Every week, millions of Americans toss their recyclables into a single bin, trusting that their plastic bottles, aluminum cans, and cardboard boxes will be given a new life.

But what really happens after the truck picks them up?

Single-stream recycling makes participating in recycling easy, but behind the scenes, complex sorting systems and contamination mean a large percentage of that material never gets a second life. Reports in recent years have found 15% to 25% of all the materials picked up from recycle bins ends up in landfills instead.

Plastics are among the biggest challenges. Only about 9% of the plastic generated in the U.S. actually gets recycled, according to the Environmental Protection Agency. Some plastic is incinerated to produce energy, but most of the rest ends up in landfills instead.

So, what makes plastic recycling so difficult? As an engineer whose work focuses on reprocessing plastics, I have been exploring potential solutions.

In cities that use single-stream recycling, consumers put all of their recyclable materials—paper, cardboard, plastic, glass, and metal—into a single bin. Once collected, the mixed recyclables are taken to a materials recovery........

© Fast Company