Bio-based flame retardants (FRs) were employed to successfully reduce the flammability of acrylonitrile–butadiene–styrene (ABS), achieving results comparable to a commercial brominated ABS product (Br-ABS); synergistic interactions between the components were responsible for the enhanced performance. In a two-phase study, eight nonhalogenated, low-toxicity FRs and combinations thereof were melt-processed with ABS at a 30 wt % FR content and screened using microscale combustion calorimetry (MCC). All 30 samples presented significantly lower peak heat release rates (PHRR; 26–43% reduction) and total heat release (THR; 16–29% reduction) than ABS. Four best-performing compositionsABS/tannic acid (TA), ABS/tannic acid/fish gelatin (TA-FG), ABS/phytic acid sodium salt (PA), and ABS/phytic acid sodium salt/tannic acid (PA-TA)were scaled up and further analyzed through cone calorimetry (CC) and mechanical testing. TA, TA-FG, PA, and PA-TA significantly lowered ABS’s PHRR in MCC (36–43% reduction) and in CC (38–65% reduction). Some samples matched commercial brominated ABS: TA in MCC and PA-TA in CC. The mechanical performances of the composites were acceptable, with an increase in modulus but a loss in toughness. Important synergistic interactions between the FRs and the ABS matrix, between TA and FG, and between PA and TA, were responsible for the reduced flammabilities.

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