The conventional isolation of cellulose nanofibers (CNFs) process involves high energy input which leads to compromising the pulp fiber’s physical and chemical properties, in addition to the issue of elemental chlorine-based bleaching, which is associated with serious environmental issues. This study investigates the characteristic functional properties of CNFs extracted via total chlorine-free (TCF) bleached kenaf fiber followed by an eco-friendly supercritical carbon dioxide (SC-CO2) treatment process. The Fourier transmission infra-red FTIR spectra result gave remarkable effective delignification of the kenaf fiber as the treatment progressed. TEM images showed that the extracted CNFs have a diameter in the range of 10–15 nm and length of up to several micrometers, and thereby proved that the supercritical carbon dioxide pretreatment followed by mild acid hydrolysis is an efficient technique to extract CNFs from the plant biomass. XRD analysis revealed that crystallinity of the fiber was enhanced after each treatment and the obtained crystallinity index of the raw fiber, alkali treated fiber, bleached fiber, and cellulose nanofiber were 33.2%, 54.6%, 88.4%, and 92.8% respectively. SEM images showed that amorphous portions like hemicellulose and lignin were removed completely after the alkali and bleaching treatment, respectively. Moreover, we fabricated a series of cellulose nanopapers using the extracted CNFs suspension via a simple vacuum filtration technique. The fabricated cellulose nanopaper exhibited a good tensile strength of 75.7 MPa at 2.45% strain.

The production of kenaf bast cellulose nanofibrillated fiber (CNF) using a combined method of supercritical carbon dioxide (SC CO2) and high-pressure homogenization as the reinforcement with biopolymer were studied. The obtained CNF was used as reinforcement in polylactic acid using the solvent casting method. The obtained CNF were verified using TEM and FTIR analysis to approve the effectiveness of the technique. The dispersion of kenaf bast cellulose nanofibrillated fiber in modified PLA was studied with scanning electron microscopy and atomic force microscopy. Further characterization, such as, mechanical, thermal, and wettability properties of the composite was also analyzed. The TEM and FTIR confirmed the formation of nanofiber, and the FTIR result showed a typical bond present in cellulose nanofibrillated fiber. The SEM and AFM showed good dispersion of the kenaf bast cellulose nanofibrilated fiber in PLA. The mechanical and thermal properties of the composite were significantly improved compared with the neat PLA. The wettability showed that the addition of CNF increased the hydrophilicity of the sample. The production of CNF through combine methods displayed comparable properties to those produced from conventional methods and the CNF preparation method in this study is simplified and adaptable for potential industrial application.

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