Rheology and Thermotropic Gelation of Aqueous Sodium Alginate Solutions

Abstract

In this work, we present the evaluation of the thermotropic gelling ability and steady-state rheology of aqueous sodium alginate (NaAlg) solutions. NaAlg is been considered due to its gelling capabilities and to determine its suitability as a film-forming agent with the potential capacity for immobilization of very potent, solid, and hydrophobic drugs. The existence of a thermally induced gelation of 1.0 to 2.5 wt.% sodium alginate solutions between 13°C to 22°C was demonstrated through three independent rheological tests: the constant-stress temperature-ramp viscosity, dynamic viscoelastic moduli, and thixotropy tests. Oscillatory dynamic tests also showed the thermoreversible nature of the NaAlg gels, but a large hysteresis between the gel formation and the gel melting was observed. The steady-state viscosity was experimentally determined as a function of shear rate for NaAlg concentrations between 1.0 to 2.5 wt.% and for temperatures from 20°C (or above T gel ) to 90°C. A viscosity master curve was constructed by applying time-temperature superposition and a semi-empirical shift factor for concentration. A power-law fluid modeladjusted to the data from 20°C to 60°C and found to provide good agreement with fitting parameters k=4.81 and n=−0.449±0.003.

Shaken flasks by resonant acoustic mixing in the biosynthesis of alginate by Azotobacter vinelandii with non‐Newtonian rheological characteristics

“…We found the ratio to be close to 1 most of the time, which indicated that the epimerases functioned throughout the culture time. Similar values can be found in the literature . However, at the highest shaking frequency of 20 g the M/G ratio varied a lot, as we observed a larger standard deviation, probably indicating the widest variety of monomer distribution at that growth stage.…”

Effect of electrostatic interactions on the ultrafiltration behavior of charged bacterial capsular polysaccharides

“…[10][11][12][13][14] The thermodynamic and hydrodynamic properties of these charged polysaccharides are quite complex, with significant changes in molecular conformation, degree of entanglement, and rigidity in different ionic strength solutions. 15 For example, Florian-Algarin and Acevedo 16 showed that aqueous solutions of sodium alginate undergo thermally induced reversible gelation at concentrations between 1 and 2.5 weight percent, with a large hysteresis between gel formation and melting.…”

Alginate gelling process: Use of bivalent ions rich microspheres

“…According to the available data in literature, the gelling process, for the Mg 2+ /alginate system, does not occur due to the weak polymer‐ion interactions ; in this study, a stable Mg 2+ /alginate gel was achieved using a solvent/nonsolvent system to collect the microspheres.…”