**3. Results**

## *3.1. Accelerated Photo-Degradation*

Average color change after 1000 h of Q-Sun exposure was calculated for each treatment group (Figure 1). The MBCC-treated wood became darker and less green. The peroxide post-treatment greatly reduced these color changes, as the wood was already darker and less green prior to Q-Sun exposure. The iron oxide-based reference treatment became less red and less yellow after Q-Sun exposure. The untreated control became darker and much less yellow. The total color change ( Δ*E*\*) was similar between the peroxide post-treatment and the iron oxide-based colorant reference, and less than the MBCC without the peroxide post-treatment and the untreated control.

Erosion measurements were quite variable but did show a significant reduction in erosion for all samples treated with copper compounds and the proprietary iron oxide colorant (Figure 2). This is consistent with the ability of copper to photo-stabilize wood [5–7,22]. Erosion was similar in MBCC-treated samples with and without peroxide post-treatment.

Figure 3 shows the samples before and after 1000 h of Q-Sun exposure. The discolored spot on three of the samples from each group is from the blue tack that was used to create a reference spot for erosion measurement. MBCC-treated wood changed from a pale green to a medium brown color. This is consistent with field observations of such material [23]. The peroxide treatment resulted in an initial brown-green color that changed to the same medium brown color as the MBCC treatment.

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**Figure 2.** Average and standard deviation of surface erosion after 1000 h of Q-Sun exposure of samples treated with micronized basic copper carbonate (MBCC) with and without peroxide post-treatment, an iron oxide-based colorant, and an untreated control.

**Figure 3.** Red pine sapwood before and after 1000 h of accelerated photo-degradation: (**a**) treated with micronized basic copper carbonate, (**b**) treated with micronized basic copper carbonate after 1000 h of accelerated photo-degradation, (**c**) treated with micronized basic copper carbonate with a peroxide post-treatment, (**d**) treated with micronized basic copper carbonate with a peroxide post-treatment after 1000 h of accelerated photo-degradation, (**e**) treated with an iron oxide-based colorant, (**f**) treated with an iron oxide-based colorant after 1000 h of accelerated photo-degradation, (**g**) untreated, and (**h**) untreated after 1000 h of accelerated photo-degradation.

#### *3.2. Black-Stain Fungal Resistance*

Black-stain fungi aggressively attacked most samples and quickly grew, causing darkening or masking of the original wood color (Figure 4). Note that the white material on some surfaces is epoxy resin from the edge seal. No color changes were observed on the uninoculated controls (Group D). A rating of 5 was assigned to the majority of samples of unweathered and weathered inoculated pine controls after only two weeks of incubation (Figure 5). The unweathered IPBC/propiconazole reference performed well and prevented any fungal growth with an average rating of 0 throughout the test for all inoculum types. The MBCC treatment was associated with lower black-stain ratings than untreated controls. Average stain ratings were near zero for inoculum group A. However, growth of the strains in inoculum groups B and C was evident on the MBCC-treated wood, with or without peroxide post-treatment. The peroxide post-treatment was associated with lower black-stain ratings than MBCC with no post-treatment for inoculum group B, but was similar for group C. MBCC is used to protect wood from fungal decay. This does not include staining fungi, though these data sugges<sup>t</sup> a possible beneficial effect.

**Figure 4.** Test assembly showing unweathered red pine sapwood covered with black-stain fungi after two weeks of incubation (**left**); unweathered red pine sapwood samples after six weeks of incubation with inoculum groups A, B, C and D (uninoculated) (**right**).

**Figure 5.** Average stain ratings over a six-week incubation for specimens exposed to strains of *Aureobasidium pullulans* from inoculum groups ( **A**–**C**).

## *3.3. Copper Leaching*

Copper leaching from the wood treated with MBCC was very low and similar to the untreated control (Figure 6). This is consistent with previous work demonstrating the low leachability of copper from wood impregnated with MBCC [24]. In contrast, copper leaching was much greater in the samples post-treated with peroxide, though this tapered off substantially after 22 days. During the leaching experiment, it was observed that water uptake during immersion was much greater in the peroxide post-treatment group (average 6.4 g) than in the no post-treatment group (average 3.4 g). This increase in water uptake may explain the greater degree of leaching observed.

**Figure 6.** Concentration of copper in leachates from wood impregnated with micronized basic copper carbonate, with and without peroxide post-treatment.

## *3.4. Copper Characterization*

**Table 1.** Average total copper measured by X-ray

The total copper content in the MBCC-treated wood measured by X-ray fluorescence is shown in Table 1. Total copper concentration averaged 5.6 mg/g in material with no post-treatment and 5.0 mg/g in material with the peroxide post-treatment. Reacted copper concentration averaged 2.62 mg/g in material with no post-treatment and 4.24 mg/g in material with the peroxide post-treatment. These data demonstrate an association between the peroxide post-treatment and increased levels of reacted copper. The reacted copper content in the wood treated with micronized copper carbonate is typical of values previously reported [21,25]. The peroxide treatment may generate more reactive sites in the wood, leading to enhanced reaction between the wood and the micronized basic copper carbonate. The peroxide reaction with lignin is known to oxidize ketonic carbonyl groups [26].

The EPR spectral parameters provide information on the electronic structure of paramagnetic copper complexes in wood. There was very little variation between material with and without peroxide post-treatment, indicating that the compounds being created during the post-treatment have very similar configuration and bonding as the reacted copper (Table 2). The Az parameter is consistent with a copper–oxygen bonding typical of the copper carboxylate bonding formed in wood [21].


fluorescence

 and reacted copper measured by EPR in



**Table 2.** Average EPR spectral data from MBCC-treated wood, with and without a peroxide post-treatment.
