Developing environmentally relevant test materials for microplastic research through UV-induced photoaging

Microplastics, defined as plastic fragments smaller than 5 mm, are pervasive pollutants which pose considerable ecological and health hazards owing to their durability and potential to cause adverse environmental effects. These particles originate mainly from the breakdown of bigger plastic debris by mechanisms such as UV-induced photodegradation, resulting in fragmentation into micro- and nanoplastics. Appropriate laboratory test materials that simulate naturally degraded plastics are essential for evaluating the environmental impact of microplastics, enhancing analytical methods, and assessing remediation pathways. In this study we generated "true-to-life" microplastics from commonly utilized plastic products through controlled photodegradation processes that replicate natural aging conditions. Two aging protocols were developed: the first consisted UV irradiation of macroplastic fragments for a duration of up to eight weeks, followed by cryogenic milling to generate microplastics; the second involved exposing pre-fragmented microplastics to UV light for the same duration. Five polymers, namely polystyrene (PS), polypropylene (PP), low-density polyethylene (LDPE), polyvinyl chloride (PVC), and polyethylene terephthalate (PET), were chosen for analysis, with PET investigated separately due to the presence of the carbonyl group, which complicates carbonyl index (CI) calculations used as a quantitative index to monitor the photo-oxidation. The surface morphology of aged microplastics was examined using Scanning Electron Microscopy (SEM), their chemical composition was investigated by near-Infrared (NIR) and Fourier-transform infrared (FTIR) spectroscopy, thermal properties were also evaluated by thermogravimetric analysis (TGA). PET degradation was further analyzed using supplementary techniques such as X-ray diffraction (XRD) and differential scanning calorimetry (DSC) to assess structural and thermal alterations. This study improves the environmental applicability of microplastic test materials, enabling more precise evaluations of microplastic behavior and degradation in real-world scenarios and providing significant insights into the possible long-term ecological impacts of microplastics.