Abiotic and Biotic Polymer Degradation to Inform Sustainable Design

Abstract

As global plastic production continues to rise, understanding environmental processes governing plastic degradation is crucial to inform the sustainable design of polymers. This thesis is structured into three chapters, each addressing critical aspects of polymer degradation: In the first chapter, I develop and apply a sequential abiotic (photodegradation and hydrolysis) and biotic degradation test to a diverse suite of 18 polymers, including novel polyhydroxyalkanoates polyesters, commercially available bio-based polymers (e.g., polylactic acid, poly-3-hydroxybutyrate), and conventional fossil-derived polymers (e.g., polypropylene, polyethylene terephthalate). Results illustrate that current biodegradation standard methods relying only on mineralization underestimate polymer degradation by up to two-fold. Simulated sunlight notably enhanced polymer degradation by mobilizing dissolved organic carbon (DOC), which proved highly biodegradable in marine environment. Chemical structural differences were clearly linked to degradation behaviors, emphasizing the utility of the developed workflow for rapidly identifying environmentally relevant degradation mechanisms, which can inform structure-property relationships for future polymer designs. In the second chapter, I delve deeper into characterizing polymer-derived dissolved degradation products. Conducting Mass Remainder Analysis (MARA) using non-target liquid chromatography–high-resolution mass spectrometry (LC-HRMS) data, we systematically identified oligomeric degradation products and homologous series of polyamide-6 (PA6), polycaprolactone (PCL), and polylactic acid (PLA). Complementary experimental approaches (retention-time shifts across varied mobile phase pH, fragmentation analysis, and spectral matching) were essential to improve structure elucidation and determine acid-base properties (pKa) and hydrophobicity (logKow and logD). The experimental findings emphasized large deviations of oligomers hydrophobicity from computational predictions, underscoring the necessity for oligomer-specific experimental data to enhance environmental fate modeling and risk assessment accuracy. In the third chapter, I investigate the fate of polymer-derived dissolved organic carbon (p-DOC) from PLA, PCL and PA6, focusing specifically on oligomer chemistry. Using natural marine microbial communities, PLA- and PCL-derived DOC demonstrated rapid biodegradation (82-85% within six days), while PA6-derived DOC exhibited resistance. Detailed analysis using high-resolution mass spectrometry and MARA revealed significant chemical structure dependence in biodegradation rates, with rapid degradation of aliphatic ester-containing cyclic and linear oligomers. Larger cyclic oligomers degraded faster, while short linear oligomers showed transient accumulation followed by degradation. PA6 oligomers exhibited limited biodegradability, with cyclic oligomers showing minimal degradation. The results emphasize the critical influence of oligomer chemistry and microbial enzymatic specificity, providing essential insights for designing sustainable polymers compatible with marine environments.