Water Barrier Properties of Resin‐Stabilized Waterborne Coatings for Paperboard

Abstract

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.

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

“…The resin-stabilized dispersion was synthesized by semibatch emulsion polymerization as reported earlier, resulting in poly(styrene–butyl acrylate) polymer particles stabilized by alkali-soluble resin (ASR) in water ( Figure 1 A). 32 The undiluted polymer dispersion was directly applied on untreated paperboard by bar coating and dried at 60 °C for 1 h ( Figure 1 B). This resulted in a transparent and glossy film having a thickness of ca.…”

“…As discussed in our previous work, these particles originate from the hard shell/soft core particles in the waterborne dispersion. 32 The hard ASR shell hinders extensive particle coalescence, causing the soft polymer particles to be trapped in an ASR matrix and retaining their initial spherical character.…”

“…Particularly, drying temperatures close to the T g of the ASR ensure softening of the shell, which is favorable for particle coalescence. 32 Therefore, the oil barrier performance was tested for coatings dried at room temperature, 60 °C, or 100 °C. Surprisingly, the drying temperature and therewith the coating morphology did not significantly influence the oil barrier performance ( Figure S3 ).…”

“…A high concentration of carboxylates is unfavorable for the water barrier performance, as the carboxylates are more hydrophilic than carboxylic acids. 32 The oil barrier performance was determined for 1- and 14-day equilibration time, and it was found that it was independent of the equilibrium time between application and measurement as shown in Figure S4 . Hence, these results indicate that, in contrast to the water barrier performance, the oil barrier is not dependent on the chemistry of the coating-substrate system, i.e., on the remaining carboxylate ion concentration.…”

“… 22 − 31 In our previous work, we showed that these ASR-based coatings provide very good water barrier performance when applied on pretreated paperboard. 32 …”