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

Microplastics (MPs), defined as plastic fragments smaller than 1 mm, arepervasive pollutants posing considerable ecological and health hazardsowing to their durability and potential to cause adverse environmentaleffects. These particles originate mainly from the breakdown of biggerplastic debris by mechanisms such as UV-induced photodegradation,resulting in fragmentation into micro-and nanoplastics. Appropriatelaboratory test materials that simulate naturally degraded plastics areessential for evaluating the environmental impact of MPs, enhancinganalytical methods, and assessing remediation pathways. In this study wegenerated ``true-to-life{''} MPs from commonly utilized plastic productsthrough controlled photodegradation processes designed to acceleratepolymer aging. Two aging protocols were developed: (i) UV irradiation ofmacroplastic fragments for up to eight weeks followed by mechanicalmilling, and (ii) UV exposure of pre-fragmented MPs over the sameperiod. Five polymers, namely polystyrene (PS), polypropylene (PP),high-density polyethylene (HDPE), polyvinyl chloride (PVC), andpolyethylene terephthalate (PET), were chosen for analysis, with PETinvestigated separately due to the presence of the carbonyl group, whichcomplicates carbonyl index (CI) calculations used as a quantitativeindex to monitor the photo-oxidation. The surface morphology of aged MPswas examined using Scanning Electron Microscopy (SEM), their chemicalcomposition was investigated by Near-Infrared (NIR) andFourier-transform Infrared (FTIR) spectroscopy, thermal properties werealso evaluated by Thermogravimetric Analysis (TGA). PET degradation wasfurther analyzed using supplementary techniques such as X-RayDiffraction (XRD) and Differential Scanning Calorimetry (DSC) to assessstructural and thermal alterations. These findings demonstrate that theproposed protocols generate MPs with consistent physicochemicalproperties, providing a model system suitable for studying MPdegradation and behavior in laboratory studies, ultimately supportingenvironmental risk assessment and mitigation strategies.