Evaluation of Microscopic Foreign Matter in Recycled Plastics Using Dynamic Image Analysis, Infrared Microscopy, and SEM-EDS

Significance of the Topic

Recycled plastics must meet strict quality standards to be used reliably in manufacturing. Microscopic foreign particles can compromise mechanical integrity, cause processing issues such as filter clogging and mold defects, and reduce final product performance. Quantitative analysis of these contaminants is essential to improve recycling processes and ensure consistent pellet quality.

Objectives and Study Overview

This study compared microscopic foreign matter in virgin and recycled polyethylene terephthalate (PET) pellets. By dissolving pellets in hexafluoro-2-propanol (HFIP) and analyzing the resulting suspensions, the research aimed to quantify particle size and concentration differences, characterize particle morphology, and identify chemical composition to guide process improvements.

Methodology and Used Instrumentation

Pellets (100 mg/mL) were dissolved in HFIP, leaving insoluble particles in suspension. The suspensions were measured directly by dynamic particle image analysis, then diluted tenfold, filtered on a silver membrane, and evaluated by infrared microscopy and SEM-EDS.

• Dynamic Particle Image Analysis System: iSpect DIA-10
• Fourier Transform Infrared Microscope: IRTracer-100 and AIM-9000
• Scanning Electron Microscope with Energy-Dispersive X-ray Spectroscopy: ProX (Phenom World)

Results and Discussion

Dynamic image analysis revealed a marked increase in particle concentration for recycled PET (≈20 240 particles/mL) compared to virgin material (≈286 particles/mL). The largest detected diameters reached ~40 µm in recycled samples versus ~10 µm in virgin. Infrared microscopy identified organic contaminants in virgin samples (cellulose- and amide-type compounds), likely from handling. SEM-EDS of recycled samples detected inorganic carbonates (elements C, Ca, O) and metallic aluminum particles. Correlation between image brightness/morphology and composition suggests that dynamic imaging can also infer particle type.

Benefits and Practical Applications

This integrated approach offers rapid, quantitative evaluation of microscopic contaminants using small sample volumes and provides actionable insights for process control and quality assurance:

• Optimizes filter selection and replacement intervals during extrusion.
• Enhances foreign-matter removal efficiency in pellet manufacturing.
• Guides investigations into contamination sources and preventive measures.

Future Trends and Potential Applications

Advancements may include automated image-based classification using machine learning, inline monitoring of molten polymers, extension to other recycled materials, and integration with process control systems for real-time quality assurance. Such developments could further reduce waste, lower production costs, and broaden the scope of recycled-material applications.

Conclusion

The combined use of dynamic particle image analysis, infrared microscopy, and SEM-EDS enables comprehensive characterization of microscopic foreign matter in PET pellets. This methodology delivers precise size and concentration data, material composition insights, and morphological information, supporting targeted improvements in recycled-plastic processing and product reliability.

References

No formal literature references were provided in the source document.