Use of calcium chloride to enhance the efficacy of polyamidoamines as flame retardants for cotton

The role of metal ions in improving the flame resistance of cotton prompted to investigate whether adding CaCl2 to the glycine-derived polyamidoamine M-GLY, an excellent intumescent flame retardant for cotton, increased its efficacy in this respect. Thermogravimetric analysis demonstrated a superior thermo-oxidative stability of cotton when treated with M-GLY/CaCl2 mixtures, particularly above 550◦C, compared to cotton treated with either MGLY or CaCl2, suggesting that they act synergistically. In horizontal flame spread tests, M-GLY/CaCl2 coatings proved to be even more efficient than M-GLY coatings. In vertical flame spread tests (VFSTs), where M-GLY failed to protect cotton even at add-ons >30%, M-GLY/CaCl2 coatings with add-ons 7% and 2%, respectively, inhibited cotton ignition producing only modest afterglow, and leaving an 82% residue. No other amino acid-derived polyamidoamine, except those containing disulfide groups, has proved as efficient in VFSTs, even at much higher add-ons. The set of data reported here prompts that the ionic interactions of calcium ions with the carboxylate groups of M-GLY induce the formation of even larger amounts of char compared to M-GLY and lets envisaging a synergistic action of these two components. This finding paves the way for the study of new polyamidoamine-based organic/inorganic flame retardants for cotton.