Polyurethane (or PU for short) is one of the most versatile synthetic materials on the market. Its uses span a never-ending list of applications, from machinery and appliances to car parts, and even bedding. Polyurethane is also widely used in footwear – especially safety footwear.
Polyurethanes are formed by reacting a polyol (an alcohol with more than two reactive hydroxyl groups per molecule) with a diisocyanate or a polymeric isocyanate in the presence of suitable catalysts and additives (American Chemistry Council).
Depending on their chemical compositions, different types of polyurethanes exist in different applications.
1. Rigid Polyurethane Foam
These foams form one of the world’s most popular, energy-efficient, and versatile insulations. They are able to significantly cut energy costs while simultaneously adding efficiency and comfort to commercial and residential properties.
Rigid polyurethane foam helps maintain uniform temperature and lower noise levels in homes and commercial properties. It is used in roof and wall insulation, insulated windows, doors, and air barrier sealants.
2. Coatings, Adhesives, Sealants and Elastomers
Polyurethane coatings can both enhance the appearance and lengthen the lifespan of a product. Adhesives and sealants made with PU offer stronger bonding and tighter seals. PU elastomers are extremely versatile – they can be molded into almost any shape, are lighter than metal, and are resistant to many environmental factors (such as extreme weather).
3. Thermoplastic Polyurethane (TPU)
TPU is highly elastic, flexible, and resistant to abrasion, impact and weather – which is why it is used to mold the sole units on safety boots. TPUs can be coloured and fabricated in a wide variety of ways, adding unlimited potential to this material.
TPU is also an elastomer which is fully thermoplastic. It is elastic and melt-processable – it can be processed through extrusion, injection, blow, and compression moulding equipment. It can also be vacuum-formed or solution-coated. It is an extremely flexible material that can be adapted to a wide range of uses, namely automotive, construction, and – of course – footwear.
4. Reaction Injection Molding
Car bumpers, electrical housing panels, and computer equipment enclosures are just some of the items made through the process of RIM. With its added design flexibility, the RIM process enables the production of parts that is not usually achievable through typical injection-molding processes. This includes the production of thick- and thin-walled parts, encapsulated inners, and foamed cores.
These polyurethanes are high strength and low weight, and can exhibit heat resistance, thermal insulation, and dimensional stability.
PU binders have the ability to bond many different types of materials together. Their main areas of use are in the manufacturing of wood panels, rubber/elastomeric flooring surfaces, and sand casting for the foundry industry. Rebond carpet underlay also uses PU binders to adhere scrap pieces of foam together in its production.
There are as many applications for PU as there are different chemical variations. In the apparel industry, fine threads of PU are combined with nylon to make more lightweight, stretchable garments. PU fibers have improved over the years in the form of spandex fibers, PU coatings, and thermoplastic elastomers. Because of the advancements in polyurethane techniques, manufacturers can now make a broad range of apparel – from man-made leather to sports clothes.
Polyurethanes are an important component in major appliances – such as rigid foams for refrigerators and thermal insulation systems used in freezers. They are also commonly used in the automotive industry. From the foam in car seats to bumpers, spoilers, and doors, all are made using polyurethane materials.
Other industries that rely on polyurethanes include building and construction, electronics, flooring, furnishings, and even medical sectors.
At Kaliber, all of our safety footwear is made with dual density polyurethane sole units. This makes them shock absorbent, oil and heat resistant, anti-slip and anti-static. The flexible nature of PU also ensures the utmost comfort across all of our shoe models.