Degradation of polypropylene : proportion of microplastics formed and assessment of their density.

In the environment, UV radiation, mechanical abrasion and the action of micro-organisms contribute to the degradation of plastics and their reduction into micro- and nanoplastics (MPs/NPs). More specifically, the action of UVs alters the structure of these materials and modifies their chemical composition1,2 via oxidation, as well as their intrinsic properties such as their crystallinity and density. Studying the change in density of plastics during their degradation is a key parameter that can provide answers as to the presence of MPs/NPs at different levels of the water column and in sediments, as well as their capacity to adsorb certain pollutants3 or to be ingested by different aquatic organisms. Moreover, not all macroplastics are transformed by mass into MPs/NPs, and other sub-degradation products may be formed and have an impact on the environment, either volatile or soluble compounds4. The aim of this study was to gain a better understanding of the degradation mechanisms of polypropylene (PP) under the form of films. During ageing in a UVs chamber, the mass of the films, their oxidation, their crystallinity rate and their density were measured. Results show that the longer the exposure time to UVs, the more the mass of solid PP decreases, highlighting a significant production of volatile compounds. At the same time, the density of residual films and fragments increased, reaching values in excess of 1.05 (the mean density of salt water), suggesting that the position of PP particles in the water column will be variable as it degrades. Also see: https://micro2024.sciencesconf.org/559493/document