This study was conducted to evaluate the physical and chemical properties of Scots pine (Pinus sylvestris L.) sapwood modified with tannin-based formulas. Wood samples were pressure impregnated with tannin solution at five different concentrations of citric acid (0, 2, 10, 20, and 40 wt/wt%). The tannin-modified samples were analyzed by mean of their weight percentage gain (WPG), leaching resistance (LR), bulking coefficient (BC), anti-swelling efficiency (ASE), Fourier-Transform Infrared (FTIR) spectroscopy, and optical microscopy, and the results were compared with unmodified sapwood and heartwood samples. It is observed that the WPG and dimensional stability of the samples increased with increasing the citric acid (CA) concentrations and the highest WPG was attained (44%) with a formulation containing 20% CA while, the BC, LR, and ASE values were considerably higher in the samples modified with 40% CA concentration as compared to other modification formulas and also the unmodified sapwood and heartwood samples. FTIR spectroscopy analyses showed higher esterification degree with higher concentrations of CA. Overall, this study suggests the potential of a fully bio-based tannin formula to improve the water-related properties of Scots pine sapwood.

Tannins are polyphenolic compounds extracted from various tree species and used in variousmapplications such as adhesives, composites, pharmaceuticals, medicines, and food and beverage production (Mubarak et al. 2023). However, tannins, especially condensed tannins, have limited reactivity with wood. Consequently, to effectively modify wood, cross-linkers and other reactive chemicals or additives must be used. In this work, we have introduced a bio-based cross-linker in a 20% tannin (Quebracho) aqueous solution. Five levels of cross-linker (0, 2, 10, 20 and 40% of total tannin solid) were used to modify Scotspine (Pinus sylvestris L.) sapwood with dimensions of 25 × 25 × 10 mm³ (radial × tangential × longitudinal). Full-cell impregnation was applied with a 60 min vacuum and pressure for 60 min. Samples were kept at room condition for 24 h, stepwise dried to avoid drying defects and cured at 140 °C for 10 h. Modified wood samples are shown in Figure 1. Weight percentage gain (WPG) and bulking coefficient (BC) after water leaching for 5 days were measured according to Donath et al. (2004).

Petrochemical-based phenol–formaldehyde (PF) adhesives are widely used in plywood production. To substitute phenol in the synthesis of PF adhesives, lignin can be added due to its structural similarity to phenol. Moreover, micro-fibrillated cellulose (MFC) can further enhance the bond performance, mechanical properties, and toughness of adhesive systems. Thus, the aim of this study was to evaluate the adhesion performance of lignin–PF (LPF) adhesives reinforced with MFC. In LPF formulations, three levels of MFC (0, 15, and 30 wt% based on the total solid content of adhesives) were added to the homogenous adhesive mixture. Three-layer plywood panels from birch (Betula pendula Roth.) veneers were assembled after hot pressing at 130 °C under two pressing durations, e.g., 60 and 75 s/mm. Tensile shear strength was measured at dry (20 °C and 65% RH) and wet conditions (water soaked at room temperature for 24 h). The results indicated that the addition of lignin reduced the strength of LPF adhesives in both dry and wet conditions compared to the control PF adhesive. However, MFC reinforcement enhanced the shear strength properties of the plywood. Furthermore, a longer pressing time of 75 s/mm slightly increased the shear strength.

Rattan cane is an important forest product with economic value. Its anatomical, physical, and biological properties vary with the cane height. This makes it difficult to select the appropriate cane diameter for harvesting. Understanding the material properties of rattan cane with different diameter sizes is important to enhance its utilization and performance for different end uses. Thus, the present study was performed on two rattan species, Calamus zollingeri and Calamus ornatus, at two different cane heights (bottom/mature and top/juvenile). Calamus zollingeri was studied at diameter classes of 20 mm and 30 mm, while Calamus ornatus was analyzed at a diameter class of 15 mm. The anatomical properties, basic density, volumetric swelling, dynamic moisture sorption, and biological durability of rattan samples were studied. The results showed that C. zollingeri with a 20 mm diameter exhibited the highest basic density, hydrophobicity, dimensional stability, and durability against mold and white-rot (Trametes versicolor) fungi. As confirmed by anatomical studies, this could be due to the higher vascular bundle frequency and longer thick-walled fibers that led to a denser structure than in the other categories. In addition, the lignin content might have a positive effect on the mass loss of different rattan canes caused by white-rot decay.

Scots pine sapwood was pretreated with two levels of propanetriol (20% and 40% w/w glycerol), and then subjected to vacuum-heat treatment (VHT) at 180°C and 200°C. The treated samples were examined with respect to their weight and volumetric changes, mechanical properties, colour changes, and dynamic water vapour sorption. The weight of the samples after VHT did not change with increasing the temperature, but it was increased in glycerol pretreated samples. Combination of glycerol pretreatment and VHT decreased the maximum swelling. Total colour change was significantly higher during VHT at a higher temperature, while no obvious trend observed in the samples pretreated with glycerol. Modulus of elasticity (MOE) and modulus of rupture (MOR) were not affected by solely VHT, but strongly decreased after glycerol pretreatment. The equilibrium moisture content (EMC) of the samples decreased by VHT. The glycerol pretreatment caused a reduction in EMC values at a relative humidity (RH) below 60%, but considerably increased the moisture sorption in the RH above 75%. VHT slightly reduced the sorption hysteresis compared to untreated wood, but an apparent reduction in hysteresis observed by glycerol pretreatment. This indicates that the flexibility of the wood cell wall polymers increases due to glycerol pretreatment, which results in decreased MOE and sorption hysteresis values.

Nowadays, the design of composite materials considering sustainability and the environmental impact of the production is conspicuous. Therefore, in this work, we focus on investigating the mechanical behaviour and structure of a new green wood-based fibrous composite material bonded with a novel polymer matrix. The constitutive prediction models employing the material and structure design approaches simultaneously are proposed here to describe the material's microstructure. The goal is speeding up trials and reducing experiments expenses by replacing tests with computer simulations. Additionally, the relationship between material behaviour and structure is established and will be later used to generate Representative Volume Elements (RVEs) for finite element analysis (FEA).

Polyurethane (PU) adhesives were prepared with bio-polyols obtained via acid-catalyzedpolyhydric alcohol liquefaction of wood sawdust and polymeric diphenylmethane diisocyanate(pMDI). Two polyols, i.e., crude and purified liquefied wood (CLW and PLW), were obtained fromthe liquefaction process with a high yield of 99.7%. PU adhesives, namely CLWPU and PLWPU,were then prepared by reaction of CLW or PLW with pMDI at various isocyanate to hydroxyl group(NCO:OH) molar ratios of 0.5:1, 1:1, 1.5:1, and 2:1. The chemical structure and thermal behavior of thebio-polyols and the cured PU adhesives were analyzed by Fourier transform infrared spectroscopy(FTIR) and thermogravimetric analysis (TGA). Performance of the adhesives was evaluated by singlelap joint shear tests according to EN 302-1:2003, and by adhesive penetration. The highest shearstrength was found at the NCO:OH molar ratio of 1.5:1 as 4.82 ± 1.01 N/mm² and 4.80 ± 0.49 N/mm² for CLWPU and PLWPU, respectively. The chemical structure and thermal properties of the cured CLWPU and PLWPU adhesives were considerably influenced by the NCO:OH molar ratio. 

Cross-laminated timber (CLT) is increasingly used in building construction worldwide. Durability of CLT against fungal attack has yet to be fully explored. Water intrusion in mass timber can yield dimensional changes and microbial growth. This study evaluated the performance of CLT coated with various water- and solvent-based stains commercially available in the United States. Twelve coatings were tested for moisture excluding effectiveness, water repellency effectiveness, volumetric swelling, and anti-swelling efficiency. Only five coatings repelled water, limiting dimensional changes. A modified version of AWPA E10-16 (2016) was performed to evaluate decay of the coated CLT samples. Weight losses were recorded after 18 weeks' exposure to the brown-rot decay fungus Gloeophyllum trabeum. In accelerated mold testing, coated CLT samples were grown in chambers containing spores of Aspergillus sp., Rhizopus sp., and Penicillium sp. for 29 d and assessed visually for mold growth. In both tests, coating C (transparent, water-based, alkyd/acrylic resin) performed the best among the tested coatings. Mold growth was completely prevented, and weight loss caused by G. trabeum was approximately 1.33%. Although coating C prevented decay for 18 weeks, coatings are not intended to protect against decay fungi. However, they may offer short-term protection during transport, storage, and construction. 

Water is one of the most significant factors for the durability of wood. A common solution is to use a coating to protect and maintain low water content. However, little knowledge exists how the underlying wood substrate affects the water sorption of coated wood. Therefore, the liquid water absorption of coated and uncoated Norway spruce heartwood and sapwood with a variety of densities was measured by letting the panels float freely in the water. The effect of one year weathering of the coatings was also included. Coated heartwood and sapwood had no difference in water absorption in opposite to uncoated spruce. The influence of heartwood and sapwood seemed to have limited impact when a coating hindered the presence of free water. Wood density had a positive effect on the absorption of coated wood, i.e. low absorption for low-density samples, in opposite to uncoated samples. Low-density characteristic also contributed to a lower increase of water absorption after weather degradation, for samples with water-borne coatings. Natural weathering enhanced the effect of wood characteristics on coated samples, likely by an increase of coating permeability.

Previous studies have shown that thermally modified wood (TMW) performs well in outdoor, above‐ground conditions in terms of resistance to wood‐decaying fungi. Yet, little is known about the development of defects such as checks and the corresponding mechanical properties of TMW in this condition. This experiment focused on the effect of 30 months outdoor above‐ground exposure (weathering) on the degree of checking, dynamic stiffness and static bending properties of thermally modified timber (TMT) of Norway spruce. Two board pairs per log were cut from 190 logs; one board of each pair was thermally modified and the other used as control. Then, 90 board pairs were exposed to the weather in south Sweden. Surface checking and axial stiffness were monitored at six‐month intervals by using digital photography and non‐destructive tests (time‐of‐flight and resonance method) to monitor changes in the material upon weathering. Finally, all boards were tested destructively in a 4‐point static bending test following EN 408 standard. Results showed that weathering had no significance influence on static bending properties of TMT even though the degree of checking was considerably higher in TMT than unmodified timber after weathering. In particular, checks along growth rings were deeper, longer and more common in TMT after weathering, especially on the pith side of boards. The maximum depth of these checks did not depend on board orientation (i.e., which side was exposed) and exceeded limits given in strength grading standards for 7% of the modified boards included. Axial dynamic stiffness determined at 6‐month intervals was less influenced by fluctuations in moisture content for TMT compared to unmodified timber, but did not confirm the increase in the degree of checking of TMT. The presence of checks from weathering did influence failure modes in TMT; horizontal shear failure became more frequent and some boards failed in compression.