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Article Excerpt
Technology, which has become synonymous with innovation, involves the application of knowledge to develop new commercial products and processes. Technology has become increasingly important as companies try to compete in a fierce and unforgiving global competitive environment. Recent restrictions on the use of the wood preservative chromated-copper-arsenate (CCA) are focusing public and government attention on technological developments in the wood protection arena, specifically the availability of alternatives to CCA. The ready availability of arsenic- and chromium-free copper-based preservatives to replace CCA is proof of the ability of chemical suppliers to innovate and produce products that are attuned to the commercial realities of the marketplace. Currently, the market requires efficacious and inexpensive preservatives that can protect wood from biological deterioration without reliance on chemicals that possess high mammalian toxicity. Environmental concerns have driven this change and are likely to sh ape future innovation in this sector.
Emerging technologies promise competitive advantage, reductions in the environmental impact of treated wood products, and the solution to seemingly intractable problems such as the treatment of refractory timbers. More generally, technology is shaping the structure of the industry as developments in other fields open up new markets, provide opportunities for product diversification, or produce substitutes such as wood-plastic lumber that displace treated timber from its traditional strongholds. This article will review the emerging chemicals, processes, and raw materials for the protection of wood.
New Preservative Systems
COPPER-BASED SYSTEMS
Large numbers of biocides originally developed for the agricultural sector are available for use as wood preservatives, e.g., various alkyl-ammonium compounds, anilides, benzimidazoles, benzothiazoles, carbamates, guanidine derivatives, imidizoles, isothiazolones, pyrethroides, substituted benzenes and lignins, sulfonamides, thiurams, triazoles, and 2,4-dinitrophenols. These chemicals, when combined with the salts or oxides of copper, zinc, iron, aluminum, zirconium, or boron, offer unlimited potential for innovation and the development of new wood preservatives. Research that is currently underway, which could produce the wood preservatives of tomorrow, is mainly focusing on the development of new biocidal combinations that resist leaching and possess fungicidal activity. Particular attention is being given to developing copper-based preservatives, which is not surprising given the efficacy of copper as a fungicide, its low mammalian toxicity and cost, and its long history of use as a wood preservative and a s a biocide in other fields, for example, horticulture and viticulture.
Multiple patents have been filed in recent years for copper-based wood preservatives. Most of the patents describe formulations consisting of a copper II salt and an organic co-biocide formulated in an ammoniacal- or amine-containing aqueous solution. For example, ACQ consists of a copper II salt, didecyldimethylammonium chloride (DDAC), ammonia (ACQ-B) or amine (ACQ-D), and water. Copper azole is based on a patent that describes a ready-to-use wood preservative containing copper sulfate, tebuconazole, cypermethrin, and boric acid as biocides formulated in an ammoniacal solution. Commercial copper-azole preservatives now in the marketplace may omit one or other of the biocides (e.g., cypermethrin or boric acid) and substitute an amine for ammonia. The inclusion of ammonia is, however, desirable when treating refractory wood species such as Douglas-fir (Pseudotsuga menziesii). The patent literature also describes copper-containing wood preservatives consisting of: 1) copper amine oxides; 2) isothiazolone and c opper-amine complexes; 3) copper-amine complexes and carboxylic acid; and 4) isothiazoline, copper-amine complexes, and carboxylic acids. The formulation of these preservatives is broadly similar; however, Battershell et al. took a different approach in their 1998 patent application, which describes a process for depositing copper dimethydithiocarbamate in wood by infiltrating wood with gaseous carbon disulphide and then impregnating it with an aqueous solution of copper ions. Recent Japanese patents also describe copper-based wood preservatives that use phenolic compounds such as pyrogallol and lignin derivatives to increase the fixation of copper-amine in wood.
ZINC-BASED SYSTEMS
Research is also focusing on alternative, non-copper-based, metal preservatives, or even metal-free systems. Preservatives based on zinc are attractive because of zinc's low cost, long history of use as a wood preservative, and ability to be formulated in a colorless form. Zinc naphthenates have been used in organic solvent-based wood preservatives for nearly 100 years. Related zinc compounds based on synthetic carboxylic acid compounds, known as zinc soaps, are effective biocides; however, they have not attracted widespread commercial interest because of the high cost...
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