The influence of clay orientation and crystallinity on oxygen permeation in dispersion barrier coatings

• Dynamic mass transport, diffusion, and the solubility was determined for dispersion barrier coatings of PVOH and kaolin.
• Clay orientation factor for the thin barrier coating was lower for the samples dried at lower temperature (60 °C).
• Oxygen permeability decreased when kaolin concentration increased (up to 5 wt% clay content) in the barrier coatings.
• The dynamic mass transport shows that a lower drying temperature, 60 °C, improved the barrier performance.

In this study oxygen permeability in dispersion barriers produced from poly(vinyl alcohol) (PVOH) and kaolin clay blends coated onto polymeric supports was investigated. To determine the oxygen permeability, two measurement methods were used: the oxygen transmission rate (OTR) and the ambient oxygen ingress rate (AOIR). It was found that with increasing kaolin content the oxygen permeability increased, up to about 5 wt% kaolin, whereafter the oxygen permeability decreased, as was expected. The increased (> 5%) kaolin loading lowered the diffusion because of an increased tortuosity. Structural information about the dispersion-barrier coatings, such as kaolin orientation and polymer crystallinity, was obtained from Fourier transform infrared spectroscopy (FTIR) and scanning electron microscopy (SEM). Kaolin orientation was influenced by the drying temperature, the thickness of the samples, and the kaolin concentration. The polymer crystallinity increased in thicker samples. The drying temperature did not show any clear effect on the crystallinity of thin samples, while for the thicker barriers, combined with a kaolin concentration lower than 20 wt%, a higher crystallinity was achieved at lower drying temperatures. This study demonstrates the strong influence of chemical and physical structures on the permeability of the investigated coatings.

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