chemoleo
Biochemicus Energeticus
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Degradable Plastics
Today I went shopping, and as usual placed items into a plastic bag.
The plastic bag said (it underwent a burntest in the meantime  ):
"This plastic bag is 100% degradable but you can still reuse it!"
The plastic start to degrade in approx. 18 months time. The whole process will take about 3 years.
The company making the bag is http://www.degradable.net/
How does it work? The company says (http://www.degradable.net/how/index.shtml)
| Quote: | The degradation process is initiated at the time the polyethylene or polypropylene is extruded by the inclusion of a small amount of a special
additive. This additive 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. Stabilisers work to ensure that a sufficiently long useful life is provided for each specific application. For
example, a refuse sack might require a useful life of say 18 months before beginning to lose its strength whereas a bread bag might only require a few
weeks.
Significantly, the d2w™ range does not need a biologically active environment to start degrading - this will happen even if the plastic is left in
the open air! This is very important if we are to address the serious litter problems caused by waste plastic. For this reason in particular, d2w™
'totally degradable' plastic is superior to 'bio-degradable' which requires the plastic to be in a biologically active environment (for example, by
being buried in the ground) before the degradation process is initiated. |
Quizically they don't say what the additive is.
Anyone heard anything about it?
What's the chemistry behind it, the products being what exactly?
Just found another page:
| Quote: | | This pro-degradant is in the form of a metal salt that causes a breakdown of the carbon-carbon bonds in the molecular chains - i.e.
chain cleavage, or scission is activated. The plastic product will become brittle and quickly disintegrate into tiny flakes. As the chains continue to
reduce in size, oxygen is permitted to bond with the carbon and produce CO2. The molecular mass quickly descends to below 40,000u and at that stage,
the material effectively becomes water wettable and micro-organisms can access the carbon and hydrogen. Carbon is used for cell wall structure etc.
and it is exhausted as CO2 and the hydrogen as H2O. This stage can accurately be described as bio-degradation. |
From http://www.degradable.net/how/in_detail.shtml
Betw 1-3% of the additive are required.
Now what is this metal salt that can cleave C-C bonds?
Never Stop to Begin, and Never Begin to Stop...
Tolerance is good. But not with the intolerant! (Wilhelm Busch)
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not_important
International Hazard
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I would expect transition metals, ignoring cost and toxicity issues Co, Fe, Ce, V, Bi, Sb, and Mn are all candidates, as is TiO2 in the proper crystal
form and polyheteroacids based on Mo and W.
The company behinds this, Symphony Environmental, has been in the news a bit over the last several years. Recently it is for extravagant claims for
this additive, earlier they were in court accused of swiping another company's patented invention ... for an additive to make plastics degrade.
In that patent, US 5854304, Co, Ce, and Fe stearates are the preferred metals. In the specific example it is cobalt stearate with citric acid as the
stabiliser or life extender; I suspect it gets oxidised first over the polyolefins.
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chemoleo
Biochemicus Energeticus
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Registered: 23-7-2003
Location: England Germany
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I found another bag being 'compostable', being manufactured by
http://www.marchant.co.uk/bio-website/intro-bio.htm
It looks like normal PE, feels like LD PE , burns like it and smells like it (paraffin).
The website doesn't unfortunately say what makes it compostable.
I'll keep it for a while and see what happens to it.
I'm yet looking for products wrapped in polylactic acid!
Never Stop to Begin, and Never Begin to Stop...
Tolerance is good. But not with the intolerant! (Wilhelm Busch)
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