Ok let’s continue talking about recycling:
Here is an overview of the steps involved in recycling plastics from beginning to end, exemplarily by using a mechanical approach.
In order to recycle your plastic, it needs to be transported to the recycling plant.
Transportation is a crucial topic because it can leave a significant footprint. Seldomly, recycling facilities are close to the collection sites. Some studies approximate that more than 45% of plastic waste is exported from the EU to Asia to be recycled.
"Fun" Fact: In 2018 China introduced a ban on 24 types of solid waste, including some plastics. While in 2016 the EU exported about 1.4 Million tons of plastic waste, by 2019 the amount was 99% smaller.
Other Asian countries including Turkey buffered the effect somewhat but significantly more plastic is burned in Europe ever since then.
Still, the plastic exported was probably just seldomly recycled... Even if, the stark footprint of container ships can lead to bigger carbon footprints than producing from virgin materials. Just for your information, railroad movement by train can reduce footprints of transportation up to 75% apparently!
Moving on…
Next up: Sorting
Have you ever asked yourself how all the various plastics jumbled together in a single bin are separated?
There are multiple methods, let us introduce the most common with mechanical recycling made up more than 95% in Europe until now:
1. Sink-Float Separation/ Gravity Based Sorting: In this process, plastic waste is introduced into a tank filled with a liquid solution, often water, with carefully controlled density. Due to the density difference, plastics such as Polypropylene (PP - remember ; ) floats to the surface while heavier plastics sink.
2. Centrifugal/Hydrocyclone Sorting: What shall I say... I think the principle is intuitive - but below is a picture to get an impression what such machines looks like:
3. Dissolution and Reprecipitation: By dissolving a mixture of plastics in a suitable solvent, some polymers can be selectively dissolved while leaving others intact. Subsequent reprecipitation or precipitation of plastics from the solution allows for its isolation and recovery in a purified form.
4. Near Infrared Radiation (NIR) Techniques: NIR spectroscopy relies on the absorption of NIR waves by molecular bonds within plastics, generating characteristic spectra that can be analyzed to identify specific polymers.
The others: There are additional methods such as Melt Flow Index (MFI) Separation that measures the flowability of molten plastics under specific conditions of temperature and pressure, Air-Gravity Based Sorting or Triboelectrostatic sorting. Of course, many more are under development.
- Read more -
Applying The Knowledge
Theoretically you could set up various bins in your lab for the different types of plastics (PP, PET, PS…) but unless you have die-hard sustainability lovers in your team, it is unlikely that they will agree to that.
Furthermore, transport to the recycling facility is difficult since they normally do not keep separate plastic streams.
However, disassembling materials, can help a lot. As seen in the graphics above, many plastics are shredded or cut into small pieces but especially when glued, you can help this process by separating individual pieces. This especially counts for removing non-plastic pieces to properly discard the plastic.
Furthermore, the plastics for tubes or tips are generally of high purity given the required quality and transparency. If items such as caps are not contaminated or tubes/tips only got in touch with Tris-Buffer, discard them in the recycling waste!
Pro Tip: Collection is often a difficult topic in many institutions given that cleaning forces are not necessarily introduced in recycling schemes. Therefore, it is crucial to make sure that they actually separate waste when they take if from your lab! Seems trivial but talking to them (or rather translating to them) can be important.
Take Away
Plastics are shipped all around the world to be recycled – until countries implement bans against waste. To separate plastics, they are often shredded and then sorted by mechanical forces (e.g., in air, fluids or by vibration), chemical approaches (dissolution) or analysis (NIR). Mechanical processes are still the most common.
In your lab, dissemble products, throw all non-contaminated waste into the recycling bin and talk to cleaning staff.
Upcoming Lesson:
Different approaches of recycling plastics to produce new products from them.
