Flame-Retardant Behavior and Nanocrystal Synthesis through Formation of Multilayers of Poly(acrylic acid) and Zinc Phosphate on Cotton Fabric

Cotton fabric with improved flame retardancy was prepared by introducing a zinc phosphate compound into cotton fabric using a layer-by-layer (LBL) deposition method with poly(acrylic acid) as a polymer electrolyte layer. In a vertical burning (VB) test, it was found that the flame retardancy improved as the number of depositions increased. As a result of thermogravimetric and inductively coupled plasma-atomic emission spectroscopy analyses, the residual amount increased to 20 wt % for the 20 deposited sample, and the weight ratio of Zn and P elements reached more than 40 wt %. As a result of SEM analysis, the cotton fibers not treated with LBL were destroyed after the VB test, but the shape of the fabric was maintained in the LBL-treated cotton fabrics. It was observed by TEM that numerous single crystals of about 10 nm formed on the surface of the sample subjected to the VB test. Through FT-IR and XPS analyses, it was confirmed that the zinc phosphate compound layer was formed by LBL deposition by the reaction between the phosphate anion and zinc cation. XRD analysis confirmed that the orthorhombic hopeite crystals produced by LBL deposition were transformed into zinc phosphate Zn₃(PO₄)₂ crystals by flame during the VB test. These results show that flame retardancy was improved by a mechanism in which a noncombustible zinc phosphate barrier was formed during firing. These results are significant in suggesting a new method for preparing zinc phosphate single crystals of about 10 nm in size and providing anticorrosion coating for cotton fabric by an environmentally friendly LBL method.