Polyurethane products have many uses. Over three quarters of the global consumption of polyurethane products is in the form of foams, with flexible and rigid types being roughly equal in market size. In both cases, the foam is usually behind other materials: flexible foams are behind upholstery fabrics in commercial and domestic furniture; rigid foams are inside the metal and plastic walls of most refrigerators and freezers, or behind paper, metals and other surface materials in the case of thermal insulation panels in the construction sector. Its use in garments is growing: for example, in lining the cups of brassieres. Polyurethane is also used for moldings which include door frames, columns, balusters, window headers, pediments, medallions and rosettes. The new iPad Smart Cover is made of polyurethane.
Polyurethane formulations cover an extremely wide range of stiffness, hardness, and densities. These materials include:
Polyurethane foam is widely used in high resiliency flexible foam seating, rigid foam insulation panels, microcellular foam seals and gaskets, durable elastomeric wheels and tires, automotive suspension bushings, electrical potting compounds, seals, gaskets, carpet underlay, and hard plastic parts (such as for electronic instruments).
| characteristics of polyurethane materials |
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The following table shows how polyurethanes are used (US data from 2004):[1]
| Application | Usage (millions of pounds) | Percentage of total |
|---|---|---|
| Building & Construction | 1,459 | 26.8% |
| Transportation | 1,298 | 23.8% |
| Furniture & Bedding | 1,127 | 20.7% |
| Appliances | 278 | 5.1% |
| Packaging | 251 | 4.6% |
| Textiles, Fibers & Apparel | 181 | 3.3% |
| Machinery & Foundry | 178 | 3.3% |
| Electronics | 75 | 1.4% |
| Footwear | 39 | 0.7% |
| Other uses | 558 | 10.2% |
| Total | 5,444 | 100.0% |
Open cell flexible polyurethane foam (FPF) is made by mixing polyols, diisocyanates, catalysts, auxiliary blowing agents and other additives and allowing the resulting foam to rise freely. Most FPF is manufactured using continuous processing technology and also can be produced in batches where relatively small blocks of foam are made in open-topped molds, boxes, or other suitable enclosurers. The foam is then cut to the desired shape and size for use in a variety of furniture and furnishings applications.
Applications for flexible polyurethane foam include upholstered furniture cushions, automotive seat cushions and interior trim, carpet cushion, and mattress padding and solid-core mattress cores.
Flexible polyurethane foam is a recyclable product. [2]
Flexible and semi-flexible polyurethane foams are used extensively for interior components of automobiles, in seats, headrests, armrests, roof liners, dashboards and instrument panels.
Polyurethanes are used to make automobile seats in a remarkable manner. The seat manufacturer has a mold for each seat model. The mold is a closeable "clamshell" sort of structure that will allow quick casting of the seat cushion, so-called molded flexible foam, which is then upholstered after removal from the mold.
It is possible to combine these two steps, so-called in-situ, foam-in-fabric or direct moulding. A complete, fully assembled seat cover is placed in the mold and held in place by vacuum drawn through small holes in the mold. Sometimes a thin pliable plastic film backing on the fabric is used to help the vacuum work more effectively. The metal seat frame is placed into the mold and the mold closed. At this point the mold contains what could be visualized as a "hollow seat", a seat fabric held in the correct position by the vacuum and containing a space with the metal frame in place.
Polyurethane chemicals are injected by a mixing head into the mold cavity. Then the mold is held at a preset reaction temperature until the chemical mixture has foamed, filled the mold, and formed a stable soft foam. The time required is two to three minutes, depending on the size of the seat and the precise formulation and operating conditions. Then the mold is usually opened slightly for a minute or two for an additional cure time, before the fully upholstered seat is removed.
The walls and ceiling (not just the insulation) of the futuristic Xanadu House were built out of polyurethane foam. Domed ceilings and other odd shapes are easier to make with foam than with wood. Foam was used to build oddly shaped buildings, statues, and decorations in the Seuss Landing section of the Islands of Adventure theme park. Speciality rigid foam manufactures sell foam that replace wood in carved sign and 3D-topography industries. PU foam is also used as a thermal insulator in many houses.
Polyurethane resin is used as an aesthetic flooring material. Being seamless and water resistant, it is gaining interest for use in (modern) interiors, especially in Western Europe.
Two Binary liquids, one of which is a polyurethane (either T6 or 16), when mixed and aerated, expand into a hard, space-filling aerosolid.
Polyurethane sealants are available in one, two and three part systems, and in cartridges, buckets or drums. Polyurethane sealants are used to fill gaps thereby preventing air and water leakage. They are also used in conjunction with inorganic insulation, such as rockwool or ceramic fibres, for firestopping. Firestops can thwart smoke and hose-stream passage.
Some raft manufacturers use urethane for the construction of inflatable boats. AIRE uses urethane membrane material as an air-retentive bladder inside a PVC shell, whereas SOTAR uses urethane membrane materials as a coating on some boats. Maravia uses a liquid urethane material which is spray-coated over PVC to enhance air retention and increase abrasion resistance.
Some surfboards are made with a rigid polyurethane core. A rigid foam blank is molded, shaped to specification, then covered with fiberglass cloth and polyester resin.
Some boat hulls have a rigid polyurethane foam core sandwiched between fiberglass skins. The foam provides strength, buoyancy, and sound deadening.
Some boat decks including U.S Navy vessels use specialized polyurethane sealants to protect from constant moisture and harsh oceanic elements. As an example, Durabak-M26 uses a custom single-part polyurethane to prevent water seepage to unwanted areas.
Polyurethane has been used to make several Tennis Overgrips such as Yonex Super Grap, Wilson Pro Overgrip and many other grips. These grips are highly stretchable to ensure the grip wraps neatly around the racquet's handle.
Polyurethane is used as a black wrapping for timepiece bracelets over the main material which is generally stainless steel. It is used for comfort, style, and durability.
A thin film of polyurethane finish is added to a polyester weave to create polyurethane laminate (PUL), which is used for its waterproof and windproof properties in outerwear, diapers, shower curtains, and so forth. PU is used in some cutting-edge swimsuits to provide buoyancy for competitive swimmers. There are restrictions as the buoyancy enhances swimming performance.
A still more popular use of polyurethane in textiles is in the form of spandex, also known as elastane or by DuPont's brand name Lycra. Polyurethane fibers in the form of spandex can stretch up to 600% and still return to their original shape. Spandex is spun with other fibers, such as cotton, nylon, or polyester, to create stretchable fibers essential for clothing for both sports and fashion.[3]
Polyurethane materials are commonly formulated as paints and varnishes for finishing coats to protect or seal wood. This use results in a hard, abrasion-resistant, and durable coating that is popular for hardwood floors, but considered by some to be difficult or unsuitable for finishing furniture or other detailed pieces. Relative to oil or shellac varnishes, polyurethane varnish forms a harder film which tends to de-laminate if subjected to heat or shock, fracturing the film and leaving white patches. This tendency increases when it is applied over softer woods like pine. This is also in part due to polyurethane's lesser penetration into the wood. Various priming techniques are employed to overcome this problem, including the use of certain oil varnishes, specified "dewaxed" shellac, clear penetrating epoxy, or "oil-modified" polyurethane designed for the purpose. Polyurethane varnish may also lack the "hand-rubbed" lustre of drying oils such as linseed or tung oil; in contrast, however, it is capable of a much faster and higher "build" of film, accomplishing in two coats what may require many applications of oil. Polyurethane may also be applied over a straight oil finish, but because of the relatively slow curing time of oils, the presence of volatile byproducts of curing, and the need for extended exposure of the oil to oxygen, care must be taken that the oils are sufficiently cured to accept the polyurethane.
Unlike drying oils and alkyds which cure, after evaporation of the solvent, upon reaction with oxygen from the air, polyurethane coatings cure after evaporation of the solvent by a variety of reactions of chemicals within the original mix, or by reaction with moisture from the air. Certain products are "hybrids" and combine different aspects of their parent components. "Oil-modified" polyurethanes, whether water-borne or solvent-borne, are currently the most widely used wood floor finishes.
Exterior use of polyurethane varnish may be problematic due to its susceptibility to deterioration through ultra-violet (UV) light exposure. All clear or translucent varnishes, and indeed all film-polymer coatings (i.e., paint, stain, epoxy, synthetic plastic, etc.) are susceptible to this damage in varying degrees. Pigments in paints and stains protect against UV damage, while UV-absorbers are added to polyurethane and other varnishes (in particular "spar" varnish) to work against UV damage. Polyurethanes are typically the most resistant to water exposure, high humidity, temperature extremes, and fungus or mildew, which also adversely affect varnish and paint performance.
Polyurethane is also used in making solid tires. Industrial applications include forklift drive and load wheels, grocery cart and, rollercoaster wheels. Modern roller blading and skateboarding became economical only with the introduction of tough, abrasion-resistant polyurethane parts, helping to usher in the permanent popularity of what had once been an obscure 1960s craze. The durability of polyurethane wheels allowed the range of tricks and stunts performed on skateboards to expand considerably. Polyurethane is also used to make small equipment tires in the lawn and garden industry for wheelbarrows, hand trucks, lawn mowers, carts, etc. They provide the bounce and feel of an air-filled tire with the benefit of no flats. They weigh about the same as air-filled tires as well, even though they are solid polyurethane all the way through. Other constructions have been developed for pneumatic tires, and microcellular foam variants are widely used in tires on wheelchairs, bicycles and other such uses. These latter foam types are also widely encountered in car steering wheels and other interior and exterior automotive parts, including bumpers and fenders.
Often electronic components are protected from environmental influence and mechanical shock by enclosing them in polyurethane. Typically polyurethanes are selected for the excellent abrasion resistances, good electrical properties, excellent adhesion, impact strength, and low-temperature flexibility. The disadvantage of polyurethanes is the limited upper service temperature (typically 250 °F (121 °C)). In production the electronic manufacture would purchase a two-part urethane (resin and catalyst) that would be mixed and poured onto the circuit assembly (see Resin dispensing). In most cases, the final circuit board assembly would be unrepairable after the urethane has cured. Because of its physical properties and low cost, polyurethane encapsulation (potting) is a popular option in the automotive manufacturing sector for automotive circuits and sensors.
Polyurethane can be used as an adhesive, especially as a woodworking glue. Its main advantage over more traditional wood glues is its water resistance. It was introduced to the general North American market in the 1990s as Gorilla Glue and Excel, but had been available in Europe much earlier.
On the way to a new and better glue for bookbinders, a new adhesive system was introduced for the first time in 1985. The base for this system is polyether or polyester, whereas polyurethane (PUR) is used as prepolymer. Its special features are coagulation at room temperature and resistance to moisture.
First generation (1988)
Second generation (1996)
Third generation (2000)
Fourth generation (present)
Advantages of polyurethane glue in the bookbinding industry:
Thermoset polyurethanes are also used as a protective coating against abrasion. Cast polyurethane over materials such as steel will absorb particle impact more efficiently. Polyurethanes have been proven to last in excess of 25 years in abrasive environments where non-coated steel would erode in less than 8 years. Polyurethanes are used in industries such as:
Polyurethane is also used in the concrete construction industry to create formliners. Polyurethane formliners serves as a mold for concrete, creating a variety of textures and art.