Determination of the Effect of Liquid Glass ( SiO 2 ) on Color Stability of Wood Stained by Natural Dyes

In this exploratory study, the effect of liquid glass (SiO2) treatment on color stability of wood stained by natural dyes was investigated. Mixing liquid glass with natural dyes produced durable, natural, and protective wood stain as expected. For natural dyes, Licorice (Glycyrrhiza glabra L.), Indigo (lsatis tinctoria L.) and pomegranate skin (Punica granatum L.) were chosen and their extracts were mixed with liquid glass and applied to Scots pine (Pinus sylvestris L.), chestnut (Castanea sativa Mill.) and mahogany (Khaya Ivorensis A. Chev.) specimens using immersion method. Coated wood specimens were tested to evaluate the protection degree of liquid glass + natural stains against discoloration using cold check test. The treated wood specimens were exposed to cold check test for different conditions; 1 h 50 °C (± 5), 1 h laboratory conditions, and 1 h -20 °C (± 2), for 20 cycles. As a result, the liquid glass treatment produced better performance against color change. However, for general defi nition, liquid glass was not found precisely effective on color stability.

"Zero VOC" even if the VOC content in it is actually not zero.EPA Method 24 allows for up to 5 g/L of VOCs as "Zero VOC" for oil-borne paints, 250 g/L as "Low-VOC" for latex paints, and 380 g/L, as "Low-VOC" for oil-borne paints (EPA, 2016).
As mentioned earlier in this study, VOCs are a cause of low indoor air quality.The United States Environmental Protection Agency (US EPA) recommended not using them in indoor environment".The synthetic dyes can be replaced with the natural ones to solve this problem.During the last few decades, growing interest in the use of natural colourants has been recognized, both in public awareness and scientifi c activity (Leitner et al., 2012; Khan et al. 2006).The majority of natural dyes are vegetable dyes from plant sources: roots, berries, bark, leaves, wood and other organic sources such as fungi and lichens.These alternative materials provide increased sustainability, renewable resources, environmentally friendly processing, reduced pollution, and green chemistry (Bechtold et al., 2003).Also, environmentally-friendly natural poisonous plant extracts, stains derived from natural dye plants, and water-based wood preservatives are being developed against wood damaging biotic and abiotic factors.There are scientifi c studies on using natural plant dye staff for wood materials.After applying natural dyes on wood specimens, color changing (Goktas et al., 2013; Peker, 2012; Goktas, 2009; Goktas, 2008 a ; 2008 b ), antimicrobial, and antifungal performances (Ozen, 2014) have been determined.Unfortunately, natural colorants and preservatives can be bleached and discolored by exposure to weather conditions.Therefore, introducing natural and durable colorant is a requirement that needs to be developed against bleaching and discoloration.
As a solution to this problem, applying liquid glass on wood materials was considered as a potential option.The liquid glass can be used to decrease the disadvantages of wood like lack of color stability and water interaction of wood (Lu et al., 2014).Also, another study showed that the addition of nano-SiO 2 modifi cation to the wood structure provides decrease in external moisture penetration, which has a negative effect on color changes (Jiang et al., 2013).The liquid glass can be sprayed on the surface within seconds and can create an anti-microbial, easy-to-clean barrier that will last from one to several years, depending on the surface (Nanopool, 2012).In this study, the coated wood specimens were tested to evaluate the protection degree of liquid glass+natural stains against discoloration using cold check test.

UVOD
Volatile organic compounds (VOCs) are chemicals used to manufacture and maintain building materials, interior furnishing, cleaning products, and personal care products."Volatile" means that these chemicals evaporate or can easily get into the air at room temperature."Organic" means that these chemicals are carbon based.The term "chemical emissions" refers to VOCs as they evaporate into the air from products (Greenguard, 2016).
VOCs are emitted as gases from certain solids or liquids.VOCs include a variety of chemicals, some of which may have short-and long-term adverse health effects.The majority of VOCs found in the indoor environments originate from building materials, indoor furnishings, cleaning supplies, consumer products and processes, such as printing, cooking, hobbies, cleaning, interior renovations and pesticide applications.
The human health risks can be decreased using organic chemicals instead of highly toxic, petroleum based ones.Human health risks may include: eye, nose and throat irritation, headaches, loss of coordination and nausea, damage to the liver, kidney and central nervous system; also some organics can cause cancer in animals, some are suspected or known to cause cancer in humans (EPA, 2016).
There are three main ways how people are exposed to chemicals: ingestion, dermal absorption, and inhalation.Ingestion occurs when materials including chemical content are swallowed or placed in the mouth.Dermal absorption occurs when chemicals come into contact with the skin.While these are both signifi cant forms of chemical exposure, the majority of everyday chemical exposure occurs through the air we breathe in our homes, offi ces, schools and other indoor environments.As mentioned earlier in this paper, these airborne chemicals are commonly referred to as volatile organic compounds (VOC's).EPA's Offi ce of Research and Development's "Total Exposure Assessment Methodology (TEAM) Study" found levels of about a dozen common organic pollutants to be 2 to 5 times higher inside homes than outside, regardless of whether the homes were located in rural or highly industrial areas (Dalsan, 2015;Greenguard, 2016).
Due to economical impacts, environmental concerns, and new regulations, paint and coating industries are signifi cantly shifting toward water-borne formulations (Stoye et al., 2006;Dalsan, 2015).Nowadays, the interest in using water-borne paints or stains in furniture manufacturing has been signifi cantly increased.Unfortunately, water-borne paints are not fully harmless because the colorants used in waterborne paints are frequently aniline based ones, where aniline is a toxic organic compound with the formula C 6 H 5 NH 2 .
There is a variety of defi nitions like; "VOC Free Paint", "Zero VOC", "Green-Product" on paint bins."Zero VOC" paint does not necessarily mean non-toxic, healthy, or safe.EPA allows the paint to be called ..........Yeniocak, Goktas, Aliyazicioglu, Colak, Yeniocak, Ozen, Ugurlu: Determination... were chosen.The specimens were prepared from the sapwood parts of the fi rst-class wood with smooth fi ber, knotless and crack-free surfaces, no color and density differences, with annual rings perpendicular to the surfaces, in accordance with TS 2470 standards (2005).
In this study, the cold check test was used to observe and investigate the behavior of the fi nishing layer.The cold check test is a practical way to understand that the changes in fi nishing layer occured because of temperature changes (Wisnofurniture, 2013).
The cold check test specimens were prepared with dimensions of 100 mm x100 mm x10 mm and were kept under suitable temperature (20±2 °C) and suitable moisture (moisture of ±12 % and relative humidity of ±65 %) conditions until they became airdried (the moisture value in furniture used under interior area conditions) in accordance with TS 2471, (2005).

Plant material and mordant agents 2.2. Biljni materijal i sredstva za fi ksiranje boje
Plant materials were purchased from domestic markets located in Turkey.The Licorice (Glycyrrhiza glabra L.), Indigo (lsatis tinctoria L.) and Pomegranate Skin (Punica granatum L.) were chosen as natural dyes.In addition to creating affi nity between dye and wood fi bre, the use of mordants change the hue of certain dyes (Shahid, 2013).Different mordants used with the same dye may darken, brighten or drastically alter the fi nal color of the dyed wood sample.The mordants used in this study were ferrous sulfate (Fe 2 (SO 4 ) 3. 7H 2 O), aluminum sulfate (Al 2 (SO 4 ) 3 .18H 2 O) and vinegar (Kimetsan Co.,Fersan Co./Turkey).Also, a synthetic dye (woodtex -Kayalar kimya Co./Turkey) has been used for comparison to natural dyes.

Extraction of dye 2.3. Ekstrakcija boje
A weighed amount of dry plant material was extracted with distilled water in a bath (Elmasonic X-tra 150 H).According to the standard procedure, the mass / volume ratio between plant material and liquid was 1:20; extraction was performed for approximately 180 min.at 45 °C.Due to the high liquor ratio, some manual stirring was applied to distribute the plant material homogenously in the liquid during the extraction period.The expected volume loss due to evaporation was compensated by the addition of water at the end of the extraction period to obtain the initial volume.
Aqueous solutions were mordanted by adding ferrous sulfate (Fe 2 (SO 4 ) 3 .7H 2 O) 3 %, aluminum sulfate (Al 2 (SO 4 ) 3 .18H 2 O) 5 %, and grape vinegar 10 % in order to stabilize the color of extracted dyes, ensure itsduralibilty on the applied material (to increase retention amount), and create color options.After mordanting, liquid glass was added to mordanted aqueous with 20 % by weight.

Dyeing experiments 2.4. Bojenje uzoraka
Air-dried wood specimens were placed into the dyebath container.The immersion method was applied for 60 min at 45 °C.Any extra solution left on the specimens was wiped with a clean cloth.Specimens were then left to air dry at 20±3 °C in a vertical position.

Color measurements 2.6. Mjerenja boje
The colors of the cold check tested coated parts were identifi ed prior to exposure using Konica Minolta CR-10 portable color reader device.Minumum four (4) repetitions (color measurmenets) were performed to analyze the colors on each specimen due to the non-homogenous color structure of wood.The identifi ed color values were classifi ed according to the coordinates Commission International de I'Eclaireage-CIELAB 1976 set in ISO 2470 standards (Figure 1).The obtained colors were indicated by numerical values of L, a, and b.Where; "L" indicates lightness from 0 % (black) to 100 % (white), "a" from green (-a) to red (+a), and "b" from blue (-b) to yellow (+b).Also, the coated parts were subjected to color measure prior to cold check test and stated as "color values prior to cold check".

Determination of color change values 2.7. Određivanje veličina promjene boje
In order to determine the color changes occured due to the cold check test cycle, Konica Minolta CR-1 (Japan) portable color reader device was used.Color changes were calculated with the following equations in accordance with ISO 2470 standards.Where; ∆L*, ∆a* and ∆b* are the changes occurring between the initial state (i) and fi nal state (f) of colors.∆E*, indicates total changes of colors occurring in L, a, and b.The highest value shows the highest color change.

REZULTATI I RASPRAVA
The color change values of the test specimens exposed to cold check test for periods of 1 h 50 °C (± 5), 1 h laboratory conditions, and 1 h -20 °C (± 2), for 20 cycles are numerically presented in Table 1 The results showed that all wood specimens, exposed to cold check test, produced negative values of ΔL*.This was attributed to chemical structure changes that occurred, especially in lignin, due to temperature differences applied through the cold check test.
For natural plant extracts, sensitive degrees to cold check test are Licorice (Glycyrrhiza glabra L.), Pomegranate skin (Punica granatum L.) and indigo (lsatis tinctoria L.) extracts.For Licorice, the best color stability (ΔE* 3,14) was determined on chestnut wood with vinegar mordant.The biggest change (ΔE* 49,08) for the same dyestuff was observed on chestnut wood treated with ferrous sulfate (Table 1).The best color stability (ΔE* 3,71) for Pomegranate skin was determined on mahogany wood with vinegar mordant.The biggest change (ΔE* 50,06) for the same dyestuff was observed on scots pinewood with ferrous sulfate (Table 2).For indigo, the best color stability (ΔE*8,89) was determined on chestnut wood with control sample (without mordant).For indigo, the biggest change (ΔE* 56, 74) for the same dyestuff was observed on the same wood with ferrous sulfate (Table 3).Wood materials colored with metal mordant mixes produced darker colors.However, researchers did not determine that mordant had negative effect on color change performances.This can be explained by the reactions between wood material and mordant mixes and defi nitely by the effect of UV irradiation on different colors.Dark colors could absorb the light up to 98 %, and transparent colors up to 11 %.Therefore, darker wood species could have undergone more color changes (Yeniocak et al., 2015).
Among wood specimens, high color changing values for cold check test were respectively observed on Scots pine, chestnut and mahogany.The reason for the differences between wood species may be due to the differences of chemical composition of wood species, and interaction of natural dyes and mordant mixes ).In addition, the treatment parameters, such as treatment time, percentage of dyes materials, application temperature and percentage of mordant may also affect the color stability.All wood specimens exposed to cold check showed negative values of ΔL*, which means that the color of all wood specimens partially turned to gray.Generally, the highest negative values (ΔL*) were observed on specimens that were treated with ferrous sulfate mordant.This result is compatible with literature studies about color changing (Yeniocak, et al., 2015) of natural dyes.The use of ferrous sulfate mordant produced high color

Figure 1
Figure 1 CIELAB-76 color system Slika 1. Sustav boja CIELAB-76 , Table 2, and Table 3. Positive (+) values of ΔL* show whitening, and negative (-) values of ΔL* indicate the color turning to gray.Positive values of Δa* indicate reddening of the colors, and negative values of Δa* show a shift towards green.Positive values of Δb* represent yellowing in color, and negative values of Δb* represent the color turning blue.