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

Dekker says Ciba is keeping a close eye on market trends, particularly the growing interest in PBT (polybutylene terephthalate) thermoplastic polyester as an alternative to nylons in electrical applications, and in halogen-free FRs for epoxies and other thermosets.

Other Developments

It's not only additive suppliers that are working on halogen-free solutions. In fact, some of the busiest developers are the major engineering plastics suppliers--although not always alone.

Ticona worked with Clariant to develop Celanex XFR, a PBT with a new patented flame retardant system based on organic phosphinates. These salt-like, halogen-free compounds are stable up to temperatures of 350[degrees]C, which makes them ideal for engineering thermoplastics in the E/E sector. Even very thin components (from 0.8mm) fulfil the strict flame retardancy requirements of the US Underwriters Laboratories (UL) 94 V-0 test.

Ticona says metal phosphinates make it possible to meet the latest high flame retardancy requirements. Flame retardant PBT compounds offer high thermal stability up to 300[degrees]C and are readily coloured. They have no significant tendency to migration or emission. GE Plastics several years ago embarked on a programme to develop halogen-free flame retardant grades of its engineering thermoplastics that had mechanical properties equal to or better than those of halogen-containing versions. The latest result of this programme is the Valox ENH family of flame retardant PBT thermoplastic polyesters that meet the UL 94 V-0 standard at 0.8mm. Estelle Cheret, GE Plastics' global product manager for Valox PBT, says that unlike other V-0 PBTs, impact strength and overall strength have not been compromised. Furthermore, electrical properties such as comparative tracking index (CTI) are actually much better than standard PBTs, and the grade easily passes the new IEC glow wire test norm, which calls for zero ignition at a wire temperature of 750[degrees]C.

The company has just launched the first grade in the ENH family, a 25 percent glass reinforced type, and grades with different fillers, as well as PBT/PC blends, will follow. GEP is using new, patented technology for its new generation compounds, which incorporate a phosphate-based FR system--Cheret declines to provide more details. Although the company still uses pentaBDE FR additives in some of its compounds, Cheret does say the goal is to have converted all FR engineering thermoplastics to halogen-free types by 2009/2010.

Development of halogen-flee flame retardant nylons has progressed faster than for thermoplastic polyesters, but development in FR nylons continues all the same. Ultramid B3UM4, a reinforced nylon 6, is one of the latest grades from BASF for circuit breakers. And two other nylons conform to the Household Appliance Standard IEC 60335-1, which was recently made more rigorous. Ultramid A3X4G7 is a totally new type of nylon 66 with 35 percent glass fibres, while Ultramid A3UG5, containing 25 percent glass fibres, has been optimised specifically to comply with the new standard since its introduction at K 2004.