A comparison of the thermal decomposition of preservatives, using thermogravimetry and rising temperature kinetics

The thermal behaviors of benzoic, sorbic and citric acids, which are three commonly used preservatives, were studied by thermogravimetry. The kinetic mechanisms of evaporation and/or decomposition in air and nitrogen were determined and compared. Benzoic acid completely evaporated via a zero-order kinetic mechanism. Sorbic acid partially evaporated by a zero-order kinetic mechanism, with the production of a transition compound. Citric acid decomposed to a transition compound by a combination of kinetic mechanisms. A majority of the process followed zero-order kinetic principles, with the evaporation of most of the sample. The activation energies of evaporation and the pre-exponential terms were calculated and compared. (C) 1998 Elsevier Science B.V. All rights reserved.