Aqueous solutions and gels of guar galactomannans (consisting of mannan backbone and galactose side groups in 2:1 ratio; see below) are used in a wide range of applications because of their natural abundance and ability to enhance viscosity in various systems. For instance, metal cross-linked guar gels are used as hydraulic fracturing fluids to create permeable channels for oil/gas flow. Subsequent to fracturing, these gels need to be degraded and their viscosity reduced so as to flush them out, leaving behind a highly permeable channel. Enzymes offer a novel and powerful way to tailor the kinetics and mechanism of the gel degradation process, thereby leading to enhanced oil/gas production. These enzymes can cleave the guar molecule at different sites (see below), giving rise to very different polymer structure. In this project, we are studying the kinetics and mechanism of enzymatic hydrolysis using rheology, size exclusion chromatography and confocal micsroscopy. Of particular interest is the correlation between molecular changes and macroscopic properties as a function of enzyme concentration and type (side chain vs. main backbone cleavage).

Our results reveal that:

guar degradation is dictated by a balance between enzyme activity and stability, with the -mannanase enzyme (main-chain cleavage) playing the most significant role in rheology modification.

polymer chain scission follows zeroth-order kinetics in contrast to existing theories on polymer degradation.

chain scission mechanisms for crosslinked gels and solutions are the same; however, the macroscopic behavior is different for the two systems.

blends of xanthan and enzymatically-modified guar exhibit a different mechanism of gel formation than previously hypothesized for these types of system.

in-situ modification of guar (in the presence of xanthan) leads to different blend rheology. This can be exploited in food processing to tailor food with novel functionalities.