UHMWPE properties
Ultra-high molecular weight polyethylene (UHMWPE) is a semicrystalline, opaque, whitish thermoplastic composed of polyethylene chains with an exceptionally high molecular weight, typically between 2 and 6 million daltons. This extreme chain length gives it the highest impact resistance among thermoplastics, along with exceptional toughness and wear resistance. It is self-lubricating, has a very low coefficient of friction — comparable to PTFE — and outstanding chemical resistance against acids, alkalis, and most solvents, except oxidizing acids. Unlike conventional polyethylenes, its very high melt viscosity prevents processing by common methods such as injection molding; powder sintering, ram extrusion, or gel spinning are used to obtain high-performance fibers.
Chemical composition
Section titled “Chemical composition”The base structure of UHMWPE corresponds to the repetition of the ethylene monomer, forming very long linear chains of -(CH₂-CH₂)- with an average molecular weight much higher than that of conventional HDPE.
| Component | Value |
|---|---|
| Chemical formula | (C₂H₄)n |
| Typical molecular weight | 2 – 6 × 10⁶ g/mol / Dalton |
| Carbon (wt%) | 85.7 % |
| Hydrogen (wt%) | 14.3 % |
| Crystallinity | 39 – 75 % (depending on processing) |
| Fiber orientation degree | > 95 % parallelism |
Mechanical properties
Section titled “Mechanical properties”Properties in base state (sintered sheet/rod)
Section titled “Properties in base state (sintered sheet/rod)”The following mechanical properties correspond to UHMWPE consolidated by sintering, without additional molecular orientation.
| Property | Value (metric / imperial) |
|---|---|
| Tensile strength | 35 MPa / 5,076 psi |
| Flexural modulus | 0.5 GPa / 72.5 ksi |
| Elongation at break | 500 % |
| Yield strain | 25 % |
| Izod impact strength (notched) | 1.06+ kJ/m / 19.9+ ft·lb/in |
| Surface hardness | Rockwell R: RR50 |
Properties in high-modulus fiber form (UHMPE / HPPE)
Section titled “Properties in high-modulus fiber form (UHMPE / HPPE)”Subjected to gel spinning and drawing, UHMWPE achieves orientations greater than 95 % and crystallinities up to 85 %, resulting in radically improved mechanical properties (indicative values for Dyneema / Spectra type fibers).
| Property | Value (metric / imperial) |
|---|---|
| Tensile strength | 2.2 – 3.0 GPa / 319 – 435 ksi |
| Elastic modulus | 80 – 170 GPa / 11.6 – 24.7 Msi |
| Linear density (tex) | variable according to denier |
| Elongation at break | 3 – 4 % |
Physical properties
Section titled “Physical properties”| Property | Value (metric / imperial) |
|---|---|
| Density | 0.945 g/cm³ / 0.0341 lb/in³ |
| Water absorption (24 h, 23 °C) | 0.01 % |
| Dynamic friction coefficient (against steel) | 0.05 – 0.11 (self-lubricating) |
| Volume resistivity | 10¹⁸ Ω·cm (log = 18) |
| Dielectric strength | 28 MV/m / 711 V/mil |
| Dissipation factor (1 kHz) | 0.0002 |
| Dielectric constant (1 kHz) | 2.3 |
Thermal properties
Section titled “Thermal properties”| Property | Value (metric / imperial) |
|---|---|
| Melting temperature (onset) | 127.7 °C / 261.9 °F |
| Maximum continuous operating temperature | 55 °C / 131 °F |
| Brittle temperature | -150 °C / -238 °F |
| HDT (0.45 MPa) | 69 °C / 156.2 °F |
| HDT (1.80 MPa) | 42 °C / 107.6 °F |
| Linear expansion coefficient | 13 × 10⁻⁵ / °C (7.2 × 10⁻⁵ / °F) |
| Limiting oxygen index (LOI) | 17 % |
| UL94 flammability rating | HB |
Applications by industry
Section titled “Applications by industry”- Medical and orthopedic industry: joint replacement components (hip, knee, spine) due to its biocompatibility and wear resistance.
- Material handling and bottling: guides, hoppers, slide plates, wear parts for filling machines and bulk solid transport.
- Food industry: professional cutting boards, work surfaces that prevent contamination and blade wear.
- Sports and recreational equipment: edge protectors for ice rinks, skate components, sports shoe reinforcements.
- Defense and ballistic protection: bulletproof vests, helmets, lightweight armor from high-modulus fibers (Dyneema / Spectra).
- Marine sector: quay fenders, high-strength ropes and lines.
- Textile engineering and machinery: bushings, bearings, self-lubricating plain bearings, moving parts of looms.
Comparison with similar materials
Section titled “Comparison with similar materials”Qualitative comparison of UHMWPE against other high-engineering thermoplastics in their most distinctive properties (indicative scale).
| Property | UHMWPE | PTFE | Nylon (PA6) | Acetal (POM) | HDPE |
|---|---|---|---|---|---|
| Friction coefficient | Very low (≈0.05‑0.11) | Very low (≈0.04) | Low (≈0.15‑0.25) | Low (≈0.2) | Low (≈0.2) |
| Abrasion resistance | Excellent | Low | Good | Very good | Moderate |
| Impact resistance (toughness) | Exceptional (highest among thermoplastics) | Low | High | Moderate | High |
| Maximum continuous service temperature | 55 °C / 131 °F | 260 °C / 500 °F | 85‑100 °C / 185‑212 °F | 85‑100 °C / 185‑212 °F | 55‑65 °C / 131‑149 °F |
| Moisture absorption | Practically zero (0.01 %) | Zero | High (up to 3 %) | Low (0.2 %) | Very low |
| Processability | Only sintering/ram | Easy sinter/mold | Injection/extrusion | Injection/extrusion | Injection/extrusion |
Frequently Asked Questions (FAQ)
Section titled “Frequently Asked Questions (FAQ)”What is the fundamental difference between UHMWPE and HDPE?
Section titled “What is the fundamental difference between UHMWPE and HDPE?”UHMWPE has a molecular weight between 2 and 6 million daltons, while conventional HDPE ranges from 200,000 to 500,000. This extreme chain length gives it much higher impact and abrasion resistance, as well as slightly higher chemical resistance, but at the cost of being unable to be processed by conventional melt methods.
Can UHMWPE be joined or glued?
Section titled “Can UHMWPE be joined or glued?”Adhesive bonding of UHMWPE is extremely difficult due to its very low surface energy (approx. 30 mN/m) and non-polar nature. For acceptable adhesion, surface treatments such as plasma, corona, or chemical etching with chromic acid are required. Mechanical fastening or heat sealing are preferable alternatives.
What is the maximum continuous service temperature of UHMWPE?
Section titled “What is the maximum continuous service temperature of UHMWPE?”The recommended continuous operating temperature for solid components is 55 °C / 131 °F. Prolonged exposure above 80‑90 °C causes softening and loss of mechanical properties, although the crystalline melting temperature begins around 127.7 °C.
Why can’t UHMWPE be injection molded?
Section titled “Why can’t UHMWPE be injection molded?”Its melt viscosity is on the order of 10⁷‑10⁹ Pa·s, millions of times higher than that of injection-moldable polyethylenes. This practically non-existent flow prevents mold filling by injection. Feasible industrial techniques are powder sintering (compression) and ram extrusion, or gel spinning for fibers.
At what temperature does UHMWPE become brittle?
Section titled “At what temperature does UHMWPE become brittle?”The material retains high toughness down to very low temperatures; embrittlement is observed below -150 °C / -238 °F. This makes it an excellent choice for cryogenic or arctic applications.
What makes UHMWPE self-lubricating?
Section titled “What makes UHMWPE self-lubricating?”Its exceptionally low coefficient of friction, from 0.05 to 0.11 against steel, is comparable to PTFE and is due to the absence of polar groups in the polyethylene chains. This non-adhesive structure prevents the formation of strong surface bonds, reducing both friction and wear without the need for external lubrication.
Sources Consulted
Section titled “Sources Consulted”- azom.com: https://www.azom.com/article.aspx?ArticleID=854
- engineeringtoolbox.com: https://www.engineeringtoolbox.com/ASTM-D3035-PE-pipes-d_2138.html
- steelnumber.com: https://www.steelnumber.com/en/steel_composition_eu.php?name_id=602