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Acetylation is a breakthrough in wood modification and has been established on industrial scale. However, concerns have been raised regarding the stability of acetylated wood under elevated temperatures, particularly during post hot-pressing processes to manufacture products such as laminated veneer lumber (LVL). At around 150 °C, the added acetyl groups might cleave off ("de-acetylation") and by that release sorption sites for water. This would increase the moisture uptake of the modified wood. In this study, the impact of hot-pressing at 150 °C on the stability of acetylated beech veneers and LVL was investigated. Fourier transform infrared (FTIR) spectroscopy showed that the chemical composition of acetylated veneers seemed to be unaffected after the heat treatment. Dynamic vapor sorption (DVS) analysis and long-term storing over saturated salt-solutions in miniature climate chambers, indicated no de-acetylation on the basis of negligible changes in wood-water interactions. The number of hydroxyl groups of heat-treated acetylated samples was similar to that of not heat-treated ones, indicating the persistence of the effects of acetylation. By the present study, a certain resilience of acetylated wood towards elevated temperature, like it may occur during hot-pressing of acetylated veneers, became apparent and illustrated the thermal stability of this chemical modification approach. [ABSTRACT FROM AUTHOR]

The combination of different wood-modification technologies to obtain improved performance is increasingly receiving attention in research. In this study, Scots pine (Pinus sylvestris) sapwood was impregnated with furfuryl alcohol (FFA) in pure aqueous 20, 40, and 60% solution strength without adding any catalyst. In a second step, the FFA was polymerized while simultaneously performing thermal modification in a closed system at 130, 150, or 180 °C. After leaching and ageing tests, the nine different combinations were tested in use class 4 applications (in contact with or very close to the ground and frequently wet) according to CEN/TS 15083-2 (2005) decay laboratory test. It was noted that even the minimum-intensity combination of 20% FFA at 130 °C resulted in maximum durability class (DC) 1 performance. On the contrary, DC 4 was assigned to thermally modified control samples, even at the maximum intensity of thermal modification. Similarly, for FFA modifications, previous research has suggested that an uptake of 35% solution strength is required to obtain an adequate durability performance in use class 4 applications. High levels of resistance against termites were also noted by corresponding termite lab tests. Moisture studies showed the combined treatments resulted in improved stability and reduced moisture uptakes. Thus, the results obtained by this study revealed synergistic performance effects, which originate from the combined thermo-chemical modification approach, and which were higher than simple accumulation of the individual performance of purely thermally or chemically modified wood. Thus, the presented findings have provided positive implications for industrial applications of thermo-chemical modification techniques and offers an array of new research opportunities. [ABSTRACT FROM AUTHOR]

The application of tree of heaven (Ailanthus altissima (Mill.) Swingle) is constrained by its poor durability and dimensional stability. Despite exhibiting promising physical and mechanical properties comparable to ash wood (Fraxinus excelsior L.), it is regarded as an invasive species and receives limited attention in wood property enhancement research. This study subjected tree of heaven to heat treatment at 180 °C and 200 °C to investigate its sorption characteristics using dynamic vapor sorption tests. The results revealed a 13% reduction in equilibrium moisture content at 95% relative humidity and 25 °C after thermal modification at 180 °C and a 25% reduction after thermal modification at 200 °C. Increasing the treatment temperature lowered the moisture content ratio to 0.76 and shortened the conditioning time by up to 10%. The highest hysteresis, ranging from 3.39% to 3.88%, was observed at 70% relative humidity. [ABSTRACT FROM AUTHOR]

Wood modification with thermosetting resins results in improved dimensional stability and durability. However, the treatment does not enhance fire resistance. To address this, Scots pine sapwood (Pinus sylvestris L.) was impregnated with thermosetting resins such as 1,3-dimethylol-4,5-dihydroxyethyleneurea, phenol-formaldehyde resin and melamine-formaldehyde resin, along with a phosphorus polyol as the flame retardant. Both weight percent gain and cell wall bulking were measured to investigate the deposition of resin and phosphorus polyol. Fire resistance was assessed through thermogravimetric analysis, Bunsen burner test and mass loss calorimeter. The inclusion of a phosphate polyol improved thermal stability, reduced flammability and heat release. Melamine-formaldehyde resin combined with phosphorus polyol demonstrated self-extinguishing capability with the heat release rate comparable to non-combustible materials inside 400 s. Moreover, the total heat release within 600 s shows an 84% reduction compared to untreated wood. [ABSTRACT FROM AUTHOR]

Wood is a commonly used material in construction. However, its application is limited due to its flammability. Modification of wood with phenol-formaldehyde resin (PF) can improve many of its inherent properties, but does not upgrade its fire resistance. To address this issue, Scots pine (Pinus sylvestris L.) sapwood was impregnated with a low molecular weight PF resin and phosphate-based flame retardant (FR). The fixation of the FR was evaluated using an accelerated ageing procedureaccording to the EN 84 standard (CEN 2020: EN 84 (2020) Wood Preservatives – Accelerated Ageing of Treated Wood Prior to Biological Testing - Leaching Procedure (Brussels, Belgium: European Committee for Standardization)). The thermal stability, flammability and heat release of treated wood were analysed before and after a leaching test. The combination of PF and FR treatment significantly improved the thermal stability, reduced flammability and decreased the heat release, as evidenced by a 82% and 86% reduction in total heat release within 600 s compared to untreated wood and pure PF-treated wood, respectively. The improved fire performance was also observed for the leached wood. [ABSTRACT FROM AUTHOR]

The durability against decay organisms is an essential material property for wood in outdoor use. A jack of all trades method for above-ground wood durability testing has been sought for decades, but until now no method has found its way into European standardization. The method of choice shall be applicable for untreated and treated wood—ideally also for wood composites. It shall further be reproducible, objective, fast, easy, and inexpensive. Finally, it shall provide high predictive power. This study was aimed at a review of results and practical experience with the Bundle test method which could serve as a standard procedure for above-ground field tests of wood-based materials. The method allows for water-trapping, creates a moderate moisture-induced decay risk typical for UC 3 situations, and was found applicable for a wide range of wood materials. The method allows for rapid infestation and failure of non-durable reference species within five years in Central Europe. Based on results from Bundle tests with different modifications and performed at different locations, a guideline has been developed. The method is recommended as a suitable tool for determining the durability of various wood-based materials including modified and preservative-treated wood and can provide data for durability classification. [ABSTRACT FROM AUTHOR]

Chemical and thermo-chemical modification processes were applied to European beech wood to make it applicable for interior applications which place high demands on aesthetics, hygrothermal and water resistance performance. In particular, the use of modified wood in kitchen tools was foreseen. Impregnation modification with a 20% DMDHEU solution, thermal modification and a combined approach of thermo-chemical modification were compared. All modification processes caused a darkening that for the high modification intensities became close to the aesthetics of some of the most renowned tropical hardwood species. The higher the modification intensity, the higher the improvement. In particular, chemical and thermo-chemical modification processes significantly decreased the liquid water uptake. As regards the mechanical performances while stiffness and strength did not change abruptly and hardness increased, the resistance towards dynamic impacts significantly decreased with every kind of modification process. Thermo-chemical modifications resulted to be an interesting way to improve most of the physical properties of wood with outstanding behaviour in terms of colour appearance and reduction of water uptake in wet environments. An increased brittleness is the weakest point for foreseen fields of application. [ABSTRACT FROM AUTHOR]

Scots pine sapwood (Pinus sylvestris L.) was modified with an aqueous solution of sorbitol and citric acid (SorCA) and a commercial phosphorus-based fire-retardant (FR). The aim of this study was to assess whether the fire behavior can be improved when the SorCA solution is supplemented by an FR and if this effect is resistant to leaching. The fire behavior of modified wood was investigated by a Bunsen burner ignition test, mass loss calorimetry (MLC) and thermogravimetric analysis (TGA). The results demonstrated a significantly improved fire-retardancy based on a decreased burning rate and a reduced mass loss in the Bunsen burner test. Also, the induced formation of a protective char barrier facilitated by the addition of a FR, reduced the heat release rate and delayed the ignition. The fire-retardant effect was still observed, to the less extent, after a cold-water (EN 84 2020) leaching of the specimens. [ABSTRACT FROM AUTHOR]

Novel approaches for a non-toxic protection of timber have been investigated and referred to as "wood modification". Especially, chemical impregnation modifications show promising opportunities to improve a wide range of wood properties. Yet, most of the available treatments resort to technically synthesized oil-based chemicals. Therefore, new ways of wood modification based on citric acid (CA) and bio-based low-molecular-weight polyols (CA-PO) – both originating from renewable resources – are under test and appear to be a promising alternative to available processes. The mode of action is expected to be a combination of both a cell wall bulking, and a cross-linking between CA-PO polyesters and wood cell wall polymers. However, the treatment process requires optimization with regard to the impregnation system and parameters for an industrial scale implementation. This paper provides a general background about CA-based solid wood treatment and its effects on the characteristics of wood. Moreover, it discusses current developments in this area and points out existing research gaps, with one focus being the process of development on an industrial scale. [ABSTRACT FROM AUTHOR]

Recent studies showed treatments with sorbitol and citric acid (SorCA) to significantly improve the dimensional stability and biological durability of wood. The industrialization of this process requires a quality control (QC) method to determine if the fixated chemicals are homogenously distributed within the piece of wood, which is essential for uniform material performance. Therefore, the objective of this work was to evaluate the use of common electromagnetic radiation-based methods to determine the degree of modification in SorCA-treated wood. Both Fourier transform infrared (FTIR) spectroscopy and near-infrared (NIR) spectroscopy have been used to create rough calibrations for the weight percent gain (WPG) prediction models. The FTIR measurements resulted in a high linear correlation between the band area ratio (BAR) and the WPG (R2 = 0.93). Additionally, a partial least square (PLS) regression of NIR spectroscopic data resulted in a model with a high prediction power (R2 = 0.83). Furthermore, X-ray density profiling emerged as a simple alternative for the QC by showing a gradient of modification chemicals inside the sample and differences in chemical uptake between earlywood and latewood. Overall, it can be concluded that the results from FTIR, NIR and X-ray densitometry can serve as indicators of impregnation chemical distribution in SorCA-modified wood. [ABSTRACT FROM AUTHOR]