AVICEL® RC-591 NF or a Colloidal Avicel is a modified microcrystalline cellulose product. It has a composition, on a dry basis, of 82-89% microcrystalline cellulose and 11-18% sodium carboxymethylcellulose, medium viscosity. It is a water-dispersible organic hydrocolloid that provides suspension stability in water based systems. When properly dispersed in water, the individual RC-591 powder particles disintegrate and form a dispersion of cellulose microcrystal aggregates. These aggregates are elongated solid particles that range in size from a few microns to a few tenths of a micron. At concentrations of less than 1% solids, Avicel RC-591 forms colloidal pseudoplastic dispersions; but at concentrations greater than 1%, thixotropic gels are formed.