Environmental tannins

In essence, due to water leaching the tannins from the bark and other chemicals in the trees themselves, these water solutions must be subjected to zero discharge by 1977, according to the new guidelines by the Environmental Protection Agency. 

This effect can be modulated by environmental factors. Significant increases were found in skin proanthocyanidin content, proportion of (-)-epigallocatechin, and average DP in berries from zones with a low vine vigor (Cortell et al. 2005). In reaction to sun exposure, skin proanthocyanidin content tends to increase, particularly trihydroxylated subunits and mDP is enhanced (Downey et al. 2004 Cortell and Kennedy 2006). Shaded fruits reached a lower maximum in proanthocyanidin content than sun-exposed ones but the contents at harvest were similar. Most authors agree that water stress had only slight effects on tannin composition (Ojeda et al. 2002 Kennedy et al. 2002 Castellarin et al. 2006). Seed flavanol composition seems hardly affected by environmental factors. 

Kawamoto, H., Nakatsubo, F. (1997). Effects of environmental factors on two-stage tannin-protein co-predpitation. Phytochemistry, 46, 479-483. 

Tannins and tannic acid occur naturally in plants. Essentially all wood and plant tissue contain tannins. Therefore, biodegradation is expected to be the major environmental fate process for tannic acid. 

This has been made possible by the development of suitable adhesive systems that are able to bond the partieles together. The synthetie adhesives offer a consistency of performance that is diffieult to aehieve with natural produets sueh as tannins, and at a cost that has enabled rapid growth to be aehieved. At the same time the adhesive systems have shown a toleranee to a range of wood properties that has enabled most wood residues sources to be used. The environmental effects of formaldehyde emissions from panels made using UF adhesives have been successfully addressed. Initially these required higher resin addition rates to offset a loss in physieal property levels, but further development has reclaimed much of this additional cost. 

One of the prime environmental objectives is the removal of suspended contaminants from water and waste streams. Water turbidity in nature is the result of colloidal clay dispersion and the color is from decayed wood and leaves (tannins and lignins) and organic soil matter. In addition to these contaminants, there are viruses, algae, bacteria, metal oxides, oils and other pollutants. In recent years, synthetic organic polyelectrolyes, in particular the cationic polymers, have been used very effectively in water treatment (3). These polyelectrolytes are high... 

The loose term renewable resources adhesives has been used to identify polymerie eom-pounds of natural, vegetable origin that have been modified and/or adapted to the same use as some classes of purely synthetic adhesives [1]. At present two classes of these adhesives exist one already extensively commercialized in the southern hemisphere and the other on the slow way to commercialization. These two types of resins are tannin-based adhesives [2] and lignin adhesives [3 ]. Both types are aimed primarily at substituting synthetic phenolic resins. In some aspects, such as performance, they closely mimic, or are even superior to, synthetic phenolic adhesives, while in others they behave in a vastly different manner from their synthetic counterparts. In this chapter we focus primarily on tannin-based adhesives because they have already been in extensive industrial use in the southern hemisphere, in certain fields of application, for the past 20 years. These adhesives are of some interest not only for their excellent performance in some applications but also for their mostly environmentally friendly composition. Lignin adhesives are treated briefly here and in detail in Chap. 28. 

The use of synthetic resins Umits somewhat the environmental attractiveness of such adhesives based on purely natural materials, while the use of tannins alone is limited at present by the relatively Umited supply of these materials [1]. Thus, the aim is to prepare an adhesive based on materials of natural origin, satisfying international standards for both performance and emission, which does not emit or even better does not contain any formaldehyde, the composition of which does not include any synthetic resins, and that is less costly and uses widely available materials. This will render wood panel adhesives based on natural materials much more acceptable both economically and environmentally. 

Lei H, Pizzi A and Du G (2008), Environmentally friendly mixed tannin/lignin wood resin , J Appl Polym Sci, 107, 203-209. 

Labieniec, M. Gabryelak, T. (2003). Effects of tannins on Chinese hamster cell line B14. Mutation Research/Genetic Toxicology and Environmental Mutagenesis, 539,127-135. 

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