How are they made?
The two basic components of polyurethanes are polyols with diisocyanates. Isocyanate is the functional group of atoms comprising one nitrogen, one carbon and one oxygen. An isocyanate that has two isocyanate groups is known as a diisocyanate. A polyol is an alcohol containing many hydroxyl (a compound containing oxygen and hydrogen) groups.
MDI (Diphenylmethane diisocyanate)
MDI is a versatile isocyanate that can be used to make flexible foams, as well as semi-rigid and rigid polyurethane plastics, and even adhesives. Its primary applications include construction insulation and adhesives, furniture interiors, automotive components and shoe soles.
TDI (Toulene Diisocyanate)
TDI is an isocyanate used primarily in the manufacture of flexible foams. Its primary applications include foam cushions for furniture and automotive components.
Polyether Polyols (PEOL)
Marketed under the Lupranol® and Pluracol® brands, the BASF polyol portfolio includes conventional PEOLs as well as polymer PEOLs. Primary applications include rigid foams and flexible foams.
Marketed under the name Lupraphen®, there are both aliphatic and aromatic grades available. They are combined with isocyanates to produce semi-rigid polyurethane plastics. Applications include cable sheathings and shoe soles.
Part of polyurethane’s flexibility stems from chemists being able to engineer on the molecular level to create different physical attributes. Mixing polyols and diisocyanates variants in different quantities and with different additives creates a wide variety of textures, hardness and rigidity. There are four different categories of polyurethane.
Flexible foams are soft, but also supportive and provide comfort. Flexible foams are durable, resilient and absorb energy. They also always return to their original shape. They’re used for cushioning for upholstered furniture, bedding, carpet cushioning, packaging, textiles and fibers, car and truck seating and more.
Rigid polyurethane foams deliver a unique combination of properties that allow them to be used in a number of ways, most notably in building insulation materials, refrigeration and water insulation. Because they are so efficient at controlling thermal transfer, thinner profiles can be used, increasing space utilization and reducing energy costs. They are also strong, yet lightweight and moisture resistant. They bond well to most substrates as well as metal skins, enhancing structural strength. They function well in temperature extremes and keep their shape under stress.
Thermoplastic polyurethane (TPU) is a segmented block copolymer comprised of hard and soft segments. The hard segment can be either aromatic or aliphatic and the soft segment either a polyether or a polyester type. This effectively means that thermoplastic polyurethanes can be created on a spectrum from hard rubber to soft plastic and can be processed via extrusion and injection, blow or compression molding equipment.
TPUs are durable and resistant to impact, abrasion, tear and weather. TPUs have literally hundreds of uses in an array of commercial, industrial and consumer products. Typical applications include caster wheels, shoe soles, glass lamination, fire hoses, irrigation hoses, reinforced tubing, wire and cable jacketing, sporting equipment from hard in-line skate wheels to soft swim fins, automotive side body moldings, airbag covers and power tools.
Coatings, Adhesives, Sealants and Elastomers
Polyurethane coatings are used wherever high strength, moisture resistance and durability are required. They give a high gloss shine to automobiles, protecting the paintwork and color with their scratch and corrosion resistant properties. They are relied on by the aerospace industry protect external parts of aircraft from extreme temperature differences.
Polyurethane adhesives provide strong bonding and tight seals and are ideal for the manufacturing and construction industries. They reduce the need for clamping, saving time and increasing flexibility. They are used in footwear manufacture, automotive interiors and windshields and to make fiberboard.
Polyurethane sealants retain their shape after being stressed, cure fast and adhere to almost anything. They are used in road repair, plumbing, construction and anywhere a high-strength, water-proof seal is needed.
Polyurethane elastomers have rubber-like properties with high load-bearing capacity and abrasion resistance, and can be molded to almost any shape. Polyurethane elastomers also have shape memory and will return to their original shape after being stressed. They are light, machined easily and are resistant to abrasion, impact, temperature, aging and microbial growth.
Their unique properties make them the material of choice for hundreds of products and applications from snowplow blades to shoe soles, from wheels for carts, boards and skates, to valves, balls and trolley wheels—the list is almost endless.