In module 2 we studied the WEEE recycling process and learned how plastics are separated from other fractions (such as metals). Now we will take a more detailed look at how the plastic fraction is sorted by polymer type through the application of different sorting methods. Additionally we will discuss how these technologies inform design for recycling guidelines.

Main Takeaways

• Sink float density separation is a commonly used sorting method. Polymer fragments are fed into a flotation bath in which they either float or sink, depending on their densities.
• Triboelectric separation is based on the differences in electrostatic properties between polymers.
• Near infrared spectroscopy is an optical sorting method that is based on how different polymers reflect light of different wavelengths.
• Avoid creating permanent connections between different polymers. If fragments remain connected after shredding, they are unlikely to be sorted and will end up as waste.
• Whenever possible also try to avoid additives, coatings, paints and polymer blends. These can contaminate the recycled stream or even alter the density of the polymer, causing it to be misidentified.

Further Reading (optional)

Below we have listed a few useful resources about plastics recycling. They are not required to complete the course.

• Ragaert, K., Delva, L., & Van Geem, K. (2017). Mechanical and chemical recycling of solid plastic waste. Waste management, 69, 24-58.
• Delva, L., Van Kets, K., Kuzmanović, M., Demets, R., Hubo, S., Mys, N. & Ragaert, K. (2019).  Mechanical Recycling Of Polymers For Dummies.
• Wang, C. Q., Wang, H., Fu, J. G., & Liu, Y. N. (2015). Flotation separation of waste plastics for recycling – A review. Waste Management, 41, 28-38.