You may have seen the recent news that Coca-Cola is ramping up its production of polyethylene terephthalate (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.
Photo of collection of empty used plastic bottles on white background. each one is shot separately provided by Picsfive via Shutterstock
This article originally appeared on GreenBlue's In the Loop blog and is reprinted with permission.
How about making these
How about making these bottles a different color or shape, so separators can differentiate.
Why must biologically derived
Why must biologically derived technical materials ONLY flow in the biological system? I think this is a huge assumption and worth critical examination. There are lots of examples of chemicals derived from plants to make recyclable technical materials like Coke is doing with PET. In fact, cellulosic plastics have been quite common place for many decades now--think about the clear plastic used on the head of your screw driver. Waste cellulose from trees has been converted chemically into feed stocks to make these plastics. I simply don't buy the notion that biologically derived materials must only yield biologically recyclable materials.
However, a real problem is when you mix biological materials with technical materials to create a hybrid that doesn't fit neatly into either the biological or technical cycle. Good examples include particleboard, plywood, and other plastic-impregnated or glue saturated plant based composites.
What concerns me with any strong move toward use of renewable materials on a super-industrial scale stems around (1) high energy & resource intensity to grow all of the materials we need, (2) there isn't enough arable land to grow all of our food, plastics/building materials, enjoy for recreation, live on, preserve, and be in balance with fragile ecosystems. Vertical farms have the potential to offer an elegant solution to these concerns, but I admit that I'm not 100% sold on those yet either.
I believe the bigger issue we should discuss is what will nutrient management of the future look like because the current design of thousands of materials don't lend themselves to be continually recycled. Also, the design of our recycling systems are pretty ineffective. PET is recycled at an abysmal rate here in the United States and can only go through a certain number of heat histories (remelting and extrusion/molding) before it breaks down, cross links, loses molecular weight and technical performance. I dream of a future where some sort of large scale digestor combines our intelligence on chemistry and biology to literally digest these materials back into feed-stocks that we can use to put back into the biological OR technical cycle no matter what their previous life was.
Why must biologically derived
Why must biologically derived technical materials ONLY flow in the biological system? I think this is a huge assumption and critical examination. There are lots of examples of chemicals derived from plants to make recyclable technical materials like Coke is doing with PET. In fact, cellulosic plastics have been quite common place for many decades now--think about the clear plastic used on the head of your screw driver. Waste cellulose from trees has been converted chemically into feed stocks to make these plastics. I simply don't buy the notion that biologically derived materials must only yield biologically recyclable materials.
However, a real problem is when you mix biological materials with technical materials to create a hybrid that doesn't fit neatly into either the biological or technical cycle. Good examples include particleboard, plywood, and other plastic-impregnated or glue saturated plant based composites.
What concerns me with any strong move toward use of renewable materials on a super-industrial scale stems around (1) high energy & resource intensity to grow all of the materials we need, (2) there isn't enough arable land to grow all of our food, plastics/building materials, enjoy for recreation, live on, preserve, and be in balance with fragile ecosystems. Vertical farms have the potential to offer an elegant solution to these concerns, but I admit that I'm not 100% sold on those yet either.
I believe the bigger issue we should discuss is what will nutrient management of the future look like because the current design of thousands of materials don't lend themselves to be continually recycled. Also, the design of our recycling systems are pretty ineffective. PET is recycled at an abysmal rate here in the United States and can only go through a certain number of heat histories (remelting and extrusion/molding) before it breaks down, cross links, loses molecular weight and technical performance. I dream of a future where some sort of large scale digestor combines our intelligence on chemistry and biology to literally digest these materials back into feed-stocks that we can use to put back into the biological OR technical cycle no matter what their previous life was.
Chemically, PET is PET. Look
Chemically, PET is PET. Look at it as one big pool and consider the proportionality of the two cycles. The plant based PET comes from carbon dioxide fixed from the atmosphere. If you want to return it to the biological cycle, just burn the PET. Since a lot of trash is already incinerated, in effect that return loop is already in place.
This article makes very good
This article makes very good points about what the goals are - keep things in the technological cycle and keep reusing them without harm (or in the interim minimizing) or they should be in the biological cycle where they will remain in the biosphere without harm. Food packaging is one that seems like it should be part of the biological cycle in totality, but obviously the technology to satisfy that criteria with preservation, transportability, etc. is not there yet.
Still, I wonder if simply advertising plant-based plastic bottle is not something of a greenwash, (and a bit misleading) since it cannot yet be composted, and still poses the same problems that regular plastic bottles pose. And do we have the lifecycle basis to claim less impact by replacing only part of the petro-plastic with bio-plastic?
Producing plant-based
Producing plant-based plastics requires less energy overall afaik (oil extraction being particularly energy intensive). So it's still a good step in the way of sustainability, even though the bottles themselves aren't "nature friendly".