Intumescent flame retardant finishing for polypropylene nonwoven fabric

This work reports our recent efforts on improving the fire safety of nonwoven polypropylene fabric by increasing surface polarity followed by a conventional finishing. The fabric was firstly surface treated in a surfactant solution containing cetyltrimethylammonium chloride under ultrasonic to increase the hydrophilicity, and then was treated by a pad-dry process with a water solution of ammonium polyphosphate and pentaerythritol. The contact angle of polypropylene fabric treated with 0.2% cetyltrimethylammonium chloride was decreased to 71° from 130° of the control sample. The flammability was evaluated by limiting oxygen index, vertical flammability test, and cone calorimetry test. The limiting oxygen index value was increased to 23.5% from 18.1%, the peak heat release rate was decreased to 159.1 from 292.5 kW/m ² , and the melt dripping was completely eliminated by the finishing treatment. Thermogravimetric analysis showed that treated polypropylene fabric samples had higher thermal stability and formed more char residue in high temperature range (above 450 °C) than the control polypropylene sample. The char morphology observation by scanning electron microscopy demonstrated that the treated fabric sample formed continuous char structure without voids, which effectively isolated underlying polypropylene fabric materials from fire and oxygen. It is proposed that decomposition compounds from both cetyltrimethylammonium chloride and ammonium polyphosphate catch free radicals in the gas phase, and the presence of ammonium polyphosphate and pentaerythritol promote char formation in the condensed phase during the burning process of polypropylene fabric.