Durability of fluoropolymer

In recent years, fluorochemical repellents have been coapplied mainly with wax dispersions made durable with cross-linking adjuvants. Although a variety of water repellents with hydrocarbon-type hydrophobes enhance the repellency and durability of fluoropolymer repellents, silicones may reduce their oil repellency... 

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]. 

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. 

Properties of fluoropolymers that have led to applications include chemical resistance, thermal stability, cryogenic properties, low coefficient of friction, low surface energy, low dielectric constant, high volume and surface resistivity, and flame resistance. Fluoropolymers are used as liners (process surface) because of their resistance to chemical attack. They provide durable, low maintenance and economical alternatives to exotic metals for use at high temperatures without introducing impurities. Electrical properties make fluoropolymers highly valuable in electronic and electrical applications as insulation, e.g., FEP in data communications. 

Wear, scoring, material flow, pitting, fracture, creep, and fatigue cause plastic and metal gears to fail. Continuous lubrication can increase the allowable bending stress by a factor of at least 1.5. However there are plastics (acetals, nylons, fluoropolymers, and others) that operate efficiently with no lubrication. There are plastics with wear resistance and durability of plastic gears makes them exceptionally useful. 

Copolymers of VF and a wide variety of other monomers have been prepared. Interpolymers of VF with TFE and other highly fluorinated monomers have been reported. Examples of the third monomers include HFP, perfluorobutylethylene, and PEVE. These polymers were found to have typical properties of fluoropolymers such as chemical resistance, thermal stability, and outdoor durability [86,87]. 

The era of fluoropolymers began with the discovery of polytetrafluoroethylene in 1938. The history of fluoropolymers, as will be seen in this book, is steeped in both scientific curiosity and serendipity— the seemingly indispensable elements of most major discoveries and inventions. There has been an explosion of fiuoropolymer applications in all facets of human affairs. Old and new technological advances have been made possible by their unique properties. From the Manhattan project in the early 1940 s, to the Apollo missions in the 1970 s, to integrated manufacturing in the late 1980 s, industries have relied on fluoropolymers for their inertness and durability. New applications are being developed everyday after more than six decades since the discovery of this plastic family. Few materials have impacted the lives of peoples as extensively as fluoropolymers. 

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. 

Table 5.13 Marketing Durability of Flame- and Plasma-Treated Fluoropolymer Insulated Wires ...

The structure of nonfluorinated monomers and their ratio to the fluorinated monomer affect repellency as well as other properties of the polymer such as melt flow and hardness. Comonomers with a cross-linking function, such as a hydroxyl, epoxy, or vinyl group, are used to increase the durability of the repellent polymer. Hybrid fluoropolymers, consisting of hydrophobic and hydrophilic segments, are discussed in Chapter 13. 

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]. 

Yi et al. reported a new type of PVDF membrane prepared by blending two very different polymers, a PVDF fluoropolymer such as Kynar with a sulfonated poly-electrolyte. The new membrane is inexpensive and displayed good performance and durability based on 1,000-h test data. 

In the chemical processing industry, for example, fluoropolymers are selected for their resistance to chemical attack. They serve as linings for carbon steel vessels, and for piping and other fluid handling components. They provide durable, low maintenance, and economical alternatives to exotic metal alloys. In these applications, fluoropolymers also offer thermal stability for use at high temperatures. And because they do not react with process streams, they help prevent contamination of products. 

Membranes which may be used in the removal of alkali metal ions by electrodialysis are those which are impermeable to anions, but which allow the flow therethrough of cations. Such cation-selective membranes should, of course, possess chemical durability, high resistance to oxidation and low electrical resistance in addition to their ion-exchange properties. Homogeneous-type polymeric membranes are preferred, for example, network polymers such as phenol, phenosulfonic acid, formaldehyde condensation polymers and linear polymers such as sulfonated fluoropolymers and copolymers of styrene, vinyl pyridine and divinylbenzene. Such membranes are well known in the art and their selection for use in the method of the invention is well within the skill of the art. 

Since ozone is very reactive and easily decomposes on contact with other substances, use of inert (and clean) materials such as fluoropolymers (e.g., poly-tetrafluoroethene (PTFE)) or glass is mandatory for sampling tubes and other parts in contact with the sample gas and water. Sample flow rate and tube diameter should be large enough to minimize decomposition loss of ozone. Particulate matter in the sample should be removed with a PTFE filter. For applications of a high ozone concentration, durable material such as stainless steel should be used. 

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