Yoshitsugu Kojima

Mechanical properties of nylon 6-clay hybrid

Various nylon 6-clay hybrids, such as molecular composites of nylon 6 and silicate layers of montmorillonite and saponite, NCHs and NCHPs, respectively, have been synthesized. To estimate the mechanical properties of these hybrids, tensile, flexural, impact, and heat distortion tests were carried out. NCH was found superior in strength and modulus and comparable in impact strength to nylon 6. The heat distortion temperature (HDT) of NCH (montmorillonite: 4.7 wt. %) was 152 °C, which was 87 °C higher than that of nylon 6. In NCHP, saponite had a smaller effect on the increase of these mechanical properties. The modulus and HDT of NCH and NCHP increased with an increase in the amount of clay minerals. It was found that these properties were well described by the contribution of the constrained region calculated from the storage and loss modulus at the glass transition temperature. According to the mixing law on elastic modulus, the following expression was obtained between the modulus E at 120 °C and the fraction of the constrained region C, E n = E c n = C , where the values of n and E c (modulus of the constrained region) were 0.685 and 1.02 GPa, respectively.

Synthesis of nylon 6-clay hybrid

It was found that montmorillonite cation exchanged for 12-aminolauric acid (12-montmorillonite) was swollen by ∊-caprolactam to form a new intercalated compound. Caprolactam was polymerized in the interlayer of montmorillonite, a layer silicate, yielding a nylon 6-clay hybrid (NCH). The silicate layers of montmorillonite were uniformly dispersed in nylon 6. The carboxyl end groups of 12-aminolauric acid in 12-montmorillonite initiated polymerization of ∊-caprolactam, and as 12-montmorillonite content became larger, the molecular weight of nylon was reduced. From the result of end-group analysis, carboxyl end groups were more than amino end groups. The difference between the carboxyl and the amino end groups was attributed to ammonium cations (-NH 3 + ) of nylon molecules, because the difference agreed with the anion site concentration of the montmorillonite in NCH. It is suggested that the ammonium cations in nylon 6 interact with the anions in montmorillonite.

Swelling behavior of montmorillonite cation exchanged for ω-amino acids by -caprolactam

Natural Na-montmorillonite was cation exchanged for the ammonium cations of various ω-amino acids [H 3 N + (CH 2 ) n −1 COOH, n = 2, 3, 4, 5, 6, 8, 11, 12, and 18]. X-ray diffraction (XRD) results suggested that the chain axes of ω-amino acids with a carbon number of eight or less were parallel to the silicate layers, and that the chain axes of those with a carbon number of 11 or more were slanted to the layers. The cation-exchanged montmorillonites form intercalated compounds with ∊-caprolactam at 25 °C. The montmorillonites intercalated with both ω-amino acid and ∊-caprolactam were studied by XRD measurement at room temperature and 100 °C. We propose a model where amino acid molecules were arranged perpendicular to silicate layers and ∊-caprolactam molecules filled the space between them. When the ∊-caprolactam was melted at 100 °C, the basal spacing for the montmorillonite increased, in which the carbon number exceeds 11. This phenomenon will be applicable to obtaining the nylon 6-clay hybrid, a molecular composite of nylon 6 and montmorillonite.

Hydrogen generation using sodium borohydride solution and metal catalyst coated on metal oxide

Abstract Sodium borohydride (NaBH4) reacted slowly with water to liberate 4 mol of hydrogen/mol of the compound at room temperature. Hydrogen generation was accelerated by applying metal–metal oxide catalysts such as Pt–TiO2, Pt–CoO and Pt–LiCoO2. As the metal crystallites size decreased and the amount increased, the hydrogen generation rate increased. It was indicated that the hydrogen generation rates using Pt and LiCoO2 were high compared with those using other metal and metal oxide, respectively. It seemed that a key finding was that use of the supercritical CO2 method produced a superior catalyst. Borohydride ion was stabilized in alkaline solution containing at least 5% by weight of NaOH. Alkaline stabilized solution of NaBH4 can be applied as a hydrogen source. We found that Pt–LiCoO2 worked as an excellent catalyst for releasing hydrogen from the stabilized NaBH4 solution.

Nylon 6–Clay Hybrid

ζ-Caprolactam was polymerized in the interlayer spacing of montmorillonite, a clay mineral, yielding a nylon 6-clay hybrid (NCH) 1) . X-ray and TEM measurements revealed that each template of the silicate, which is 10 A thick, was dispersed in the nylon 6 matrix and that the repeat unit increased from 12 A in unintercalated material to 21 A in the intercalated material. Thus NCH, is a “polymer based molecular composite” or “nanometer composite”. NCH, when injection-molded, shows excellent properties as compared to nylon 6 in terms of tensile strength, tensile modulus and heat resistance. Heat distortion temperature increased from 65 °c for nylon 6 to 152 °c for NCH, containing 4 wt% (1.6 vol%) of clay mineral.

Recycling process of sodium metaborate to sodium borohydride

Abstract Sodium borohydride ( NaBH 4 ) was synthesized by reacting sodium metaborate ( NaBO 2 ) with magnesium hydride ( MgH 2 ) or magnesium silicide ( Mg 2 Si ) by annealing (350– 750° C ) under high H 2 pressure (0.1– 7 MPa ) for 2– 4 h . As the temperature and the pressure increased, the yield increased to have a maximum value (97–98%) at 550° C under 7 MPa , but the value was independent of time. A concept for converting NaBO 2 back to NaBH 4 using coke or methane is described.

Solid state NMR study on the thermal decomposition pathway of sodium amidoborane NaNH2BH3

The thermal decomposition pathway of sodium amidoborane (NaAB; NaNH2BH3) has been investigated in detail by using solid state NMR spectroscopy. 23Na MAS/3QMAS NMR spectra suggested that NaH and an amorphous Na–N–B–H phase started to be formed as decomposition products even at 79 °C, although NaAB was prepared from NaH and NH3BH3 by ball milling at room temperature. Based on the quantitative analyses of the 23Na MAS spectra, we proposed a decomposition reaction to 200 °C to be NaNH2BH3 → Na0.5NBH0.5 + 0.5NaH + 2.0H2. The hypothetical phase Na0.5NBH0.5 is amorphous, where the basic molecular unit of the original NaAB is polymerized into a [–BN–]n network structure. It was also found that the diammoniate of diborane (DADB) and polyaminoborane (PAB) were not formed during the decomposition of NaAB, which are both key compounds on the pyrolysis of ammonia borane (AB).

Hydrogen generation by electrolysis of liquid ammonia

Hydrogen gas is generated by the electrolysis of liquid ammonia which has high hydrogen capacity of 17.8 mass%. The metal amides are used as supporting electrolytes to dissolve the amide ion in liquid ammonia. The results presented here indicate that liquid ammonia is promising as an energy medium for hydrogen storage and generation.

Hydrogen adsorption and desorption by potassium-doped superactivated carbon

Potassium-doped superactivated carbon can adsorb 1.6 wt % of hydrogen at room temperature under 5 MPa. This value was greater than that of potassium-doped graphite (hydrogen adsorption capacity: 1.0 wt %). Kinetics of the hydrogen adsorption of the potassium-doped superactivated carbon was remarkably improved. The hydrogen stored in the potassium-doped superactivated carbon was mainly released at high temperatures (440–1370 K). The high hydrogen adsorption capacity and the improved kinetics of this system may be derived from the small-sized graphen and the high surface area.

The reaction process of hydrogen absorption and desorption on the nanocomposite of hydrogenated graphite and lithium hydride

The lithium-carbon-hydrogen (Li-C-H) system is composed of hydrogenated nanostructural graphite (C(nano)Hx) and lithium hydride (LiH). C(nano)Hx is synthesized by ball-milling of graphite under a hydrogen atmosphere. In this work, the reaction process of hydrogen absorption and desorption on the Li-C-H system is investigated. The C(nano)Hx-LiH composite can desorb about 5.0 mass% of hydrogen at 350 degrees C with the formation of Li2C2 until the second cycle. However, the hydrogen desorption amount significantly decreases from the third cycle. Furthermore, it is shown by using gas chromatography that a considerable amount of hydrocarbons is desorbed during the rehydrogenation process. These results indicate that the amount of reaction between the polarized C-H groups in C(nano)Hx and LiH is reduced due to a decrease in the C-H groups by losing carbon atoms under the hydrogen absorption and desorption cycles.