Part 2 of Green Innovation: Recycling Plastics Series

The bulk of sorting, at least at the consumer-level, is done by the plastic collection agencies. However, in industrial-scale recycling – where businesses sometimes send their plastics without sorting them – different methods are used. Northstar’s article on the subject discusses how these plastics can be sorted with water and heat.

By placing plastics in water, their density (relative to water) can be determined. Typically, LDPE, HDPE, and PP plastics will sink while PET, PVC, and PS plastics will float.

When heating the plastics with a flame, the plastic’s identification is more precise. The plastics that float should also produce a blue flame with white smoke. Those that have a waxy smell are usually LDPE or HDPE, but the plastic with a sweet smell is typically PP.

Of the plastics that typically sink, each has their own properties when burning. If, when melting, it has a burnt-sugar smell, the plastic is likely PET. If the plastic ignites only at higher temperatures (with a blue/green flame), it is likely PVC. Finally, if the plastic does not drip and has black, sooty smoke, it is likely PS.

It’s pretty clear, however, that this process is time-consuming and inefficient for large batches of unsorted plastics. To solve this issue, a group of researchers designed a way to process almost 1.4 tonnes of plastic every hour – with computers.

They use the unique fluorescence patterns of plastics to identify and separate them. For more information on the process check out this research paper. In the future, I may create a post about the topic, so stay ready!

If you liked this post, be prepared for Part 3 of the Green Innovation: Plastics Recycling series.