Abstract
The oriented strandboard (OSB) has less dimensional stability than plywood, but they are competitive panels and have been used for similar ends. The wood-water relation variables, such as thickness swelling and water absorption, express this OSB dimensional instability and can be explained by two main factors: wood hygroscopicity and imposed hot-pressing stresses. The objective of this present paper was to propose a thermal post-treatment as a method to improve OSB dimensional stability by decreasing wood hygroscopicity and releasing hot-pressing stress. OSB panels from Pinus taedawood were produced in laboratory, and their characteristics were: single layer, 0.8 g/cm3; 8% phenolic resin and without wax. The OSB panels were treated in a laboratory press at 250 °C for about 4, 7 and 10 minutes. The wood-water relation variables, thickness swelling (TS), water absorption (WA), equilibrium moisture content (EMC) and springback or permanent thickness swelling (PTS) were determined and compared with untreated panels. The results showed that the proposed thermal treatment was effective to reduce TS, EMC and PTS, but didn’t affect WA which was affected by panel density reduction. The longer the treatment the higher the dimensional stability, and panel weight loss could be used as predictive variable for the efficiency of the treatment.
Zusammenfassung
OSB hat zwar eine geringere Dimensionsstabilität als Sperrholz, aber dennoch ist es für viele Verwendungen ein wettbewerbsfähiges Produkt. Parameter wie Dickenquellung und Wasseraufnahme verdeutlichen die Dimensionsstabilität von OSB. Diese lässt sich durch zwei Hauptfaktoren erklären: zum einen durch die Hygroskopizität von Holz und zum anderen durch die beim Heisspressen eingebrachten Spannungen. Ziel dieser Veröffentlichung ist es, eine Wärmenachbehandlung als ein Verfahren zur Verbesserung der Dimensionsstabilität von OSB vorzuschlagen, welche die Hygroskopizität des Holzes verringert und die Spannungen durch das Heisspressen abbaut. Labor-OSB-Platten aus Pinus taeda Holz wurden mit folgenden Eigenschaften hergestellt: einschichtig, 0,8 g/cm3; 8% Phenolharz, kein Wachs. Diese Platten wurden in einer Laborpresse bei 250 °C für ungefähr 4, 7 und 10 Minuten behandelt. Die Parameter Dickenquellung (TS), Wasseraufnahme (WA), Gleichgewichtsfeuchte (EMC) sowie reversible und irreversible Dickenquellung (PTS) wurden bestimmt und mit den Werten von unbehandelten Platten verglichen. Die Ergebnisse zeigten, dass mit der Wärmebehandlung zwar die Parameter TS, EMC und PTS verringert werden konnten, WA jedoch davon nicht beeinflusst wurde. Diese wird durch die abnehmende Rohdichte der Platte beeinflusst. Mit zunehmender Dauer der Wärmebehandlung verbesserte sich die Dimensionsstabilität. Der Masseverlust der Platten ist ein gutes Mass für die Wirksamkeit der Behandlung.
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Del Menezzi, C., Tomaselli, I. Contact thermal post-treatment of oriented strandboard to improve dimensional stability: A preliminary study. Holz Roh Werkst 64, 212–217 (2006). https://doi.org/10.1007/s00107-005-0052-1
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DOI: https://doi.org/10.1007/s00107-005-0052-1