The life-story of plastic butter tubs

, Delorme Astrid, Verney Vincent, Askanian Haroutioun, Roussel Erwann, Voldoire Olivier, Delor-Jestin Florence, Koumba Gaelle Bissagou, Peiry Jean-Luc.

In this work, plastic debris has been introduced into the environment to be exposed to various environmental conditions such as moisture, heat, sunlight or microbial action. Prolonged exposure to these environmental factors action causes polymers to degrade, fragment into smaller pieces and cleaved into small molecules. We investigate the degradation pathways of five identical plastic butter tubs made of polypropylene (PP), positioned in five different locations near a French wild river, in which one was buried in sediments (after having being artificially pre-weathered in lab conditions), two were placed by the riverbank, and two in the vegetation. At each location UV radiation, moisture and temperature were monitored and samples of each plastic tub were taken frequently for 506 days. Changes in the chemical structure were followed with rheology by studying the viscoelastic properties of the polymer as a function of time. Despite, being located in different places which resulted in different UV-radiation exposure and temperature variations, the plastic butter tub followed similar trends, in that after an initial decrease in the viscosity of the polymer, we observe an increase in the overall viscosity after a longer exposition to environmental conditions (506 days) which suggests that a chain recombination mechanism is occurring within the polymer. This is a rather unusual observation since PP is known to, generally, undergo chain scission when it is aged, as indicated by a lowered viscosity. The conclusion is that such experiments in natural conditions may be very instructive to understand the fate of abandoned plastic wastes in the environment. However, a more robust methodology must be built-up with more samples to be able to assess longer times.

View online