Abstract:

Objective Polyester/cotton fabric (PC) combines the comfort, air permeability of cotton and stability, high mechanical of polyester, and it is widely used in aerospace, home decoration and other fields. However, the PC produces heat and smoke when burning, accompanied by a serious melting phenomenon, which seriously endangers people's life and health and property safety. The combustion will produce a "wick effect", making the combustion process more intense. Therefore, it is essential to improve the flame retardant performance of PC.

Method To improve the flame retardant property of PC, by using phytic acid (PA) from biology to provide a phosphorus source and chitosan (CS) to provide nitrogen source and carbon source, the expansion flame retardant system was constructed on the surface of PC by the impregnation-baking process to prepare flame retardant polyester/cotton fabric (PC-PA/CS) which improved the flame retardant property of PC.

Results The optimal preparation process of PC-PA/CS was determined by the limiting oxygen index (LOI) value: baking temperature was 160 ℃, baking time was 120 s, CS concentration was 30 g/L, and PA concentration was 400 g/L. The LOI value of flame retardant polyester cotton fabric reached to 28.7%. Infrared spectrum analysis showed that the flame retardant finishing liquid composed of PA and CS was successfully deposited on the surface of polyester/cotton fabric. From the scanning electron microscopy images, the fibers in PC showed obvious dents after pretreatment. After flame retardant treatment, the dents on the fiber of PC-PA/CS surface disappeared and the surface became smooth, with a uniform coating on the surface. Compared with PC, after flame-retardant finishing, the decomposition temperature of cotton with PC-PA/CS was advanced from 377 ℃ to 256 ℃, the maximum decomposition rate of fabric was reduced, and stable char layer can be formed. And the char residual rate is increased to more than 25% at 800 ℃ in N₂. Flame retardant finishing has succeeded in improving the thermal stability of polyester and cotton fabric. The results of cone calorimetry test showed that the maximum heat release rate (PHRR) and total heat release (THR) of PC were 145.86 kW/m² and 2.75 MJ/m², respectively. The PHRR and THR of PC-PA/CS were 96.96 kW/m² and 2.06 MJ/m², respectively, which decreased by 33.53% and 25.10%, respectively, showing that the coating had good thermal inhibition ability. The combustion growth rate index (FGR) was decreased from 6.34 kW/(m²·s) to 3.88 kW/(m²·s), and the fire safety of the fabric was increased. The breaking strength of PC was 50.62 N, while that of PC-PA/CS decreased to 48.86 N which remained above 95% of original fabric. The introduction of CS reduced the influence of thermal and acidic environment on the mechanical properties of fabrics. The introduction of flame retardant coating formed a stable expanded carbon layer on the surface during the combustion process of the fabric, which improved the flame retardant performance of the fabric and has a condensed phase flame retardant mechanism.

Conclusion PC-PA/CS was successfully prepared by dipping-baking method, using PA and CS of biomass to form an expansion flame retardant system together with PC. The LOI value of PC-PA/CS increased significantly from 17.8% to 28.7%, and the droplet phenomenon disappeared, showing excellent flame retardant property. The introduction of flame retardant coating improved the thermal stability and char residual rate of the fabric. Flame retardant finishing effectively reduced the heat release and improved the fire safety of PC. When the fabric was burned, it can form a stable expanded char layer, increased the degree of graphitization of the char layer, and improved the flame retardant performance of PC, which had the flame retardant mechanism of condensed phase.

Key words: polyester/cotton blended fabric, chitosan, phytic acid, flame retardant finishing, biomass expansion flame retardant system, functional textile