Application of a novel testing device to characterize the layer adhesion of co-extruded polymer sheets

Co-extrusion is a common and efficient way to produce polymer products out of various layers with different materials tailoring their properties. Adhesion between the individual layers is crucial for the overall performance of the multi-layer product. The existing methods to characterize layer adhesion, such as delamination tests, peel-off test, and tensile-shear tests, were originally developed for testing adhesive joints, composites, and laminates and have limited applicability to co-extruded polymer products. In this study, first the existing methods for a two-layer polymer sheet using various compatible materials are evaluated. These combinations formed strong interfaces which could not be characterized with the existing methods. Next, a novel layer adhesion testing device which is capable to apply pure shear loads at the interface is presented. Using this testing device enables characterization of the strong interfaces of the co-extruded sheets with adhesive failure observed. Finally, tests with various interfacial overlapping lengths are performed and yield strength, failure strength, and the energy absorbed are evaluated to proof the suitability of the novel testing device to characterize layer adhesion in multi-layer polymer sheets.