Note: This is the first article of a three-part series covering plastics in barrier packaging (1) trends, (2) material/process advances and (3) applications.
Despite being costly, plastic barrier packaging has established itself in the food and beverage sector because it can prevent oxygenation and thus degradation of contents. It is being used to increase shelf life, protect flavor profiles and maintain food appearance without adding preservatives.
Knowing what the next "green" sustainable trends are in the packaging world from an emerging plastics material, processing and application standpoint is a must in order for companies to enhance their environmental credentials. Let's take a look at some key sustainable plastics barrier packaging trends.
Biodegradable soft drink bottle grade polyglycolic acid (PGA) is a good starting point. The competitive environment of the food and beverage business has led packaging producers to develop innovative materials that allow manufacturers to preserve the quality, original odor, original color and taste of products as well as extend their shelf life in the market.
PGA is a biodegradable, thermoplastic polymer and the simplest linear, aliphatic polyester. With a high gas barrier to carbon dioxide and oxygen, controllable hydrolysis and excellent mechanical strength PGA is ideally suited for high-performance packaging as well as other applications.
However, industrial-scale production of PGA has proven elusive. Glycolic acid polymerizes easily through esterification, but the water byproduct then tends to hydrolyze the ester bond, chopping up the polymer into short strands. Attempts to drive off the water with heat only speed up the unwanted reaction. Production of PGA has been therefore limited to relatively small-scale operations for the manufacture of surgical sutures.
Researchers have now developed a high-volume, cost-effective manufacturing process for PGA. Kureha researchers found a way to make glycolide: a dimer. At the right dimer concentration in the right solvent, the dimer rings are opened to polymerize into a high molecular weight polymer. PGA offers:
- Gas barrier that is 100 times greater than PET (polyethylene terephthalate). It is also a 2-3 times (up to 10 times) greater barrier in multilayer PET bottles than MXD6 amorphous nylon. This makes it possible to reduce the amount of PET used in these bottles by approximately 20 percent and retain the barrier against carbon dioxide loss.
- Melting point close to PET simplifying coinjection of bottle preforms
- Unlike EVOH (ethylene vinyl alcohol), PGA does not suffer a dramatic fall-off in barrier performance under high humidity
- No tie layers needed in PET/PGA/PET constructions
- Hydrolytic properties/polyester chemistry make it compatible with industrial PET recycling processes
Kureha PGA LLC has constructed facilities to commercially produce Kuredux PGA using breakthrough technology that produces PGA from natural gas. The company has 40-plus patents on the process it will use at its Belle, West Virginia, plant (4,000 metric tonnes per year capacity).
The targeted application is multilayer PET bottles for carbonated soft drinks and beer. In multilayer construction, PGA has also been shown to enhance the gas and moisture barrier of bio-based polymers such as PLA.
Continuing, let's take a look at high-barrier silicone oxide coated flexible biofilm. While all commercially available polylactic acid (PLA) films meet ASTM D6400 compostability requirements and have good clarity, sealability and dead fold, their main drawbacks are poor temperature resistance and poor barrier properties.
The application of a silicone oxide (SiOx) 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 standards 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 and high gloss, and they allow metal detection as well as have excellent combined barrier against gases, water vapor and aromas. SiOx-coated PLA film from Amcor Flexibles is produced using Amcor silicon oxide coating technology. Ceramis biodegradable film features are as follows:
Amcor
Ceramis-PLA renewable and compostable film.
- High transparency
- High gloss
- Very good stiffness
- Excellent combined barrier against gases, water vapor and aromas
- Allows metal detection
- High bonding of the SiOx coating to the base films
- Suitable for use on established converting machines
- Made from annually renewable resource corn starch
- Fully biodegradable
- Various gauges available
Standard-gauge 20-micron Ceramis-PLA finds application in food grade lidding foil for trays (thermoformed or rigid), and all types of food pouches.
Finally, nanocomposite technology is leading the way for packaging innovation in the plastic container and flexible film industries, offering enhanced properties such as lighter weight materials, greater barrier protection and increased shelf life. Nanocomposites appear capable of approaching the elusive goal of converting plastic into a super barrier — the equivalent of glass or metal — without upsetting regulators.
A nanoclay-enhanced bottle barrier layer is a good example. With nanoclay supplier Nanocor, Mitsubishi Gas Chemical has developed Imperm, nanocomposite/MXD6 nylon blend featuring extraordinary oxygen and carbon dioxide barrier properties for use in multilayer PET bottles.
The grade uses nanoclay to impart significantly higher resistance to permeation by oxygen, carbon dioxide and moisture. This nanocomposite retains high clarity, making it an ideal core layer in multilayer PET bottles for such demanding applications as beer and carbonated soft drinks.
The Imperm 103 grade, containing a low loading of nanoclay particles, has a four-fold improvement in oxygen barrier and twice the carbon dioxide barrier properties of unmodified MXD6 nylon, while moisture resistance is increased by 200 percent. Imperm 103 also adheres to PET without a tie layer.
It offers good clarity with 1.5 percent haze as resin and 4 percent haze in bottles has good recyclability, good retort ability and maintains most other properties of unmodified MXD6 nylon. Imperm 103/PET multilayered bottles can be made thinner with equivalent protection to a single-layer PET bottle. They can therefore be compacted more readily and thus may contribute to volume reduction and resource savings in the recycle stream.
The barrier bottles have been used for carbonated beverages, juices, salad dressings and condiments. Also commercialized were thermoformed sheet grades for multilayer thermoformed deli containers and polyolefin packaging film grades for flexible multilayer film snack food packaging.
Nanocor
Imperm oxygen permeability.
