Microporous transition metal phosphide flame retardant toughened PA6 composites with excellent thermal conductivity and ferroelectric response

Polyamide 6 (PA6) is a widely used engineering polymer with excellent mechanical and thermal properties. However, its inherent flammability, low thermal conductivity, and limited understanding of its nanomechanical and ferroelectric properties limit its engineering applications in high-performance composites. Herein, we fabricate a multi-functional PA6 composite with excellent flame retardancy, enhanced thermal conductivity, and improved ferroelectric response using Microporous Transition Metal Phosphides (MTMP). An optimal 3 wt% MTMP loading resulted in 83 % and 87 % improvement in the fire performance index and the flame retardancy index, respectively. Furthermore, a 30 % reduction in fire growth rate, a 67 % improvement in the smoke-to-heat release ratio, a 35.8 % increase in the LOI value, and a V-0 rating was achieved due to the enhanced radical quenching and condensed phase mechanism of MTMP. The thermal conductivity improved by ∼205 % and the maximum polarization of the composite reached 1.53 μC-cm⁻² at 200 Kv/cm. The average permittivity increased to 83.8 with an approximate capacitance of 14.8 pF at the least resistance of ∼1.63 GΩ due to the enhanced ferroelectric response resulting from the charge storage and field-induced phase switching effects of MTMP. A significant improvement in nanoindentation hardness and Young's modulus was obtained with a 129 % improvement in the bulk material tensile strength due to the physically restrictive topological polymer chain interlock mechanism. This study offers an important perspective on the development of multi-functional polymer composites with potential applications in the energy, electronics, aerospace, and automotive sectors.