If you've ever had to separate different types of plastic for recycling, then you'll know how much it slows down the recycling process. Now, imagine how much harder it is for staff receiving huge amounts of unsorted plastic at municipal recycling plants. New technology developed at Ludwig Maximilians Universitat in Munich, however, identifies plastic types automatically.
In the new system, plastic items are exposed to a brief flash of light which causes them to fluoresce. Photoelectric sensors then measure how long it takes for that fluorescence to fade. Because different types of plastic polymers have different fluorescence lifetimes, a measurement of that lifetime can reliably identify the plastic in question.
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Even in its present form, the technology can sort up to 1.5 tons (1.4 tonnes) of plastic per hour. According to the researchers, this figure meets the specifications required for its application on an industrial scale.
"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 project leader, Prof. Heinz Langhals.
A paper on the research was recently published in the journal Green and Sustainable Chemistry.