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Fig. 2 EDX-7200
Fig. 1 Recycled PET Fiber (Left) and Virgin PET Fiber (Right)
Principle and Overview
Metal catalysts such as antimony (Sb) and germanium (Ge) are
used in the synthesis of PET resin. These catalyst metals have
been reported to be useful indicators of material origin.
1),2)
For
example, Sb and Ge are frequently detected together in
material-recycled PET, whereas only one catalyst metal is
detected in chemically recycled PET and virgin PET. This likely
reflects the fact that material-recycled PET is derived from a
mixture of feedstocks using different catalysts.
ICP-AES (ICP optical emission spectrometry) and ICP-MS (ICP
mass spectrometry), which are commonly applied to catalyst
metal analysis, provide high sensitivity and accuracy. However,
they require pretreatment to convert the sample into a solution,
thereby lengthening the analytical workflow. By contrast, EDX
can measure solid samples directly, making it well-suited to
applications requiring rapid results, such as incoming material
inspection and in-line analysis in molding plants. Because EDX is
non-destructive, it is also suitable for multimodal analytical
workflows.
On the other hand, some commercially available handheld EDX
instruments do not support elements such as Sb and Ge. At the
same time, higher-end systems may not offer the specifications
or price range needed for industrial deployment. The EDX-7200
supports a broad range of elements with excellent cost
performance. This article describes the analysis of Sb and Ge in
PET using this instrument.
Table 1 Quantitative Results
Introduction
Establishing a sustainable circular economy is a major societal
challenge, and recycling plastic materials such as PET
(polyethylene terephthalate) plays a particularly important role
in reducing environmental impact. Large numbers of PET
bottles and molded products are used every day in the food and
beverage sectors. To recycle these materials safely and reliably,
technologies are required that can accurately identify their
origin. In practice, however, appearance and conventional
physical properties alone are insufficient to distinguish virgin
material from recycled material, creating a need for a more
reliable identification method.
For rapid identification in industrial settings, a method requiring
little or no pretreatment is highly desirable. In some cases, non-
destructive analysis is also needed to enable subsequent
application of other analytical techniques. This article presents a
practical approach in which metal catalysts present in PET are
detected by EDX (Energy-Dispersive X-ray Spectroscopy) and
used to distinguish material-recycled PET from virgin PET.
EDX enables the identification of recycled PET.
Measurements are quick and simple, require no cumbersome pretreatment, and can be automated using a multi-sample turret.
The instrument offers excellent cost-performance and supports the detection of a wide range of elements.
Identification of Virgin PET and Recycled PET
by X-ray Fluorescence Spectrometry
Xu Yan
Energy Dispersive X-ray Fluorescence Spectrometer EDX-7200
Samples
• Virgin PET fiber: 1 sample
• Recycled PET fiber (material recycling): 1 sample
Fig. 1 shows the samples. JIS testing showed that the two
samples had nearly identical tensile strength.
Results
Samples were placed in sample cups, sealed with 5 μm
polypropylene film, and measured directly. An EDX-7200
instrument (Fig. 2) was used. The two samples were analyzed
sequentially using the optional turret unit. Fig. 3 shows the
samples mounted on the turret.
Fig. 3 Samples Mounted on the Turret
Fig. 4 overlays the profiles obtained from the two samples, and
Table 1 summarizes the quantitative results of Ge and Sb
calculated by the FP (Fundamental Parameter) method using
the automatic balance function.
For the virgin PET fiber, Sb was detected, whereas Ge was not. In
contrast, both Sb and Ge were detected in the recycled PET fiber.
These results are consistent with previous reports and confirm
that EDX can effectively distinguish recycled PET from virgin PET.
Ge (ppm) Sb (ppm)
Virgin PET Fiber - 87.8
Recycled PET Fiber 19.3 92.2
