Hydrolytic degradation of PLA nanocomposites: impact of cellulose nanocrystal surface chemistry and dispersion state

Cellulose nanocrystals (CNCs) are promising biodegradable fillers for poly(lactic acid) (PLA), but their influence on PLA degradation, particularly the relationship between the surface chemistry and dispersion of CNCs and hydrolytic degradation behavior, remains incompletely understood. Herein, we systematically investigate the hydrolysis of PLA composites incorporating unmodified and polymer-grafted CNCs. Results show that polymer grafting enhances the hydrophobicity of CNCs and improves their dispersion within the PLA matrix. Unexpectedly, unmodified CNCs exhibit negligible impact on PLA hydrolysis, whereas grafted CNCs accelerate hydrolytic degradation regardless of whether they are modified with hydrolysis-resistant poly(methyl methacrylate) (PMMA) or hydrolysis-sensitive poly(vinyl acetate) (PVAc). Morphological observation and X-ray diffraction/scattering analysis reveal that PLA and its composites follow a bulk erosion mechanism during hydrolysis. On one hand, the well-dispersed CNCs create additional pathways for hydrolytic media to penetrate the material interior. On the other hand, the grafted PVAc enriched at the interfaces undergoes preferential hydrolysis, thereby further amplifying the promoting effect of CNCs on PLA degradation. This research sheds light on the hydrolytic degradation behavior of PLA/biomass-filler composites and provides fundamental insights for designing PLA composites with tailored degradation profiles.