Preservative formulations

Historically, wood preservatives have been thought of in terms of their solubility in either water or oil-type solvents (Ibach, 1999). Thus we have so called oil-bome and water-borne preservative systems. More recently that classification has become less relevant, because, with advances in formulation chemistry active ingredients can be formulated with either type of solvent, while others may be emulsions or suspensions. Water-based preservatives often include some type of co-solvent such as an amine or ammonia to keep one or more of the active ingredients in solution. Each solvent has advantages and disadvantages depending on the application. 

Water-based preservatives are often used where cleanliness and paintability of the treated wood are required. Typically, wood treated with a water-based preservative has little or no odour when compared to oil-based preservatives. However, unless supplemented with a water repellent, the water-based systems do not confer any dimensional stability to the treated wood. In addition, water-based preservatives that utilize copper as a fungicide may not adequately protect hardwood species under conditions that favour soft rot attack. Some water-based preservatives can increase the rate of corrosion of mild steel fasteners. 

Copper has been a primary ingredient in wood preservative formulations for over a eentury because of its excellent broad-speetrum fungieidal properties, low 

Each preservative has unique characteristics that might affect its suitability for a particular application. These include factors such as appearance, odour, toxicity, wood species compatibility and availability. The discussion that follows provides a basic background to a wide range of preservative systems. Some of these systems are still in use today, while others have been phased out and others are currently under development. Further discussion of preservative systems can be found elsewhere (Ibach, 1999 Nicholas, 1973b Richardson, 1993 Schultz and Nicholas, 2003). It will be readily apparent from this section that the transition away from traditional heavy metal broad spectrum biocidal compounds to organic chemistries has added significant complication to the wood preserving industry as a whole. 

Marine borers present a severe challenge. Some preservatives that are very effective against decay fungi and insects do not provide protection in seawater.Thus, despite severe reservations about the continued use of creosote and CCA these remain the only viable treatments currently available. Creosote is most commonly used, preventing attack by all marine borers except Limnoria tripunctata. 

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AppHcations of mercury include use in batteries (qv), chlorine and caustic soda manufacture (see Alkali and chlorine products), pigments (see Pigments, inorganic), light switches, electric lighting, thermostats, dental repair (see Dental materials), and preservative formulations for paints (qv) (1—3). As of the end of the twentieth century, however, increased awareness of and concern for mercury toxicity has resulted in both voluntary and regulatory reduction of mercury usage (see also Mercury compounds). 

Preservative molecules are used up as they inactivate microorganisms and as they interact non-specifically with the significant quantities of contaminant dirt also introduced during use. This will result in a progressive and exponential decline in the efficiency of the remaining preservative. Preservative capacity is a term used to describe the cumulative level of contamination that a preserved formulation is likely to cope with before becoming so depleted as to become ineffective. This will vaiy with preservative type and complexity of the formulation. 

Indoor household dust samples gathered by a vacuum cleaner from rooms with furniture treated with a wood-preserving formulation were analyzed for CDDs (Christmann et al. 1989b). The wood-preserving... 

Christmann W, Kloeppel KD, Partscht H, et al. 1989b. PCDD/PCDF and chlorinated phenols in wood preserving formulations for household use. Chemosphere 18 861-865. 

Biocidal applications. The use of quaternary ammonium salts in disinfecting systems for household and industrial cleaners has been known for many years [95, 96]. Alkyl-benzyldimethyl quaternaries, alkyltrimethyl quaternaries, and dialkyldimethyl quaternaries are the more commonly used biocidal quaternary ammonium salts [16]. Recently, dialkyldimethyl quaternary ammonium salts have received renewed attention as potential wood preservatives to replace the heavy metal types [97]. Metal-free wood preservative formulations containing dialkyldimethyl ammonium salts with non-halide anions, such as carboxylates, borates, and carbonates, have been developed [98, 99]. 

Table 4. The amount of PCDEs in technical chlorophenols and chlorophenol-based wood preservative formulations...

I. Stability of multidose, preserved formulation epoetin alfa in syringes for three and six weeks. Am. J. Health-Syst. Pharm. 2003, 60, 464-A68. 

Preservative formulations that contain copper and chromium salts reportedly promote afterglow in treated wood subjected to fire. Once the treated wood starts to burn or glow, the wood may continue to glow until the entire member is consumed, even when no flame is present (38, 39). This characteristic can cause serious problems in utility poles, fenceposts, and highway signs, structures that might be... 

In recognition that the deterioration hazard varies with end-use, many countries have developed hazard class or use category systems that specify those preservative formulations that are suitable in particular situations, the amount of preservative to be used (its retention ), and the depth to which the preservative must penetrate the wood (Morrell and Preston, 1995) (Table 9.2). As might be expected there is considerable overlap between these end-use categories. 

CCB and CCP are similar in many respeets to CCA except for the fact that the arsenic is replaced by boron in CCB and by phosphate in CCP. Most commonly used in Europe, both formulations were developed in part to address concerns about the toxicity of the arsenic in CCA. CCB and CCP are less efficacious than CCA and in the absence of arsenic the fixation processes are compromised. The systems still contain significant levels of chromium, which faces significant regulatory pressure from the Biocidal Products Directive in Europe. In the longer term the future for preservative formulations containing chromium is questionable. 

Copper azole is another recently developed water-based preservative formulation that relies primarily on copper solubilized in ethanolamine and an organic trizaole co-biocide. The first copper azole formulation developed contained 49% copper, 49% boric acid, and 2% tebuconazole. More recently, a formulation containing 96% copper and 4% tebuconazole has been used. As with ACQ formulations the copper in copper azole systems provides the primary fungicide and insecticide activity. The azole component provides protection against copper tolerant fungi. 

In many respects a ground contact or fresh water immersion environment represents a very consistent and high exposure hazard the same cannot necessarily be said of all above ground applieations. In certain situations, for example where moisture or organic debris ean colleet, the above ground environment may present a deterioration hazard similar to a ground contact exposure. This can be particularly problematic to the wood preservative formulator and treater. Here, the heavy duty preservatives discussed in the previous section may be more appropriate for such applications, especially in critical structural members. 

In summary, although there is considerable evidence that parabens can penetrate into the skin, permeation and systemic availability of intact compounds are likely to be considerably reduced by transcutaneous and systemic metabolism. Furthermore, since these preservatives are present at concentrations of 0.1-0.2 percent w/w in topical pharmaceutical formulations, in-use dermal exposure to these compounds will be relatively low. In the cosmetic industry, there is a trend toward preservative-free and self-preserving formulations (Kabara and Orth 1997). However, before starting down this road, the pharmaceutical formulator must consider the potential implications on the efficacy and safety of the product. 

Xyligen . [BASF AG] Active ingredients for wood preservative formulations additives to glues for wood applic. 

Polychlorinated diphenyl ethers (PCDE) were found in the ng/g range in cod liver oils [138]. The PCDE profiles were compared with those of PCDEs in chlorinated phenols, wood preserving formulations, and fly ash. The primary source of PCDEs are chlorophenols but sources other than those investigated appear to be involved as well. The majority of PCDEs found in cod liver oil are mono- or di-ortho- substituted and also have chlorines in the meta and para positions. 

Uses Emulsifier, suspending agent, thickener, stabilizer, binder in foods, cosmetics, pharmaceuticals, industrial applies. adhesives leather dressing textile printing and sizing dyes hair-wave preps. printing inks food preservative, formulation aid, cryst. inhibitor pharmaceutical tablet excipient and binder in dentifrices... 

The use of quaternary ammonium compounds as biocides in wood preservation formulations is increasing rapidly. Their low toxicity and biodegradable properties, combined with their favourable adsorption characteristics, have led to an increase in the popularity of these products as an alternative to other wood preservative formulations such as pentachloraphenate (PCP) and chromated copper arsenate (CCA). Due to growing environmental pressure, the use of these latter products is declining and the development of alternative wood preservatives is gaining momentum. 

Used by themselves, or in combination with other modem biocides - such as systematic fungicides, bactericides or insecticides - the long-alkyl-chain quaternary ammonium compounds offer a useful tool in the development of new environmentally acceptable wood preservative formulations. The most commonly used quaternary ammonium compounds are coco(fractionated) benzyldimethylammonium chloride and didecyldimethylammonium chloride. 

After studying the relevant documentation, one will often find that commercial technical preservatives are not always highly toxic substances or preparations. The preservatives formulated with the appropriate know-how are highly effective products with very good toxicological properties. In addition, the so-called relative toxicity should be considered, i.e. the effect of the preservative on the total toxicity of the water-mixed coolant after dilution beyond the relevant use-concentrations, e.g. 1 1000. 

This chapter aims to summarise this subject area, focussing on the most commonly encountered types of wood degrade, their recognition and the range of wood preservative formulations used to prevent degrade. 

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