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Fixation mechanism of ammoniacal copper wood preservatives Xie, Changshi

Abstract

This thesis describes the first comprehensive study of the chemistry of ammoniacal copper based wood preservatives, including the fixation of copper and nitrogen in treated wood; and the identification of the cause of the black color in treated Douglas-fir heartwood. The effects of enhanced nitrogen content in ammoniacal copper solution treated wood on the decay by three rotting fungi were investigated. Taxifolin, a Douglas-fir heartwood extractive was isolated and identified using ultraviolet (UV), infrared (IR), nuclear magnetic resonance (NMR) and mass spectrometry (MS). It was confirmed that taxifolin reacted with ammoniacal copper solutions to form a black copper-nitrogen-taxifolin complex. Nitrogen fixation in ammonium hydroxide treated wood was studied through the reaction of ammonium hydroxide solution with wood and its components. It was found that carbonyl and carboxylic groups in lignin and hemicelluloses can react with ammonia to fix nitrogen in wood. The fixation mechanism of copper and nitrogen in ammoniacal copper treated wood was studied through the reaction of vanillin, a lignin mode l compound, with an ammoniacal copper solution. The green copper complex formed was extensively studied using infrared (IR), electron spin resonance (ESR) elemental analysis an d X-ray single crystallography an d identified to be a vanillin-copper ammonia complex. An X-ray structural analysis of a single crystal of the complex enabled the structure to be known. In the complex both the methoxy and phenolic oxygen atoms of guaiacyl units were coordinated to the copper, together with nitrogen from ammonia forming a six coordinated complex. This was first determination of a crystal structure of copper-lignin model complex which may describe important bond formations occurring during the fixation of copper and nitrogen from ammoniacal copper wood preservatives. The effect of enhanced nitrogen in ammoniacal copper treated wood on the decay was studied. Wood treated with higher concentrations of ammonium hydroxide solution showed an increased decay resistance to both P. placenta and a slightly enhanced resistance to T. versicolor fungus. However, for G. trabeum the weight losses of the ammonium hydroxide treated-wood was slightly increased relative to the control. Ammoniacal copper treated wood with low copper retention showed increased decay resistance to both T. versicolor and G. trabeum. The nitrogen in the complex can not be used by fungi for their growth. However, the ammoniacal copper treated wood with low copper retention was easily attacked by P. placenta due to its ability to form insoluble copper oxalate in copper treated wood.

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