What Is Polyetherimide (PEI)?
Polyetherimide (PEI) is a high-performance, amorphous thermoplastic. It is a robust and transparent polymer. It has a high glass transition temperature (217°C). It consists of repeating aromatic imide units.
PEI offers an excellent balance of properties like:
- High strength and rigidity
- Dimensional stability
- Good electrical insulation properties
- Resistance to flame, chemical, and high temperature
It can be easily processed as its toughness remains stable over a wide temperature range. These assets make it a chosen alternative to metals & other high-performance plastics. Suitable for aerospace, medical devices, electronics, and several other applications.
What are the characteristics of polyetherimide?
Polyetherimide (PEI) is an amorphous, high-performance polymer known for its exceptional thermal, mechanical, and chemical properties.
Physical Properties:
PEI is an amorphous polymer. Unlike semi-crystalline polymers, it does not have a defined crystal structure, which contributes to its transparency and inherent toughness. Its amorphous nature allows it to exhibit consistent properties over a wide temperature range.
Dimensional Stability:
PEI is an ideal material of choice to produce complex parts with very tight tolerances. The polymer exhibits excellent dimensional stability even when used under high-temperature and high-humidity conditions.
Electrical Properties:
PEI has excellent electrical insulation properties. High volume resistivity and insulation resistance are retained after exposure to high-humidity environments. It has a less pronounced O2 sensitivity. It can be conveniently doped to get high conductivity.
Thermal Properties and Fire Resistance:
PEI is a high-temperature specialty polymer. Most of the PEI compounds pass UL94V-0 standard without adding flame retardant. PEI can withstand temperatures up to 200°C for prolonged periods and can endure short-term exposure to temperatures as high as 340°C.
Mechanical Properties:
PEI has high strength, high rigidity, and low degradation characteristics even in high-temperature conditions. It also shows excellent fatigue endurance and creep resistance. PEI has a lower elongation to break, a higher cost, and is rather brittle. Today, PEI is available in different forms and grades such as compounds, fibers, filaments, films, and coatings.
Chemical Properties:
PEI has good chemical resistance. It is unaffected by alcohols, ketones, chlorinated aliphatic compounds, esters, liquid ammonia, etc. It also tends to be affected by dilute HCl, nitric acids, and concentrated sulfuric acid. It is insensitive to moisture and has good weatherability.
What is polyetherimide used for?
Electronic and Electrical Applications
Owing to its high temperature resistance, excellent dimensional stability, exceptional toughness, and superior rigidity, PEI becomes an ideal material of choice in E&E market.
- Offers outstanding flow and low shrinkage for precision molding of connectors and sockets
- Provides superior stiffness and mechanical integrity for reliable assembly, and
- Is the most stable material choice for all soldering methods
PEI compounds also have UL94 V-0 flammability ratings without the use of flame retardant additives. Special low flash grades have been developed to meet the needs of high precision molding applications. In the electrical / electronic sector, Polyetherimide is also used to manufacture a range of articles including bobbins and connectors, hard disk drives, electronic housings, sockets, switches and relays. The key trend influencing PEI growth in electrical / electronic applications is substitution of other lower temperature polymers.
Automotive Applications
Polyetherimide (PEI) applications in the automotive market have seen strong growth mainly due to its ability to replace metal, thermosets, and other types of plastic, in more demanding applications. It is an ideal choice for automotive parts exposed to:
High temperatures, Automotive fluids, or Mechanical stress
PEI is a lighter weight alternative to metals, resistant to corrosion by salts and all automotive fluids. The ability to mold complex parts to tight tolerances and insert molding capability accommodate multiple component integration.
Under-the-hood is the largest application area for PEI followed by electrical parts. PEI applications in automotive include fuel injection systems, coolant systems, water pump impellers, thermostat holder, electric brakes, switches, bulb housing, and so on.
It is rarely used for the manufacture of interior or exterior auto parts.
Industrial Applications
PEI has been replacing metal alloys, thermosets, and many other thermoplastics in mechanical engineering applications. The thermal stability and broad chemical resistance of Polyetherimide make it exceptionally well suited to service in very hostile chemical environments.
It finds uses in many heavy industrial applications, including some outside the arena of reinforced injection molding compounds
- It is used in fiber extrusion as well as in non-stick and chemical resistant coatings
- It is well suited to manufacture mechanically and thermally highly stressed molded parts
- In machine construction and precision engineering, PEI is used for various components such as pumps, valves, and piping
- It can also be found in oil field equipment such as lift and centrifugal pump components, oil patch drop balls, rod guides, and scrapers
- In the heating, ventilation, and air conditioning (HVAC) equipment sector, Polyetherimide is used for compressors, mufflers/reservoirs, hot water circulation components, induced draft blower housing, motor relays and switches, power vent components, and thermostat components
Medical and Healthcare Applications
PEI compounds (typically glass reinforced grades) are used in medical applications such as surgical instruments and device components & parts that require high dimensional stability, strength, and heat resistance. PEI fibers are also used in medical fibers and membranes.
What is the difference between PEI and ULTEM?
One of the most common questions we’re asked about PEI and Ultem is, “Is there any difference between the two?”
The truth is, Ultem is the brand name for a type of PEI. A good way to think about it is the difference between a Band-Aid and an adhesive bandage. Both PEI and Ultem are polyetherimide. However, PEI is a single material, while the Ultem brand includes other advanced polyimide materials.
Depending on the polyimide material that fits closest to your ideal range of mechanical strength, thermal stability, or price range, you might choose PEI or Ultem for your component design.
By the time you’re looking to transform your design from raw material into a component, you’ll want to select the most appropriate materials for your purpose.
Is polyetherimide toxic?
Polyetherimide is generally considered to be a safe and non-toxic material. PEI can pose a risk to human health and the environment if not handled properly or used inappropriately. Hence, it is important to follow proper safety protocols and guidelines.
