Understanding and Improving the Oil and Water Barrier Performance of a Waterborne Coating on Paperboard

[Image: see text] Using paperboard as packaging material is more sustainable than using plastic. To be a viable replacement, however, the barrier properties of paperboard need to be improved. Applying a waterborne barrier coating for both oil and water is an attractive method to improve the barrier performance of paperboard food packaging. However, not much is known about the oil and water barrier properties and penetration pathways of such coatings. Here, an alkali-soluble resin (ASR)-stabilized waterborne emulsion polymer was prepared and applied on untreated paperboard. Its performance as oil and water barrier coating was investigated, and the penetration pathways for both oil and water through the coating are discussed. The presence of surface defects in the coating applied on the paperboard strongly affects both the oil and water barrier properties, but the coating’s morphology and chemical nature only play a major role in the water barrier performance. The optimal barrier performance for oil and water was achieved when adding 5 wt % isopropanol (IPA) to the dispersion and applying two coating layers on paperboard. The IPA improves film formation and reduces the number of surface defects, which is explained by a more favorable spreading coefficient of the coating over the paperboard substrate. These insights will help to improve the oil and water barrier properties of polymer-coated paperboard for more sustainable packaging applications.