High pressure-induced structural effects in plastic packaging

Abstract

Today, flexible vacuum packages are predominantly used for products to be subjected to high pressure treatment. However, tray packages with a modified atmosphere are in demand, which provide a high failure rate with respect to gas and water vapour permeability and packaging integrity. Methods to follow permeation processes under high pressure were developed and used together with optical microscopy, confocal scanning laser microscopy, Raman spectroscopy and atomic force microscopy to identify the mechanisms for changes in permeability and damage to the packaging materials. Single film samples and pouch packages filled with model products were studied. Results indicate a reversible decrease in the coefficients of diffusion and permeation under the impact of high pressure, due to the compression of the polymeric bulk. Irreversible changes in the polymeric materials are associated with gases in the packaging head space, which cause high local temperatures and create damage due to rapid deliberation upon the pressure drop at the end of the high pressure cycle

The Effect of High Pressure Processing on the Integrity of Polymeric Packaging – Analysis and Categorization of Occurring Defects

“…could show directly by in situ studies that during high‐pressure treatment, the permeation coefficients of benzoic acid through polyamide 6 (PA6) and of β‐ionone through low‐density polyethylene (PE‐LD) decrease reversibly upon an increase of pressure during the treatment. After pressure release, the permeability returns to its initial value within the accuracy of the measurement . Similar findings were published by Schmerder et al .…”

“…The observation of a temporary change of the permeation coefficient can be explained via the free‐volume model for diffusion in polymers . The model is based on the assumption that within or throughout an ordered matrix, there are discrete cavities, which may be either fixed or mobile.…”

“…In a failure analysis, Richter et al . detected an increase of crystallinity in a damaged area of a PE‐LD layer of a PET/PE‐LD multilayer at 600 MPA and 30°C by Raman spectroscopy …”

Influence of selected packaging materials on some quality aspects of pressure-assisted thermally processed carrots during storage

“…Single and combinations of PET, PE, PP, and EVOH films are some of the commonly used as packaging materials for high-pressure pasteurization (Juliano, Koutchma, Sui, Barbosa-Canovas, & Sadler, 2010). Co-extruded films with polymeric barrier layers, adhesive laminated films on a polymer base or inorganic layers such as aluminum foil (a few micrometers thick) or vacuum deposited coating (nanometer levels thick) are also used (Richter, Sterr, Jost, & Langowski, 2010).…”

The Influence of High Pressure Treatment and Thermal Pasteurization on the Surface of Polymeric Packaging Films

“…But the discussion of the SEM‐images has been more or less descriptively or has served as fortification for specific assumptions, for example that inorganic coatings are not suitable for high pressure processing (HPP). Nevertheless the surface of the packaging is of importance: The surface is the interface between food and packaging and thereby an influencing factor when considering migration aspects or the topic ‘white spots’, whose appearance in food and packaging cannot be explained thoroughly . For a better understanding of packaging–food‐high pressure interactions a comprehensive evaluation of the influence of HPP on the surface of polymeric films is required.…”