Divergent marine biodegradation of cellulose acetate and cellulose propionate: Substituent chemistry controls microbial interactions and environmental persistence

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The marine biodegradation of cellulose esters remains poorly understood, particularly when polymers with similar chemical compositions exhibit different degradation behaviors due to differences in ester substituents. Herein, the biodegradation behaviors of cellulose acetate (CA) and cellulose propionate (CP) films were compared under identical flow-through seawater aquaculture conditions. Biodegradation was evaluated using biochemical oxygen demand measurements according to the Organization for Economic Co-operation and Development (OECD) 301F protocol and was complemented by surface characterization, microbial community analysis, and kinetic modeling. Despite having the same degree of substitution (DS = 2.5), CA exhibited moderate biodegradation and reached 27.1% mineralization after 119 days, whereas CP showed negligible biodegradation (2.3%) over the same period. Kinetic modeling estimated an apparent half-life of ∼137 days for CA and 2110 days for CP, indicating pronounced differences in environmental persistence. Surface analyses revealed greater erosion and denser biofilm formation on CA films than on CP films. Microbial community analysis showed an enrichment of taxa previously associated with hydrolytic activity on CA, whereas CP films supported biofilms dominated by taxa associated with surface colonization and biofilm persistence. Fourier-transform infrared spectroscopy revealed preferential ester-bond cleavage in CA, providing complementary mechanistic evidence of degradation. Although neither polymer met the OECD criteria for ready biodegradability, persistence-based metrics clarified their relative environmental risks. These results demonstrate that subtle differences in ester substituents drive divergent biodegradation pathways through structure-microbe interactions. The findings also highlight the importance of persistence-informed evaluation frameworks for bioplastics intended for marine and aquaculture applications.