Effect of Cryo-Milling on PLA/CNC and PLA/Calcium Carbonate Nanocomposites: A Comparison Study

This study examines a new approach for improving the dispersion of hydrophilic fillers into a hydrophobic polymer matrix, a long-standing challenge that often limits the thermal and mechanical performance of biocomposites. We investigated two different types of fillers—natural cellulose nanocrystals (CNC) and mineral calcium carbonate (CaCO₃)—introduced into polylactic acid (PLA) at five different volume fractions. PLA-based biocomposite films were fabricated using physical mixing and cryo-milling methods, followed by hot pressing to study their effects. Cryo-milling was explored as a promising strategy to enhance filler distribution within the matrix. Thermal properties, crystallization behavior, and mechanical performance were characterized using differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), and tensile testing. CNC addition slightly lowered the glass transition temperature (Tg), while CaCO₃ raised it; both fillers promoted crystallization, although overall crystallinity remained relatively stable. Mechanically, tensile strength and strain decreased with filler addition, but CNC composites, particularly those prepared by cryo-milling, retained better ductility. Both CNC and CaCO₃ increased the modulus of PLA composites, with CaCO₃ providing a greater improvement. Although cryo-milling improved nanoparticle dispersion within the PLA matrix, better interfacial bonding is still needed. Future strategies, such as surface modification of fillers—like PEG-coating CNC—are recommended alongside improved mixing methods to optimize composite performance for sustainable applications.