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Nanodiamond Fabrication of Superhydrophilic Wool Fabrics Shadi Houshyar, Rajiv Padhye, Robert Shanks, and Rajkishore Nayak Langmuir, Just Accepted Manuscript • DOI: 10.1021/acs.langmuir.8b02191 • Publication Date (Web): 06 May 2019 Downloaded from http://pubs.acs.org on May 8, 2019
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Nanodiamond Fabrication of Superhydrophilic Wool Fabrics Shadi Houshyar1*, Rajiv Padhye2, Robert A Shanks3, Rajkishore Nayak4
1 College
of Science, Engineering and Health, School of Engineering, RMIT University, Melbourne, 3000, Australia Centre for Materials Innovation and Future Fashion, College of Design and Social Context, School of Fashion and Textiles, RMIT University, Brunswick, 3056, Australia 3 College of Science, Engineering and Health, School of Applied Sciences, RMIT University, Melbourne 3000, Australia 4 School of Communication and Design (Fashion Merchandising), RMIT University Vietnam, Ho Chi Minh City, Vietnam 2
*Corresponding Author; Shadi Houshyar; Email:
[email protected] Abstract Nanodiamonds (ND) have been gaining impetus in fields such as medicine and electronics. ND has been widely used to modify polymer surfaces and composites for improved functionality. There has been limited research on ND application in regard to textile substrates. In this study, we presented a sustainable coating method, adapted to functionalized ND particles, coated onto wool fabric surfaces to enhance hydrophilicity. The application of an ND coating was found to increase wool hydrophilicity due to the presence of additional polar groups, shown by Fourier transforms infrared spectrometry, which increased surface energy and fiber roughness. Scanning electron microscopy images revealed that the polar ND coated wool scales demonstrated improved fiber hydrophilicity. Water absorbency, wicking and contact angle for coated fabrics confirmed significant improvement in hydrophilicity, which was directly related to the concentration of ND particles. The optimal concentration of ND was therefore selected to coat the wool fabric. Furthermore, tensile strength and abrasion resistance of the coated fabrics were increased due to the exceptional mechanical properties of ND. Keywords: Nanodiamond, wool fabric, hydrophilicity, SEM, FTIR, abrasion resistance
Introduction Wool is a widely used fiber for clothing materials. Characteristics such as low bulk density, hydrophilicity and warmth provide comfort. Wool fibers are able to absorb a large amount of moisture and display the highest regain among natural fibers (1-3). An epicuticle membrane on the surface of the wool fiber reduces potential moisture absorbency. This is a fatty layer, with 18-methyl eicosanoic acid covalently bound to the protein layer of the wool cuticle via a thioester linkage. Water absorption and liquid transport of wool fibers are limited when epicuticles are present (1,4,5). This impacts the comfort of the wearer and limits wool fiber applications for many industries, including sport (1,4-7). Previous research has focused on removing or masking the epicuticle membrane to improve hydrophilicity and to increase the transport properties of wool fibers (2,6,8) Processes such as corona discharge, non-thermal plasma and enzyme treatment have been used to enhance the hydrophilicity of wool fibers. The disadvantages of these processes include lowered durability of finishes, higher cost, damage to the fabric surface and environmental hazards. Plasma treatment, for
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instance, requires expensive equipment (8-13). The hydrophilicity of the treated fabric also depends on storage conditions and decreases gradually in air. Enzyme treatment eliminates the fatty layer and risks damaging the structure of the wool fibers (14-16). The development of a sustainable, one-step, low cost technique for enhancing the hydrophilicity of wool fibers is, therefore, a challenge that has yet to be addressed (1,17-20). The super-hydrophobicity or superhydrophilicity of a fabric surface depends on chemical composition and surface topographical morphology[21]. The micro/nanostructure of low surface energy materials is a key to controlling the wettability of the surfaces (8,18,21-23). Nanodiamond (ND) particles for coating and grafting are gaining attention due to their unique physical properties, such as mechanical stability, extreme hardness, low fraction coefficient, high corrosion resistance, transparency, high thermal conductivity and chemical stability (24-27). ND is transparent in the visible and IR-range, yet highly absorptive to sunlight. It can be moulded into fibers, or coated and grafted to the surface of fibers or other shapes to harness its useful properties. The application of diamond like-carbon (DLC), gold nanoparticles, diamond and carbon nanotube in the preparation of hydrophobic/hydrophilic textiles is an attractive innovation (20,22,28). The application of ND to create a super-hydrophilic wool fabric has not yet been investigated. ND has the potential to provide an effective coating for wool to create a hydrophilic surface. This is due to the available functional groups such as hydroxyl and carboxyl groups present on the surface of the NDs. These groups are able to attach to the surface of the wool to create a permanent, stable coating, while the remaining hydrophilic groups support a hydrophilic wool surface [28]. Fig. 1 describes the mechanism for increasing the hydrophilicity of wool fibers with the application of ND, which increases the number of polar groups. Wool Fiber Wool Fiber
R
H
N
C
H
OH
O
+
R
N
C +
H O
O
O-H
O
Fig. 1. Schematic diagram of the nanodiamond coating on wool fibers
Although there have been many recent articles on surface modification using ND, none have specifically focused on improving the hydrophilicity of wool. ND powder may be used to increase the hydrophilicity of the wool fabric, while improving other performance properties such as tear strength and abrasion resistance. The aim of this study is to prepare and evaluate the influence of an ND coating on the mechanical and thermal properties of wool fabric. The ND concentration in the application solution, hence the amount of ND available for adsorption on wool fibers, and the concentration dependence of thermal, structural and mechanical properties is investigated. The evaluation of water absorbency and water contact angle are used as a measurement of hydrophilicity and reported as a function of ND concentration, to characterize the coated wool fiber properties.
Experimental Materials Plain woven grey wool fabrics used in this research were kindly contributed by Macquarie Textiles, Australia. All fabrics were conditioned for at least 24 h in a standard atmosphere with the controlled relative humidity (RH of 60 ± 3 %) and temperature (20 ± 20 °C) as per standard. The warp and weft count (English or Ne), thread and areal density were determined following standard test methods ISO 7211/5 and ISO 7211/2 [29], respectively. The mass per unit area was calculated following standard [30] using five specimens. The constructional details of the fabric are shown in Table 1: ACS Paragon Plus Environment
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Table 1. Constructional details of wool fabrics Warp count (Ne)
Weft count (Ne)
16 (2/32)
16 (2/32)
Threads/cm End 24
Picks 24
Areal density (g/m2) 195
Fabric samples of 40 cm × 40 cm were cut and purified by washing in isopropanol for 20 min using an ultrasonic bath to remove surface impurities. The fabric samples were rinsed with distilled water and dried at 60 °C for 2 h then conditioned in a standard testing atmosphere as detailed above. Detonation nanodiamond (DND) was supplied by Guangzhou Jiechuang Trading Co. Ltd (China, Figure 1 (a,b), average particle size w< 10 nm, having afflomerate size of ~ 20-50 µm, as determined by scanning electron microscopy (SEM)). Acetic acid (99.5 % purity), acetone and other chemical-reagents, were obtained from Sigma Aldrich, Australia. Deionized water was used for all experimental processes.
Preparation of DND suspension and superhydrophilic fabrics A DND suspension was prepared by adding 0.1 %·w/w, 0.2 %·w/w and 0.3 %·w/w DND in deionized water, which were abbreviated as W1, W2 and W3, respectively. A blank solution was prepared with 0 %·w/w DND as a control and abbreviated as W0. These suspension liquids were then sonicated at room temperature for 120 min to provide a mixture without visible agglomerates as shown in Fig. 2 (c and d)[31]. Acetic acid was used to adjust the DND suspension to pH = 5. The weight ratio of wool fabric to water was 1:30. (a)
(b)
(c)
(d)
Fig. 2. DND images (a) TEM and (b) SEM(on carbon tape), DND suspension in deionized water: (c) before and (d) after ultrasonication Dip coating was used to apply the DND onto the surface of the wool fabric samples. The samples were immersed in a DND dispersion with the temperature raised from an ambient temperature (25 °C) to 50 °C over a 30 min and held at 50 °C for a further 30 min, followed by drying in a hot air oven at 60 °C for 12 h. The dip coating system was placed in a sonicator bath during the process. The samples were tested for mechanical, surface chemical and hydrophilic properties, to record the effect of the DND coating on those properties. The results are which are discussed below.
Mechanical properties Mechanical properties of the fabric samples were evaluated by measuring tensile strength and abrasion resistance. The tensile strength of the untreated and treated fabric samples was tested using an Instron Universal Test Instrument (Model 3300, Single Column, with Bluehill software), at a gauge length of 50 mm and a strain rate of 100 mm.min-1. Five test specimens of 20 cm (l) × 2 cm (w) were used for the tensile strength in warp direction for each fabric and tested in accordance with ISO Standard [32]. An average of five readings was reported for breaking strength and breaking elongation, which was calculated using Bluehill Software. Abrasion resistance was determined following the Australian standard [33] using a Martindale Abrasion Tester. Each fabric specimen was mounted in a specimen holder with a foam backing and then rubbed against a standard abradant with a semi-random Lissajous motion. A total weight of 0.595 kg was used
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during the test, which is equivalent to a nominal pressure of 12 kPa. Each fabric was tested with four samples and the results averaged. Final results were observed in terms of the number cycles the samples were able to withstand before multiple ruptures occurred in the fabric.
Scanning Electron Microscopy Analysis (SEM) Scanning electron microscopy (SEM) and energy dispersive X-ray (EDX) spectroscopic measurements were performed with a scanning electron field-emission microscope (Quanta FE-SEM) at an accelerated voltage of 15 kV in a low vacuum mode. The specimens were coated with platinum (thickness ~10 nm) using a Gatan precision etching and coating system (PECS). To determine the distribution of DND on the fiber surface, X-ray net counts were obtained at random locations on the stub with a collection time of 1000 s. The elemental composition was determined by EDX software from EDX distribution mapping.
Fourier Transform Infrared Spectrometry (FTIR) analysis Fourier transform infrared (FTIR) spectroscopy was performed to identify types of chemical bonds and functional groups in the structure of both the untreated and treated fabric samples. FTIR spectra were collected using a PerkinElmer Spectrometer (Spectrum-400). The number of scans per spectrum was 4 and the FTIR spectra were collected in the wavenumber range of 4000 – 650 cm–1.
Thermal properties Thermal degradation as a function of environmental exposure was characterized using thermogravimetry (TGA). Samples of approximately 5 mg were cut from each specimen and accurately weighed in the weighing balance. A PerkinElmer thermogravimetric analyzer (Pyris 1) was used for the measurements. Temperature was scanned from 25 to 850 °C at 10 °C/min under a nitrogen purge of 10 mL/min, with purge gas switched to air with the same flow at 700 °C. The mass loss after switching to air was due to the combustion of carbon residue formed during the scan because of the high carbon content of the fibers resulting from dehydration. The TGA was calibrated using Curie temperature standards and a reference mass. The data are represented as a mass fraction and its derivative with time, as a function of temperature.
Surface water management properties The water absorbency of all fabric samples was calculated by placing each specimen onto the surface of water in a beaker for 0, 30, 60 and 120 s at room temperature (~ 20 °C). All samples were then pad dried and the pickup water weighed. Wicking was tested by the vertical suspension of a fabric above a reservoir of distilled water with its lower edge immersed. The wicking time was measured when water reached each in a sequence of marks [34]. Three samples of each fabric were tested for water absorbency and wicking and the results were averaged. Water contact angles and surface energy of the fabric samples were measured using a contact angle apparatus (Data Physics OCA20) with automatic fitting of droplet contours. Three samples of each fabric were used for all tests and the results were averaged. Five specimens of 8 cm × 8 cm were cut from each fabric and tested on an SDL Atlas Moisture Management Tester (MMT) in accordance with standard [35]. A saline solution of 0.9 % was prepared using sodium chloride (NaCl), which was used for the tests. The saline solution was released from the standard spray nozzle of the instrument for 20 s in the center of the fabric on the skin side. The change in the electrical resistance between each series of concentric sensors was recorded individually using top and bottom sensors. The dynamic liquid transfer process and data measurements were automatically monitored and recorded.
Results and discussion SEM and EDX The aim was to develop smart wool textiles with superhydrophilicity, higher abrasion resistance and tensile strength by coating with the DND. The fabric color changed slightly after dip coating with the ACS Paragon Plus Environment
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DND dispersion, due to impurities present in the DND solution. The morphological changes resulting from the deposition of various amounts of DND on the surface of the wool fabrics were investigated by SEM as shown in Fig. 3. (a)
(b)
(c)
(d)
Fig. 3. SEM images of (a) pristine wool fiber (W0); and treated wool fibers, (b) W1, (c) W2 and (d) W3
It is apparent from the images of the surface of the pristine wool fiber, in Fig. 3 (a), that the surface is smooth with prominent scales extruding from the surface. Fig. 3 (b, c, d) reveals the presence of DND on the fiber surface after dip coating. This indicates that the wool fibers have been effectively coated with a thin film of DND and the tips and scale of the wool fibers were masked. The coating thickness on the fiber was improved by increasing the amount of DND in the dispersion. This suggests that DND deposition has modified the surface of the wool fiber with an evident smoothing of the tips of the scales and the surface of the fibers without adverse effects on the morphology of the pristine fiber in the micrometer range. The data obtained from the EDX measurement is shown in Table 2, which represents the chemical composition of the DND-layer coated wool fiber. From Table 2, it can be observed that the intensity of the carbon peaks from DND treated surfaces were much stronger than that of the untreated surface, indicating the existence of a DND layer coated onto the wool fiber surface. The DND carbon element content on the surface of W3 is higher than those of W2 and W1, due to an increased DND concentration on the wool fiber. Table 2. Surface chemical composition of untreated (W0) and treated wool fibers (W1, W2, W3) Element
W0
W1
W2
W3
C1s
72.1
75.6
77.1
79.1
O1s
25.2
21.5
19.9
17.1
S2p
3.8
3
2.9
2.7
FTIR Spectroscopy FTIR spectroscopy was performed to determine the chemical composition of the DND coated wool fabric. The FTIR spectra have been presented in Fig. 4.
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0.12
W0 W1 W2 W3 ND
0.1
Absorbency
0.08 0.06 0.04 0.02 0 4000
3500
3000
2500
2000
1500
1000
Wavenumber (cm-1) Fig. 4. FTIR spectrum of untreated (W0) and treated Wool fibers (W1, W2 and W3, respectively)
Characteristic peaks for wool fibers are present at 1641 cm-1, 1540 cm-1 and 1242 cm-1 for amide I (induced by the stretching carboxyl bond), amide II (induced by the bending N-H and stretching C-N) and amide III (induced by the stretching C-C and C=O bending), respectively. As shown in Fig. 4, DND has hydroxyl (OH) and carboxyl (-COO–) groups on the surface, which can interact with the active groups in the wool fiber (Fig. 1). The -OH (3000-3960 cm-1) and -NH peaks (induced by the stretching amine salt, 2960 cm-1) are significantly reduced for the W3 fabric compared to the other fabrics, due to hydrogen bonding and the interaction of the amine group with the carboxyl group in DND, as shown in Fig. 1(37, 38).
Thermal degradation
100
0
90 80
-0.05
70 -0.1
60 50 40
-0.15
30 20
-0.2
Derivative Weight (mg/min)
TGA of the untreated and treated wool fabrics are presented in Fig. 5. A weight loss of 2.60 % was obtained for all fabric samples before 220 °C, suggesting the presence of a volatile component, probably water, due to the high moisture regain of wool fibers.
Weight (%)
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W1 W2 W3 W0 W0 W1 W2 W3
10 0
-0.25 0
100
200
300
400
500
600
700
800
900
Temperature (°C) Fig. 5. TGA of untreated (W0) and treated wool fibers from fabrics (W1, W2 and W3, respectively)
Figure 5 showed that both the untreated and treated fabrics experienced a significant weight loss after 220 °C due to thermal degradation. However, the untreated fabric (W0) has a lower offset temperature (∆T ~10 °C) of 309 °C with a higher weight loss of 76.2 % followed by W1, W2 and W3, respectively. However, for the treated fabrics the weight loss occurred between 400 to 500 °C due to increased carbonaceous residue being formed in the treated samples in addition to the residue of DND, caused by the presence of DND. Thermal degradation started at a lower temperature for untreated samples in ACS Paragon Plus Environment
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comparison with the treated fabric, as the DND caused a delay in volatilization of degradation products due to adsorption. Upon switching from nitrogen to air at 700 °C, carbonaceous residue was observed from the cotton substrate and DND oxidized. Sample W3 had a residual mass of around 5% by 850 °C, which approximately equal to the fraction of DND particles on the treated fabric.
Hydrophilicity Water contact angle, absorbency, wicking and moisture management properties of the untreated and treated fabrics were measured to determine the activity of DND treatment on wettability of the wool fibers. The water contact angle of untreated wool fabric is in the range of 119-125° as shown in Fig. 6, due to the use of unscoured wool fabric. However, after treatment with DND, water droplets were absorbed, disappearing rapidly after about < 2 s. This indicates that DND treatment of the wool fabric resulted in improved surface wetting, due to the existence of polar functional groups on the surface of the fabric. The amount of DND coating on the fabric impacted the contact angle; the fabric with the lowest amount of DND (W1), exhibited the lowest contact angle of less than 20° (Fig. 6 (a). A contact angle close to zero for W2 and W3, Fig. 6 (c,d) may be due to the higher amount of hydrophilic functional groups on the surface of the fabrics, attracting and absorbing water droplets more quickly. (a)
(b)
0.57mm
(c)
(d)
0.57mm
0.57mm
0.57mm
Fig. 6. Contact angle of a water droplet on (a) untreated wool fabric (W0), (b) treated wool fabric, W1, and (c) W2 (d) W3
The results for water absorption and wicking tests are shown in Fig. 7 (a) and (b), respectively. Treatment with DND increases the water absorbency and wicking of the wool fabric significantly, supporting the results from the contact angle measurement. 250
W0 W1
200
W2 W3
150 100
Time (s)
Water absorbency (%)
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60
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70
W0
60
W1
50
W2 W3
40 30 20
50
10 0 30
60
Time (sec) (a)
90
120
0 1
2
3
4
5
Relative distance
6
(b)
Fig. 7. (a) Water absorbency and (b) wicking properties of untreated (W0) and treated wool fabrics (W1, W2 and W3, respectively)
The water absorbency of untreated and treated wool fabrics over a period of 120 s is reported in Fig. 7(a). W3 exhibited the greatest rate of absorbency due to the highest amount of DND on the surface of the fabric. Surface roughness and surface energy play an important role in fabric. All treated fabrics exhibited higher surface energy and roughness compared to the untreated fabrics. The amount of DND increased the surface roughness of the wool fabrics. The surface energy of the untreated wool fiber was low due to
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the low hydrophilic nature of the wool fiber compared to the treated fabrics. However, coating the fibers with DND resulted in the presence of increased hydrophilic groups (-OH, -COOH groups) on the wool surface and reduced the wettability of the fabric due to the fiber nature (cuticle). As a result, surface energy of the wool fabrics improved after treatment with DND. As the concentration of the DND application solution increased, the number of polar groups on the surface of the treated wool fabric was also increased, further enhancing the hydrophilic properties of the wool fabric. However, there was an optimum concentration for DND layer on wool surface. W3 initially absorbed more water (
