A Smart Cotton Fabric With Temperature Sensitive Moisture Management Property By An N-Vinylcaprolactam Based Polymer Finishing

doi:10.21203/rs.3.rs-1440944/v1

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A Smart Cotton Fabric With Temperature Sensitive Moisture Management Property By An N-Vinylcaprolactam Based Polymer Finishing

https://doi.org/10.21203/rs.3.rs-1440944/v1

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In this study, it was aimed to develop a smart cotton fabric with temperature-sensitive wetting and water vapor permeability management functions. For this purpose, n-vinyl caprolactam (VCL) based poly(2-hydroxyethyl-6-(vinyl amino)hexanoate) (PHEVAH) polymer was synthesized by free radical addition polymerization method. The produced polymer was cross-linked onto the cotton fabrics using 1,2,3,4-butanetetracarboxylic acid. Before the synthesis, VCL was hydrolyzed with ethylene glycol in toluene to open its ring structure and obtain a new monomer with different functional group and molecular weight. The synthesis of the PHEVAH polymer with average molecular weight of 4000 g/mole was confirmed by ¹H-NMR spectroscopy. Its lowest critical solution temperature (LCST) was determined at around 34°C. The surface morphology of the fabrics coated by the polymer were confirmed by SEM images. The temperature-sensitive hydrophilicity and wettability of the fabrics were determined by wetting time and water uptake tests and contact angle measurements. At temperatures above the LCST of the polymer, the hydrophilic character of the fabrics turned to hydrophobic. Their surface contact angles increased and water uptake values decreased. The vapor permeability of the fabrics treated with low concentration polymer was significantly high as compared to untreated fabric. Consequently, the fabrics was able to control water vapor permeability by changing their temperature-dependent hydrophilic/hydrophobic character and porosity resulting from swelling or shrinkage of the polymer molecules. Besides, PHEVAH polymer formed a flexible coating on the fabric surface and did not increase the bending rigidity of the fabrics.

Smart textile

temperature-sensitive polymer

stimuli responsive

cotton fabric.

Today, with the increase in people's living standards, their expectations from textile products are also changing. In parallel with increasing demand, fundamental principles of science are now increasingly used in manufacturing of smart textiles. Smart textiles are defined as textiles which are able to sense and respond to changes in their environment. Some of the type of the smart textiles are fibers or textiles having automatic acclimatizing properties, containing one of the phase change materials, shape memory materials and temperature-sensitive materials. The passive comfort of a standard clothing is regulated by choosing the material and construction and inadequate to manage heat transfer between the body and environment in dynamic environment and at changeable activity levels. The main benefit of the smart textiles with automatic acclimatizing properties is to create a thermoregulation system to cause a change in the thermal comfort properties of the textile in dynamic environment and at changeable activity levels. Thanks to these features, they have become an indispensable especially in products where thermo-physiological comfort is at the forefront such as sportswear, medical clothing and work wear (Jocic 2016; Korkmaz-Memiş and Kaplan 2020).

One of the materials used to fabricate textiles with automatic acclimatizing properties and improve the thermal comfort of clothes is temperature-sensitive or thermo-responsive polymers (Chen et al. 2017; Liu et al. 2014; Wang and Yu 2015; Wang et al. 2020; Xiao et al. 2017). These polymers respond to change in temperature and have a special activation temperature known as the lowest critical solution temperature (LCST). Around the LCST, they undergo a phase transition and their hydrophilic-hydrophobic character changes (Crespy and Rossi 2007; Demirbağ and Alay-Aksoy 2019; Jian and Xu 2014). At temperatures below the LCST, the polymer displays hydrophilic character and soluble in water (swollen state). The water solubility of the most polymers increases as the temperature increases, the temperature-sensitive polymer with an LCST decrease their water solubility as the temperature increases (Xiao et al. 2017). As a result of the swollen polymer molecules on the fabric surface closing the pores of the fabric, the heat transfer is limited in cool environment and is supported keeping the body temperature. However, increased hydrophilicity will also prevent moisture transfer from stopping completely. At temperatures above the LCST, the hydrophobic interactions between polymer molecules increase and the polymer shrinks (shrinkage state), resulting the pores of the fabric surface to open. The moisture transmission ability of the fabric increases. Considering the fabric thermal comfort is directly related to moisture permeability, this reaction of temperature-sensitive polymers to temperature change will significantly improve thermal comfort of the fabrics (Gu et al. 2019). The most common used one of the temperature-sensitive polymers is Poly(N-isopropylacrylamide) (PNIPAM) which has the LCST between 30–32°C (Gautam and Yu 2020). According to the literature survey, the homopolymer or copolymers based on PNIPAM have been applied to the fabrics to enhance the thermo-physiological comfort (Lavric et al. 2012; Lubben et al. 2017; Sun et al.2017; Wang et al. 2017).

Poly(N-vinylcaprolactam) (PVCL) was another important temperature-sensitive polymer type. Although PNIPAM has been commonly chosen, the PVCL is a better alternative due to its higher biocompatibility (Xiao et al. 2017). It has been synthesized as a homopolymer and generally a copolymer and applied to fabrics. Shtanko et al. (2003) realized synthesis of pH and temperature-sensitive poly(vinylcaprolactam-co-acrylic acid) (P(VCL-co-AA)) copolymer in different solvents by free radical polymerization method. In the study, it revealed the compositions and molecular weights of the copolymers synthesized in different solvents were different. Their molecular weights vary between 7500 − 26.400 g/mole and the LCST values vary in the range of 33–35°C. Kozanoğlu et al. (2011) polymerized VCL monomer at different temperatures, 50°C, 60°C and 70°C using AIBN initiator in hexane solvent. The researchers claimed the polymer synthesis took place via the carbon-carbon double bond (C = C) without any change in the caprolactam ring in the structure of the polymer and the LCST value of the polymer changed in the range of 32–34°C. Xiao et al., (2017) prepared poly(vinyl caprolactam-co-hydroxyethyl acrylamide) P(VCL-co-HEAA) polymer by copolymerization of vinyl caprolactam and N-hydroxyethyl acrylamide by free radical solution polymerization. The LCST of the P(VCL-co-HEAA) was 34.5°C. The cotton grafted this copolymer fabric exhibited thermo-responsive behavior and its water vapor permeability decreased at elevated temperature. Sun et al. (2017) synthesized a thermo-responsive copolymer from chitosan based oligosaccharide and VCL by free radical polymerization method. The copolymer was infiltrated into CaCO₃ particles to prepare thermo-sensitive porous microgels containing drug. The microgel was incorporated to the cotton fabric by pad-dry-cure method using citric acid as cross-linker. It was found the microgel-loaded fabrics provided drug release behavior in response to temperature and the drug release increased at temperature above the LCST of the copolymer. Crespy et al. (2009) synthesized the copolymers of the vinyl caprolactam with methacrylic acid and acryloyl chloride by free radical polymerization. The temperature-sensitive properties of the cotton fabrics coated by copolymers were proved by monitoring their swelling in distilled water as a function of temperature. Besides, the values of water vapor permeability for coated fabrics were exceed those of the uncoated fabric at high humidity (80%) and temperature (40°C).

In this study, unlike the literature, a new temperature-sensitive smart polymer based on VCL monomer was synthesized. The synthesized new polymer was applied to the cotton fabric in order to produce a smart fabric with temperature-sensitive wetting and water vapor permeability function. The polymer was synthesized by free radical polymerization of the monomer obtained by hydrolysis of the VCL monomer with ethylene glycol in toluene solution. The synthesis of the polymer was confirmed by ¹H-NMR spectroscopy. The synthesized PHEVAH polymer was applied to the cotton fabric at two concentrations (3% and 5%) by a double-bath impregnation method. To investigate the temperature-sensitive hydrophilic/hydrophobic behavior of the fabrics, the wetting time and water uptake tests and contact angle measurements were done. Besides, the change in water vapor permeability depending on change in temperature was measured at temperatures below and above the LCST. The effect of polymer application on the mechanical properties of the fabrics was measured by tear strength and bending stiffness tests. Besides, durability of the thermo-responsive property of the copolymer-applied fabrics was investigated after repeated washings.

2.1. Materials

VCL (Sigma-Aldrich) was used as monomer to synthesize the temperature-sensitive polymer and ethylene glycol was used to hydrolyze the VCL monomer. 2,2'-Azobis (2-methylpropionitrile) (AIBN) (Sigma-Aldrich) was used as initiator. Toluene was used as solvent in the synthesis of the polymer.

The synthesized polymer was applied to a scoured and bleached, plain weave, 100% cotton fabric having a weight of 151 g/m². The fabric supplied from Söktaş (Turkey) has 61 threads per cm in the warp direction and 38 threads per cm in the weft direction. 1,2,3,4-Butane tetracarboxylic acid (Sigma Aldrich) was used as cross-linker and sodium hypophosphite (Sigma Aldrich) was used as a catalyst. For the cationization process of cotton fabric, Setamordant T (supplied from Setaş (Turkey)) was used as cationizing agent, Triton X 100 (Sigma Aldrich) used as surface active material and sodium hydroxide used to increase the solubility of the cationizing agent.

2.2. Synthesis and characterization of the polymer

VCL based polymer was synthesized by the free radical polymerization method in our previous studies (Demirbağ et al. 2017). During the polymer synthesis, firstly, VCL monomer (1 g) was hydrolyzed in the mixture of ethylene glycol (EG) and monomer (1/1 mol) in 30 ml of toluene solution at room temperature for 5 hours afterward stirring continued at 50°C for 15 minutes. The new monomer named as 2-hydroxyethyl-6-(Vinyl Amino) Hexanoate (HEVAH) using Chemsketch Software was obtained (Scheme 1). Then, the new monomer was polymerized adding AIBN solution in toluene (0.08 g AIBN dissolved in 5 ml toluene) in monomer solution. Prepared solution was poured to test tubes and was degassed with nitrogen for 2 minutes. Polymer reaction was carried out in oil bath at 80°C for 8 hours to obtain powder polymer (PHEVAH) as shown in Scheme 1.

¹H NMR spectroscopy methods was performed to confirm the chemical structure of the synthesized polymer and the molecular weight was measured by cryoscopy method (Demirbağ-Genç and Alay-Aksoy 2021). The ¹H-NMR analysis was carried out on a Bruker 400 MHz instrument and deuterated dimethyl sulfoxide was used as solvent.

The LCST value of the synthesized polymer was determined by monitoring the turbidity of the polymer solution (1% concentration in water) while it heating from 30°C to 40°C with 1°C increment.

2.3. Preparation of the temperature-sensitive cotton fabric

The cotton fabric was pretreated by Setamordant T by exhausted method at 80°C for 40 minutes to cationize the cotton cellulose before polymer application. The pretreated cotton fabric was treated by the polymer using a double bath impregnation method. The fabrics were impregnated by the first bath solution containing BTCA cross-linker and it catalyst SHP and dried at 80°C and cured at 160°C for five minutes. In the study, the BTCA/SHP ratio was selected as 4:1 and 3.75 g BTCA cross-linker per 1 g polymer was used. In the second bath, the pre-treated fabric kept in polymer solution for 1 hour and then passed from the foulard, dried at 80°C and cured at 160°C. In our previous study, the polymer solution with 3% (w/v) concentration was applied to the fabric (Demirbağ-Genç et al. 2019). In this study 5% polymer concentration was applied to the polymer fabric. The fabrics were labeled as CF-PHEVAH-3 (3% polymer content fabric), CF-PHEVAH-5 (5% polymer content fabric). In addition, to examine the effect of BTCA application on the fabric, two different amounts of BTCA used in polymer application were applied to the fabrics and these fabrics were named BTCA-3 and BTCA-5.

2.4. Characterization of temperature-sensitive cotton fabric

Grafting yield of the PHEVAH polymer on the fabric was calculated from Eq. 1. In the Eq. 1, W₁ and W₂ is weight of the fabric sample before and after the grafting process, respectively.

\(\text{G}\text{Y} \text{%} =\frac{\mathbf{W}2-\mathbf{W}1}{\mathbf{W}1}\) Eq. (1)

The morphology, wetting time and temperature-sensitive behaviors of the CF-PHEVAH-3 fabric was determined in our previously study (Demirbağ-Genç et al. 2019). In this study, the same test and analysis were carried out for CF-PHEVAH-5 fabric. Moreover, contact angle measurement, water uptake and vapor permeability tests of the CF-PHEVAH-3 and CF-PHEVAH-5 fabrics were performed to examine the fabric properties related to temperature-sensitive active thermo-physiological clothing comfort.

The morphology of the fabrics was investigated using Scanning Electron Microscopy (SEM, Phillips XL-30S FEG model). Sinking behavior of the fabrics in water at different temperature was examined to investigate temperature-sensitive properties of the fabrics. In the test, the fabrics were left into the water at 20°C and 40°C. The sinking of the fabric to the bottom of the water meant its hydrophilic character, while remaining of the fabric on the water surface demonstrated its hydrophobic character. The temperature-sensitive wetting time of the fabrics was measured according to the AATCC 79 test standard. The contact angle measurements were carried out on the surface of the fabrics whose temperature was gradually rose from 25 to 50°C in the air environment having a relative humidity of 10–25%. Measurements were made by a sessile drop method using a goniometer (Dataphysics OCA 15 plus model instrument) and a CCD camera. The fabric surface temperature was controlled using a Fluke Ti100 Thermal Imager. The temperature-sensitive water uptake property of the fabrics was determined in the temperature range of 25°C to 35°C with a temperature increase of 2°C (Demirbağ and Alay-Aksoy 2019; Kulkarni et al. 2010). The water vapor permeability of the fabrics at temperatures above (40°C) and below (20°C) the LCST of the PHEVAH polymer were investigated regarding to the modified BS 3424 control dish method (Demirbağ and Alay-Aksoy 2019). The fabric samples conditioned under standard atmospheric conditions (20 ± 2°C, 65 ± 4% relative humidity) for 24 h were tested.

In the study, the fabrics were washed ten times at 30°C for 30 minutes according to the TS EN 20105-C06: 2001 standard to investigate the durability of the temperature-sensitive properties of the fabrics against repetitive washes. The water uptake test of the washed fabrics was repeated. Tear strength and bending rigidity tests were performed according to TS EN ISO 13937-2: 2014 standard and TS 1409 standard, respectively. The statistical significance of the test results was evaluated by Tukey HSD (Honestly Significant Difference) Multiple Comparison Test (α = 0.05) with SPSS 20.0 software package.

3.1. Characterization of the PHEVAH polymer

3.1.1.¹H-NMR analysis of the polymer

Chemical structure of the new monomer HEVAH and the polymer PHEVAH synthesized was examined by ¹H-NMR analysis. The ¹H-NMR spectra were shown in Fig. 1. The protons belonging to vinyl groups displayed as "b" and "c" in the molecular formula of the monomer appeared at 4.36 ppm ad 4.59 ppm, respectively. CH₂ groups, indicated by "a" in the molecular formula, appeared at 1.53 ppm in the spectrum. CH₂ groups (e) close to the N-H group were revealed at 1.67 ppm, and CH₂ groups (f) close to the C = O group were revealed at 2.57 ppm. The peak revealed at 7.25 ppm in the spectrum of the monomer belongs to the N-H group (d). While the proton in the alcohol group was seen at 0.9 ppm, the CH₂ groups near the alcohol group (g) were revealed at 3.59 ppm. As seen from the spectrum of the polymer, the peaks of the monomer were displaced in the spectrum of the polymer. Additionally, it was determined that the peaks of vinyl groups did not completely disappear, but their density decreased significantly. The peak that appears at 4.80 ppm in the spectrum of the polymer was the characteristic peak of dimethylsulphoxide used as a solvent for analysis. The findings showed the PHEVAH polymer synthesis was successful even though the synthesized polymer sample containing monomer residue.

3.1.2. Molecular weight of PHEVAH Polymer

The number average molecular weight of the PHEVAH polymer was determined as 4000 g/mole. According to the value, the synthesized polymer was concluded to have low molecular weight.

3.1.3. LCST point of the PHEVAH polymer

The temperature-sensitive polymers are insoluble in water at temperatures above their LCST because of increasing interaction between hydrophobic groups in their molecules. Interaction between their hydrophobic groups causes the phase separation in their aqueous solutions and their solution becomes to be turbidity (Xiao et al. 2017). The temperature at which the aqueous solution of the temperature-sensitive polymer began to cloudy is accepted as its LCST. In the study, LCST values of the PHEVAH polymers were determined by analyzing the images of their aqueous solutions taken at temperatures in the range of 30°C and 40°C. As seen from Fig. 2, turbidity of polymer solution started almost 34–35°C and its LCST value was determined as 34°C, which is close to human body temperature (Demirbağ et al. 2017).

3.2. Characterization of the PHEVAH polymer incorporated fabric

3.2.1. Grafting yield of the PHEVAH Polymer

The amount of polymer applied to the fabric structure was determined as grafting yield. The values were calculated as 11.43% for CF-PHEVAH-3 fabric and 13.34% for CF-PHEVAH-5 fabric. The increase in the polymer concentration applied to the fabric slightly increased the amount of polymer transferred to the fabric.

3.2.2. SEM micrograhs of the PHEVAH incorporated fabrics

The SEM images of the untreated fabric CF-PHEVAH-3 and CF-PHEVAH-5 were given in Fig. 3. According to the SEM images, the surface of the fabrics treated with polymer was covered. However, the coating on the CF-PHEVAH-3 fabric surface was not homogeneous and contained polymer fractions associated with lower polymer concentration. The fiber surfaces on the CF-PHEVAH-5 fabric were smoother and homogeneously coated and the polymeric coating substantially filled the spaces among the fibers.

3.2.3. Temperature-sensitive wetting property of the PHEVAH polymer incorporated fabrics

The temperature-sensitive hydrophility of the fabrics were examined their sinking behavior in the water and the wetting time test. Both untreated fabric and polymer applied fabrics sank in water with 20°C and exhibited hydrophilic character (Fig. 4). Unlike the untreated fabric, polymer applied fabrics suspended on the surface of water at 40°C. Decreasing adhesion force between the PHEVAH polymer and water molecules caused to exhibit the fabric hydrophobic character. This finding was approved by wetting time test. There was no effect of the change in temperature on the wetting time of the untreated fabric and it was determined as 0 s at both temperatures. However, wetting time of the PHEVAH-5 fabric rose from 3 s at 20°C to 47.80 s [with a standard deviation of 3.90] at 40°C, and its hydrophilic character changed to hydrophobic as a function of the increasing temperature. A similar change was also confirmed for fabric with a lower concentration of polymer applique. The wetting time of the CF-PHEVAH-3 fabric was measured as 3.40 s at 20°C and 31.00 s [with a standard deviation of 7.20] at 40°C (Demirbağ-Genç et al. 2019).

In the study, contact angle measurements on the fabrics having different temperatures was also carried out to evaluate their temperature-sensitive wettability behaviors and the results were given in Fig. 5a. The contact angle values of the untreated fabric used as control fabric couldn't measure because of its high hydrophility. The contact angle of the polymer-applied fabrics increased especially between 30–40°C which is around the LCST value (34°C) of PHEVAH polymer. The maximum angle was measured as 64.25° and 49.95° for CF-PHEVAH-3 and CF-PHEVAH-5, respectively. The increase in the contact angles resulting from rising in temperature indicated the wettability decreased. However, it was not high enough to explain the hydrophobic character (θ > 90°) as expected. The reason which the expected high contact angle value could not be reached despite the hydrophilic character of the polymer on the fabric surface was related to the decrease in the surface smoothness of the fabric as a result of the polymer coating. Similar result was obtained for PNIPAM polymer grafted cotton fabric in our previous studies (Demirbağ and Alay-Aksoy 2019; Demirbağ and Alay-Aksoy 2021). Especially with increasing polymer concentration, a smoother surface was obtained, which caused the contact angle of CF-PHEVAH-5 to be lower. Especially with increasing polymer concentration, a smoother surface was obtained, which caused the contact angle of CF-PHEVAH-5 to be lower (Fig. 3).

3.2.4. Determination of the temperature-sensitive water uptake property of the fabrics

Figure 5b shows the water absorption values of the fabrics. In the study, pretreated fabrics (cationized fabric and BTCA applied fabrics) were used as control samples. As seen from the figure, the water uptake values of the pretreated fabrics were not affected by the temperature increase. However, especially at high concentrations, BTCA application significantly reduced the water absorption capacity of fabrics regardless of temperature change (from 110% for cationized fabric to 70% for BTCA 5% concentration). This decrease was a result of the esterification reaction of the free hydroxyl groups interacting with the water molecules in the structure of the cellulose with BTCA (Alay-Aksoy and Genç 2015; Ji et al. 2019).

On the other hand, the sudden decrease in water uptake values of the polymer applied fabrics as a function of the increase in the temperature was observed. The decrease carried out between 29°C and 37°C for the CF-PHEVAH-3 and between 29°C and 33°C for the CF-PHEVAH-5 (Fig. 5b). The lowest water uptake values of the CF-PHEVAH-3 and CF-PHEVAH-5 fabrics at temperatures above LCST were detected as 54.2% and 50%, respectively. In contrast to the pretreated fabrics, the decrease in the absorption capacity of the polymer applied fabric was a result of becoming dominant of hydrophobic groups in the PHEVAH polymer macromolecule above the LCST. This finding indicated the synthesized PHEVAH polymer incorporated cotton fabrics exhibited comparable temperature-sensitive water absorption property to the PNIPAM applied cotton fabric. In our previous study, cotton fabric containing PNIPAM changed the hydrophilic character of PNIPAM around the LCST value. The difference in water absorption ability of low concentration (3%) PNIPAM grafted cotton fabric at temperatures below and above the LCST value was approximately 41%. (Demirbağ-Genç and Alay-Aksoy, 2021) In another study in the literature, the water absorption ability of cotton fabric incorporating 16% concentration poly(2-(2-methoxyethoxy)ethoxyethyl methacrylate-co-ethylene glycol methacrylate decreased by 34.6% (Chen et al. 2017). In this study, this decrease for low concentration PHEVAH polymer-containing fabric was 52%. From these findings, it was concluded that the decrease in the water uptake ability of the fabric due to the increase in temperature was more pronounced compared to other studies.

The water uptake test results after repeated washings were given in Fig. 5c to investigate the durability of the temperature-sensitive properties of the fabrics. As seen from the Fig. 5c, temperature-sensitive water uptake ability of the fabrics was not significantly influenced from repeated washings until 5th wash. The fabrics kept their ability until 5th wash. However, after tenth washing, the difference between water absorption capacity values of the fabrics at temperature above and below the LCST value diminished and their temperature-sensitive water uptake features were weakened.

3.2.5. Determining of the temperature-sensitive water vapor permeability of the fabrics

To investigate the temperature-sensitive water vapor permeability of the fabrics, the water vapor permeability test was performed at 20°C (T < LCST) and 40°C(T > LCST), and the results were presented in Fig. 6. The untreated fabric had the highest water vapor permeability at 20°C. Cationization process and BTCA application caused the decrease in the water vapor transmission of the fabric significantly. Hydrophobic character of the fabric increased by the reduction of the OH groups in the cellulose molecule as a results of the reaction with cationizing agent and BTCA. Additionally, crosslinking of the fibers caused to block the pores of the fabrics resulting hindering the water vapor permeability. However, PHEVAH polymer application on the pretreated fabric caused to increase water vapor permeability of the fabrics. The CF-PHEVAH-3 fabric exhibited statistically the same water vapor permeability as the untreated fabric (p > 0.05). This increasing resulted from the increasing hydrophility of the fabric after polymer application but it limited by fabric pores closed by swelling polymer molecules at higher concentrations (CF-PHEVAH-5).

Above the LCST (at 40°C), water vapor permeability of the fabrics increased because of the evaporation of more water molecules at high temperature compared to the measurement results obtained at 20°C. According to the test results at 40°C, the water vapor permeability of the fabrics treated with BTCA decreased significantly compared to the untreated fabric (p < 0.05) However, polymer application increased the permeability of the pretreated fabrics and tolerated the loss caused by pretreatments. Even, the water vapor permeability of the CF-PHEVAH-3 fabric (5593,00 g/m²/h) increased over the untreated fabric (5104.75 g/m²/h) and the difference was statistically significant. Above the LCST, polymer macromolecules on the fabric returned from swollen state to puckered state and the fabric pores were opened resulting in more water molecules passes through. However, unexpectedly, the water vapor permeability of the CF-PHEVAH-5 fabric was less than the untreated and CF-PHEVAH-3 fabrics. Water vapor permeability is related to porosity and hydrophilicity (Save and Jassal 2005). The smoothly covering the fabric surface by high amount of polymer in the CF-PHEVAH-5 fabric (seen in SEM images) limits the porosity opened by shrinkage of the polymer, resulting in less water vapor transmission.

As a result, the CF-PHEVAH-3 and CF-PHEVAH-5 fabrics exhibited temperature-sensitive water vapor permeability changing their hydrophilic character and porosity as function of temperature. The increasing hydrophilic character and shrinkage of the polymer molecules were key parameter effecting the thermo-responsive water vapor permeability of fabrics. The hydrophilic character of the polymer below the LCST caused to increase the water vapor permeability of the fabrics. The shrinkage of the polymer molecules on the fabric above their LCST increased the porosity of the fabric and accordingly water vapor permeability. In the literature, there was finding that the water vapor permeability of the cotton fabric grafted by poly(vinylcaprolactam-co-hydroxyethyl acrylamide) polymer using BTCA decreased at elevated temperature (Xiao et al. 2017). However, generally the temperature-sensitive polymers including PNIPAM and PVCL and their copolymers provide to increase the water vapor permeability at temperatures above the LCST (Demirbağ and Alay-Aksoy 2019: Demirbağ-Genç and Alay-Aksoy, 2021; Sun et al. 2017). Additionally, in this study it was concluded the low concentration PHEVAH polymer incorporated fabrics exhibited important level higher water vapor permeability property above the LCST compared to untreated fabric. However, other studies concerning thermo-responsive polymer applied fabric reported the water vapor permeability was lower compared to untreated fabric. Here, it was proved the synthesized polymer offers an opportunity to obtain significantly higher water vapor permeability at high temperatures compared to untreated fabric (Sun et al. 2017; Xiao et al. 2017).

3.2.6. Test results of the bending rigidity and tear strength of the fabric

The effect of polymer application on the bending rigidity and tear strength of the fabric was investigated and the test results were given in Table 1. PHEVAH polymer application had no significantly affect the bending rigidity of the fabric (p > 0.05). However, the treatment with BTCA with 5% concentration caused to increase the bending rigidity significantly (p < 0.05) because of limiting the movement of fiber elements cross-linked by BTCA. Nevertheless, the CF-PHEVAH-5 fabric had similar bending rigidity statistically with other fabrics, although the BTCA-5 fabric had statistically highest rigidity. The PHEVAH polymer application resulted in a reduction of the bending stiffness of the fabrics. With this finding, it was concluded that the PHEVAH polymer formed a flexible coating on the fabric surface.

In this study, the effect of polymer application on the fabric tenacity was assessed by tear strength test. Tearing strength is described as the sequential breakage of yarns or groups of yarns. The restricted movement of the yarns in the fabric results in the lower tear strength. On the contrary, loose and open fabric constructions allow yarns to move and group together, resulting in a high tear strength (Eryürük and Kalaoğlu 2015). Additionally, decrease in tear strength may be attributed to acidic pH of the application bath as well as reduced yarn slippage to resist tearing. Normally, bending rigidity and tear strength are related to each other and the increasing bending rigidity causes the yarns to break one by one and reduces the warp tear strength (Bulut and Sular 2015; Kim et al. 2002). However, while the bending stiffness of the PHEVAH-containing fabrics did not increase significantly, the tear strength decreased significantly (p < 0.05). This reduction was associated with reduced yarn strengths due to the acidic pH of the application bath (pH 4).

Table 1

The bending rigidity and warp tear strength test results
Sample	Bending rigidity test results (mg.cm) [SD]	Warp Tear strength test results (N) [SD]
Untreated fabric	170.74 [21.81]	4.94 [0.01]
BTCA-3	193.36 [11.39]	2.51 [0.00]
BTCA-5	209.43 [7.00]	1.98 [0.06]
CF-PHEVAH-3	174.99 [7.22]	1.43 [0.06]
CF-PHEVAH-5	179.57 [18.62]	1.30 [0.07]

In this study, temperature-sensitive VCL-based a new polymer (PHEVAH) was synthesized and coated on the cotton fabric to product smart textile material. The synthesis of the polymer was proved by ¹H-NMR spectroscopy method and its molecular weight was determined as 4000 g/mole. Its LCST was determined as 34°C which was close to the human body temperature.

The polymer was coated successfully on the fabric surface by applying with double bath impregnation method. The polymer layer on the surface of the fabric was proved by SEM images. The fabric test results confirmed their hydrophilic character at temperatures below the LCST turned into hydrophobic at temperatures above the LCST. As a result of the increase in surface hydrophobicity, the contact angle of the fabrics increased at temperatures above the LCST. However, the contact angles were not measured high enough to explain the hydrophobic character due to a smooth polymer layer formed on the fabric surface. In addition, water vapor permeability of the fabrics changed as a function of the temperatures. The hydrophilic character of the polymer at temperature below the LCST caused to increase the water vapor permeability of the polymer incorporated fabrics compared to pretreated fabrics. Even, the water vapor permeability of the lower concentration polymer-containing fabrics was the same value statistically as that of untreated fabric. However, increasing polymer concentration hindered the increasing of vapor permeability because of the closing the fabric pores resulting from swelling polymer on the fabric. In contrast, shrinkage of the polymer molecules on the fabric above their LCST increased the porosity of the fabric and accordingly water vapor permeability. As a results, a new temperature-sensitive polymer for fabrication of smart cotton fabrics with thermally switchable hydrophilicity was synthesized and proved it able to perform adjustable wettability and moisture management depending on variable temperature. However, it was necessary to optimize the amount of polymer applied to the fabric so that the fabrics could perform intelligent moisture method under variable temperature conditions and effectively support the thermal comfort of the garment.

Acknowledgment

This work was financially supported by the Süleyman Demirel University (Project No. 4486-D2-16).

Conflict of interest: The authors declare that they have no conflict of interest.

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Scheme 1 is available in the Supplementary Files section.

Scheme1.png
Scheme 1. Schematic representation (a) and reaction (b) of the hydrolysis of VCL based monomer with ethylene glycol, the molecular structures of the obtained new monomer (c) and the synthesized polymer (d).

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You are reading this latest preprint version

A Smart Cotton Fabric With Temperature Sensitive Moisture Management Property By An N-Vinylcaprolactam Based Polymer Finishing

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Version 1

Abstract

Figures

1. Introduction

2. Experimental

2.1. Materials

2.2. Synthesis and characterization of the polymer

2.3. Preparation of the temperature-sensitive cotton fabric

2.4. Characterization of temperature-sensitive cotton fabric

3. Results And Discussion

3.1. Characterization of the PHEVAH polymer

3.1.2. Molecular weight of PHEVAH Polymer

3.1.3. LCST point of the PHEVAH polymer

3.2. Characterization of the PHEVAH polymer incorporated fabric

3.2.1. Grafting yield of the PHEVAH Polymer

3.2.2. SEM micrograhs of the PHEVAH incorporated fabrics

3.2.3. Temperature-sensitive wetting property of the PHEVAH polymer incorporated fabrics

3.2.4. Determination of the temperature-sensitive water uptake property of the fabrics

3.2.5. Determining of the temperature-sensitive water vapor permeability of the fabrics

3.2.6. Test results of the bending rigidity and tear strength of the fabric

4. Conclusion

Declarations

References

Scheme

Supplementary Files

Status:

Version 1