Determining the influence of variable additive, filler, and dye concentrations in plastics on their fluorescence behavior via spectrometry and FD-FLIM

TL;DR

This study explores how additives, fillers, and dyes in plastics affect their fluorescence behavior, showing that these components complicate plastic identification using FD-FLIM.

Contribution

The paper introduces a logarithmic model to describe how varying concentrations of additives, fillers, and dyes influence plastic fluorescence lifetimes.

Findings

Additives, fillers, and dyes in plastics cause overlapping fluorescence lifetimes, making plastic identification difficult.

A logarithmic model accurately captures the concentration-dependent fluorescence lifetime behavior of plastics.

FD-FLIM's effectiveness for plastic analysis is limited without considering multiple excitation/emission states.

Abstract

Microplastic (MP) pollutes our terrestrial and aquatic ecosystems due to their uncontrolled discharge into our environment. The analysis of MP contamination is still a challenge, although significant improvements are made for different environmental matrices. Using mass-based particle analysis methods such as thermal extraction and desorption-gas chromatography/mass spectroscopy (GC/MS) or pyrolysis GC/MS, essential parameters such as the MP’s morphology, size, and shape cannot be obtained, which are indispensable to assess the hazard of the respective particles. Raman, micro-Fourier transform infrared, and attenuated total reflectance spectroscopy are particle-based analysis methods, which are time-consuming due to the high purification effort. Thus, novel, reliable, and time-efficient methods for MP analysis are required. Previously, studies showed the potential of frequency domain fluorescence lifetime imaging microscopy (FD-FLIM) to identify plastics’ type, shape, size, and morphology, and distinguishing these from natural materials. However, only pure plastic granules were investigated, omitting that commodity plastics accumulating in our environment contain various additive, filler, or dye concentrations. To circumvent the dependency of additive, filler, and dye concentrations, we investigated the fluorescence spectra and lifetimes of three plastic types, individually composed with two fillers, three additives, and two dyes in six different concentrations. We heuristically modeled the dependency of the concentration on plastics’ fluorescence lifetime using a logarithmic model with a high correlation and showed that identifying the plastic types is hardly possible when fillers, additives, or dyes are added in various concentrations because of their superimposing fluorescence lifetimes. However, further research has to be conducted to investigate different emission states of fluorescence to optimize the FD-FLIM method, as only one excitation wavelength and emission band was used for the investigations.

The online version contains supplementary material available at 10.1007/s00216-026-06361-0.

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