Based on polyhexamethylene guanidine phosphate (PHMGP)/ammonium polyphosphate (APP)/PHMGP/potassium alginate (PA)-carbon nanotube (CNT)

a unique quadlayer (QL) hybrid organic-inorganic film is built via layer-by-layer self-assembly to protect cotton fabric from fire.Fourier Transform Infrared and Ultraviolet-visible Spectroscopy indicate that PHMGP

APP

PA and CNT respectively grow linearly during the assembly process.Insulation resistance measurement reveals that

because of the cross-linked CNT network formed in assembly coating on fiber

10 QL coating makes a decrease by orders of magnitude

from 1.8×1010 Ω·cm to 9.1×104 Ω·cm

in the electrical resistivity of cotton fabric

which implies that the electrical conductivity of cotton has been improved greatly.Characterizations of thermal and combustion behaviors for all fabrics show that QL coating performs an excellent flame retardant effect on cotton

which is stronger than that of PHMGP/APP bilayer coating (P/A).P/A coating has stronger catalytic effect on the thermal decomposition of the cotton with respect to the QL coating of equal weight.This can be confirmed by the lower T-5% and Tmax1.However

the QL coated fabric shows higher Tmax2 and more left residue as compared to the corresponding P/A coated fabric

indicating the formation of more thermally stable char by the combination of PA-CNT with PHMGP/APP intumescent system.With increasing quadlayers coated on fabric

the burning time reduces gradually

and afterglow phenomenon disappears as well.Additionally

the coated fabric also leaves more unburned area and residual char with intact structure after combustion.Undeformed fibers are observed in 10 and 20 QL after burning

and numerous small bubbles appear on their residual fiber surfaces

indicating the formation of abundant expansion char during burning.It can also be seen that CNTs in the residue form a cross-linking network char on the fiber surface.This cross-linked network inhibits the inflation of bubbles

in favor of the formation of multicellular char.Thus

the enhanced flame retardant effect of this QL assembly coating is attributed to the formation of intumescent network structure during burning by introducing PA-CNT network into PHMGP/APP intumescent coating.Fourier transform infrared spectra and X-ray photoelectron spectroscopy of the residue char further reveal that the enhanced flame retardant effect on cotton is attributed to the powerful cooperative heat barrier action of intumescent flame retardant coating and CNT physical barrier layer

which is formed on the surface of fiber during burning.