LMU researchers have developed 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.
A team of researchers led by Professor Heinz Langhals of LMU’s Department of Chemistry has taken a significant step which promises to markedly expedite the recycling of plastic waste. They have developed a technique which provides for automated recognition of their polymer constituents, thus improving the efficiency of recycling and re-use of the various types of plastic.
The technique takes advantage of the polymer-specific nature of the intrinsic fluorescence induced by photoexcitation. “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,” Langhals explains. Details of the new method appear in the latest issue of the journal “Green and Sustainable Chemistry”.
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 photoexcitation 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.
Turning bottles into windcheaters
Unlike metals, the quality of which often suffers during the recycling process itself, recycled plastics can be processed quite efficiently. “Polymers represent an interesting basis for the sustainable cycling of technological materials. The crucial requirement is that the recycled material should be chemically pure. In that case, bottles made of PET, for example, can be relatively easily turned into synthetic fiber for use in waterproof windcheaters,” says Langhals.
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.
Contamination levels as low as 5% are sufficient to significantly reduce the quality of the reformed product. The reason for this “down-cycling” effect is that, as a general rule, polymers tend to be immiscible, as they are chemically incompatible with one another.
Remelting of polymer mixtures therefore often leads to partitioning of the different polymers into distinct domains separated by grain boundaries, which compromises the quality of the final product. For this reason, high-quality plastics are always manufactured exclusively from pristine precursors – never from recycled material.
The new method developed by the LMU team could, however, change 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,” says Langhals. Indeed, the use of fluorescence lifetime measurements permits the identification and sorting of up to 1.5 tons of plastic per hour. In other words, the method in its present form already meets the specifications required for its application on an industrial scale.
(Green and Sustainable Chemistry, 2014)
Luise Dirscherl | Eurek Alert!
Litter is present throughout the world’s oceans: 1,220 species affected
27.03.2017 | Alfred-Wegener-Institut, Helmholtz-Zentrum für Polar- und Meeresforschung
International network connects experimental research in European waters
21.03.2017 | Leibniz-Institut für Gewässerökologie und Binnenfischerei (IGB)
The Institute of Semiconductor Technology and the Institute of Physical and Theoretical Chemistry, both members of the Laboratory for Emerging Nanometrology (LENA), at Technische Universität Braunschweig are partners in a new European research project entitled ChipScope, which aims to develop a completely new and extremely small optical microscope capable of observing the interior of living cells in real time. A consortium of 7 partners from 5 countries will tackle this issue with very ambitious objectives during a four-year research program.
To demonstrate the usefulness of this new scientific tool, at the end of the project the developed chip-sized microscope will be used to observe in real-time...
Astronomers from Bonn and Tautenburg in Thuringia (Germany) used the 100-m radio telescope at Effelsberg to observe several galaxy clusters. At the edges of these large accumulations of dark matter, stellar systems (galaxies), hot gas, and charged particles, they found magnetic fields that are exceptionally ordered over distances of many million light years. This makes them the most extended magnetic fields in the universe known so far.
The results will be published on March 22 in the journal „Astronomy & Astrophysics“.
Galaxy clusters are the largest gravitationally bound structures in the universe. With a typical extent of about 10 million light years, i.e. 100 times the...
Researchers at the Goethe University Frankfurt, together with partners from the University of Tübingen in Germany and Queen Mary University as well as Francis Crick Institute from London (UK) have developed a novel technology to decipher the secret ubiquitin code.
Ubiquitin is a small protein that can be linked to other cellular proteins, thereby controlling and modulating their functions. The attachment occurs in many...
In the eternal search for next generation high-efficiency solar cells and LEDs, scientists at Los Alamos National Laboratory and their partners are creating...
Silicon nanosheets are thin, two-dimensional layers with exceptional optoelectronic properties very similar to those of graphene. Albeit, the nanosheets are less stable. Now researchers at the Technical University of Munich (TUM) have, for the first time ever, produced a composite material combining silicon nanosheets and a polymer that is both UV-resistant and easy to process. This brings the scientists a significant step closer to industrial applications like flexible displays and photosensors.
Silicon nanosheets are thin, two-dimensional layers with exceptional optoelectronic properties very similar to those of graphene. Albeit, the nanosheets are...
20.03.2017 | Event News
14.03.2017 | Event News
07.03.2017 | Event News
30.03.2017 | Physics and Astronomy
30.03.2017 | Studies and Analyses
30.03.2017 | Life Sciences