Ultra-high molecular weight polyethylene (UHMWPE) is a unique polymer with outstanding physical and chemical properties. It’s most notable characteristics include the chemical inertness, lubricity, impact resistance, and abrasion resistance. These characteristics make UHMWPE the material of choice in a wide range of industrial applications, such as pickers for textile machinery, lining for chutes and dump trucks in mining sites, runners for bottling production lines, as well as bumpers and siding for ships and harbors. Over 90% of the UHMWPE produced worldwide is used in industrial applications. UHMWPE also has been used in orthopedics as a bearing material in artificial joints.
UHMWPE belongs to a family of polymers called polyethylene which consists of only H and C elements. Polyethylene is a polymer formed from ethylene (C2H4) monomer. The chemical structure of polyethylene can be expressed as –(C2H4)n–, where n is the degree of polymerization or the number of the repeating ethylene unit. The below schematic demonstrates the chemical structures of ethylene and polyethylene:
When ethylene is polymerized the result is relatively straight polymer chains. From the main chain they can branch out. We get different kinds of Polyethylenes from the varying degree of branching in their molecular structure. There are several kinds of polyethylene (LDPE, LLDPE, HDPE, UHMWPE), which are synthesized with different molecular weights and chain architectures. For UHMWPE, the molecular chain can consist of as many as 200,000 ethylene units. In other words, the molecular chain of UHMWPE contains up to 400,000 carbon atoms.
LDPE (Low Density Polyethylene) is highly branched which makes it difficult to crystallize and thus causes the low density. It has outstanding clarity in film for food packaging. It’s density of 0.91-0.925g/cm3.
LLDPE (Linear Low Density Polyethylene) has a significant number of short branches. Its polymer chains are able slide against each other upon elongation unlike entangled chains of LPDE. This gives LLDPE improved mechanical properties relative to LDPE. It has a density of 0.91-0.94g/cm3.
MDPE (Medium Density Polyethylene) has less branching then the HDPE which makes it less notch sensitive and has better stress cracking resistance than HDPE. It has a density range of 0.926 - 0.94 g/cm3
HDPE (High Density Polyethylene) has minimal branching of its’ polymer chains which make it easier to crystallize and thus denser than other types. It is more rigid and less permeable then the LDPE. It has a density of 0.941-0.965g/cm3.
UHMWPE (Ultra High Molecular Weight Polyethylene) has extremely long chains, with molecular weight numbering in the millions usually between 3 to 7 million. Such longer polymer chains serve to transfer load more effectively to the polymer backbone by strengthening intermolecular interactions. This causes the material to be very tough and gives it the highest impact strength of the polyethylenes. Also UHMWPE exhibits excellent impact strength and abrasion resistance. These characteristics make UHMWPE the preferred material in a wide range of industrial applications. It has a density of 0.928-0.941 g/cm3.
LDPE (Low Density Polyethylene) is highly branched which makes it difficult to crystallize and thus causes the low density. It has outstanding clarity in film for food packaging. It’s density of 0.91-0.925g/cm3.
LLDPE (Linear Low Density Polyethylene) has a significant number of short branches. Its polymer chains are able slide against each other upon elongation unlike entangled chains of LPDE. This gives LLDPE improved mechanical properties relative to LDPE. It has a density of 0.91-0.94g/cm3.
MDPE (Medium Density Polyethylene) has less branching then the HDPE which makes it less notch sensitive and has better stress cracking resistance than HDPE. It has a density range of 0.926 - 0.94 g/cm3
HDPE (High Density Polyethylene) has minimal branching of its’ polymer chains which make it easier to crystallize and thus denser than other types. It is more rigid and less permeable then the LDPE. It has a density of 0.941-0.965g/cm3.
UHMWPE (Ultra High Molecular Weight Polyethylene) has extremely long chains, with molecular weight numbering in the millions usually between 3 to 7 million. Such longer polymer chains serve to transfer load more effectively to the polymer backbone by strengthening intermolecular interactions. This causes the material to be very tough and gives it the highest impact strength of the polyethylenes. Also UHMWPE exhibits excellent impact strength and abrasion resistance. These characteristics make UHMWPE the preferred material in a wide range of industrial applications. It has a density of 0.928-0.941 g/cm3.
The table below compares the properties of HDPE and UHMWPE:
In summary:
HDPE Material Characteristics
• Good machinability
• Good chemical resistance
• Impact resistant
• Easy to fabricate
• Good weldability
• Low moisture absorption
HDPE Applications:
• Chemical tanks like fuel tanks
• Cutting boards
• Water pipe flanges (HDPE pipe grade)
• Outdoor and indoor playground systems
• Marine construction (pile guards, bumpers, anti-skid surfaces)
• Light-duty tank, chute, and bin linings
• Outdoor cabinetry and furniture
UHMWPE Material Characteristics
• Great chemical resistance
• Great Impact resistant
• Self-lubricating
• Easy to fabricate
• High friction and wear resistant
• Good machinability
• No moisture absorption
UHMWPE Applications:
• Chute, hopper, and truck bed liners
• Wear strips and guide rails
• Star wheels and idler sprockets
• Conveyor components
• Packaging machinery parts
• Food processing machinery parts
• Bumpers, pile guards, and dock fenders
