Waste Cotton Fabric/Zinc Borate Composite Aerogel with Excellent Flame Retardancy

A waste cotton fabric (WCF)/zinc borate (ZB) composite aerogel with flame resistance was successfully synthesized through zinc borate immobilized in the cellulose aerogel by in situ formation by dissolving a waste cotton fabric in NaOH/urea aqueous solution. Morphology and composition were studied by scanning electron microscopy, energy-dispersive spectroscopy, X-ray diffraction, and X-ray photoelectron spectroscopy. The thermal stability and flame retardancy with thermogravimetric analysis and ignition tests as well as microscale combustion calorimetry were tested. The results show that zinc borate is dispersed evenly in the pore and on the surface of the aerogel and has no significant effect on the porous structure of the WCF/ZB composite aerogel. In addition, the introduction of zinc borate can significantly improve the mechanical properties of composite aerogels. The compressive strength of pure WCF aerogels and WCF/ZB-9 aerogels increases from 0.028 to 0.70 MPa. The composite aerogel exhibits excellent thermal stability, flame retardancy, and self-extinguishing properties, which can effectively suppress heat release, and the heat release rate reduces from 190.70 to 5.45 W/g for the pure WCF aerogel and WCF/ZB-9 aerogel. Heat release capacity and total heat release of the pure WCF aerogel and WCF/ZB-9 aerogel decrease from 12.1 to 1.6 kJ/g and from 213 to 7 J·g^–1 k^–1, respectively. The WCF/ZB aerogel from the waste cotton fabric can be potentially applied to lightweight flame retardant fields.