The recyclability of modern paper and cardboard products increasingly depends on details that, until now, have been difficult to evaluate objectively. A particular challenge is posed by paper coatings with barrier properties, adhesive joints, or printing, which can be reintroduced into the paper as sticky contaminants during the paper recycling process and may interfere with the paper manufacturing and further processing. In particular, adhesive contaminants made of acrylates or acetates can cause the paper web to stick during drying on the paper machine, leading to holes, tears, or even web breaks on the paper machine, or severely impairing further processing. Until now, sheet stickiness has been evaluated using manual sheet stickiness tests, which are highly subjective.
As part of a research project, a novel peel test device was therefore developed that, for the first time, replicates the classic sheet stickiness test under defined and reproducible conditions. The goal of the project is to develop an objective methodology for evaluating sheet stickiness in recyclability studies of paper and cardboard products.
Real-world peeling processes under controlled conditions
The new testing apparatus enables peel tests of specimens bonded in soft-to-soft and soft-to-rigid configurations on a tensile testing machine. A key component of the apparatus is a movable peel table that generates a smooth and continuous separation motion—similar to the actual peeling of bonded sheets in a practical sheet adhesion test.
In this process, laboratory sheets can be separated either from a paper backing or from a metal backing. Since the specimen setups vary depending on the backing material, the apparatus was designed to allow for the flexible implementation of different clamping and mounting configurations.
Simultaneous force and temperature measurement
A distinctive feature of this testing technology is the combined measurement of mechanical and thermal processes during the peeling process. As the bonded materials are separated, the system continuously measures the peeling forces that occur. At the same time, temperature changes are recorded with spatial resolution directly in the peel gap using a thermal imaging camera.
This not only allows the adhesion properties of the materials to be quantitatively determined but also enables a detailed analysis of the physical processes during the separation process. The combination of force and temperature measurement opens up new possibilities for investigating adhesive mechanisms and material interactions.
Objective data instead of subjective evaluation
With the new testing apparatus, a manual sheet adhesion test—which was previously heavily based on experience—becomes a reproducible measurement method. The data obtained enables significantly better comparability of different material systems and supports the development of paper and cardboard products suitable for recycling.
Contribution to More Sustainable Packaging Solutions
As requirements for recyclability and the circular economy increase, so does the need for standardized test methods for fiber-based packaging. The peel tester provides an important foundation for this.
Through the objective measurement of sheet tack, material developments can be evaluated more precisely, recycling processes can be better understood, and more sustainable packaging solutions can be developed more quickly.
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