Innovation in Preservation Enabled by High-Barrier Composite Films

A composite film thinner than a strand of hair is made by precisely stacking multiple material layers. It can extend the shelf life of chilled fresh meat from a few days to nearly one month.

After 20 days of refrigerated storage, a tray of chilled fresh meat can still retain its bright red color and fresh texture. The key lies in its packaging film. In recent years, composite materials made from PE (polyethylene), PA (nylon), and EVOH (ethylene vinyl alcohol copolymer) have become an important technology in food preservation.

Research by Inner Mongolia Agricultural University found that vacuum-packed chilled meat using PE/EVOH/PE and PE/PA/EVOH/PA composite films could remain within its shelf-life requirements for up to 25 days. By comparison, chilled meat packaged in a conventional PA/PE composite film exceeded the applicable microbial safety limit on day 22.

1. Three materials, three different roles

PE, PA, and EVOH complement one another, forming the core of high-barrier packaging.

PE offers moisture resistance, flexibility, easy heat sealing, and low cost, making it suitable for the inner and outer layers. Its weaknesses are relatively poor oxygen resistance and limited puncture resistance.

PA provides high strength, toughness, and puncture resistance. It remains flexible at low temperatures and also offers a certain degree of oxygen barrier performance.

EVOH serves as the main oxygen-barrier layer. Its ability to block oxygen is far greater than that of PE, helping slow oxidation and spoilage. However, EVOH is sensitive to humidity and therefore needs protection from other materials.

2. From five layers to eleven

A single material cannot easily provide oxygen and moisture resistance, heat sealability, and puncture protection at the same time. This is why multilayer co-extrusion technology was developed.

A typical structure uses PE as the inner and outer layers for moisture protection and heat sealing. EVOH is placed in the middle as the oxygen-barrier core, while PA improves mechanical strength and helps protect the EVOH layer. Adhesive or tie layers are added between the materials to maintain structural integrity.

A patent published in late 2024 describes the following eleven-layer co-extruded film structure:

LLDPE/UHMWPE/PE-g-MAH/PA-g-C(n)/PE-g-MAH/EVOH/PE-g-MAH/PA-g-C(n)/PE-g-MAH/UHMWPE/LLDPE-EVA

In this structure, graphene-grafted nylon resin, or PA-g-C(n), is used to improve film strength. Test results showed a tensile strength above 40 MPa, elongation at break above 550%, and puncture resistance above 130 N.

3. An invisible barrier for food preservation

Chilled fresh meat is one of the most typical applications for these composite films. Studies show that when packaged with PE/EVOH/PE or PE/PA/EVOH/PA films, the meat experiences relatively slow purge loss during 25 days of storage, while pH and total microbial counts remain within the relevant freshness and safety ranges.

For seafood, exporters in Qingdao have used PE/EVOH/PA/EVOH/PE five-layer co-extruded films for vacuum packaging. The method can extend the shelf life of cooked shellfish to as long as 10 months while preserving much of its original flavor and texture.

Depending on the food and preservation requirements, composite films can also be used for:

• Pouch packaging: Suitable for sauces and dairy products; nitrogen can be added or air can be removed.

• Stretch packaging: An EVOH/PA/PE co-extruded bottom film is thermoformed tightly around the product.

• Modified-atmosphere packaging: High-barrier trays and lidding films are combined with oxygen, carbon dioxide, nitrogen, or other gas mixtures to extend shelf life and maintain meat color.

4. Performance, cost, and environmental considerations

EVOH greatly reduces oxygen transmission and slows oxidation. PE blocks water vapor, helping prevent moisture loss or absorption. PA improves puncture and impact resistance, reducing the risk of package failure.

Compared with glass bottles and metal cans, composite films are lighter and can lower transportation costs. Data from Shanghai Chuangfa Packaging Materials Co., Ltd. indicate that multilayer co-extruded films can cost 10% to 20% less than conventional composite films.

Multilayer co-extrusion can also reduce the use of adhesives and organic solvents, lowering the risk of solvent residues. However, because different materials are combined in one structure, recycling still depends on effective separation and reuse systems.

5. From food packaging to other industries

The applications of PE, PA, and EVOH composites extend well beyond food packaging.

In chemical transportation, eleven-layer co-extruded films can be used as inner liners for container flexitanks. These liners can carry up to approximately 24,000 liters of liquid and meet the tensile, elongation, and puncture-resistance requirements of rail transport.

In automotive manufacturing, multilayer fuel tanks made from EVOH and high-density polyethylene are lighter than metal tanks and can reduce fuel evaporation.

In healthcare, EVOH-based materials can be used in medical devices such as blood-dialysis membranes. In textiles, their bonding properties can support the development of functional materials.

From simple plastic bags to five- and eleven-layer co-extruded films, food packaging is evolving from basic containment to precision protection. A film only a few micrometers thick can combine oxygen resistance, moisture protection, heat sealing, and puncture resistance—helping extend shelf life and reduce transport losses.