Glass with fluorocarbon

Most architectural fabrics are usually flexible composites comprised of glass fibers coated with fluorocarbons to resist wind, mechanical forces, and outdoor environmental degradation. The airport terminal in Saudi Arabia, and the roofs for the Hubert Humphrey Dome in Minneapolis and the Tokyo Dome Stadium are a few examples of the successful use of architectural fabrics. 

Acetal translucent crystalline polymer is one of the stiffest TPs available. It provides excellent hardness and heat resistance, even in the presence of solvents and alkalies. Its low moisture sensitivity and good electrical properties permit direct competition with die-cast metal in a variety of applications. In addition, acetal has extremely high creep resistance and low permeability. Acetal is also available as a copolymer (Hoechst Celanese Corp. s Celcon) for improved processability. The homopolymer (DuPont s Delrin) has a very low coefficient of friction and its resistance to abrasion is second only to nylon 6/6. Acetals are frequently blended with fibers such as glass or fluorocarbon to enhance stiffness and friction properties. Acetal is not particularly weather-resistant, but grades are available with UV stabilizers for improved outdoor performance. Acetal, whether homopolymer or copolymer, is not used to any significant degree in forming structural foams. 

Figure 16.2 Fluorous small-molecule microarrays. Small-molecule histone deacetylase (FiDAC) binders are noncovalently immobilized onto a glass slide coated with fluorocarbon compounds. An antibody labeled with a fluorescent dye recognizes HDAC proteins. See color plate 16.2.

The stopcocks must be greased with fluorocarbon lubricant because of the corrosive effect of Cl30g, unless one prefers to use the glass valves su ested by Bodenstein. 

Packed columns are typically made of stainless steel and have outside diameters of 1/4 or 1/8 inch and lengths of 2 to 10 feet. For applications requiring greater inertness, alternative materials have been used including glass, nickel, fluorocarbon polymers (Teflon ), and steel that is lined with glass or Teflon . Copper and aluminum are conveniently soft for easy bending, but are not recommended due to their reactivity. 

With the exception of glass-reinforced fluorocarbons, such as polytetrafluoroethylene and fluo-rinated ethylene-propylene, most all materials can be ultrasonically welded. Table 5-5 compares the welded strength of several glass-reinforced materials. However, horn wear problems can arise from the abrasiveness of the fiberglass. This problem is usually minimal with less than 20% glass. Welds can be made with glass levels between 20 and 35% but some wear will result. Strong welds cannot be assured at levels above 35% due to insufficient fusable resin . 

Polymers used for seat and plug seals and internal static seals include PTFE (polytetrafluoroeth ene) and other fluorocarbons, polyethylene, nylon, polyether-ether-ketone, and acetal. Fluorocarbons are often carbon or glass-filled to improve mechanical properties and heat resistance. Temperature and chemical compatibility with the process fluid are the key selec tion criteria. Polymer-lined bearings and guides are used to decrease fric tion, which lessens dead band and reduces actuator force requirements. See Sec. 28, Materials of Construction, for properties. 

A major development in fluoroplastks is the recent small scale production of Teflon AF, a noncrystaUme (amorphous) fluorocarbon polymer with a high glass transition temperature (240 °C) This optically transparent TFE copolymer is soluble m certan fluorocabons and has the same chemical and oxidative stability as crystallme TFE homopolymers [5]... 

Flame resistance The underwriters ruling on the use of self-extinguishing plastics for contact-carrying members and many other components introduces critical material selection problems. All TSs are basically self-extinguishing. Nylon, polyphenylene oxide, polysulfone, polycarbonate, vinyl, chlorinated polyether, chlorotrifluoroethy-lene, vinylidene fluoride, and fluorocarbon are examples of TPs that may be suitable for applications requiring self-extinguishing properties. Cellulose acetate and ABS are also available with these properties. Glass reinforcement improves these materials considerably. 

Moisture Deteriorating effects of moisture are well known as reviewed early in this chapter (OTHER BEHAVIOR, Drying Plastic). Examples for high moisture applications include polyphenylene oxide, polysulfone, acrylic, butyrate, diallyl phthalate, glass-bonded mica, mineral-filled phenolic, chlorotrifluoroethylene, vinylidene, chlorinated polyether chloride, vinylidene fluoride, and fluorocarbon. Diallyl phthalate, polysulfone, and polyphenylene oxide have performed well with moisture/steam on one side and air on the other (a troublesome... 

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