Self-poled PVDF/recycled cellulose composite fibers utilizing cellulose nanocrystals to induce PVDF β-phase formation through wet-spinning as a flexible fabric piezoelectric sensor

In general, PVDF (Polyvinylidene fluoride) needs polarization treatment to exhibit its piezoelectric properties. Introducing nanofillers or applying stretching during the processing can promote the β-phase transformation in PVDF, achieving self-polarization. Herein, by incorporation of cellulose nanocrystals (CNCs), continuous β-phase enriched PVDF/cellulose composite fibers are prepared via wet spinning and drawing, in which the cellulose is recycled from waste cotton textiles to improve the wet spinnability of PVDF and reduce the cost. The obtained composite fibers are woven into fabrics and subsequently assembled into a flexible sensor, exhibiting excellent piezoelectric performance (d33 = 26.2 pC/N) without requiring additional polarization treatment. It generates an open-circuit voltage of 12 V and a short-circuit current of 100nA, much higher than those of the previously reported piezoelectric PVDF sensors with high-voltage polarization. This fabric-based flexible sensor also exhibits notable characteristics, including stable output signals and heightened sensitivity, thereby fulfilling the demands for monitoring both minute and extensive human movements. Furthermore, it shows great potential for widespread use in sound sensing for human-machine interfaces. The self-poled PVDF composite fibers offer the advantage of being easily woven together with other fiber materials, which contributes towards the development of self-powered flexible piezoelectric fabric sensors.