Engineering sulfonated rigid organic particles for fire-safe polycarbonate combining high transparency and enhanced mechanical property

• A sulfonated organic rigid particle (sSANNa) was synthesized. • sSANNa effectively maintained the high transparency of PC at a low addition. • sSANNa endowed PC with superior flame retardancy due to its catalytic effect. • sSANNa enhanced the toughness of PC. Despite great advances in overcoming the inherent flammability of polycarbonate (PC), it remains highly challenging to achieve a property portfolio of flame retardancy, mechanical properties and transparency. To ameliorate this issue, a sulfonate organic rigid particle (sSANNa) was synthesized by incorporating sodium sulfonate into the acrylonitrile-styrene copolymer (SAN) molecular chain. Only 0.5 wt% sSANNa endowed the resultant PC/0.5sSANNa composite with desired flame-retardancy, including limiting oxygen index (LOI) of 34.0 % and vertical burning (UL-94) V-0 rating, and well-preserved optical properties. The peak heat release rate (PHRR) and total smoke release (TSR) of PC/0.5sSANNa were respectively decreased by 23 % and 15 % compared to pure PC, attributing to the organic sulfonates promoting the formation of a denser char layer during combustion. Meanwhile, PC/0.5sSANNa showed an enhanced notch impact strength reaching 76.9 kJ·m −2 due to the craze induction mechanism of sSANNa and improved interfacial interaction between PC matrix and sSANNa. This work establishes a promising design strategy for creating transparent, flame-resistant yet tough PC composites by integrating sulfonate and organic rigid particles, expecting to broaden the high-tech applications of PC (e.g. transparent fireproofing board, covers for unmanned vehicles and architectural lighting equipment).