Determination of Color, Whiteness Index, and Glossiness Properties in Wax Applied American white oak (Quercus alba) Wood

Wood is one of the most important natural raw material sources used by humans. Its significant role as a renewable resource is attributed to its widespread availability, as well as its properties such as hardness, strength, elasticity, and lightness. Additionally, its ability to be shaped and the capacity to improve certain properties, along with qualities like nail and screw holding capabilities and adhesiveness, contribute to its importance. Thanks to these favorable characteristics, wood material finds thousands of applications today [1].

Wood materials left exposed to outdoor conditions in their natural state are susceptible to various biotic and abiotic hazards. Therefore, it may be necessary to impregnate them or apply protective coatings, especially for those of aesthetic significance [2].

Wood surface treatments have been employed since ancient times to overcome inherent limitations, enhance aesthetic appeal, ensure cleanliness, and provide protection against external elements. In furniture production, various wood species and surface finishes are utilized, each offering distinct structural properties that influence their application. These variations in structural and surface properties are critical factors that define and restrict the use of varnish systems in different contexts [3].

Young worker bees produce wax, which is secreted as a liquid from four pairs of wax glands located on the ventral surface of their abdominal tergites. This liquid wax spreads over the surface of these plates and solidifies upon exposure to air, forming a single wax scale on each tergite. These scales appear as small wax flakes on the lower part of the bee’s body. A worker bee produces eight wax scales every 12h. The size of the wax glands is dependent on the worker bee’s age: they reach their maximum size around 12 days old and gradually decrease from the eighteenth day until the end of their life [4].

This study seeks to fill a research gap in the literature, where wax-based treatments have been extensively studied in various modifications or in their natural state across different wood species [5-30]. Studies have reported the application of wax-based chemicals prepared using various methods on wood materials. However, there is a notable lack of investigation into the surface properties after applying three different coat numbers of wax specifically on American oak wood. Below are summarized details about this particular tree species.

American oak (Quercus alba) has been valued by several Native American tribes for its antiseptic and astringent properties and has been used medicinally to treat various ailments. The bark was chewed to treat mouth sores [31]. Heartwood generally shows a moderate level of resistance to decay. It finds extensive use in various applications such as railroad ties, lumber, mine supports, barrel-making, fence posts, fuelwood, cladding, and more. Highquality white oak is especially preferred for making tight barrels. Its durability against decay makes it a popular choice for ship and boat planking as well as curved components. Moreover, it is utilized in doors, flooring, railway equipment, agricultural tools, carpentry, furniture, and a wide range of other products [32]. In terms of its composition, the cellulose content in American oak wood is 38.11%, lignin is 25.01%, ethanol-cyclohexane soluble extractives are 2.03%, and hot water solubility is 3.16% [33]. Waxes are also applied to drawer slides and edges, as well as on surfaces that need to be slippery, such as skis, to reduce friction. Waxes can be softened with heat [34].

In this study, color, glossiness, and whiteness index values were determined on surfaces obtained by applying wax at different coat numbers on American white oak (Quercus alba) wood.

For this research, American white oak (Quercus alba) wood sourced commercially was cut into dimensions of 100 x 200 x 20mm. The wood surfaces underwent sanding with 80, 100, and 120 grit sandpapers using a vibration sander before being cleaned with compressed air. A wax-based oil mixture, comprising natural and synthetic waxes (neutral color, 30% dry residue, paste-like appearance, characteristic odor, water-dispersible but not soluble, pH 7.6), was applied to the wood surfaces in 1, 2, and 3 coats using a brush.

Glossiness, much like color and light intensity, is a psychophysical quantity that requires standardized illuminating and observing conditions [35]. Glossiness tests were conducted using the ETB- 0833 model gloss meter device according to the ISO 2813 [36,37] standard. These tests were performed at three different angles (20 °, 60 °, and 85 °) in both perpendicular and parallel directions to the wood fibers.

Whiteness index (WI*) values were measured using the Whiteness Meter BDY-1 device, evaluating both parallel and perpendicular orientations to the wood fibers, following ASTM E313-15e1 [38] standards.

The color change of the samples was assessed using the CS-10 (CHN Spec, China) device, following the ASTM D 2244-3 [39] standard [CIE D65 light source, CIE 10 ° standard observer; illumination system: 8/d (8°/diffuse illumination)]. In the literature, ΔC* is referred to as chroma difference or saturation difference, and ΔH* is referred to as hue difference or shade difference [40]. The total color differences were computed utilizing the formulas provided.

Definitions for other parameters [ΔC*, Δa*, Δb*, and ΔL*] can be found in Table 1 [40]. The criteria for visually assessing the calculated ΔE* color difference are outlined in Table 2, in accordance with DIN 5033 [41].

Table 1:The definitions of ΔC*, Δa*, Δb*, and ΔL* [40].

Table 2:Comparison criteria for ΔE* evaluation [41].

Using statistical software and measurements from the study, calculations have been conducted to determine maximum measurement values, minimum mean values, analysis of variance, standard deviations, homogeneity groups, and percentage (%) change rates.

Table 3 shows the analysis of variance results for color parameters. In all tests for color parameters, the number of coats factor was found to be significant (Table 3).

Table 3:Analysis of variance results for color parameters.

Table 4 displays the measurement results for color parameters. With wax applications, decreases were found in ho and L* values, while increases were observed in C*, a*, and b* values (Table 4).

In the a* parameter, the highest result was observed in the samples treated with 2 coats of wax (9.59), while the lowest result was found in the control samples (6.23). a* test, the greatest increase was observed in the samples with 2 coats of wax, showing a rise of 53.93%, while the smallest increase was recorded in the samples with 1 coat of wax, at 22.95% (Table 4).

The highest L* value was found in the control group samples (64.14), while the lowest value was obtained on surfaces treated with 2 coats of wax (53.93). The smallest decrease rate in L* was observed with 1 coat wax application (%6.53), whereas the highest decrease rate was seen in the experimental samples with 2 coats of wax (%15.92) (Table 4).

Table 4:Measurement results for color parameters.

In the b* value test, the highest rate of increase was observed in the samples treated with 2 coats of wax at 27.65%, whereas the lowest rate of increase was found in the samples treated with 1 coat of wax at 18.26%. For the b* parameter, the highest result was found in the samples treated with 2 coats of wax (24.19), while the lowest result was obtained in the control samples (18.95) (Table 4).

When looking at C* parameter, the highest increase rate was obtained in the samples treated with 2 coats of wax at 30.48%, while the lowest increase rate was found in the samples treated with 1 coat of wax at 18.60%. For C* value, the lowest result was observed in the control samples (19.95), whereas the highest result was seen in the samples treated with 2 coats of wax (26.03) (Table 4).

Regarding the results for the ho parameter, after wax applications, the minimum decrease rate was 0.93% with 1 coat, and the maximum decrease rate was 4.82% with 2 coats. In ho parameter, the lowest result was found on the surfaces of samples treated with 2 coats of wax (68.34), while the highest result was obtained on the control samples where no wax application was done (71.80) (Table 4).

Table 5 presents the results for total color differences. The ΔH* values were determined to be 0.54 for 1 coat of wax, 1.34 for 2 coats of wax, and 1.02 for 3 coats of wax. For all wax applications, the ΔL* values were found to be negative (darker than the reference), while the Δa*, Δb*, and ΔC* values were positive (indicating the samples were redder, yellower, and clearer/brighter than the reference, respectively). The ΔE* values were found to be 5.62 for 1 coat of wax, 11.96 for 2 coats of wax, and 10.57 for 3 coats of wax. When comparing the color change criteria, applying 1 coat of wax resulted in a “very distinct” category (3.0 - 6.0), while applying 2 to 3 coats of wax resulted in a “strong” category (6.0 - 12.0) (Table 5).

Table 5:Results for total color differences.

Table 6 presents the analysis of variance results for whiteness index (WI*) values. The number of coats factor was found to be significant in whiteness index (WI*) values in both directions (⊥ and ║) (Table 6).

Table 6:Analysis of variance results for whiteness index (WI*) values.

Table 7 displays the measurement results for whiteness index (WI*) values. Decreases were observed in WI* tests in both directions. The control samples exhibited the highest values (⊥: 19.56 and ║: 14.60). The lowest WI* results were found in the experimental samples treated with 2 coats of wax (⊥: 12.50 and ║: 6.98). Decrease percentages for applications of 1, 2, and 3 coats were found to be %31.19, %36.09, and %28.43 for WI* ⊥, respectively, and %34.79, %52.19, and %28.36 for WI* ║, respectively (Table 7).

Table 7:Measurement results for whiteness index (WI*) values.

In the literature on wax studies, it has been reported that applying different numbers of coats affects the whiteness index (WI*) values [ebony Africa (Diospyros crassiflora Hiern.) [9], lemon (Citrus limon (L.) Burm.) [8], magnolia (Magnolia grandiflora L.) [15], American black cherry (Prunus serotina) [30], American walnut (Juglans nigra L.) [12], plum (Prunus domestica L.) [16], olive (Olea europaea L.) [23], ebony Macassar (Diospyros celebica Bakh.) [26].

The analysis of variance results for glossiness values are presented in Table 8. In all grades and directions, the number of coats factor was found to be significant in glossiness values (Table 8). Table 9 presents the measurement results for glossiness (║ and ⊥, 20 o, 60 o, and 85 o) values. Increases were observed in glossiness values with the application of multiple coats in all grades and directions. The lowest glossiness values were found in the control samples (⊥20 o: 0.41, ⊥60 o: 2.38, ⊥85 o: 0.91 and ║20 o: 0.30, ║60 o: 2.63, and ║85 o: 1.70). The highest glossiness values were obtained on surfaces treated with 3 coats of wax (⊥20 °: 0.80, ⊥60 °: 4.78, ⊥85 °: 6.08 and ║20 °: 0.75, ║60 °: 5.44, and ║85 °: 9.24). The highest increase rates were observed with the application of 3 coats in all grades and directions wax (⊥20 °: 95.12%, ⊥60 °: 100.81%, ⊥85 °: 568.13% and ║20 °: 150.00%, ║60 °: 106.84%, and ║85 °: 443.53%) (Table 9).

Table 8:Analysis of variance results for glossiness values.

Table 9:Measurement results for glossiness (║ and ⊥, 20o, 60o, and 85o) values.

In the existing literature concerning wax studies, it has been noted that altering the number of applications influences the values of glossiness [magnolia (Magnolia grandiflora L.) [15], olive (Olea europaea L.) [23], ebony Africa (Diospyros crassiflora Hiern.) [9], lemon (Citrus limon (L.) Burm.) [8], American walnut (Juglans nigra L.) [12], American black cherry (Prunus serotina) [30], plum (Prunus domestica L.) [16], ebony Macassar (Diospyros celebica Bakh.) [26].

Conclusion

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• Abstract
• Introduction
• Material and Method
• Statistical Analysis
• Findings and Discussion
• Conclusion
• References

The ΔE* values were measured as 5.62 for 1 coat of wax, 11.96 for 2 coats of wax, and 10.57 for 3 coats of wax. Wax applications led to decreases in L* and ho values, while showing increases in a*, C*, and b* values. In this study, it has been observed that different results were obtained with the application of varying numbers of wax layers.

References

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• Abstract
• Introduction
• Material and Method
• Statistical Analysis
• Findings and Discussion
• Conclusion
• References

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