Xanthan properties

Rinaudo M., Milas M., Xanthan properties in aqueous solution, Carbohyd. Polyrrt, 2(4), 1982, 264-269. 

Xanthan Gum. As a result of a project to transform agriculturally derived products into industrially usefiil products by microbial action, the Northern Regional Research Laboratories of the USDA showed that the bacterium TCanthomonas campestris - noduces a polysaccharide with industrially usefiil properties (77). Extensive research was carried out on this interesting polysaccharide in several industrial laboratories during the eady 1960s, culminating in commercial production in 1964. 

Properties. Xanthan gum is a cream-colored powder that dissolves in either hot or cold water to produce solutions with high viscosity at low concentration. These solutions exhibit pseudoplasticity, ie, the viscosity decreases as the shear rate increases. This decrease is instantaneous and reversible. Solutions, particularly in the presence of small amounts of electrolyte, have exceUent thermal stabiHty, and their viscosity is essentially constant over the range 0 to 80°C. They are not affected by changes in pH ranging from 2 to 10. 

Health nd Safety Factors. The toxicological and safety properties of xanthan gum have been extensively investigated (82). On the basis of these studies, the EDA issued a food additive order in 1969 that allowed the use of xanthan gum in food products without specific quantity limitations. 

Uses. The unique properties of xanthan gum make it suitable for many appHcations for the food, pharmaceutical, and agricultural industries (79). 

Welan has similar properties to xanthan gum except that it has increased viscosity at low shear rates and improved thermal stabiUty and compatibihty with calcium at alkaline pH (90). The increased thermal stabiUty has led to its use as a drilling mud viscosifter especially for high temperature weUs. The excellent compatibihty with calcium at high pH has resulted in its use in a variety of specialized cement and concrete appHcations. 

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... 

Applications. The high heat tolerance and good salt compatibiUty of welan gum indicate its potential for use as an additive in several aspects of oil and natural gas recovery. Welan also has suspension properties superior to xanthan gum, which is desirable in oil-field drilling operations and hydraulic fracturing projects. It is compatible with ethylene glycol, and a welan—ethylene glycol composition that forms a viscous material useful in the formulation of insulating materials has been described (244). 

Xanthan gum [11138-66-2] is an anionic heteropolysaccharide produced by several species of bacteria in the genus Aanthomonas A. campestris NRRL B-1459 produces the biopolymer with the most desirable physical properties and is used for commercial production of xanthan gum (see Gums). This strain was identified in the 1950s as part of a program to develop microbial polysaccharides derived from fermentations utilizing com sugar (333,334). The primary... 

Commercial locust bean gum is the ground endosperm of the seeds of the locust bean (carob) tree. The general properties of locust bean gum are similar to those of guar gum. Differences are its low cold-water solubiUty and its synergistic gelation with kappa-carrageenan, furceUaran, and xanthan... 

The unusual properties of xanthan undoubtedly result from its stmctural rigidity, which in turn is a consequence of its Linear, ceUulosic backbone that is stiffened and shielded by the trisaccharide side chains. The conformation of xanthan in solution is a matter of debate. It does appear that the conformation changes with conditions. 

Microcrystalline ceUuloses ate marketed under the trade name Avicel. The physical characteristics of microcrystalline ceUuloses differ markedly from those of the original ceUulose. The ftee-flowiag powders have particle sizes as smaU as 0.2—10 p.m. Avicel ceUuloses coated with xanthan gum, guar gum, or carboxy-methylceUulose to modify and stabilize their properties are also available. The Avicel products are promoted for use ia low calorie whipped toppiags andiciags andia fat-reduced salad dressiags and frozen desserts (see Fat substitutes). 

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. 

The intermolecular interactions stabilise the helices and greatly influence the properties of exopolysaccharides in solution, ie solubility, viscosity and gel-formation. A strong interaction or good-fit between molecules will lead to insolubility, whereas poor interaction will lead to solubility of exopolysaccharides. The interactions between molecules is influenced by the presence of side-chains. For example, cellulose is insoluble but introduction of a three monosaccharide side-chain into the cellulose chain gives the soluble xanthan. Small changes in the structure of the side-chains can alter the molecular interactions and thus properties of the exopolysaccharide. 

Xanthan does not in itself form gels, despite the strong intermolecular interactions which occur in solution. However, some of the rheological properties of xanthan have... 

Xanthan has some unique properties and high activity at low concentrations and is commercially the most important exopolysaccharide. Food products account for approximately 60% of xanthan use, 15% is accounted for by toothpaste, textiles and crop protection products, 10% in the oil industry and the remainder in miscellaneous industrial/consumer applications. 

Xanthan gum is the most important exopolysaccharide used commercially, its unique properties making it ideal for an extraordinary range of applications Table 7.5. 

Several new exopolysaccharides such as welan and rhamsan produced by Alcaltngettes spp may supercede xanthan for some industrial applications. These are based on the same repeat tetrasaccharide backbone of glucose, glucuronic acid, glucose and rhamnose but differ in the substituents rhamsan has a disaccharide side chain and welan a monosaccharide. Both are stable at high temperature and have excellent pseudoplastic properties. 

H. Liu and Y. Zhang. Rheological property of the xanthan biopolymer flooding systems. J Univ Petrol, China, 19(4) 41-44, August 1995. 

Milas, M. and Rinaudo, M., Investigation on conformational properties of xanthan in aqueous solutions, in Solution Properties of Polysaccharides, Brant, D. A., Ed., ACS Symp. Ser., No. 150, American Chemical Society, Washington, D.C., 1981, 25-30. 

Sato, T., Norisuye, T., and Fujita, H., Double stranded helix of xanthan dimensional and hydrodynamic properties in 0.1 M aqueous sodium chloride,... 

Milas, M., Rinaudo, M., and Tinland, B., Comparative depolymerization of xanthan gum by ultrasonic and enzymic treatments. Rheological and structural properties, Carb. Polym., 6, 95, 1986. 

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... 

Oleaginous bases consist of vegetable oil thickened with agents such as aluminum monostearate, colloidal silica, and xanthan gums. The lubricant properties of the oil make these formulations less adhesive than water bases. 

Stabilizing agents are used to maintain drilling fluid rheological properties at highly elevated downhole temperatures. Chromium and chromium-free lignosulfonates, polyglycol ethers, sodium polystyrene sulfonate-co-maleic anhydride), and a melanin polymer have been used in this application. Additives such as sodium diethyldi-thiocarbamate have been used to stabilize aqueous polysaccharides such as xanthan gum (18). 

Both nonionic and anionic surfactants have been evaluated in this application (488,489) including internal olefin sulfonates (487, 490), linear alkylxylene sulfonates (490), petroleum sulfonates (491), alcohol ethoxysulfates (487,489,492). Ethoxylated alcohols have been added to some anionic surfactant formulations to improve interfacial properties (486). The use of water thickening polymers, either xanthan or polyacrylamide to reduce injected fluid mobility mobility has been proposed for both alkaline flooding (493) and surfactant enhanced alkaline flooding (492). Crosslinked polymers have been used to increase volumetric sweep efficiency of surfactant - polymer - alkaline agent formulations (493). 

Xanthan has several undesirable properties. It ordinarily forms microgel particles that can plug permeability(137), it is expensive relative to other natural polysaccharide gel agents, and it resists degradation by ordinary gel breaker additives. These features have kept xanthan applications in fracturing gels to a minimum. Some literature(138) on xanthan has appeared. 

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