The Effects of Sodium Antimonate on the Flame Retardancy and Mechanical Properties of Thermoplastic Polyurethane Composites

Abstract

Thermoplastic polyurethane (TPU) is highly versatile yet inherently flammable, restricting its use in fire-safe applications. This study incorporates sodium antimonate (SA) into TPU via melt blending (0–10 wt%). Through a comprehensive suite of analytical techniques—including thermogravimetric analysis (TGA), Fourier transform infrared spectroscopy (FT-IR), universal testing, and cone calorimetry—the effects of SA on the various properties of the material were investigated. Quantitative analysis reveals that 10 wt% SA delivers the best flame retardancy, reducing the peak heat release rate by ~50% (from 605 to 310 kW/m2) and total heat release by ~40% (from 32 to 19 MJ/m2), while increasing the char residue from 9.84% to 13.89%. However, to retain mechanical robustness, the SA content must be capped at ≤5 wt%. This ensures that the material retains 30% of its fracture elongation and a tensile strength of 1.7 MPa; higher loadings cause severe embrittlement due to particle agglomeration. Mechanistically, SA acts via a dual-phase mode—promoting a dense insulating char layer in the condensed phase and quenching reactive radicals in the gas phase. These findings establish a practical balance between fire safety and mechanical performance, offering a clear guideline for the rational design of flame-retardant TPU composites.