Pigment loading level effects on water barrier properties in barrier coating formulations, TAPPICon25

To create moisture vapor barrier papers, barrier coatings can be formed on paper using dispersion coating methods. These coatings consist of latexes and pigments to enhance the barrier coatings in terms of barrier properties, cost efficiency, and blocking tendency, for example.1 These formulations aim to reduce the permeability of the coatings by creating tortuosity and improving the uniformity of the coating.2 Models predict that vapor permeability decreases with increasing pigment volume concentration (PVC).3 In practice, continually increasing the PVC in dispersion coatings does not yield continuous improvement and may even lead to an effective decrease in barrier properties.4 Questions remain regarding the origin of this discrepancy between experiments and theory for latex and pigment based barrier coatings.BR>
The shape and nature of the pigments have been indicated as the origin of this deviation.5 Additionally, hydrophilic surfactants in the latex have been also suggested to reduce the moisture barrier by creating channels for water diffusion in the coating.6 To explore these effects of additives on barrier properties, we synthesized latexes using surfactants and through a Pickering emulsion method using montmorillonite (MMT). These latexes were compared in coating formulations. Coatings with MMT, with and without surfactants, demonstrated a PVC where a minimal water vapor transmission rate (WVTR) was observed such that increasing PVC led to worse barrier properties. This behavior was attributed to the formation of a percolating network of hydrophilic pigments in the coating allowing for water diffusion along the surface of the MMT pigments.

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