Abstract

Background: Halogen free flame retarded Polyamide 6 and 66 are fibres and engineering plastics of great commercial interest. Therefore, an important amount of papers and data as well as technical solutions exist. Nevertheless, for further progress there is a lack of principal results.

Methods: Heats of combustion and degradation with their corresponding temperatures and residues were measured on polyamides and their flame retardants. Thermodynamic balances of heat and weight were established. They lead to chemical formulas, which have to be consistent with the balances. This procedure enables the description of degradation and the composition of residues and chars like aluminium phosphate, C3N4 graphite and graphite phosphorous pentoxide. Using the ideal gas equation the amount of evolved gases is estimated. Furthermore, thermodynamic theory can predict the expansion of intumescent flame retardants and indicate the existence of hydrogen bonds between polyamides and melamine cyanurate. Intumescent coatings, which are sprayed or painted on surfaces, are the most efficient flame retardants for devices with low area to volume ratios. Another advantage of intumescent flame retardants is to be seen in their foamed insulating char, which delays the time of failure of the fire protected building part.

Conclusion: The thermodynamic procedure allows the quantitative description of decomposition under fire and emphasizes the favourite position of intumescent flame retardants in the ranking of efficiency.

Keywords: Combustion, differential scanning calorimetry, extrusion, flame retardants, polyamide, thermodynamics.

Graphical Abstract