Unique nanobrick wall nanocoating for flame-retardant cotton fabric via layer-by-layer assembly technique

Unique quadlayer assembly film of polyhexamethylene guanidine phosphate (PHMGP)/ammonium polyphosphate (APP)/PHMGP/α-zirconium phosphate (α-ZrP) was constructed on cotton fabric to achieve excellent flame-retardant modification. X-ray diffraction and attenuated total reflection Fourier transform infrared spectroscopy confirmed that PHMGP, APP, and α-ZrP grew linearly in the layer-by-layer assembly process. Thermogravimetric analysis was carried out to assess the thermal stability of the coated fabric, and the relevant results showed that cotton fabric were effectively protected by the assembly coating during burning. The microscale combustion calorimetry results indicated that the coated fabric showed smaller values of the peak heat release rate and total heat release than the uncoated one. Characterizations of burning behaviors of all fabrics in vertical configuration revealed that the nanobrick wall coating obviously decreased the burning time, thoroughly eliminated the afterglow phenomenon, and significantly enhanced the residue char left after burning. Moreover, the unique nanobrick wall coating provides an enhanced flame-retardant effect as compared to the PHMGP/APP, PHMGP/α-ZrP and APP coatings. The scanning electron micrograph and Fourier transform infrared spectra of the residue chars revealed that the excellent flame retardancy of the coated cotton was attributed to the catalytic charring of the intumescent component and the protection of the unique nanobrick wall as an reinforced barrier layer during burning.