ZrO2 nanocomposite inducing thermal barrier and self-cleaning properties on protein fibers

Accepted Manuscript Citric acid/ZrO2 nanocomposite inducing thermal barrier and self-cleaning properties on protein fibers Mazeyar Parvinzadeh Gashti, Arash Almasian PII: DOI: Reference:

S1359-8368(13)00185-6 http://dx.doi.org/10.1016/j.compositesb.2013.04.037 JCOMB 2365

To appear in:

Composites: Part B

Received Date: Revised Date: Accepted Date:

20 December 2012 12 March 2013 7 April 2013

Please cite this article as: Gashti, M.P., Almasian, A., Citric acid/ZrO2 nanocomposite inducing thermal barrier and self-cleaning properties on protein fibers, Composites: Part B (2013), doi: http://dx.doi.org/10.1016/j.compositesb. 2013.04.037

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Citric acid/ZrO2 nanocomposite inducing thermal barrier and self-cleaning properties on protein fibers Mazeyar Parvinzadeh Gashti1*, Arash Almasian2

1- Department of Textile, Islamic Azad University, Shahre rey Branch, Tehran, Iran 2- Department of Environmental Research, Institute for Color Science and Technology, Tehran, Iran

*Email: [email protected] Tel: +98-9123137115 Fax: +98-21-22593135

Abstract: The present research carried out to stabilize nano-ZrO2 on the wool fabric using citric acid (CA) as a crosslinking agent and sodium hypophosphite (SHP) as a catalyst under UV irradiation. The influence of the amount of nano-ZrO2 on the performance of wool fiber was investigated by the use of Fourier transform infrared spectroscopy (FTIR), thermo-gravimetric analysis (TGA), scanning electron microscopy (SEM), energy dispersive X-ray spectroscope (EDX) and reflectance spectrophotometer (RS). The possible interactions between nano-ZrO2 particles, cross-linking agent and wool free radicals were elucidated by the FTIR spectroscopy. Results indicated that the stabilized nano-ZrO2 enhances the thermal stability of wool. Photo-catalytic activities of the coated wool were evaluated through degradation of methylene blue (MB) under UV irradiation.

Keywords: A. Fabrics/textiles; B. Thermal properties; D. Chemical analysis

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1. Introduction: Inorganic oxides are well-known ceramic materials with diverse applications in nano-composites, building materials, cements, potteries, papers, textile coatings, pharmaceuticals, adsorbents, ion exchangers, separators, paints, plastics, pesticides, cosmetics and catalysts due to their great abundance, low cost and particular properties [1-6]. Aluminium oxide, silicone dioxide, zinc oxide, chromium (III) oxide, cadmium oxide, iron(III) oxide, copper(I) oxide, manganese dioxide, calcium oxide and titanium dioxide are used for these purpose. One of the most commercially available inorganic oxides is zirconium dioxide sometimes known as zirconia with three structural isomorphs [7-13]. It is prepared through base precipitation of zirconium hydroxide, followed by thermal calcination. Its monoclinic phase is stable below 1000°C, however the intermediate tetragonal and cubic phases are stable above 1200°C and 2285±15°C, respectively [14-16]. Zirconia is widely used in various products including thermal shields, jet and diesel engines, insulators, abrasives, enamels, ceramic glazes, oxygen sensors, fuel cell membranes, adsorbents, electroceramics and dental restorations due to its hardness, shock wear, strong acid and alkali resistances, low frictional resistance and high melting temperature [17-19]. Nowadays, application of inorganic nano-particles on textiles would be a good alternative to conventional materials and consequently, they can open up a new opportunity for multi-functional modification of fibers. For this purpose, a great number of researches have been carried out for coating of nano-particles on textiles using different methods including, impregnation in colloidal dispersion of nano-oxides [20]; grafting of particles [21,22]; UV irradiation to enhance coating [23,24] and functionalisation by sol–gel coatings [25-28]. Some researchers studied the photocatalytic activity of TiO2 coated wool through self-cleaning of different stains [29-34]. We have recently fabricated a hydrophobic textile via dip-coating with a silica-polycarboxylic acid dispersion without any side-effect on the color and morphology of fibers [35]. Antibacterial, mothproofing, antibiotic, and antistatic properties were easily achieved on wool by the conventional pad-dry-cure method using the nano-sized silver colloid [36,37]. 2

Another field of study which has recently been of special interest is the application of cross-linking agents for stabilization of nano-particles on the wool fiber due to the fact that there is no attraction between them. Non-formaldehyde-emitting cross-linking agents containing carboxylic acids such as 1,2,3,4- butanetetracarboxylic acid, CA, succinic acid, maleic acid, glyoxal and glutaraldehyde are used for this purpose. These materials can form different linkages with the peptide chains of wool using a phosphorus catalyst in the structure of cross-linking agent [38-45]. Previous researches have been focused on the sol-gel method, layer-by-layer fabrication technique and cross-linking agent for stabilization of silica, silver and titanium dioxide on the wool surface. However, as far as we know, none of the recent research studies has focused on photo-catalytic properties of nano-ZrO2 on wool using a cross-linking agent. Attempts were made in the present study to investigate thermal and self cleaning properties of CA/ZrO2 nanocomposite coated wool fibers.

2. Experimental 2.1. Materials Standard knitted wool fabric from SDC enterprises limited was used. Nonionic detergent was provided by SDL Technologies for scouring of the wool fabric. Monoclinic nano-ZrO2 powder was supplied by the German, PlasmaChem GmbH with an average particle size of 15 nm and specific surface area of 130±20 m2/g. CA, SHP, cetyltrimethyl ammonium bromide (CTAB) and MB were supplied by Merck Chemical Co., Germany.

2.2. Methods Wool fabrics were scoured with a 0.5% nonionic detergent. The L:G (liquor to good ratio) of the scouring bath was kept at 40 : 1 for 30 min at 50°C. Stabilization of the particles on wool was performed by a four step method. First, different colloidal dispersions were prepared by mixing 1, 3, 6 and 9% (o.w.f) nano-ZrO2, CTAB and deionized water (The ratio of nano-ZrO2 : CTAB was 3

kept at 2 : 1). The colloidal dispersions were then treated with an ultrasonic machine at 50°C for 2 h to reduce the particle sizes. Second, a 8% (o.w.f) CA with SHP (5% o.w.f) were added to the dispersions of nano-ZrO2 under ultrasound vibration at 40°C for 20 min. Third, the wool fabrics were padded (85% wet pick up) in prepared solutions. The treated fibers were dried at 60°C for 10 min and cross-linking of the fabrics was conducted by UV irradiation (Germicidal UV lamp from Keosan Enterprise Co. Ltd: 15W/0.3A, UV-C, λmax=250 nm) at ambient temperature for 30 min. The irradiated fibers were then rinsed with a large amount of deionized water to remove residual nano-ZrO2, CA and SHP for three times. The fabrics were dried completely at 40°C in an oven.

2.3. Analytical methods: 2.3.1. Fourier-transform infrared spectroscopy (FTIR): The chemical compositions of the fabrics were examined by the FTIR spectroscopy [Bomem-MB 100 Series (Hartmann and Broun)rsqb].

2.3.2. Thermo-gravimetric analysis: The thermal degradation analysis (TGA) of the samples was performed on a TGA-PL thermoanalyzer from UK. In each case, a 5 mg sample was examined under a N2 at a heating rate of 5°C/min from room temperature to 600°C.

2.3.3. Microscopic characterization: The surface of fibers was investigated using a Scanning Electron Microscope (SEM XL30, Philips). Samples were first coated with a thin layer of gold (w10 nm) by Physical Vapor Deposition method (PVD) using a sputter coater (SCDOOS, BAL-TEC). The presence of zirconia on the fiber surface was also determined by energy dispersive X-ray microanalysis (EDX) attached to the SEM.

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3.3.4. Self cleaning properties of coated wool: A 5 μl of 5% MB was introduced onto the wool sample and it was irradiated under a UV lamp at ambient temperature for 40 h and 80 h. The distance between the sample and the lamp was 40 cm. The self-cleaning properties of the fabric were determined using a Gretagmacbeth COLOREYE 7000A spectrophotometer integrated with an IBM-PC. CIELAB color coordinates (L*, a*, b*, C*, h°) and color differences (ΔE) of the samples were calculated for 10° observer and D65 illuminant according to equation 1. Reflectance curves (R∞(λ)) were also converted to the corresponding Kubelka-Munk ratio (K/S)λ of the one constant theory using equation 2.

ΔE=[(Δa*)2+(Δb*)2+(ΔL*)2]1/2 (1) (K/S)λ = (1- R∞(λ))2/ 2R∞(λ)

(2)

3. Results and discussion: 3.1. Structural information by FTIR spectra: It has been previously described by some researchers that ZrO2 can be used as a photo-catalyst for decomposition of CO2 and various organic compounds. The surface of ZrO2 is struck by UV light (hv) resulting to excitation of valence band (vb) electrons and jumping to the conduction band (cb). Highly reactive electron (e-) and hole pairs (h+) are produced after this step and the negative charge is increased in the conduction band (e-cb). Furthermore, the reactive electrons interact with

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dissolved O2 molecules to form super oxide radical anions resulting to formation of HO2 radicals.

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Moreover, the positive holes react with water molecules to form OH radicals. Figure 1 shows the mechanism for photo-reduction phenomenon of nano-ZrO2 under UV irradiation [46-48]. On the other hand, UV irradiation of wool causes scission of the main functional groups including carboxyl and hydroxyl bonds as well as cystine linkages which may result in formation of alkyl, alkoxy and alkyl peroxy radicals. This photo-chemical deterioration results in both yellowing and 5

changes in mechanical properties of fiber [49-53]. Figure 2 illustrates various free radicals formed in wool by UV light. The infrared spectra of the untreated and CA cross-linked wool as well as the sample coated with CA/9% ZrO2 nanocomposite are shown in Figure 3. The N-H stretching and bending vibrations in wool usually appears at 3100-3500 cm-1 and 1550-1640 cm-1 respectively, depending on the type of amide (primary and secondary), chemical environment (solid and liquid) and intra- or intermolecular hydrogen bonds. The C=O stretching vibration band appears in the normal region between 1630 and 1670 cm-1 which usually overlaps with N-H bending [54-56]. Figure 3a assigned N-H stretching of a secondary amide at 3251 cm-1 as expected for wool. The bands at 1634 cm-1 are also characteristic of N-H stretching vibration which overlaps with C=O vibration. The weak C-H stretching, CH2 out of plane bending, C-O-C asymmetric stretching and S-O-S (cystine monoxide) vibrations in wool appear at 2919, 835, 1232 and 1072 cm-1, respectively. Other weak bands appear at 3759 and 3682 cm-1 are attributable to O-H stretching vibrations in free primary and secondary alcohols [56]. Figure 3b showed that after UV irradiation of CA treated wool, the intensity of the bands at 3850, 3673 and 1634 cm-1 increased and new band appeared at 3206 cm-1. These changes are due to interaction between CA radicals and the free radicals of wool forming esteric and etheric linkages. Other changes are appearance of a band at 2347 cm-1 and increment of the intensity of the bands at 1235 and 2920 cm-1 in the cross-linked wool due to amidification reaction [57].

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Researchers showed that OH radicals generated from the photo-reduction of nano-ZrO2 are able to degrade CA. They stated that oligocarboxylic acids such as CA may form carboxylic acid terminated surfaces on ZrO2 and TiO2, and the proposed main route is a hole attack (Figure 4) [58]. This result is also supported by other authors for the photo-reduced succinic acid in the presence of nano-TiO2 under UV irradiation [59,60]. As it can be seen in Figure 3c, after embedding of wool with CA/nano-ZrO2 nanocomposite, the bands at 3566 and 3376 cm-1 appeared in comparison with

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the cross-linked wool. This could be due to generation of H2O as a product of cross-linking between CA and wool free radicals. Increment in the intensity of a band at 1634 cm-1 and shifting of a band at 1079 to 1056 cm-1 can be expressed as the photo-reduction of CA and generation of the aldehydes in the presence of nano-ZrO2. Two mechanisms can be explained by FTIR results for cross-linking of wool with CA in the presence of nano-ZrO2: Firstly, the free radicals obtained on CA can directly bind to wool free radicals producing etheric and esteric cross-linkages. Secondly, CA molecules containing aldehyde groups are formed by UV irradiation which may react with amine, carboxyl and hydroxyl groups of wool using a phosphorous catalyst by dehydration (Figure 5a,b) [61-63]. Increase in the intensity of bands at 746 and 668 cm-1 is also attributed to the successful stabilization of nano-ZrO2 particles on the wool surface. As we used acidic pH for impregnation bath, formation of Zr4+ cations is expected. Free carboxylate anions of the crosslinked CA have high affinity towards the positive charges of zirconia leading to the electrostatic interaction as it is illustrated in Figure 5a. This tendency is also further supported by other authors [38,40,42,43,64-66].

3.2. Determination of thermal properties: Figure 6 illustrates the thermal degradation of the untreated wool and those cross-linked with CA/nano-ZrO2 nanocomposites under UV light. As it can be seen, the TGA curves of wool consist of three regions of initial, main, and char decomposition. In the first stage, the changes of the thermal properties and the weight loss of fibers are due to some physical damages occur mostly in the amorphous regions of the polypeptide chains. The main thermal stage occurs in the second region, where the weight loss is significant [67]. It was demonstrated that the thermal degradation in this region takes place in the α-helice crystallites of wool. Moreover, the onset temperature at which the thermal degradation of keratin and other histological components in wool begins, is about 230-250°C [68]. Production of char occurs at the third region at higher temperatures of 400°C. This process continues by releasing water and carbon dioxide molecules and increasing the carbon and charred residues [69]. The sample cross-linked with CA/3% ZrO2 nanocomposite 7

showed higher degradation temperatures in comparison with the untreated wool. Increase in nanoZrO2 concentration caused a greater increase in the thermal resistance. The weight of the residue at 600°C (Wt600ºR) increased for the coated samples compared with the untreated wool, ranging from 6 to 25%. This improvement of the thermal properties is ascribed to the high heat resistance, the heat insulation effect and the mass transport rate exerted by the nano-ZrO2 particles themselves which is one measure of the flame retardancy. On the other hand, the interaction between wool, nano-ZrO2 and CA was fairly strong which effectively restricted the motions of the molecular segments in wool. This result is incidentally consistent with our result obtained from the FTIR spectra [61-63,70,71].

3.3. Microscopic characterization The SEM images of the untreated wool and the samples cross-linked with CA/ZrO2 nanocomposites are shown in Figure 7a-f. It can be observed that the untreated fiber has overlapping scales with no deposition of the cross-linking agent and nano-particles. It was observed from Figure 7b showed that CA covered the surface of wool compared with the untreated sample. The high magnification SEM images of the wool fibers cross-linked with CA/1% ZrO2 nanocomposite show formation of few aggregated nano-ZrO2 on the wool surface. It is evident that increment in nano-ZrO2 content in nanocomposite coating increased the aggregated particles on the fiber surface [67,68]. Figure 8a-f show the presence of chemical elements on the surface of fibers as investigated by the EDX analysis. In these patterns, Au peaks clearly show a successful sputter coating on the fiber surface. The EDX analysis of the cross-linked wool illustrates more efficient interactions between the wool surface and nano-ZrO2 leading to the presence of Zr. Several factors affect on the ability of nano-particles to aggregate on the textile surfaces of including size, mobility, end-group functionality, relative composition and molecular architecture. It was mentioned previously from the FTIR spectra of samples that cross-linking reactions between 8

wool and CA free radicals are performed. It seems that these interactions are strong enough to enable deposition of nano-ZrO2 particles on the wool surface as a result of their high surface area. We have confirmed this phenomenon in cases where the nano-particles were incorporated into the inorganic-organic hybrid coatings [20-24].

3.4. Self cleaning properties of wool samples: Table 1 and Figure 9 present the color co-ordinates and the (K/S)λ curves for MB stained wool textiles after UV irradiation. The images of samples before and after UV irradiation are also shown in Figure 10. The color values were evaluated in the CIELAB color space, the three axes being L*, a*, and b*. The L* is the color coordinate which represents the lightness of samples and can be measured independently of color hue. Any decrease in the lightness of samples could be concluded as the lower reflectance of textiles. The a* stands for the horizontal red–green color axis. The b* represents the vertical yellow–blue axis. The C* represents the brightness or dullness of the samples. Any increase in the C* of samples could be concluded as greater brightness of the nanocomposite. The hue angle (h°) stands for hue, which is the actual color recognized by the human eye and identified as orange, yellow, beige, brown, pink, or any of the other colors visible to humans. It is expressed in degrees, with 0° being a location on the +a* axis, continuing to 90° for the +b* axis, 180° for -a*, 270° for -b*, and back to 360° = 0°. Differences in color coordinate of samples before and after UV irradiation are defined by ΔE [70]. As it can be seen in Table 1, the wool samples cross-linked with CA/9% ZrO2 nanocomposite showed higher L* values, lower redness and lower brightness after UV irradiation for 40 and 80 h. Results obtained from Figure 9 indicated that the K/S values for the UV irradiated samples were lower in comparison with that of unexposed to UV lamp. This can be due to decomposition of MB stains and photo-catalytic activity of nano-ZrO2 particles embedded in coating. The migrated

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electrons and holes of zirconia may produce OH radicals which are able to degrade MB stains [33,71,72]. Figure 11 shows the mechanism for photo-catalysis of MB by ZrO2 under UV irradiation. At the initial step, the functional groups of C_S+=C is degraded to sulfoxide groups which subsequently

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may undergo a second attack by OH radicals. This may produce sulfone molecules, causing the

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definitive dissociation of two benzenic rings. Degraded products can be attacked by a third OH radical for giving a sulfonic acid which finally releases the SO42− ions [73].

Conclusion: Nano-ZrO2 and CA were used for generation of self-cleanable wool. The nanocomposite was stabilized by a reaction of CA and wool free radicals. This process resulted in electrostatic interaction of Zr4+ cations to the carboxylate anions of CA. The FTIR spectra showed that CA contains carboxyl groups, which seems to increase the interfacial interactions and bonding with the amine or hydroxyl end groups of wool by generation of ester and ether linkages. Results obtained from TGA demonstrated an enhancement of thermal properties of coated samples. This can be as a result of the high heat resistance, heat insulation effect and the mass transport barrier of nano-ZrO2 particles embedded in coating. Moreover, the nano-ZrO2 cross-linked wool promotes the photo. degradation process of MB due to production of OH radicals after UV irradiation.

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Figure 1: Photo-reduction phenomenon of nano-ZrO2 under UV irradiation [46-48].

Figure 2: Free radicals produced in wool by UV irradiation [49-53].

Figure 3: FTIR spectra of the untreated and CA cross-linked wool as well as the sample coated with CA/9% ZrO2 nanocomposite.

Figure 4: The possible photo-reduced CA products in the presence of nano-ZrO2 [58]

Figure 5: The possible cross-linking reactions catalyzed with nano-ZrO2 under UV irradiation [6163]. Figure 6: Thermal degradation curves of (A) untreated wool, (B) CA cross-linked wool, (C) wool cross-linked with CA/3% ZrO2 nanocomposite under UV light, (D) wool cross-linked with CA/6% ZrO2 nanocomposite under UV light, (E) wool cross-linked with CA/9% ZrO2 nanocomposite under UV light.

Figure 7: SEM images (a) untreated wool fiber at 2μm, (b) wool fiber cross-linked with CA under UV light at 2μm, (c) wool fiber cross-linked with CA/1% ZrO2 nanocomposite under UV light at 2μm, (d) wool fiber cross-linked with CA/3% ZrO2 nanocomposite under UV light at 2μm, (e) wool fiber cross-linked with CA/6% ZrO2 nanocomposite under UV light at 2μm, (f) wool fiber cross-linked with CA/9% ZrO2 nanocomposite under UV light at 2μm.

Figure 8: Energy dispersive X-ray analysis of (a) untreated wool fiber, (b) wool fiber cross-linked with CA under UV light, (c) wool fiber cross-linked with CA/1% ZrO2 nanocomposite under UV light, (d) wool fiber cross-linked with CA/3% ZrO2 nanocomposite under UV light, (e) wool fiber

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cross-linked with CA/6% ZrO2 nanocomposite under UV light, (f) wool fiber cross-linked with CA/9% ZrO2 nanocomposite under UV light.

Figure 9: (K/S)λ curves of MB stained wool samples cross-linked with CA/9% ZrO2 nanocomposite before UV irradiation, and after UV irradiation for 40 and 80 h.

Figure 10: Wool textiles stained with MB, (a) Sample cross-linked with CA/9% ZrO2 nanocomposite before UV irradiation, (b) Sample cross-linked with CA/9% ZrO2 nanocomposite after UV irradiation for 40h, (d) Sample cross-linked with CA/9% nanocomposite after UV irradiation for 80h. Figure 11: Mechanism of the possible routes for the photo-catalytic degradation of MB by ZrO2 under UV [73].

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Figure1

Figure 1

Figure2

Figure 2

Figure3

Figure 3

Figure4

Figure 4

Figure5

Figure 5

Figure6

Figure 6

Figure7

a

b

c

d

e

f

Figure 7

Figure8

Figure 8

Figure9

Figure 9

Figure10

Figure 10

Figure11

Figure 11

Table 1: The color co-ordinates for MB stained wool samples cross-linked with CA/9% ZrO2 nanocomposite after UV irradiation for 40 and 80 h Methylene blue stained Sample

L*

a*

b*

C*

h˚

ΔE

Before UV irradiation

37.14

-10.05

-27.30

29.09

249.79

-

After UV irradiation for 40 h

51.47

-6.78

-1.23

6.89

190.25

29.93

After UV irradiation for 80 h

56.56

-4.78

4.83

6.80

134.68

37.92

17