Thermogravimetric analysis, flame retardancy

Three flame retardants were compared in this study, namely, a brominated polycarbonate oligomer (58% bromine), a brominated polystyrene (68% bromine), and a brominated triaryl phosphate ester (60% bromine plus 4% phosphorus). These are described in Table I. Figures 1 and 2 compare the thermal stability of the brominated phosphate with commercial bromine-containing flame retardants by thermogravimetric analysis (TGA) and by differential scanning calorimetry (DSC). The brominated phosphate melts at 110°C and shows a 1% weight loss at 300°C. Brominated polycarbonate and brominated polystyrene are polymeric and are not as volatile at elevated temperatures as the monomeric flame retardants. 

Figure 1. Thermogravimetric Analysis (TGA) of Brominated Flame Retardants - 10°C/min. under nitrogen...

Application of difiFerential thermal analysis and thermogravimetric analysis techniques to the pyrolysis of cellulose is obviously complicated by the complexity of the reactions involved, and the corrections and simplifying assumptions that are required in calculating the kinetic parameters. Consequently, these methods provide general information, instead of accurate identification and definition of the individual reactions (and their kinetics), which are traditionally conducted under isothermal conditions. The data obtained by dynamic methods are, however, useful for comparing the efiFects of various conditions or treatments on the pyrolysis of cellulose. In this respect, the application of thermal analysis for investigating the effect of salts (and flame retardants in general) on the combustion of cellulosic materials is of special interest and will be discussed later (see p. 467). 

The fact that flame retardants and salts alter the kinetics, as well as the products, of the pyrolysis reactions is confirmed by the investigations of Tang and Neil involving thermogravimetric and differential thermal analysis methods (see Section 11,6 p. 446). These investi-... 

Figure 3 shows a thermogravimetric analysis performed on the two molding compounds. The scans show that the molding compound based on the stable bromine CEN has a 15-20°C increase in thermal degradation temperature over the standard compound. Even though the stable bromine CEN is more thermally stable than standard resins, it still supplies the bromine necessary to achieve the desired flame retardancy properties. 

Several Co2 +, Sn2 +, Pr3 +, Cu2 +, Cu1 +, and Fe3+ compounds were used for flame retardation of epoxy-based polymers 176). Zarkhina et al.177) have shown that Mn2 +, Cr3 + and Ce3 + compounds reduce the temperature of initiation of the thermooxidative decomposition of the same polymer by 80-100 °C, but the rate of the decomposition itself is lower than that of the unmodified polymer. Thermogravimetric and differential thermal analysis have shown that Men+ have no influence on the thermal decomposition of the polymer in the absence of an oxidative atmosphere. 

As a resnlt of this and further studies by thermogravimetric analysis (TGA), solid-state NMR and electron probe microanalysis, Dabrowski and co-workers [27] conclude that melamine polyphosphate is an efficient flame retardant additive in polyamide-6,6 (glass fibre reinforced or not). The glass fibres are shown to strongly inflnence the fire performance of the intumescent FR material. A reactivity between the additive and the glass fibre and the formation of alumino-phosphates was demonstrated. These species might be responsible for the improvement of the FR behaviour particularly in the conditions of the LOI test. 

Wang and co-workers [105] studied the thermal degradation of flame-retarded PE-magnesium hydroxide-PE-co-PP/elastomer composites using thermogravimetric analysis. 

Backus and co-workers [1] investigated the thermal degradation in air of rigid urethane foams by thermogravimetric analysis (TGA), differential thermal analysis (DTA), infrared (IR), and other techniques. Three commercial foams were studied a polyether urethane foam 1, a flame-retardant polyether urethane foam 2, and a chlorinated polyester urethane foam 3 (Table 5.1). 

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