Simultaneous Coloration and Functionalization of Wool, Silk, and

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Simultaneous Coloration and Functionalization of Wool, Silk, and Nylon with the Tyrosinase-Catalyzed Oxidation Products of Caffeic Acid Sha-Sha Sun, Tieling Xing, and Ren-Cheng Tang* National Engineering Laboratory for Modern Silk, College of Textile and Clothing Engineering, Soochow University, 199 Renai Road, Suzhou 215123, P. R. China S Supporting Information *

ABSTRACT: The use of polyphenol oxidases in low environmental impact biotechnology is launching a new dyeing technology in textile industry. In this work, the simultaneous coloration and functionalization of wool, silk, and nylon fabrics with the tyrosinase-catalyzed oxidation products of caffeic acid were investigated. The occurrence of polymerization of caffeic acid resulting in colored quinone derivatives was confirmed by UV−visible and Fourier transform infrared spectroscopies. The treated fabrics showed distinct color with excellent rub fastness and staining fastness but weak light fastness and color change fastness. The color depth of dyed fabrics depended greatly on the dosage of tyrosinase employed in the preparation of caffeic acid oxidation products and the pH of dyebath. The multifunctionalities of dyed fabrics such as deodorizing ability, UV protection capacity, antioxidant activity and hydrophilicity were achieved. Tyrosinase-catalyzed caffeic acid products can be used as potential colorants and functional finishing agents. valuable dyeing properties.24 A red sulfonic azoanthraquinone dye through laccase-catalytic coupling of aromatic amine monomer displayed lower toxicity than other commercial red dyes and had good dyeing properties for nylon.25 The dyes from the laccase-catalyzed conversion of aromatic amines had an affinity for wool fibers.26 In addition, the colorless dye precursors, such as guaiacol, vanillin, ferulic acid, catechol, catechin, rutin, quercetin, etc., have been used to the in situ dyeing of textile fibers in the presence of polyphenol oxidases.27−36 Hydroxycinnamic acids, such as caffeic acid, chlorogenic acid, sinapic acid, ferulic acid, p-coumaric acid, and their derivatives are widely distributed in plants. They have attracted much attention because of their various biological and pharmacological activities (anti-inflammatory, antioxidant, antimutagenic, and anticarcinogenic).37 Treatment of hydroxycinnamic acids with laccase results in a variety of oxidation and coupling products depending on their aromatic ring substituents and reaction conditions.38 Ferulic acid, caffeic acid, and chlorogenic acid had been grafted onto textile fibers by polyphenol oxidases-catalyzed reactions for achieving antimicrobial and antioxidant finishing effects.36,39,40 The aim of this research is to study the feasibility of using tyrosinase-catalyzed caffeic acid (CA) oxidation products as eco-friendly colorants and functional finishing agents in the simultaneous coloration and functionalization of textile fibers. In this work, the tyrosinase-catalyzed CA oxidation products were first prepared and characterized, and then applied to the coloration of wool, silk, and nylon fabrics using the conven-

1. INTRODUCTION The development of synthetic dyes and dyeing industries is now facing many hindrances including environmental pollution, high labor costs, and legislative limitation.1−4 These difficult situations become the impetus for finding new types of ecofriendly synthetic dyes,3,4 and new energy saving and emission reduction techniques.5 With this goal, novel multifunctional cationic, disperse, acid, and reactive dyes were synthesized, and their dyeing and finishing properties were evaluated.6−14 Besides, the application of natural dyes in textile processing has also been increasing because of their high environmental compatibility, lower toxicity and allergic reaction, and most of plant-based dyes have a wide range of functional and medicinal properties, such as UV protection,15 antimicrobial and antioxidant activities,16−22 and deodorizing ability.23 These synthetic and natural functional dyes can be applied to the processing of textiles to achieve the simultaneous coloration and functional finishing effects with potential benefits in saving time and energy, increasing production and efficiency, and reducing effluent load. As far as the new ways of dye synthesis are concerned, the technological potential of polyphenol oxidases used as ecofriendly biocatalysts has been recognized. Usually the biocatalytic procedures offer the advantages of mild reaction conditions, and low waste and toxicity. Polyphenol oxidases including tyrosinase, laccase and catechol oxidase can oxidize phenolic compounds to phenoxyl radicals, which next undergo nonenzymatic reactions to form colored dimeric, oligomeric and polymeric products. The enzymatic synthesis of dyes primarily with laccases from different resources has been described in literature.1 Some of the enzymatically synthesized dyes could be applied to textile dyeing. Some of stable dyes generated by coupling of phenolic and nonphenonic precursors in the presence of immobilized white rot fungi exhibited © XXXX American Chemical Society

Received: December 4, 2012 Revised: May 21, 2013 Accepted: June 6, 2013

A

dx.doi.org/10.1021/ie303350z | Ind. Eng. Chem. Res. XXXX, XXX, XXX−XXX

Industrial & Engineering Chemistry Research

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Nicolet 5700 FTIR spectrometer (Thermo Fisher Scientific Inc., U.S.A.) by a KBr pellet method. All the IR data were collected from 32 scans with a resolution of 4.0 cm−1. 2.5. Color Measurement and Color Fastness Test. The CIE L*, C*, and h color coordinates (Lightness [L*], chroma [C*], and hue [h]) and the apparent color depth (K/S) were measured by a HunterLab UltraScan PRO reflectance spectrophotometer (Hunter Associates Lab. Inc., USA) using illuminant D65 and 10° standard observer. Each sample was fold twice so as to give a thickness of four layers. The washing and rubbing fastness of dyeings was tested according to ISO 105-CO1 and ISO 105-X12, respectively. A multifiber fabric was attached to the treated sample so as to detect color migration. The light fastness was tested according to ISO 105B02, and the fabrics were exposed to xenon arc lamp for 10 h in a standard testing condition. 2.6. Evaluation of Hydrophilicity. Hydrophilicity of the fabrics was evaluated by measuring the contact angle and the wetting time of a water droplet on the surface of the fabrics. The contact angles of distilled water on the surface of fabrics were measured using an OCA 20 contact angle and drop shape analyzer (DataPhysics Instruments GmbH, Germany) equipped with an imaging system. Each sample was carried out three times, and the average value was recorded. In the wetting time test, a drop (20 μL) of distilled water from a height of 1 cm was placed on the surface of fabric. The wetting time for a drop of distilled water to sink into the sample was recorded. Each sample was measured three times, and the average value was reported. 2.7. Evaluation of Functional Properties. The ultraviolet protection factor (UPF) of fabrics was determined in a UV1000F ultraviolet transmittance analyzer (Labsphere Inc., USA). Each sample was tested four times at different positions, and the average of the data was used. The antioxidant activity of fabrics was evaluated using the DPPH radical scavenging assay reported by Kokol by means of measuring the decrease in the absorbance of DPPḢ at 517 nm.21 In this experiment, the solution of DPPḢ was prepared daily. Briefly, 3 mL of 0.1 mM DPPḢ solution in ethanol was mixed with 300 mg of fabric and 7 mL of ethanol. The reaction mixture was stored in the dark at room temperature for 30 min and then the absorbance was measured. The experiment was carried out in triplicate. The DPPḢ scavenging activity was calculated using the following equation:

tional dyeing technique. The dyeing properties of the CA oxidation products were determined, and the hydrophilicity, UV protection capacity, antioxidant activity and deodorizing ability of the resultant dyeings were assessed.

2. EXPERIMENTAL SECTION 2.1. Materials. Mushroom tyrosinase (E.C.1.14.18.1, 965 U/ mg) was purchased from Worthington Biochemical Corp., USA. Caffeic acid (3,4-dihydroxycinnamic acid, CA) with purity above 98% was obtained from Wuhan Yuancheng Group, China. 2,2-Diphenyl-1-picrylhydrazyl (DPPH) was bought from Sigma-Aldrich (Shanghai) Trading Co. Ltd. A cationic fixing agent (Tinofix FRD) was kindly provided by Huntsman International LLC. All other chemicals used were of analytical reagent grade. The scoured and bleached wool fabric up to the standard GB/T 7568.1−2002 was purchased from Shanghai Textile Industry Institute of Technical Supervision. The scoured, woven silk fabric of crepe de Chine and the scoured, woven semidull nylon fabric were obtained from Wujiang Zhiyuan Textile Co. Ltd., China. The specifications of these fabrics are given in Table S1 of the Supporting Information. 2.2. Preparation of Tyrosinase-Catalyzed CA Oxidation Products and Their Application to Coloration of Wool, Silk, and Nylon. Ten millimolar CA solution was prepared with 4% (v/v) ethanol in phosphate buffer (pH 6.5). The oxidation reaction was started by adding 16 U/mL tyrosinase and incubated at 25 °C for 240 min. Dyeing of wool, silk, and nylon with the tyrosinase-catalyzed CA oxidation products was started at 70 °C using a 25:1 liquor ratio. After 10 min (tyrosinase inactivation), the temperature was elevated at a rate of 2 °C/min up to 95 °C, at this temperature the dyeing was continued for 60 min. At the end of dyeing, the dyed samples were removed, rinsed thoroughly in tap water, and allowed to dry in the open air. All the experiments were performed in open and conical flasks housed in a XW-ZDR low-noise oscillated dyeing machine (Jingjiang Xinwang Dyeing and Finishing Co. Ltd., China). To assess the effect of tyrosinase dosage employed in the preparation of CA oxidation products on the color depth of dyed fabrics, various concentrations of tyrosinase (0−18 U/ mL) were used. To estimate the effect of sodium sulfate, varying concentrations (0−25 g/L) were used in the dyebath. To study the effect of pH of dyebath, Britton−Robinson buffers (H3PO4−HAc-H3BO3/NaOH) were used to adjust pH over a range between 3 and 7. To attempt to improve the color fastness of CA oxidation products, the dyed fabrics were treated in the solution of a cationic fixing agent (8% omf Tinofix FRD) at 50 °C for 20 min. 2.3. UV−vis Spectrophotometric Analysis. The formation of colored products by tyrosinase catalyzed oxidation was monitored using a Shimadzu 1800 UV−vis spectrophotometer (Shimadzu Co., Japan). Five millimolar CA with 2 and 8 U/mL tyrosinase at pH 6.5 was incubated. After tyrosinase introduction, the change in the spectrum of CA solution was detected at different time points. 2.4. FT-IR Analysis. After removing the solvent with a rotary evaporator, the reaction products were dissolved in hot methanol followed by separation using pumping filtration to remove undissolved phosphate buffer and tyrosinase. The filtrate solution was dried with a rotary evaporator, and the final products were obtained through drying under vacuum and used for structural analysis. FT-IR spectra were recorded with a

antioxidant activity (%) = 100 ×

Acon − A sam Acon

(1)

where Acon is the initial absorbance of the DPPḢ , and Asam is the absorbance of the remaining DPPḢ in the presence of sample (fabric). The deodorizing ability of fabrics was tested as follows: a proper amount of odor substrate (1000 mg/m3 ammonia) was injected into a 4 L airtight polyethylene vessel. The fabric (1 g) was suspended in the vessel at 25 °C and 40% relative humidity for 60 min. The initial and residual concentrations of ammonia were measured by a corresponding gas detector tube with GASTEC GV-100S gas sampling pump (GASTEC Co., Japan). The deodorizing ability described as deodorizing rate was calculated according to the following equation: deodorizing rate (%) = 100 × B

Ccon − Csam Ccon

(2)



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where Ccon and Csam are the concentrations of ammonia in the vessel in the absence and presence of fabric, respectively.

3. RESULTS AND DISCUSSION 3.1. Enzymatic Oxidation of CA. The tyrosinase-catalyzed oxidation reaction of CA was investigated using UV−vis absorption spectra. The relevant results are depicted in Figure S1 of the Supporting Information (2 U/mL tyrosinase) and Figure 1 (8 U/mL tyrosinase), respectively. As shown in

Figure 2. UV−vis spectra of the solutions of CA oxidation products obtained using different tyrosinase dosages and thermal inactivation (10 mM CA).

ture,39,41,42,44−46 the final colored products of tyrosinasecatalyzed CA oxidation after a relatively long time and thermal inactivation of tyrosinase should be quinone oligomers. As the UV−vis spectra of the tyrosinase-catalyzed CA oxidation products varied with reaction time and thermal inactivation of tyrosinase, and a visual color change was also observed, the reproductibility of the formation of the CA oxidation products should deserve close attention. In the subsequent experiments, a reaction time of 280 min and thermal inactivation of tyrosinase were used so as to obtain the relatively stable oxidation products. To analyze the chemical groups in the tyrosinase-catalyzed CA oxidation products, the FI-IR analysis was carried out and depicted in Figure S2 (Supporting Information). In the case of CA spectrum, characteristic phenolic O−H stretching was at 3433.6 cm−1 and phenolic O−H in-plane bending at 1298.9 cm−1. The peaks at 3232.8, 3026.3, and 2568.3 cm−1 were attributed to O−H stretching vibration bands for carboxyl group. CO stretching and CC stretching vibrations were seen at 1645.3 and 1619.5 cm−1, respectively. Three absorption bands between 1450 and 1620 cm−1 were due to aromatic skeletal vibration. The other bands at 1280.0 and 1218.2 cm−1 belonged to the phenolic C−O stretching and CHCH inplane bending.47−49 The spectrum of CA oxidation products exhibited different profiles as compared to CA. A broad peak was spread over the range of 3500−2500 cm−1, indicating that the strong hydrogen bond interactions occur because of the existence of the obviously increased hydroxyl and carboxyl groups in CA oxidation products. The strong absorption band at 1604.2 cm−1 attributed to a combination of CC stretching and aromatic skeletal vibrations exhibited increased intensity, and the band at 1518.5 cm−1 assigned to aromatic skeletal vibration also displayed a significant increase in intensity. This implies the increased number of aromatic rings and carbon double bond in CA oxidation products. Two new bands appeared at 1387.7 and 1268.3 cm−1, and the bands of O−H bending vibrations of CA located at 1376.7, 1352.9, 1298.9, and 1218.2 cm−1 showed great shifts. In addition, a new band appeared at 1078 cm−1, which was attributed to the C−O−C stretching of aromatic− aliphatic ether, supposing the formation of benzodioxane moiety50 and also a consequence of the C−C linkage of phenolic acids.41 On the basis of the analyses of UV−vis and FT-IR spectra and earlier work,39,41,42,44−46 it may be presumed that the tyrosinase-catalyzed CA oxidation products consist mainly of

Figure 1. UV−vis spectra of CA solution (5 mM) in the presence of 8 U/mL tyrosinase at pH 6.5.

Supporting Information Figure S1 and Figure 1, a tailed broad absorption band appeared in the region between 400 and 550 nm during the period of CA oxidation. The band had a maximum absorbance at about 476 nm corresponding to a visible dark orange color. The profiles of these spectra in the visible region are similar to those reported in the literature for the oxidation of CA by laccase from Trametes versicolor.41 In addition, the spectral analysis of the control solution, containing only CA, showed no spectrum variation with time, indicating that no substantial autoxidation took place. Thus, the emergence of the new absorption band suggests the formation of colored products during the oxidation of CA. From Supporting Information Figure S1 and Figure 1, it is clear that the absorption intensity of colored products increased with both time and tyrosinase dosage, indicating the formation of the more colored substances. It is worthwhile to note that the absorption band became broader after a long period of oxidation with a color change from relatively orange to stable reddish brown. These facts suggest that a certain change has occurred in the chemical structure characteristics of the colored products accompanying the extension of oxidation time. An additional analysis about the spectra of the CA oxidation products subjected to thermal inactivation of tyrosinase is depicted in Figure 2. It was found that the absorption band further broadened after thermal inactivation, suggesting that the colored products varied in chemical structure characteristics during heating. The tyrosinase can oxidize and convert CA to reactive oquinones, which undergo oligomer forming reactions with other quinones,39,41 as well as a complex set of nonenzymatic autoxidation reactions.42,43 The broadened absorption band of the colored products with time and thermal inactivation of tyrosinase indicates that small and unstable molecular quinones changed into relatively large and stable ones by virtue of further polymerization with increased conjugation length. According to the present experimental results and the earlier literaC



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caffecin-like oligomers, dimers originated by C−C coupling between benzene rings, cycloligans, colored quinone oligomers, and their derivatives. The representative structures of these products are presented in Figure 3.

Figure 5. Effect of Na2SO4 concentration on the color depth of wool, silk, and nylon fabrics (10 mM CA, 16 U/mL tyrosinase; dyeing at pH 6.5).

However, the dyeing acceleration of Na2SO4 is not prominent. Therefore, the experiment about the influence of pH of dyebath on the color depth of the fabrics was further carried out. As shown in Figure 6, the color depth of three fabrics was greatly dependent on the pH of dyebath, and the highest color Figure 3. Representative structures of the tyrosinase-catalyzed CA oxidation products.

3.2. Dyeing Properties of the Tyrosinase-Catalyzed CA Oxidation Products. The dyeing properties of the CA oxidation products for wool, silk, and nylon fabrics were determined in terms of the effects of tyrosinase dosage, Na2SO4 concentration, and pH of dyebath on the color depth of dyed fabrics. Taking the fact into consideration that high temperature can increase the diffusion of CA oligomers within fiber substrates, the dyeing process was carried out at 95 °C. Figure 4 shows that the color depth of three fabrics increased with increasing tyrosinase dosage, but the increment in color

Figure 6. Effect of pH of dyebath on the color parameters of wool, silk, and nylon fabrics (10 mM CA, 16 U/mL tyrosinase).

depth and the lowest lightness (the lower L* value, the darker the color) were achieved at the pH of around 4−5. This finding can be explained in terms of the mechanism by which the colored products of CA oxidation are adsorbed onto fibers. Wool, silk, and nylon fibers are amphoteric in nature, and exhibit different charge characteristics at different pH values, which have an important role on the adsorption of anionic adsorbates in solution. On the other hand, as the charge character and water solubility of the colored products of CA oxidation are closely related to pH, the CA oxidation products can exhibit negative charges due to the dissociation of carboxyl groups in them. When the pH is below the isoelectric point of amphoteric fibers, the uptake of the colored products of CA oxidation occurs primarily by electrostatic interaction between the anionic carboxyl groups in the colored products and the protonated amino groups in the fibers, although other forces of interaction, such as hydrogen bonding and van der Waals force also contribute to the affinity of the colored products to fibers. The electrostatic interaction between the colored products and the fibers ensures the highest uptake of the colored products by

Figure 4. Effect of tyrosinase dosage on the color depth of wool, silk, and nylon fabrics (10 mM CA; dyeing at pH 6.5).

depth became small when the tyrosinase dosage exceeded 8 U/ mL. Figure 5 shows that the color depth of three fabrics increased slightly with an increase in Na2SO4 concentration. Theoretically, both the carboxyl group-containing colored products of CA oxidation and three fibers are anionic in character under the condition of pH 6.5. The repulsive charges between colored products and fibers can be overcome by adding neutral salts such as Na2SO4, which have the effect of screening the negative charges on the surface of fibers. D



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Table 1. Color Fastnesses of the Fabrics Dyed with the Tyrosinase-Catalyzed CA Oxidation Products before and after Post Treatment of a Cationic Fixing Agent wash staining fabrics

light

rub (dry/wet)

Wool Silk Nylon

3 1 1

4−5/4−5 5/5 5/5

Wool Silk Nylon

4 3 1

5/5 5/5 5/5

color change

wool

acrylic

control 5 5 5 5 5 5 treatment of a cationic fixing agent 2−3 5 5 3 5 5 4−5 5 5 2 2 5

fibers at pH 4−5, expressed as the highest K/S and the lowest L* of fabrics in Figure 6. When the pH is much lower (e.g., 3 and 4 for nylon dyeing, and 3 for wool dyeing), the dissociation of the colored products is negatively affected, and thus the reduced quantity of the free anionic colored products leads to a decrease in the quantity of the colored products adsorbed by wool and nylon fibers by virtue of electrostatic interaction. At the higher pH values (6 and 7), the lower color depth of the dyed fabrics is also caused by the reduced contribution of electrostatic interaction to total adsorption of the colored products. From Figure 6, it is found that the hues (h values) of the dyed wool, silk, and nylon fabrics exhibited certain variation, and changed with the pH of dyebath. The change in hue might be caused by the fact that various components of CA oxidation products had different extents of adsorption on the fibers, and their adsorption varied with the pH of dyebath. As a result of the fluctuation in color depth and hue, the variation in the chroma of the dyed fabrics occurred with the pH of dyebath. From the point of view of textile dyeing, the reproductibility of the colors of the dyed fabrics is of great importance. According to the influence of the pH of dyebath on the hues and color depth of the dyed fabrics, it is suggested that pH had better be controlled within the range of 4−5. 3.3. Color Fastness of the Fabrics Dyed with the Tyrosinase-Catalyzed CA Oxidation Products. Textiles are subjected to frequent washing, rubbing, and lighting during their usage. Hence the resistance of the dyes on textiles to these conditions is important. In practical applications, the textiles for different purposes have varied requirements for color fastness. The color fastness of the dyed wool, silk, and nylon fabrics with the products of CA enzymatic oxidation was assessed and listed in Table 1. The fastness rating of the dyed nylon fabric was excellent for washing, while those of the dyed wool and silk fabrics were excellent for staining but poor for color change. This result is probably due to the high affinity of the colored CA oxidation products to nylon fibers. All the dyed fabrics exhibited very good dry and wet rubbing fastness, indicating the good diffusion and penetration of the colored CA oxidation products into fiber substrates. However, the poor light fastness of all the dyed fabrics was observed. The dyed wool had relatively high light fastness (rating 3), which should be attributed to its higher color depth. The poor resistance of the dyed fabrics to light may be caused by the fact that the colored products with multiple hydroxyl groups are susceptible to photo-oxidation on exposure to light. Thus the fabrics dyed with the products of CA enzymatic oxidation are not suitable

polyester

nylon 6,6

cotton

acetate

5 5 5

5 5 5

4−5 4−5 4−5

5 5 5

5 5 5

4−5 5 5

4−5 5 4−5

5 5 5

for the applications having the requirements for the high color fastness to light. Taking the relatively poor wash color fastness in terms of color change, as well as the existence of the carboxyl groups in the CA oxidation products into consideration, a cationic fixing agent (Tinofix FRD) was applied to the post treatment of the dyed fabrics with the aim of improving the color fastness. The results in Table 1 show that after fixation treatment the color change fastness of the dyed wool and silk fabrics was improved by 0.5 and 1 ratings, respectively. This should result from the electrostatic interaction between the cationic groups in the fixing agent and the carboxyl groups in the CA oxidation products. From Table 1, it can be interestingly noted that after fixation treatment the light color fastness of the dyed wool and silk fabrics was improved by 1 and 2 ratings, respectively. The electrostatic interaction between the fixing agent and the CA oxidation products might hinder the photo-oxidation of the multiple hydroxyl groups in the CA oxidation products, and accordingly improve the light color fastness of the dyed fabrics. 3.4. Hydrophilicity and Functional Properties of the Dyed Fabrics. The products of tyrosinase-catalyzed CA oxidation are a mixture of various components as described above. During the process of their application to wool, silk and nylon fabrics, both colored and noncolored components can be adsorbed by the fibers. Thus the properties of the dyed fabrics would be likely to be changed, although the extent of the uptake of each component by the fibers is difficult to be determined. In the present work, the hydrophilicity, UVprotection property, antioxidant activity, and deodorizing ability of the dyed fabrics were evaluated. Hydrophilicity. The hydrophilicity of a fabric can be characterized using the contact angle and wetting time of a water droplet. The smaller the contact angle and the shorter the wetting time, the more hydrophilic the surface of the fabric is. Wool fiber contains a large amount of polar and hydrophilic groups, but its cuticle scale surface is covered by a thin layer of fatty acids, which are covalently bound to the protein matrix of the epicuticle and confer hydrophobic character to this fiber.51 Nylon is a hydrophobic fiber in nature because of the existence of methylene groups and the lack of hydrophilic groups. Since silk fabric possesses tremendously good hydrophilicity, its contact angle and wetting time was not determined in this work. The wetting times and contact angle values of dyed wool and nylon fabrics were measured and shown in Table 2. The control wool and nylon (treated only with buffer) had contact angle values above 90° and showed very long wetting times, revealing their hydrophobic surfaces. No substantive variation in contact angle and wetting time was observed for E



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Table 2. Wetting Times and Contact Angle Values of Wool and Nylon Fabrics wetting time (min)

contact angle (deg)

treatments

wool

nylon

wool

nylon

control CA CA oxidation products

>30 >30 10.7

10.4 10.3 3.8

130.4 126.8 113.8

115.7 111.7 82.1

tyrosinase treated (date not shown) and CA treated wool and nylon, suggesting that tyrosinase and CA are not likely to improve the hydrophilicity of samples. In the case of the dyeing with the CA oxidation products, the contact angles decreased from 130.4° to 113.8° for wool, and from 115.7° to 82.1° for nylon, respectively, and at the same time the wetting times were obviously shortened. The increase of hydrophilicity is further demonstrated by the images of water droplet captured on the surfaces of undyed and dyed nylon fabrics (Figure S3 of the Supporting Information). The improvement of hydrophilicity should be due to the adsorption of hydrophilic CA oxidation products on the surface of fibers. It is possible that the hydrophobic segment of the CA oxidation products is embedded into the interior of fibers, while their hydrophilic moiety, that is, their hydroxyl and carboxyl groups is left on the surface layer of fibers. The distribution of the hydrophilic moiety of the CA oxidation products on fiber surface contributes to an increase in the hydrophilicity of wool and nylon. Here, it has to be mentioned that according to British Standard 4554:1970 (Method of Test for Wettability of Textile Fabrics), the fabrics that give the water absorption time exceeding 200 s are considered to be unwettable.52 Although the wool and nylon fabrics dyed with the CA oxidation products exhibited the obviously reduced wetting times (10.7 min for wool, and 3.8 min for nylon) and the improved hydrophilicity, they still belonged to the nonwettable fabrics. UV-Protection Properties. The sunlight ultraviolet radiation in the range between 100 and 400 nm is subdivided into UV-C (100−280 nm), UV-B (280−315 nm), and UV-A (315−400 nm). Since UV-C radiation is mostly adsorbed by the ozone layer in the upper atmosphere, the protection performance of textiles against UV-A and UV-B radiation is evaluated when the effect of ultraviolet radiation on human health is considered. The solutions of hydroxycinnamic acids such as caffeic acid, ferulic acid, coumaric acid, sinapic acid, chlorogenic acid, etc. usually exhibit two UV absorption bands in the UV−vis spectra, one being at 295 nm or so, the other being approximately at 315 nm. 41 Thus hydroxycinnamic acids possess good absorption capacity in the UV-A and UV-B region, and can be used as UV protection agents. In our previous work, the extract of honeysuckle whose main chemical component is chlorogenic acid was found to be a natural UV-absorbing agent with relatively good durability to light radiation and laundering when applied to wool finishing.53 Hence, the UV-protection properties of the wool, silk, and nylon fabrics dyed with and without the products of tyrosinase-catalyzed CA oxidation were evaluated according to Australia Standard/New Zealand Standard AS/NZS 4399:1996,54 and the results are shown in Figure 7. The UPF values of the wool, silk, and nylon fabrics (control samples) were 26.0, 7.3, and 44.9, respectively. Silk fabric showed the poor UV protection capability due to its lightweight fabric character, while nylon fabric had the good UV protection

Figure 7. UPF values of the wool, silk, and nylon fabrics dyed with the tyrosinase-catalyzed CA oxidation products (10 mM CA).

property indicated by a high UPF due to the presence of a small amount of titanium dioxide in the interior of this fiber. The fabrics treated with CA exhibited a remarkable increase in UPF as expected, which have similarity with wool treated with the extract of honeysuckle (chlorogenic acid).53 This finding supports the use of hydroxycinnamic acids as UV protection agents. From Figure 7, it can be clearly seen that the dyeing with the products of tyrosinase-catalyzed CA oxidation further improved the UPF values of the fabrics as compared to CA treatment. Furthermore, the improvement in UPF increased with increasing dosage of tyrosinase employed in the process of CA oxidation. This can be explained by the fact that CA oligomers have higher affinity to the fibers than CA and corresponding larger uptake by the fibers because of the existence of more aromatic rings and carbon−carbon conjugated double bonds in their structure. Both the more UV-absorbing moiety and the larger uptake of CA oxidation products can endow the fibers with higher UV protection performance. Antioxidant Activity. The antioxidant activity is one of the most important properties of bioactive textiles, and the radical scavenging textiles can deactivate highly reactive and harmful species such as active oxygen radicals. Textiles can be endowed with antioxidant activity by means of the adsorption of antioxidant compounds. Hydroxycinnamic acid compounds are an important source of antioxidants and possess excellent antioxidant activity.55,56 Antioxidant activity was expected on the fabrics treated with CA and its tyrosinase-catalyzed oxidation products. The antioxidant activity values of original wool, silk, and nylon fabrics were 1.03, 0.37, and 7.56, respectively, revealing the poor radical scavenging ability of original fabrics. As can be seen in Figure 8, the three fabrics treated with CA exhibited considerably enhanced antioxidant activity, which originates from their adsorption capacities to CA as CA have the inhibition ability of radical scavenging due to the hydrogendonating phenolic hydroxyl groups in its structure. In the case of the fabrics dyed with the tyrosinase-catalyzed CA oxidation products, with increasing dosage of tyrosinase employed in the preparation process of the oxidation products, the three fabrics showed further increased antioxidant activity. This may be attributed to the combination impacts of the peculiar adsorption and structural characteristics of the CA oxidation products. The CA oxidation products have higher affinity to fibers than their parent compound due to their larger conjugated system or hydrophobic moiety, and accordingly higher extent of adsorption on fibers. Moreover, some CA oxidation products possess more hydrogen-donating phenolic F



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adsorption by virtue of neutralization operating between ammonia and the carboxyl groups in fiber contributes to the deodorizing performance toward ammonia. As shown in Figure 9, wool and silk fabrics showed obviously increased deodorizing ability after treated with CA. All the three fabrics dyed with the tyrosinase-catalyzed CA oxidation products had the highest deodorizing ability. This can be explained by the fact that the adsorption of the CA oxidation products on fibers increase the amount of carboxyl groups on fiber surface. The results of deodorizing power indicate that the products of tyrosinasecatalyzed CA oxidation may be developed as a deodorizing agent applied to textile finishing.

4. CONCLUSIONS The products of tyrosinase-catalyzed CA oxidation were prepared and successfully applied to the coloration and functionalization of wool, silk and nylon fabrics using the conventional dyeing technique. The UV−vis and FT-IR spectra provided evidence for the coupling reaction of CA and the formation of colored quinone oligomers. The tyrosinase-catalyzed CA oxidation products exhibited good dyeing properties for wool, silk, and nylon fabrics. The color depth of dyed fabrics was greatly dependent on the dosage of tyrosinase employed in the CA oxidation process and the pH of dyebath, but slightly related to the concentration of Na2SO4 in dyebath. The fastness ratings of dyed fabrics were excellent for staining and rubbing but poor for light and color change; the washing and light color fastness of the dyed wool and silk fabrics could be improved by the post treatment of a cationic fixing agent. Overall, these dyed fabrics are not suitable for the applications with high light fastness requirements. The tyrosinase-catalyzed CA oxidation products could endow the dyed fabrics with a variety of functional properties. The dyed wool and nylon fabrics exhibited decreased contact angles and shortened adsorption times of water droplet, indicating the obvious improvement of hydrophilicity. The dyed fabrics showed enhanced UV protection capacity, antioxidant activity in inhibition of DPPH, and deodorizing ability toward ammonia. The tyrosinase-catalyzed CA oxidation products may be developed as potential colorants and functional finishing agents which can be applied for the simultaneous coloration and functionalization of textiles. The potential and promising application fields of the relevant products are likely to be healthcare and medical textiles whose functionalities are emphasized, but whose requirements for color characteristics are relatively low. In future, the problems of poor light and washing fastness for color change should be further solved.

Figure 8. Antioxidant activity of the wool, silk and nylon fabrics treated with CA and its tyrosinase-catalyzed oxidation products, measured as the reduction of the DPPH radicals (10 mM CA).

hydroxyl groups that are likely to amplify the antioxidant activity. Both the two possible reasons can explain the improvement of the antioxidant properties of the dyed fabrics. Figure 8 also shows that the dyed wool and nylon exhibited higher antioxidant activity than silk, which might be attributed to their higher adsorption capacities to the CA oxidation products. The antioxidant activity measurements of the dyed fabrics reveal that the products of tyrosinase-catalyzed CA oxidation may exhibit medical actions toward human body by contact with textile fabrics. Deodorizing Ability. There are many bacteria and microbes in our environment, which produce diverse odors when they propagate. In everyday life, the main odor substances of the malodor elements including sweat, excretion, cigarette, and garbage odors are ammonia, acetic acid, isovaleric acid, methyl mercaptan, trimethylamine, etc. Among these odors, ammonia is one of the most common pernicious gases, especially in new buildings and newly renovated houses, as well as in some livestock farms, lavatories, and special workshops.57 Since the deodorizing performance of textiles has drawn considerable attention, it is interesting to evaluate the deodorizing ability of the fabrics dyed with the products of tyrosinase-catalyzed CA oxidation toward ammonia. Figure 9 shows that the deodorizing ability of the original fabrics toward ammonia increased in the order of nylon < silk < wool. The order of deodorization is consistent with the previously reported result,23 and with the contents of carboxyl groups in these fibers. This suggests that the chemical

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ASSOCIATED CONTENT

S Supporting Information *

Specifications of the fabrics used, UV−vis spectra of the solution of CA and tyrosinase (2 U/mL), FT-IR spectra of tyrosinase-catalyzed CA oxidation products, and images of water droplet captured on the surface of nylon fabric. This material is available free of charge via the Internet at http:// pubs.acs.org.

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AUTHOR INFORMATION

Corresponding Author

*Address: National Engineering Laboratory for Modern Silk, College of Textile and Clothing Engineering, Soochow University, 199 Renai Road, Suzhou 215123, P. R. China.

Figure 9. Deodorizing ability of the wool, silk and nylon fabrics treated with CA and its tyrosinase-catalyzed oxidation products toward ammonia (10 mM CA, 16 U/mL tyrosinase). G



Article

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Tel.: +86 512 6716 4993. Fax: +86 512 6724 6786. E-mail: [email protected]. Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS This study was funded by the National Nature Science Foundation of China (51203107), Suzhou Research Program of Application Foundation (SYG201117), Graduate Student Research and Innovation Program of Jiangsu Province (CXZZ12_0822), Jiangsu Provincial Natural Science Foundation of China, and the Priority Academic Program Development (PAPD) of Jiangsu Higher Education Institutions.

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Simultaneous Coloration and Functionalization of Wool, Silk, and

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