Torlon PAI Properties — Mechanical, Thermal & Wear Data

Torlon polyamide-imide holds a unique position among engineering thermoplastics: it delivers the highest unfilled tensile and compressive strength of any melt-processable thermoplastic while sustaining continuous service at 500°F (260°C) — a combination no other single-polymer stock shape matches. The data below covers all three commercial stock-shape grades (4203, 4301, 4540) across mechanical, thermal, electrical, and tribological axes.

At a glance:

• Tensile strength (4203): 21,000 psi — highest of any unfilled engineering thermoplastic in stock-shape form
• Compressive strength: 36,000 psi — greater than PEEK (16,000 psi) and nearly double Vespel SP-1 (18,000 psi)
• Continuous use temperature: 500°F; glass transition (Tg): 537°F; no crystalline melt point
• Creep resistance exceeds PEEK, PPS, and Ultem at equivalent temperature and stress
• Flexural modulus 700,000 psi — stiff at temperature, enabling precision geometric tolerances
• Water absorption among the lowest of any polyimide-family material: 0.28% (24h ASTM D570)

Mechanical Properties

Tensile and Compressive Strength

Torlon 4203 achieves 21,000 psi tensile strength — approximately 45% higher than virgin PEEK (14,500 psi) and 65% higher than Ultem 1000 (15,200 psi). More importantly for bearing and structural applications, its compressive strength of 36,000 psi is exceptional for a thermoplastic, enabling sustained contact stresses that would cause PEEK or nylon to creep or yield.

The filled grades (4301, 4540) trade modest tensile strength for tribological performance. Graphite and PTFE additions are not inert fillers — they form a low-friction transfer film on the mating surface, which reduces adhesive wear and heat generation at the interface. The penalty in tensile strength is approximately 15–20% for 4301 and up to 25% for 4540 relative to 4203.

Creep and Sustained Load

Creep resistance at elevated temperature is where Torlon most clearly surpasses competing thermoplastics. Under a 4,000 psi compressive stress at 400°F (204°C), PEEK exhibits measurable creep deformation within hours. Torlon 4203 under identical conditions shows deformation an order of magnitude lower. This is attributable to the rigid imide ring in the backbone, which resists chain-segment mobility even as temperature approaches Tg.

For thrust washers and bearing pads where dimensional stability under load determines service life, this creep advantage is often the deciding factor in specifying Torlon over PEEK.

Fatigue and Impact

The Izod impact strength of 1.7 ft-lb/in (4203, notched) is moderate — lower than polycarbonate or PEEK but comparable to glass-filled grades of many engineering thermoplastics. Torlon is not a first-choice material for high-impact shock loads; it is a precision structural and tribological material.

Fatigue endurance under cyclic bending is excellent relative to stiffness, largely because the material's high modulus minimizes strain amplitude for a given stress cycle.

Thermal Properties

Temperature Capability

The absence of a crystalline melt transition means Torlon does not undergo the abrupt property drop that semicrystalline polymers like PEEK or PPS exhibit at their melting points. Torlon softens gradually as it approaches Tg (537°F), retaining useful structural stiffness up to and slightly beyond the 500°F continuous-use rating.

Thermal Expansion and Dimensional Stability

A CTE of 16 × 10⁻⁶ in/in/°F (flow direction) is moderate for a thermoplastic — lower than nylon and acetal, comparable to PEEK. Designers should account for anisotropy in compression-molded stock: the transverse CTE (18 × 10⁻⁶) is slightly higher than the flow direction. For assemblies that transition across a wide temperature range, differential thermal expansion relative to aluminum (13 × 10⁻⁶) or steel (6.5 × 10⁻⁶) must be incorporated into clearance calculations.

Flammability

Torlon burns with extreme reluctance. Its LOI of 43% requires an oxygen-enriched atmosphere to sustain combustion — ordinary air (21% O₂) will not support continued burning. UL 94 V-0 is achieved without flame retardant additives, a significant advantage for aerospace and semiconductor applications where halogenated additives are problematic.

Electrical Properties

The unfilled 4203 grade provides the best electrical insulation of the three grades. Graphite-filled grades (4301, 4540) are electrically conductive through the graphite network and are not suitable for electrical insulation. For connector bushings, wafer-handling components, or electrical stand-offs that require insulation, specify 4203.

Volume resistivity of 7 × 10¹⁶ Ω·cm places 4203 firmly in the insulator category. The dielectric constant of 3.9 at 1 MHz is stable with temperature, varying less than 5% from ambient to 400°F — an advantage in RF and microwave component applications.

Tribological (Wear & Friction) Properties

Torlon's tribological performance depends strongly on grade selection and operating conditions.

PV (Pressure × Velocity) Limit

The PV limit defines the product of bearing contact pressure (psi) and sliding velocity (ft/min) at which a bearing material begins to overheat and fail. Torlon 4301 at 35,000 psi·fpm and 4540 at 50,000+ psi·fpm dramatically exceed what PEEK (typically 10,000–15,000 psi·fpm unfilled) can sustain dry.

At high velocity, the graphite and PTFE lubricants in 4301 and 4540 form a thin transfer film on the metal counterface, reducing friction and heat generation. This self-lubricating behavior persists over extended cycle counts, unlike grease-lubricated systems that require periodic replenishment.

Wear Against Mating Surfaces

The hardest mating surfaces yield the lowest wear rates. Ground stainless steel (Ra ≤ 16 μin) or hard chrome are preferred counterfaces. Avoid soft aluminum or uncoated copper alloys — surface ploughing accelerates initial wear. Graphite-filled Torlon against a 60 HRC hardened steel shaft under appropriate PV conditions routinely achieves 10,000+ hours of service without measurable dimensional loss.

Chemical Resistance

Torlon's chemical resistance is good across most organic solvents and aliphatic media, but it is susceptible to attack by strong alkalis and sustained steam exposure above 250°F. Strong base cleaning agents should not be used in maintenance of Torlon components.

Properties vs. Competing Materials

For deeper comparison analysis, see Torlon vs. PEEK and the Torlon comparisons index.

More related guides

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Applications

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Industries

• Aerospace
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Compare to other materials

• Peek Vs. Pai Torlon
• Torlon Vs. Vespel

Frequently asked questions — Pai Torlon FAQ