Xanthan gum solution

Solutions of welan are very viscous and pseudoplastic, ie, shear results in a dramatic reduction in viscosity that immediately returns when shearing is stopped, even at low polymer concentrations (230). They maintain viscosity at elevated temperatures better than xanthan gum at 135°C the viscosity half-life of a 0.4% xanthan gum solution is essentially zero, whereas a welan gum solution has a viscosity half-life of 900 minutes (230). The addition of salt to welan solutions slightly reduces viscosity, but not significantly. It has excellent stabiUty and theological properties in seawater, brine, or 3% KCl solutions... 

In addition to the normal problems of completely dissolving particles of water-thickening polymers, xanthan gum contains insoluble residues which decrease polymer injectivity. Various methods of reducing insolubles content and improving xanthan solution injectivity are available (80—87). None appears economically viable. Oxygen scavengers (88) and bactericides (77,89) are commonly used to stabili2e injected polyacrylamide and xanthan gum solutions (90—102). 

Prepare a 1% solution of xanthan gum with the inclusion of a preservative. Slowly add the vegetable gum to water and stir until thoroughly hydrated. Add the calcium carbonate, followed by the amphoteric surfactant, the nonionic surfactant and the xanthan gum solution. 

A.W. Chow and G.G. Fuller, Response of moderately concentrated xanthan gum solutions to time-dependent flows using two-color birefringence, J. Rheol., 28, 23 (1984). 

The basic assumption of the impeller viscometer approach is that the shear rate constant is independent of the rheologic properties of the fluid. This assumption allows the helical impeller viscometer to be calibrated using Newtonian and non-Newtonian fluids. The calibration results for guar and xanthan gum solutions ranging in concentration from 0.5 to 1.5% produced a single value of k = 10.8, which is sufficient to represent all the data. 

Pastor, M. V., Costell, E., Izquierdo, L., and Duran, L. (1994). Effects of concentration, pH and salt content on flow characteristics of xanthan gum solutions. Food HydrocoU. 8 265-275. 

A heteropolysaccharide (xanthan gmn) vehicle also prodnces longer ocular surface contact time and has been incorporated into a once-daily timolol gel formulation (Falcon gel-forming). Twenty-one minntes after instillation, 12% of a reference solution, 25% of the xanthan gum solution, and 39% of Gelrite solution remain on the ocnlar snrface (see Figure 2-8). 

Figure 7-7 Estimated Oral Shear Rates by Cutler et al. (1983) are Indicated by Circles. Closed circles are of xanthan gum solutions the dotted line represents the middle of the curve determined by Shama and Sherman (1973).

The viscosity of xanthan gum solutions is increased in the presence of ceratonia. This interaction is used synergistically in controlled-release drug delivery systems. 

Xanthan gum is a stable material. Aqueous solutions are stable over a wide pH range (pH 3-12), although they demonstrate maximum stability at pH 4—10 and temperatures of 10-60°C. Xanthan gum solutions of less than 1% w/v concentration may be adversely affected by higher than ambient temperatures for example, viscosity is reduced. Solutions are also stable in the presence of enzymes, salts, acids, and bases. 

The viscosity of xanthan gum solutions is considerably increased, or gelation occurs, in the presence of some materials such as ceratonia, guar gum, and magnesium aluminum silicate. This effect is most pronounced in deionized water and is reduced by the presence of salt. This interaction may be desirable in some instances and can be exploited to reduce the amount of xanthan gum used in a formulation see Section 7. 

Xanthan gum solutions are stable in the presence of up to 60% water-miscible organic solvents such as acetone, methanol, ethanol, or propan-2-ol. However, above this concentration precipitation or gelation occurs. 

The USPNF 23 also includes a monograph for xanthan gum solution. A specification for xanthan gum is contained in the Food Chemicals Codex (FCC). 

Rochefort, W.E. Middleman, S. Relationship between rheological behavior and drag reduction for dilute xanthan gum solutions. In Drag Reduction in Fluid Flows Techniques for Friction Control, Sellin, R., Moses, R., Eds. Ellis Horwood West Sussex, U.K., 1989 69-76. 

We have already mentioned that xanthan gum solutions are tolerant to both acids and bases. Solutions of xanthan gum also have excellent compatibility with many surfactants, water-miscible solvents, and other thickeners. As an anionic polysaccharide, xanthan gum is most stable with anionic surfactants (up to 20% active), nonionic surfactants (up to 40% active), and amphoteric surfactants (up to... 

FIG. 5.17 Viscosity as a function of pH for xanthan gum solutions at 0.2 and 0.5% solids. (Reproduced with permission from CP Kelco ApS, Copyright 2004, CP Kelco, San Diego, CA.)... 

The number of passes required through an orifice to form a well-dispersed solution depends on the polymer concentration. The reservoir characteristics are needed for the final design of the orifice mixing system. Details of mixing of xanthan gum solutions were presented in an earlier study (7). ... 

The xanthan gum solutions that are filtered prior to aging do not lose their viscosity to an appreciable extent over a period... 

The viscosities of xanthan gum solutions can be maintained quite well for 6 or 8 months if the solutions are mixed properly and filtered prior to aging. The degradation affects the injec-tability of these solutions rather than the viscosity. 

In the capillary viscometer, the slip phenomena can also be observed due to inhomogenous flow (Cohen and Metzner, 1986 de Vargas et ai, 1993). Therefore, the influence of the slip phenomenon must be considered when analyzing the data. In the case of 0.2% xanthan gum solution, the slip velocity is an increasing function of the wall shear stress and also of the length to diameter ratio UD. However, the slip velocity becomes independent of UD at large UD (de Vargas et ai, 1993). 

Xanthan gum solutions are remarkably resistant to thermal degradation. 

Exposure to temperatures as high as 80 C for extended periods has little effect on the viscosity of xanthan gum solutions. This resistance to thermal degradation is enhanced by the presence of... 

Xanthan gum will dissolve in acids such as 5% acetic acid and remain stable for several months unless the temperature is elevated. Also, xanthan gum is soluble directly in 5% sodium hydroxide solutions. Sodium hydroxide solutions of 0-15% can be thickened, provided the gum is pre-dissolved in water prior to adding the sodium hydroxide solution. These highly alkaline, thickened solutions have exceptional viscosity stability. Water miscible compounds such as ethanol are compatible with xanthan gum solutions up to concentrations of 50%. Solutions, emulsions, and gels that contain xanthan gum have excellent freeze-thaw resistance and many applications in the food industry. 

Drag reduction of xanthan gum solutions is greatly reduced at high salt concentrations [Rochefort and Middleman, 1987]. From their rheological measurements, Rochefort and Middleman concluded that the xanthan molecules underwent a transition from a highly extended semiflexible coil with disordered backbone structure, to a collapsed, semirigid rod with an ordered backbone structure at high salt concentrations. 

Garcia-Ochoa, F.F., and Gomez, E. (1998), Mass transfer coefficient in stirred tank reactors for xanthan gum solutions, Biochemical Engineering Journal, 1(1) 1-10. 

Suaysompol, K. Effects of ionic species on turbulent drag reduction of xanthan gum solutions. M.S. Thesis Arizona State University (1983). 

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