Featured Research

from universities, journals, and other organizations

Novel recycling methods: Fluorescent fingerprint of plastics

Date:
August 21, 2014
Source:
Ludwig-Maximilians-Universitaet Muenchen (LMU)
Summary:
A new process has been developed that 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 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.
Credit: © alexandro900 / Fotolia

Researchers at Ludwig-Maximilians-Universitaet (LMU) in Munich 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.


Story Source:

The above story is based on materials provided by Ludwig-Maximilians-Universitaet Muenchen (LMU). Note: Materials may be edited for content and length.


Journal Reference:

  1. Heinz Langhals, Dominik Zgela, Thorben Schlόcker. High Performance Recycling of Polymers by Means of Their Fluorescence Lifetimes*. Green and Sustainable Chemistry, 2014; 04 (03): 144 DOI: 10.4236/gsc.2014.43019

Cite This Page:

Ludwig-Maximilians-Universitaet Muenchen (LMU). "Novel recycling methods: Fluorescent fingerprint of plastics." ScienceDaily. ScienceDaily, 21 August 2014. <www.sciencedaily.com/releases/2014/08/140821141347.htm>.
Ludwig-Maximilians-Universitaet Muenchen (LMU). (2014, August 21). Novel recycling methods: Fluorescent fingerprint of plastics. ScienceDaily. Retrieved October 2, 2014 from www.sciencedaily.com/releases/2014/08/140821141347.htm
Ludwig-Maximilians-Universitaet Muenchen (LMU). "Novel recycling methods: Fluorescent fingerprint of plastics." ScienceDaily. www.sciencedaily.com/releases/2014/08/140821141347.htm (accessed October 2, 2014).

Share This



More Matter & Energy News

Thursday, October 2, 2014

Featured Research

from universities, journals, and other organizations


Featured Videos

from AP, Reuters, AFP, and other news services

Japan Looks To Faster Future As Bullet Train Turns 50

Japan Looks To Faster Future As Bullet Train Turns 50

Newsy (Oct. 1, 2014) — Japan's bullet train turns 50 Wednesday. Here's a look at how it's changed over half a century — and the changes it's inspired globally. Video provided by Newsy
Powered by NewsLook.com
US Police Put Body Cameras to the Test

US Police Put Body Cameras to the Test

AFP (Oct. 1, 2014) — Police body cameras are gradually being rolled out across the US, with interest surging after the fatal police shooting in August of an unarmed black teenager. Duration: 02:18 Video provided by AFP
Powered by NewsLook.com
Raw: Japan Celebrates 'bullet Train' Anniversary

Raw: Japan Celebrates 'bullet Train' Anniversary

AP (Oct. 1, 2014) — A ceremony marking 50 years since Japan launched its Shinkansen bullet train was held on Wednesday in Tokyo. The latest model can travel from Tokyo to Osaka, a distance of 319 miles, in two hours and 25 minutes. (Oct. 1) Video provided by AP
Powered by NewsLook.com
Robotic Hair Restoration

Robotic Hair Restoration

Ivanhoe (Oct. 1, 2014) — A new robotic procedure is changing the way we transplant hair. The ARTAS robot leaves no linear scarring and provides more natural results. Video provided by Ivanhoe
Powered by NewsLook.com

Search ScienceDaily

Number of stories in archives: 140,361

Find with keyword(s):
 
Enter a keyword or phrase to search ScienceDaily for related topics and research stories.

Save/Print:
Share:  

Breaking News:

Strange & Offbeat Stories

 

Space & Time

Matter & Energy

Computers & Math

In Other News

... from NewsDaily.com

Science News

Health News

Environment News

Technology News



Save/Print:
Share:  

Free Subscriptions


Get the latest science news with ScienceDaily's free email newsletters, updated daily and weekly. Or view hourly updated newsfeeds in your RSS reader:

Get Social & Mobile


Keep up to date with the latest news from ScienceDaily via social networks and mobile apps:

Have Feedback?


Tell us what you think of ScienceDaily -- we welcome both positive and negative comments. Have any problems using the site? Questions?
Mobile iPhone Android Web
Follow Facebook Twitter Google+
Subscribe RSS Feeds Email Newsletters
Latest Headlines Health & Medicine Mind & Brain Space & Time Matter & Energy Computers & Math Plants & Animals Earth & Climate Fossils & Ruins