Abstract
Alkyl ketene dimer (AKD) was used as a hydrophobic agent for PF-bonded particleboards. In contrast to conventionally used paraffin, AKD can be covalently bonded to the chip surface by esterification with wood hydroxyl groups. FTIR analyses before and after toluene extractions indicated that only a small amount of the applied AKD is chemically bonded. Wettability studies on veneer strips suggested that particularly the bonded AKD accounts for the surface hydrophobicity.
A subsequent spraying of AKD and PF resin on the chips that were pressed for 15, 30, and 60 s mm-1 (Process 1) did not result in decreased thickness swelling and water uptake as compared to the control boards. In Process 2, chips were cured (130 °C/6, 12, 24 h) prior to pressing (15 s mm-1) which did not impart significant hydrophobicity either. The low efficacy of AKD as hydrophobic agent in Process 1 is attributed to the hydrolysis of AKD by water vapor during pressing. The low hydrophobic effect of AKD in Process 2 is ascribed to a saponification of esters between AKD and wood hydroxyl groups by the alkaline PF resin.
Zusammenfassung
Alkylketendimer (AKD) wurde als Hydrophobierungsmittel für PF gebundene Spanplatten verwendet. Im Gegensatz zu konventionell eingesetztem Paraffin kann AKD die Hydroxylgruppen des Holzes verestern und so auf der Spanoberfläche fixiert werden. FTIR Analysen vor und nach Toluolextraktionen ergaben, dass lediglich eine geringe Menge des aufgebrachten AKD kovalent gebunden vorlag. Untersuchungen der Benetzbarkeit von Furnierproben zeigten, dass hautsächlich das gebundene AKD die Hydrophobierung bewirkt.
Das schrittweise Aufsprühen von AKD und PF Leim auf die Späne, die nachfolgend bei 15, 30 und 60 s mm-1 verpresst wurden (Prozess 1), ergab keine Verringerung der Dickenquellung und Wasseraufnahme im Vergleich zu den Kontrollplatten. Im zweiten Prozess wurden die mit AKD beaufschlagten Späne vor dem Pressen (15 s mm-1) getrocknet (130 °C/6, 12, 24 h), was ebenfalls zu keiner nennenswerten Hydrophobierung der Platten führte. Die geringe Wirksamkeit von AKD im ersten Prozess wird auf eine Hydrolyse des AKD durch Wasserdampf während des Pressens zurückgeführt. Die geringe Hydrophobierung im zweiten Prozess basiert vermutlich auf einer Verseifung der Ester zwischen AKD und den Hydroxylgruppen des Holzes durch den alkalischen PF Leim.
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Hundhausen, U., Militz, H. & Mai, C. PF-bonded particleboards from AKD-modified chips . Eur. J. Wood Prod. 68, 143–149 (2010). https://doi.org/10.1007/s00107-009-0358-5
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DOI: https://doi.org/10.1007/s00107-009-0358-5