How does the new polyurethane REACH regulation affect manufacturers?

New regulations coming on August 24, 2023, requiring construction training for materials containing diisocyanates, have raised concerns about polyurethane adhesives. These materials are widely used in industrial facilities to bond metals, plastics and even glass due to their reasonable cost, good adhesion, high peel strength and good impact resistance.

Polyurethanes can be used to make rigid and flexible foams, as well as varnishes and coatings, adhesives, potting compounds and fibers. The most common use of polyurethane is foam, which accounts for about two-thirds of the total amount of polyurethane used.

About 6% of the world's polyurethane is used in adhesives and another 3% in sealants. Polyurethane adhesives are available in one-component (1K) and two-component (2K) formulations, and the basic chemical reaction is the same for both types. They are usually thermosets, but there is another type of polyurethane thermoplastic hot melt adhesive, which is usually polyester-based.

Advantages of polyurethane adhesives

Polyurethane adhesives have excellent adhesion to a wide range of materials – they bond plastics, metals and synthetics well. Polyurethane adhesives have lower surface energy than epoxy adhesives and therefore have better wetting and adhesion to plastic substrates. There are many types of polyurethane adhesives – they can be formulated with different cure lifetimes, while viscosity grades can range from self-leveling to non-slumping and curing grades from very soft to very hard.

Polyurethane adhesives have good performance characteristics: extremely toughness, high peel strength, suitable for gap filling. Because they are impact, solvent, weather and abrasion resistant, they are popular in outdoor applications. Importantly, they are relatively low-cost materials that are easy to apply and cure (typically, these adhesives cure at room temperature, but heating speeds up the curing process). To achieve the best results, manufacturers need to mix well in the right proportions.
Polyurethane chemistry

Polyurethanes are formed by reacting isocyanates (a highly reactive, low molecular weight chemical) and polyols (organic compounds containing multiple hydroxyl groups). Other ingredients include pigments for coloring, fillers for mechanical reinforcement and reduction of total costs, plasticizers for increased flexibility, flame retardants and smoke suppressants to reduce flammability and smoke production during combustion, and UV absorbers and antioxidants to reduce degradation.

Both polyols and isocyanates are hygroscopic and react with moisture, and industrial users must understand this. If isocyanates react with water, they form unstable carbamic acid, which breaks down to form urea and carbon dioxide gas. Therefore, the entrained moist air when mixing can lead to blistering or the formation of bubbles, which may affect aesthetics. If foaming is desired, choosing the appropriate catalyst can inhibit or facilitate the reaction.

Isocyanates and safety

The most widely used isocyanate in polyurethane adhesives is diisocyanate, which has two isocyanate groups. There are two main types of diisocyanates used in polyurethane adhesives: toluene diisocyanate (TDI) and methylenediphenyl diisocyanate (MDI). In polyurethane adhesives, they are used up during the reaction, which means that diisocyanates are virtually absent in finished or cured materials.

Their chemical reactivity means that exposure to isocyanates when handling polyurethane adhesives prior to curing poses several health risks, including irritation of skin and mucous membranes, chest tightness and difficulty breathing. The main potential effects of harmful exposure are occupational asthma and other lung problems, as well as irritation of the eyes, nose, throat and skin. In addition, isocyanates include compounds classified as potential human carcinogens and are now known to cause cancer in animals.

New restrictions

Following a review by the European Parliament, the REACH restrictions on aliphatic and aromatic diisocyanates (which continue to apply in the UK) were published on 4 August 2020 and came into force on 24 August 2020. These restrictions mean that, from August 24, 2023, training is mandatory for all professional and industrial users working with products with a total monomeric diisocyanate concentration greater than 0.1%.

Like any chemical, diisocyanates are safe if disposed of in accordance with relevant risk management and health safety measures. The purpose of these restrictions is to ensure that this is done so that adverse effects from exposure to diisocyanates in the workplace and throughout the supply chain are minimized.
The restriction requires adhesive and sealant manufacturers to provide end-users with training information on the safe use of diisocyanates and, from February 24, 2022, ensure that all polyurethane products requiring safety training are marked with the following statement: As of August 24, 2023, appropriate training must be carried out before using the product in the industrial or professional field.

Under the new requirements, employers are responsible for providing appropriate training to all employees exposed to diisocyanate-containing substances. The format of the training is not prescribed, and many training courses are available online free of charge or at low cost. The European Adhesives and Sealants Industry Association (FEICA) provides financial support for the training of its members and their customers in the form of coupon codes that make training materials related to Polyurethane Adhesive and sealant applications freely available.

In addition to providing training, employers must collect evidence of successful completion of the training program, such as certificate logs. The training certificate is valid for five years and needs to be renewed after five years.

Alternative ways

Another option for industrial users is to specify the use of polyurethane adhesives with a total concentration of less than 0.1% diisocyanate monomer. Currently, there are new advanced polyurethane adhesive materials based on micro-emission technology that do not require training if specified, helping businesses avoid the cost, management and time burden associated with new mandatory training while ensuring high standards of health and safety (H&S).

Importantly, these new materials retain all the advantages of polyurethane, namely good adhesion, fast curing and good environmental resistance. Micro-emitting products may even bring additional economic benefits due to health and safety – because their emissions are very low and there may be fewer warning icons on the label.

With August 24 just around the corner, industrial users of polyurethanes will need to decide whether to train their teams or adopt new micro-emission technologies. Either approach keeps manufacturers productive while prioritizing employee safety.