The influence of the initial size on the fragmentation kinetics of polymers based on experimental results has not been deeply investigated so far. In this work, the fragmentation kinetics during photodegradation of polyethylene (PE) microplastics in abiotic water were investigated and compared to the fragmentation of macroscopic PE films with a surface of several square centimeters. In both cases, the weathering was performed in situ to avoid any contamination and the focus was on the detection of colloidal fragments, i.e. with sizes less than 1 µm. The chemical modifications associated with weathering and ageing were measured for the films using infra red and Raman spectroscopy.  The results showed that colloidal PE particles do not fragment in smaller particles during weathering. However, during the same time of exposition, the macroscopic PE film was fragmented with the smallest fragments having a size of around 200 µm. No colloidal plastics could be detected in the water despite the fact that chemical oxidation of the film and modification of its crystallinity were found to have occurred during weathering. Once the water was dried, a few particles were detected that had the spectral signature of aged PE, but it is not clear in what form this PE was present in the water before drying (particles vs aggregation of short polymer chains). These results confirm that the fragmentation from macro to microplastics for a PE film exposed to photodegradation is quite rapid whereas, at the conditions of this study (no strong mechanical abrasion during weathering, abiotic conditions), PE nanoplastics were not formed in significant quantities implying that they are not produced or only at a rate slower than investigated here. Surface-ablation appeared also to be very limited. Nevertheless, such processes could be more important in natural environments through the presence of microorganisms at the surface or of abrasives. Bulk fragmentation did take place at larger length scales but the fact that micrometric PE particles did not exhibit any size decrease over more than 40 weeks of photodegradation suggests that the existence of a size limit below which the rate fragmentation of plastics would strongly decrease should be considered. The factors that may influence this size limit should be further investigated.

Transition size in polymer fragmentation processes may slow down nanoplastics production in the environment

Macromolecular Chemistry: The Second Century

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ACS Spring 2020 National Meeting & Expo

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.