Microcrystalline cellulose is a purified, naturally occurring fraction of cellulose, the most abundant natural polymer on earth. It is composed of anhydroglucose units linked together through a P (1-4) glycosidic bond (FMC Corp., 1993a). It is a hydrophilic, water insoluble, linear, high molecular weight polymer consisting of ordered, crystalline areas. In commercial colloidal grades and aggregrate grades, microcrystalline cellulose comprises 75 to 95% by weight of the composition. The remaining 5 to 20% is a soluble hydrocolloid, the type and level varying between different products, as shown in Table 7A.1. Sodium carboxymethyl cellulose, the soluble component in RC/CL colloidal grades, is an anionic water-soluble polymer derived from cellulose. The AC colloidal grades of microcrystalline cellulose are co-processed with calcium alginate, a structural polymer composed of mannuronic and guluronic acids, extracted from the cell walls of brown seaweeds (Imeson, 1994). RCN aggregrate grades are co-processed with guar gum, a galactomannan extracted from plant seeds and composed of a mannose backbone with galactose side-chains. In these co-processed products, the soluble hydrocolloids are associated with the microcrystalline cellulose by hydrogen bonds to give an integrated structure. Different products contain different levels and specific types of each hydro-colloid depending on the targeted application and desired properties.
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