Enriched huntite as a green flame retardant: thermal and physical behaviors in polyurethane matrices

Abstract

Flame retardants are crucial for operational safety in strategic sectors such as aerospace, automotive, and electronics. However, traditional flame retardants pose significant environmental and health risks due to toxic gas emissions. Consequently, sustainable "green" alternatives like huntite have gained increasing attention. Huntite enhances the thermal stability of polymers through endothermic decomposition, releasing inert gases that suppress combustion without generating toxic byproducts. Polyurethanes (PU) are highly valued in industry for their mechanical strength and flexibility; however, their susceptibility to thermal degradation and structural instability at elevated temperatures restricts their broader application. To meet strict fire safety and performance standards, the development of heat-resistant, multifunctional PU composites is essential. This study investigates the interaction between the polyurethane matrix and the huntite mineral to evaluate its potential as an eco-friendly flame-retardant system. The structural interactions, dispersion behavior, and chemical properties of the resulting PU-huntite composites were systematically characterized using X-ray diffraction (XRD) and Fourier-transform infrared (FTIR) spectroscopy. Flotation-enriched huntite (85.9% purity, d80 = 46.86 µm) was successfully integrated into polyurethane films (optimized thickness of 200 µm) at loadings of 0.1, 0.3, 0.5, 1.0, and 3.0 wt.%. XRD analysis revealed the retention of the broad amorphous halo (2θ = 10°–25°) along with the emergence of the characteristic huntite reflection at 2θ = 31.8° at 3.0% loading. FTIR spectroscopy confirmed a purely physical incorporation through the appearance of the carbonate (CO32-) band at 870–880 cm-1 and overlapping bands at 1400–1500 cm-1, while the stability of the carbonyl (C=O) peak at 1730–1740 cm-1 confirmed that the polymer backbone remained unaltered. Furthermore, functional evaluations demonstrated that huntite incorporation substantially enhances the hiding power and opacity of the composite films, with the opacity value reaching 83.3% at the maximum 3.0% mineral loading. These findings validate that huntite not only serves as a promising sustainable flame retardant but also significantly improves the light-blocking performance of polyurethane matrices for advanced structural and protective coating applications.