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Polyester/cotton fabric swith blend ratios of 0/100, 11/89, 20/80, 30/70, 50/50, and 65/35 were investigated via thermogravimetric analysis in both nitrogen and air atmospheres. The samples were heated from ambient to 750°C at a heating rate of 5°C min −1 . The same fabrics were analyzed after treatment with tetrakis (hydroxymethyl) phosphonium chloride-urea-poly(vinyl bromide) (Thpc-urea-PVBr) flame retardant. Weight losses observed during pyrolysis were assigned to the cotton and polyester portions of the blends. Both cotton and polyester thermally decompose to yield gases and solid char byproducts. In nitrogen the 100% cotton fabric undergoes one major weight loss between 270 and 370°C, with the maximum rate of weight loss, 0.15 mg/min-mg occurring at 346°C. Thermal decomposition of the 100% polyester occurs over a range of 335–470°C, with the peak rate of weight loss, 0.11 mg/min-mg, measured at 416°C. In an air atmosphere, both volatile gases and solid char by- products of pyrolysis undergo combustion. The combustion reactions are associated with measured weight losses. The maximum rate of weight loss for the cotton portion increases to 0.25 mg/min-mg and occurs at 317°C. The maximum rate of polyester decomposition remains the same in both air and nitrogen, but the temperature decreases to 405°C.

Flame-retardant polyester/cotton fabrics are increasing in importance in the apparel and household fabrics market. Phosphorus-nitrogen flame-retardant systems developed for 100% cotton are not necessarily effective for polyester/cotton blends. Bromine effectively imparts flame-retardant properties of polyester resins. It has been theorized that systems containing both bromine and phosphorus should be suitable for polyester/cotton blends. A thermoanalytical study was undertaken to elucidate the effect of bromine in flame-retardant polyester/cotton blend fabrics. Fabrics having various ratios of polyester to cotton were treated with THPOHNH3, which is particularly effective on 100% cotton, and with THPC-urea-PVBr, which was designed for 50/50 polyester/cotton blends. For comparison, data are also presented on a 50/50 polyester blend fabric treated with THPOHNH3 and with THPC—urea flame retardants plus tris(2,3-dibromopropyl) phosphate in a two-step application. TG and DSC data were obtained in atmospheres of either nitrogen or air, using a DuPont 990 Thermal Analysis System2. The thermal changes are assigned to decompositions of cotton, polyester, char, and resin finish. A comparison is made of the effects caused by the different flame-retardant finishes. Ol values and FF 3-71 data are reported.