How Do We Close the Loop for Non-biodegradable Plant-based Plastic?

Adam Gendell

You may have seen the recent news that Coca-Cola is ramping up its production of PET made with plant-based glycol instead of petroleum-derived glycol. In the language of sustainability, this would be described as replacing a non-renewable feedstock with a renewable feedstock. This isn’t a new concept for those of us who are immersed in the sustainability community, but this beginning-of-life change introduces a bit of complexity when it comes to the end-of-life for the PET. What does sustainable recovery look like for this material?

Let’s first refresh our memories on the basic concept of sustainable recovery. The SPC’s Definition of Sustainable Packaging refers to both biological closed loop cycles as well as technological closed loop cycles, which are two distinct concepts. The idea behind a biological closed loop cycle is that living things are built from nature’s inputs, and when they die they must give those inputs back to the natural environment. This ensures that nature won’t run out of inputs for new living things–nature’s closed loop, if you will.

Conversely, the idea behind a technological closed loop cycle is that non-living things don’t automatically renew themselves (at least not at a rate that’s anywhere close to being useful), and their use will only be sustainable in the long run if we keep using the finite amount that exists and avoid total depletion. Therefore instead of giving these materials back to nature (“discarding” might be a better word than “giving”), we must keep them in use by people–a technological closed loop.

So what about this PET with its plant-based constituent? The first complexity is that only a portion is plant-based, so the PET is also composed of some things that ought to stay within a technological closed loop. There’s no easy way (yet) to separate the different constituents and put them in their respective preferable recovery systems.

The other complexity is that there must be a mechanism by which the plant-based material may return to nature and participate in the biological cycle. Even if the first complexity were resolved by making PET entirely from plant-based materials (which is not truly possible today, considering all the catalysts and polymer chemistry whatsits that are not made from plants), the PET would still be an inherently non-biodegradable material. While that helps traditional PET stay in the technological cycle, it prevents it from returning to the biological cycle. I wonder, could the always-controversial biodegradability additives finally have a home? Probably not, but it still makes one wonder what the answer would look like.

Fortunately for Coca-Cola, and anyone else who’s thinking big and making major changes to the way packaging is made, innovation is crucial and the “complexities” can usually be worked out in time. Right now we don’t have a perfectly sustainable way of making and recovering plastic at all, regardless of whether it’s made from plants or petroleum. In the long run, it certainly can be argued that plant-based feedstocks are a step in the right direction. To get there, we just have to keep innovating away the complexities.

3 Responses to How Do We Close the Loop for Non-biodegradable Plant-based Plastic?

  1. Brent Eubanks says:

    My question is, is the plant-based PET really a biological nutrient any longer? I understand the need to keep the loops separate to avoid contamination and balanced to avoid depletion. But in this case, the material in question is basically just a carbon-oxygen-hydrogen compound – that’s a renewable resource from plants, so material depletion isn’t really an issue. Contamination of the recovery stream is, of course. But is plant-based PET so different from regular PET that it cannot be treated as a technological nutrient?

    If the answer is “yes, the materials are different and cannot co-mingle”, then I have to question the value of using the plant-based input in the first place. The offsetting of petroleum inputs is a small benefit (shades of greenwashing) compared to the hassle of dealing with a bio/techno hybrid material.

  2. Adam Gendell says:

    Hi Brent,

    Great comment. Unfortunately, it gets a long answer…

    The plant-based PET is chemically identical to traditional petroleum-based PET, so it does not contaminate the recycling stream. In fact, this is why it’s such a breakthrough – most plant-based polymers don’t mimic traditional polymers, and hence they sometimes do contaminate the recycling streams of traditional plastics. This new plastic does not.

    Conversely though, most plant-based polymers are biodegradable, so they are readily able to be returned to the biological cycle. That’s one of the reasons why non-biodegradable plant-based PET raises such an interesting question. This technology takes something from the biological cycle and creates something that can live in the technical cycle.

    This has all kinds of intriguing implications; for instance, from a carbon standpoint, it may mean that we can sequester atmospheric carbon in plants and store it for a period of time in plastic.

    But, no plastic can live forever in the technical cycle. Currently there are no technologies that recover plastic without loss of quality, and until that changes it prevents the opportunity for any kind of plastic packaging to live endlessly in a technological closed loop*.

    But, fortunately, as you mention, we’re talking about renewable resources from plants here. So, it’s okay if they’re not endlessly recyclable. Eventually, even after a few trips around the technological loop, these containers are destined for disposal, and this is where we still have an opportunity to complete the biological closed loop. We just have to figure out how to return them there.

    Why is that necessary? According to estimates from the EPA, the U.S. generates around 27 billion pounds of plastic packaging each year. If we were to take 27 billion pounds of plants out of the biological cycle every year without returning anything, then yes, theoretically it would create a harmful imbalance to the ecosystem and the practice would not be sustainable in the long term.

    Conventional wisdom does tell us not to mix our biological nutrients with our technical nutrients. This new material, though, suggests that it’s beneficial to mix the cycles as long as the right things eventually end up in the right loops.

    Interesting, huh?

    * I should note that some chemical recycling technologies do come close to recovering 100% of the plastic input with no loss of quality, but in addition to perfecting those technologies, we would also have to collect 100% of plastic packaging – not likely possible (though not theoretically impossible).

  3. polythenepam says:

    Years ago, driven mad by plastic trash, I decided to boycott plastic.I kinew nothing of the product.Some time later and I have cut alot of plastic from my life,and, I know little more about the product. That is down to wonderful blogs and articles like this one. Many thanks for posting. x. Pam.

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