Molecular and crystal structures of cellulose in severely deteriorated archaeological wood

Abstract

Preservation and conservation of archaeological wooden artifacts is extremely challenging due to a lack of knowledge about the hierarchical structure of preserved cellulose. Herein we report on the comparative analysis of eight archaeological and four recent wood samples from three archaeological sites in China by a variety of methods, including micro-morphology, Fourier Transform Infrared Spectrum, X-ray scattering, chromatographic analysis of wood sugars, and solid state 13C CP/MAS NMR. Results show that deterioration on the microscale is clearly related to a fragmentation of both the cellulose crystallite structure and the cellulose microfibrils. Slightly deteriorated archaeological wood features cellulose crystallites and microfibrils, comparable to non-degraded recent wood, whereas severely deteriorated wood shows higher porosity of the wood cell wall, fragmented cellulose aggregates instead of fibrils and nearly no crystallinity. Alterations in molecular structures resulted in advanced degradation of both amorphous and crystalline cellulose domains. Only a small amount of cellulose was preserved. The data allows to assume highly fragmented but still partially crystalline cellulose lamellas.Graphical abstract