<p>The increasing demand for biodegradable plastics calls for materials that not only degrade the environment but also exhibit sufficient mechanical strength for practical use. Poly(butylene succinate) (PBS) is a promising candidate in this regard, but its relatively unpredictable degradation behavior remains a limiting factor. In this study, PBS-based materials were synthesized via in-situ polymerization by incorporating three additives: cellulose nanocrystals, citric acid, and polyethylene glycol. The synthesized samples were evaluated in terms of mechanical properties, hydrolysis under various pH conditions, enzymatic degradation using two lipases, and biodegradation in freshwater ecosystems. The differences in degradation behavior linked to the type of additive indicate that the structure of the PBS polymer is crucial in determining its response to hydrolytic, enzymatic, and microbial degradation conditions. This study advances beyond the simple degree of degradation and systematically characterizes the degradation pathways and rates that vary with each additive. These findings establish a fundamental mechanism for designing PBS-based biodegradable materials, and allow for the customization of their degradation properties according to the intended environment of use.</p> Graphical abstract <p></p>