人工降解饱水木材制备方法与光谱研究

Preparation and Spectra Study of Artificially Degraded Waterlogged Wood

考古出土/出水的饱水木质文物保存状态千差万别,内部降解不均匀、差异大,又有取样的限制,造成许多必需的材性定性定量分析和保护效果评价测试难以进行,因此亟需开发实验室可控制备的人工降解饱水木材技术,以获取大量重复性好、性质均匀的样品供研究使用。以健康黄松为原料,探索使用NaOH-真空浸渍-高压水热的联用法制备人工降解饱水木材,取得了初步的成功。制备的人工降解饱水木材的最大含水率(MWC)为260%,340%和575%,分别达到国际上普遍认定的低、中、高度降解饱水考古木材的MWC水平。红外光谱(FTIR)显示制备的人工降解饱水木材纤维素结构保存较为完好,氢键部分断裂;半纤维素显著降解,主链、侧链有断裂现象,1732 cm^(-1)特征峰消失;木质素有部分降解,1508 cm^(-1)处木质素芳香环骨架振动等吸收峰相对强度降低并发生偏移。近红外反射光谱(NIR)显示,制得的样品的三大素均发生降解,半纤维素降解程度最高,木质素次之,木质素相对含量升高,表现为C═O相对含量增加。在1536~1580 nm区域形成宽峰且峰强度降低,表明纤维素结晶区分子内部、分子间氢键结构均发生断裂。NaOH-真空浸渍-水热联用法与国际上现用的常压高浓度NaOH浸渍法相比,所需NaOH溶液浓度从50%以上降低到1%、处理时间从数月缩短至10 h,制备效率大大提升,所制得的饱水木材的最大含水率显著增大,与考古木材相近,细胞壁化学结构降解程度显著增大。NaOH-真空浸渍-水热联用法有望实现在实验室可控、快速、大量制备不同降解程度的人工降解饱水木材,对饱水木质文物保护水平的提高具有一定的促进意义。

The preservation states of excavated/salvaged waterlogged wooden artifacts vary greatly.The inhomogeneity of degradation and restricted acquirement of sampling make many necessary qualitative or quantitative analyses of wood properties and protection effect evaluation tests difficult to carry out.Therefore,it is urgent to develop a laboratory-controlled artificial degradation method to obtain sufficient waterlogged wood samples with good repeatability and uniform properties for preservation method research.This paper selected sound Pinus sp.wood to make artificially degraded waterlogged wood by NaOH-vacuum impregnation-hydrothermal combined method.The maximum water content(MWC)of the artificially degraded waterlogged wood was 260%,340%and 575%,respectively,corresponding with the widely recognized degradation states level of low,medium and high degraded waterlogged archaeological wood according to their MWCs.Fourier transform infrared spectroscopy(FTIR)results indicated that the cellulose structure of the wood was well preserved though the hydrogen bond partially broke.Hemicellulose was degraded significantly,the main chain,as well as side chain,were broken,and the characteristic peak at 1732 cm^(-1) disappeared;Lignin was partially degraded,and the relative intensity of the vibration absorption peak of aromatic lignin ring at 1508 cm^(-1) decreased and shifted.Near-infrared reflectance spectroscopy(NIR)showed that all the three major components in the samples were degraded.Hemicellulose was the most degraded,followed by lignin.The increase of relative content of lignin,reflected by the increase of relative content of C═O.A broad peak was formed in the 1536~1580 nm region with decreased peak intensity,indicating that the hydrogen bond structure within and between molecules in the cellulose crystallization region was broken.Compared with traditional methods,the concentration of NaOH solution using the combined method was reduced from more than 50%to 1%,and the treatment time was significantly shortened from several months to 10 hours,which proved that the degradation efficiency was greatly improved.The MWC and the degradation degree of the chemical structure of wood cell wall of artificially degraded waterlogged wood was many controller and higher than that of the existing methods.The state and performance of artificial waterlogged wood in this research were similar to archaeological wood.