Ensuring a high degree of water repellency of polyester textile materials by treating them with supercritical carbon dioxide

Abstract

It was shown that an ultrathin continuous fl uoropolymer fi lm that replicates the microrelief of the fi bres forming the fabric is formed on the surface of polyester fabric when it is treated with a solution of a low-molecular-weight fraction of polytetrafl uoroethylene in supercritical carbon dioxide. The protective coating formed is ultrahydrophobic and has extremely low water absorption. An additional increase in the degree of hydrophoby of polyester fabric can be attained by using the chemical method of preliminary modifi cation of the fabric which gives the surface of the polyester fi bres additional roughness.There is an increasing demand for water-resistant textiles on the textile materials market, so that the problem of obtaining household and industrial fabrics with high hydrophoby is pressing. Water-repellent fi nishing of textile materials is to give them the capacity of not being wet with water while retaining air and vapor permeability. The contact angle of wetting  -the angle between the tangent to the surface of a drop of liquid at the point of contact of three phases (solid, liquid, and gas) and the surface of a solid, measured inside the liquid phase [2], is the basic index of the hydrophoby of a material, and it should be greater than 90°. Investigators have focused attention on highly hydrophobic -ultra-( > 120°) and superhydrophobic ( > 150°) -materials [3]. The ability of a material with a fl at, smooth, nonporous surface to be wet by liquids is described by Young's equation [2]:where  sg is the surface tension on the solid-gas interface;  sl is the surface tension on the solid-liquid interface;  lg is the surface tension on the liquid-gas interface. A real textile material has a biporous (micro-and macropores) system with a different degree of development. When such materials react with a liquid, it is necessary to take into account the appearance of forces of capillary suction. In this case, the Laplace equation [2], which correlates the capillary pressure (P c ) with the surface tension of the liquid ( lg ) and the average capillary radius (r c ) applies:It follows from Eq. (2) that the capillary pressure will approach zero with no wetting of the capillary walls. It is necessary to consider that Eq. (1) only holds for smooth surfaces, while textile materials are rough. One of two types of wetting takes place on rough surfaces [3]: homogeneous, where the liquid totally fi lls the cavities on the entire surface of the solid, and heterogeneous, where the liquid is in contact with the surface which has cavities totally or partially fi lled with air. For this reason, for describing the effect of roughness on the contact angle of wetting, either Wenzel's equation (3) (for

Giving polyester textile materials high water repellency by treating them with a solution of tetrafluoroethylene telomers

“…2b). In contrast to the smooth and uniform coating formed from a solution of ultradisperse polytetrafl uoroethylene in supercritical carbon dioxide [4,5], the telomeric fi lm is weakly attached to the fabric has a less complete, nonuniform structure. An abrasive effect was used to remove the excess telomer weakly attached to the substrate and to give the structure a protective fi lm with greater ordering [6].…”

“…Nontraditional methods of making polyester fabrics water repellent by using fl uoropolymers were developed by the "Fluoropolymer Materials and Nanotechnologies" consortium. The method of making polyester fabric water repellent by treating it with a solution of ultradisperse polytetrafl uoroethylene in supercritical carbon dioxide is examined in detail in [4,5]. Another promising method of making synthetic fabrics waterrepellent is to form a protective coating on their surface by application of tetrafl uoroethylene telomers from solution in acetone [6].…”

“…We previously demonstrated the possibility of additionally increasing the water repellency of textile material by regulating the level of nanoroughness of the fi bres forming it [4]. Since the surface properties of textile materials, including their microrelief, can be changed by modifying the fi bres, we evaluated the effect of a chemical method of modifi cation (activation) of polyester fi lms and fi bres treated with Cherfl on [16].…”

Composites with Hydrophobic Surfaces

“…Fluoroplastics that are soluble in organic solvents can be deposited on fiber and material surfaces from solutions. An interesting method for depositing fluoroplastic coatings using tetrafluoroethylene telomers in acetone was reported [7].The goal of the present work was to compare the abilities of F-2M fluoroplastic in DMF and F-4D fluoroplastic in an aqueous suspension to produce a hydrophobic surface. Carbon-carbon composite sheets (CS Toray) (Japan), pilot batches of Russian sheets (PS RF), and a nonwoven composite produced in Russia (NC RF) were treated with water repellents.…”

“…Fluoroplastics that are soluble in organic solvents can be deposited on fiber and material surfaces from solutions. An interesting method for depositing fluoroplastic coatings using tetrafluoroethylene telomers in acetone was reported [7].…”