Thermal analysis of ammonium, mono-, di- and triethanolammonium alginates

Thermal behaviour of ammonium (NH(4)alg), mono- (MEAalg), di- (DEAalg) and triethanolammonium (TEAalg) salts of alginic acid (Halg) was investigated by thermogravimetry (TG) and differential scanning calorimetry (DSC). Salts were prepared by the direct reaction of alginic acid with the ammonium hydroxide and with the respective ethanolamines. After preparation the compounds were lyophilized during 24 h and characterized by FTIR spectroscopy and elemental analysis (C, H and N). Under air the compounds exhibited three successive thermal decomposition steps: dehydration, decomposition of the polymeric matrix and finally, burning of carbonaceous residue. Under nitrogen two steps (dehydration and decomposition) were observed. The stability order of this series of compounds was: TEAalg this series of compounds was: TEAalg < DEAalg < NH(4)alg < Halg approximate to MEAalg. DSC curves between -50 and 150 degrees C did not show any thermal events suggesting that after lyophilization probably non-freezing type water is present in the system.