Effectively improving flame retardancy levels of finished cotton fabrics only by simple binary silicon-boron oxide sols

This work aims to improve the thermal stability and flame retardancy of cotton fabrics treated just by a single SiO 2 , a single B 2 O 3 and their binary composite sol–gel systems. Tetraethyl orthosilicate (TEOS) and tributyl borate were used as precursors. The sols were coated onto cotton fabrics via dipping-baking processes. Techniques including Diffuse Reflectance Infrared Fourier Transform Spectroscopy (DRIFTS), X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), Scanning electron microscope (SEM), energy-dispersive X-ray spectroscopy (EDS), thermogravimetric analysis (TGA), limiting oxygen index (LOI) and vertical burning test (VBT) were used to investigate the surface functional groups, elemental compositions, crystal structures, surface morphologies, elemental contents, thermal stability and flame retardancy levels of original and sols-treated cotton fabrics, respectively. The results show that the sols converted gel coatings are successfully deposited on the cotton fabric surfaces. SiO 2 -B 2 O 3 sol finishing cotton fabric shows the best flame retardancy. It shows the highest char residue rate (43.82%), the highest LOI (25.7%) and ΔLOI/Δm (7.0%/g), the lowest after-flame time (10.0 s) and after-glow time (0.0 s without a smoldering process), a relatively complete and continuous char residue after a VBT. The SiO 2 and B 2 O 3 sol–gel systems play more synergistic effects than competitive effects in flame retarding a cotton fabric. A SiO 2 gel shows effects of a high melting point, a structural support and dimensional stability, while a B 2 O 3 gel shows a fusing capability and a longer pyrolysis process.