Effect of Sonication and Nano TiO2 on Thermophysiological Comfort Properties of Woven Fabrics.

The main aim of the present study was to investigate the effects of ultrasonic irradiation on thermophysiological comfort properties of TiO2-coated fabrics. The results were evaluated on the basis of heat and mass transfer as well as air permeability performances. Alambeta, a permetester, an air permeability tester, and a moisture management tester were used for thermal evaluation and air and moisture transportation, respectively. Hundred percent pure cotton and polyester woven fabrics were used for this study. Moreover, the study explains the effect of sonication on surface roughness of textile woven fabrics. TiO2 nanoparticles were deposited onto selected fabrics by sonication. Surface topography, changes regarding surface roughness, and the presence of nano TiO2 were evaluated by scanning electron microscopy (SEM), energy dispersive X-ray (EDX) analysis, X-ray diffractometry (XRD), and inductively coupled plasma atomic emission spectroscopy (ICP-AES). Furthermore, standard test methods were carried out to evaluate physical and overall thermophysiological comfort properties, i.e., thermal conductivity, thermal absorptivity, relative water vapor permeability, absolute evaporative resistance, air permeability, and overall moisture management capacity of TiO2-treated and untreated samples.

Introduction

One of the most desirable and demanding attributes of textile products is thermophysiological comfort that can be evaluated by heat transfer, moisture transportation, and air permeability. This salient feature helps consumers to select an appropriate fabric for wearing under hot and cold climate, respectively. In general, clothing comfort is divided into many categories, but from an experimental point of view, the most important and significantly effective categories are thermophysiological comfort and sensorial comfort. In this study, we focused on thermophysiological comfort properties of cotton and polyester woven fabrics. Dalbaşi and Özçelik Kayseri worked on comfort properties of multicellular linen fabrics subjected to different enzymatic and softening finishing treatments. They proposed that enzyme types had a significant effect on the thermal conductivity of the treated fabrics. Moreover, samples subjected to an enzymatic treatment provided maximum thermal resistance for linen shirt fabrics.[1] Azeem et al. investigated the thermophysiological comfort properties of multifilament polyester fabrics, and their results showed that nanofilament polyester had significantly higher thermal conductivity compared with pure cotton and pure coolmax fabrics. Furthermore, a higher value of thermal absorptivity induced a cool feeling in nanofilament polyester samples, whereas due to low thermal absorptivity, coolmax samples exhibited a warm feeling.[2] In a different study, Arumugam et al. investigated the thermal properties of three-dimensional (3D) warp knitted spacer fabrics. They concluded that thickness of the fabric is the most influential parameter that affects water vapor permeability and thermal conductivity. They further explained that water vapor permeability is a function of fabric thickness and porosity.[3] In another experimental study, Zahra et al. reported results regarding thermophysiological comfort of plain woven fabrics and explained that fabric type and weave structure play major roles in enhancing the comfort of textile products.[4] Mansoor et al. developed a novel method and proposed a mathematical model for the prediction of thermal resistance and other thermophysiological properties of textile knit structures in dry as well as wet states. They prepared plain socks with different fibers and evaluated the results in comparison with the thermal foot model. They explained that moisture content is an important factor for the measurement of thermal conductivity and filling coefficient.[5] Many other researchers worked on thermophysiological comfort of textiles and reported their results in recent years.[6−10]

Titanium dioxide (TiO2) is a widely used material in textile industries for multiple applications.[11−14] TiO2 has been considered as a durable photocatalyst and multifunctional material due to its use in diversified applications ranging from paints to sunscreens, hydrogen storage to dye-sensitized solar cells, and water purification to self-cleaning applications.[15] In recent years, researchers have reported the deposition of nano TiO2 onto different textile substrates for photocatalytic, photovoltaic, and other functional applications.[16−22] The use of ultrasonic energy (sonication) for synthesis and deposition of nanomaterials onto textile substrates has been considered as one of the most economical, facile, and eco-friendly approaches. Sonication is based on the principle of acoustic cavitation. In liquids, ultrasonic irradiations induce physicochemical changes and generate infinite quantity of unstable bubbles. Due to pressure difference, these bubbles violently collapse with each other and produce heat energy with an increase in local temperature and pressure up to 5000 K and 20 MPa, respectively, with a cooling rate of 1010 K s–1. In our previous study, we have successfully synthesized and deposited nano TiO2 onto textile fabrics through sonication.[23] In light of the above discussion, it has to be noted that information regarding the thermophysiological comfort properties of nano TiO2-coated textile substrates is very limited. As far as we searched, no significant literature based on the relationship of ultrasonic irradiations and thermophysiological comfort properties of textile substrates was found. Therefore, we propose a novel study that explicitly describes and elaborates the effects of ultrasonic irradiations and nano TiO2 onto thermophysiological properties of cotton and polyester fabrics. Moreover, we believe that this approach is unique in its scope and can be further extendable for other types of textile substrates.

Results and Discussion

Scanning Electron Microscopy (SEM) and Energy Dispersive X-ray (EDX) Analysis

Figures and 2 illustrate results regarding the morphology and surface topography of untreated and treated samples of cotton and polyester woven fabrics. SEM micrographs were taken at magnification 5.00k and 10.00k times for cotton samples (S1 (untreated) and S3 (treated)) and 250× and 10.00k times for polyester samples (S10 (untreated) and S12 (treated)), respectively. Figures a and 2a show very clean and smooth surfaces of cotton and polyester samples as no treatment was applied on them. Figures c and2c are the higher-magnification SEM micrographs that were taken to visually judge the percentage deposition of nano TiO2 onto treated samples. A homogenous distribution of nano TiO2 and a quasispherical shape of deposited particles was observed during investigation, as depicted in Figures b,c and 2b,c for cotton and polyester, respectively. It was also observed that due to sonication the entire surface of the fabric sample was covered by nanoparticles as the particles overwhelmingly attached with the surface as a thick smooth layer and strongly aggregated.

Figure 1

SEM micrographs for cotton fabric (a) untreated sample S1, (b) sample S3, and (c) sample S3 with higher magnification.

Figure 2

SEM micrographs for polyester fabric (a) untreated sample S10, (b) sample S12, and (c) sample S12 with higher magnification.

Moreover, EDX analysis was carried out to detect elements, their composition, and their weight percentage present in prepared samples. The overall EDX results for samples S1, S3, S10, and S12 for cotton and polyester fabrics, respectively, are illustrated in Figure . The EDX spectrum of samples S3 (Figure b) and S12 (Figure d) confirmed the presence of nano TiO2 in cotton and polyester samples, respectively, whereas no Ti elemental peak was identified in the case of sample S1 (Figure a) and S10 (Figure c) for cotton and polyester samples as no treatment was applied to these samples. Furthermore, a higher weight percentage of Ti element in these samples indicates higher deposition of nano TiO2 over diverse textile substrates, which practically explains the benefits of sonication in textile and materials science. The results achieved by EDX are in good agreement with SEM results.

Figure 3

EDX spectra for cotton fabric (a) sample S1 and (b) sample S3 and for polyester fabric (c) sample S10 and (d) sample S12.

X-ray Diffractometry (XRD) Analysis

XRD is a standard tool to evaluate the crystal structure of samples on the basis of crystal lattice. The collected XRD patterns for all of the selected samples (S3, S6, S9, and S12) confirmed the existence of pure anatase crystals of nano TiO2 in both fabrics. The results showed that all of the obtained peaks under XRD analysis matched with the International Center for Diffraction Data (ICDD) Powder Diffraction File (PDF: 00-21-1272). The highest peak for all of the samples obtained at 2θ = 25.4° is the characteristic crystalline peak for pure anatase TiO2 that follows [101] plane reflection, as presented in Figure . In addition, a series of crystalline peaks at 2θ = 38, 48, 53.8, 55, and 62° follow [004], [200], [105], [211], and [204] planes, respectively. Furthermore, no other phases (impurities), i.e., rutile and brookite, were found during the XRD analysis.

Figure 4

XRD patterns of samples S3, S6, S9, and S12 fabricated by sonication.

Inductive Couple Plasma Atomic Emission Spectroscopy (ICP-AES) Analysis

ICP-AES analysis of samples S2, S3, S5, S6, S8, S9, S11, and S12 confirmed the presence of nano TiO2 onto used cotton and polyester fabrics. However, no traces of TiO2 were found on untreated samples. Moreover, for the absolute amount of nano TiO2 deposited onto investigated materials, the characteristic peak of Ti was counted as observed in emission spectra and results are reported in Table . The total deposited amounts of nano TiO2 for samples S3, S6, S9, and S12 are 990, 965, 972, and 985 ppm, respectively.

Table 1

Constructional Parameters of Used Fabrics in Detail and Results of ICP-AES Analysis

sample ID	composition	weave	TiO2 deposition [ppm]	GSM [g m–2]	thickness [mm]
S1	100% cotton	plain		110	0.25
S2	100% cotton	plain	355	113	0.29
S3	100% cotton	plain	990	116	0.31
S4	100% cotton	plain		224	0.66
S5	100% cotton	plain	370	227	0.68
S6	100% cotton	plain	965	230	0.70
S7	100% polyester	plain		118	0.32
S8	100% polyester	plain	401	122	0.35
S9	100% polyester	plain	972	125	0.38
S10	100% polyester	plain		230	0.66
S11	100% polyester	plain	395	232	0.75
S12	100% polyester	plain	985	235	0.79

Thermophysiological Comfort Analysis

The overall results for thermophysiological comfort properties, i.e., thermal conductivity, thermal absorptivity, relative water vapor permeability, evaporative resistance, air permeability, and overall moisture management capacity of all of the samples with varied amounts of nano TiO2, are presented (see the Supporting Information) and discussed one by one in this section. The discussion regarding the results for all comfort-related properties is a depiction that comfort is a function of thickness, the deposited amount of nano TiO2, and sonication time. Moreover, regression analysis was done to estimate the influential tendency of the investigated parameters on observed responses as well as to assess the strength of their dependency for acceptance or rejection. A regression equation for a linear relationship was derived for each comfort property with its respective coefficient of determination (R2).

Thermal Conductivity

Thermal conductivity is one of the most important, influential, and significant criteria used to estimate thermal comfort of textiles. The results regarding thermal conductivity of all samples (untreated and treated) are presented in Figure a. In general, a higher value of thermal conductivity indicates more heat transfer from skin to fabric surface and eventually provides a cool feeling and vice versa. This condition is ideal for a hot environment especially for summer as a higher value of thermal conductivity makes the phenomenon of heat transfer easier. The values of thermal conductivity were higher for all of the treated samples of cotton fabrics (S2, S3, S5, and S6) and polyester fabrics (S8, S9, S11, and S12) than their respective untreated samples, i.e., S1 and S4 for cotton and S7 and S10 for polyester, respectively, as illustrated in Figure a. The results depict that the applied treatment induced a positive effect on surface porosity of both textile fabrics. The results explain that the deposition of nano TiO2 onto cotton and polyester fabric samples significantly covered the void spaces presented on the surface, which results in reduction of trapped air inside the fiber volume and hence increases the thermal conductivity for all of the treated samples. Second, a higher amount of TiO2 anchored on the surface eventually increased the thickness of treated samples, which provided higher thermal conductivity values as the portion of air reduced. The achieved results for thermal conductivity are in good agreement with the findings of Dalbaşi and Özçelik Kayseri.[1]

Figure 5

(a) Thermal conductivity of all of the tested samples for cotton (S1–S6) and polyester (S7–S12) fabrics. (b) Thermal conductivity of used woven fabrics as a function of thickness.

Figure b explains the results for thermal conductivity as a function of thickness of all of the observed samples. Here, a critical point to be noted for better understanding of this novel study is that thickness itself is a function of the deposited amount of nano TiO2, which means the overall comfort properties are directly related to the anchored nano TiO2 onto fabric samples and the deposition itself is a result of sonication. Therefore, the results related to thickness are elaborated and discussed for the overall thermophysiological comfort properties of used woven fabrics.

The trend line illustrates an increased tendency of thermal conductivity with the augmentation of thickness, as shown in Figure b. The parameters of the regression equation and the value of the R2 coefficient statistically explain the dependency of thermal conductivity on the thickness of observed samples. A strong positive linear relationship and a strong dependency trend was observed for thermal conductivity and thickness of textile substrates. Hence, the investigated woven textile fabrics are the perfect option for summer wear.

Thermal Absorptivity

Thermal absorptivity is another influential parameter and a subject of great interest to evaluate the warm-cool feeling. Generally, a lower value of thermal absorptivity indicates a warmer feeling when a fabric gets in touch with the skin and vice versa. The results regarding thermal absorptivity of all of the samples (untreated and treated) are presented in Figure a. The values of thermal absorptivity were higher for all of the treated samples of cotton fabric (S2, S3, S5, and S6) and polyester fabric (S8, S9, S11, and S12) than of their respective untreated samples, i.e., S1 and S4 for cotton and S7 and S10 for polyester, respectively, as demonstrated in Figure a. These results revealed that treated fabric samples provide a cool feeling on touch. The results are quite obvious as the deposition of nano TiO2 reduced the air gap between the fabric and the skin. So the total area of contact increases, which results in a higher value of thermal absorptivity. The obtained results show a positive impact of the applied treatment on thermal absorptivity of both textile fabrics.

Figure 6

(a) Thermal absorptivity of all of the tested samples for cotton (S1–S6) and polyester (S7–S12) fabrics. (b) Thermal absorptivity of used woven fabrics as a function of thickness.

Figure b explains the results of thermal absorptivity as a function of thickness for all of the developed samples. Here, thickness is a function of the deposited amount of nano TiO2, which means that the overall comfort properties are directly related to the anchored nano TiO2 onto fabric samples. Therefore, thickness results are elaborated and discussed for the overall thermophysiological comfort properties of used woven fabrics. The overall obtained results for thermal absorptivity are in good agreement with the findings of Arumugam et al.[3]

The trend line illustrates an increased tendency of thermal absorptivity with augmentation of thickness, as shown in Figure b. The parameters of the regression equation and the value of the R2 coefficient statically explain the dependency of thermal absorptivity on the thickness of developed samples. A positive linear relationship with a dependency trend was observed for thermal absorptivity and thickness of textile substrates.

Relative Water Vapor Permeability (RWVP)

RWVP is a nonstandardized parameter that has a practical influence on the overall thermophysiological comfort properties of textiles. The closer the RWVP value to 100, the more is the permeability of the substrate. The obtained results for RWVP are illustrated in Figure a. The results explain that an increment in thickness reduced the RWVP value both for cotton and polyester fabrics. In addition, an increment in the mass per unit area for both types of fabric leads to diminution of their respective RWVP. However, a homogenous deposition and longer sonication provided a carrier pathway for water vapor transportation that slightly enhanced the value of RWVP for both fabrics, respectively.

Figure 7

(a) Relative water vapor permeability of all of the tested samples of cotton (S1–S6) and polyester (S7–S12) fabrics. (b) Relative water vapor permeability of used woven fabrics as a function of thickness.

Figure b explains the results of RWVP as a function of thickness for all of the developed samples. The trend line shows a decreasing tendency of RWVP with the augmentation of thickness, as presented in Figure b. The parameters of the regression equation and the value of the R2 coefficient statistically explain the RWVP dependency on the thickness of used materials. A negative linear relationship and a strong dependency trend were observed for RWVP and thickness of the textile substrates. The overall achieved results for RWVP are in good agreement with the findings of Angelova et al.[6]

Absolute Evaporative Resistance (Ret)

The results of absolute resistance of the investigated fabric samples against water vapors are illustrated in Figure a,b, respectively. The results revealed that an increment in thickness of a fabric sample increased the tendency toward augmentation of evaporative resistance for both types of fabric. However, after sonication and TiO2 deposition, a significant diminution was observed for evaporative resistance. These results further enlighten us on the scope of sonication not only for the synthesis of novel materials but also for the enhancement of comfort properties of textiles.

Figure 8

(a) Absolute evaporative resistance of all of the tested samples of cotton (S1–S6) and polyester (S7–S12) fabrics. (b) Absolute evaporative resistance of used woven fabrics as a function of thickness.

Figure b depicts that evaporative resistance is a function of thickness, and the trend line shows an increasing tendency of evaporative resistance with the augmentation of thickness. Parameters of the regression equation and the value of the R2 coefficient statically explain the dependency of evaporative resistance on the thickness of used materials. A positive linear relationship and a dependency trend were observed between evaporative resistance and thickness of the textile substrates. The overall obtained results for evaporative resistance are in good agreement with the findings of Zhou et al.[24]

Air Permeability

Another important parameter to indicate the overall thermophysiological comfort properties of textiles is air permeability as it performs a crucial role in transporting moisture from the human body to the outer or external atmosphere. In general, air permeability of textiles is dependent on the pore size distribution through which air permeation takes place. The results related to air permeability of all samples (untreated and treated) are presented in Figure a. Values of air permeability significantly decreased for all of the treated samples of cotton fabric (S2, S3, S5, and S6) and polyester fabric (S8, S9, S11, and S12) than those of their respective untreated samples, i.e., S1 and S4 for cotton and S7 and S10 for polyester, as illustrated in Figure a. The results revealed that the applied treatment (deposition of nano TiO2) hinders the porosity by accumulating inside the void spaces and blocks the pores. Moreover, the deposition of nano TiO2 onto cotton and polyester fabric samples creates difficulties in the air pathway, which decreases air permeability. The overall achieved results for air permeability are in good agreement with the findings of Shaid et al.[10]

Figure 9

(a) Air permeability of all of the tested samples of cotton (S1–S6) and polyester (S7–S12) fabrics. (b) Air permeability of used woven fabrics as a function of thickness.

Figure b shows the results of air permeability as a function of thickness, and the trend line illustrates a decreasing tendency of air permeability with the augmentation of thickness. Furthermore, parameters of the regression equation and the value of the R2 coefficient statistically explain the dependency of air permeability on the thickness of used materials. A negative linear relationship and a random distribution were observed for air permeability and thickness of the textile substrates.

Overall Moisture Management Capacity (OMMC)

OMMC is another influential indicator and an important parameter for thermophysiological comfort evaluation of textiles. OMMC describes the capacity of a textile substrate to transfer liquid in all of the three dimensions of a substrate. The results for OMMC of all of the samples (untreated and treated) are presented in Figure a. The value of OMMC ranges from 0 to 1, and a higher value (closer to 1) of OMMC indicates better moisture management properties of textiles and vice versa. The values of OMMC were higher for all of the treated samples of cotton fabric (S2, S3, S5, and S6) and polyester fabrics (S8, S9, S11, S12) than those of their respective untreated samples, i.e., S1 and S4 for cotton and S7 and S10 for polyester, as illustrated in Figure a. However, an increment in thickness causes a diminution in OMMC for polyester fabric. The results show that the applied treatment (sonication, deposition of nano TiO2) augmented the positive effect on the moisture management properties of both textile fabrics. The authors precisely explained the benefits of sonication for the synthesis of nanomaterials, photocatalytic applications, polymer composites, and functional textiles in previous studies.[12,22] During sonication, the acceleration of fluid flow inside a fiber’s internal structure and the swelling of the textile substrate due to acoustic cavitation result in better moisture management properties.[12] The overall achieved results for OMMC are in good agreement with the findings of Mishra et al.[8]

Figure 10

(a) OMMC of all of the tested samples of cotton (S1–S6) and polyester (S7–S12) fabrics. (b) OMMC of used woven fabrics as a function of thickness.

Figure b shows the results of OMMC as a function of thickness, and the trend line depicts a slight increase in OMMC with the augmentation of thickness, as presented in Figure b. Furthermore, parameters of the regression equation and the value of the R2 coefficient statistically explain the dependency of OMMC on the thickness of used materials. A positive linear relationship and random distribution were observed for OMMC of the textile substrates.

A twinkling comparison of all of the samples for the overall thermophysiological comfort properties investigated in this study is presented in a spider plot, as illustrated in Figure . The spider plot is based on the original experimental values.

Figure 11

Spider plot for a twinkling comparison of the overall thermophysiological comfort properties of used woven fabrics.

Washing Stability (Reusability)

Finishing applications impart coloring effects to fabrics. Therefore, the durability of simultaneously synthesized and anchored nano TiO2 onto both fabric samples against washing was evaluated according to the ISO 105 C06 (B1M) test method. This approach is used as a direct method to evaluate washing durability. According to this standard, each washing cycle completed with 4 g L–1 detergent at 50 °C for a 45 min time interval. The samples were removed from the solution, and the amount of Ti+4 ions was estimated by ICP-AES analysis. The experiment was repeated for five cycles, and samples were rinsed and dried at 60 °C for 15 min after each washing cycle. In a distinctive process, the total number of Ti+4 ions appearing in the solution was considered as a measure of durability against washing. A higher amount of Ti+4 ions indicates lower durability and vice versa. The maximum contents of Ti+4 ions present in the solution after the fifth cycle were 34, 39, 28, 38, 83, and 78 ppm for samples S2, S3, S6, S8, S9, and S12, respectively. The obtained results are quite positive and reveal that on average only 7% TiO2 was removed from treated samples after the fifth washing cycle, whereas the sample by sample percentages were 9.5% for S2, 3.9% for S3, 2.9% for S6, 9.4% for S8, 8.5% for S9, and 7.9% for S12. These results indicate that nano TiO2 developed by sonication onto different fabric samples was strongly attached to the fabric surface as its minimal quantity was removed even after five washing cycles, as illustrated in Figure . These results confirm the stability and reuse of developed samples for industrial applications.

Figure 12

Reusability and washing stability of different samples.

Conclusions

The aim of this study was to investigate the overall thermophysiological comfort properties of different types of woven fabrics with varying thickness and amounts of nano TiO2 anchored by sonication. The following conclusions were drawn for overall thermophysiological comfort properties of used fabrics on the basis of a comprehensive experimental study significantly based on heat and mass transfer as well as air permeability.

The thickness of fabric is a noteworthy parameter that affects the overall thermophysiological comfort properties, especially thermal conductivity and thermal absorptivity. Moreover, statistically significant results were found for thickness and thermal conductivity with an R2 value of 0.8862. By keeping the comfort feeling of woven fabrics in mind, this result depicts that the applied method (sonication) and deposition of nano TiO2 resulted in improvements in thermal conductivity values as their amount or level increased. In addition, the thermal conductivity of polyester fabric was higher than that of cotton fabric in a parallel comparison of thickness, the deposited amount of nano TiO2, and sonication time.

A remarkable consistency was observed for thermal absorptivity values for untreated and treated samples of both cotton and polyester fabrics. Thickness of the textile substrate played a metaphorical role in the case of thermal absorptivity, as discussed above. The results for thermal absorptivity were statistically significant with an R2 value of 0.4044. The value of R2 is a little lower for thermal absorptivity as an abnormal distribution was observed during regression analysis. Furthermore, these results show that sonication and deposition of nano TiO2 improved the values of thermal absorptivity to some extent.

Surface morphology and structure of the used textiles before and after treatment play a crucial role in determining the overall thermophysiological comfort properties. The behavior of moisture transportation is strongly dependent on porosity. The results of RWVP decreased for both types of fabric as the amount of nano TiO2 and thickness of the fabric increased. The diminution of RWVP was the reflection of lower porosity of treated samples. The results for RWVP were statistically significant with an R2 value of 0.5985. Furthermore, the distribution of nano TiO2 somehow disrupted the porosity and lowered the value of RWVP.

The results of absolute evaporative resistance increased for both types of fabrics as the amount of nano TiO2 and thickness of the fabric increased in contrast to RWVP. However, after sonochemical deposition of nano TiO2, a diminution was observed for both types of fabrics regarding the results of absolute evaporative resistance. The latter result was the effect of sonication as the ultrasonic waves untied the fiber structure and allowed the fluid to pass through. The results for evaporative resistance were statistically significant with an R2 value of 0.4997.

The results of air permeability decreased for both types of fabric as the thickness and amount of nano TiO2 increased. The results for air permeability were statistically significant.

The results of OMMC increased for both types of fabric. However, a decrease in OMMC values for polyester fabric was observed with an increase in thickness. The results for OMMC were statistically significant.

Besides the inspirational findings of this novel and thematic study, there were some other influential parameters of heat and mass transfer, i.e., thermal diffusivity, thermal resistance, heat flux, wetting, accumulative one-way transport index, etc., that could affect thermophysiological comfort to a significant level. Therefore, for a deeper comfort zone, these parameters will be investigated in our future studies.

This study explains that the deposition of nano TiO2 improves the characteristics of different fabrics for better thermophysiological applications. However, this study does not conclude that such modifications are unique for nano TiO2 only. It may be possible that the deposition of other metal oxide nanoparticles brings similar changes to the same fabrics. Therefore, in a parallel study, we are investigating zinc oxide nanoparticles.

Materials and Methods

Materials

For this research, cotton and polyester (100% pure) woven fabrics were used as received from the Department of Material Engineering, Technical University of Liberec, Czech Republic. Titanium tetrachloride (TiCl4) and isopropanol ((CH3)2CHOH) were received from Sigma-Aldrich. These chemicals were used as received without any further processing during the synthesis of nano TiO2.

Physical Testing

Before physical testing, the fabrics were first conditioned at standard atmospheric conditions, i.e., 20 ± 2 °C temperature and 65 ± 2% relative humidity for 24 h in accordance with the standard test method ASTM D 1776-16. The fabric mass, i.e., gram per square meter (GSM), was determined by the standard test method ASTM D 3776. The thickness of the fabric was calculated according to the standard test method ASTM D 1777-96 (2019) with an SDL thickness meter at a pressure of 100 Pa. Details of constructional parameters of all of the fabric samples are presented in Table .

Synthesis and Deposition of Nano TiO2

Nano TiO2 was synthesized and coated onto textile samples according to the same procedure reported in our previous investigation.[12] In this unique study, cotton fabric was immersed in a vessel containing TiCl4, isopropanol, and water under an ultrasonic system (Bandelin Sonopuls HD 3200, 20 kHZ, 200 W, 50% efficiency) to complete the reaction mechanism. TiCl4 was hydrolyzed in the presence of isopropanol and water. The effective power of ultrasonic waves emitted in the solution was 100 W cm–2 experimentally determined by calorimetric measurement. The graphical representation of the proposed mechanism is illustrated in Figure . The simultaneous synthesis and deposition of nano TiO2 onto fabric samples, morphological and topographical changes, as well as surface roughness were evaluated by SEM. UHR-SEM Zeiss Ultra Plus with an accelerating voltage of 2 kV was used for SEM analysis. An EDX spectrophotometer was utilized to evaluate the elemental percentage of the deposited materials on the surface of fabric samples. EDX analysis was performed at a 10 kV accelerating voltage. To confirm the pure anatase crystals of nano TiO2, XRD analysis was performed using an X’Pert PRO X-ray diffractometer under Cu Kα radiation with wavelength λ = 0.15406 nm, with a scanning angle (2θ) range 10–70° and with a step size of 0.02° at a voltage and current of 40 kV and 30 mA, respectively. The obtained results were compared with standard patterns in the ICDD file (PDF: 00-21-1272) for the authenticity of pure TiO2 crystals. The exact amount of nano TiO2 deposited onto fabric samples by sonication was calculated by ICP-AES. PerkinElmer optima 2100 DV was used for ICP-AES analysis.

Figure 13

Schematic illustration of the proposed system and experimental study.

Thermophysiological Comfort Properties

For the thermal conductivity coefficient (λ) [W m–1 K–1] and thermal absorptivity (b) [W s1/2 m–2 K–1] of all of the prepared samples, the Alambeta instrument was used, which was developed by Sensora, Czech Republic. Alambeta measures the thermal properties of a sample in both transient and steady states. Alambeta additionally measures the thickness of a fabric. The working principle of Alambeta is based on the thermal conductivity coefficient that calculates the net amount of heat passing through a material having an area of 1 m2 within 1 s and covering a distance of 1 m with a temperature difference of 1 K. The thermal conductivity coefficient (λ) is calculated by the following equation.In eq , Q represents the net amount of heat flow, h is the sample thickness, A is the cross-sectional area through which heat flows, t is the total time taken for heat flow, and ΔT is the temperature gradient.

Thermal absorptivity (b) is the measure of the warm-cool feeling. Higher thermal absorptivity gives more cool feeling and vice versa when the body gets in touch with fabric. Thermal absorptivity is calculated by eq The permetester was used for the measurement of relative water vapor permeability (RWVP) [%] and absolute evaporative resistance (Ret) [m2 Pa W–1] that play an important role for determining thermophysiological comfort. The permetester is based on heat flux sensing. The experiments for RWVP and Ret were performed through the standard test method ISO 11092-2014. These two parameters evaluate the net water vapor transport capacity of a fabric sample. RWVP is calculated by the following equationIn eq , qf and qo represent the heat loss with and without a fabric sample, respectively, from the measuring head.

Air permeability is a function of porosity of a material. Higher air permeability means that the sample is more porous and vice versa. Air permeability of all of the fabric samples was measured by the SDL ATLAS air permeability tester according to the standard test method ISO 9237-1995. The air pressure for air permeability test was 100 Pa.

The moisture management property, i.e., the overall moisture management capacity (OMMC), is another important property of thermophysiological comfort of textiles. OMMC was measured by an instrument named the moisture management tester (MMT). The AATCC 195-2009 standard test method was followed to investigate the OMMC. The OMMC represents the ability of a textile substrate to deal with moisture.

Statistical Analysis

The results regarding thermophysiological comfort properties of woven fabrics subjected to sonication and incorporation of nano TiO2 were statistically evaluated by regression analysis.