Delamination onset and design criteria of multilayer flexible packaging under high pressure treatments

• Delamination occurrence in bi-layer polymer packages under high pressure is addressed.
• Delamination is ascribed to mismatch of the mechanical moduli of the laminated films.
• Interfacial failure localizes near the welded flexible package sides.
• Mismatch of mechanical properties of the films promote high interlaminar stresses.
• Good practices derived for designing flexible packaging for high pressure treatments

Delamination phenomena frequently occur when multi-layer flexible polymeric films are employed for high pressure treatments of food packaging for pasteurization and sterilization purposes, thus potentially limiting the reliability of this treatment technology. The motivation of delamination is however not yet well understood. For this reason, to catch the key factors leading to interlaminar stress fields which can be prodromal to localized delamination events, the issue of mechanical failure of bi-layer structures under high pressure is thoroughly addressed in the present work, by constructing analytical models and Finite Element based numerical simulations. The theoretical results highlight the crucial role played by the mismatch of Young's moduli and Poisson ratios of the laminated film sheets in promoting delamination. These outcomes are in full agreement with experimental findings obtained by performing tests on high pressure-treated food multilayer packages realized coupling different polymeric materials, that is polypropylene-polyethyleneterephthalate, polypropylene-cast polyamide and polypropylene-bioriented polyamide.Industrial relevanceHigh pressure processing is a promising food preservation method endowed with minimal quality loss. To allow a safe use of this technique one cannot address the sole issues related to the effect of treatment on food itself, but also suitability of packaging materials to be used for this technology. In this contribution the attention is focused on multilayer flexible packaging with the aim of supplying guidelines for the proper choice of film structures able to withstand the loads associated with high pressure treatments.