Viscoelastic Properties of Amylose-Amylopectin Gels

Abstract

The viscoelastic properties of aqueous gels of amylose, amylopectin, and their blends were investigated using three types of rheometers, which are able to cover more than 8 decades of frequency range.
The viscoe lastic behavior of aqueous gels of amylopectin can be explained by assuming reversible temporary cross-links with long relaxation times due to hydrogen bond and physical entanglements. Highly branched chains of amylopectin suppress the formation of three- dimensional networks and reduce the equilibrium elasticity of the gels.
On the other hand, amylose aggregates easily with each other. These aggregates are linked with other aggregates, and these cross-linked crystallites may contribute to the three-dimensional character of the network.
The slope of the logari thmic modulus vs. logarithmic concentration plot for amylose gels is as high as approximately 4.0, which corresponds to that for crystalline gels.
The maximum of retardation spectrum decreased with increasing conce ntration, irrespective of compositions in gels. With increasing concentration the maximum shifts to longer time for aqueous gels of amylopectin, whereas the maximum shifts markedly to shorter time for those of amylose-amylopectin blends. These phenomena were explained as follows: the presence of the amylose fraction restricts the relaxation mechanisms with longer relaxation times due to the relaxation of amylopectin fractions, which form highly branched chains but not three-dimensional networks.