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Degree of fixation of amine copper solutions in Scots pine (Pinus sylvestris) Lucas, Nolwenn A.

Abstract

Amines are solvents used in copper based wood preservatives. Understanding their influence on chemical fixation in wood is crucial for improvements to be made to the fixation of copper. In this study, Scots pine sapwood blocks were treated with monoethanolamine copper and ethylenediamine copper solutions. The influence of chemical factors, such as copper concentration and amine to copper mole ratio in the treating solution, and the physical factor temperature, were investigated. Chemical analysis of treated wood showed that monoethanolamine and ethylendiamine have different influences on the fixation chemistry of copper. As well, copper concentration and amine to copper ratio are directly related to copper retention and the amine to copper mole ratios in treated wood. The minimum wood preservative retention required by the American Wood Preservers' Association (AWPA) and Canadian Standard Association (CSA) is met with low solution concentration (0.5%) treatment. This exploratory work suggests that there is a 1:1 mole ratio of amine to copper in both monoethanolamine copper and ethylenediamine copper treated wood after leaching. Furthermore it implies that an amine-copper-wood complex is primarily formed during fixation and is supported by further spectroscopic analysis. However, the formation of copper precipitate, unbound to amine, may be produced at high solution concentrations, and at temperatures above 60°C. The copper leaching resistance can be improved from one week at ambient temperature to one hour at temperature above 60°C. In general, spectroscopic analysis showed that there are no significant changes on the spectra as the temperature is increased, nor for increased duration of post-treatment time at any temperature. Further analysis demonstrated that heating may not produce a large amount of copper(I) species (< 1%), however, extended exposure to X-rays during analysis promoted the reduction of copper(II). This study also suggests that an ammonia/monoethanolamine mixture in copper based preservatives has minor effects on copper fixation. Amine-copper-wood compound formation is preferred, but some copper(II) carbonate precipitate may form during ammonia evaporation. The addition of ammonia to monoethanolamine copper solution noticeably improved the leaching resistance of copper.

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