Visualizing local phase distribution and crystalline evolution in polymer-protein composite electrospun nanofibers by Raman mapping and structural analysis

Elucidating crystallization in biodegradable polymer composite fibers requires both bulk thermal/structural analysis and spatially resolved characterization of local crystalline domains and phase distribution. Herein, one-dimensional poly(lactic acid)/silk fibroin (PLA/SF) composite nanofibers with different compositions were fabricated by electrospinning, and their isothermal crystallization behavior was systematically investigated using differential scanning calorimetry (DSC), X-ray diffraction (XRD), and Raman mapping spectroscopy. DSC analysis combined with Avrami kinetics demonstrated that silk fibroin acted as an effective bio-based nucleating agent, shortening the crystallization onset time and half-time while increasing the crystallization rate and crystallinity of PLA. Fibers crystallized at 105 °C exhibited faster crystallization and higher crystallinity than those treated at 125 °C, whereas treatment at 125 °C favored the formation of more ordered PLA α-crystals, as supported by temperature-dependent XRD results. Beyond the bulk information obtained from DSC and XRD, Raman mapping provided direct spatial visualization of PLA/SF phase distribution, local PLA crystalline regions, and silk fibroin β-sheet structures before and after isothermal treatment. The mapping results revealed good component dispersion without obvious phase separation and showed that isothermal crystallization generated finer and more dispersed crystalline domains within the composite fibers. This work demonstrates that integrating Raman mapping with thermal and diffraction analyses provides a powerful approach for revealing phase heterogeneity, localized crystallinity, and crystallization kinetics of electrospun biodegradable polymer-protein composite fibers.