Wool dyeing using Ziziphus bark extract as a natural dye: studies on the dyeing, antibacterial, and antioxidant characteristics

Considering the growing importance of natural colorants and sustainable products, the research on application of natural dyes has been focused on new color resources, identification, and standardization of natural dyes. Hence, the extraction of natural colorants available in Ziziphus bark was performed by ultrasound technique and its application on the wool yarn to produce the antioxidant and antibacterial fibers. The optimal conditions for the extraction process were as follows: ethanol/water (1/2 v/v) as solvent, concentration of Ziziphus dye 14 g/L, pH 9, temperature 50 °C, time 30 min, and L.R ratio 50:1. Moreover, the effect of important variables for application of Ziziphus dye on the wool yarn was investigated and optimized temperature 100 °C, concentration of Ziziphus dye 50% o.w.f., time for dyeing 60 min and pH 8, and L.R 30:1. The reduction values of Gram-negative and Gram-positive bacteria on dyed samples at optimized condition were 85% and 76%, respectively. Moreover, the antioxidant property of dyed sample was 78%. The color variations on the wool yarn were produced with diverse metal mordants, and color fastness properties were measured. Ziziphus dye not only can be used as an origin for a natural dye, but also provided the antibacterial and antioxidant agent on the wool yarn, which can be a step towards the fabrication of green products.


Introduction
A main group of ecological contaminations is the synthetic dyes and severe health risks and troubles in environmental balance produced by excessive usages of these dyes (Ahmad Khan et al. 2014;Bulut and Akar 2012;Sadeghi-Kiakhani et al. 2018;Adeel et al. 2022;Rehman et al. 2022). In the face of these problems, the application of natural dyes as the biodegradable sources has been explored by many researchers (Zia et al. 2019;Teklemedhin and Gopalakrishnan 2018). Depending on the sources of natural dyes, they can produce the wide range of hues (Baaka et al. 2017a;Adeel et al. 2022). The demand of consumers for natural dyes is more inclined to use natural dyes due to their harmony, quality, and environmental compatibility (Kasiri and Safapour 2015;Ali et al. 2009;Mehrparvar et al. 2016). In recent decades, the introduction, extraction, and dyeing of textiles with new natural dyes is one of the topics that motivated the scientists .
Ziziyphus spina-christi plant grows wild in parts of tropical Asia and Africa. It is a family of Rhamnacese and, originally, is grown in the subtropical, arid, and semi-arid regions of Iran and grows well in the southern provinces, Fars, Hormozgan, Bushehr, Khuzestan, Kerman, and especially, south of Sistan and Baluchestan (Fazelinasab and Mirzaei 2017). The shrubs of this plant are resistant to heat and drought and have various pharmacological applications (Nkafamiya et al. 2013;Buyukakinci et al. 2021;Eser and Yavas 2021). The bark of Ziziphus has been widely used in the biological activities such as antioxidant, antimicrobial, and cardio protective properties (Kafamiya et al. 2013), and Responsible Editor: Philippe Garrigues the other parts of this tree exhibit many valuable properties while its bark is much more effective (Jian et al. 2017). The active potential coloring component of the Ziziphus bark is triterpenoids and their saponins, favonoids, and cyclopeptide alkaloids which are responsible for imparting the yellowish to reddish-brown color (Salih et al. 2021). Antimicrobial activity of aqueous and ethanolic extraction of leaves of Ziziphus was reported against various bacteria (Lomchoey et al. 2018). Also, Chungkrang et al. studied the dyeing and color fastness properties of wool yarn with bark of Ziziphus. They declared that different mordants were produced different shades with good to excellent color fastness properties (Chungkrang et al. 2018).
In recent years, the development of the extraction efficiency of natural compounds has been performed by different technologies such as microwave and ultrasound (Zeković et al. 2017;Khan et al. 2018). The extraction of natural dyes with improving absorption of dye has been supported by ultrasonic, ultraviolet, microwave, plasma, and gamma radiations (Baaka et al. 2017b). Among the mentioned techniques, ultrasonic radiation is proper in terms of useful and energy-saving (Adeel et al. 2018;Haji et al. 2018). The extraction of colorants by ultrasonic-assisted extraction (UAE) has been reported by researchers since 1963 (He et al. 2016;Cai et al. 2016;Sharmila et al. 2016;Alexandru et al. 2013), so that the extraction efficiency can enhance by increasing the power of ultrasound from 20 to 100 kHz. Irradiation of ultrasound in liquids cause to form micro-bubbles, and exciting them can disrupt the cell walls of plants, and consequently, the active ingredients in the plant move in the solution phase. It should be noted that heat can also improve the extraction process and transfer effective ingredients to the solution phase (Assami et al. 2012).
Wool fibers are susceptible to micro-organism growth and attack due to high moisture absorption. Bacteria can damage the fibers and be harmful to human bodies. Therefore, it is necessary to perform antimicrobial finishing on natural fibers such as wool. This finishing can be done with various chemicals, which many of them are harmful to the environment . To prevent the growth of microbes, which were liable for various contaminations, many antibacterial drugs were manufactured in the world (Al-juraifani 2011). However, resistant to several antibacterial drugs was produced by these drugs through the genetic mutation of microorganisms (Gupta et al. 2016). Furthermore, the serious risks for the internal organs of the human related to the extensive use of the chemical drugs may provide by side effects (Huang et al. 2017). Therefore, researchers have focused on medicinal plants to solve the restriction of chemical medicines. Natural compounds are extensively applied for medicinal purposes in various societies as rich sources of antibacterial drugs. Some useful phytochemicals such as tannins, flavonoids, glycosides, cyclopeptide alkaloids, peptides, and sterols terpenoids have been isolated from Z. lotus root bark (Borgi et al. 2008). Due to the presence of these compounds, this species has ecological, economical, analgesic, antipyretic, antiviral, anti-inflammatory, and antidiabetic activities (Weinges and Schick 1995;Sudhersan et al. 2003;Niamat et al. 2012).
One of the most important groups of environmentally friendly materials with the least amount of hazards for humans during their photosynthesis is natural dyes. In addition to coloring of products, some of these dyes have perceptible antioxidants and antimicrobial properties. Therefore, these materials can be used to perform multifunctional processes in one step and produce the goods with harmony dye, antioxidant, and antimicrobial properties (Shafei et al. 2018;Lee et al. 2013). It is mentioned that the extraction process of natural dyes can be performed comparatively economy than the production costs of synthetic dyes. Also, the capability of industrial performance has fewer environmental risks, if the extraction and application of natural dyes can be optimized.
Dyeing of fibers using natural dyes with antibacterial and antioxidant properties is considered as a green method, which can save energy, time, water, and chemicals. As far as we considered, the optimization of extraction of natural dyes from Ziziphus bark in order to produce wool dyed samples with antibacterial and antioxidant properties has been reported for the first time in the present study. The extracted colorants were characterized by UV-visible and FTIR technique. The dyeing of wool yarns with extracted colorants was carried out by different mordants via pre, post, and simultaneous methods. The colorimetric data and colorfastness properties of the dyed wool samples against wash, light, and rub were determined. Also, the effect of Ziziphus bark extract on the antioxidant and antibacterial properties of wool samples was evaluated.

Materials and equipment
The Ziziphus plant was prepared from the Zahedan capital of Sistan and Baluchestan Province, Iran, during the month of March 2021. The barks of this plant were collected and dried in a dark environment, so that the available compounds in Ziziphus barks are preserved as much as possible. A smooth powder was obtained via ground. The bleached and scoured wool yarn with specification of 200Tex/fourfold was supplied from Azarbarf Tabriz. The mordants such as stannous chloride (SnCl 2 ·2H 2 O), aluminum sulfate (Al 2 (SO 4 ) 3 ·18H 2 O), iron sulfate (FeSO 4 ·7H 2 O), and copper sulfate (CuSO 4 ·5H 2 O) were used to produce different hues on the wool samples dyed with Ziziphus barks. The rest of the chemicals used in this study were laboratory grade. The water used for preparation of dyeing solution was distilled. UV-visible Cecil 9200 double-beam spectrophotometer was utilized to determine the spectrophotometric properties of dye solutions. Also, the colorimetric properties of dyed wool yarns were measured by a Gretag Macbeth spectrophotometer model 7000 A. also, the color eye and observer degree were D65 illumination and 10°, respectively.
The maximum absorption wavelength (λ max ) of Ziziphus bark extract was obtained at 425 nm and is consistent with previous reports (Chungkrang et al. 2018). Hence, the optimization of extraction process was measured by spectrophotometer at this wavelength in extracts.

Mordanting procedures
The mordanting process was performed in three ways: before, after, and simultaneous dyeing and mordanting together in one bath. The mordants used on the woolen yarn were Al 2 (SO 4 ) 3 (5%owf), CuSO 4 (5%owf), SnCl 2 (1%owf), and Fe 2 SO 4 (1%owf). Pre-mordanting process was carried out using (liquor ratio) L.R of 50:1 at boiling temperature for 60 min. After mordanting, the dyeing process was performed on the wool samples. In the simultaneous method of mordanting and dyeing, dye and mordant are introduced into the solution simultaneously, and the operation is performed in one step. Post-mordanting method after dyeing, the mordanting was performed. The samples were placed in baths with L.R 50:1, and mordanting was completed at boiling temperature for 60 min.

Dyeing of wool yarns with Ziziphus bark
After extraction, the influence of significant parameters for instance dye concentration, temperature, time, and pH on dyeing process were optimized. The wool dyeing was performed at a liquor ratio (L.R) of 100:1, 50:1, and 30:1 with the dye bath being maintained at diverse pHs (4, 7, and 8).
The reflectance spectrophotometer equipped with software was used to calculate automatically CIEL*a*b* (CIE means International Commission on Illumination, L* is the luminance, a* is the red-green axis, and b* is the blue-yellow axis), and color strength (K/S) values of dyed samples from the reflectance values at the proper wavelength (Korifi et al. 2013).

Colorfastness testing
The washing fastness of dyed samples was evaluated via the standard ISO 105 C06 C2S:1994 (E) method. In accordance with this standard, the samples were washed at 60 °C for 30 min. After drying, the samples were analyzed by gray scale. ISO 105 B02:1988 (E) was used to evaluate the light fastness of dyed samples. In this test, the samples were exposed to xenon arc lamp, and then, the color fading of the wool samples was determined by blue reference samples. The colorfastness to rub of dyed samples was performed through ISO 105-X12:1993 (E) standard. Rubbing fastness was performed by a crockmeter in both dry and wet types, and then, the staining on the white adjacent test fabric was evaluated by the gray scale.

Antibacterial test
The antibacterial activities of dyed samples against Escherichia coli (E. coli) and Staphylococcus aureus (S. aureus) bacteria were measured by AATCC 100-2004 standard test (Pinho et al. 2010). After incubation at 37 ± 2 °C for 18 h, the reduction percentage of the bacterial count (R) of dyed samples was determined by the surviving cells of dyed reduction in the number of colony-forming units (CFU) (B) with respect to untreated control sample (A) (Eq. 1).

Antioxidant activity test
The raw and dyed wool samples were evaluated by free radical scavenging test by using α,α-diphenyl-β-picrylhydrazyl (DPPH) (Ghaheh et al. 2017). Briefly, wool samples (1 g) were immersed in methanol (40 mL) containing DPPH (0.15 mM) and keep in dark media at ambient temperature for 30 min. The absorbance of samples at λ = 517 nm was measured by UV-spectrophotometer, so that the antioxidant percent can be measured via absorbance of solution for dyed samples (C) and raw wool (D) (Eq. 2):

Results and discussion
Extraction process

Effect of solvent
The plants containing polyphenols ingredients can be extracted at different solvents. The significant parameters such as the type and part of plant to be extracted, nature of the bioactive compounds, and the availability of solvent are effective in selecting of solvent (Pandey and Tripathi 2014;Sasidharan et al. 2011;Altemimi et al. 2017). The preferred active ingredients can be extracted by polar and non-polar solvents (Gupta et al. 2012).
The extraction of Ziziphus bark in various solvents was performed, and the absorption is given in Fig. 1. Results indicated that methanol has a higher efficiency in extraction process, which it can be related to the complexity of the structure of the available colorants in the Ziziphus bark, the penetration strength of the solvent into plant, the difference in polarity, and diverse solubility of colored components in the plant into the solvent. It is obvious from the data that methanol is the proper solvent for extraction of both phenolic and flavonoid (Djeridane et al. 2006;Medini et al. 2014;Nobossé et al. 2018). The application of methanol in extraction process of many plants as a suitable solvent was suggested (Truong et al. 2019).
In many cases, the mixture of solvents increases the extraction efficiency and can have a synergistic effect. It has been mentioned that the extraction of flavonoid compounds can improve through combination of organic solvents with water. Therefore, diverse ratios of water and methanol were prepared, and the extraction process of Ziziphus bark was carried out, and the effects of methanol/water ratios on the absorption of extracted solutions are presented in Fig. 2. Results showed that the absorbance value of mixture of methanol/water 1/2 was the more than pure water or methanol (Sultana et al. 2009). Also, by increasing the ratio of water in the solvent, the extraction efficiency improved, which it can be associated to enhance in the polarity of the solvent, the better penetration of the solvent in the structure of Ziziphus bark, and the better solubility of the color compounds in the plant. On the other hand, water can increase the swelling of the internal pores of the plant, and as a result, effective plant compounds can be extracted better (Wang et al. 2008). Hence, the ratio of methanol/water (1/2) was considered for the extraction of Ziziphus bark.

Effect of pH
The effect of pH is another factor influencing the extraction process. Changing the pH can alter the solubility of color compounds in natural dyes. As shown in Fig. 3, among the three different environments of pH 4, 7, and 9, Ziziphus bark has higher dye absorption at the pH of the base with λ max 510 nm. Therefore, pH 9 can be considered as the optimal pH for the dye extraction process. In addition of these alkalis, this process increases the color yield. It was suggested that the extraction of natural dyes containing phenolic groups in alkaline media had positive effect (Liu et al. 2009;Merdan et al. 2017).
Since the phenolic compounds present in the extract are significantly higher than the proanthocyanidin contents (Bardakci et al. 2019), therefore, the more soluble  . 2 The extraction of natural colorants from Ziziphus bark with different ratios of methanol/water, (a) methanol/water 1/1, (b) methanol/water 2/1, and (c) methanol/water 1/2, dye value 14 g/L, temperature 50 °C, time 30 min, and pH 7 compounds are extracted by increasing of pH, and as a result, color absorption increases (Scheme 1).

Effect of temperature
The extraction was performed at various temperatures (30, 50, and 70 °C) to select the appropriate range of temperature (Fig. 4). Temperature can be influenced on the solubilization of colorant compounds in the solution and the shifting of dye molecules from inside the plant into the solution (Jing et al. 2015). Results showed that the solubility and amount of absorption dramatically increased by increasing the temperature. But with increasing temperatures from 50 to 70 °C, there is not much change in the amount of absorption. Increasing the temperature can collapse the cell wall of plant and improve the solubility of compounds, but rising the temperature up to the optimum temperature possible degrade the temperature-sensitive of natural compounds and reduce the extraction efficiency. Flavonoid compounds such as anthocyanins are sensitive to temperature, so excessive temperature may cause their destruction. Hence, in order to hamper the destruction of the phenolic compounds, the permissible limit of temperature increase must be respected (Shafiq et al. 2021). Thus, the optimum temperature for extraction of Ziziphus bark was chosen 50 °C.

Effect of time
The extraction of Ziziphus bark was performed at various times (15, 30, and 45 min) (Pedro et al. 2016). According to Fig. 5, the extraction reached equilibrium from 15 to 30 min and then dropped after this time. Increasing the time for more than 15 min in ultrasound condition may damage the sensitive compounds in plant, and as a result, the amounts of absorption and efficiency of extraction decrease. So, the time equals 30 min can be considered as the optimal for the extraction process.

Effect of quantity of solvent to solute
Ziziphus bark was extracted in various ratios of solvent to solute (30:1, 50:1, and 70:1), and results are shown in Fig. 6. It is detected that by increasing in ratio of solvent to solute up to 50:1, the absorbance of solution decreases. When the ratio of solvent to solute is raised up from 30:1 to 50:1, the absorbance is increased. In the ratio of 70:1 solvent to solute, the solution becomes diluter other than 50:1, and the amount of absorption decreases. Therefore, ratio 50:1 is considered as an optimum ratio and is sufficient to extract the solute and solvent.

Effect of concentration of Ziziphus bark
The extraction was investigated in the range of 2, 6, 10, 14, and 18 g/L in order to optimize the concentration of Ziziphus bark. The results of Fig. 7 show that with increasing dye concentration, the amount of absorbance also increased. In general, by increasing the amount of dye, the solvent penetrates a larger amount of plant tissues and extract more dyes into the solvent, resulting in a higher release of dye from Ziziphus bark (Maran et al. 2013). The results show that 7 g/L of Ziziphus bark is the best concentration for extraction.
The optimal conditions for the extraction process were as follows: ethanol/water (1/2 v/v) as solvent, concentration of Ziziphus dye 14 g/L, pH 9, temperature 50 °C, time 30 min, and L.R ratio 50:1. All of the parameters are significant in the extraction process and in some cases have synergistic effect; however, results indicated that pH and concentration of Ziziphus dye are two effective parameters in the extraction process.

Optimization of dyeing process
The significant parameters, for instance time, temperature, concentration of Ziziphus bark, and pH of dyeing, were optimized in wool dyeing, and color strength (K/S) was determined.

Effect of pH
The absorption of the dye molecules on the textile is influenced by the pH of the dyeing bath (Mehrparvar et al. 2016;Elshemy 2011). Also, pH can affect the surface charge of fiber and dye. As shown in Fig. 8, increasing the pH from 4 to 7 has been able to increase the amount of color strength and absorption of dye. Since this dye has alkaloid compounds, it becomes positively charged and the possibility of interaction with the anionic groups of wool fiber (COOH) is provided. pH 7-8 is above the isoelectric range of wool yarn, and in this condition, the number of carboxylic acid groups on wool fiber is relatively more than acidic media. Thus, ionic interactions were formed between alkaloid of Ziziphus bark and carboxylic acid groups of wool fiber, and consequently, the color strength was increased in neutral and alkali media (Ali et al. 2009;Son et al. 2007). The results exhibited that the difference in absorption of dye between pH 7 and 8 is insignificant, so pH 7 was considered as the optimal pH of dyeing process. The chemical structure of the

Effect of temperature
The dye absorption on the wool yarn was investigated at various temperatures 60-100 °C. The color strength of wool yarn was increased at higher temperatures (Fig. 9). Improvement of the solubility of colorant ingredients in Ziziphus bark, swelling of the internal pores of the fiber, and the diffusion of dye molecules from the dyeing bath into the fiber can become easier, and consequently, the absorption of dye increases (Kumari et al. 2020;Ahmad Khan et al. 2014). So, the perfect temperature was considered 100 °C for wool dyeing with Ziziphus bark.

Scheme 2 The chemical structures of the colorants in
Ziziphus bark at various pH amounts on the wool Fig. 9 The color strength of samples dyed with Ziziphus bark at various temperatures (dyeing conditions: pH 7, t = 60 min, C dye = 50% o.w.f., L.R 50:1)

Effect of time
The dyeing of wool samples with Ziziphus bark was performed at T = 100 °C for different durations from 15 to 120 min. The absorption of dye increased with the increase of dyeing time. Also, in time, 60 min, the amount of dye absorption on the wool yarn is completed, and this time can be considered as the equilibrium time in dyeing process. With the increase of dyeing time at 100 °C, on the one hand, the solubility of the dye molecules increases, and they migrate towards the fiber pores, and on the other hand, the fiber pores become the more swell, and the molecules are attracted to the inner pores and adsorptive sites of the fiber (Ahmad Khan et al. 2014). Finally, in 60 min, the absorption of the dye on the wool and in the dyeing bath achieves equilibrium, and the sites of the fiber are saturated. So, the suitable time for dyeing of wool with relatively satisfactory Ziziphus bark absorption is recommended, 60 min Mirnezhad et al. 2017) (Fig. 10).

Effect of initial concentration of Ziziphus bark
Various initial concentrations of Ziziphus bark (5-100% o.w.f.) were used for dyeing of wool yarn at 100 °C for 60 min, and K/S values of samples were measured (Fig. 11). It was found that increasing in initial concentration of Ziziphus bark up to around 50% o.w.f. has a direct effect on dye absorption, so that the color strength of wool yarn increased significantly (2.5 units). In low concentrations of Ziziphus bark, since the molecules of dye have high affinity to the wool fiber and the accessibility of them to adsorptive sites of the fiber is quicker, the absorption of dye happens straightforwardly. In addition of the amount of the Ziziphus bark in dyeing solution, the sites in the fiber are filled by the dye molecules, and at a concentration of 50%o.w.f., the adsorptive sites in fiber are saturated, and it is not possible to absorb the more dye molecules, and consequently, the interactions between the dye molecules and wool fibers were completed Ahmad Khan et al. 2014). In this concentration, adsorptive sites on wool fiber were occupied by dye molecules, and a slight increase in dye absorption occurred in further initial dye concentration. So, the optimal concentration of Ziziphus bark was chosen 50% o.w.f. for dyeing of wool yarns.

Effect of liquor ratio
The wool yarns were dyed with Ziziphus bark in various liquor to good ratio (30:1, 50:1, and 100:1) (Fig. 12). It was observed that color strength value decrease by increasing liquor ratio from 30:1 to 100:1, but it has not provided a significant difference on dye absorption. However, this factor affects the uniformity of the dyeing process and water and energy consumption, and also, the access of dye molecules to adsorptive sites of fiber is slower in a higher volume of dye solution. Therefore, by considering all aspects, the L.R 50:1 was chosen as the optimal condition. Generally, the maximum absorption of Ziziphus bark on the wool yarn can be achieved under the following conditions: the concentration of Ziziphus bark 50% o.w.f., time 60 min, pH 7, temperature 100 °C, and L.R 30:1.

Effect of mordant
Dyeing properties of the dyed textiles with natural dyes depend on the mordant. The color variation and improvement of colorfastness of many natural dyes on the textiles are produced by the mordant. In many cases, the type of mordant, the chemicals used during mordanting, and the method of mordanting affect the hue and quality of dyed the textile. Also, it has been stated that the mordant is very significant related to natural dyes in natural dyeing   Variation shades on dyed samples with Ziziphus bark were found using different mordants and mordanting process, so that post-mordanting with Fe and pre-mordanting with Cu will show the more colorfastness ratings. Generally, the more color fastness ratings for natural dye is dependent to chelate bonding between dye molecules/mordant/fiber system (Scheme 3) (Pervaiz et al. 2016;Gedik et al. 2013).

Colorfastness properties
In Table 4, the colorfastness properties of wool samples in the presence of various mordants are presented. The color change ratings of washing fastness were obtained 3-4, 4, and staining on adjacent white fabrics was insignificant (4-5).
The slight staining results were observed in rubbing fastness of dyed samples in wet and dry states (4-5). The mordanting with any of the inorganic salts clearly improved the lightfastness of the dyed samples from 4 (moderate) to 6-7 (very good). This can be attributed to the complex formation and coordination of the natural dyes with the mordants on the fiber surface (Chungkrang et al. 2018;Baaka et al. 2017b).

Antibacterial activity
The reduction percent of bacteria and inhibition zone of dyed samples with Ziziphus bark at different concentrations are presented in Table 5. The presence of high alkaloids, saponins, anthraquinones, and phenolic compounds in the Ziziphus bark produced noticeably antibacterial activities, so that Ziziphus bark at concentration of 100 o.w.f.% will be able to provide an acceptable antibacterial percent on wool yarn. It was found that the reduction percentage of Gram-negative bacteria is higher than that of Gram-positive, which can be attributed to the membrane structure of them. A thin layer of peptidoglycan is bordered on the cell wall of Scheme 3 The proposed interaction between metal/dye/wool system Gram-negative bacteria, which an outer membrane containing lipopolysaccharide is surrounded itself, while there is no outer membrane in Gram-positive bacteria, but layers of peptidoglycan are available that they are many times thicker than the Gram-negative bacteria.

Antioxidant property
The antioxidant activity of the wool dyed with Ziziphus bark in various concentrations was investigated by using the DPPH test (Fig. 13). In methanol as a media, the radical of DPPH is soluble and stable. Also, it has a deepviolet color at λ max 517 nm. The reaction of antioxidant agents with DPPH stable radical can produce an electron or hydrogen atom (Song et al. 2017). Thus, the radical of DPPH reduce to 2,2-diphenyl-1-hydrazine (DPPH-H) or a substituted analogous hydrazine (DPPH-R). This phenomena cause to color change of solution from deepviolet to colorless or pale-yellow. UV-visible spectrophotometer is a suitable equipment to determine antioxidant activity of compounds with antioxidant potentials (Song et al. 2017). The Ziziphus bark comprises high amount of anthraquinone, phenolic, saponin, and alkaloid compounds that all of them have antioxidant activities. It is well known that antioxidant agents can reduce the attack of free radical on DNA, and consequently, mutations that cause cancer are disallowed (Weinges and Schick 1995;Sudhersan et al. 2003). Due to carcinogenicity effect and serious health problems of synthetic antioxidant agents, the natural antioxidant agents from safer sources have been developed. The application of Ziziphus bark on the wool yarns showed that the dyed samples preserve above 80% antioxidant activity. Therefore, Ziziphus bark can be used not only for dyeing of textiles but also for producing antioxidant and antibacterial properties on medical textiles (Weinges and Schick 1995;Sudhersan et al. 2003;Niamat et al. 2012).

Conclusion
The extraction of Ziziphus bark was optimized under ultrasound condition and was applied on wool yarns. Optimum dyeing conditions were determined, and the colorimetric data and colorfastness properties of dyed samples in the presence of different mordants and methods were investigated. Results indicated that the extract of Ziziphus bark has acceptable color strength on wool yarn and acceptable colorfastness ratings, and variations of colors have been produced by different mordants. Post-mordanting with Fe and pre-mordanting with Cu improved the dyeing and colorfastness properties of wool samples. It was found that Ziziphus bark extract not only has a suitable dyeing ability on wool yarn but also has an acceptable potential to render antibacterial and antioxidant properties. Therefore, it is possible to produce multi-functional wool yarn dyed with a natural dye with antibacterial and antioxidant properties in an environmentally friendly procedure.