Functionalized GO nanoplatelets with folic acid as a novel material for boosting humidity sensing of chitosan/PVA nanocomposites for active food packaging

Humidity sensing materials play a pivotal role for serving as the essence of moisture sensors to trap surrounding water molecules through hydrophilic interaction, chemical bonding, or hydrogen bonds, therefore enhancing the sensor conductivity. Thus, this work addresses a highly efficient humidity sensing material based on folic acid (FA) functionalized graphene oxide (GO) which was prepared for consolidating inside chitosan (CS)/polyvinyl alcohol (PVA) (80/20) blend by the solvent casting approach. The structure of GO and its decoration were ratified by X-ray diffraction (XRD), Fourier transform infrared (FT-IR) and UV–vis spectroscopies. Three GO-FA contents (i.e., 10, 20, and 30 vol%) were utilized to fabricate the renewable CS/PVA nanosensors. The morphology of fabricated sensors was characterized by XRD and scanning electron microscopy (SEM). SEM images showed that the miscibility and dispersibility of GO-FA nanoplatelets in the CS/PVA matrix are better at 10 and 20 vol%, although the tensile strength increased to 69.40 MPa for the nanocomposite film containing 30 vol% GO-FA compared to the blank specimen. Moreover, other investigations such as Raman spectroscopy and antibacterial activities were performed on the CS/PVA sensors. The humidity sensing properties were carried out over a broad range of relative humidity from (7–97% RH) and frequency (100 Hz-100 kHz). The data revealed that 1 kHz was considered to be the optimum frequency. Furthermore, the obtained outcomes from humidity-sensing tests at 1 kHz showed that the sensor C10 had higher sensitivity with ultrafast response/recovery times (2.6 s/3.5 s) compared to other nanosensors, to be used in intelligent food packaging and preservation.