Design and characterisation of bicomponent polyamide 6 fibres with specific locations of each flame retardant component for enhanced flame retardancy

Bicomponent filaments of polyamide 6 (PA6) were produced with core/sheath geometries containing aluminium diethyl phosphinate (AlPi), and/or a montmorillonite nanoclay located individually or together in the sheath or core. A characterisation protocol based on thermogravimetric analysis (TGA) under both flowing air and nitrogen and pyrolysis combustion flow calorimetry (PCFC) enabled the effects of AlPi, clay and atmospheric oxygen to be assessed on PA6 thermal degradation. Knitted fabrics were assessed for flammability by vertical strip testing, which demonstrated that the relative location of the clay and flame retardant has a significant effect on burning behaviour. Correlation of the TGA/DTG, PCFC and burning sample results were discussed in terms of the effects of the roles of atmospheric oxygen and flame retardant components on the thermal degradation of PA6, especially when located in the sheath. •Bicomponent PA6 filaments produced with flame retardant and clay in sheath or core.•Fibres characterised for tensile, morphological, TGA/DTG, PCFC, and flammability behaviour.•TGA of PA6 in air promotes char formation, influencing flame retardancy with AlPi/clay.•Superior flame retardancy obtained when both AlPi and clay present in sheath of filaments.•Combined condensed and gas phase action of AlPi in air together with clay determine FR properties.