Engineering S/Si-containing rigid organic particles for transparent, tough, flame-retardant polycarbonate composites

Due to increasingly stringent industrial safety standards and environmental regulations, achieving a desirable property portfolio of flame retardancy and other functional properties is essential for expanding the practical applications of polycarbonate (PC). To address this challenge, two S/Si-containing rigid organic particles with different molecular weight (LNSiAS and HNSiAS) were synthesized by incorporating sulfonate groups and siloxane segments into an acrylonitrile-styrene copolymer (SAN) backbone. The molecular weight and sulfonated degree of the flame retardants were tuned by adjusting the polymerization temperature and the dosage of the sulfonating agent. The resulting PC/LNSiAS and PC/HNSiAS composites exhibited enhanced flame retardancy, superior smoke suppression, and high transparency. With only 0.5 wt.% flame retardant, PC/0.5LNSiAS and PC/0.5HNSiAS achieved a vertical burning (UL-94) V-0 rating, with limiting oxygen index (LOI) values exceeding 29%. The peak heat release rate (PHRR) of PC/1LNSiAS and PC/1HNSiAS were reduced to 323.9 and 307.8 kW/m², representing decreases of 15.8% and 20.0%, respectively, compared with neat PC. Meanwhile, the total smoke production (TSP) reduced by 22.0% and 11.3%, respectively. LNSiAS maintained the high impact resistance of PC but reduced the tensile strength and elongation at break, which were mitigated by increasing the molecular weight of the additive. The well-preserved notched impact strength was attributed to good compatibility and strong interfacial interactions between the flame retardants and the PC matrix, facilitating efficient energy dissipation. This work provides a feasible strategy for developing flame-retardant, transparent, and tough PC composites, broadening the application scope of PC in sectors such as illumination, construction, and the automotive industry.