Dilute xanthan solution

Methods of analysis. The total protein concentration of crude solutions, including cellular proteins, was determin by the biuret method (72). With dilute xanthan solutions, this method was not sensitive enough, and a spectrofluorometric assay was carried out. This method consisted of an acid hydrolysis of the samples followed by derivatization with o-phthaldialdehyde and HPLC analysis on a Cl8 reverse column of the amino acids released, using spectrofiuorescence as the detection nKxie. 

In packed beds of particles possessing small pores, dilute aqueous solutions of hydroly2ed polyacrylamide will sometimes exhibit dilatant behavior iastead of the usual shear thinning behavior seen ia simple shear or Couette flow. In elongational flow, such as flow through porous sandstone, flow resistance can iacrease with flow rate due to iacreases ia elongational viscosity and normal stress differences. The iacrease ia normal stress differences with shear rate is typical of isotropic polymer solutions. Normal stress differences of anisotropic polymers, such as xanthan ia water, are shear rate iadependent (25,26). 

In this study we use electron microscopy (EM) to study xanthan strandedness and topology both in the ordered and disordered conformation. Correlation of data obtained from electron micrographs to physical properties of dilute aqueous solution on the same sample will be used to provide a working hypothesis of the solution configuration of xanthan. Electron micrographs obtained from xanthan of different origins will be compared to assess similarities and differences in secondary structure at the level of resolution in the used EM technique. 

The viscosity of xanthan solutions is also distinct from that of flexible polyelectrolyte solutions which generally shows a strong Cs dependence [141]. In this connection, we refer to Sho et al. [142] and Liu et al. [143], who measured the intrinsic viscosity and radius of gyration of Na salt xanthan at infinite dilution which were quite insensitive to Cs ( > 0.005 mol/1). Their finding can be attributed to the xanthan double helix which is so stiff that its conformation is hardly perturbed by the intramolecular electrostatic interactions. In fact, it has been shown that the electrostatic persistence length contributes only 10% to the total persistence length even at as low a Cs as 0.005 mol/1 [142]. Therefore, the difference in viscosity behavior between xanthan and flexible polyelectrolyte... 

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. 

Xanthan Solutions. Specimens of xanthan were obtained from Kelco Co. (Kelzan) and from Dr. P. Sandford, then at U.S.D.A. Northern Regional Laboratory, and were purified by the method described by Holzwarth. ( ) An aqueous stock solution containing V 0.5% xanthan was prepared by addition of distilled deionized water that had previously been filtered through 0.1pm Milllpore filters (to remove bacteria, dust, etc.). This solution was dialyzed for four days against filtered distilled deionized water. Other than for the first solutions used for the thermal studies, sodium azide (0.02%) was added to the stock solutions to retard bacterial growth. Solutions at different concentrations were prepared by dilution with 0.02% aqueous sodium azide. Preparations before and at different intervals after filtration were checked for possible bacterial growth by examination of shadowed specimens in a Jeol lOOB electron microscope. Bacterial cells were not seen in xanthan solutions that had been filtered through 0.22)im Milllpore filters these solutions remained sterile for over a month. 

The direct addition of protein-rich ingredients such as com steep liquor or yeast extract to xanthan solutions also affected the rheological behavior of both diluted purified solutions and concentrated broth solutions. Aggregation effects on macromolecules chains and thixotropy phenomena have been observed. These effects are greatly dependent on salt content, pH, and nature of proteins, whether these proteins were added to xanthan solution or came from the fermentation medium. 

After a preliminary analysis of the influence of the production mode on xanthan characteristics, this study was focussed on the effects of the origin and concentration of proteins on the state of aggregation of xanthan in solution estimated by rheological measurements. In a first while, purification treatments were applied to dilute polymer solutions in order to try to separate proteins from xanthan and thus to evaluate the amount and effect of proteins linked to the polysaccharide backbone. In the second phase of this study, the direct addition of proteins to dilute or concentrated xanthan solutions was analyzed, and the effects of salt, pH and origin of proteins were investigated. 

Viscosimetric determinations. The Newtonian intrinsic viscosity of the xanthan molecule was determined by measuring the viscosities of several dilute polymer solutions with a Contraves Low-Shear viscometer. Extrapolation at zero polymer concentration of the reduced specific viscosity gave the value of the intrinsic viscosity, and the Huggins constant was calculated from the slope of the curve. 

Addition to purified and diluted solutions of xanthan. For this study, it was necessary to prepare a non-aggregated xanthan solution which was obtained by extensive ultrafiltration of a commercial xanthan sample which was initially non-aggregated. The absence of aggregation was confirmed by the Huggins constant which was 0.4 and the intrinsic viscosity which was 6.7 m kg. This corresponds to a molecular weight of 4.8x10 daltons. This xanthan solution was adjusted at a polymer concentration of 0.4 g.l"l in a protein-rich solution such as com steep liquor (CSL). Before use, the com steep solution was centrifuged and only the clear supernatant was added to the xanthan solution. The solvent was 0.1 M sodium chloride and the ratio of protein to xanthan was 10% (w/w). 

Rheological measurements were performed on xanthan solutions prepared by dilution of broths, 48(X) CX, A, C or powder Rhodopol 23, adjusted at similar polymer concentrations (between 5 and 7 g.l ). The effects of the addition of a protein-rich solution and of other parameters such as salinity and pH were further investigated. 

Xanthan samples from four commercial manufacturers were studied in synthetic reservoir brines and a dilute NaCl solution. The samples included broth and powdered xanthan products. The weight-average molecular weight, M, for each sample was measured in the different solvents by low angle light scattering. was not affected by the brine composition, and no... 

Fig. 3. Filterability of dilute polysaccharide solutions (500 ppm active polymer) of xanthan gum broths.

A classic example is the master curve obtained for concentrated polystyrene solutions in n-butylbenzene (94). The method is also applicable for dilute aqueous solutions of poly(acrylamide), xanthan gum and poly(ethylene oxide). In the case of polyelectrolytes, the method gives satisfactory results only in limited concentration ranges. Further refinements have to be added to the general method (95). 

Sato, T., Norisuye, T., and Fujita, FI., Double-stranded helix of xanthan in dilute solution evidence from light-scattering, Polymer J., 16, 341, 1984. 

Xanthans from several different sources were used in this study Xanthan samples A, B and C were kindly provided as freeze dried powder of ultrasonic degraded xanthan by Dr. B. Tinland, CERMAV, Grenoble, France. The molecular weights of these samples were determined experimentally in dilute solution by Dr. B. Tinland. Xanthan D was kindly provided as pasteurized, ultrafiltrated fermentation broth by Dr. G. Chauveteau, Institut Francais du Petrole, France. Xanthan E was kindly provided as a freeze dried sample from Dr. I. W. Sutherland, Edinburgh, Scotland. Xanthan F was obtained as a commercial, powdered material (Kelzan, Kelco Inc., a Division of Merck, San Diego CA.). Xanthan G was obtained as a commercial concentrated suspension (Flocon 4800, Pfizer, New York, NY)... 

Almost every biological solution of low viscosity [but also viscous biopolymers like xanthane and dilute solutions of long-chain polymers, e.g., carbox-ymethyl-cellulose (CMC), polyacrylamide (PAA), polyacrylnitrile (PAN), etc.] displays not only viscous but also viscoelastic flow behavior. These liquids are capable of storing a part of the deformation energy elastically and reversibly. They evade mechanical stress by contracting like rubber bands. This behavior causes a secondary flow that often runs contrary to the flow produced by mass forces (e.g., the liquid climbs the shaft of a stirrer, the so-called Weissenberg effect ). 

Almost every biological solution of low viscosity [but also viscous biopolymers like xanthane and dilute solutions of long-chain polymers, e.g., carboxymethyl-cellulose (CMC), polyacrylamide (PAA), and polyacrylnitrile (PAN)] displays... 

Time constants based on molecular theories have been derived for rod hke and bead-spring models (Bird et al., 1977b Ferry, 1980). For example, Whitcomb and Macosko (1978) showed that the conformation of xanthan gum in solution is rod like with some flexibility. The bead-spring model has found extensive use in the literature on polymers. The development of molecular theory for dilute solutions of linear... 

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