Part of the polyethylene family, UHMW and HDPE are thermoplastics with distinct characteristics. In this article, we will discuss their respective applications and the properties that set them apart.
UHMW-PE (ultra-high-molecular-weight polyethylene)
Ultra-high-molecular-weight polyethylene (UHMW-PE or simply UHMW) is a high-performance plastic known for its low coefficient of friction. Its English name refers to its molecular structure.
"UHMW has a density of approximately 940 kg/m3, about 3 times lighter than aluminum.”
Alex Tremblay Frenette, Eng.
The main advantages of UHMW
Thanks to its extremely long molecular chain, this plastic is highly resistant to abrasion and impacts while being noticeably light. Indeed, UHMW has a density of approximately 940 kg/m3, lower than that of water (1000 kg/m3). UHMW offers numerous advantages, such as:
- excellent abrasion resistance
- excellent impact resistance
- reduced impact and friction noise
- good chemical resistance
- a low coefficient of friction
It is also available in both self-lubricating grade and metal detectable grade.
Thanks to its versatility and advantageous combinations of mechanical properties, UHMW fulfils numerous needs and is therefore used by various industries. In the manufacturing sector, UHMW is employed to design mechanical parts, guides, wear strips, gears, anti-friction liners, conveyor parts and chutes, among others. White UHMW is often confused with PFTE (Teflon) because of its low coefficient of friction; however, the former is much lighter and more affordable than the latter.
In addition, UHMW is food grade approved and therefore popular with the food industry. It is indeed frequently used in the manufacture of rollers, chain guides, conveyor parts and chute liners. UHMW that may come into contact with food include TIVAR® 1000, TIVAR® HPV, TIVAR® MD and TIVAR® H.O.T.
To learn more about high-performance plastics used in the food industry, click here!
UHMW is also commonly used in the natural resources sectors. Thanks to its properties, it represents an efficient choice to optimize the transportation of bulk materials. It is mainly used in the manufacture of abrasion-resistant liners because its low coefficient of friction helps reduce clogging in chutes. In addition, the strength of UHMW liners protects equipment while optimizing the flow of raw material. For instance, TIVAR® 88-2 is an efficient liner material, as its low dynamic coefficient of friction (0.08) allows bulk material to slide easily over its surface. It also reduces impact and friction noise generated by bulk material. High-performance UHMW liners can be welded, increasing their service life while reducing the risk of material infiltration..
Thanks to the injection of various additives that improve certain basic properties of the resin, high-performance plastics, such as UHMW, possess an extremely wide range of properties.
As previously mentioned, standard UHMW resins perform well at temperatures of up to 180 °F (82 °C). Others, such as TIVAR® H.O.T., have been specifically developed to withstand even higher temperatures. Those plastics will therefore last up to 10 times longer than standard UHMW when subjected to extreme temperatures. Specifically, they can be used in environments where continuous temperatures reach 230 °F (110 °C) and can tolerate peaks of up to 275 °F (135 °C).
Metal detectable UHMW
This type of UHMW contains a metal additive that allows it to be detected by a standard industrial metal detector while remaining relatively lightweight. When used in food environments, polyethylene materials, such as TIVAR® MD (MD stands for metal detectable), represent a significant asset because they reduce the risk of contamination by a foreign body, facilitating the identification of contaminants such as plastic parts or fragments that have fallen on the production line. Although still little known in North America, they are now a standard in Europe in terms of food safety.
This type of UHMW is obtained by adding an oil or wax lubricant to the resin. Self-lubrication eliminates the need for external lubrication since the plastic lubricates itself as it moves. Several UHMW of the TIVAR® family are self-lubricating: TIVAR® 1000, TIVAR® HPV and TIVAR® Ceram P®.
Like UHMW-PE, HDPE (high-density polyethylene) belongs to the polyethylene family and is used by various industries. The name HDPE refers to its molecular structure. Like UHMW, HDPE is food grade approved; for example, SANALITE is used in the manufacture of cutting boards.
The main advantages of HDPE
HDPE has advantages that are similar to UHMW, such as good chemical and impact resistance. It is also
- easily machinable
- resistant to abrasion
- easy to weld (more so than UHMW)
Since it can be easily moulded or welded according to specific needs, HDPE is mainly used in the food, medical and chemical sectors. It is also frequently used in the manufacture of water or chemical storage tanks.
How to choose between UHMW and HDPE
Although these two plastics are quite similar, they do possess their own distinctive characteristics. To make the right choice, it is important to evaluate the environment in which the plastic must perform; for more demanding applications, UHMW will, in many cases, be more appropriate than HDPE. Also, the coefficient of friction of HDPE (0.20) is much higher than that of UHMW (0.08). UHMW will therefore be a more suitable choice for applications that require a reduction of friction and wear.
When to choose HDPE
- For applications that require a specific shape obtained only through moulding
- For oversized parts that need to be welded
- For water storage tanks
- For chemical storage tanks
- For easy-to-clean food-grade cutting boards
- For outdoor parts or units
When to choose UHMW
- For mechanical parts subjected to high levels of stress
- For components subjected to high levels of frictional stress
- To reduce system wear and friction
- To reduce the risk of food contamination (through metal detection)
- For noise-reducing liners
HDPE is a versatile plastic suitable for a wide variety of applications. However, it is preferable to opt for one of the many UHMW grades for applications burdened by heavy stress.
To learn more about polyethylene, view our article, "What is polyethylene?”