Nanodiamond decorated phosphor-silicone thermally conductive PA6 composites with excellent flame retardancy, nanomechanical and thermo-pyroelectric response

Abstract

Polyamide 6 (PA6) is a widely used engineering polymer, valued for its mechanical strength and ease of processability. However, its inherent flammability, low thermal conductivity, and weak ferroelectric response restrict its applicability in advanced composite materials. In this study, a multifunctional PA6 composite was developed using phosphor-silicone decorated nanodiamonds (NDSiP), resulting in enhanced fire safety, improved thermal conductivity, superior pyroelectric response, and strengthened nanomechanical properties. The composite demonstrated a 40.7 % reduction in peak heat release rate (PHRR) and a 160 % increase in the flame retardancy index (FRI), achieving a V-0 rating and a limiting oxygen index (LOI) of 31.2 %. MD-ReaxFF simulations confirmed that the flame-retardant mechanism primarily occurred in the condensed phase, evidenced by a significant C–C peak shift towards 1.42 Å and 1.16 Å, corresponding to graphitic structure bond distances, induced by the presence of ND and oxidized phosphor-siloxane carbonaceous clusters. The thermal conductivity of the composites increased by 302 %, accompanied by substantial improvements in remnant polarization (0.208752 µC/cm2), switching polarization (0.72 µC/cm2), average permittivity (66.0), capacitance (19.5 pF), and resistivity (1.37 GΩ). Additionally, a notable enhancement in the pyroelectric coefficient (−∂P/∂T) was observed, attributed to the enhanced phase transition behavior of NDSiP within the PA6 matrix. Moreover, the composites exhibited exceptional heat dissipation capabilities, driven by the phonon heat transport effect of ND, making them suitable for thermal management applications. Significant improvements in nanoindentation hardness and Young's modulus were achieved, alongside a 123 % increase in tensile strength, highlighting the strong interfacial bonding between PA6 and NDSiP.