Different Way to Look at Surface Starch for Improved Film Formation and Barrier Properties, 2000 Papermakers Conference Proceedings

Francis Aloi, Ralph M. Trksak, Victor Mackewicz--Surface starches have traditionally been characterized by their Brookfield viscosity at a given solids, while coating additives are characterized by their rheology. Brookfield viscosity, however, is not indicative of actual viscosity in the size-press. It has been estimated that surface starch formulations are exposed to much higher shear rates at the size-press nip and extreme hydrodynamic forces. Unique surface starches based on hydrophobic starch esters, exhibit a pseudoplastic or shear-thinning rheology, similar to coating additives. The shear-thinning viscosity profile enables the starch to have a higher viscosity before and after contact with the size-press nip. This viscosity profile results in better runnability and improved film formation. Better film formation can be used to provide porosity reduction, improved printability, reduced overall starch pick up and improved opticals. Enhanced barrier properties, such as oil and grease resistance, can also be achieved. Recently, liquid polymers, based on a similar shear-thinning viscosity profile, have been developed.