Relationship between the Carbonyl Index (CI) and Fragmentation of Polyolefin Plastics during Aging

Thecarbonyl index (CI)-fragmentation relationshipwill contribute to more accurate MP mass balance models, since itsuggests a simple method to assess the fragmentation potential ofa polyolefin particle. The durability of plastics in the marine environmenthas emergedas a crucial environmental issue. However, the contribution of severalfactors and the threshold point after which a plastic product generatessecondary micro- and nanoplastics is still unclear. To investigatethe interaction of environmental parameters with the physicochemicalproperties of polyethylene (PE) and polypropylene (PP) films in themarine environment, polyolefin films were subjected to weatheringin emulated coastal and marine environments for 12 months, focusingon the relationship between radiation load, alteration on the surface,and subsequent generation of microplastics (MPs). The weight averagemolecular weight (M (w)) was found to bestrongly correlated with the generated particles and the Feret diameter,implying the generation of secondary microplastics at decreased M (w). A significant and strong relationship betweenthe carbonyl index (CI) and the Feret diameter for PP films weatheredon beach sand was identified. This CI-fragmentation relationshipinvolves three sequential stages and suggests that spontaneous fragmentationoccurs at CI values above 0.7.

Automated summary

The CI-fragmentation relationship can be used to accurately predict the fragmentation potential of polyolefin particles in MP mass balance models. The durability of plastics in the marine environment and the threshold point for the generation of secondary microplastics are still unknown. This study investigated the interaction between environmental parameters and the physicochemical properties of PE and PP films, finding a strong correlation between molecular weight and the generation of microplastics. Additionally, a significant relationship between CI and Feret diameter was identified for PP films weathered on beach sand.