Fast Facts and Frequently Asked Questions
Countless polyurethane products made possible with aliphatic diisocyanates (ADI) chemistry are important to America’s economy, particularly for paint and coatings used in the construction and transportation sectors. ADI chemistry can help save consumers and businesses money through improved durability in a wide range of products that use polyurethane-based coatings and sealants, such as automobiles and homes.
- ADIs are typically used in many types of coatings, adhesives, sealants and elastomer (CASE) applications.
- Production of ADIs and their end-use products employ thousands of workers in facilities across the nation. For example, the U.S. paint and coatings industry employed 315,700 workers in 2019, adding some 4,000 jobs from the previous year.1 Considering that many paint and coating products rely on ADI chemistry, their economic impact is significant.
- The United States exported $2.2 billion in paint and coatings products in 2020.1
- Automotive clearcoats are usually acrylic urethane-based formulations that use ADIs to offer a wide range of performance benefits such as aesthetics, gloss, weather, UV and impact resistance, and durability.
- The majority of automotive refinish coatings are two-component systems, based upon ADIs and acrylic polyols. Using these raw materials provides certain qualities in the end-product, including high shine, high UV resistance and durability, and also relatively fast cure speeds. Traditionally, auto refinishing has been a major market segment for two-component polyurethane solvent-borne coatings based on ADIs and acrylic polyols.
- ADIs are also used in construction sealants. For exterior applications, they help provide durability, weather resistance and stability. They are also used in high performance polyurethane elastomers.
- Small volumes are used in specialty applications including leather finishing formulations, textile and fiber treatments, inks, thermoplastic polyurethane (TPU) sheets used in glazing applications. For these and other specialty applications, ADIs provide UV protection and durability.
- ADIs are considered specialty materials. They are used in smaller quantities than their aromatic counterparts and are estimated to represent less than 5% of overall isocyanate consumption in the North American polyurethane industry.2
These are just a few of the many ways that aliphatic diisocyanates are making a positive contribution to the U.S. economy. ADIs are important chemical building blocks in the production of products we count on every day and improve our quality life. For more information, visit the Consumer Safety and Aliphatic Diisocyanates page.
Chemistry of Diisocyanates
Diisocyanates are a family of versatile chemical building blocks used to make polyurethane products, such as rigid and flexible foams, coatings, adhesives, sealants and elastomers. Many of the products that we rely upon every day for improved quality of life are enhanced by diisocyanates. Diisocyanates are incredible chemical building blocks which countless products rely upon for comfort, insulation, weather-resistance, adhesion, durability, and flexibility.
There are two primary aromatic diisocyanates: toluene diisocyanate (TDI) and methylenediphenyl diisocyanate (MDI). Together, they comprise over 90% of the overall diisocyanate consumption in the North American polyurethane industry, with aliphatic diisocyanates accounting for the balance. TDI is used primarily in the production of flexible foams. MDI, the second type of aromatic diisocyanate, comes in two forms: Pure MDI and polymeric MDI (PMDI). Pure MDI is used in the production of a variety of polyurethane products like coatings, adhesives, sealants and elastomers (CASE). PMDI is a highly versatile product used to produce a wide variety of rigid, flexible, semi-rigid, and polyisocyanurate and thermoset foams.
While aromatic diisocyanates are primarily used to make polyurethane foam products, aliphatic diisocyanates are specialty intermediate chemicals often reacted to form polyisocyanates, which are used to make color-stable and durable polyurethane coatings, adhesives, sealants and elastomers. The most common types of aliphatic diisocyanates include hexamethylene diisocyanate (HDI), methylene dicyclohexyl diisocyanate or hydrogenated MDI (HMDI), and isophorone diisocyanate (IPDI). Aliphatic diisocyanates are sold primarily to industrial customers who use them as binders or hardeners during manufacturing processes. Both aromatic and aliphatic diisocyanates are manufactured in closed-loop systems that are monitored for compliance with environmental, health and safety regulations.
TDI is used in the production of polyurethanes, primarily for flexible foam applications, including bedding and furniture, carpet underlay, as well as packaging applications. TDI is also used to manufacture coatings, adhesives, sealants, and elastomers. In transportation applications, TDI is used to help make automobile parts lighter, leading to improvements in vehicle fuel efficiency and thus energy conservation.
MDI is used in the production of polyurethanes for many applications. MDI is primarily used to make rigid polyurethane foams such as insulation for your home or refrigerator. Insulation made with MDI can help conserve energy. Some additional uses of MDI in polyurethanes include coatings, adhesives, sealants, and elastomers found in items such as paints, glues, and weather resistant materials. These polyurethane products are then used to make many types of footwear, sports and leisure items, truck bedlining products and, to a much lesser extent, some specialty flexible foams. MDI can also be used as a binder for wood and to produce mold cores for the foundry industry.
The most widely used aliphatic diisocyanate is HDI. HDI-based products, like polyisocyanates, are primarily used to manufacture industrial coatings where high performance capability, such as UV stability and weather resistance, is required. HDI-based products are used to manufacture a variety of products, including automobiles, aircraft, flooring, furniture, safety equipment, machinery, medical devices and infrastructure projects.
HMDI serves as a building block for the preparation of chemical products, reactive intermediates and polymers such as polyurethane dispersions (PUDs), elastomers, and thermoplastic polyurethanes (TPUs). Products based on HMDI may be useful in coatings for flooring, roofing, and textiles, as well as elastomers, optical products, adhesives, and sealants.
Isophorone diisocyanate (IPDI) is used to produce IPDI-based products (i.e., polyisocyanates, polyurethane dispersions) that are primarily used in polyurethane coatings. These IPDI-based products are used by industrial customers to manufacture various coatings for automobiles, flooring, roofing, machinery, and textile applications. They are also used in cast elastomers, adhesives, sealants, and as crosslinkers for powder coatings.
Diisocyanates can and have been used safely for many years in a wide variety of applications. Safety data sheets (SDSs) help users understand the potential hazards of diisocyanates and the recommended protective measures to be taken when handling. These safe use and handling measures can include workplace practices, use of personal protective equipment and engineering controls, as well as worker training and medical surveillance.
Manufacturers are committed to the safe use and handling of diisocyanates. Industry — in conjunction with government agencies — provides guidance and support on the safe use and handling of diisocyanates. One example is the voluntary Alliance between OSHA and industry, which is designed to foster safer and more healthful American workplaces operating with diisocyanate chemicals along the polyurethane value chain. Additionally, there are a variety of federal, state and local regulations that apply to manufacturers during the manufacturing process.
Diisocyanates are among the chemicals known to cause asthma in the workplace, however the incidence of diisocyanate-related asthma has been decreasing. Recent data show a consistent picture of a decline in asthma rates associated with diisocyanates over the last decade even as production rates of diisocyanates have increased. The reduction in diisocyanate-related occupational asthma is primarily due to a variety of industry product stewardship activities, including education and training, enhanced worker awareness, improved work practices, use of less volatile diisocyanate forms (e.g. pre-polymers), improved engineering controls (e.g., containment and/or ventilation), better medical surveillance programs, minimization of peak exposures, and continuing emphasis on compliance with existing exposure standards. These product stewardship efforts are key to further reductions in cases.
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Each person may respond differently, or not at all, to a stimulus, including an allergen. However, it has been demonstrated through epidemiology studies of workers in diisocyanate industries and animal studies that a susceptible person/animal must encounter an irritating dose of a diisocyanate through inhalation before respiratory sensitization occurs. Although a numerical threshold has not been agreed upon, it is accepted by a wide variety of researchers and medical professionals that “peak” irritating inhalation exposures are necessary in order to induce sensitization to diisocyanates.
Scientific evidence shows that diisocyanates are not carcinogenic under the relevant and primary routes of human exposure, which are via inhalation or dermal contact. Nonetheless, despite more recent and reliable data indicating otherwise, in 1986, the International Agency for Research on Cancer (IARC) classified toluene diisocyanate (TDI) as “possibly carcinogenic to humans.” The IARC carcinogenicity classification for TDI is based solely on one conceptually and technically flawed study performed over 30 years ago by the National Toxicology Program (NTP). The IARC carcinogenicity classification for TDI is based on an unrealistic exposure scenario and is not reflective of current scientific consensus.
Fully cured polyurethane products do not contain diisocyanates. In other words, the diisocyanates that once existed before completion of the curing process are no longer present and therefore cannot be transferred to a consumer via the air or by direct contact with the product. EPA specifies that “[c]ompletely cured products are fully reacted and therefore are considered to be inert and non-toxic.” The vast majority of diisocyanates are manufactured for industrial and commercial use. Potential exposures to uncured diisocyanates in some adhesives and sealants products that are available to consumers are expected to be very low or negligible under anticipated conditions of use, and once they are fully cured (by reaction with moisture), those diisocyanates are no longer present.
Consumer products containing uncured diisocyanates generally are accompanied by product safety information like warning labels, which can include the characteristics of the chemicals, their approximate cure time, and how to properly protect oneself while handling the product. Manufacturers of products with uncured diisocyanates emphasize to users the importance of carefully reading the labels for information about potential health effects, chemical properties and how to control exposure.
The vast majority of diisocyanates manufactured are for industrial and commercial use. Overall, consumer exposures to unreacted diisocyanates are expected to be of very low magnitude and frequency under anticipated conditions of use. EPA notes that “polyurethane products, such as mattresses, pillows, and bowling balls, are considered completely cured products before they are sold.” EPA also states that “[c]ompletely cured products are fully reacted and therefore are considered to be inert and non-toxic.” Oftentimes, the diisocyanates used in consumer products are lower vapor pressure varieties, such as polyisocyanates and prepolymers. Consumer products containing uncured diisocyanates (e.g. certain coatings, adhesives and glues) generally are accompanied by product safety information like warning labels, including the characteristics of the chemicals, their approximate cure time, and how to properly protect yourself while handling the product. The chemical industry makes the safety and responsible use of its products a priority. A robust system of laws and industry initiatives oversees the development and use of chemical products, enhances scientific understanding and makes safety information available to the public.
Diisocyanates are used in the manufacture of many polyurethane products that we rely on every day (e.g., foam in mattresses, foam in furniture cushions, shiny finish on our cars, etc.) It is important to recognize however that once the curing process is fully completed, the polyurethane products do not contain diisocyanates. Therefore, diisocyanates do not emit from fully cured polyurethane products, and those polyurethane products do not cause consumer exposure to diisocyanates.
These conclusions are supported by EPA which specifies that “[c]ompletely cured products are fully reacted and therefore are considered to be inert and non-toxic.” This means that even though we use diisocyanates to make a lot of different products, they’re not detectable or present by the time these products are fully cured. They were transformed during the chemical reaction into the finished polyurethane product. (Note: There are some adhesives and sealants products on the market that initially contain uncured diisocyanates; however following completion of the curing process (via reaction with surface moisture or moisture in the air) those diisocyanates are no longer present). Check out the following whiteboard video that further explains the reactivity of diisocyanates chemistry, the incredible chemical building block.
Curing refers to the reaction that occurs between the two primary chemicals used to form a polyurethane product. These primary chemicals are commonly referred to as the “A-side” (diisocyanate) and “B-side” (polyol or other co-reactant). The A-side material is highly reactive and curing typically begins shortly after mixing with the B-side material. The cure time varies depending on the type of polyurethane product being produced, the ingredient formulations and other factors in the manufacturing process. Polyurethane products such as mattresses, pillows, furniture cushions, car seating, refrigerator insulation, footwear, ski bindings and inline skates are believed completely cured and therefore considered “inert” before they are sold. This means that the original reactive ingredients, diisocyanates and polyols, are no longer present in their original form in the fully cured polyurethane product. As a result of the reaction, they were transformed during production into the finished polyurethane product.
The United States chemical industry is committed to complying with applicable federal, state and local regulations, and evaluates products before they reach the marketplace for health, safety and environmental compliance. Diisocyanates have been used since the late 1940s, and their safety and environmental impact have been well studied. Diisocyanates are regulated under the authority of the Environmental Protection Agency (EPA), the Occupational Safety and Health Administration (OSHA) and other government agencies. Federal and state authorities have set exposure safety limits for diisocyanate emissions to protect workers in production facilities and individuals in surrounding communities. The environmental, health and safety benchmarks are based on science and reviewed by government officials with the goal of protecting workers and communities. Companies can face significant civil and criminal penalties for noncompliance.
Diisocyanates have been used for decades (since the 1940s) and studied extensively. A robust database of scientific information exists and is available to the value chain, regulatory bodies, and general public. The industry provides extensive health and safety information at no cost, for workers and facilities using these chemistries. The resources include technical information on hazard communication, ventilation, industrial hygiene, safe handling guidance, environmental emissions reporting and testing, first aid, emergency response and disposal.
To our knowledge, there are no existing regulations banning the use of diisocyanates. In June 2013, OSHA undertook a National Emphasis Program (NEP) to evaluate facilities handling diisocyanates in which over 800 inspections occurred. The NEP was subsequently cancelled due to little evidence supporting the notion of widespread over-exposure. Moreover, in 2017, OSHA entered into a positive educational Alliance with industry in order to develop and disseminate best work practice information. Diisocyanate technology is a chemistry where innovation is vigorous and manufacturing continues to thrive. Diisocyanates are incredible chemical building blocks that enable countless products we rely on every day for comfort, insulation, weather-resistance, adhesion, durability, flexibility and improved quality of life.