Environmental Question #19 ["Biodegradable" Greenwashing]

Courtesy of Reddit user u/dscoZ

Q: I’ve read that a lot of “biodegradable” plastics need special environments to break down which are not common in most cities, so it’s really just a greenwashing technique by companies selling their products. That being said, are there any materials that seem promising in terms of actual recyclability and biodegradability that are feasible for inexpensive packaging and things like that?

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A: The greenwashing you're talking about is specifically about the "compostable" plastic PLA, which is the cheapest and most common alternative plastic available. PLA is an interesting case study, because it is a bioplastic that biodegrades completely into nontoxic products if it is exposed to bacteria and held at 60C (140F) for a week. In an industrial composting center, the fermentation from the giant compost heap can easily produce temperatures that high, but the average person's backyard compost heap won't get anywhere near that hot. That makes it so that when PLA is disposed of properly it is seen as a huge green win, but the problem is that it doesn't get disposed of properly most of the time. I would hesitate to call it greenwashing, because there is nothing inherently hazardous or polluting about the material itself, but it is impractical for how our waste management systems are currently set up. You're right though that since most PLA is not properly disposed of, most of it ends up in the environment where it will effectively never biodegrade.

There are biodegradable plastics both already in existence and currently being developed that have a lot of utility, but feasibility is a more complex question. For example, there is a biodegradable plastic called PHB that has been available for more than a decade now. PHB is the natural energy storage molecule for bacteria in the same way that fat is the natural energy storage molecule for us, so to manufacture PHB factories feed lots of bacteria plant scraps to fatten them up, then kill them to extract the PHB. It might sound weird that PHB is a naturally occurring plastic, but there are actually lots of naturally occurring plastics. Starch is a plastic and so is DNA, as freaky as it sounds. PHB feels just like regular plastic, and since it is literally bacteria food, bacteria will eat it in any environment, meaning it has practically universal biodegradability. There are even some companies that make PHB straws, and you'd never know it isn't made of regular plastic. (Sometimes they also use the term PHA instead of PHB. They are subtly different bacteria energy storage molecules that have different physical properties, such as PHA is more flexible than PHB, but for the purposes of biodegradation the difference doesn't matter. Here's an example of a company that makes PHA straws: https://www.phadeproducts.com/ . I have never worked on biodegradable plastics for straws and have no affiliation with this company. I just stumbled across them because I used one of their straws at a restaurant one time.)

The problem with PHB though, and by extension most other biodegradable plastics, is cost. Currently most conventional non-biodegradable plastics cost about $1 per pound, but PHB costs about $3 per pound. For a cup or straw manufacturer working with slim margins, this makes PHB unviable to use while making a profit. Efforts are being made to bring that cost down and to invent cheaper biodegradable plastics, but so far conventional plastic is so cheap that it's difficult to compete with.

Ultimately the best replacement for disposable plastics isn't biodegradable plastics, it's reusable materials as I discuss in the post I linked above. As I discuss in detail in that post, there are some situations where biodegradable plastics are the best tool for the job, so I believe we should continue to develop them for those purposes. However, most of the time we would be better off returning to a less disposable mindset for society in general.

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