Development of Eco-Friendly synergistic intumescent flame retardants for enhanced thermal stability and fire resistance of biomass TPU composites

Abstract

This study presents the development of a novel synergistic intumescent flame retardant (IFR) composed of tetraethoxysilane (TEOS) and bio-based chitosan (CS) as the carbon source, ammonium polyphosphate (APP) as the acid source, and melamine cyanurate (MCA) as the gas source. The novel TEOS/CS/APP/MCA (TCAM) IFR, which exhibited both reactive and coupling compatibility, was incorporated into biomass thermoplastic polyurethane (TPU) at varying loadings to fabricate TPU/TCAM composites. Comprehensive analysis and characterization demonstrated that the TPU composite with 20% TCAM loading exhibited superior flame retardancy and thermal stability. Vertical combustion tests (UL-94) revealed that TCAM incorporation eliminated melt dripping and enabled the TPU/TCAM 20% composite to achieve the highest V-0 rating, while the limiting oxygen index (LOI) increased significantly from 22% for neat TPU to 28%. Cone calorimetry test results indicated substantial reductions in the peak heat release rate, total heat release, and peak smoke production rate. Thermogravimetric analysis (TGA) revealed a remarkable increase in char residue from 0.52 wt% for pure TPU to 17.78 wt% for TPU/TCAM 20%, highlighting the formation of an expanded char layer that effectively served as a barrier in the condensed phase. Furthermore, TCAM demonstrated free radical quenching in the gaseous phase and synergistic flame retardancy, as confirmed by FTIR, TG-IR, SEM, XPS, and Raman spectroscopy analyses. This work verified the effectiveness of bio-based chitosan in enhancing the flame retardancy of biomass TPU, offering a high-performance and sustainable solution aligned with the principles of the circular economy.