Gums, like starch and cellulose, are carbohydrate polymers. They differ from them in that the monomeric unit may be a sugar other than glucose, and the chemical configuration and the way in which the units are joined are different. The molecular weight of gums is usually between 200,000 and 300,000, that is, about 1500 monomer units. Guar is a typical gum. It consists of a chain of mannose units joined by 1,4-glycosidic linkages, and attached to every other
mannose unit is a pendant galactose unit.
Source Rheology Modifiers
Plant seeds Guar gum, locust bean gum
Seaweed extracts Alginates, carrageenan, agar
Tree exudates Gum arabic, karaya gum, gum tragacanth
Citrus fruits Pectin
Animal skin and bones Gelatin
Fermentation Xanthan gum
Each gum has characteristic properties slightly different from other gums. Frequently, the commercially important differences lie in the rheological properties of the dispersions of the gums in water. Gums may be chemically modified just as cellulose is, and the most useful derivatives are carboxymethyl, hydroxypropyl, and dimethylaminoethyl gums.
The applications of gums are wide. Guar gum is the most important and may be considered typical. It has many times the thickening power of starches and may be used in combination with them. Its derivatives are useful in flocculation for precipitating mineral slimes and as a suspending agent for ammonium nitrate that not only leads to a much cheaper explosive than dynamite or nitroglycerin but also to one that is more effective, because it assumes the shape of the cavity where the blast is to start.
Carboxymethyl guar gum is an anionic material useful as a print gum paste. This means that it serves as a binder for a pigment used to impart colour and design to cloth. In contrast, diethylaminoethyl guar gum is cationic and is used in paper manufacturing. It is a particularly effective flocculant of “fines,” the very fine cellulose particles in the paper matrix, onto which it adsorbs. By helping to retain the “fines,” it increases the yield of product and, since fewer “fines” are in the water that drains from the machine, the pollution problem is diminished. Guar itself strengthens the paper by hydrogen bonding to the fibers and helping them achieve a linear rather than a random configuration.