Assessment of wood microstructural changes after one-stage thermo-hydro treatment (THT) by micro X-ray computed tomography

The microstructural changes in a selection of softwoods and hardwoods resulting from thermo-hydro treatment (THT) at 160°C were examined by means of a state-of-the-art micro X-ray computed tomography. A dedicated X-ray scanning and volumetric processing protocol was developed. All reconstructed volumes had an approximate voxel pitch between 0.8 and 1.2 μm3. The microstructures of the same needle-shaped specimens before and after THT were visualized, and the individual parameters (maximum opening and lumen volume) for various cell types were quantified and compared. The highest values of substance volume were recorded for the ash sapwood (81%) and spruce specimens (72%). After THT, a significant correlation was found between the mass loss determined by gravimetry and the X-ray volume loss. The largest change occurred in the lumen volume of several tissue components, such as libriform fibers, tracheids, and ray parenchyma. The average aspen fiber volume reduction after THT was 31%, a value 2.6 times higher than the volume reduction of the average vessels. The porosity of ash sapwood increased from 41 to 56%, whereas the porosity of birch decreased from 34 to 29%

Potential of X-ray computed tomography for 3D anatomical analysis and microdensitometrical assessment in wood research with focus on wood modification

Studying structure and chemistry of wood and wood-based materials is the backbone of all wood research and many techniques are at hand to do so. A very valuable modality is X-ray computed tomography (CT), able to non-destructively probe the three-dimensional (3D) structure and composition. In this paper, we elaborate on the use of Nanowood, a flexible multi-resolution X-ray CT set-up developed at UGCT, the Ghent University Centre for X-ray Tomography. The technique has been used successfully in many different fields of wood science. It is illustrated how 3D structural and microdensitometrical data can be obtained using different scan set-ups and protocols. Its potential for the analysis of modified wood is exemplified, e.g. for the assessment of wood treated with hydrophobing agents, localisation of modification agents, pathway analysis related to functional tissues, dimensional changes due to thermal treatment, etc. Furthermore, monitoring of transient processes is a promising field of activity too

Penetration of Wood Preservatives into Thermally Modified Birch and Pine Wood

The objective of the present study was to investigate the interaction between Cu-containing preservatives and birch (Betula spp.) and pine (Pinus sylvestris L.) wood, modified at a relatively mild temperatures (150 – 180ºC). The disposition of wood to absorb water was evaluated by capillary absorption (CA) tests through the specimens’ tangential and radial surface. Changes in wood drying characteristics due to thermal modification (TM) were evaluated by monitoring wood moisture dynamics after impregnation. In order to assess the capacity of wood to absorb preservatives, a vacuum/pressure process was used to impregnate small specimens for which uniform saturation into the entire volume can easily be reached. Quantitative determination of copper Cu content in the specimens was performed by using atomic absorption spectroscopy (AAS). The fixation of the absorbed Cu was evaluated by subjecting the specimens to leaching procedures according to EN 84 and assessing the ratio of retained Cu in the specimens. The CA test showed deceleration of capillary absorption in TM birch wood through both surfaces, with similar absorption rates regardless of treatment temperatures. A significant increase in the absorption rate through the tangential surface was recorded for TM pine wood and the increase was greater for specimens treated at higher temperatures. The results of moisture content monitoring showed a similar reduction in the drying rate due to thermal modification regardless of species. Comparing wood of one species with similar densities, less preservative was absorbed by TM wood. However, the results of AAS showed that, in comparison with unmodified wood, 10% (birch) and 25% (pine) more Cu per one gram of wood was introduced during impregnation. Nevertheless, TM also resulted in higher Cu leaching rates for both species

STUDY OF THE STRUCTURE OF WOOD-RELATED BIOPOLYMERS BY SORPTION METHODS

The potentialities of different vapour sorption methods are analized for the investigation of the microstructure of wood sorbents (wood, cellulose and lignin) as a particular case of biopolymers. There are two important distinctions in the sorption behaviour of biopolymers from traditional rigid sorbents, namely, the dependence of the characteristics of the porous structure on the thermodynamic properties of the sorbate, and the manifestation of the sorption hysteresis over the whole region of the sorption–desorption isotherm. The reason for these distinctions is the low rigidity (low values of modulus of elasticity) of biopolymers, hence, their considerable deformability under the action of sorption forces, resulting in the cleavage of interstructural bonds. This process, manifesting itself phenomenologically as swelling, depends on the activity of the sorbate and results in the appearance of porosity and a new surface. The criterion for the activity of the sorbate is close values of the solubility parameters of the polymer and the sorbate. Inert substances are adsorbed on the surface of large morphological formations and characterise the intact structure of the sorbent, while active sorbates cause the swelling of these formations and penetrate them, which enables a study of the microstructure of sorbents. In the desorption process, the cleaved bonds are restored, blocking a part of the sorbate in the polymer’s structure, which results in the appearance of sorption hysteresis, not connected directly with the porous structure of the sorbent

Novel Alkyd - Linseed Oil Emulsion Formulations for Wood Coatings

All water-borne coatings need surfactants in order to reduce the free energy of the various interfaces of the system, thus providing kinetic stability to the formulation. Surfactants are used as binder emulsifier and as pigment dispersant, they are needed to improve wetting on low energy substrates, to control foaming during application and processing, and to prevent film defects caused by surface tension gradients (Hellgren A.-C et al, 1999). The purpose of this experiment was to obtain a water-based emulsion, suitable as a coating for wood protection and, at the same time, reduce or eliminate the presence of co-solvent, which is usually always present also in water-based coatings

Novel Alkyd-Linseed Oil Emulsion Formulations for Wood Coatings

In this experiment an oil-in-water emulsion, suitable as a coating for wood surface protection, was obtained. The main components of this emulsion were linseed oil and an alkyd, mixed at a ratio of 1:2. The experiments were conducted to find a valid combination of solubilizing agents, capable of giving a stable emulsion. Several surfactants, obtained from different producers, were tested. The main factors considered were the nature of the surfactant and its hydrophilic-lipophilic balance (HLB). Our results confirmed that the most suitable surfactants were ethoxylated non-ionic types with a high HLB value, while surfactants based on the gemini technology showed a poor efficiency due to scarce solubility in water, which led to the separation of phases. Once the optimal emulsion composition was obtained, hydrothermally treated and untreated aspen wood samples were coated to evaluate the degree of coating absorption for two different substrates

Enhancing Thermally Modified Wood Stability against Discoloration

Thermal modification of wood has gained its niche in the production of materials that are mainly used for outdoor applications, where the stability of aesthetic appearances is very important. In the present research, spectral sensitivity to discoloration of thermally modified (TM) aspen wood was assessed and, based on these results, the possibility to delay discoloration due to weathering by non-film forming coating containing transparent iron oxides in the formulation was studied. The effect of including organic light stabilizers (UVA and HALS) in coatings as well as pretreatment with lignin stabilizer (HALS) was evaluated. Artificial and outdoor weathering was used for testing the efficiency of different coating formulations on TM wood discoloration. For color measurements and discoloration assessment, the CIELAB color model was used. Significant differences between the spectral sensitivity of unmodified and TM wood was observed by implying that different strategies could be effective for their photostabilization. From the studied concepts, the inclusion of the transparent red iron oxide into the base formulation of the non-film forming coating was found to be the most effective approach for enhancing TM wood photostability against discoloration due to weathering

Conditions Influencing Mould Growth for Effective Prevention of Wood Deterioration Indoors

Effective prevention of mould growth indoors is still an important topic considering that mould growth is frequently observed in buildings, it causes serious health hazards and can irreversibly damage infected objects. Several studies have been conducted and mould growth models developed. Despite that, some potentially important aspects such as water damage and spore contamination have received only little attention. The objective of the present study was to investigate the effect of the initial moisture content of wood and spore contamination on mould development indoors. The mould tests were performed in constant temperature (10, 20 and 30 °C) and relative humidity (91% and 97%) conditions. The results show that wetting of wood specimens prior to the test significantly accelerates mould growth at a temperature of 10 °C. For the other temperatures, the effect was insignificant. Similar results were obtained for the test involving dry (conditioned at RH 50%) and conditioned specimens (RH 91% or RH 97%). The results regarding initial spore contamination show that significantly longer periods are required for mould to develop without spore contamination at 10 °C and 20 °C, while at 30 °C the effect is relatively small

Change of the Properties of Pine Wood on the Initial Stage of Decay by Wood-Rot Fungi

The microstructure of pine wood at the first stage (10 days) of exposure to brown-rot (Gloeophyllum trabeum and Porta placenta) and white-rot (Coriolus versicolor) fungi after extraction of low-molecular hydrophilic products of degradation by hot water was investigated by the water vapour sorption method. The content and composition of monosaccharides in the extracts were determined by the GLC-method. After washing of sound wood, the pore volume of the sample in the region of pore sizes D ~ 1.5 nm increases. The same maximum appears on the curves of pore volume distribution in size after exposure of wood to brown-rot fungi: after washing, this maximum is shifted into the region of lesser pore sizes. The extraction of low-molecular products with water does not change essentially the wood structure, but results in the enhancement of its hydrophility. The most essential changes in the wood microstructure are caused by white rot, namely, the wood surface becomes more hydrophobic, and the pore volumes in the whole region of their sizes decrease dramatically. The composition of monosaccharides in the water extracts of the samples decayed by P. placenta and C. versicolor, as well as the control sample is the same (xylose, arabinose and galactose); only after the exposure to G. trabeum, new components (glucose and mannose) appear besides the above-mentioned ones