Role of package headspace on multilayer films subjected to high hydrostatic pressure

Abstract

The objective of this study was to systematically examine the effect of high‐pressure processing and package headspace on package integrity and properties. Working pressures were 400 and 600 MPa, and starting vessel temperatures were 30°C, 60°C, and 90°C. Coextruded and laminated multilayers packaging films were studied: film A: (PA/EVOH/PP) and film B: (PET‐AlOx‐OC/PA6/PP), respectively. The films were made into pouches (0.05 m × 0.10 m) and filled with 30‐mL water as a model food. Various headspace volumes (0, 0.05, 0.10, 0.15, 0.20, 0.25, and 0.30‐cc air/mL H2O) were introduced into the packaging before processing. Imaging was used to quantify defects such as the formation of white spots on the package surface and delamination of film layers. The results showed that the headspace level and processing initial temperature had a greater effect than the operating pressure on visual defects. The package with 0% headspace did not show any physical damage to the tested films. Furthermore, thermal and mechanical analyses showed that the coextruded film A had better resistance to testing conditions than the laminated structure of film B. The X‐ray diffraction results showed that film B had more defects than film A that altered the crystalline structure. Visual observation revealed white spots and delamination in the inside layer (PP) in both films. The same processing conditions affected the oxygen and water vapour transmission rates of film B more than film A. This work provides a basic guideline to select the right headspace for a given type of packaged food whenever heat and pressure are used simultaneously.

High‐pressure treatment of water‐filled co‐extruded polylactide films: Effect on microstructure, barrier, thermal, and rheological properties

“…Packaging seals remained intact in all treated films and there was no leakage or hole in the pouches. The obtained results differ from the earlier reports on HP treatment on laminated films (e.g., bilayer metPET, PET/LLDPE, PA/EVOH/PP) (Al‐Ghamdi et al., 2019; Sansone et al., 2014). It was reported that films processed under HP or a combination of HP and high temperature resulted in visual defects (white spots) and delamination of the outer film.…”

“…Al‐Ghamdi et al. (2019) made a similar observation for PA/EVOH/PP and PET‐AlOx‐OC/PA6/PP films, where the overall thicknesses of the films were not affected after the HP processing. Pouches sustained the largest exerted pressure of 600 MPa for 15 min, and no deformation or any form of visual defects were detected in pouches (e.g., blisters, opacification, and delamination).…”

“…Such an improvement in the barrier properties of the films could be attributed to the coextrusion process that reduces the effective diffusion coefficient of both water vapor and oxygen molecules in the film as compared to the single-layer PLA film. Pressure independency of the barrier properties of various multilayer films at ambient temperatures has been reported in the literature (Al-Ghamdi et al, 2019). Conversely, application of pressure and temperature in combination (600 MPa/90 • C/10 min) had a significant effect on the OTR of multilayer films (Al-Ghamdi et al, 2019;Júnior et al, 2020).…”

High‐pressure processing effects on the barrier properties of flexible packaging materials

“…For the PET printing /PET met /LDPE coex laminate, the increases in WVTR and OTR are justified by the microscopic damage presented on the surface of the material, as reported in a previous study (Marangoni Júnior, de Oliveira, Dantas, et al, 2020). In addition, other studies in the literature, where metallized structures or other coatings, processed by different high‐pressure conditions were also evaluated, resulting in discontinuation of metallization after high‐pressure processing (Al‐Ghamdi, Sablani, Rasco, & Cánovas, 2019; Ayvaz et al., 2012; Bull et al., 2010; Caner, Hernandez, & Pascal, 2000; Galotto, Ulloa, Guarda, Gavara, & Miltz, 2009; Galotto et al., 2010), which was not possible to evaluate the material studied due to the presence of printing on the outer layer of PET.…”

Multilayer packaging: Advances in preparation techniques and emerging food applications

“…Microscopic analysis of a multilayer film surface can be done using scanning electron microscopy (SEM) to help in the detection of swelling, delamination, surface cracks, and holes after processing (Marangoni Júnior, Cristianini, Padula, & Anjos, 2019). The changes occurring in the crystal structure and crystal size of the polymers when undergone processing can be visualized in X‐ray diffraction (Al‐Ghamdi, Rasco, Tang, Barbosa‐Cánovas, & Sablani, 2019). Positron annihilation lifetime spectroscopy (PALS) is an informative technique that can be used for characterization of valance defects in crystals and voids volumes in polymers (Tang, Selim, Dhawan, Varney, & Barbosa‐c, 2014).…”