Degradable Plastics- the dissolving grocery bag
by Lloyd Alter, Toronto 
on 08.24.05
"A British company, Symphony Plastic Technologies plc, has developed an innovative, practical and safe solution to the huge environmental problems caused by the millions of tonnes of plastic waste clogging up our planet." They have also developed a truly slick website covering their invention Degradable Plastics, an additive that "works to break down the carbon-carbon bonds in the plastic leading to a lowering of the molecular weight and eventually to a loss of strength and other properties." ie- give them enough time and they disintegrate. We are of two minds on this- it is great that they have developed a product that can eliminate the visual clutter of refuse bags and plastic waste everywhere, but another part of me says that we should not be picking up new bags every time we go to the store, and we should not be tossing the ones we do get into the street. The issue is not the bags- to quote the immortal Pogo, "we have met the enemy, and he is us" ::Degradable Plastics
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Does this mean:
How about biodegradable bubble wrap, and more publicity about the corn-based packing peanuts? That stuff's at least as bad as grocery bags.
My question is what happens to the molecules that "disintegrate" from these plastic bags? They still exist. They're just smaller. Do they rinse down into the water supply? Do they pollute rivers and kill fish? Do they become inert and essentialy do no harm whatsoever?
I couldn't find any information on the website that discusses the molecular components left behind by the degraded plastic. Currently, when plastics do degrade (after a very long time) the byproduct is toxic to living things. I would imagine they would highlight this concern if they were, in fact, making the plastics inert. Is it possible that increasing the degradation of plastics, before we are prepared counter the toxic side-effects, is even more dangerous than the clutter of solid waste?
Because outright grocery bag bans are happening or being proposed in many developing economies (they plug sewers up and mess the coutryside beyond belief) this sort of technology is the holy grail for polymer pellet formulators. THey want to be able to sell an additive that goes right into existing plastic film extruding equipment so they can use the new product to argue against the bans. The problem as I see it is that governments and NGO's don't have the technical savvy in those places to ask the right questions and then validate the answers. There's no easy way around that problem so Lloyd's approach and the comments are what need to be addressed.
I dug around on the site and found ">this pdf.
Chemically speaking, polyethylene is made up of very long chains of carbon, saturated with hydrogen atoms (also known as hydrocarbon chains). There may be trace amounts of a catalysts and other chemicals used in the processing of the plastic, or dyes and plasticizers depending on use. So, if you take polyethylene and start breaking carbon-carbon bonds at random, at first you'll just be reducing the length of the long carbon atom chains, and making the material more brittle. Eventually, though, the chains will be so short that it won't be fitting to call it polyethylene any more; some shorter hydrocarbon chains are known as paraffin wax. Shorter still would get you paraffin oil and kerosone oil in some order, if I understand it correctly, and then eventually, you'd get down to to butane (4 carbons), propane (3 carbons), ethane (2) and methane (1). The impression I get is that bacteria can start chowing down on hydrocarbon chains long before they're short enough to be considered wax or oil.
Wikipedia has decent entries on paraffin and polyethylene.
Argh, bad link in that last post, I meant to post this link: http://degradable.net/downloads/Pyxis_Biodegradation_300705.pdf
(link)
Sorry about that.
There's more info on the polymer breakdown in the link to a pdf by Gerald Scott at the bottom of the 'How does it work? in detail' page.
It kind of goes like Ike suggests, but even better because the polyolefins degrade into more delicious (for microbes anyway) carboxylic acids rather than paraffins, waxes, etc.
One note on those corn oil products: most of that is from GMO corn (demand was low so they needed another output). So if you happen to be against GE stuff, make sure your corn plastics are clean (which is tough if it's made in the US because of pollen dispersal).
Check these links for more in depth information on Oxo-biodegradable plastic:
http://www.omnipac.com.au/media/DegradablePlastics.pdf
http://www.omnipac.com.au/media/CompostingPatterns.pdf
http://www.omnipac.com.au/media/OxobiodegradablePlastics.pdf
http://www.omnipac.com.au/degradablePlastics.php#3
URGENTLY LOOKING FOR SPECIFIC SELF DISSOLVING "PLASTIC-LIKE" BAG.
We are calling on established producer(s) of self dissolving bags to provide us with a bag or other container to hold chemical powders which are added to a process containing caustic solution. The container must be strong enough to contain the chemical while in storage for weeks at a time yet dissolve quickly once thrown into the caustic containing mix tank. More details will be provided to prospective suppliers upon reply to James Bergoffen, Riverside Specialty Chemicals, Tel 212-769-3440 or e-mail "riverchem@prodigy.net". Requirement will be for several thousand bags per year.