Thin Al2O3 Barrier Coatings Grown on Bio-Based Packaging Materials by Atomic Layer Deposition (Ohuet Biopohjaisille Pakkausmateriaaleille Atomikerroskasvatetut Al2O3-Barrierpinnoitteet)

摘要

Growing environmental concerns related to the use of non-biodegradable polymers in the packaging industry have led to the need for new materials. Currently, these conventional polymers are widely used due to their relatively low cost and high performance. Bio-degradable plastics and fibre-based materials have been proposed as a solution to the waste problems related to these synthetic polymers. Fibre-based packaging materials have many advantages over their nonbiodegradable competitors, such as stiffness vs. weight ratio and recyclability. However, poor barrier properties and sensitivity to moisture are the main challenges restricting their use. Application of a thin coating layer is one way to overcome these problems and to improve the barrier properties of such materials. Atomic Layer Deposition (ALD) is a well suited technique for depositing thin inorganic coatings onto temperature-sensitive materials such as polymer-coated board and paper and polymer films. Thin and highly uniform Al2O3 coatings have been deposited at relatively low temperatures of 80, 100 and 130 deg C onto various bio-based polymeric materials employing the ALD technique. The work demonstrates that a 25-nm-thick ALD-grown Al2O3 coating significantly enhances the oxygen and water vapour barrier performance of these materials. Promising barrier properties were revealed for polylactide-coated board, hemicellulose-coated board as well as various biopolymer (polylactide, pectin and nanofibrillated cellulose) films after coating with a 25-nm-thick Al2O3 layer. Extremely thin Al2O3 coatings can improve the properties of biopolymers, enabling the use of these renewable polymers in the production of high-performance materials for demanding food and pharmaceutical packaging applications. The future roll-to-roll ALD technology for coating polymers with inorganic thin films will increase the industrial potential of these materials and could lead to further opportunities for their commercialization.