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This study reports the effects of post-draw processing on the structural and functional properties of electrospun poly(vinylidene fluoride-co-hexafluoropropylene) (PVDF-HFP) nanofibers. Previous studies have independently demonstrated the potential of the electrospinning process or the post-drawing process to enhance the piezoelectric properties of PVDF nanofiber, and thin film structures respectively. However, post drawing electrospun nanofibers has been difficult to achieve. To overcome this limitation, a parallel automated track device was implemented to post-draw thousands of individual PVDF-HFP electrospun nanofibers per minute. Relationships were established showing that yield strength, Young's modulus, and piezoelectric output were enhanced with increasing draw ratio. The normalized voltage output of PVDF-HFP nanofibers post-drawn to a draw ratio of 3 increased by four-fold compared to undrawn control. We hypothesize that polymer chain and crystal alignment in the direction of the fiber axis, which were increased by post drawing, resulted in enhanced voltage output of PVDF-HFP nanofibers under mechanical stimulation.

The study reports a nanomanufacturing method that facilitates post-drawing of electrospun polymer nanofibers. Post-drawing is critical in conventional microfiber processing to enhance mechanical strength, but has been difficult to implement with nanofibers. Here, a parallel automated track collector was designed to permit continuous processing of thousands of individual nanofibers per minute under highly controllable drawing conditions. Post-drawing systematically induced macromolecular alignment and altered the chemical bond composition of polycaprolactone nanofibers with increasing draw ratio. The strength and stiffness of fibers with a draw ratio of 4 were enhanced by 7 and 15 times respectively and their mechanical properties exceeded previously reported values for conventional and nanoscale polycaprolactone structures.