A critical evaluation of the degradation state of dry archaeological wood from Egypt by SEM, ATR-FTIR, wet chemical analysis and Py(HMDS)-GC-MS

Abstract

An in-depth investigation was undertaken of the chemical changes to wood induced by degrading agents in dry burial environments. The degradation state of eleven wood samples from dry archaeological sites in Egypt was evaluated by combining the information obtained by scanning electron microscopy (SEM), wet chemical analysis (WCA), attenuated total reflectance Fourier transform infrared spectroscopy (ATR-FTIR) and analytical pyrolysis gas chromatography mass spectrometry with in situ silylation (Py(HMDS)-GC-MS). The samples belonged to five different wood species (Faidherbia albida, Ficus sycomorus, Taxus baccata, Pinus sylvestris and Tamarix sp.) and came from three different archaeological sites corresponding to three different time periods (from ca. 1700 BC to ca. 1700 AD). The results were compared with sound reference wood of the same species. SEM enabled a fungal attack to be identified in some of the samples. WCA highlighted the preferential loss of lignin or carbohydrates in these samples, but also showed unusually high values of water-soluble substances in most of them. FTIR spectra acquired before and after the extraction of the samples revealed that this soluble fraction generally contained depolymerised carbohydrates and/or lignin units. Py(HMDS)-GC-MS was applied without any sample pre-treatment and was used to assess the alteration/depolymerisation of the individual wood components, thus complementing the picture regarding the chemical changes. The results showed that, unlike waterlogged archaeological wood, most of the degraded wood components â\u80\u93 depolymerised carbohydrates and/or lignin â\u80\u93 had not leached away from the dry wood matrix, and thus complicated the interpretation of data. The commonly used parameters, such as the H/L (holocellulose/lignin) ratio, failed to give a correct evaluation of the wood degradation when both carbohydrates and lignin were degraded. The preservation conditions of the samples were very variable, from very good to a high depletion of carbohydrates, to the preferential depletion of lignin, or comparable levels of carbohydrate and lignin degradation. This was sometimes observed within the same wood species and the same archaeological site. This highlighted how difficult the interpretation can be in order to correctly evaluate the multiple causes of degradation affecting dry archaeological wood. An analytical approach using complementary techniques appears to be essential

Investigation of biomass surface modification using non-thermal plasma treatment

“…The FTIR absorbance of the pulverized EFB samples are shown in figure 5, while the assigned wavelengths for the major functional groups and bonds are recorded in table 1. The observed absorbance is similar to those reported in literature [1,20,28,29]. Figure 5(a) shows changes in the absorbance (at medium intensities) that are representative of the lignin content, which are observed for C-H bonds for aromatics in syringyl and guaiacyl at 1109 cm −1 [1,20] (ref.…”

A review of analytical methods for assessing preservation in waterlogged archaeological wood and their application in practice

“…This can then be weighed to provide a percentage ash composition [17,81]. Determination of ash content does not reveal the composition of the ash but allows the correction of other analytical methods [66]. If necessary, the composition of this ash can be further analysed, for example by chemical extraction or instrumental methods suitable for elemental analysis [82].…”

“…Microscopy is most commonly used to examine the mode of decay, as characteristic decay patterns can help identify the type of biological attack [64,65]. However, the sample region analysed under the microscope may not be representative of the entire object; therefore microscopy tends to be used alongside other analytical methods which assess a greater bulk of the sample, for example Loss of wood substance or Gravimetric analysis (Acid insoluble lignin/TAPPI methods) [45,66]. Microscopy is non-quantitative, so consistency between analysts in terms of the conclusions drawn regarding the levels of decay is difficult to achieve.…”

Navigating conservation strategies: linking material research on alum-treated wood from the Oseberg collection to conservation decisions

“…In alum-treated woods, polysaccharides formed during pyrolysis are mainly anhydrosugars, which may be considered an index of holocellulose degradation. In sound woods, the most abundant holocellulose category is made up of cyclopentenones such as 3-hydroxy-2-hydroxymethyl-2-cyclopentenone, and E-2,3-dihydroxy-cyclopent-2-enone [31,32]. The second most abundant group is composed of anhydrosugars which are mainly represented by levoglucosan (1,6-anhydro-beta-d-glucopyranose).…”