Barrier properties of latex/kaolin coatings

Abstract

The inclusion of plate-like pigments such as kaolin to a styrene–butadiene dispersion is a well-known approach for enhancing barrier properties. Latex coatings containing kaolin with different treatments were evaluated. The in situ dispersion of kaolin in latex-bound coatings were characterised by Focused Ion Beam (FIB) imaging, X-ray diffraction (XRD) and Scanning Electron Microscopy (SEM). The effects of parameters such as the kaolin particle size distribution (PSD) and aspect ratio (AR), and the particle orientation distribution on the barrier properties of coatings were investigated. It is found that the barrier properties of the composites are independent of PSD and are mainly dominated by the AR distribution range and the degree of disorientation of the kaolin platelets (given a similar volume concentration of flakes). Large platelets with high AR contribute more to the improvement of barrier properties than do small platelets with low AR. Finally, the influence of platy pigments on the water vapor permeability was simulated using traditional models, which shows good agreement with the experimental data.