Study on flame-retardant and UV-protection properties of cotton fabric functionalized with ppy–ZnO–CNT nanocomposite

Abstract

Cotton fabric was modified with 1,2,3,4-butanetetracarboxylic acid as cross-linking agent in the presence of sodium hypophosphite as catalyst. Polypyrrole–zinc oxide (ppy–ZnO) and polypyrrole–zinc oxide–carbon nanotube (ppy–ZnO–CNT) composites were also prepared by an in situ chemical polymerization method. The composite sol was coated on the cotton fabric using a pad-dry-cure technique. This coated cotton fabric was characterized by FE-SEM with EDAX, XRD, UV-DRS and FT-IR analyses. Flame-retardant and UV-protection properties of the coated cotton fabric were tested and compared with those of uncoated fabric. The ppy–ZnO–CNT composite-coated cotton was found to possess better properties than uncoated cotton.

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1. Introduction

Cellulose is the most abundant biopolymer found on the earth. It has many excellent properties such as biodegradability, biocompatibility and eco-friendliness.¹ In recent years, textile industries have been focusing on improving its functional properties,^2–7 such as fire-retardant, UV-protection, self-cleaning and antibacterial properties. Textile finishers worldwide are considering a global challenge in materials to make garments comfortable and multifunctional. Attempts have been made to meet the challenges using nanomaterials with a view to introducing new functional properties to textiles. High-performance textile materials are greatly appreciated by a more discerning and demanding consumer market. Nanoparticles of metal oxide-ceramics have been used to incorporate functional properties into textiles. Common metal oxides such as titanium oxide (TiO₂), zinc oxide (ZnO), cupric oxide (CuO) and magnesium oxide (MgO) are in use for providing functional properties.⁸ Ultraviolet (UV)-resistant cotton fabrics were developed by coating with ZnO and TiO₂ nanoparticles. Nano-ZnO-coated cotton yarns were found to withstand knitting operations.⁹ Among the transition metal oxides, zinc oxide (ZnO) has received considerable interest for the fabrication of polypyrrole (ppy) hybrid materials because of its variety of applications in optoelectronic devices. Zinc oxide has high refractive index and thermal stability, offers ultraviolet protection, and has good transparency, high electron mobility and a wide band gap of 3.37 eV.^10,11 ZnO nanorods grown on cotton fabrics possessed an ultrahigh UV protection factor of 379.14. This indicates an excellent protection against UV radiation in comparison with untreated cotton fabrics.¹² Coating of cotton with ppy by in situ oxidative chemical polymerization at room temperature altered the combustion process of cellulose, and such coated cotton could have potential applications as technical textiles with antistatic (low electrical resistance), heat-generation, hygroscopic, antibacterial and high-temperature-resistance properties.¹³ Polyethyleneterephthalate–ppy textile complexes incorporating different anionic dopants have been treated between 60 and 150 °C to investigate effects of short-term heating on conductivity and stability; 80 °C did not significantly change the final resistance of the conducting textile, while 125 °C was the most effective. Sulphonic group-containing dopants were found to be effective in improving the conductivity and stability.¹⁴ Cotton was functionalized with carbon nanotubes (CNT) using a simple surface coating method. Due to the reinforcement and protection effects of the CNT modification, the cotton exhibited enhanced mechanical properties, extraordinary flame retardancy, and improved UV-blocking and super-water-repellent properties. Considering the novel physical properties of CNT, the functionalization of textile material with CNT would be of great importance for both fundamental research and practical applications.¹⁵ CNT were coated by an exhaustion method and stabilized on cotton using 1,2,3,4-butanetetracarboxylic acid (BTCA) as cross-linking agent and sodium hypophosphite (SHP) as catalyst. CNT-modified surface increased the thermal stability.¹⁶

From the literature, it is observed that a flame-retardant finish on cotton fabric is very important for many applications, such as military, buildings and protective clothing. In the present work, it was aimed to develop crosslinked cotton coated with nanocomposites (ppy–ZnO and ppy–ZnO–CNT) for UV-protection and flame-retardant finishes.

2. Experimental

2.1. Material and method

Woven cotton grey fabric of 80 counts was obtained from South Indian Textile Research Association (SITRA), Coimbatore. It was pretreated by a one-pot method with a recipe of 0.4 mL HCl, 3.9 g Na₂CO₃, 1.9 g NaOH and 1.9 mL H₂O₂ in 200 mL water. Fabric (8 cm × 4 cm) was immersed in the pretreatment bath at 80 °C for 90 min. ZnO (Sigma-Aldrich, 97%) with an average size of 50 nm, BTCA (Alfa Aesar, 98%), ammonium persulfate (APS) (Alfa Aesar, 98%), single-wall CNT (Sigma-Aldrich, 97%), SHP (SD fine, 98%), polyethylene glycol (Alfa Aesar, 98%) and pyrrole (Sigma-Aldrich, 98%) were purchased and used.

2.2. Synthesis of polypyrrole

Pyrrole was purified by double distillation before use. Pyrrole (0.3 M) was dissolved in 500 mL de-ionized water. After 10 min, APS (0.06 M) in 100 mL de-ionized water was added drop-wise into the solution mixture. The content was stirred for 24 h at 20 °C. Methanol was used to stop the reaction whenever necessary. Formation of black precipitate was considered as the completion of the reaction. It was filtered and washed with different solvents such as de-ionized water, methanol and acetone. Then the resultant sample was dried at 30 °C for 12 h in a vacuum oven.¹⁷

2.3. Synthesis of ppy–ZnO and ppy–ZnO–CNT composites by in situ polymerization

Pyrrole (0.3 M) was dissolved in 500 mL de-ionized water. After 10 min, BTCA (0.1 M) and SHP (1 g) were added. Molar ratio of the material was taken. Stirring was carried out for 30 min at room temperature. Required amount of NaOH was added to bring the pH to neutral. APS (0.06 M) was prepared in 100 mL de-ionized water. ZnO (0.25 g) was mixed with the solution. The solution was sonicated for 30 min leading to a milky white colloidal form. This was added drop-wise into the solution and stirring was carried out for 9 h at 20 °C. This mixture was kept overnight for the formation of a black-coloured composite. It was filtered and washed with different solvents such as de-ionized water, methanol and acetone and dried at 30 °C for 6 h in a vacuum oven. This resulted in a ppy–ZnO composite at 1 : 1 ratio. This procedure was extended to prepare ppy–ZnO composites at 1 : 2 and 1 : 3 ratios. This latter ratio was further used with addition of CNT to form a 1 : 3 : 1 composite. The composite ratios were designated as C₁ (1 : 1), C₂ (1 : 2), C₃ (1 : 3) and C₄ (1 : 3 : 1).

2.4. Coating sol preparation

The ppy–ZnO and ppy–ZnO–CNT composite sols were prepared by mixing with polyethylene glycol (2 mL). Then, 6 mL deionized water was added into 100 mL absolute ethanol and stirred vigorously at room temperature for 30 min until a homogeneous solution was obtained. Then, 4 mL ammonia was added drop-wise into this solution and kept under ultrasonic irradiation for 30 min to form ppy–ZnO and ppy–ZnO–CNT composite sols. These sols were used for coating of fabric using a pad-dry-cure method.¹⁸ The padded fabrics were air-dried and cured at 180 °C for 5 min in a hot-air oven. The ppy–ZnO and ppy–ZnO–CNT nanoparticles were coated on the fabrics due to an exchange reaction with –OH groups of cotton.

3. Results and discussion

3.1. XRD patterns of ppy, ppy–ZnO (1 : 1, 1 : 2, 1 : 3) and ppy–ZnO–CNT (1 : 3 : 1) composites and composite-coated cotton

Fig. 1 shows the XRD patterns of ppy, ZnO and ppy–ZnO composites (C₁, C₂, C₃ and C₄). Fig. 1a shows the sharp diffraction peaks of ZnO, implying that the ZnO is crystalline in nature. The peaks correspond to the planes of (100), (101), (102), (110) and (103).¹⁹ Fig. 1b shows the diffraction pattern of ppy, which has a broad peak at 2θ = 24.78° indicating the amorphous nature of the polymer.²⁰ Fig. 1c and d show an amorphous nature. It is clear that no sharp peaks were observed. Crystalline peaks in the XRD patterns were observed by increasing the concentration of ZnO from C₁ to C₄ in the composites. From Fig. 1e and f, it is clearly noticed that sharp crystalline peaks corresponding to ZnO were observed in the patterns of C₃ and C₄ composites. The crystallite size of ppy–ZnO calculated by using Scherrer's formula was found to be 15 nm. All the peaks match very well with the standard ZnO of hexagonal structure (JCPDS card 06-7848). The XRD patterns of polypyrrole-functionalized ZnO have a broad peak at lower diffraction angles, ∼22°, which indicates their amorphous nature with no clear indication of crystalline morphology. This broadening of peaks can be confirmed to be the result of the spreading of the polypyrrole chains around ZnO.²¹ An additional sharp peak is seen at (002) plane (Fig. 1f), which indicates the presence of CNT.²² The decrease in the intensities of the ZnO peaks in the pattern of the ppy–ZnO–CNT functionalized composite indicates an average size of about 40–70 nm (Fig. 1f).

Fig. 1 XRD patterns of (a) pristine ZnO, (b) ppy, and (c) C₁, (d) C₂, (e) C₃, (f) C₄ composites.

As a result of composite XRD (Fig. 1), ppy, C₃ and C₄ composites were optimized with a crystalline nature. These composite sols were coated on cotton fabric. Fig. 2 shows the XRD patterns of uncoated cotton, and ppy-, C₃- and C₄-coated cotton. Fig. 2a shows no sharp diffraction peaks for the uncoated cotton. Fig. 2b shows the diffraction pattern of ppy-coated cotton, indicating the amorphous nature of the polymer. The peaks observed at 31.6°, 36.1° and 56.4° are correlated with the formation of hexagonal ZnO and were assigned to (100), (101), (102), (110) and (103) diffractions of hexagonal ppy–ZnO composite fabric (Fig. 2c).²³ All the peaks were well matched with the values from the standard (JCPDS card 06-7848). The strong and sharp diffraction peaks indicate that the ppy–ZnO is well crystallized. The crystallite (002), (100), (002) and (110) planes are shown in Fig. 2d. The peaks were well matched with the values from the standard (JCPDS card 89-7213). The equal ratio of ppy–ZnO shows strong peaks. It was observed that the ZnO particle interacts on the polypyrrole surface.

Fig. 2 XRD patterns of (a) uncoated cotton fabric, (b) ppy-coated cotton, (c) C₃-coated cotton and (d) C₄-coated cotton.

3.2. FT-IR analysis

Fig. 3 represents the FT-IR spectra of uncoated cotton, pristine ppy-coated cotton, ppy–ZnO composite-coated cotton and ppy–ZnO–CNT composite-coated cotton. The bending vibration of water molecules (H–O–H) is observed at 1687 cm⁻¹ in the spectrum of uncoated fabric (Fig. 3a). The cellulose bands observed at 1024 and 1157 cm⁻¹ correspond to the bending vibration of C–O, whereas the asymmetric stretching vibration of glucose ring is observed at 1103 cm⁻¹.^24,25 The spectrum of ppy shown in Fig. 3b confirmed the formation of ppy. The peak at 1588 cm⁻¹ corresponds to the stretching vibration of C–C in the pyrrole ring.^26–28 The peak observed at 1687 cm⁻¹ for the untreated fabric (Fig. 3a) is shifted to 1716 cm⁻¹ which may be due to the cross-linking between cotton and BTCA (Fig. 3c and d).²⁹ The peak at 1387 cm⁻¹ corresponds to C–H in-plane deformation modes. Ppy shows characteristic C–N and C–H stretching vibrations of pyrrole at 1271 cm⁻¹ and 1017 cm⁻¹ respectively. The stretching mode of ZnO appears at around 868 and 870 cm⁻¹ due to metal oxide bond. These significant changes in peak positions and broadening reveal that there is no simple mixture of ppy and ZnO and can be attributed to some chemical interactions between active sites in ppy, CNT and ZnO that change the polymer conformation (Fig. 3c and d).³⁰

Fig. 3 FT-IR spectra of (a) uncoated cotton, (b) ppy-coated cotton, (c) C₃-coated cotton and (d) C₄-coated cotton.

3.3. SEM analysis

The SEM study confirms that ppy–ZnO nanocomposites are grafted on the fabric surface after washing. The uncoated fabric shows a plain surface when compared to ppy-, C₃- and C₄-coated fabrics. Fig. 4c shows spherical ppy–ZnO nanocomposites adhering to the fabric surface, whereas needle-like small agglomerated ppy–ZnO–CNT nanocomposite particles are seen in Fig. 4d. EDAX analyses indicate the presence of zinc, oxygen, and carbon in the coated fabric. The spherical and needle-shaped morphologies of ppy–ZnO were examined through EDAX. From these studies, the elemental wt% of C₄-coated fabric (2.20 wt%) is found to be increased when compared to that of the C₃-coated fabric (1.28 wt%). These results confirm the effective coating of the nanoparticles on the surface of the cotton fabric. The weight gain of the original cotton fabric after being coated with ppy–ZnO and ppy–ZnO–CNT nanoparticles is tabulated in Table 1.

Fig. 4 FE-SEM images with EDAX analyses of the (a) uncoated, (b) ppy-coated, (c) C₃-coated and (d) C₄-coated cotton fabrics.

Table 1 The weight gain of the original cotton fabric and composite-coated cotton fabrics

Sample	Weight gain (%)
Ppy-coated cotton	17.3
C1-coated cotton	18.1
C2-coated cotton	19.3
C3-coated cotton	20.6
C4-coated cotton	21.5

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3.4. TGA-DTA analysis

Flammability is an important issue in the clothing and textile areas as it can lead to bodily injuries and property loss. Flammability of textile products is defined by characterizing their burning behavior, in particular ease of ignition and sustained burning after ignition. The flame retardancy of polymer nanocomposites has been fully investigated based on thermogravimetric analysis (TGA). TGA and DTA curves are shown in Fig. 5a and b. The samples were heated from 0 to 600 °C at a heating rate of 10 °C min⁻¹ under a nitrogen flow rate of 20 mL min⁻¹. TGA curves summarize the thermal degradation of the uncoated cotton and that of the C₃-coated cotton and C₄-coated cotton (Fig. 5a). As seen from the figure, the TGA curves of cotton consist of three regions, 1, 2, and 3, as initial, main, and char decomposition regions, respectively. In the first stage, the changes of the thermal properties and the weight loss of fibers are due to some physical damages occurring mostly in the amorphous region of the cellulose. In this stage mass loss between 50 °C and 205 °C is due to the loss of water and unreacted substances. The main thermal stage occurs in the second region, where the weight loss between 205 °C and 440 °C indicated the decomposition of polymer chains. The weight loss is significant. It is stated by other researchers that glucose together with all kinds of combustible gases are generated in this region.³¹ They found that thermal degradation in this region takes place in the crystalline region of cellulose fibers. The production of char occurs in the third region at a higher temperature of 540 °C. This process is continued further by de-watering and charring reactions, releasing water and carbon dioxide, and increasing the carbon and char residues.³² The sample cross-linked with CNT and BTCA showed higher degradation temperature in the second region. This improvement of thermal properties is attributed to the high heat resistance, the heat insulation effect, and the mass transport barrier toward cellulose molecular chains exerted by the CNT themselves which are a measure of flame retardancy. DTG curve shows that the burning step is broadened by the presence of ppy, and therefore the associated heat of combustion is spread in a wider range of temperatures. These findings point out that ppy alters the combustion process of cellulose, when coated with ppy–ZnO–CNT. Finally, the residual weight at 390 °C for all the coated samples is more than double that for cotton (Fig. 5b).

Fig. 5 TGA (a) and DTA (b) curves of uncoated fabric, ppy–ZnO composite-coated fabric and ppy–ZnO–CNT composite-coated fabric.

3.5. UV-blocking

According to wavelength, UV light can be subdivided into three bands: UVA (320 or 315 to 400 nm), UVB (290 to 315 or 320 nm), and UVC (100–290 nm). Terrestrial solar UV consists of only UV with a wavelength of 290–400 nm, because UVC and some UVB are absorbed by the stratospheric ozone in the earth's atmosphere. Light radiation of wavelength 280–400 nm permits tanning of the epidermis. Rays of wavelength 290–320 nm (UVB) cause erythemas and skin burns, which can inhibit skin tanning. Radiation of wavelength 320–400 nm (UVA) is known to induce skin tanning, but can also cause skin damage, especially to sensitive skin which is exposed to sunlight for a long period of time. Examples of such damage include loss of skin elasticity, the appearance of wrinkles, promotion of the onset of erythemal reaction, and the inducement of phototoxic or photoallergic reactions. In addition, all types of UV can cause a photochemical effect within polymer structures, which can lead to the degradation of some polymers. Obviously, the treatment of textiles with UV-blocking techniques can also improve their service lifetime.

Ultraviolet protection factor (UPF) measurements were made with a Jasco V-670 spectrophotometer, with the aim of determining the transmittance of the UV radiation in the conditioned samples, thus evaluating the UV protection properties. This test provides the average UPF value of the sample, after analysis. UV-blocking properties of uncoated cotton, and ppy-, C₁-, C₂-, C₃- and C₄-coated cotton are shown in Fig. 6 and the values are tabulated in Table 2. UPF was computed using the following equation:

where S_λ is spectral irradiation of the skin in UV region (280–400 nm); E_λ is relative erythemal spectral effectiveness; T_λ is spectral transmittance of the fabric; Δ_λ is an increment relating to wavelength; and λ is wavelength in nanometers.

Fig. 6 Transmittance versus wavelength for differently treated samples in UV analysis. (a) Uncoated cotton, (b) pyrrole-coated cotton, (c) C₁-coated cotton, (d) C₂-coated cotton, (e) C₃-coated cotton, (f) C₄-coated cotton.

Table 2 Effect of ratios of ppy–ZnO and ppy–ZnO–CNT composites coated on cotton for UV protection of uncoated and composite-coated cotton fabrics

Composition	UPF value	UV protection
Uncoated cotton	6	Not considerable
Ppy-coated cotton	13	Not considerable
C1-coated cotton	17	Good
C2-coated cotton	22	Good
C3-coated cotton	28	Good
C4-coated cotton	40	Excellent

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Fig. 6 shows the UV transmission curves of uncoated cotton and coated cotton samples. Fig. 6a indicates that almost 45% of UVA and UVB can penetrate into the uncoated cotton. In samples coated with C₁, C₂, C₃, and C₄ the transmittance values decrease which confirms the presence of UV-blocking material (ZnO nanoparticles) in the coated cotton. These particles are able to absorb wavelengths less than 358 nm. In curve c, a decrease in transmittance (39%) is observed. This may be due to higher possibility of contact between UV wavelength and particles in the presence of BTCA–ZnO molecules.³² Curves d, e and f show decreases in the value of transmittance of 36%, 34%, and 28% respectively. The results show that at high concentration, CNTs can provide perfect UV blocking to the coated cotton fabric. UV-blocking results reveal that when the ratio of ZnO increases, the UV-blocking efficiency also increases. UPF values of 28 and 40 were observed for C₃- and C₄-coated samples respectively.

3.6. Evaluation for flame retardancy

Fig. 7 shows the combustion process of pristine cotton fabric, ppy-coated cotton fabric, and C₃- and C₄ composite-coated fabric. Due to the surface CNT coatings, the color of the treated cotton looks gray. The untreated cotton fabric and the composite-treated cotton samples were hung on a metal supporter, and then the samples were ignited with a lighter simultaneously. As shown in Fig. 7, the untreated cotton sample catches fire immediately and, with the progress of burning, the untreated cotton sample burns to ashes completely. However, the C₃ and C₄ composite-coated cotton did not burn at all and was just charred at the edge, forming a stiff sinter (transfer of CNTs on the cotton substrates was observed during combustion). The results in Fig. 7 provide direct evidence of the flame-retardant effect of CNT on cotton textiles. The results of the vertical flammability test are summarized in Table 3. The results indicate that the performed treatment decreased the flammability of the coated samples. Noticeably, BTCA cross-linked with ppy–ZnO and ppy–ZnO–CNT composite were effective in reducing the flammability of coated fabrics in the presence of SHP. The cotton fabric coated with C₃ and C₄ composite showed decreased char length and increased char yield. These results confirmed the impregnation of phosphorus on coated fabric. The flammability of uncoated and coated samples is compared in Fig. 7. C₄-coated fabric shows low char yield compared to other fabrics due to the uniform deposition of the composite.

Fig. 7 Images of vertical flame testing of the uncoated and composite-coated cotton fabrics (ppy, C₁, C₂, C₃ and C₄).

Table 3 Effect of different ratios of ppy–ZnO and ppy–ZnO–CNT composites on flammability of untreated and treated cotton fabrics

Sample	Flammability (45 °C)
	Char length (cm)	Char yield (%)
Untreated cotton	2.0	85
Ppy-coated cotton	1.9	65
C1-coated cotton	1.5	90
C2-coated cotton	1.0	92
C3-coated cotton	0.5	93
C4-coated cotton	0.4	98

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Table 4 Physical properties of uncoated, and ppy-, C₁-, C₂-, C₃-, C₄ composite-coated fabrics

Specimen	Absorbency (seconds)	Tensile strength (lbf)		Tearing strength (lbf)		CRA (W + F) (°)
		Warp	Weft	Warp	Weft
Uncoated	6	63.5	52.5	3.8	3.2	120
Ppy	6	64.5	53.4	3.7	3.6	121
C1	7	66.5	59.4	3.4	3.1	115
C2	7	65.1	58.7	3.5	3.1	125
C3	8	66.5	59.2	3.7	3.2	135
C4	10	74.5	60.2	3.8	3.3	140

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The efficient composite sols of C₃ and C₄ were applied to military uniform, designated as MC₃ and MC₄ respectively. The char length of uncoated fabric is 7.5 cm and char yield is 72%. MC₃ coating shows a char length of 5.5 cm and char yield of 80%. The char length of MC₄ coating is 3.5 cm and char yield is 68%. This shows it to be more efficient than the other coated fabrics (Fig. 8).

Fig. 8 Images of vertical flame testing of the uncoated and composite-coated cotton fabrics (ppy, MC₃ and MC₄).

Results of Table 3 indicate that the performed treatments decreased the flammability of the treated samples. Evidently, BTCA cross-linked with ppy–ZnO and ppy–ZnO–CNT composite-coated fabric are effective in reducing flammability of treated fabrics in the presence of SHP. Char length of samples was measured in the vertical flammability test and is reported in Table 3. The differences in the burning behaviour and char length in vertical flame test for uncoated sample compared to the composite-coated fabrics are shown in Fig. 7. The results showed that the treatment decreased the flammability of the samples. It can be concluded that increasing the ZnO and CNT ratios leads to a decrease of the fabric flammability (Table 3). It is interesting to note also that the charred surface of the C₃- and C₄-coated samples was very uniform indicating that the nanoparticles uniformly covered the fabric surface.

3.7. Physical properties of the fabrics (Table 4)

Water absorbency of coated fabric was compared to that of uncoated fabric. The absorbency was superior for fabric coated with C₃ and C₄ composites. The tensile strength of C₄-coated fabric with catalyst has enhanced performance compared to the other coated samples. This may be ascribable to the intermolecular and intramolecular crosslinking which reduces the possibility of getting an even stress distribution, causing a reduction in the capacity to resist load. Tearing strength of sample C₃ is improved compared to the uncoated sample. This may be due to the crosslinking ability of BTCA, hindered by the presence of hydroxyl groups in the structure. Sample coated with composite showed a moderate increase in CRA (crease recovery angle) values. CRA of composite sample C₄ reached up to 140°, when compared to uncoated fabric. This shows that the crosslinking effected by the esterification reaction of coated cotton imparted a better crease recovery behaviour. This may be ascribable to the fact that BTCA has one more carboxylic acid group which bonds to the adjacent carbons in the molecular backbones.³³

3.8. Washing stability

From Table 5, the uncoated and C₁-, C₂-, C₃-, and C₄-coated samples show a low char length after the flammability test for all applied washing conditions. After 10 cycles of washing with tap water, these samples show a significantly low char length compared to untreated cotton fabric. Hence these samples were chosen for further thermal decomposition studies.

Table 5 Washing stability of uncoated and composite-coated cotton fabrics

Cleaning agent	No. of washing cycles	Uncoated	Char length (cm)
			ppy	C1	C2	C3	C4
Tap water	5	2.0	1.5	1.6	1.5	1.4	1.9
	10	Char	Char	0.3	Char	Char	0.3
Detergent solution (0.3%)	5	1.5	1.4	1.3	0.5	0.4	1.2

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4. Conclusions

Fabrics coated with composites prepared from carboxylic acids and catalysts without metal oxide were evaluated for flame retardancy. BTCA with SHP as catalyst effectively increased the char formation. Ppy–ZnO and ppy–ZnO–CNT sols were obtained using the sol–gel method and then coated onto cotton fabric using a pad-dry-cure method. The nanoparticles deposited on the fabric surface show stability both before and after washing, which is confirmed through SEM-EDAX analysis. The flammability of C₄-coated fabric was found to be 0.4 cm, which was better than that of uncoated fabric. The UPF value of C₃- and C₄-coated cotton was found to be 28 and 48 respectively. Thus the results obtained suggest that ppy–ZnO–CNT coated cotton fabrics will be promising multifunctional textile materials for military and UV-protection applications.

Acknowledgements

The authors would like to thank the DST PURSE, UGC project (1656/2013) for funding to carry out this research work. The authors are grateful to the School of Physics, Alagappa University, Karaikudi for the provision of XRD analysis.

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