Rheological Characterization of Commercial Alginate Solutions With High Viscosity and Its Effect in the Production of Microparticles

The viscoelastic behaviour of high viscosity sodium alginate salts (NaAlg) is analysed through capillary, rotational and extensional rheometry. Alginate salts are commonly used as biopolymer in several applications i.e. scaffolds for tissue engineering, cell and drugs encapsulation or gelling agents in the food industry.

These polysaccharides are usually characterized from a known and invariable chemical composition. In this work we study commercial NaAlg samples, with slight chemical changes between batches but a general rheological behaviour. We found that the polyelectrolyte character of the samples affects the interaction between polymeric chains due to the variation of ionic strength in the lower concentration regime of solutions. However, free-salt behaviour holds for higher concentrations, showing a transition to a neutral polymer behaviour for the highest concentrations, as data from rotational rheometry points out.

We also examined thoroughly the extensional regimes suffered by medium-high viscosity concentrations after a controlled stretching process. The analysis of adimensional numbers (namely Ohnesorge, Elastocapillary and Deborah numbers) describing the different time and elasticity scales for the process enables us to predict the predominant extensional behaviour (inertia, viscous or elastic predominance).

Finally we studied the effects of this rheological behaviour in the destabilization and breakup of jets in order to produce biocompatible microparticles.