BIOdegradability or DEgradability ?
End of Life is an over emphasized aspect of a self-serving LIfe Cycle Analysis ( LCA ).
It's a classic 2 + 2 = " what do you want it to be ? "
In any case, the big unknown is how the consumer will dispose of the item - above ground as litter or conscientiously curbside recycled. It is interesting to note that the recycling rate for polyethylene terephthalate #1 is stuck in the low 30% range. It is the most recyclable of all plastics, yet the consumer persists in not recycling it two out of three times.
There are two approaches to accelerated degradation:
BIOdegradable and DEgradable usually referred to as "OXObiodegradable". This article will define both and give a few examples. We are completely objective because we have chosen to wait and see for many reasons. ( more on this later ). The schools of thought have been at loggerheads for over a decade.
We have been approached by suppliers from other countries who have done impressive studies ostensibly to prove their products are degradable in some fashion. They will have only limited success in the USA until they are blessed by the Biodegradable Products Institute "BPI ".
The compliance standard for compostable is ASTM D 6400. Perhaps because they got there first, the Biodegradable Products Institute is the accepted standard for biodegradable plastics.
There are 2 definitions of BIO degradable compostable -" home" and "commercial".
The difference has to do with the mass of the item. A thick thermoformed tray made from the same resin, e.g. PLA, used for packaging salads must be transported to a commercial facility which reaches higher heat which backyard compost piles cannot achieve. Really ?
The expectation is the consumer will segregate the tub and send it to - where ???
Polly Lactic Acid ( PLA ) was the front runner in the biodegradable space. Thicker gauges do not break down in a backyard compost pile. It must be transported to a commercial composter. That requires extra effort by the consumer and fossil fuels to transport. No matter. It is the darling of the Biodegradable Plastics Institute which has come to be the gold standard of biodegradable plastics in the USA anyway. Most feedstocks for compostable are derived from agricultural sources. For this reason, they are referred to as "BIOpolymers". PHA is an example.
It is important to understand that polymer resins derived from agricultural sources are not by definition degradable. Braskem's " green " resins are an example. Their polypropylene and polyethylenes are derived from the natural by-product of sugar production - ethane.
They did a marketing number on the entire planet. Until recently, they were oversold. Lego swallowed the pitch hook, line and sinker. Their blocks have the same half life as plastic derived from evil fossil fuels. In an ironic twist, they set up shop in La Porte, TX to make a billion pounds of polypropylene from natural gas. At the press conference, the CEO praised the US feedstock situation which was a tacit endorsement of fracking.
The OXO degradable approach is to weaken the the polymer chains to make them susceptible to the triggers of light and heat. The compliance standard is ASTM D 6954-04.
Even thin plastic oxobiodegradable films do not degrade when buried because they are not exposed to the triggers.
The crux of the debate is whether or not OXO's are biodegradable or do they just create smaller bits of plastic which are harmful ? So far there is no clear repeatable evidence that oxobiodegradables lead to consumption by microbes.
There has been a proliferation of self-serving degradability standards to account for the wild card of disposal environment. ASTM D 5511 claims to be a propos for disposal above ground.
In any nascent industry there is a dynamic growth curve; degradable polymers is no exception. The plastics industry refers to the growing throng of degradable additive manufacturers as " additive cowboys " because it is a new frontier ripe for patent medicine hustlers.
Here are some links to OXO additive manufacturers:
There is a third category emerging - additives which make other components in a multilayer structure BIO degrade through some sort of contagion action. Biologiq is a major proponent. They recently hit a grand slam by getting their additive specified for Wal Mart's apple bags.
It will be amusing to watch this play out.
Circa 2007, WalMart was gung ho about PLA. It went off the rails when merchandise packaged in PLA put on the shelf in May turned into flakes by July.
No major petrochemical company ( resins are all made by petrochemical companies ) has embraced biodegradable polymers. The closest was Dow Chemical. They sold out their interest in Nature Works long ago. The reason is simple. Remember the triggers of light and heat ? Common sense dictates that it would not take long for railcars sitting out in Texas heat to become a hot mess. It's like comedy - the problem is timing.
The good news is the FTC is taking this seriously and is cracking down.
Caveat: Do your own due diligence. Take the advice of Missourians. Ask the marketers to show you repeatable verifiable results proving compliance with a specific accepted standard, not a home brew. For good measure, ask how they will come to your aid when the FTC initiates action against you.