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This answer to another question brought up the point that "recycling" of plastic is often more accurately "downcycling." From Wikipedia:

Downcycling, also referred to as cascading, describes the recycling of waste in cases where the recycled material is of lower quality and functionality than the original material.

How is this effect quantified in the case of plastics? For instance, if I send in 100 high-quality plastic water bottles for recycling, what sorts of things can be made from the resulting materials? And what after that? How many steps are there? At what point do the intermediate steps become unusable?

  • What sort of plastic? – Graham Chiu Mar 14 '18 at 22:26
  • @GrahamChiu any sort -- I'm interested in whatever data is available on the topic. – LShaver Mar 14 '18 at 23:18
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HDPE plastic is usually shredded, melted and then pelletized where the pellets are then used to create new HDPE products. It can theoretically be recycled indefinitely except that usually contamination appears from other plastic fibres and the contents of HDPE containers so that this is practically limited to 7-8 recycles. One company, Carbios, has developed an enzymatic approach to recycle PET to potentially allow infinite recycling, and they are attempting to expand their process to include other plastics.

For many non-food HDPE products it is cheaper to purchase recycled pellets to use in manufacturing than to use virgin plastics. If one considers plant containers etc to be of a lower utility than food containers then one could say that this is downcycling of the plastic.

Recycling HDPE has many benefits. For example, it is more cost efficient to produce a product from recycled HDPE than it is to manufacture ‘virgin’ plastic.

HDPE, like many plastic polymers, is produced using considerable amounts of fossil fuels and it takes a total of 1.75kg of oil to manufacture just 1kg of HDPE.

Because it is not autoclavable it is not possible to do non-destructive sterilization of food containers made from HDPE.

https://www.azocleantech.com/article.aspx?ArticleID=255

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    I don't understand the logical connection between these two statements: "However, some industries that use HDPE for their products eg. garden pots, ropes etc it is cheaper to use recycled HDPE than purchase virgin HDPE. And this is why it is downcycled.". Can you clarify this part of the answer? Why does "cheaper to use recycled" result in it being "downcycled"? – Jean-Paul Calderone Mar 15 '18 at 15:33
  • It's cheaper for whatever product to use recycled hdpe than virgin. The food industry prefers virgin. – Graham Chiu Mar 15 '18 at 19:36
  • Do you have any references for your claim that HDPE can be recycled indefinitely? – THelper Mar 16 '18 at 10:24
  • Thanks for sharing, but the article is about PET and it says they are working on achieving this. I am not able to find any article that says HDPE can be recycled infinitely, but I did find this article where they say it can be recycled at least 10 times – THelper Mar 16 '18 at 11:33

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