Their efficacy, particularly of divalent ions, is ascribed to their Lewis acid-basic strength, on which the ability to stabilize specific reaction intermediates depends. On the other hand, it is well- known that several polyamidoamines obtained by reacting natural a-amino acids with N,N’-methylenebisacrylamide through an environment-friendly process, that is, in water solution and at room temperature, act as flame retardant of cotton. Their action is due to their ability to activate during oxidation the formation of an expanded char, or intumescence, on cotton at temperatures from 350 to 500°C, protecting it from combustion.

This premise prompted to study the effect of the addition of CaCl 2 to the glycine-derived polyamidoamine coded M-GLY, an excellent intumescent flame retardant for cotton. Thermal analyses demonstrated a superior thermo-oxidative stability of cotton when treated with M-GLY/CaCl 2 mixtures, particularly above 550°C, compared to cotton treated with either M-GLY or CaCl2, suggesting that they act synergistically.

In horizontal flame spread tests, M-GLY/CaCl 2 coatings are even more efficient than M- GLY coatings. In the severe vertical flame spread tests, where M-GLY failed to protect cotton even at very high concentrations, M-GLY/CaCl 2 coatings with low amounts of both components inhibited cotton ignition producing only modest afterglow. No other amino acid-derived polyamidoamine, except those containing disulfide groups, has proved as efficient in vertical flame spread tests.

The proposed mechanism of action is 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. This finding paves the way for the study of new polyamidoamine- based organic/inorganic flame retardants for cotton.

Read the full article