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FAQs GLOSSARY


Chemistry of Diisocyanates


Worker Safety


Consumer Safety


Regulatory Review


Chemistry of Diisocyanates

Q: What are diisocyanates?
A: Diisocyanates are a family of 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 safer, tougher and more comfortable through the use of polyurethanes, which are made possible by diisocyanates. Diisocyanates are incredible chemical building blocks which countless products rely upon for comfort, insulation, weather-resistance, adhesion, durability, and flexibility.

Polyurethane chemistry is complex, but the basics are relatively easy to understand. Polyurethanes are produced from the reaction of diisocyanates (A-side) with polyols and other chemical additives tailored to specific manufacturing techniques (B-side). Because a variety of diisocyanates and a wide range of polyols can be used to produce polyurethane (and the reaction speed can be adjusted), a broad spectrum of materials can be produced to meet specific application needs. But, once A-side and B-side are mixed and reacted to form a polyurethane, they no longer exist in their original form and the diisocyanates are fully reacted away.

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Q: What is the difference between aromatic and aliphatic diisocyanates?

A: 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 elastomers, sealants, adhesives and coatings. 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 act as building blocks to form 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 carefully monitored for compliance with environmental, health and safety regulations. 

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Q: What is toluene diisocyanate (TDI) and why is it important?

A: TDI is a chemical used in the production of polyurethanes, primarily for flexible foam applications, including furniture, bedding and carpet underlay, as well as packaging applications. TDI is also used in the manufacture of coatings, sealants, adhesives and elastomers. In transportation applications, TDI helps produce lighter automobile parts, which saves weight and leads to improvements in fuel efficiency and energy conservation. 

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Q: What is methylenediphenyl diisocyanate (MDI) and why is it important?

A: MDI is a chemical used in the production of polyurethanes for many applications. MDI is used primarily in the production of rigid polyurethane foams used for insulation for your home or refrigerator, but has many other uses as well. Insulation made with MDI can help consumers save on their heating and cooling costs and 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.   

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Q: What is hexamethylene diisocyanate (HDI) and why is it important?

A: The most widely used aliphatic diisocyanate is HDI. HDI is an intermediate chemical used to produce HDI-based products (i.e., polyisocyanates). These HDI-based products are primarily used in the manufacture of industrial coatings where high performance capability, such as UV stability and weather resistance, is required. HDI-based products are used in the manufacture of a variety of products, including automobiles, aircraft, flooring, furniture, safety equipment, machinery, medical devices and infrastructure projects.  

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Q: What is methylene dicyclohexyl diisocyanate, or hydrogenated MDI (HMDI), and why is it important?

A: 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. 

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Q: What is isophorone diisocyanate (IPDI) and why is it important?

A: Isophorone diisocyanate (IPDI) is an intermediate chemical 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.

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Worker Safety

Q: Can diisocyanates be used safely? 

A: 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. A variety of federal, state and local regulations apply to manufacturers before the product even reaches the marketplace. Additionally, industry -- in conjunction with government agencies -- provides additional guidance and support on the safe use and handling of diisocyanates. One example of this is the voluntary Alliance between OSHA and industry designed to foster safer and more healthful American workplaces operating with diisocyanate chemicals along the polyurethane value chain. 

» Learn more

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Q: Are diisocyanates the leading cause of occupational asthma? 

A: Diisocyanates are among chemicals known to cause asthma in the workplace, however the incidence of diisocyanate-related asthma has been decreasing. Despite the fact that diisocyanates do not rank as the leading cause, nor in the top 10 leading causes, of occupational asthma, some articles continue to reference old data. 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. » Learn more 

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Q: Is it true that there is no airborne threshold limit to prevent sensitization to diisocyanates? 

A: 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 widely accepted by researchers and medical professionals that “peak” irritating inhalation exposures are necessary in order to induce sensitization to diisocyanates.  

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Q: Are diisocyanates carcinogens?

A: Scientific evidence shows that none of the diisocyanates would be carcinogenic under the relevant and primary routes of human exposure, which are via inhalation or dermal contact. In 1986, the International Agency for Research on Cancer (IARC) misclassified toluene diisocyanate (TDI) as “possibly carcinogenic to humans.” This listing is flawed and is unsubstantiated by credible scientific evidence. 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. 

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Consumer Safety

Q: Are there risks to consumers when using polyurethane products made from diisocyanates?

A: 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, and once they cure (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. 

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Q: How are consumers protected from potential exposures to diisocyanates?

A: 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. 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.

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Q: Are diisocyanates contributing to the increased rate of asthma in the general population?

A: Fully cured polyurethane products do not expose adults or children to diisocyanates in everyday life. An exposure potential must exist in order for diisocyanates, or any substance, to contribute to asthma rates in the general population. Concerns that adults and children are exposed to diisocyanates in everyday life from fully cured products or from environmental exposures have not been supported by reliable scientific evidence. EPA acknowledges that “cured” polyurethane products are considered “inert” with no exposure potential under intended use. 

In 2007, the North Carolina Department of Health and Human Services (NCDHHS) and the Agency for Toxic Substance and Disease Registry (ATSDR) conducted a joint study of environmental exposure to TDI and potential community health effects. The study results were released in May 2010 and did not find evidence of significant health-related exposure concerns associated with communities near plants using TDI. » Learn More

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Q: Are diisocyanates emitted from finished polyurethane products?

A: 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 that these and other types of fully cured 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 the original reactive ingredients - the diisocyanate and polyol or co-reactant - are no longer present in their original form in the cured polyurethane product. 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 curing (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.  

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Q: How does “curing” take place during formation of a polyurethane product?    

A: 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 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.  

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Regulatory Review

Q: How are diisocyanates regulated?

A: The United States chemical industry is committed to complying with all 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 both workers in production facilities and 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. 

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Q: How significantly have diisocyanates been researched? 

A: Diisocyanates chemistry has 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. 

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Q: Are diisocyanates being phased out due to regulation? 

A: To our knowledge, there are no existing regulations banning the use of diisocyanates. In June 2013, OSHA undertook a National Emphasis Program (NEP) targeting 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. 

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