Montmorillonite pigment effects on the water barrier properties of paper coated with latexes synthesized through surfactant and Pickering emulsion methods

Pigments are often added to improve the barrier performance of dispersion coatings on paper, but they only are beneficial up to a limited pigment volume concentration (PVC). In this study, the use of montmorillonite (MMT) as pigment was explored in latex emulsions synthesized using surfactant and Pickering emulsion methods to explore the origins of this limitation. MMT was used to synthesize dispersion coatings for paper consisting of poly (styrene-co-butylacrylate) latex and compared with those synthesized using sodium dodecyl sulfate (SDS) surfactant. The Pickering, surfactant, and commercial coating systems with MMT decreased the water vapor transmission rate (WVTR), reaching minimum values at 1.2 %, 2 %, and 0.4 % PVC, respectively. At higher PVC values, the WVTR of all systems increased, which was attributed to the MMT pigments creating pathways for water transport. Moreover, similar pore volumes were found in all the latex films, indicating that the decrease in barrier properties as PVC increased was not caused by pore generation. The hydrophilicity of the MMT pigment was found to contribute to the observed minimum and lower barrier properties with increasing PVC. This work demonstrates that addition of pigments to the latex can be beneficial to improve paper barrier properties up to a certain level beyond which the pigments form percolation networks along the interfaces between MMT and the polymer, reducing the barrier properties.