A Systematic Study on the Degradation Products Generated from Artificially Aged Microplastics

Abstract

Most of the analytical studies focused on microplastics (MPs) are based on the detection and identification of the polymers constituting the particles. On the other hand, plastic debris in the environment undergoes chemical and physical degradation processes leading not only to mechanical but also to molecular fragmentation quickly resulting in the formation of leachable, soluble and/or volatile degradation products that are released in the environment. We performed the analysis of reference MPs–polymer micropowders obtained by grinding a set of five polymer types down to final size in the 857–509 μm range, namely high- and low-density polyethylene, polystyrene (PS), polypropylene (PP), and polyethylene terephthalate (PET). The reference MPs were artificially aged in a solar-box to investigate their degradation processes by characterizing the aged (photo-oxidized) MPs and their low molecular weight and/or highly oxidized fraction. For this purpose, the artificially aged MPs were subjected to extraction in polar organic solvents, targeting selective recovery of the low molecular weight fractions generated during the artificial aging. Analysis of the extractable fractions and of the residues was carried out by a multi-technique approach combining evolved gas analysis–mass spectrometry (EGA–MS), pyrolysis–gas chromatography–mass spectrometry (Py–GC–MS), and size exclusion chromatography (SEC). The results provided information on the degradation products formed during accelerated aging. Up to 18 wt% of extractable, low molecular weight fraction was recovered from the photo-aged MPs, depending on the polymer type. The photo-degradation products of polyolefins (PE and PP) included a wide range of long chain alcohols, aldehydes, ketones, carboxylic acids, and hydroxy acids, as detected in the soluble fractions of aged samples. SEC analyses also showed a marked decrease in the average molecular weight of PP polymer chains, whereas cross-linking was observed in the case of PS. The most abundant low molecular weight photo-degradation products of PS were benzoic acid and 1,4-benzenedicarboxylic acid, while PET had the highest stability towards aging, as indicated by the modest generation of low molecular weight species.

Nano/Microplastics Capture and Degradation by Autonomous Nano/Microrobots: A Perspective

“…[ 46–48 ] The latter allows qualitative and quantitative determination of degradation products, which permits the evaluation of degradation pathways and potential secondary pollution. For instance, pyrolysis‐gas chromatography‐mass spectrometry (Pyr‐GC‐MS) provided information on byproducts formed during the aging of various microplastics, [ 49 ] while size exclusion chromatography (SEC) disclosed the reduction of their molecular weight due to the induced oxidation. Smaller microplastics (<100 µm), and thus nanoplastics, are challenging to handle by Pyr‐GC‐MS.…”

“…[46][47][48] The latter allows quali-tative and quantitative determination of degradation products, which permits the evaluation of degradation pathways and potential secondary pollution. For instance, pyrolysis-gas chromatography-mass spectrometry (Pyr-GC-MS) provided information on byproducts formed during the aging of various microplastics, [49] while size exclusion chromatography (SEC) disclosed the reduction of their molecular weight due to the induced oxidation. Smaller microplastics (<100 µm), and thus nanoplastics, are challenging to handle by Pyr-GC-MS. [50] Contrarily, matrix-assisted laser desorption/ionization-time-offlight mass spectrometry (MALDI-TOF MS) is an ionization technique that offers mass spectra of high-molecular-weight polymers, including plastics, with a resolution of the individual n-mers within the polymer mass distribution.…”

On-Line Thermally Induced Evolved Gas Analysis: An Update—Part 1: EGA-MS

“…Instrumental analytical techniques based on analytical pyrolysis and thermal analyses provide qualitative and mass-based quantitative information and have a high potential to become of general use in the analysis of microplastics. La Nasa et al reviewed the research carried out to date in the analysis of microplastics by analytical thermal and pyrolysis techniques [ 229 , 230 , 231 ].…”

Risk for the release of an enormous amount of nanoplastics and microplastics from partially biodegradable polymer blends

“…9,16,19 In addition, an increasing number of studies show that the highly degraded secondary NMPs contain a greater content of hazardous substances than pristine NMPs due to the presence of degradation products such as monomers, oligomers and oxidative products. [20][21][22][23] Therefore, it is particularly crucial to understand the degradation-induced formation process of NMPs in various environmental conditions for better prediction of NMP emissions. 16,[24][25][26][27][28] Most studies focus on pure plastics, [24][25][26][27] and overlook an important source for NMPs: the degradation of polymer blends.…”