Ultem Sheet (PEI)
Ultem® or Polyetherimide (PEI) is an amorphous engineering thermoplastic. It is characterized by high heat resistance — CUT = 338°F (170°C), high strength and modulus, as well as excellent electrical insulating properties, which are stable over wide ranges of temperature and frequency. Its molecular structure consists of alternating aromatic imide and ether groups. Imide groups provide strength at high temperatures, while flexible ether group linkages ensure relatively easy processing. Unmodified polyetherimide resin is transparent with an amber tint.
Polyetherimide has good creep resistance as indicated by its apparent modulus of 350,000 psi (3,410 MPa) after 1,000 hours at 180°F (82°C) under an initial applied load of 5,000 psi (34.5 MPa). The coefficient of linear thermal expansion is 3.1 x 10-5 in/in-°F (0.56 x 10-4/°C) for the base resin, but can be as low as 1.1 - 0.8 x 10-5 in/in-°F (0.19 - 0.14 x 10-4/°C) in glass-filled grades. Moisture absorption is also low, giving the material excellent dimensional stability in a variety of environments. Although unfilled PEI is not a particularly good bearing material, internally lubricated PEI, particularly carbon fiber filled grades, do show good friction and wear characteristics.
Polyetherimide resists a broad range of chemicals, though chemical resistance is strongly dependent on stress. Compatibility has been demonstrated with aliphatic hydrocarbons and alcohols including gasoline and gasohol, mineral-salt solutions, dilute bases and fully halogenated hydrocarbons. The polymer is attacked by partially halogenated solvents such as methylene chloride by strong bases and aromatic hydrocarbons such as benzene and toluene. Stress, applied or internal, can significantly reduce the chemical resistance of PEI. Resistance to UV radiation is good even in unfilled grades; change in tensile strength after 1,000 hours of xenon arc exposure is negligible. PEI is resistant to gamma radiation. Strength loss was less than 6 percent after 500 megarads exposure to cobalt 60 at one mrad/hr. Hydrolitic-stability tests show more than 85 percent of the tensile strength is retained after 10,000 hours of boiling water immersion. The material is also suitable for short-term steam exposure as in autoclaving, though repeated autoclaving will cause crazing after about 900 cycles. Dielectric constant remains virtually constant between frequencies of 60 and 109 Hz. Both dielectric constant and dissipation factor (loss) are relatively insensitive to temperature. High dielectric strength and resistivity combined with low dielectric constant and loss make PEI an excellent electrical insulator. Arc resistance (128s) exceeds the UL electrical requirements for sole support of live parts. Principal areas of use for polyetherimide resin include electrical/electronic, automotive, aerospace and specialty applications. PEI APPLICATIONS
• High-voltage circuit-breaker housings
• Integrated circuit chip carriers for accelerated testing at
• Noncombustible plenum connectors
• High-temperature bobbins, coils, fuseblocks and wirecoatings
• Printed-wiring boards
• Jet-engine components
• Aircraft interior and electrical hardware components
• Microwave applications, replacing glass in medical lamps
• Under-the-hood automotive components