**1. Introduction**

The service life of wood products in exterior applications is often limited by loss of appearance rather than loss of structural integrity [1]. As a result, there is a need for wood protection treatments to protect the appearance of the wood as well as against biodegradation by decay and insects. 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 [5–8]. One of the most widely used residential wood protection treatments in North America is micronized copper azole (MCA), which includes micronized basic copper carbonate (CuCO3·Cu(OH)2) (MBCC) as the primary biocide. Treatment with MBCC gives wood a pale blue/green color. Commercial products often add a colorant to give the MBCC-treated wood a more natural-looking brown color [9]. For exterior preserved wood, iron oxides dominate the market due to their low cost, the wide range of colors that are possible, their photo-protective effects, their compatibility with preservative formulations and their positive health and environmental profiles [10]. However, the color still fades over time.

It was observed that, in service, wood treated with copper-based preservatives tends to go from green/blue to a brown color as the surface of the wood oxidizes [11]. The use of peroxide to generate stable color complexes in wood impregnated with transitional metal compounds has been reported by Auger [12]. In the present work, we explored this approach using wood impregnated with MBCC followed by a peroxide post-treatment. The aim was to understand the e fficacy of this approach in yielding a brown, photo-stable wood surface with the potential to eliminate or reduce the need for the addition of colorants.

MBCC-treated wood with a peroxide post-treatment could potentially also a ffect preservative efficacy. MBCC has proven to be an e ffective wood preservative due to the slow solubilization of MBCC and reaction of this solubilized copper with the wood cell wall [13–15]. Oxidation of the wood surface was hypothesized to increase the amount of reacted copper, which could potentially increase biological e fficacy.

#### **2. Materials and Methods**

These experiments assess the performance of wood pressure-treated with MBCC, with and without a peroxide post-treatment. Specimens were evaluated for their resistance to color change and erosion following accelerated photo-degradation, and their resistance to disfigurement by artificially inoculated and incubated black-stain fungi under optimal conditions. An additional experiment examined the impact of the peroxide post-treatment on copper leaching and on the formation of reacted copper in the wood.

Red pine (*Pinus resinosa*) sapwood was used as a wood substrate throughout these experiments. MBCC was obtained from Timber Specialties Co. (Campbellville, ON, Canada). An iron oxide-based colorant formulation was used as a reference in the accelerated photo-degradation experiment. The MBCC and the iron oxide-based colorant were applied to wood by vacuum-pressure impregnation to target gauge concentrations of 4.0 kg of MBCC per cubic meter of wood and 2.0 kg of iron oxide-based colorant per cubic meter of wood, respectively.

The peroxide post-treatment consisted of a one-minute dip in a 20% solution of aqueous hydrogen peroxide adjusted to pH 6 with a dilute solution of sodium hydroxide at room temperature on air-dried samples. The 20% solution was prepared from a 30% hydrogen peroxide concentrate (Fisher Scientific, Ottawa, ON, Canada, ACS Reagent Grade). The conditions described above were determined based on a series of tests to optimize the peroxide treatment conditions. These tests are described in Appendix A. Factors evaluated included peroxide concentration, pH, storage time, drying and the impact of wood type (heartwood vs. sapwood).
