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The modification by impregnation of veneers for the production of plywood with phenol–formaldehyde resins is a well-known method to improve the dimensional stability and fungal resistance. Because phenol is obtained from non-renewable resources, finding substitutes has been a topic of research. Due to similarities in chemical structure and availability, lignin cleavage products present a promising alternative. In this study, microwave-assisted pyrolysis cleavage products of softwood kraft lignin have been used to substitute 30% of phenol in phenol–formaldehyde resins. Scots pine veneers were impregnated with the resin, and five-layered plywoods were produced. The influence of the substitution on the bonding quality, the dimensional stability, and the leaching of resin from the specimens were studied. Mechanical properties such as the bending strength, the modulus of elasticity, as well as the dynamic impact bending strength of the plywood were analyzed. Both treatments led to plywood with good dimensional stability, and the resin was stable against leaching. The substitution of phenol with lignin cleavage products led to slightly reduced brittleness of the specimens compared to pure phenol–formaldehyde resin. This study presents a method to reduce the use of non-renewable resources, increase the use of currently underutilized lignin sources, and produce plywood with promising properties for exterior applications. [ABSTRACT FROM AUTHOR]

Acetylation of wood with acetic anhydride reduces the wood–moisture interaction, improves the dimensional stability and resistance against biodegradation. However, the adhesive bonding is affected by the modification, which is crucial to manufacture engineered wood products, such as laminated veneer lumber (LVL). In this study we report the bonding of 8-layered acetylated beech (Fagus sylvatica L.) LVL boards to 2-layered LVL beams. The beams were glued together at room temperature adding three common load-bearing construction adhesives: melamine–urea–formaldehyde (MUF), phenol–resorcinol–formaldehyde (PRF), and one-component polyurethane (PUR). The bonding performance was tested by assessing its dry and wet tensile shear strength (TSS) and wood failure percentage (WF). Also evaluated were the material's density and moisture content (MC). The surface was characterized prior to bonding by its pH, roughness, and contact angle (CA). The adhesive penetration was observed by fluorescence microscopy. Aside from MUF, applying PRF and PUR adhesives achieved good bonding performance on acetylated LVL and references. Acetylated LVL displayed a more hydrophobic behaviour, a higher pH, a somewhat smoother surface, and an increased density. [ABSTRACT FROM AUTHOR]

Experiments on finger-jointing acetylated beech (Fagus sylvatica L.) laminated veneer lumber (LVL) have been made. The specimens were examined on its wet tensile shear strength (TSS) using three adhesives, including phenol resorcinol formaldehyde (PRF), one-component polyurethane (PUR) (without primer), and melamine urea formaldehyde (MUF). Contact angles (CA) of uncured and drop-applied MUF, PRF, and PUR adhesives on freshly cut finger-joints were evaluated. Surface roughness was measured using a laser-scanning-microscope (LSM). Results showed that PRF bonded acetylated specimens had highest wet TSS, followed by specimens with PUR bonding. MUF performed poorly, which was most likely caused by its inadequate water resistance and changes in chemical reactions due to remaining acetic acid. Acetylated finger-joints had a topography similar to untreated joints. Moreover, CA were just barely lower for MUF and PRF on acetylated wood than on untreated references. [ABSTRACT FROM AUTHOR]

The overall aim of this study was to investigate the durability of acetylated beech (Fagus sylvatica L.) laminated veneer lumber (LVL) against wood-destroying basidiomycetes. The secondary objective was to test whether the specimen size affects the mass loss and durability assessment of wood-material under test. The durability test was based on the pre-standard prEN 113-3. Six materials (acetylated beech LVL, untreated beech LVL, beech solid wood, pine sapwood (Pinus sylvestris L.), larch (Larix decidua Mill.) 3-layer slab, larch solid wood) were tested using three specimen geometry designs (50 × 25 × 15 mm3 as well as 50 × 50 × 19 mm3 with and without sealed edges) against Coniophora puteana, Rhodonia placenta, Gloeophyllum trabeum, Trametes versicolor, and Pleurotus ostreatus. The durability assessment was made using the arithmetic mean and median percentage mass loss (ML), the relative ML (x-values), and the decay susceptibility index (DSI). It was found that mass loss was affected by the test fungus, the material, and the specimen size and design, with the latter being the most essential factor in this study. In addition, the assessment parameter had a significant effect on the durability classification. Furthermore, small differences in ML resulted in different durability classes (DC) in some cases, whereas large differences in ML did not. However, acetylated beech LVL was always considerably durable (DC 1) against all tested fungi independent of the specimen design and durability assessment method. [ABSTRACT FROM AUTHOR]