Hierarchical alignment of nanophase separation in TPU/cellulose nanocrystal composite fibers via electrospinning: A pathway to enhanced mechanical performance

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This study provides an in-depth structural analysis of hard-segment (HS) nanodomains in thermoplastic polyurethane (TPU) and TPU/cellulose nanocrystal (CNC) electrospun nanofibers and directly correlates nanoscale morphology with macroscopic mechanical performance. CNCs (0–5 wt%) were incorporated into TPU via electrospinning at take-up velocities of 440 and 1320 m/min. Synchrotron-based small-angle X-ray scattering (SAXS), interpreted through a hierarchical lamellar grain model, revealed two distinct morphologies: oriented lamellae and fragmented “oblique-herringbone” structures. At low draw speed, CNCs acted as structural templates promoting preferential domain orientation, whereas high draw speed induced fragmentation regardless of CNC content. Quantitative SAXS analysis identified systematic variations in lamellar long period, grain width ( IB σ ), and grain tilt ( ϕ ) with CNC addition, with optimal domain dimensions achieved at 3 wt% CNC. These structural parameters directly reflected changes in tensile performance: the widest lamellar grains corresponded to peak tensile strength, while increased domain orientation and packing density enhanced modulus. This integration of nanodomain mapping and mechanical analysis establishes a clear structure–property relationship and offers a framework for tuning performance in sustainable, high-strength TPU-based nanofibers.