Elucidating the Mechanism of Enhanced Strength and Degradability in Polylactic Acid via 2D Raman Imaging

Polylactic acid (PLA) is a biobased, biodegradable polymer whose broader industrial deployment is limited by a trade-off between mechanical robustness and hydrolytic degradability. Using Chemicals Informatics (CI), we previously identified promising small-molecule additives, adipic acid and 3,3′-dithiodipropionic acid, that could resolve this contradiction. Here, we employ Raman spectroscopy to visualize the spatial distribution and evolution of these additives in PLA during hydrolysis, using both surface and cross-sectional mapping at multiple time points. We show that adipic acid and 3,3′-dithiodipropionic acid are more uniformly distributed in the PLA matrix than the comparative additives in the initial state, suggesting improved compatibility with PLA. During hydrolysis, the additive-rich domains progressively decrease in the Raman images, indicating redistribution or removal of the additives from the matrix, which is consistent with the observed increase in degradability. Distinct morphological signatures, such as block-like domains for adipic acid and layered structures for 3,3′-dithiodipropionic acid, are resolved, elucidating the mechanistic pathways by which CI-selected additives simultaneously enable strength and degradability. This work demonstrates the power of combining informatics-guided selection with spectroscopic visualization to rationally design biodegradable polymer formulations.