Peroxide Post-Treatment of Wood Impregnated with Micronized Basic Copper Carbonate

Rod Stirling,Gabrielle Boivin,Adnan Uzunovic,Stacey Kus,John N. R. Ruddick

doi:10.3390/coatings10121213

Abstract

Wood is vulnerable to significant color changes when used in exterior applications. Some copper-based wood preservatives use colorants to minimize this color change. This paper examines the ability of a peroxide post-treatment to turn wood impregnated with micronized basic copper carbonate (CuCO3·Cu(OH)2) (MBCC) a stable brown color. MBCC-treated wood, with and without peroxide post-treatment, along with associated controls were evaluated for color change, erosion and black-stain fungal resistance after exposure to artificial photo-degradation. The impact of the peroxide treatment on copper leaching was assessed in a laboratory experiment, and the impact on copper reactivity was assessed by electron parametric resonance (EPR) spectroscopy. Peroxide post-treatment of wood pressure impregnated with MBCC was shown to reduce color change by more than 50% compared to controls. Erosion due to photo-degradation and colonization by black-stain fungi were lower in samples treated with MBCC than in untreated controls and were relatively unaffected by peroxide post-treatment. The peroxide post-treatment was associated with increased amounts of mobile copper. This led to increased susceptibility to leaching and to a more than 60% increase in the amount of copper than had reacted with the wood.

Highlights

The service life of wood products in exterior applications is often limited by loss of appearance rather than loss of structural integrity [1]
We explored this approach using wood impregnated with micronized basic copper carbonate (MBCC)
The natural looking mid-brown color produced by the peroxide post-treatment of MBCC impregnated wood suggests that an attractive and fade resistant brown color at point of sale could be achieved

Summary

Introduction

The service life of wood products in exterior applications is often limited by loss of appearance rather than loss of structural integrity [1]. Weathering is a complex series of interactions between moisture, UV and visible light, oxygen, and surface-colonizing fungi [2]. Changes in color arise largely from the photo-degradation of lignin and the colonization by surface-inhabiting black-stain fungi [3]. A wide range of inorganic UV absorbers can be used to improve color stability [4]. This includes copper, which is already present in many residential preservative formulations. Copper-based wood preservatives are known to photo-stabilize lignin and slow the rate of surface degradation and color change from weathering [5,6,7,8]. One of the most widely used residential wood protection treatments in

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