Sally Brown

July 5, 2017 | General

Connections: Perspectives On Plastics


Sally Brown

Sally Brown
BioCycle July 2017

I am perfectly fine with Leonardo da Vinci and JS Bach as our legacy contributions to the future. However I just read an article that suggested that plastic distribution in both oceans and in soils is a “key geological indicator of the Anthropocene,” the first geological age to be named as a result of other than natural forces. While I will admit to having had an extensive collection of Bach CDs  (polycarbonates), I am not OK with the plastic (versus the music) being the signature achievement of our civilization.
The term “plastic” is a general category that covers a wide range of carbon-based compounds. The actual definition of plastic means something that is capable of being shaped or molded. A select few naturally occurring compounds either have this property or can be altered to have it. Rubber, gum and resin are some examples. The first real man-made plastic, invented in 1907, was called Bakelite, which is now relegated to sites like Ebay where you can find old bracelets.
Our understanding of how to make different types of plastics and how to use them has since exploded. We made about 2 million tons of plastic in 1950 and make 300 million tons a year now — equivalent to about 88 lbs/person/year. This is projected to grow to 40 billion tons by 2050, enough to wrap the planet with cling wrap 6 times over.
Modern day plastics are made from petrochemicals; about 8 percent of the fossil deposits currently mined go to produce plastic. While the vast majority of the plastics currently produced share this common ingredient, processes used to make them and properties of the final products are different. About 15 to 20 main types of plastic are currently in broad scale use. And most plastics produced since the 1950s are still around somewhere (Ebay likely only accounts for a miniscule volume).

Recycling Is Complicated

About 15 to 25 percent of plastic produced in Europe is recycled. Rates in the U.S. are below 5 percent, with plastic, becoming the least recycled and most common waste material. One reason for the low rate is that recycling plastic is a real challenge. While so many types of plastics start with that prefix “poly,” how they behave and how they can be repurposed varies considerably. For example, all plastics have a large number of repeating chemical units (polymers) as their backbone, but they often have different side chain attachments that make it hard for different materials to mesh. If you try to mix polypropylene (used in packaging, clothing and carpets) and polyethylene (plastic bags and films, containers) together, you will end up with layers of each rather than a single product. Layers, while a great concept for dressing in a variable climate, mean that the resulting mixture has limited strength and so limited use.
The strength and value of the plastic in part derives from the length of the polymers that form the backbone of the materials. In cases where mixing and melting is possible, the resulting poly tends to be shorter in polymers and so less valuable. In the future it may be possible to design polymers that can integrate without losing chain length and associated value but this is the task of chemical engineers and not recycling officials (Ignatyev et al., 2014).
Therefore, to reuse plastics you have to be able to separate the different types. Because there are so many types with such a broad range of uses, many of which include multiple types of “polys,” this is not straightforward on either a municipal level or a commercial level. Recycling options for plastics in different communities reflect this complexity. Here in Seattle I can recycle bubble wrap and grocery bags but not the bags that you put produce in. The CD cases that held my Bach recordings go in the trash as well.
This confusing guidance is likely due in part to undeveloped markets for certain types of plastics and difficulties in sorting the wide range of materials that are out there. More sophisticated sorting technologies would likely lead to the acceptance of a broader range of materials allowed in recycling programs. I read about one that shoots beams of light at the waste and then measures the different levels of fluorescence from the different plastics as a way to sort them. These have promise and are likely to develop in both sophistication and accuracy but won’t be cheap, thus the value of the sorted materials will need to be high.

End Uses

Much of the plastic that is recycled is melted and formed into pellets that are reused. You can buy both clothes and carpets made from recycled plastics. Or you can just make more bottles. Polyethylene terephthalate (PET) bottle recycling increased 53 percent from 2002 to 2014. As of 2014 the recycled PET pellets were selling for $0.05 more than the virgin ones. This price difference was due in part to a glut of virgin PET, produced as demand for this material is expected to increase. This differential may not ruin the market for recycled material as some bottle manufacturers are mandating a certain percentage of recycled materials in their production. Price and/or regulatory requirements will be key factors in maintaining and growing demand for recycled plastics.
If we can’t figure out a way to recycle plastics, they can always be burned for their energy value. These materials did come from the same fossil deposits that power our cars. A report by Columbia University noted that the 28.8 million tons of plastics that were landfilled in the U.S. in 2008 have the energy equivalence of 36.7 million tons of coal (Themelis et al., 2011). While not my idea of a highest and best use, it certainly tops plastic washing up on tropical beaches.
Identifying technologies that can successfully recycle plastics, through improved separation technologies or through production of materials that can melt together are both viable options. We are a long way from that world. And then I just read a recent study that identified a caterpillar that can eat polyethylene grocery bags (Bombelli et al., 2017). Also a bit of a stretch. But imagine if you will a vacation in the South Pacific with your cottage powered by solar, your favorite version of Bach’s Brandenberg concertos playing from your electronic device made from recycled plastic composite and the beach filled with seashells. That is a future and a legacy worth working towards.
Sally Brown is a Research Associate Professor at the University of Washington in Seattle and a member of BioCycle’s Editorial Board.


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