Starch-based bio-latex redistribution during paper coating consolidation

Starch-based bio-latex has been widely studied for the purpose of partially substituting petroleum-based latex as coating binder due to its environmental-friendly and sustainable natures. To engineer coating structure, it is essential to understand the bio-latex distribution during coating layer drying. In this work, bio-latex concentration at the surface and along the thickness direction of model coatings on a non-absorbent film consolidated under various conditions was detected with ATR-IR, ESCA and Cryo-SEM techniques in order to understand whether bio-latex redistribute during coating drying and how the migration occurs. The results showed that bio-latex particles moved differentially with respect to kaolin clay pigment toward the coating surface and accumulated at surface during the initial liquid drying period, however, they deprived from coating surface in the end and aggregated at the top region of coating layer. A mechanism was proposed to explain this unexpected finding, which was attributed to the sphere-like morphology with nano or submicron size and highly hydrophilic, water-swollen natures of starch-based bio-latex binder. The small-sized bio-latex particles migrated to the surface due to their higher Brownian mobility relative to pigment initially, and in the later drying stage would move back into the coating pores with water because of its water affinity as the air-water interfaces receded from the surface into the capillaries.