Repellent Finishing with Fluoropolymers

Fluoropolymers are used for repellent finishing of fabrics made of synthetic and natural fibers. Formulations for cellulosic fabrics include cross-linking reactants to increase durability of fluoropolymer finishes, to impart wrinkle resistance, wash and wear, and durable press properties. Cross-linking reactants of the melamine, triazine or modified triazine, carbamate, or glyoxal type are used. Because fluoropolymers, unlike silicones, do not soften the fabric, softeners may be needed. Coapplication with cross-linking reactants may also require lubricants, such as nonionic polyethylene dispersions, to assure satisfactory sewing properties of the fabric. A typical formulation for polyester-cotton rainwear and outerwear is shown in Table 12.2 [148]. 

Fluoropolymer repellent finishes are applied by padding, spraying, or exhaust. Generally, the fabric is padded, dried at 120-180°C, and cured for 1-3 min at 150-182°C. The coapplied adjuvants and resins may require the fabric to be process washed and dried at 150-175°C. Fluorochemicals (e.g., CH2=CH-COO(CH2)2C8Fn) [149] have been applied to fabrics by plasma coating as well. 

Producers of fluoropolymer repellents require that textiles meet minimum oil- and water-repellency specifications to bear the producer s label. The durability of repellency to laundering and dry cleaning is also specified (Table 12.3) [148]. 

All fabrics, fibers and blends of fibers for all uses except flat woven rainwear and all upholstery fabrics 90 80 80 5 4 4 

Note A tolerance of 10 is allowed on Spray Test Ratings. A tolerance of 1 is allowed in Oleophobic Test Ratings. 

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Repellent finishes are usually compatible with easy-care and durable press finishes and many softeners. However, most silicone products interfere with the oil repellency of fluorocarbon finishes and should generally be avoided in an oil-repellent formulation. This is a remarkable contrast to the incorporation of silicone segments in the backbone chain of fluoropolymers, which generates a special soft handle. 

Hydrocarbon-based repellents are relatively inexpensive but they repel only water. They do not impart oil and soil repellency to textiles. In contrast, fluorinated repellents provide oil and soil repellency as well as water repellency. However, the higher cost of fluorinated repellents limits their applications. To lower the cost of repellent finishing, fluoropolymers are usually coapplied with hydrocarbon-type repellents. With a hydrocarbon repellent as an extender, fluorinated repellents can be used at a lower concentration without an adverse effect on repellency [43-57]. 

The characteristics of fluoropolymers are summarized in Table 1. Thermal and chemical resistance is in general with most of plastics, elastomers and perfluorinated membranes. Weather resistance with the outdoor durability for more than 20 years is specific for fluorinated paint resins. Surface properties such as water and oil repellency are provided by acrylic polymer-based textile finishes and coatings with long-chain per-fluoroalkyl groups. Electrical properties as well as a low refractive index are important for optoelectronics applications like optical fibers. 

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