Page 204 - Engineering Plastics Handbook

Thermoplastic Polyetherimide (PEI) 177

volumes do not justify the cost of cutting steel tooling in which to mold
parts. Fine-denier fibers, which are useful in some flame-retardant appli-
cations, have also been drawn from various PEI resins [47, 48].
Because they are thermoplastic, PEI resins can be easily recycled via
grinding up old parts and remelting them to form new shapes. This can
be done with both post-industrial and post-consumer recycle. In some
cases, such as automotive lighting, metallized reflectors may be reused
to make parts without removing the thin metal layer [49]. As in all recy-
cling operations, care must be taken to keep the recyclate free of con-
tamination. In addition, since PEI resins can undergo degradation under
abusive processing, parts containing recyclate must be tested to ensure
they meet all end-use and regulatory requirements.
Thermoplastic PEI resins can be formed into either low-density or
high-density (structural) foams [50, 51]. Structural-foam resins (10 to
30% density reduction) are useful in forming large parts with reduced
weight, improved flow, and few sink marks. Both gas injection and
chemical-blowing agents may be used. Low-density foams (>50% den-
sity reduction) are used as panels in transport applications where
strength, ignition resistance, and sound damping are possible benefits.
PEI resins may also be processed by using profile extrusion (single or
multilayer), blow molding, or gas-assist molding.
As molded, PEI resins have very smooth, glossy surfaces. These sur-
faces may be directly metallized by vacuum sputtering or similar
processes [52]. Parts can be metallized as molded with no base coating or
secondary operation. They show good metal adhesion [53]. Metal-coated
PEI resins are used in a variety of lighting applications as reflectors for
high-temperature use such as projectors and automotive forward light-
ing. Their excellent dimensional stability makes them especially valuable
where precise focus of the reflected light is important.

Applications
PEI resins have been used in a variety of applications such as electri-
cal connectors, internal computer parts, printed-circuit boards, flexible
circuits, optical fiber connectors, fire helmets, large appliances, aircraft
interiors, trays, microwave cookware, reflectors, motor parts, gears,
pumps, lubrication systems, wire coating, industrial applications, bear-
ings, small appliances, films, and fibers. Polyetherimides are used in a
wide range of applications. A few of the key markets for PEI resins and
some of the benefits they bring to the application are summarized below.
■ Food service: resistance to greases and oils, microwave- and dish-
washer-safe, good practical impact, repeated food-contact compliant,
and stain-resistant