Plastics - Uses, problems, and solutions

Updated: Aug 6

Plastics cause many environmental problems. Used the right way, however, their intrinsic advantages may actually make them environmental benefactors.

If you want to know more, read this article.

Plastics receive a lot of bad press (and, yes, we use the word ‘plastics’ indiscriminately here — just as indiscriminately as it is used in most of the aforementioned bad press).




This bad press is not entirely unjustified.


However, it should be directed less at the material itself than at its (mis)use as it is this misuse and lack of proper recycling that’s causing the problems.


There are many different kinds of plastics in widespread use.


And the literature regarding its manufacture, use, and the problems associated with it fills libraries.


In this article we shall concentrate on one particular kind of plastic material.


The material of our interest, answers to the beautiful name of polyethylene terephthalate — a bit of a mouthful perhaps, so, for short it’s also called PET.


It is what your cola-bottle is made of.



Image by LauraTara from Pixabay


As it is, PET is a fantastically useful and environmentally beneficial material. The last bit may sound a little surprising at first but it is nonetheless true.


Consider this simple back-of-the-envelope calculation.


And this is really nothing more than a back-of-the-envelope estimation, it is not proper thermodynamics. However, it does illustrate the point.


(If you’re scared of a little maths, please skip this section and go directly here 👊🏼.)




- A 1.0 l PET bottle weighs around 60 g.
- A 0.7 l glass bottle weighs around 600 g. [REF1]
- The melting point of PET is approx. 250 °C,
- That of glass is approx. 1000 °C.[REF2, REF3]
- The heat capacities of PET and glass are 1.3 kJ/kg/K and 0.8 kJ/kg/K, respectively.[REF4, REF5]

In the form of an equation, it looks like this:
Q = m x C x ΔT
where Q is the amount of energy in Joules,
m is the mass in grams,
C is the heat capacity in Joules per gram per Kelvin, and
ΔT is the temperature difference in Kelvin

👊🏼 Plugging the above numbers into this equation yields 18 and 470 kJ for PET and glass per bottle, respectively —


a significant energetic advantage for PET.

NB: This is the energy required to melt enough material to make one bottle. It is not the energy required to produce the material in the first place.


If you would like to experience another advantage of PET all you need to do is go to the shop, buy three bottles of water (bottles once in glass and once in PET) and carry them home in your shopping bag.


On your arrival at home you will feel less tired if the bottles were made of PET.


The same reduction in weight also applies to lorry loads of bottles where it results in reduced fuel consumption.


Drinks bottles are only one application of PET.


The same reduction in weight also applies to lorry loads of bottles where it results in reduced fuel consumption.


PET is used in many other forms as well such as spun fibres (e.g. the fleece in your fancy outdoor jacket is made from it) or thin films (e.g. the electromagnetic tapes used in audio cassettes is made of PET — the older generation may remember this).



Of course life isn’t quite this simple.


Glass bottles can be reused more often than PET bottles
and
PET discarded into the environment has the tendency to break down into microscopic particles which then accumulate in animals with negative consequences for food chains.

The problem with plastics (and remember: in this article we take PET as pars pro toto) is less one of the material itself than one of a lack of reuse and/or recycling.



https://images.app.goo.gl/h48uTic4y3WSg6Fs6


PET lends itself favourably to recycling, for instance it is often made into fibres, non-food containers, or building materials such as polyurethane foams.


Turning used PET bottles into fibres for clothing or carpets demonstrates one problem with recycling plastics:


A piece of waste is prevented from being sent to a landfill site.

That is an advantage.


However, the reformed plastic material (a piece of clothing or carpet) will, once it reaches the end of its useful life, most likely be sent to a landfill site,


in other words, the negative impact in the environment is delayed, not averted.

In addition to that, while the recycling rate of PET bottles is reasonably high there are many other kinds of PET-based packaging which are not recycled to anything near the same extent, such as the so-called clam-shell packs for anything from pastry products to fresh fruit to meat.


Some steps are being taken in the right direction.


The EU has banned some plastic products such as straws and Q-tips.[REF6]



https://images.app.goo.gl/VUHABhsKj4Af82Re6


In the US, the American plastics and resin producers have pledged to reach full circularity by 2040.[REF7]


Considering the worldwide increase in plastics production and use this might be criticised as too little too late but it is a step in the right direction all the same.

Innovative solutions


Let’s say, we’ve solved he problem of the low recycling rate of plastics:


What do we do with all the plastic products that are being returned by the customers?

Here are two innovative solutions:


Plastic roads


The Dutch company KWS wants to build roads out of plastic instead of the more traditional tarmac.


They claim that roads built with their technology last 3 times longer, are built 70% faster, are 4 times lighter, and are completely circular.[REF8]


And if plastic could be recycled ad infinitum?


The French company Carbios has developed an enzymatic method that transforms the plastic polymers back into the respective monomers.


This means that at the end of its useful life a PET bottle can be converted into its constituent monomers, and these monomers can then be re-polymerised to make yet another bottle (or whatever else).


This approach lends itself particularly well to polyesters (such as PET).[REF9]


To sum it all up:
Plastics are not at the end of their road.
Used wisely and recycled properly they can form an integral part of a circular economy.

REFERENCES

[1] https://www.hoellensprudel.de/sortiment/masse-gewichte-einheiten.html [Last accessed on June 21st 2020]

[2] https://en.wikipedia.org/wiki/Polyethylene_terephthalate [Last accessed on June 21st 2020]

[3] https://en.wikipedia.org/wiki/List_of_physical_properties_of_glass [Last accessed on June 21st 2020]

[4] http://www.goodfellow.com/E/Polyethylene-terephthalate.html [Last accessed on June 21st 2020]

[5] https://www.engineeringtoolbox.com/specific-heat-solids-d_154.html [Last accessed on June 21st 2020]

[6] https://www.europarl.europa.eu/news/en/press-room/20190321IPR32111/parliament-seals-ban-on-throwaway-plastics-by-2021 [Last accessed on June 21st 2020]

[7] https://www.americanchemistry.com/Media/PressReleasesTranscripts/ACC-news-releases/US-Plastics-Producers-Set-Circular-Economy-Goals-to-Recycle-or-Recover-100-Percent-of-Plastic-Packaging-by-2040.html [Last accessed on June 21st 2020]

[8] https://www.plasticroad.eu/en/ [Last accessed on June 21st 2020]

[9] https://carbios.fr/en/technology/biorecycling/ [Last accessed on June 21st 2020]

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