Yutaka Ohkoshi

Synthesis of titanium carbide from a composite of TiO2 nanoparticles/methyl cellulose by carbothermal reduction

Abstract Titanium carbide (TiC) was synthesized from a composite constituted of nano-sized TiO 2 particles (ca. 5 nm in diameter) and methyl cellulose (MC) via carbothermal reduction in an Ar flow. The composite was converted into titanium oxycarbide by heating at 1050°C. With the increase of heating temperature, the lattice parameter of the titanium oxycarbide phase increased while the oxygen content in the specimen decreased, especially above 1300°C. That is, low oxygen content (0.60–2.32 wt%) TiC could be prepared from the composite by heating above 1300°C, which was a considerably lower temperature compared to that employed in the conventional carbothermal reduction methods that use a mixture of TiO 2 and carbon powders.

Preparation and structure of copper nanoparticle/poly(acrylic acid) composite films

Composite films consisting of metallic Cu nanoparticles dispersed in poly(acrylic acid) (PAA) have been prepared by reduction of Cu 2+ from the copper salt of PAA above 220°C under a H 2 atmosphere. Optical absorption properties and structures have also been investigated by UV/VIS, WAXD, TEM and IR. Spherical Cu particles were found to be homogeneously dispersed in the PAA and the diameters of the particles were in the range 10-16 nm. The composite films exhibited an optical absorption peak centered at ca. 570 nm, which was attributed to surface plasmon resonance of Cu nanoparticles. The composite film made by heat treatment at 220 C was less stable because Cu particles in the film were oxidized to Cu 2+ ions within several weeks, while the composite films prepared by heating above 230°C were stable and the Cu particles in their films were not oxidized. The stability of the Cu nanoparticles in PAA is suggested to be related to the formation of ketone groups by condensation reactions between carboxylic acids of PAA above 230°C.

Direct Measurement of Fiber Temperature in the Continuous Drawing Process of PET Fiber Heated by CO2 Laser Radiation

Abstract Poly(ethylene terephthalate) (PET) fiber was heated by carbon dioxide laser radiation during the continuous drawing process. Numerical calculation shows that the PET fiber can be heated much more rapidly and uniformly by heat radiation than by convective heat transfer through the fiber surface. During CO2 laser heated drawing, temperature in the vicinity of a neck-like deformation can be measured on-line with high precision, because the neck-like deformation is located within a range of 0.5 mm. We measured the fiber temperature profiles on the drawing process by IR thermometer that has a range resolution of 0.355 mm. The temperature at which neck-like deformation of the fiber initiates is higher than Tg when draw ratio is less than 4.5, but lower than Tg when draw ratio is more than 5.5. The maximum fiber temperature in the drawing process increases with draw ratio, up to 208°C for a draw ratio of 6.0. The rate of orientation-induced crystallization in the drawing process was estimated by comparison of measured temperature profiles with calculated temperature profiles.

Effects of Take-up Speed of Melt Spinning on the Structure and Mechanical Propertiesof Maximally Laser Drawn PA9-T Fibers

Abstract A new semiaromatic polyamide, PA9-T, was melt-spun at take-up speeds from 200 to 1000m min−1. The as-spun fibers were drawn with CO2 laser-heated drawing to their maximal draw ratio (DRmax). The drawing stress was recorded during this process. The effects of take-up speed of melt-spinning on maximally drawn fibers were characterized through measurements of density, birefringence, wide-angle X-ray diffraction, crystal orientation, tensile testing, and dynamic viscoelastic analysis. All as-spun fibers were essentially amorphous and their birefringence and density increased slightly with the increase of take-up speed. Lower take-up speeds yielded higher DRmax values, and fibers drawn to their DRmax exhibited superior structure and mechanical properties. The tensile strength and Youngs modulus achieved were the highest reported to date for PA9-T: 737 MPa and 5.8 GPa, respectively.

States of water in poly(vinyl alcohol)/poly(sodium l-glutamate) blend hydrogels

Abstract Tough and rubber-like physically crosslinked hydrogels were prepared by blending of concentrated aqueous solutions of poly(vinyl alcohol) (PVA) and poly(sodium L-glutamate) (PSLG) in an autoclave under 2 atm pressure at 120°C. There are three types of water in every blend hydrogel, i.e. free water, unfrozen water (namely bound water), and frozen bound water. Unfrozen water content increases with increasing PSLG content because of the increase in the number of the ionic -COONa group, which has many bonding sites with the water molecular. Heat of thawing per unit weight of water, i.e. free and frozen bound waters, not containing unfrozen water (ΔHw), estimated for hydrogels having various water contents, was obtained by dehydration and was smaller than that of free water. Spin lattice relaxation time (T1), obtained by pulsed nuclear magnetic resonance measurement, decreases with increasing PSLG content. These results for ΔHw and T1 are caused by the interaction between water and ionic -COONa groups of the PSLG molecules.

States of water in poly(vinyl alcohol) hydrogels

Abstract Poly(vinyl alcohol) (PVA) hydrogels with various water contents were prepared from 10 wt% aqueous solutions of mixtures of PVA and anionic poly(styrene sulfonic acid) sodium salt (NaPSS) by casting, dehydrating, and then extracting NaPSS. The existence of three types of ice were suggested by differential scanning calorimetry (DSC) measurements for every frozen hydrogel. In the frozen hydrogels the states of water, except unfrozen water, were ice of free water and disordered ice crystals. The mobility and activation energy for motion of water molecules in unfrozen hydrogels were investigated by using pulsed nuclear magnetic resonance (PNMR) measurements. It was concluded that there are two states of water in the unfrozen hydrogel, i.e. unfrozen water and disordered water which is mainly formed in narrow apertures in the hydrogel. The discrepancy between the DSC and PNMR measurements was explained by a structural transformation during cooling.

Introduction of copper iodide fine particles into a poly(acrylic acid) matrix via a complex of polymer–polyiodide ions

In this study, an organic–inorganic nanocomposite material of cross-linked poly(acrylic acid) (PAA) doped with fine particles of copper iodide (CuI) was prepared. The preparation method of the composite involved the complexing of PAA film with polyiodide ions such as I3− and I5− by immersion in an iodine–potassium iodide (I2–KI) aqueous solution, and then reaction with CuCl in aqueous hydrochloric acid, resulting in the in-situ formation of CuI fine particles within the PAA matrix. The crystal form of CuI in the composite was identified as γ-CuI using X-ray diffraction, and the amount of CuI could be varied by changing both the concentration of the I2–KI solution and the frequency of performing the doping procedure to introduce CuI into the matrix. This preparation method, using polyiodide ions as a precursor, has an advantage in that a large amount of metal iodide, such as CuI, can be easily formed, and it is regarded as a unique method for the preparation of organic–inorganic composites.

Diameter Profile Measurements for CO2 Laser Heated Drawing Process of PET Fiber

Abstract Poly (ethylene terephthalate) (PET) fiber was heated by carbon dioxide laser radiation in the continuous drawing process. By this procedure, the position of the deformation region could be fixed precisely in the air. The location of neck-like deformation fluctuated within a range of about 0.2 mm for draw ratios of 4.0 to 4.5 and within a range of about 0.5 mm for draw ratios of 5.5 to 6.0, but the location fluctuated over a range of 1.0 mm for a draw ratio of 5.0. Fiber diameter profiles, which were used to calculate Hencky strain rate profiles and apparent elongational viscosity profiles, were obtained from high-speed video camera images of the deformation region. Regardless of draw ratio, apparent elongational viscosity exhibited almost the same minimum value. Apparent elongational viscosity is much lower than the value obtained by measurement at a low, constant strain rate, but the elongational stress acting at the point where apparent elongational viscosity begins to increase steeply (Hencky strain of about 1.0) is of the same order of magnitude as the reported value. For draw ratios less than 5.0, the temperature where apparent viscosity is lowest is about 100 to 120°C, which corresponds to the flow temperature of amorphous PET, whereas for draw ratios exceeding 5.0 the temperature where apparent viscosity is lowest is about 80°C, which corresponds to the glass transition temperature. Thus, the former corresponds to so-called neck-like deformation typically observed in high-speed spinning, and the latter corresponds to necking typically observed in cold drawing. These two types of deformation appear in turns for a draw ratio of 5.0, and therefore the location of the deformation region fluctuates greatly. This measurement system can be used as a high-strain-rate elongational rheometer for analyzing practical polymer processing systems, which can easily measure the precise on-line deformation history with a time resolution in the μs level.

High-Strength PET Fibers Produced by Conjugated Melt Spinning and Laser Drawing

Abstract The mechanical properties of conjugated-spun and laser drawn poly(ethylene terephthalate) (PET) fibers were investigated. The as-spun fibers used for the laser drawing were made by conjugated melt spinning with the copolymer of p-hydroxybenzoicacid and 2-hydroxy-6-naphthoicacid or polystyrene. The PET fibers prepared by conjugated spinning could be laser drawn to higher draw ratios under lower drawing stresses. The drawn fiber could be re-drawn up to a higher total draw ratio. Thus, a PET fiber having a tensile strength of 1.14 N/tex could be produced.

Visualization of a pillar-shaped fiber bundle in a model needle-punched nonwoven fabric using X-ray micro-computed tomography

In the needle-punching process, the barbs of a needle catch fibers and orient them along the thickness direction of the fabric. The oriented fibers form a pillar-shaped fiber bundle, which acts as a bonding point of the fabric. The structure of the pillar-shaped fiber bundle thus governs the mechanical properties of needle-punched nonwoven fabric, and both are largely affected by the needle-punching conditions. However, the three-dimensional structure of pillar-shaped fiber bundles and their development under different needle-punching conditions have not been revealed. In the present study, we visualized the three-dimensional structure of a pillar-shaped fiber bundle in needle-punched nonwoven fabric, employing X-ray micro-computed tomography (XCT) on the basis of the difference in the X-ray absorption coefficient between polyethylene terephthalate (PET) and polyethylene fibers. For a material density ratio of less than 1.4 and PET fibers having a diameter of 40 µm, the pillar-shaped bundles of PET fibers were visualized by erasing 20-µm polyethylene fibers in XCT images. Furthermore, we investigated the effects of the penetration depth of the needle on the development of pillar-shaped fiber bundles. The number of fibers constituting a pillar largely increased at a penetration depth of 19.0 mm, and pillars protruded from the bottom surface of the fabric and formed a stitch structure. The XCT applied in this study is thus effective in analyzing the structure of pillar-shaped fiber bundles quantitatively without affecting the structure of the nonwoven fabric.