How to Choose the Right Plastic
Acetal (Delrin) is a common engineering thermoplastic with excellent dimensional stability. It’s perfect for high precision parts requiring rigidity, excellent mechanical strength, and low friction. It’s a logical next level up from HDPE. Acetal is available in both copolymer and homopolymer form. Acetal homopolymer is known by the brand name Delrin, produced by DuPont. Because many of their properties are within 10% of each other, acetal copolymer and homopolymer (Delrin) are often interchangeable. The acetal copolymer may, however, be more appropriate where hot water performance is key. The copolymer has less porosity than Delrin, and thus a slightly lower water absorption rate. This can be critical for moist applications such as plumbing, impellers, pumps, valve and valves stems. Delrin, on the other hand, has a greater crystalline structure, giving it improved mechanical strength and creep resistance over copolymer acetal. Common applications for both forms of acetal including bearings, bushings, electrical components, gears, rollers, and pump and valve parts.
Acrylic is available in a large number of opaque and translucent colors, or in an optically clear form. Acrylic is more flexible and shock resistant than glass. It is known for excellent weathering and long service life, high light transmission, and abrasion resistance. Indeed, acrylic has the greatest surface hardness of any thermoplastic. It is resistant to UV and chemical damage, easily cleaned, cut or machined. It is corrosion resistant and a good insulator. Common applications include: Window glazing, machine guards, signs, skylights, transparent manifolds, lighting fixtures, furniture, table tops, POP and trade show displays, camera lenses, aquariums, toys, and incubators.
ABS (Acrylonitrile Butadiene Styrene) is a common thermoplastic noted for its relative low cost and toughness. It is an easily machined, rigid plastic with high impact strength. ABS provides a good balance between chemical resistance, mechanical toughness, electrical insulating properties, wide temperature ranges, and dimensional stability. Because of its good dimensional stability, ABS is often used for preproduction prototypes. It is also used for pipes and fittings, valve bodies, and in material handling equipment.
Chlorinated Polyvinylchloride is available in both opaque and transparent sheet form. It has high temperature strength and excellent flammability properties, as well as exceptional corrosion resistance and good mechanical properties. Because it meets the FM4910 flammability standard, CPVC is often called for in clean room settings.
Polyethylenes are available in a range of densities and formulations, and represent the largest volume of thermoplastic polymer in use today. They are characterized by toughness, excellent chemical resistance and electrical properties, and near-zero moisture absorption. They have good impact resistance, and HDPE’s self-lubricating properties make it useful in applications such as rollers and skids which need a non-stick, low-friction material. HDPE is available in black and “natural” (off-white) colors.
Nylon is known for excellent abrasion resistance, good wear, and low coefficient of friction. Nylon is most often used for various wear components such gears, cams, bearings, valve seats, and other parts requiring wear resistance, low coefficient of friction, and quiet operation. Because it is available in USDA approved and FDA compliant grades, it is also used in food processing applications. Nylon is available in several grades. “Nylon 6/6” is the most widely used, and has the lowest permeability by gasoline, mineral oil and fluorocarbon refrigerants. Other types include Nylons 11 and 12, which absorb less moisture and therefore have better dimensional stability and electrical properties.
An extremely strong and stiff plastic material. It is often used in high temperature environments where other thermoplastics would lose their mechanical properties. PAI has excellent dimensional stability with an extremely low coefficient of thermal expansion (CTE) making it an excellent choice for applications that require machining to tight tolerances. PAI is available in a variety of formulations including electrical, bearing and wear, and glass-filled grades.
Ultem is a semi-transparent, high temperature plastic material with extremely high strength and stiffness. Ultem is resistant to hot water and steam and can withstand repeated cycles in a steam autoclave. Ultem has outstanding electrical properties and one of the highest dielectric strengths of any thermoplastic material. Ultem is used when superior strength, stiffness, or temperature resistance is required. Ultem is available in glass-filled grades with enhanced strength and stiffness.
PEEK is a strong and stiff plastic material that is often used in applications where performance at high temperatures is required. PEEK has outstanding chemical resistance as well as resistance to steam and hot water. It has very low creep. Virgin PEEK or unfilled PEEK is naturally abrasion resistant. Bearing grade PEEK has enhanced bearing and wear properties.
Polycarbonate is a transparent, strong, and stiff thermoplastic with outstanding impact resistance. Its toughness and optical clarity make polycarbonate an ideal material for machine guards, indoor and outdoor signs, architectural glazing, face shields, skylights, and point-of-purchase displays. Polycarbonate rod and plate have excellent dimensional stability and are easy to machine. Machine grade polycarbonate is commonly used for electrical components, manifolds, sight glasses, and semiconductor machinery parts.
Polypropylene is a thermoplastic known for exceptionally good resistance to many chemical solvents, bases and acids. This makes it ideal for a wide range of laboratory and industrial applications. Polypropylene is a rugged material, easily machined, with good mechanical strength, impact resistance, and moisture resistance. Common applications include semiconductor equipment and components, wet benches and laboratory equipment, and chemical tanks.
PSU is an amber, semi-transparent, heat-resistant, high performance engineering thermoplastic. It has excellent mechanical, electrical and improved chemical resistance properties relative to polycarbonate. Polysulfone’s properties remain relatively consistent over a broad temperature range, from -150°F to 300°F. It is hydrolysis resistant for continuous use in hot water and steam at temperatures up to 300°F. Polysulfone offers high chemical resistance to acidic and salt solutions, and good resistance to detergents, hot water and steam. It is often used to replace polycarbonate when higher temperatures, improved chemical resistance, or the ability to withstand an autoclave is required. Common uses include analytical instrumentation, medical devices and semiconductor process equipment components.
Polytetrafluoroethylene (Teflon being a common brand name) is the most chemically resistant plastic known. Only a few chemicals will react with it. It has a very low coefficient of friction, and it is difficult to make anything stick to PTFE. It has excellent thermal and electrical insulation properties. PTFE’s mechanical properties are low compared to other engineering plastics, although its properties remain at useful levels through a very broad temperature range.
When corrosion resistance is key, consider PVC (polyvinyl chloride). It’s chemically nonreactive, and can be machined to close tolerances. It also has excellent electrical properties, low moisture absorption, good dimensional strength, and good compressive strength. PVC also has good flame resistance, and can be chemically bonded (glued). PVC’s disadvantages include poor weatherability, relatively low impact strength, and high weight. It’s easily scratched, and possesses a comparatively low heat distortion point. PVC is often used for corrosion resistant tanks, ducts, fume hoods, and pipe.
UHMW-PE is a polyethylene with excellent abrasion resistance and an extremely low coefficient of friction. It has high impact strength and excellent chemical resistance. On the other hand it suffers relatively high thermal expansion. UHMW-PE is commonly used in applications requiring maximum abrasion resistance and impact strength, with a low friction coefficient. Examples include conveyor belt wear strips, guide rails, bearings, and chute linings.