Natural Weathering Reduces Spectroscopic Identifiability of Common Plastics

Area of Science:

• Environmental Science
• Materials Science
• Analytical Chemistry

Background:

• Microplastic pollution assessment is hindered by the lack of understanding regarding plastic degradation over time.
• Systematic studies on the natural weathering of multiple plastic types are scarce.
• Reliable identification of aged plastics is crucial for accurate pollution assessment.

Purpose of the Study:

• To investigate the impact of natural weathering on the identification of common polymers.
• To compare the degradation patterns of different plastic types under outdoor weathering conditions.
• To assess how weathering affects polymer identification using Raman and FTIR spectroscopy.

Main Methods:

• Exposure of nine common polymers (including ABS, PC, PET, PP, HIPS) to 12 months of outdoor weathering.
• Surface cleaning using ethanol wiping to minimize alteration before analysis.
• Polymer identification using Raman and FTIR spectroscopy, supported by optical microscopy and scanning electron microscopy (SEM).

Main Results:

• Confidence in polymer identification decreased with increased weathering for ABS, PC, PET, PP, and HIPS.
• Raman spectroscopy showed reduced identifiability faster than FTIR spectroscopy.
• Oxidative degradation was indicated by changes in specific chemical groups (vinylidene, C-O, C=O), with ABS, PP, and HIPS showing the most significant alterations.
• Black plastics demonstrated greater resistance to oxidation than white plastics.
• Macroplastic fragmentation was observed to directly produce microplastics.

Conclusions:

• Natural weathering progressively reduces the reliability of polymer identification, leading to potential underestimation of microplastic pollution.
• Accurate environmental monitoring requires accounting for polymer-specific degradation, analytical techniques, and pigmentation.
• Understanding weathering effects is essential for developing effective strategies to combat plastic pollution.