German scientists develop new technique to sort plastics


Researchers at Ludwig Maximilians Universität (LMU) in Munich have developed a new process that will allow the rapid separation of different plastics.

Led by Professor Heinz Langhals of LMU’s Department of Chemistry, a technique has been developed that allows for automated recognition of the constituents of a polymer, thus making sorting more efficient.

The technique takes advantage of the polymer-specific nature of the intrinsic fluorescence induced by photoexcitation.

Professor Langhals said: “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.

“With this process, errors in measurement are practically ruled out. For any given material, one will always obtain the same value for the fluorescence half-life, just as in the case of radioactive decay.”

Using this fluorescence technique could permit the sorting of up to 1.5 tonnes of mixed plastics per hour according to the LMU scientists, which would allow for its application on an industrial scale.