These combine very high strength, good temperature and abrasion resistance, exceptional dimensional stability, and low coefficient of thermal expansion. They compete with nylon (but with many better properties) and with metal die castings (but are lighter). Chemical resistance is good except for strong acids. Typical applications are water-pump parts, pipe fittings, washing machines, car instrument hous- ings, bearings, and gears.
Acrylics (Methylmethacrylate, PMMA)
These are noted for their optical clarity and are available as sheet, rod, tubings, etc., as Perspex (U.K.) and Plexiglas (
Acrylonitrile-Butadiene-Styrene (ABS)
This combination of three monomers gives a family of materials which are strong, stiff, and abrasion resistant with notable impact-resistance properties and ease of processing. The many applications include pipes, refrigerator liners, car-instrument surrounds, radiator grills, telephones, boat shells, and radio and television parts. Available in medium, high, and very high impact grades.
Cellulosics
“Cellulose nitrate” is inflammable and has poor performance in heat and sunlight. Its uses are therefore limited. Cellulose acetate has good strength, stiffness, and hardness and can be made self-extinguishing. Glass-filled grades are made. Cellulose acetate-butyrate (CAB) has superior impact strength, dimensional stability, and service temperature range and can be weather stabilized. Cellulose proprionate (CP) is similar to CAB, but has better dimensional stability and can have higher strength and stiffness. Ethyl cellulose has better low-temperature strength and lower density than the others. Processing of cellulose plastics is by injection molding and vacuum forming. Applications include all types of moldings, electrical insulation, and toys.
Ethylene-Vinyl Acetate (EVA)
This material gives tough flexible moldings and extrusions suitable for a wide temperature range. Thematerial may be stiffened by the use of fillers and is also specially formulated for adhesives. Applications include all types of moldings, disposable liners, shower curtains, gloves, inflatables, gaskets, and medical tubing. The material is competitive with polyvinyl chloride (PVC), polyethene, and synthetic rubbers,
and is also used for adhesives and wax blends.
Fluorocarbons
This class of polymers, characterized by fluorine substitution, has outstanding chemical, thermal, and electrical properties and is characterized by the following four main classes of structures. Polytetrafluoroethylene (PTFE), known commercially as Teflon or Fluon, is the best-known material and resists all known chemicals, weather, and heat, has an extremely low coefficient of friction, and is “non-stick.” These materials are inert with good electrical properties. They are nontoxic, nonflammable, and have a working temperature range of –270 to 260°C. They may be glass filled for increased strength
and rigidity. They do not melt and they must be formed by sintering of powders. Applications include chemical, mechanical, and electrical components, bearings (plain or filled with glass and/or bronze), tubing, and vessels for “aggressive” chemicals.
Fluoroethylenepropylene (FEP), unlike PTFE, can be processed on conventional molding machines and extruded, but thermal and chemical resistance properties are not quite as good. Ethylenetetrafluoroethylene (ETFE) possess properties similar to but not as good as those of PTFE.However, the material exhibits a thermoplastic character similar to that of polyethylene which gives it a very desirable molding behavior.
Perfluoroalkoxy (PFA) is the fourth group of fluorinated polymers. These materials have the same excellent properties as PTFE, but the compound is melt processible and, therefore, suitable for linings for pumps, valves, pipes, and pipe fittings.
Ionomers
These thermoplastics are based on ethylene and have high melt strength, which makes them suitable for deep forming, blowing, and other similar forming processes. They are used for packaging, bottles,moldings for small components, tool handles, and trim. They have a high acceptance of fillers.
Polymethylpentene
Polymethylpentene (TPX) is a high-clarity resin with excellent chemical and electrical properties and the lowest density of all thermoplastics. It has the best resistance of all transparent plastics to distortion at high temperature — it compares well with acrylic for optical use, but has only 70% of its density. It is used for light covers, medical and chemical ware, high-frequency electrical insulation, cables, micro-wave oven parts, and radar components. It can withstand soft soldering temperatures.
Polyethylene Terephthalate
Polyethylene terephthalate (PETP) and modified versions thereof have high strength, rigidity, chemical and abrasion resistance, impact resistance in oriented form, and a low coefficient of friction. It is attackedby acetic acid and concentrated nitric and sulfuric acids. It is used for bearings, tire reinforcement,bottles, automotive parts, gears, and cams.
Polyamides (Nylons)
The polyamides are a family of thermoplastics, e.g., Nylon 6, Nylon 66, and Nylon 610, which areamong the toughest engineering plastics with high vibration-damping capacity, abrasion resistance,inherent lubricity, and high load capacity for high-speed bearings. They have a low coefficient of frictionand good flexibility. Pigment-stabilized types are not affected by ultraviolet radiation and chemicalresistance is good. Unfilled nylon is prone to swelling due to moisture absorption. Nylon bearings maybe filled with powdered molybdenum disulfide or graphite. Applications include bearings, electrical
insulators, gears, wheels, screw fasteners, cams, latches, fuel lines, and rotary seals.
Polyethylene
Low-density polyethylene (orinally called polythene) is used for films, coatings, pipes, domestic mold-ings, cable sheathing, and electrical insulation. High-density polyethylene is used for larger moldingsand is available in the form of sheet, tube, etc. Polyethylene is limited as an engineering material because of its low strength and hardness. It is attacked by many oxidizing chemical agents and some hydrocarbonsolvents.
Polyketone, Aliphatic
Aliphatic polyketones are relatively strong, tough, ductile polymeric resins derived from equal propor-tions of ethylene and carbon monoxide with an additional few percent of higher olefin for property and processibility adjustment. Their physical, thermal, and mechanical properties are similar to polyamides and polyacetals. Mechanical properties are characterized by preservation of high levels of stiffness,
toughness, and strength over a broad temperature range. Resistance to hydrolysis, swelling, and perme-ation provides broad chemical resistance. Relatively new in commercial supply, they find application ingears, machine components, and similar engineering applications. Tribological performance is very good,and in particular they have a low coefficient of friction and a low wear factor against steel. The electrical
properties of the neat polyketone are typical of those of polar, semicrystalline thermoplastics.
Polyethersulfone
Polyethersulfone is a high-temperature engineering plastic — useful up to 180°C in general and some grades have continuous operating ratings as high as 200°C. It is resistant to most chemicals and may be extruded or injection molded to close tolerances. The properties are similar to those of nylons.Applications are as a replacement for glass for medical needs and food handling, circuit boards, general electrical components, and car parts requiring good mechanical properties and dimensional stability.
Polystyrene
This polymer is not very useful as an engineering material because of brittleness in unmodified forms, but it is well known for its use in toys, electrical insulation, refrigerator linings, packaging, and numerous commercial articles. It is available in unmodified form as a clear transparent resin and also in clear and opaque colors. High-impact forms are achieved by compounding with butadiene or other rubbery resins and heat-resistant forms are achieved by the use of fillers. Polystyrene can be stabilized against ultraviolet radiation and also can be made in expanded form for thermal insulation and filler products. It is attacked by many chemicals, notably aromatic hydrocarbon solvents, and by ultraviolet light.
Polysulfone
Polysulfone has properties similar to nylon, but these properties are retained up to 180°C compared with 120°C for nylon, which greatly expands the range of applications. Its optical clarity is good and its moisture absorption lower than that of nylon. Applications are as a replacement for glass for medicalneeds and chemistry equipment, circuit boards, and many electrical components.
Polyvinyl Chloride
This is one of the most widely used of all plastics. With the resin mixed with stabilizers, lubricants, fillers, pigments, and plasticizers, a wide range of properties is possible from flexible to hard types, in transparent, opaque, and colored forms. It is tough, strong, with good resistance to chemicals, good low- temperature characteristics and flame-retardant properties. PVC does not retain good mechanical per-formance above 80°C. It is used for electrical conduit and trunking, junction boxes, rainwater pipes and gutters, decorative profile extrusions, tanks, guards, ducts, etc.
Polycarbonate
Polycarbonate is an extremely tough thermoplastic with outstanding strength, dimensional stability, and electrical properties, high heat distortion temperature and low-temperature resistance (down to –100°C).It is available in transparent optical, translucent, and opaque grades (many colors). Polycarbonates have only fair resistance to chemicals as evidenced by the stress cracking caused by many solvents. The weathering tendencies can be stabilized against ultraviolet radiation by the use of proper additives.
Polycarbonate compounds are used for injection moldings and extrusions for glazing panels, helmets, face shields, dashboards, window cranks, and gears. Polycarbonate is an important engineering plastic.
Polypropylene
Polypropylene is a low-density, hard, stiff, creep-resistant plastic with good resistance to chemicals, good wear resistance, low water absorption, and is relatively low cost. Polypropylene can be spun into filaments, converted into weaves, injection molded, and is commonly produced in a large variety of forms. Glass-filled polypropylene is widely used for its enhanced mechanical properties. It is used for food and chemical containers, domestic appliances, furniture, car parts, twine, toys, tubing, cable sheath, and bristles.
Polyphenylene Sulfide
Polyphenylene sulfide is a high-temperature plastic useful up to 260°C. Ambient temperature properties are similar or superior to those of nylon. It has good chemical resistance and is suitable for structural components subject to heat. Glass filler improves strength and enables very high heat resistance to 300°C. Uses are similar to those of nylon, but for higher temperatures.
Polyphenylene Oxide
This is a rigid engineering plastic similar to polysulfone in uses. It can be injection molded and hasmechanical properties similar to those for nylon. It is used for automotive parts, domestic appliances,and parts requiring good dimensional stability. Frequently, the commercially available product is blended (or “alloyed”) with polystyrene which acts as a cost-effective extender.
Posts
