Thermogravimetric analysis study of the mechanism of pyrolysis of untreated and flame retardant treated cotton fabrics under a continuous flow of nitrogen

Abstract

Samples of unmodified cotton fabrics and cotton fabrics finished with various flame retardant treatments at commercial levels of application were subjected to thermogravimetric analysis in a continuous flow of nitrogen. The relative thermal stabilities of the fabric samples were investigated using various heating rates. Each sample was found to give a characteristic TG curve with three distinct regions. This could be interpreted as an indication of the decomposition occurring in three stages, viz. dehydration, volatile evolution (with char formation) and char removal. All the flame retardant treatments lowered the temperature at which volatiles first appeared. Attempts were made to calculate Arrhenius parameters for the volatile evolution processes using a technique developed at Salford. It was found that fabric samples treated with the commercial condensed phase active-flame retardants, namely ammonium polyphosphate (Amgard TR, Albright and Wilson Ltd) a phosphonopropionamide (Pyrovatex CP, Ciba-Geigy Ltd) and a phosphonium salt-urea-polycondensate (Proban CC, Albright and Wilson Ltd) raise the activation energy compared to that of the untreated cotton fabric. Volatile evolution probably occurs via three-dimensional diffusion. Cotton fabrics treated with the commercial vapour phase-active flame retardants ammonium polyphosphate-ammonium bromide (Amgard CD, Albright and Wilson Ltd) and an antimony(III) oxide-aliphatic bromide (Flacavon, Shill and Seilacher) yielded TG curves which were too complex for simple interpretation.