Characterization of Wattle Tannin Based Adhesives for Tanzania

Abstract

Wattle tannin-based urea formaldehyde (UF) adhesives for exterior grade plywood panels were formulated and tested. Laboratory work was conducted in Canada and plant trials in Tanzania. Tests showed that tannin-based adhesives gave quite good plywood which met the Canadian Standard Association (CSA) exterior grade requirements under press conditions similar to those currently employed for UF (control) adhesives. Formulations containing formaldehyde and oil instead of paraformaldehyde were found to be slightly less reactive under mill conditions. For particleboard, hydrolysis of the tannin was required for producing adhesive with acceptable viscosity and "pot life" for commercial applications. The hydrolysis of tannin also improved mechanical properties of particleboard. Relatively long press cycles or high press temperatures were required to produce particleboard panels with aged modulus of rupture (MOR) strength above the CSA exterior grade requirements. Prior to particleboard making, size exclusion chromatography (GPC) and differential scanning calorimetry (DSC) were performed on tannin, hydrolysed tannin, tannin-UF adhesive and commercial PF and UF adhesives. GPC indicated, possibly due to aggregation, that the tannin average molecular weight increased upon heating in the presence of alkali. The thermal or kinetic cure characteristics of the tannin-based adhesives, which are activation energy, enthalpy of cure and reaction order, were determined to be comparable with those of UF adhesives. Tannin hydrolysis lowered the activation energy for cure and this resulted in lower press times, as shown in test results. IntroductionThe demand for imported wood adhesives in Tanzania is estimated at 1000 metric tonnes per annum. While Tanzania is importing tonnes of urea-formaldyde (UF) adhesives at high costs (US $ 0.75/kg), it is exporting at relatively low cost (US $ 0.45/kg) highly reactive tannin extract from the bark of the black wattle tree (Acacia mearnsii) which could be used as the main ingredient in the formulation of exterior grade wood composite adhesives (Dalton and many others).

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.…”

Rheology of tannin-added phenol formaldehyde adhesives for plywood

“…In our experiments the average glue consumption in the preparation of boards was approx. 250 g/m 2 (in double glue line), clearly lower than the one used by other researchers, 350-450 g/m 2 (Olivares and Sellers 1994;Calvé et al 1995;Santana et al 1996;Zhao et al 1996).…”