Effect of manganese and cobalt ions on flame retardancy and thermal degradation of bio-based alginate films

Abstract

Bio-based cobalt alginate and manganese alginate films were prepared by a facile ionic exchange and casting approach. Their flame retardancy, thermal degradation, and pyrolysis properties were investigated by vertical burning (UL-94), limiting oxygen index (LOI), thermogravimetric analysis, microscale combustion calorimetry (MCC), thermogravimetric analyzer coupled with Fourier transform infrared analysis (TG–FTIR), and pyrolysis–gas chromatography–mass spectrometry (Py–GC–MS). It showed that cobalt alginate film had much higher LOI value (45.0 %) than those of manganese alginate film (30.7 %) and sodium alginate film (24.5 %). Moreover, cobalt alginate film passed UL-94 V-0 rating, while manganese alginate and sodium alginate films showed no rating. Importantly, peak of heat release rate of cobalt alginate and manganese alginate in MCC test was much lower than that of sodium alginate, suggesting that the addition of cobalt ion and manganese ion decreases the release of combustible gases. TG–FTIR and Py–GC–MS results indicated that cobalt alginate and manganese alginate produced much less gaseous products than that of sodium alginate. Finally, a possible thermal degradation mechanism of cobalt alginate and manganese alginate had been proposed. The results provided useful information for understanding flame-retardant mechanism of alginate as well as for designing bio-based materials with excellent fire-retardant properties.