Plastic High resistivity

Traditionally, hood interiors were made from asbestos sheets, which had both good chemical and good heat resistance. Their main problem was that they absorbed any liquid that was spilled on them. Asbestos has now lost its favor because of its toxic properties. Modem hoods usually have interiors of highly resistant plastic, often fiberglass reinforced. Such surfaces are easy to keep clean, but their temperature resistance may be limited. 

See also resistance (electrical) resistivity high-resistivity plastics. 

Bisphenol A. One mole of acetone condenses with two moles of phenol to form bisphenol A [80-05-07] which is used mainly in the production of polycarbonate and epoxy resins. Polycarbonates (qv) are high strength plastics used widely in automotive appHcations and appHances, multilayer containers, and housing appHcations. Epoxy resins (qv) are used in fiber-reinforced larninates, for encapsulating electronic components, and in advanced composites for aircraft—aerospace and automotive appHcations. Bisphenol A is also used for the production of corrosion- and chemical-resistant polyester resins, polysulfone resins, polyetherimide resins, and polyarylate resins. 

Electrical Properties. Poly(methyl methacrylate) has specific electrical properties that make it unique (Table 4). The surface resistivity of poly(methyl methacrylate) is higher than that of most plastic materials. Weathering and moisture affect poly(methyl methacrylate) only to a minor degree. High resistance and nontracking characteristics have resulted in its use in high voltage appHcations, and its excellent weather resistance has promoted the use of poly(methyl methacrylates) for outdoor electrical appHcations (22). 

Precipitation Hardening Alloys. Copper alloys that can be precipitation hardened to high strength are limited in number. In addition to the metallurgical requirement that the solubiUty of the added element(s) decrease with temperature, the precipitated phase that forms during aging must be distributed finely and have characteristics that act to resist plastic deformation. 

Plastic Materials In comparison with metalhc materials, the use of plastics is limited to relatively moderate temperatures and pressures [230°C (450°F) is considered high for plastics]. Plastics are also less resistant to mechanical abuse and have nigh expansion rates, low strengths (thermoplastics), and onlv fair resistance to solvents. However, they are lightweight, are good thermal and elec trical insiilators, are easy to fabricate and install, and have low fric tion factors. 

Polypropylene has a chemical resistance about the same as that of polyethylene, but it can be used at 120°C (250°F). Polycarbonate is a relatively high-temperature plastic. It can be used up to 150°C (300°F). Resistance to mineral acids is good. Strong alkalies slowly decompose it, but mild alkalies do not. It is partially soluble in aromatic solvents and soluble in chlorinated hydrocarbons. Polyphenylene oxide has good resistance to ahphatic solvents, acids, and bases but poor resistance to esters, ketones, and aromatic or chlorinated solvents. 

The high thermal stability of the carbon-fluorine bond has led to considerable interest in fluorine-containing polymers as heat-resistant plastics and rubbers. The first patents, taken out by IG Farben in 1934, related to polychlorotri-fluoroethylene (PCTFE) (Figure 13.1 (a)), these materials being subsequently manufactured in Germany and the United States. PCTFE has been of limited application and it was the discovery of polytetrafluoroethylene (PTFE) (Figure... 

NBR adhesives are characterized by high resistance to oils and plasticizers, excellent heat resistance and superior adhesion to metallic substrates. 

Chemical Reactivity - Reactivity with Water No reaction Reactivity with Common Materials Reacts violently with aluminum. May cause fire on contact with common materials such as wood, cotton, straw. Iron, steel, stainless steel, and copper are corroded by bromine and will undergo severe corrosion when in contact with wet bromine. Plastics are also degraded/ attacked by bromine except for highly fluorinated plastics which resist attack Stability During Transport Stable Neutralizing Agents for Acids and Caustics Not pertinent Polymerization Not pertinent Inhibitor of Polymerization Not pertinent. 

Plastics are highly resistant to a variety of chemicals. They have a high strength per unit weight of material therefore, they are of prime importance to the designer of chemical process equipment. Their versatility in properties has provided new and innovative designs of equipment. They are excellent substitutes for expensive nonferrous metals. 

Figure 9-6V. Jaeger Tri-Packs high-performance packing fabricated of corrosion resistant plastic. Used by permission of Jaeger Products, Inc.

Lenses for safety glasses are made from highly impact resistant plastics such as modified acrylics and polycarbonate. They will resist puncture from flying objects and offer the exceptional eye protection. They can be molded to prescription requirements. 

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