Natural Dyeing and UV Protection of Raw and Bleached / Mercerised Cotton

Dyeing with natural dyes extracted from curcuma, green tea, avocado seed, pomegranate peel and horse chestnut bark was studied to evaluate the dyeability and ultraviolet (UV) blocking properties of raw and bleached/mercerised cotton fabrics. 20 g/l of powdered plant material was extracted in distilled water and used as a dyeing bath. No mordants were used to obtain ecologically friendly fi nishing. The colour of samples was measured on a refl ectance spectrophotometer, while UV-blocking properties were analysed with UV-Vis spectrophotometer. The results showed that dyeing increased UV protection factor (UPF) to all samples, however much higher UPF values were measured for the dyed raw cotton samples. The highest UPF values were obtained on both cotton fabrics dyed with pomegranate peel and green tea extracts, giving them excellent protective properties (UPF 50+). The lowest UPF values were obtained by dyeing cotton with avocado seed extract and curcumin. Dyeing with selected dyes is not stable to washing, so the UV-blocking properties worsen after repetitive washing. However, raw cotton samples retain their very good UVblocking properties, while bleached/mercerised cotton fabrics do not provide even satisfactory UV-blocking properties. No correlation between CIE L*a*b*, K/S and UPF values were found.

eir advantages compared to natural dyes are lower prices, better colour fastness and wider range of shades.On the other hand, the awareness of their harmful, carcinogenic and not bio-degradable properties became present among certain parts of society [2,3].Environmentally conscious manufacturers are trying to decrease harmful consequences on human health and environment using natural dyes.Due to their biodegradability and functional properties natural dyes are also used in food, pharmaceutical and cosmetic industry [4].e major problem associated with dyeing of cotton with natural dyes is their inadequate colour fastness [5].In addition to their dyeing properties, some natural dyes also have UV-blocking and antimicrobial properties.
e UV-blocking properties of textile substrates dyed with natural dyes are of great interest, because the Sun-caused allergies and skin damages (i.e.sunburn, erythema, photo-aging and photocarcinogenesis) have increased in recent years [6].
e purpose of our research was to dye cotton fabrics with natural dyes, i.e. extracts of curcuma rhizome, green tea leaves, avocado seed, pomegranate peel and horse chestnut bark.e objective of the research was to evaluate the dyeability and UVblocking properties of dyed raw and bleached/mercerized cotton without using any mordants.

Curcuma rhizome
Curcuma rhizome (Curcuma longa) belongs to the ginger family (Zingiberaceae).It probably originates from South or Southeast Asia.Firstly, it was cultivated as a dye, later it was used as a spice, for cosmetic and medicinal purposes.e dyeing constituent of curcuma rhizome is the polyphenolic pigment curcumin (Figure 1) [7].Due to the keto and enol tautomeric conformations in solid state or liquid, the colour of curcumin depends on a pH of the solution; alkali solution results in red and acid solution in yellow colour [8].Adeel S. and Osman E. [9] showed that the extract of curcuma might be an alternative for yellow synthetic dyes due to good colour strength and acceptable colour fastness.e best result was obtained when cotton and curcuma powder were UV-irradiated.
e acid-treated cotton dyed with cationised curcumin yielded excellent UV protection property and good durability to home laundering [10].e result is classi ed as an excellent UV protection due to interaction between cationic curcumin cation and cellulosic citrate anion.
e colour fastness of cotton samples dyed with turmeric extract is generally better when using mordants [4].eir application can also in uence on the nuance of the nal colour.

Green tea
Green tea is produced from Camellia sinensis leaves.It originates from China and is nowadays worldwide spread.Tea polyphenol mostly consists of catechin (Figure 2), which is a very e ective UV absorber.Catechin is one of the natural phenols and antioxidants [11].Due to antioxidant and deodorization functions on natural bres, many researches were carried out using green tea as a dye [12].It was found that hot extraction of red, black and green tea provided cotton fabrics with UVblocking properties [13].e UV-protection factor (UPF) was mostly connected to the method of extraction as well as the colour of the tea.e green tea showed the lowest UPF value.Kim S. [14] increased the adsorption of green tea extract with chitosan mordanting of cotton fabrics, and its ability for UVA and UVB protection.e UV protection generally increased approximately by 7%, which is similar value to a cellulose fabric dyed with green tea and metal mordant.

Avocado seed
Avocado (Persea americana) belongs to the Lauraceae family.e cultivation of this fruit originates from Mexico.It is best known as an important protein and lipid supplier in human diet.e seed accounts for 16% of total avocado weight, and is an under-utilized resource and today classi ed as a waste which contributes to the environmental pollution [15,16].Avocado seeds and pulp are full of hydroxycinnsmin acids, catechins and procyanidins which have antioxidative and antimicrobial properties [17].e extracts of avocado seed showed antibacterial properties against several strains of Streptococcus agalactiae [18].e seeds could also be used as a source of natural dye.e colour of the extract is supposedly connected to the procyanidins, the oligomeric compounds, formed from catechin (Figure 2) and epicatechin (Figure 3) molecules [19,20].Currently no reported research was performed in dyeing of textiles with avocado seed extract.e UV-blocking properties have not been studied yet as well.

Pomegranate peel
Pomegranate (Punica granatum) belongs to the Punicaceae family.It originates from Persia and is nowadays a common plant in the countries with warm climates.Pomegranate peel contains phenolics, avonoids and tannins.It also contains pigments called anthocyanidins (Figure 4).ose pigments are further divided into pelargonidins, cyanidins and delphinidins [22][23][24][25].e nal colour of 100% cotton samples dyed with pomegranate peel extract can vary from yellow, brown to black and is a result of the used mordant.When using metal salt, better colour strength is obtained [22].However, it was found that mordanting process was not essential for dyeing cotton with pomegranate peel extract [23].Cotton, wool and silk fabrics dyed with pomegranate peel extract showed excellent deodorising performance with high wash fastness [24].
e UV-blocking properties of cotton dyed with pomegranate peel have not been evaluated yet.

Horse chestnut bark
Aesculus hippocastanum is one of the representatives of the Sapindaceae family.Native range of the plant is Balkan [30,31].Bark contains two di erent types of coumarins glycosides; aesculine and fraxine.Aesculin (Figure 5) is a good UVB absorber and has the maximum absorbance at 346 nm and another peak at 250 nm [30].Another important substance is a group of tannins (Figure 2 and 3).ey also have good antioxidant and antimicrobial properties [30,31].ere was no evidence of using horse chestnut bark as a dye or as a UV-blocking substance.
e curcuma rhizome powder and green tea crushed leaves were used as received.
e avocado seed, pomegranate peel and horse chestnut bark were cut in smaller pieces, washed in cold deionised water and 0.5 g/l non-ionic surfactant, rinsed thoroughly and dried.e dried plants were then grinded to powder using a blender.e extracts were prepared by immersing 20 g/l of powder from each plant in cold distilled water.e temperature of the solutions was then increased to a boiling and held at that temperature for 5 minutes.A erwards all solutions were le to cool for two hours and then ltered.e prepared extracts were used for dyeing cotton fabrics.

Dyeing of cotton fabrics
Dyeing of raw and bleached/mercerised cotton fabrics with prepared plant extracts was performed in stainless-steal asks of Launder-o-meter apparatus at 60 °C for 60 minutes.e liquor to goods ratio was 20:1.A erwards dyed samples were rinsed in cold deionised water and air-dried at room temperature.

Durability to washing
e dyed samples were washed in laboratory apparatus Launder-o-meter in accordance with EN ISO 105-C06 standard.e size of the samples was 100 x 40 mm, the wash bath contained 4 g/l ECE phosphate reference detergent B, the bath volume was 150 ml, the temperature of washing was 40 °C and the washing lasted for 30 minutes.Ten stainless steel globules were added to each bath to perform washing equal to ve domestic washings.e samples were rinsed twice a er washing in deionised water and air dried at room temperature.

Colour measurements
where ∆L* is the lightness di erence, ∆a* is a difference on red-green component and ∆b* is the difference in blue-yellow component between standard and a batch.
e colour strength (K/S values) from the re ectance measurement was calculated based on equation 2: where R represents the re ectance, K means the absorbance and S represents the scattering of the sample.
Dye uptake was determined from K/S values according to equation 3: where R D is the re ectance of dyed sample and R O is the re ectance of undyed sample.

UV protection factor measurements
UV protective properties of the cotton samples were analysed on a Varian CARY 1E UV/VIS spectrophotometer containing Solarscreen so ware and a DRA-CA-301 integration sphere.e transmittance measurements and calculations of the ultraviolet protection factor (UPF) were carried out according to the AATCC TM 183 standard.2).From the results of ∆L*, ∆a* and ∆b*, only one common characteristic between dyed raw and bleached/mercerised cotton sample can be found: the bleached/mercerized samples are lighter than raw samples (∆L* > 0). is can be expected since the samples of the bleached/ mercerised do not contain the natural pigment, which is present in the samples of a raw cotton [32].
e CIE L*a*b* values (Table 1) and the colour differences (Table 2) represent valuable information on the colour of dyed textiles, but cannot give the information on the uptake of the dye on the textile substrate.Although the low CIE L* values are connected to the higher uptake, when textiles are dyed with synthetic dyes, this relationship is not necessarily true when textiles are dyed with natural dyes [33,34].e dye uptake (∆K/S) results of studied natural extracts are presented in Figure 6. e dye uptake of each natural dye is very similar for both cotton substrates, although the dyed bleached/mercerised cotton is much lighter than the dyed raw cotton (Table 1 and 2).e dye uptake of curcumin and avocado seed extract is slightly higher on bleached/mercerised cotton, while the dye uptake of green tea, pomegranate peel and horse chestnut extracts is slightly higher on raw cotton.ese results indicate that raw and bleached/mercerised cotton have very similar uptake of studied natural dyes, and that uptake depends more on the dye structure than on the presence or absence of pigments and other non-cellulosic compounds on the cotton.In Figures 7 and 8 the colour strength values (K/S) of dyed raw and bleached/mercerized cotton samples before and a er repetitive washings are presented.Dyeing with curcumin and pomegranate peel extract gives higher K/S values (2.30 < K/S > 5.23) (Figures 7  and 8), while dyeing with green tea, avocado seed and horse chestnut bark extracts gives lower K/S values (0.43 < K/S > 0.80).Repetitive washing lowers the K/S values, which indicates not a very stable fastness of natural dyes to washing (Figures 7 and 8).
e K/S values greatly reduce on both substrates already a er the rst wash for the samples dyed with curcumin and pomegranate peel extract (Figure 7 and 8).From Figures 7 and 8 it could be concluded that washfastness is better for the samples dyed with avocado seed, horse chestnut bark and green tea, however the samples have low K/S values even at the beginning of the performed washings.From the CIE L*a*b* results (Table 1) it is clear that the latter samples have poor colour wash stability since they become much lighter a er repetitive washing.[35].Raw cotton samples dyed with green tea and horse chestnut bark extracts are also rated into the excellent UV protection category (50+) (Figure 9).eir UPF values are 73 and 55, respectively.However, dyeing the bleached/mercerised cotton with the same extracts does not yield so high UPF values.While dyeing of bleached/mercerised cotton fabric with green tea extract provides very good UV protection (UPF = 26), dyeing with horse chestnut bark extract does not (UPF = 12) (Figure 9).e sample is not even UV rateable.Dyeing cotton substrates with avocado seed extract and curcumin gives the lowest UPF values (Figure 9 and 10).Dyed raw cotton samples have the UPF values 25 and 26, respectively, which rates the samples in the very good UV protection category (Figure 9).e UPF values of avocado seed extract and curcumin dyed bleached/mercerised cotton samples are only 8 and 10, respectively, which is not UV rateable.It is indicated in the literature that dark coloured fabrics with high K/S values transmit less UV radiation than lighter shaded fabrics with lower values [36][37][38][39].However, the results of our research show that the upper statement cannot be generalised for all dyes, especially not for natural dyes.with horse chestnut bark extract and have moderate to low UPF values.From these results no correlation between CIE L*, K/S and UPF was established.
e reason why one or the other natural dye gives higher or lower UPF values to the cotton samples is most likely connected to the chemical structure of dye and its ability to absorb light near UV region than to its dyeing properties. is conclusion is supported by the fact that textiles nished with organic UV absorbers that are colourless compounds that absorb in wavelength from 280 to 400 nm have excellent UV protective properties [40,41].Although dyeing cotton samples with pomegranate peel extract gave remarkable UPF results, the e ect is not stable to washing (Figures 9 and 10).Even after the rst performed washing, the UPF is drastically reduced, i.e. from 260 to 80 for raw cotton (Figure 9), and from 84 to 20 for bleached/mercerised cotton (Figure 10).While the UV protection category of raw cotton dyed with pomegranate peel extract remains excellent until the twel h wash, this does not apply to dyed bleached/mercerised cotton.e latter is a er the rst and sixth wash characterised as a fabric with good UV protection properties (UPF ∼ 20).A er the twel h performed wash, the UPF values are further decreased to the point where raw cotton is rated as a fabric with very good UV protective properties (UPF = 30), while the bleached/mercerised cotton is not rateable anymore (UPF = 14).e green tea extract performed similar as pomegranate peel extract, with the exception that the decrease in UPF values a er the rst wash already classi es the dyed bleached/mercerised cotton into the unrateable UV protection category (UPF < 15).e raw cotton dyed with green tea extract remains in the very good UV protection category even a er the twel h wash (UPF = 26).Dyeing with curcumin and avocado seed extract already gave inferior UPF results comparing to other studied dyes, and this is probably why no drastic changes in UPF values were found after repetitive washing.

Conclusion
Raw and bleached/mercerised cotton fabrics were dyed with the extracts of plant parts, such as green tea leafs, curcuma rhizome, avocado seed, pomegranate peel and horse chestnut bark.e dye uptake results show similar adsorption of natural dyes onto both substrates.e CIE L*a*b* colour values and colour strength values (K/S) of dyed samples were not in correlation with the UV protection factor (UPF) values.All dye extracts increased the UPF of cotton fabrics, in the following order: avocado seed < curcumin < horse chestnut bark < green tea < pomegranate peel.While all dyed raw cotton samples performed as textiles with at least very good UV protective properties, the bleached/mercerised cotton fabric performed also as a non-rateable.e results showed that extremely high UPF values and UV protection could be Mercerised Cotton Tekstilec, 2017, 60(2), 126-136 achieved by dyeing raw or bleached/mercerised cotton fabric with pomegranate peel or green tea extracts.However, the fabrics as such do not perform well a er repetitive washing.Further research should be performed in the area of increasing the fastness to washing by using ecologically friendly compounds and modi cations.

A
re ectance spectrophotometer Spectra ash 600 PLUS-CT (Datacolor) was used for measuring CIE L*a*b values and re ectance (R) of the samples.Colour di erences from the CIE L*a*b* colour values were calculated in accordance with the equation 1:

Figure 6 :
Figure 6: Dye uptake (∆K/S) of studied natural dyes on raw and bleached/mercerized cotton

Figure 7 :
Figure 7: Colour strength (K/S values) of unwashed and washed raw cotton samples dyed with natural dyes

Figure 8 :
Figure 8: Colour strength (K/S values) of unwashed and washed bleached/mercerised cotton samples dyed with natural dyes

Figure 9 :
Figure 9: UPF values of unwashed and washed raw cotton samples dyed with natural dyes

Table 1 :
results of the CIE L*a*b* colour values of dyed raw and bleached/mercerized cotton samples before and a er repetitive washings are presented in Table1.With the increasing number of washings, the lightness of samples is increasing (CIE L* values), while the colour values on the red-green axis (CIE a*) and on the CIE L*a*b* colour values of unwashed and washed raw and bleached/mercerized samples dyed with studied natural dyes values move from red to the green axis.All other dyed samples, regardless of the number of washings, are positioned on the positive part of the CIE a* and CIE b* axis (on red and yellow axis).In Table2the colour di erences (∆E ∆E ab * values are higher than 1, meaning that the di erences are visible.e calculated ∆E ab * values for curcumin dyed samples (∆E ab * = 8.85) are the highest, and for pomegranate peel extract dyed samples the lowest (∆E ab * = 2.93) (Table e ab *) and the differences in lightness (∆L*) on red-green axis (∆a*) and on yellow-blue axis (∆b*) between dyed raw and bleached/mercerised cotton samples are presented for each dyeing extract (i.e.curcumin, green tea, avocado seed, pomegranate peel or horse chestnut bark).e

Table 2 :
e colour di erence (∆E ab *) and di erences in lightness (∆L*), on red-green axis (∆a*) and on yellow-blue axis (∆b*) between dyed raw and bleached/mercerised cotton samples Tekstilec, 2017, 60(2), 126-136 Our results show that samples dyed with avocado seed extract have the lowest UPF values and are among the lightest samples with low K/S values.e samples dyed with pomegranate peel extract that have the highest UPF values are not among the darkest samples and have moderate K/S values.For example, the samples dyed with curcumin with the highest K/S values and lightness have very low UPF values.e darkest samples with low K/S values are those dyed Mercerised Cotton Tekstilec, 2017, 60(2), 126-136