Enzymatic reactions in water soluble polymer solutions: Rheology and kinetics.

摘要

The main objective of this research is to explore the use of enzymes to control the rheology of aqueous solutions containing polysaccharides and thereby, understand the interrelationship between the enzymatic modification and the resulting rheological consequences.; In the first part of the project, we focus on modifying the structure of guar galactomannan using three glycosidase enzymes, beta-mannanase, beta-mannosidase and alpha-galactosidase, at different combinations and proportions. We investigate the effect of synergistic hydrolysis by multiple enzymes in terms of viscosity reduction patterns during the hydrolysis reactions. We develop a mathematical model based on Michaelis-Menten kinetics to predict the changes in molecular weights and molecular weight distribution during the hydrolysis reaction. The model is evaluated using the molecular weight distribution data measured during the depolymerization of guar using beta-mannanase enzyme. We also develop a rheokinetic model combining the kinetic model with the viscosity-molecular weight relationship. The rheokinetic model is used to estimate the kinetics parameters by tracking changes in steady shear viscosity during the enzymatic reactions. The effects of the combined action of enzymes on degradation rates are quantified in terms of variation in rate constants and other model parameters.; In the second part of the project, we focus on modulating the rheology of synthetic polymer that is not biodegradable. Our approach is to modulate intermolecular interaction between the polymer molecules by adding cyclodextrins. The synthetic polymer used in this study is a hydrophobically modified associative polymer. The polymer has a comb-like structure with hydrophobic groups randomly attached to the polymer backbone. The intermolecular interaction between the hydrophobic groups forms a transient network resulting in the thickening of the solution containing them. The cyclodextrins encapsulate the hydrophobes, disrupts the network, and causes a reduction in viscosity and other viscoelastic properties. Subsequent degradation of the cyclodextrin using an amylase enzyme enables complete recovery of the original rheological properties. We develop mathematical models to study the thermodynamics of cyclodextrin-hydrophobe complexation and the kinetics of the enzymatic reactions. We show that the model parameters can be estimated by measuring changes in the rheological properties during the cyclodextrin-hydrophobe complexation and subsequent enzymatic degradation process. (Abstract shortened by UMI.)