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.

Plastic barrier packaging technology is driven by safety, convenience and quality. Growing demand for convenience foods and "ready meals" created by busier lifestyles and increased disposable income are reflected in high growth in food packaging. Food-purchasing decisions are based on taste and appearance, as well as convenience, making excellent barrier quality to maintain product freshness vital in food packaging.

No. 1 with the public is food safety, and active or barrier packaging that can help prevent spoilage or contamination is in strong demand. Consumers want easy-to-open, see-through, economic packaging that also protects against oxygen, water vapor and aromas.

Let’s start by delving further into high barrier coated flexible biofilm. While all commercially available PLA (polylactic acid) films meet ASTM D6400 compostability requirements and have good clarity, sealability and dead fold, its main drawbacks are poor temperature resistance and poor barrier properties. The application of SiOx (silicone oxide) clear barrier layer to the PLA film greatly enhances its barrier properties without negatively impacting the compostability of the base PLA film. The improvements in barrier properties achievable are virtually independent of the thickness of the base film.

Ceramis-PLA is a fully biodegradable film with a high barrier against oxygen and water vapor. The films are in conformity with DIN EN standard and also comply with the U.S. standard ASTM D 6400. These films have high bonding of the SiOx coating to the base films. They have high transparency, high gloss, and allow metal detection as well as have excellent combined barrier against gases, water vapor and aromas. SiOx coated PLA film from Amcor is produced using Amcor silicon oxide coating technology.

A second solution to the PLA barrier issue is application of a metalized barrier layer to the PLA film. This inorganic layer does not negatively impact the compostability of the base PLA film. Improvement in barrier properties with this layer is independent of the thickness of the base film. Celplast Metallized Products Ltd. has demonstrated that a very high-barrier all-PLA package can be achieved with a two-ply structure of reverse printed Ceramis-PLA (SiOx coated PLA) laminated to Enviromet metallized PLA (a biodegradable barrier film supplied by Celplast).

Amcor Flexibles
One week MAP (Modified Atmosphere Package) shelf life comparison using PLA film (T) without and (B) with SiOx Coating

Amcor Flexibles
SiOx coated PLA barrier map (The barrier map compares the barrier properties of plain 80-g PLA film to SiOx-coated PLA, and the coated PLA laminated to another 80-g PLA layer. These properties are overlayed on a barrier map showing the barrier requirements of typical food packaging applications)

Amcor Flexibles
Metalized PLA barrier map (The barrier map, showing barrier requirements of typical food packaging applications, compares barrier properties of plain 80-g PLA film to metalized PLA, and the metallized PLA laminated to an 80-g plain PLA. Even higher barrier properties are possible by laminating metallized PLA to an SiOx coated PLA layer)

Next, multiple lessons were learned by Fabri-Kal in transitioning to PLA thermoforming. Fabri-Kal is one of the largest thermoformers in North America. It made the transition commercializing its Greenware PLA drink and portion cups. PLA properties were well-suited to the cold-drink cups that Fabri-Kal produced. It had similar shrink to PET (polyethylene terephthalate) and the company which was already making a line of PET cups had the tooling for PET. It looked like a drop-in technology; however, there were lessons to be learned.

PLA crystallizes at a much lower temperature than PET and gets much stickier during the transition phase from amorphous to crystalline which caused problems when crystallizing regrind.

  • PET doesn't melt at the same temperature as PLA.
  • The material is very sensitive to contamination. PET and PS (polystyrene) won't melt at the low temperatures used to process PLA. A speck of unmelted PS will show up white in a clear PLA cup and a bit of unmelted PET will appear like a dimple.
  • The Fabri-Kal older equipment was difficult to clean out to run PLA. UnaDyn redesigned their crystallizer so that it can be cleaned thoroughly with no trap points for dust, as PLA can be very dusty. They also added more access points to facilitate cleaning and a new lump catcher at the bottom of the crystallizer to trap and remove PLA agglomerates, which can occur even with good temperature control.
  • Equipment had poorer control at lower operating temperatures.

PLA trims easily because of its relative brittleness, but finished product must be handled more carefully than PET. Greenware is now 10 percent of Fabri-Kal's business and growing at 15 percent per year — even during the recent recession, and despite being a premium-priced product.

Greenware PLA Drink and Portion Cups

Finally, let’s review compostable cellophane disposable barrier films. Compostable packaging materials have typically been used in applications where their inherent permeability is an advantage, and thus were technically excluded from packaging applications that required excellent barrier properties. Cellophane films generally offer good gas barrier properties but must be coated to impart moisture barrier properties. Uncoated cellulose films are highly permeable to water vapor whilst still providing an excellent barrier to micro-bacteria, flavors and aromas.

NatureFlex NK from Innovia films is a transparent, flexible, high-barrier cellophane film that is heat-sealable and compostable. NatureFlex films are based on renewable wood-pulp sourced from managed plantations, from suppliers operating sustainable forestry programs (Forest Stewardship Council or similar). In addition to biodegradability/compostability, the film offers a moisture barrier approaching co-extruded OPP (oriented polypropylene). It has the best moisture barrier of any biopolymer film currently available and is achieved via Innovia’s unique coating technology.

Innovia Films
NatureFlex NK film construction

Innovia Films
NatureFlex NK film wrapped cereal bars

The film maintains good print and conversion receptivity as well as heat-sealability on both sides. NK film is formulated to provide enhanced moisture barrier by the addition of a small amount of PVdC (PolyVinyledene Chloride). NatureFlex NK (available in 80 to 180 gauges) offers:

  • Excellent moisture barrier (0.65g/100 in2/day at 100ºF, 90 percent RH)
  • Good barrier to gases and aromas
  • Excellent transparency and gloss
  • Heat-sealable on both sides
  • Superb dead-fold properties

NatureFlex films are certified to both EU (EN13432) and U.S. (ASTM D6400) composting standards. Innovia Films have fully commercialized a NatureFlex film together with a proprietary sealant layer.