Effects of zinc-based flame retardants on the degradation behaviour of an aerospace epoxy matrix

Flame behaviour is a fundamental requirement for advanced aerospace composites. In this work, a commercial, low-viscosity epoxy system, typically used in liquid infusion composite processes, and its mixtures with three different zinc-based flame retardants (ZB, ZS, ZHS) at different weight percentages has been investigated by cone calorimetry and thermogravimetric analysis. Cone calorimetry has been performed to verify the flame retardancy effects induced by each filler composition. Nevertheless manufacturability issues require the evaluation of the rheological changes induced by filler on the unloaded matrix system. Rheological tests have been, therefore, performed to identify the maximum concentration of filler. Based on these results thermogravimetric tests have been performed to investigate thermal degradation kinetics of selected systems. The feasibility of Kissinger and Flynn-Wall-Ozawa method for the determination of characteristic degradation kinetics parameters has been evaluated and results were analysed. A simplified decomposition model was assumed to analyse epoxy degradation behaviour; it was found that this model gives appreciable matching with experimental TGA curve trend for neat epoxy whereas for the filled compounds additional stages were assume to occur.