Volume 79, Issue 12

The alternating arrangement of earlywood (EW) and latewood (LW) in wood growth reflects an optimization structure, where anatomical differences lead to varying properties. This study analyzed the stabilization characteristics of hygro-deformation in Chinese fir, and compared the dimensional responses of intact growth rings and with those of isolated EW and LW during step-wise desorption and adsorption. During both desorption and adsorption, both LW and EW exhibited rapid hygro-deformation initially, followed by stabilization. The stabilization of dimensional changes lagged behind stabilization of moisture content based on evaluating their rates of change. Isolated EW showed significant reductions in hygro-deformation compared to when LW was present, due to the removal of LW’s restraining effect. The radial and tangential shrinking differences in EW before and after isolation were 0.40 and 0.46 %, respectively, as relative humidity decreased from 97 % to 0. The corresponding values were 0.58 and 0.71 % during adsorption (0 → 97 % RH). These results highlight the impact of EW-LW interaction on the hygro-deformation of Chinese fir and are helpful to elucidate the complex nature of wood-water relations.

Formaldehyde-free, bio-based wood modification processes are gaining importance. One well-developed method is modification with citric acid and sorbitol as a copolymer (SorCA). However, some studies report that citric acid (CA) alone can be used for modification. In our previous paper, we showed that although the addition of sorbitol leads to a higher weight percent gain (WPG), the cell wall bulking (CWB), chemical fixation and impact bending strength were only marginally different compared to modification with pure citric acid. This study compares water-related properties, namely (1) dimensional stability and (2) swelling and shrinking behaviour, (3) water vapour uptake, (4) liquid water absorption and release and (5) capillary water uptake (CWU). Modification with pure citric acid resulted in higher dimensional stability compared to modification with SorCA. Dynamic vapour sorption (DVS) measurements showed that the modification with CA leads to a higher reduction in water vapour uptake. Liquid water uptake and release tests on the other hand revealed that, after leaching, SorCA-modified samples exhibited significantly lower water absorption. In summary, this study identified that while the addition of a copolymer has little effect on dimensional stability and water vapour sorption, it exerts a clear positive influence on liquid water absorption.

The temperature and relative humidity (RH) have an impact on the moisture absorption rate, moisture distribution, and swelling behavior of wood, which can lead to wood absorptive rheological phenomena such as swelling stress and swelling strain. This study examined the absorption and rheological characteristics of heat-treated (HT) and conventionally kiln-dried (CKD) North American alder wood under different conditions (50, 70, and 90 °C at 90 % RH) from an absolutely dry state to target moisture content (MC) levels (5 %, 10 %, and 15 %). The results showed that heat treatment significantly reduced the moisture absorption rate, the difference in MC, and the radial swelling ratio of the wood, with maximum reductions of 0.94-points, 1.54-points, and 0.89-points, respectively. The differential swelling between wood’s surface and core generates stresses and swelling strains ( ε E , ε V , ε M ). These stresses showed a trend opposite to that of the drying stress. Heat treatment notably reduced the mechano-sorptive swelling creep strain (MSCS) in North American alder wood (47.3 % lower at 70 °C and 0.7 % lower at 90 °C). In contrast, there were no significant differences in free swelling strain, elastic swelling strain, and viscoelastic swelling creep strain between HT and CKD wood.

Eucalyptus benthamii has been identified as one of the main forest species for planting in the southern region of Brazil due to its resistance to low temperatures. Current studies with the species are restricted to forestry and the processing of wood from short-rotation plantations. However, the greatest added value occurs in processing, where the application of paints and varnishes can change the characteristics of the wood. The objective of the study was to evaluate the colour changes of E. benthamii wood, coming from long rotation plantations, subjected to artificial weathering, with two finishing products. The surfaces of the pieces were treated with marine varnish and power stain and subjected to three cycles in the weathering chamber (240 h, 480 h, and 720 h), following the standard ASTM G154 (2006. Standard practice for operating fluorescent light apparatus for UV exposure of nonmetallic materials (ASTM G154-06)). To measure colourimetric parameters, a Konica Minolta colourimeter (model CR-400) was used. The artificial weathering process caused darkening of the wood and a very appreciable variation in the surface colour after 240 h. After 720 h, all samples showed a tendency towards a yellow–brownish tone, with a standardisation in colour after accelerated ageing. This characteristic is interesting for marketing, considering consumers’ preference for the natural colour of wood.

A more systematic, multiscale characterization of the mechanical properties of lignocellulosic materials, such as wood and bamboo, is needed so that manufacturers can better tailor their properties for specific end-uses. Nanoindentation was used to assess the mesoscale elastic modulus ( E S N I ${E}_{S}^{NI}$ ) and Meyer’s hardness ( H ) of secondary cell wall layers (SCWL) in Moso bamboo, and S 2 SCWL and compound corner middle lamella (CCML) in loblolly pine. The anisotropic SCWL was tested in both longitudinal and transverse directions. The effects of moisture content (MC) were studied by testing specimens conditioned between 1 % and 92 % relative humidity (RH). Both pine and bamboo SCWL exhibited many of the same features in their MC- and orientation-dependent E S N I ${E}_{S}^{NI}$ and H results, which suggested that the features were general characteristics of SCWL from different plants. A new transition in plasticity was observed around 2–4 % MC in which the SCWL transverse H had a sudden 20 % decrease. For comparison to literature plasticity S 2 SCWL uniaxial compression flow stress ( σ ) measurements made using micropillar compression testing, a H -derived uniaxial compression flow stress ( σ H ) was calculated using established methods. The σ H compared well to the literature σ , which supported that both H and σ can be used to similarly study plastic deformation mechanisms.

Wood modification is essential to enhance the performance and longevity of wood as a material while maintaining its natural and sustainable characteristics. By modifying wood, its properties can be significantly improved without the need for toxic preservatives. Thus bio-based wood modification is vital for enhancing wood properties sustainably, reducing environmental impact, and meeting the demand for eco-friendly, non-toxic, and renewable material solutions. In this study, bio-based formulae were used on pine sapwood for enhanced decay and weathering resistance. Quebracho tannin solutions (20 %) with different concentrations of citric acid (CA) as a cross-linker were prepared and then vacuum-pressure impregnated in Scots pine sapwood before curing them at 140 °C. The durability performance of untreated and tannin-impregnated wood samples was assessed against accelerated weathering, mould growth and brown rot decay fungus Coniophora puteana (Schumach.) P. Karst. Experimental results showed that the weathering resistance was apparently improved by tannin modification with higher levels of CA, as reflected by color stability, crack formation and contact angle. While tannin modification increased mould susceptibility, the decay resistance was notably enhanced in all modified wood samples. The acidity of the formulas at high CA levels may increase the risks of hydrolytic degradation of wood, and thus, low CA concentrations (e.g. 2 %) appear optimal for balancing performance and chemical stability. These findings underscore the potential of 100 % bio-based tannin–CA systems to enhance wood durability, offering a promising pathway for sustainable wood protection strategies.

Thermal treatment is a widely used bamboo modification method, but how moisture in the treatment atmosphere influences the hygroscopicity and dimensional stability of thermally modified bamboo is still poorly understood. In this study, the effects of dry thermal (N 2 T), hygrothermal (HGT), hydrothermal (HDT), and combined hydrothermal-dry thermal (HD&N 2 T) treatments on the chemical composition, hygroscopicity, and dimensional stability of Moso bamboo were comparatively investigated. The hygroscopic behavior of bamboo depended not solely on the number of accessible hydroxyl groups, but also on the porous structure of bamboo. The presence of moisture facilitated the degradation of hemicellulose and amorphous cellulose, but HDT treatment with excessive moisture largely deteriorated the dimensional stability of bamboo due to cell softening and collapse. Upon N 2 T treatment, lignin condensed with degradation products of polysaccharides, resulting in the highest crosslinking degree, the fewest sorption sites (7.1 mmol/g), the largest hysteresis value, and a significantly improved dimensional stability with an anti-swelling efficiency (ASE) of 27.3 %. HGT modified bamboo with the lowest hemicellulose content and a moderate crosslinking degree showed the most enhanced dimensional stability, with an ASE of 34.2 %. This study highlights the critical role of moisture in determining the properties of thermally modified bamboo.