Effects of divalent metal ions on the flame retardancy and pyrolysis products of alginate fibres

Abstract Several different divalent metal ions have been incorporated into sodium alginate by ion exchange and the effects of divalent metal ions on the flame retardancy and pyrolysis products of divalent metal alginate fibres and alginic acid fibres have been examined. Various analytical methods were used. Results from thermogravimetric analysis (TG) indicated that barium ions, copper ions, and zinc ions induced formation of higher amounts of char than did alginic acid fibres. Limiting oxygen index (LOI) results indicated that the LOI values of divalent metal alginate fibres were higher than that of alginic acid fibres. Cone calorimetry (CONE) results showed that the heat release rate (HRR), total heat release (THR), and total smoke release (TSR) of divalent metal alginate fibres were lower than those of alginic acid fibres, suggesting that the incorporation of divalent metal ions into alginate fibres not only improved the flame retardancy, but also inhibited gas generation. Scanning electron microscopy (SEM) images of the residues after CONE indicated that the divalent metal alginate fibres produced denser, more consistent residues than alginic acid fibres did. The pyrolysis behaviour, tested by pyrolysis–gas chromatography–mass spectrometry (Py-GC/MS), showed that there were fewer main pyrolysis products produced by combustion of divalent metal alginate fibres than by combustion of alginic acid fibres, and that pyrolysis of the divalent metal alginate fibres was incomplete. A general mechanism for flame retardancy of divalent metal alginate fibres is proposed.