Objective Fire hazard has caused great losses to human life and property, and textile fire is one of the main causes of fire disaster. As the mostly used chemical fiber in the world, polyester fiber is widely used in clothing, home textiles, transportation and other fields. However, it is a flammable material, and its burning is accompanied with serious dripping of droplets, which is prone to cause secondary injuries and fire spread. Therefore, it is of great significance to modify the polyester fabrics for flame-retardant and anti-dripping performance. Method Alkali washing and plasma treatment were employed to pretreat polyester(PET) fabric, which activated and etched the PET fiber, so as to improve the infiltration and adhesion of flame-retardant as well as the flame-retardant durability. After that, methyl phosphonic acid (5-ethyl-2-methyl-2-oxo-1,3,2-dioxo-5-yl) methyl methyl ester (EMD) and N-phenylmaleimide (N-PMI) were compounded to form a phosphorus-nitrogen synergistic system for the leaching treatment of polyester fabric. By combining the flame-retardant of EMD with the crosslinking and char formation promotion property of N-PMI, the flame-retardant and anti-dripping performance of polyester fabric could be simultaneously improved. Results Scanning electronic microscopy(SEM) and Fourier transform infrared spectroscopy (FT-IR) results showed that the impurities on the surface of the polyester fabric were significantly reduced after alkali washing, and the grooves generated by plasma etching were obviously visible in the fiber surface (Fig. 1 and Fig. 2). After leaching and finishing, EMD and N-PMI were uniformly adhered to the surface of PET fiber. The limiting oxygen index (LOI) and vertical burning test results showed that the LOI value of PET-EMD (PET treated with EMD only) was significantly increased, but the droplet phenomenon was not improved (Tab. 2). The LOI value of PET-N-PMI (PET treated with N-PMI only) was not increased much, but the droplet dripping is obviously reduced. In contrast, the flame-retardant and anti-dripping performance of polyester fabric treated by both EMD and N-PMI (PET-E+N) were enhanced with different features. The LOI value of PET-E+N reached 35.1% (83.8% higher than that of pure polyester fabric), which was higher than that of PET-EMD and PET-N-PMI, indicating the synergistic flame-retardant performance of EMD and N-PMI. In addition, PET-E+N extinguished immediately after leaving the fire source, and no dripping occurred during the combustion process, reaching flame-retardant grade B1. The introduction of N-PMI can promote the char formation of PET, and the char residues of PET-N-PMI at high temperature were 1.2 times higher than that of pure PET (Fig. 3). Furthermore, cone calorimeter test suggested that the peak heat release rate and total heat release of PET-E+N were 48.6% and 20.8% lower than that of pure PET, respectively (Fig. 4 and Tab. 4). The results also demonstrated that EMD would provide flame suppression effect, and N-PMI could promote the char formation, therefore, PET-E+N displayed outstanding barrier effect. PET-E+N burned to form a dense, continuous and porous char layer (Fig. 5 and Fig. 6), playing a critical role in blocking and protecting during combustion and implying that PET-E+N exhibits a typical condensed phase flame-retardant mechanism. Moreover, PET-N-PMI and PET-E+N both displayed an apparent exothermic peak (around 265 °C) after the melting peak(Fig. 7), indicating that the existence of N-PMI promoted the crosslinking of PET during melting and played a role of "high temperature self-crosslinking". This is believed the deep reason for anti-dripping effect induced by N-PMI. Conclusion On the basis of alkali washing and plasma pretreatment, EMD and N-PMI were selected to construct a new phosphorus-nitrogen synergistic flame-retardant system with the characteristics of "intelligent self-crosslinking" and employed to improve the flame-retardant and anti-dripping performane of polyester fabrics. The flame-retardant mechanism was deeply studied. Results show that the constructed flame-retardant system could effectively improve the flame-retardant and anti-dripping performane of polyester fabrics. Meanwhile, the mechanical properties and air permeability of the fabric are not obviously affected. This study provides a theoretical basis for flame-retardant and anti-dripping modification of polyester fabric. © 2023 China Textile Engineering Society. All rights reserved.
