Abstract: Thermoplastics flammability remains a considerable threat during fire incidents. Conventionally, halogen-free fire retardant (FR) additives are incorporated into thermoplastics to reduce fire hazards. However, the incorporation of FR additives compromises the mechanical properties (most notably, toughness) of thermoplastics, which has impeded the development of thermoplastic products that possess both high mechanical and fire retarding performances. This study reports an in situ nano-fibrillation strategy to fabricate thermoplastics that exhibit fire retarding properties and a combination of high stiffness and toughness. The proposed composites were composed of in situ thermoplastic polyester elastomer (SBC) nanofibers within a polystyrene (PS) matrix containing hexagonal boron nitride (hBN) as the FR additive. The presence of elastomeric nanofibers successfully mitigated the losses in mechanical performances caused by the incorporation of 2 wt% hBN. Specifically, the inclusion of 15 wt% SBC nanofibers significantly enhanced the toughness of the PS-hBN composite by 350% with negligible effects on the stiffness as compared to neat PS. Furthermore, the presence of nanofibers resulted in synergies with hBN to fabricate composites with enhanced fire retarding performance since the total heat release (THR) of PS-hBN composite decreased from 212 to 189 MJ m^-2 with 10 wt% nanofibers. Thus, nanofibers behave as a multifunctional component that compensated for the losses in mechanical performances caused by hBN incorporation, while enhancing the fire retarding performance. This strategy can be effectively implemented to fabricate the next generation of polymer composites with high fire retarding and mechanical properties for various applications including energy storage packs for batteries and electronics.

Key words: Nano-fibrillated composite, Elastomeric nanofiber, Toughened polystyrene, Flame retardantHexagonal boron nitride