Many sportswear manufacturers are using thermoplastic polyurethanes today. Because of their strength and durability, they are ideal for air chambers used on balloons, cyclists’ helmets and on fabric laminates such as ballast compensators for scuba divers and even as anti-scratch layers. They are placed on the bottom of inflatable boats as well. Their tensile and abrasion resistance and ease of manufacture explain their long-lasting performance.
The air chambers used in balls, helmets, shoes and other equipment have to be solid for a long time and kept intact against maltreatment of all kinds such as blows, pressures, squeezing and pushups. In addition to these mistreatments, they have to withstand natural inclemency including extreme temperatures and humidity. Thermoplastic polyurethanes give these air chambers the necessary tensile and burst strength with elasticity and flexibility needed to withstand the blows. They have excellent flexural fatigue strength and retain their properties in all kinds of excessive conditions including extreme heat and cold. And since they do not contain plasticizers, they retain their properties during a long useful life.
Another advantage is the ease of manufacture. It is a material with which you work easily and it simplifies production and reduces costs. It can be manufactured in many ways i.e. punching or sealing at high frequencies, thermoformed, vacuum formed, hot rolled or adhesive glued with other polyurethanes or other materials. It can be stamped or screen-printed. The best polyurethane air chambers are often used in footballs, volleyball or rugby balls and to shape cycling helmets, hockey skates and athletic footwear. Gel chambers are used for orthopedic or anti-shock insoles in footwear.
Other sports applications that use thermoplastic polyurethanes are compresses that circulate cold water to the wounds suffered by athletes in the joints. This type of product not only benefits from TPU chambers to contain and circulate the fluids in question but also uses laminated thermoplastic polyurethanes tissue to protect the wounds with a wrapper that does not lose flexibility at very low temperatures.
The strength and durability of the thermoplastic polyurethanes makes it an excellent material to laminate it on various types of fabrics, a combination that is used in a wide variety of sporting goods. Depending on the needs, a very thin layer is applied that provides resistance to tension and abrasion as well as impermeability, and it also serves as a versatile adhesive to glue together many materials.
Laminates for ballast compensators in underwater sport use polyurethanes for their resistance to abrasion and fatigue caused by pushups. On the other hand, the laminate facilitates the design of waterproof systems which is essential for underwater equipment and other applications.
They can be sealed dielectrically instead of having to be sewn which explains that they are products without sutures. In addition, there are protective articles such as rug hull pads, which use thermoplastic polyurethanes as an adhesive between a layer of fabric and insulating foam for better outer protection. These laminates are also used for stickers, decals or patches with numbers or names that are printed on a fabric with an iron.
Thermoplastic polyurethanes laminates are also often used in camping equipment. They are waterproof but let the air pass through and give protection, durability and impermeability to the fabrics of tents and backpacks and rainwear. There are inflatable camping mattresses that have a non-woven foam pad glued to the fabric or nylon with thermoplastic polyurethanes. These mattresses are usually wrapped in backpacks with other materials and yet have to remain sufficiently inflated on uneven, rugged and often rocky terrain. Thermoplastic polyurethanes provide these mattresses with strength and durability to keep their different layers inseparable and avoid holes through which air escapes.
Let’s start by talking about the structure property relationship of a thermoplastic polyurethanes. It has a structure that gives it properties that other types of polymers do not possess and that make them very useful for high performance applications such as the following;
- Excellent abrasion resistance
- Excellent mechanical properties combined with great elasticity
- High resistance to tearing
- Very good resistance to oils and fats
- Very good elasticity at low temperatures
Traditionally thermoplastic polyurethanes are classified into two major groups according to their nature;
- Polytetrahydrofuran generally based on polyether
- TPUs based on polyester generally derived from adipic acid
Polyether-based TPUs have better resistance to hydrolysis, better resistance to microorganisms and better flexibility at lower temperatures, on the other hand, they have better resistance to thermo-oxidation and better resistance to oils and fats. There will be new polyether based TPUs for applications where there is high resistance to hydrolysis and TPUs of different hardness based on copolymer polyether together with the best features of TPUs based on polyether and polyester, making good resistance to combined hydrolysis with a good resistance to thermooxidation and excellent mechanical properties.
New Trends and Developments
The best prospects for TPUs are centered on the area between conventional rubber and rigid thermoplastics. Technological applications and new designs strive to take advantage of their unique properties to create innovative products at reasonable prices.
They tend to have long injection cycle times, and consequently, their production is less profitable. These products can be obtained by the addition of plasticizers to harder TPUs, but it is always a compromise for the problems that said additive entails exudation and loss of mechanical properties. A potentially interesting market is the soft plastic-free TPUs for articles that require high mechanical properties and good resistance to solvents.
TPUs with High Temperature Resistance
The developments in this field are interesting in two sectors of application. The market requires products that have a high melting point to be in continuous contact with hot areas. This is the case of polyurethane films used in the automotive industry. This sector requires high elasticity and very good resistance to temperature. The property most valued in this case is the compression set, which should be as low as possible at high temperatures. Polycaprolactone copolyester base TPUs are especially recommended for this application.
Highly Stable TPU to Light
Yellowing by exposure to light is a major drawback in some applications. The use of effective combinations of UV absorbers and the use of aliphatic isocyanates enables TPUs to be obtained with high light stability. These products have poorer mechanical properties and are more expensive, but they are also good candidates for biomedical applications because of their low toxicity. The challenge is to obtain high quality products with very good stability to light and competitive prices.
Thermoplastic Polyurethanes as an Alternative to Plasticized PVC
These are special formulations of thermoplastic polyurethanes powder applied by rotational sintering in the automotive industry. It is used to coat interior parts of the car that require imitation skin feel.
Phases of the Process
- Placement of the powder in the previously heated mold.
- Application of vacuum and rotation or vibration of the mold to distribute powder evenly by its hot surface where it melts and covers it in the form of skin.
- Mold cooling
- Transfer of the ‘skin’ to the surface of the piece to be coated
The product applied by this system must have the following basic requirements;
- Homogeneous fusion
- Adequate melt viscosity
- Very fine granulometry
- Easy demolding
- High resistance to light
- Color stability
The thermoplastic polyurethanes also has very good adhesion to polyethylene foam, behaves better at extreme temperatures and is more pleasant to the touch than other polymers used in this application.