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Polyamides | fl ame retardants


A variety of halogen- free fl ame retardants are available for polyamide resins. Clariant head of fl ame retardant development Dr Sebastian Hörold details the options available to compounders


Formulating fi re retardant PAs


For some 15 years now, the use of various halogen-free fl ame retardants (HFFRs) has been increasing in engineering thermoplastics in general and in polyam- ides in particular. They have now become the main fl ame retardant systems for such polymers, due to their good environmental credentials and ability to meet end use requirements without compromising safety. The growth in HFFRs has been spurred by regula- tions such as RoHS (Restriction of Hazardous Substanc- es), REACH (Regulation on Registration, Evaluation, Authorisation and Restriction of Chemicals) and WEEE (Waste Electrical and Electronic Equipment). These are all European but similar regulations exist today in many other countries. Also having an infl uence, although less so, is the new


pan-European fi re protection standard for railway passenger vehicles, EN 45545, which comes fully into force in March 2016. The new standard specifi es test methods and limit values and establishes requirement sets (R1 to R26) for components. For materials used in connectors, for example, R22 and R23 are the maximum applicable requirement sets (the fi rst is for internal applications, the second for external), mandating values for Limiting Oxygen Index (LOI), smoke density and the toxicity of any gas produced. Hazard levels HL1 to HL3 indicate the testing severity, with HL3 being the most severe. There are no norms or laws currently calling for fl ame retardance in automotive components and


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systems, except for the US Federal Motor Vehicle Safety Standard (FMVSS) 302 for interior components (FMVSS 302 is a fl ame spread test - foams, fi lms and textiles need fl ame retardants to pass it but injection moulded parts normally do not). However, the industry is clearly moving in the direction of increased fi re safety, as evidenced by the publication of the US National Fire Protection Association (NFPA) guide to fi re and hazard (NFPA 556) at the end of the last decade. The bulk of fl ame retarded polyamides are used in


electrical and electronic applications, as well as in civil engineering and in transportation. Automotive has been emerging as a key development area, since materials need to offer a particularly high performance mix of mechanical, electrical and fl ammability characteristics for applications such as battery housings, connectors, sensors and – perhaps for the future - fuel cell separators. Automotive applications account for around 45% of the total market for injection moulded polyam- ides, but today most of them are not fl ame retarded. More than a quarter of the total market for injection moulded polyamides is accounted for by electrical and electronic applications, the overwhelming majority of which call for stringent fl ammability requirements, often UL 94 V0—and this is increasingly called for at wall thicknesses down to 0.4 mm. Close to 10% of the total market is accounted for by general industrial and engineering applications – for example in circuit


Above:


Optimising the performance of fl ame retarded polyamides requires an in-depth


understanding of the different additive options available


December 2015 | COMPOUNDING WORLD 31


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