Juvenile and mature wood of Abies pinsapo Boissier: sorption and thermodynamic properties

Abstract

For industrial processes, it is important to study the hygroscopicity and thermodynamic properties of juvenile and mature wood. Samples of Abies pinsapo Boiss. collected in the natural areas of the species in Spain were used to study these properties in both types of wood. The equilibrium moisture contents were obtained, and the 15, 35 and 50°C isotherms were plotted following the Guggenheim-Anderson-Boer-Dent model. The thermodynamic parameters were calculated using the integration method of the Clausius-Clapeyron equation. Chemical analyses, infrared spectra and X-ray diffractograms were applied to assess chemical modifications and possible changes in the cell wall structure. The chemical composition of the mature wood shows a decrease in the lignin and hemicelluloses content and an increase in the extracts and a-cellulose. The sorption isotherms for the three temperatures studied are higher in the mature wood than in the juvenile wood. Causes of this include the higher content of a-cellulose, the higher crystallinity index and the shorter crystallite length in the mature wood. No difference was found between the juvenile and mature wood in relation to the point of inflexion where the multilayer starts to predominate over the monolayer (approximately 30 %). In terms of the thermodynamic properties, the heat involved is greater in desorption than in adsorption, and more heat is involved in the mature wood than in the juvenile wood.

Thermodynamic analysis of water vapour sorption behaviour of juvenile and mature wood of Abies alba Mill.

“…The predominance of the multilayer over the monolayer around 30 % RH concurs with the results obtained in earlier studies of other softwoods [14,34,61,62], indicating that this value is independent of tree age and the position of the wood in the tree.…”

“…The GAB model constants do not follow a distribution with the temperature (Table 2), concurring with findings for other types of wood [14,28,55]. The C g value is positive due to the strong exothermic interaction between the water molecules and the sorption sites [56][57][58].…”

“…All the experimental EMC values are higher in the mature wood and the fitted isotherms of the mature wood are above those of the juvenile wood (Table 1; Fig. 1), concurring with authors who studied other species, both softwoods and hardwoods [8,10,11,14]. The explanation for this behaviour must be sought in the chemical composition of the two types of wood.…”

“…In relation to chemical composition, the distribution pattern of the various compounds throughout the radial direction of the tree has been determined by other authors in various softwood and hardwood species [14,16,23,[63][64][65][66]. However, because the only coincidence is the increase in cellulose at a greater distance from the pith, no set distribution pattern can be established [19,67].…”

“…Hill et al [13] concluded that there was no relation between the sorption isotherms and the location of the sample in the tree in the wood of Picea sitchensis. Esteban et al [14] obtained higher EMC in mature wood of Abies pinsapo than in its juvenile wood. Hill et al [15] determined differences between the hygroscopic response of the earlywood and the latewood of Larix kaempferi that were more pronounced as the distance from the pith increased.…”