Rheology of tannin-added phenol formaldehyde adhesives for plywood

Abstract

Exterior-grade plywood boards were prepared with tannin-added phenol-formaldehyde adhesives, obtained through copolymerisation at room temperature of tannins with previously elaborated resols. The practically Newtonian rheological behavior of the resols is modified after copolymerisation with tannins, obtaining adhesives with pseudoplastic behavior. This is of great interest in industrial applications as it allows 250 g/m 2 adhesive consumption in double glue line, which is significantly lower than the aprox. 400 g/m 2 allowed by commercially available phenol-formaldehyde adhesives. The adhesives prepared with resols containing 36% reactive solids, the tannins representing aprox. 20%, has permitted the preparation of eucalyptus plywood boards exceeding the requirements of the European norm for exterior grade plywood. Rheologie von PF-Harzen mit Tanninzusatz für SperrholzSperrholzplatten für Außenverwendung wurden mit PFHarzen unter Zusatz von Tanninen hergestellt. Der Kleber wurde durch Kopolymerisation des Tannins mit Resolen bei Raumtemperatur erhalten. Das praktisch Newton'sche Fließverhalten der Resole wird nach der Kopolymerisation mit Tanninen zu einem pseudoplastischen Verhalten verändert. Dies ist von großem Interesse für die industruielle Anwendung, da es einen Verbrauch von nur 250 g/m 2 je doppelter Klebeline erlaubt. Dies ist bedeutend niedriger als die etwa 400 g/m 2 , die bei kommerziell erhältlichen Harzen nötig sind. Die hier hergestellten Harze enthalten etwa 36% reaktive Harze, wovon ca. 20% Tannine darstellen. Mit diesen Harzen konnten Eukalyptus-Sperrhölzer hergestellt werden, welche die Anforderungen der europäischen Normen für Außenverwendung übersteigen.

Acacia mangium Tannin as Formaldehyde Scavenger for Low Molecular Weight Phenol-Formaldehyde Resin in Bonding Tropical Plywood

“…Tannin-based adhesives have been studied by many researchers for the past 30 years [3,[7][8][9][10][11][12][13][14]. Nowadays, tannins are commercially produced: e.g., mimosa tannins in Brazil, South Africa, India, Zimbabwe and Tanzania.…”

Eco‐friendly tannin‐phenol formaldehyde resin for producing wood composites

“…It could be partially substituted in industrial phenol formaldehyde adhesives. Because of their ability in reducing gel time and pressing time, polyphenolic compounds of bark extracts has been used as accelerators application of PF resins in particleboard and plywood manufacture (Vazquez et al, 1996(Vazquez et al, , 2002(Vazquez et al, , 2003Pizii, 1997, 2001;Nemli et al, 2004;Calve et al, 1995). Tannins Condenced tannins used in the previously described studies are very generally extracted from the bark of various trees: pine, pinus radiat and pinaster, grape pomace, mimosa, etc.…”

“…It could be partially substituted in industrial phenol formaldehyde adhesives. Because of their ability in reducing gel time and pressing time, polyphenolic compounds of bark extracts has been used as accelerators application of PF resins in particleboard and plywood manufacture (Vazquez et al , 1996, 2002, 2003; Trosa and Pizii, 1997, 2001; Nemli et al , 2004; Calve et al , 1995). Tannins are complex phenolic compounds of two main categories: hydrolysable and condensable tannins.…”

Effects of Pinus pinaster bark extracts content on the cure properties of tannin-modified adhesives and on bonding of exterior grade MDF

“…One alternative that has been successfully developed in plywood manufacture involves the co-polymerization reaction of Pinus pinaster bark tannins with a phenol-formaldehyde resin [1]. The substitution of phenol by tannins was approximately 30%.…”