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Tannin-based adhesives for bonding high-moisture Eucalyptus veneers: Influence of tannin extraction and press conditions

Tanninkleber zum Verleimen sehr feuchter Furnierblätter: Einfluß der Tanninextraktion und der Preßbedingungen

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Abstract

The alkaline extraction of tannins from Pinus pinaster bark was studied as regards the influence of solid/liquid ratio, extraction time and NaOH concentration on the yield and Stiasny number of the extracts precipitated at pH 2. The extract with the highest Stiasny number(97) was copolymerized with a previously prepared resol to afford a resin with a 1∶1 phenol/tannins ratio. Plywood boards of Eucalyptus globulus bonded with this resin at board humidities of 10 or 16%, temperatures of 130 or 185°C and press times of 5 or 8 min all passed the WBP knife test (with one exception for the longer press time). We conclude that this resin is superior to commercial phenol-formaldehyde resins as regards its tolerance to moisture in plies and adhesive, its press time requirement, and its ability to bond veneers of woods known for their high levels of adhesive-repellent substances.

Zusammenfassung

Die Alkaliextraktion von Tanninen aus Pinus pinaster wurde untersucht im Hinblick auf den Einfluß des Flottenverhältnisses, der Extraktionszeit und der NaOH-Konzentration auf die Ausbeute und die Stiasnyzahl der Extrakte nach Ausfällen bei pH2. Der Extrakt mit der höchsten Stiasnyzahl (97) wurde mit Resol copolymerisiert, so daß sich ein Phenol-Tannin-Verhältnis von 1∶1 ergab. Alle Sperrhölzer, die aus Eukalytus-globulus-Furnieren mit Feuchten von 10 oder 16% mit diesem Harz verleimt waren (Preßtemperaturen 130 oder 185°C, Preßzeiten 5 oder 8 Minuten), bestanden entsprechende Qualitätstests. Eine Ausnahme bildeten Sperrhölzer, die bei längerer Preßzeit hergestellt waren). Dieses Tanninharz erscheint uns kommerziellen PF-Harzen überlegen in Hinsicht auf seine Feuchtetoleranz in Furnier und Harz, die Preßzeit und das Bindevermögen auch für Hölzer, die als schwerverleimbar gelten.

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Authors and Affiliations

  1. Department of Chemical Engineering, University of Santiago de Compostela, Avda. de las Ciencias s/n, 15706, Santiago de Compostela, Spain

    G. Vázquez, G. Antorrena, J. González & J. C. Alvarez

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  1. G. Vázquez
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  2. G. Antorrena
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  3. J. González
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  4. J. C. Alvarez
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Vázquez, G., Antorrena, G., González, J. et al. Tannin-based adhesives for bonding high-moisture Eucalyptus veneers: Influence of tannin extraction and press conditions. Holz als Roh-und Werkstoff 54, 93–97 (1996). https://doi.org/10.1007/s001070050144

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  • DOI: https://doi.org/10.1007/s001070050144

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