If you have driven to work, gone for a jog, gotten a good night’s rest or opened your refrigerator lately, chances are that you have encountered a special type of plastic—polyurethane. Polyurethanes are a polymer composed of a chain of organic units, joined by urethane links.
Although not yet a “household name,” polyurethanes are prevalent in everyday life. Polyurethanes pad your car’s steering wheel and seats, form the soles of your shoes, cushion your mattress and help keep your fridge cold, among many other uses.
A highly versatile material, polyurethane can be flexible (foams for furniture or mattresses) or rigid (spray polyurethane foam and polyiso board insulation for buildings). Polyurethanes’ superior insulating properties and ability to be molded into any shape also make them ideal for many commercial and residential applications.
Buildings account for almost 40 percent of the total energy consumed in the U.S. In commercial buildings, heating, cooling and ventilation consume 34 percent of the energy used onsite. The building envelope provides a boundary between the interior of the building and the outdoor climate, and is designed to perform as an effective thermal barrier, maintaining a comfortable indoor environment. Polyurethane insulation products continue to grow in popularity as they provide some of the highest thermal resistance values, contributing to high energy efficient building envelopes.
Foam plastic insulation products like polyurethane insulation are projected to enjoy significant growth. The Freedonia Group reports that, “demand for foamed plastic insulation, which accounted for the second-largest share of the market in 2011, is expected to rise 7.3 percent per year to $3.9 billion in 2016.” According to Principia Consulting, “the shift to more stringent codes will drive the trend to higher R-values overall. Foams, which have a higher share in high R-value applications, will be the major beneficiaries of this trend.”
POLYURETHANES IN COMMERICAL BUILDINGS
Polyurethanes have a long history of use in construction. They are formed from the reaction between isocyanate and hydroxyl groups, a reaction that was discovered in the 19th century and further developed during World War II as scientists searched for a replacement for rubber. The first commercial application of the polyurethane polymer was developed between 1945 and 1947 in coatings and adhesives.
Flexible foams were commercialized in 1953, followed with rigid foams like polyurethane insulation for buildings in 1957. Spray polyurethane foam roofing systems have been applied since the 1960s. Hospitals, schools, offices buildings, cold storage facilities and retail stores are just a few of the commercial structures that use polyurethanes for insulating and roofing.
Today, spray polyurethane foam is one of the world’s most popular, energy-efficient and versatile type of insulation. However, there are many other forms of polyurethane insulation—including polyisocyanurate foam, one-component foam, insulated metal panels and structural insulated panels—that can also offer significant design versatility while making commercial and residential properties more efficient and comfortable.
TYPES OF POLYURETHANE INSULATION PRODUCTS
Polyisocyanurate foam: Polyiso chemistry is a modified form of the polyurethane reaction, with higher levels of isocyanate used to generate the polyisocyanurate molecule, which imparts greater fire resistance to the polymer. Polyiso insulation typically comes in a rigid board form.
Spray polyurethane foam is produced when a mixture of fast-reacting, foam-forming ingredients are combined at the moment of application. SPF can be applied to almost any substrate that is clean, dry, and free of dust. SPF performs as both an insulation material and an air sealant to help create a tight building envelope. In 2012, SPF insulation was a $1 billion market at the manufacturer level, and over $2 billion in installed value.
One-component polyurethane foam, applied mainly from pressurized containers, is used to seal doors and windows in construction as well as to fill gaps, for example around pipes or in walls and floors.
Sandwich/insulated metal panels consist of a foam core and two metal faces. As composites, these have excellent load-bearing properties, making them especially suitable for self-supporting roofs and walls, and other applications with structural requirements.
Structural insulated panels are engineered panels made of a thick layer of polyurethane or polyiso foam sandwiched between two layers of oriented strand board, plywood or fiber-cement. SIPs are used throughout a building: the framing, flooring, ceilings and roofs and as a single-piece exterior sheathing.
BENEFITS OF POLYURETHANE INSULATION
The rise of polyurethane insulation can be attributed to its promise of significantly reduced energy consumption. According to the U.S. Department of Energy, as much as 40 percent of a building’s energy is lost due to air infiltration. One of the best and most practical solutions to reduce greenhouse gas emissions is improving a building’s insulation, thus reducing the heating and cooling loads and reducing the energy consumption.
Polyiso board is a roofing insulation of choice for many new, low-slope commercial construction projects. It has high thermal resistance, cost-effectiveness, superior fire performance, and compatibility with various membrane adhesives. Polyiso sheathing board is available for use as wall insulation in residential and commercial buildings.
With its very high R-value (around 6 per inch), builders turn to SPF to both insulate and air seal, as well as lower noise levels. By creating an air barrier, SPF can also minimize the pollutants, pollen and moisture that often infiltrate buildings. It also adds structural strength; studies have shown that SPF can actually help a building withstand high winds and hurricanes.
One-component polyurethane foam also works as an air barrier. One-component foam is ideal for weatherization— the process of modifying a building to reduce energy consumption—because it contains two key elements in one product: insulation and air sealing. A study by the American Society of Heating, Refrigerating and Air Conditioning Engineers found that sealing of existing homes with one-component spray polyurethane foam (foam-in-a-can) pays for itself in an average of 4 months and provides a 7-year return on investment of 4,400 percent.
In addition to their structural properties, IMPs give architects and engineers extensive choice in project design. They can be produced in various dimensions (length, width and thicknesses), and feature different joints, metal surface profiles, embossments, colors and high thermal insulation values. The growth of sandwich/insulated metal panels has also been supported by their simple, fast and cost-effective installation process.
As their name implies, structural insulated panels provide both structural support and superior insulating properties. They form a dense, continuous air barrier and offer efficient thermal performance that can reduce energy usage. SIPs are also able to withstand high winds and seismic forces. SIPs are lightweight and smaller panels can be installed by one person.
HEALTH AND SAFETY BEST PRACTICES
Some types of polyurethanes, like SPF, are reacted on-site and have health and safety requirements set forth by the Occupational Safety and Health Administration. Before applying SPF, consult the manufacturer for more information on health and safety issues. Select a professional SPF applicator, who is trained, and work with subtrades to address what constitutes a safe work environment. The SPF applicator can also provide information about recommended times before reentering the area and ventilation.
Another factor to keep in mind is that a building insulated with spray foam can be very tight due to the absence of fresh air infiltrating through cracks and gaps. A building insulated with SPF is inherently very thermally efficient with a tight envelope. This means that temperature loads will be greatly reduced, but latent (humidity) loads will likely remain where they have been. Adequate fresh air ventilation and design for good humidity removal to address these changes are important. Using mechanical fresh air exchange can often address issues associated with improper ventilation.
Most rigid polyurethane foam insulation products are formulated with fire retardant additives to reduce the rate of fire growth, and allow time for occupants to leave a building in the event of a fire. In most cases, the fire retardants selected have undergone rigorous risk assessments. Consult with your supplier for specific questions on the fire retardants in the products you select.
There are many resources available for contractors, building owners and architects who would like to learn more. For architects or contractors wishing to specify polyurethane products, visit the websites www.whysprayfoam.org, www.spraypolyurethane.org, www.pima.org, and www.metalconstruction.org/imp to find excellent information about using polyurethane products safely and effectively. W&C
Monica Karamagi chairs the Outreach Committee of the Center for the Polyurethanes Industry of the American Chemistry Council. CPI serves as the voice of the polyurethanes industry in North America, promoting its development and coordinating with polyurethane trade associations across the globe. Karamagi is also the regional marketing and industry affairs manager for the Polyurethanes Division of Huntsman Corporation.
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