Solvent Evaporation-Controlled Stereocomplexation in PLLA/PDLA Films for Sustainable Packaging

The formation of stereocomplex (SC) crystallites in poly(L-lactide) (PLLA)/poly(D-lactide) (PDLA) blends has attracted significant attention due to its potential to enhance the performance of biodegradable polymer films. In this study, the effect of solvent evaporation kinetics on the crystallization behavior, microstructure, and functional properties of PLLA/PDLA blend films was systematically investigated. Films with various blend ratios were prepared under open-lid (fast evaporation) and closed-lid (slow evaporation) conditions. Differential scanning calorimetry (DSC), wide-angle X-ray diffraction (WAXD), and small-angle X-ray scattering (SAXS) analyses revealed that slow solvent evaporation significantly promotes stereocomplex formation, particularly at the equimolar (50:50) composition, resulting in a higher degree of crystallinity and a more compact structure compared to fast evaporation conditions. These structural changes were directly correlated with improved functional properties. The optimized PLLA/PDLA (50:50) films exhibited a substantial reduction in water vapor permeability from 22.7 to 3.11 g·mm/m2·day·kPa (~86% decrease) and a marked decrease in microbial growth, as evidenced by reduced total plate count (TPC) values compared to neat polymers. The enhanced barrier performance and reduced microbial proliferation were attributed to the reduced free volume and increased tortuosity associated with densely packed stereocomplex crystallites, as supported by DSC and WAXD results. These findings demonstrate the importance of solvent evaporation kinetics in tailoring structure–property relationships to control stereocomplex formation and multiscale structural organization, providing a practical strategy for biodegradable packaging films.