Film Formation Mechanism of Aqueous Polymer Particle Dispersions for Barrier Coating Applications

Dispersion coatings are promising barrier solutions for fiber-based packaging. Among the advantages of water-borne dispersion coatings are easier repulping, recyclability, and composting of fiber packaging compared to other types of coatings. Dispersion coatings can replace fluorochemicals, which pose health hazards in food packaging. The film formation mechanism is the basis for developing barrier dispersion coatings, as a flawless coating structure is a prerequisite for good barrier properties. However, developing cost-efficient dispersion coatings with good film formation properties combined with good barrier and converting properties remains challenging. In this work, we implement atomic force microscopy (AFM) imaging in air and water to study the film formation mechanisms at the nanoscale of a series of styrene-acrylic copolymer barrier dispersion coatings with different surfactant/stabilizer systems and correlate these findings with the barrier properties of the coatings determined by common methods. In particular, AFM is used to characterize the morphology of the films prepared under different conditions, illuminating the effect of both the core polymer chemistry and stabilizing system on film formation. The relationship between the film morphologies and barrier properties of the coatings is subsequently revealed. In addition to AFM, another surface-sensitive technique, quartz crystal microbalance with dissipation monitoring (QCM-D), is used to evaluate the interaction of the dispersion coating particles with cellulosic substrates. The significant impact of the chemical structure of the stabilizer system of the dispersion on the barrier properties of coatings is unraveled by using this approach. Overall, this work reveals the predictive capacity of the AFM technique for evaluating the barrier properties of dispersion coatings.