We evaluated the stacking uniformity characteristics using various multi-nozzle patterns of mass-scale electrospinning equipment (nozzle 680 EA, width 1,000 mm). For the test, polyether sulfone (PES), and a polymer mixed solution was prepared by mixing dimethylformamide (DMF) and N-methyl-2-pyrrolidone (NMP) as solvents at a constant volume ratio. Cetyltrimethylammonium bromide (CTAB) was added to improve the electrospun below at the critical concentration of PES polymer. All experimental variables of electrospinning were fixed. In the multi-nozzle pattern, 12 nozzles arranged in the horizontal direction constituted one column, and a total of four columns were arranged in one set in an intersecting arrangement. The four multi-nozzle patterns were configured with inter-nozzle spacing of 75 mm, 78 mm, 80 mm, and 83 mm, respectively. For property evaluation, scanning electron microscopy (SEM), weight analysis, pore analysis, and air permeability measurement were performed, and the performance as an air filter was measured by a filter filtration performance test. Test results confirmed that the uniformity of fiber lamination improved as the multi-nozzle pattern changed from 75 to 83.

Field emission (FE) applications, essential in cutting-edge technologies like microwave devices and particle accelerators, increasingly utilize carbon nanomaterials like graphene and carbon nanotubes. However, their production encompasses complex challenges, and structural intricacies affect their efficacy. In this research, we advanced the development of graphene fibers using a wet-spinning method, marking a progression in FE applications. The process entailed control of fiber coagulation and draw ratios to optimize their internal structure. Furthermore, we introduced a continuous reduction technique to increasing the electrical conductivity of the graphene fibers. The produced fibers showed threshold electric fields of 1.1, 1.0, 0.8 and 0.6 V/μm, maximum currents density of 1.09, 1.19, 1.22 and 1.25 A/cm2. Field enhancement factor (β) 9900, 10216, 12007 and 20830 showed marked improvement correlating with increased draw ratios, highlighting their field emission properties. This study illuminates the potential of graphene fibers as FE materials, paving the way for future advancements in this domain.

In this study, the transient curtain coating process is computationally carried out via the in-house code developed using a finite element method(FEM). Incorporating sophisticated auto-remeshing techniques, our numerical implementaion for FEM not only captures the complex flow dynamics inherent in this curtain coating process but also adapts to the rapid deformations observed at important flow zones in the curtain coating flow. The stability and accuracy of the proposed computational model have been rigorously tested against a spectrum of flow rates, viscosities, and substrate speeds, proving its robustness and reliability. As we continue our research, we aim to further enhance these simulation algorithms identifying optimal operating conditions that could be key in ensuring consistent quality across materials with different rheological properties in the curtain coating process.

Zirconium diboride (ZrB2) and hafnium diboride (HfB2) fibers have not been studied as extensively as metal carbides and nitrides for transition metal solid solutions due to a lack of processing technology. However, their remarkable physical properties make them ideal for high-temperature applications. In this study, we investigated the mechanical properties of solid solution diboride using ab initio calculations. Specifically, we focused on the (Zr1-xMx)B2 and (Hf1-xMx)B2 (M=Ti, V, Cr, Zr, Nb, Mo, Hf, Ta, and W) compositions. Our findings revealed that ZrB2 and HfB2 have high Young’s moduli of 524.12 and 551.41 GPa, respectively. Additionally, the solid solutions of (Zr0.25Ti0.75)B2 and (Hf0.25Ti0.75)B2 showed superior shear and Young's modulus. We also compared the mechanical properties of titanium-doped diboride solid solutions with undoped ZrB2 and HfB2 at high temperatures. Our study provides valuable insights into the potential development of diborides as ceramic fibers tailored for hightemperature applications.

The correlation between the imidization degree of polyimide fibers and characteristics of activated carbon fibers was studied. Poly(amic acid) solution was spun by dry-jet wet spinning method and poly(amic acid) fibers were transferred into polyimide fibers by heat treatment of IR heater at 300 oC, 400 oC, 500 oC, 600 oC. Polyimide fibers were carbonized and activated at 900 oC. The imidization degree was investigated using FT-IR. The chemical structure was traced by FT-IR, elemental analyzer(EA) and x-ray diffraction(XRD). Thermal properties were analyzed with DSC and TGA. Mechanical properties were measured with single fiber tester(favimat). Specific surface area and pore characteristics were analyzed by BET method. The surface morphologies were observed by FE-SEM. The imidization degree of polyimide fibers increased up to 500 oC but decreased at 600 oC. The thermal and mechanical properties of polyimide fiber exhibited a dependency on the imidization degree. The mechanical properties and compact morphologies of activated carbon fiber strongly depended on the imidization degree of polyimide fiber. Activated carbon fiber was showed the maximum tensile strength value of 898 MPa and specific surface area composed of micropores value of 920 oC/g at IR heater temperature of 500 oC and the imidization degree of 96%.

PP (polypropylene), which was previously used for general purposes, has a chemical structure that is difficult to decompose and has become a cause of environmental pollution. Therefore, a composite material was manufactured by adding TPS (thermoplastic starch), which can be biodegraded under composting conditions. The manufactured composite material was UV (photo oxidized) treated with cycle C according to the ASTM D 6954 standard for composite biodegradation. In the case of the UV-treated composite material, the molecular weight was reduced by 98.1% due to photo oxidation, and the melting peak was shifted to 132 oC and 43.6%. % melting enthalpy decreased. As a result of the analysis, it was confirmed that defects occurred in the composite material and polymer chains were broken due to photo-oxidation. The composting biodegradability test was conducted in accordance with ISO 14855-1, and after 180 days, the decomposition rate was 53.1% for TPS-PP composite material and 8.9% for UV-TPS-PP composite material, which is due to the photo oxidation process in the case of UV-TPS-PP composite material. It is judged that the degree of decomposition of gelation is low. Through continued research, it is judged that additional research is needed on how gelation occurs in PP due to photo-oxidation caused by UV treatment.

Nanofibers with ultrafine diameters (< 50 nm) have been reported to exhibit a significant surface area and a high filtration efficiency. Recently, the ionic surfactants have been used for fabricating nanofibers with ultrafine diameters. However, the use of ionic surfactants is not desirable because of the electrophoretic behavior and following instability of the ions with the high electric potential during the electrospinning process. In this study, hierarchical nanofiber assemblies including ultrafine nanofibers with diameters < 50 nm were designed by utilizing heterogenous molecular interactions of different types of polymers with high dipole moments (polyacrylonitrile (PAN), poly(vinylidene fluoride-cohexafluoropropylene) (PVdF-HFP)), and their filtration performances were evaluated based on EN 143 standard. The fraction of nanofibers with ultrafine diameters was adjusted from 4% to 46%, and the b-phase fraction of PVdF increased from the initial 71.6% to a maximum of 85.37%. Among various PAN/PVdF samples, the PAN/PVdF 3:7 represented the highest efficiency of 87.6% even at low basis weight due to its ultrafine diameter, and all samples demonstrated efficiency exceeding 99.3% as basis weight increased. In conclusion, this study successfully achieved process stability and excellent filtration performance by establishing a method to manufacture hierarchical nanofiber assemblies without the use of ionic surfactants, relying solely on the interaction of heterogeneous polymers.