Quantitative Analysis of Recycled Plastics Using FTIR – Individual Calculation Method –

Importance of the Topic

The rapid growth of plastic waste has driven the need for reliable, rapid methods to quantify the main polymer components in recycled materials. Accurate determination of polyethylene (PE), polypropylene (PP), polystyrene (PS), and polyethylene terephthalate (PET) content enables manufacturers to maintain quality standards and optimize recycling processes.

Study Objectives and Overview

This work evaluates a screening method using Fourier transform infrared spectroscopy (FTIR) with an individual calculation approach. The aim is to compare its performance against conventional nuclear magnetic resonance (NMR) analysis. The study focuses on developing calibration curves from samples with known compositions and applying them to unknown recycled plastic sheets.

Analytical Methodology and Instrumentation

An IRAffinity-1S FTIR spectrometer equipped with a Quest single-reflection attenuated total reflection (ATR) accessory was employed. Key parameters included a resolution of 4 cm⁻¹, 20 accumulations, Happ-Genzel apodization, and DLATGS detection in absorbance mode. Sample sheets were pressed against the ATR zinc selenide prism to collect spectra over 400–1800 cm⁻¹ without any chemical pretreatment.

Main Results and Discussion

Calibration curves for PE (719 cm⁻¹), PP (841 cm⁻¹), PS (698 cm⁻¹), and PET (1721 cm⁻¹) showed a linear relationship between corrected peak height and polymer concentration. Five known samples yielded consistent infrared spectra, enabling quantitation of two unknown samples. FTIR results agreed within 6 wt% of NMR values for major components, with greater variability at low concentrations. Sheet-form samples ensured reliable prism contact and reproducible measurements, while trace component analysis exhibited higher scatter.

Benefits and Practical Applications

• Eliminates time-consuming solvent extraction and NMR sample preparation.
• Enables rapid screening of recycled plastics in quality control.
• Supports compliance with container and packaging recycling regulations.

Future Trends and Applications

Advances may include expanding calibration datasets to improve accuracy, integrating chemometric algorithms for multicomponent deconvolution, and adapting ATR-FTIR for automated on-line monitoring in recycling plants. Portable FTIR instruments could facilitate field audits and mobile testing services.

Conclusion

The individual calculation method using ATR-FTIR provides a fast, cost-effective alternative to NMR for quantifying major polymer fractions in recycled plastic sheets. While minor components and low-level analysis require further refinement, this approach shows strong potential for routine quality control in the circular plastics economy.