Ryton® PPS compounds are inherently flame resistant. All Ryton® PPS compounds have UL 94 V-0 and many have UL 94 5VA non-flammability ratings without using flame retardant additives. The limiting oxygen index, another good method of comparing the flammability of various materials, is the minimum percentage of oxygen in a test atmosphere that allows the plastic to support continued combustion. The limiting oxygen index of Ryton® PPS compounds is about 50%, making them among the most flame resistant plastics.
When comparing flammability ratings of engineering plastics, it is important to note that many require flame retardant additives to be classified UL 94 V-0. Flame retardant additives tend to be detrimental to the mechanical and electrical properties of a plastic. Most common flame retardant additives break down after a single pass through an injection molding machine, so parts molded using regrind will not be as flame retardant as parts molded from virgin material. Furthermore, the thermal degradation of flame retardant additives can produce toxic, corrosive off gasses. Since Ryton® PPS compounds require no flame retardant additives, regrind is as flame resistant as virgin material and the other undesirable effects of using flame retardant additives are also avoided.
