Tannin-based

Pizzi, A., Roll, W. and Dombo, B., United States patent USP 5,532,330. Heat-curable tannin-based binding agents. Assigned to Rutgerswerke AG, 1996. 

Multiblended inhibitors based on tannins, for use in either closed loop HW systems or steam raising boiler plants. Tannin-based multiblends are often offered as an alternative to sulfite-based multiblends. 

Tannin-based multiblends cannot incorporate amines directly into their formulations (unlike sulfite-based multiblends). The neutralizing amine component must be added separately when using tannin multiblends. 

The tannin-based, multiblend formula shown here is designed for steam-raising boiler plants operating at up to 200 to 220 psig (say, 15 bar). 

Tannin reserve to be maintained at 100 to 150 ppm, other parameters as per standard recommendations. The tannin-based closed-loop formula, also shown, is designed for use at 1,500 to 2,000 ppm product in the system, which provides approximately 180 to 240 ppm tannin reserve. Various modifications to these formulations exist for example, 0.5 to 1.0% diethylhydroxylamine (DEHA) may be added to improve passivation when used in simple HW heating systems. 

For HW, LP steam, and many lower pressure industrial operations, sulfite or sulfite derivatives have proved to be excellent scavengers and suitably cost-effective, provided the MU requirements are not too high and FW temperatures not too low. Alternatively, tannin-based products provide a similar degree of effectiveness without the contribution to TDS and, in practice, almost irrespective of FW oxygen content. 

Where sodium sulfite is added as a component of multifunctional or one-drum products designed for smaller boilers, no cobalt catalyst is added because of the cobalt alkaline precipitation problem. Consequently, if the FW temperature is low this type of formulation is unsuitable because the sulfite requirement will be too high and the available reaction time too short. Probably a tannin-based, one-drum product would be more suitable (although here again there may be a problem because tannin-based products, unlike sulfite cannot be mixed with amines). 

In addition, even where foaming is not a specific problem in a boiler, carryover may occur, especially in lower pressure boilers with very high TDS (i.e., over 10,000 to 15,000 ppm TDS) because of the collapse of surface bubbles. This leads to BW aerosol generation and entrainment of the spray in steam. Under these circumstances, antifoam agents such as polyamides are useful in preventing these entrainment problems. Furthermore, the antifoaming action of polyamides is often enhanced by protective colloid materials such as tannins, and consequently, formulations containing polyamide emulsions in an alkaline tannin base are available. 

Tannin-Based Chemistry Multiblend, One-Drum Programs Materials Formulation... 

It is not usual for unopened drums of nitrite-based chemical to degrade, and the product should remain in good condition for several years. However, it is possible for tannin-based corrosion inhibitors to degrade, even in unopened drums. Under warm conditions (such as storage in a boil-erhouse) and in the absence of a small amount of suitable microbiocide in the formulation, plastic drums containing tannin products may swell considerably because of microbiological degradation and gas formation. Care is needed to avoid accidents. 

In this chapter, the development of a thermosetting adhesive from soda bagasse lignin is described. The research has concentrated on the development of interior-grade adhesives for particleboard. The local market for exterior boards is smaller than that for the interior panels, and adhesives for exterior boards are already covered by an excellent range of tannin-based adhesives. 

Interest in use of condensed tannins as components of adhesive formulations began about three decades ago. While research studies have been carried out in widely scattered laboratories around the world, three major areas of activity can be distinguished. These are 1) development of bark extracts and commercial production facilities on the west coast of North America, 1953 to 1975 2) application of tannins in adhesive formulations in South Africa based on indigenously produced mimosa (wattle) tannin, early 1970 s to the present and 3) a resurgence of interest in pine bark as raw material for tannin-based adhesives, beginning in the middle 1970 s. Each of these activities has been characterized by parallel efforts on structural identification of the tannins and development of unique methods for incorporating the isolated tannins into adhesives. 

Tannin-Based Adhesives for Finger-Jointing Wood... 

Research vs. Industrial Practice with Tannin-Based Adhesives... 

Problems and facts that in the author s personal experience arise in the industrial application of tannin-based adhesives for timber sometimes indicate lack of correspondence with laboratory practice and results. These are often problems related to unusual characteristics of the adhesive itself, or of its application technique, which could not be noticed during research under laboratory conditions, but the existence of which could easily jeopardize successful implementation of laboratory technology into industrial practice. Correcting the credibility gap between research focus and industrial usage is seen as a critical step toward market expansion for these new products. Important considerations are consistency of tannins, extracts and adhesives properties due to the natural raw material variability formulation in cold-setting adhesives and application conditions (such as wood moisture and adhesive-content or pressing time) in particleboard adhesives. These problems have been overcome in use of wattle tannin-based adhesives as shown by a visual comparison of tannin-, phenolic-, and melamine-bonded particleboards exposed to the weather for 15 years and the growing use of tannin-based adhesives in other countries. 

Figure 5. World production and use of wattle tannin-based adhesives.

Progress in the use of condensed tannins in adhesive formulations might be expected to be more rapid than is the case for lignins because of the impetus provided by the commercialization of wattle tannin-based adhesives and because of the extraordinarily high reactivity of tannins in reactions with formaldehyde. This reactivity offers an opportunity to substitute tannin for resorcinol (currently priced at about 1.80/lb) instead of phenol (about 0.40/lb). Now that wattle tannins have been successfully introduced, their application can be expected to continue to expand. The situation remains difficult, on the other hand, for use of conifer bark tannins in adhesives. Herb Hergert is certainly... 

Recent progress in the characterization of numerous tannins has enabled the investigation of the biological activities of these compounds on the basis of structural differences in a way similar to that used for die other types of natural organic compounds such as alkaloids, terpenoids and flavonoids. Besides astringency, a fundamental property of tannins, based on strong affinity to biopolymers such as proteins and polysaccharides, various biological and pharmaceutical activities beneficial to human healdi, have been found. 

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. 

---