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Article

Wear-Resistant Hydrophobic Coatings from Low Molecular Weight Polytetrafluoroethylene Formed on a Polyester Fabric

by
Natalia P. Prorokova
*,
Tatyana Yu. Kumeeva
and
Igor V. Kholodkov
G.A. Krestov Institute of Solution Chemistry of the Russian Academy of Sciences, 153045 Ivanovo, Russia
*
Author to whom correspondence should be addressed.
Coatings 2022, 12(9), 1334; https://0-doi-org.brum.beds.ac.uk/10.3390/coatings12091334
Submission received: 26 July 2022 / Revised: 2 September 2022 / Accepted: 6 September 2022 / Published: 14 September 2022
(This article belongs to the Special Issue Efficiency of Coatings Formed in Various Ways)
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Abstract

:
The paper presents a comparative analysis of the surface structure and morphology of hydrophobic coatings formed on a polyester fabric from various types of low molecular weight tetrafluoroethylenes by a new method. The low molecular weight compounds used include: ultrafine polytetrafluoroethylene of the FORUM® trademark prepared through thermo-gas-dynamic decomposition of industrial polytetrafluoroethylene waste, and tetrafluoroethylene telomers, synthesized by radiation-chemical initiation from fluoromonomers in acetone, butyl chloride and trimethylchlorosilane solutions. The formation of coatings consists in deposition of low molecular weight tetrafluoroethylenes from solutions in supercritical carbon dioxide and organic solvents. The contact angle and water absorption of the polyester fabric with coatings containing the specified water-repellents are determined. The resistance of the achieved effect to various types of wear—washing, dry cleaning and abrasionis evaluated. The hydrophobic properties of the fabric are found to be affected by the coating plasticity characterized by the stiffness coefficient. The importance of this indicator to targeted changes in fabric properties is proved. All the considered types of low molecular weight polytetrafluoroethylene (PTFE) are shown to be effective water-repellents for the polyester fabric.

1. Introduction

Achieving high hydrophobicity in fabrics is a difficult problem, both in theory and in practice. Wetting of fibers and fabrics made from them obeys theoretical regularities characteristic of all materials [1,2,3,4,5]. According to them, hydrophobic fabrics are expected to have the lowest possible surface energy and multimodal roughness that can ensure homogeneous wetting of the surface. The surface energy can be lowered by changing the surface chemical composition. The most common way to do that is to cover the fabric surface with a coating formed by a substance with lower surface energy (a water-repellent). The multimodal roughness is usually achieved by texturing the fabric surface.
However, multimodality plays a bigger role in fabrics than in other materials. Fabrics are known to be made of interwoven yarns of cylindrical shape. It means the surface of a fabric consists of numerous convex elements.
Work [6] reports that cylindrical surfaces have a bigger contact angle than flat ones. Besides, the authors of [4,7] established that due to its complex structure of interwoven yarns, a fabric can be assumed to possess multimodal roughness. These factors facilitate fabric hydrophobing.
However, requirements for consumer properties of finished fabrics make it more difficult to solve the problem of providing fabrics with water-repellent properties. For example, after hydrophobing, fabrics must remain breathable, i.e., retain their high air- and vapour-permeability values. It means that a coating formed by a water-repellent must only cover the surface of the yarns without filling the space between them. However, hydrophobing must not make the fabric too rigid. This sets additional requirements for the stiffness of a water-repellent-based coating, a parameter that characterizes its plastic properties [8]. A prerequisite is also the resistance of the achieved effect to severe wear-abrasion, washing, and dry cleaning, i.e., the coating adhesion to the fibrous material must be high. Besides, works [9,10,11] show that the most important feature of fabric hydrophobicity is low water absorption—the sample ability to absorb liquid when fully immersed in water for an hour. It is evident that low water absorption of a fibrous material can be ensured if the coating does not have defects that would let water in. Therefore, high performance of a fabric can be preserved during its treatment with water-repellents if the surface of every yarn is covered with a coating of moderate stiffness and high adhesion to the fiber. The coating formed must be uniform and defect-free. Besides, to ensure that the fabric multimodality continues to affect the fabric wetting process, the coating must reproduce the micro- and nanorelief of the fiber, i.e., must be ultrathin. But the main requirement for water-repellents is low surface energy.
The lowest surface energy is characteristic of polytetrafluoroethylene coatings; however, their formation on a fabric is still technologically unfeasible. Other fluorine-containing compounds have a little higher surface energy [12]. In the past, the most common industrial water-repellents were perfluorooctanoic acid derivatives. But these compounds were found potentially carcinogenic [13]. And restrictions on their use were imposed. However, there are a large number of other fluorine-containing compounds that can be used as fabric water-repellents. For example, in works [14,15], highly hydrophobic coatings are made from fluoroalkylsilane-based compounds and in [16,17] from polytetrafluoroethylene-based ones. However, all these water-repellents are insoluble in water and, hence, are mostly deposited on a fabric in the form of emulsions or dispersions. This deposition method produces thick nonuniform coatings with a lot of defects. Although the processed fabric has high contact angle values, the effect achieved is metastable as the fabric does not have low water absorption. The coatings formed are not sufficiently resistant to wear either.
The authors of this article proposed a new method of production of high quality hydrophobic fabrics. It consists in the formation of a fluorine-containing coating on a fabric from solutions in non-traditional solvents rather than from emulsions or dispersions [18]. To minimize the surface energy of the fibrous material, we used polytetrafluoroethylene as a water repellent. Since high molecular weight polytetrafluoroethylene is insoluble in all solvents, it was suggested to use low molecular weight tetrafluoroethylene as the water-repellent. It represents tetrafluoroethylene oligomers capable of forming coatings on the fiber surface and providing them with properties similar to those of polytetrafluoroethylene [18,19,20].
There are two approaches to obtaining tetrafluoroethylene oligomers soluble in a number of solvents and possessing film-forming properties. The first one consists in thermo-gas-dynamic decomposition of industrial polytetrafluoroethylene waste [21]. The obtained ultrafine polytetrafluoroethylene (UPTFE) of the FORUM® trademark consists of a mixture of perfluorinated linear –CF2– chains with the average number of links n~100. It contains low and high molecular weight fractions [21]. Its low molecular weight fractions contain, on average, 10–20 monomer units and dissolve in supercritical carbon dioxide (SC-CO2) [22]. SC-CO2 was selected as the medium for hydrophobing the fabrics due to its unique set of properties. Its dissolution and transport properties, ability to be totally removed from the fabric after the process is completed, and low critical parameters together with relative inertness make SC-CO2 a medium suitable for realizing a number of finishing treatment processes in textile fabrics [23,24,25,26,27]. SC-CO2 leads not only to high solubility of hydrophobic compounds but also to absolute surface wettability of hydrophobic polymer materials.
Another way to produce tetrafluoroethylene oligomer solutions capable of film formation is their synthesis from fluoromonomers by telomerization. Telomerization is a special type of polymerization realized in the presence of compounds (telogens)—effective chain transfer agents that act as solvents at the same time [28]. One of the most important telomerization methods is radiation-induced telomerization [28]. The application of initiation γ-radiationallows telomerization to be realized at room temperature without introducing special reaction initiators or catalysts into the system. In this case, the reaction is initiated by radicals formed under the action of the solvent (telogen), in which the synthesis is carried out. The use of different telogens in radiation-induced telomerization is known to produce different hydrogen-, oxygen-, chloro- and bromine-containing end groups that largely determine the properties of the obtained telomers (solubility, adhesion, hydrophobicity, abrasion resistance and others). Changing the synthesis parameters (telogen, monomer concentration, and radiation dose) makes it possible to obtain telomers with the chain length from several units to hundreds of units [20,29,30]. Works [11,18,20,30,31,32,33,34,35,36,37] show that tetrafluoroethylene telomers synthesized and dissolved in acetone, butyl chloride and trimethylchlorosilane with the chain length of 20–30 monomer units possess a combination of film-forming properties, good adhesion and high thermal stability. These properties of the telomers make them promising water-repellents for fibrous materials.
Radiation-induced telomerization of TFE in solvents leads to the formation of telomers with the common formula R1–(TFE)n–R2, where n is the chain length, R1 and R2 are the end groups representing solvent molecule fragments. When telomers are synthesized in acetone (C3H6O), the end groups can be H, CH3, COCH3 and CH2COCH3 [38,39], in butyl chloride (CH3(CH2)3Cl)–H, Cl, and C4H8Cl [35,40] and in trimethylchlorosilane (C3H9ClSi)–Cl, –(CH3)2ClSi and –(CH3)3Si [11,37]. UPTFE FORUM® does not have such end groups. Thus, it is evident that the coatings formed from tetrafluoloethylene oligomers through PTFE destruction or TFE monomer telomerization have different water-repellent properties, although they are similar to each other in their chemical composition. It can be supposed that additional influence on the coating water-repellent properties is produced by the medium, in which these coatings are deposited–SC-CO2 for UPTFE FORUM® and acetone, butyl chloride and trimethylchlorosilane for TFE telomers synthesized in these solvents. Thus, the problem of which tetrafluoroethylene oligomer type is the most effective water-repellent remains to be solved.
Tetrafluoroethylene oligomer preparations without hydrophilic groups in their structure are the most effective when used for hydrophobing synthetic fabrics. Despite the fact that synthetic fibrous materials are made from fibers that are considered hydrophobic, they absorb a drop of water almost immediately, i.e., they need hydrophobing. In the last few decades, the most popular fabrics have been those made from polyethylene terephthalate fibers (polyester fabrics). That is why the object of research in this work was polyester fabrics. They were studied as an example to compare the effectiveness of the hydrophobing effect of low molecular weight tetrafluoroethylene prepared by different methods: thermo-gas-dynamic decomposition of industrial polytetrafluoroethylene waste and radiation-induced synthesis of fluoromonomers in acetone, butyl chloride and trimethylchlorosilane solutions.

2. Materials and Methods

The object of the study was a plain weave polyester fabric with the area weight of 180 ± 10 g/m2, warp yarn number of 216 ± 4 per 10 cm and weft yarn number of 203 ± 4 per 10 cm (produced by Y.R.C. Textile Co., Ltd., Bangkok, Thailand) purchased in a regular store. In some of the experiments, we used a 15 µm thick polyester film with the area weight of 19.5 ± 0.1 g/m2 (produced by ShuyangGenzon Novel Materials Co., Ltd., Suqian, Jiangsu, China).
The water-repellents we applied were low molecular weight polytetrafluoroethylenes prepared by two methods. One of the water-repellents was ultrafine polytetrafluoroethylene of the FORUM® trademark (Institute of Chemistry, Far East Branch of the Russian Academy of Sciences, Vladivostok, Russia) (UPTFE) prepared by thermo-gas-dynamic decomposition of industrial polytetrafluoroethylene waste [41]. Its morphology, structure and properties are described in detail in work [21]. The other water-repellent type was tetrafluoroethylene (TFE) telomers synthesized using radiation initiation from fluoromonomers in a number of organic solvents (Institute of Problems of Chemical Physics of the Russian Academy of Sciences, Chernogolovka, Russia). In this work, we applied TFE telomers synthesized in acetone (TFE/AC), butyl chloride (TFE/BC) and trimethylchlorosilane (TFE/TMCS). Their synthesis procedure and properties are described in detail in works [35,36,37,38,39,40].
The UPTFE coating was deposited from an SC-CO2 medium on an experimental apparatus (the scheme is given in work [42]) at a temperature of 90 °C, pressure of 20 MPa for 60 min., with the sample placed coaxially. After the sample exposure under the required conditions, we removed the solvent by dropping the pressure in the cell cooled to 42–44 °C (the temperature exceeding the critical value for SC-CO2 by 10–12 °C) to avoid the formation of the solvent liquid phase. The coating formation parameters were experimentally validated in works [43,44].
The carbon dioxide (OAO BKZ, Linde Gas AGA, Balashicha, Russia) complied with GOST 8050-85 and had 99.998% purity. According to the substance certificate, the moisture volume fraction in CO2 did not exceed 5 × 10−6 vol.%.
The monomer used in the telomer synthesis was gaseous tetrafluoroethylene (TFE) (C2F4, produced and supplied by OOO Polymer Plant of Kirovo-Chepetsky Chemical Plant, Kirovo-Chepetsk, Russia) containing 0.02% impurities. The solvents for the radiation-induced synthesis of telomers were: acetone (C3H6O, produced and supplied by Sigma-Aldrich, Hamburg, Germany, 99.9%), butyl chloride (1-chlorobutane) (C4H9Cl, produced and supplied by Fluka, Hamburg, Germany, 99%), and trimethylchlorosilane (C3H9ClSi, produced and supplied by Sigma-Aldrich, 99%). We used ethyl acetate (EA) (C4H8O2, produced and supplied by “Sigma-Aldrich”, 99.8%) and acetone to dilute the telomer solutions. TFE, TMCS, acetone and EA were not subjected to special purification.
The polyester fabric samples were processed using solutions of TFE/AC and TFE/BC telomers diluted with acetone and TFE/TMCS telomers diluted with ethyl acetate up to a concentration of 2%. We submerged the TFE fabric samples in a solution of telomers for ~10 s. The fabric impregnation was repeated several (up to 3) times. After each impregnation, we dried the fabric samples at T = 20−25 °C for 24 h to remove the solvent. At the final stage, after the drying, we subjected the samples to thermal treatment at T = 150 °C for 1 min. As a result, the samples had one-, two- and three-layer telomer coatings.
The IR spectra were recorded on an Avatar ESP 360 type spectrometer (produced by Nicolett, Markham, ON, Canada) by the method of multiple attenuated total reflectance (MATR) using a zinc selenide crystal with a 12-fold reflection in the range from 700 to 1500 cm−1.
We measured the contact angle of wetting with water by the conventional Owens-Wendt method [45]. The fabric water absorption was determined according to GOST 3816-81 (ISO 811-81) as the amount of water held by a fabric sample after its full submersion in the liquid for one hour. Ten parallel measurements were made.
The fibrous material texture and coating morphology were studied with a VEGA 3 SBH scanning electron microscope (TESCAN) and a Solver P 47-PRO atomic-force microscope (NT-MDT).
The abrasion resistance of the hydrophobicity effect was determined by measuring the change in the contact angle of a TFE fabric with a telomer coating after the fabric was subjected to abrasion 100 times. The abrasive effect consisted in the simultaneous action of normal applied load and shear load produced by a horizontal force. Such effect was realized using a special TP-4 apparatus for evaluating the dye resistance to abrasion. A fabric sample was pulled onto the apparatus stage and abraded with a calico piece fixed onto a protruding rubber stopper. The abrasion was produced by shifting the stage by 10 cm forward and backward a required number of times. The total force applied by the stopper to the stage was 9.8 N. Ten parallel measurements were made. The apparatus scheme is given in work [46].
The coating stiffness was evaluated by the force spectroscopy method using a Solver-47Pro atomic-force scanning probe microscope (NT MTD, Zelenograd, Russia). The method is based on measuring the cantilever displacement (deflection degree) at different distances between the probe and the sample. The procedure is described in detail in works [8,47]. The adhesion was determined by Hooke’s law based on the known stiffness coefficient of the probe used (3.5 N/m) when the probe moved away from the surface. The relative stiffness was characterized by the relative cantilever deflection when the probe approached the surface. The error of these measurements was ~5%.

3. Results and Discussion

Deposition of the low molecular weight PTFE fraction or TFE telomers on a polyester fabric or film leads to the formation of a coating, the composition of which is similar to that of polytetrafluoroethylene (PTFE), on its surface. This result is seen in the IR-spectra in Figure 1.
As Figure 1 shows, the highest intensity bands in the UPTFE spectrum, also characteristic of UPTFE FORUM® [48], are observed around 1153and 1208 cm−1. They are attributed to the stretching vibrations of the –CF2– groups [48]. The spectra of the processed fabric (a) 2, (b) 2 and 3 have similar bands, unlike the spectra of the initial fabric (a) 1, (b) 1, which indicates the formation of a fluorine-containing coating on the fabric surface. The formation of a coating with PTFE properties on the polyester fabric surface is also confirmed by the X-ray diffraction, energy-dispersive, gravimetric, elemental and thermal analyses [18,43,44,49,50].
To maintain the high air and vapor permeability of the hydrophobized fabric, the formed PTFE coating should not overlap the inter-yarns space. On Figure 2 shows images of the initial polyester fabric (Figure 2a) and fabrics with PTFE coatings (Figure 2b,c) obtained by scanning electron microscopy. Comparison of these images shows that there is no PTFE in the inter-yarns space, i.e., the coating is formed only on the surface of each polyester fabric yarns.
Applying energy-dispersive analysis we determined the coating composition. Figure 3 shows examples of energy-dispersive spectra of the samples with fluoropolymer coatings. A quantitative analysis showed that the coating formed by depositing UPTFE FORUM® from an SC-CO2 medium contains ~1.2% fluorine, whereas the coatings formed from TFE telomer solutions contain from ~1.4% to 3.3% fluorine. This means the coatings are extremely thin.
Additional information about the coating morphology was obtained by studying the coatings deposited on a polyester film by the atomic-force microscopy method. The study results are shown in Figure 4.
The figure shows that, when deposited from an SC-CO2 solution, the coating is extremely uniform and ultrathin (Figure 4b). As can be seen from the histogram (Figure 4c), the average thickness of the resulting coating is several tens of nanometres. Deposition of telomer solutions on a polyester fabric and subsequent thermal treatment also lead to the formation of a continuous fluoropolymer coating on the fiber surface (Figure 4d–g). As can be seen from the histogram along the height of the TFE/AC telomer coating (Figure 4e), its thickness reaches several hundreds of nanometers. The telogen type and radiation dose applied in telomer synthesis and, hence, the type of end groups they contain affect the quality of the film formed. The coating formed from TFE/AC and TFE/TMCS telomer solutions is somewhat less ordered than the one deposited from a solution of the low molecular weight PTFE fraction in SC-CO2. The use of TFE/AC telomer solutions results in the formation of a more uniform coating. Interestingly, the morphology of the coatings is noticeably different, which may be caused by their different plastic properties [51].
The ultrathin coatings formed reproduce the fiber microrelief. They are also characterized by nano-scale roughness that makes an additional contribution to the multimodal roughness of the fibrous material. As work [50] shows, the roughness of the coating formed by UPTFE FORUM® from an SC-CO2 medium can be increased by introducing a cosolvent into the supercritical fluid.
Table 1 presents the characteristics of the water-repellent properties of the polyester fabric processed with solutions of UPTFE FORUM® in SC-CO2 and TFE telomers in acetone, butyl chloride and trimethylchlorosilane. For comparison, the table also shows the characteristics of the polyester fabric processed with Nuva TTH (Clariant, Gendorf, Germany), a fluorine-containing preparation that has proven effective in practice.
The evaluation of the water-repellent properties of the polyester fabric processed with a solution of the low molecular weight UPTFE FORUM® fraction from an SC-CO2 medium shows that the modified fabric has an extremely big contact angle—137°. Of special importance is that it also has a low water absorption value—3.7%, whereas the use of the highly effective Nuva TTH preparation only gives the value of 12%. The water absorption in the initial fabric is 38%. The use of TFE telomers also ensures that the polyester fabric becomes highly hydrophobic, although less hydrophobic than in case when UPTFE FORUM® is used, with the contact angle equaling 123–132°. This is evidently caused by the bigger thickness of the coating, which reduces the positive effect of its multimodal roughness on the fibrous material hydrophobicity. The maximum increase in the contact angle is achieved when TFE/BC telomers are used; the lowest water absorption is observed in the fabric with a TFE/TMCS telomer coating.
The stability of the achieved hydrophobicity was evaluated based on the contact angle of the processed fabric after a number of tests. The data obtained are given in Table 2.
The table shows that the coatings formed by low molecular weight PTFE on polyester fabrics are extremely wear-resistant. This significantly increases the stability of the coatings based on the highly effective Nuva TTH preparation used in industrial production. A comparison of the properties of the coatings containing UPTFE FORUM® and TFE telomers shows that they all are highly resistant to washing and dry cleaning. However, the coatings containing TFE telomers are much more abrasion-resistant. This may be the result of the difference in the plasticity of the coatings containing UPTFE FORUM® and different TFE telomers, which is reflected in the morphology of the coatings. The difference in the surface structure makes it possible to evaluate the plastic properties of the coatings by force spectroscopy, which is implemented using an atomic force microscope [52]. The force spectroscopy method is based on direct interaction between the surface atoms and the microscope probe. At a distance of about one angstrom between the atoms of the sample and the atoms of the probe, repulsive forces act, and at large distances, attractive forces appear. The force acting on the probe from the surface causes bending of the probe console. The bending value can be used to obtain information about the rigidity of the surface at individual points. The stiffness coefficients are given in Table 3.
The table shows that the UPTFE FORUM® coating is more rigid than those formed by TFE telomers. Evidently, when higher plasticity coatings containing TFE telomers are subjected to abrasion, the nonfixed fluoropolymer excess is removed from the polyester fabric surface, making it more uniform and increasing its quality.
The images of the fluoropolymer coating on the polyester film before and after the exposure to abrasion are shown in Figure 5.
The histograms indicate that abrasion makes the coating more uniform.
Interestingly, the stiffness coefficient, which can be used to evaluate the plasticity of a coating, is not normally determined by researchers, but is an important feature affecting the quality and durability of fabric hydrophobing, as well as its other consumer properties. For example, a comparison of the data in Table 1 and Table 3 shows that the coatings of low stiffness cannot guarantee sufficiently low water absorption in a polyester fabric. At the same time, if the stiffness is too high, coatings can have a negative effect on the mechanical characteristics of a fabric and the comfort of its use. Thus, it is necessary to determine the optimal values of coating stiffness for each type of water-repellent agents to achieve high hydrophobicity and preserve good consumer properties in a fabric.

4. Conclusions

In this work, we implemented a new way of providing a polyester fabric with hydrophobic properties, which consists in deposition of tetrafluoroethylene oligomers from solutions on the surface of every yarn forming the fabric. It was established that the ultrathin coatings formed have properties similar to those of polytetrafluoroethylene and reproduce the micro- and nanorelief of the yarn. We carried out a comparative analysis of two types of tetrafluoroethylene oligomers as water-repellent agents for a polyester fabric: ultrathin polytetrafluoroethylene FORUM® obtained by thermo-gas-dynamic decomposition of industrial polytetrafluoroethylene waste and tetrafluoroethylene telomers synthesized by radiation-chemical initiation from fluoromonomers in acetone, butyl chloride, and trimethylchlorosilane solutions.
The coating formed on the polyester fabric during its processing with low molecular weight UPTFE FORUM® from an SC-CO2 medium has a thickness of several tens of nanometres and is highly ordered and extremely wear-resistant. The polyester fabric with such a coating has a contact angle of wetting of 137 degrees and extremely low water absorption.
Solutions of TFE telomers synthesized in acetone, butyl chloride and trimethylchlorosilane make it possible to cover the fabric fiber surface with a coating that forms a thin (300–600 nm thick) fluoropolymer film after thermal treatment. Such coating is thicker and rougher, has higher plasticity and is even more wear-resistant than the one obtained using UPTFE FORUM®. After the coating deposition, the fabric has a smaller contact angle (123–132 degrees). The water absorption varies depending on the telomer type and times of coating deposition. The biggest contact angle is achieved by using TFE/BC telomer solutions; the lowest water absorption in the fabric is observed when TFE/TMCS telomer solutions are applied.
Thus, it was established that solutions of low molecular weight PTFE, regardless of the preparation method, are effective water-repellent agents for polyester fabrics and can provide the fabrics with a big contact angle and low water absorption. The main difference between them is in the plasticity of the coatings, characterized by the stiffness coefficients. We showed that stiffness is an important feature affecting the quality and durability of the hydrophobic treatment of a fabric, as well as its other consumer properties.

Author Contributions

Conceptualization, N.P.P.; methodology, T.Y.K.; software, I.V.K.; validation, N.P.P., T.Y.K. and I.V.K.; investigation, N.P.P., T.Y.K. and I.V.K.; resources, T.Y.K.; data curation, N.P.P.; writing—original draft preparation, N.P.P.; writing—review and editing, N.P.P.; visualization, N.P.P.; supervision, N.P.P.; funding acquisition, N.P.P., T.Y.K. and I.V.K. All authors have read and agreed to the published version of the manuscript.

Funding

This work was funded by the Russian Foundation for Basic Research and Ivanovo region government as part of project No. 18-48-370005-r_centre_a.

Institutional Review Board Statement

Not applicable.

Informed Consent Statement

Not applicable.

Data Availability Statement

Not applicable.

Acknowledgments

The authors would like to thank Kiryukhin, D.P.; Kushch, P.P.; Kichigina, G.A.—for synthesizing the tetrafluoroethylene telomers. The work was done on the equipment of the Center for Joint Use of Scientific Equipment “The Upper Volga Region Center of Physico-Chemical Research” and Center for Joint Use of Ivanovo State University of Chemistry and Technology.

Conflicts of Interest

The authors declare no conflict of interest.

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Coatings 12 01334 g001 550
Figure 1. IR absorption spectra (MATR method): (a) 1 is the initial polyester fabric; 2 is the fabric processed in SC-CO2 with UPTFE FORUM® at a pressure of 20 MPa and temperature of 90 °C; 3 is UPTFE FORUM®; (b) 1 is the initial polyester fabric; 2 is the fabric processed with a TFE/AC solution; 3 is the fabric processed with a TFE/BC solution; 4 is PTFE.
Figure 1. IR absorption spectra (MATR method): (a) 1 is the initial polyester fabric; 2 is the fabric processed in SC-CO2 with UPTFE FORUM® at a pressure of 20 MPa and temperature of 90 °C; 3 is UPTFE FORUM®; (b) 1 is the initial polyester fabric; 2 is the fabric processed with a TFE/AC solution; 3 is the fabric processed with a TFE/BC solution; 4 is PTFE.
Coatings 12 01334 g001
Coatings 12 01334 g002 550
Figure 2. Image of the polyester fabric:(a) is the initial polyester fabric; (b) is the UPTFE FORUM® deposited from an SC-CO2 medium; (c) is the TFE/BC telomers [32,43]. The study method is scanning electron microscopy.
Figure 2. Image of the polyester fabric:(a) is the initial polyester fabric; (b) is the UPTFE FORUM® deposited from an SC-CO2 medium; (c) is the TFE/BC telomers [32,43]. The study method is scanning electron microscopy.
Coatings 12 01334 g002
Coatings 12 01334 g003 550
Figure 3. Energy-dispersive analysis of the polyester fabric samples:(a) processed with a UPTFE FORUM® solution in SC-CO2 (the content of the elements: C—63.21%; O—35.63%; F—1.15%); (b) after a three-time deposition of a 1.5% solution of TFE/AC telomers (the content of the elements: C—63.75%; O—34.86%; F—1.39%).
Figure 3. Energy-dispersive analysis of the polyester fabric samples:(a) processed with a UPTFE FORUM® solution in SC-CO2 (the content of the elements: C—63.21%; O—35.63%; F—1.15%); (b) after a three-time deposition of a 1.5% solution of TFE/AC telomers (the content of the elements: C—63.75%; O—34.86%; F—1.39%).
Coatings 12 01334 g003
Coatings 12 01334 g004a 550Coatings 12 01334 g004b 550
Figure 4. Images of the polyester film surface: (a) before processing; (b) with a coating deposited from a UPTFE FORUM® solution in SC-CO2; (c) height histogram of the coating deposited from a UPTFE FORUM® solution in SC-CO2; (d) with a TFE/AC telomer coating; (e) height histogram with a TFE/AC telomer coating; (f) with a TFE/BC telomer coating; (g) with a TFE/TMCS telomer coating. The study method is atomic-force microscopy. The representation method is phase contrast.
Figure 4. Images of the polyester film surface: (a) before processing; (b) with a coating deposited from a UPTFE FORUM® solution in SC-CO2; (c) height histogram of the coating deposited from a UPTFE FORUM® solution in SC-CO2; (d) with a TFE/AC telomer coating; (e) height histogram with a TFE/AC telomer coating; (f) with a TFE/BC telomer coating; (g) with a TFE/TMCS telomer coating. The study method is atomic-force microscopy. The representation method is phase contrast.
Coatings 12 01334 g004aCoatings 12 01334 g004b
Coatings 12 01334 g005a 550Coatings 12 01334 g005b 550
Figure 5. Images of a 5 × 5 µm polyester film surface with a coating formed from TFE/AC telomers (phase representation)—(a,c)—and histograms of the peak heights of these surface areas—(b,d): (a,b) are the initial coating; (c,d) are the coating after abrasion. The study method is atomic-force microscopy.
Figure 5. Images of a 5 × 5 µm polyester film surface with a coating formed from TFE/AC telomers (phase representation)—(a,c)—and histograms of the peak heights of these surface areas—(b,d): (a,b) are the initial coating; (c,d) are the coating after abrasion. The study method is atomic-force microscopy.
Coatings 12 01334 g005aCoatings 12 01334 g005b
Table
Table 1. Water-repellent properties of the polyester fabric with coatings containing UPTFE FORUM® and a variety of TFE telomers.
Table 1. Water-repellent properties of the polyester fabric with coatings containing UPTFE FORUM® and a variety of TFE telomers.
Times of DepositionContact Angle, °Water Absorption, %
0Water is absorbed immediately.38.0 ± 0.9
Fabric with a UPTFE FORUM® coating deposited from a solution in SC-CO2
1137 ± 33.7 ± 0.2
Fabric with a FE/AC telomer coating
2127 ± 222.4 ± 0.2
3127 ± 218.2 ± 0.2
Fabric with a TFE/BC telomer coating
2131 ± 210.3 ± 0.2
3132 ± 24.9 ± 0.2
Fabric with a TFE/TMCS telomer coating
2125 ± 21.2 ± 0.1
3123 ± 22.4 ± 0.2
Fabric with a Nuva TTH coating
1 (30 g/L)132 ± 412.0 ± 0.2
Table
Table 2. Hydrophobicity resistance to different types of wear.
Table 2. Hydrophobicity resistance to different types of wear.
Contact Angle before Processing, °Contact Angle after Processing, °
100 Abrasion Cycles25 Washings25-Time Dry-Cleaning
Fabric with a UPTFE FORUM® coating deposited from a solution in SC-CO2
137 ± 3129 ± 2133 ± 2134 ± 2
Fabric with a TFE/AC telomer coating
127 ± 2135 ± 2124 ± 2132 ± 2
Fabric with a TFE/BC telomer coating
132 ± 2138 ± 2127 ± 2132 ± 2
Fabric with a TFE/TMCS telomer coating
123 ± 2124 ± 2124 ± 2129 ± 2
Fabric with a Nuva TTH coating
132 ± 4111 ± 4103 ± 5120 ± 5
Table
Table 3. Stiffness of the coatings formed on the polyester fabric by different methods from solutions of low molecular weight PTFE.
Table 3. Stiffness of the coatings formed on the polyester fabric by different methods from solutions of low molecular weight PTFE.
Method of Coating Formation from Low Molecular Weight PTFECoating Stiffness
Coating containing UPTFE FORUM® deposited from solutions in SC-CO20.054
Coating containing TFE/AC telomers0.015
Coating containing TFE/BC telomers0.024
Coating containing TFE/TMCS telomers0.042
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Prorokova, N.P.; Kumeeva, T.Y.; Kholodkov, I.V. Wear-Resistant Hydrophobic Coatings from Low Molecular Weight Polytetrafluoroethylene Formed on a Polyester Fabric. Coatings 2022, 12, 1334. https://0-doi-org.brum.beds.ac.uk/10.3390/coatings12091334

AMA Style

Prorokova NP, Kumeeva TY, Kholodkov IV. Wear-Resistant Hydrophobic Coatings from Low Molecular Weight Polytetrafluoroethylene Formed on a Polyester Fabric. Coatings. 2022; 12(9):1334. https://0-doi-org.brum.beds.ac.uk/10.3390/coatings12091334

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Prorokova, Natalia P., Tatyana Yu. Kumeeva, and Igor V. Kholodkov. 2022. "Wear-Resistant Hydrophobic Coatings from Low Molecular Weight Polytetrafluoroethylene Formed on a Polyester Fabric" Coatings 12, no. 9: 1334. https://0-doi-org.brum.beds.ac.uk/10.3390/coatings12091334

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