Conducting Leathers for Smart Product Applications - Industrial

In other words, the treated leathers absorb the entire visible spectrum of wavelength. Hence, the color of the treated leathers is black, as also can ...
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Conducting Leathers for Smart Product Applications Jima Demisie Wegene† and Palanisamy Thanikaivelan*,‡ †

Leather Garment & Goods Manufacturing Technology Directorate, Leather Industry Development Institute, P.O. Box 24692 Code 1000, Addis Ababa, Ethiopia ‡ Centre for Leather Apparel & Accessories Development, Central Leather Research Institute (Council of Scientific and Industrial Research), Adyar, Chennai 600 020, India S Supporting Information *

ABSTRACT: Leather is a unique consumer material possessing a variety of properties such as strength, viscoelasticity, flexibility, and longevity. However, the use of leather for smart product applications is a challenge since it is an electrically insulating material. Here, we report a simple method to produce conducting leathers using an in situ polymerization of pyrrole. The concentrations of pyrrole, ferric chloride, and anthraquinone sulfonic acid and the number of polymerization were optimized to produce maximum conductivity in the treated leathers. The coating of polypyrrole in the treated leathers was probed using Fourier transform infrared spectroscopy, X-ray diffraction, and electron microscopic analysis. We also show that the treated leathers are black through reflectance measurements, thereby suggesting that the use of toxic and expensive dyes can be avoided for coloration process. We further demonstrate that the treated leathers, with a maximum conductivity of 7.4 S/cm, can be used for making conductive gloves for operating touch-screen devices apart from other smart product applications.

1. INTRODUCTION Leather, made up of collagen fiber bundles, is a unique material used in a variety of applications due to its durable and flexible properties.1 Some important applications of leather are production of leather garments, goods, footwear, upholstery, gloves, sport goods, etc. However, currently leather does not find any smart or advanced applications such as flexible or wearable electronics, or wearable biomonitoring garment, etc. This is because leather is an insulator and does not conduct electricity.2 Materials need to have electrical conductivity properties for smart or advanced product applications. Smart products are specializations of hybrid products with physical realizations of product categories and digital product descriptions that provide characteristics such as situated, personalized, etc. Conductive polymers are extensively used for a variety of applications including smart products. Polypyrrole is one among them and known to possess high conductivity, easy synthesis, good environmental stability, and less toxicity.3,4 However, the infusible and insoluble nature of polypyrrole owing to its strong interchain bonding causes severe limitations on its processing. One way to avoid this difficulty is to prepare a conductive composite by depositing the conductive polymer on the substrate through in situ chemical polymerization techniques.3−5 In-situ chemical polymerization is relatively simple, easy to control, does not require the destruction of the substrate and provides reasonably good conductivity.6−8 Conductive leathers can be used for producing leather gloves for operating touch-screen devices such as smart phone, tablet, iPod, etc.9 A conductive leather glove gives precise control over touch-screen devices without having to remove the gloves in heavy winter season. Therefore, conductive leather is highly demanded in cold season to operate touch-screen devices comfortably. Conductive leather can also find application in manufacturing smart garments. The commercial techniques © 2014 American Chemical Society

involve application of conductive agents such as carbon black, carbon nanotubes, graphite, silver, copper, gold, etc. on the surface of the leather during finishing9 or embroidering a conductive thread on the fingers and thumbs or knitting a conductive complex on the whole glove so that electrical impulses are passed to touchscreens. However, aforementioned techniques do not provide uniform electrical conductivity all over the surface and three-dimensional fibrous network across the cross section. Further, all the techniques reported for introducing electrical conductivity in leather require a separate coloration or dyeing process. Here, we report a simple method to prepare conducting and colored leathers for smart or advanced product applications. Sheep nappa white crust leathers were chosen as the substrate and coated with polypyrrole through in situ polymerization of pyrrole such that both conductivity and color is obtained. Achieving both functions (conductivity and color) in a single chemical treatment avoids expensive and toxic dyes. Polymerization conditions were optimized to obtain maximum conductivity in leather. The surface morphology of the treated leathers was also studied.

2. EXPERIMENTAL SECTION 2.1. Materials. Pyrrole (purity >98%) was purchased from Sigma-Aldrich and used without further purification. Ferric chloride was procured from Himedia Laboratories Pvt. Ltd., India, and used as oxidant. The dopant, anthraquinone-2sulfonic acid sodium salt monohydrate (AQSA, 97% purity), was purchased from Sigma-Aldrich and used as received. Sheep Received: Revised: Accepted: Published: 18209

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nappa white crust leathers of Indian origin with fairly uniform size of 4 ± 0.5 sq.ft. and thickness of 0.9 ± 0.1 mm were procured from a tannery in Chennai. 2.2. Optimization of Reaction Parameters. Polymerization of pyrrole on leather substrate was carried out using ferric chloride as oxidant and AQSA as dopant.10 Pyrrole was dissolved in AQSA solution with vigorous stirring for 30 min. Then leather (8 × 8 cm2) was soaked in pyrrole/AQSA solution for 1 h through continuous stirring. Oxidant solution was added to the above mixture to initiate polymerization. Concentrations of monomer, dopant, and oxidant, and number of polymerization were varied in order to find the optimum treatment conditions that can provide maximum conductivity. Experiments were performed by varying pyrrole concentration (0.05, 0.10, 0.15, 0.20, 0.30, and 0.40 M), ferric chloride concentration (0.15, 0.2, 0.25, 0.30, 0.35, 0.40, and 0.45 M), and AQSA concentration (1, 5, 10, 30, 60, and 100 wt % where % was based on weight of pyrrole). While varying one parameter, the remaining two were held at constant level. The constant levels of pyrrole, ferric chloride, and AQSA concentrations were 0.15 M, 0.30 M, and 10 wt % (% based on weight of pyrrole), respectively. The molar concentration of pyrrole and ferric chloride was calculated separately before mixing the solutions together. The amount of water used for dissolving pyrrole and ferric chloride was retained equally throughout the experiments. Polymerization was carried out for 2 h in a bath at 5 ± 2 °C. Finally PPy-coated leather was washed four times with distilled water and dried at room temperature prior to measurement of resistance. To study the effect of number of polymerization on conductivity of leather, the concentrations of ferric chloride and AQSA were fixed at 0.30 M and 10 wt % (% based on weight of pyrrole), respectively, and pyrrole concentration was varied from 0.1 to 0.3 M. While these concentrations were employed for single in situ polymerization in one bath, half of the concentrations of reactants were employed in each of the two baths for double in situ polymerization. In double in situ polymerization, leather was first treated in the first bath containing half of concentrations of reactants and polymerization was carried out for 2 h in a bath at 5 ± 2 °C. Treated leather was washed four times with distilled water and dried at 35 °C. Then this leather was further treated in a second bath containing the remaining half of the concentrations of reactants following a similar procedure. Finally, treated leathers were washed four times with distilled water and dried at 35 °C. All the dried leathers were analyzed for resistance. 2.3. Characterization. The electrical conductivity of PPycoated leathers was calculated by measuring resistance using a two-probe method as given in eqs 1 and 2. Surface resistivity of the square specimen was obtained by measuring resistance (R) between two ends of the specimen and applying the following equation.

R s = RW /L

In all the experiments, the electrical resistance values were measured three times on the grain side of the treated leather and an average resistance of the sample was calculated. 2.4. Bulk Production. For the bulk experiments, two halves of sheep nappa white crust leathers (2 sq ft each) were taken and treated with reaction parameters that yield higher conductivity through single and double in situ polymerization. For single in situ polymerization, the leather was treated in 0.3 M of pyrrole and AQSA (10 wt % based on weight of pyrrole) solution for 1 h in a drum at 10 rpm. Ferric chloride solution (0.80 M) was added to the drum to initiate the polymerization. Polymerization was carried out for 2 h in the drum at 5 °C. Finally, single in situ PPy-coated leather was washed four times with distilled water and dried at 35 °C prior to measurement of resistance as described above. For double in situ polymerization, leather was first treated in 0.15 M of pyrrole and AQSA (10 wt % based on weight of pyrrole) solution for 1 h in a drum at 10 rpm. Ferric chloride solution (0.40 M) was added to the drum to initiate the polymerization. Polymerization was carried out for 2 h in the drum at 5 °C. PPy-coated leather was washed four times with distilled water and dried at 35 °C. This leather is again treated following the same procedure as mentioned to obtain double in situ PPy-coated leather. Treated and untreated leathers were further characterized using Fourier transfrom infrared (FTIR) spectroscopic measurements using a PerkinElmer FTIR spectrometer (USA) in KBr medium in the region of 4000−500 cm−1. The X-ray diffraction (XRD) patterns of the samples were obtained using a Rigaku miniflexII, desktop X-ray diffractometer with Cu Kα (λ = 1.5418 Å) radiation operating at 30 kV and 15 mA. Scanning was carried out in the 2θ range from 5 to 80° at a scan speed of 2° per minute. The surface morphology of treated and untreated leathers was examined using a scanning electron microscope (Vega3 SB, Tescan, Czech Republic). Rubbing fastness (dry and wet) of the samples was carried out according to ISO 11640:1993 test method.11 Samples from treated leathers were obtained according to ISO 2418:2002 procedure12 and conditioned at 19.2 °C and relative humidity of 69.7% as per the ISO 2419:2012 method.13 Reflectance measurements for the control and treated leathers were measured using a Milton Roy Color Mate HDS instrument. The color parameters namely, L, a, b, h, and C, which represent lightness, red and green axis, yellow and blue axis, hue, and chromaticity, respectively, were also recorded. The total color difference (ΔE) and hue difference (ΔH) were calculated using equations below:14 ΔE =

ΔL2 + Δa 2 + Δb2

(3)

ΔH =

ΔE2 − ΔL2 − ΔC 2

(4)

where ΔL = lightness difference; Δa and Δb = difference in a and b values; ΔH = hue difference; and ΔC = chromaticity difference. ΔL, Δa, Δb, and ΔC were calculated by subtracting the corresponding values for treated leathers from that of control leathers.

(1)

where Rs is surface resistivity, R is resistance of the sample, W is width of the sample, and L is length between electrodes.

3. RESULTS AND DISCUSSION 3.1. Electrical Conductivity Characteristics. The electrical conductivity of treated leather is a function of extent of PPy deposition on leather substrate. In-situ polymerization of PPy on leather substrate comprises two processes: deposition onto a leather substrate and polymerization in a reaction bath.

conductivity (S/cm) = 1/(surface resistivity × thickness of leather in cm) (2) 18210

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Figure 1. Effect of different polymerization parameters on the conductivity of leather. (a) Effect of monomer concentration on conductivity of leather (FeCl3 0.30 M, AQSA 10 wt % of pyrrole, polymerization time 2 h, temperature 5 ± 2 °C and single in situ polymerization). Digital images of leathers with increasing concentration of pyrrole is also shown to demonstrate the changes in color; (b) Effect of oxidant concentration on the conductivity of leather (pyrrole 0.15 M, AQSA 10 wt % of pyrrole, polymerization time 2 h, temperature 5 ± 2 °C and single in situ polymerization); (c) Effect of dopant concentration on the conductivity of leather (pyyrole 0.15 M, FeCl3 0.30 M, polymerization time 2 h, temperature 5 ± 2 °C and single in situ polymerization).

may be attributed to the formation of a more ordered structure at lower temperature. 3.2. Effect of Monomer Concentration. The effect of change in concentration of pyrrole on the conductivity of leather/PPy composite is shown in Figure 1a. In general, leather is an insulator having a surface resistance above 200 MΩ. In Figure 1a, as the monomer concentration increases, conductivity of leather increases linearly up to 0.3 M pyrrole. A further increase in the concentration of monomer beyond 0.3 M did not yield a significant increase in the conductivity of leather. It could occur because the excess monomer in the reaction bath can form a homopolymer in the solution but not on leather. The conductivity of the coated leather greatly depends on the thickness of the coating layer and chemical nature of the leather. At lower monomer concentration (10 wt %) resulted in a significant decrease in the conductivity of leather. This may be due to the high competition of AQSA with chloride anion during the polymerization reaction and increase in the intermolecular chain separation owing to higher concentration of AQSA thereby resulting in reduced interchain hopping of charge carriers. Similar observations have been reported on the effect of dopant concentration on electrical conductivity.20 Therefore, the optimum AQSA concentration required to get maximum conductivity in leather is determined as 10 wt %, which is economically advantageous than the quantity reported earlier for various other systems.20,21 3.5. Effect of Number of Polymerization. The effect of number of polymerization on the conductivity of leather is shown in Figure 2. It is evident that the conductivity of leather is much higher for double in situ polymerization when compared to single step polymerization. It is seen that the effect of number of polymerization on conductivity of leather is insignificant at lower monomer concentration (≤0.15 M) and more substantial as monomer concentration increases. This is because the formation of homopolymer in the solution is reduced and uniform coating is obtained for double in situ polymerization. This may be due to more absorption of monomer into leather substrate in two steps of the double in situ polymerization since drying after first step helps to achieve enhanced absorption. 3.6. Surface Morphology. Scanning electron microscopic images showing the surface of untreated and treated leathers are shown in Figure 3. Insets shown in the SEM images are a magnified view of the selected portion of the images. The

Figure 2. Effect of number of polymerization on the conductivity of leather at different monomer concentration (FeCl3 0.30 M, AQSA 10 wt % of pyrrole, polymerization time 2 h, temperature 5 ± 2 °C).

micrograph of untreated leather (Figure 3a) shows a clear, smooth surface and hair pores free from any foreign particles. On the other hand, the micrographs of treated leathers show polymeric particles of PPy coated on the surface which can be attributed to the conducting nature of treated leathers. It is seen that some area of leather is free from PPy particles (Figure 3b). Interestingly, the leather coated with double in situ polymerization shows a continuous film of compacted PPy particles without much free space indicating higher coating and conductivity (Figure 3c). Hence, it is demonstrated that as the number of polymerization increases, the degree of deposition of PPy increases and a continuous film is formed. SEM images showing the cross-section of the leathers treated with single and double in situ polymerized PPy exhibit increased coating thickness reaching up to 3 μm as the number of polymerization increased (see Supporting Information, Figure S1). Hence, reaction parameters such as soaking time, polymerization time, reactant concentration, and number of polymerization can be tailored to control the coating thickness and uniformity of coating film. 3.7. Infrared Spectroscopy. Figure 4a shows the FTIR spectra of control (white crust sheep nappa leather) and experimental leathers treated with single and double in situ polymerization of pyrrole. The FTIR spectra of control leather possess characteristic peaks corresponding to amide I (1700− 1600 cm−1), amide II (1600−1500 cm−1), and amide III (1300−1200 cm−1) bands.22 Further it also shows an additional peak at 1458 cm−1 corresponding to aliphatic side chain groups of amino acids present in collagen. These characteristic peaks of collagen are not significantly altered upon single and double in situ polymerization of pyrrole as evidenced from Figure 4a. Nevertheless, the appearance of characteristic bipolaron bands at 1177 and 910 cm−1, corresponding to N−C stretching and CC in-plane bending of pyrrole ring, confirms the formation of polypyrrole on the leather surface after single and double in situ polymerization of pyrrole.20,21 An additional characteristic band at 790 cm−1 is assigned to the C−H out-of-plane PPy ring deformation vibrations. It is shown that the variations in the N−C stretching band indicate the presence of free electrons of the bipolarons near the N−C bond in PPy.23 Because of the bipolarons, charge hopping takes place in the PPy chain, thereby the treated materials become conductive.23,24 Here, it is 18212

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Figure 3. SEM micrographs showing the grain surface of (a) untreated sheep nappa white crust leather and leathers treated with (b) single in situ polymerized PPy (pyrrole 0.3 M, FeCl3 0.8 M, AQSA 10 wt % of pyrrole, polymerization time 2 h and temperature 5 ± 2 °C) and (c) double in situ polymerized PPy (pyrrole 0.15 M, FeCl3 0.4 M, AQSA 10 wt % of pyrrole, polymerization time 2 h and temperature 5 ± 2 °C for each step of in situ polymerization). Insets show magnified view of the select portion of images.

Figure 4. (a) FTIR spectra of sheep nappa white crust leather and leathers treated with single and double in situ polymerization of pyrrole (pyrrole 0.3 M, FeCl3 0.8 M, AQSA 10 wt % of pyrrole, polymerization time 2 h and temperature 5 ± 2 °C); (b) XRD patterns of single and double in situ polymerized polypyrrole thin film coated on the leather (pyrrole 0.3 M, FeCl3 0.8 M, AQSA 10 wt % of pyrrole, polymerization time 2 h and temperature 5 ± 2 °C).

seen that the N−C stretching band is more pronounced for the leather treated with double in situ polymerization of pyrrole indicating more conductivity in the treated leathers in comparison to single in situ polymerization of pyrrole. 3.8. X-ray Diffraction Analysis. X-ray diffraction patterns of experimental sheep nappa crust leathers treated with single

and double in situ polymerization of pyrrole are shown in Figure 4b. The control crust leather shows a broad peak around 20° exhibiting its amorphous nature (see Supporting Information, Figure S2). The surface of leathers coated with PPy through in situ polymerization also shows amorphous peaks due to their polymeric nature. Although both control and 18213

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leathers is black, as also can be seen from the inset of Figure 5. The color measurement data of the control and treated leathers are given in Table 1. It is seen that the lightness index for the polypyrrole treated leathers is much lower than that of control leathers. On the other hand, the hue index for the polypyrrole treated leathers is much higher than that of control leathers. Whereas the indexes for the color axis (a and b) are not altered much between control and polypyrrole treated leathers. Hence, it is inferred that the color of the control leather is whitish, and the treated leathers are black. These results are in agreement with the reflectance data. 3.10. Dry and Wet Rubbing Fastness. Although the in situ polymerization of pyrrole on the leathers resulted in in situ generated black conducting leathers without employing toxic dyes, the color fastness of the treated leathers need to be analyzed. As can be seen (see Supporting Information, Table S1), dry as well as wet rubbing fastness for leathers treated through both single and double in situ polymerization are more than that of the standard requirement. Further, dry rub fastness for leathers treated through double in situ polymerization is slightly higher. This may be due to higher absorption of reactants into leather owing to a long polymerization time, which reduces excess monomer deposition on the surface. 3.11. Application Study. Bulk produced double in situ PPy-coated leather showed a conductivity value of 7.4 S/cm. To demonstrate the ability of PPy-coated highly conducting leathers for operating the touch screen-devices, both control and treated leathers treated with double in situ polymerization of pyrrole were used to touch and operate an iPad mini device (see Supporting Information, Movie S1). As can be seen, control sheep nappa white crust leather, not coated with PPy, could not operate the device. On the other hand, PPy coated sheep nappa black crust leather can easily navigate through the pages and operates the device nicely. Hence, it can be seen that the PPy-coated conducting black leathers developed in this study can be potentially used for smart or advanced product applications with an additional advantage of avoiding toxic dyes during leather manufacture.

PPy-treated leathers exhibit similar diffraction patterns, PPytreated leathers display a small peak at low angle scattering and a broad peak at a higher angle. It is known that collagen also exhibits a low angle peak with a d spacing of 11.07 Å signifying the intermolecular lateral packing.25 Here, the PPy-treated leathers exhibit a d spacing of 10.04 Å probably due to the interactions between PPy and collagen.25 The broad peak observed at 22.2° for the PPy-treated leathers may comprise few suppressed higher order peaks indicating the paracrystalline nature of PPy as interpreted by Nogami.26,27 These higher order peaks are generally due to interplanar spacing of PPy lattice chain, average molecular packing distances of the PPy aromatic rings and face-to-face distance between PPy chains. 3.9. Color Measurements. The percentage reflectance values against visible wavelength for the control and treated leathers are shown in Figure 5. In principle, the color of the

Figure 5. Reflectance spectra of uncoated and coated leather with PPy using single and double in situ polymerization (pyrrole 0.3 M, FeCl3 0.8 M, AQSA 10 wt % of pyrrole, polymerization time 2 h and temperature 5 ± 2 °C). Inset shows the digital image of the PPycoated leather through double in situ polymerization.

4. CONCLUSION A simple process to prepare conducting and self-colored leathers through in situ polymerization of pyrrole is demonstrated. Highly conducting leathers with a conductivity value of 7.4 S/cm were prepared using 0.3 M of pyrrole, a dopant concentration of 10 wt % of pyrrole, oxidant concentration of 0.8 M (2.67 ferric chloride to pyrrole molar ratio) and double in situ polymerization at 5 °C. The extent of deposition of PPy increases as the number of polymerization increases thereby leading to a continuous film as seen under the microscope. FTIR confirms the formation of polypyrrole on the leather surface as well as the presence of a prominent N−C stretching band in double in situ polymerized leather, proving higher conductivity compared to single in situ polymerized leather. X-ray diffraction analysis suggests para-crystallinity in the PPy-treated leathers. The PPy-treated leather was shown to

leather will be shown as a decrease in the reflectance value at the absorption maximum. Absorption maximum is the wavelength at which the reflectance is minimum. It is seen that there is no specific reflectance minimum for the control leather. A major reflectance minimum is seen around 575 nm while the reflectance values for the wavelength region 370 to 500 nm are low, which shows that the absorption is maximum in this entire wavelength region. Further, the reflectance values are in the range of 35 to 70% for the wavelength region 370 to 600 nm. This means that the color of the control leather samples is whitish. In the case of leathers treated with single or double in situ polymerization, the reflectance values range between 7 and 9% without any specific reflectance minimum. In other words, the treated leathers absorb the entire visible spectrum of wavelength. Hence, the color of the treated

Table 1. Color Measurement Data of Control and PPy-Coated Leathers leather sample

L

a

b

c

H

ΔL

Δa

Δb

ΔC

ΔE

ΔH

control single in situ polymerization double in situ polymerization

80.10 34.82 34.60

−3.227 −0.555 −0.788

4.322 −0.254 −0.527

5.394 0.610 0.948

126.768 204.582 213.76

−45.28 −45.50

2.672 2.439

−4.576 −4.849

−4.784 −4.446

45.589 45.822

2.278 3.105

18214

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(12) ISO 2418:2002. Leather. Chemical, physical and mechanical and fastness tests. Sampling location; International Organization for Standardization: Geneva, 2002. (13) ISO 2419:2012. Leather. Physical and mechanical tests. Sample preparation and conditioning; International Organization for Standardization: Geneva, 2012. (14) Ayyasamy, T.; Thanikaivelan, P.; Chandrasekaran, B.; Rao, J. R.; Nair, B. U. Development of an integrated wet finishing process: Manufacture of garment leathers. J. Am. Leather Chem. Assoc. 2004, 99, 367. (15) Kang, E. T.; Neoh, K. G.; Ong, Y. K.; Tan, K. L.; Tan, B. T. G. X-ray photoelectron spectroscopic studies of polypyrrole synthesized with oxidative iron(III) salts. Macromolecules 1991, 24, 2822. (16) Sakkopoulos, S.; Vitoratos, E.; Dalas, E. Conductivity degradation due to thermal aging in conducting polyaniline and polypyrrole. Synth. Met. 1998, 92, 63. (17) Dalas, E.; Sakkopoulos, S.; Vitoratos, E. Thermal degradation of the electrical conductivity in polyaniline and polypyrrole composites. Synth. Met. 2000, 114, 365. (18) Gubbels, F.; Blacher, S.; Vanlathem, E.; Jerome, R.; Deltour, R.; Brouers, F.; Teyssie, P. Design of electrical composites: Determining the role of the morphology on the electrical properties of carbon black filled polymer blends. Macromolecules 1995, 28, 1559. (19) Kuhn, H. H.; Kimbrell, W. C.; Fowler, J. E.; Barry, C. N. Properties and applications of conductive textiles. Synth. Met. 1993, 57, 3707. (20) Kaynak, A.; Beltran, R. Effect of synthesis parameters on the electrical conductivity of polypyrrole-coated poly(ethylene terephthalate) fabrics. Polym. Int. 2003, 52, 1021. (21) Kim, S. H.; Oh, K. W.; Bahk, J. H. Electrochemically synthesized polypyrrole and Cu-plated nylon/Spandex for electrotherapeutic pad electrode. J. Appl. Polym. Sci. 2004, 91, 4064. (22) Ashokkumar, M.; Thanikaivelan, P.; Krishnaraj, K.; Chandrasekaran, B. Transforming chromium containing collagen wastes into flexible composite sheets using cellulose derivatives: Structural, thermal, and mechanical investigations. Polym. Compos. 2011, 32, 1009. (23) Vishnuvardhan, T. K.; Kulkarni, V. R.; Basavaraja, C.; Raghavendra, S. C. Synthesis, characterization and a.c. conductivity of polypyrrole/Y2O3 composites. Bull. Mater. Sci. 2006, 29, 77. (24) Selvan, T.; Spatz, J. P.; Klok, H. A.; Möller, M. Gold− polypyrrole core−shell particles in diblock copolymer micelles. Adv. Mater. 1998, 10, 132. (25) Thanikaivelan, P.; Narayanan, N. T.; Pradhan, B. K.; Ajayan, P. M. Collagen based magnetic nanocomposites for oil removal applications. Sci. Rep. 2012, 2, 230 (7p). (26) Nogami, Y.; Pouget, J. P.; Ishiguro, T. Structure of highly conducting PF6−-doped polypyrrole. Synth. Met. 1994, 62, 257. (27) Warren, M. Electronic and Structural Effects on the Electrochemistry of Polypyrrole. MS Thesis, University of British Columbia, Vancouver, Canada, 2005.

be black in color without employing any toxic dyes and also able to operate touch-screen devices thereby demonstrating its potential for smart or advanced product applications. Nevertheless, the coated PPy can loose its conductivity due to the removal of dopant anions during use or wash care, which is an inherent deficiency of polypyrrole. Studies to overcome the challenge of retaining the conductivity of PPy during usage in advanced products can be explored in the future.

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ASSOCIATED CONTENT

S Supporting Information *

SEM images showing the cross section of control and PPycoated leathers, XRD of control sheep nappa white crust leather, color fastness of PPy-coated leathers, and a movie showing the ability of PPy-coated leather for operating touchscreen devices. This material is available free of charge via the Internet at http://pubs.acs.org.

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AUTHOR INFORMATION

Corresponding Author

*Email: [email protected]; [email protected]. Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS J.D.W. acknowledges the Twinning Project funded by Government of Ethiopia that enabled his stay at Central Leather Research Institute, Chennai. Authors thank CSIR for providing financial support under XII plan project “S&T Revolution in Leather with a Green Touch” (STRAIT-CSC0201) project scheme; CSIR-CLRI Communication No. 1075.

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REFERENCES

(1) Gautieri, A.; Vesentini, S.; Redaelli, A.; Buehler, M. J. Hierarchical structure and nanomechanics of collagen microfibrils from the atomistic scale up. Nano Lett. 2011, 11, 757. (2) Kabat, F. Lineman safety belt. US Patent 2127034, 1938. (3) Lee, J. Y.; Cho, S. H.; Song, K. T. In Handbook of Conductive Polymers; Skotheim, T., Reynolds, J., Eds.; CRC Press: New York, 2007. (4) Nabid, M. R.; Entezami, A. A. A novel method for synthesis of water-soluble polypyrrole with horseradish peroxidase enzyme. J. Appl. Polym. Sci. 2004, 94, 254. (5) Gasana, E.; Westbroek, P.; Hakuzimana, J.; De Clerck, K.; Priniotakis, G.; Kiekens, P.; Tseles, D. J. Electroconductive textile structures through electroless deposition of polypyrrole and copper at polyaramide surfaces. Surf. Coat. Technol. 2006, 201, 3547. (6) Chandrasekhar, P. Conducting Polymers, Fundamentals and Applications: A Practical Approach; Springer Publication: New York, 1999. (7) Malinauskas, A. Chemical deposition of conducting polymers. Polymer 2001, 42, 3957. (8) Oh, K. W.; Hong, K. H.; Kim, S. H. Electrically conductive textiles by in situ polymerization of aniline. J. Appl. Polym. Sci. 1999, 74, 2094. (9) Leto, G.; Wager, D. J. Material for use with a capacitive touch screen. US Patent Application 20120128995, 2012. (10) Wegene, J. D.; Thanikaivelan, P.; Krishnaraj, K.; Phebe, K.; Chandrasekaran, B. A novel bi-functional leather for smart product applications and a process for the preparation there of. Indian Patent Application 1269Del2014, 2014. (11) ISO 11640:1993. Leather. Tests for colour fastness. Colour fastness to cycles of to-and-fro rubbing; International Organization for Standardization: Geneva, 1993. 18215

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