Extrusion-Coated Polymer Layers

There is a deep relationship between the molecular structure of a polymer and its bulk properties. The University of Copenhagen and Tetra Pak are using X-ray scattering to study structure-property relationships in packaging materials.

Keeping food safe, fresh and appetising requires good materials for wrapping or packing. To achieve all the functions required by the packaging (such as heat insulation, keeping light out, and keeping taste in) requires a complex stack of many layers. The polymer polyethylene is one of the important components in these packing layers, which is due to its excellent chemical resistance.
When packaging is produced, speed is paramount, and it is important to understand the properties of all the components exactly as used in practice. In some of the applications of polyethylene in Tetra Pak’s packaging, this means very thin films that are cooled from molten polymer very quickly. Polyethylene will generally form some amount of crystals as it cools, and it is important the amount of crystalline polymer and how it is oriented so that this can be related to the performance of the film as a barrier.

Read the interesting one pager about this project: X-ray scattering from thin polymer layers.

Techniques and Methods

Tetra Pak have worked with the LINX team at the University of Copenhagen (KU) to characterise extruded films of polyethylene in a form as similar as used in packaging as possible. Very thin (micrometre-scale) were produced by Tetra Pak and studied as produced and under stretching, as might be encountered in production or consumer use. The LINX team at KU used both wide-angle X-ray scattering (WAXS) to study the molecular structure and crystallinity and small-angle X-ray scattering (SAXS) to study the nanoscale lamellar structure. By calculating as many properties of the films as possible from the WAXS and SAXS data, it should be possible to determine if there are any correlations between structure and performance that can help Tetra Pak predict performance of grades of polyethylene as well as to provide useful experimental inputs into computer modelling of the packaging process.

Project Information

Participants: Tetra Pak, University of Copenhagen.
Start date, end date:
October 2018 – January 2020.
Structural characterization of extrusion-coated polymer layers by SWAXS (FP04.005, Colloid materials).