Identification of Virgin PET and Recycled PET by X-ray Fluorescence Spectrometry

Significance of the Topic

The reliable identification of virgin versus recycled polyethylene terephthalate (PET) is critical for safe recycling, quality control, and establishing traceability within a circular economy. Metal catalyst residues (notably antimony and germanium) incorporated during PET polymerization provide a chemical fingerprint that can distinguish material origin. A rapid, non-destructive, and low‑cost analytical workflow suitable for industrial environments enables incoming material inspection, in‑line monitoring at molding plants, and supports regulatory and safety assessments of recycled streams.

Objectives and Overview of the Study

This application study evaluated the capability of an energy‑dispersive X‑ray fluorescence spectrometer (EDX‑7200) to discriminate virgin PET from material‑recycled PET by detecting catalyst metals (Sb, Ge) directly in solid fiber samples. The goals were to demonstrate: quick, low‑preparation elemental screening; the typical elemental signatures of virgin versus recycled PET; and the operational suitability of the EDX‑7200 for routine industrial use, including multi‑sample automation via a turret.

Methodology

Two PET fiber samples were analyzed: one virgin PET fiber and one material‑recycled PET fiber. Both showed comparable tensile properties by JIS testing, illustrating that physical properties alone could not reliably indicate origin. Samples were placed in sample cups, sealed with 5 μm polypropylene film, and measured directly without chemical pretreatment. Measurements were performed sequentially using an optional multi‑sample turret.

Instrumental Setup

The method used the Shimadzu EDX‑7200 energy‑dispersive X‑ray fluorescence spectrometer. Key instrumental parameters and choices included:

• Quantification approach: Fundamental Parameters (FP) method with automatic balance function.
• Detector: Silicon Drift Detector (SDD).
• X‑ray tube: Rhodium (Rh) target.
• Collimator diameter: 10 mm.
• Tube voltage: 50 kV; tube current set to auto.
• Atmosphere: air; samples analyzed through thin polypropylene film (non‑destructive).
• Integration time and measurement sequencing: short integration for rapid screening (example: 20 s per condition reported), turret used for automation.

Main Results and Discussion

Elemental profiles overlaid for the two fibers revealed clear differences in catalyst content. Quantitative FP results were:

• Virgin PET fiber: Sb detected at ~87.8 ppm; Ge not detected.
• Recycled PET fiber: Sb detected at ~92.2 ppm; Ge detected at ~19.3 ppm.

These observations align with literature reports that material‑recycled PET often contains both Sb and Ge because recycled feedstocks originate from varied production routes and catalysts. Virgin PET commonly shows a single catalyst signature (Sb or Ge depending on synthesis route), while chemically recycled PET may show a different pattern. The ability of EDX to detect Sb and Ge directly in solids enabled rapid discrimination between the two fibers.

Benefits and Practical Applications

Key practical advantages demonstrated by this approach include:

• Non‑destructive, direct analysis of solid samples—no digestion or wet chemistry required, preserving samples for follow‑up testing.
• Rapid throughput and ease of use suitable for incoming inspection, quality control, and plant in‑line checks.
• Compact and cost‑effective compared with high‑sensitivity but higher‑effort methods (ICP‑AES, ICP‑MS) that require sample dissolution.
• Automation capability via a multi‑sample turret increases reproducibility and labor efficiency.

The method is particularly useful as a screening tool to flag suspected recycled material for further confirmatory testing or to support material traceability and QA workflows when combined with physical property data.

Limitations and Considerations

• EDX typically has higher detection limits than ICP‑based techniques; low‑level trace elements may be below EDX limits of detection.
• Matrix effects and peak overlaps require careful calibration and the use of FP quantification to improve accuracy.
• Not all handheld or low‑cost EDX devices detect Sb and Ge reliably; instrument selection (such as the EDX‑7200) matters for element coverage.

Future Trends and Potential Applications

Opportunities to expand and enhance this approach include:

• Integration with chemometric models and classification algorithms to automate origin assignment and handle complex mixed‑feedstock signatures.
• Standardization of measurement protocols, reference materials, and limits of decision to support regulatory acceptance and cross‑laboratory comparability.
• Improved detector and software capabilities to lower LODs, resolve spectral overlaps, and expand detectable element ranges (beneficial for detecting other additives/contaminants).
• Combining EDX screening with complementary techniques (e.g., thermal analysis, FTIR, or ICP after targeted digestion) to provide a multi‑modal material characterization framework.
• Deployment in recycling facilities and supply chains to enable real‑time sorting and quality control, thereby strengthening circular‑economy practices.

Conclusion

Energy‑dispersive X‑ray fluorescence analysis using the EDX‑7200 provides a practical, fast, and non‑destructive method to distinguish recycled PET from virgin PET by detecting catalyst metals (Sb and Ge) directly in solid samples. While EDX does not replace the sensitivity of ICP techniques for trace quantification, it offers an effective screening and QC tool with strong operational advantages for industrial deployment. When combined with physical testing and confirmatory analyses, this workflow supports safer and more traceable recycling streams and contributes to circular‑economy objectives.

References

1. Ohkado Y, Kawamura Y, Mutsuga M, Tamura H, Tanamoto K. Metals in Recycled Polyethylene Terephthalate and Discrimination Method for Its Use. Journal of the Food Hygienic Society of Japan. 2005;46(3):109–116.
2. Ministry of the Environment. Guidance on investigation methods for products containing recycled plastics (by resin type), Document No. 000040692; Polyethylene terephthalate (PET) fibers. Section 4.8.