Zaihan Jalaludin

A rheological description of the water vapour sorption kinetics behaviour of wood invoking a model using a canonical assembly of Kelvin-Voigt elements and a possible link with sorption hysteresis

Abstract The dynamic vapour sorption behaviour of two Malaysian hardwoods, acacia (Acacia mangium Wild) and sesendok (Endospermum malaccense Bent ex Müll. Arg.) was studied over a narrow temperature range (20–40°C). The rate of sorption or desorption of water into or out of the wood cell wall was considered to be limited by the viscoelastic behaviour of the material and the sorption kinetics was accordingly analysed in terms of a canonical series of Kelvin-Voigt elements. A two series and three series model have been applied to the kinetic data and the results are compared. Characteristic times and moisture contents were obtained from the models. The Arrhenius equation was used in conjunction with the reciprocals of the characteristic times to calculate the activation energy and activation entropy of sorption, and the Gibbs free energy of activation for the sorption process was also determined. This is the first time that entropy of activation and Gibbs free energy of activation for sorption processes with wood have been reported. Interpretation of these data invokes a model describing the polymeric relaxation processes occurring within the cell wall during adsorption or desorption. A possible link between sorption kinetics, polymeric relaxation processes, and sorption hysteresis is discussed.

Analysis of the water vapour sorption isotherms of thermally modified acacia and sesendok

Abstract Two Malaysian hardwoods, acacia (Acacia mangium) and sesendok (Endospermum malaccense), that had been subjected to oleo-thermal modification were studied to determine their sorption isotherm behaviour using a dynamic vapour sorption apparatus. All the specimens were thermally modified using palm oil at three different temperatures (180, 200 and 220°C) and three different times (1, 2 and 3 h). The results showed that there was a reduction in equilibrium moisture content at each target relative humidity due to the heat treatment, but that the two wood species showed different behaviour in this respect. The adsorption isotherms were analysed using the Hailwood and Horrobin model, with excellent fits to the experimental data. The monolayer water and polylayer water were both reduced at a range of relative humidity values of the treated samples, although behaviour between the two wood species differed. Heat treatment resulted in an increase in hysteresis ratio, which was probably due to the increase in matrix stiffness of the cell walls.

Analysis of water vapour sorption of oleo-thermal modified wood of Acacia mangium and Endospermum malaccense by a parallel exponential kinetics model and according to the Hailwood-Horrobin model.

Abstract Two Malaysian hardwoods, acacia (Acacia mangium Wild.) and sesendok (Endospermum malaccense Bent. ex Müll. Arg.) that had been previously subjected to oleo-thermal modification, were studied to determine their dynamic sorption kinetic behaviour. All specimens were thermally modified in palm oil at 180°C, 200°C, and 220°C and 3 h treatment time. Data were analysed using the parallel exponential kinetics (PEK) model, and excellent fits to the experimental data were obtained. The relation between the monolayer water and polylayer water was also examined by the Hailwood-Horrobin (H-H) model at a range of relative humidity (RH) values. The PEK model divides the sorption kinetics curve into a fast and slow sorption processes. Characteristic times of the two processes at various RH showed sorption hysteresis with all of the specimens only in the slow process. However, with mass change data, sorption hysteresis occurred with both the slow and fast processes. By comparing H-H and PEK models, it was found that the fast and slow sorption process of untreated and treated E. malaccense could possibly be linked, respectively, to monolayer and polylayer formation from 5 to 40% RH. No such correlation was found for A. mangium, however.

Influence of earlywood/latewood and ring position upon water vapour sorption properties of Sitka spruce

Abstract Variation in the water vapour sorption kinetics of the stemwood of Sitka spruce (Picea sitchensis (Bong.) Carr.) has been studied, with respect to possible variations between earlywood and latewood and between different annual ring positions from pith to bark. The sorption kinetics was analysed using the parallel exponential kinetics (PEK) model that has recently been introduced by this laboratory for studies with wood. Significant differences in kinetic parameters were found between ring positions, corresponding to differences between juvenile wood and mature wood that contrast with previously reported work in the literature. Differences were also found in the sorption kinetics of earlywood and latewood in agreement with the literature. Thus far, there has been no satisfactory explanation as to the physical interpretation of the PEK model and in this paper it is argued that the kinetic behaviour is consistent with what would be expected for sorption with a viscoelastic material. Analysis of the PEK data using the Kelvin–Voigt model has proved that it is possible to obtain values for the wood cell wall stiffness and viscosity that are in broad agreement with previously published values in the literature.