Interplay between the Molecular Structure of Lignin and the Degradation Process of PLA/Lignin Materials

Blending lignin in polylactide (PLA) could simultaneously promote lignin valorization and tackle the limitations of PLA. Still, the lack of compatibility between lignin and PLA typically requires chemical modification of lignin's hydroxyl groups, which could affect the already slow biodegradation rate. Here, the impact of the molecular structure of different lignin types on the properties and degradation processes of PLA/lignin films was investigated. Alkaline lignin and Kraft lignin were blended with PLA as received and after acetylation and/or fractionation. The PLA/lignin materials were aged under hydrolytic and simulated industrial composting conditions. During hydrolytic degradation, PLA/lignin materials with acetylated lignin showed an accelerated degradation rate during the early stages, as a consequence of lignin deacetylation and the release of acetic acid that catalyzed ester hydrolysis. Our results demonstrate that the molecular structure and weight of lignin influence both the physicochemical properties and morphology of the films, as well as the subsequent degradation process.