Construction of a P–N–Si flame retardant coating on the cotton fabric with the integration of biomass carbon dots and ammonium polyphosphate

In order to improve the flame retardancy of cotton fabric, a kind of biomass carbon dots (CDs) particles were interspersed in the ammonium polyphosphate (APP) layer to achieve a new efficient CDs-based APP (CDs-APP) composite flame retardant by the integration technology. Then the CDs-APP layer was coated on the surface of cotton fabric. The microstructure and thermal stability of CDs-APP particle were characterized by the Transmission electron microscopy (TEM), Fourier infrared spectroscopy (FTIR) and X-ray diffraction (XRD). The mass ratio of CDs to APP was 15.52%, which contains the C, O, N, Si and P elements, accounting for the 28.86%, 42.29%, 19.01%, 2.58% and 6.26%, respectively. The flame-retardant mechanism of CDs-APP was investigated by the limiting oxygen index (LOI), vertical combustion, cone calorimeter, thermogravimetric and thermogravimetric-infrared analysis. The results showed that, when the content of CDs-APP was about 10%, the LOI value of cotton fabric rose to 36.1%. The burning time and damage length have reduced to 4.5 s, 5.6 cm, respectively. And the fabric achieved B1 level. The addition of CDs-APP decreased the total heat release, heat release rate, total smoke emission and smoke emission rate of cotton fabric, among the peak-heat release rate has decreased by 55.78%. By quantifying the flame-retardant modes of CDs-APP, it displayed the superposition of physical barrier effect, flame inhibition effect and catalytic charring effect, accounting for 45.96%, 8.62% and 47.85%, respectively.