The aim of this study was to investigate effects of natural weathering on color stability of Scots pine (
Wood is one of the most important natural materials used for aesthetic, engineering, and structural applications [
This study investigates the effect of natural weathering on color stability of Scots pine and Oriental beech wood impregnated with copper-based wood preservatives including TN-E, AD-KD5, and CCA and applied with PV or SV. The effect of 3- and 6-month natural weathering on color stability was evaluated.
Wood specimens were prepared from air-dried sapwood of Scots pine and Oriental beech for impregnation treatment with dimensions of 10 (radial) × 100 (tangential) × 150 (longitudinal) mm. They were oven dried at
The wood specimens were impregnated with 4 percent aqueous solution of CCA, AD-KD5, and TN-E according to the ASTM D1413-07e1 [
SV and PV were supplied by merchants and used according to the producer’s instructions. The viscosity of the varnishes was determined according to the manufacturer’s directions and was found to be 18 s (DIN 4 cup) at
Wood specimens were prepared for weathering exposure according to ASTM D7787 [
Weather conditions of Mugla from March to August in 2011.
Months | Mar | Apr | May | Jun | Jul | Aug |
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Average temperature (°C) | 8.6 | 11.7 | 16.4 | 22.8 | 27.9 | 27.5 |
The highest temperature (°C) | 19.9 | 21.7 | 29.1 | 35.9 | 38.4 | 38.1 |
The lowest temperature (°C) | −4.9 | 1.4 | 6.8 | 13 | 12.1 | 13.5 |
Sunbathing time (hour) | 5.4 | 5.5 | 6.8 | 10 | 11.2 | 10.4 |
The number of the rainy days | 11 | 17 | 9 | 6 | 0 | 0 |
Rainfall per month (kg/m2) | 29.8 | 80.4 | 59.4 | 17.4 | 0 | 0 |
Humidity (%) | 74.6 | 75.2 | 67.8 | 53.6 | 38.8 | 39.2 |
The exposure rack was positioned so that the exposed specimens were at an angle of 45° facing south. Wood specimens were set outside for weathering exposure according to ASTM G7/G7M-13 [
The CIE
The CIE
In this study, synthetic or polyurethane varnish was applied to Scots pine and Oriental beech wood specimens after being impregnated with three different chemicals except for the control specimens. The wood specimens were exposed to natural weathering for two periods, 3 months and 6 months. The effects of natural weathering on color stability of impregnated and varnished wood materials are evaluated in this section. Retentions of different impregnation solutions on Scots pine and Oriental beech wood are given in Table
Retentions of wood specimens.
Impregnation solution | Concentration (%) | Retention (Kg/m3) | |
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Scots pine | Oriental beech | ||
CCA | 4 | 32.7 | 27.6 |
AD-KD5 | 4 | 30.7 | 23.1 |
TN-E | 4 | 35.5 | 28.8 |
Retentions were calculated as 30.7 to 35.5 kg/m3 in Scots pine and 23.1 to 28.8 kg/m3 in Oriental beech. The highest retention amounts determined in Scots pine and Oriental beech treated with TN-E were 35.5 kg/m3 and 28.8 kg/m3, respectively. The lowest retention amounts determined in Scots pine and Oriental beech treated with AD-KD5 were 30.7 kg/m3 and 23.1 kg/m3, respectively.
Table
The color changes of Oriental beech before and after natural weathering.
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Before natural weathering | After 3-month natural weathering | After 6-month natural weathering | ||||||||||||||||||||
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Mean | SD | Mean | SD | Mean | SD | Mean | SD | Mean | SD | Mean | SD | Mean | SD | Mean | SD | Mean | SD | Mean | SD | Mean | SD | ||
Control | 10 | 62.30 | 7.60 | 10.78 | 1.38 | 21.78 | 3.01 | −9.84 | 1.40 | −9.83 | 1.26 | 9.94 | 1.31 | 17.10 | 2.60 | −19.35 | 2.55 | −12.3 | 1.87 | −8.63 | 1.05 | 24.50 | 3.14 |
PV | 10 | 68.07 | 7.35 | 12.60 | 1.20 | 27.04 | 4.19 | 8.92 | 1.23 | −5.37 | 0.62 | 9.36 | 1.20 | 14.00 | 1.93 | −14.78 | 1.89 | −9.66 | 1.33 | −10.07 | 1.09 | 20.33 | 2.34 |
SV | 10 | 63.54 | 5.46 | 12.74 | 1.48 | 28.11 | 3.71 | 7.87 | 0.83 | −5.65 | 0.66 | 8.45 | 1.23 | 12.86 | 1.49 | −13.18 | 1.92 | −10.16 | 1.18 | −9.75 | 0.84 | 19.29 | 2.24 |
CCA + PV | 10 | 60.53 | 5.57 | 12.15 | 1.56 | 28.51 | 3.93 | 7.78 | 0.95 | −3.53 | 0.45 | 8.25 | 1.25 | 11.88 | 1.45 | −13.63 | 2.07 | −7.85 | 0.96 | −7.53 | 0.69 | 17.44 | 2.41 |
AD-KD5 + PV | 10 | 54.27 | 6.13 | 14.77 | 1.42 | 28.73 | 4.48 | 7.60 | 1.01 | −3.39 | 0.53 | 7.26 | 0.89 | 11.04 | 1.47 | −11.35 | 1.40 | −9.41 | 1.25 | −5.18 | 0.59 | 15.63 | 2.44 |
TN-E + PV | 10 | 38.69 | 3.52 | 3.14 | 0.43 | 10.06 | 1.39 | 5.86 | 0.71 | −3.97 | 0.55 | 6.95 | 0.77 | 9.92 | 1.20 | −5.87 | 0.65 | −6.81 | 0.82 | −6.95 | 0.63 | 11.36 | 1.57 |
CCA + SV | 10 | 61.46 | 5.10 | 11.90 | 1.42 | 28.96 | 4.89 | 6.92 | 0.78 | −5.48 | 0.65 | 5.84 | 0.66 | 10.58 | 1.20 | −13.02 | 1.47 | −8.86 | 0.91 | 8.73 | 0.72 | 18.01 | 2.14 |
AD-KD5 + SV | 10 | 58.21 | 6.46 | 12.43 | 1.70 | 27.50 | 3.77 | 6.83 | 0.96 | −5.38 | 0.74 | 5.89 | 0.77 | 10.50 | 1.48 | −10.56 | 1.38 | −9.13 | 1.29 | −7.81 | 0.87 | 16.00 | 2.19 |
TN-E + SV | 10 | 35.51 | 4.40 | 2.83 | 0.33 | 8.87 | 1.22 | 6.55 | 0.81 | −4.83 | 0.57 | 5.86 | 0.73 | 10.03 | 1.24 | −6.85 | 0.85 | −7.19 | 0.89 | −7.24 | 0.90 | 12.29 | 1.45 |
Before natural weathering, while
After 3-month natural weathering,
After 6-month natural weathering, the
The color changes of Scots pine before and after natural weathering are shown in Table
The color changes of Scots pine before and after natural weathering.
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Before natural weathering | After 3-month natural weathering | After 6-month natural weathering | ||||||||||||||||||||
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Mean | SD | Mean | SD | Mean | SD | Mean | SD | Mean | SD | Mean | SD | Mean | SD | Mean | SD | Mean | SD | Mean | SD | Mean | SD | ||
Control | 10 | 70.52 | 9.31 | 6.52 | 0.83 | 27.81 | 4.23 | −21.49 | 3.27 | 4.25 | 0.54 | 2.22 | 0.27 | 22.02 | 2.82 | −30.07 | 4.27 | −4.26 | 0.52 | −13.2 | 1.69 | 33.15 | 4.91 |
PV | 10 | 78.85 | 10.09 | 7.66 | 0.88 | 32.36 | 4.47 | −13.71 | 1.89 | 5.84 | 0.85 | 5.92 | 0.64 | 16.03 | 1.52 | −23.65 | 3.26 | −1.7 | 0.18 | −8.84 | 1.02 | 25.31 | 3.67 |
SV | 10 | 75.44 | 11.01 | 7.41 | 0.86 | 32.56 | 3.78 | −12.83 | 1.49 | 5.81 | 0.65 | 4.34 | 0.37 | 14.74 | 1.71 | −21.01 | 2.43 | −4.3 | 0.37 | −6.85 | 0.79 | 22.51 | 2.97 |
CCA + PV | 10 | 71.2 | 10.82 | 6.25 | 0.80 | 29.50 | 3.60 | −12.12 | 1.31 | 4.12 | 0.57 | 5.21 | 0.48 | 13.82 | 1.81 | −18.49 | 2.26 | −1.19 | 0.11 | −3.84 | 0.49 | 18.92 | 2.61 |
AD-KD5 + PV | 10 | 73.94 | 9.09 | 8.35 | 1.30 | 41.24 | 5.48 | −11.17 | 1.63 | 5.11 | 0.80 | 5.67 | 0.64 | 13.53 | 1.30 | −17.46 | 2.32 | −1.88 | 0.21 | −5.26 | 0.82 | 18.33 | 2.86 |
TN-E + PV | 10 | 45.02 | 5.18 | 4.31 | 0.59 | 12.49 | 1.51 | −7.37 | 0.89 | 3.55 | 0.49 | 5.92 | 0.54 | 10.10 | 1.41 | −8.24 | 1.03 | −6.43 | 0.59 | −5.95 | 0.94 | 12.03 | 1.66 |
CCA + SV | 10 | 70.98 | 8.02 | 6.96 | 0.83 | 28.51 | 2.94 | −10.39 | 1.17 | 5.28 | 0.63 | 7.95 | 0.66 | 14.11 | 1.68 | −17.37 | 1.96 | −5.64 | 0.47 | −6.21 | 0.74 | 19.29 | 2.30 |
AD-KD5 + SV | 10 | 72.82 | 9.54 | 8.61 | 1.18 | 42.06 | 5.93 | −10.17 | 1.43 | 3.54 | 0.48 | 7.76 | 0.86 | 13.27 | 1.82 | −15.88 | 2.24 | −3.68 | 0.41 | −6.34 | 0.87 | 17.53 | 2.40 |
TN-E + SV | 10 | 47.71 | 5.92 | 3.26 | 0.38 | 15.86 | 1.97 | −6.24 | 0.77 | 2.98 | 0.35 | 7.65 | 0.95 | 10.31 | 1.22 | −11.34 | 1.41 | −6.37 | 0.79 | −5.85 | 0.69 | 14.26 | 1.68 |
Total color changes (
While the
Total color changes (
The highest
As the result, the best color stability was TN-E with PV coating for both Oriental beech and Scots pine wood specimens. TN-E treatments both slowed down photodegradation by retarding the formation of carbonyl groups. The light resistance of TN-E-treated wood likely results from Cu (II) chelating with functional groups in wood. These chelates can photostabilize wood and retard the formation of carbonyl groups [
Wood materials used in exterior applications are exposed to several climate factors including solar radiation, water, temperature changes, wind, and erosion [
Initially, Scots pine and Oriental beech control wood specimens had lighter, natural reddish, and yellowish color tones. Varnishing them increased lightness, yellowness, and redness of the color of the wood surface, but impregnating them decreased lightness of the wood specimens compared to control specimens. The lightness values of all the specimens decreased within natural weathering. However, untreated (control) wood specimens exhibited higher color changes than the other specimens in all stages of natural weathering.
It can be concluded that untreated (control), solely varnished, and both impregnated and varnished wood specimens shifted from red to green on the red-green scale and from yellow to blue on yellow-blue scale with increasing exposure times in natural weathering. The highest total color change was observed on the untreated (control) Scots pine after 3- and 6-month natural weathering. The total color changes of untreated Oriental beech specimen were less than that of untreated Scots pine specimens. Finally, the best color stability was obtained by impregnation with TN-E before PV coating for both Oriental beech and Scots pine wood specimens after the natural weathering. The impregnated wood with copper-based formulations before PV coating was more effective in stabilizing wood color. The photostabilization of wood by copper-based impregnation may be explained by the retarding of the formation of carbonyl groups and reduced delignification during weathering.
The authors declare no conflict of interests.