Preparation And Properties Of Cellulose Nanofiber/Carbon Nanofiber Composites From Coconut Palm Petiole

In recent years, extracting cellulose derivative from natural fibers has received much attention for their superior properties, such as high specific strength, biodegradability, low density and low cost. These advantages make cellulose nanofibers promising candidates in the fields of reinforcing agent, pharmaceutical packaging, and electromagnetic interference materials, etc. Carbon nanofibers(CNF) possess fantastic applications in the fields of adsorbing materials, conductive materials and catalyst support, attributed to their large surface area, high aspect ratio and novel web-like networks.In this study, coconut palm petiole was used as a starting material to fabricate cellulose nanofibers(Cell NF) and CNF. Cell NF was prepared by mechanical treatments combined with chemical pretreatments, and CNF was prepared by pyrolyse the freeze-dried Cell NF.Cell NF/CNF composite membrane was prepared by mixing method. The obtained Cell NF,CNF and their composite membrane were characterized and analyzed by Fourier infrared(FT-IR), X-ray diffraction(XRD), Scanning electron microscopy(SEM), etc. The main conclusions are as follows:(1) Cell NF was successfully isolated from coconut palm petiole by chemical modification followed by mechanical treatments, i.e. grinding, ultrasonication and homogenization. Most of hemicellulose and lignin was removed from the palm petiole fibers by chemical treaments, and the subsequent mechanical treatments make the diameter of the Cell NF between 50–100 nm,and the aspect ratio of Cell NF over 1000. Among the three types of treatments, the film prepared by grinding(F1) showed the tensile strength and Young's modulus of 106.83 MPa and2.19 GPa, respectively. Compared to the film prepared by grinding, the film prepared by grinding/ultrasonication(F2) and grinding/ homogenization(F3) had an increase of 46.6% and50.2% in tensile strength, and 35.2% and 66.2% in Young's modulus, respectively. At a wavelength of 600 nm, the regular light transmittance at room temperature of sample F1, F2 and F3 was 73.3%, 76.1% and 78.1%, respectively.(2) Freeze drying creates sufficient space between the individual fibers, results in the preservation of fibrous morphology during carbonization. Longer holding time(10 hours) at240 ? and slower heating rate from 240 to 400 ? were critical to preserve the original fibrous structures of the precursive Cell NF after pyrolysis. The diameter of fibers decreased slightly with increasing pyrolysis temperature, but when the maximum pyrolysis temperature was over 800 ?, the decrease became negligible and the diameter was distributed over 10-70 nm.(3) The surface active groups increased after the oxidation treatments, which can enhance the degree of wettability and adhesion between the matrix material and CNF.(4) CNF possessed a three dimensional network structure, it can intercalate into 2 layers of Cell NF and stack with them like a sandwich. Meanwhile, the surface of the composite membrane were uniform, which indicated that CNF can combine with Cell NF well and form chemical bonds and lamellar structures by physical crosslinking. Therefore, the strength of the materials was improved greatly with increasing content of CNF. When the ratio of CNF to Cell NF was 1:1 in weight, the composite membrane showed the tensile strength and Young's modulus of 25.4 MPa and 1.12 GPa, respectively. When the ratio was 1:6, the composite membrane had an enhancement of 166% and 113% in tensile strength and Young's modulus,respectively.(5) CNF has a certain electronic conductivity, and the electronic conductivity of the composite membrane was 180.3 S/cm when the ratio of CNF to Cell NF was 1:1 in weight. Along with the increasing content of Cell NF, the electrical conductivity decreased, because CNF itself had no electrical conductivity.