Plastics – what they are and why are they so hard to get rid of

When the deepest ever dive plunged 11 kilometers into the Mariana Trench it returned to the surface world with two types of evidence. The first was of four new species that could offer exciting insight into the origins of our planet. The second was plastic.

At the very deepest point on our planet where no human had ever ventured, Victor Vescovo found a plastic bag and lolly wrappers. 

Despite brands dropping plastic from their packaging and entire countries moving away from single-use plastic, how is it we’re still swimming in the stuff? 

Why is plastic so sturdy?

The reason plastic has become so useful and ubiquitous in today’s society is exactly why has left us in this heaping mess: plastic is strong, flexible and doesn’t break down easily. It was made to last forever, and forever it is lasting.

The earliest iteration of mass-producible plastic was developed in 1909 to rival entirely natural materials. Before that it was rubber latex made from plants, shellac from beetle secretions, and celluloid from plant cellulose.

The chemist Leo Baekeland developed Bakelite, and for the first time, the synthetic light weight, durable material entered the global market.

Isabel Thomlinson, PhD researcher from University of Bath’s Centre for Sustainable Chemical Technologies, says the molecular structure of plastic is what makes it so hard to break down.

It is composed of “very long molecules called polymers, which can consist of many thousands of atoms linked together in a chain,” she says. “The sheer size of the molecules gives plastics their well-known properties – solid, strong, tough, flexible.”

Not all plastics are created equal

While the most common plastics are made from crude oils, you may have seen a few different symbols on your takeaway coffee cups or sandwich boxes. These different classifications, such as compostable and biodegradable, hint at different methods of disposal, recycling or reuse. 

Recyclable

Recyclable plastics can theoretically be recovered, sorted and reused to make a new product. What you may not realise however is that most plastics can only be recycled once or twice, and that generally has to be into something that doesn’t hold food or meet stringent strength requirements as the plastic’s quality diminishes with recycling.

And unfortunately, even the most recyclable plastics, such as PET, or poly(ethylene terephthalate), can be hard to recycle as they pick up additives and other contaminants along the way. 

it becomes hard (or impossible) to completely clean even the plastics labeled recyclable

Additives such as dyes, fillers and flame retardants, as well as food particles can get in the way. When tossed together in our bins and at the recycling plant it becomes hard (or impossible) to completely clean even the plastics labeled recyclable without loss of performance or aesthetic.

The government supported group NetWaste compiled this list to help us understand what can and cannot be recycled.

• Read our explainer on ewaste.

Bioplastics

Bioplastics are made from plants or other organic materials, rather than crude oil. Their molecular structure means that in theory they can be naturally assimilated or converted into CO2 by microorganisms (ie decompose).

However, there is no regulated time requirements for this process, and according to Thomlinson it can take many years under some conditions. 

“These plastics are generally not designed to degrade without special treatment,” she says, which means if they leak into the environment as litter they can be just as harmful as standard plastics made from fossil fuels. 

Compostable

To be certified compostable in Australia, plastics must be proven to break down under industrial composting conditions in less than 12 weeks and produce no harmful substances. 

Ms Thomlinson says industrial composting conditions usually refer to “the necessary balance of heat, moisture, air and microorganisms to efficiently compost food and other compostable waste” – conditions that can be tricky to replicate at home. 

It is important to note that compostable plastics do not break down to the same standards when mixed with other types of plastics.

• Read our explainer on creating your own home compost

So what’s the problem?

Unless these specific conditions are met, plastic, as Vescovo discovered, does not break down. In fact, without the required infrastructure and systems in place to deal with their specific needs, all kinds of plastics can become harmful.

not one of the tested plastic bags broke down completely

One study out of the University of Plymouth tested five types of plastic, including compostable, biodegradable and conventional plastic, in three different conditions: underground, exposed to the air and sunlight, and submerged in the sea.

The study found that not one of the tested plastic bags broke down completely in all environments. In fact, the “biodegradable” plastics tested underground and in the sea were so intact they were still able to carry over two kilograms of shopping. 

What if we could recycle plastics infinitely? 

This is the question asked by researchers from the US Department of Energy’s Lawrence Berkeley National Laboratory, or Berkeley Lab. The answerpublished in the journal Nature Chemistry was poly(diketoenamine), or PDK.

PDK is the plastic equivalent of a Lego playset. According to Berkeley Lab it can be broken down at a molecular level and “then reassembled into a different shape, texture, and colour again and again without loss of performance or quality.”

In theory, with the right systems in place, PDK could close the loop on plastic recycling

Unlike traditional PET and other plastics, PDK requires nothing but an acid bath to clean it of any additives and start the recycling process. From these building blocks, PDK can be recreated as lunch boxes or phone cases forever.

In theory, with the right systems in place, PDK could close the loop on plastic recycling so the only discoveries we make on the sea floor from now on are strange fish and crustaceans.