Polyetherimide (PEI), a high-performance thermoplastic known as Ultem, is valued in aviation for its strength and flame resistance.

Background and Evolution

PEI was developed in the early 1980s by General Electric (later SABIC), entering commercial use as Ultem by 1982. Its aviation adoption began with aircraft like the Boeing 767, replacing metals in interiors and fittings due to its toughness. It remains key in modern planes like the Boeing 777, prized for its balance of properties.

How Polyetherimide is Used

PEI, a rigid amber plastic, is molded into:

• Interior Cladding: Forms cabin panels and overhead bins, enhancing safety and durability.
• Electrical Connectors: Shapes housings and terminals, resisting heat and shorts.
• Structural Fittings: Used in brackets and seat supports, bearing moderate loads.
• Galley Components: Constructs trays and carts, withstanding wear and heat.

Why Polyetherimide is Used

• High Strength: Offers tensile strength (~90–105 MPa), supporting structural roles.
• Flame Resistance: Self-extinguishing, meets FAA flammability standards (e.g., FAR 25.853), ideal for cabin safety.
• Heat Tolerance: Operates up to 200°C, suited for electrical and galley zones.
• Lightweight: At 1.27 g/cm³, cuts mass compared to metals, aiding efficiency.
• Transparency: Provides optical clarity in some grades, useful for visible parts.

Technical Specifications

• Density: 1.27 g/cm³, lighter than PEEK.
• Melting Point: ~217°C (amorphous, softens), robust for moderate heat.
• Hardness: 85–95 Rockwell R, tough and durable.
• Dielectric Strength: ~30 kV/mm, strong insulation.

Comparison to Alternative Materials

• PEEK: More heat-resistant and stronger, but costlier.
• Polycarbonate: Clearer and cheaper, but less heat-tolerant.
• PPS: Similar heat resistance, but less transparent and flexible.
• ABS: More affordable, but weaker and less flame-resistant.

PEI excels in strength and fire safety.

Role in Modern Aviation

In aircraft like the Airbus A320 and Boeing 737 MAX, PEI reinforces interiors, connectors, and fittings, ensuring durability and compliance. It pairs with polycarbonate for clarity and PEEK for high-heat roles, boosting safety in models like the Boeing 777.

Environmental and Economic Considerations

• Production: Moderate energy use, with high material costs.
• Cost: Pricier than ABS, offset by longevity and safety.
• Recycling: Reprocessable, though aviation additives may limit reuse.

Future Trends

Reinforced PEI or cost-reduced grades could widen its use, though PEEK may dominate in extreme applications.

Summary

PEI’s strength, flame resistance, and heat tolerance make it essential for aviation’s interiors and connectors. From its 1980s debut, it has bolstered safety and performance, securing a versatile role.