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In order to improve the flame retardancy of knitted cotton fabrics and investigate the flame-retardant mechanism of the system formed by ammonium polyphosphate (APP) and chitosan (CS), flame-retardant knitted cotton fabrics coated with APP and CS were successfully prepared by layer by layer assembly. APP and CS formed the intumescent flame-retardant system, in which CS acted as the carbon source agent and APP acted as both the acid source and foaming agent. The surface micromorphologies before and after flaming of coated knitted cotton fabrics were exploited by scanning electron microscopy. The flammability, combustion behaviors, thermal degradation properties and flame-retardant mechanism of this system were investigated by vertical burning test, cone calorimetry test and thermogravimetric analysis coupled with Fourier transform infrared analysis in N2 atmosphere, respectively. Compared with the control sample, the deposition of APP and CS endowed the knitted cotton fabrics with improved flame retardancy, higher residual chars, lower heat release rate and total heat release, while increased the smoke production. Improved flame-retardant behaviors are attributed to the thermally stable residual chars, more release of inflammable gases and potential free radical scavengers (PO·) in the gaseous products, named the combination of the condensed-phase and gaseous-phase flame-retardant mechanism. [ABSTRACT FROM AUTHOR]

Highlights • We have rephrase the highlights:1.Fire retardant cotton fabrics were prepared based on APTES, chitosan and sodium phytate by LBL. • The addition of chitosan further improved the fire retardancy of coated cotton fabrics. • The deposition of APTES, chitosan and sodium phytate obviously reduced the release of inflammable gases, and increased the release of nonflammable gases. Abstract Chitosan was added to cotton fabrics coated with sodium phytate and 3-Aminopropyl triethoxysilane (APTES) to further enhance the fire retardant property by the layer-by-layer (LBL) assembly. The surface morphologies before and after flaming and structure of coated cotton fabrics were evaluated by scanning electron microscopy and Fourier transform infrared analysis. The thermal degradation properties, fire retardancy, and combustion properties of this system were investigated by Fourier transform infrared analysis, thermogravimetric analysis coupled with Fourier transform infrared analysis (TG-FTIR) in the N 2 atmosphere, the thermogravimetric analysis in air atmosphere, limiting oxygen index test (LOI), vertical burning test and cone calorimeter test, respectively. Sodium phytate, chitosan and hydrolyzed APTES were successfully deposited and well distributed on the surface of cotton fibers. The LOI value of the coated cotton fabric with 15BL was 29.0%, and it extinguished at once in the vertical burning test, while the coated cotton fabrics with 5BL and 10BL were burned out. The deposition of sodium phytate, chitosan and hydrolyzed APTES led to the decrease of heat release rate, total heat release, total smoke release and smoke production rate. The promoted fire retardancy was assigned to thermally stable residuals formed on the surface of cotton fibers, which prohibited heat/mass transfer from combustion zone to polymer degradation zone. TG-FTIR results indicated that flame retardant cotton fabrics produced more nonflammable gases (CO 2 and H 2 O) and less combustible gases than them of the control sample did, increasing flame retardant properties of flame retardant cotton fabrics. [ABSTRACT FROM AUTHOR]