The use of mechanical analyses, scanning electron microscopy and ultrasonic imaging to study the effects of high-pressure processing on multilayer films

The effects of high-pressure processing (HPP) on the mechanical and physical characteristics of eight high-barrier multilayer films were investigated. These films were PET/SiOx/LDPE, PET/Al2O3/LDPE, PET/PVDC/nylon/HDPE/PP, PE/nylon/EVOH/PE, PE/nylon/PE, metallised PET/EVA/LLDPE, PP/nylon/PP and PET/PVDC/EVA. In addition, PP was evaluated as a monolayer film for comparison purposes. Pouches made from these films were filled with distilled water, sealed, then pressure processed at 600 and 800 MPa for 5, 10 and 20 min at a process temperature of 45 °C. Pouches kept at atmospheric pressure were used as controls. Prior to and after HPP, all films were tested for tensile strength, percentage elongation and modulus of elasticity (at 50 cm min^-1) and imaged by scanning electron microscopy (SEM) and C-mode scanning acoustic microscopy (C-SAM). Results showed no significant changes in tensile strength, elongation and modulus of elasticity of all films after HPP. However, significant physical damage to metallised PET (MET-PET) was identified by SEM and C-SAM. Thus it could be concluded that MET-PET is not suitable for batch-type high-pressureprocessed food packaging. It can also be concluded that the other materials investigated during this study are suitable for batch-type high-pressure -processed food packaging.