Water Barrier Properties of Resin-Stabilized Waterborne Coatings for Paperboard

The replacement of plastic packaging by paperboard can significantly contribute to meeting sustainability goals in important application fields, such as in food packaging. The (water) barrier properties of paperboard-based products need, however, to be improved. Waterborne coatings offer an environmentally friendly possibility to enhance these barrier properties, which in turn highly depend on the coating chemistry and film formation. Here, the relation between the characteristics of a waterborne coating and its water barrier performance is investigated. A waterborne polymer dispersion is prepared by emulsion polymerization, using an alkali-soluble resin (ASR) as stabilizing agent. The ASR-stabilized dispersion is applied as a coating on paperboard. During this application, the carboxylate groups of the ASR are converted to uncharged carboxylic acids. The coatings are characterized by Fourier-transform infrared spectroscopy (FTIR), atomic force microscopy (AFM), and scanning electron microscopy (SEM), and the water barrier properties are evaluated by dynamic vapor sorption (DVS) and the Cobb method. It is found that the water barrier performance is dominated by the carboxylate concentration remaining in the film, which is dependent on the moisture content. High drying temperatures improve particle deformation and polymer flow during coating formation, but do not influence the water barrier performance.