When you think of polylactic acid (PLA), you think of NatureWorks. They've been able to take sugar (from corn or cane or what ever) and using a fermentation process, produce lactic acid. The acid is then dimerized into the lactide which is then polymerized. That process is pretty straightforward as far as a mass balance is concerned. The sugar is a carbohydrate, C6H12O6, and the lactic acid is half of this, C3H6O3.
So now NatureWorks has announced that the are co-developing a process to make lactic acid from methane. That's quite a change. 3 CH4 + 3 O2 --> C3H6O3 + 3 H2O. That's also a lot of produced water that has to be dealt with. And so much for making the PLA from bio-based feedstocks.
It's not as if PLA derived from methane can't be differentiated from that derived from glucose. The biobased plastic will have C-14 isotopes that can be easily picked up by a good mass spec, while the petroleum-based PLA will lack this. [*]
I can see wanting to cash in on the cheap methane like many other plastic suppliers are, but also I imagine the marketing and PR people will be putting in lots of long hours trying to figure out how to greenwash this plastic. Further, it's not as if PLA is competing with any of the polyethylene that will mostly be the big winner from frack gas. PLA is most often competing against polyester (PET), and to a lesser extent polyproplyene (PP). All the way around, I find this a very strange move by Natureworks. Or am I missing something?
[*] This same presence/lack of C-14 is what led the Tour de France to strip the title from an American winner. No, not Lance Armstrong, but Floyd Landis. Landis was found to have an unusually high level of testosterone is his urine, and more importantly, that testosterone was lacking in the necessary amount of C-14, meaning that it was synthetic. Busted!
The greenest of possible worlds would be PLA from landfill methane. There'd be a profit incentive to capture more landfill methane. If you're taking methane that would otherwise be vented and using it to make plastic (that likely won't degrade in landfills), you can be carbon negative.
I can't believe that landfills would provide a large enough volume of methane to make it usable (and that the volume would be consistently generated at a near constant rate).
Research regarding methane as a warming agent usually identified bovines as the largest source of methane if I recall correctly. It we want free-range cattle however (I certainly do), then collection becomes a challenge.
According to Mango Materials (using data from USDA methane to market study), the vented methane just from California would be 100 million pounds of phb plastics (Assuming PLA may be similar). The advantage of that methane is that it's almost free as a source material. Re: methane, 18% of methane production is from agriculture, but only a small amount of that is directly from the cows, a large part of it is rotting waste.
Source (Mango/landfills) - http://www.nsf.gov/discoveries/disc_summ.jsp?cntn_id=131553&org=NSF
Methane discussion - http://epa.gov/climatechange/ghgemissions/gases/ch4.html
Methane can be either fossil fuel based or biobased, since anaerobic digestion creates biogas which is about 60% methane and about 40% carbon dioxide, so making PLA from methane CAN be sustainable, if you get it from anaerobically digested plant material, instead of from fossil natural gas.
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