Evolution of Pigments in Artificially Aged Polyethylene Plastics: A Raman Study

The degradation mechanisms of polymers under UV exposure and the evolution of additives are a major concern due to their potential toxicity to humans and the environment. Vibrational spectroscopies are commonly used for the analysis of these processes. Raman spectroscopy offers a key advantage by detecting both organic and inorganic compounds with enhanced sensitivity through resonance, while infrared spectroscopy is less sensitive to low‐concentration additives. This paper highlights a new qualitative method, based on Raman spectroscopy, for the investigation of the degradation path of plastics additives, in particular pigments. The limitations and advantages are discussed in detail, with a focus on Raman‐resonant amplification of the spectral signature. Applied to commercial polyethylene containing either inorganic (titanium dioxide) or organic (PR254) pigments, this approach was validated by two artificial aging configurations. Dry and humid UVA exposure was performed during 3, 7, 15, 30, 60, and 120 days. Raman spectroscopy provides access to the study of aged surface samples, where degradation occurred. More severe degradation of the polymer matrix was observed under humid conditions compared to dry exposition. The observed relative reduction in the Raman signature of pigments indicates either the release or degradation (bond breaking or oxidation) of the pigments. Examination of the aged Raman spectra revealed no significant difference between dry and humid UVA aging, suggesting that UVA radiation was the predominant. Our study demonstrates the value of resonance Raman spectroscopy in investigating the degradation processes of plastics in the environment.