Mechanical Reinforcement and Early-Stage Deterioration of Cellulose Nanocrystal-Reinforced Isosorbide-Based Polycarbonate Nanocomposites Under Humid Soil Exposure

Recently, the development of biomass-based polymers has attracted a great deal of attention as a sustainable alternative to petroleum-based plastics. However, the relatively limited mechanical properties of these bio-derived polymers often require reinforcement through the inclusion of nanofillers, while the environmental durability of such nanocomposites remains insufficiently understood. In this regard, we prepared nanocomposites composed of isosorbide-based polycarbonate (ISB-PC) and surface-modified cellulose nanocrystals (CNCs), and examined the effect of nanofillers on the mechanical properties and their retention under humid soil exposure. Interestingly, the initial reinforcement effect provided by CNCs rapidly decreased during the early stage of exposure, and the mechanical properties of the ISB-PC composites eventually converged toward those of pristine ISB-PC within a relatively short time. Based on the time-dependent changes in mechanical properties and mass loss, we propose that the mechanical deterioration was associated with physical changes in the polymer matrix, accompanied by the formation of macroscale cavities within the films. Our results suggest that initial reinforcement does not necessarily ensure sustained mechanical performance under humid soil exposure.