Polysulfone Properties — PSU vs PPSU Data
Polysulfone (PSU) and polyphenylsulfone (PPSU) share the same aromatic sulfone backbone but differ enough in mechanical toughness, heat resistance, and hydrolytic stability to occupy distinct application niches. PSU delivers 10,200 psi tensile strength and a 374°F glass transition; PPSU raises toughness, Tg (428°F), and sterilization durability significantly. This page consolidates datasheet-level property values for both grades, with context for interpreting each figure in real application scenarios.
At a glance:
- PSU tensile strength 10,200 psi; PPSU 10,500 psi — similar stiffness, PPSU markedly tougher
- Tg: PSU 374°F (190°C), PPSU 428°F (220°C) — PPSU handles higher sustained heat
- Both hydrolytically stable; PPSU rated 1,000+ autoclave cycles vs. moderate for PSU
- Low water absorption: PSU 0.30%, PPSU 0.37% (24h immersion)
- Chemical resistance: excellent vs. dilute acids/bases, poor vs. chlorinated solvents and ketones
- Density: PSU 1.24 g/cc, PPSU 1.29 g/cc — both lighter than aluminum (2.7 g/cc)
Mechanical Properties
Polysulfone is a rigid, amorphous thermoplastic. Its mechanical profile sits closer to engineering-grade plastics than commodity resins — stiff enough for structural components, ductile enough to avoid brittle fracture under impact loading.
Tensile and Flexural Data
Both grades are stiffer than polycarbonate (flexural modulus ~345,000 psi) and considerably stiffer than nylon 6 (~175,000 psi). PSU has a marginally higher modulus than PPSU, making it the better choice for applications where deflection under sustained load is the primary concern. PPSU's higher elongation at break reflects its greater ductility.
Impact and Hardness
PPSU's notched Izod impact resistance is approximately twice PSU's — a significant practical difference in clinical settings where trays and cassettes sustain mechanical loading from instrument placement, stacking, and autoclaving. The unnotched Izod gap is even larger, indicating PPSU's substantially greater resistance to crack propagation from a pre-existing notch or scratch.
Notch sensitivity matters in autoclave tray design. Sharp internal corners and aggressive machined radii concentrate stress in both grades, but PSU is more likely to crack from a tight corner radius under impact. Design with minimum 0.030" inside radii, larger where possible.
Thermal Properties
The sulfone group's thermal stability underpins both grades' elevated Tg values relative to polycarbonate (Tg ~280°F / 138°C).
Thermal Data Table
The 50°F gap in continuous use temperature between PSU and PPSU is not trivial. In applications approaching the 300°F ceiling — high-temperature process equipment, high-pressure steam fittings, repeated 132°C autoclave cycling — PPSU provides meaningful safety margin. PSU parts operating near their Tg risk dimensional distortion under load; PPSU remains stable.
Autoclave and Sterilization Resistance
Steam sterilization at 270°F (132°C) is a standard hospital cycle. PSU tolerates intermittent autoclaving, but studies document tensile strength loss at extended cycle counts — relevant for any device that cycles daily over months of service life. PPSU retains over 95% of tensile strength through 1,000 autoclave cycles, making it the only sulfone grade specified for high-volume clinical use.
For a detailed grade and sterilization-cycle comparison, see the polysulfone grades guide.
Hydrolytic Stability
Hydrolytic stability — resistance to property loss from water, steam, or aqueous chemicals — is polysulfone's defining advantage over polycarbonate in wet environments. The polycarbonate ester bond hydrolyzes over time under steam, leading to molecular weight reduction and surface crazing. Polysulfone's ether-sulfone linkages do not hydrolyze under conditions typical of steam sterilization or hot-water service.
Long-Term Water Immersion
These figures reflect Solvay published data for Udel and Radel resins. PSU performs adequately for moderate steam exposure; PPSU is the specification material for high-cycle clinical applications.
Chemical Resistance
Resistant (No Attack or Slight Attack)
- Dilute mineral acids (sulfuric, hydrochloric, phosphoric at low concentrations)
- Dilute alkalis (sodium hydroxide up to ~10%)
- Alcohols (isopropanol, ethanol) — note: prolonged exposure may cause slight surface stress
- Aliphatic hydrocarbons (hexane, mineral spirits)
- Aqueous salt solutions, detergent solutions
- Hospital-grade disinfectants: quaternary ammonium compounds, iodophors, hydrogen peroxide vapor (as used in VHP sterilizers)
Not Resistant (Avoid)
- Chlorinated solvents: methylene chloride, chloroform, trichloroethylene — these dissolve polysulfone
- Ketones: acetone, MEK, cyclohexanone
- Aromatic hydrocarbons: toluene, xylene, benzene
- Esters: ethyl acetate, butyl acetate
- Concentrated acids and bases
- Chlorine bleach (sodium hypochlorite) above approximately 200 ppm
Isopropanol (IPA) at 70% concentration — standard hospital surface disinfectant — is generally compatible with both PSU and PPSU at room temperature for brief contact times. Prolonged IPA immersion of stressed parts may cause stress cracking. Unstressed surfaces wiped with IPA pose minimal risk.
Electrical Properties
Polysulfone's electrical properties make it a candidate for electronic components requiring dimensional stability at elevated temperatures.
Electrical values for PPSU are similar. For applications where electrical insulation is the primary requirement, Ultem PEI offers comparable or superior dielectric properties with higher temperature ratings.
Optical Properties
Both grades transmit visible light in the amber range. The transparency allows visual inspection of fluid levels or tray contents in medical applications.
PPSU is slightly darker amber than PSU. Neither grade is available as clear or in standard opaque colors without compounding, which is not typical for stock shapes.
Creep and Long-Term Mechanical Performance
Polysulfone, like all thermoplastics, is subject to creep (slow deformation under sustained load) at elevated temperatures. At room temperature, creep in PSU and PPSU is minimal for stress levels below 1,000 psi. As service temperature approaches the continuous-use ceiling, the allowable stress for creep-limited design decreases.
For sustained-load applications operating at or above 250°F, design with a safety factor of at least 3× against the short-term tensile strength value. Polysulfone's time-dependent modulus (creep modulus) at 150°C (302°F) after 1,000 hours of loading is approximately 200,000–250,000 psi depending on grade and stress level — roughly 60% of its room-temperature flexural modulus. This reduction should be factored into structural designs for autoclave tray components that bear instrument weight repeatedly at sterilization temperatures.
For creep-critical applications at temperatures above 300°F, PEEK provides meaningfully better creep resistance by virtue of its semicrystalline structure, which maintains stiffness more effectively near its service temperature ceiling.
Comparing Polysulfone to Key Alternatives
The comparison underscores that polycarbonate is the better choice for room-temperature optical clarity and high impact resistance, but cannot compete in sterilization-intensive applications. PEEK dominates at extreme temperatures and in aggressive chemical environments but costs several times more per pound. Polysulfone is the rational choice between these poles for medical, food processing, and hot-water applications.
See the polycarbonate vs. polysulfone comparison for a detailed head-to-head.
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