Sustainable fire-retardant coating for Nylon-cotton fabric from wastewater-recycled struvite

Nylon-cotton blend (NYCO) fabric is widely used in military uniforms and work-wear due to its durability and comfort, but it is highly flammable. Since the currently available fire retardant coatings release toxic fumes causing adverse health and environmental effects, there is a pressing need for a bio-safe fire retardant for NYCO. One potential solution is struvite—magnesium ammonium phosphate hexahydrate (MgNH<sub>4</sub>PO<sub>4</sub> . 6H<sub>2</sub>O)—which can be recycled from wastewater. We investigated whether struvite, alone or combined with naturally occurring plant-based compounds, such as tannic acid (TA) and phytic acid (PA), could be developed as a sustainable and bio-safe fire retardant for NYCO. Using a simple dip-coating procedure, we treated the NYCO fabric with TA, PA, and/or struvite. We determined the surface functionalization of the treated NYCO fabrics utilizing gravimetry, Fourier-transform infrared spectroscopy, and scanning electron microscopy. We confirmed results from other studies that showed the fire-retardant properties of PA treatment on NYCO. We then demonstrated that NYCO fabric treated with struvite, alone or combined with TA, exhibited reduced flammability and a lower maximum temperature during burning, as assessed by a modified vertical flame test (as outlined by ASTM D-6413). Our study suggests that wastewater-recycled struvite, alone or combined with TA, may be an effective phosphorus-based bio-safe fire retardant for NYCO. Moreover, using struvite recycled from wastewater has an additional benefit of preventing residual phosphorous from reaching aquatic bodies; which in turn; may mitigate eutrophication.