Koji Nakane's research while affiliated with University of Fukui and other places

Inspired by a three‐dimensional (3D) structure, we demonstrate 3D aluminum nitride (AlN) nanofibers fabricated by a freeze‐drying technique using polyvinyl alcohol (PVA)/boehmite precursor nanofibers. After applying hot pressing, a series of PVA/boehmite precursor nanofibers were prepared with varying PVA‐to‐boehmite ratios (30/70 wt%, 50/50 wt%, and 70/30 wt%). Our findings reveal that the thermal conductivity of the AlN composite nanofibers is significantly affected by the relative proportions of PVA and boehmite, where the ratio of PVA should be more significant than that of boehmite. We produced AlN nanofibers at a lower temperature (1500°C) than the theoretical formation temperature of AlN (1664°C). The minimum specific surface area and pore volumes were 8.39 m²/g and 0.0166 cm³/g, respectively, at 1500°C. X‐ray photoelectron spectroscopy spectra measured 38.27% aluminum and 23.55% nitrogen in AlN nanofibers. The aligned AlN nanofibers mat was impregnated with polyurethane (PU), which showed good thermal conductivity in the planar (4.1–13.6 W/(m·K)) and thickness (1.5–4.9 W/(m·K)) directions at 18–56 vol% AlN nanofibers content. The heat‐dissipating sheet also showed superior electrical insulating (1.2 × 10¹² Ω/cm²) properties. In this study, the author sought to develop a heat‐spreading material made of thermally conductive, but electrically insulating PU/AlN nanofibers that could efficiently dissipate heat from electric devices.

Polyolefins are a widely accepted commodity polymer made from olefinic monomer consisting of carbon and hydrogen. This thermoplastic polymeric material is formed through reactive double bonds of olefins by the addition polymerization technique and it possesses a diverse range of unique features for a large variety of applications. Among the various types, polyethylene and polypropylene are the prominent classes of polyolefins that can be crafted and manipulated into diversified products for numerous applications. Research on polyolefins has boomed tremendously in recent times owing to the abundance of raw materials, low cost, lightweight, high chemical resistance, diverse functionalities, and outstanding physical characteristics. Polyolefins have also evidenced their potentiality as a fiber in micro to nanoscale and emerged as a fascinating material for widespread high-performance use. This review aims to provide an elucidation of the breakthroughs in polyolefins, namely as fibers, filaments, and yarns, and their applications in many domains such as medicine, body armor, and load-bearing industries. Moreover, the development of electrospun polyolefin nanofibers employing cutting-edge techniques and their prospective utilization in filtration, biomedical engineering, protective textiles, and lithium-ion batteries has been illustrated meticulously. Besides, this review delineates the challenges associated with the formation of polyolefin nanofiber using different techniques and critically analyzes overcoming the difficulties in forming functional nanofibers for the innovative field of applications. Graphical abstract

Aluminum nitride (AlN) nanofibers were formed by heating polyvinyl alcohol (PVA)/boehmite precursor nanofibers at various temperatures in nitrogen gas flow. We designed AlN nanofiber as an effective thermal conductive filler to create long linear heat-transfer pathways in the resin. Aligned AlN nanofiber mats were fabricated using electrospinning of PVA/boehmite composite aqueous solution and were impregnated with polyvinyl butyral (PVB) solutions. The obtained sheets containing the aligned AlN nanofiber 47, 52, and 54 vol% had excellent thermal conductivity, 22, 21, and 19 W/(m·K), for aligned nanofibers direction in the sheet. The PVB/AlN nanofibers composite sheet also showed good electrical insulating properties below 1.0 × 10¹² Ω/cm². Graphical Abstract

Ultrafine nanofiber from polyacrylonitrile (PAN)/ethylene co-vinyl alcohol (EVOH) with a diameter of a few hundred nanometers was prepared through solution electrospinning. In this study, EVOH was employed as a precursor for the purpose of decreasing the diameter of electrospun fibers. The effect of different EVOH content in weight percentages incorporated with PAN on the fiber diameters was investigated. A successive and drastic reduction in fiber diameter was observed with the increase of EVOH in the blend. Moreover, the fiber diameter was further reduced after isopropanol (IPA) treatment. Scanning electron microscopy (SEM), differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), and Fourier transform infrared (FTIR) spectroscopy were used to investigate the fiber morphology, thermal attributes, degradation behavior, and the chemistry of electrospun nanofiber respectively. The diameter of PAN/EVOH nanofibers found ranged from 47 nm to 880 nm, and after IPA treatment observed from 41 nm to 719 nm. The diameter of PAN/EVOH blend fiber was found to be 514 nm, 319 nm, and 116 nm for the EVOH content of 25%, 50%, and 75% correspondingly. After IPA treatment (at the content of 75%), the lowest PAN nanofiber diameter was discovered to be 102 nm. In the DSC heat flow, melting temperature (T m ) of electrospun nanofibers manufactured from pure PAN, pure EVOH, PAN/EVOH blend, and IPA treated were detected at 290 ⁰ C, 182 ⁰ C, 301 ⁰ C, and 271 ⁰ C separately. The blend nanofiber (50/50) exhibited a distinctive single melting peak in DSC and the T m was shifted upward from 290°C (as observed in pure PAN) to 301°C. In addition, on the TGA curve the degradation temperature of blend nanofiber (50/50) extended up to 289°C which surpasses the pure PAN's value of 280°C. Both DSC and TGA analyses demonstrated the enhancement of the thermal properties of blend nanofiber. Due to its smaller diameter and improved thermal properties, the developed nanofiber may find use in air filtration and protective clothing.

We investigated the additive ionic liquid (IL) type dependence on the crystal structure of poly(vinylidene fluoride) (PVDF) nanofibers. As additive ILs, we used imidazolium based ILs with different cation and anion sizes. From differential scanning calorimetry (DSC) measurements, we found that there is a proper amount for the additive IL to promote PVDF crystallization, and the proper amount is influenced by the cation size, not by the anion size. In addition, it was found that IL itself inhibited the crystallization, but IL can promote crystallization under the presence of DMF.

Polyvinyl alcohol (PVA)/beryllium sulfate (BeSO4) precursor nanofibers are fabricated by electrospinning technique, mixing PVA aqueous solution with BeSO4 salt. The productivity is increased by adding polyethyleneimine (PEI) with PVA/BeSO4 spinning solution. The beryllium oxide (BeO) nanofibers are obtained by calcinating the PVA/BeSO4/PEI precursor nanofiber heated at 1000 °C or above. The crystallographic structure of BeO nanofibers is examined by X-ray diffraction. The thermal behaviors of the pure PVA nanofibers, BeSO4 salt, and PVA/BeSO4/PEI precursor nanofibers are studied by thermogravimetry analysis. The BeO nanofiber diameters are reduced with the increase in calcination temperatures. The specific surface area of the PVA/BeSO4/PEI precursor nanofibers is around 36.9 m² g⁻¹, and that of the BeO nanofibers calcined at 1200 °C is about 11.9 m² g⁻¹. The pore properties deteriorate due to sintering and blockage as the calcination temperature increases. This work introduces mesoporous BeO nanofibers for the very first time.

Polyvinyl alcohol/beryllium sulfate/polyethyleneimine (PVA/BeSO4/PEI) precursor nanofibers (NFs) was first fabricated to obtain PVA/BeSO4/PEI electrospun NFs by electrospinning technology, finally manufactured beryllium oxide (BeO) NFs followed by various heat treatment methods. The minimum calcination temperature for pure BeO NFs was 1000 °C, and the minimum specific surface area (5.1 m2 g-1) and pore volumes (0.0128 cm3 g-1) were at 1300 °C. 46.18% Be and 53.82% O was measured in BeO NFs by X-ray photoelectron spectroscopy. BeO NFs were then impregnated with polyurethane (PU) aqueous solution to make PU/BeO NFs heat-dissipating sheet. This heat-dissipating sheet showed superior thermal conductivity (14.4 W m-1 K-1) at 41.4 vol% BeO NFs content. The electrical insulating properties of the heat-dissipating sheet were likewise excellent (1.6 × 1012 Ω □-1). In this study, the author attempted to create a thermally conductive but electrically insulating PU/BeO NFs heat-dissipating sheet that could effectively eliminate generated heat from electric equipment.

The image created by Mohammad Zakaria and colleagues depicts a super‐efficient nanofibrous membrane made of ultra‐fine polypropylene nanofiber. The membrane's compact fibrous mesh structure was created using PP nanofiber, resulting in optimal porosity, good hydrophobicity, and a smaller mean pore size with a narrower distribution. The nanofibrous membrane's filtration performance for dyeing wastewater has also demonstrated the potential for finer PP nanofiber. The developed nanofibrous membrane, which filtered wastewater very close to drinking water, rejected 99.95 percent of the color. The commercial PP membrane, on the other hand, can only reject 17.38 percent of color from wastewater. DOI: 10.1002/app.52657

A fibrous membrane being prepared from nanofiber is of great demand for super‐efficient filtration of industrial wastewater. This study reported a highly efficient noanofibrous membrane made of superfine polypropylene (PP) nanofiber with an average diameter of only 228 nm and that had also demonstrated a direct influence of fiber diameter on its properties and performance for textile wastewater purification. The PP nanofibers were prepared with a varying content of PP/ethylene‐co‐vinyl alcohol (EVOH) blends from which the EVOH matrix was removed after electrospinning. Subsequently, the PP nanofibrous membranes were manufactured using the prepared PP nanofibers via a simple wet‐laid process. The fiber diameter turned out to be an important factor in the surface properties and pore characteristics of the PP nanofibrous membrane. The finer PP nanofiber constructed a compact fibrous mesh structure of the membrane leading to an optimum porosity, a high hydrophobicity, and a smaller mean pore size with a narrower distribution. The filtration performance of the nanofibrous membrane for dyeing wastewater has also evidenced the potentiality of the finer PP nanofiber. Moreover, in comparison with the commercial PP fibrous membrane, the developed PP membrane was found to be more promising.