lundi 5 janvier 2009

Point of view: Oxo-biodegradable VS Hydro-biodegradable plastics

I publish here a comment that has been left following my post:
Are biodegradable plastics sustainable?

My question: Are Oxo plastics Degradable or Biodegradable?

It is vital not to confuse oxobiodegradable and hydro-biodegradable plastics.

Ordinary plastic and recycled plastic can now be made oxo-biodegradable.

This is done by including d2w additive which makes it degrade, then biodegrade, on land or at sea, in the light or the dark, in heat or cold, in whatever timescale is required, leaving NO fragments NO methane and NO harmful residues. Oxo-bio can be tested according to American Standard 6954, and is made from a by-product of oil refining which used to be wasted, so nobody is importing extra oil to make it.

There is little or no additional cost, it can be recycled and it is certified safe for food contact. For general info see If all plastic were oxo-biodegradable there would be no North Pacific Garbage Patch.

“Compostable” (or hydro-biodegradable) plastics, usually made from crops, are up to 400% more expensive, many of them are not strong enough for use in high-speed machinery, and they emit methane (a powerful greenhouse gas) in landfill. Also, it is wrong to use land, water and fertilizers to grow crops for bioplastics and biofuels, which drives up the cost of food for the poorest people. See eg The Guardian newspaper (UK) 26th April 2008

Compostable plastic makes sense only if there are industrial composting facilities to receive it in sufficient quantity. Also, as it is expensive to separate compostable plastics from other plastics, many industrial composters do not want plastic of any kind in their feedstock.

Home composting of plastic packaging should not be encouraged, as it is often contaminated with meat or fish residues, and temperatures may not rise high enough to kill the pathogens.

Compostable plastics will damage the recycling process if they get into in a normal plastic recycling waste stream.

They are not really "renewable" either. Just consider the hydrocarbons burned by machines which clear the land, plough the land, make the fertilizers and pesticides, transport them to the farm, sow the seeds, spray the crops, etc.

The same applies to growing cotton or jute to make durable bags. These rapidly become unhygienic if a tomato is squashed or milk is spilled, and become a durable form of litter, but they can be made from washable oxo-bio plastic to last up to 5 years.
Oxo-bio plastics degrade in the upper layers of a landfill, so they will take up less space, but they are completely inert deeper in the landfill in the absence of oxygen. They do not emit methane at any stage.

Paper bags use 300% more energy to produce, they are bulky and heavy and are not strong enough when wet. They will also emit methane in landfill.

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