Papermaking is the largest non-food application for starches globally, consuming millions of metric tons annually. In a typical sheet of copy paper for instance, the starch content may be as high as 8 percent.
In the wet part of the papermaking process, typically cationic starches, which have a positive charge bound to the starch polymer, are used.
Cationic starches, together with other retention and internal sizing agents, help to give the necessary strength properties to the paper web formed in the papermaking process (wet strength) and to the final paper sheet (dry strength).
In the dry end of the papermaking process, the paper web is rewetted with a starch-based solution. The process is called surface sizing. Starches used typically are chemically or enzymatically de-polymerized at the paper mill or by the starch industry (oxidized starch).
Starch is also used in paper coating as one of the binders for the coating formulation, which is a mixture of pigments, binders and thickeners. Coated paper has improved smoothness, hardness, whiteness and gloss, and thus improves printing characteristics.
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