Norimasa Okui

High‐speed melt spinning of bicomponent fibers: Mechanism of fiber structure development in poly(ethylene terephthalate)/polypropylene system

High-speed bicomponent spinning of poly(ethylene terephthalate)(PET)(core) and poly-propylene (PP) (sheath) was carried out and the structure development in the individual components, PET and PP, was investigated. The orientation and crystallinity development in the PET component was enhanced as compared to that of the single-component spinning while the PP component remained in a low orientation state and had a pseudohexagonal crystal structure even at high take-up speeds. To clarify the mutual interaction between the two components in bicomponent spinning, a semiquantitative numerical simulation was performed. The simulation results obtained using the Newtonian fluid model showed that the solidification stress in the PET component was enhanced while that of the PP component was decreased in comparison with the corresponding single-component spinning. This is due to the difference in the temperature dependence of their elongational viscosity. Simulation with an upper-convected Maxwell model as the constitutive equation suggested that significant stress relaxation of the PP component can occur in the spinline if the PET component solidifies earlier than does PP. Based on the structural characterization results, and the simulation results, it was concluded that the difference in the activation energy of the elongational viscosity and solidification temperature between the two polymers are the main factors influencing the mutual interaction in the bicomponent spinning process.

Layer-by-layer polycondensation of nylon 66 by alternating vapour deposition polymerization

Nylon 66 thin films were prepared by layer-by-layer polycondensation. Two kinds of bifunctional monomers were deposited alternatively onto the substrate. The films showed the highly ordered structure with the molecular orientation normal to the substrate. It was found that the thickness and the molecular weight of the nylon 66 film could be effectively controlled by the number of deposition reaction cycle. The molecular weight of the film was proportional to the film thickness.

Co-crystallization behaviour and melting-point depression in poly(ethylene terephthalate-co-1,4-cyclohexylene dimethylene terephthalate) random copolyesters

Abstract The crystallization behaviour of the poly(ethylene terephthalate- co -1,4-cyclohexylene dimethylene terephthalate) (P(ET/CT)) random copolyesters is studied by d.s.c. analysis. ET units can crystallize with complete rejection of the CT units from the crystals, whereas CT units can co-crystallize with incorporation of ET units to some extent, resulting in a minimum melting temperature at an intermediate composition of about 30–40 mol% CT. A good linear relation is found between the compositions at which the melting point exhibits a minimum experimentally in various random copolyesters and those at which the cohesive energies for two components estimated by group contribution methods are identical.

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.

Preparation and piezoelectricity of β form poly(vinylidene fluoride) thin film by vapour deposition

Abstract Thin films of poly(vinylidene fluoride) (PVdF) and VdF oligomer were prepared by vapour deposition. PVdF was thermally decomposed in a vacuum system, when the polymer was heated above 300°C in the crucible. Low molecular weight fractions in PVdF were evaporated at temperatures below 300°C without the thermal decomposition. The thin films exhibited the β form with molecular orientation parallel to the substrate when PVdF and VdF oligomer were deposited onto the substrate at temperatures below — 150°C. Piezoelectricity was observed for the as-deposited film without poling treatment. The piezoelectric constant d 33 of the film prepared from VdF oligomer was about 15 times larger than of that prepared from PVdF.

Preparation of polyvinylcarbazole thin film with vapor deposition polymerization

N-vinylcarbazole (NVCz) was evaporated toward a substrate of a glass slide coated with silver 100 nm thick with the existence of a redheated filament. The processes of vapor deposition polymerization (VDP) and annealing were observed with in-situ infrared reflection absorption spectroscopy. The filament temperature of 2300 K and the substrate temperature of 266 K were effective to retard the re-evaporation of deposited NVCz. After NVCz was deposited on the above conditions and then annealed at 285 K, the resulting VDP film had a number average molecular weight of 1.1 × 104 and a polymer yield of 88%.

Molecular orientation behavior of paraffin thin films made by vapor deposition

Abstract The molecular orientation behavior of paraffin thin films prepared by the vapor deposition method was investigated. The molecular orientation in the thin film could be controlled by the substrate temperature, the deposition rate, the lenght of the molecular chain and other parameters. Of these parameters, the degree of supercooling, defined as the difference between the melting temperature of the sample and the substrate temperature, was found to be the most important factor influencing the molecular orientation in the film. It is supposed that the degree of supercooling affects the adsorption-desorption process and the molecular motions on the substrate, such as translation, rotation and precession modes. Among these modes, the precessional motion is assumed to play an important role in the formation of the thin film with the molecular orientation perpendicular to the substrate.

In-situ study on alternating vapor deposition polymerization of alkyl polyamide with normal molecular orientation

Abstract The film formation mechanism during the alternating vapor deposition polymerization was studied by monitoring the change in the amount of adsorbate during the deposition. Azelaoyl dichloride (ADC) monomers can be chemisorbed onto the diaminoheptane (DAH) layer and form a mono-molecular layer with a normal molecular orientation. DAH monomers can be chemisorbed onto the ADC layer and form a multi-molecular layer on the surface of the chemisorbed DAH layer with the normal molecular orientation. Polyamide thin film with a layered structure like an Langmuir-Blodgett film was obtained by use of the alternating vapor deposition polymerization method, similar to the atomic layer epitaxy method.

High-Speed Melt Spinning of Sheath-Core Bicomponent Polyester Fibers: High and Low Molecular Weight Poly(ethylene Terephthalate) Systems

Sheath-core bicomponent spinning of high molecular weight poly (ethylene terephthalate) (hmpet, IV = 1.02 dl/g) and low molecular weight pet (lmpet, IV = 0.65 dl/g) is done at a take-up velocity range of 1 to 7 km/min. The structures of the individual components in the as-spun bicomponent fibers are characterized. Orientation and orientation-induced crystallization of the hmpet component are enhanced, while those of the lmpet component are suppressed in comparison to corresponding single component spinning. Numerical simulation with the Newtonian model shows that elongational stress in the hmpet component is enhanced and that of the lmpet decreases during high-speed bicomponent spinning. The difference in elongational viscosity is the main factor influencing the mutual interaction between hmpet and lmpet, which in turn affect spinline dynamics, solidification temperature, and structural development in high-speed bicomponent spinning. Simulation with an upper-convected Maxwell model shows that considerable stress relaxation can occur in the lmpet component if the hmpet component solidifies before lmpet. A mechanism for structural development is also proposed, based on the simulation results and structural characterization data.

Direct formation of polyimide thin films by vapor deposition polymerization

Abstract Polyamic acid films and polyimide films were prepared by vapor deposition polymerization at three substrate temperatures, 25°C, 125°C and 175°C. At substrate temperatures below 125°C, poly(amic acid) films were formed and those annealed above 125°C transformed to polyimide films. At substrate temperatures above 175°C, polyimide thin films were formed directly on the substrate. Wide-angle X-ray diffraction and IR spectra obtained using transmission and reflection-absorption (RAS) methods confirmed that the molecular chains in all films tended to align perpendicular to the substrate surface. The film prepared at 125°C had greater molecular orientation perpendicular to the substrate than those prepared at 25°C. The polyimide film prepared at a high substrate temperature exhibited greater thermal stability than those prepared at a low substrate temperature.