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We can’t recycle black plastic, but now we can use its carbon for renewable energy

Jun 26, 2019

The big problem with plastics is that though they last for a very long time, most are thrown away after only one use. Since plastics were invented in the 1950s, about 8,300m metric tonnes (Mt) have been made, but over half (4,900 Mt) is already in landfill or has been lost to the environment. In 2010 alone, an estimated 4.8 to 12.7 Mt went into the oceans.

Only a small proportion of the hundreds of types of plastics can be recycled by conventional technology. But there are other things we can do to reuse plastics after they’ve served their original purpose. My research, for example, focuses on chemical recycling, and I’ve been looking into how food packaging can be used to create new materials like wires for electricity.

In chemical recycling you use the constituent elements to make new materials. All plastics are made of carbon, hydrogen and sometimes oxygen. The amounts and arrangements of these three elements make each plastic unique. As plastics are very pure and highly refined chemicals, they can be broken down into these elements and then bonded in different arrangements to make high value materials such as carbon nanotubes. In theory, the only side products from doing this should be oxygen and hydrogen.

Carbon nanotubes are tiny molecules with incredible physical properties. Think of a piece of chicken wire wrapped into a cylinder. This is what the structure of a carbon nanotube looks like. When carbon is arranged like this it can conduct both heat and electricity. These two different forms of energy are each very important to control and use in the right quantities, depending on your needs.

For our new study, we took plastics – in particular black plastics, which are commonly used as packaging for ready meals and fruit and vegetables in supermarkets, but can’t be easily recycled – and stripped the carbon from them, then built nanotube molecules from the bottom up using the carbon atoms.

Nanotubes are 80,000 times thinner than a human hair, in fact they are virtually as thin as DNA strands. But being made of carbon-carbon bonds also gives them diamond-like strength. They are so strong they’re considered the ideal material for a proposed space elevator.

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