PET (Ertalyte) Properties — Mechanical, Thermal & Wear Data
Ertalyte (bearing-grade PET-P) properties are driven by its semi-crystalline structure: high stiffness (600,000 psi flexural modulus), excellent compressive strength, low friction, and near-negligible moisture absorption. This datasheet covers mechanical, thermal, electrical, tribological, and chemical resistance values for Ertalyte natural and Ertalyte TX (PTFE-filled) in stock-shape form.
At a glance:
- Tensile strength: 11,600 psi; flexural modulus: 600,000 psi
- Continuous use temperature: 212°F (100°C); HDT at 264 psi: 185°F (85°C)
- Water absorption (24 hr): 0.10% — one of the lowest in engineering thermoplastics
- Coefficient of friction (dry vs steel): ~0.25 unfilled; ~0.10 Ertalyte TX
- FDA 21 CFR 177.1630 compliant for both natural and TX grades
- Density: 1.41 g/cc; Rockwell hardness: M94
Mechanical Properties
Ertalyte's mechanical profile is flat relative to temperature up to its HDT. The semi-crystalline structure resists creep better than amorphous thermoplastics — a critical feature for sustained-load bearing applications.
Tensile, Compressive, and Flexural Data
Impact and Hardness
Grade Comparison: Ertalyte vs Ertalyte TX
Ertalyte TX's lower mechanical properties (tensile strength, modulus) are the trade-off for dramatically improved tribological performance. For structural parts under high tensile load, use unfilled Ertalyte. For dry-running bearing and bushing service, TX pays back in extended part life.
Thermal Properties
Temperature Considerations
Ertalyte's HDT at 264 psi (85°C) is modestly lower than its continuous-use rating (100°C) because HDT is measured under a specific bending load. In actual bearing applications, the working temperature must account for frictional heat rise — particularly in dry-running, high-speed applications where surface temperature can exceed ambient by 20–40°C. Ertalyte TX's lower friction coefficient reduces this heat rise substantially.
Above 100°C continuous, consider PEEK, PPS (Ryton), or PAI (Torlon) depending on the chemical environment. For applications where temperature is the only driver and cost is a priority, see the PET comparisons guide for alternatives.
Electrical Properties
Ertalyte is a good electrical insulator. These values are not grade-controlled (the material is not used in precision electrical applications), but they confirm that Ertalyte parts carrying incidental electrical loads or requiring isolation from current-conducting equipment are suitable without modification.
Tribological Properties (Wear and Friction)
This is where Ertalyte earns its place. Bearing-grade PET-P was engineered for sliding wear service — its low friction and excellent wear resistance against metals make it a premier choice for unlubricated or marginally lubricated bearings.
How These Numbers Translate to Practice
A wear factor (K) of 65 for unfilled Ertalyte places it in the same performance tier as standard acetal in dry sliding. Ertalyte TX at K ~8 is comparable to PTFE-filled acetal grades or low-friction nylon composites. The combined effect of lower K and lower friction coefficient means TX bearings run cooler and last significantly longer in dry service.
In wet (water or process fluid) sliding, both Ertalyte grades maintain their tribological properties because moisture absorption is minimal. Nylon, by contrast, softens and loses compressive strength when saturated, causing bearings to creep and fail under load. This wet performance advantage is Ertalyte's strongest argument in food-processing and wash-down bearing applications.
Physical and Chemical Properties
Chemical Resistance Summary
| Reagent | Resistance | Notes |
|---|---|---|
| Water / aqueous solutions | Excellent | Negligible absorption; dimensional stability maintained |
| Dilute acids (pH > 3) | Excellent | Acetic, citric, phosphoric at typical food-plant concentrations |
| Dilute alkalis | Good | NaOH at <10%; some surface attack at higher concentrations |
| Aliphatic hydrocarbons | Excellent | Mineral oil, petroleum-based lubricants |
| Aromatic hydrocarbons | Moderate | Toluene, xylene cause swelling — avoid prolonged immersion |
| Alcohols | Excellent | IPA, ethanol, methanol |
| Ketones (acetone) | Moderate | Some swelling — verify for prolonged contact |
| Strong oxidizing acids | Poor | Concentrated H₂SO₄, HNO₃ attack polymer backbone |
| Chlorinated solvents | Poor | Methylene chloride, TCE attack PET |
| Hydraulic fluids | Excellent | Petroleum and fire-resistant types |
Ertalyte's chemical resistance is significantly better than acetal in dilute acid environments common in food processing (citric, acetic, phosphoric acids). However, chlorinated cleaning solvents will attack Ertalyte. Specify Ertalyte for alkaline or neutral wash-down environments; for chlorinated cleaner exposure, consult before specifying.
Moisture Absorption — Why It Matters for Bearings
Moisture absorption deserves special attention for bearing-grade materials:
| Material | 24-hr Absorption | Saturation Absorption | Dim. Change Sat. |
|---|---|---|---|
| Ertalyte (PET-P) | 0.10% | 0.26% | <0.05% |
| Acetal (Delrin) | 0.22% | 0.90% | ~0.20% |
| Nylon 6/6 | 1.60% | 9.00% | 2.00% |
| Nylon 6 | 1.80% | 9.50% | 2.50% |
For a bearing bored to H7/g6 fit, nylon saturation swelling can close the running clearance entirely, causing seizure. Ertalyte's 0.05% dimensional change at saturation is essentially negligible — parts retain their machined dimensions throughout service in wet environments.
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