Modification of beech veneers with N-methylol-melamine compounds for the production of plywood

Abstract

Rotary cut beech (Fagus sylvatica L.) veneers were treated with two formulations based on N -methylolmelamine (NMM): (1) NMM solution (NMM-1, 10% solid content), (2) fatty acid modified NMM dispersions containing paraffin (with an aluminium salt as catalyst, mNMM-2, 5% solid content). Five treated veneers were bonded with phenol formaldehyde (PF) adhesive to produce plywood in two different processes.The plywood treated with NMM-1 displayed increased shear strength in comparison to the controls, whereas the treatments with mNMM-2 diminished the shear strength of the plywood to different extents. Treatment with NMM-1 also enhanced other mechanical properties of the plywood as compared to water-treated control plywood such as Brinell hardness, modulus of elasticity and bending strength. The plywood treated with mNMM-2 showed only slight changes of these mechanical properties compared to the control plywood.The plywood specimens were subjected to cyclic water submersion and oven-drying. The treatment with mNMM-2 caused greater reduction in water uptake and thickness swelling than NMM-1; the degree of delamination depended on the process. The plywood treated with NMM-1 exhibited lower equilibrium moisture content than that treated with mNMM-2. The formaldehyde emission of NMM-1-treated plywood was much higher than that of the control and the mNMM-2-treated plywood. Das mit NMM-1 behandelte Sperrholz wies im Vergleich zu den Kontrollen eine erhöhte Scherfestigkeit auf, wäh-rend die Behandlung mit mNMM-2 die Scherfestigkeit des Sperrholzes in unterschiedlichem Ausmaß reduzierte. Die Behandlung mit NMM-1 erhöhte außerdem andere mechanische Eigenschaften wie die Brinellhärte, den Elastizitäts-modul und die Biegefestigkeit. Das mit mNMM-2 behandelte Sperrholz zeigte im Vergleich zum Kontrollsperrholz nur leichte Veränderungen der genannten mechanischen Eigenschaften.Die Sperrholzproben wurden einem zyklischen Test bestehend aus Tauchen in Wasser und Ofentrocknung unterzogen. Die Behandlung mit mNMM-2 verursachte eine stärke-re Abnahme der Wasseraufnahme und der Dickenquellung als NMM-1; der Grad der Delaminierung war dabei vom Prozess abhängig. Das mit NMM-1 behandelte Sperrholz zeigte eine niedrigere Gleichgewichtsfeuchte als das mit mNMM-2 behandelte. Die Formaldehydabgabe von NMM-1-behandeltem Sperrholz war sehr viel höher als die der Kontrolle und des mNMM-2-behandelten Sperrholzes. Eur.

Optimization of reaction parameters and characterization of glyoxal-treated poplar sapwood

“…After modification with glyoxal, the WU was significantly reduced and decreased with increasing curing temperature. This phenomenon may be explained by the higher condensation degree of glyoxal; thus, much network was formed, and in addition, at higher curing temperature, more cross-linking may be formed, leading to lower WU (Trinh et al 2012). When the temperature was higher than 120°C, the changing trend was not obvious, which was similar to the ASE shown in Fig.…”

“…Clearly, glyoxal modification significantly affected the surface of the modified wood and greatly improved the hydrophobic ability on the wood surface. The increased contact angle may be attributed to the less hydrophilic hydroxyl and less porous wood surface because of the cross-linking reaction and filling effect of the curing hydrophobic glyoxal (Trinh et al 2012). With the addition of the glycol, the contact angle further increased, indicating that the addition of glycol improved the hydrophobic ability of the modified wood.…”

Plywood made from plasma-treated veneers: melamine uptake, dimensional stability, and mechanical properties

“…4b, 5b, 6b, 7b), since all variants show equal weight loss, attributed to accessory material of wood. differences between parallel and perpendicular test direction, an observation that has already been reported in several studies [29,34]. For compressive strength, only marginal differences could be observed between reference 0 , reference and plasma samples independent of grain direction of the outer layers (whereas ''reference 0 '' shows the highest value in perpendicular direction and ''plasma'' in parallel direction, respectively).…”

“…Trinh et al tested the bending strength of five-layer plywood samples made from vacuum-impregnated beech veneers with melamine resin (solution solid content 5-10%) and bonded with phenol formaldehyde (PF) resin [34]. Dieste et al presented similar results of plywood samples made from DMDHEU vacuum-impregnated beech veneers [39].…”

The influence of curing conditions on the chemical distribution in wood modified with thermosetting resins

“…In commercial processes for the production of resin-treated plywood, veneers are pre-dried after impregnation. Afterwards, they are either cured at higher temperatures in the veneer dryer (Stamm and Seborg 1942) or in a combined step in the hot press simultaneously with curing the glue (Wepner 2006;Dieste et al 2009;Trinh et al 2012). Varying a number of manufacturing variables, Millett et al (1943) found that drastic drying ([ca.…”