Measurement of Microplastics and Use of Thermal-Damaged Plastics Library

Significance of the Topic

Microplastics, defined as plastic fragments under 5 mm, pose growing threats to marine ecosystems and human health. Their ubiquity along coastlines demands reliable analytical methods to identify polymer types, determine sources, and guide mitigation strategies.

Objectives and Study Overview

This study demonstrates the use of a compact FTIR spectrophotometer combined with a thermal-damaged plastics spectral library to rapidly identify environmentally degraded microplastic samples collected from a sea coast. The aim is to overcome limitations of standard FTIR libraries when analyzing UV-degraded materials.

Methodology

Environmental microplastics were sampled from shoreline sediments, exhibiting diverse shapes and colors. Attenuated Total Reflection (ATR) FTIR was used to acquire surface absorption spectra with a light penetration depth of several micrometers. Spectral matching employed a thermal-damaged plastics library containing reference spectra of thirteen common polymers in unheated form and after heating at 200–400 °C. This approach leverages similarities between thermal and UV-induced oxidative degradation patterns.

Instrumentation

• IRSpirit™ Compact FTIR: portable footprint (< A3 size), dual-side access, high signal-to-noise ratio, and class-leading resolution.
• QATR™-S ATR accessory (diamond prism): integrated into the IRSpirit sample compartment for easy ATR measurements.

Main Results and Discussion

Two representative microplastic particles (white and red, ≤ 5 mm) were analyzed under the following conditions: 4 cm⁻¹ resolution, 40 scans, Happ-Genzel apodization, and DLATGS detector. Spectral matching indicated the white fragment as polypropylene heated at 200 °C for 4 h and the red fragment as polyethylene heated at 200 °C for 2 h. These matches suggest both samples underwent oxidative degradation similar to UV exposure.

Benefits and Practical Applications

• Rapid, non-destructive identification of degraded microplastics without extensive sample preparation.
• Portable instrumentation supports field surveys and coastal monitoring.
• Thermal-damage library extends qualitative capabilities to weathered plastics often unrecognized by standard libraries.

Future Trends and Potential Applications

Advancements may include expansion of degradation libraries to cover broader environmental conditions and integration with micro-imaging FTIR mapping for spatial characterization. Automated spectral matching and machine learning could further enhance throughput and accuracy in pollution monitoring.

Conclusion

The combination of ATR-FTIR with a thermal-damaged plastics library enables swift qualitative analysis of UV-degraded microplastics. This workflow enhances the reliability of polymer identification in environmental samples, aiding research and remediation efforts.

Reference

1. Hiroshi Yamanoi (2007), The Mechanisms of Polymer Degradation Discoloration and Stabilization, Journal of the Materials Life Society, Japan, 19(3), 103–108.
2. Yoshio Oki (1973), Degradation of Plastic Materials, Journal of the Metal Finishing Society of Japan, 24(4), 229–238.