Posted in: Chemistry, IBM Research-Almaden

From garbage to gold: How advances in plastic recycling can help save the environment

Growing up in Seattle made me aware and interested in the environment and its conservation, particularly through recycling. I wanted to help develop technologies that would protect the unique and delicate ecosystem that I saw around me.

recycling

IBM researcher Jeannette Garcia at work

To channel this interest, I got my PhD. in organic synthesis and catalysis — focusing on small-molecule bond forming and breaking reactions — at Boston College. I was attracted to IBM Research by Jim Hedrick’s work PET depolymerization (PET is a common polymer used in plastic bottles and food containers). Less than a year after joining IBM, I had my first breakthrough: the discovery of a high-strength and fully degradable thermoset.

Encouraged by this discovery, today I continue to work as a polymer chemist at IBM Research – Almaden with the aim of applying chemistry to improve the environment and human health.

This led my colleague AliReza Rahimi and me to recently publish a review in Nature Reviews Chemistry, Chemical recycling of waste plastics for new materials production.” The review describes technologies available for sorting and recycling plastic solid waste into feedstocks — as chemical building blocks that can be used for new products — as well as state‑of‑the-art techniques to chemically recycle commercial plastics.

Globally we produce around 150 million tons of plastic solid waste. If we were to recycle it all, we could save around $176 billion dollars per year in terms of energy. Given this significance and the fact that recycling is of interest to many — some 90 percent of Americans believe it’s important — I’d like to share some insight from our nine page review on the types of recycling available and their potential.

There are currently four methods used in plastics recycling:

  • Primary (closed-loop): Primary recycling is the most commonly encountered method of plastic recycling and requires that the polymer is recycled for the same initial use. For example, a recycled bottle is used as material for a new bottle. However, very little post-consumer plastic is recycled in this manner due to purity requirements.
  • Secondary (mechanical): Also known as downgrading or down-cycling, this method uses recycled plastics for production of a product with a lower value use, such as using recycled PET bottles to make carpet.
  • Tertiary (chemical): This process requires the use of a catalyst, and currently is very energy intensive. The temperatures required can be around 300-500 degrees Celsius (572-932 degrees Fahrenheit). If technology were developed to enable chemical recycling of polymers back to the petroleum-derived starting material (known as a monomer), then the isolation and reuse of these starting materials would enable the decoupling of current plastic prices from the current price of crude oil. There are many opportunities in this space to design new catalysts and processes that less energy intensive than current methods.
  • Quaternary (energy recovery): Plastic is burned and energy recovered in the form of heat. It is possible to obtain approximately 36,000 kJ/kg from incinerating plastic. By comparison, recycling plastic saves about 60-90,000 kJ/kg. Therefore, incineration as an end-of-life treatment regimen for plastics ultimately cannot compete with recycling in terms of overall energy savings.

Although mechanical recycling is currently the most commonly used recycling method, its drawback is that plastics have to go through a melt-and-remold process, which causes the materials to lose important properties such as strength, flexibility, or clarity. In theory, if chemical recycling methods were developed that enabled 100 percent breakdown for plastics to monomer, then the plastic could be recycled an infinite number of times!

One can think of chemical recycling like Legos, where the monomer is the individual Lego piece and the polymer is represented when you link all the pieces together into something larger. Once constructed, you can take it apart again and then rebuild the same thing or perhaps something else. Building the large piece is analogous to polymerization (plastic production) and taking it apart is like a chemical recycling process.

recycling

Cutting up old CDs for recycling

Because the process enables chemical and structural flexibility we can use chemical recycling approaches to make “value add” materials from waste plastics. In an example of this, we demonstrated that its possible to break down e-waste (in the form of waste CDs) chemically and use the monomer to make a high-performance thermoplastic, polysulfone, that can be used to purify water and in high-temperature medical equipment.

Another approach is to design plastics that have a built-in, triggerable mechanism for taking them apart chemically. Self-immolative polymers, which have been studied for decades and can be used for lithography, sensors, and drug delivery applications, are examples of a controlled approach to polymer deconstruction. However, often self-immolative polymers are not very robust and can be sensitive to things like heat, light or mechanical stress. In order to access high-performance revertible polymers, polymer chemists can design the networks in such a way as to target properties such as strength, rigidity, and environmental robustness in the material, while incorporating chemical structures that can be taken apart under the right stimulus. My first breakthrough at IBM Research is an example of this — a strong thermoset polymer that could be selectively reverted in acid.

Overall, formulating polymers and plastics that can be broken down and catalysts for the breakdown of commercially used polymers will be critical for treating plastics that have been discarded in the environment and, ultimately, for decreasing society’s dependence on virgin materials directly produced from petroleum.

Polymers that are currently slowly decomposing for the next 500 years in landfills, or floating in the ocean, can be thought of as a preserved source of crude oil. This is ultimately why it’s time to start thinking of them as resources and of garbage as gold.

Jeannette Garcia is one of MIT Tech Review’s 2015 35 Innovators Under 35, one of Business Insider’s 17 IBM Research Rock Stars, and the recipient of the Individual World Technology Award in Materials. In 2016, Garcia was named as one of Foreign Policy’s Top 100 Global Thinkers. In 2017, she was the first recipient of the ACS POLY Division’s Young Industrial Polymer Chemist Award and chosen as a YWCA Emerging Leader. She has authored over 34 papers, has over 70 patents granted and pending and is an IBM Master Inventor. Her work has been featured in The New York Times, CNN, Wall Street Journal, Scientific American and HBO VICE.

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recycling

Jeannette Garcia

Polymer chemist, IBM Research