In marine ecosystems, plastics undergo primarily abiotic degradation through photo-oxidation by UV light, thermodegradation, and hydrolysis. In order to understand the extent, ecological effects, and lifetimes of waste plastics in marine environments, it is necessary to quantify how these synthetic polymers degrade under natural environmental conditions and the variability in degradation conditions among materials of different sizes, surfaces areas, differing commercial compositions and formulations. Herein, we report systematic measurements of polymer fragments recovered from marine animals and beaches in the Pacific Ocean to first determine the polymer type, then measure chemical composition, molar mass distribution, and branching content within each fragment. A small subset of polypropylene samples were also sectioned to probe differences of the outer surface composition relative to the unexposed core. These resultant slices were characterized by x-ray photoelectron spectroscopy (XPS), high temperature size exclusion chromatography (HT-SEC) with tetra-detection, and differential scanning calorimetry (DSC). Sections within the same parent fragment all demonstrated a clear decrease in the number and weight average molar masses, a broader molar mass distribution, a high degree of oxidation, and greater incidence of foreign chemical elements relative to materials sampled from the internal material core. Among all polypropylene fragments measured, molar mass decreases were predominately due to chain scission, as very little long chain branched content was observed by differential viscosity measurements. Trends in the data, both from within slices of the same sample, as well as comparisons between different plastic fragments will also be discussed. This research can be used to aid the marine scientific community for sampling plastic marine debris, by providing them with alternate techniques of identification, quantitative degradation measurements, and (ultimately) information to develop improved quantitative models of polymer degradation in marine ecosystems.

Quantitative chemical, thermal, and molecular mass measurements of recovered ocean plastics

2019 Fall National Meeting

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