Chemical and Mechanical Differences between Historic and Modern Scots Pine Wood

Abstract

Timber is one of the most common historic building materials, but relatively little is known about how it ages in situ. Here we investigate historic and modern Scots pine to determine any chemical or mechanical differences between them. Fourier-transform infrared (FTIR) microscopy was used to investigate differences in the chemical composition of Scots pine (Pinus sylvestris L.) timber, comparing small samples from historic beams about 500 years old with modern timber. The hemicellulosic acetyl content was reduced by about half in the historic samples, uniformly across the thickness of the beams. A chemical mechanism was therefore suggested for the loss of acetyl groups, as has been observed in paper. In paper, deacetylation and the resulting release of acetic acid are accompanied by loss of strength. Mechanical testing of the historic timber was difficult because the available length of the samples along the grain was only 20 mm. After developing a miniaturized compression test developed for the purpose, it was shown that the relative stiffness of the historic Scots pine samples was reduced by about half compared to modern material.

Beyond Heritage Science: A Review

“…Often, such studies utilize materials that are historic in age but not in terms of significance. Studies into parchment and wood, for example, have aimed to understand the decay pathways of complex biological polymers that are exposed to variable environmental conditions with a view to offering guidance on storage conditions [6,7].…”

Analysis of the Natural Aging of Silver Fir (Abies alba Mill.) Structural Timber Using Dendrochronological, Colorimetric, Microscopic and FTIR Techniques

“…It is possible to correct the baselines of the spectra so that linear baselines are drawn between the same frequencies for each spectrum, resulting in a more reproducible peak analysis of the spectra [8,[23][24][25]. The absorbance at flattening frequencies was subtracted from the uncorrected spectra to produce baseline-corrected spectra (Figure 4).…”

“…This peak is assumed to be specific to lignin as it corresponds to a stretching vibration mode on the benzene ring, which occurs mainly in the lignin polymer [23,26,27]. The averaged absorbance values of the fingerprint and the peak at 1509 cm −1 were then evaluated in a similar manner (Equation (1), Figure 4) [8].…”

“…The hemicelluloses in softwoods are represented by glucomannans and glucuronoxylans, only the former being acetylated [28,29]. The ratio was then calculated (Equation (2), Figure 4) [8]:…”

“…Natural aging of wood most frequently shows changes in hemicelluloses, which are the least stable components [5][6][7]. FTIR spectroscopy and chemical analytical studies confirm a decrease in the proportion of free hydroxyl groups, which in turn leads to a decrease in hygroscopicity and thus greater dimensional stability of aged wood [8,9]. Natural aging of wood may also be accompanied by an increase in the degree of crystallinity of cellulose [10], as evidenced by the formation of new intermolecular bonds in amorphous regions.…”