There is no staple polymer that can provide a barrier to moisture and oxygen, the twin elements to which pre-packed viability of the majority of food products are most susceptible. Unless the objective is a clear-cut either/or in terms of prevention, the likelihood is that a multi-layer solution will be required. Not only does co-extrusion impact on price, but also mixed materials may not be recyclable: an added potential difficulty to be addressed if and when flexible packaging recovery becomes a reality within the UK.
In broad terms, it's the polyamides (for example, nylon) and polyesters (PET) for oxygen; and polypropylene (PP) or better still, polyethylene (PE) for moisture and also its excellent sealing attributes. Further degrees of barrier capability, for example suitability for microwaving, stem from those base-points, explains PAFA's David Tyson.
"Each plastic has different properties – these are the building blocks to create the requirement of the film. Some are created to withstand high temperatures, moisture, grease, oils and so on; some are intended to seal in flavour or seal out air; some are for strength; some are for flexibility; some are for economical reasons. It's just a matter of choosing the material to suit the purpose that you want the packaging to achieve."
Practical packagingThere is currently pressure to simplify the number of materials used, particularly in plastic packaging. The rationale is to recycle more and to have more common materials. Tyson rebuts: "That's fine, so long as you don't remove some of the properties that protect the contents. Studies have shown that the energy used to produce the actual content inside can be up to 20 times the energy taken to produce the packaging. I believe that the packaging's got to be driven by the application and not the end-of-life scenario."
And those applications can be highly sophisticated. Amcor Flexibles' retortable HeatFlex pouch solution for microwaving at temperatures of 180°C, for example, comprises co-extruded layers of a transparent high barrier laminate-coated PET film; a polyamide secondary layer and a further PP layer on the inside.
As the converting division within the BPI Group, bpi.consumer VMB is the largest supplier of fresh produce flexible packaging applications to UK multiples, processing over 12,000 tonnes per year of mostly PE and PP. Using the same external barrier film components, modified atmosphere packaging (MAP) figures high on the agenda; for example, co-extruded BOPP packs customized to have a high O2 permeability to extend the shelf life of Tesco own-label trimmed leeks and sweet corn.
"If we can reduce food waste by using optimized packaging solutions and customizing the packaging to the specific end-use, then we can not only reduce that waste but we can also make a big commercial impact on the levels of scrap experienced by retailers," says business development manager Robin Gilmour. "It does add cost, but it more than pays for itself in extended shelf-life. Otherwise, the retailers wouldn't buy it, would they?"
Either as a straightforward filmic solution or else as a laminate coating, PVDC (poly-vinylidene chloride) has the capability to withstand both oxygen and moisture. Innovia, for example, applies it to its basic cellophane films and also BOPP grades for its PropaFresh packs.
"If you look at the PP sector, traditionally, if you want to improve the aroma barrier then you'll add an acrylic coating – but if a gas barrier is really critical, then it'll require a PVDC coating," says global marketing manager Andy Sweetman. "On the other side, you'll have basic cellulose film and polymers such as PVOH and EVOH, which provide very good gas barrier properties as long as you keep them dry. Sitting in the middle of that construction you'll have PVDC. It's a dual-purpose barrier solution with a coating on the top."
Coated polyester films can offer a barrier to both oxygen and moisture, but aren't sealable. So in addition you'd need a PE or PP layer, which would also provide rigidity, points out Amcor Flexibles innovations manager Uwe Obermann, who also raises the potential conflict between barrier technology and green concerns.
"Environmental issues are an increasing factor in terms of reduction of layer thickness or the overall material consumption."
Cost of laminate is another issue; replacing transparent aluminium oxide-coated foil with other combinations, such as metallised PET or OPP films, even though the aluminium foil provides the best barrier to light, moisture and oxygen.
"With new material constructions you can't achieve everything; the customer has to reduce his requirement of certain packaging applications if he wants to go for a more eco-friendly alternative."
Amcor business manager Frank Nielsen takes that marketing dilemma one stage further. "While increased cost for a barrier film does pay for itself in extended shelf-life, working capital and turnaround time are factors very much in focus right now, which means that if the supply chain is robust and very responsive you could actually see a decline in demand for barrier properties."
Nielsen adds that there is a trend towards reducing order volume but increasing frequency of delivery in order to avoid the need for a barrier film.
Natural selectionBiopolymer films score highly with environmentalists. The difficulty is that while there's an inbuilt gas barrier there's also high permeability to moisture. "Innovia has resolved that with NatureFlex NK by using our coating technology to allow the use of small amounts of a different material that reinforces the barrier without compromising biodegradability," claims Andy Sweetman.
"You can work with very small amounts; they must be non-toxic, and must satisfy the very rigorous EN13432 composting regulation to prove that the overall solution is biodegradable, compostable and has no toxicity issues. It can be an onerous process. Taking a new material through the testing programme will entail at least six months' work."
NatureWorks is also looking at extending the remit of its PLA 'Ingeo' polymer into moisture barrier applications, says European business development manager Eamonn Tighe. "There are a number of additives that can be used: some of them bio-based, some of them not; some of them compostable, some of them not, and which will meet the barrier requirements of whatever application you need."
Tighe admits that Ingeo is not the packaging industry's 'silver bullet', but he also points out: "Many of the fossil-fuel derivative plastics have been optimised over a significant period of years; we've only been around for five." Biopolymers may still have much to prove, but their sustainable origins may mean they face fewer barriers in the green debate.
Nanotechnology
Still in its infancy - but the recipient of around $6bn of investment in R&D per annum, estimates industry consultant Neil Farmer – the commercialization of nanotechnology looks set to drive flexible filmic barrier packaging performance significantly further.
"Lighter weight or even using less film can be a benefit, but often the biggest gain is extended shelf-life," says bpi.consumer VMB's Robin Gilmour. "If you take bananas - the single biggest sales line by value through the multiples - we can add two extra days without any organoleptic (taste) effect by using minute particle ethylene scavengers approved for direct contact with food. The consequent 2% or so waste reduction can equate to a saving of tens of millions of pounds to the retailer."
Farmer, meanwhile, enthuses that "all plastics, especially biopolymers, will soon contain nano-additives to boost performance and provide additional active and bio-active functionalities." But others are less convinced. "It's interesting and we're watching what's happening, although not yet working on it," says Amcor Flexibles innovations manager Uwe Obermann. "There's a risk that because of their minute size, nano-particles could migrate into the content."
For the past five years, the US army has equipped its combat troops with emergency ration packs made from cellulose with 0.5-nanometre-wide gaps. Facilitating 99% toxin-free rehydration regardless of the liquid quality employed, these packs are activated by anything from infected water to the body's own natural effluent.
While it might not be something to try at home, the result is that a nanotechnology-enhanced pouch containing a day's rations can be reduced down from 3.5kg to just 0.4kg. It certainly brings a whole new meaning to taking the piss.
Source--- 
"This cup grew up in Blair, Nebraska. It's made entirely of corn. It's 100% compostable. It will disappear no matter what you do with it." 
"This cup grew up in Blair, Nebraska. It's made entirely of corn. It's 100% compostable. It will disappear no matter what you do with it." 
“The study found that Ingeo™ compares favorably with rPET even when a producer chooses not to lightweight a clamshell,” said Steve Davies, NatureWorks director of Communications and Public Affairs. “The study also showed that the next generation of Ingeo™ biopolymer, which will be available in 2009, offers further improvements in eco-profile and clearly outperforms 100 percent rPET in head-to-head comparisons.” 
Systematic diagram of individualization of nano-sized plant cellulose fibrils by direct surface carboxylation using TEMPO catalyst. (Image: Dr. Isogai/University of Tokyo). 
