Polyanionic Cellulose

Cellulose Basics

Cellulose is a naturally occurring fibrous material derived from wood or cotton that is insoluble in water. It is a linear polysaccharide composed of anhydroglucose unit (A.G.U.) linked through glycosidic bonds (1-4 ß Glycosidic linkages). The number of A.G.U.s in the polymer chain defines the Degree of Polymerization (D.P.) which corresponds to the length of the fiber. Each A.G.U. is characterized by three OH-groups -- potential sites for etherification.

Cellulose solubility can be altered by etherifying the reactive OH-groups with either chloroacetic acid or sodium chloroacetate to produce carboxymethyl cellulose (CMC). By controlling the reaction conditions, the degree of etherification can be regulated very precisely to achieve desired product properties.  The degree of etherification is defined as the degree of substitution (DS), corresponding to the average number of etherified OH-groups for the A.G.U.Polyanionic Cellulose (PAC) is chemically a carboxymethyl cellulose that is characterized by a high degree of substitution. Depending upon the starting cellulose raw material and the level of substitution, PAC is classified as premium quality or standard quality.

Polyanionic Cellulose Choices

Premium Quality Polyanionic Cellulose (PAC) is typically made out of cotton linters and is characterized by an extremely high degree of substitution to ensure effective fluid loss control properties, shale inhibition, and salt tolerance. It is useful for water-based drilling fluids as well as in low density brines.

Standard Quality PAC is usually made with a blend of cotton linters and wood pulp, and is characterized by more substitution than standard carboxymethyl cellulose, but less substitution than premium quality PAC. Standard quality PAC is appropriate for water-based drilling fluids, but Premium Quality PAC is a better choice for filtration control, salt tolerance, and shale inhibition.