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  • Enhanced Method for Recycling Plastics: Fluorescent Fingerprint

    Enhanced method for Recycling plastics: Fluorescent fingerprint

    A team of researchers at Ludwig-Maximilians-Universitaet (LMU) in Munich have claimed to develop a new process which will greatly simplify the process of sorting plastics in recycling plants. The method enables automated identification of polymers, facilitating rapid separation of plastics for re-use.

    The team is led by Professor Heinz Langhals of LMU's Department of Chemistry. The technique takes advantage of the polymer-specific nature of the intrinsic fluorescence induced by photo excitation.

    Recycling of plastic is the general process of recovering scrap and waste plastics reprocessing them into useful products which may be in a completely different form from its original.

    Plastics are also recycled during the manufacturing process of plastic goods such as polyethylene film and bags.

    The vast majority of technical polymers are processed as thermoplastics, i.e., they are melted at high temperature and the finished article is produced by injecting the molten material into an appropriate mold, where it allowed to set. Reheating of recycled plastic can, however, lead to deleterious alterations in its properties of the material unless the sorted material is of high purity.

    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. Photoelectric sensors then measure the intensity of the light emitted in response to the inducing photo excitation to determine the dynamics of its decay. Because the different polymer materials used in the manufacture of plastics display specific fluorescence lifetimes, the form of the decay curve can be used to 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," says Langhals.

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