Note: This is the second article of a three-part series covering plastics in barrier packaging (1) trends, (2) material/process advances and (3) applications.

With new plastic barrier materials, let's start by taking a look at layered barrier film material comparisons. Depending on product sensitivity, it is vital to provide food packaging protection with proper barrier components to ensure product shelf life.

Some products are susceptible to moisture, oxygen and/or other gases. Barrier films often consist of multilayers or coated films designed to be impervious to gas and moisture migration as single-layer films are in general quite permeable to most gases.

Frequently used layered barrier film materials include:

  • Polyproylene (PP): Mechanical properties and water vapor barrier
  • Polyethylene (PE): Sealing/water vapor barrier
  • Metallocene linear low-density polyethylene (mLLDPE): Good optical and mechanical properties
  • Polyamide (PA, nylon): Aroma/oxygen barrier with stiffness
  • Ethylene vinyl alcohol (EVOH): High oxygen barrier — EVOH provides excellent barrier properties to gas and water vapor. It is also environmentally friendly and clear; however, it is not suitable for high temperature processes.
  • Ethylene vinyl acetate (EVA): Good for sealing
  • Polylactic acid (PLA): Biodegradability

Topas Advanced Polymers
Oxygen versus water vapor permeation rates for barrier plastics.

Various approaches can be taken to improve barrier properties in the plastics packaging sector:

  • Barrier layers can be applied onto the plastic using vacuum coating (e.g. aluminum or transparent oxides such as aluminum oxide or silicon oxide applied to PET or BOPP films)
  • Multiply layer structures can be used
  • Nanoparticles can be compounded into the polymer matrix to form a nanocomposite that inhibits gas permeability

Next, an emerging film extrusion cyclic olefin copolymer (COC) is filling a performance gap. This COC film extrusion grade delivers a unique combination of greater heat stability and robust extrusion performance.

COC resins are amorphous polymers that offer transparency, moisture barrier, high strength and biocompatibility. Topas 7010F-600 from Topas Advanced Polymers features a heat distortion temperature (HDT) of 100 degrees C and strong extrusion capabilities for multilayer food packaging that withstand hot fill conditions.

Topas Advanced Polymers
Cyclic olefin copolymer (COC) polymer structure (left) and COC resin samples (right).

The material is typically used in multilayer structures with polyolefins and barrier resins such as PA and EVOH. It is used to produce a range of multilayer packaging film applications including metallized film, twist film, hot fill and shrink labels in thicknesses up to 100 microns.

This unique COC grade can be processed on conventional extrusion equipment. It can be run on blown film systems with or without grooved feed extruders at process temperatures of 230 degrees C or above and can also be processed on thin cast film lines with low haze over a wide process temperature range.

Continuing on in compostable/sustainable materials, a sustainable barrier film is gaining market traction in Europe. Tons of legume byproducts produced annually in Europe are discarded and the disposal of this part is costly for the food industry and damaging to the environment. The Leguval project is looking to develop new protein films and coatings that improve barrier properties in biodegradable package film while maintaining package biodegradability.

A three-year research project, funded by the Seventh Framework Programme from the EU, Leguval is handled by a consortium from four European member states. It combines the expertise of four European R&D centers (CNR-IPCF UOS, SSICA, Tecnalia and Polieko) that will provide contract research services to three industry associations (Consebro, PCS, Assocomaplast) and four companies (Iris, Thenos, RDX, Tuba) related with the food and plastics industry.

The leftover biomass of protein extraction will be used as an additive for the polymer matrix to improve properties of the plastic materials and as a source of biogas by anaerobic digestion.

Legume based biopackaging raw material.

The average chemical composition of by-product legumes includes:

  • 21 percent dry residue
  • 6 percent protein
  • 3.5 percent starch
  • 8 percent fibers
  • 2 percent sugars

Leguval will finalize the industrialization steps prior to the commercialization of the developed vegetal protein coating for plastic films that could replace currently used expensive synthetic oxygen barrier layers.

Finally, let's review an advance in flexible-film high barrier development, namely ultra-high-barrier metallized biaxially oriented polypropylene (BOPP) film. Torayfan PC5 metallized BOPP film developed by Toray Plastics (America) Inc. is a versatile ultra-high oxygen-and-moisture barrier film that can be used in tri-laminations, as a foil replacement and as an overwrap lamination or wrapper.

One side is designed with an ultra-high-barrier layer resistant to crazing. The other side is corona treated for excellent bond strength in cold-seal adhesive applications and in extrusion and adhesive three-ply laminations. The PC5 BOPP film is available in 60 gauge (15 um, or micron) and is designed to run on horizontal form fill seal (HFFS) and vertical form fill seal (VFFS) packaging equipment.

Toray Plastics (America)
Torayfan PC5 metallized BOPP film (left) and barrier package examples (right).

Key features are:

  • Guaranteed ultra-high oxygen barrier — gas flushable
  • Guaranteed moisture barrier
  • Noncraze metal surface
  • Excellent bonding of pressure sensitive adhesives (cold seals)
  • Excellent bonding in extrusion and adhesive three-ply laminations

Torayfan PC5 is a durable, cost-effective replacement for foil in a typical paper/PE/foil/PE packaging structure. Typical structures include:

  • Release film/ink/adhesive/PC5/patterned cold seal
  • PA 10/ink/adh/PC5/adhesive/PE
  • F61W/ink/PE/PC5/PE
  • Ink/Paper/PE/PC5/PE
  • O.L./ink/Board/PE/PC5/PE
  • O.L./ink/PC5/PE/Board/PE

In conclusion, the principal function of plastics barrier packaging is protection and preservation from external contamination. This function involves retardation of deterioration, extension of shelf life and maintenance of quality and safety of packaged food.

Packaging protects food from environmental influences such as heat, light, the presence or absence of moisture, oxygen, pressure, enzymes, spurious odors, microorganisms, insects, dirt and dust particles, gaseous emissions, and so on. All of these cause deterioration of foods and beverages.

Prolonging shelf life involves retardation of enzymatic, microbial and biochemical reactions through various strategies such as temperature control; moisture control; addition of chemicals such as salt, sugar, carbon dioxide, or natural acids; removal of oxygen; or a combination of these with effective packaging. Precise integration of the product, process, package and distribution is critical to avoid recontamination.

The ideal packaging material should be inert and resistant to hazards and should not allow molecular transfer from or to packaging materials. Other major functions of packaging include containment, convenience, marketing and communication.

Containment involves ensuring that a product is not intentionally spilled or dispersed. The communication function serves as the link between consumer and food processor. It contains mandatory information such as weight, source, ingredients, and now, nutritional value and cautions for use required by law.

Product promotion or marketing by companies is achieved through the packages at the point of purchase. Secondary functions of increasing importance include traceability, tamper indication and portion control.

New tracking systems enable tracking of packages though the food supply chain from source to disposal. Packages are imprinted with a universal product code to facilitate checkout and distribution control.