Analysis of a polytetrafluoroethylene coating deposited onto polyester fibers from supercritical carbon dioxide

Abstract

A low-molecular-weight polytetrafl uoroethylene coating deposited onto a polyester textile material from supercritical carbon dioxide with the aim to make the material hydrophobic was analyzed. The hydrophobic properties of the coating were examined in comparison with those of the hydrophobizing agent produced by Nuva (Switzerland).The most effective surface modifi ers used for making the surface unwettable are fl uorinated hydrocarbons having low surface energy (18.5-26 mJ m -2 ) [1]. In hydrophobization of textile materials, these substances are traditionally used in the form of suspensions or emulsions [2].Surface modification of fibrous materials causes changes in their structure and surface energy, which is a direct manifestation of intermolecular interactions. It should be noted that the surface free energy is determined by surface forces, which rapidly decrease with the depth [3]. Therefore, to make the surface hydrophobic, it is suffi cient to apply an ultrathin layer of an appropriate material onto a high-energy surface [4].Today polyester fibers play an important role in industry [5]. The majority of them are produced from poly(ethylene terephthalate) (PET). These fi bers are widely used owing to their cheapness, feasibility of dressing, and suffi cient strength and wear resistance, but are insuffi ciently hydrophobic.To obtain a hydrophobic material, additional modifi cation aimed to decrease its surface energy by deposition of a stable low-energy coating is necessary. The hydrophobizing agents used in textile industry cannot ensure formation of a high-quality hydrophobic coating on the PET surface, because they are diffi cultly soluble in the traditionally used aqueous medium.Among the known materials, polytetrafl uoroethylene (PTFE) has the lowest surface energy. However, it is practically insoluble in all the known solvents, its processing is diffi cult, and its adhesion is poor [6]. The negative properties of PTFE are due, to some extent, to the high molecular weight of the polymer. Therefore, coatings are usually deposited from emulsions and suspensions of specially synthesized fl uorinated substances of lower molecular weights [7-10]. However, with this deposition procedure, the coatings are contaminated with trace amounts of emulsifi ers [2]. To attain the required effect, multiple layers of a fl uorinated substance are deposited in succession onto a support [11].The problem of depositing ultrathin polymeric coatings can be solved by using supercritical carbon dioxide (SC CO 2 ) as a solvent for fl uorinated hydrophobizing agents [12]. This solvent is characterized by high solubility of nonpolar substances in it and by absolute wettability of the material being modifi ed. Owing to unique dissolving properties, high diffusion mobility, and easy complete removal from the material after the end of the process, SC CO 2 shows promise for wide use in diverse branches of chemical technology. The supercritical state of carbon dioxide is attained at relatively low parameters (P c = 7.39 MPa, T c = 31.6°С...

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“…In this concern, solving the above discussed difficulties of PTFE in the textile processing is a common expectation of in textile industry. The developed methods (emulsion dipping, laminating composite method, and sputter coating) [8,9] are mainly based on coating of PTFE materials on the fabric, which will invalidate the fabric washability, [10] air permeability, [11] comfort, [12] style. [13] Moreover, the high molecular weight of PTFE makes it difficult to adhere to the fabric surface and the coating on fiber surface is uneven because of Plateau-Rayleigh instability.…”

“…Why in most cases PTFE materials are only used in industrial textiles and seldom used in apparel textiles? The reason is that the small dielectric constant value of PTFE makes it easy to generate static electricity during friction, [ 8 ] which will result in the failure of normal production of PTFE fabric, let alone high‐speed production. Specifically, the static electricity will cause unclear shedding (warp yarn weaving opening), mechanical failures or even major accidents.…”

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

“…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].…”

Giving Improved and New Properties to Fibrous Materials by Surface Modification

“…When applied from solutions, some of these oligomers are capable of forming coatings on the surface of filaments with properties similar to those of polytetrafluoroethylene [220,221]. Fluorinated oligomers, obtained either by thermal degradation of fluoropolymers [207,[222][223][224][225][226][227] or by synthesis from fluoromonomers [3,207,211,221,[228][229][230][231][232], are the basis of such coatings. The use of organosilicon compounds as hydrophobizers also significantly reduces the surface energy of fibrous materials [233][234][235][236].…”

“…Fabrics and nonwovens are formed by cylindrical fibers and threads, which are characterized by a higher water contact angle than flat films of the same chemical composition [260]. In addition, in previous works [223,224,261,262] it was shown that fabric has a multimodal roughness, due to its complex weave. These factors create favorable conditions for the hydrophobization of fibrous materials and contribute to the achievement of higher water contact angle compared to the treatment of films of similar chemical composition with the same hydrophobizer.…”