Thermal degradation of carboxymethylcellulose in different salty forms

Carboxymethylcellulose (CMC) salts in different counter-ion forms were obtained and characterized by FTIR, CP-MAS C-13 NMR and EDX spectroscopies. Additionally, thermogravimetry (TG) was used to evaluate the degree of humidity and the thermal stability. In general, CMC samples having Li+, Na+ and K+ as counter-ions showed a high hydrophilic character, absorbing more than 50% in weight of water, while for CMC having Mg2+, Ca2+, Ba2+ and others cations the hydrophilic character was lower than the former, absorbing less than 30% of water. All of the CMC salts showed lower thermal stability than their cellulose parent, Typical values of T-m, in degrees C, and E-a, in kJ mol(-1), were for cellulose: T-m = 349.11, E-a = 178.8 +/- 8.4; CMCK: T-m = 283.61, E-a = 152.9 +/- 1.0 kJ mol(-1); CMCCa: T-m = 305.67, E-a = 167.2 +/- 5.2 kJ mol(-1). Different kinetic models were found for the CMC salts as Sestak-Berggren, reaction order and Johnson-Mehl-Avrami. (C) 2009 Elsevier B.V. All rights reserved.