Enhanced flame retardancy level of a cotton fabric treated by an ammonium pentaborate doped silica-KH570 sol

Tetraethoxysilane (TEOS), γ- (methacryloyloxy) propyltrimethoxysilane (KH570) and ammonium pentaborate (AP, NH ₄ B ₅ O ₈ ) were used as a precursor, silane coupling agent and flame retardant additive to prepare a series of single (SiO ₂ ), composite (SiO ₂ -KH570) and doped (SiO ₂ -KH570-AP) sols via sol-gel processes. The sols were post finished to cotton fabrics through dipping-curing methods. Results show that as-prepared sol-gel systems are successfully deposited on cotton fabrics. SiO ₂ -KH570-AP@COT shows the highest initial pyrolysis temperatures (296.4°C), char residue rate (31.5%), LOI (24.0%) and ΔLOI/Δm (4.75%/g), the most beneficial after-flame time (14.1 s) and after-glow time (0.0 s), the most complete char residue (30.0 cm), the second highest maximum pyrolysis temperature (356.6°C) and an effective synergistic effectiveness parameter (>1.0). Its flame retardancy is mainly promoted by both individually positive and jointly synergistic actions of silica sol (strong physical barrier and structural support effects in enhancing thermal stability and providing char frame), KH570 (strong coupling effect in combining components and reinforcing interface properties between components and cotton fibers) and AP (release of water molecules for cooling burning zone, diluting and isolating oxygen and gaseous products and promoting char formation). The flame-retardant treatment deteriorated the tensile strength of cotton fabrics.