Flame retardants: is the customer always right? Brominated additives are a bete noire for OEMs trying for a green image, but perhaps for the wrong reasons. What then is the future for halogen-based flame retardants?

Plastics Engineering, July, 2007 by Peter Mapleston

Tetrabromobisphenol-A (TBBPA) is the most widely used BFR, predominantly as a reactive flame retardant in epoxy laminates for printed circuit boards (it becomes an integral part of the polymer). It is also used as a non-reactive additive in thermoplastics, mostly ABS.

Many scientific studies have been conducted on TBBPA in the framework of a European risk assessment programme. The overall risk assessment is expected to be finalised by the end of this year. However, the human health part of the report has already concluded that TBBPA is safe. TBBPA's environment risk assessment concluded that no risk has been identified for reactive use, while the final environmental report, completed in March 2007, identified a low risk for the additive use of TBBPA in water and sediment.

The European Brominated Flame Retardant Industry Panel (EBFRIP), based in Brussels, believes that the risks identified for additive application are manageable through its Voluntary Emissions Control Action Programme (VECAP). The programme's aim is to make sure that BFRs are locked into products, where they are not harmful to the environment. It is now running in the six main European user countries for decabroms: UK, Belgium, Germany, Netherlands, France, and Italy.

But if you really don't want bromine, what choices do you have? They are increasing.

Alternatives

Since beginning commercial production of its Exolit OP organic phosphorus-based flame retardants in late 2004, Clariant has been steadily expanding the range. Latest types, based on phosphinates, are tailored to the requirements of OEMs in the electrical and electronics industry. In addition to the main fields of application, which are glass fibre reinforced nylons and thermoplastic polyesters, they have proven their efficiency in printed circuit boards, adhesives and sealants.

Recently developed for PCBs, Exolit OP930/935 is not hygroscopic, is non-toxic, has an extremely low solubility in water and in common solvents, and does not hydrolyse in the presence of water to form phosphoric acid. It starts to decompose at over 300[degrees]C, which is high enough to withstand lead-free soldering temperatures and is also in the range at which most of the epoxy resins will decompose. It can be used alone or in combination, for example with aluminium hydroxide as a synergist to reduce the total filler content.

Ciba is still a relatively small player in the flame retardants business as a whole, but is working hard on increasing the use of its melamine-based flame retardants. Melamine based FRs have been used for some time in polyamides, for such electrical products as circuit breakers, switch gear, terminal blocks and the like.

The companys most recent addition is Melapur 200, a high temperature resistant grade based on melamine polyphosphate. It was originally developed for glass fibre reinforced nylon 66, but Eelco Dekker, Ciba's global new business development manager for flame retardants, says it is now being accepted in a much broader range of polymers. The company is promoting its use, often in synergistic blends with other additives, in demanding applications in E/E, public transportation and other areas.