Flame-retardant ramie fabrics with APP: flame retardancy, flame-retardant mechanism and mechanical properties

In this study, ammonium polyphosphate (APP) coating was constructed on ramie fabrics (RFs) by a simple and easy dip-pad-bake method to acquire flame-retardant ramie fabrics (RF-APP). With the weight gain of APP of about 5%, RF-APP passed the vertical flame test, the afterflame time and afterglow time were both 0 s, the damaged length was only about 80 mm, and the limiting oxygen index value reached 28.6%. The data obtained from cone calorimetry test showed that both the heat and smoke production released were greatly reduced during burning. Meanwhile, the fire growth rate index also decreased significantly. The above facts indicated that the fire safety of RF-APPs had been visibly improved. Through analyzing the gas phase products and condensed phase products, it was concluded that APP promoted the catalytic dehydration of the fabrics to form denser char layers and suppressed the generation of flammable gases to achieve excellent flame retardancy. The tensile strength of RF-APPs remained basically unchanged. The simple preparation method of RF-APPs, which required only APP, provides a feasible solution for further preparation of flame-retardant natural fibers reinforced composites.