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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]

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]

Haematoxylum campechianum is most prevalently used as dyewood; its use for furniture, flooring, or fencing is only of regional importance, which might be due to lacking data about its technological properties. Therefore, small specimens were cut from H. campechianum stems from plantations in the lowlands of the Usumacinta delta in Mexico. The latter were subjected to laboratory decay and moisture studies. Water vapour sorption, liquid water uptake, and swelling of H. campechianum appeared much lower in comparison with most European grown wood species and similar to tropical hardwoods such as Tectona grandis. After removal of water-soluble ingredients, water vapour sorption of H. campechianum specimens further decreased, which assigned such ingredients a somewhat hydrophilic character. Mean mass losses (ML) due to decay by white, brown, and soft rot fungi in laboratory tests were <5%. On the basis of a dose-response model, wetting ability factors and ML values from decay tests predicted an outdoor performance similar to T. grandis and Intsia bijuga. Based on this preliminary property profile, H. campechianum can be recommended for both outdoor (e.g. fencing, outdoor decking, railing) and indoor applications (e.g. flooring, manufacturing of furniture, wall and ceiling panels, decoration artwork). [ABSTRACT FROM AUTHOR]

Bloodwood (Haematoxylum campechianum L.) native to Central America has been known as dye source since the prehistoric times by the Maya. Nowadays, bloodwood is increasingly used for plantations but its use for furniture, flooring, or fencing is only of regional importance. The reason is seen in lacking knowledge of its properties. To expand that knowledge, this Part 1 of the two-part study series investigated the anatomy and the discolouration due to leaching of heartwood of H. campechianum. Anatomical characteristics were described qualitatively and quantitively using scanning electron microscopy and X-ray micro-computed tomography. Detailed wood anatomical data are presented, together with numerical analyses of cell parameters. Apart from wood anatomy, colourimetric analyses were obtained after 10 leaching cycles. The colour change of the wood due to water exposure was determined measuring in CIE L*a*b* colour system. In addition, the extinction of the leachate was determined spectrophotometrically after each leaching cycle. The resulting colour change was evaluated according to colour change after each cycle. The most prominent change in colour was observed for the first cycle due to leaching. Because of the extensive leaching of extractives, further investigation might address the effect of leaching of water-soluble extractives on adhesion properties of bloodwood. [ABSTRACT FROM AUTHOR]

Citric acid together with sorbitol (SorCA) have been used to modify wood and improve its properties, such as dimensional stability and biological durability, which partly result from its swelling and sorption behavior. However, the underlying mechanism of water interaction with SorCA-treated wood is very complex and not fully understood. Previous research confirmed cell wall bulking and suggested cross-linking, however the extent of their contribution to moisture-induced changes has not been researched. This study investigated the effect of SorCA treatment on sorption properties of wood in the hygroscopic range (0–95% RH). Scots pine sapwood (Pinus sylvestris L.) was chemically modified with an aqueous SorCA solution at different treatment levels and measured by dynamic vapor sorption (DVS). The observed permanent increase in oven-dry dimensions did not result in a decreased swelling compared to untreated specimens. It was ascribed to the excessive expansion of cell wall matrix caused by a degradation of cell wall constituents by the acidic impregnation solution. However, a reduction in moisture content in comparison to untreated reference was detected. Present findings suggest that the SorCA polyester structure is altered after impregnation inside the wood and affects its sorption behavior by covalent bonding and, presumably, cross-linking with wood polymer constituents. [ABSTRACT FROM AUTHOR]

Chemical modification is increasing the durability of wood against biological deterioration. Usually, the effect of a new treatment on the durability of wood is screened in laboratory decay tests, where durability classes are assigned on the basis of the mass loss (ML) caused by degrading fungi. The aim of this study was to demonstrate how non-fixated chemicals in modified wood may affect fungal ML measurements and corresponding durability classification when wood samples are incubated under humid conditions for long periods. Wood blocks were treated with solutions of 1,3-dimethylol-4,5-dihydroxyethyleneurea (DMDHEU), methylated DMDHEU (mDMDHEU) and 1,3-dimethyl-4,5-dihydroxyethyleneurea (DMeDHEU) and subjected to consecutive cold-water leaching cycles. Significant amounts of non-fixated chemicals were removed from the wood by three leaching cycles and might lead to ML mistaken as response of fungal decay. Consequently, the treated material was assigned erroneously by up to four durability classes (DC) worse than material which did not include leachable, non-fixated chemicals. Thus, for a reliable durability classification of chemically modified wood, prolonged leaching procedures are recommended to assure that the measured ML is entirely attributed to fungal decay. [ABSTRACT FROM AUTHOR]

Cyclic N-methylol compounds have been used for cell wall impregnation modifications of wood. Besides an improved decay resistance and dimensional stability, the modifications resulted in a decrease of wood's dynamic strength properties. However, the mechanisms behind a significant loss in dynamic strength are not fully understood yet. In this study, wood blocks were treated with the N-methylol compounds 1,3-dimethylol-4,5-dihydroxyethyleneurea (DMDHEU) and methylated DMDHEU (mDMDHEU) and the N-methyl compound 1,3-dimethyl-4,5-dihydroxy-ethyleneurea (DMeDHEU). In order to study the factors that control the changes of wood performance under dynamic loads, single (impact bending strength, IBS) and multiple dynamic impact (resistance to impact milling, RIM) tests were applied. It became evident, that reductions in IBS and RIM increased with increasing solid content, formaldehyde content and catalyst concentration of the impregnation solutions, but were not affected by a cold-water leaching. Differences in structural integrity of wood modified with N-methylol and N-methyl compounds were more pronounced than those of IBS. Therefore, RIM appeared more sensitive to changes on cellular level, as a higher degree of co-condensation of the N-methylol compounds with cell wall polymers was expected in comparison with the N-methyl compound. [ABSTRACT FROM AUTHOR]

Chemical wood modification has been used to modify wood and improve its decay resistance. However, the mode of protective action is still not fully understood. Occasionally, outdoor products made from chemically modified timber (CMT) show internal decay while their outer shell remains intact. Hence, it was hypothesized that wood decay fungi may grow through CMT without losing their capability to degrade non-modified wood. This study aimed at developing a laboratory test set-up to investigate (1) whether decay fungi grow through CMT and (2) retain their ability to degrade non-modified wood. Acetylated and 1,3-dimethylol-4,5-dihydroxyethyleneurea (DMDHEU) treated wood were used in decay tests with modified 'mantle specimens' and untreated 'core dowels'. It became evident that white rot (Trametes versicolor), brown rot (Coniophora puteana) and soft rot fungi can grow through CMT without losing their ability to degrade untreated wood. Consequently, full volume impregnation of wood with the modifying agent is required to achieve complete protection of wooden products. In decay tests with DMDHEU treated specimens, significant amounts of apparently non-fixated DMDHEU were translocated from modified mantle specimens to untreated wood cores. A diffusion-driven transport of nitrogen and DMDHEU seemed to be responsible for mass translocation during decay testing. [ABSTRACT FROM AUTHOR]

The efficacy of chemical wood modification is closely related to the permeability of the wood species and the cell wall deposition of the reagent, causing a permanent swelling ("bulking effect"). This study aimed to analyze how rubberwood (Hevea brasiliensis Müll. Arg.) and English oak (Quercus robur L.) may be affected by chemical wood modification, although they are known to show either variations in permeability or being less permeable. Thin clear veneers were treated with 1,3-dimethylol-4,5- dihydroxyethyleneurea (DMDHEU) which resulted in significantly reduced moisture-induced swelling and increased the resistance to static and dynamic indentation loads. The results evidenced significantly lower liquid uptakes in English oak compared to rubberwood, which directly affected the weight percent gains (WPGs) and restricted the range for potential improvements of the material properties. Surprisingly, rubberwood showed a lower cell wall bulking, which, in comparison with English oak, indicated less DMDHEU monomers entering the cell walls and rather being located in the cell lumens. Atypical for treatments with cell wall penetration chemicals, no further decrease in maximum swelling (SM) was detected with increasing bulking in rubberwood specimens. English oak showed higher variations in DMDHEU distribution within treated veneers and between earlywood and latewood areas, effecting a less homogeneous performance. [ABSTRACT FROM AUTHOR]

As wet wood is prone to degradation by wood-destroying fungi, the monitoring of the moisture content (MC) of wood can be used to quantify the risk of fungal infestation. Fungal decay alters the sorption and electrical conductivity of wood, and thus the goal of the present study was to measure the electrical resistance (R) of wood after fungal decay as a function of MC. Scots pine sapwood (Pinus sylvestris L.) and European beech wood (Fagus sylvatica L.) were submitted to decay by Coniophora puteana (a brown rot fungus, BR) and Trametes versicolor (a white rot fungus, WR) and the mass loss (ML) due to the fungal metabolism was measured. The sorption isotherms were determined by dynamic vapor sorption (DVS), and comparative gravimetric- and R-based MC measurements were conducted. BR and WR reduced the sorption of wood and lowered its R in the hygroscopic range, where the decay led to an overestimation of wood MC, while wood MC was dramatically underestimated above fiber saturation (FS). Specimens showed an MC well above FS if measured directly after harvesting and an increased R compared to undecayed wood at a given MC. BR-decayed specimens were dried and rewetted, and such specimens showed an elevated R beyond FS. In the case of WR-decayed wood, the R was reduced at a given MC. [ABSTRACT FROM AUTHOR]