Providing UV Protection Features for Woolen Fabric Using Buckthorn Dye

ABSTRACT In recent years, many different properties of natural dyestuffs that do not harm the environment and human have been discovered as a result of the search for dyestuffs. Buckthorn based dyes can be considered in this respect, and so they were tested in this study. The berries and leaves of the buckthorn bush trees were used. While dyeing the fabric, along with the dyeing process, other properties that can be added have been investigated. Wool fabrics with no metal salts and with five different metal salts were dyed with natural dye sources at 100°C for 1 hour. After dyeing, all samples were dried at room temperature. Then, the dyed wool samples’ CIE L*a*b* and color efficiency values (K/S) were determined from the obtained colors to show the usability of buckthorn in dyeing. Color fastness to washing, rubbing, perspiration, and light fastness of the samples were also tested, and results were determined in the range of 3–5 points. The T% values between 0.08 and 0.35 for UVA and between 0.09 and 0.18 for UVB were observed in all trials. It has been determined that fabrics treated with buckthorn berries/leaves can provide a protective feature against the harmful rays of the sun.


Introduction
The use of natural stuffs in textile finishing has started to be a promising topic in the textile industry. Due to the harm caused by petroleum-based dyestuffs to the environment and human health, research and development in the textile dye industry are particularly focused on renewing producing natural dyestuffs for a sustainable future (Thakker and Sun 2021). By 2024, it is expected that the global market share of natural dyes would increase by $5 billion or more. The compound annual growth rate would be 11% from 2018 to 2025 (Natural Dyes Market). Natural dyestuffs are widely used as colorants in the textile, food, pharmaceutical, cosmetic, leather, and lacquer industries today. There are a wide variety of plant-based dyestuffs and many different parts of plants, such as roots, stems, branches, leaves, bark, flowers, seeds, and fruit, can be used as the colorants (Samanta and Konar 2011). Phenolic compounds are the most commonly found structures in plants (Khoddami,Wilkes,and Roberts 0000), and plants produce flavonoids to protect themselves against external factors such as frost, drought, fungal/microbial activities, and UV radiation (Giusti and Wallace 2009). Therefore, in addition to the ability of plant-based natural dye sources to dye textile materials Davulcu et al. (2014); Benli and Bahtiyari (2015)(a); Benli and Bahtiyari 2016;Benli (2017); Mia et al. (2022) in recent years, many properties such as antimicrobial (Han and Yang 2005;Singh et al. (2005); Gawish et al. (2017); Yılmaz et al. (2020(a)); Yılmaz et al. (2020(b)); Jiang et al. (2022), antioxidant (Andreeva et al. 2004), anti-viral (Rachel and Hussain 2019) and UV protection (Grifoni et al. 2009;Hou et al. 2013;Karabulut and Atav 2020;Benli and Bahtiyari 2021;Mia et al. 2021) have been discovered. The sun is the main source of energy on the globe. Only a small portion of UV light is made up by solar energy, and the atmosphere absorbs it depending on its wavelength. Ozone, water vapor, and CO 2 in the stratosphere absorb the bulk of high-energy UV-C and around 90% of UV-B radiation. Thus, 94% of the radiation that comes to Earth is UV-A, which penetrates the skin deeply, while only 6% of UV-B comes to surface (Sankaran et al. 2021). Exposure to the sun's harmful UV rays causes a variety of health problems and plays a causal and determining role in acute and chronic skin damage as well as cancer (Afaq and Mukhtar 2001). Therefore, the skin should be protected from the harmful rays of the sun. Today, clothes can gain protective properties by a number of chemical substances (TiO 2 , ZnO) (Khan et al. 2018;Mavrić, Tomšič, and Simončič 2018;Sivakumar et al. 2013). From an ecological point of view, the toxicity of chemicals such as ZnO to environmental bacterial species is of great importance (Dağlıoğlu et al. 2016;Londono et al. 2017;Ma, Williams, and Diamond 2013). Hence, providing protection with environmentally friendly methods is also very important in terms of sustainability and the environment. In this context, the importance of detecting and applying natural materials and structures that have protective properties against the harmful UV rays of the sun has emerged. Researchers are currently exploring natural dyestuffs to ensure the UV protection of garments as ultraviolet radiation (UVR) begins to reach the Earth due to damage to the ozone layer. UV radiation can harm human beings and that is why the UV protection property of garments has become the main concern of garment manufacturers. As is known, natural fibers are widely used in summer garments because of their excellent comfort properties, but these fibers have very poor UV protection (Kociç et al. 2019). Natural resources such as dyer's woad, madder, logwood, brasilwood, lavender, and weld have been reported as dyestuff providing UV protection properties to the textile materials (Grifoni et al. 2009(Grifoni et al. , 2011(Grifoni et al. , 2014. In this study, the dyeing and UV protection properties of buckthorn (Rhamnus petiolaris Boiss) (Figure 1), a previously unexplored herbal resource from this point were investigated. Buckthorn has been known for centuries. Buckthorn berry dye plant, an old Turkish dyestuff, has a very important place in natural dyestuff sources (Böhmer et al. 2002;Cardon 2007). The main dyestuff present in the aqueous extract from the dried buckthorn is reported to be a glycoside derivative of rhamnetin (Romani, Zuccaccia, and Clementi 2006), and the barks have a lot of flavonoids such as chrysophanol, physcion, emodin (Tanker and Ertan 1971), and quercetin glycosides (Deveoglu 2012). During the 15 th and 17 th centuries, these plants were used to produce yellow colors on a variety of carpets (Deveoglu 2019) too. Apart from its usage as a dyestuff, little research has been done on buckthorn's other properties.
Comlekcioglu et al. reported that R. petiolaris was found to be the most efficient antimicrobial agent on wool yarn against certain microorganisms (Comlekcioglu et al., 2017). Davulcu et al. (2014) shown that polypropylene could be dyed via buckthorn through the incorporation of hyper-branched polyester amide into the polymer prior to fiber spinning via buckthorn (Davulcu et al. 2014). Rocchetti et al. (2019) determined the antioxidant activities of methanol and aqueous unmature fruit extracts of buckthorn using radical scavenging activities (Rocchetti et al., 2019). In this study, not only the dyeing ability but also the UV protection properties of buckthorn plant-based natural dyestuffs were investigated.

Materials
In this study, the berries and leaves of dried Anatolian Buckthorn (Figure 1), obtained from the local market, were used as a natural dyestuff source. All natural sources were separately ground into a powder before being used for the finishing of the fabrics. In the study a wool fabric at a weight of 200 g/m 2 was used. It was a 2/1 twill fabric and it was in pretreated form so ready for the dyeing.

Mordanting-dyeing
Since the mordants are generally substantive against both the colorant and the fiber and make bonds with the dye on the fiber to form an insoluble precipitate, it is used to improve dye adsorption and Buckthorn Bush Tree

Buckthorn berries
Buckthorn leaves The ground Buckthorn berries The ground Buckthorn leaves fastness. Different mordanting techniques such as pre-, post-, or simultaneous mordanting, have been used for centuries. By utilizing different metal salts, which are frequently polyvalent metallic ions that form a complex with the fiber and the pigment, the same dyestuff sources could produce distinct hues or even different colors (Zarkogianni et al. 2011). Simultaneousmordanting methods (dye source and metal salt are applied simultaneously to textile material) (Erdem and Bahtiyari 2018) were used for the finishing of wool in this study. This method was performed at a material to liquor ratio of 1:40 for one hour at 100°C. After the herbal sources were prepared for dyeing, they were added to the bath with the fabrics and mordants if necessary. The used herbal source amount was arranged to be equal to the fabric to be dyed. Like the study by Yılmaz (2020) In the dyeing process ( Figure 2), natural dye sources (without a previous extraction) and mordants (if necessary) were added directly to the dye bath (water at pH:7) and the dyeing procedure started. After that, dyed fabrics were rinsed, followed by a hot wash with 1 g/L nonionic surfactant for 10 minutes. Subsequently, warm and cold rinses were managed too. And finally, dyed wool fabrics were dried at room temperature.

Color analysis
The dyed wool fabrics were evaluated in terms of color efficiencies (K/S) and CIE L*a*b* color space values by using a Konica Minolta 3600d spectrophotometer (D65/10°). L* describes lightness (100 = white, 0 = black); a* measures redness or greenness; b* measures yellowness or blueness in the CIE system. The K/S value was calculated by Kubelka -Munk equation 1 (McDonald 1997). (1) Where K is the absorption coefficient, S is the scattering coefficient, and R is the fabric's reflectance at peak wavelength.

UV-Vis absorption
A UV/VIS spectrophotometer (PG Instrument T70) was used to obtain the absorbance curves of the tested natural dye sources. Berries and leaves of buckthorn were tested separately. Water was used as the solvent. Extracts were obtained by taking the amount of fruit and leaves required for dyeing and boiling them at 100°C for one hour. The absorbance curve of these extracts was determined ( Figure 3).

Measurement of UV-protective properties
As in our previous study (Benli and Bahtiyari 2021), the UV-protection properties of the samples were measured with the help of the EN 13758-1.2001. standard. The UV-transmittance rates of the undyed and dyed samples were determined. The UV-protection factor (UPF) and ultraviolet transmittance rates (TUVA and TUVB) were calculated (Hou et al. 2013).

SEM analysis
The surface changes of the selected samples were determined by scanning electron microscopy (SEM) (Zeiss LS-10).

Results and discussion
In the present study, buckthorn berries and leaves were used as a natural dye source. Generally, there is a complex relationship between the dye molecule, metal salt, and fiber. This complex structure was shown in different studies (Haji, Mehrizi, and Sharifzadeh 2016;Uddin 2014, Benli 2022. The aim of this study was to investigate the protective properties of the dyed wool fabrics with natural dyestuffs against harmful UV rays emitted by the sun.

UV-protective properties
Every textile material serves a different purpose for defense against many elements, including heat, mechanical strain, bad weather, physical, chemical, and biological dangers, electric and electronic dangers, explosions, etc. Since all kinds of protection cannot be provided by a single textile, the development of various protective clothing has gained importance. UPF values of textile materials are affected by chemical composition and fiber structure (Sankaran et al. 2021). According to a study by Schuicrer (1997), natural fibers like cotton, wool, and silk have lower UV absorption rates than synthetic fibers like PET (Schuicrer 1997). It has been reported that dyed cotton fabrics show higher UPF compared to undyed and bleached cotton (Sankaran et al. 2021). Srinivasan and Gatewood (2000) stated that depending on the concentration of dyes in the fabric and the absorptivity of dyes in the UV area, the application of dyes can significantly affect the UV protection offered by a fabric (Srinivasan and Gatewood 2000). In general, it is understood that the UV protection property of the fabric improves with the dyeing of the textile surface. It is reported that the UV-blocking capacity of natural dye sources depends on the functional groups' absorption properties, such as those of flavonoids, anthraquinones, terpenoids, aromatic conjugated systems, etc., that are present in plants (Ammayappan and Jose 2015). In Table 1, UV protection properties of selected dyed samples were shown. The results for the undyed wool fabrics were almost identical to those obtained in our previous study (Benli and Bahtiyari 2021). In this study, the UV protection values of undyed wool fabrics are 8.24% (T(UVA)) and 0.5% (T(UVB)), respectively. The T% values between 0.08 and 0.35% for UVA and between 0.09 and 0.18 for UVB were determined in all trials. In addition, the UPF rating values were determined as 50 + .By dyeing with tested natural sources, a significant increase in UV-Protection features has been gained even in mordant-free dyeings too. But beyond this, it was also found that the transmittance level of the samples changed with the metal ion used in dyeing, and hence, the dyed samples showed significantly higher UV protective properties. However, there can be some shifts in the obtained results due to the use of different mordants. For each used natural dye source, the higher UV protection was obtained via dyeing with iron sulfate, and the sample with the lowest transmittance (UVA: 0.08%; UVB: 0.09%) was observed in the sample dyed with buckthorn berry in the presence of iron ions. The sun's harmful rays (UVB) transmittance rates of selected samples are listed as follows for the dyeing with buckthorn berries, from the higher to the lower; unmordanted-dyed sample (0.18) > Al-dyed sample (0.16) > Sn-dyed sample (0.14) > Cr-dyed sample (0.13) > Cu-dyed sample (0.12) > Fe-dyed sample (0.09). It was also observed that the used natural dye source has an effect on the obtained UV protection features. So, the so-called sequence for dyeing with buckthorn leaves becomes as follows: Sn-dyed sample (0.17) > unmordanted/Al-dyed sample (0.16) > Cu-dyed sample (0.15) > Cr-dyed sample (0.14) > Fe-dyed sample (0.12). It could be stated that the UV protection properties change depending on the presence and type of mordant materials. The UV protection capacities of the samples dyed with buckthorn leaves were lower than the UV protection capacities of the samples dyed with buckthorn berries. A similar trend was observed in the case of using mordant. But it should be taken into account that, in addition to the direct effect of the used natural dye source and mordants, the obtained colors can also be responsible for the obtained results, as reported previously (Ghazi, Couteau, and Coiffard 2010). It can be stated that the UV protection properties of dyed wool fabrics are higher than the leaves of the Buckthorn berry. Table 1 shows the samples in addition to the UV protection feature results.
From this, it is clearly understood that clothes that protect from the harmful rays of the sun can be produced using natural materials using buckthorn berries and leaves. It is mentioned in the introduction that there are various natural sources that show UV protective properties by using different natural materials. In their studies, Rather et al. reported different approaches. In one, UV protection was obtained by dyeing woolen fabrics with peanut shells, which was an agricultural waste for sustainable natural dye production (Rather et al. 2021a). In the other study, it was stated that the waste water from Cinnamomum camphora natural dye, which shows sustainable UV protective and antioxidant properties in dyeing wool fabric, can be reused (Rather, Zhou, and Li 2021b).

Color analysis
Buckthorn is an old natural dye source, and the main dye component can be reported as quercetin, emodin, or kaempferol (Donmez et al. 2017;Karadag, Buyukakinci, and Torgan 2020;Poulin 2018). The bath of blank dyeing, which means it contains only natural dye sources in the dyeing process without the addition of fabric and any mordant, was centrifuged after the dyeing process. By this way, an extraction from the natural sources is managed, which is normally occurring in dyeing processes. After centrifugation, the absorbance of the extracts was taken without dilution, and the diagrams are given below in Figure 3. The absorbance curve of the natural dye extracts shown in Figure 3 indicates the color of the solutions. The UV-Vis spectrum of the solution of ground buckthorn leaves and berries extracted in aqueous medium was taken separately. It was previously stated in different studies that the UV-Vis absorption spectrum of a typical flavonoid comprises two maxima between 240-285 nm (band II) and 300-550 nm (band I). It was also reported that the absorption range of anthocyanidins and anthocyanin is between 465 and 560 nm (Andersen and Markham 2005), and 437 nm is the maximum UV absorption wavelength for emodin (Sucheta et al. 2011;Ţebrencu et al. 2015). Likewise, a peak was observed in the range of 400-500 nm. In addition to the absorbance curve of the dye extract, the colors that came out by the use of buckthorn berries and leaves in simultaneous dyeing and mordanting were analyzed and presented in Table 2. One of the most important results obtained is the dyeability of wool fabric with buckthorn berries and leaves without using any metal salt. It was found that by solely using these natural sources, the coloration of the wool can be managed, and it was determined that the colors obtained with the change of the natural source also changed. At the end of dyeing, wool fabrics dyed with buckthorn berry and buckthorn leaves without any mordant showed mustard yellow (a*: 8.24, b*: 40.94) and brown-beige (a*: 2.77, b*: 26.62) respectively. In trials carried out without using metal salt, the color efficiency (K/S) values were as follows: buckthorn berry (21.74) > buckthorn leaves (6.63). Among them, it was seen that the highest color efficiency (K/S) can be obtained with buckthorn berry. It is stated that a general trend of an increase in K/S values due to mordanting reveals that the extracted dye molecules can form metal complexes with positively charged mordant ions. At the same time, the L* value was as follows: buckthorn berry (54.03) < buckthorn leaves (65.19). Besides, the hue degree (h °) was as follows; buckthorn berry (78.63) < buckthorn leaves (84.07). In addition to the trials without using metal salt, their colors were examined using five different metal salts as mordanting agents. The colors belonging to dyed samples obtained from the dyeing via mordants are presented in Table 1. When the colors obtained are generally evaluated, dark brown, dark yellow, and brown-red colors are seen when buckthorn berry is used. Via the use of buckthorn leaves, brown-yellow tones were brought out (Table 1).
When the data obtained from dyed samples (Table 2) with buckthorn berries were examined in detail, the following results can be highlighted. In the case of using iron, copper, aluminum, tin, chromium ions, bitter brown (a*: 3.85, b*: 17.74), brown (a*: 9.4, b*: 35.84), dark yellow (a*: 10.11, b*: 42.51), red brown (a*: 19.18, b*: 53.95), and burgundy (a*: 17.85, b*: 26.36) colors were obtained, respectively. The darkest color tone was obtained from the dyeing combination using buckthorn berry and iron ions ( Table 1). The ability of some transition metal ions to form coordination complexes allows them to tightly interact with natural dye molecules, resulting in the production of intense color on cloth. The transition metal mordants, such as ferrous sulfate, generate many complexes with the dye molecules, usually octahedral ones with coordination number 6 (Uddin 2014). Furthermore, different color efficiencies from wool fabrics dyed with buckthorn berries were obtained by using different mordanting agents. The highest color efficiency (24.65) was obtained from the experiment with tin salt, and the lowest K/S value (4.52) was obtained from the fabric sample dyed with chrome. Besides, the highest L* (49.1) value was obtained from the experiment that used tin salt, and the lowest L* value (31.99) was obtained from the fabric samples that were dyed in the presence of iron ions. Hue degrees (h°) were as follows: chrome (55.9) < tin (70.43) < copper (75.31) < alum (76.62) < iron (77.76).
In dyeing with buckthorn leaves, the colors were changed by the mordants, as in the dyeing with berries. As seen in Table 1 from the photos of the samples, one of the significant color changes came out of the dyeing with tin chloride. The color became nearly yellow and a*: 3.58 and b*: 46.62 values were measured. In that case, the lightest color has been obtained with an L* value of 70.25. Instead of tin, by using iron-based mordants, the color gets darker and the darkest color among those dyed with the leaves was obtained by the L* value of 41.61. In this case, a* is 1.38 and b* is 12.88. The colors dyed in the presence of KAl(SO 4 ) 2 .12 H 2 O and K 2 Cr 2 O 7 were closer to each other when compared with the samples dyed in the presence of other mordants. This case can be seen from the CIE L*a*b* values of the samples and photos as well. Moreover, for all the leave-based dyed samples, the hue angles were in the range of 82-86° but color efficiencies differed from each other. The highest one was seen in dyeing with copper, and in this case, the color efficiency was 14.99. The lowest K/S (4.52) was seen in dyeing with K 2 Cr 2 O 7 . But as a generalization, it can be said that the K/S of the samples dyed with berries is higher than the ones dyed with leaves, and whereas the darker shades were obtained via the berries.

Color fastness properties
Protein fibers contain many different amino acids with a number of functional groups that provide binding opportunities for all kinds of colorants (Pailthorpe 1992). Mordants are widely used to provide better color fastness and to obtain a wide color range from natural dyes with limited color range. The color fastness test results of the wool fabrics dyed using buckthorn berries and leaves were presented in Table 3. When the color fastness test results were examined, it was determined that the results obtained from all trial sets were in the range of 4-5 points for the fastness against washing, rubbing, and perspiration. Meanwhile, the light fastness was between 3-5. From the test results reported in Table 3, both berries and leaves can be used for obtaining samples with high washing fastness. But in berry-based dyeing, a bit lower fastness has come out. The staining on wool values were 4/5. However, with the use of buckthorn leaves, the washing fastness values were 5 in almost all cases. The same tendency is valid for the rubbing fastness values too.
In the rubbing fastness test, 5 values were obtained in all samples dyed with buckthorn leaves. But especially for wet rubbing fastness, the samples dyed with berries were a bit lower but still good. The values were 4 and 4/5 and changed depending on the mordant. Perspiration fastness was another tested fastness property. It was seen that for the unmordanted dyed samples in berry-based dyeing, the value was 4 for acidic perspiration in staining on wool. But except in this situation, the values are higher than 4/5 for both tested natural dye sources.
All dyed samples' artificial light fastness values were obtained from low to medium (3-5). The lowest light fastness, which was 3, was obtained from the fabrics dyed with buckthorn leaves without the use of any mordant. With the use of berries without the use of mordant, the light fastness value was 4. Moreover, it was found that in the case of using solely natural sources, the light fastness values were lower and by the addition of mordants, the light fastnesses were improved by nearly 1-2 points. In terms of light fastness, the mordants had significantly important effects on the obtained results and solely the use of leaves caused the lowest value. In light of the obtained results from the dyeing with buckthorn, it was concluded that both berries and leaves can be useful for coloration and functionalization of the wool. But the use of berries is more commonly known. So, a cop dyeing with the extract of berries without the use of any mordant was conducted for the yarns constituted of Viscose-Acrylic (30/70) as seen in Table 4. By this way, it was planned to show the usability of natural dyeing with buckthorn in an industrial aspect. The dyeing process was carried out in the factory environment with the dyeing recipes optimized as a result of the laboratory studies. The berries of the buckthorn plant were used as the dye source. The dyestuffs were extracted from the related plant in a Soxhlet system by water prior to cops dyeing. In the extraction process, a plant amount equal to the weight of the material to be dyed was extracted for 4 hours, and the obtained extract was used directly as a dye bath in the cop dyeing machine.
From Table 4, it can be seen that a uniform dyeing with the extract of berries can be obtained in dyeings without using mordants. Meanwhile, as in fabrics, a mustard yellow in a brown shade was obtained. Meanwhile, an SEM view of the surface structure of the dyed sample revealed the smoothness and cleanness of the surface.

Conclusions
Today, various applications are made on clothes to protect the human skin from the harmful rays of the sun. In those applications, non-environmentally friendly and hazardous chemicals can be used. Recently, very intensive research has been carried out on natural resources with UV protection properties. In this study, woolen fabrics were dyed using a natural material derived from a vegetable source (buckthorn), and at the same time, dyed fabrics gained protection properties against harmful UV rays. And thus, this practice became an example of sustainable and environmentally friendly processes. It was observed that good results can be obtained in terms of color fastness values, UV protection properties, and coloration without using metal salt. However, metal salts are very important in terms of UV protection and also for light fastness. When different metal salts are used as mordanting agents, it was seen that although they are the same natural dye sources, very different color tones, color fastness properties, and UV transmittance ratios can be obtained. The most important reason for this difference is thought to be caused by the formation of a complex structure formed by the metal ions and the dye molecule. When these ions are combined with the chemical structure called quercetin found in buckthorn, it has been observed that the UV protection properties are changed. As a result, it could be said that the fabrics treated with buckthorn berries and leaves can act as a protective shield against the harmful sun's UV rays, and in the meantime, different colors and fastnesses can come out by using different metal salts.

Highlights
• Herbal sources can provide alternatives for gaining UV protective properties to textiles.
• Textile materials can acquire UV protective properties by dyeing with berries and the leaves of buckthorn.
• UV protective properties are obtained simultaneously with different colors and sufficient fastness properties by treating with berries and the leaves of buckthorn. • This method may be a viable way to reduce the use of synthetic UV protectors.

Disclosure statement
No potential conflict of interest was reported by the author(s).