PI – polyimide (Vespel®, TECASINT, Duratron PI)
The highest-temperature plastic: continuous use near 290 °C, no melting
Polyimide is a polymer that does not melt: it decomposes first. That is why it works continuously near 290 °C, with peaks above that, and keeps dimensional stability and low creep where all other thermoplastics soften. It is sintered directly into rods, plates and parts. It absorbs moisture and is attacked by strong bases.
Designations and equivalents
| System | Designation |
|---|---|
| Abbreviation (ISO 1043) | PI |
| Trade names | TECASINT 2011 natural (Ensinger); Duratron D7000 PI (MCAM); Vespel SP-1 / SP-21 (DuPont) |
Standards by product form
| Form | Standard |
|---|---|
| Rod, sheet and sintered parts | Manufacturer's specification (DuPont Vespel, Ensinger TECASINT, MCAM Duratron) |
| Machined part to drawing | ISO 2768 tolerance or as per drawing |
Composition and filler
Nominal composition
| Component | Content |
|---|---|
| Polyimide | 100% (natural grade) |
| Filled grades | graphite, MoS₂ or PTFE (bearing grades) |
Mechanical properties
Typical values from the stock-shape manufacturer's catalog, 23 °C; ISO/ASTM methods as per the source
| Property | Value |
|---|---|
| Tensile strength | 130 MPa |
| Modulus of elasticity (tensile) | 3,600 MPa |
| Elongation at break | 8% |
| Compressive strength | 170 MPa |
| Hardness | Shore D 90 |
| Notched impact | 9.3 kJ/m² |
Typical physical and thermal properties
| Property | Value |
|---|---|
| Density | 1.38 g/cm³ |
| Maximum continuous service temperature | 290 °C |
| Maximum short-term temperature | 450 °C |
| Minimum service temperature | -50 °C |
| HDT (1.8 MPa) | 319 °C |
| Melting point or glass transition | 352 °C |
| Linear thermal expansion | 43-44 µm/m·K |
| Thermal conductivity | 0.22 W/m·K |
| Water absorption (24 h) | 0.47% |
| Water absorption (saturation) | 4% |
| Dielectric strength | 34.3 kV/mm |
| Flammability (UL 94) | V-0 |
Calculate the weight of PI – polyimide (Vespel®, TECASINT, Duratron PI) bar, plate or pipe →
Chemical resistance
| Medium | Resistance |
|---|---|
| Acids | Good in dilute acids |
| Bases (alkalis) | Poor (alkalis and amines attack polyimide) |
| Solvents | Very good |
| Hydrocarbons and oils | Very good |
| Steam and hot water | Limited (hydrolysis in steam) |
Stock forms and sizes
- Rod (round bar)
- Sheet (plate)
- Tube and bushing
- Parts sintered directly to shape
- Raw material: rod (round bar), sheet (plate) and tube, cut to size
- Machined part to drawing or sample, in the same order as the metal parts
- Lot certificate of conformity; FDA/EU 10/2011 declaration when the grade allows
Service temperature, machining and assembly
| Item | Usual practice |
|---|---|
| Service temperature | Continuous service up to 290 °C, short peaks up to 450 °C; minimum -50 °C (unloaded; under load, limited by HDT and creep). |
| Annealing (stress relief) | Not applicable: sintered, stable material. |
| Bonding and welding | Bonding with high-temperature adhesives after preparation. |
| Machining | Machines with carbide tooling; the material is abrasive and brittle in thin sections. |
Typical applications
- Insulators and supports at high temperature and in vacuum
- Washers and bushings for engines and turbines
- High-temperature valve seats
- Parts for semiconductor and glass equipment
Alternatives: PAI (Torlon) up to 260 °C with higher strength; PEEK when 260 °C is enough.
Frequently asked questions
Which standards cover PI?
Rod, sheet and sintered parts: Manufacturer's specification (DuPont Vespel, Ensinger TECASINT, MCAM Duratron). Machined part to drawing: ISO 2768 tolerance or as per drawing.
Up to what temperature can PI be used?
Continuous service up to 290 °C, short peaks up to 450 °C; minimum -50 °C (unloaded; under load, limited by HDT and creep).
Which materials can replace PI?
PAI (Torlon) up to 260 °C with higher strength; PEEK when 260 °C is enough.
Does polyimide melt?
No. Polyimide decomposes before melting, so it is sintered rather than injection molded; it works above the service temperature of PEEK.
