What is the impact of the new polyurethane REACH regulation on manufacturers?

New regulations that will be introduced on August 24 this year require construction training for materials containing diisocyanates, which has drawn attention to polyurethane adhesives. These materials are widely used to bond metals, plastics and even glass in industrial facilities due to their reasonable cost, good adhesion, high peel strength and good impact resistance.

Polyurethane can be used to make hard and soft 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 single-component (1K) and two-component (2K) formulations, and the basic chemical reaction is the same for both types. They are usually thermoset materials, 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 variety of materials - they bond well to plastics, metals and synthetic materials. The surface energy of polyurethane adhesives is lower than that of epoxy adhesives, so they have better wettability and adhesion on plastic substrates. There are a wide variety of polyurethane adhesives - they can be formulated for different curing lives, and viscosity grades can range from self-leveling to non-slump paste, and curing grades can range from very soft to very hard.

Polyurethane adhesive has good performance characteristics: strong toughness, high peel strength, suitable for gap filling. Because they are resistant to impact, solvents, weather and wear, 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 accelerates the curing process). For best results, manufacturers need to mix adequately in the right proportions.

Chemical composition of polyurethane

Polyurethanes are formed by the reaction of 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 total cost reduction, plasticizers for increased flexibility, flame retardants and smoke suppressors for reducing flammability and smoke produced during combustion, and UV absorbers and antioxidants for reducing degradation.

Both polyols and isocyanates are hygroscopic and react with moisture, and industrial users must be aware of this. If the isocyanate reacts with water, it forms an unstable carbamic acid, which breaks down to form urea and carbon dioxide gas. As a result, the moist air enfolded during mixing can lead to the formation of bubbles or bubbles, which may affect aesthetics. If foaming is desired, selecting the appropriate catalyst can inhibit or promote the reaction.

Isocyanates and safety

The most widely used isocyanate in polyurethane adhesives is the diisocyanate, which has two isocyanate groups. There are two main types of diisocyanates used in polyurethane adhesives: toluene diisocyanate (TDI) and methylene diphenyl diisocyanate (MDI). In polyurethane adhesives, they are used up during the reaction, which means that there is almost no diisocyanate present in the finished or cured material.

Their chemical reactivity means that exposure to isocyanates when handling polyurethane adhesives before curing poses a number of health risks, including skin and mucous membranes irritation, chest tightness, and breathing difficulties. The main potential effects of harmful exposure are occupational asthma and other lung problems, as well as eye, nasal, throat and skin irritation. In addition, isocyanates include compounds classified as potentially carcinogenic to humans and are now known to cause cancer in animals.

New restriction

Following a review by the European Parliament, the REACH limits 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, all professional and industrial users of products with a total concentration of monomer diisocyanate greater than 0.1% will have to be trained.

As with any chemical, diisocyanates are safe if handled in accordance with relevant risk management and health and safety measures. The aim 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 minimised.

The restriction requires adhesives and sealants manufacturers to provide end users with training information on the safe use of diisocyanates and, as of February 24, 2022, ensure that all polyurethane products that require safety training are marked with the following statement: As of August 24, 2023, appropriate training must be conducted prior to the use of the product in industrial or professional fields.

Under the new requirements, employers are responsible for providing appropriate training to all employees who come into contact with substances containing diisocyanates. The form of training is not specified, and many training courses are available online for free or at a 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 the application of polyurethane adhesives and sealants freely available.

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

Alternative mode

Another option for industrial users is to specify the use of polyurethane adhesives with a total concentration of diisocyanate monomers of less than 0.1%. There are a number of new advanced polyurethane adhesive materials based on microemission technologies that do not require training if specified, helping companies 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. Microemission products may even bring additional economic benefits for health and safety - because their emissions are so low, there may be fewer warning ICONS on the label.

As August 24 approaches, industrial users of polyurethane need to decide whether to train their teams or adopt new microemission technologies. With employee safety as a priority, either approach allows manufacturers to maintain productivity.