Xanthan dispersibility

Xanthan gum was shown to be stiffer than CMC and alginate all three are ionic polysaccharides, with CMC having slightly more flexibility than alginate under identical conditions (R. C. Clark, 1992). The invariant nature of xanthan dispersion properties is attributed to the stability of the tertiary structure. The indifference of this gum to salt is explained by its already rigid conformation (Morris, 1976). 

Random-coil polysaccharides make strong films, because they are given to a high incidence of long-life contact points for the same reason, they are good carriers of flavor. Notably, concentration had no effect on flavor release from a nongelling xanthan dispersion (Baines and Morris, 1988). 

Figure 4-42 Values of Yield Stress of Starch-Xanthan Dispersions Relative to those of the Starch-Water Dispersions (YSA SO) and Relative Mean Granule Diameters (D/DO) Plotted against Values of c[j) of Xanthan Gum waxy maize (WXM), cross-linked waxy maize (CWM), and cold water swelling (CWS).

Achayuthakan et al. (2006) studied vane yield stress of Xanthan gum-stareh dispersions. The intrinsic viscosity of Xanthan gum was determined to be 112.3 dl/g in distilled water at 25°C. In addition, the size of the granules in the dispersions of the studied starches waxy maize (WXM), cross-linked waxy maize (CWM), and cold water swelling (CWS) were determined. The values of yield stress of the starch-xanthan dispersions relative to those of the starch-water dispersions (YSA"S0) and relative mean granule diameters (D/DO) plotted against values of c[ ] of xanthan gum are shown in Figure 4-42. With the values of YS/YSO being less than 1.0, there was no synergism between CLWM starch and xanthan gum. 

Table 4-13 contains the static yield stresses of the xanthan dispersions in water (Column A), of the three starches in water (Column B) and their sum (Column C), and those of the mixed starch-xanthan dispersions (Column D). One can say that there is synergism between xanthan and starch if values in Column D are higher than those in Column C if they are lower, there is antagonism. From the table, it seems that WXM (except with 1% xanthan concentration) and CWS starches exhibited synergistic... 

The fact that the polymer dispersion coefficient is larger over a range of flow rates for the low-concentration xanthan/tracer floods is shown in Figure 7.4. In this low-concentration flood, the chloride dispersion coefficient is almost identical to the value found experimentally in the absence of polymer. Thus, it can be concluded that the presence of polymer, at least in low concentration, has no effect on the passage of the chloride (an inert tracer) through the tortuous pore space within the sandstone core. However, there is clearly an effect at play which causes the xanthan dispersion to be larger than that of the chloride. 

Dextran is soluble in water, but water-insoluble dextrans also exist. Dextran dispersions have lower viscosity in comparison with xanthan dispersions, but are relatively resistant to hydrolysis. 

Low molecular weight (1000—5000) polyacrylates and copolymers of acryflc acid and AMPS are used as dispersants for weighted water-base muds (64). These materials, 40—50% of which is the active polymer, are usually provided in a Hquid form. They are particularly useful where high temperatures are encountered or in muds, which derive most of their viscosity from fine drill soHds, and polymers such as xanthan gum and polyacrylamide. Another high temperature polymer, a sulfonated styrene maleic—anhydride copolymer, is provided in powdered form (65,66). AH of these materials are used in relatively low (ca 0.2—0.7 kg/m (0.5—2 lb /bbl)) concentrations in the mud. 

For products intended to remain stable dispersions for an extended period, a particle size of 2 p.m or less is desirable. A thickening agent is usuaUy added after the reaction has been completed and the mixture is cooled in order to prevent settling and agglomeration. Examples of thickeners are guar gum, xanthan gum, and hydroxyethylceUulose. The final products are generaUy between 40 and 50% soUds, with a viscosity of 1500 5000 mPa-s(=cP). 

Bacterial Cellulose. Development of a new strain of Acetobacter may lead to economical production of another novel ceUulose. CeUulon fiber has a very fine fiber diameter and therefore a much larger surface area, which makes it physicaUy distinct from wood ceUulose. Its physical properties mote closely resemble those of the microcrystalline ceUuloses thus it feels smooth ia the mouth, has a high water-binding capacity, and provides viscous aqueous dispersions at low concentration. It iateracts synergisticaUy with xanthan and CMC for enhanced viscosity and stabUity. 

For suspensions primarily stabilized by a polymeric material, it is important to carefully consider the optimal pH value of the product since certain polymer properties, especially the rheological behavior, can strongly depend on the pH of the system. For example, the viscosity of hydrophilic colloids, such as xanthan gums and colloidal microcrystalline cellulose, is known to be somewhat pH- dependent. Most disperse systems are stable over a pH range of 4-10 but may flocculate under extreme pH conditions. Therefore, each dispersion should be examined for pH stability over an adequate storage period. Any... 

This product dispersion should be uniformly mixed and levigated. Xanthan gum dispersion should be uniform and smooth. 

Add, in small quantities, the remaining half of magaldrate cake or powder and disperse well. Mix for 1 hour and then remove heat. (Adjust the speed of the agitator and of the homogenizer to maintain the mobility of suspension.) Separately blend silicon dioxide colloidal with xanthan gum and disperse the blend in glycerin, with constant mixing. 

Prepare Part A by slowly adding vegetable gum and xanthan gum to the water. Continue agitating until smooth dispersion is obtained. 

When a liquid dispersion contains non-adsorbing polymers there will be a layer of liquid surrounding each dispersed species that is depleted in polymer, compared with the concentration in bulk, solution. This causes an increase in osmotic pressure in the system compared with what it would be were the dispersed species absent. If the dispersed species move dose to each other then the volume of solvent depleted is reduced, reducing the overall osmotic pressure, which provides a driving force for flocculation. Xanthan gum, added in low concentrations, can cause depletion flocculation [291]. 

Ionization offers dispersed polyanions short-term protection from deposition through shielding with H30+ counterions. The hydration of xanthan is enhanced by its containing a charged, trisaccharide side-chain repeating unit (Sanofi, 1988). 

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