Adhesion Failure
Mechanical failure occurs when the specialized adhesive resin used to join incompatible polymer layers in a multi-layer film fails to maintain a permanent bond. During tie layer delamination, the structural integrity of the barrier packaging is lost as the individual plies separate from one another. Structural failure renders the material unfit for use in modified atmosphere packaging or liquid containment where gas barriers are mandatory.
Interfacial Stress
Thermal and mechanical forces during the coextrusion process or subsequent converting steps can exceed the chemical bond strength at the interface. If the tie resin is not compatible with both the polar barrier layer and the non-polar structural layer, the molecular entanglement at the boundary will be insufficient. The cooling rate at the chill roll also influences the development of these bonds, as rapid cooling can sometimes trap stresses that later lead to separation.
Chemical degradation of the adhesive resin during processing may further weaken the interface, especially if the melt temperature exceeds the stable range for the polymer.
Product Integrity
Separation of the layers typically leads to the total loss of the oxygen or moisture barrier, as gas can bypass the protective layer through the gaps. In food packaging, this failure often results in premature spoilage or the ingress of external contaminants. Testing involves T-peel strength measurements where the force required to pull the layers apart is quantified and compared against the minimum specification for the specific application.
