Surface modification of cellulose nanofibers with graphene nanoplatelets for the fabrication of high-performance biocomposites

Abstract

A self-assembled biocomposite nanopaper with high toughness, ductility, and tensile strength was produced by the incorporation of graphene nanoplatelets (GNP) into cellulose nanofibers (CNF). This was achieved through noncovalent functionalization of CNF with very low GNP concentrations of 0.25%, 0.5%, and 1%. It is proposed that GNP functions as a ball-bearing lubricating agent that partially disrupts hydrogen bonds and introduces noncovalent C–H···π interactions between its aromatic structure and the hydrophobic domains of CNF. The relationship between the material's structure and properties was established using a combination of characterization techniques, including Raman spectroscopy, Fourier transform infrared spectroscopy (FTIR), wide-angle X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), and tensile testing. FESEM results showed a layered fibrous network, while Raman spectroscopy confirmed the noncovalent functionalization. XRD analysis indicated that hydrogen bond alteration led to a reduction in crystallinity and a modification of cellulose crystal size. The presence of interfacial interactions was further supported by FTIR results. These crucial interactions resulted in controlled fibril slippage, where hydrogen bonds rupture and reformation repeatedly during mechanical testing. This led to a simultaneous enhancement of toughness, ultimate tensile strength, and strain-to-failure. These properties were improved by 210% (34.1 ± 1.8 MJ/m³), 47% (158.3 ± 4.5 MPa), and 191% (35 ± 2.5%), respectively.