Design of flame-retardant PAN composite fiber with smoke inhibition, toxicity reduction and mechanical reinforcement based on ion- and UV-induced thermal oxidation technology

Polyacrylonitrile (PAN) fiber is widely applied in textile and industrial fields, whereas their inherent flammability and release of toxic gases severely restrict their high-safety applications. In this work, an intumescent flame retardant (TP@Gly) was successfully synthesized via a one-step Mannich reaction using tea polyphenols, glyphosate and formaldehyde. The PAN spinning solution was blended with TP@Gly to prepare modified fiber (TP@Gly/PAN) via wet spinning. Subsequently, flame-retardant PAN fiber (O/UV-TP@Gly/PAN) was obtained by treating TP@Gly/PAN with UV-induced thermal oxidation. The results indicated that ion- and UV-induced thermal oxidation obviously promoted generation of thermostable conjugated trapezoidal structures of PAN molecular chains at 180 °C. Therefore, O/UV-TP@Gly/PAN exhibited a high LOI value of 31.5%. Cone calorimetry tests demonstrated that O/UV-TP@Gly/PAN achieved excellent flame retardant and smoke suppression performance by dramatically reducing the peak heat release rate, total smoke production rate and CO production rate by 69.6%, 82.9% and 91.7%. Moreover, the release of toxic HCN was effectively restrained, further verifying the superior fire safety performance. The tensile strength of O/UV-TP@Gly/PAN increased from 13.35 cN/tex to 20.12 cN/tex. This study provided a facile and effective strategy for the preparation of flame-retardant PAN fiber.