Effects of α- and β-Chitin on the Mechanical Properties and Molecular Interactions of Electrospun PLLA Nanofibers

Poly(L-lactic acid) (PLLA) nanofibers are promising materials for biomedical and packaging applications; however, their inherent brittleness limits applications requiring both stiffness and ductility. Here, α- and β-chitin, differing in molecular packing and hydrogen-bonding characteristics, were incorporated into electrospun PLLA nanofibers at a PLLA/chitin mass ratio of 10:1. Both chitin types enhanced the mechanical properties of PLLA, increasing tensile strength by 1.4- and 1.6-fold and Young’s modulus to 83.7 and 79.7 MPa for PLLA/α-chitin and PLLA/β-chitin, respectively. PLLA/α-chitin exhibited higher yield strength and more uniform fiber morphology, whereas PLLA/β-chitin showed substantially greater ductility and toughness with pronounced necking behavior. Thermal, spectroscopic, and diffraction analyses revealed distinct structural responses associated with the two chitin forms. α-Chitin produced a constrained hydrogen-bonded environment that restricted PLLA chain mobility. In contrast, β-chitin preserved greater chain mobility and promoted a more heterogeneous local molecular environment. Despite its lower overall crystallinity, PLLA/β-chitin exhibited a distinct secondary melting feature, suggesting localized chain organization and a limited nucleation effect rather than enhanced bulk crystallization. These findings demonstrate that chitin structure provides a practical design parameter for balancing stiffness and toughness in PLLA nanofiber composites, broadening their potential applications in the biomedical and packaging fields.