The difference in the recyclability of plastic types can be down to how they are made; thermoset plastics contain polymers that form irreversible chemical bonds and cannot be recycled, whereas thermoplastics can be re-melted and re-molded.

The most mature of the advanced recycling technologies is called pyrolysis, which is the application of heat — upwards of 500°C — in the absence of oxygen to break down plastics into their component parts. This typically produces a cocktail of end products, including oils, diesel, naphtha, waxes and monomers.

Technologies like depolymerisation, pyrolysis, and gasification are gaining traction in chemical recycling. Depolymerisation breaks down plastic polymers into their monomer units, which can then be used to produce new plastic products.

In a study published today in Nature Sustainability , researchers successfully engineered microbes to make biological alternatives for the starting ingredients in an infinitely recyclable plastic known as poly(diketoenamine), or PDK.