Water Vapour Sorption and Moisture Transport in and Across Fibre Direction of Wood

Water vapour sorption experiments are frequently used to characterise the absorption and desorption of water in wood during transient conditions in relative humidity. When interpreting such experiments, it is still unclear to what extend the resulting time-dependent change of sample mass (i.e. sorption kinetics) is influenced by moisture transport, sorption and sorption related processes. To evaluate the impact of water vapour diffusion under such transient conditions, this study investigates the sorption kinetics of small wood samples with different lengths of transport pathways in and across fibre direction. For this purpose, water vapour sorption experiments on Norway spruce ( Picea abies ) samples were performed under identical climatic conditions at ambient air pressure and ambient standard temperature. The results showed that sample thickness has an impact on the sorption kinetics along the whole tested range of relative humidity. Differences between the sorption kinetics for samples in and across fibre direction were considerable at low relative humidity, indicating the relevance of water vapour diffusion through the lumen-pit-ray system. In contrast at high relative humidity, differences between the sorption kinetics for samples in and across fibre direction started to disappear while the impact of sample thickness was still considerable. Therefore, it seems as if an additional or modified process that depends on the number of sorption sites becomes relevant at an increased moisture content of wood. This process, as well as the increasing uptake and release of water across fibre direction, should be further investigated to gain a better understanding of the absorption and desorption of water in wood.

Water Uptake as a Crucial Factor on the Properties of Cryogels of Gelatine Cross-Linked by Dextran Dialdehyde

We investigated the water sorption properties of macroporous cryogels of gelatine (Gel) and dextran dialdehyde (DDA) prepared via cryogelation at 260 K and following the freeze drying processes. Water vapour sorption isotherms for aerogels were studied at 293 K by two independent methods: static-gravimetric and dynamic vapour sorption (DVS) over a water activity range of 0.11–1.0. Experimental data were fitted by use of the Brunauer–Emmett–Teller (BET) and Guggenheim–Anderson–de Boer (GAB) models. The BET model (for a water activity range of 0.1 ≤ p/po ≤ 0.5) was used to calculate the sorption parameters of the studied cryogels (the monolayer capacity, surface area and energy of interaction). In comparison with BET, the GAB model can be applied for the whole range of water activities (0.1 ≤ p/po ≤ 0.95). This model gave an almost perfect correlation between the experimental and calculated sorption isotherms using nonlinear least squares fitting (NLSF). Confocal Laser Scanning Microscopy (CLSM) was used to confirm the structural differences between various DDA:Gel cryogel compositions. Thermogravimetric analysis and DSC data for aerogels DDA:Gel provided information regarding the bonded water loss, relative remaining water content of the material and the temperature of decomposition. Estimation of the amount of bound water in the cryogels after the freeze drying process as well as after the cycle of treatment of cryogels with high humidity and drying was performed using DSC. The results of the DSC determinations showed that cryogels with higher gelatin content had higher levels of bonded water.

The Use of Starch Drying Kinetics Curves for Experimental Determination of Its Specific Surface Area

The most popular method for the calculation of specific surface area is its determination from water vapour sorption isotherms. The study presented here has been designed for the purpose of optimisation and selection of the conditions of drying so as to allow the determination of specific surface area from plotted curves of the drying process. The results indicate that drying curves can be used as the basis for the determination of specific surface area, the values of which do not differ statistically significantly (α = 0.05) from those determined from isotherms of water vapour sorption (adsorption/desorption).

Water vapour sorption behaviour and physico-mechanical properties of methyl methacrylate (MMA)- and MMA–styrene-modified batai (Paraserianthes falcataria) wood

The purpose of this study was to determine the applicability of methyl methacrylate (MMA) and MMA–styrene in treating batai (Paraserianthes falcataria) wood. The effectiveness of the treatment was evaluated based on Fourier transform infrared spectroscopy (FTIR) analysis, physico-mechanical properties of the treated wood, and moisture sorption isotherm using dynamic vapour sorption (DVS) apparatus. Physico-mechanical properties of the modified batai wood were improved. The MMA-treated batai wood showed better improvement in terms of physical and mechanical properties compared to the MMA–styrene-treated batai wood. The equilibrium moisture content (EMC) for untreated batai wood was higher than that of treated samples. At 95% RH, the EMC for untreated batai wood was 20.7%, whereas the EMC for MMA- and MMA–styrene-treated samples was 7.9 and 8.8%, respectively. The findings indicate that the modified batai wood absorbed less moisture compared to the untreated batai wood. Moreover, the untreated batai wood had larger hysteresis loop than the treated batai wood. The highest hysteresis value was observed at 80% RH for untreated batai wood (3.8%), followed by MMA–styrene-treated batai wood (1.7%) and MMA-treated batai wood (1.2%). Both MMA and MMA–styrene proved to be effective treatments for batai wood because they reduced its hygroscopicity.

Dynamic vapour sorption protocols for the quantification of accessible hydroxyl groups in wood

This study investigated several key parameters of deuterium exchange measurements in a dynamic vapour sorption apparatus to optimise the measurement protocol for hydroxyl (OH) group accessibility determination. The impact of changing the sample mass, the deuterium oxide (D2O) vapour exposure time and the rate of change in moisture content (dm dt−1) during the drying steps on the measured OH group accessibility were analysed. A sample mass of more than 10 mg, an exposure to D2O vapour of at least 10 h and a dm dt−1 of 0.0005% min−1 over a 10-min period during the drying steps gave the most reliable results. We also investigated the necessity of adding a method stage that eliminates the effect of inclusion compounds (ICs). The addition of an initial drying and wetting stage enabled the release of entrapped solvents.