An approach for improved 3D formability of paper

Paper has a long and successful history not only as information carrier but also as a source of various packaging materials. Moreover, paper-based packaging is experiencing stable market growth even in developed countries in contrast to steady decline of printing papers demand. Plastic packaging is the major competitor for paper-based packaging, even though it is not as "green" as paper in terms of recyclability, biodegradability and renewability of raw materials. The poor ability of paper to be formed in thermoforming processes has been a limiting factor for its use, for example, in modified atmosphere packaging. The inability of paper to be formed into the 3D-shapes is primarily related to low extensibility of paper and board under the forming conditions. The improvement of 3D-formability is the key for enabling novel types of paper-based packaging and further competitiveness of the whole industry. The primary objective of this work was to improve 3D-formability of paper to a level which would allow utilizing it for the production of tray-like shapes for packaging of food. This aim was realized by the utilization of several methods, including: mechanical modification of fibres, addition of agar and gelatine, and in-plane compaction of the fibre web, concluded by unrestrained drying to allow free shrinkage of paper. Formable paper samples were formed to 3D-shapes using several laboratory-scale forming devices to proof the developed approach for the improvement of formability. As a result of the treatments applied to fibres and paper, extensibility of paper was raised from 4% to around 20% points, with the potential to be up to 30% in MD. Tray-like shapes with the depth of 20-40 mm were obtained using the thermoforming method.