n the early days of the plastics industry, polymers were generally considered low-cost, low-quality alternatives to metals, wood products and ceramics. During the past 40 years, however, plastics technology has advanced dramatically. Today, plastics provide significant performance advantages over other classes of materials in many demanding applications.

The purpose of this article is to highlight key benefits of plastics compared with other materials. These advantages can serve as discussion points as IAPD members educate customers, develop new applications and expand the market for plastic materials.

Plastics and composites have specific gravities ranging from 0.91 to 2.24. These values are lower than those of many commercially available ceramics and metals. This low density provides numerous benefits in machinery design, including reduced power requirements for moving parts, fuel savings and lower stress on mechanical drive systems.

Thermoplastic composites reinforced with glass or carbon fiber offer high strength and modulus, or stiffness. This makes them suitable for applications such as drones and military equipment, where strength and lightweight performance are required.

One major advantage of polymer materials is their toughness and impact resistance. A plastic coffee cup, for example, is generally more durable than a ceramic cup, which is prone to brittle fracture.

Performance plastics such as high-molecular-weight polyethylenes maintain ductility even at cold winter temperatures. That is why they are specified for applications such as truck bed liners and animal feed troughs. High-performance polymers such as PEEK and polyimide maintain ductility at cryogenic temperatures below minus 150 degrees Celsius. This makes them suitable for cryogenic bearings and seals.

Unfilled thermoplastics are softer than metals or ceramics, with modulus values ranging from 70 kpsi to 700 kpsi, compared with 10,000 kpsi for 6061-T6 aluminum and 30,000 kpsi for zirconia ceramic. This lower stiffness allows plastics to conform to mating metal surfaces and create tight seals under relatively light mechanical loads.

Materials such as nylon, acetal, PTFE and PEEK are used for sealing applications, including valve seats and gaskets. They are soft enough to form seals against metal while remaining stiff enough to prevent leak paths for pressurized fluids.

Polymers including nylon, acetal, PTFE and ultra-high-molecular-weight polyethylene are often specified for sliding wear applications. Plastic components can achieve low friction and low wear rates by depositing microscopic transfer films onto mating metal surfaces. Plastics also tend to cause minimal wear on mating metal components, supporting long service life.

In contrast, metal-on-metal contact typically requires external lubrication. This may be undesirable in industries such as food processing, pharmaceuticals, aerospace and semiconductor manufacturing. Unlubricated metal contact can result in severe wear known as galling.

Road salt, moisture and other corrosive chemicals can quickly degrade wood products and metals. Performance plastics often perform well in these environments. Rigid polyurethane foams, for example, have replaced wood in many carved outdoor signs. Thermoformed plastic body panels are also used instead of painted sheet metal in agricultural and construction equipment because of their resistance to corrosion.

Manufacturers can control the appearance and feel of plastic parts, including color, gloss and texture, without secondary operations such as painting, plating or powder coating. As a result, plastics are used in applications such as office furniture, retail point-of-purchase displays, aircraft interiors and architectural wall coverings.

Electrical grades of plastics, including Noryl, Ultem, PEEK and thermoset laminates, are used as insulators because of their high dielectric strength and resistance to arcing. Metals are unsuitable for these applications because of their electrical conductivity.

Performance plastics such as PTFE, polyethylene and polycarbonate are also transparent to radio frequency, or RF, signals because of their low dielectric constants and dissipation factors. This allows them to be used as radomes to protect antennas without significantly attenuating RF transmissions.

Plastics can be molded into complex shapes with short cycle times and relatively low processing temperatures compared with metals and ceramics. This enables production of intricate parts with minimal labor. For example, a plastic machine housing can be thermoformed in a single process. A similar sheet metal housing may require bending, welding and painting.

IAPD member companies continue to develop new materials and processes that expand the market for performance plastics. Examples include formulations with enhanced friction and wear characteristics, decorative sheet materials and thermoplastic composites with mechanical properties approaching those of metals.

Plastics vs. metals: Plastics are lightweight, corrosion-resistant and electrically insulating. They are also transparent to RF signals.

Plastics vs. ceramics: Plastics are lightweight, durable, and easier to machine and mold into complex shapes.

Plastics vs. wood products: Plastics resist rot and moisture-related degradation and do not require coatings to maintain appearance or weatherability.