Degradation of a Water-Soluble Polymer:  Molecular Weight Changes and Chain Scission Characteristics

Abstract

Computer simulations in conjunction with molecular weight distributions, obtained from gel permeation chromatography (GPC), are used to obtain physical insights on the mechanisms of degradation of guar galactomannan, a naturally occuring polysaccharide. Two different modes of degradation, sonication and enzymatic hydrolysis, are compared. Both modes of guar degradation reveal similar features in terms of changes in molecular weights, a rapid reduction followed by a slow decrease. However, the molecular weight distributions are significantly different, with ultrasonication leading to a narrowing of the molecular weight distribution and enzymatic hydrolysis resulting in its broadening. Sonication of guar results in a random degradation of chains, so that all bonds have equal probability of cleavage. In contrast, enzymatic degradation does not follow any of the typical modes of chain scission (random, Gaussian, and central), indicating that enzymatic hydrolysis of guar does not obey a "single scission" pathway. Plots of the zero shear viscosity, η o, as a function of number-average molecular weight, Mn, show enzymatically degraded guar to possess a much higher viscosity compared to a sonicated guar, at the same Mn. This contrasts the behavior of zero shear viscosity, ηo, vs weight-average molecular weight, Mw, where both systems are identical despite the large differences in polydispersity. We infer that, for polydisperse systems, the steady shear rheological properties are not very sensitive to the entire molecular weight distribution and can be adequately described by Mw, the molecular weight average that is primarily controlled by the high molecular weight fraction.

Optimization of enzymatic hydrolysis of guar gum using response surface methodology

“…Partially hydrolyzed guar gum (PHGG) has attracted attention as a water-soluble dietary fiber as it shows physiological effects such as increasing defecating frequency and lowering the pH of feces of both healthy men and constipated women and reducing serum cholesterol, free fatty acid, and glucose concentrations in humans (Greenberg and Sellman 1998;Heini et al 1998;Trinidad et al 2004;Minekus et al 2005;Stewart and Slavin 2006;Yoon et al 2006). PHGG can be produced by enzymatic hydrolysis, acid hydrolysis, irradiation, microwave and ultrasonication techniques (Tayal and Khan 2000;Cheng et al 2002;Singh and Tiwari 2009;Gupta et al 2009a). For food applications, PHGG production is preferred using enzymes like endo-β-D-mannanase (Yoon et al 2008) and pectinase (Shobha et al 2005).…”

Fracturing fluid cleanup by controlled release of enzymes from polyelectrolyte complex nanoparticles

“…Tayal et al [55,56] applied gel permeation chromatography (GPC) to measure the molecular weight of the polymers during the degradation process. The GPC showed that average molecular weight decreases significantly during the degradation of guar while the molecular weight distribution broadens significantly.…”

“…Studying the enzymatic degradation of guar-borate hydrogel using β-mannanase, α-galactosidase and combination of both, Tayal et al [55][56][57] recognized three different degradation regimes in plots of rheological moduli ( G′ and G ′ ′ ) and the complex viscosity vs. frequency. They made their guar samples in water containing 0.5M sodium chloride and 0.05M sodium thiosulfate.…”

“…They indicated that both moduli curves vs. frequency shift down significantly by time. Tayal et al [55][56][57] also stated that the plateau region decreases over the time and disappears after the network is completely broken. After this point, G ′ ′ is higher than G′ and the system behaves as a solution.…”

“…The mentioned sites can be cleaved by endo-and exo-β-mannanase and α-galactosidase enzymes respectively. Tayal et al [55][56][57][58] indicated that insufficient α-D-galactosidase in an enzyme package results in short mannose chains, which cannot be degraded further because of steric hindrances from the galactose side chains. On the other hand, insufficient endo-β-mannanase results in unsubstituted mannose chains thus forming insoluble residues.…”