Galactomannans viscosities

Anionic galactomannans, which are derived from guar gum, in which the hydroxyl groups are partially esterified with sulfonate groups that result from 2-acrylamido-2-methylpropane sulfonic acid and l-allyloxy-2-hydroxypropyl sulfonic acid [1872], have been claimed to be suitable as thickeners. The composition is capable of producing enhanced viscosities, when used either alone or in combination with a cationic polymer and distributed in a solvent. 

Two fundamental properties determine much of the behavior of polymers the molecular weight and the conformation (molecular shape). Because of the very high viscosities of even dilute solutions of galactomannans, determinations of the molecular weight are technically difficult. 

Robinson, G., Ross-Murphy, S. B., and Morris, E. R. (1982). Viscosity-molecular weight relationships, intrinsic chain flexibility, and dynamic solution properties of guar galactomannan. Carbohydr. Res. 107 17-32. 

The viscosities of solutions of xanthan, unlike those of all other water-soluble polymers, do not decrease as the temperature is raised. They are unaffected by temperature between 0 °C and 100 °C. And even though it is an anionic polymer, its solution viscosity is not affected by pH or most salts, i. e., although ionic, it behaves as if it were a neutral gum. Xanthan interacts synergistically with guar gum and locust bean gum (both galactomannans) (O Sect. 4.2). An increase in solution viscosity results from its interaction with guar gum. Heat-reversible gelation results from its interaction with locust bean gum. 

In an earlier work [27], several enzymes (lipase, hemicellulase, and protease) were shown to have noticeable effects on the viscosity of guar solutions. Guar typically contains more than 80% soluble galactomannans, 7% proteins, 2-3% fatty acids, and small amoimts of insoluble galactomaimans and cellulosics [28]. 

---