5-7 OCTOBER

ISFR

2011

155

TOLEDO (SPAIN)

HIGH PERFORMANCE RECYCLING SYSTEM FOR SHREDDED PLASTICS
BY USING RAMAN IDENTIFICATION
H. Kawazumi1, A. Tsuchida2, K. Arikata2 Y. Tsuchida2, H. Hasuo3 and T. Oosaki3
1 School of Industrial Technology, Kinki University, Iizuka, Japan
2 Saimu Corporation, Iizuka, Japan
3 Fukuoka Industrial Technology Center, Chikusino, Japane-mail: kawazumi@fuk.kindai.ac.jp

Abstract
Raman Spectroscopy is able to identify plastic components, similar to infrared absorption. This paper shows the potential
application of Raman spectroscopy to waste plastic recycling when massive and accurate sorting processes are required.
We developed a high-speed Raman apparatus for scanning with an appropriate wavelength region of less as 1.5
milliseconds, and a precise analyzing methodology. Spectroscopic identification could show additives and deterioration of
the plastics. This technique is successfully implemented into the online sorting in a shredded plastic recycling plant withmore than three hundred cycle decisions per second in one laser line. A practical-scale demonstration facility with fifty
Raman apparatuses is constructed including the preprocessing system of specific gravity classification tank and metal
remover for shredded plastics from used home appliances.

Keywords: material recycling, plastic sorter, waste plastics, home appliances, Raman spectroscopy.

1. Introduction
There is a growing need for plastic recycles globally. The
classification of each kind of post-consumer plastic is thecrucial technology for the material and chemical recyclingthat is very effective for saving natural resources andenergy. However, few technique provides enoughperformance in respect of both speed and accuracy inthe recycle industry. Spectroscopic identifica-tions suchas infrared (IR) and near-IR (NIR) reflectancemeasurements are one of sophisticated candidates in thereliability comparing batch-screening techniques via
specific gravity differences. In laboratoies, IR measurement is a common method used to identify kinds ofplastics via molecular vibration information. Raman
scattering measurement also provide similar information
about the molecular structures. Such spectroscopic
methods can definitively classify plastics [1]. In thisFig. 1. Plastic sorting system with Raman spectroscopyinteriores libro.indd 155

paper, we present the applicability of Raman
spectroscopy to industrial-scale waste plastic recyclingthat requires massive processing [2]. Figure 1 presents ascheme of the plastic sorting system in which Raman
identifiers were implemented.

2. Materials and Methods
In Japan, a law encourages the recycle of the resourcesof home appliances and states that the used appliances(air-conditioner, refrigerator, TV and washing machine)
should be collected by their distributors and sent torecycle plants operated by electronics companies. The
collected appliances amounted up to 0.64 million tons in2009. The shredded plastics as feedstock in our sorting
system are excreted from these used home appliancesand should be classified into main three kinds of plastics;
polypropylene (PP), polystyrene (PS) and acrylonitrilebutadiene-styrene (ABS) polymers.
We have also developed the compact, high-speed andsensitive, home-made Raman spectrometer that isspecialized for the plastic sorting. An optical part consistsof a 785-nm high-power diode laser operated at 2 watts
and a backside incident FFT-CCD detector of 1024 x 58
pixels. The optical system is designed to achieve highoptical throughput with the appropriate resolution of 20
cm-1. A data analysis part is embedded in a field
programmable gate array circuit that is used instead of a
CPU to reduce the signal processing time.
An overall sorting process is as follows; removing metalparts and electric wires by using magnetic force,classifying the shredded plastic mixture into PP and
PS/ABS roughly in a water tank based on the specificgravity difference. Then the plastic pieces are fed under

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the Raman identifier by a high-speed (100 m/min.) belt
conveyor. At the end of the conveyor a series of pulsed
air guns sorts the identified plastic piece in synchronizedtiming. The fifty Raman identifiers in an array work
parallelly in the one conveyor lane for the massive
amount processing of 600 Kg / hour.

3. Results and Discussion
Raman spectra of PP, PS and ABS are shown inFig.2. The samples are real waste plastics with whitecolor and move in the speed of 100m/min. The
measurement time is 3 ms without graphical displaying
and the amount of Raman shift in horizontal axis
corresponds in the direct pixel position of the CCD
detector for the fast identification. A bottom axis shows
the common representation in the unit of cm-1. Even in
the 3-ms measurement, they show the spectroscopic
features with sufficient signal-to-noise ratio for theidentification. A peak around 2300 cm-1 could distinguish
ABS from PS; both plastics did not classify by thespecific gravity separation.

(DeBDE) in the measurement time of 100 ms. A Raman
spectrum shows sharp peaks generally comparing IRand NIR one. The measurement in a fraction of a second
provides a clear peak originating from a carbon-brominebond at the arrow indication in Fig. 2.
The implemented identification algorism seeks thepresence of normalized peaks simply. We are also
developing the multivariate analysis technique based on
Mahalanobis’ generalized distance for data mining. This
off-line analysis could provide the information about
deterioration of the waste plastics.
Figure 4 presents an example of the performanceof our waste plastic sorting system developed. The upper
charts show the content percentages before and after
sorting for the suspending samples in the specificgravity-separation water tank and the lower for thesettling. The purity of 98 % is obtained and its degradation is mainly affected by operation of the pulsed airguns.
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Fig. 2. Raman spectra of plastics in 3-ms measurement
The waste plastics contain many kinds of additives
to improve the property for wide range applications of thepolymers. High quality recycles such as a closed loop
one require the sort and removal of the plastics
containing the certain amount of the additives. Especiallybrominated flame retardants that is one of RoHSregulated chemicals must be reduce less than 0.1 %. Fig.
2 shows the Raman spectra of prepared standard
samples of PP containing Decabromodiphenyl Ether㻻㼠㼔㼑㼞㻞㻑㻿㻻㻾㼀㻼㼂㻯㻝㻠㻑 㻭㻮㻿㻝㻝㻑㻝㻜㻜㻜㻿㼑㼠㼠㼘㼕㼚㼓㻌㻿㼍㼙㼜㼘㼑

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Fig. 4. Performance of the waste plastic sorting system
based on Raman spectroscopy

4. Conclusions
In this paper we could successfully demonstrated
that the applicability of Raman spectroscopy to theindustrial-scale post-consumer plastic recycling with theacceptable performance in comercial stages. Thisidentifying technique based on the Raman scattering
could be applied not only the waste samples but also thefresh products for the quality control.

References[1] V.Allen, J.H. Kalivas, and R. G. Rodriguez, “PostConsumer Plastic Identification Using Raman Spectroscopy” Applide Spectroscopy, 53 (1999), 672.
[2]H. Kawazumi, Y. Tsuchida, Japan Patent No. 2008209128, 2008.

Acknowledgment
Authors have had the financial support from The Ministryof Economy, Trade and Industry of Japan.
Fig. 3. Raman spectra of PP containing DeBDE

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