RHEOLOGICAL PROPERTIES OF ALGINATE GELS

Rheological properties of alginate gels formed in various ways were studied using a parallel plate viscoelastometer and an Instron. All the gels studied exhibited linear viscoelastic behaviour. The creep compliance-time response was fitted by a model consisting of a Maxwell element in series with two or three Kelvin-Voigt elements. Despite the fact that alginate gels are non-thermoreversible the crosslinks do not appear to be permanent. Gels formed with an alginate containing a high proportion of mannuronic acid residues are weaker and more elastic than gels prepared with an alginate predominantly composed of guluronic acid residues. When the level of calcium in the gel was high, the reciprocal of the creep compliance was proportional to the square of the polysaccharide concentration. A reduction in calcium level for a given polysaccharide concentration resulted in a more elastic gel. The nature of the temperature dependence varied with the degree of crosslinking and time of measurement after application of stress. The results were explained by assuming that the creep compliance could be regarded as the sum of two components: a time independent factor given by the theory of rubber elasticity, or some modification of this, and a time dependent factor associated with the breakage of crosslinks.