Kazuyuki Yabuki

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.

Heat resistance properties of poly(p‐phenylene‐2,6‐benzobisoxazole) fiber

The high temperature properties of Poly(p-phenylene-2,6-benzobisoxazole) (PBO) fiber are examined and compared with those of the p-Aramid fiber. In particular, the temperature dependence of tensile strength of the PBO fiber is reported for the first time. The PBO fiber has 100°C higher decomposition temperature than the p-Aramid fiber, and the amount of toxic gases in combustion is much smaller than the p-Aramid fiber. Although the relative strength decreased proportionally in the range of room temperature to 500°C, the PBO fiber has 40% of the strength at room temperature even at a temperature of 500°C. After thermal treatment at 500°C for 60 s, the PBO fiber retained 90% of its original strength. The PBO fiber is expected to substitute for asbestos, which is still used as a heat resistant cushion material.

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.

History of Super Fibers: Adventures in Quest of the Strongest Fiber

The high-strength and high-modulus fibers have been widely spread into many industrial applications since the last quarter of the twentieth century. Key technologies leading to the industrial success of the fibers are the molecular designs of rigid polymers giving rise to a spontaneous molecular organization and the gel spinning of flexible polymers. The continuous efforts of a great number of researchers in this field over 40 years are summarized in this chapter.

Controlled Orientation and Morphology of High Modulus and High Strength Fibers.

高分子の配向.配列制御技術の近年のもっとも大きな実りのひとつは.液晶紡糸.ゲル紡糸といった高強度.高弾性率繊維の製造技術である.これらの繊維化技術のキーテクノロジーは流動.伸長場による配向制御であり.本稿では.こうした外場中での高分子の構造形成に関する最近の話題を概説した.

Degradation of polyester tire cord in rubber.

ポリエステルタイヤコードのゴム中での疲労現象を明らかにする目的で, ゴム中におけるポリエステルタイヤコードの熱化学劣化について検討した. 170°Cの高温加硫による劣化試験後, ポリエステルタイヤコードをゴムより取り出し, 引張り強力, 極限粘度及びカルボキシ基量を測定した. 結果は次のように要約される. ポリエステルのゴム中でゐ強力低下は, 主として加水分解により引き起こされる分子鎖の切断に起因する. 強力低下と分子鎖の切断量とには直線関係が認められ, この関係は, 特殊な配合の場合を除き, ゴム種に関わらずゴム中でのポリエステルの劣化に当てはまる. 低分子量の脂肪族アミンを含む天然ゴムの場合, ゴム中の劣化に関しては, アミン分解の寄与が認められるが, 主たる反応はアミンが触媒作用を果たす加水分解である. 加硫促進剤は非アミン系といえどもゴム中のポリエステルの加水分解における触媒としての作用を果たす.

FATIGUE-FRACTOGRAPHY OF POLY (ETHYLENE TEREPHTHALATE) TIRE CORDS

The fatigue behavior of Poly (ethylene terephthalate) (PET) tire cords were investigated as functions of degree of polymerization and twist number of tire cords both of which were the major factors governing the fatigue properties.The fatigue tests were conducted by means of a Goodyear tube and a Goodrich disk fatigue testers. After the fatigue tests, tire cords isolated from rubber were examined by an optical microscope in a view point of fractography.The results are summarized as follows:(1) The higher the degree of polymerization of PET tire cord, the greater the resistance to compression-induced fatigue.(2) In the tube fatigue test, the fatigue life considerably depends on the temperature of tube. The tube temperature was found to be affected by the degree of polymerization of PET tire cord.(3) In the case of disk fatigue test, a fibrillation was observed at the very early stage of fatigue test.(4) The structural deterioration such as occurrence of kinkband was observed only in the cases of low degrees of polymerization or low twist number which are considered as giving the cords a very severe fatigue condition.