Influence of mass transfer on gelation time using VIPS-gelation process for chitin dissolved in LiCl/NMP solvent—Modelling and experimental study

A non-isotherm mass transfer model is developed for gelation of chitin induced by non-solvent. The system studied in this paper concerns chitin dissolved in LiCl/N-methyl-2-pyrolidone (NMP) at different concentrations ranging from 0.5 to 5% (w/v), and the water as the non-solvent. The gelation is induced by the absorption of water vapours using the vapour induced phase separation (VIPS)-gelation process. The model incorporates coupled heat and mass transfer and due to the very low chitin concentration involved, binary diffusion within the solution was assumed using temperature- and composition-dependent mutual diffusion coefficient. The model was validated using experimental data of gravimetric measurements. The experiments were conducted in a fabrication chamber with controlled process parameters (RH, temperature and air flow conditions) at different chitin concentrations in the initial solution and two temperatures (20 °C and 40 °C). The numerical results were in good agreement with the experimental data, therefore the model has no adjustable parameter for fitting the curves. Then the model was used to predict the composition of the chitin solution at the gelation time, in order to investigate the influence of the non-solvent intake and the solvent extraction involved in the gelation mechanisms. The gelation time was determined by rheological measurements. Results exhibit that the temperature has a great impact on the gelation time through the chitin chains mobility, the interchain association and the mass transfer kinetics. Furthermore, the critical solvent quality that induces the gelation was shown to be correlated to the chitin concentration in the initial solution. Moreover, the chitin chemical structure does not influence the mass exchanges, but the gelation time is reduced using a chitin source characterized by a higher molecular weight and a higher degree of deactylation.