Summary
Condensed tannins such as wattle (Mimosa) extract can be partially modified, through hydrolysis of a benzyl ether link and consequent opening of the flavonoid heterocyclic ring, through sulphitation. The introduction of a sulphonic group in the flavonoid structure and the heterocyclic ring opening produces tannin solutions of lower viscosity. While the sulphonic group introduced is deleterious to the strength and water resistance of simple tannin-formaldehyde adhesives, a moderate degree of sulphitation is inconsequential on the strength and water resistance of tannin-formaldehyde adhesives fortified with small amounts of simple phenolic resins used to enhance cross-linking in such a network. Their low viscosity renders these sulphited tannin adhesives particularly useful in applications, like particleboard manufacture, where this is needed.
Zusammenfassung
Kondensierte Tannine, wie z. B. Wattle (Mimosa) Extrakte, können, durch Hydrolyse einer Benzyläther-Bindung und nachfolgende Öffnung des flavonoid heterozyklischen Ringes, durch Sulphitation teilweise modifiziert werden. Die Einfuhrung einer Sulphongruppe in die Flavonoidstruktur und die Öff-nung des heterozyklischen Ringes. ergeben Tannin-Lösungen von niedriger Viskositat. Die Stärke und Wasserfestheit einfacher Tannin-Formaldehyd-Klebstoffe werden durch die eingeführte Sulfongruppe nachteilig beinflußt. Dieselben Eigenschaften von Tannin-Formaldehyd-Klebstoffen, die mit kleinen Mengen phenolischer Harze zur Verbesserung der Querverbindung behandelt sind, bleiben jedoch unbeeinflußt nach mäßiger Sulfitation. Zufolge der niedrigen Viskosität dieser sulfitierten Tannin-Klebstoffe sind selbige besonders geeignet zur Herstellung von Preßspanholz, bei der diese Klebstoff eigenschaft wichtig ist.
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Now at the National Timber Research Institute, CSIR, Pretoria, R.S.A.
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Pizzi, A. Sulphited tannins for exterior wood adhesives. Colloid & Polymer Sci 257, 37–40 (1979). https://doi.org/10.1007/BF01539014
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DOI: https://doi.org/10.1007/BF01539014