Generation of nanoplastics during the photoageing of low-density polyethylene

In this work, we studied the hydrolytic and photochemical degradation of three low-density polyethylene (LDPE) materials, within the size range of microplastics (MP). The MPs were exposed to mechanical agitation and UV irradiation equivalent to one year of solar UVB + UVA in a stirred photoreactor. Flow cytometry was used to track the formation of small (1-25 μm) MPs by applying Mie's theory to derive the size of MP particles from scattering intensity readings. The calculation was based on a calibration with polystyrene (PS) beads. The results showed that the generation of 1-5 μm MP reached 10⁴-10⁵ MPs in the 1-25 μm range per gram of LDPE. ATR-FTIR and micro-FTIR measurements evidenced the formation of oxygenated moieties, namely hydroxyl, carbonyl, and carbon-oxygen bonds, which increased with irradiation time. We also found evidence of the production of a high number of nanoplastics (<1 μm, NPs). The Dynamic Light Scattering size of secondary NPs was in the hundreds of nm range and might represent up to 10¹⁰ NPs per gram of LDPE. Our results allowed the unambiguous spectroscopic assessment of the generation of NPs from LDPE under conditions simulating environmental exposure to UV irradiation and used flow cytometry for the first-time to track the formation of secondary MPs.