Amorphous cobalt borate nanosheets grown on MoS2 nanosheet for simultaneously improving the flame retardancy and mechanical properties of polyacrylonitrile composite fiber

It is a great challenge to achieve efficient flame retardance with no mechanical deterioration to polymers. In this study, novel sandwich-like cobalt borate nanosheets-molybdenum disulfide (CoBi-MoS2) hybrids are synthesized by a facile aqueous-phase synthesis approach at room-temperature, and employed as nanofillers for PAN fiber. The amorphous CoBi nanosheet with surface Lewis pairs and potential flame-retardant characteristics acts as interfacial compatibilizer and cooperative flame-retardant, enabling simultaneous improvement in both flame-retardant and mechanical properties of 2 wt% CoBi-MoS2/PAN composite fiber. Compared with pure PAN fiber, the peak heat release rate, peak smoke production rate and peak CO production rate of 2 wt% CoBi-MoS2/PAN composite fiber are decreased by 46.2%, 45.7% and 62.9%, respectively. The gaseous and condensed phase analysis reveals that the catalytic redox activity, cross-linked charring and physical barrier effect of the CoBi-MoS2 are responsible for the flame-retardant enhancements of PAN composite fiber. Simultaneously, the 2 wt% CoBi-MoS2/PAN composite fiber exhibits a 58.7% and 49.1% improvement in tensile strength and elongation at break compared to pure PAN fiber.