Material Identification of Plastics Throughout Their Life Cycle by FTIR Spectroscopy

Significance of the Topic

Plastic materials are indispensable across numerous industries, making precise identification at each stage of their life cycle critical for quality control, regulatory compliance, and environmental protection. Fourier transform infrared (FTIR) spectroscopy provides a fast, non-destructive, and cost-effective method to distinguish polymer types in raw feedstocks, finished products, recycled streams, and environmental debris.

Study Objectives and Overview

This application demonstrates a streamlined workflow using the Agilent Cary 630 FTIR spectrometer with attenuated total reflectance (ATR) to identify five representative samples spanning the plastic life cycle. The aim is to validate a combined use of an Agilent ATR demo library and a user-generated polymer spectral library for rapid, reliable material identification.

Methodology

Five samples were selected to cover key stages: a glycerol plasticizer (starting material), an LDPE nurdle (raw pellet), a polystyrene coffee lid (finished product), a recycled PET water bottle, and polypropylene beach debris (weathered waste). Spectral data were collected over the 4000–650 cm⁻¹ range with 64 background scans and 64 sample scans at 4 cm⁻¹ resolution. The Similarity search algorithm was applied against both the Agilent ATR demo library and a user-generated library built from standard polymer samples, including PS, PP, HDPE, LDPE, PET, PVC, PC, PMMA, POM, PA, and PTFE.

Instrumentation

• Agilent Cary 630 FTIR Spectrometer
• Diamond ATR Sampling Module
• Agilent MicroLab Software for guided acquisition and library management

Main Results and Discussion

All five samples achieved high hit quality indices (HQI > 0.97), confirming accurate polymer identification: glycerol (HQI 0.996), LDPE nurdle (0.996), PS lid (0.978), PET bottle (0.986), and PP debris (0.989). The MicroLab software provided color-coded confidence levels, simplifying result interpretation and minimizing user errors.

Benefits and Practical Applications

• Quality assurance of raw materials and final plastic products
• Verification of recycled polymer streams to maintain purity
• Identification of environmental plastic debris for pollution monitoring
• Intuitive software interface reduces training requirements and operational errors

Future Trends and Opportunities

Emerging directions include expanding spectral libraries to cover composite polymers and weathered materials, integrating machine learning for automated match scoring, and deploying portable FTIR-ATR instruments for in-field analysis in recycling facilities and environmental surveys.

Conclusion

The Agilent Cary 630 FTIR-ATR system combined with MicroLab software delivers a robust, turnkey solution for polymer identification throughout the plastic life cycle. High confidence hit indices and simplified workflows support diverse applications in manufacturing, recycling, and environmental research.

References

• Rhodes CJ. Plastic Pollution and Potential Solutions. Science Progress. 2018;101(3):207–260.
• British Plastic Federation. Plastics Applications. Accessed May 2023.