Synthesis and evaluation of an efficient, durable, and environmentally friendly flame retardant for cotton

An efficient and durable formaldehyde-free flame retardant consisting of an ammonium salt of pentaerythritol tetraphosphoric acid (APTTP) was prepared by a solventless synthesis and characterized by Fourier-transform infrared (FT-IR) spectroscopy and nuclear magnetic resonance. The flame retardancy of the treated cotton fabric was enhanced, as assessed by limiting oxygen index (LOI), vertical flammability, and cone calorimetry measurements. The collected results demonstrated that cotton fabrics treated with APTTP exhibited high flame retardancy and excellent durability. Cotton fabric treated with a 140 g/L APTTP solution showed a LOI of 43.8%, and this value reduced to 26.9% after 50 laundering cycles. No after-flame and after-glow phenomena were presented during vertical flammability tests for all cotton fabrics treated with different concentrations of APTTP. Cone calorimetry results revealed a significant reduction in the intensity of the heat release rate and total heat release peaks. X-ray diffraction revealed that the crystalline particles of cotton fibers treated with APTTP were slightly affected compared with those of control sample. FT-IR spectroscopy results revealed that APTTP was grafted on the cotton fibers. Scanning electron microscopy showed that the surface of the treated cotton fibers remained smooth, while thermogravimetric analysis confirmed that the treated cotton fibers easily decomposed to form char. It was proposed that the flame retardant mechanism of APTTP occurred in the condensation phase.