Sorption and thermodynamic properties of wood of Pinus canariensis C. Sm. ex DC. buried in volcanic ash during eruption

Abstract

The hygroscopicity and thermodynamic properties of Pinus canariensis wood buried in volcanic ash, dating from 1100 BC, were studied and compared with recently felled juvenile and mature wood of the same species. The sorption isotherms were obtained by the saturated salt method at 35 and 50 °C. The isotherms were fitted using the Guggenheim-Anderson-de Boer model. The thermodynamic parameters were determined following the Clausius-Clapeyron integration method. To understand the behaviour of each type of wood, the chemical composition, infrared spectra and X-ray diffractograms were determined for each sample. The mature wood has a higher sugar content and lower extractive content than the juvenile and the buried wood. For both temperatures, the isotherm of the mature wood is above the isotherm of the juvenile wood and this, in turn, is above the isotherm of the buried wood, primarily influenced by the higher cellulose and hemicellulose contents and lower extractives content in the mature wood, resulting in a higher number of accessible -OH groups. Degradation of the buried wood due to high temperatures explains why its isotherms are below the isotherms of the recent wood. The energy involved in the desorption process is greater than in adsorption. Similarly, more energy is involved in the mature wood than in the juvenile wood, and the energy involved in the juvenile wood is greater than in the buried wood.

Changes in cell wall components of Pinus sylvestris L. wood after 300 years in contact with salt (NaCl)

“…This occurred because the desorption process requires greater energy than the adsorption process (Siau 1995;Avramidis 1997). Similar results were obtained in other studies on old wood of different species in various ageing situations (Esteban et al 2008a(Esteban et al ,b, 2009(Esteban et al , 2010Fernandez et al 2014;Simon et al 2017a). As EMC increases, net isosteric heat decreases, and the decrease is more pronounced in desorption than in adsorption.…”

“…As in other studies (Simon et al 2017a), the most significant changes occurred in the extractives content and were greater in the salt-covered wood (10.2%) than in the new wood (4.1%); this is because ageing typically results in higher extractives content in wood (Fengel 1991). The crystallinity indices (CrI%) showed significant differences between the two types of wood (Table 4) and were lower in the old wood, agreeing with similar studies on archaeological wood (Esteban et al 2008b(Esteban et al , 2009Guo et al 2018).…”

“…This result indicates the lower availability of -OH groups in the water sorption process in the salt-covered wood, which is more important in desorption than in adsorption due to the mechanical barrier of the salt in the cell wall. In studies on other species that had been buried, submerged, or buried under volcanic ash (Esteban et al 2006(Esteban et al , 2008a(Esteban et al ,b, 2009(Esteban et al , 2010Simon et al 2017a), the RH values from which the multilayer predominates over the monolayer remained at around 30 to 40%, 15 °C despite the chemical changes in the cell wall. The new wood was in this RH range, but the salt in contact with the wood substantially modified this point of inflexion, and the monolayer became saturated at lower RH values.…”

“…In the latter two studies, the adsorption-desorption isotherms of the old wood were above those of recently felled wood of the same species, mainly due to the increase in active -OH sites. Simon et al (2017a) demonstrated polysaccharide degradation due to high temperatures and the high percentage of extractives in Pinus canariensis C. Sm. ex D.C. wood buried in pyroclastic ash after an eruption about 3,000 years ago, resulting in lower EMC in the wood buried in ash than in recently felled wood of the same species.…”

Influence of alkaline delignification time on the moisture uptake behaviour of hemp

“…Lignin behaves as an easily accessible moisture-absorbing material that contributes to sorption via its carboxyl and both aliphatic and phenolic hydroxyl groups (Simon et al, 2017;Guo et al, 2016). When removed, causes significant alterations on the fibre surface and in accessibility (Yang et al, 2018).…”