Tooru Kitagawa

Morphological study on poly-p-phenylenebenzobisoxazole (PBO) fiber

Morphological survey on new PBO fiber (Zylon®) was conducted by X-ray and transmission electron microscopic studies. Crystal size, orientation of the crystal, fibrils, microvoids, and fine structure were discussed. It was found that the molecule in the fiber showed high orientation (more than 0.99 in Hermanns orientation function for heat-treated fiber) and relatively small crystal sizes in the longitudinal (160 A) and the transverse (110 A) directions. Crystal modulus estimated by extrapolation to perfect orientation on the plot of the fiber modulus as a function of fiber orientation (Northolts method) shows discrepancy from the crystal modulus directly obtained by X-ray scattering. This discrepancy means that the Northolts model is insufficient to describe the Youngs modulus of PBO fiber. Microvoids elongated to the fiber direction were examined by small-angle X-ray scattering and transmission electron microscopic methods. The diameter of the microvoids was 20 A to 30 A and the fiber had a very thin microvoids-free layer (0.2 μm). Preferential orientation of the a-axis of crystal in the fiber was also confirmed. Summarizing these results, a structure model of the PBO fiber was proposed.

An analysis of deformation process on poly-p-phenylenebenzobisoxazole fiber and a structural study of the new high-modulus type PBO HM+ fiber

This study is concerned with fiber structure of new high-modulus type PBO fiber. Crystal modulus and molecular orientation change with stress was surveyed. Standard-modulus type PBO (AS) fiber has hysteresis effect to applied stress while high-modulus type PBO (HM) fiber shows reversible change. In order to raise actual PBO fiber modulus higher, nonaqueous coagulation process was adopted with conventional heat treatment. The fiber (HM+) so made gives 360 GPa in the Youngs modulus and an absence of small-angle X-ray scattering pattern that is characteristic for aqueous-coagulated PBO fiber with heat treatment (Zylon™ HM). The crystal structure form and crystal size for the HM+ fiber are the same as those of the HM fiber.

An investigation into the relationship between processing, structure, and properties for high-modulus PBO fibers. II. Hysteresis of stress-induced raman band shifts and peak broadening, and skin-core structure

This paper is the second of a series of studies to elucidate the relationship between the structure and mechanical properties of poly(p-phenylene benzobisoxazole) (PBO) fibers processed in different ways. Deformation hysteresis effects with stress and strain have been followed using Raman Spectroscopy and are discussed in terms of modulus improvement and fiber morphology. Selected-area electron diffraction has been employed upon longitudinal ultra-thin section of the fibers to detect the differences in skin-core structure. It is found that the stress–strain curve and Raman band shifts with stress and strain in PBO as-spun (AS) fibers show noticeable mechanical hysteresis. This indicates that plastic structural changes occur upon loading in tension, which may give the fibers a more homogeneous structure. No significant mechanical hysteresis is found for the commercial AS and heat-treated (HM), and new (HM+) PBO fibers. The HM+ fiber is found to show a more enhanced skin-core structural difference than the AS and HM fibers even though it has the highest Youngs modulus.

A relationship between the stress distribution and the peak profile broadening of meridional X‐Ray diffraction from poly‐p‐phenylenebenzobisoxazole (PBO) fiber

Poly-p-phenylenebenzobisoxazole (PBO) is one of the rigid-rod polymers, the fiber of which shows high modulus and high strength. For these high mechanical properties to be understood, an analysis of the deformation process occurring in the fiber under stress was inevitable. For this purpose, X-ray diffraction measurements were carried out for the fiber under stress. The diffraction peak broadened as the degree of applied stress was increased. According to a Hosemann analysis, in the PBO fiber only the crystalline order was changed along the fiber axis in the crystal structure under deformation, whereas a change in the crystallite size was not detected. The external stress induced heterogeneous stress distribution to the molecule in the crystal; this distorted the X-ray diffraction peak profile, which followed Hosemanns theory.

Novel Fine Structures in Poly-p-phenylenebenzobisoxazole Fibers Induced by Water Vapor, Hot Water, and Non-Aqueous Coagulation I Molecular Orientation Along the Fiber Axis and Fine Structures

This article is concerned with describing novel structural features of the water vapor coagulated Poly-p-phenylenebenzobisoxazole fiber in comparison with other PBO fibers made with hot liquid water and non-aqueous coagulation. Micro-focus X-ray diffraction was adopted to see the skin-core difference of molecular orientation and crystal size along the fiber-radius direction. Low temperature differential scanning calorimetry (DSC) was performed to elucidate the structural features of never-dried fibers made with the different coagulation techniques. Comparison of micro-focus X-ray diffraction profiles from the different positions on the fiber suggests less anisotropy of preferential orientation for the water vapor coagulated fiber. The fiber made through water vapor coagulation showed a large skin-core difference in molecular orientation with structural inhomogeneity along the fiber axis.

Novel Fine Structures in Poly-p-phenylenebenzobisoxazole Fibers Induced by Water Vapor, Hot Water, and Non-Aqueous Coagulation II Random and Radial Preferential Orientations of the Crystal a-Axis

The preferential orientation of the a-axes of poly-p-phenylenebenzobisoxazole (PBO) crystals in PBO fibers made with differential coagulation processes is characterized. Electron diffraction and micro-focus X-ray diffraction were carried out for this purpose. To estimate the alignment quantitatively a two-phase model is proposed and the calculated X-ray diffraction profiles fit well with the measured profiles. Water vapor coagulation at high temperature gave mostly almost random preferential orientation while a non-aqueous coagulation produced radial orientation. The fibers made with hot liquid water coagulation were characterized as a middle form between the limits of radial and random orientations.

Effects of hydrophilicity of rigid-rod polymers on the formation of poly-p-pyridylenebenzobisoxazole fibers

This study investigates the fiber structure of a newly developed poly-p-pyridylenebenzobisoxazole fiber. The molecular structure resembles that of poly-p-phenylenebenzobisoxazole fiber, which has a rigid-rod backbone structure with a thin-planar shape; thus, a similar preferential radial orientation of the molecular planes normal to the fiber axis is expected. We have focused on the change of fiber structures induced by copolymerizing hydrophilic groups in a rigid-rod backbone of PBO. The preferential orientation of the crystal planes in various positions of the fiber, the molecular orientation along the fiber axis and the crystal size were analyzed by micro-focus X-ray diffraction. The difference in molecular orientation and crystal size in the various positions was related to the formation of the crystal structure induced by radial preferential orientation of the (200) crystal plane sourced from the rigid-rod backbone structure with the thin-planar shape.

Spectroscopic studies of electron spin resonance and Raman scattering on novel hybrid poly-p-phenylenebenzobisoxazole (PBO) fibers with copper phthalocyanine

ABSTRACT As was shown in the previous study using X-ray analyses, poly-p-phenylene benzobisoxazole fibers can accommodate copper phthalocyanine molecules with a molecularly-dispersed state in the fiber structure. It is necessary for us to investigate the presence/absence of chemical interactions between the two molecules mentioned above for the purpose to make clear the mechanism why such characteristic structures with the well dispersion of copper phthalocyanine molecules in the hybrid fiber were realized. Spectroscopic analyses based on electron spin resonance and Raman scattering were adopted. Because the copper phthalocyanine molecule take a plane form having D4h symmetry in an ideal state, the spectra from the molecule would express the consequences based on its symmetry as the shape of the spectrum; the presence of characteristic bands in the spectra would be a proof of the existing state of copper phthalocyanine and poly-p-phenylene benzobisoxazole molecules in the hybrid fiber. It is found that both the spectroscopic methods suggested that there were no chemical bond observed between the two molecules of copper-phthalocyanine and poly-p-phenylene benzobisoxazole in the hybrid fiber.

Thermal Conductivity of poly-p-phenylene-2,6-benzobisoxazole Film along the In-Plane Axis in the 10–300 K Temperature Range

Abstract The thermal conductivities of compression molded thin films of poly-p-phenylene-2,6-benzobisoxazole (PBO) were measured in directions along an in-plane axis in the 10–300 K temperature range by a steady-state heat flow method, with interest in the use of the material for superconductivity applications. The thermal conductivities of the PBO films increased from 0.3 W/mK to 9.0 W/mK with increasing temperature from 10 K to 300 K and these were much higher than those of polyimide films, epoxy resin and glass fiber reinforced plastics at all temperatures. The 9.0 W/mK at 300 K was 60% of that of stainless steel (SUS304). It was 6 W/mK at 150 K, which was half that of SUS304 and was 3.3 W/mK at 77 K, which was 33% of that of SUS304. The thermal conductivities of the PBO films were lower than those of a cloth of high strength ultrahigh molecular weight polyethylene fiber reinforced plastics in the 30 K–180 K temperature range and were almost equivalent to its values in the 180 K–300 K temperature range. The main contribution to the thermal conduction in the PBO films was from thermal phonon conduction along the molecular chains. Although many kinds of high thermal conductivity polymeric materials have been prepared by a uni-directional drawing process or by adding high thermal conductive additives, the PBO film showed high thermal conductivity without a uni-directional drawing process or high thermal conductive additive.

Effects of Thermal History in the Fiber Production on Preferential Orientations of Molecular Planes of Rigid-Rod Polymers along the Radial Direction Normal to the Fiber Axis

ABSTRACT The research described in this article was primarily concerned with the preferential orientations of crystal planes along the radial direction normal to the fiber axis, using fibers of poly-p-phenylenebenzobisoxasole as an example. The focus is placed on the formation of the preferential orientation during the dry-jet wet spinning fiber production process for rigid-rod polymers in which, after coagulation, the fibers are washed and dried at low temperatures. It is suggested that the formation of the radial or random preferential orientation was determined in the coagulation and washing processes, based on an analysis of micro-focus X-ray diffraction intensities in a synchrotron radiation facility.