Phase transition kinetics and rheology of gelatin-alginate mixtures

The present study reports systematic rheological data of binary aqueous mixtures of gelatin and alginate up to a concentration ratio of 1:1. The mixtures were prepared and rheologically studied with respect to the gelation point, melting point, and kinetics. The effect of the polysaccharide concentration on the sol gel and gel sol transitions is presented for concentrations up to 5% (w/w). Under small amplitude oscillatory shearing conditions, both transitions were shifted to higher temperatures. The kinetic study showed that the storage modulus will continue to increase in time under isothermal conditions, even if the rate of increase is considerably reduced. Furthermore, all binary gels exhibited a higher storage modulus than the pure gelatin gels at 5 degrees C. The increase was 9 and 24% for 5 and 2.5% gelatin, respectively. Assuming that the storage modulus is directly related to the amount of the triple helixes, all isothermal data could be successfully described by the kinetic gelation model proposed by Djabourov, Leblond, & Papon (1988a, 1988b). The excellent agreement between the rheological data and the gelation model confirm that this model can effectively predict the long-term elastic properties of the binary mixtures. Using isolated prototype modules, discrete gel specimens were formulated at 5 degrees C. Large amplitude oscillatory shear measurements (LAOS) showed that these specimens were still intact after the tests. The gels that were prepared directly on the rheometer plate exhibited strain hardening behavior during LAOS deformations. A nonlinear stress analysis of the Lissajous plots confirmed this finding. (C) 2016 Elsevier Ltd. All rights reserved.