Creating a more recyclable plastics
Scientists in the US have created what they hope could be the most recyclable type of plastic yet.
The Department of Energy researchers believes that polydiketoenamine – or PDK – will be able to be repeatedly reprocessed into different shapes, textures and colours without any loss of quality.
The key to this is that, unlike with conventional plastics, the molecules which PDK is made of can be easily separated from other chemicals which have been added to them during manufacturing, by dipping the plastic in strong acid.
The research was undertaken at the Lawrence Berkeley National Laboratory in California and published in Nature Chemistry.
The problem with plastic
Plastics are made of polymers – long chains of identical smaller molecules, called monomers. Other chemicals are then often added to give the plastic certain properties, such as plasticisers, which make it flexible, dyes, flame retardants or fillers, which make it tough.
But these chemicals are often so tightly bound to the monomers that they stay in the plastic even after it’s been processed at a recycling plant. During recycling, plastics with different chemical compositions – hard plastics, flexible plastics, clear plastics, coloured plastics – are mixed together and melted down to make new material. But because those added chemicals are still there, and there are now a whole load of different chemicals from different plastics, it’s hard to predict what properties the new plastic will have.
This unpredictability means that only about 20 to 30 per cent of even the most recyclable types of plastic is reused. The rest is incinerated or sent to landfill. For example, plastic bags, straws and many toys aren’t recycled.
Where PDK can help
Humans produce 300 million tons of plastic waste every year.
“Plastic upcycling is a grand challenge, and we’ve seen the impact of plastic waste leaking into our aquatic ecosystems,” explained team leader Brett Helms, a staff scientist at the Molecular Foundry.
With PDK, however, the added chemicals bond to the polymers in a different way from other plastics. “The immutable bonds of conventional plastics are replaced with reversible bonds,” Helms explained. The acid helps to separate the monomers from the added chemicals and from each other, so they can be remade into new polymers without inheriting the colour or other features of the original material.
“That broken black watchband you tossed in the trash could find new life as a computer keyboard if it’s made with PDK,” Helms told ABC News.
The researchers now hope to develop PDK plastics with a range of thermal and mechanical properties for uses including textiles, 3D printing, and foams, and to incorporate plant-based materials and other sustainable components.
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