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Synthesis, characterization, and developmentof thermally enhanced cotton fabric usingnanoencapsulated phase change materials containingparaffin waxM. Karthikeyana, T. Ramachandranb & O.L. Shanmugasundaramc

a Faculty of Industrial Safety Engineering, K S Rangasamy College of Technology,Tiruchengode, Indiab Karpagam Institute of Technology, Coimbatore, Indiac Faculty of Textile Technology, K S Rangasamy College of Technology, Tiruchengode, IndiaPublished online: 14 Feb 2014.

To cite this article: M. Karthikeyan, T. Ramachandran & O.L. Shanmugasundaram (2014) Synthesis, characterization, anddevelopment of thermally enhanced cotton fabric using nanoencapsulated phase change materials containing paraffin wax,The Journal of The Textile Institute, 105:12, 1279-1286, DOI: 10.1080/00405000.2014.886368

To link to this article: http://dx.doi.org/10.1080/00405000.2014.886368

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Synthesis, characterization, and development of thermally enhanced cotton fabric usingnanoencapsulated phase change materials containing paraffin wax

M. Karthikeyana*, T. Ramachandranb and O.L. Shanmugasundaramc

aFaculty of Industrial Safety Engineering, K S Rangasamy College of Technology, Tiruchengode, India; bKarpagam Institute ofTechnology, Coimbatore, India; cFaculty of Textile Technology, K S Rangasamy College of Technology, Tiruchengode, India

(Received 27 October 2013; accepted 17 January 2014)

The objective of this study was to develop a thermoregulated cotton fabric using novel nanoencapsulated phase changematerial that contains paraffin wax as core and urea-formaldehyde as the shell material using in-situ polymerizationmethod. The nanocapsules were fixed on the fabric surface using pad-dry-cure method. The morphology and chemicalstructures were measured using scanning electron microscope and Fourier transform infrared spectroscopy, respectively.The thermal properties and stabilities were measured using differential scanning calorimetry and thermogravimetricanalyzer. The fabric properties such as tensile strength, water absorption, and abrasion resistance were also studied. Theaverage diameter of the nanocapsules was found to be 256 nm. The latent heat energy storage capacity of the fabriccontaining 20 and 40 wt.% nanocapsules was 1.52 and 1.91 J/g, respectively.

Keywords: paraffin wax; nanoencapsulation; thermoregulated cotton

Introduction

Exposure to extreme heat results in occupation illnessand injuries such as heat stress, heat exhaustion, heatcramps, and heat rashes. Heat stress is the overall heatburden on the body from the combination of bodyheat generated while working and clothing restrictions(Zheng, Zhu, Tian, Chen, & Sun, 2012). Extreme hotenvironments, where temperature is above 35°C forliving and above 32°C for working lead to heat stress(Tian, Zhu, Zheng, & Nei, 2011; Zhao, Zhu, & Lu,2009). In foundries, steel-mills, bakeries, smelters, glassfactories, and furnaces, extremely hot or molten materialis the main source of heat. Outdoor environmentsinclude construction, oil and gas well operations, andlandscaping also increase the risk of heat stress (Yanget al., 2007). To overcome these problems, researchershave been studying smart textiles or intelligent textiles.Smart textiles are those that can sense and react toenvironmental conditions or stimuli from mechanical,thermal, chemical, electrical, and magnetic sources.Smart textile materials can be classified into passive andactive smart textile materials. Active smart textilematerials that can sense and react to the environmentalconditions are heat storage material, thermoregulatedtextile, heat evolving fabric, water-vapor absorbing, andelectrically heated suits; whereas, passive smart textilescan only sense the environmental conditions (Onofrei,Rocha, & Catarino, 2010). One of the fundamentalfunctions of clothing is to improve the comfort of the

wearers and provide insulation against hot conditions,providing a barrier between the skin and environment.Workers working in hot environments require clothingwith good thermal-regulated properties (Wang et al.,2008).

Phase-change materials (PCMs) can absorb or releasestored energy when the material changes from solid toliquid or vice versa. PCMs can be classified as organicand inorganic. Organic PCMs have more uses because oftheir outstanding properties. Paraffin is the best exampleof organic PCMs. Paraffin as PCMs has attracted moreinterest owing to its high latent heat, due to the fact thatit is chemically inert, nontoxic, noncorrosive, and easilyavailable in the market. Currently, numerous researchgroups have widely studied the thermal properties ofparaffin wax for the development of diverse heat storagematerials (Sarier & Onder, 2012). All these studies haveshown that paraffin wax absorbs, stores, and releases agreat amount of heat repeatedly during phaseconversions between solid and liquid phases. PCM hasbeen used to manufacture thermoregulated textiles toimprove the comfort of the wearer. PCMs are entrappedin microcapsules or nanocapsules to prevent leakageduring melting (Mondal, 2008).

Microencapsulation or nanoencapsulation is aprocess of covering the core material with polymersuch as shell material. The term microcapsules is usedto describe particles with diameter between 1 and1000 μm, whereas particles smaller than 1 μm are called

*Corresponding author. Email: mkk_textile@rediffmail.com

© 2014 The Textile Institute

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nanocapsules or nanoparticles (Sarier & Onder, 2012).The shell materials can be formed by varioustechniques such as in situ polymerization (Jin, Wang,Liu, & Yang, 2008), interfacial polymerization (Chen,Liu, & Lee, 2012), complex coacervation (Uddin, Zhu,& Hawlader, 2002), and spray drying (Borregueroet al., 2011). Among these, in situ polymerization isthe most widely used for the encapsulation of PCMscapable of producing strong capsules and also suitablefor textile applications (Mondal, 2008; Salaün, Devaux,Bourbigot, & Rumeau, 2010a; Zhao & Zhang, 2011).

Shin, Yoo, and Son (2005) successfully synthesizedmicrocapsules using in situ polymerization containingn-eicosane and melamine-formaldehyde as the core andshell material, respectively. The result showed that theparticle size was 1.89 μm. Sarier and Onder (2007)prepared microcapsules containing urea-formaldehyde(UF) as shell materials with different core materials suchas n-hexadecane, n-octadecane, and n-eicosane. The resultshowed that the microcapsules containing n-eicosane andn-hexadecane were 69.1 μm and their latent heat storagecapacities were 51.7 and 54.8 kJ/kg, respectively. Fang,Chen, and Li (2010) fabricated microcapsules containingparaffin and silicon dioxide (SiO2) as the core and shellmaterial, prepared through Sol–Gel method. The scanningelectron microscope (SEM) results showed that paraffinwas encapsulated in the shell of SiO2. The differentialscanning calorimetry (DSC) results showed that the latentheat of microcapsules was 165.68 kJ/kg. Li, Zhang, Xu,and Zhang (2007) synthesized nanocapsules usingminiemulsion polymerization containing n-hexadecaneand UF as the core and shell material, respectively. Theaverage size of the nanocapsules was 270 nm and thelatent heat increased from 114.6 to 143.7 kJ/kg, whichrelated to the amount of surfactant.

Nanoencapsulated PCMs have attracted moreresearchers recently. Nanoencapsulated PCMs havepotential applications in textiles and in the manufactureof thermoregulated fibers and fabrics (Sarier & Onder,2012). The encapsulated PCMs have been applied to thetextile materials using various methods such as coating,laminating, finishing, and foam manufacturing (Mondal,2008). Salaün, Devaux, Bourbigot, and Rumeau (2010b)produced microPCMs using in situ polymerizationcontaining 77 wt.% of n-hexadecanol/n-eicosane binarymixtures in the core. The prepared microPCMs wereincorporated into cotton fabric using polyurethanebinder. The result showed that the treated cotton fabricusing polyurethane binder had good thermoregulatingproperties during the first 30 s with altering thepermeability. Sánchez, Sánchez-fernandez, Romero,Rodríguez, and Silva (2010) prepared microcapsulescontaining paraffin wax as core and polystyrene as theshell material using suspension-like polymerization andincorporated into the fabric structure using binder. The

results showed that the coated textile materials with35 wt.% microcapsules had higher latent heat capacity.

In this study, we first aimed to prepare thenanoencapsulated PCM using in situ polymerizationcontaining paraffin wax and UF as the core and shellmaterials, respectively. The prepared nanocapsules coatedon the cotton fabric with 20 and 40 wt.% nanocapsules(which related to the binder agent); the thermoregulationproperties of the cotton fabric after coating were alsoinvestigated. Furthermore, tensile strength, waterabsorption, and abrasion property were also studied.

Experimental

Materials

Paraffin wax was used as the core material (Hi-Media,Mumbai). Urea (Hi-Media, Mumbai) and Formaldehydeof 37–41 wt.% (Merck, Mumbai) were used as theshell-layer. Sodium dodecyl sulfate (SDS) supplied byHi-Media with purity 99%, was used as emulsifier.Sodium hydroxide (purity-97%) (Sigma-Aldrich) andpolyvinyl alcohol (purity-99.9%) (Sigma-Aldrich) wereused as pH controller and stabilizing agent, respectively.Hydrochloric acid supplied by Sigma-Aldrich with purityof 35% was used as activator.

Preparation of the nanocapsules

Nanocapsules containing paraffin wax and UF polymerwere prepared by in situ polymerization method. In thismethod, the pre-polymer solution was prepared by adding24 g of urea and 14.8% formaldehyde into 100 mL water.The mixture was stirred and adjusted to pH 8.5–9 with anaqueous solution of 10% sodium hydroxide. The mixturewas then continuously stirred at 70–75°C for 1 h toprepare the pre-polymer solution. Next, 16 g of paraffin,2.9 g/L of SDS, and 100 mL of water were emulsifiedmechanically at 80°C with a stirring rate of 2500 rpm for45 min. Subsequently, 1.8 g/L of PVA was added to themixture to stabilize the emulsion. Finally, the preparedpre-polymer solution was added to the above emulsion,and the emulsion mixture was stirred at a rate of 1000rpm. The pH was reduced to the range of 5–5.5 by addingdilute hydrochloric acid into the mixture. The mixture wasagitated continuously at a stirring rate of 600 rpm for 1 h,and the temperature was slowly reduced to 35°C. Theresulting nanocapsules were filtered, washed, and dried inan oven at 70°C for 8 h to remove water.

Coating the nanocapsules onto the cotton fabric

A 100% cotton fabric was used as the textile material.The properties of the cotton fabric are given in Table 1.The fabric was bleached with 0.2 g/L H2O2, washed, anddried in an oven at 50°C for 20 min. The prepared

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nanocapsules contain two different compositionsincluding 20 and 40 wt.% nanocapsules related to binderagent that were added onto the textile material usingpad-dry-cure method. The treated fabric with 20 wt.%nanocapsules is coded as ncf1 and 40 wt.% is coded asncf2. The coating compositions were stirred for 1 h at800 rpm. The cotton fabric is cut to the size of 40 × 40cm was soaked into the coating materials for 10 min andthen, passed through a padding mangle at a speed of 20m/min. The pressure of 5 kgf/min was maintained toremove excess solution (Karthikeyan, Ramachandran, &Shanmugasundaram, 2013). The fabric was conditionedfor 24 h prior testing (24°C and 65% RH) and paddedwith an expression of 80% wet pickup, dried at 80°Cwith speed of 25 m/min, and cured at 120°C with speedof 35 m/min for 3 min. The nanocapsules were fixedonto the cotton fabric using a polyurethane bindingagent. The polyurethane binding agent helps to firmlybinding the nanocapsules with cotton fabric. Thenanocapsules were mixed with polyurethane bindingagent at 30°C using mechanical stirrer.

Testing of textile materials

The tensile strength and extension at maximum load ofthe fabric were measured using an Instron 3360 seriestensile tester in accordance with ISO 13934. The size ofthe test samples was 60 × 300 mm. In this test, fivesamples were tested both in warp and weft direction.The samples were conditioned for 24 h prior to testingand maintained at temperature of 20°C and 65% RH.Tensile test was carried out at a gage length of 100 mmwith strain rate of 50 mm/min.

The water absorbency property of the samples wascalculated by the time taken for the fabric to absorb adrop of water as per AATCC 79 standard (2010). Thesample was cut to a size of 200 × 200 mm and mountedon an embroidery hoop such that the side of the sampleto be tested was face up and free from wrinkles. In thistest, the nozzle of a burette was placed 10 ± 1.0 mmabove the specimen surface and one drop of distilledwater was allowed to fall on the cloth. Then, the time

taken for the drop of water to be completely absorbed,that is, the time taken for the drop of water to lose itsreflectivity, was calculated. Three samples were testedand averaged the readings.

The abrasion resistance test was carried out using anabrasion resistance tester (Martindale method) inaccordance with EN ISO 12947. The size of the testsamples that were used was 38 mm in diameter. Threesamples were prepared and averaged the readings. Thetest specimen was placed face down into the base of thespecimen holder. The test was carried out until twoseparate threads were completely broken down.

Characterization

The morphology and particle size of the samples wereanalyzed using SEM. The SEM measurements wereperformed using a Quanta 200 FEG-SEM. All thesamples were coated with conductive layer such as goldto prevent charging of nonconductive cotton fabrics. Theparticle size of the nanocapsules was measured usingparticle size analyzer (Nanophox, 1–1000 nm). FTIRspectra of the paraffin and nanoencapsulated paraffinwere recorded using FTIR spectrometer with thescanning range 4000 and 500 cm−1 (IR Affinity-1,DLATGAS; Shimadzu) at 60°C using KBr pellets. TheKBr disks were made by pressing the mixture, whichcontained 10 mg of samples with 100 mg of KBr at apressure of 125 kg/cm2. The total number of scans was32 and background was scanned with scanning conditionresolution of 1 cm−1. DSC measurements of thenanocapsules and treated samples were carried out usingNETZCH DSC 204 and the enthalpy was measuredbetween 0 and 120°C with a scanning rate of 10 and30°C/min, respectively. The thermal stability of thenanocapsules was evaluated using a thermogravimetricanalyzer (TGA; Diamond; Perkin–Elmer, USA) with ascanning rate of 10°C/min and temperature range from 0to 800°C under nitrogen atmosphere.

Results and discussion

Morphological analysis and particle size of thenanocapsules

The surface morphology of the nanoencapsulated PCMwas obtained using SEM, as shown in Figure 1.Figure 1(a) shows the core material such as paraffinwax before encapsulation. The nanocapsule showssmooth surface and spherical shape, as shown inFigure 1(b) and (c). It can also be seen from the SEMimages that nanocapsules are partially agglomerated.The SEM images reveal that the UF shell materialencapsulated the paraffin wax and prevents the leakageof the melted paraffin. From Figure 2, the average

Table 1. Fabric properties.

Properties Particulars

Fabric type Plain weaveEnglish count (Ne) Warp 40

Weft 40Fiber analysis Warp 100% cotton

Weft 100% cottonEnds/Inch 131Picks/Inch 71Areal density (g/m2) 141 ± 2.55Fabric thickness (mm) 0.33 ± 0.00816

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particle size of the nanocapsules was found to be256 nm. The size of the nanocapsules is within a rangeof 200–400 nm. The prepared nanocapsules also showbimodal distribution compared to the SEM images.

FTIR analysis of the nanocapsules

The FTIR spectra of the paraffin wax and nanocapsulesare shown in Figure 3. The absorption peak at 1466 cm−1

is attributed to the C–H bending, the multiple absorptionpeaks around 3000–2800 cm−1 are associated with thealiphatic C–H stretching vibration and the absorption peak

at 720 cm−1 is assigned to the group of CH2 inplanevibration (Figure 3(a)). These characteristic peaksrepresent the core material, the paraffin wax. The

Figure 1. SEM micrographs of paraffin wax (a); nanocapsules (b), and (c).

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Figure 3. FTIR spectra of (a) core material and (b)nanocapsules.

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absorption peak at 1645 cm−1 is attributed to the–C=O stretching vibration, and the absorption peak at1550 cm−1 is assigned to the group of –C–N– stretchingvibration (Figure 3(b)). These are characteristic peaksassigned to the UF shell materials conforming that theparaffin wax was well encapsulated in the shells of UFpolymers (Zin, Wang, Liu, & Yang, 2008).

Thermal properties of the nanocapsules

The thermal properties of the nanocapsules wereevaluated using DSC instrument. The DSC curve of thenanocapsules is shown in Figure 4. From Figure 4(a)and (b), the first phase change peak that occurs at about48.3 and 46.2°C corresponds to the solid–solid phasetransition, whereas the second phase change peak atabout 68 and 64.3°C correspond to the solid–liquidphase transition. The latent heat enthalpy of the paraffinwax and nanocapsules was 154.2 and 74.2 J/g. It wasimportant to note that the melting point temperature ofthe nanocapsules is close to that of the paraffin. Hence,it indicates that the shell layer of nanocapsules do notinfluence the properties of the phase change behavior ofparaffin.

The encapsulation ratio of the resultant nanocapsulescan be calculated using the following Equation (1)(Alkan, Sari, & Karaipekli, 2011):

Encapsulation ratio ¼ DHnanocapsules

DHparaffin� 100; (1)

where ΔHnanocapsules and ΔHparaffin are the enthalpy ofprepared nanocapsules and paraffin wax, respectively.Then, the encapsulation ratio was found to be 48%. TheUF shell wall can be successfully utilized to encapsulatethe PCM to absorb latent heat energy. Therefore, thenanoencapsulated PCM helps to prevent the liquidleakage of the paraffin wax during the phase transitionfrom solid to liquid at 64.3°C.

Thermal stability of the nanocapsules

The thermal stability of the nanocapsules was evaluatedby using TGA instrument. Figure 5 shows the TGAcurves of the paraffin wax and nanocapsules. Thenanocapsules show two-step degradation, whereas thecore paraffin materials showed single-step thermaldegradation. The nanocapsules exhibited a 78% firstmass loss peak between 205 and 420°C and a 16%second mass loss peak occurred between 420 and 613°C.The weight loss of 1.34% occurred at 250°C and suddenweight loss between 250 and 400°C were observed forparaffin wax, shown in Figure 5(a). The weight loss ishigher for nanocapsules upto 400°C compared with theparaffin wax. After 400°C, the second-step thermaldegradation starts and shows lower weight losscompared to the paraffin wax (Figure 5(b)). This findingis due to the influence of the shell material and showsgood thermal stability compared to the paraffin wax.

Morphology of the treated fabrics

The SEM images of untreated and treated cotton fabricsare shown in Figure 6. Figure 6(a) shows themorphology of the untreated cotton fabrics. InFigure 6(b) and (c), SEM images show nanocapsulesdistributed homogenously over different locations on thecotton fabrics. The coated nanocapsules have a smoothand regular surface that coated the surface of the fabric.

Testing of nanocapsules coated fabric

The tensile strength measurements of the treated anduntreated fabric are given in Table 2. The maximum loadand tensile extension at maximum load of the fabricwere also observed and recorded. The tensile strength ofthe treated fabric ncf1 decreased compared with theuntreated fabric. The treated fabric ncf2 shows increasedtensile strength compared with the treated fabric ncf1.This may be attributed to the presence of 40 wt.%nanocapsules related to binder agent on the coatedfabric. In general, the addition of the chemical finishesto the cotton fabric resulted in deterioration of the tensilestrength of the fabric. The tensile strength of the treated

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Figure 4. DSC curves of (a) core material and (b)nanocapsules.

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sample ncf2 and ncf1 had decreased strength comparedto the untreated fabric. This may due to the addition ofthe coating materials. The extension at maximum load ofthe treated sample ncf1 and ncf2 does not showconsiderable changes compared to untreated fabric.

The water absorbency measurements of the treatedand untreated fabrics are shown in Figure 7. Theuntreated fabric had more time to absorb water. Thismay be due to the fact that the untreated sample hadmore protruding fibers on its surface. The treated fabricshowed quick water absorption characteristics than theuntreated fabric. This finding is due to the polar OHgroups present in the cellulosic cotton that make theuntreated fabric more hydrophilic than the fabrics treated

with hydrophobic nanocapsules. The treated fabric ncf1took more time to absorb water compared to the treatedfabric ncf2. This may be attributed to the highconcentration nanocapsules with related to the binderagent in the treated fabric ncf2.

The abrasion resistance measurements of the treatedfabrics are shown in Figure 8. The test was conducted todetermine the mass loss after 10,000 cycles and alsountil the fabric threads on the abraded surface brokedown. The results show that there is obvious differencein mass loss between treated fabric ncf1 and ncf2. Thelowest mass sample loss occurred for the treated fabricncf2 compared to other treated fabric. The treated samplencf2 were abraded after 11,000 cycles, whereas thetreated fabric ncf1 and untreated fabric were abradedafter 10,000 cycles. This is due to the high amount ofloaded nanocapsules related to the binder agent.According to the results, treated fabric ncf2 shows gooddurability and had more uniform surface compared to theother treated fabric and untreated sample.

Thermal properties of the nanocapsules treated fabrics

The thermal properties of the treated fabrics wereevaluated using DSC instrument. The phase changeproperties of the treated fabrics are shown in Figure 9.The melting temperatures and the latent heats of meltingof the treated fabrics are summarized in Table 3. Thelatent heat of the treated fabric is different due to theamount of nanocapsules increased from 20 to 40 wt.%related to binder agent. The latent heat energy storagecapacity of the treated fabric ncf1 and ncf2 was 1.52 and1.91 J/g, respectively. The treated fabric ncf1 shows

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Figure 5. TG curves of (a) core material and (b)nanocapsules.

Figure 6. SEM images of (a) cotton fabric, (b) nanocapsules coated fabric (ncf1), and (c) nanocapsules coated fabric (ncf2).

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lower latent heat energy storage than the treated fabricncf2. Compared to the previous study (Karthikeyanet al., 2013), the thermoregulated property of treatedfabric was higher than the untreated fabric, when thenanocapsules were prepared through the same route withpolyethylene glycol as core and UF as shell material.But, the latent heat capacity of treated fabrics wasenhanced compared to untreated fabric. This resultshowed that the latent heat storage capacity of thethermo-regulated textiles depends on the amount of thenanocapsules added onto the fabric and the amount ofnanocapsules added on the fabric with nanocapsule/binder ratio. The latent heat of the textile decreased asthe amount of the nanocapsules decreases. In addition,the latent heat energy storage value can be improved

through selection of core and shell material, amount ofsurfactant, and stirring rate.

Conclusion

Firstly, nanoencapsulated paraffin wax was successfullyprepared using in situ polymerization method. Theprepared nanocapsules showed smooth and regularsurface. The average diameter of the nanocapsules wasfound to be 256 nm. The latent heat enthalpy and themelting temperature of the nanocapsules were 74.2 J/gand 64.3°C, respectively. The nanocapsules exhibitedgood thermal stability. Secondly, the preparednanocapsules were coated on the cotton fabric usingpad-dry-cure method. The latent heat energy storage

Table 2. Tensile strength properties of untreated andnanocapsules treated fabrics.

Sample codeTensile

strength (N)Tensile extension atmaximum load (mm)

ncf1 263.3 ± 0.2 22.9 ± 0.01ncf2 282.1 ± 0.1 23.4 ± 0.12Untreated fabric 283.4 ± 0.49 22.3 ± 0.05

Figure 7. Water absorbency rate of untreated and treatedfabric.

Figure 8. Mass loss of the treated fabrics against abrasion.

Delta H= 1.91 J/g Peak = 55.45°C

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Figure 9. DSC curves of nanocapsules treated fabric (a) ncf1and (b) ncf2.

Table 3. Thermal properties of the treated fabrics.

Sample Onset point (°C) Tm (°C) ΔHm (J/g)

ncf1 42.37 55.2 1.52ncf2 40.2 55.45 1.91

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capacity of the treated fabrics ncf1 and ncf2 was 1.52and 1.91 J/g, respectively. The results showed thattreated fabrics had average tensile strength, quick waterabsorption, and were more resistant to abrasion. Further,the treated fabric with 40 wt.% nanocapsules is suitablefor developing thermoregulated cotton fabric againstthermal hazards. Finally, the treated fabrics withnanocapsules enhance the capacity of thermoregulatedproperty compared to untreated fabric.

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