Bio-Based Flame Retardant Superhydrophobic Coatings by Phytic Acid/Polyethyleneimine Layer-by-Layer Assembly on Nylon/Cotton Blend Fabrics

The inherent flammability and hydrophilicity of nylon/cotton (NC) blend fabrics limit their practical applications. Traditional hydrophobic treatments often involve fluorinated compounds or nanomaterials, which raise environmental concerns and exhibit poor durability. To address these issues, this study developed a sustainable multifunctional finishing strategy. Initially, the nylon/cotton blended fabric was pretreated with 3-glycidyloxypropyltrimethoxy silane (GPTMS). An intumescent flame retardant coating based on bio-derived phytic acid (PA) and polyethyleneimine (PEI) was constructed on NC fabrics via a layer-by-layer (LBL) self-assembly process. Subsequently, polydimethylsiloxane (PDMS) was grafted to reduce surface energy, imparting synergistic flame retardancy and superhydrophobicity. The treated fabric (C-3) showed excellent flame retardant and self-extinguishing behavior, with no afterflame or afterglow during vertical burning and a char length of only 35 mm. Thermogravimetric analysis revealed a residual char rate of 43.9%, far exceeding that of untreated fabric (8.6%). After PDMS modification, the fabric reached a water contact angle of 157.8°, indicating superior superhydrophobic and self-cleaning properties. Durability tests showed that the fabric maintained its flame retardancy (no afterflame or afterglow) and superhydrophobicity (WCA > 150°) after 360 cm of abrasion and five laundering cycles. This fluorine-free, nanoparticle-free, and environmentally friendly approach offers a promising route for developing multifunctional NC fabrics for applications in firefighting clothing and self-cleaning textiles.