Safety aspects of polymer films with thin Al₂O₃ barrier

Atomic layer deposition (ALD) is an efficient tool for improving the barrier properties of polymer films and polymer coated papers/paperboards. However, adequate barrier properties are only one of the key requirements set for food packaging materials, while other properties have only been studied to a limited extent. The main safety aspects related to polymer films with a thin ALD grown Al₂O₃ layer are presented in this paper. Although ALD methods for preparing thin films can be classified as part of nanotechnology, ALD grown Al₂O₃ thin layers do not fall under the European Commission's definition of nanomaterial, even though the thickness of the layer is in the nanoscale. Al₂O₃ is also accepted as an additive for plastics in contact with food. In abrasion tests ALD grown films did not increase the number of airborne particles in the surrounding air. ALD films on reference silicon wafers and oriented polymers were exposed directly to specific food simulants and the key material properties were evaluated. Finally, the films were also tested for migration. The Al₂O₃ layer was affected by the simulant exposure, and the degree of impact depended also on the base film. As a conclusion ALD grown Al₂O₃ thin layers require an additional protective layer.