Even after years of application worldwide the recycling process of plastic materials is still far from perfection. For example, the plastic recovered from separate collection is never used to produce high quality products because of its low chemical purity; in fact contamination levels as low as 5% are sufficient to significantly reduce the quality of the new products.

Now, however, a team of researchers at the Department of Chemistry of Ludwig Maximilians Universität (LMU) in Munich, Germany, have developed a new process, which is expected to greatly improve and simplify plastics sorting in recycling plants.

This technique provides for automated recognition of the polymer constituents of plastic objects, thus improving the efficiency of recycling and re-use of the various types of plastic; it takes advantage of the photoexcitation effect, which in the case of plastics is highly polymer-specific. As prof. Langhals, the head of the research team, 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".

The new technique, which is the subject of a patent application, will make the automated sorting of plastic feasible, since it permits the identification and sorting of up to 1.5 tons of plastic per hour, and much more reliable.

More information are available on the LMU website