Summary of 12 Key Properties of Polyurethane Elastomers

At Nord Wheel, we are deeply committed to the research and development of polyurethane elastomers to enhance wheel performance from the material level. We manufacture wheels using four primary polyurethane systems: TDI, MDI, NDI, and PPDI. Based on years of innovation, we’ve summarized the following key properties of polyurethane elastomers—insights we hope are valuable to customers, partners, and industry professionals alike.

1) Hardness

Polyurethane elastomers span a wide hardness range—from Shore A10 to Shore D80—without requiring filler additives. They maintain excellent elasticity and elongation even at high hardness levels. In contrast, conventional rubber must rely on fillers (which reduce elasticity) to achieve similar hardness. Above Shore D75, rubber loses significant elasticity, and at D85 or higher, it is no longer considered an elastic material.

2) Mechanical Strength

Polyurethane elastomers offer exceptional mechanical performance across several dimensions:

Young’s Modulus & Tensile Strength: While Hooke’s Law only applies at low elongations (~2.5%), polyurethane elastomers exhibit significantly higher modulus values than most elastomers, bridging the range between rubber and plastic.
Tear Strength: Especially in polyester-based systems, tear strength can exceed that of natural rubber by more than 2x.
Load-Bearing Capacity: Polyurethane’s ability to increase hardness without sacrificing elasticity enables high load-bearing capacity—unlike many conventional rubbers with hardness limitations.

3) Wear Resistance

Polyurethane elastomers deliver outstanding abrasion resistance, typically in the range of 0.03–0.20 mm³/m, or 3–5 times better than natural rubber. Their high tear strength plays a key role. However, they do exhibit a relatively high coefficient of friction (usually >0.5). To reduce frictional heat and wear, additives such as molybdenum disulfide, graphite, silicone oil, or PTFE powder are recommended. Friction increases with softer materials and higher surface temperatures, peaking around 60°C.

4) Oil & Chemical Resistance

Polyurethane elastomers—particularly polyester-based types—are highly resistant to fuels and mineral oils, outperforming general-purpose rubber and comparable to nitrile rubber. However, they swell and degrade in alcohols, esters, ketones, and aromatic hydrocarbons at elevated temperatures. Halogenated solvents may also cause degradation. Even minimal water contamination (as little as 0.02%) in oil can significantly affect material performance by migrating into the elastomer.

5) Water Resistance

Polyurethane elastomers exhibit excellent water resistance at room temperature. Based on accelerated testing:

Polyester elastomers: Lose 50% tensile strength after ~10 years in water at 25°C
Polyether elastomers: Reach the same threshold only after ~50 years

Polyether-based systems are markedly superior for long-term moisture exposure.

6) Heat & Oxidation Resistance

In inert environments (e.g., nitrogen), polyurethane performs well at elevated temperatures. At room temperature, it also resists oxygen and ozone. However, the combined effect of heat and oxygen accelerates aging:

Long-term air use: up to 80–90°C
Short-term exposure: up to 120°C
Onset of oxidative degradation: around 130°C

Among formulations, polyester-based elastomers generally outperform polyether types in thermal-oxidative resistance. Within those families, poly(hexamethylene adipate) systems perform best.

7) Low-Temperature Performance

Polyurethane elastomers retain flexibility at extremely low temperatures, with brittle points as low as -50°C to -70°C. Some formulations, like PCL-TDI-MOCA, remain non-brittle even below this range. However, common polyester-based polyurethanes may crystallize in the cold, becoming brittle and unsuitable for sealing applications below -20°C. At low temperatures:

Hardness, strength, and stiffness increase
Rebound and elongation decrease

8) Vibration Absorption (Damping)

Polyurethane elastomers display strong hysteresis behavior under alternating stress, dissipating energy as internal heat. Key factors:

The attenuation coefficient quantifies energy absorption
Performance depends on material formulation, temperature, and vibration frequency
Maximum damping occurs when vibration frequency ≈ molecular relaxation time
At room temperature, polyurethane absorbs 10–20% of vibration energy—exceeding nitrile rubber

Note: Hysteresis-induced heat raises the material’s temperature, increasing rebound but reducing damping. These trade-offs should be balanced in vibration-control design.

9) Electrical Insulation

Polyurethane elastomers offer good electrical insulation at operating temperatures, comparable to chloroprene rubber and phenolic resins. Their castable and thermoplastic versatility makes them ideal for potting compounds and cable jackets.

10) Radiation Resistance

Among synthetic polymers, polyurethane elastomers demonstrate excellent resistance to high-energy radiation, retaining performance at doses of 10⁵–10⁶ Gy. However, light-colored or transparent formulations may discolor—similar to aging effects in heated or UV-exposed environments.

11) Fungal Resistance

Polyether polyurethanes: Excellent resistance (Grade 0–1), nearly mold-free
Polyester polyurethanes: Prone to mold and unsuitable for tropical/humid conditions without additives

For such environments, formulations must include fungicides (e.g., copper-8-hydroxyquinoline, BCM) at 0.1–0.5% to inhibit microbial growth.

12) Biomedical Compatibility

Medical-grade polyurethane is:

Non-toxic
Non-allergenic
Non-irritating
Non-pyrogenic

Extensively validated through toxicology and animal studies, polyurethane is considered one of the most promising synthetic materials in biomedical applications.