The promise of sustainable manufacturing can feel elusive or empty. When can we call a company or a product sustainable? That’s a question someone asked me after a talk I gave recently. My facetious answer was “never.”
The full answer is more nuanced. As I told the audience member, just claiming sustainability does no good without real data on greenhouse gas emissions, resource use, and toxicity. It also exposes a company to being called out for greenwashing, and rightly so.
It’s About Materials
If there is such a thing as sustainable manufacturing, it needs to start with product design. Design, in turn, relies on material inputs. Choices in which materials to use and how to procure them affect everything from water and energy consumption to repairability.
When sourcing materials, manufacturers don’t always consider long-term social and environmental impacts. The key concerns are performance, availability, and cost. Those are still essential, but companies can do more.
It feels easiest to continue business as usual. That mean designing and making products the way it’s “always” been done or choosing suppliers with whom you have years-long or decades-long relationships. That’s not the only way to do things.
Five Questions to Ask
We can all add sustainability to the equation by asking some questions when choosing materials.
- Where does the material originate? That means more than considering the country where the supplier is based. When you trace the supply chain all the way back to raw material extraction or recycled content, you get insights into the environmental and social impact of the materials you use.
- What alternatives are available that can meet your needs for strength, weight, durability, chemical compatibility, or other factors? By keeping an open mind, you might discover something that is equal or even better in performance with less negative impact.
- How can product design affect how much material you need or how many materials you need to incorporate? By considering materials choices early in the design process, you may find ways to save resources.
- How long is availability expected to continue? When considering availability, look beyond the obvious question of whether supplier A or B can deliver the quantity you need each month. Sustainability means thinking longer term. Will the material as sourced still be available years from now?
- What does the entire product lifecycle look like? Can components be repaired or replaced if something breaks? What are the options for the product after it no longer works or the customer doesn’t want it any longer, and how do your materials choices affect the options?
Thoughtful consideration of these questions can help move toward a more circular economy.
Circularity and Recycling
I want to clarify something up front. Circularity and recycling are not the same thing.
Slapping a “recyclable” label on your product or packaging doesn’t make it circular. The item may or may not actually get to a recycling facility. Even if it does, it might not actually get processed into a new item, or it might go to a dead end where it gets reused once (the open-loop path in the diagram below).
When it comes to recycling, plastics are especially problematic. There are limits to the number of times most plastics can get recycled without losing quality. Another problem is that toxic additives in many plastics give them desirable properties like their ability to be easily molded into any shape. Each time plastics are recycled, more of these additives enter the manufacturing process.
Absolute vs Relative Circularity
If circularity isn’t recycling, what is it? In an ideal circular economy, consumption would be completely decoupled from resource extraction. There would be no need to extract any more raw materials from the earth to make products because all inputs would be materials that are renewable or have already been extracted.
This fictional ideal represents 100% circularity. It’s fictional because it’s impossible to achieve.
Absolute circularity would mean that once a ton of raw material is extracted and turned into a usable product, that ton would stay in use forever. That’s not possible—the laws of physics dictate that there is some loss along the way in every processing or recycling step. There is no such thing as a perpetual motion machine.
Reducing leaks in the cycle (external facing arrows) increases circularity. Absolute circularity would mean no leaks.
Instead, the goal is to increase relative circularity, where each ton of raw material is reused as many times as possible before being discarded into a landfill or burned for fuel. Unfortunately, even though people talk about increasing circularity, the world is moving in the opposite direction. Global circularity dropped from 9.1% in 2018 to 7.2% in 2023, according to the Circularity Gap Report.
The reason for the drop in circularity is expanded material extraction and production. Plastics are a key example.
Conventional plastics, which have become ubiquitous in the past 50 years, are relatively new. The first commercial plastics were introduced in the early twentieth century. Most plastics in common use today were invented between 1930 and 1960.
The past 60 years have seen explosive growth in the amount of plastic being produced annually. Available data doesn’t look promising for those who want to curb production and improve circularity.
Recycled Content
One common misconception about circularity is that by increasing the recycled content in products, manufacturers have solved the problem. Greater recycled content can drive more circularity, but not as much as you might think.
Companies that make products from aluminum or steel can improve circularity by sourcing recycled metals, subject to availability. However, the recycling process still requires energy to grind and melt incoming metal. Does that energy come from fossil fuels or renewables? The answer matters.
In another example, the trend of making textiles from recycled water bottles might sound good on the surface. Surely keeping polyethylene terephthalate (PET) in circulation is better than extracting more oil to make new polyester fabrics, right?
Extrapolating a bit, if all polyester clothing were made from recycled PET bottles, that increases the market for them. It gives producers another excuse to keep making billions of plastic bottles every year. And it gives clothing makers an excuse to sell more clothing at higher prices because of the “green” label.
Then there’s the issue of microplastics shedding and potentially toxic additives. Recycled PET does nothing to eliminate those concerns and might exacerbate them.
There are alternatives. Using recycled PET starts with the assumption that clothing needs to be made from polyester. Many other fibers are available. Plants and animals (including humans) yield materials that can be spun into yarn or thread. Starting with an open mind and considering all the five questions I listed above may yield surprising results.
Final Thoughts
Engineered materials can be impressive. When I took my first materials science course in college, I was so fascinated by the idea that engineers could tailor material properties with slight changes in composition or processing that I pursued a PhD in Materials Science.
It wasn’t until years later that I considered the negative impacts resulting from some of these fascinating materials. That got me thinking about the importance of looking beyond material properties to consider how new materials development might help or hurt people and the natural environment.
Now when I talk to students or business professionals, I ask questions that challenge their assumptions. In turn, I ask them to do the same when they lead projects, design products, or consider the next step in their careers.
If society is to move to a more circular economy that relies less on extractive practices, materials scientists can play a starring role. I find that both an exciting prospect and a difficult challenge. Are you up for it?
Footnotes
1. Geyer, Roland, Jenna R. Jambeck, and Kara Lavender Law. 2017. “Production, Use, and Fate of All Plastics Ever Made.” Science Advances 3 (7). https://doi.org/10.1126/sciadv.1700782 [1950-2015 data]
2. OECD. 2022. “Plastics Use by Type.” OECD Library. Paris. 2022. https://www.oecd-ilibrary.org/environment/data/global-plastic-outlook/plastics-use-by-type_ad13eab0-en?. [2020-2022 data].
