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Ultra High Molecular Weight Polyethylene (UHMW) is one the most widely used thermoplastic materials today. It is defined as having a minimum molecular mass (molecule length) of 3.2 million; some resins go as high as 7.5 million (for reference, HDPE = ~1MM, LDPE = ~500,000)
UHMWPE advantages in its virgin form:
- odorless, tasteless, and nontoxic
- highly resistant to corrosive chemicals except oxidizing acids
- almost no moisture absorption
- extremely low coefficient of friction (comparable to PTFE (&#;Teflon®&#;))
- self-lubricating
- excellent abrasion resistance, especially wet (~15X better than carbon steel)
- highest impact resistance of any thermoplastic (IZOD = no break)
Easily modified, this base material is used in applications as diverse as cargo dock impact bumpers to dump truck liners to food equipment to orthopedic joint replacements. Essentially a &#;poor man&#;s Teflon®&#;, it shares similar properties, with some significant limitations.
Like PTFE, UHMW cannot be melt processed, as this breaks down the molecular chain. It is made using compression and heat to &#;fuse&#; the material below its melting point. It is available in compression molded sheets up to 8&#; x 20&#;, and ram-extruded rod, tubes & profile shapes.
The largest industrial markets for UHMW are food processing and heavy equipment, both primarily for bearing & wear components. For such applications, the limitations versus nylon or acetal are:
- Heat Resistance &#; the heat deflection temperature is 116&#;F, compared to ~200&#;F
- Thermal Expansion &#; UHMW changes at 2X the rate of nylon with temperature changes
- Compressive Strength &#; its compressive strength = psi, versus 15,000 psi for nylon &#; UHMW&#;s safe working load is psi maximum
- Inserts &#; since the material is only 25%as strong as nylon, larger / specialty inserts with a foot extension on the bottom (prevents pull-through), and limited torqueing is needed
Where food contact is not an issue, reprocessed UHMW is a cost effective alternative. Using clean regrind mixed with virgin black resin yields a material with the same low friction, low moisture absorption and impact resistance of virgin at lower material cost. Due to the inclusion of the larger regrind particles, it is actually slightly harder and some OEMs prefer it over virgin.
There many modifications of UHMW available, including colors; UV stabilized; lubricant filled (solid, oil or MoS2), ceramic filled; anti-static/conductive; metal/X-ray detectable; high temperature.
This last version needs come clarification. Some mills offer an anti-oxidant filled UHMW touted to withstand 275&#;F &#; HOWEVER -THE HEAT DEFLECTION TEMPERATURE IS THE SAME AS VIRGIN, 116&#;F! What the 275F means is that, where pure virgin UHMW starts to oxidize (turn brown) over time @ ~175&#;F, this version adds ~100&#;F heat resistance before oxidation.
Too much information? Give us a call, the experts at WS HAMPSHIRE can walk you through all the data to find the right material for your needs &#; you&#;re in the right place!
Tom Connelly is a self proclaimed &#;street engineer&#; with over 40 years in the plastics industry.
Polyethylene is the most commonly used plastic in the world, but how do you know if it&#;s the right yarn for your application? Consider the attributes of ultra-high-molecular-weight polyethylene (UHMWPE) - a very tough subset of polyethylene that has a strength to weight ratio 8-15 times greater than steel.
Want more information on UHMWPE Plant? Feel free to contact us.
Commonly known by the trade names of Spectra® and Dyneema®, UHMWPE plastics and yarns are primarily used for:
- Ballistic uses (Body Armor, Armor Plating)
- Sports and leisure (skydiving, skiing, boating, fishing)
- Ropes and cordage
- Bulk material handling
- Porous parts and filter
- Automotive industry
- Chemical industry
- Food processing and beverage machinery
- Mining and mineral processing equipment
- Manufacturing equipment
- Civil engineering and earthmoving equipment
- Transport-related applications, including truck trays, bins and hoppers.
As you can see UHMWPE has a diverse range of uses from manufacturing to medical as well as in wire and cable applications. This is due to its long list of benefits which meet specific requirements for many different jobs.
The advantages of UHMWPE include, but are not limited to:
- Excellent resistance to stress and high resistant to cracking
- Abrasion wear resistance &#; 15 times more resistant to abrasion than carbon steel
- Its 40% Stronger than Aramid yarns
- Its strong chemical resistance - highly resilient to most alkalis and acid, organic solvents, degreasing agents and electrolytic attack
- It&#;s non-toxic
- Excellent dielectric properties
- Self-lubricating &#; very low coefficient of friction (comparable to PTFE)
- Non-staining
- FDA approved for use in food and medical applications
- Low specific gravity &#; will float in water
While this may sound like an ideal material, there are also a few disadvantages you should be aware of. UHMWPE has a lower melting point (297° to 305° F) than many common polymers, therefore it&#;s not suitable for high temperature applications. It also has a low coefficient of friction which can be a drawback depending on the application. UHMWPE yarns can also develop &#;creep&#; under a constant load, which is a process of gradual elongation of the fibers. Some people may consider the price to be a disadvantage, however when it comes to UHMWPE, less is more. Given the strength of this material you would not need to buy as much as you would with other materials.
Still wondering whether or not UHMWPE is right for your product? Service Thread develops and delivers engineered yarns and sewing threads to solve product and processing problems for our customers. Proactive, personalized service is wound into everything we do. Contact us to find out what fiber is best for your application.
Information on other high performance fibers:
Vectran&#; vs. Aramid
What is Vectran&#;?
Para-Aramid vs. Meta-Aramid
Kevlar® Alternatives
Aramid Applications
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