Hydrophobic modification of cellulose nanofibers by gallic acid and the application in pressure sensing

Via rational molecular structure design and using gallic acid (GA) for hydrophobic modification of cellulose nanofibers (CNF), the "polymer dipole" CNF-GA with hydrophilic main chains and hydrophobic side chains was prepared, which improved the poor piezoelectric properties of CNF used for preparing pressure sensors. Due to the appearance of the side chains, the elongation at break of the CNF-GA-2, compared with CNF, was enhanced by 186 %, and the excellent tensile strength, puncture load, and tearing strength were displayed. Moreover, the significant glass transition temperature (T_g) near the human body temperature was exhibited for CNF-GA, making it possible to be applied in temperature sensing. Most importantly, the CNF-GA-2 showed the maximum hydrophobicity, with a contact angle of 76.77°. Finally, the CNF-GA-2/MXene nanocomposite film was prepared by the CNF-GA-2 with MXene through vacuum filtration. The results indicated that the film had excellent piezoelectric properties (d₃₃ = 63.283), the generated stable induced voltage (125.6 mV), the preferable piezoresistive performance (ΔR/R₀ = 2.15), the fast response/recovery time (48/61 ms), which could achieve dynamic and static responses. Moreover, this film could be used for real-time detection of limb movements (such as wrists).