Doctor-Blade-Assisted Casting for Forming Thin Composite Coatings of Montmorillonite and Poly(vinyl alcohol)
Anna Marie LaChance, Zaili Hou, Maria M. Farooqui, Shantal A. Carr, Jordan M. Serrano, Catherine E. Odendahl, Megan E. Hurley, Tessa E. Morrison, Jacqueline L. Kubachka, Nia T. Samuels, Allyson T. Barrett, Yajing Zhao, Alysha M. DeGennaro, Luyi Sun, Montgomery T. Shaw
Abstract
Montmorillonite (MMT) nanosheets were coassembled with poly(vinyl alcohol) (PVA) chains and applied to a poly(ethylene terephthalate) (PET) substrate via doctor-blade-assisted casting. The resulting coated PET had vastly improved oxygen barrier properties, thanks to the highly ordered layered structure of the MMT nanosheets creating tortuous paths for molecular diffusion. The layering and ordering of MMT nanosheets on a solid substrate are controlled by an array of factors, some of which can be controlled by the coating process. To this end, parameters, including total solids in suspension, suspension volume, blade speed, and blade land length, were varied across orders of magnitude to determine their impact on the final coating quality. The turbidity of the films was quantified using ultraviolet–visible (UV–vis) spectroscopy. The structure of the nanocoating layers was verified via X-ray diffraction (XRD). Finally, the overall performance of the coatings was assessed via oxygen transmission rate (OTR) measurements, which gives an indication of the nanosheet assembly structure. This continuous coating technique has unique implications for vapor barriers such as food packaging materials, biomedical devices, and construction materials.