Cladding-free thermal drawing for scalable reel-to-reel manufacturing of piezoelectric coaxial polyvinylidene fluoride fibers

The thermal drawing process (TDP) offers a promising route for fabricating long functional fibers from macroscopic multimaterial preforms; however, its potential is currently restricted by two critical bottlenecks: the difficulty in integrating highly conductive, flexible electrodes and the processing constraints imposed by conventional shear-based rheological assessments. Because such assessments cannot capture tensile rupture behavior, semi-crystalline polymers typically require a cladding material that stabilizes the drawing process but limits scalability. Here, we overcome these limitations by introducing a highly conductive silver nanowire (AgNW)-coated polymeric core electrode and a thermal elongation (TE) test that directly evaluates extensional deformation across diverse material systems. Guided by the TE test, we demonstrate cladding-free thermal drawing of a semi-crystalline polyvinylidene fluoride (PVDF) homopolymer, with synchronous feeding of the AgNW-coated nylon core (17 Ω/cm). Eliminating the cladding enables a seamless, continuous post-treatment workflow, including in situ corona discharge poling. The resulting piezoelectric coaxial fiber exhibits a remarkably high peak-to-peak output voltage of 9.4 V under 0.5% tensile strain and demonstrates exceptional mechanical durability, retaining 87.3% of its initial signal after 10,000 bending cycles at a 1 mm radius. All processes are fully integrated into a reel-to-reel system, establishing a scalable pathway toward mass production of flexible piezoelectric fibers for wearable sensing applications.