Polysaccharides solubility behavior

Some polymers such as poly(acrylic acid) or polyacrylamide precipitate from aqueous solutions when cooled (normal solubility behavior) whereas others such as poly(ethylene oxide), poly(propylene oxide), or poly(methacrylic acid) phase separate when heated (inverse solubility behavior). Solution turbidimetiy is often used to obtain plots of phase-separation temperatures termed cloud point vs concentration for fixed solvent conditions. Changes in ionic strength, molecular weight, and addition of co-solvents or structure breakers affect the shapes of phase behavior curves. The important conclusion of such studies is that the total free energy of the polymer and water must be considered to predict phase behavior. The structin-e and dynamics of water surroimding polynucleotides, proteins, polysaccharides, and lipids are also major determinants of biological activity (8-10). 

The various groups of pectic substances are usually characterized by their solubility behavior. Polygalacturonides, like other polyuronides, can be quantitatively estimated by the amount of carbon dioxide formed upon heating with hot acid. Pectic substances of all sorts have been commonly determined by the formation and weighing of water-insoluble pectic acid or calcium pectate but unfortunately it is difficult to get these precipitates free from impurities (particularly other polysaccharides) present in the material analyzed. Today, the most common method of estimation is the spectrophotometric measurement of the colored complex formed upon the addition of alcoholic carbazole to the material to be analyzed after alkali treatment and heating with concentrated sulfuric acid. ... 

As the unsubstituted polysaccharides are rarely stable in solution, soluble derivatives must almost invariably be used, and a study of the unavoidable degradation accompanying the preparation of such derivatives is also essential. The use of soluble derivatives may not be entirely satisfactory as there is the possibility that linear natural polymers might aggregate in solution (compare the behavior of certain synthetic polymers, e.g., polyvinyl chloride24). A similar effect may occur in the presence of... 

A large number of molecular weight measurements have been made on glycogens from various sources. The natural material, in contrast to the behavior of starch fractions, appears to be stable in aqueous solution, and measurements have been made on the unsubstituted polysaccharide as well as on soluble derivatives. 

Polymers that have been suggested for mobility control in oil reservoirs include polyacrylamides, hydroxy ethyl cellulose, and modified polysaccharides which are produced either by fermentation or by more conventional chemical processes. In this paper the solution properties of these polymers are presented and compared for tertiary oil recovery applications. Among the properties discussed are non-Newtonian character for different environmental conditions (electrolytes and temperature), filterability, and long term stability. The behavior of these water soluble polymers in solution can be correlated with the effective molecular size which can be measured by the intrinsic viscosity technique. A low-shear capillary viscometer with a high precision and a capability of covering low shear rates (such as 10 sec - - for a 10 cp fluid) has been designed to measure the viscosities. The measurement of viscosities at such slow flow conditions is necessitated... 

Although pectins are not employed as thickening agents, pectin solutions exhibit the non-Newtonian, pseudoplastic behavior characteristic of most polysaccharides. As with solubility, the viscosity of a pectin solution is related to the molecular weight, DE, and concentration of the preparation and the pH and presence... 

Tara gum is the galactomannan obtained from the seed of Tara shrub, Caesalpinia spinosa, mostly found in northern Africa and Peru of South America. The main polysaccharide chain is formed of (1 4)-llnked 3-D-mannopyranosyl units, with single a-D-galactopyranosyl units attached with average three main chain units via (1 6]-linkages. Molecular weight of tara gum may fall between 300,000 and 1,000,000. It is 70% soluble in cold water and hydrated 100% at temperature above 80°C showing pseudoplastic behavior in solution. 

Gum arable is the gummy exudate obtained from Acacia trees in Africa, primarily in Sudan. It is a highly branched polysaccharide containing both neutral monomers and uronic acids covalently attached with proteinaceous fractions, rendering its excellent function as an extensively used emulsifier with molecular weight about 250,000. It is highly soluble, producing low viscosity solution even at 40% concentration. The solution shows Newtonian behavior with constant viscosity at different shear rates. 

Polymers belong to the group of macromolecular substances. They are comprised of one or several kinds of repeating units called mers interconnected with chemical bonds and ordered according to certain statistics. Some macromolecular substances are built from the low-molecular moieties, mutual arrangement of which can be hardly described by any statistics (for example humin substances). The latter should not be designated polymers . In other words, all polymers are macromolecular substances but not all macromolecular substances are polymers. In this chapter, we will deal almost exclusively with synthetic and man-made polymers. The important exceptions represent polysaccharides, especially cellulose and its derivatives. Cellulose is the most abundant organic polymer on the earth. The behavior of polysaccharides in many aspects resembles that of synthetic polymers. Polysaccharides are often chemically modified to adjust both their solubility and utility properties. Chemical modification of polysaccharides results in the specific class of natural/synthetic polymers. 

Amphoteric polysaccharides are challenging to formulate they can be soluble when cationic or anionic, but insoluble in their zwitterionic form. These polyglycans can also have complex chemistries in the presence of salts and surfactants. Salts can modify the pH at which amphoteric polymers become zwitterionic. Surfactant behavior is more complex. When the amphoteric polymer is cationic, it is incompatible with anionic surfactants... 

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