How do recyclable plastics work?


© Paul Taylor/Corbis

So what's the deal with plastic recycling?

I know, it's easy to just throw it all in the bin and let God sort it out. But there's a bit more to it than that.

As explained in "How Plastics Work," oil-based plastics don't degrade, but many types can be recycled. We're talking the likes of PP, LDPE, HDPE, PET, and PVC. But just because a plastic can be recycled doesn't mean it's always economically feasible to do so. In other words, check the instructions from your local recycling service to see what's accepted.

But when it comes time to breathe new life into dead polymers, here's how it goes down:

  1. First up, inspectors weed out contaminants and bad plastics.
  2. Then recyclable plastics are shredded and washed.
  3. The resulting plastic shreds are separated based on density.
  4. Next, the shreds are dried and melted.
  5. Now it's time to drain that molten plastic through a series of screens.
  6. Then the molten plastic is cooled and shredded into pellets.
  7. Finally, recyclers sell these plastic pellets right back to the plastic companies.

Bioplastics such as corn plastic offer a biodegradable alternative, but be careful chucking it in with the oil-based plastics. Even a relatively small amount of bioplastic can contaminate conventional plastic recycling, preventing the salvaged plastic from being reused. Sadly, bioplastics don't necessarily break down in your backyard compost heap either. Corn plastic, for instance, only composts in the hot, moist settings of a commercial composting facility.

Plastics certainly introduce a number of complications, but they've proven rather irreplaceable. At least for now.


About the Author: Robert Lamb spent his childhood reading books and staring into the woods — first in Newfoundland, Canada and then in rural Tennessee. There was also a long stretch in which he was terrified of alien abduction. He earned a degree in creative writing. He taught high school and then attended journalism school. He wrote for the smallest of small-town newspapers before finally becoming a full-time science writer and podcaster. He’s currently a senior writer at HowStuffWorks and has co-hosted the science podcast Stuff to Blow Your Mind since its inception in 2010. In his spare time, he enjoys traveling with his wife Bonnie, discussing dinosaurs with his son Bastian and crafting the occasional work of fiction.