Earth Week Chemsplainer: Why is it so difficult to recycle plastics?

During a recent interview, Erin Stache, assistant professor of chemistry, unpacked several of the items she uses in educational talks: a plastic newspaper bag, a coffee cup lid, a detergent bottle, a plastic water bottle, Tupperware, a PVC pipe. She makes the point that these six items are all the same kind of plastic, and yet their inherent differences would require almost as many ways to recycle them.  

This simple demonstration underscores the biggest problem facing plastics today: how can researchers come up with a process that recycles at least the most common forms? The quick answer is, they can’t. It is a far more complex challenge than the public is led to believe. Here is Stache’s take on what we should know about recycling.

Why aren’t we able to recycle more plastic?

The simple answer is that it’s incredibly complicated. Because of the massive scope of the problem, there isn’t one overarching solution. “Plastic” is a generic term for thousands if not hundreds of thousands of different products, encompassing the types of materials from a glue or paint to a hard thermoplastic like a tire. These all fall under the generic umbrella of “plastic.”

As a result, we’re talking about a whole range of properties and materials. The idea that a one-size-fits-all solution is going to solve this problem is just not realistic. While mechanical recycling may work for one type of polymer, it’s ineffective for another. We need to have the appropriate infrastructure in place for each specific type of plastic recycling.

Can you provide an example?

Take your shampoo bottles: those are multiple types of polymeric materials. They usually have adhesive or glue, which is a different type of polymer that you have to have a process for. And then you have different colors, white, black, blue bottles, all caused by different pigmented additives. There could be co-polymers or additives that act as plasticizers, small molecules, dyes, other fillers – multiple, chemically distinct materials within a single product – and all of this must be considered. So, when I say it’s complicated, I mean it’s incredibly complicated.

To put a positive spin on this, plastics really have enabled so much in our modern society. We would not have modern medicine, efficient transportation, transportation of goods across the country and across the world. Plastics are the cheapest, lightweight materials, and alternatives often have added environmental or opportunity costs.

As a researcher, where do you start?

It comes down to fundamentals and practicality. As a society, we were able to develop these materials because people understood the fundamental science of polymerization to make them. The process of making these materials is a downhill process – it’s very easy energetically. But if you want to recycle it, you have to go back up that hill, which is far more energy-intensive.

As researchers, we can develop unique solutions, but then we ask the question: what is the cost of this recycling process? We can develop the most perfect recycling strategy in the lab, but is it something that’s going to be economically feasible? The balance of efficiency and practicality must be well struck.

How is your research contributing?

In the Stache Lab, we’re using something called photothermal conversion so we can convert light to photothermally depolymerize these plastics … just by using sunlight. We’re developing these techniques using standard LEDs and examining irradiation intensity, different photothermal agents, understanding how they incorporate into the polymers themselves, how they influence the properties of the plastic, how they impact the shelf life of materials.

It’s an important problem, and I go to work every day knowing that I’m working on something that impacts every person and ecosystem on the planet.

What can the public do to really make a difference now?

The public needs to appreciate that most materials aren’t being recycled, and so bringing that awareness into your daily practices by reducing your plastic consumption … presumably, that would help.  We take so many things for granted, do so much out of convenience. Take-out containers, plastic utensils, straws …. Ask yourself, do I need to use this single use plastic, or can I develop a new practice to avoid it?

Certainly, find out about your local recycling centers and the types of plastics they accept and recycle so you don’t throw in plastics that aren’t going to be recycled. Finding creative solutions to reuse plastic waste materials at home can be fun projects while extending the lifetime of plastics, one piece at a time.