New Insights toward Casein/Polyvinyl Alcohol Electrospun Nanofibrous Webs as a Piezoelectric-Cum-Triboelectric Energy Harvester

Herein, a hybrid piezoelectric-cum-triboelectric energy harvesting device has been fabricated very successfully by using a casein/polyvinyl alcohol (PVA)-based electrospun nanofibrous (NF) web. At first, the casein powder has been synthesized by using cow milk in the laboratory. Thereafter, the casein nanofiber has been prepared by the electrospinning method with the help of the PVA polymer since casein is not spinnable as a single component due to its higher tendency to form intermolecular hydrogen bonds among the surrounding casein molecules. The PVA polymer has been used to create a secondary bond with the casein molecule so that casein can be easily spinnable by the electrospinning process. The synthesized casein molecules and the developed casein/PVA NF web have been characterized. Various structural analysis techniques (Fourier transform infrared and X-ray diffraction) have been used to confirm the presence of different functional groups (−OH, C═O, −NH, and −CONH) and the crystallinity, respectively, in the blend of casein and the PVA polymer. For confirming the piezoelectric behavior of the casein/PVA solution cast film, the ferroelectric property has been analyzed by the P–E hysteresis loop. The developed hybrid solution cast film has shown a remnant polarization of ∼33 μC/cm2. Finally, energy harvesting performances have been measured by simple finger tapping and by the standard testing method. The energy harvesting device has shown an output voltage and a current of ∼20 V and ∼37 μA, respectively, by repeated finger tapping on the device, while ∼195 mV output voltage and ∼0.018 μA current have been found to be generated in the case of the standard testing method. Furthermore, this device could glow "IITD text" made of 20 light-emitting diodes at a time by simple finger tapping on the device. This directly substantiates that the developed device can be of practical use in different niche applications.