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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]

This study demonstrates acetylation with acetic anhydride, one of the few industrial wood modification techniques on the market, to increase the dimensional stability and durability of laminated veneer lumber (LVL) made from beech wood (Fagus sylvatica L.). After being acetylated, veneers were hot-bonded to LVL using phenol-formaldehyde resin (PF) or phenol-resorcinol-formaldehyde resin (PRF). The bonding performance (bonding shear strength (BSS) and wood failure (WF)) was tested under the following three conditions: 20°C and 65% RH, water immersion, and rigorous boiling-drying-boiling cycle. Additionally, using the same specimen sizes on a second sample set, the moisture content (MC) and dimensional stability were determined. Results indicate that the PRF resin provided the strongest bonding performance on acetylated LVL and references. Acetylated LVL had higher BSS in wet conditions than untreated controls, especially after boiling in water, which could be attributed to less wood-water interaction at the cell wall level after acetylation. [ABSTRACT FROM AUTHOR]