Polyurethanes are formed by reacting a polyol (an alcohol with more than two reactive hydroxyl groups per molecule) with a diisocyanato or a polymeric isocyanate in the presence of suitable catalysts and additives. Because a variety of diisocyanatos and a wide range of polyols can be used to produce polyurethane, a broad spectrum of materials can be produced to meet the needs of specific applications.
The nature of the chemistry allows polyurethanes to be adapted to solve challenging problems, to be molded into unusual shapes and to enhance industrial and consumer products. Polyurethanes can be found in liquid coatings and paints, tough elastomers such as roller blade wheels, rigid insulation, soft flexible foam, elastic fiber or as an integral skin.
History of Polyurethanes
The origin of polyurethane dates back to the beginning of World War II, when it was first developed as a replacement for rubber. The versatility of this new organic polymer and its ability to substitute for scarce materials spurred numerous applications. During World War II, polyurethane coatings were used for the impregnation of paper and the manufacture of mustard gas resistant garments, high-gloss airplane finishes and chemical and corrosion-resistant coatings to protect metal, wood and masonry.
Formulations, additives and processing techniques continue to be developed, such as reinforced and structural moldings for exterior automotive parts and one-component systems. Today, polyurethanes can be found in virtually everything we touch—desks, chairs, cars, clothes, footwear, appliances, beds as well as the insulation in our walls and roof and moldings on our homes.
Flexible polyurethane foam is used as cushioning for a variety of consumer and commercial products, including bedding, furniture, automotive interiors, carpet underlay and packaging. Flexible foam can be created in almost any variety of shapes and firmness. It is light, durable, supportive and comfortable. Flexible polyurethane foam accounts for about 30 percent of the entire North American polyurethane market, and is used largely for bedding, furniture and in the automotive industry.
Rigid polyurethane and polyisocyanurate (polyiso) foams create one of the world’s most popular, energy-efficient and versatile insulations. These foams can significantly cut energy costs while making commercial and residential properties more efficient and comfortable. According to the U.S. Department of Energy, heating and cooling account for about 56 percent of the energy use in a typical U.S. home, making it the largest energy expense for most homes. To maintain uniform temperature and lower noise levels in homes and commercial properties, builders turn to rigid polyurethane and polyisocyanurate foam. These foams are effective insulation materials that can be used in roof and wall insulation, insulated windows, doors and air barrier sealants.
Polyurethane elastomers (PU) are part of the polyurethane group, and castable polyurethane elastomers are thus only a small part of the global polyurethane production and use. PU elastomers are formed by combining hard (isocyanate) and elastic (polyol) parts, and changing these selections creates the superior qualities of the polyurethane elastomers. Polyurethane elastomers are superiour in following features:
resistance to abrasion
resistance to chemicals (oil, gas)
Polyurethane elastomers can be used virtually everywhere. Snowplow blades are made with polyurethane to reduce road damage caused by metal scraping the roads. Wheels for shopping carts, skateboards, roller coasters, and heavy trash containers are all produced from polyurethane, due to its high load-bearing capacity and abrasion resistance. And since polyurethane elastomers can be so easily machined, they can be molded and processed for custom uses such as valves, snow blower augers, balls, and factory fixtures.
Many modern coatings, whether for vehicles and cables, floors and walls, or bridges and roads, contain polyurethanes, which safely and effectively shield exposed surfaces from the elements and various forms of pollution, so that they look better and last longer.
The durability, corrosion resistance and weather resistance of polyurethanes makes them suitable for coating all kinds of surfaces. Applications range from concrete constructions like bridges and motorway structures, to steel railway carriages and wooden furniture.
Polyurethanes are so versatile that they are also available in the form of glues that can safely bind together quite different materials, such as wood, rubber, cardboard or glass. Construction projects, in particular, take advantage of polyurethane glues. Packaging manufacturers and producers of exterior furniture, both of whom require resilience and strength in their products, also frequently rely on polyurethane adhesives. Polyurethane’s adhesive properties are also exploited in the manufacture of high-performance composite wood products. Composite wood products made from sustainable forestry resources are a real alternative to panel products produced from large mature trees that have taken years to grow.
Polyurethane sealants provide excellent stress recovery to retain shape after being bent or pulled, fast curing rates and even adherence to non-primed concrete. Polyurethane adhesives and sealants can also be painted to match the surrounding surfaces, while some bonding agents cannot be painted.
Polyurethane and Hybrid Adhesives & Sealants are advanced, one-part formulations that require no mixing or special application tools. 3M’s POWER Line products cure with atmospheric moisture to form durable, resilient, long-lasting bonds ideal for:
• Truck, trailer, bus and another vehicle panel mounting
• Marine OEM deck-to-hull joining, through-hull fastening, deck fitting and more
• Roof flashings, through-wall pipe and cable sealing andother construction applications
• Concrete sealing and expansion joint filling
• Marine and specialty vehicle window bonding and glazing
• Many other applications in a wide range of industries
When scientists discovered that polyurethanes could be made into fine threads, they were combined with nylon to make more lightweight, stretchable garments. Over the years, polyurethanes have been improved and developed into spandex fibers, polyurethane coatings and thermoplastic elastomers.
Because of today’s advances in polyurethane techniques, manufacturers can make a broad range of polyurethane apparel from man-made skins and leathers used for garments, sports clothes and a variety of accessories.
Polyurethanes are an important component in major appliances that consumers use every day. The most common use for polyurethanes in major appliances is rigid foams for refrigerator and freezer thermal insulation systems. Rigid polyurethane foam is an essential and cost-effective material that can be used for meeting required energy ratings in consumer refrigerators and freezers. The good thermal insulating properties of rigid polyurethane foams result from the combination of a fine, closed-cell foam structure and cell gases that resist heat transfer.
Polyurethanes are used throughout cars. In addition to the foam that makes car seats comfortable, bumpers, interior “headline” ceiling sections, the car body, spoilers, doors and windows all use polyurethanes. Polyurethane also enables manufacturers to provide drivers and passengers significantly more automobile “mileage” by reducing weight and increasing fuel economy, comfort, corrosion resistance, insulation and sound absorption.
Today’s homes demand high-performance materials that are strong, yet lightweight; perform well, yet are easily installed; and are durable, but also versatile. Polyurethane helps conserve natural resources and helps preserve the environment by reducing energy usage. With its excellent strength-to-weight ratio, insulation properties, durability and versatility, polyurethane is frequently used in building and construction applications. Both the affordability of these versatile materials and the comfort they provide homeowners have made polyurethane components part of homes everywhere.
Polyurethane is used all over the house. In floors, flexible foam padding cushions your carpet. In the roof, reflective plastic coverings over polyurethane foam can bounce sunlight and heat away, helping the house stay cool while helping reduce energy consumption. Polyurethane building materials add design flexibility to new homes and remodeling projects. Foam-core panels offer a wide variety of colors and profiles for walls and roofs, while foam-cored entry doors and garage doors are available in different finishes and styles.
Polyurethanes play a major role in modern materials, such as composite wood. Polyurethane-based binders are used in composite wood products to permanently glue organic materials into oriented strand board, medium-density fiberboard, long-strand lumber, laminated-veneer lumber and even strawboard and particleboard.
Often referred to as “potting compounds,” non-foam polyurethanes are frequently used in the electrical and electronics industries to encapsulate, seal and insulate fragile, pressure-sensitive, microelectronic components, underwater cables and printed circuit boards.
Polyurethane potting compounds are specially formulated by developers to meet a diverse range of physical, thermal and electrical properties. They can protect electronics by providing excellent dielectric and adhesive properties, as well as exceptional solvent, water and extreme temperature resistance.
Either as a foam underlay or on top as a coating, polyurethanes can make the floors we walk on every day more durable, easier to maintain and more aesthetically pleasing. Using flexible polyurethane foam as a carpet underlay in residential or commercial applications can significantly increase the lifespan of the carpet, protect its appearance, provide added comfort and support and can reduce ambient noise.
Polyurethanes are also used to coat floors, from wood and parquet to cement. This protective finish is resistant to abrasion and solvents, and is easy to clean and maintain. With a polyurethane finish, a new wood, parquet or cement floor wears better and longer, while an old floor can be refinished to look new again.
Polyurethane, mostly in the form of flexible foam, is one of the most popular materials used in home furnishings such as furniture, bedding and carpet underlay. As a cushioning material for upholstered furniture, flexible polyurethane foam works to make furniture more durable, comfortable and supportive.
Millions of Americans enjoy boating each year. Part of boating’s ongoing popularity is thanks to improvements in boating technology, to which polyurethane materials make an important contribution.
Polyurethane epoxy resins seal boat hulls from water, weather, corrosion and elements that increase drag, affect hydrodynamics and reduce durability. Boaters today can have the comforts of home on the water, thanks in part to flexible polyurethane foam. In addition, rigid polyurethane foam insulates boats from noise and temperature extremes, provides abrasion and tear resistance, and increases load-bearing capacity all while adding minimal weight. Thermoplastic polyurethane is also great for use in the maritime industry. It is elastic, durable and an easily processed substance, well suited for wire and cable coatings, engine tubing, drive belts, hydraulic hoses and seals and even ship molding.
Polyurethanes are commonly used in a number of medical applications, including catheter and general purpose tubing, hospital bedding, surgical drapes, wound dressings and a variety of injection-molded devices. Their most common use is in short-term implants. Polyurethane use in medical applications can be more cost-effective and provide for more longevity and toughness.
Polyurethane packaging foam (PPF) can provide more cost-effective, form-fitting cushioning that uniquely and securely protecting items that need to stay safely in place during transit. PPF is widely used to safely protect and transport many items, such as electronic and medical diagnostic equipment, delicate glassware and large industrial parts. A versatile on-site solution for many packaging challenges, PPF can save time and be more cost-effective by providing a custom-fit container with each shipment.