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Compostable Packaging Finally Here

February 7, 2010

This week, Frito Lay announced it is introducing its SUN CHIPS brand of multigrain chips in a new bag that will compost in about 14 weeks.  I think this is a major step forward for the packaging industry, to get a high-profile consumer goods marketer to adopt an innovation such as this.

 

SUN CHIPS Compostable Bag

The New Compostable Bag for SUN CHIPS

 

The secret behind this is a film called polylactide or PLA, that is derived from corn or other plant-based sugars.

PLA is notable for to reasons:

  1. It is derived from a renewable resource
  2. It will biodegrade within about 90 days down to CO2 and water.

As a result, PLA gets points for sustainability and for being truly biodegradable..

PLA was developed by Natureworks, a subsidiary of Cargill Corp.  Dextrose, or sugar, is fermented, in a process similar to making yogurt, to create lactic acid.  Lactic acid is a naturally occurring material that makes yogurt tangy and makes your muscles ache after a work-out.  From lactic acid, a molecule called lactide is created.  The water is removed, and the lactide crystallized to create the high-performance polymer – polylactide (PLA) – which they brand Ingeo™.

Another aspect of PLA is that it is not only from a renewable resource, but also has a lower carbon footprint compared to manufacture of petroleum-based polymers.  Manufacturing PLA produces 43% less greenhouse gases and uses 48% less non-renewable energy (NREU) than traditional polymers like PET, polyethylene, polystyrene and other commonly used packaging polymers. (http://www.natureworksllc.com/the-ingeo-journey/eco-profile-and-lca.aspx)

To complete the cycle, PLA is compostable.  According to Natureworks’ website, PLA undergoes a 2-step degradation process.  First, the moisture and heat in the compost pile split the polymer chains apart, creating smaller polymers, and finally, lactic acid.  Microorganisms in compost and soil consume the smaller polymer fragments and lactic acid as nutrients.  Since lactic acid is widely found in nature, a large number of organisms metabolize lactic acid.   The end result of composting is carbon dioxide, water and humus, a soil nutrient.

This degradation process is temperature and humidity dependent.  Municipal composting operates at high enough temperatures and humidity to ensure the PLA will completely biodegrade.  However, in backyard composters, temperature and humidity are not so well controlled by householders, so it’s not so easy to claim PLA will compost in backyards.  Because municipal composting systems are operated as a controlled process, they also are better able to provide the oxygen required for aerobic digestion of the hydrocarbons in the polymer.

A limiting factor for PLA is its relatively poor barrier to water vapor, oxygen, and CO2.  PLA’s water-vapor transmission rate is significantly higher than for PET, PP, or PVC.  PLA’s oxygen barrier is better than that of high impact polystyrene but is still significantly lower than those of PET, PP, and PVC.  Consequently, PLA’s role in blow molding is at present restricted to short-shelf-life products, dry goods, and refrigerated items.

BARRIER PERFORMANCE OF CLEAR RESINS
Polymer MVTR Oxygen Permeation CO2 Permeation
PLA 21 40 183
HIPS 10 300-400 NA
Nylon 6 23 3 NA
PET 1 3-6 15-25
PP 0.7 150 NA
PVC 2 5-20 20-50
ag-mil/100 in.2-day. bcc-mil/100 in.2-day-atm.

One way of overcoming this might be to vacuum metalize the PLA film, which would dramatically improve its water vapour and oxygen barrier.  So far, I have not seen this in commercial use, though perhaps in the SUN CHIPS product, this may have been done already.  Another approach might be to laminate with other films to selectively add barrier properties while optimizing the cost of the film.

My understanding is that PLA is currently priced at a premium to PET or OPP, two commonly used packaging films. The volume Frito Lay represents could be sufficient critical mass to enable the production of PLA to be more efficient and therefore become more price-competitive.

Among the suppliers of PLA film is BI-AX International, who market their product under the EVLON brand name.

Clearly, development of PLA as a packaging material will help divert a significant amount of waste from municipal landfills.  As other feedstocks are developed to drive down the cost of making PLA, it should supplant PET and polypropylene or PVC in many applications.

I can only hope the introduction of SUN CHIPS new package will be the start of a positive trend for the better.

As a side note, my company, The Packaging Alliance, sells a courier pack for wines called VinGARD that is compostable ad is made from recycled materials, but I think I’ll save this for another posting.

I want to acknowledge two especially helpful resources for writing this posting. First is the Natureworks site itself, which has a lot of useful information. Second is an article by Robert Leaversuch,of Packaging Technology. (http://www.ptonline.com/articles/200203fa2.html)

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