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Polyimide (PI) Plastic: High-Temperature Performance Beyond PEEK
Key Properties of Polyimide
· Glass transition temperature: above 360°C — classic grades do not melt
· Continuous service temperature: up to 250°C; short-term peaks to 300°C
· Tensile strength: 70–100 MPa, retained well at elevated temperature
· Excellent radiation resistance — among the best of any organic material
· Very low outgassing — suitable for vacuum and space applications
· Inherent self-lubricating behaviour with good wear performance
· Operates from cryogenic temperatures to sustained high heat
PI vs PEEK: A Practical Comparison
Property | PI | PEEK |
Continuous service temp (°C) | ~250 (short-term 300+) | 250 |
Glass transition (°C) | >360 | 143 |
Tensile strength (MPa) | 70–100 | 90–100 |
Radiation resistance | Outstanding | Good |
Chemical resistance | Good (weak in strong alkalis) | Excellent |
Processing | Compression sintered (classic grades) | Melt-processable |
Relative cost | Higher | High |
PEEK remains the more versatile choice thanks to melt processability and broader chemical resistance. PI earns its premium where temperatures exceed PEEK’s comfort zone for long durations, where radiation is present, or where outgassing must be minimal.
Common Applications
· Semiconductor — test sockets, high-temperature carriers, wafer handling tools
· Aerospace — bearings, seals, electrical insulators exposed to heat and radiation
· Vacuum systems — low-outgassing spacers and insulators
· Industrial machinery — hot-runner insulators, high-speed wear rings
Machining Considerations
Because classic PI grades cannot be remelted, components are produced by compression sintering stock shapes and then precision machining. Carbide tooling, sharp geometries, and controlled heat build-up are essential. NAGOMER supplies PI stock shapes and finished parts machined to customer drawings.
Grades and Filler Options
PI stock shapes are offered in several formulations, each trading a little of one property for more of another. Unfilled PI delivers the best electrical insulation, lowest outgassing, and the classic amber appearance valued in vacuum and test equipment. Glass-fibre filled grades (typically 30%) raise stiffness and dimensional stability for structural jigs and hot fixtures, at some cost in insulation performance. Graphite-filled grades cut friction and boost wear life for bearings, seal rings, and thrust washers running at temperatures where PEEK-based composites are marginal. Black grades add a measure of light screening for optical assemblies. NAGOMER can advise on the right grade and machine finished components from certified stock with full traceability.
To compare PI with other high-temperature plastics, see our PEEK vs PEI (ULTEM) comparison and PPS GF40 vs PEEK guide.
FAQ
Q1: Can polyimide be injection moulded?
Classic PI grades cannot — they are compression sintered from powder and then machined. Some modified thermoplastic polyimides can be melt processed, but standard PI stock shapes are sintered.
Q2: How does PI compare to PEEK at high temperature?
Both serve continuously at 250°C, but PI’s glass transition is far higher (>360°C versus 143°C), so it stays stiffer at peak temperatures and tolerates short excursions to 300°C and beyond.
Q3: Is PI suitable for vacuum applications?
Yes. Its very low outgassing makes PI a preferred insulating and structural material in vacuum chambers and space hardware.
Q4: What colour is PI plastic?
Typical PI stock shapes are amber-brown to dark brown or black, depending on grade and filler.
Q5: Is PI more expensive than PEEK?
Generally yes, reflecting its synthesis route and compression sintering process. Use PI only where its temperature, radiation, or outgassing advantages are genuinely needed.
Evaluating PI for extreme-temperature components? Contact NAGOMER for material selection advice and machined PI parts to your drawing.
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NAGOMER — Professional Engineering Plastics Solutions
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