Silica-encapsulated red phosphorus for flame retardant treatment on textile

Red phosphorus (RP) particles are commercially available as a flame-retardant additive for polymers. Conventionally, RP is encapsulated with a protective organic coating. In the present work, we propose an alternative approach for the encapsulation of RP with an inorganic SiO2 shell (SiO2@RP), to be employed in textiles. The silica shell was obtained by two steps sol-gel of tetraethyl orthosilicate (TEOS) precursor in RP aqueous dispersion. A homogenous silica shell was consistently achieved. The chemical structure and morphology of the as-obtained powder were characterized by Fourier Transform Infrared (FTIR) spectroscopy, X-ray diffraction (XRD) and scanning electron microscopy (SEM). The effect of the silica coating on the thermal stability of RP was investigated through thermogravimetric coupled-differential thermal analysis (DT-TGA) that revealed improved thermo-oxidative stability. The application of the prepared coated and uncoated RP as flame retardant additives for fabric back-coating is then investigated. Only the fabrics treated with SiO2@RP successfully self-extinguished the flame during flammability test, based on BS-5852 normative, achieving the no-ignition classification required for a practical application. The proposed fully inorganic encapsulation strategy opens up to new and efficient flame retardant solutions based on RP that can potentially be exploited in several application fields.