How will the new regulations affect manufacturers using PU adhesives?

Kevin Brownsill, Technical Head: Learning and Development of the adhesives specialist intertronicsDiscusses the chemistry of PU and how the new REACH requirements will affect manufacturers.

New law requiring training for handling materials containing diisocyanates coming on the 24th^th August this year has drawn attention to polyurethane adhesives (PU). These materials are widely used in industrial facilities for joining metals, plastics and even glass, due to their reasonable cost, good adhesion, high peel strength and good impact resistance.

Polyurethanes are polymers composed of organic units linked by urethane linkages. They are used to make rigid and flexible foams, and to make varnishes and coatings, adhesives, potting compounds, and fibers. Their most common application is in foam, which makes up about two thirds of all polyurethane use.

Globally, 6% of polyurethane is used in adhesives, and 3% in sealants. PU adhesives are available in one part (1K) and two part (2K) formulations, both types exhibiting the same basic chemical reactivity. They are usually thermoset materials, but PU thermoplastic hot melts are available, which are typically polyester based materials.

Advantages of PU adhesive

Polyurethane adhesives provide excellent adhesion to a wide range of materials – they bond well to plastics, metals and composites. Their surface energy is lower than that of epoxy adhesives, which can result in better wetting and adhesion to plastic substrates. A wide range of PU adhesives are available – they can be formulated with varying pot lives, in viscosity grades from self-levelling to non-slump paste, and in grades that cure from very soft to very hard. Let’s go

Polyurethane adhesives offer good performance characteristics: they are extremely tough, have high peel strength, and are suitable for filling gaps. They are popular in outdoor applications due to their resistance to impact, solvents, weather and abrasion. Importantly, they are relatively low-cost materials that are easy to apply and cure (typically, these adhesives cure at room temperature, although the process can be accelerated by heat). For best results, the manufacturer will need a good mix in the right proportions.

PU chemistry

Polyurethanes are formed by the reaction between an isocyanate (a highly reactive, low molecular weight family of chemicals) and a polyol (an organic compound containing multiple hydroxyl groups). Other components include pigments for color, fillers for mechanical reinforcement and to reduce overall cost, plasticizers to increase flexibility, flame retardants and smoke suppressants to reduce flammability and smoke generation when burned, and UV absorbers and antioxidants to reduce degradation.

Both polyols and isocyanates are hygroscopic and will react with moisture, and it is important that industrial users are aware of this. If isocyanate reacts with water, it forms an unstable carbamic acid, which decomposes to form urea and carbon dioxide gas. Therefore, the moist air trapped in the mixture may form foam or bubbles, which may not be aesthetically desirable. Selecting the proper catalyst can either suppress or promote the reaction should foaming be desired.

Isocyanates and Safety

The most widely used isocyanates in polyurethane adhesives are diisocyanates, which contain two isocyanate groups. There are two main types of diisocyanate used in polyurethane adhesives: toluene diisocyanate (TDI) and methyldiphenyl diisocyanate (MDI). In polyurethane adhesives, they are used during reaction, meaning that virtually no diisocyanates are present in the finished or cured material.

Their reactive chemistry means that there are some health risks associated with isocyanate exposure when handling PU adhesives before curing, including skin and mucous membrane irritation, chest tightness and difficulty breathing. The main potential effects of hazardous exposures are occupational asthma and other lung problems, as well as irritation to the eyes, nose, throat and skin. In addition, isocyanates include compounds classified as probable human carcinogens that cause cancer in animals.

new restrictions

Following review by the European Parliament, the REACH ban on aliphatic and aromatic diisocyanates (which applies in the UK) was published 4 .^th August 2020 and became effective on August 24, 2020. These restrictions mean that, 24^th By August 2023, training is required for all professional and industrial users of products with a total monomeric diisocyanate concentration of >0.1%.

Like any chemical, diisocyanates are safe when handled in accordance with relevant risk management and health and safety measures. These restrictions aim to ensure that this happens, with the aim of reducing adverse effects induced by exposure to diisocyanates in the workplace and throughout the supply chain.

The ban requires adhesives and sealant manufacturers to provide information on training on the safe use of diisocyanates to end users and, from 24^th February 2022, ensure that all PU products that require safety training are labeled with the following statement: By 24^th August 2023 Adequate training is required prior to industrial or commercial use of this product.

Under the new requirements, employers are responsible for providing adequate training for all employees who are exposed to substances containing diisocyanates. The format is not specified and many training courses are available online and are either free, or low cost. The Association of the European Adhesive and Sealant Industry (FEICA) is offering its members financial support in the form of voucher codes for the training of member organizations and their customers, providing training materials related to PU adhesive and sealant applications free of charge.

In addition to providing training, employers must also collect evidence of successful completion of training programs, such as a log of certifications. Training certificates last for five years, after which they need to be renewed.

alternative approach

Another possibility for industrial users is to specify PU adhesives with total monomeric diisocyanate concentrations of <0.1%. There are new, pioneering polyurethane adhesives based on micro-emission technology, which means training is not required if you specify those products, helping businesses avoid the cost, administrative and time burdens associated with new mandatory training, while ensuring high standards of Health and Safety (H&S).

Importantly, these new materials retain all the advantages of PU, in that they have good adhesion, rapid curing and good environmental resistance. Micro-emission products may also bring additional H&S benefits – because their emissions are so low, they are less likely to carry a warning sign on the label.

with 24^th As August draws near, industrial users of PU have a decision to make, team up, train or adopt new, micro-emission technology. Either approach enables makers to maintain productivity while prioritizing the safety of their teams.