Atomic layer deposition onto polymer surfaces

The goal was to study polymer films and coated paperboard as base substrates for atomic layer deposition (ALD), to understand the parameters affecting layer growth and functional properties, to characterize thin layers, and to assess their safety and sustainability. Barrier properties of most polymer films studied were improved by Al₂O₃ thin layers. The relative improvement was the most significant with cellulose and polyester films, while certain plastic additives completely prevented thin layer growth. Polymer pre-coatings on fiber-webs have to be smooth and have good film forming properties. Layer growth starts by sorption of precursors onto and into the polymer surface followed by chemical reactions with the polar oxygen groups of the polymer and a possible formation of an interphase. This is followed by cluster formation and growth through clusters. The amount of oxide needed to cover the polymer depends on its' surface chemistry. Surface chemistry of polymer film has an impact on the layer growth and final functional properties. Polymer pretreatments prior to the ALD can be used to improve the barrier properties. Ozone can activate difficult surfaces, and the barrier properties can be adjusted by choosing the oxygen source. In addition, deposition temperature should be as high as possible. Mechanical properties of oxide layers were improved by combining thinner oxide and inorganic-organic hybrid layers into a nanolaminate. In addition, a contact between the oxide layers and the bacteria promoted antimicrobial activity. Uniform Al₂O₃ barrier layers do not seem to fall under the EU's definition of nanomaterial. Migration of Al₂O₃ to food simulants was low. However, ALD coated polymers require a top layer to protect the oxide layer from stresses, to prevent dissolution and to act as a sealant.