Some (almost) Final Thoughts on Plastics

Image result for polymer

Image source: https://www.sciencenewsforstudents.org/article/explainer-what-are-polymers

Another Earth Day has come and gone and sometimes it feels like we’re no closer to reaching the goal of a sustainable and stable balance between the needs of human society and those of the rest of the inhabitants of our planet.  While I spend most of my time focusing on energy systems, this side trip into plastics, solid waste and recycling has been very elucidating.  Like the rest of the sustainability puzzle, the issues are complex, highly interwoven and the solutions unclear at best.  It’s like trying to untie a massive tangle of yarn not wanting to make any cuts in the continuous strand.

Here are a few random thoughts as I move back to more comfortable territory.

Plastics are amazing. Of all the materials breakthroughs in human history (wood, bronze, iron, steel, etc) I suspect the development of plastics has had the largest impact on society as measured by economic growth and widespread improvement in quality of life.  They bring us great benefits and those benefits should not be overlooked.

“Plastics” is a term applied to a wide range of materials, the vast majority of which are synthesized using petroleum as a feedstock.  They are a form of fossil fuel (diverted to other uses)  By at least one estimate, about 4% of the worlds’ petroleum production goes to the production of plastics.

In spite of the impressive effort put into recycling programs across the country, nearly half of the energy content in municipal solid waste is now ‘non-biogenic‘.  In other words, if you extract the energy from a typical city garbage truck by burning it, you’ll find that the majority of the energy you get will come from the plastic that has been thrown out. (remember, paper cardboard and wood are all from trees).  ( Wonky aside:  yes, there’s a semantic trap here because, technically speaking, plastics are indeed biogenic since petroleum originated in pre-historic plants, but that’s not how the Energy Information Administration  sees it.)

Plastics are remarkably stable compounds. That’s why we use them. It’s also why they don’t readily break down in the environment. Some are susceptible to becoming brittle when exposed to UV radiation, but that just makes them  shatter into smaller pieces of less polymerized plastic.  Many of the so-called biodegradable plastics build on this by readily breaking down, not into the component elements of carbon, hydrogen and oxygen, but into smaller pieces of plastic.

That stability is a curse when it comes to recycling. Much of the plastic we use is formed chemically in the shape it is needed. Much if it cannot simply be “re-melted” and reformed. Those plastics are the ones that are shredded and turned into something else entirely, often of lower value than the original. Those plastics that can be re-melted and re-formed are plagued by problems of contamination and color, which makes the creation of new products from old plastics particularly problematic.

So this all adds up to the fact that, while we’ve been led to believe that plastics are recyclable, they really aren’t.  And the problem is just getting worse, as I’ll explore in my next post.

 

 

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May 16, 2018 at 1:54 am Leave a comment

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