Bismuth subcarbonate nanoplates for thermal stability, fire retardancy and smoke suppression applications in polymers: A new strategy

Bismuth subcarbonate ((BiO)2CO3·xH2O) nanoplate, a bismuth-containing layered nanomaterial, is successfully applied in improving fire safety properties of polymers for the first time. The introduction of (BiO)2CO3·xH2O (≤6.2 wt%) into poly(methyl methacrylate) (PMMA) matrix by in situ polymerization method enhances the thermal stability, flame retardancy and smoke suppression properties remarkably including increased onset degradation temperature (T0.1, by 58 °C) and mid-point degradation temperature (T0.5, by 24 °C), and decreased peak heat release rate, total heat release, toxic volatile organic products (VOP) and smoke density. Morphological studies of PMMA/(BiO)2CO3·xH2O nanoplate composites by Scanning electron microscopy (SEM) and Transmission electron microscopy (TEM) suggest that (BiO)2CO3·xH2O nanoplates are well dispersed in the PMMA matrix. Thermal decomposition behaviors investigated by Thermogravimetric analysis (TGA) and char analysis studied by Fourier transform infrared spectra (FTIR) demonstrate the catalytic charring effect of (BiO)2CO3·xH2O to PMMA matrix. Due to the char formation during degradation, the toxic VOP amount and smoke evolution from PMMA combustion are reduced. Meanwhile, thermal decomposition of (BiO)2CO3·xH2O can release carbon dioxide (CO2) and water, which was evidenced by thermogravimetric analysis/infrared spectrometry (TGA-IR) results. The (BiO)2CO3·xH2O nanoplates combines several flame-retardant strategies including the char formation, dilution effect of CO2 and water, and physical barrier effect, and thus enhance the thermal stability, flame retardancy and smoke suppression of PMMA/(BiO)2CO3·xH2O composites simultaneously.