Using charcoal, ATR FTIR and chemometrics to model the intensity of pyrolysis: Exploratory steps towards characterising fire events

Widely used charcoal analysis method in paleo studies involving NaOCl results in loss of charcoal formed below 400°C

“…The variability in bleaching within temperature groups could be the result of heterogeneity in the wood samples or due to variations in temperature across the heating surface in the oven. A recent study (Constantine et al, 2021) using the same production methods as this experiment applied FTIR and chemometrics to model charring intensity (CI) across species and temperatures. That study showed that there is variation in the infrared spectra within and between species charred in identical conditions.…”

Chemical Characterization of Waterlogged Charred Wood: The Case of a Medieval Shipwreck

“…Moreover, specific bands assigned to wood components such as hemicelluloses (~1737 cm −1 ), lignin (~1510 and 1269 cm −1 ) and cellulose (1026 and ~898 cm −1 ) [23] and generally all bands in the "fingerprint" region 1500-900 cm −1 [23,28] are absent, displaying the chemical changes caused by pyrolysis as well [29]. Nonetheless, the charred sample spectrum presents broad bands at ~1708 cm −1 , due to the acidic C=O groups, characteristic of low temperature charcoals' spectra [11,13] and a broad band at 1610-1590 cm −1 due to lignin aromatic C=C skeletal vibrations, which have been also reported to increase in intensity with increasing charring [29].…”

“…Nonetheless, an increase in absorption at 1030 and 1060 cm −1 has been observed indicating respectively the pronounced aromatic nature of the semi-charred wood, since this absorption band also indicates aromatic in-plane C-H deformation and changes in cellulose structure [34,35] along with the formation of aliphatic alcohols during heating [31,35]. The charred archaeological sample infrared spectrum (Figure 4e) appears typical to charcoals where the broad band at 3400-3320 cm −1 representing the -OH stretching vibration of water and the peaks at 3000-2800 cm −1 , due to aliphatic C-H stretching vibration derived from methyl, methylene, and methine group, are absent, as these bands decrease in intensity with increasing temperature [11,13,28,29]. Moreover, specific bands assigned to wood components such as hemicelluloses (~1737 cm −1 ), lignin (~1510 and 1269 cm −1 ) and cellulose (1026 and ~898 cm −1 ) [23] and generally all bands in the "fingerprint" region 1500-900 cm −1 [23,28] are absent, displaying the chemical changes caused by pyrolysis as well [29].…”

“…Nonetheless, it is well known that thermal decomposition of wood is accompanied by major chemical changes in hygroscopicity, viscosity, cell wall structure, color, density, and loss of mass and strength [4][5][6][7][8]. Moreover, it is also documented that these alterations depend on variables related not only on the wood, such as density, moisture content, permeability, species, size, grain direction, and surface protection [7,9], but also on the heating scenario, which incorporates the heat flux (temperature and duration) and the environment surrounding the wood like the oxygen concentration [7,[9][10][11][12][13]. All these factors which influence pyrolysis, combustion, and the charring rate of wood justify the coexistence of charred, semi-charred, and uncharred wood in the shipwreck.…”

Catchment vegetation and erosion controlled soil carbon cycling in south-eastern Australia during the last two glacial-interglacial cycles

“…Late Glacial and Holocene fire activity in the Thirlmere catchment is further refined by charring intensities, as inferred from Attenuated Total Reflectance Fourier Transform Infrared spectra from the same core (Constantine et al, 2021) and increasing Late Glacial to Holocene sedimentary SPAC contents (Fig. 4, .…”