Abstract
Non-fortified, non-modified tannin extracts, rather than chemically-modified tannin adhesives intermediates, can be used as effectively to produce excellent exterior grade particleoboard at fast pressing times of industrial singnificance, with considerable advantages in both handling and cost. This can be achieved by simple pH-controlled reactivity adjustments of the tannin extract in the glue mix. This new concept is shown to be applicable to all types of polyflavanoid tannin extracts: Pine, mimosa, pecan, quebracho, and gambier tannin extracts are compared as regards their performance and capabilities. The new concept applied to the faster-reacting tannins, such as pine tannin and pecan tannin extracts, is shown to produce fast hot-pressing rates and excellent high moisture content tolerances which are undreamed of for the slower-reacting tannins, modified or non-modified, which are traditionally associated with thermosetting wood adhesives. Industrially used techniques to control well viscosity and pot-life of the glue-mixes of accelerated tannin adhesives are also presented.
Zusammenfassung
Nicht-verstärkte und unmodifizierte Tanninextrakte können anstelle von chemisch modifizierten Tanninen zur Herstellung hochwertiger Spanplatten für die Außenverwendung eingesetzt werden. Sie ermöglichen kurze Preßzeiten und bieten sowohl auf der Kostenseite als auch in der Handhabung bedeutende Vorteile. Dies kann durch einfache pH-Steuerung der Reaktivität des Tanninenextraktes im Klebstoffgemisch erreicht werden. Das neue Konzept konnte für alle Typen von Polyflavonid-Tanninen bestätigt werden. So wurden Tanninextrakte aus Kiefern, Mimosa, Hickory, Quebracho und Gambir (Katechu) auf ihre Verwertbarkeit untersucht. Mit den schnell-reagierenden Tanninen aus Kiefern und Hickory konnten sehr kurze Preßzeiten und ausgezeichnete Feuchtetoleranzen gegenüber den Spänen erzielt werden, die bisher bei herkömmlichen, langsam-reagierenden Tanninklebern unvorstellbar waren. Weiterhin werden industrielle Verfahren zur Kontrolle der Viskosität und der Topfzeit der Klebstoffgemische aus diesen beschleunigt reagierenden Harzen vorgestellt.
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References
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Dedicated to Prof. Dr. D. Fengel on occasion of his retirement
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Pizzi, A., Stephanou, A. Fast vs. slow-reacting non-modified tannin extracts for exterior particleboard adhesives. Holz als Roh-und Werkstoff 52, 218–222 (1994). https://doi.org/10.1007/BF02619095
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DOI: https://doi.org/10.1007/BF02619095