Best of plastics: Barrier packaging
Monday, September 26, 2016
Note: This is the second of a five-part "best of" series covering trends, material/process advances and applications in electrical and electronics, barrier packaging, medical, bioplastics and 3-D printing.
Value and health are currently driving barrier technology in food packaging. Increasingly busy lifestyles are reflected in growing consumer demands for convenience foods, ready meals and eating "on the go," resulting in high growth in food packaging.
With the increasingly global customer base of food retailing, food packaging requires longer shelf life and monitoring of food safety/quality based on international standards. The rising popularity of convenience foods means global demand for food packaging will reach $140 billion by the end of 2016.
Consumers expect not only product protection from packaging, but they also want to see the food they buy; they want it to be safe to eat; they want it to stay fresh for a longer period; and above all, they want it to be tasty. Food purchasing decisions are based not only on convenience, but also on taste and appearance, making excellent barrier quality to maintain product freshness vital in food packaging to extend shelf life and to protect brand image.
Food safety is the number one issue with the public, and active/barrier packaging that can help prevent spoilage or contamination is in strong demand. Recalls can be particularly damaging to both the brand image and the company's bottom line. Most companies understand the added expense of improving packaging to help prevent recalls — a liability case is often far less than the cost of losing many customers because of an unhealthy or unsafe product.
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.
Topas Advanced Polymers
Oxygen versus water vapor permeation rates for barrier plastics.
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/O2-barrier with stiffness
- Ethylene vinyl alcohol (EVOH): Excellent barrier properties for 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
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).
- Multiple layer structures can be used.
- Nanoparticles can be compounded into the polymer matrix to form a nanocomposite that inhibits gas permeability.
Next, 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 while still providing an excellent barrier to microbacteria, 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 (FSC - Forest Stewardship Council or similar).
In addition to biodegradability/compostability, the film offers a moisture barrier approaching co-extruded oriented polypropylene (OPP). It has the best moisture barrier of any biopolymer film currently available and is achieved via Innovia's unique coating technology.
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 polyvinyledene chloride (PVdC). NatureFlex NK (available in 80 to 180 gauges) offers:
- Excellent moisture barrier (0.65g/100 in2/day (at 100 degrees F, 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.
NatureFlex NK film construction (left) and NatureFlex NK film wrapped cereal bars (right).
Continuing in smart packaging, MicVac microwave pasteurized ready meals have been developed. Chilled ready meals are a growing trend with today's busy lifestyle, increased single- or two-person households, increased disposable income, and increasing westernization of food habits across major countries. These leading factors are driving demand for convenient meal options, especially ready meals.
A unique packaging concept for chilled ready meals provides an extended refrigerated shelf life greater than 30 days at 8 degrees C., thanks to microwave pasteurization technology. Sweden's MicVac is the developer of the unique microwave pasteurization technology.
In the process, raw food ingredients in a PP tray with a peelable PA (polyamide or nylon)/PP flexible film lidding is heat sealed in place. Accurate control of sealing pressure/temperature ensures the lidstock/tray seal is strong enough to withstand internal pressure during pasteurization and consumer heating, yet remains easy to peel away when the heated food comes out of the consumer’s microwave.
MicVac pasteurization process (left) and a microwave pasteurization ready meal (right).
Just before the lidding material is applied to the filled trays, a custom labeler from European Labeling System GmbH punches a small hole in the lidstock and applies over the hole a unique MicVac valve. The servo-driven film transport of the SealPac tray-sealer helps deliver the accurate hole-punching and label-positioning that are required. SealPac GmbH developed a special application device for the patented MicVac valve on its tray sealers.
The patented MicVac valve, designed so that it can open and close multiple times, opens to release internal pressure created as the food releases steam during cooking/pasteurization or reheating by the consumer. The contents of the tray are cooked/pasteurized in 4-10 minutes using microwave energy, depending on the size of the food particulates, versus 2-3 hours pasteurization in a steam oven or autoclave retort.
As soon as the pasteurization process is completed, the trays are cooled and the MicVac valve closes. Steam trapped inside the tray condenses, causing a vacuum within the package. This causes the bottom of the specially developed FlexTray to curve upward while the lidding film is pulled down toward the food contents. Consumers are able to reheat the product in their microwave in only about 3 minutes, with the valve releasing the steam of the food once again.
The final result is a cooked, pasteurized and vacuum packed product with excellent quality in taste, nutrition and texture, which can be presented attractively on the retail shelves — even vertically. MicVac has signed a cooperation agreement with Curwood/Bemis. The cooperation will make the unique MicVac technology for chilled ready meals available in North, South and Central America. Curwood, a technological leader in high-barrier packaging, is part of Bemis Company, Inc.
In conclusion, consumers insist on easy-to-open, see-through packaging while also requiring protection against oxygen, water vapor and aromas that remain economical. Environmental, regulatory and public policy issues are also impacting the design of barrier plastic packaging.
Packaging waste is a growing environmental concern, and consumers are seeking ever more sustainable packaging choices driving food packagers to look for bioplastic materials with good barrier properties. The presence of oxygen-sensitive unsaturated fats are fueling development of active/barrier packaging in flexible and rigid formats, as the result of trends toward natural/organic foods featuring heart-healthy fats.
Active packaging interacts chemically with the food inside the package to safeguard against product degradation from exposure to oxygen and/or moisture. By making use of a combination of active and barrier packaging, processors can increase shelf life, protect flavor profiles and maintain the food’s appearance/texture — all without adding preservatives to the product formulation.
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