Polymer Film Micro Fracture Mechanisms under High Strain Shear in Folding Boxboard Creases
High strain shear during boxboard creasing causes polymer film micro fractures when local elongation exceeds film yield capacity along the outer bend radius.
Tie Layer Adhesion
Interfacial Bonding
Coextruded multilayer packaging structures require functional adhesive resins to join dissimilar polymer films and paperboard substrates. Achieving effective tie layer adhesion prevents layer separation between polar materials like paper or ethylene vinyl alcohol and non-polar polymers like polyethylene. Converters evaluate bond strength to ensure structural integrity and barrier permanence in barrier packaging applications.
Bond Evaluation
Functional tie layers utilize modified polyolefins containing reactive maleic anhydride groups that form covalent and hydrogen bonds with paper fibres or polar polymer surfaces. Evaluating tie layer adhesion involves ninety-degree or one-hundred-eighty-degree peel testing according to ASTM D903, measuring the force required to peel laminated layers apart. Extrusion variables, including melt temperature, line speed, layer thickness, and air gap residence time, dictate chemical bonding and mechanical interlocking across the interface.
Inadequate oxidation or cold melt temperatures during extrusion reduce interfacial bonding, causing premature delamination during carton folding or heat sealing operations. Microscopic inspection of failure surfaces determines whether bond failure is adhesive at the interface or cohesive within the tie resin or paper substrate.
Delamination Threshold
Interfacial bonding degrades when process temperatures drop below activation thresholds required for chemical reaction. Exposure to high moisture, chemical contents, or deep freeze conditions can weaken interfacial bonds, leading to package failure.