The Many Forms and Functions of Thermoplastic Polyurethane

Thermoplastic polyurethane (TPU) is an elastomer that is fully thermoplastic. Like all thermoplastic elastomers, TPU is elastic and melt-processable. Further, it can be processed on extrusion as well as injection, blow and compression molding equipment. It can be vacuum-formed or solution-coated and is well suited for a wide variety of fabrication methodologies. TPU can even be colored through a number of processes. But more so than any other thermoplastic elastomer, TPU can provide a considerable number of physical property combinations making it an extremely flexible material adaptable to dozens of uses.

This is partly because TPU is a linear segmented block copolymer composed of hard and soft segments. The hard segment can be either aromatic or aliphatic. Aromatic TPU's are based on isocyanates such as MDI while aliphatic TPU’s are based on isocyanates like H12 MDI. When these isocyanates are combined with short-chain diols, they become the hard block. Normally it is aromatic, but when colors and clarity retention in sunlight exposure is a priority, an aliphatic hard segment is often used.

The soft segment can either be a polyether or polyester type, depending on the application. For example, wet environments generally require a polyether-based TPU while oil and hydrocarbon resistance often demand a polyester-based TPU. For even greater utility, the molecular weight, ratio and chemical type of the hard and soft segments can be varied.

This versatility results from the unique structure of TPU that results in high resilience, good compression set, plus resistance to impacts, abrasions, tears, weather, and even hydrocarbons. TPU offers flexibility without the use of plasticizers as well as a broad range of hardness’s and high elasticity. In fact, TPU bridges the material gap between rubbers and plastics. Its range of physical properties enables TPU to be used as both a hard rubber and a soft engineering thermoplastic. TPU’s can be sterilized, welded, easily processed, colored, painted, printed, die-cut and slitted. They have low temperature flexibility and, in some grades, exhibit biocompatibility, hydrolytic stability, optical clarity, plus flame retardant and anti-static properties.


TPU Compounds

Further, TPU can be compounded for use in numerous applications where greater structural integrity is required, such as for automotive body side moldings. For example, when mixed with glass fiber or mineral fillers, TPU’s properties of abrasion resistance, paintability, high impact strength and good low temperature flexibility all become enhanced, and the compound also demonstrates good fuel and oil resistance and high melt flow characteristics.

In addition, TPU is an outstanding contributor of polymer blends. When added to polyvinyl chloride (PVC), TPU improves compression set, abrasion resistance and low temperature flexibility. The addition of TPU also improves toughness and impact resistance of acetal.

When added to polycarbonate or acrylonitrile-butadiene-styrene (ABS), a TPU resin with a nominal flexural modulus of 18,000, produces compounds with flexural modulus values up to 150,000 psi. In this way, specialized compounds can be made that improve the properties of polycarbonate or ABS or other plastics.

TPU Applications

These properties make TPU extremely useful for hundreds of products.

  • Architectural Glass Lamination
  • Auto-Body Side Molding
  • Automotive Lumbar Supports
  • Caster Wheels
  • Cattle Tags
  • Constant Velocity Boots (Automotive)
  • Drive Belts
  • Film and Sheet
  • Fire Hose Liner
  • Flexible Tubing
  • Food Processing Equipment
  • Footwear - sport shoe soles
  • Hydraulic Hoses
  • Hydraulic Seals
  • Inflatable Rafts
  • In-Line Skates
  • Magnetic Media
  • Medical Tubing / (+IV) Biomedical Apparatus
  • Mining Screens
  • Sporting Goods
  • Swim Fins and Goggles
  • TPU Coated Fabrics
  • Wire and Cable Coatings

Helping the industry and marketplace to harness the tremendous versatility of TPU is the Center for the Polyurethanes Industry which works to expand the worldwide use of thermoplastic polyurethane by promoting its features and benefits, reducing barriers to the use of TPU and by serving as an industry-wide forum for issue identification and resolution.

Whether for its outstanding toughness, durability or processing ease, TPU is a versatile performer that bridges the gap between rubber and plastics.

spotlight

The polyurethane industry, working together through the American Chemistry Council's (ACC) Center for the Polyurethanes Industry (CPI) and the Spray Polyurethane Foam Alliance (SPFA), has launched an enhanced product stewardship program to support further understanding of the benefits of spray polyurethane foam and its continued safe use and handling. A part of this outreach, a new Spray Polyurethane Foam Health and Safety website, www.spraypolyurethane.com, has been launched by CPI and SPFA that contains new materials, literature and posters to increase understanding of spray polyurethane foam (SPF) product stewardship information.

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