Project description:A low carbon yield is a major limitation for the use of cellulose-based filaments as carbon fiber precursors. The present study aims to investigate the use of an abundant biopolymer chitosan as a natural charring agent particularly on enhancing the carbon yield of the cellulose-derived carbon fiber. The ionic liquid 1,5-diazabicyclo[4.3.0]non-5-enium acetate ([DBNH]OAc) was used for direct dissolution of cellulose and chitosan and to spin cellulose-chitosan composite fibers through a dry-jet wet spinning process (Ioncell). The homogenous distribution and tight packing of cellulose and chitosan revealed by X-ray scattering experiments enable a synergistic interaction between the two polymers during the pyrolysis reaction, resulting in a substantial increase of the carbon yield and preservation of mechanical properties of cellulose fiber compared to other cobiopolymers such as lignin and xylan.
Project description:Multiwalled carbon nanotube (MWNT)/cellulose composite nanofibers have been prepared by electrospinning a MWNT/cellulose acetate blend solution followed by deacetylation. These composite nanofibers were then used as precursors for carbon nanofibers (CNFs). The effect of nanotubes on the stabilization of the precursor and microstructure of the resultant CNFs were investigated using thermogravimetric analysis, transmission electron microscopy and Raman spectroscopy. It is demonstrated that the incorporated MWNTs reduce the activation energy of the oxidative stabilization of cellulose nanofibers from ∼230 to ∼180 kJ mol(-1). They also increase the crystallite size, structural order, and electrical conductivity of the activated CNFs (ACNFs). The surface area of the ACNFs increased upon addition of nanotubes which protrude from the fiber leading to a rougher surface. The ACNFs were used as the electrodes of a supercapacitor. The electrochemical capacitance of the ACNF derived from pure cellulose nanofibers is demonstrated to be 105 F g(-1) at a current density of 10 A g(-1), which increases to 145 F g(-1) upon the addition of 6% of MWNTs.
Project description:The kraft lignin's low molecular weight and too high hydroxyl content hinder its application in bio-based carbon fibers. In this study, we were able to polymerize kraft lignin and reduce the amount of hydroxyl groups by incubating it with the white-rot fungus Obba rivulosa. Enzymatic radical oxidation reactions were hypothesized to induce condensation of lignin, which increased the amount of aromatic rings connected by carbon-carbon bonds. This modification is assumed to be beneficial when aiming for graphite materials such as carbon fibers. Furthermore, the ratio of remaining aliphatic hydroxyls to phenolic hydroxyls was increased, making the structure more favorable for carbon fiber production. When the modified lignin was mixed together with cellulose, the mixture could be spun into intact precursor fibers by using dry-jet wet spinning. The modified lignin leaked less to the spin bath compared with the unmodified lignin starting material, making the recycling of spin-bath solvents easier. The stronger incorporation of modified lignin in the precursor fibers was confirmed by composition analysis, thermogravimetry, and mechanical testing. This work shows how white-rot fungal treatment can be used to modify the structure of lignin to be more favorable for the production of bio-based fiber materials.
Project description:Carbon fibers (CFs) are fabricated by blending hardwood kraft lignin (HKL) and cellulose. Various compositions of HKL and cellulose in blended solutions are air-gap spun in 1-ethyl-3-methylimidazolium acetate (EMIM OAc), resulting in the production of virtually bead-free quality fibers. The synthesized HKL-cellulose fibers are thermostabilized and carbonized to achieve CFs, and consequently their electrical and mechanical properties are evaluated. Remarkably, fibers with the highest lignin content (65%) exhibited an electrical conductivity of approximately 42 S/cm, surpassing that of cellulose (approximately 15 S/cm). Moreover, the same fibers demonstrated significantly improved tensile strength (∼312 MPa), showcasing a 5-fold increase compared to pure cellulose while maintaining lower stiffness. Comprehensive analyses, including Auger electron spectroscopy and wide-angle X-ray scattering, show a heterogeneous skin-core morphology in the fibers revealing a higher degree of preferred orientation of carbon components in the skin compared to the core. The incorporation of lignin in CFs leads to increased graphitization, enhanced tensile strength, and a unique skin-core structure, where the skin's graphitized cellulose and lignin contribute stiffness, while the predominantly lignin-rich core enhances carbon content, electrical conductivity, and strength.
Project description:For highly efficient heat dissipation of thin electronic devices, development of film materials that exhibit high thermal conductivity in the in-plane direction is desired. In particular, it is important to develop thermally conductive films with large in-plane anisotropy to prevent thermal interference between heat sources in close proximity and to cool in other directions by diffusion. In this study, we developed flexible composite films composed of a uniaxially aligned carbon-fiber filler within a cellulose nanofiber matrix through liquid-phase three-dimensional patterning. The film exhibited a high in-plane thermal conductivity anisotropy of 433%, with combined properties of a thermal conductivity of 7.8 W/mK in the aligned direction and a thermal conductivity of 1.8 W/mK in the in-plane orthogonal direction. This remarkable thermal conductivity and in-plane anisotropy showed the ability to significantly cool powder electroluminescent devices formed on the composite film and also to cool two heat sources in close proximity without thermal interference. In addition, the carbon-fiber filler could be extracted from the composite films by heat treatment at 450 °C and reused as a thermally conductive material.
Project description:In this study, Cellulose-based carbon fibers (CBCFs) were prepared from cellulose after phenol liquefaction and curing. The characteristics and properties of CBCFs were examined by scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), Raman spectroscopy and X-ray photoelectron spectroscopy (XPS). The results showed that, with increasing carbonization temperature, the La, Lc, and Lc/d(002) of CBCFs increased gradually, whereas the degree of disorder R decreased. The -OH, -CH₂-, -O-C- and phenyl group characteristic absorption peaks of CBCFs reduced gradually. The cross-linked structure of CBCFs was converted into a graphite structure with a six-ring carbon network during carbonization. The surface of CBCFs were mainly comprised of C-C, C-O, and C=O. The tensile strength, carbonization yield and carbon content of CBCFs obtained at 1000 °C were 1015 MPa, 52%, and 95.04%, respectively.
Project description:A method was developed in which cellulose (CEL) and/or chitosan (CS) were added to keratin (KER) to enable [CEL/CS+KER] composites to have better mechanical strength and wider utilization. Butylmethylimmidazolium chloride ([BMIm(+)Cl(-)]), an ionic liquid, was used as the sole solvent, and because the [BMIm(+)Cl(-)] used was recovered, the method is green and recyclable. Fourier transform infrared spectroscopy results confirm that KER, CS, and CEL remain chemically intact in the composites. Tensile strength results expectedly show that adding CEL or CS into KER substantially increases the mechanical strength of the composites. We found that CEL, CS, and KER can encapsulate drugs such as ciprofloxacin (CPX) and then release the drug either as a single or as two- or three-component composites. Interestingly, release rates of CPX by CEL and CS either as a single or as [CEL+CS] composite are faster and independent of concentration of CS and CEL. Conversely, the release rate by KER is much slower, and when incorporated into CEL, CS, or CEL+CS, it substantially slows the rate as well. Furthermore, the reducing rate was found to correlate with the concentration of KER in the composites. KER, a protein, is known to have secondary structure, whereas CEL and CS exist only in random form. This makes KER structurally denser than CEL and CS; hence, KER releases the drug slower than CEL and CS. The results clearly indicate that drug release can be controlled and adjusted at any rate by judiciously selecting the concentration of KER in the composites. Furthermore, the fact that the [CEL+CS+KER] composite has combined properties of its components, namely, superior mechanical strength (CEL), hemostasis and bactericide (CS), and controlled drug release (KER), indicates that this novel composite can be used in ways which hitherto were not possible, e.g., as a high-performance bandage to treat chronic and ulcerous wounds.
Project description:Nanocomposite materials made from cellulose show a great potential as future high-performance and sustainable materials. We show how high aspect ratio cellulose nanofibrils can be efficiently aligned in extrusion to fibers, leading to increased modulus of toughness (area under the stress-strain curve), Young's modulus, and yield strength by increasing the extrusion capillary length, decreasing its diameter, and increasing the flow rate. The materials showed significant property combinations, manifesting as high modulus of toughness (~28-31 MJ/m3) vs. high stiffness (~19-20 GPa), and vs. high yield strength (~130-150 MPa). Wide angle X-ray scattering confirmed that the enhanced mechanical properties directly correlated with increased alignment. The achieved moduli of toughness are approximately double or more when compared to values reported in the literature for corresponding strength and stiffness. Our results highlight a possibly general pathway that can be integrated to gel-spinning process, suggesting the hypothesis that that high stiffness, strength and toughness can be achieved simultaneously, if the alignment is induced while the CNF are in the free-flowing state during the extrusion step by shear at relatively low concentration and in pure water, after which they can be coagulated.
Project description:The trend across the whole of society is to focus on natural and/or biodegradable materials such as cellulose (Cell) over synthetic polymers. Among other usage scenarios, Cell can be combined with electroactive components such as multiwall carbon nanotubes (CNT) to form composites, such as Cell-CNT fibers, for applications in actuators, sensors, and energy storage devices. In this work, we aim to show that by changing the potential window, qualitative multifunctionality of the composites can be invoked, in both electromechanical response as well as energy storage capability. Cell-CNT fibers were investigated in different potential ranges (0.8 V to -0.3 V, 0.55 V to -0.8 V, 1 V to -0.8 V, and 1.5 V to -0.8 V), revealing the transfer from cation-active to anion-active as the potential window shifted towards more positive potentials. Moreover, increasing the driving frequency also shifts the mode from cation- to anion-active. Scanning electron microscopy (SEM) and energy dispersive X-ray (EDX) spectroscopy were conducted to determine the ion species participating in charge compensation under different conditions.
Project description:Sheep wool is one of the most common wastes derived from agriculture and also a great source of keratin. In this study, chemical reduction and alkali hydrolysis methods of extracting keratin from wool were studied for the purpose of reusing the waste wool, and the products were used to fabricate wet-spun hybrid fibers by mixing with PVA. The comparative yield of the two extraction methods was investigated, and the optimal precursor concentration ratio for keratin extraction was identified. The effects of keratin concentration and wet-spinning flow rate on the mechanical properties of fabricated fibers were studied. Therefore, this study encourages the further investigation of wool keratin-based hybrid biomaterials, which could provide a new way to reuse waste wool.