徐州出土汉代棺木用材树种鉴定及其化学性质

Species identification and chemical analysis of coffin wood in the Han Dynasty excavated in Xuzhou

木材是人类日常生活的常见材料,也是从古至今人类文明与民族文化的重要载体。伴随着考古发掘工作的进行,来自不同地区、不同朝代的大量木质文物出土并需要持续保护,因此掌握出土木质文物所用的木材树种情况,并研究其化学组分的降解状态,可为制定合理的木质文物修复和保护方案提供科学依据。通过对徐州万达汉墓墓群中1号与4号墓出土棺木进行取样和对标准三切面的切片进行观察,根据三切面显微构造特征对棺木所用木材树种进行鉴定,经与标准切片比对,结果表明M1c、M1oc、M4c、M4oc棺木树种分别为楠木(Phoebe sp.)、硬木松(Pinus sp.)、梓木(Catalpa sp.)、榉木(Zelkova sp.)。进一步采用荧光显微镜与傅里叶变换红外光谱、X射线衍射相结合的方法,分析棺木的主要化学组分降解情况。结果表明:与现代健康材相比,古木在长期埋藏过程中,木材的主要多糖类化学组分纤维素和半纤维素降解严重,纤维素结晶度降低;古木各类型细胞中木质素的自发荧光效应均减弱,且红外光谱分析表明木质素化学结构发生改变;古木在埋藏过程中木材的整体构造保存较好,但主要化学组分发生了降解,这与其地下饱水低氧的埋藏环境有很大关系。

Wood is the commonly used material in human life. Together with the archaeological excavation work, a huge amount of wooden products have been unearthed and need to be protected in different regions and different dynasties depending on the excavation sites. It is important to identify the wood species of the archaeological wooden products and accurately analyze the degradation of the chemical components in the archaeological wooden artifacts. The identification results and chemical data could provide a scientific foundation to formulate a reasonable plan for the restoration and protection of archaeological wooden artifacts. The four coffin samples from tombs numbered No.1 and No.4 in the Wanda tombs of the Han Dynasty were selected during excavations in Xuzhou, Jiangsu Province. The wood samples collected from coffin were sliced to obtain three standard direction sections, which were the transverse direction, radial direction and tangential direction. The microscopic structural characteristics of the three directions from different samples were compared with the standard sections carefully. The results indicated that the wood species of M1c, M1oc, M4c and M4oc coffin were phoebe ( Phoebe sp.), hard pine ( Pinus sp.), catalpa ( Catalpa sp.) and zelkova( Zelkova sp.), respectively. The fluorescence light microscopy (FLM), Fourier transform infrared spectroscopy (FT-IR) and X-ray diffraction (XRD) were used to analyze the degradation of the chemical components (mainly cellulose, hemicellulose and lignin)in the coffin wood from anatomical and chemical aspects. The results indicated that the crystallinity of cellulose decreased and the polysaccharide (cellulose and hemicellulose) in the archaeological wood degraded seriously during the long-term burial, compared with the sound wood. The auto-fluorescence effect of lignin in all types of the archaeological wood cell walls was weakened, especially for the hard pine. The chemical structure of lignin was altered according to the FT-IR analysis results, being revealed by that the absorbance peak at 1245 cm^-1 for sound wood changed into two absorbance peaks at 1268 and 1225 cm^-1 for the archeological wood samples. However, comparing the four species, phoebe kept its anatomical structure and chemical components with better condition than others. The overall morphological structures of the archaeological wood were still intact, but the chemical degradation occurred to the main components in burial condition owing to their close connections to water-saturated and hypoxic burial soil environment.