- PSU, PPSU, and PES belong to the same family (polysulfones) — all share a backbone with sulfone (–SO₂–) groups, but differ in the linker between them, giving each a completely different personality.
- PSU is the entry-level sedan (cheap, serviceable, struggles in extremes); PPSU is the off-road SUV (toughest impact resistance, 800+ cycles of 134 °C steam); PES is the all-purpose business car (the pharma industry's favorite).
- The cost of the wrong pick: PSU under repeated 134 °C steam will stress-crack; PES exposed to DMSO will turn brittle.
- This article uses a 14-row comparison table, three common pitfalls, and benchmarks against other membrane materials — 10 minutes to master the family.
- Semiconductor-grade PSU/PPSU/PES products can claim pore sizes down to 1 nm – 0.1 µm, paired with ICP-MS / LPC extractables control.
- Who is the polysulfone family? Three structural stories
- PSU: the entry-level sedan
- PPSU: the off-road SUV
- PES: the all-purpose business car (pharma's favorite)
- 14-row comparison table: the differences at a glance
- When to pick which? Decision cards
- Three common pitfalls
- Cross-comparison with PVDF / Nylon / MCE
- FAQ
Who is the polysulfone family? Three structural stories
Polysulfones are a polymer family sharing one common feature: a backbone containing sulfone groups (–SO₂–) linking two aromatic rings. This structure delivers three shared advantages:
The differences among the three resins all come down to what's "sandwiched" between the –SO₂– groups:
- PSU (Polysulfone): contains a bisphenol A "isopropylidene" group (–C(CH₃)₂–) in the middle. Representative resins: Solvay Udel®, BASF Ultrason® S.
- PPSU (Polyphenylsulfone): features a "biphenyl" linker — fully aromatic structure. Representative: Solvay Radel® R, BASF Ultrason® P.
- PES (Polyethersulfone): the simplest — alternating ether linkages (–O–) and sulfone groups, no isopropylidene, no biphenyl. Representative: Solvay Veradel®, BASF Ultrason® E.
PSU: the entry-level sedan
PSU is the "elder brother" of the polysulfone family — the cheapest, easiest to process, but weakest in heat and chemical resistance.
Typical applications
- UF/MF hollow fiber membrane body and support layer: hemodialysis membranes (pore size down to 40 nm), wastewater reclamation, backwashable UF systems.
- Food and beverage industry: juice clarification, dairy concentration, brewing.
- Cost-sensitive UF applications: industrial wastewater reuse, rural water supply systems.
Limitations
PSU contains bisphenol A in its structure and is unsuitable for long-term contact with food and medical products (although the membrane body itself does not contact food directly, more manufacturers are choosing BPA-free PES / PPSU as alternatives). It cannot withstand repeated 134 °C steam sterilization — stress cracking emerges after dozens of cycles.
PPSU: the off-road SUV
PPSU is the "muscle car" of the family — its fully aromatic structure delivers impact resistance, repeated steam sterilization tolerance, and stress-crack resistance, but processing is the most difficult and the price is the highest.
Typical applications
- Filter housings / cartridge shells: pharmaceutical-grade filter housings, sterile sampling bag connectors.
- Repeatedly sterilized instruments: orthopedic surgical instrument trays, surgical instrument baskets.
- Baby bottles / medical tableware: BPA-free alternatives, dishwasher-safe at high temperatures.
- Aviation / rail transit interiors: flame-resistant, impact-resistant, lightweight.
Limitations
PPSU is rarely used as the membrane material itself — its melt flowability is poor and processing is difficult; it serves primarily as rigid structural components. Membrane bodies remain dominated by PSU / PES.
PES: the all-purpose business car (pharma's favorite)
PES is the "all-rounder" of the polysulfone family — Tg up to 225 °C, extremely low protein binding, very high flux, excellent chemical resistance. It practically monopolizes the biopharma sterile filtration market.
Structural feature: asymmetric membrane
Commercial PES membranes typically use an asymmetric structure: a dense top layer for precise retention plus a coarse-pore lower layer for support and flow. A single membrane balances high retention with high flow rate — the key reason PES dominates pharma final filtration over other membrane materials.
Typical applications
Common pore sizes and bubble points
| Pore size | Application | Bubble Point (water) |
|---|---|---|
| 1 nm – 0.1 µm | Semiconductor EUV / advanced process chemicals (PSU/PESU high-cleanliness grades) | Per manufacturer spec |
| 0.1 µm | Mycoplasma removal | ≥ 5.4 bar (78 psi) |
| 0.22 µm | Sterilizing-grade filtration | 3.1–3.5 bar (45–50 psi) |
| 0.45 µm | Clarification, pre-filtration | 2.0–2.4 bar (29–35 psi) |
| 0.65 / 0.8 µm | Coarse-particle clarification | 1.4–1.7 bar (20–25 psi) |
| 1.2 µm | Coarse filtration, pretreatment | 0.9–1.1 bar (13–16 psi) |
14-row comparison table: the differences at a glance
| Item | PSU | PES | PPSU |
|---|---|---|---|
| Glass transition temperature Tg | 185–187 °C | 220–225 °C | 220 °C |
| Heat deflection temperature HDT | 174 °C | 204 °C | 207 °C |
| Long-term service temperature | 160 °C | 180–200 °C | 180 °C |
| Steam sterilization temperature | 121 °C | 134 °C | 134 °C |
| Sterilization cycle life | Tens to ~100 | Hundreds | 500–1000+ |
| Density g/cm³ | 1.24 | 1.37 | 1.29 |
| Hydrolysis resistance | Good | Excellent | Outstanding |
| Acid / alkali resistance | Good | Excellent | Outstanding |
| Resistance to ketones / chlorinated / aromatic hydrocarbons | Poor (attacked) | Moderate | Better |
| H₂O₂ sterilization tolerance | Not tolerant | Moderate | Tolerant |
| Transparency | Pale yellow translucent | Amber | Amber |
| BPA-free | No (contains bisphenol A) | Yes | Yes |
| Price tier | $ (lowest) | $$ (medium) | $$$ (highest) |
| Primary form | UF / MF membrane body | MF / sterile membrane body | Filter housing / structural parts |
When to pick which? Decision cards
Three common pitfalls
Cross-comparison with PVDF / Nylon / MCE / PTFE
Putting PES (the most common membrane material in the polysulfone family) into the biopharma membrane arena:
| Membrane | Protein binding | Flow rate | pH range | Typical use |
|---|---|---|---|---|
| PES (hydrophilic) | Very low | Highest | 1–14 | Sterile filtration, media, buffers (first choice) |
| PVDF | Low | Medium | 1–13 | Protein analysis, HPLC, trace-solvent samples |
| Nylon 66 | High | Medium | 6–13 | General aqueous solutions, chromatography (not for proteins) |
| MCE (mixed cellulose ester) | High | Medium | 4–8 | Microbiological detection, sterility testing |
| PTFE (hydrophilic) | Low | Low | 1–14 | Strong acid/alkali, HPLC mobile phases, organic solvents |
FAQ
What's the difference between PSU and PES in hemodialysis membranes?
Both are used as dialysis membrane bodies. PSU is the classic (used widely in Fresenius F60/F80 series), with pore sizes down to 40 nm for high-flux dialysis. PES is more popular in newer-generation products due to higher Tg and lower complement activation. Clinical choice still follows physician and nephrology team protocols.
Why is PPSU 3–5× more expensive than PSU?
Three reasons: (1) biphenyl monomer is more expensive than bisphenol A; (2) PPSU has high melt viscosity, requiring processing temperatures above 380 °C — energy-intensive; (3) demand is far smaller than PSU, so economy of scale is weaker. But for medical instruments needing 800+ high-temperature sterilization cycles, PPSU's longevity amortizes per-use cost effectively.
Do market-grade PES 0.22 µm filters vary much in contact angle?
Significantly. Unmodified PES has a contact angle around 83.5° (hydrophobic); lightly modified versions are around 60–70°; deeply hydrophilized (PVP blending + grafting) can reach 30–50° (highly hydrophilic). Pharma-grade vendors typically use deep modification, but cheap knockoffs may only do surface coating — washing several times reverts them to hydrophobic state. Request contact-angle / flow-rate measurement reports from the vendor.
Can PPSU filter housings really be sterilized 1000 times?
In practice, yes, given proper conditions. Solvay Radel® R, tested under 134 °C saturated steam, shows noticeable mechanical degradation only after 800 cycles; even past 1000 cycles, tensile strength retains over 80% of original value. The conditions: detergents free of alkylphenol ethoxylates, and operating pressures within spec.
Can polysulfone membranes be sterilized by gamma (γ-ray) radiation?
Yes, but with dose limits. PES and PPSU show < 5% mechanical change at the standard 25–50 kGy dose; above 100 kGy, yellowing and brittleness emerge. EtO (ethylene oxide) sterilization and electron beam sterilization are both well compatible.
References
- BASF Ultrason® E / S / P Product Brochure (PSU / PES / PPSU specifications)
- Solvay PPSU Radel® Design Guide (with 800–1000 cycle steam sterilization data)
- Wikipedia — Polysulfone (chemical structure and family classification)
- Cobetter — PES Membrane Technical Notes (asymmetric structure and biopharma applications)
- PMC — Review of PES Hydrophilic Modification (contact angle 83.5° → 50° mechanism)
- Econe — Bubble Point and Integrity Performance (PES integrity test measurements)
- Aberdeen Tech — Autoclavable Plastics (PPSU 1000-cycle sterilization validation)
- Honyplastic — Understanding the Polysulfone Family (PSU / PPSU / PES)
- Tuntun Plastic — PSU vs PES vs PPSU Comparison