Enhancing the flame resistance of cotton by exploiting the interaction between calcium chloride and an aspartic acid-derived polyamidoamine

In this work, the ability of Ca2+ ions to enhance the efficacy of the aspartic acid-derived polyamidoamine M-ASP as a flame-retardant of cotton was investigated. M-ASP bears two carboxyl groups per repeat units that are negatively charged at all pH's and can ionically interact with Ca2+ ions. Moreover, IR analysis confirmed that Ca2+ ions form Lewis's acid/base interactions with the amide groups of M-ASP. Thermogravimetric analysis demonstrated that Ca2+ ions improve the thermal and thermo-oxidative stability of cotton treated with M-ASP. The observed effect was greater than previously observed for cotton treated with glycine-derived polyamidoamine M-GLY, which bears only one carboxyl group per repeat unit. In horizontal flame spread tests, M-ASP/CaCl2 protected cotton more efficiently than M-ASP. The effect of Ca2+ ions on cotton/M-ASP was greater than on cotton/M-GLY, both in terms of higher residue and reduced flaming and afterglow combustion times. In vertical flame spread tests, while M-ASP failed to stop cotton combustion, M-ASP/CaCl2 coatings with add-ons 12% and 2%, respectively, inhibited cotton ignition, producing modest afterglow, and leaving an almost intact mass. The efficacy was greater than that of M-GLY/CaCl2 coatings, for which 19% M-GLY add-on was required. These findings demonstrate that the interaction of Ca2+ ions with the cotton/alpha-amino acid-derived polyamidoamine systems remarkably improves their flame retardancy, to an extent depending on the PAA chemical structure. The high hydrophilicity of M-ASP/CaCl2 and the low add-on adopted allowed obtaining pleasant to the touch coatings and did not noticeably change the hand of the fabrics compared to untreated cotton.

Automated summary

This study investigates the enhancement of cotton flame retardancy through the interaction between Ca2+ ions and aspartic acid-derived polyamidoamine (M-ASP). The presence of Ca2+ ions improves the thermal stability of cotton treated with M-ASP, surpassing the efficacy of glycine-derived polyamidoamine (M-GLY). Horizontal flame spread tests demonstrate that M-ASP/CaCl2 provides better protection for cotton compared to M-ASP, and the effect of Ca2+ ions on cotton/M-ASP is greater than on cotton/M-GLY. In vertical flame spread tests, M-ASP fails to stop cotton combustion, but M-ASP/CaCl2 coatings with low add-ons inhibit cotton ignition and leave almost intact mass.