08 September 2014

Flash of genius could make light work of plastic sorting process

Recycling can pay off for UK circular economyA team of Researchers in Munich has developed a new process which they claim could simplify the process of sorting plastics in recycling plants.


The new technique, which is the subject of a patent application, involves exposing particles of plastic to a brief flash of light which causes the material to fluoresce.


The development team has been led by Prof Heinz Langhals, who explained: ‘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.”


Photoelectric sensors then measure the intensity of the light emitted in response to the inducing photoexcitation to determine the dynamics of its decay, which helps identify their chemical nature. ‘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,’ said Langhals.


The technique has the potential to prove extremely useful, as the reheating of recycled plastic can lead to harmful alterations in the properties of the material, demonstrating that sorted material should be of high purity.


The new method developed by the scientists could help with this. ‘The waste problem can only be solved by chemical means, and our process can make a significant contribution to environmental protection, because it makes automated sorting feasible,’ said Langhals.