Note: This is the third article of a three-part series covering plastics in barrier packaging (1) trends, (2) material/process advances and (3) applications.
Safety, convenience and quality drive food packaging technology. Increasing demands for fresh packaged food, consumer convenience and manufacturers' concern for longer shelf life are driving the market for global advanced barrier-packaging technology for the food and beverage market.
The growing demand for convenience foods and "ready meals" created by busier lifestyles and increased disposable income are reflected in the high growth of food packaging. The public's top concern is with 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. Government policy and regulations are also impacting barrier plastic packaging design.
Let's take a look at some recent applications in this field, starting with oxygen-scavenger nanocomposite barrier layer application development.
Honeywell Specialty Polymers has commercialized Nanocor's nanoclays in nylons for barrier layer applications in multilayer PET bottles and other packaging applications. The company initially directed its Aegis nylon 6 nanocomposites at PET beer bottles with its Aegis OXCE (or OX), a grade that makes use of a proprietary oxygen-scavenging "polydiene entity" dispersed in the polyamide nanocomposite, which is formulated for use where high oxygen barrier is required.
This dual-acting formulation uses passive nanoclay barrier material that blocks O2 entry, while the active O2 scavenger also absorbs any O2 from the head space and bottle contents. The material was widely noted on the introduction of the Hite Pitcher beer bottle from Hite Brewery Company in South Korea. Aegis OXCE forms the barrier layer in the three-layer product, which is said to have a 26-week shelf life comparable to the performance of glass bottles.
In addition, it provides an excellent barrier against CO2, while delivering glass-like clarity, recyclability and good adhesion to PET. Aegis OXCE also handles well in the co-injection stretch blow-molding process and demonstrates superior resistance to delamination.
In related nonbottle packaging applications, historically other Aegis nanocomposite grades such as Aegis NC (without oxygen scavenger) have been developed to replace EVOH (ethylene vinyl alcohol) in films and pouches. These Aegis grades cost less than EVOH and provide a better barrier, thereby allowing lightweighting possibilities.
They also have superior puncture resistance and, as the small nanoparticles do not interfere with light transmission, have good clarity. Aegis NC type materials could potentially be used as a coating replacement for nylon 6 in paperboard juice cartons or as the base resin for cast or blown films.
In cartons, the material provides approximately three times better oxygen barrier than nylon 6, has greater rigidity/less bulging, and is also less hygroscopic. In films, Aegis NC type systems can also be used as a nylon replacement for deli cuts packaging.
These type resins could approximately double nylon 6's heat resistance and increase tensile modulus, flexural modulus and flexural strength by 30-50 percent, providing the opportunity to move from a foil toward an all-polymer material. They also become a possible candidate for high-barrier shelf stable foods in a semi-rigid container.
Next, let's review sustainable whey-based protein barrier packaging, Whey is produced during cheese manufacture and is available in large quantities.
The Wheylayer Consortium (of 14 partners from seven EU countries led by the Fraunhofer Institute for Process Engineering and Packaging IVV) is working to develop an economic sustainable packaging material that will make use of the excellent barrier properties of whey protein against oxygen and humidity. In the food industry, the oxidation of fats, oils and other food components produces off-flavors, off-colors and nutrient loss so that protection against oxygen is an important requirement of food packaging.
Common synthetic polyolefin films such as polyethylene (PE) and polypropylene (PP) are excellent moisture barriers, but must be coated or laminated with synthetic polymers including ethylene vinyl alcohol (EVOH) and polyvinylidene chloride (PVdC) copolymers to provide an oxygen barrier. The resulting polymeric structures, while effective in minimizing permeation of oxygen, water vapor and odor, are characterized by poor reuse due to difficulties in separating each layer for appropriate recycling.
Whey coating on plastic film provides good barrier properties with acceptable mechanical integrity and can improve recyclability/reuse of the plastic layer by removing the whey protein chemically or enzymatically. Initial studies have shown that it is possible to completely dissolve the barrier coating from the substrate, without leaving any residues.
Additionally, active antimicrobial/antioxidative compounds naturally present in whey can be used to extend food shelf life. The end materials are whey protein formulations with good barrier properties, adhesion and mechanical integrity, preventing delamination and brittle fracture.
The oxygen barrier properties — oxygen transmission rate (OTR) of less than 2 grams per square meter decibar of atmospheric pressure — and a water vapor barrier — water vapor transmission rate (WVTR) of less than 20 g/m2 dbar for a whey layer thickness of 100µm (microns) — suggest that whey protein coating may be used to replace synthetic polymer coatings such as EVOH and PVdC otherwise used to improve barrier properties of conventional packaging substrates.
Finally, the United States military, with Hydration Technologies Inc. (HTI), developed porous plastic bags "X Pack" coated in nanoclays that filter water. The pouch outer container can be filled, via the large red port, with dirty water from any puddle. Clean water passes via forward osmosis through the bag's nanoclay coating into the inner clean drink container.
Bacteria — including poliomyelitis,one of the smallest bacteria types — and other contaminants are filtered out. Pouches can also contain dried food, which is rehydrated by the incoming clean water. Future versions will rehydrate food by taking in moisture from the air.
HTI technology is based on a proprietary hydrophilic membrane filter that allows water to pass through, yet blocks the smallest of contaminants. Water is driven across the membrane by osmotic pressure created by a standard sport drink powder on the clean side of the membrane to the inner 1.75 liter hydration pouch. The process can be repeated three times per day for 10 days.
Because the HTI systems use osmotic pressure instead of hydraulic pressure, they do not clog or foul as do other filtration systems. Several versions of the water purifier are available, including one that can be used 10 times a day for 10 days.
