Pucha Zhou

Polyacrylonitrile/lignin sulfonate blend fiber for low-cost carbon fiber

Polyacrylonitrile/lignin sulfonate (PAN/LS) blend fibers were spun via a wet spinning process. The fiber structure, mechanical properties and thermal stability of the precursor fibers were studied by FT-IR, SEM, tensile tester, and TG-DSC. Results indicated that there was no chemical crosslinking between PAN and LS during the process of wet spinning. PAN and LS had good compatibility in the blend fibers. LS could weaken the skin of the blend fibers and reduce the fiber structure defects. The increase of dope concentration could improve the fiber structure and mechanical properties. LS blending with PAN could reduce fiber weight loss in the thermal stabilization process, and most importantly the precursor fibers could be stabilized rapidly without fiber fusion. Through polymer blending and wet spinning, this study provided a promising way to prepare a precursor fiber for carbon fiber.

Nitrogen- and oxygen-enriched 3D hierarchical porous carbon fibers: synthesis and superior supercapacity

A nitrogen- and oxygen-enriched hierarchical porous carbon fiber was fabricated by phase-separable wet-spinning and the subsequent chemical activation of polyacrylonitrile (PAN) precursors. The wet-spinning could readily offer an interpenetrating 3D meso-/macro-porous network owing to the phase-separation of PAN in the coagulation bath (DMSO/H2O), caused by the different solubility of PAN in DMSO and H2O, and the different content of PAN in the fiber and the coagulation bath. The latter chemical activation introduced abundant small-sized nanopores within the meso-/macro-porous network skeleton. The obtained hierarchical porous carbon fiber exhibited a high specific surface area of 2176.6 m2 g−1 and a large pore volume of 1.272 cm3 g−1, and was highly doped with heteroatoms of nitrogen and oxygen. When it was used as a supercapacitor electrode, high performance of reversible specific capacitances of 329 F g−1 at 0.1 A g−1 and 223 F g−1 at 20 A g−1 as well as the capacitance retention of 97.6% after 2000 cycles were achieved in a two-electrode cell.

Layered NiO/reduced graphene oxide composites by heterogeneous assembly with enhanced performance as high-performance asymmetric supercapacitor cathode

A layered NiO/reduced graphene oxide composite (NiO/RGO) was prepared by a facile heterogeneous assembly approach with subsequent in situ thermal reduction. The two-dimensional hydroxide and graphene oxide nanosheets achieved nanoscale dispersion in the composites, with high interfacial interaction between each other. The as-obtained material exhibits a high specific capacitance of 782 F g−1 at 0.5 A g−1 and an excellent cycling stability with 94.1% retention at 2 A g−1 after 3000 cycles in a three-electrode system. To further evaluate the NiO/RGO electrode for practical application, an asymmetric supercapacitor NiO/RGO//AC was fabricated using the NiO/RGO as cathode and AC as anode. It exhibits maximum energy density of 32.5 W h kg−1 at a power density of 375 W kg−1 and even retains 19.78 W h kg−1 at 7500 W kg−1. This asymmetric device also shows a high cycling stability along with 92.7% retention after 3000 cycles, and is able to light up an LED bulb. The success of the NiO/RGO composite sheds light on designing advanced hybrid materials for next-generation supercapacitive energy storage.

Preparation and characterization of high boiling solvent lignin-based polyurethane film with lignin as the only hydroxyl group provider

A novel diisocyanate-modified lignin-based polyurethane (LPU) film was facilely prepared using renewable lignin as the only hydroxyl group provider at ambient temperature and pressure for the first time. The lignin was extracted through a modified high boiling solvent (HBS) method with 1,4-dioxane as the solvent, and then dried through freeze drying. The ash content of the HBS lignin sample was about 0.25%, which was lower than for other lignins. The HBS lignin had a large number of hydroxyl groups, which indicated the potential value in substitution of polyols in the synthesis of polyurethane (PU). From the results, the LPU film possessed high performance in hardness, solvent resistance and hydrophilicity with no need for further modification. The LPU film also had high tensile strength with a maximum value of 41.6 MPa. In order to investigate the thermal properties of the LPU film, thermal gravimetric analysis (TGA) and thermogravimetric infrared analysis (TGA-FTIR) were performed, and the LPU film was stable at 114 °C in air and an N2 atmosphere. This study developed a novel LPU film which could show promising future applications as a coating and base.

Novel wearable polyacrylonitrile/phase-change material sheath/core nano-fibers fabricated by coaxial electro-spinning

This study focused on the preparation of wearable polyacrylonitrile (PAN)/phase-change material (PCM) sheath/core nano-fibers by coaxial electro-spinning technology. PAN was used as the sheath material to make fibers comfortable to human skin, and isopropyl palmitate and paraffin oil were used as sample PCMs. The electro-spinning conditions are critical for encapsulating a PCM by a PAN shell and forming a uniform sheath–core structure. Our experiments show that these PCMs could be well encapsulated in PAN hollow fibers and function to stabilize environmental temperature in a narrow range. This study provides a versatile and feasible way to fabricate PAN/PCM sheath/core homo-thermal nano-fibers with various temperature stabilization windows. Using these homo-thermal nano-fibers as clothing materials will be able to abate people’s discomfort during a sudden environmental temperature change.

Effect of Bath Concentration on Coagulation Kinetics at the Early Stage during Wet Spinning of PAN Copolymer Nascent Fibers

A mathematical model was proposed to simulate the effect of bath concentration on coagulation kinetics at the early stage of wet spinning for the poly(acrylonitrile-co-vinyl acetate)/dimethylsulfoxide (DMSO)/water system. The dependence of critical precipitation time, components concentration distribution, and the radius of nascent fibers on the concentration of DMSO in the DMSO/water coagulation bath were estimated by solving the model equation numerically. The experimental results indicated the model was suitable to simulate the dynamic features of the early stage of the coagulation process. The critical precipitation time was found to increase with bath concentration. The mode of phase separation was changed from instantaneous demixing to delayed demixing as DMSO bath concentration increased. The simulation results showed that bath concentration influenced the phase separation path which determined the polymer concentration distribution in the spinning solution. As a result, nascent fibers with different structures would form in wet spinning and a radial homogeneous structure would be obtained when the DMSO bath concentration increased to some extent.

Dynamic Self-Stiffening and Structural Evolutions of Polyacrylonitrile/Carbon Nanotube Nanocomposites

The self-stiffening under external dynamic strain has been observed for some artificial materials, especially for nanocomposites. However, few systematic studies have been carried out on their structural evolutions, and the effect of the types of nanofillers was unclear. In this study, we used a semicrystalline polymer, polyacrylonitrile (PAN), and various types of carbon nanomaterials including C60, carbon nanotube (CNT), and graphene oxide (GO). An external uniaxial dynamic strain at small amplitude of 0.2% was applied on the prepared nanocomposite films. It was observed that PAN/CNT exhibited significant self-stiffening behavior, whereas PAN/GO showed no response. Systematic characterizations were performed to determine the structural evolutions of PAN/CNT film during dynamic strain testing, and it was found that the external dynamic strain not only induced the crystallization of PAN chains but also aligned CNT along the strain direction.

Polyacrylonitrile-based turbostratic graphite-like carbon wrapped silicon nanoparticles: a new-type anode material for lithium ion battery

We investigated a new-type anode material for silicon (Si) nanoparticles wrapped in polyacrylonitrile (PAN)-based turbostratic graphite-like carbon, and discovered an interesting phenomenon that the battery capacity increased rather than decreased with the increase of cycling numbers. The carbonaceous matrix formed by PAN-based turbostratic graphite-like carbon could accommodate the volume change of Si nanoparticles and make the pulverized Si nanoparticles to keep good contact with the working electrode, thus to enable the full lithiation of Si and improve the battery capacity. As a result, the capacity of the anode material reached 680 mA h g−1, about twice as that of the commercial anode material, with only 9.8 w% silicon content. We also provided a new anode material preparation method that was easy to be industrialized, including using the PAN precursor and the preoxidation process to ensure the high carbon yield and the relatively high graphitization degree of the anode material. Some findings in this study are helpful to more clearly understand the lithiation–delithiation process of Si-based anode materials, as well as the basic strategy of increasing the Si-based anode material capacity.