Kinetics of biopolymer gelation—Implications of a cascade theory description for the concentration, molecular weight, and temperature dependences of the shear modulus and gel time

The kinetic progress of biopolymer gelation is measured in terms of the shear modulus–time curve available from mechanical spectroscopy. Attention is focused on the gel time, and on the limiting value of the modulus attained at long time. A theoretical treatment of these quantities is presented based on cascade theory. This model can take on a reversible, or irreversible, form depending on differential equations defining the growth of the degree of cross-linking α(t), i.e., depending on whether a crosslink equilibrium is assumed or permanent branched crosslinking competes with irreversible intramolecular cyclization. Application of this model to limiting modulus–concentra- tion and modulus–temperature data is illustrated using results for a low DE pectin–calcium system. The model’s ability to explain modulus–molecular weight data is also demonstrated using literature data for kappa carrageenan gels. Where gel time–concentration data are concerned, success is much more limited, however, and this problem is discussed.