Spectroscopically evaluating composition and crystallinity changes to PET controls during production and weathering using polarization dependent OPTIR

Published

September 26, 2026

Author(s)

Danuta Liberda Matyja, Hsiuchin Huang, Tae Joon Cho, Li Piin Sung, John Pettibone

Abstract

Detection of micro and nanoplastic (MNP) particles in diverse matrices and subsequent chemical identification are analytical challenges being extensively researched. Methods capable of MNPs detection are only beginning to be developed, because of challenges associated with the high sensitivity and selectivity requirements needed to distinguish plastics from carbon backgrounds. Based on these challenges, the ability of mid-infrared photothermal (MIP) microscopy to collect IR spectra with submicron spatial resolution has resulted in growing research efforts to develop methods for MNPs detection and chemical characterization. Here, we applied a commercially available, polarization dependent MIP system, OPTIR, to extend IR-based methods for films to structurally and chemically heterogeneous polymeric particle controls. Because polymer crystallinity is critical for stability, the ability to estimate crystallinity was paramount for developing practicable particle assessments in addition to chemical composition. We examined a well-studied system, pristine and UV-exposed polyethylene terephthalate (PET) control samples. Previously reported IR methods for determining crystallinity in bulk PET through glycol conformer fractions were combined with advanced structural determination methods to characterize thick and opaque films using azimuthal angle and Herman's in-plane orientation function. We defined UV irradiation induced photo-oxidation signatures as a function of depth in cross-sectioned films using K-means clustering. Using the OPTIR and data processing tools developed for films, we successfully demonstrated the first extension of chemical and structural mapping to small, UV-weathered CM particles.

Citation

Analytical Chemistry

Pub Type

Journals

Download Paper

https://doi.org/10.1021/acs.analchem.6c01918

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Keywords

microplastics, nanoplastics, mid-infrared photothermal microscopy, spectroscopy, imaging

Citation

Liberda Matyja, D. , Huang, H. , Cho, T. , Sung, L. and Pettibone, J. (2026), Spectroscopically evaluating composition and crystallinity changes to PET controls during production and weathering using polarization dependent OPTIR, Analytical Chemistry, [online], https://doi.org/10.1021/acs.analchem.6c01918, https://nps-ext.nist.gov/nps/nps_public_api/api/Publication/file/961270 (Accessed October 29, 2026)

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