Halogen-free Intumescent Flame Retardant for ABS/PA6/SMA Alloys

The intumescent flame-retardant system of acrylonitrile-butadiene-styrene (ABS) copolymer/polyamide 6 (PA6)/styrene-maleic anhydride (SMA) alloys (ratio 80/20/6) with ammonium polyphosphate (APP) was evaluated by the limiting oxygen index (LOI) and UL-94 tests. Furthermore, the different effects of various synergistic charring agents on the flame retardancy of the ABS/PA6/SMA alloys were also investigated, including caged bicyclicphosphates (PEPA), thermoplastic phenolic resin (TPPFR), epoxy resin (E-44), and Zeolite 4A. The results indicate that PA6 can act as a very efficient carbonization agent and intumescent flame retardant for ABS/PA6/SMA alloys. When the content of APP was 25 wt%, the LOI value of the ABS/PA6/SMA/APP system was 29 and with a UL-94 test rating of V-1; when the content of APP was 35 wt%, the UL-94 test rating was V-0. The higher the molecular weight of PA6, the better the flame retardancy of the ABS/PA6/SMA/APP system. The ABS/PA6/SMA alloy shows a much better charring performance and flame retardancy when the mass ratio of APP/PEPA or APP/E-44 is 20/5, or APP/Zeolite 4A is 22/3. The expansion and dense carbon layer formed on the surface of the complex after burning were observed by scanning electron microscopy (SEM).