Fabrication of flame retardant coating on cotton fabric by alternate assembly of exfoliated layered double hydroxides and alginate

Abstract

In our current work, a layer-by-layer flame retardant coating, assembled from MgAl layered double hydroxides (MgAl-LDH) and alginate, was firstly fabricated onto the surface of cotton fabric for the purpose of reducing its flammability. First, the MgAl–NO₃ LDH was prepared by the hydrothermal method, then it was exfoliated into the positively charged nanosheet in the presence of formamide. Second, the coating deposition on cotton fabrics was carried out by alternately immersing the fabrics into MgAl-LDH suspension and alginate solution. In the vertical flame test, the cotton fabric coated with 20 bilayers could preserve almost 70% of the weave structure after the burning, while pure cotton fabric was completely burned out. The test by microscale combustion calorimetry revealed that the cotton fabrics only with 3.52 wt% coating could obtain 34.6% reduction in peak heat release rate and 25.6% reduction in total heat release compared with those of the pure one. In addition, as evidenced by thermogravimetric analysis-Fourier transform infrared spectroscopy results, the decreased amount of volatilized pyrolysis products and toxic volatiles (CO) during the degradation of coated cotton fabrics was another important factor to improve the flame retardancy. The notable improved flame retardancy of coated cotton fabrics is attributed to the fact that the MgAl-LDH filled coating can form an inorganic protective layer, which can act as a barrier to retard the transfer of heat, oxygen, and the diffusion of volatilized pyrolysis products between the combustion zone and underlying cotton fibers.