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Even after so many years, why haven't we yet come up with a solution to the plastic problem ?

Why are plastics so hard to decompose via chemical or physical processes into something harmless or useful ?

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closed as too broad by Gaurang Tandon, aventurin, Mithoron, airhuff, Todd Minehardt May 10 '18 at 2:20

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    $\begingroup$ Its not hard, its expensive and the cost of new plastics has been so low that it was not worthwhile. Awareness of the 'plastic problem' is pretty recent and still has not reached some places. $\endgroup$ – Waylander May 9 '18 at 12:43
  • $\begingroup$ I was looking at more like - you leave paper, cotton, organic stuff on the ground , it disappears in a few days-weeks , why does plastic stay there for years ? $\endgroup$ – theenigma017 May 9 '18 at 12:48
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    $\begingroup$ Think about the chemical structure of the materials and what holds them together, mostly proteins and polysaccharides so esters, amides and acetal linkages. Thousands of enzymes evolved to cleave them. Plastic OTOH are all C-C bonds, fewer enzymes do this. $\endgroup$ – Waylander May 9 '18 at 12:54
  • $\begingroup$ Oh i see.... :p $\endgroup$ – theenigma017 May 9 '18 at 13:01
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The (ironic? funny?) thing is, we have this great treasure of petroleum that we use to create many plastics precisely because nature once invented a chemical substance that could be built enzymatically, but, at that point in time, not be destroyed enzymatically. It was a great success, because organisms that built with it were built for eternity - you could gnaw them, but it would not benefit you because nobody could metabolize it. This giant wealth of indestructible organic matter accumulated and accumulated, and even existed for geological timeframes, getting submerged under sand and mud, slowly degenerating to become petroleum. Most lifeforms never caught up, which is why even today cows need special gut bacteria to crack the building blocks of the grass they eat. without them, they would benefit from the grass as much as we do - not at all. The grass would come out just as it went in, just more chewed. ---- So with the plastics that we produce, we have a similar conundrum, there are enzymes to break many of them down, but the creatures that posess them do not rely on them, and therefore do not produce a great deal of them. That's good because otherwise your Tupperware bowl might start being decomposed, and it's bad because all the plastic garbage (or its degenerated form) will be around for a very long time indeed (as were the plants that degenerated into petroleum - hundreds of millions of years, and that material is still around!).

Chemically and physically the problem is not as big. The real problem is economics: To make a plastic bag, investment on the order of one tenth of a cent is necessary - so why not make one for every single piece of consumer goods? To store a discarded plastic bag on a trash-heap? A hundreth or thousandth of a cent. But to clean off all the muck, sort them, recycle them? Two tenths of a cent. So a hundred percent more investment than to produce a new one, and ten to a hundred times more than to just stash it. This is where the government (could/should?) step in: Just tax the shit out of petroleum, and the industry will suddenly find it cheaper to recycle - and then they will, because already they can. (Why tax petroleum, not plastic-generation? Because what's needed for recycling is energy, and if it's just the plastic-generation that's taxed, the industry will burn petroleum to make energy to recycle plastic which would really defeat the purpose...)

You could also genengineer organisms to metabolize most plastics efficiently, but (apart from the (again: main point) economic problems) that would have serious consequences in regards to CO2 (metabolizing ultimately means reducing to CO2), technical safety (currently we rely on plastics ability to not be eaten in a plethora of use cases), and biological safety (who is to tell what might come from those super-metabolizers?) - so the safer way would be to go with the technical solution. Which ist just a matter of economics.

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Most plastics are reusable . The problem is wastes are mixes of various different plastics and other materials . The cost to reliably separate them into specific materials is greater than the cost to make new plastic.

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