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).

In this study, a combination of three chemicals (cashew nut shell liquid, sulfited wattle tannin and copper(ii) chloride) has been used to develop an environmentally friendly termite preservative. Cashew nut shell liquid (CNSL) is a by-product of cashew nut kernel processing factories and its use in the preservative formulations minimises the wastes from the factory as well as the amount of conventional hazardous preservatives from entering the environment. The formulated preservatives were tested for their ability to preserve wood blocks from a soft wood, ponderosa pine (Pinus ponderosa) and a hard wood, trembling aspen (Populus tremuloide). Sulfonated wattle tannins alone or combined with copper chloride at different concentrations, and cashew nut shell liquid (CNSL) without or with copper chloride were used in treating the 14 3 14 3 14 mm wooden blocks from the two wood species. The samples were exposed to termite attack in the surveyed fields in Arusha and Moshi, Tanzania. After 108 days exposure, evaluation of termite attack by measuring the weight losses and damage showed that the test wood treated with the combinations 40% CNSL + 1% CuCl 2 and 40% CNSL + 2% CuCl 2 were among the least damaged.