Water-borne Barrier Coating Based on Poly(vinyl alcohol) Nanocomposite

Abstract

Plastic recycling rates have remained in the single digits and most plastic waste ends up in landfills and oceans. One of the reasons is the difficulty in recycling plastic film, sometimes considered impossible. In container and package applications, multiple films are used combined to prolong shelf life by providing both oxygen and water barrier properties, but these layers are difficult to separate at a commercial scale. An important solution to enable recycling is to create single material plastic films, but the current monolayer film candidates may lack the necessary barrier properties. Therefore, we are designing an ultra-thin 'super barrier' coating for single-layer plastic films, enhancing barrier properties while ensuring full and easy recyclability. Nanocomposite Poly(vinyl alcohol) (PVA) /nano-clay is an existing waterborne coating formulation that significantly slows down oxygen’s transport speed across the film. However, it needs an unacceptably low concentration (< 10wt%) to ensure processability and solvent removal is inefficient. In this work, modified PVA copolymer was prepared by chain-scission reaction. It shows high solubility (> 30wt%) in water at room temperature. Moreover, transparent film with 30wt% nano clay loading was produced using solvent casting method. The film also exhibited narrow XRD peaks. Since high transparency and narrow XRD peak only appears when nano clay forms orientation, self-assembly induced by solvent evaporation might occur using this modified PVA copolymer. In addition to properties related to barrier performance, the material exhibited favorable rheological properties that enable processability using conventional coating methods at high nano-clay loading (30wt%) and reasonable coating solid weight (30wt%).