Simplified structure of the condensed phase of fire retarded PA6 nanocomposites in TGA as related flammability

• Replacement of halogenated fire retardants is a burning issue.
• Alternatives such as nanoparticles and phosphinates are considered in this work.
• Fire retardancy and flammability is investigated by examining the mass residue during pyrolysis.
• The residue is examined by TGA, STDA and FTIR.

This paper concerns with the analysis of the nature of the mass residue of PA6 and its nanocomposites in nitrogen. To assess the structure of the condensed phase during pyrolysis, this study presents thermal (by TGA in nitrogen) and condensed phase analysis of the residue (by FTIR-ATR) of PA6 nanocomposites consisting of phosphorous based flame retardants (FR) and/or nanoparticles (based on modified Montmorillonite clay). The thermal analysis reveals that the nanoparticles do not change the pyrolysis kinetics of PA6 whereas the FR does. The FR and NC used in the polymer nanocomposites (PNC) are capable of changing the structure of the char compared with pure PA6, where the char structure consists of polycyclic aromatic hydrocarbons (PAH) whereas the PA6 does not leave any considerable amount of mass residue. This residue analysis for decomposition samples in TGA in Nitrogen of the PA6/FR/NC composites complements previously published work for gas phase analysis ( FTIR-gas) as well as cone calorimeter characterization for their flammability. The overall aim, addressed here also, is to find out to what extent microscale measurements (e.g. TGA/FTIR/DSC/ATR) can be used a priori to delineate the flammability of polymer fire retarded composites. It is shown that FTIR-gas and FTIR (ATR) residue can be used to determine the fire retardant action (solid and/or gaseous) only qualitatively.