摘要
为探究沉船考古木材内外部位的降解特征,选择“小白礁Ⅰ号”沉船遗址出水的一件饱水考古木材样品,通过分区取样获得其剖面“外层”与“内核”部位的样品。经鉴定样品为龙脑香属(Dipterocarpus sp.)木材,并进一步采用光学显微镜(OM)、扫描电子显微镜(SEM)、衰减全反射傅里叶变换红外(ATR-FTIR)和动态水蒸气吸附(DVS)等方法综合分析考古木材内外部位的降解差异。结果表明,外层木材最大含水率(MWC)高达687%,内核木材MWC为246%。外层木材所有类型细胞均降解,而内核木材部分木纤维细胞保存完好,呈现被侵蚀细菌降解的模式。SEM形貌分析显示外层木材细胞壁具多孔“海绵”结构。FTIR确定了外层木材细胞壁残余化学组分主要为木质素,而内核木材保留了部分纤维素,结合主成分分析(PCA)表明纤维素是判别外层与内核木材降解差异的特征化学组分,层次聚类分析(HCA)判定样品剖面存在降解过渡区。DVS分析发现外层木材吸湿平衡含水率高于内核木材,借助H-H模型拟合吸附等温曲线,进一步揭示外层与内核木材的水分吸附性能差异与细胞壁化学组分及孔隙结构有关。综合分析方法阐释了“小白礁Ⅰ号”沉船饱水考古木材非均一性降解特征,实现了木材内外部位保存状况的准确判定,为饱水木质文物的保护及利用积累了科学基础数据。
Ancient wooden shipwrecks excavated from the marine environment are a significant part of cultural heritage.Investigating the degradation characteristics of waterlogged archaeological wood from shipwreck remains is not only crucial to study the mechanisms of wood decay in buried underwater environments,but also essential for the development of conservation techniques tailored to waterlogged wooden cultural relics.The degradation of waterlogged archaeological wood exhibits variability.This study focused on the waterlogged Dipterocarpus sp.wood remains from the archaeological excavation of the XiaobaijiaoⅠ,an ancient Chinese shipwreck.Internal and external sampling was conducted to explore the degradation characteristics.In this study,comprehensive characterization methodologies,including physical parameters analysis,optical microscopy(OM),polarized light microscopy(PLM),scanning electron microscopy(SEM),attenuated total reflectance-Fourier transform infrared spectrometry(ATR-FTIR),and dynamic vapor sorption(DVS)were employed to characterize the degradation differences between the internal and external parts of waterlogged archaeological wood.The results indicate that there was significant degradation difference between the internal and external parts of waterlogged archaeological wood,with the degraded areas clearly divided into the“outer layer”and“inner core”.The maximum water content(MWC)of the outer layer wood reached 687%,while the MWC of the inner core wood was 246%.The outer layer of wood was severely degraded,with the majority of the cells heavily decayed,and the birefringence of cellulose crystals having disappeared;furthermore,the secondary wall of the wood fibers exhibited a porous“spongy”structure,while only the middle lamella remained intact.The inner core wood was moderately degraded,with intact wood fiber cells coexisting with decayed cells,presenting the decay pattern of erosion bacteria.The FTIR results revealed that the residual chemical components in the cell walls of the outer layer of wood primarily consisted of lignin,while the inner core wood retained partial cellulose.The combination of FTIR spectrometry and principal component analysis(PCA)enabled accurate identification of severely and moderately degraded types.PCA loading curve analysis confirmed that cellulose was the main chemical component that distinguished the degradation difference between the outer layer and inner core wood.The hierarchical clustering analysis(HCA)of FTIR spectra identified the existence of a degradation transition zone between severely and moderately degraded wood.DVS analysis revealed the difference in moisture sorption properties between the outer layer and inner core wood.The Hailwood-Horrobin model was utilized to fit the sorption isotherms,allowing for the calculation of monolayer and multilayer adsorbed water contents in wood samples exhibiting various degrees of degradation.The results indicated that the equilibrium moisture content of the outer layer wood was higher than that of the inner core wood.This disparity was primarily attributed to the difference in the porous structure of the wood cell walls and cellulose content between the outer layer and inner core wood.Specifically,the porous cell wall structure of the outer layer of wood facilitates an increase in monolayer adsorbed water content,while the higher cellulose content in the inner core wood results in an elevation in multilayer adsorbed water content.This study employed a comprehensive analytical approach with innovations in sampling and FTIR analysis.Based on the positional differences in wood degradation,samples were collected from both the outer layer and inner core regions.By integrating chemometric analysis methods with FTIR spectrometry,the degree of wood degradation was rapidly determined on the basis of microscopic diagnosis,thereby enhancing the accuracy of assessing the preservation state of waterlogged archaeological wood.Furthermore,based on the investigation of microstructural and chemical components,the moisture sorption properties of wood cell walls at different degradation levels were characterized,and the influence of changes in cell wall structure on the hygroscopicity of waterlogged archaeological wood was further explored.This study revealed that the erosion bacteria were the main degraders for the XiaobaijiaoⅠ,and elucidated on the heterogeneous characteristics of degradation in shipwreck waterlogged archaeological wood,providing a perspective for understanding the mechanisms of wood decay in underwater burial environments.
作者
李仁
张治国
金涛
孙满利
铁付德
殷亚方
LI Ren;ZHANG Zhiguo;JIN Tao;SUN Manli;TIE Fude;YIN Yafang(School of Cultural Heritage,Northwest University,Xi’an 710127,China;China-Central Asia"the Belt and Road"Joint Laboratory on Human and Environment Research(Northwest University),Xi’an 710127,China;Key Laboratory of Cultural Heritage Research and Conservation(Northwest University),Ministry of Education,Xi’an 710127,China;Research Institute of Wood Industry,Chinese Academy of Forestry,Beijing 100091,China;Wood Specimen Resource Center of National Forestry and Grassland Administration,Beijing 100091,China;National Center for Archaeology,Beijing 100013,China;Ningbo Municipal Institute of Cultural Heritage Management,Ningbo 315012,China)
出处
《文物保护与考古科学》
北大核心
2024年第6期91-102,共12页
Sciences of Conservation and Archaeology
基金
国家重点研发计划资助(2020YFC1521800)
国家留学基金委国家建设高水平大学公派研究生项目资助(CSC201903270023)
中国博士后科学基金面上资助项目(2022M722575)。
关键词
饱水考古木材
小白礁Ⅰ号
降解特征
木材细胞壁
水分吸附性能
Waterlogged archaeological wood
XiaobaijiaoⅠ
Degradation characteristic
Wood cell wall
Moisture adsorption property
