Preservative-wood interaction

Another detrimental effect of preservative-wood interaction is the formation and buildup of colloidal material in the treating solutions as it is recycled. This particulate matter arises from an interaction between the preservative chemicals and wood components and often results in a significant decrease in the penetrability of the treating solution (54). 

PhD thesis. University of Canterbury, Christchurch, New Zealand Bull DC (2001) The chemistry of chromated copper arsenate II. Preservative-wood interactions. Wood Science and Technology, 34 459-66 Bunn EH (1981) The nature of the resource. New Zealand Journal of Forest Science, 26(2) 162-99... 

The wood preservation properties of [Bu3Sn(IV)r compounds are strongly related to the interactions between cellulose and the organotin(IV) cation and are... 

Ammonium Fluoride or Malt Salt, NH4F, mw 37.04, wh poisonous crysts sp gr 1.31, mp — decomp by heat w/o melting sol in cold w. Prepd by interaction of Amm hydroxide with HF, followed by crystn. Used in glass etching, textile mordant, wood preservation and in analytical chemistry (Refs 1 2)... 

The mechanism of interaction of the CCA preservative with the wood structure was initially elucidated by Dahlgren [3, 4] and Dahlgren and Hartford 5]. Subsequently, this scheme was modified by Pizzi [6, 7, 8, 9], who studied the kinetics of reactions between CCA or CCA component elements and cellulose or lignin model compounds. The kinetic data combined with results from analysis of reaction precipitates were used to determine the distribution of preservative elements between the major compounds in the wood structure. A summary of the products formed when CCA reacts with wood is presented in Figure 1. 

Before proceeding with potential interactions between preservative chemicals and the wood substrate, it will be necessary to describe briefly the pertinent chemical and physical properties of the commercial wood preservatives as well as some new biocides that may have future potential in wood preservation. 

Macrodistribution. The ability of any wood preservative to control biodegradation is affected by the macrodistribution of the chemical within the wood product being protected. The macrodistribution of a preservative is influenced by three basic factors wood characteristics, treating process, and characteristics of the treating solution. Consideration of the principles of flow in wood and of the factors that influence the treatment of wood are covered in Chapters 3 and 4 14, 15). Suffice it to say that when the preservative has been distributed through the wood, fixation will occur either through chemical interaction between the preservative and the wood structure, between the preservative components themselves, or by physical deposition as a result of solvent loss. These fixation mechanisms are covered in the section on microdistribution. 

Inorganic Salt Preservatives. Inorganic compounds used to formulate wood preservatives are normally water soluble. As a result, the salts deposited in the wood are susceptible to leaching unless they are transformed to insoluble compounds or are chemically fixed to the wood substrate. Indeed, such conversions do occur as a result of interactions between some of the salts and the wood substrate. Both single element and multicomponent reactions are involved in the fixation mechanisms copper and chromium are the most reactive of the possible components. 

Needless to say, the fixation of inorganic chemicals in wood by interaction with the wood substrate and extractives is beneficial and greatly improves the durability of these preservatives. Contrarily, other interactions provide less desirable reactions. For example, under certain circumstances copper and zinc can become so tightly bound to the wood that their efficacy as wood preservatives is reduced. This result occurs when copper acetate and zinc acetate are used to treat wood (53). In this form, these elements are salts of acetic acid and they form ion-exchange bonds with the wood components that are stable in the weak acid environment and cannot be ionized readily by water. Conversely, this reduction in efficacy does not occur when copper sulfate and zinc chloride are used because they are salts of strong acids and the pH of the environment prevents insolubilization of these elements by the wood. 

Lebow ST and Morrell JJ (1995) Interactions of ammoniacal copper zinc arsenate (ACZA) with Douglas fir. Wood and Fiber Science, 27(2) 105-18 Lebow ST and Tippie M (2001) Guide for minimizing the effect of preservative-treated wood on sensitive environments. USDA, Forest Service, Forest Products Laboratory, General Technical Report FPL-GTR-122... 

Pentachlorophenol and arsenical compounds are also used in wood preserving. For this reason, it is likely that they will be found with creosote at hazardous waste sites. However, there is no information available on the potential interactions of creosote with pentachlorophenol or arsenical compounds. 

The dye can be photographed and quantified using various fluorescence-monitoring apparatus, e.g. the FIVES (fluorescence interactive video exposure system) fluorescent monitor, developed at the Health and Safety Laboratories in the UK (Roff 1994), and has been used to determine the dermal exposure of workers using wood-preservative fluids (Roff 1997). 

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