Thermal decomposition of flame retarded formulations PA6/aluminum phosphinate/melamine polyphosphate/organomodified clay: Interactions between the constituents?

The aim of this article is to investigate the thermal decomposition in pyrolytic and oxidative conditions of a phosphorous flame retardant (combination of melamine polyphosphate and aluminum phosphinate: AlPi-MPP) alone as well as in combination with an organo-modified clay (o-MMT) and of polyamide 6 formulations containing these additives. The gases evolved during the decomposition have been analyzed using TGA-FTIR. A detailed condensed phase study has been carried out combining X-ray diffraction (XRD) analyses and 27Al, 31P and 13C solid-state nuclear magnetic resonance (NMR) measurements on samples heat treated at different characteristic temperatures. It is demonstrated that no reaction leading to the formation of new species between the additives or the additives and the matrix occurs. However, Lewis acid/base interactions are highlighted resulting in the catalytic decomposition of the components particularly under nitrogen. Under air, the combined action of oxygen and Lewis interactions leads to an even more catalyzed decomposition process. Mechanisms of thermal decomposition are proposed.