German scientists say they have spotted a way to sort plastics for recycling much more speedily – and it’s all down to fluorescent light.
The technique hinges on automated recognition of a plastic item’s polymer make-up – i.e. the molecules it is made of.
Professor Heinz Langhals at Ludwig-MaximiliansUniversitat (LMU)’s Department of Chemistry explains: “Plastics emit fluorescent light when exposed to a brief flash of light, and the emission decays with time in a distinctive pattern.
“Thus, their fluorescence lifetimes are highly characteristic for the different types of polymers, and can serve as an identifying fingerprint.”
Details of the new method are published in the latest issue of the journal “Green and Sustainable Chemistry”.
The development could be important because to re-use plastics, typically by melting them down and injecting them into a mould, they need to be “chemically pure”, says the scientist.
Even a plastic contaminated 5% by another material can be a problem.
The LMU researchers have applied to patent their new technique.