Repellency of Fabrics

The resistance of a fabric to wetting and penetration of a liquid, such as water or oil, depends on the chemical nature, geometry, and roughness of the fiber surfaces and the capillary spacings in the fabric. 

The hydrostatic pressure, AP, required to force a liquid through a fabric is given by the Laplace equation 

The pressure required for the penetration of fabrics through spaces between the yarns is given by [61] 

The apparent receding contact angle Bw is related to the receding contact angle for 

The nature of the support under the repellent fabric and its compressibility are important [66,67]. Penetration is more likely to occur on a rigid support than on a compressible surface. The wettability of the liner under the fabric can also affect the repeilency of the garment. An absorbent liner can increase wetting, whereas a repellent liner can function as a second line of defense against penetration by water. 

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Fig. Xm-3. Effect of contact angle in determining water repellency of fabrics.

ISO 9865 1991, Textiles, Determination of Water Repellency of Fabrics by the Bundesmann Rain Shower Test, International Standards Organization, Geneva, 1991. 

Water repellence of fabrics made of p-aramide, which were coated with a basic sol (pre-hydrolyzed alkoxysilane, crosslinking agent, ethanol) modified with an additional hydrophobizing agent... 

Repellents Not Using Human Bait (No Attractant). A treated strip of fabric and a control strip are lowered iato a container of crawling arthropods such as ticks, fleas, and mites. After a predetermined time, the strips are lifted, the animals remaining are counted, and the percentage repeUency is determined. 

Table 10.49 Oil and water repellency of cotton fabrics treated with perfluorinated acrylic polymers [502]...

For application of these fluorochemical finishes to textile fabrics, an extremely important factor is their formulation into suitable aqueous emulsions or dispersions. The quality of the formulation has a critical influence on stability during storage and application, as well as the efficacy of treatment and durability [501,502]. In particular, the choice of surfactant(s) for emulsifying or dispersing must ensure good stability with freedom from deposition on rollers, yet must not impair the water and oil repellency of the finished fabric. No individual product fulfils all requirements hence specifically formulated products are available for certain fibre types. 

The application of water-repellent finishes to fabrics actually involves a chemical reaction between the material and the finish. Cellulose-based fibers such as cotton possess hydroxyl (-OH) groups that exist on the surface of fabrics spun and woven from the fiber. The basic structure of cellulose portrayed in Fig. 7.6.1 reveals... 

AATCC methods for determining water repellency are AATCC 22 (spray test) and AATCC 70 (tumble jar dynamic absorption test). In the spray test, water is sprayed against the taut surface of the test specimen to produce a wetted pattern the size of which depends on the repellency of the fabric. Evaluation is by comparing the pattern with a series of patterns on a standard chart. The latter method evaluates the percentage by weight of water absorbed by a sample after dynamic exposure to water for a specified period of time. 

The semipermeable membrane proposed for the demineralization of sea water is based on H. L. Calendar s theory that osmosis takes place through the membrane as vapor, condensing at the opposite membrane surface. The actual membrane being used consists of two sheets of untreated cellophane separated by a water-repellent powder, such as a silicone-coated pumice powder. The vapor gap is maintained by an air pressure in excess of the pressure on the sea water and the cellophane sheets support the capillary surfaces, which will withstand pressures up to 1500 p.s.i. A number of successful experiments are reported with over 95% desalinization. The present effort is directed toward obtaining reproducible experimental results and better methods of fabricating the vapor gap. 

TABLE 1. Water/alcohol and oil repellency testing of fabrics modified with perfluoroacrylate monomer to confer a hydrophobic/oleophobic repellent surface. 

Advantages of silicone water repellents include a high degree of water repel-lency at relatively low (0.5-1 % owf) on weight of fabric concentrations, very soft fabric hand, improved sewability and shape retention, and improved appearance and feel of pile fabrics. Some modified silicone repellents can be exhaust applied (to pressure-sensitive fabrics). 

Four samples of treated fabric are subjected to simulated rain for 10 min. The fabrics (placed on inclined cups and sealed at the edges) are in constant motion and the side of the fabric not exposed to the rain is subjected to a rubbing action. The repellency of the fabric is determined by the appearance of the wetted side, the amount of water absorbed by the fabric and the amount of water passing through the fabric. This test requires an elaborate special apparatus. 

Conditions for high repellency of finished fabrics inclnde a close-packed textile structnre with small inter-yam spaces (therefore better woven than knitted) with fine yams (preferably microfibres or microfilaments) and a uniform distribution of the repellent finish. This last condition is enhanced by the removal of protmding surface fibres by singeing or shearing. 

Silicones and flnorocarbon polymers cannot easily be stripped off, especially when they are crosslinked. As it is the natnre of repellent finishes to reduce adhesion, there are problems with backcoating and laminating of fabrics finished by padding flnorochemicals. One solntion is the one side application of the repellents by nip-padding, spray, foam or sqneegee techniques. 

This fibre and fabric modification is based on photophysical and photochemical processes induced by exposure to plasma gases. Reactive gases are used to create chemical fibre surface modifications such as repellency of water, oil and soil and higher fibre resistance against aggressive chemicals. These modifications are mainly restricted to the fibre surface to avoid damaging the fibre bulk, for example... 

PERSISTOL SIN is a sillcone-type impregnating agent for the water-repellent finishing of fabrics of all types. According to the type of substrate, it is necessary to use CONDENSOL I New or CONDENSOL II. 

From 1.0 to 2.0% of AQUAFILM on the weight of fabric is generally enough to impart dry-soil resistant/soil repellent properties. 

ARIDRY SS-80 has been developed as a specialty water repellent to be used where many other hand builders and auxiliaries are used without sacrificing a high degree of water repellency. ARIDRY SS-80 is a one-package zirconium product that incorporates a blend of emulsifiers that lend an inherent uniqueness to the product. ARIDRY SS-80 can be applied to many types of fabrics but is particularly effective on rayon linings. 

Primary Use Water repellent and softener for all types of fabrics... 

DOW CORNING 75 emulsion is a reactive, methyl silicone emulsion especially designed for use as a water repellent for all types of fabrics. When used with a catalyst, it provides water repellency used alone it functions as a fabric softener. 

Gives fullness to fabrics safe to use in water repellent of fluorochemical finishes durable to laundering when applied with resins--starch derivative. 

Durable water repellent and fluorocheraical extender NORANE 100 repellent provides durable water repellent properties to cellulosic, cellulosic/synthetic blends, and synthetic fabrics, when used with fluorocheraicals it reduces the required amount of fluorochemical needed for water repellent properties. NORANE 100 repellent also improves hand and sewing properties of fabrics while providing excellent water spray resistance. 

Organometallic Complexes. Wemer-type complexes of chromium and long-chain carboxjUic acids, eg, stearic acid, are water repellents for fabrics of natural and synthetic fibers. The complexes have a small market in the textile industry. 

A new process of water repelling-waterproofing of fabrics depends in part upon cataphoresis. The Tate electrical process of water-repelling waterproofing, as dis-... 

Standard Test h [ hi, ,(Y ).SlandardTestMethodfor Alcohol Repellency ofNomvoven Fabrics, INDA, Association of the Nonwoven Fabrics Industry, Cary, North Carolina, 1992. 

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