Smart textile framework: Photochromic and fluorescent cellulosic fabric printed by strontium aluminate pigment

Carbohydrate Polymers 195 (2018) 143–152

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Carbohydrate Polymers journal homepage: www.elsevier.com/locate/carbpol

Smart textile framework: Photochromic and fluorescent cellulosic fabric printed by strontium aluminate pigment ⁎

T

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Tawfik A. Khattab , Mohamed Rehan , Tamer Hamouda Textile Industries Research Division, National Research Centre, 33 El-Behouth Street, Dokki, Giza 12311, Egypt

A R T I C LE I N FO

A B S T R A C T

Keywords: Inorganic pigment Screen printing Photochromism Fluorescence Smart cellulosic fabric

Smart clothing can be defined as textiles that respond to a certain stimulus accompanied by a change in their properties. A specific class herein is the photochromic and fluorescent textiles that change color with light. A photochromic and fluorescent cotton fabric based on pigment printing is obtained. Such fabric is prepared by aqueous-based pigment-binder printing formulation containing inorganic pigment phosphor characterized by good photo- and thermal stability. It exhibits optimal excitation wavelength (365 nm) results in color and fluorescence change of the fabric surface. To prepare the transparent pigment-binder composite film, the phosphor pigment must be well-dispersed via physical immobilization without their aggregation. The pigmentbinder paste is applied successfully onto cotton fabric using screen printing technique followed by thermal fixation. After screen-printing, a homogenous photochromic film is assembled on a cotton substrate surface, which represents substantial greenish-yellow color development as indicated by CIE Lab color space measurements under ultraviolet light, even at a pigment concentration of 0.08 wt% of the printing paste. The photochromic cotton fabric exhibit three excitation peaks at 272, 325 and 365 nm and three emission peaks at 418, 495 and 520 nm. The fluorescent optical microscope, scanning electron microscope, elemental mapping, energy dispersive X-ray spectroscopy, fluorescence emission and UV/Vis absorption spectroscopic data of the printed cotton fabric are described. The printed fabric showed a reversible and rapid photochromic response during ultra-violet excitation without fatigue. The fastness properties including washing, crocking, perspiration, sublimation/heat, and light are described.

1. Introduction Smart textiles are usually defined as garments that can sense and react to environmental conditions or external stimuli, such as light, pH, temperature, pressure, solvents of different polarities, mechanical or magnetic effects, chemicals, and electricity (Gashti & Eslami, 2015; Gashti, Ebrahimi, & Pousti, 2015; Gashti, Pakdel, & Alimohammadi, 2016; Parvinzadeh Gashti, 2014). For instance, smart clothes can release medication or moisturizer onto the skin, assist regulate the muscular vibrations during athletic activities, and even release materials able to control body temperature. Smart fabrics can also change their color, lighting up in patterns or even display pictures and video (Gashti & Eslami, 2015; Gashti et al., 2015, 2016; Parvinzadeh Gashti, 2014). Generally, there are three major components that must be present in smart garments including sensing, actuating, and controlling units. Production of smart clothes is generally based on the traditional textile manufacturing technologies, such as weaving, knitting, embroidery, and textiles finishing, coating and laminating. Textiles modifications or

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finishes, and miniaturized electronic devices can also generate smart garments or electronic textiles (e-textiles) that enable digital components to be embedded in such textiles imparting the ability to communicate, transform, and conduct energy (Gashti & Gashti, 2013; Nooralian, Gashti, & Ebrahimi, 2016; Ojuroye, Torah, Beeby, & Wilde, 2017). Smart textiles that generate adequate responsiveness are prone to enhance their protective purpose as a consequence of an external stimulus such as pressure (Lee et al., 2015), temperature (Chowdhury, Joshi, & Butola, 2014), UV intensity (Gorjanc et al., 2017), pH (Rosace et al., 2017), or electrical field (Choi & Jiang, 2006). An example of smart textiles could be photochromic textiles that transform their color upon exposure to light (Cheng, Lin, Brady, & Wang, 2008). Photochromism is a photo-induced transformation process between two optical absorption states in which a compound in the solid state or in solution changes color when exposed to light and then reverts back to its original color upon removal of external light stimulus (Kawata & Kawata, 2000). This fascinating color-changing technology has received

Corresponding authors. E-mail addresses: [email protected] (T.A. Khattab), [email protected] (M. Rehan).

https://doi.org/10.1016/j.carbpol.2018.04.084 Received 29 November 2017; Received in revised form 15 April 2018; Accepted 21 April 2018 Available online 23 April 2018 0144-8617/ © 2018 Elsevier Ltd. All rights reserved.

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pigments. As a result, the photochromic fabric usually has poor properties that still need to be improved to satisfy consumer expectations, as the photochromic and fluorescent visual effects rapidly fade out with prolonged exposure to light, perspiration, heat, continuous washing, and rubbing (di Nunzio et al., 2008; Feczkó et al., 2013; Peng et al., 2015). The immobilization of inorganic pigment phosphor at low concentration onto binder-thickener printing matrix before their incorporation on fabric surface via screen-printing methodology can be considered as a potential strategy for the fabrication of photochromic fabrics with enhanced color-exchange properties, dye stability, and comfort. Oxide-based strontium aluminate pigment phosphor doped with divalent europium are extremely advantageous to provide photochromic and fluorescent functionalities to textile substrates while maintaining the original textile properties such as appearance, color fastness, handle, and touch. Up to now, there are different long-lasting luminescent materials have been developed as different primary color emitters, such as CaAl2O4:Eu2+/Nd3+ or SrMgSi2O6:Eu2+/Dy3+ for blue (Lin, Tang, Zhang, Wang, & Zhang, 2001; Yamamoto & Matsuzawa, 1997), MgAl2O4:Mn2+ or SrAl2O4:Eu2+/Dy3+ for green (Matsuzawa, Aoki, Takeuchi, & Murayama, 1996; Wang, Jia, & Yen, 2003), and Y2O2S:Eu3+,Mg2+/Ti4+ or CaS:Eu2+/Tm3+/Ce3+ (Smet, Moreels, Hens, & Poelman, 2010; Wang, Zhang, Tang, & Lin, 2003) for red. The SrAl2O4:Eu2+/Dy3+ has been verified to be an excellent long persistent phosphor due to its higher brightness, longer persistence time (> 10 h), with photo, chemical and physical stabilities (Kumar, Kedawat, Kumar, Dwivedi, & Gupta, 2015; Qin et al., 2013). In addition, the photochromic layer is nontoxic, non-radioactive, and can be recycled (Qiu et al., 2007; Rojas-Hernandez et al., 2018). Consequently, the fabrication of cost-effective high-tech textiles with tuneable photoswitchable properties, excellent fabric handle, high durability and improved fastness properties such as washing, perspiration, sublimation, crocking and light fastness through their printing with aqueous binder-containing inorganic pigment phosphor is an innovative approach, opening new horizons to the development of more effective and stable smart garments. To the best of our knowledge, the fabrication of light-responsive color changeable textiles employing screen-printing of aqueous binder and strontium aluminate pigment has not been reported. Herein, we report the design and application of strontium aluminate pigment on cellulosic fabrics by screen-printing for smart textile purpose.

great attention in science to afford a variety of industrial products such as packaging, cosmetics, sunglasses and ophthalmic lenses, optical data storage, memories, optical switches, sensors and displays (Garai, Mallick, & Banerjee, 2016; Kunzelman, Gupta, Crenshaw, Schiraldi, & Weder, 2009). This intensified perceptibility of materials colored with photochromic or fluorescent colorants is an advantage in preparing colored advertisements, road and traffic signs, and information descriptions (Garai et al., 2016). The use of photochromism in textiles can offer innovative opportunities to accomplish smart garments capable of blocking UV radiation, sensing environmental changes, security printing, brand protection, sports clothing, fashion garments, clothing for special services such as fire brigades and the police, fabric-based electronic image displays, security barcodes, sensor systems, solar heat, light management and attractive decorations (Jamshaid & Mishran, 2014; Little & Christie, 2010; Otley, Invernale, & Sotzing, 2013; Qiu, Zhou, Lü, Zhang, & Ma, 2007; Rojas-Hernandez, Rubio-Marcos, Rodriguez, & Fernandez, 2018). Furthermore, photochromic effects can be applied in military clothing to provide camouflage that is responsive to light as an external energy stimulus (Hu, 2008). Stimuli-responsive and active protective garments have the advantages of their easy maintenance including washing and drying, extremely large specific surface and low specific weight with enhanced strength, tensibility and elasticity. Workability without altering the manufacture technology, potential incorporation of these types of sensors into structures of protective garments, in addition to their cost and accessibility, are also considerable advantages. Photochromic fabrics can be produced without compromising their comfort, easy care and hygiene. Therefore, this challenges researchers to develop new photochromic and fluorescent smart textiles (Arkhipova, Panchenko, Fedorov, & Fedorova, 2017; Christie, Morgan, & Islam, 2008; Luo, Tang, Zhu, Xu, & Qian, 2015). It is possible to classify photochromic fibres into different groups: those which emit the color when activated by visible light and those which emit the color when activated by ultraviolet radiation. Photochromic fibres and/or fabrics made from different substrates (e.g., cotton, polyester, nylon, acrylic, wool, and polyamide) have been produced by different dyeing procedures through the incorporation of photochromic organic molecules, mostly spirooxazine-based colorants. Dyeing of garments using photochromic organic dyes results in a number of problems associated with the dyeing procedure such as dye degradation, limited interaction between dye and fibre matrix due to low dye uptake and decreased dye diffusion into the fibres, total inhibition of photochromism, constraints imposed by the hardness of the matrix, and low washing and light fastness characteristics. Some of these drawbacks can be overcome by processing dyes into pigments using microencapsulation processes; although this methodology tends to increase the stability of the photochromic compounds, it usually confers a certain harshness and stiffness on the fabric, compromising the comfort of the user (di Nunzio, Gentili, Romani, & Favaro, 2008; Fan & Wu, 2017; Fan, Zhang, & Wang, 2015; Feczkó, Samu, Wenzel, Neral, & Voncina, 2013; Peng et al., 2015). Alternatively, photo-switchable textiles can be produced by simple technique called screen-printing using aqueous binder containing organic photochromic dyes, which prevents the problems related to dyeing and eventual incompatibility between the colorant and the substrate. The aqueous-based pigment-binder screen-printing method is a simple and cost-effective technique that can be processed to develop printing matrices, which are excellent hosts for both of organic and inorganic pigments. Pigment printing is not only the oldest but also the easiest coating technique as far as simplicity of application is concerned. More than 80% of the printed merchandise is based on pigment printing due to its apparent advantages, such as versatility and ease of near final print at the printing stage itself (Hoeng, Denneulin, ReverdyBruas, Krosnicki, & Bras, 2017; Pinto et al., 2016). Most of these coloration techniques use organic photochromic colorants which are characterized by low photostabilty and high cost compared to inorganic

2. Experimental details 2.1. Materials and chemicals Desized, scoured and bleached 100% cotton fabrics (Plain weave) were supplied by El-Mahalla El-Kobra Company, El-Mahalla, Egypt. The fabric specifications were as follows: fabric weight 150 g/m2, thickness 0.40 mm, micronaire (3.88 μg/inch), weft 30 yarn/cm, and warp 36 yarn/cm. The fabrics were scoured, by El-Mahalla El-Kobra Company, in aqueous solution having a liquor ratio of 1:50 and containing 2 g/L of non-ionic detergent solution (Hostapal; Clariant, Swiss), 5 g/L sodium hydroxide and 2 g/L of sodium carbonate at 90° C for 60 min to get rid of waxes and impurities, followed by rinsing in cold water, and finally dried at room temperature. The scoured cotton fabrics were bleached with hydrogen peroxide solution (20 ml, 35% H2O2), sodium silicate (2 g/L), sodium hydroxide (2 g/L) and 2 g/L of non-ionic detergent solution (Hostapal; Clariant, Swiss) at a liquor ratio of 1:50 for 1 h at 90 °C. Binder additive, thickener alcoprint PTP, and Reactive Red AEF were supplied by Dystar, Egypt. Strontium carbonate (SrCO3), Aluminium oxide (Al2O3), Europium (III) oxide (Eu2O3), Dysprosium (III) oxide (Dy2O3) and Boric acid (H3BO3). All the raw materials employed in this experiment were supplied by Sinopharm Chemical Reagent Co. Ltd, China.

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2.2. Preparation of the pigment

04).

The strontium aluminate phosphor pigment (Sr0.95Al2O4: Eu2+ 0.02, were prepared according to literature procedure by high-temperature solid-state reaction (Guo & Ge, 2013; Yan, Zhu, Guo, & Ge, 3+ 2014). The Sr0.95Al2O4: Eu2+ 0.02, Dy0.03 complex was prepared by mixing the powder materials, SrCO3, Al2O3, Eu2O3 and Dy2O3, according to the mole ratios of the elements, (molar ratio of Sr:Al:Eu:Dy = 1:2:0.01:0.02) and adding 5% of H3BO3 (molar ratio 0.2) as a flux, which were dissolved in approximately 100 ml of absolute ethanol and followed by ultrasonic dispersion with 25 kHz for 20 min in order to get a homogeneous mixture. Subsequently, the mixtures were dried at 90° C for 24 h, ground in a planetary high-energy ball mill for 2 h and sintered at the 1300° C over 3 h with a heating rate of 10° C min−1 in a powered carbon reduction atmosphere. The sintered products were remilled and sieved to get the desired strontium aluminate pigment phosphor activated by Eu2+, Dy3+.

2.5. Evaluation of the photophysical properties

Dy3+ 0.03)

In order to acquire the UV–vis spectra of the samples, the UV lamp (λmax = 365 nm and 6 W) was placed 4 cm above the fabrics and the measurements were carried out at room temperature. In a preliminary experiment, the UV–vis absorption spectra of the fabrics before and after UV irradiation were obtained to determine the maximum wavelength of absorption (λmax) of the colored form. In a second experiment, after the fabrics were irradiated during 1 min with UV light, the light source was turned off and the absorbance at λmax vs. time was monitored. 2.6. Colorimetric measurements and color fastness The color of the printed cotton fabrics before and after UV irradiation was measured using a Chroma meter Konica Minolta CR-400 with a D65 illuminant (daylight, color temperature 6504 K), a 2° standard observer function and an 8 mm diameter illumination area. The colorimetric values were determined using the CIE (International Commission on Illumination) Lab color space, which is a three dimensional system with the coordinates L* (lightness), a* (green/red) and b* (blue/yellow); L* assumes values from 0 (darkest black) to 100 (brightest white), a* denotes red when it is positive and green when negative, and b* defines yellow when it is positive and blue when negative. In this experiment, fabrics were irradiated for 1 min with a UV lamp (λmax = 365 nm and 6 W) placed 4 cm above. The lamp was removed and the colorimetric measurements were reported directly. The color strength of the printed samples expressed as K/S was evaluated by high reflectance technique. The color strength expressed as K/S was assessed by applying the Kobelka Munk equation. The color fastness of the treated fabrics was tested according to ISO standard methods. The specific tests were ISO 105-X12 (1987) for color fastness to rubbing; ISO 105-C02 (1989) for color fastness to washing and ISO 105 E04 (1989) for color fastness to perspiration (Emam, Mowafi, Mashaly, & Rehan, 2014; Khattab et al., 2017; Rehan et al., 2017).

2.3. Fabrication of photochromic cotton substrates Before applying the stimuli-responsive printing paste, the knitted cotton garments were dyed using Reactive Red AEF to afford a dark redcolored hue. The dyeing’s carried out using a liquor ratio of 1:50. The dye-bath was prepared by adding dye (2% owf; weight of fabric) and sodium chloride (60 g/dm3) to distilled water at room temperature. Wet cotton fabric was added to the dye-bath and left for 30 min, and then the temperature was raised to 60° C and left for 20 min. Fixation was conducted subsequently for 40 min using sodium carbonate (20 g/dm3) at 60° C. The dyed fabrics were rinsed thoroughly by hot tap water and soaped in a soap solution (5 g/dm3) soap power, 5 min) at 90° C, then rinsed thoroughly under tap water and finally air-dried. The printing stock paste was obtained by the direct incorporation and homogeneous dispersion of ammonium hydroxide (0.1 wt%), diammonium phosphate (0.1 wt%) and binder additive (15 wt%) were mixed with distilled water (82.8 wt%). The synthetic thickener alcoprint PTP (2 wt%) was then introduced and the paste was stirred using a high shear mixer for 10 min to allow full viscosity to develop. The phosphor pigment SrAl2O4:Eu2+, Dy3+ (0.04, 0.08, 0.14, 0.20, and 0.30 wt%) was then added to the mixture with stirring using a high shear mixer for 15 min. If the viscosity of the printing pastes decreases, a slight amount of the thickener is added to maintain consistent viscosity values of the pastes at 21,000 cps at rate of shear of 2.180. All printing pastes were applied to 100% cotton fabrics using the flat printing screen. The final printed fabrics were left to dry at room temperature followed by thermal fixation at 160° C for 4 min in an automatic thermostatic oven (Werner Mathis Co., Switzerland). The printed fabric was then rinsed with hot tap water at 50 °C followed by tap water at ambient temperature and finally dried.

2.7. Reversibility and fatigue resistance The color change properties and the technical performance of the printed fabrics characterized by colorimetry. The optimally printed samples were irradiated with UV light for 4 min and then left in the dark for 5 min to fade back to their original unexposed states. This irradiation and fading cycle was repeated 21 times. Both fluorescence emission and excitation absorbance values were measured after each cycle, and then compared with the values recorded after the original UV exposure.

2.4. Characterization and measurements 2.8. Evaluation of antimicrobial activities Field emission scanning electron microscope (FE-SEM) on a Quanta FEG 250 (Czech Republic) was used to investigate the morphology analysis coped with Energy Dispersive Spectroscopy analysis (TEAM −EDX Model). Fluorescent optical microscope images were recorded on LEICA DM2500 microscope (EBQ 100-04). Steady-state fluorescence emission spectra and excitation measurements of the printed cotton substrates were evaluated by a JASCO spectrofluorometer FP-8300. The instrument provides corrected excitation spectra directly; the fluorescence emission spectra were corrected for the characteristics of the emission monochromator and for the detection photomultiplier response. The fluorescence emission spectra were recorded by excitation at absorption maxima, and the excitation spectra were recorded at fluorescence emission maxima. A UV lamp of λ = 365 nm at a power of 6 was employed as UV irradiation source. Fluorescent optical microscope images were recorded on LEICA DM2500 microscope (EBQ 100-

The antimicrobial activities of printed cotton samples were tested against Escherichia coli as gram-negative bacteria, Staphylococcus aureus as gram-positive bacteria and Candida albican as fungi. The antimicrobial test was performed quantitatively using the standard test method according to the AATCC test method 100–1999 for microbial counting (Emam et al., 2014). 2.9. Evaluation of UV protection UPF (Ultraviolet Protection Factor) was studied to verify the UV shielding protective performance for the printed cotton fabrics. In this study, the evaluation of the UPF of sun protection fibre products defined in AS/NZS 4399:1996 by using the UPF calculation system of a UV/Vis spectrophotometer (AATCC Test Method 183:2010-UVA 145

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S are reported in Table 2, where L* corresponds to the lightness, a* denotes the green-red characteristics, and b* denotes the blue-yellow features. The coloration measurements, screening results and photochromic effect before and after exposure to UV irradiation are shown in Table 2. All the obtained samples possess red hue similar to the original cotton fabric before printing. The color strength is expressed as K/S value and color data is evaluated by high reflectance technique. In both cases, before and after exposure to UV irradiation, a large decreased K/ S value is monitored to indicate a change to lower faded color strength. A negligible change is monitored in the K/S value upon increasing pigment phosphor concentration from 0.04 to 0.30 wt%. Furthermore, upon increasing the pigment concentration, all printed cotton fabrics do not display significantly different L*, a* and b* values compared to the blank red-colored unprinted cotton fabric. In absence of UV irradiation, no change is detected in the K/S value of the red-color cotton fabric before and after printing which proof the transparency of the printed film on cotton due to the very low concentration of pigment phosphor. These results reflect the best coloration measurements are obtained at 0.08 wt% pigment phosphor concentration in printed film matrix. Therefore, we discuss bellow the color fastness properties for the 0.08 wt% sample as shown in Table 3. The exposure to UV irradiation leads to a decrease in λmax value of the printed film from 525 nm to 510 nm. The color space values (L*, a* and b*) of the printed cotton fabric with different pigment phosphor concentrations are measured before and after exposure to UV irradiation. The original color of cotton fabric is red; with low L* value 26.85, comparatively high a* value 37.01 and low b* value 4.66. Whereas, L* is increased while a* and b* values are decreased after UV irradiation. The increased L* value indicates a whiter/pale hue. The decreased a* and b* positive values represents a change in the hue from red to greenish-yellow. After exposure to UV irradiation, the printed garment is instantly changed from red to greenish-yellow, within a fraction of second. All fabrics presented decreased a* and b* values, revealing a contribution from red and yellow components that are responsible for the development of different combinations of greenish-yellow intensities and/or degrees after UV irradiation. For the printed fabrics, a* > b*, meaning that, for these fabrics, the red component is more influential than the yellow component, resulting in the development of a greenish color; for the fabrics, a* < b*, indicating a higher contribution of the yellow component, which is responsible for the appearance of a yellowish color after irradiation.

Transmittance). 3. Results and discussion Organic photochromic materials usually face steric hindrance when encapsulated in films as a print or inside any matrix. Consequently, this inhibits the optical performance of the photochromic organic dye (Lee, Park, Kim, & Yi, 2008). On the other hand, the inorganic photochromic colorants do not face the same effects because their photophysical transformation is not accompanied by structural transformation as in the case of organic photochromic dyes, leading to better photochromic performance (Liu & Xu, 2003). The prolonged exposure of organic photochromic molecules to UV light can induce their degradation and gradual diminution of their photochromic response which result in low photostability, limiting their application in outdoor environments or under strong UV light (di Nunzio et al., 2008). It was previously reported that the oxide-based strontium aluminate pigment phosphor doped with divalent europium is highly photostable under UV radiation, presenting enhanced resistance to fatigue and fast reversibility between coloration and decoloration processes (Liu & Xu, 2003). Such inorganic phosphor pigments are presently used for various goods utilizing their long afterglow characteristics, for example, switches, lights, articles for use in darkroom, handrails, luminous indications such as wall indications, guidance signs, escape tools, other phosphorescent indications such as phosphorescent safety marks, ornamental articles, table cloths, and toys (Arkhipova et al., 2017; Ma, Yuan, Wang, & Zhou, 2009; Rojas-Hernandez et al., 2018; Van den Eeckhout, Smet, & Poelman, 2010). Due to employing the highly stable oxide-based strontium aluminate pigment phosphor as photochromic substrate, there will be no need for incorporating a quencher UV stabilizer in the printing layer, hydrophobic treatment of the porous surface, or covering the coating film layer with an additional silica layer; which are usually used to enhance the photostability and durability of organic pigment-based photochromic garments. Most of the above treatments usually reduce the washing and rubbing durability. The extra silica coating layer increases the fabric rigidity. Furthermore, both of amino and hydroxyl groups present in the chemical structure of UV stabilizers such as hindered amine light stabilizers leads to more hydrophilic nature of the printed layer (Christie et al., 2008; Feczkó et al., 2013; Iacono, Budy, Moody, Smith, & Smith Jr, 2008; Peng et al., 2015). 3.1. Characterization of treated fabrics

3.3. Evaluation of photochromic properties The morphological and elemental composition of the SrAl2O4: Eu2+ 3+ Dy on cotton fabrics was performed. The SEM images of the treated cotton surface via screen-printing, presented in Fig. 1a; display that, the treated surface coated with clusters of orthorhombic or/and hexagonal microstructures of strontium aluminate. The elemental composition was investigated by EDX diagrams which are the electronic support images (Fig. 1b). The composition in atomic% and weight% of two different locations on the fabric surface are summarized in Table 1. The elemental composition on printed cotton fabric is quite similar in both regions. This confirms that the distribution of SrAl2O4: Eu2+ Dy3+ on cotton fabric surface is uniform and recognized at a very low concentration. The elemental mapping of the photochromic printed fabric was also studied to verify the elemental distribution of the phosphor pigment on cotton surface (Fig. 2).

The strontium aluminate pigment phosphor is incorporated on the surface of cotton fabric by the screen-printing process (Fig. 3). The fabrics were dyed with red reactive dye to afford dark color background that enhances the visual greenish-yellow photochromic effect. The photochromic effect is more obvious to the naked-eye on dark garments as the produced light greenish-yellow color under UV irradiation is highly detectable by naked-eye on a dark surface. All the printed fabrics exhibit instant and reversible photochromic and fluorescent properties under UV light. However, only printed garment with low pigment concentration at 0.08 wt% can develop fast reversibility. On the other hand, printed garments with pigment concentration more than 0.20 wt% develop an afterglow effect leading to slow decoloration/reversibility. After irradiation of the fabric with UV light (λ = 365 nm) for 1 min at room temperature, the light source is turned off, and the fading absorbance measured at the wavelength of maximum absorption (λmax) is monitored as a function of time. The photochromic and fluorescence effects are confirmed by UV–vis excitation and fluorescence emission spectroscopy, through the appearance of a broad and strong absorption bands in the visible region as shown in Figs. 4 and 5, with λmax ≈ 272, 325 and 365 nm, whose absorption intensities quickly faded with time upon removal of the light source. In correspondence, three emission peaks appear at 418, 495 and

3.2. Colorimetric measurements The colorimetric measurements are a relatively simple and easy to use technique. Based on the change in the reflection spectrum, the K/S and CIE (L*, a*, b*) system are employed to measure the garment sensor abilities. The color-change properties and technical performances of the photochromic fabrics (photostability and fatigue resistance) are also evaluated using the CIE Lab color space. The values of L*, a*, b*, and K/ 146

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Fig. 1. SEM images (a) and EDX diagram (b) of the printed cotton fabric (pigment conc. 0.08 wt%).

Table 1 The composition in weight% and atomic% of two different regions for printed cotton fabric (pigment conc. 0.08 wt%). Samples

Region 1 Region 2

C

O

Al

Sr

Dy

Eu

Wt.%

At.%

Wt.%

At.%

Wt.%

At.%

Wt.%

At.%

Wt.%

At.%

Wt.%

At.%

59.15 58.84

67.21 66.89

38.27 38.51

32.13 32.36

0.81 1.03

0.41 0.52

1.41 1.24

0.22 0.19

0.19 0.21

0.02 0.02

0.17 0.17

0.01 0.02

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Fig. 2. Elemental mapping of the printed cotton fabric (pigment conc. 0.08 wt%). Table 2 Coloration measurements of printed cotton fabrics at different pigment concentrations. Pigment wt%

0.04 0.08 0.14 0.20 0.30

L*

a*

b*

λmax (nm)

k/s

Before

After

Before

After

Before

After

Before

After

Before

After

26.85 25.21 27.54 29.30 28.06

27.51 27.33 31.76 34.65 32.12

37.01 38.65 38.98 37.21 38.09

33.92 32.44 33.97 31.10 29.78

5.11 5.21 6.43 6.02 6.18

4.23 4.72 4.69 4.98 4.80

22.33 22.82 22.92 22.37 22.70

19.08 19.53 19.25 19.38 19.90

525 525 520 520 525

510 510 505 505 510

520 nm. The printed cotton fibres display greenish-yellow fluorescence indicated by florescence microscopic images under exposure to UV irradiation (Fig. 6). The UV–vis excitation spectra of printed fabric at 0.08 wt% are monitored upon increasing the exposure time (from 0 to 70 s) under UV irradiation. The stepwise increase of the exposure time under UV irradiation results in a gradual increase in the absorbance values together with consequent color change to yellow which is reversibly converted back into its original red color upon removal of the effect. The intensity of the fluorescence peak located at shorter wavelength (418 nm) decrease, while simultaneously on fluorescence peaks at longer wavelengths (495 and 520 nm) increase in intensity.

level of durability and photostability is satisfactory. A very good sublimation/thermal fastness is recorded, and there is no significant difference between hot pressing at 180 and 210 °C. The handle of the printed fabric is assessed based on their flexural rigidity (mg.cm) and bending modulus (kg/cm2). The results indicated a negligible increase in stiffness compared to original unprinted fabric. The high durability and photostability of the photochromic and fluorescent cotton fabric indicates the high strength of the organic-inorganic printed layer matrix.

3.4. Durability and photostability

Reversibility, photostability and fatigue resistant are measured by reporting the UV/Vis absorbance upon irradiation after running light, wash, rubbing, heat, perspiration fastness standard tests. For technological purposes, the materials should exhibit high fatigue resistance upon repeated and continuous coloration and decoloration cycles. Therefore, the fatigue resistance properties of the printed cotton fabrics are tested under alternating UV irradiation/darkening steps. The color change properties and the technical performance of the printed fabrics characterized by colorimetry. The sample of printed fabric are irradiated with UV light for 4 min and then left in the dark for 5 min to fade back to their original unexposed states. This irradiation and fading

3.5. Reversibility and fatigue resistance

The screen-printed cotton fabrics show softness to the touch and good handling. After washing, no differences are observed for the fabrics to which the pigment is applied. In absence of UV irradiation, in general, the depth of color shade and fastness properties of the printed fabric is very good to excellent as shown in Table 3. In the presence of UV irradiation, the durability of the printed photochromic and fluorescent fabric against washing, perspiration, light, sublimation and rubbing is assessed by monitoring the changes in absorption and fluorescence intensities after exposure to UV irradiation. The overall

Table 3 Fastness properties of the cotton fabric before and after printing of the pigment phosphor in absence/presence of UV irradiation. Pigment Phosphor sample with Conc. 0.08 wt %

Shade

Wash Alt.

a

Perspiration St.

a

Acidic Alt.

Before Printing After Printing After UV Irradiation

Red Red Greenish-Yellow

4–5 4 4

4–5 4 4

Rubbing

a

4–5 4 4

Basic a

Alt.

4–5 4 4

4–5 4 4

St.

a

St.

Sublimation

Dry

Wet

180 ˚C

210 ˚C

4–5 3–4 3–4

4–5 3 3

4–5 4 4

4–5 4 4

Light

a

4–5 4 4

6–7 6 6

The light fastness is evaluated using the blue scale (1 and 2-very poor, 3-poor, 4-fair, 5-good, 6 and 7-very good and 8-excellent). Printing paste: ammonium hydroxide (0.1 wt %), diammonium phosphate (0.1 wt%), binder additive (15 wt%), and synthetic thickener (82.8 g; 2 wt% dispersed in distilled water). a Alt. = alteration in color; St. = staining on cotton. 148

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Fig. 3. Photographs of the screen-printed cotton fabric (0.08 wt%) before and after UV (λ = 365 nm) Irradiation for 1 min at room temperature.

Fig. 4. UV–vis excitation absorption (4a) and fluorescence emission (4b) spectra of the 0.08 wt% cotton fabric (before and after printing) after being irradiated with UV light (λ = 365 nm) for 70 s. Fig. 5. UV–vis excitation absorption (5a) and fluorescence emission (5b) spectra of the 0.08 wt% printed cotton fabric after being irradiated with UV light (λ = 365 nm) for different time periods.

cycle is repeated 21 times. Both fluorescence emission and excitation absorbance values are measured after each cycle, and then compared with the values recorded after the original UV exposure. A fast and full reversibility of the color and fluorescence emission can be easily achieved. There is no photochemical fatigue nor is deterioration detected after numerous repetitive cycles of irradiations. The reversibility of the coloration-decoloration sensing effect towards light stimulus is

monitored by exposure to UV irradiation at room temperature and maintaining it for a fixed time (5.0 min). The UV–vis excitation and fluorescence emission spectra are recorded again after removal of the effect. The same procedure is repeated for 21 cycles. The changes in the 149

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Fig. 6. Fluorescence optical microscopy images of the printed cotton fabric before (6a) and after (6b) UV irradiation.

ratio of the absorbance at 365 nm; and emission peak at 520 nm of printed fabrics are recorded for each cycle. As is shown in Fig. 7, at least for this many cycles it is clear that this process exhibits high reversibility towards UV-irradiation sensing without fatigue. 3.6. Antimicrobial properties The antimicrobial activities of samples against gram-negative bacteria namely; Escherichia coli, gram-positive bacteria namely; Staphylococcus aureus, and fungi namely; Candida albican, were evaluated by using the plate agar count approach. The percentages of the antimicrobial reduction induced by printed cotton samples were summarized in Table 4. It was very clear that, samples with 0% of phosphor have no inhibition effect on the reduction% pathogenic microorganisms. On the other hand, the cotton fabrics coated by phosphor displayed antimicrobial resistance ranging from poor; well, very well to excellent antimicrobial resistance properties depending on the pigment concentration. 3.7. UV protection properties Ultraviolet protection factor (UPF) can directly evaluate the UVblocking activity of the cotton fabrics. The UPF of the cotton samples was measured and represented in Table 5. It was noted that, the UPF values of the pigment coated cotton fabrics were higher than that of the blank fabrics. The blank dyed cotton fabrics have high UPF, due to its color. The reasons for UV protection of pigment could be attributed to the mechanism of the high UV absorption property which is ascribed to 3+ the electronic structure of the pigment (Sr0.95Al2O4: Eu2+ 0.02, Dy0.03) making such pigment phosphor a suitable material for UV protection. 4. Conclusion A photochromic fluorescent film of phosphor pigment on textile fabric with a function of conversion from near UV light to visible light is Table 4 Antimicrobial properties of treated fabrics. Pigment wt%

Fig. 7. Changes in the ratio of the absorbance values at 525 and 510 nm (7a), and the emission value at 520 nm (7b); of printed fibres (pigment conc. 0.08 wt %) before and after UV irradiation (365 nm) at ambient temperature and atmospheric pressure for 21 cycles.

0 0.04 0.08 0.14 0.20 0.30

150

Anti-bacterial (Bacterial Reduction%) Escherichia coli (Gram −ve)

Staphylococcus aureus (Gram +ve)

Anti-fungal (Fungal Reduction %) Candida albican

0.00 32 ± 40 ± 56 ± 73 ± 86 ±

0.00 33 ± 44 ± 59 ± 75 ± 89 ±

0.00 0.00 0.00 0.00 10 ± 1.0 10 ± 1.0

1.4 1.2 1.1 1.2 1.3

1.1 1.6 1.1 1.0 1.3

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Table 5 UV protection of treated fabrics. Pigment wt%

UPF

0 0.04 0.08 0.14 0.20 0.30

588 1302 1518 1828 2866 2927

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achieved. Inorganic pigment phosphor is successfully incorporated on knitted cotton fabric by a screen-printing process to introduce both photochromic and fluorescent effects. This method is rapid, easy to handle, cost-effective, and reproducible, without compromising the garment’s aesthetic properties such as handling and comfort. The screen-printing paste is prepared by direct immobilization of oxidebased strontium aluminate pigment phosphor doped with divalent europium into aqueous binder. Typically, the fabric printed with strontium aluminate pigment showed better color fastness properties than those printed with organic pigments. The color changeable garments exhibit very good to excellent washing, perspiration, light, sublimation and rubbing fastness after exposure to UV irradiation. In absence of UV light, no changes in fastness properties are monitored for cotton fabric before and after printing of the pigment phosphor. The photo- and thermal stability, high reversibility and fatigue resistance of printed samples make them very promising smart garments for generic applications in specific areas such as brand protection, military camouflage, and security printing. Acknowledgements Technical support from Textile Industries Research Division, National Research Centre, Cairo, Egypt; is gratefully acknowledged. Appendix A. Supplementary data Supplementary data associated with this article can be found, in the online version, at https://doi.org/10.1016/j.carbpol.2018.04.084. References Arkhipova, A. N., Panchenko, P. A., Fedorov, Y. V., & Fedorova, O. A. (2017). Relationship between the photochromic and fluorescent properties of 4-styryl derivatives of N-butyl-1, 8-naphthalimide. Mendeleev Communications, 27(1), 53–55. Cheng, T., Lin, T., Brady, R., & Wang, X. (2008). Fast response photochromic textiles from hybrid silica surface coating. Fibers and Polymers, 9(3), 301–306. Choi, S., & Jiang, Z. (2006). A novel wearable sensor device with conductive fabric and PVDF film for monitoring cardiorespiratory signals. Sensors and Actuators A: Physical, 128(2), 317–326. Chowdhury, M., Joshi, M., & Butola, B. (2014). Photochromic and thermochromic colorants in textile applications. Journal of Engineered Fabrics & Fibers (JEFF), 9(1). Christie, R. M., Morgan, K. M., & Islam, M. S. (2008). Molecular design and synthesis of Narylsulfonated coumarin fluorescent dyes and their application to textiles. Dyes and Pigments, 76(3), 741–747. di Nunzio, M. R., Gentili, P. L., Romani, A., & Favaro, G. (2008). Photochromic, thermochromic, and fluorescent spirooxazines and naphthopyrans: A spectrokinetic and thermodynamic study. ChemPhysChem, 9(5), 768–775. Emam, H. E., Mowafi, S., Mashaly, H. M., & Rehan, M. (2014). Production of antibacterial colored viscose fibers using in situ prepared spherical Ag nanoparticles. Carbohydrate Polymers, 110, 148–155. Fan, F., & Wu, Y. (2017). Photochromic properties of color-matching, double-shelled microcapsules covalently bonded onto cotton fabric and applications to outdoor clothing. Journal of Applied Polymer Science, 134(15). Fan, F., Zhang, W., & Wang, C. (2015). Covalent bonding and photochromic properties of double-shell polyurethane-chitosan microcapsules crosslinked onto cotton fabric. Cellulose, 22(2), 1427–1438. Feczkó, T., Samu, K., Wenzel, K., Neral, B., & Voncina, B. (2013). Textiles screenóprinted with photochromic ethyl cellulose–spirooxazine composite nanoparticles. Coloration Technology, 129(1), 18–23. Garai, B., Mallick, A., & Banerjee, R. (2016). Photochromic metal–organic frameworks for inkless and erasable printing. Chemical Science, 7(3), 2195–2200. Gashti, M. P., & Eslami, S. (2015). A robust method for producing electromagnetic

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