Overview
PES (polyethersulfone, also written PESU) is the highest-Tg member of the commercial sulfone polymer family — 220–228°C, depending on grade and manufacturer. Continuous service to ~180°C in air. Transparent honey- amber. Inherently UL94 V-0. The polymer was developed in the 1970s by ICI and is now sold primarily as BASF’s Ultrason E and Solvay’s Veradel PESU.
Where PPSU (Radel R) is the high-impact, hot-water-cycling reusable medical-instrument polymer, PES sits a step toward higher Tg and lower impact. The dominant commercial application is not injection molding or machining at all — it’s ultrafiltration (UF) hollow-fiber membranes for drinking water, food/beverage filtration, gas separation, and reverse osmosis substrates. BASF supplies Ultrason E flake by the tonne to membrane producers like Pentair, Dow, and DuPont, who dissolve it in NMP or DMAc and spin it into hollow-fiber bundles.
For the machinist or designer, PES shows up as:
- Drinking-water plumbing fittings (NSF/ANSI 61)
- Hot beverage and food-service equipment
- Dental and medical instrument housings
- Aerospace electrical connectors and composite matrix
- Transparent industrial sight glasses operating above 150°C
- High-temperature FDM filament (growing but smaller than PPSU AM)
The sulfone family — PES vs PSU vs PPSU vs PEI
| Property | PSU (Udel) | PES (Ultrason E) | PPSU (Radel R) | PEI (Ultem) |
|---|---|---|---|---|
| Tg (°C) | 187 | 220–228 | 220 | 217 |
| Continuous service °C | 150 | 180 | 180 | 170 |
| Notched Izod (J/m) | 60–70 | 85–95 | 600–700 | 50 |
| Cost vs PPSU | -30% | -20% | baseline | -10% |
| Steam autoclave cycles | ~100 | ~300–500 | 1,000+ | ~100 |
| Membrane production | rare | dominant | possible | rare |
| Solvent solubility | broad | NMP/DMAc/DMF | narrower | narrower |
The sulfone-family selection logic, in shop-floor terms:
- Need 1,000+ autoclave cycles? PPSU.
- Need membranes? PES.
- Need transparent + V-0 + cost-sensitive? PSU (Udel) or PES.
- Need maximum Tg in a thermoplastic that machines well? PES.
- Need everything PES does plus higher impact? PPSU at 20–30% more cost.
Machining notes
PES machines similarly to PPSU with these differences:
- Heat sensitivity is greater — thermal conductivity 0.18 W/m·K vs PPSU’s 0.34 W/m·K. Flood coolant is more important; cutting speeds should be 10–20% slower.
- Stress crazing is more likely — PES is more sensitive to residual extrusion stress than PPSU. Anneal stock at 175–200°C for 1–2 hr/inch before tight-tolerance work.
- Avoid polar solvents in finishing — even tap water with strong detergents is fine, but methylene chloride, DMF, or NMP traces from parts cleaning will craze stressed regions.
Practical recipe for turning Ultrason E rod:
- Sharp carbide or HSS, positive rake
- Speed: 250–500 SFM
- Feed: 0.005–0.012 in/rev
- Flood coolant strongly recommended
- Anneal before final tolerance passes
Bonding and welding are real options. Solvent welding with methylene chloride or MEK works (designed-in solvent solubility is helpful here). Ultrasonic and hot-plate welding bond cleanly. Adhesives bond reliably on properly cleaned surfaces.
Membrane chemistry — PES’s principal commercial story
The dominant volume application for PES has nothing to do with machinable stock shapes. Ultrason E flake is the global workhorse polymer for ultrafiltration hollow-fiber membranes:
- Dissolved in NMP or DMAc at 15–25% concentration
- Spun through annular spinneret into water coagulation bath
- Phase inversion creates the asymmetric porous wall structure
- Result: hollow-fiber membranes with narrow pore distribution
The properties that make PES the right base polymer:
- Hydrolytic stability — survives years in continuous water service
- Wide pH compatibility (0–13) — tolerates chlorination cleaning and caustic regeneration
- Mechanical toughness — fiber walls handle backflushing cycles without rupture
- Soluble in polar aprotic solvents — required for the casting process
- High purity / low extractables — necessary for drinking-water contact (NSF/ANSI 61)
For drinking-water applications, the world’s UF membrane installed base — Pentair, DuPont, GE/SUEZ, Toray — is largely PES-based.
Variant guidance — which PES grade
- Ultrason E 2020 P — BASF’s general-purpose injection grade. Default for IM components. Tg 225°C, HDT 205°C, yield 88 MPa.
- Ultrason E 6020 P — higher MW grade for membranes and tougher structural parts. Slightly higher Tg (228°C) and toughness.
- Veradel PESU 3000P / A-301 — Solvay’s PES equivalent. Direct alternative when Solvay supply chain matters.
- GF30 (Ultrason E 2010 G6 / Veradel AG-330) — pick for structural high-temperature parts where transparency is not required. Significant CTE reduction.
- CF20–CF30 PES — aerospace structural and EMI-shielded high-temp parts.
- Medical grade — USP Class VI / ISO 10993 grades for dental and trial-implant applications. PPSU is the more common medical sulfone but PES is selected for higher-Tg medical needs.
- Stock shapes (TECASON E / Sustason PES) — for machining. Anneal before tight-tolerance work.
Failure modes worth designing around
Polar solvent attack is the dominant in-service failure mode. NMP, DMAc, DMF, DMSO, and methylene chloride dissolve PES at room temperature. The membrane producers exploit this; finished-part designers must avoid it. Verify cleaning chemistry compatibility before specifying PES in any environment where these solvents could appear.
Stress crazing from incompatible cleaning agents on stressed parts. Anneal machined parts (175°C for 1–2 hr/inch) before service. Even “safe” cleaning agents can craze PES if residual machining stress is high enough.
UV degradation — yellowing and surface crazing on continuous outdoor exposure. Indoor and protected installations are unaffected through normal service life.
Reduced impact resistance vs PPSU — PES notched impact is 5–8× lower than PPSU. For instrument trays and drop-tested medical devices, PPSU is the correct sulfone; PES is for parts where Tg and clarity matter more than impact.
Processing window narrower than PPSU — PES melt is more sensitive to overheating; brittle parts and yellow tint indicate processing above 380°C. Stay within BASF’s recommended 340–380°C melt range.
Applications by industry
- Water filtration — the dominant commercial application by tonnage. Ultrafiltration hollow-fiber membranes for drinking water purification, point-of-use filters (hospitals, hotels), industrial process water, food and beverage clarification, biopharmaceutical buffer filtration.
- Hot-water plumbing — fittings and manifolds for high-temperature hot-water distribution. NSF/ANSI 61 compliant grades.
- Coffee and hot-beverage equipment — espresso machine boiler components, hot-water dispenser hoods, brewing equipment housings.
- Medical and dental — sterilizable instrument housings, dental tray components, trial implants where Tg matters more than impact (PPSU is more common for high-impact uses).
- Aerospace — high-temperature electrical connectors and insulators, composite matrix for CF/PES structural prepregs, interior components meeting FAR 25.853 FST.
- Hydrogen energy — battery cell components, fuel-cell membrane electrode assembly sub-gaskets (overlapping application space with Radel HYRA).
- Industrial transparent windows — sight glasses and process windows operating above 150°C where glass or quartz is impractical.
- Additive manufacturing — high-temperature FDM filament for parts requiring Tg above 200°C.