Abstract: In order to improve the flame retardant effect of acrylonitrile-butadiene-styrene copolymer(ABS)/ammonium polyphosphate(APP)/poly(p-ethylene terephthalamide）(PETA)System,some commonly used synergists，such as zinc borate(ZB)，red phosphorus(RP ) and ZB, wereseparately introduced into the ABS/APP/PETA system. The improvement in the flame retardancycaused by the synergists was investigated using the limiting oxygen index(LOI）test，UL-94（vertical flame)test，thermogravimetric analysis(TGA)，and scanning electron microscopy（SEM）.Without adding the synergists, the ABS/APP/PETA(70/22. 5/7. 5)system gave LOI=30 and V-0 in the UI, 94 test.After adding 2. 5 phr ZB and 4 phr RP, the LOI value increased to 41%and the UI, 94 grade remained V-0. Meanwhile, ZB was effective in enhancing the thermal stability and the char residue ratio of the ABS/APP/PETA system and RP was effective in improving the char residue ratio markedly. In addition, the ABS/APP/PETA/ZB/RP(70/22.7. 5/2. 5/4) system formed more uniform and compact intumescent charred layers.

Key words: synergist, acrylonitrile-butadiene-styrene copolymer, ammonium polyphosphate, poly(p-ethylene terephthalamide), intumescent flame retardant