A novel flame retardant system of AMP and KH570-modified silica sol for cotton fabrics

Tetraethoxysilane (TEOS) and γ-(methacryloyloxy) propyltrimethoxysilane (KH570) were used to prepare a single silica (SiO2) sol and a silica-5'-adenosine monophosphate (AMP, bio-based substance) hybrid sol via sol-gel processes. Then, the prepared series of sols were successively applied onto the cotton fabric (COT) surface through a dipping-baking method. Fourier infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), scanning electron microscope (SEM), energy dispersive spectroscopy (EDX), thermogravimetric analysis (TGA), limiting oxygen index (LOI), vertical flammability test (VFT), and cone calorimetry test (CCT) were used to characterize the functional groups, surface element compositions, crystal structures, microscopic morphologies and surface element distributions, thermal stability and flame retardancy levels of original (raw), and treated cotton fabrics. Results show that the series of sols are successfully converted to gels and coated onto the cotton fabric surfaces. AMP-SiO2-KH570@COT shows the best flame retardancy with the highest char residue rate (48.7%) (6.5 times that of raw cotton fabric), and a LOI value of 27.7% (non-flammable level). It can self-extinguish with a char length of only 8.2 cm in a VFT. It shows reduced total heat release (THR) and peak heat release rate (PHRR) by 3.8% and 48.5% and has the longest ignition time (43 s) in a CCT. The SiO2 sol-converting gel modified with KH570 clearly improves the interfacial compatibility with the cotton fabric and effectively isolates heat and oxygen. Meanwhile, the AMP gel pyrolyzes the phosphate group at high temperatures to accelerate the carbonization degrees of cotton fibers. These components show good synergistic flame-retardant effects.