Thermal Decomposition Kinetics of Polyamide 6 Composites containing Sulphur- and Phosphorus-based Flame Retardants

The thermal degradation behaviour and degradation kinetics of polyamide 6(PA6) composites containing guanidine sulfamate–based flame-retardant systems were investigated using thermogravimetric techniques. Thermogravimetric (TG) and derivative thermogravimetric (DTG) measurements were performed in air at a constant heating rate of 10 °C min^-1 to evaluate degradation pathways, decomposition rates, and char-forming behaviour. The incorporation of flame-retardant additives alters the degradation pathway of PA6 by initiating early decomposition while enhancing thermal stability at elevated temperatures through improved char development. The GS–DP system exhibits effective condensed-phase action, with maximum char formation achieved at an OH:S ratio of 0.92, whereas the addition of montmorillonite reduces char yield due to its catalytic influence on polymer degradation. In contrast, the GS–OP system shows the most effective flame-retardant performance, producing the highest char residue through the combined action of condensed-phase stabilization and gas-phase inhibition. Thermal degradation kinetics was evaluated using model-based Coats–Redfern, Broido, and Horowitz–Metzger methods applied to single-heating-rate TG data. Kinetic analysis indicates that the degradation of PA6 and its composites follows a first-order reaction mechanism, with reduced activation energy values for flame-retarded systems reflecting facilitated yet controlled degradation that favours efficient char formation. Overall, the results demonstrate that flame-retardant formulation and its influence on degradation kinetics play a critical role in improving the fire resistance of PA6 composites.