Enzymatic Reactions in Water Soluable Polymer Solutions: Rheology and Kinetics

Abstract

The polysaccharides are being used in a variety of applications because of their biocompatibility, biodegradability and natural abundance. The enzymes, because of their specificity, offer a powerful method to modify the structure of the polysaccharides. The structural modifications alter the interaction of the polysaccharides with other synthetic and biopolymers that determine the physiochemical properties of the polymer solutions. In this regard, we explore the use of enzymes to modify the rheology of solutions containing polysaccharides and thereby, understand the interrelationship between the enzymatic modification and the resulting rheological consequences.

In the first part of this research, we modify the structure of guar galactomannan using three glycosidase enzymes, β-mannanase, β-mannosidase and α-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 rheokinetic model combining a kinetic model with the viscosity-molecular weight relationship. The rheokinetic model is used to estimate the kinetic 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 this research, we focus on modulating the rheology of hydrophobically modified associative polymer that has a comblike 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 polymer solution. Although the hydrophobic interactions are important from the rheological standpoint; it is often desirable to modulate these interactions. This is achieved by adding cyclodextrins that encapsulate the hydrophobes within their hydrophobic cavity, and causes reduction in viscoelastic properties of the polymer solution. 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.