Tannin extraction

More recently, a modification of the system described by Kreibich has been used extensively in industry with good success. Part A of the adhesive is again a standard phenol-resorcinol-formaldehyde (PRF) cold-setting adhesive, with powder hardener added at its standard pH. Part B can be either the same PRF adhesive with no hardener and the pH adjusted to 12, or a 50 to 55% tannin extract solution at a pH of 12-13, provided that the tannin is of the condensed or flavonoid type, such as mimosa, quebracho, or pine bark extract, with no hardener [118,135-137], The results obtained with these two systems are good and the resin not only has all the advantages desired but also the use of vegetable tannins and the halving of the resorcinol content makes the system considerably cheaper [118,135-137]. 

Molan, A. L., Hoskin, S. O., Barry, T. N. and McNabb, W. C. (2000). Effect of condensed tannins extracted from four forages on the viability of the larvae of deer lungworms and gastrointestinal nematodes . Veterinary Record, 147(2), 44-8. 

Tannins are polyphenols that occur only in vascular plants such as leaves, needles, barks heartwood, seeds and flowers. Tannins exist primarily in condensed and hydrolysable forms. Natural tannin extracts have been employed since the turn of the last century in leather industry. Recent development of their industrial uses as adhesives, flocculants, depressants, viscosity modifier agents and more recently as corrosion inhibitors reflects their importance as industrial raw materials. Electrochemical studies have shown that tannins extracted from the barks of mangrove trees are excellent corrosion inhibitors of steel at very low pH. The mechanism of inhibition at this pH was due to the chemisorption of tannin molecules while at higher pH, inhibition was achieved via formation of ferric-tannates [6]. 

Edwards and Jones (31) identified the condensed tannin extracted from cotton plant bracts as a tannin-like polymer of 5, 7, 3, 4 tetrahydroxyflaven 3-4 diol (THF). They demonstrated nonspecific precipitation with IgG, IgM, IgA, five myeloma IgG s and positive gel diffusion reactions with heavy and light chains. Fab and Fc pieces of IgG. Nevertheless, they refuted this reaction as a true antigen-antibody reaction, and subsequently suggested that byssinosis was not an immune complex mediated pulmonary disease. 

Labcratory rat / Sericea lespedesa tannin extract (Lespedeza cuneata Leguminosae [AD]). (26)... 

Figure 4. Binding of a protein (hemoglobin) to several tannin extracts (tannic acid, sugar maple tannins, yellow birch tannins, quebracho tannins see 29) at various pH values. Ranges of microbial chitinase activity, NPV activity, and Bt toxicity are given. See text for discussion and references.

Process Variations. The conventional techniques for tea manufacture have been replaced in part by newer processing methods adopted for a greater degree of automation and control. These newer methods include withering modification (78), different types of maceration equipment (79), closed systems for fermentation (80), and fluid-bed dryers (81). A thermal process has been described which utilizes decreased time periods for enzymatic reactions but depends on heat treatment at 50—65°C to develop black tea character (82). It is claimed that tannin—protein complex formation is decreased and, therefore, greater tannin extractability is achieved. Tea value is believed to be increased through use of this process. 

An Analysis of Wine for Tannin Extracted from Wood... 

At present, there is increasing interest in the use of CM for the production of wines with long aging potential, involving maturation in oak. Thus, at the end of the first step, contact between the wine, pomace, and the lees may be extended from a few days to months. When the effects of AM are considered to be appropriate, relative to the nature of the product expected (e.g., color or tannin extraction) some wine producers use pumping over, combined with the addition of macerating enzymes. The latter facilitate is improved extraction of quality-related compounds. 

When P. radiata bark is extracted by sulfite-carbonate, the solution viscosities are much lower. For example, Woo (30) reported a viscosity of 1,600 mPa-s for a 45% solution of Tannaphen, a commercial tannin extract from P. radiata bark that contains approximately 70% proanthocyanidins. When extracted with sulfite-carbonate, the proanthocyanidins will be partly depolymerized 31), which will cause a fall in viscosity. Whether the very high viscosities observed for aqueous extracts by Yazaki and Hillis 29) are due to the P, radiata proanthocyanidins being of much higher molecular weight than other conifer tannins or due to complexation of the proanthocyanidins with the polysaccharide fraction 32) remains to be shown. 

Selection of the End-Joint Profile. Because the purpose of this work was to determine whether a portion of the phenol-resorcinol-formaldehyde adhesive used in structural end-joints could be replaced by tannin extracts from southern pine bark, it was necessary to use a structural end-joint profile design. The profile chosen was the design used by many U.S. plants for the manufacture of structural end-joints. A reproduction in natural size with a drawing showing the exact dimensions is shown in Figure 1. 

Nonemulsifiable and emulsifiable polymeric methylene diisocyanates (Desmodur VP PU 1520 A 31 and 1520 E, Messrs. Bayer, West Germany) were combined with maize starch and solutions of tannin extract or protein. 

The gluing experiments were done with commercially available starch, proteins (casein, glutin) and tannins of mimosa Acacia spp.), Pinus radiatay and quebracho (Schinopsis spp.) and with tannins extracted from the bark of spruce (Picea abies) and common pine (Pinus sylvestris). The extractions were carried out with water or organic solvents under alkali and/or sulphite conditions on a laboratory scale aiming at optimization of yield and polyphenolic extract content. After extraction, the solutions were concentrated under reduced pressure and freeze dried. One pine bark extract was modified with phenol. A summary of the tannin extracts and their properties is given in Table I. 

Adhesives from Diisocyanates and Tannins. The tannin extracts were mixed as powders or solutions with nonemulsifiable or emulsifiable diisocyanate. The potlife of the formulations of extract powders with nonemulsifiable diisocyanate was sufficient the viscosities of the mixtures remained nearly constant for more than 5 hours. With extract solutions, the viscosity of the glue increased... 

Table I. Extraction Conditions and Properties of Tannin Extracts...

Table III. Strength and Wood Failure of Plywood1 Bonded with Formulations of Diisocyanate (PMDI) and Tannin Extracts (50% Solutions)...

Table IV. Mechanical Properties of 13-mm Particleboard1 Bonded with Unmodified Tannin Extracts and with Tannin Extracts Diisocyanate (PMDI) Formulations2...

Four types of condensed tannins were studied in the adhesive dips 1) extracts from pecan nut pith obtained by digestion with aqueous sodium sulfite-sodium carbonate solutions, 2) purified tannins from southern pine bark, 3) extracts from southern pine bark obtained by digestion with aqueous sodium sulfite-sodium carbonate solutions, and 4) tannins extracted with acetone-water solutions from peanut skins. 

The sulfite extract performed nearly as well as the peanut skin tannin in bonding to nylon. Use of a tannin sulfonate derivative does not seem to hinder the development of strong bonds (compare peanut skin and sulfite extracts from pine bark). Likewise, the presence of carbohydrates in the tannin extracts does... 

The pecan pith extract was the best of the tannin extracts examined in bonding to polyester cord. Pullout forces using this extract to totally replace resorcinol were nearly twice as high as in the standard dip. The purified pine bark extract also gave very good results. One commonality in these two extracts... 

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