Acacia mearnsii

Proanthocyanidins Mimosa Acacia mearnsii) bark taimin. Linear (+) DHB 305... 

The resorcinol-pattern proanthocyanidins are widely used not only for leather tanning, but also for a range of other commercial products, particularly as adhesives for plywood and fiberboard (6,7). Wattle tannin is produced from sustained-yield forests of Acacia mearnsii. largely in southern Africa (6,8). Some of the impetus at least to develop other uses for wattle tannin, apart from... 

Ambient pressure has been used for the extraction of Radiata pine bark, although different conditions have been used for the tannin extraction of wattle (Acacia mearnsii) bark. This is largely due to our previous experience that the application of temperatures higher than lOO C decreases the extracted yield from the bark. 

The tannins of some woods, acacias, chestnuts and oaks - and also their barks -were once of importance for the tanning of leather. Yet they have adverse influence on gluing (inhibiting polymerization of adhesives) and in pulping. Today, in the state of Rio Grande do Sul, Brazil, 100,000 ha of Acacia mearnsii provide short fibre for chip export while the 27-28% tannin in its bark supports another industry. 

No wax emulsion was added to the board to avoid the introduction of another factor that could have limited formaldehyde emission. To this glue mix were added 2 %, 5 % and 10 % UF resin solids by mass of commercial mimosa (wattle, Acacia mearnsii formerly mollissima) bark extract, a commercial flavonoid-type tannin extract. 

Drewes, S.E., D.G. Roux, H.M. Saayman, S.H. Eggers, and J. Feeney Some Stereochemically Identical Biflavanols from the Bark Tannins of Acacia mearnsii. J. Chem. Soc. (C), 1302 (1967). 

Churms S C, Merrifield E H, Stephen A M, Stephen E W 1978 Evidence for sub-unit structure in the polysaccharide gum from Acacia mearnsii. S Afr J Chem 31 115-116... 

It should be noted that the distribution of regio- and/or stereoisomers obtained by these syntheses is not always reflected in the natural products. Haslam s observations of procyanidins dominated by the C-8 linked dimers (133-136) may be due to enzymic control of the location of substitution in these plants. A similar situation exists in the dimeric proanthocyanidins isolated from Acacia mearnsii bark (27, 28). Here fisetinidol-(4)8->8)-catechin predominates and no fisetinidol-(4a 8)-catechin was observed in the plant extracts. In contrast fisetinidol-(4a- 6)-catechin was the principal product and significant amounts of the C-6 substituted isomer were also obtained from biomimetic syntheses (28). 

The profisetinidins have been studied intensively by Roux s school at The University of the Orange Free State, Bloemfontein, South Africa. The heartwoods of Acacia mearnsii and Colophospermum mopane contain a series of 2R isomers and these compounds have all been synthesized (Tables 7.6.9 and 7.6.10). The commercially important quebracho tannins from Schinopsis and Rhus contain a series of 2S isomers and these compounds have also been synthesized recently. Fifteen dimers, nine trimers, and nine tetramers have now been thoroughly de-... 

Drewes S E, Ilsley A H 1969 Dioxane-linked biflavanoid from the heartwood of Acacia mearnsii. J Chem Soc (C) 897-900... 

Roux D G, Ferreira D, Botha J J, Garbutt DCF 1976 Heartwood extracts of the black wattle Acacia mearnsii) as a possible source of resorcinol. J Appl Polym Sci Polym Symp 28 1365-1376... 

The Type 1 proanthocyanidins are distributed almost ubiquitously in the woody plants, whereas Type 2 proanthocyanidins are confined to certain families in the Leguminosae and Anacardiaceae (see Sect. 7.7.3.1), often co-existing with Type 1 proanthocyanidins either in the same or different organs of the plant. However, the Type 2 tannins are of pre-eminent importance commercially as currently the two most important sources of condensed tannins for industrial applications are wattle Acacia mearnsii) bark and quebracho Schinopsis spp.) wood, which are both of this type (Chap. 10.3). Our current knowledge of these tannins is almost entirely due to the efforts of David Roux and his colleagues over the past three decades. 

Approximately 200000 tons of quebracho Schinopsis sp.) and 100000 tons of wattle (Acacia mearnsii) tannins are produced world-wide annually. Although statistics are not so accurate, about 200000 tons of vegetable tannins derived from other plants such as hemlock (T uga sp.), chestnut (Castanea sp.), oak (Quercus sp.) and myrobylan (Terminalia sp.) extracts add to this for a total world production thought to be about 500000 tons per year, (see also Chap. 1.1). 

Most of the recent efforts to develop uses for the condensed tannins have centered on their application in wood adhesives. Reviews by Pizzi (182, 186) and others (15, 78, 87, 93, 208) provide references to several hundred papers and patents on this subject. Despite world-wide research efforts on other sources of tannins, particularly since the 1972-1973 petroleum shortage, the mimosa or wattle tannins extracted from the bark of black wattle Acacia mearnsii) remain the major source of condensed tannins exploited commercially for adhesive manufacture. Of the approximately 100000 tons of wattle tannin produced annually, only about 10000 tons are used in wood adhesives, predominantly in South Africa but also in Australia and New Zealand (186). The extensive use of wattle tannins by the wood products industry of South Africa is impressive indeed, as these tannins have partly replaced phenol and resorcinol usage in adhesives for bonding of particleboard, plywood, and laminated timbers (182, 186, 213). Three factors have contributed to the success in use of wattle tannin-based adhesives, namely the comparatively high costs of phenol and resorcinol in the Southern Hemisphere, their resorcinolic functionality and low molecular weight and, perhaps most importantly, the commitment by the research and industrial communities of these countries to reduce the reliance of the forest products industry on petroleum-based adhesives. 

Grainger, C., T. Clarke, M.J. Auldist, K.A. Beauchemin, S.M. McGinn, G.C. Waghom and R.J. Eckard, 2009. Potential use of Acacia mearnsii condensed tannins to reduce methane emissions and nitrogen excretion frxnn grazing dairy cows. Can. J. Anim. Sci. 89, 241-251. 

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