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Thread: Why don't plastics last forever?

  1. #1 Why don't plastics last forever? 
    Forum Freshman
    Join Date
    May 2010
    An honest question!

    Plastics are polymers. The monomers, such as propylene, are reacted over catalyst so that they develop long chains and "cross-links" to give the polymer some rigidity.

    When exposed to the atmosphere and in particular the sunshine, the polymer chains are damaged by UV light and/ or oxygen from the air.
    So, manufacturers of uPVC windows use anti-UV chemicals in their profile extruders.
    (by the way, uPVC is unplasticised PVC).

    Similarly with polythene, PP, PET, etc.

    Plastics can be re-used, as in India where they use PP flagons for water storage/ transport.

    Plastics can be recycled, as in UK where they are chipped-up and mixed with fresh material before "new" bottle manufacture. (But, the new bottles are not quite as good as "virgin" bottles)

    PET bottles can be chipped and subjected to "solid phase polymerisation" to get rid of the moisture which otherwise causes degradation of the recycled product. This is expensive, consuming capital plant, people-power, and fuel.

    Is there a better way, such as de-polymerisation, which regenerates the monomers, which would then have to be separated by distillation?

    Then, we wouldn't need to send any plastics to landfill.

    Go green Think green Act green
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  3. #2  
    Forum Professor
    Join Date
    Sep 2007
    Polyhydroxybutyrate - and the microbes that make them and consume them.

    Polyhydroxybutyrate (PHB) is a polyhydroxyalkanoate (PHA), a polymer belonging to the polyesters class that was first isolated and characterized in 1925 by French microbiologist Maurice Lemoigne. PHB is produced by micro-organisms (like Alcaligenes eutrophus or Bacillus megaterium) apparently in response to conditions of physiological stress. The polymer is primarily a product of carbon assimilation (from glucose or starch) and is employed by micro-organisms as a form of energy storage molecule to be metabolized when other common energy sources are not available. Microbial biosynthesis of PHB starts with the condensation of two molecules of acetyl-CoA to give acetoacetyl-CoA which is subsequently reduced to hydroxybutyryl-CoA. This latter compound is then used as a monomer to polymerize PHB.[1]

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  4. #3  
    New Member
    Join Date
    Sep 2010
    Many areas do not recycle all kinds of plastic. On the bottom of the bottle there should be a number in a triangle. This is a 'Process Number'. Ask your local Council whether they have facilities in place to recycle plastic of that particular number. They will normally recycle plastic milk bottles.
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  5. #4  
    Join Date
    Oct 2008
    Thomas Friedman (an acceptably "responsible conservative" pundit, I hope?) has a recent essay , widely published in newspapers throughout the US, on one aspect of the progress of plastic recycling in various countries. It's a matter of government interference in "the market", essentially, which is of course abhorrent in the US (where the public is expected to handle any refuse that industry finds more profitable to simply discard into the environment).

    On the physical side, in addition to various bacteria (which are evolving greater competence) UV light degrades most plastics, as does heat and physical abrasion.
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