Takeshi Kikutani

Activated carbon fibers and films derived from poly(vinylidene fluoride)

Abstract Activated carbons having different ranges of pore sizes from those derived by the conventional heat-treatment of organic compounds have been produced by carrying out a part of the conversion process through a liquid phase chemical treatment. Poly(vinylidene fluoride) (PVDF) was chosen as a starting polymer by taking into account the processability of this polymer into various geometries. The PVDF fibers and films were converted to activated carbons by using the combination of chemical dehydrofluorination with a strong base, high-temperature heat-treatment and activation in a carbon dioxide gas. The resulting activated carbon film exhibited superior methylene blue adsorption of 538 mg g−1. Formation of a rigid skeleton during dehydrofluorination accounted for the ability of dehydrofluorinated PVDF to maintain its macroscopic precursor geometry during high-temperature heat-treatment and the formation of pores with large sizes.

Fiber Structure Formation in High-Speed Melt Spinning of Polyamide 6/Clay Hybrid Nanocomposite

Polyamide 6 (PA 6)/clay hybrid (NCH) nanocomposites containing 2 and 5 wt% of clay were melt spun at take-up velocities from 1 to 5 km/min, and the effect of clay on the fiber structure formation was investigated. As the reference, neat PA 6 was spun at take-up velocities from 1 to 7 km/min. The NCH fibers showed higher crystallinity in the whole take-up velocity range, although there was no remarkable crystallinity dependence on the clay content. The birefringence of NCH fibers exceeded that of neat polymer only in the low take-up velocity region (i.e., up to 3 km/min). The orientation-induced crystallization was observed to start at about 2 km/min for NCH and at 4 km/min for neat PA 6. Also, at these take-up velocities, the peaks of α-form crystals appeared in the wide-angle X-ray diffraction equatorial (WAXD) scans, indicating that the orientation-induced crystallization was related to the direct formation of α-form crystals in the spinline. The NCH fibers were superior in Youngs modulus; however, their tenacity was higher only in the low take-up velocity region in which the crystallization in the spinline of neat PA 6 did not occur yet. That variation of tenacity was attributed to the molecular orientation, whereas the modulus was supposed to be determined by the stiffness of intercrystalline regions.

Fine structure and physical properties of polyethylene/poly(ethylene terephthalate) bicomponent fibers in high-speed spinning. I. Polyethylene sheath/poly(ethylene terephthalate) core fibers

The high-speed melt spinning of sheath/core type bicomponent fibers was performed and the change of fiber structure with increasing take-up velocity was investigated. Two kinds of polyethylene, high density and linear low density (HDPE, LLDPE) with melt flow rates (MFR) of 11 and 50, [HDPE(11), LLDPE(50)], and poly(ethylene terephthalate) (PET) were selected and two sets of sheath/core combinations [HDPE(11)/PET and LLDPE(50)/PET bicomponent fibers] were studied. The fiber structure formation and physical property effects on the take-up velocities were investigated with birefringence, wide-angle X-ray diffraction, thermal analysis, tensile tests, and so forth. In the fiber structure formation of PE/PET, the PET component was developed but the PE components were suppressed in high-speed spinning. The different kinds of PE had little affect on the fine structure formation of bicomponent fibers. The difference in the mechanical properties of the bicomponent fiber with the MFR was very small. The instability of the interface was shown above a take-up velocity of 4 km/min, where the orientation-induced crystallization of PET started. LLDPE(50)/PET has a larger difference in intrinsic viscosity and a higher stability of the interface compared to the HDPE(11)/PET bicomponent fibers.

Structural Control of Polyamide 6/Clay Nanocomposite Fibers by In-Line Drawing Process

High-speed melt spinning and in-line drawing of polyamide 6/clay hybrid (NCH) nanocomposite was carried out and the structure as well as the tensile properties of obtained fibers were investigated. In comparison with neat polyamide 6 (PA6) drawn at 50°C and 120°C, the NCH fibers drawn at 170°C showed higher crystallinity reaching 60% and higher content of a crystalline form. For both neat and hybrid fibers very high tenacity of 1 GPa was attained whereas the modulus was 15% higher for NCH filaments and reached 9.5 GPa. Since the molecular orientation was lower in NCH than in PA 6 filaments, the involvement of both crystalline structures and rigid clay particles in the stress transmission behavior was suggested as the reason for excellent tensile properties of nanocomposite fibers.

DYEING BEHAVIOR OF HIGH-SPEED SPUN POLY(ETHYLENE TEREPHTHALATE) FIBERS IN SUPERCRITICAL CARBON DIOXIDE

The dyeing behaviors for several types of high-speed and normal speed spun poly (ethylene terephthalate) fibers were compared in supercritical CO2 fluid. At lower temperature and pressure, the high-speed spun fibers, which had inherently larger crystallite sizes and lower birefringence, showed a larger dye uptake than the other fibers. However, when the supercritical conditions were elevated to 125°C and 230 bar, the dye uptake of both types increased markedly and the difference in dye uptake between the fibers became small. This suggests that the swelling of fibers in supercritical CO2 fluid exceeded a certain degree and then the diffusion of dye molecules was promoted. The swelling also promoted the rearrangement of molecular chains and permitting cold crystallization to occur. The modification of fiber structure through the dyeing in supercritical CO2 fluid was serious especially for the fibers whose inherent structure was not so well developed.

Fine structure and physical properties of polyethylene fibers in high-speed spinning. II. Effect of catalyst systems in linear low-density polyethylene

Linear low-density polyethylene (LLDPE) fibers, obtained from the melt-flow rate (g/10 min) of 45 and 50, which were polymerized by a metallocene catalyst and a Ziegler–Natta catalyst, respectively, were produced by a high-speed melt-spinning method in the range of take-up velocity from 1 to 6 km/min. The change of the fiber structure and physical properties with increasing take-up velocity was investigated through birefringence, wide-angle X-ray diffraction (WAXD), differential scanning calorimetry (DSC), a Rheovibron, and a Fafegraph-M. The birefringence increased linearly with increasing take-up velocity and that of LLDPE(45) was higher than that of LLDPE(50). With increasing take-up velocity, the crystal orientation of LLDPE transformed the a-axis orientation into a c-axis orientation. In the dynamic viscoelastic behavior of LLDPE(45) fibers with high-speed spinning, the intensity of the crystalline relaxation peak was decreased and the temperature of that was shifted lower. But that of LLDPE(50) could not be observed. The tensile strength and initial modulus were increased and the elongation was decreased with increasing take-up velocity. LLDPE(45) fibers were preferred to LLDPE(50) in mechanical properties owing to the increase of crystal and amorphous orientation factor. The change of birefringence with take-up velocity affected both the initial modulus and the tenacity uniformly.

Fine-structure and physical properties of polyethylene fibers in high-speed spinning. I. Effect of melt-flow rate in the high-density polyethylene

High-density polyethylene (HDPE) fibers, obtained from a melt-flow rate (g/10 min) of 11 and 28, was produced by a high-speed melt-spinning method in the range of take-up velocity from 1 to 8 km/min and from 1 to 6 km/min, respectively. The change of fiber structure and physical properties with increasing take-up velocity was investigated through birefringence, wide-angle X-ray diffraction (WAXD), differential scanning calorimetry (DSC), a Rheovibron, and a Fafegraph-M. With an increase in take-up velocity, the birefringence showed a sigmoidal increase, which has distinct changes in the range of 1–5 km/min. Throughout the whole take-up velocities, the birefringence of HDPE(11) was higher than that of HDPE(28). With increasing take-up velocity, the crystalline orientation was transformed from a-axis orientation to c-axis orientation. These crystalline relaxations are confirmed by the tan δ peak of high-speed spun HDPE fibers. The intensity of the crystalline relaxation peak decreases with increasing take-up velocity in both HDPE(11) and HDPE(28). As above, the crystalline relaxation peaks shift to lower temperature with increasing take-up velocity. With increasing take-up velocity, the ultimate strain decreases while both specific stress and the initial modulus increase. The mechanical behavior may be closely related to, as investigated by birefringence, orientation of the amorphous region, etc., the take-up velocity.