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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 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]

Glyoxal-based condensation resins like 1,3-dimethylol-4,5-dihydroxyethyleneurea (DMDHEU) have been used to modify wood and improve its resistance against decaying fungi. High biological durability of DMDHEU-treated wood has already been confirmed in laboratory and field tests in the past. However, the modes of protective action behind an improved decay resistance are not fully understood yet. Furthermore, it is questionable how the use of formaldehyde-poor N-methylol and formaldehyde-free N-methyl compounds instead of DMDHEU affects the moisture behavior and durability, respectively. In this study, wood blocks were treated with N-methylol (DMDHEU, methylated DMDHEU) and N-methyl compounds (1,3-dimethyl-4,5-dihydroxyethyleneurea; DMeDHEU). Untreated and modified specimens were exposed to different moisture regimes and wood-destroying fungi in order to study the indicators that control changes in the wetting ability and decay resistance. Both N-methylol and N-methyl compounds decreased the water uptake and release and increased the durability of Scots pine sapwood from 'not durable' (DC 5) to 'very durable to durable' (DC 1–2). However, high fluctuations were observed in water uptake and release as well as mass loss (ML) caused by fungal decay, when modified specimens were tested without passing through a cold-water leaching. Consequently, a significant effect of the leaching procedure according to EN 84 on the durability classification could be established. The latter appeared more pronounced for treatments with N-methyl compounds compared to N-methylol compounds. Finally, wetting ability (kwa) and resistance indicating factors (kinh) enabled a forecast of high biological durability for both treatments with N-methylol and N-methyl compounds under real service life conditions. [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]

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Durability-based designs with timber require reliable information about the wood properties and how they affect its performance under variable exposure conditions. This study aimed at utilizing a material resistance model (Part 2 of this publication) based on a dose–response approach for predicting the relative decay rates in above-ground situations. Laboratory and field test data were, for the first time, surveyed globally and used to determine material-specific resistance dose values, which were correlated to decay rates. In addition, laboratory indicators were used to adapt the material resistance model to in-ground exposure. The relationship between decay rates in- and above-ground, the predictive power of laboratory indicators to predict such decay rates, and a method for implementing both in a service life prediction tool, were established based on 195 hardwoods, 29 softwoods, 19 modified timbers, and 41 preservative-treated timbers. [ABSTRACT FROM AUTHOR]

Service life planning with timber requires reliable models for quantifying the effects of exposure-related parameters and the material-inherent resistance of wood against biotic agents. The Meyer-Veltrup model was the first attempt to account for inherent protective properties and the wetting ability of wood to quantify resistance of wood in a quantitative manner. Based on test data on brown, white, and soft rot as well as moisture dynamics, the decay rates of different untreated wood species were predicted relative to the reference species of Norway spruce (Picea abies). The present study aimed to validate and optimize the resistance model for a wider range of wood species including very durable species, thermally and chemically modified wood, and preservative treated wood. The general model structure was shown to also be suitable for highly durable materials, but previously defined maximum thresholds had to be adjusted (i.e., maximum values of factors accounting for wetting ability and inherent protective properties) to 18 instead of 5 compared to Norway spruce. As expected, both the enlarged span in durability and the use of numerous and partly very divergent data sources (i.e., test methods, test locations, and types of data presentation) led to a decrease in the predictive power of the model compared to the original. In addition to the need to enlarge the database quantity and improve its quality, in particular for treated wood, it might be advantageous to use separate models for untreated and treated wood as long as the effect of additional impact variables (e.g., treatment quality) can be accounted for. Nevertheless, the adapted Meyer-Veltrup model will serve as an instrument to quantify material resistance for a wide range of wood-based materials as an input for comprehensive service life prediction software. [ABSTRACT FROM AUTHOR]

The service life of wood in outdoor use under humid conditions is mainly determined by its material resistance and the exposure situation. Different standards such as EN 350 (2016) point on the relevance of wood's resistance against moisture for its expected service life. Recently, different standardized but also numerous nonstandardized methods were suggested to test the water permeability of wooden materials. In the context of this study, different European-grown soft- and hardwoods, tropical hardwoods, modified wood and wood treated with water- and oil-borne preservatives were subjected to floating and submersion tests according to CEN/TS 16818 (2018) and different short-term water uptake and release tests. Moisture performance data from field tests with the same materials were analyzed and used to assess the predictive power of different laboratory moisture indicators. The moisture characteristics suggested by CEN/TS 16818 (2018)—rm168 (residual moisture content after water uptake and release processes) and res312 (residue as a percentage of the absorbed moisture)—showed the little potential to predict the outdoor moisture performance of the tested materials. In contrast, the mean moisture content during absorption and desorption (MCmean) predicted well the outdoor moisture performance of the materials under test. Short-term water uptake and release of small specimens also showed high predictive power. [ABSTRACT FROM AUTHOR]