variations for both studied species with an average value of nearly 85% as obtained by the reference method. The lignin concentration maps were somewhat different. The Eucalyptus hybrid presents a broader distribution (20 to 45%) while for Mahogany it is nearly constant, around 25%, with localized regions presenting contents of 45 to 65% of lignin. The reference method showed that the mean lignin content of both species is 27%. The cellulose and lignin concentration maps agree with the biological functions of the anatomic structures observed in the images.

纤维素与木质素的定量分析对于木材分析而言兼具重要意义，其价值体现在木材化学组成解析以及商业化、工业化应用两大维度。在此研究背景下，本研究采用拉曼成像光谱法（Raman image spectroscopy）对大果桃花心木（Swietenia macrophylla King，俗称桃花心木Mahogany）以及桉树杂交种（尾叶桉×细叶桉 E. urophylla × E. camaldulensis）木材表面的纤维素与木质素分布进行定量测定。通过多元曲线分辨算法（multivariate curve resolution procedure）获取了相对浓度分布图。所拟合得到的纤维素与木质素拉曼光谱，与现有文献报道的光谱结果保持一致。两种受试树种的纤维素浓度分布均呈现相似的变化趋势，其平均含量经参考方法测定约为85%。而木质素的浓度分布则存在一定差异：桉树杂交种的木质素分布范围更广（20%~45%）；桃花心木的木质素含量基本维持恒定，约为25%，仅存在局部区域的木质素含量可达45%~65%。参考方法测定结果显示，两种受试树种的平均木质素含量均为27%。纤维素与木质素的浓度分布结果，与成像观测到的木材解剖结构的生物学功能相契合。