| In this project, our objective was to produce chitosan thermally reversible gels by non covalent interactions with different acidic solutions. In the first step, we tested various acids (organic and inorganic) varying their valence, their chain length and their chemical structure, aiming to explore gelation feasibility and explain it in terms of solution physicochemistry, and to select two systems (one potential food system and one for comparison). In the second step, parameters such as polymer concentration, solvent concentration, counter-ion type, time and temperature have been examined to see their effect on gelation. Different techniques such as rheology, differential scanning calorimetry, pH-metry and polarizing optical microscopy were used to investigate gelation mechanisms.; Gelation kinetics were also explored at 10°C and a constant frequency (6,28 rad.s-1). It was found that it occurred in three steps: gelation incubation; rapid increase of G' , and a slow stage where G' reached equilibrium due to the molecular controlled diffusion. At the gel point, scaling laws derived from percolation theory gave a relaxation exponent n of 0,55 for chitosan-oxalic and chitosan-phosphoric gels. (Abstract shortened by UMI.)... |
