Bio-based phytic acid and urea interfacial layer by layer assembly for flame-retardant cotton

•LBL technology is applied to prepare a bio-based flame- retardant coating (U@PA-Na) by a sequential assembly of positively charged urea (U) and negatively charged sodium phytate (PA-Na) solution in water medium.•The U@PA-Na system possess the characters of safety, non-toxic, and high efficiency in flame retardant.•The flammability and forced combustion tests show that the bio-based flame-retardant system with good washing resistance can significantly improve the flame retardant of cotton fabric, greatly reducing the fire risk.