Fire Retardance in Polyamide‐6,6. The Effects of Red Phosphorus and Radiation‐Induced Cross‐Links

The combustion performance of polyamide 6,6 (PA-6,6) can be improved by the addition of red phosphorus provided it is intermolecularly cross-linked upon irradiation with 60 Co-γ-rays in the presence of triallyl cyanurate (TAC). At a content of 5 wt.-% the latter promotes cross-linking, both in the presence and absence of O 2 , by a factor of about 100. From a variety of combustion tests with samples containing red phosphorus and having been γ-irradiated in the presence of TAC it turned out that an improved fire resistance of PA-6,6 is achieved if the red phosphorus content is at least 7 wt.-%. In this case test samples were self-extinguishing and the UL 94 rating corresponded to V-0. IR analysis of the solid residue brought about evidence for the reaction of red phosphorus with the polymer.