Thermogravimetric study of water affinity of gelatin materials

Abstract

Gelatin materials in the form of thin films were prepared using film-forming gelatin solutions with pH value of 2.5–6.8; interaction of gelatin with water in the films and in the solutions was studied. Thermogravimetric analysis at temperature up to 200 °C was used to identify and characterize free and bound water present in dried films. To simulate the water–gelatin interaction and to interpret thermogravimetric data, quantum chemical calculations along with the studies on the films swelling were performed. For both free water and bound water, the parameters of thermal desorption process were found to be affected by pH of film-forming solution. The observed changes in content of free and bound water and in apparent activation energies of water thermal desorption may be attributed to the growth of the quantity of negatively charged groups in gelatin molecules upon pH increase and to the changes in film structure and water affinity resulting from the charged groups interaction. Thus, by varying pH of the solution, one may influence the affinity of the films with respect to water and change the properties and usability of gelatin materials.