Flame retardance polymer degradation processes

Many phosphorous additives act as flame retardants in this way in hydroxyl containing polymers such as cellulose. During the polymer degradation process, phosphorus acids are produced which lead to char via phosphorylation and dehydration reactions. Relatively low quantities of phosphorus compounds are needed to impart a reasonable degree of flame retardancy. Several boron additives behave in a similar way by the promotion of carbonaceous char through esterification and dehydration reactions. 

Davies, R.D. Gilman, J.W. VanderHart, D.L. Processing degradation of polyamide 6-montmorillonite nanocomposites in Proceedings of the 13th Conference on Advances in Flame Retardant Polymers, Stamford, CT, 2002. 

TVA-FTIR allows method development for online detection and quantification of degradation products, as they are formed in the TVA experiment. Stevenson et al [944] have used TVA and SATVA as a platform for spectroscopic investigations of polymer degradation processes, as in case of PMMA and poly(bisphenol A, 2-hydroxypropylether). The kinetics of thermal and thermo-oxidative degradation and characterisation of the various degradation products of polystyrene alone and in the presence [949] of the flame retardant IDBP were investigated using TVA, FTIR and GC-MS. Other applications of TVA in problems in polymer chemistry have been reported [943,952]. The method is now near defunct. 

It might be assumed that, as condensed-phase flame retardants function by modifying the normal thermal degradation processes of polymers, they would also function as thermal stabilizers and that thermal antioxidant stabilizers would show flame-retardant properties. However, these statements are rarely the case, and to understand why, it is necessary to compare the mechanistic aspects of flame retardance as discussed earlier with those of thermal degradation and thermal oxidation as well, briefly alluded earlier, and in the case of the latter, the Bolland and Gee mechanism,17 in Scheme 2.1. 

In some cases, several of these processes occur simultaneously, depending on the sample size, the heating rate, the pyrolysis temperature, the environment, and the presence of any additives. Although polymer degradation schemes can be greatly altered by the presence of comonomers, side-chain substituents, and other chemical constituent factors, the ultimate thermal stability is determined by the relative strengths of the main-chain bonds. Many additives and comonomers employed as flame retardants are thermally labile and as a result the thermal stability of the polymer system is reduced. In order to reduce the observed effects of the flame-retardant additives on the thermal stability of the polymeric materials, more thermally stable and hence inherently flame-resistant polymers are of increasing interest. 

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