Peel-Cling Test Cyclic
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Peel-Cling test cyclic
Fundamentals of the test method
The peel-cling test for stretch films in the packaging industry is used to evaluate self-adhesion (i.e., the adhesion of films to themselves). These packaging films are used, for example, in agriculture or for pallets to secure loads during transport or storage.
The peel-cling test according to ASTM D 5458 [1] is used to characterise the cling behaviour of stretch films. This test method measures the force required to separate a film strip with a defined area from a fixed backing film made of identical material.
| Fig. 1: | Setup of the peel-cling test with a modified test arrangement |
The measuring principle is based on fixing the bottom foil on a 20° inclined plane by placing the foil on and under the wedge and tightening it with a rotary knob. The foil must lie on the base without bubbles or creases. A 1-inch (25.4 mm) wide strip of film is then placed in the centre of this film and rolled on with a brush or roller to remove any creases or bubbles, with a clamp attached to the lower end with a thread. This thread is guided by a deflection roller to the clamping device (see also: specimen clamping) of a universal testing machine. If a modified test device with a raised deflection roller and a 20° inclined support table is used (Fig. 1), the thread is in a horizontal starting position at the set preload.
Recording of force–deformation diagrams
During the peeling process, the thread lifts until it reaches the cling line, whereby the diagram is recorded as shown in Fig. 2.
| Fig. 2: | Registered force–deformation curves in the peel-cling test |
Ideally (red diagram), the thread is first tensioned until the preload FV is reached, and then the cling force can be determined based on the linear increase in the test force. With the cling force FCling, peeling causes an increase in deformation at constant force. However, tests show a clear start-up behaviour (blue diagram), which can be attributed to the elastic deformation and bending effects of the peel film. At the same time, however, no constant level of cling force (black diagram) is determined; instead, there is an average increase in force, the course of which is characterized by oscillations. These oscillations are comparable to a “stick-slip process,” in which crack propagation, or in this case further peeling, only occurs after a certain amount of energy has been applied. The increase in average force is obviously due to the non-constant test conditions, as the actual peel angle changes continuously during the test.
Further development of the cling test
The transition between elastic deformation and the pure peel process is difficult to detect experimentally due to vibrations. One solution here is to perform cyclic tests, which have often been used in the past to determine the elastic limit (see: modulus of elasticity) of metallic materials. In the simplest case, a load increase test with the force interval ΔF is performed at a constant crosshead speed. As long as the elastic deformation of the film is dominant, the next load level is reached, the load is relieved, and the next cycle begins with increased force. Once the cling force is reached, no further increase in force is possible and the peel process begins with an almost constant load level (Fig. 3). Such tests can also be performed with force or deformation control (see: tensile test control) if sufficiently sensitive force and strain measurement technology is available, and are also significantly more meaningful for plastics due to their viscoelastic deformation behaviour [3, 4].
| Fig. 3: | Registered diagrams in the cyclic peel-cling test |
See also
References
| [1] | ASTM D 5458 (1995; reapproved 2025): Standard Test Method for Peel Cling of Stretch Wrap Film |
| [2] | Rennert, M., Fiedler, S., Nase, M., Menzel, M., Günther, S., Kressler, J., Grellmann, W.: Investigation of the Migration Behavior of Polyisobutylene with various Molecular Weights in Ethylene/α-olefin Copolymer Blown Stretch Films for Improved Cling Properties. Journal of Appl. Polymer Sci. 131 (2014) 4861–4874, DOI: https://doi.org/10.1002/app.40239 |
| [3] | Rennert, M., Nase, M., Reincke, K., Arndt, S., Lach, R., Androsch, R., Grellmann, W.: Influence of Low-Density Polyethylene Blown Film Thickness on the Mechanical Properties and Fracture Toughness. Journal of Plastic Film and Sheeting 29 (2013) 4, 327−346, DOI: http://dx.doi.org/10.1177/8756087913483751 |
| [4] | Rennert, M.: Fracture Mechanics Investigation of Autohesive Interfacial Interactions of Polyethylene Stretch Wrap Films. Promotion. Martin-Luther-University Halle-Wittenberg. November 16, 2018. (see AMK-Library under B 1-29) (Content) |