Highly efficient, transparent, and environment-friendly flame-retardant coating for cotton fabric

Environmentally friendly flame-retardant coatings for fabrics urgently need to have both high efficiency and transparency, but their development faces severe challenges. In this study, we reported a highly flame-retardant coating without halogen and formaldehyde via a facile one-pot sol–gel approach derived from ammonium polyphosphate (APP), sodium alginate (SA), and tetraethoxysilane (TEOS). In this system, SA serving as a negatively charged stabilizer can effectively inhibit APP agglomeration and further co-gelatinize with TEOS, thus leading to high transparency (transmittance in the visible region >90%) and colorlessness of the coating. Meanwhile, SA as a charring agent, APP as both acid and blowing sources, and TEOS as a silicon source together constructed a P/N/Si-containing hybrid intumescent system, so that the coating showed highly flame-retardant efficiency for cotton fabric at an ultralow loading of 10 wt%, much superior to other coatings previously reported. The resultant cotton fabric showed a high limiting oxygen index of 31%, self-extinguishing ability in the vertical burning test. Additionally, the total heat release value and total smoke production significantly decreased by 63.5% and 70.0%, respectively in the cone calorimeter test, while the mechanical property remained almost unchanged. The mechanism analysis confirmed that the dense P/N/Si-containing graphitized char layer formed in the condensed phase could effectively prevent the release of heat and the diffusion of combustible gases. This work provides new insights into the design and fabrication of the flame-retardant coating combined with the advantages of high efficiency, environment friendliness, transparency, and colorlessness.