Abstract:For the production of high-quality parts from recycled plastics, a very high purity of the plastic waste to be recycled is mandatory. The incorporation of fluorescent tracers ("markers") into plastics during the manufacturing process helps overcome typical problems of non-tracer based optical classification methods. Despite the unique emission spectra of fluorescent markers, the classification becomes difficult when the host plastics exhibit (strong) autofluorescence that spectrally overlaps the marker fluores… Show more
“…Second, the use of TGFS to suppress the negative influences of the plastics' AF (see Time-gated Fluorescence Spectroscopy (TGFS) section) is impossible with organic markers because their fluorescence decay time constants are very small, in the nanosecond range, and thus comparable to those of the AF decay of plastics. 2…”
Section: Fluorescent Labeling Of Plasticsmentioning
confidence: 99%
“…Figure 3 shows the pulse train and basic timing diagram in order to explain the concept of TGFS. The reader is referred to our previous study 2 for more details about the optimization of the pulsing parameters and the hardware implementation. Figure 3.In TGFS, the excitation light is periodically switched on (symbolized by I) and off (0) with time period T and pulse duration t p .…”
Section: Fluorescent Labeling Of Plasticsmentioning
confidence: 99%
“…This is why it is all the more important for TGFS measurements to use an efficient and sensitive sensor and pay special attention in order to keep the noise at a low level. 2…”
Section: Prototype Of the Time-gated Fluorescence Spectroscopy Measurmentioning
confidence: 99%
“…Second, the use of TGFS to suppress the negative influences of the plastics' AF (see Time-gated Fluorescence Spectroscopy (TGFS) section) is impossible with organic markers because their fluorescence decay time constants are very small, in the nanosecond range, and thus comparable to those of the AF decay of plastics. 2 Third, organic markers are susceptible to photobleaching when incorporated in polymers. 12 This may lead to the situation that products exposed to the sun's radiation during their life cycle will have lost most or even all of their unique marker fluorescence emissions before they arrive at the recycling facilities.…”
Section: Fluorescent Markersmentioning
confidence: 99%
“…Short life cycles of consumer products additionally deteriorate the situation with megatons of plastic waste ending up on landfills, in oceans (and thus in the food chain in form of micro-plastics) as well as in incineration plants year after year. [1][2][3][4] In light of all this, plastic recycling is essential to help solve the problem. Currently, plastics of different types and grades are often mixed together in the recycling process.…”
Plastics have many unrivaled properties and are thus indispensable materials with an ever-increasing production. Since the plastics recycling rates are still small, the plastic waste that ends up on landfills, in the environment including oceans, and incineration plants also steadily grows. Large-scale automated sorting of waste plastics may help solve the problem. However, most state-of-the-art approaches are limited to a (very) small number of plastic types that can be simultaneously sorted and have severe difficulties with black plastics. The labeling of plastics with fluorescent tracers (“markers”) during their production has the potential to enable the fast and highly reliable classification and automated sorting of many different plastic types simultaneously. Unfortunately, the unique marker fluorescence (“optical fingerprint”) might be obscured by the autofluorescence (AF) often emitted by plastics. Recently, we have shown that time-gated fluorescence spectroscopy (TGFS) can be successfully applied to eliminate the influences from AF. In this study, we present the prototype of a TGFS measurement system for the classification and sorting of plastics and evaluate its performance in a typical industrial situation. With 150 000 investigated plastics flakes from 10 different plastic types that were labeled with binary combinations of six fluorescent markers, an overall plastics recovery rate (mean true positive rate [Formula: see text]) of 99.76%, and a plastics purity (positive predictive value [Formula: see text]) of 99.88% were achieved. Additional simulations that were carried out based upon the experiments allow a prediction of the performance as a function of the signal-to-noise (S/N) ratio such that various system parameters can be adapted to the particular situation.
“…Second, the use of TGFS to suppress the negative influences of the plastics' AF (see Time-gated Fluorescence Spectroscopy (TGFS) section) is impossible with organic markers because their fluorescence decay time constants are very small, in the nanosecond range, and thus comparable to those of the AF decay of plastics. 2…”
Section: Fluorescent Labeling Of Plasticsmentioning
confidence: 99%
“…Figure 3 shows the pulse train and basic timing diagram in order to explain the concept of TGFS. The reader is referred to our previous study 2 for more details about the optimization of the pulsing parameters and the hardware implementation. Figure 3.In TGFS, the excitation light is periodically switched on (symbolized by I) and off (0) with time period T and pulse duration t p .…”
Section: Fluorescent Labeling Of Plasticsmentioning
confidence: 99%
“…This is why it is all the more important for TGFS measurements to use an efficient and sensitive sensor and pay special attention in order to keep the noise at a low level. 2…”
Section: Prototype Of the Time-gated Fluorescence Spectroscopy Measurmentioning
confidence: 99%
“…Second, the use of TGFS to suppress the negative influences of the plastics' AF (see Time-gated Fluorescence Spectroscopy (TGFS) section) is impossible with organic markers because their fluorescence decay time constants are very small, in the nanosecond range, and thus comparable to those of the AF decay of plastics. 2 Third, organic markers are susceptible to photobleaching when incorporated in polymers. 12 This may lead to the situation that products exposed to the sun's radiation during their life cycle will have lost most or even all of their unique marker fluorescence emissions before they arrive at the recycling facilities.…”
Section: Fluorescent Markersmentioning
confidence: 99%
“…Short life cycles of consumer products additionally deteriorate the situation with megatons of plastic waste ending up on landfills, in oceans (and thus in the food chain in form of micro-plastics) as well as in incineration plants year after year. [1][2][3][4] In light of all this, plastic recycling is essential to help solve the problem. Currently, plastics of different types and grades are often mixed together in the recycling process.…”
Plastics have many unrivaled properties and are thus indispensable materials with an ever-increasing production. Since the plastics recycling rates are still small, the plastic waste that ends up on landfills, in the environment including oceans, and incineration plants also steadily grows. Large-scale automated sorting of waste plastics may help solve the problem. However, most state-of-the-art approaches are limited to a (very) small number of plastic types that can be simultaneously sorted and have severe difficulties with black plastics. The labeling of plastics with fluorescent tracers (“markers”) during their production has the potential to enable the fast and highly reliable classification and automated sorting of many different plastic types simultaneously. Unfortunately, the unique marker fluorescence (“optical fingerprint”) might be obscured by the autofluorescence (AF) often emitted by plastics. Recently, we have shown that time-gated fluorescence spectroscopy (TGFS) can be successfully applied to eliminate the influences from AF. In this study, we present the prototype of a TGFS measurement system for the classification and sorting of plastics and evaluate its performance in a typical industrial situation. With 150 000 investigated plastics flakes from 10 different plastic types that were labeled with binary combinations of six fluorescent markers, an overall plastics recovery rate (mean true positive rate [Formula: see text]) of 99.76%, and a plastics purity (positive predictive value [Formula: see text]) of 99.88% were achieved. Additional simulations that were carried out based upon the experiments allow a prediction of the performance as a function of the signal-to-noise (S/N) ratio such that various system parameters can be adapted to the particular situation.
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