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Fast Facts and Frequently Asked Questions

Sahar Osman-Sypher

Diisocyanates Fast Facts

  • In 2018, United States demand for pure MDI was 381.4 million pounds and 2,349.7 million pounds for polymeric MDI. Demand for TDI was 538.5 million pounds.1
  • To meet this demand, production of diisocyanates in the United States employs thousands of workers in facilities across the nation. When you consider that polyurethane production relies on DII chemistry, the economic and job impact becomes even more significant as noted below.
  • The business of diisocyanates-based polyurethane is a $38.8 billion enterprise and a key element of the U.S. economy. The industry directly employs 57,500 Americans and operates in nearly 1,000 locations across the United States.2
  • Indirectly, the industry supports an additional $50.5 billion in output and supports more than 205,800 additional jobs in other sectors of the economy. In total, the industry supports about 260,000 jobs and $89.3 billion in output.2
  • Polyurethane products are used in industries across the economy generating more than $300 billion in output and employing more than 1 million workers.2
  • The U.S. Environmental Protection Agency's (EPA) Energy Star program estimates that by adding insulation and sealing air leaks, you could save up to 11 percent on your monthly energy bills.3 Advancements in polyurethane-based insulation technologies rely on DII chemistry.
  • The U.S. Department of Energy estimates that 48 percent of the energy used in a home goes to heating and cooling.4  Spray polyurethane foam insulation made with DII chemistry is an important solution in improving your home’s energy efficiency, along with other types of polyurethane foam designed for building and construction needs.
  • DII chemistry is critical in the development of countless polyurethane products that help keep us safe, such as bike helmets, impact-absorbing foam panels in vehicles, flotation devices and even hurricane resistant safety glass.
  • With a focus on developing innovative products and reducing the nation’s reliance on fossil fuels, diisocyanates can be reacted with natural oil polyols derived from vegetable oils to develop an array of polyurethane products containing renewable resource content.

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.

Worker Safety

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.

Consumer Safety

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.

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.

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.

Regulatory Review

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.

Considerations for Isocyanate Wipe Sampling

The wipe sampling methodology was developed as a qualitative tool for education and housekeeping improvement. Wipes are useful in detecting isocyanate contamination on surfaces and/or objects that workers might expect to be clean (e.g., doorknobs, handrails, tools, safety glasses, pencils) or for determining if surfaces are clean after decontamination activities. In this mode they can be used to indicate areas which need to be cleaned or, when this is impractical, where PPE is required. The presence of dirt, grime or other components, however, can affect the shade of the indicator color so that interpretation beyond a semi-quantitative determination of high, low, or not contaminated may be difficult.

The manufacturer can provide a color wheel which may be useful in evaluating isocyanate surface contamination (ideally from surfaces that are clean with respect to dirt and grime). However, difficulties can exist when interpreting the wipe sampling results due to the variability from the reader’s color perception and if the color is not consistent across the wipe pad. For example, if particles with reactive isocyanate groups are picked up by the pad, a non-homogeneous discoloration may result. For quantification, a defined area needs to be “wiped” and this is not always possible (e.g., doorknobs). Furthermore, such data is most beneficial if it can be interpreted in terms of potential for exposure (i.e., transferability from the contaminated surface to unprotected skin) and to aid in decision making with regard to increased risk reduction measures. Even then, care must be taken as it should be understood that it is not only the monomers that will give a color reaction, but also the oligomeric NCO-species or partly reacted NCO-species which could be partially bound to the surface and not readily transferable to the skin.

To conclude: Wipes are useful qualitative tools and not designed to provide reliable quantification of isocyanates on surfaces.

Potentially, but care needs to be exercised. For example, the wipe sampling methodology can provide a qualitative assessment of the presence of an unreacted isocyanate species but cannot determine if the contact will result in transfer to (unprotected) skin. Further, wipes should be used as recommended by the manufacturer. They are sold with mineral oil as a developing solution. Use of more aggressive or polar solvents may (1) enhance the extraction of free diisocyanate from within the polyurethane material in a manner that is not representative of skin contact, or (2) solubilize the reaction chemistry of the wipe allowing it to cause discoloration of the polyurethane product due to reaction with a bound, partially reacted diisocyanate. This surface discoloration would not indicate a transferable exposure to skin and could be misleading if the process is not understood.

To conclude: Wipes are useful qualitative tools, but care should be exercised in using this tool in accordance with the manufacturer’s recommendations.

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