PEI (Ultem) Injection Moulding: Properties & Design Guide
PEI (polyetherimide), best known under the Sabic trade name Ultem, is an amorphous high-performance thermoplastic combining continuous service temperature of 170°C, UL 94 V-0 flame retardance, and structural strength approaching PEEK — at materially lower cost. Nordmould recommends PEI for demanding thermal, electrical, and medical applications where PC cannot tolerate the temperature and PEEK cannot be justified on cost.
What are the mechanical and thermal properties of PEI (Ultem)?
PEI is amorphous, meaning it has no crystalline melting point and no critical mould temperature threshold for crystallisation. This simplifies processing relative to PEEK and PPS, particularly for complex thin-walled geometries. The trade-off is lower chemical resistance compared to semi-crystalline polymers of similar thermal rating.
| Property | Unfilled PEI | 10% GF PEI | 30% GF PEI | Test Standard |
|---|---|---|---|---|
| Tensile Strength | 105 MPa | 131 MPa | 165 MPa | ISO 527 |
| Flexural Modulus | 3,300 MPa | 4,800 MPa | 8,300 MPa | ISO 178 |
| Izod Impact (notched) | 50–55 J/m | 55 J/m | 80 J/m | ISO 180 |
| Heat Deflection Temp (1.82 MPa) | 210°C | 210°C | 215°C | ISO 75 |
| Continuous Use Temp | 170°C | 170°C | 170°C | — |
| Density | 1.27 g/cm³ | 1.34 g/cm³ | 1.51 g/cm³ | ISO 1183 |
| Mould Shrinkage | 0.5–0.7% | 0.3–0.6% | 0.1–0.3% | ISO 294-4 |
| Water Absorption (24 h) | 0.25% | 0.20% | 0.17% | ISO 62 |
| Dielectric Strength | 28–33 kV/mm | 25–30 kV/mm | 22–28 kV/mm | IEC 60243 |
| Limiting Oxygen Index | 47% | — | — | ISO 4589 |
PEI's dielectric strength of 28–33 kV/mm is among the highest available from a standard injection-moulding material, supporting its widespread use in high-voltage electrical components and insulating substrates.
Where is PEI (Ultem) injection moulding used?
PEI's combination of thermal stability, electrical insulation, inherent flame retardance, and regulatory compliance for medical applications puts it at the centre of a well-defined set of demanding sectors.
Medical and dental: Sterilisable trays and instrument holders (autoclave and ETO compatible), reusable surgical instrument handles, dental prosthetic frameworks, fluid manifolds for dialysis and infusion equipment, and components for imaging systems. Ultem 1010's USP Class VI status and autoclave stability make it a direct competitor to stainless steel tray systems at significantly lower part weight.
Aerospace and aircraft interiors: Seat components, overhead bin structures, ducting, cable management parts, and structural brackets in aircraft interiors. PEI's UL 94 V-0 rating at thin walls and low smoke/toxic emission in combustion meet FAR 25.853 requirements that govern aircraft interior plastics.
Electrical and electronic: High-voltage connector housings, circuit board burn-in sockets, SMD test fixtures, transformer bobbins, and motor insulation components. The dielectric strength and dimensional stability at temperature make PEI standard for components that must maintain electrical isolation under thermal cycling.
Semiconductor: Wafer-handling components, burn-in boards, and process equipment parts where both chemical exposure and elevated temperatures are present.
Industrial automation: End-of-arm tooling, lightweight robotic grippers, and sensor housings where weight reduction and thermal resistance are both required.
What are the moulding characteristics of PEI?
PEI is processable but demanding. Its amorphous nature makes it more forgiving than PEEK or PPS in terms of crystallisation sensitivity, but the very high melt temperature and hygroscopic nature demand careful process control.
Melt temperature: 340–400°C. Consistent barrel temperature is essential; localised overheating above 420°C causes thermal degradation — discolouration, molecular weight reduction, off-gassing. Barrel purge between PEI and lower-temperature materials is mandatory to avoid degraded material contaminating the next production run.
Mould temperature: 65–175°C. As an amorphous material, PEI does not require a specific mould temperature for crystallisation. Higher mould temperatures (above 130°C) significantly improve surface finish, reduce residual stress, and improve fatigue life. For optical or cosmetic surfaces, heated tooling at 150–175°C is recommended.
Injection pressure: 100–170 MPa. PEI's melt viscosity is moderate; thin walls and long flow paths require higher pressures. Adequate venting is important as PEI is prone to burns at trapped-air locations.
Drying: 150°C for 3–4 hours in a dehumidifying dryer to below 0.02% moisture. PEI is significantly more hygroscopic than PEEK; drying must not be shortened.
Tooling: Hardened tool steel is strongly recommended. PEI's high processing temperatures and mould pressures accelerate wear in aluminium tools. P20 or H13 steel is appropriate; gate land areas should be hardened.
Shrinkage: 0.5–0.7% for unfilled grades, essentially isotropic due to amorphous structure — similar to PC. This predictable shrinkage makes PEI reliable for precision-fit assemblies without complex gate-location planning.
Chemical compatibility: PEI is attacked by partially halogenated solvents and some ketones. Mould release agents, cleaning solvents, and assembly adhesives must be compatible with PEI chemistry — a meaningful constraint for parts that will be cleaned in service.
Which PEI grades and variants are available?
| Grade | Key Feature | Primary Application |
|---|---|---|
| Ultem 1010 | USP Class VI, FDA, standard general purpose | Medical, food contact, general industrial |
| Ultem 1000 | General purpose (non-food) | Industrial, electrical |
| Ultem 2210 | 10% glass-filled | Moderate stiffness increase, better weld lines |
| Ultem 2310 | 30% glass-filled | High structural loads, HDT 215°C |
| Ultem CRS5001 | ESD-safe, static-dissipative | Semiconductor fixtures, IC handling |
| Generic PEI resins | Off-patent alternatives to Sabic Ultem | Cost-sensitive industrial applications |
Since Sabic's foundational Ultem patents expired, multiple generic PEI resin manufacturers have entered the market. For non-critical industrial applications where USP or FDA compliance is not required, generic PEI grades offer meaningful material cost reduction. Nordmould sources both branded Ultem and qualified generic PEI on request.
What are PEI's advantages and limitations?
Advantages:
- Continuous use temperature of 170°C — well above PC, nylon, and POM
- UL 94 V-0 inherently, without halogenated additives; low smoke and toxic gas on combustion
- USP Class VI and ISO 10993 compliant grades for medical applications
- Amorphous structure — predictable, isotropic shrinkage simplifies tooling
- Exceptional dielectric strength for electrical insulation applications
- High specific strength — lighter than metals for equivalent load-carrying capacity
- Autoclave sterilisable (134°C) without measurable property degradation
Limitations:
- Susceptible to attack by halogenated solvents and some ketones — verify chemical compatibility carefully
- High melt temperature (340–400°C) requires specialised processing equipment
- More hygroscopic than PEEK or PPS — rigorous drying essential
- Hardened steel tooling strongly recommended — tooling investment higher than for commodity polymers
- Translucent amber natural colour; truly transparent grades require careful processing
- Higher material cost than PC, nylon, or POM — justified only when thermal or regulatory requirements demand it
When should you choose PEI over alternative materials?
PEI vs PEEK: PEI is significantly less expensive and simpler to process (amorphous, no crystallisation threshold). Choose PEI when the application requires continuous service up to 170°C, UL 94 V-0, and either medical-grade compliance or electrical insulation performance. Choose PEEK when continuous temperature exceeds 200°C, when broader chemical resistance is needed, or when implant-grade biocompatibility certification is required.
PEI vs PPS: PPS offers better chemical resistance and a higher continuous temperature ceiling, with lower material cost for certain grades. Choose PEI for complex thin-walled geometries (amorphous processing is more predictable) and where higher impact resistance is needed. Choose PPS where chemical exposure includes ketones or halogenated solvents that would attack PEI.
PEI vs PC: Choose PEI when the part must operate above 125°C continuously, requires V-0 flame rating, or must survive repeated autoclave cycles. PC is the lower-cost, easier-to-process choice for applications under 120°C where optical clarity is an asset.
Is PEI recyclable?
PEI is not collected in municipal recycling streams. Clean, single-grade production regrind can be reprocessed at up to 20–30% with virgin material for non-critical applications. The high processing temperature and chemical sensitivity make PEI regrind management more demanding than for commodity polymers. For medical or food-contact grades, regrind must undergo the same qualification process as virgin material — in practice, most medical PEI parts are moulded from virgin material only. Nordmould can discuss regrind use protocols and, where performance allows, alternative materials with better end-of-life pathways.
Frequently asked questions
What is the heat deflection temperature of PEI (Ultem)?
Standard unfilled PEI (Ultem 1010) has a heat deflection temperature of approximately 210°C at 1.82 MPa and a continuous use temperature of approximately 170°C. Glass-filled grades (Ultem 2210, 2310) reach HDT of 210–215°C. This places PEI well above nylon, PC, and POM while remaining significantly more affordable than PEEK.
Does Ultem (PEI) qualify for medical and food-contact applications?
Yes — Ultem 1010 is USP Class VI and ISO 10993 compliant, and is used extensively in sterilisable medical trays, surgical instruments, dental components, and fluid-handling systems. It withstands autoclave sterilisation (134°C, repeated cycles) without significant property loss. Specific grades also carry FDA food-contact compliance.
Does PEI need to be dried before injection moulding?
Yes — PEI is hygroscopic and requires thorough drying before processing. Standard drying is 3–4 hours at 150°C in a dehumidifying dryer to below 0.02% moisture. Insufficient drying causes hydrolytic degradation at melt temperature, producing splay, voids, and reduced mechanical properties.
What are the melt and mould temperatures for PEI injection moulding?
PEI melt temperature is typically 340–400°C. Mould temperature of 65–175°C is recommended — higher mould temperatures improve surface finish and reduce residual stress. PEI is amorphous, so unlike PEEK or PPS there is no crystallisation threshold to respect; mould temperature can be varied more freely to balance cycle time and part quality.
How does PEI compare to PEEK for structural applications?
PEI is significantly less expensive than PEEK and offers good structural performance to 170°C continuous. PEEK surpasses PEI above 200°C continuous, offers better chemical resistance (particularly to ketones and halogenated solvents which attack PEI), higher impact toughness, and validated implant-grade options. For most applications under 180°C, PEI is the cost-rational choice.
Is PEI (Ultem) inherently flame retardant?
Yes — PEI achieves UL 94 V-0 at 0.8 mm wall thickness without halogenated flame retardant additives. Its limiting oxygen index (LOI) is approximately 47%, meaning it does not sustain combustion in normal air. Low smoke and low toxic gas emission during combustion make PEI preferred for aircraft interiors, mass transit, and healthcare environments.
What grades of PEI (Ultem) are available for injection moulding?
Key grades include: Ultem 1010 (standard, medical/food compliant), Ultem 2210 (10% GF, higher stiffness), Ultem 2310 (30% GF, high stiffness for structural parts), Ultem 1000 (general purpose, slightly lower cost than 1010), and Ultem CRS5001 (ESD-safe, semiconductor-grade). Generic PEI resin is available from multiple suppliers as Sabic's Ultem patent protection has expired.
Can PEI injection-moulded parts be bonded or solvent-welded?
PEI bonds well with structural epoxies and cyanoacrylates after surface preparation. Solvent welding uses methylene chloride or similar aggressive solvents — these must be handled under appropriate safety controls. Ultrasonic welding is also viable and is a common assembly method for PEI enclosures and instrument housings.
Submit your STEP file to Nordmould for a free DFM review — we will confirm whether PEI is the correct grade for your thermal and regulatory requirements and flag any drying, gating, or wall-thickness risks early.