One-Step Synthesis of a Novel Intrinsically Flame-Retardant Thermoplastic Polyamide 6 Elastomer: Structure, Properties, and Spinnability

Despite great advances in thermoplastic polyamide elastomers (TPAEs), it is still a significant challenge for preparing flame-retardant TPAEs with facile strategies. In this work, a series of novel intrinsically flame-retardant TPAEs (PA6PTMG-xCEPPAs) containing polyamide 6 as the hard segment, poly(tetramethylene glycol) (PTMG) as the soft segment, and 2-carboxyethyl phenyl phosphonic acid (CEPPA) as a phosphorus-based flame-retardant unit were successfully synthesized through a facile one-step synthetic method. The properties of as-prepared PA6PTMG-xCEPPA were fine-tuned by varying the CEPPA content after determining the ratio of soft and hard segments. Results showed that increasing the CEPPA content significantly enhanced the flame retardancy of PA6PTMG-xCEPPA. The resultant PA6PTMG-4CEPPA and PA6PTMG-6CEPPA could obtain limiting oxygen index (LOI) values of approximately 25.0 and 28.4%, respectively, both meeting V-0 rating in UL-94 tests. The flame-retardant mechanism can be ascribed to involve char layer formation in the condensed phase and free-radical quenching in the gas phase. However, with increasing CEPPA unit content, the intrinsic viscosity, thermal properties, crystallinity, mechanical properties, and spinnability of the as-prepared PA6PTMG-xCEPPA decreased. Fortunately, PA6PTMG-4CEPPA with superior flame retardancy still presented excellent spinnability, and the corresponding elastic fibers had 83.3% elongation at break and 1.57 cN/dtex tensile strength, indicating its outstanding comprehensive properties. Therefore, the as-prepared intrinsically flame-retardant TPAEs possess promising potential for widespread application across various industrial sectors.