The Regulating Effect of Cellulose Nanofibers on the Structure and Properties of Polylactic Acid/Bio‐Nylon 11 Composites

Cellulose nanofibers (CNFs) selectively localize in the polyamide 11 (PA11) phase of polylactic acid (PLA)/PA11 immiscible blends, regardless of whether PA11 is the continuous or dispersed phase, due to favorable interfacial interactions, as confirmed by morphological and thermodynamic analysis. CNFs‐reinforced composites were fabricated via melt processing using functional masterbatches (PLA‐g‐CNFs and PA11‐g‐CNFs). At low loadings (0.5–1.0 wt%), CNFs significantly enhance flexural strength and thermal stability, with improved stress transfer and restricted polymer chain mobility contributing to the performance gains. In contrast, higher CNFs loading (up to 3.0 wt%) leads to nanofiller agglomeration, acting as stress concentrators and resulting in reduced tensile strength and ductility. The use of functional masterbatches enables precise control over CNFs dispersion and interfacial design, allowing optimal composite performance through synergistic regulation of filler content and phase localization. Microstructural observations confirm uniform CNFs distribution at low loadings and increasing heterogeneity at higher concentrations. Crystallization behavior analysis reveals accelerated nucleation kinetics in CNF‐containing systems. Overall, the incorporation of low‐loading CNFs via tailored masterbatches effectively improves the stiffness, strength, and thermal resilience of immiscible PLA/PA11 biocomposites, demonstrating a viable strategy for high‐performance sustainable materials.