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 th e shear modulus-time curve available from mechanical spectroscopy. Att ention is focused on the gel time, and on the limiting value of the mo dulus attained at long time. A theoretical treatment of these quantiti es is presented based on cascade theory. This model can take on a reve rsible, or irreversible, form depending on differential equations defi ning the growth of the degree of cross-linking alpha(t), i.e., dependi ng on whether a crosslink equilibrium is assumed or permanent branched crosslinking competes with irreversible intramolecular cyclization. A pplication of this model to limiting modulus-concentration and modulus -temperature data is illustrated using results for a low DE pectin-cal cium system. The model's ability to explain modulus-molecular weight d ata is also demonstrated using literature data for kappa carrageenan g els. Where gel time-concentration data are concerned, success is much more limited, however, and this problem is discussed. (C) 1995 Society of Rheology.