Analyzing Microscopic Contaminants Embedded in Recycled Plastic

Significance of the Topic

Effective characterization of microscopic contaminants in recycled plastics is crucial for maintaining material performance and achieving sustainability targets in a carbon-neutral society. Trace impurities can affect mechanical properties, appearance, and safety of plastic products, making rapid and accurate analysis essential for quality control in recycling processes.

Study Objectives and Overview

This application note demonstrates a streamlined workflow for detecting, identifying and quantifying microscopic contaminants embedded in recycled polyethylene (PE) and polypropylene (PP) films. By combining infrared high-speed mapping microscopy with particle analysis software, the method aims to rapidly screen large sample areas while obtaining detailed chemical and morphological data.

Methodology and Instrumentation

The workflow consists of three key steps:

• Film Preparation: Recycled plastic pellets are pressed into a 100 µm-thick film using a thermal press.
• High-Speed IR Mapping: Transmission spectra are collected across a 2 370 × 1 470 µm area with single scans to detect IR peaks. Where peaks are found, a configurable number of repeated scans (up to 50) enhance signal quality.
• Particle Analysis: Detected spectra for each contaminant type are loaded into a particle analysis program to determine count, size and shape metrics.

Used Instrumentation:

• Microscope: IRTracer-100 with AIMsight infrared microscope
• Software: AMsolution control, high-speed mapping module, particle analysis program
• Optics & Settings: Transmission mode; spectral resolution 8 cm⁻¹; 50 scans; SqrTriangle apodization; mirror speed 30 mm/s; aperture 30 µm × 30 µm; step size 30 µm; detector T2SL
• Mapping Parameters: Area 2 370 × 1 470 µm; noise threshold 0.01; peak detection level 0.15; exclusion ranges 3 200–2 000 cm⁻¹ and 1 700–700 cm⁻¹

Key Results and Discussion

High-speed mapping successfully distinguished contaminant spectra from the PE/PP background by excluding base-material absorption regions. Two major contaminant types were identified:

• Cellulose fibers
• Polybutyl methacrylate (PBMA) particles

The particle analysis detected 74 contaminants over the mapped area, with PBMA particles approximately twice as numerous as cellulose. Size distributions based on short and long diameters revealed fiber morphology for cellulose and more rounded shapes for PBMA.

Benefits and Practical Applications

The combined high-speed mapping and particle analysis approach delivers:

• Rapid screening of large sample areas with minimal noise
• Chemical identification without contaminant extraction
• Quantitative particle counts and size distributions
• Analysis time reduced by a factor of fifteen compared with full-area repeated scanning

This methodology supports quality assurance in plastic recycling, microplastic research, and contamination control in production streams.

Future Trends and Potential Applications

Advancements may include integration of automated sample handling for higher throughput, machine-learning-based spectral classification to expand contaminant libraries, and adaptation to other polymer matrices. Coupling infrared mapping with complementary techniques such as Raman imaging or scanning electron microscopy could further enhance multi-modal characterization capabilities.

Conclusion

An infrared high-speed mapping microscope paired with particle analysis software provides a fast, non-destructive, and reliable solution for detecting and quantifying microscopic contaminants in recycled plastics. The approach enhances quality control processes and contributes to more efficient recycling workflows.

Reference

• High-Speed Measurement of Microplastics Smaller than 100 µm Collected on a Filter and Efficient Analysis—Application News No. 01-00994-EN