Rheology Modifier
The water soluble polymer acts as a rheology modifier and water retention aid in paper coating formulations. Formulators use carboxymethyl cellulose to control the viscosity of aqueous suspensions, preventing the water from separating from the pigment particles. It is produced by reacting natural cellulose with monochloroacetic acid in an alkaline medium.
The use of this additive is restricted to aqueous systems where the pH remains alkaline.
Coating Performance
High-speed blade coaters subject the coating color to extreme shear rates that demand precise control over fluid behavior. When carboxymethyl cellulose is added to the formulation, the viscosity at high shear drops, allowing the coating to level out smoothly on the paper surface. This behavior prevents defects such as streaks and scratches on the finished sheet.
The presence of the polymer also keeps the water from migrating too quickly into the raw paperboard.
Binding Mechanism
Electrostatic repulsion and hydrogen bonding between the cellulose derivative and the pigment particles determine the stability of the mixture. The anionic charges on the polymer chains repel the negatively charged clay particles, keeping them suspended evenly throughout the mixture. This suspension ensures that the coating maintains a uniform density during storage and application.
