Barrier Plastics
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Barrier plastics
General information
You cannot simply use any plastic film for food packaging. Barrier composite films with improved shelf life are used for this purpose. As a prerequisite, the packaging film must be food-compatible and have certain barrier properties that are derived from the respective food and its intended use [1]. In general, barrier properties are understood to mean no or very low permeability to gases (e.g. oxygen), vapours (e.g. water vapour) and aromas. The molecular transport of liquid and gaseous substances through non-porous materials is defined as permeation. Figure 1 shows selected foods and their corresponding barrier properties. Water vapour permeability is normally expressed in g/m² per day. Moisture decreases from 85 % to 0 % during the packaging test [2–5].
| Fig. 1: | Required packaging functionalities for food and pharmaceutical products [4, 5] |
Critera for evaluating barrier properties
The interaction of plastics with liquid and gaseous substances, which is determined by the macromolecular structure of the polymer, is considered a decisive factor in assessing barrier properties. In addition, gas transmission depends on the type of permeating gas, the partial pressure difference between the inside and outside, the surface structure and the film thickness. The permeation process can be divided into three steps. First, the substance is adsorbed onto the material surface. Then, the dissolved substance diffuses through the material in the direction of decreasing concentration. Finally, the substance is desorbed from the other side of the material (Fig. 2) [3, 6–8].
| Fig. 2: | Schematic diagram of a permeation process through a polymer [7] |
Unfortunately, many polymers have an insufficient barrier effect. The most important barrier plastics and their corresponding barrier values are shown in Fig. 3.
A particular hazard in food production and preservation is the transport of oxygen through plastic film. Oxidation causes fats in sausage and cheese, for example, to spoil, resulting in a change in colour. In fruit juices, oxygen also causes the products to turn brown. In addition, oxygen promotes the growth of microorganisms, which leads to very rapid spoilage of food [9].
| Fig. 3: | Water vapour and oxygen permeability at 23 °C [4] |
Figure 3 shows that polyethylene vinyl alcohol (abbreviation: EVOH) has the best barrier properties against both oxygen and water vapour. Denser EVOH offers the best solution in the packaging industry, especially for sensitive foods. The EVOH copolymer not only has effective gas barrier properties, but is also characterised by excellent processing properties. The property profile of this semi-crystalline plastic can be adapted to the application by selecting the right ratio of ethylene and vinyl alcohol. The EVOH types depending on the ethylene content and the resulting variation in the property profile can be seen in Fig. 4 [10].
| Fig. 4: | EVOH types and their property profiles depending on ethylene content [10] |
In general, the barrier performance of EVOH copolymer depends on the crystallinity set in the material during manufacture. In addition, the barrier properties of EVOH copolymer can be improved by reducing the ethylene content. However, the barrier effect against oxygen can also be negatively influenced by the amount of moisture absorbed from the environment, as the EVOH copolymer is hygroscopic. The amount of moisture (see: test climate) absorbed from the environment depends on the temperature and relative humidity of the application area. The oxygen permeability as a function of relative humidity is shown in Fig. 5. It should be noted, however, that compared to other materials, such as low-density polyethylene (abbreviation: PE-LD) and biaxially oriented polypropylene film (abbreviation: BOPP), the EVOH copolymer provides the best barrier performance even at high humidity.
| Fig. 5: | Barrier properties depending on relative humidity and EVOH type [11] |
When selecting the type of EVOH, all parameters such as barrier performance, processing techniques and the environmental conditions corresponding to the application must be coordinated with each other depending on the ethylene content in order to best fulfil the requirements of the end application. One disadvantage is the high price of this polymer, which reflects its excellent properties [10–13]. A cost-effective alternative is slightly permeable PA.
Barrier effect of nanoparticles
In conjunction with nanotechnology (see: microplastic & nanoplastic), it has even been possible to significantly improve the barrier effect against oxygen compared to films made of pure PA (Fig. 6).
| Fig. 6: | Barrier properties of pure polyamide (abbreviation: PA) film and PA nanoparticle film [9] |
The improvement in the barrier effect can be explained by the fact that the gaseous molecules have to travel a longer diffusion path when penetrating the film due to the layered silicates embedded in the PA6 (see: layer silicate-reinforced polymers). Figure 7 shows that the gaseous molecules, e.g. unwanted oxygen molecules, must first migrate around the layered silicate platelets before they can completely penetrate the film. It is also known from the literature that the layered morphology (see: microscopic structure) can achieve an extreme reduction in permeability compared to other morphology types (Fig. 7).
| Fig. 7: | Barrier effect of nanolayer silicates [9, 14, 15] |
The new plastic film is therefore not only more cost-effective, but also twice as dense as pure PA. However, it should be noted that its barrier properties are still not optimal compared to EVOH. It is therefore recommended that the new PA film with nano-barriers be used for less sensitive foods [9, 14–16]. In general, it can be said that different requirements for barrier effectiveness must be met depending on the food product. Packaging films that look the same differ in their composition. The specific requirements of a food product can be met by combining different barrier plastics with each other using multi-layer systems or blending technology.
See also
- Testing plastic packaging
- Film testing
- Peel properties of peel systems
- Microplastic & Nanoplastic
- Smart Materials
References
| [1] | Voronko, J.: Herstellung und Charakterisierung von Barriere-Werkstoffen auf Basis von PP-PA6/ Nanoschichtsilikat- und PP-EVOH-Blends. Martin-Luther- Universität Halle-Wittenberg, Diplomarbeit (2010) (see AMK-Library under B 3-171) |
| [2] | Birus, T.: Sorgfältig auswählen – Eigenschaften von Kunststofffolien. Pharma + Food, Edition 1 (2007) |
| [3] | Vasko, K.: Schichtsysteme für Verpackungsfolien mit hohen Barriereeigenschaften. Technische Universität München, (Dissertation) (2006) |
| [4] | Langowski, H.-C.: Anwendung der Nanotechnologie in Materialien für den Lebensmittelkontakt. see: Link to the article on www.bfr.bund.de (last accessed January 18, 2026) |
| [5] | Freisinger Tage – Neuentwicklungen und Trends bei Barrierematerialien und flexiblen Verpackungen. TWB Forum Wissenschaft. Verpackungs-Rundschau, Edition 7 (2000), pp. 42–44 |
| [6] | Müller, K.: O2-Durchlässigkeit von Kunststoffflaschen und Verschlüssen – Messung und Modellierung der Stofftransportvorgänge. Technische Universität München, (Dissertation) (2003) |
| [7] | Hanika, M.: Zur Permeation durch aluminiumbedampfte PP- und PET-Folien. Technische Universität München, (Dissertation) (2004) |
| [8] | Ilschner, B., Singer, R. F.: Werkstoffwissenschaften und Fertigungstechnik. 4th Edition, Springer, Berlin Heidelberg (2016) (ISBN 978-3-6425-3890-2) |
| [9] | Sicher umhüllt – Nanoteilchen machen Durethan®-Folien dicht und glänzend. Research – Das Bayer-Forschungsmagazin, Edition 15 (2003) |
| [10] | Houssier, D., Teniers, C.: Eval (EVOH) und TPU für sehr flexible Barriere-Folien. PU Magazin, Jahrgang 5, Edition December/January (2005/2006), pp. 264–267 |
| [11] | Kuraray Co. Ltd.: Vorstellung der EVAL-Harze. Technische Datenblätter |
| [12] | Abad, M. J., Ares, A, Barral, L., Cano, J., Diez, F. J., Garcıa-Garabal, S., Lopez, J., Ramirez, C.: Use of a sodium ionomer as a compatibilizer in polypropylene/high-barrier ethylene-vinyl alcohol copolymer blends: The processability of the blends and their physical properties. Journal of Applied Polymer Science, Vol. 94 (2004), pp. 1763–1770; https://doi.org/10.1002/app.21107 |
| [13] | Barriere im Einsatz. Neue Verpackung, Ausgabe 7 (2001) 50–52 |
| [14] | Haas, K.-H.: Nano für die Produktion – Prozesse optimieren. 4. Nanotechnologie-Forum Hessen (2007) |
| [15] | Sangerlaub, S.: Perspektiven der Nanotechnologie für verpackte Lebensmittel. BÖLW Fachtag: Nanotechnologie in der Lebensmittelwirtschaft, Berlin (2008) |
| [16] | Chow, W. S., Mohd Ishak, Z. A., Karger-Kocsis, J., Apostolov, A. A., Ishiaku, U. S.: Compatibilizing effect of maleated polypropylene on the mechanical properties and morphology of injection molded polyamide 6 / polypropylene/organoclay nanocomposites. Polymer, Vol. 44 (2003), Issue 24, pp. 7427–7440; https://doi.org/10.1016/j.polymer.2003.09.006 |