Yasuo Gotoh

Toward "strong" green nanocomposites: polyvinyl alcohol reinforced with extremely oriented cellulose whiskers.

To exploit the maximum potential of cellulose whiskers (CWs), we report here for the first time the successful fabrication of nanocomposites reinforced with highly oriented CWs in a polymer matrix. The nanocomposites were prepared using polyvinyl alcohol (PVA) and a colloidal suspension of cotton-derived CWs. The macroscopically homogeneous PVA-CW suspensions were extruded into cold methanol to form gel fibers followed by a hot drawing. Compared to the neat PVA fiber, the as-spun fiber containing a small amount of CWs (5 wt % of solid PVA) showed higher drawability, leading to an extremely high orientation of CWs with the matrix PVA. The stress-transfer mechanism, a prime determining factor for high mechanical properties of nanocomposites, was studied by X-ray diffraction. The stress on the incorporated CWs was monitored by applying an in situ nondestructive load to the composite fibers. The applied stress to the whole sample was found to be effectively transferred to the CWs inside the composites, suggesting strong interfacial bonding between the filler and the matrix. Effective stress transfer to the oriented whiskers resulted in outstanding enhancement in mechanical properties of the nanocomposites.

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.

Physical properties and dyeability of silk fibers degummed with citric acid.

Silk fibers from Bombyx mori silkworm was degummed with different concentration of citric acid, and the physical properties and fine structure were investigated to elucidate the effects of citric acid treatment. The silk sericin removal percentage was almost 100% after degumming with 30% citric acid which resulted in a total weight loss of 25.4% in the silk fibers. The surface morphology of silk fiber degummed with citric acid was very smooth and fine, showed perfect degumming like traditional soap-alkali method. The tensile strength of silk fiber was increased after degumming with citric acid (507MPa), where as the traditional soap-alkali method causes to decrease the strength about half of the control silk fiber (250MPa). The molecular conformation estimated by Fourier transform infrared spectroscopy and the crystalline structure evaluated from X-ray diffraction curve stayed unchanged regardless of the degumming with citric acid and soap. The dye uptake percentage of silk fiber degummed with citric acid decreased slightly, about 4.2%. On the other hand, the dye uptake percentage of silk degummed with soap was higher which indicates the disordering of the molecular orientation of the laterally ordered structure, accompanied with the partial hydrolysis of silk fibroin molecules by the alkali action of soap. The thermal properties were greatly enhanced by soap and citric acid degumming agents. Dynamic mechanical thermal analysis showed silk degummed with citric acid is more stable in higher temperature than that of soap. With heating at above 300 degrees C, the silk degummed with citric acid shows an increase in storage modulus and an onset of tan delta peaks at 325 degrees C and the melt flow of the sample was inhibited. The degumming of silk fibers with citric acid is safe and the results obtained are quite promising as a basis for possible future industrial application.

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.

Fabrication of carbon fibers from electrospun poly(vinyl alcohol) nanofibers

Carbon fibers were fabricated from electrospun poly(vinyl alcohol) (PVA) nanofibers. Electrospun PVA nanofibers were treated with iodine vapor for different periods, subsequently carbonized at different temperatures, and the structural changes of the PVA nanofibers were analyzed. The nanofibers iodinated at 80 °C for 24 h led to a good carbon yield of 21% when carbonized at 1200 °C. The influence of metal nanoparticle on the fabrication of carbon fiber and its properties was also investigated by the addition of a metal salt, nickel(II) acetate tetrahydrate [(CH3COO)2 Ni·4H2O], to the PVA spinning solution. Noticeably, after incorporation of nickel (Ni) nanoparticle continuous electrospinning was realized at lower polymer concentration than that of neat PVA. Moreover, smaller fiber diameter and a higher carbon yield (~34%) were obtained after carbonization. Transmission electron microscopy observation of the carbon fibers revealed that the addition of Ni-nanoparticles accelerated the formation of a graphitic structure at a lower carbonization temperature of 1200 °C.

Structural characteristics and properties of Bombyx mori silk fiber obtained by different artificial forcibly silking speeds

To study the spinning condition of natural biopolymer silk, the silk fibers were directly acquired from Bombyx mori silkworm, N140 x C140 by a simple artificial forcibly silking method at the speed of 60, 120, 180 and 240 cm min(-1), respectively and its microstructure and physical properties were evaluated. The fine silk fibers (about 8 microm) were obtained at faster spinning speed, 240 cm min(-1). The tensile properties of silk fibers were remarkably increased with raising the forcibly spinning speeds. The beta-sheet structure contents of silk fibers obtained at higher speed were considerably increased. The fibers obtained by different spinning speeds exhibited a fairly similar X-ray crystallinity, while the degree of molecular orientation increased with decreasing the fiber diameter. The fine silk fibers obtained at higher speed (240 cm min(-1)) exhibited a slightly higher thermal stability, as shown by the upward shift of differential scanning calorimetry (DSC) decomposition temperature.

Properties of highly syndiotactic poly(vinyl alcohol)

Abstract The physical properties of a highly syndiotactic poly(vinyl alcohol) (PVA, diad syndiotacticity ( r )=69%) and a commercial, atactic PVA ( r =54%) were examined. The highly syndiotactic PVA was derived from poly (vinyl acetate) prepared through the radical polymerization of vinyl acetate in (CF 3 ) 2 CHOH. The solubility, gelation behavior, melting point, and crystallization rate were drastically affected by the tacticity of the main chain. Some of the properties were measured using fiber samples prepared by the gel spinning technique. The fiber obtained from the syndiotactic PVA had a melting point of 274°C. This is the highest melting point reported for PVA. These effects of tacticity on the polymer properties are ascribed to the difference in intermolecular and/or intramolecular hydrogen bonding. A polymer chain with higher r content may form more regular and therefore more rigid hydrogen bonding between the polymer chains in the bulk sample. Such a detailed study on the effects of tacticity on the properties of PVA has not been reported so far.

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.

Temperature dependence of the elastic modulus of the crystalline regions of poly(ethylene 2,6-naphthalate)☆

Abstract The temperature dependence of the elastic modulus E 1 of the crystalline regions of poly(ethylene 2,6-naphthalate) (PEN-2,6) in the direction parallel to the chain axis has been investigated up to 228°C by X-ray diffraction. The E 1 value of PEN-2,6 was 145 GPa at room temperature, which is about 40% greater than that of poly(ethylene terephthalate) ( E 1 =108 GPa). The axial chain contraction coefficient was constant from 22 to 228°C, and correspondingly the value of E 1 remained unchanged up to 228°C. The deformation mechanism is considered to remain unchanged up to 228°C and the skeletal conformation of PEN-2,6 in the crystalline regions is stable against heat. It is reasonable to conclude that stress is homogeneous throughout the sample.

Mechanistic studies on the formation of silver nanowires by a hydrothermal method.

Silver (Ag) nanowires were fabricated from silver chloride (AgCl) by the hydrothermal method. The successful formation of Ag nanowires relied on the low solubility of AgCl as a precursor and the structural change of glucose to polymer on the Ag nanowire (protective layer). The Ag(+) ion concentration in the reaction solution containing AgCl was initially low, but after a reaction time of over 12 h, Ag(+) gradually reduced to Ag metal. Transmission electron microscope, Raman spectrometery, and X-ray photoelectron spectroscopy revealed that the surface of the obtained Ag nanowires possessed a carbon-rich layer with a carboxyl group, and the Ag(+) ion coordinated with the carboxyl group of this layer. The difference in the surface-free energy of Ag crystals changed the crystal growth rate that impelled the anisotropic growth of the Ag particles. By examining various reaction conditions, it was determined that the ratio of Cl(-) to Ag(+), reaction temperature, and reaction time are important factors for successful preparation of Ag nanowires. Under the reaction condition that the molar ratio of Cl(-) to Ag(+) at 160 °C for 24 h is above equimolar concentration, uniform Ag nanowires were successfully prepared.