Are Plastics Biodegradable?

Professor Plastics

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Plastic bag

To many people, the term “biodegradable plastics” sounds like a contradiction in terms, sort of like a square circle. As usual, reality is a bit more complicated.

First, let’s define biodegradable. From a scientific standpoint, the term most commonly refers to materials that can be broken down by microorganisms into organic matter, largely composed of common elements such as carbon, nitrogen, oxygen, and so on – elements that can be utilized by living organisms. (Thus ends the science lesson.)

Some things biodegrade faster than others – many vegetables can biodegrade in a month or so while leather shoes can take many decades. Other than the material itself, the key to biodegradability is the environmental conditions surrounding the material.

Why? (OK, a little more science …)

To biodegrade, organic materials require air, water, light or a combination of these elements so microorganisms can do their job. Remove any or all of these elements, and biodegradation can be slowed dramatically. That’s why our Declaration of Independence in the National Archives, made from parchment (thin animal skin), is displayed in a carefully controlled atmosphere. Air, water and light would cause it to biodegrade.

Another example … remember the Dead Sea Scrolls? Made from parchment and papyrus, both materials that can biodegrade, the scrolls survived two millennia in caves. Once removed from the caves, they began to biodegrade quickly.

What’s this have to do with plastics? Can air, water and light cause plastics to biodegrade? In other words, are plastics biodegradable?

Many plastics do not biodegrade to any significant degree, regardless of environmental conditions, while some do so very slowly if exposed to air, water and light – both types are best recycled or used for their stored energy.

Some plastics have been engineered to biodegrade reasonably quickly – and here’s the important part – in a large composting facility that intentionally accelerates biodegradation in a highly controlled environment using copious air, water and light. These plastics also will break down eventually if left alone in the environment – but much more slowly since the environment does not “intentionally accelerate” biodegradation. However, similar to other biodegradable materials, they likely will not break down in modern landfills that basically store waste and are designed to retard biodegradation.

Read More: Plastic bag recycling at home

So … biodegradability of plastics depends largely on the type of plastic and where it ends up.

That’s the scientific explanation in a nutshell. A few caveats:

  • When science meets the law, labeling consumer products as “biodegradable” gets a little tricky (the topic of a future lesson).
  • Some materials such as glass, aluminum and many plastics do not “bio” degrade, although they will “degrade” physically over a very long time (I also will tackle this topic in the future).
  • Today there are only a handful of large composting facilities in the U.S. that accept consumer products.
  • Biodegradable plastics must be separated from plastics that are being recycled (another future lesson topic).