To Recycle A Shoe

Is this the way?

If you haven’t seen this story by Reuters then it’s worth a read. If that story seems too long let me quickly summarize it for you.

Dow and Singapore decided that recycling athletic shoes sounds like a good idea and using the outsole and midsole of an athletic shoe would be an ideal material to downcycle into running tracks. Reuters decided to investigate more and had about 12 shoes with trackers and followed them to see where the shoes would end up in the recycling process. They ended up in the Philippines. Being sold as used shoes.

The implications that I got from this story are that Dow appears to either be 1) lying to the public about this program or 2) too stupid to know they are being duped by their partners. If implication 1 is closer to the truth, then what else is Dow lying about when it comes to recycling and why are they doing it? Perhaps it’s to look good:

On the evening of Oct. 6, Fong and other partners in the Singapore shoe recycling program stepped onto the stage of an elegant ballroom at the Equarius Hotel beach resort on Sentosa Island, just off the mainland. There they were presented with the “Most Sustainable Collaboration” award at a glitzy event hosted by the Singapore International Chamber of Commerce, the city-state’s oldest business association.

The risk doesn’t seem to be worth this award to me for Dow. Why risk the little bit of brand trust you might have for recycling something as simple as shoes? So people buy more polyurethanes or feel less guilty about buying a fresh pair of Nikes every year? I think it is more likely that Dow just didn’t care to follow-up on if their partners were actually recycling the shoes. Actually recycling shoes is quite difficult.

Having worked in shoe manufacturing for a hot minute (~13 months) I feel somewhat qualified to at least speak to some of the challenges I see in the modern athletic shoe business. All of the old Shoe Dogs in the audience feel free to call me out in the comments when I get it wrong.

Old Shoe Dogs

Shoe manufacturing is not an easy business. There are up to 67 individual parts of a shoe with a whole host of design characteristics that when slightly off can render a whole container of shoes worthless. If the toe spring is just a little bit too much an athletic shoe can go from looking like it might help you run faster to making you look a bit more like an elf from a movie. The “toe spring” is that slight uplift in the toe of your shoe. No toe spring might mean you are wearing a pair of Converse All-Stars and too much you might be auditioning for a part in “Elf 2” with an older Will Farrell and Zooey Deschanel playing your parents.

Toe spring and a whole host of other seemingly mundane components and design characteristics are what make a modern shoe. It’s a mixture of material selection, manufacturing process controls, and design that need to come together into an article that costs as little as possible to make and can yield a maximum profit. It’s why the labor of their construction is in places like rural northern Vietnam and Bangladesh.

This is the place where Shoe Dogs can really shine. I think if the journalists of the Reuters story had asked an actual Shoe Dog if recycling shoes is possible they probably would have laughed and said something like, “Yeah, but it might cost you. Happy to consult and help you figure it out.” This translates to, “hell no, but the fact that you are asking me indicates you have no idea what you are talking about so I might as well fleece you for as much money as I can before you figure that out.”

I’m no Shoe Dog, but if I’ve learned anything about my time in shoe manufacturing it’s that the sticking point on recycling is the glue.

Modern Shoe Construction

I won’t bore you with the details on older shoe construction technologies such as goodyear welt construction, but modern athletic shoes are 100% reliant on synthetic glues keeping the outsole, midsole, and upper connected. These glues are designed to ensure that materials of the shoe will fail before the bond holding them together fails.

This means that it’s nearly impossible to reliably separate a midsole from the outsole and this is a problem since the outsole is often some sort of rubber and the midsole is either an ethylene vinyl acetate foam (EVA) or a polyurethane (PU). Some shoes like Allbirds are just foam attached to an upper and it’s why when their minimal amount of tread wears out you are slipping around in the rain. An inability to separate your midsole from the outsole or the upper cleanly introduces a mixture of materials that is either 1) more costly to finish separating or 2) contaminates your recycling process. Also, there is a significant amount of labor separating the two components that it makes the process non-trivial even if you have the right equipment.

The reason the glues are made this way is that the consumer wants their shoes to last as long as possible. Imagine buying a pair of Nikes that cost $220 dollars and a year into owning them the outsole starts to delaminate from your midsole. Unacceptable to most people I think. Repeated wear of a shoe until the outsole is ground down completely due to friction is an acceptable mode of wearing out, but the glue failing is often seen as unacceptable. Wearing out an outsole is a kind of material failure that feels right, but a glue losing adhesive strength is not.

There is a part of us that wants our shoes to last as long as possible. This might be different for everyone and getting a year or two out of some shoes might be acceptable while someone else wants five years or maybe a collector wants 10 years. Either way,the glue cannot fail until we are ready to be “finished” with our shoes. Designing an adhesive chemistry that can fit the needs of everyone from a function standpoint is challenging and then add in sustainability goals and it’s even more difficult.

But let’s say we figured out the sticking problem and we can cleanly separate the outsole from the midsole from the upper. We still need to grind the outsole and midsole into small enough particles to get incorporated into a binder and then reapplied as a running track. That means cooling down these flexible materials until they are rigid (below their glass transition temperature) and grinding them into little particles (yeah, probably some microplastics in there too). All of this costs money, if we can separate the shoe components, and in the end it’s likely that the recycled shoes are on cost parity or maybe slightly more expensive than virgin materials. Also, I suspect the uppers of the shoes are just disposed of because the stitching makes it even harder to separate the different materials. Seems like a lot of effort, time, and money to make us feel better about buying some Nikes. How many running tracks do we actually need to build and is that juice worth the squeeze?

It’s Everything. Not Just Packaging.

The more use cases you see for synthetic polymers the easier it is to spot them in everyday life. The paint on the walls to the shoes on your feet to the elastic in the waistband of your underwear. Is modern athletic shoe construction and our attitude towards a somewhat durable good all wrong? I’m still wearing some Timberlands from 4 years ago (they are still waterproof too) and I plan to continue wearing them for years to come. Maybe our material selection priorities have been warped and instead of designing the material in our lives for longevity and repair we focus on articles that are “of the moment.”

I’m sure that whenever I’m “finished” with my Timberland boots I can probably donate them to a secondhand seller and they will find new life on some new feet. If we want companies to design shoes or other things we consume with a recycling end of life option we need to consider that our patterns of use and expectations towards the things we consume need to change as well. I get some dopamine the more times I can reuse a plastic bag and it would also be nice to know there was an easy path towards recycling.

The problems with recycling are all along the value chain from producers to converters to consumers to material recovery. Ironically, a few weeks before this story came out my wife came home with a bag for our unwanted shoes with the promise that they would get recycled. I was skeptical that they would actually get recycled and after reading the story above I’m even more skeptical that our shoes are getting recycled or even downcycled into something more useful. I’m also hopeful that someone will eventually figure this all out. Given the chance to do it again I’d probably go for it because someone else wearing my old shoes is better than them getting recycled anyway.

Maybe a polymer chemist fresh out of graduate school with big dreams will team up with an old Shoe Dog from Maine and they will develop an adhesive that debonds on command. Just need to figure out what that command might be chemically.

Even old dogs can learn new tricks.

Tony

Shoe Dog is a great read and I’m excited to watch the new movie Air.