fl ame retardants | Polyamides
Figure 1: DSC data shows phosphinate fl ame retardants based on P-P synergism, such as Clariant’s Exolit series, can provide an extended processing window
at low addition rates and parts have good electrical and mechanical properties. They can also be coloured. Typical density of a 30% glass reinforced PA66 retarded with such a system is around 1.46 g/cm3
. Compared to
compounds containing the brominated polystyrene/ antimony trioxide system, 14% less total material by weight is consumed to make the same number of injection moulded parts using phosphinates.
Improving synergists Over the last few years, it has been found that the nitrogen synergist limits thermal stability of the polyamide compounds and a great deal of work has gone into creating systems that use a different syner- gist. Clariant has identifi ed and now commercially produces a suitable phosphorus-based fl ame synergist. Phosphinates based on phosphorus-phosphorus (P-P) synergism are distinguished by their enhanced processing stability. DSC data (Figure 1) indicate a processing window considerably wider than phospho- rous-nitrogen (P-N) systems, red phosphorus, and brominated types.
Right: Demand for fl ame retarded
polyamides is
growing across all market sectors
Cone calorimeter tests show that new P-P systems
have heat release rate curves similar to those of P-N types. Flammability ratings and glow wire performance are also similar. With a system such as Clariant’s Exolit OP 1400, for example, it is possible to achieve a V0 rating at thicknesses down to 0.4 mm. Exolit OP 1400 provides very good electrical proper- ties such as comparative tracking index (CTI), so it is especially good for polyamides as used in connectors, circuit breakers, switches, and the like. It has enhanced processing stability, with no blooming, and has a negligible effect on the mechanical properties of the compound. And a PA66 GF30 compound fl ame retarded with a P-P system has a signifi cantly lower smoke toxic- ity index than one using a P-N system, because less hydrogen cyanide (HCN) is produced. Smoke density is also lower, which makes this system useful for railway and other transport applications. Polyamides with glass fi bres and Exolit OP 1400 can achieve the highest safety level under EN 45545, HL 3, due to their high LOI together with low smoke density and toxicity.
Processing performance As noted earlier, polyamide 66 generally requires fl ame retardants that can resist processing temperatures of up to around 300°C, and it is not unknown for temperatures to reach as h igh as 340°C. Polymer degradation, formation of decomposition products and discolouration can all occur when additives with insuffi cient thermal stability are compounded and processed. Differential scanning calorimeter (DSC) analysis shows that that reinforced PA66 compounds containing phosphinate fl ame retardants synergized with phosphorus have the broadest processing window of any fl ame retarded PA66. Clariant currently produces Exolit OP 1400 in a pilot plant but it is in the process of extending capacity. A fully commercial plant is scheduled to come into operation during the fi rst quarter of 2016. Several compounders are already producing
34 COMPOUNDING WORLD | December 2015
www.compoundingworld.com
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