A macromolecular flame retardant for polyamide 6 and its filaments with enhanced fire safety, tensile and UV-blocking performance

In the pursuit of enhancing the fire safety of polyamide 6 (PA6), the addition of flame retardants generally leads to hydrogen bond dissociation, which results in detrimental effects on the mechanical properties of PA6 composites and impedes processing and application in the textile field. In this study, a macromolecular flame retardant, PPB, designed with hydrogen bond donor-acceptor spacing aligned with PA6, was synthesized to increase the number of hydrogen bonds. The addition of 10 wt% PPB to the PA6 matrix (PA6/PPB10) endowed the composite with the limiting oxygen index (LOI) increased to 31.6 % and V-0 rating in the vertical burning (UL-94) test. PA6/PPB10 also exhibited significant enhancement in tensile strength by 12.6 % compared to pure PA6 and demonstrated a superior ultraviolet protection factor (UPF) value of 573, greatly exceeding the value of 3 for PA6. The quenching effect, diluting effect in the gas phase, and hydrogen bond interactions between PPB and PA6 backbones imparted PA6/PPB composites with satisfactory flame retardancy and mechanical properties. As a representative example, PA6/PPB10 was melt-spun into filaments with a pleasing tenacity of 3.6 cN/dtex and self-extinguishing capability within 5 s after ignition, confirming the sustained comprehensive properties after spinning and drawing into filaments.