Certain brominated flame retardants

Bromine is a key component in many flame retardant systems and it has been incorporated into numerous successful commercial products. Many of these employ the bromine in the form of brominated organic compounds or polymers. It is important to note, therefore, that the RoHS Directive is not proscribing the use of all brominated flame retardant but instead only particular types: polybrominated biphenyls and two examples of the polybrominated diphenyl ethers (pentabromodiphenyl ether and octabromodiphenyl ether). As with the other materials proscribed, the difficulty with respect to end-of-life electronics will be in determining where they have been used.

Brominated flame retardants are widely used in electronics products; for example, they are found in semiconductor encapsulants, PCBs, cables and connectors, as well as in equipment housings. It is important to distinguish between those that are reacted into thermoset polymers and those that are added to meltable polymers such as those that are injection moulded to form housings and casings. It is the latter non-reactive brominated flame retardants that are of most concern because they can migrate more easily and thus cause health and environmental problems. It is examples of these that are being proscribed by the RoHS Directive. Reactive brominated flame retardants such as the tetrabromobisphenol-A based compounds used in semiconductor encapsulants and most PCBs are not proscribed by the RoHS Directive.

Pentabromodiphenyl ether has been used as a flame retardant in epoxide, phenolic and unsaturated polyester based resins. It is still used as a flame retardant in some low cost printed phenolic circuit board materials (e.g. FR2), and these would find use in consumer electronics such as TVs. (The plastic housings of TVs sold in Europe have, for some years, been non-flame retarded).

Over 95% of the octabromodiphenyl ether produced finds use in acrylonitrile butadiene styrene (ABS) resins, which are often used in covers and casings for electrical or electronic equipment. Other reported uses are in nylon and low density polyethylene, polycarbonate, phenol-formaldehyde resins and unsaturated polyesters, as well as in adhesives and coatings.

Polybrominated biphenyls have not been used as flame retardants for some time and so the likelihood of them being found in the electronics manufacturing chain is extremely low. There is a remote possibility that they may still be encountered in older products that have come to the end of their lives and are due to be recycled. As a wide range of plastics are likely to be encountered in many electronic and electrical assemblies, the only way to be sure that they do not contain the proscribed brominated flame retardants is to check with the individual component suppliers.