Shear flow behaviors of poly(p‐phenylene benzobisoxazole) spinning dope

In this study, the shear flow properties of Poly(p‐phenylene benzobisoxazole) (PBO)/poly(phosphoric acid) (PPA) spinning dope were studied by means of capillary rheometer. The effect of shear stress, temperature, PBO concentration, and PBO molecular weight on the apparent viscosity of PBO/PPA dope was discussed. The results showed that the apparent viscosity of the dope decreased with the increase of the shear stress and the temperature. The flow behavior index increased with the increase of temperature, which indicated that the non‐Newtonian behavior of the dope became weaker at high temperature. Moreover, it was also found that at high shear stress, the apparent viscosity of the dope was insensitive to the temperature, PBO molecular weight, and PBO concentration. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Synthesis and Properties of Poly[p-(2,5-dihydroxy)-phenylenebenzobisoxazole] Fiber

The novel polymer poly[p-(2,5-dihydroxy)-phenylenebenzobisoxazole] (PBOH) fiber was synthesized in the presence of 2,5-dihydroxyterephthalicacid (DHTA) and 4,6-diamino-1,3-benzenediol in poly(phosphoric acid) (PPA) using typical polycondensation conditions. The crystalline solutions of liquid PBOH in PPA were spun into fibers using dry-jet wet spinning. Furthermore, the thermostability and mechanical properties of PBOH were compared with poly(p-phenylene-2,6-benzoxazole) (PBO) in order to investigate the relationship between the chain structure and properties. The results indicated that the thermal degradation temperature of PBOH was above 750K and the tensile strength of the PBOH fiber was 3.1GPa, which were much lower than those of PBO fiber. The compressive strength of PBOH fiber was 331 M Pa, which was slightly higher than that of PBO fiber. In addition, molecular simulation was employed to explain why the compressive strength of PBOH fiber did not increase significantly compared to PBO fiber.     

PBO纤维生产工艺的研究

以4,6-二氨基间苯二酚盐酸盐(DAR)和对苯二甲酸(TPA)制成复合盐,再以多聚磷酸为溶剂,添加五氧化二磷,制备出PBO聚合物。通过双螺杆挤出机和喷丝板挤出,在水溶液中凝固成型,经过洗涤、干燥等过程,最终卷绕成型。制成的纤维抗拉强度可以达到33 cN/dtex,制成的PBO聚合物特性粘度可以达到56 dL/g。     

Synthesis and characterization of a rigid-rod dihydroxy poly(<Emphasis Type="Italic">p</Emphasis>-phenylene benzobisoxazole) fiber with excellent surface and axial compression properties

A series of dihydroxy poly(p-phenylene benzobisoxazole) (DHPBO) were prepared by introducing binary hydroxyl polar groups into poly(p-phenylene benzoxazole) PBO macromolecular chains and the effects of hydroxyl polar groups on surface wettability, interfacial adhesion and axial compression property of PBO fiber were investigated. Contact angle measurement showed that the wetting process both for water and for ethanol on DHPBO fibers were obviously shorter than that on PBO fibers, implying DHPBO fibers have a higher surface free energy. Meanwhile, single fiber pull-out test showed that DHPBO fibers had higher interfacial shear strength than that of PBO fibers. Scanning electron microscope proved that there was more resin remained on the surface of DHPBO fibers than on PBO fibers after pull-out test. Furthermore, axial compression bending test showed that the introduction of binary hydroxyl groups into macromolecular chains apparently improved the equivalent bending modulus of DHPBO fibers.     

Promoting the adhesion of high‐performance polymer fibers using functional plasma polymer coatings

Plasma‐copolymerized functional coatings of acrylic acid and 1,7‐octadiene were deposited onto high strength, high modulus, poly‐p‐phenylene benzobisoxazole (PBO) fibers. X‐ray photoelectron spectroscopy (XPS) with trifluoroethanol derivatization confirmed that the PBO fibers were covered completely with the plasma copolymer and that the coating contained a quantitative concentration of carboxylic acid groups. Microdebond single filament adhesion and interlaminar shear strength (ILSS) tests were used to evaluate the interfacial strength of epoxy resin composites containing these functionalized PBO fibers. Both the interfacial shear strength (IFSS) obtained from single filament tests, and the ILSS of high volume fraction composites were a function of the surface functionality of the fibers so that there was a good correlation between ILSS and IFSS data. The tensile strengths of single fibers with or without coating were comparable, demonstrating that the fiber surface was not damaged in the plasma‐coating procedure. Indeed, the statistical analysis showed that Weibull modulus was increased. Therefore, plasma‐polymerized coatings can be used to control the interfacial bond between PBO fibers and matrix resins and act as a protective size for preserving the mechanical properties of the fibers. POLYM. COMPOS., 2009. © 2008 Society of Plastics Engineers     

Influence of oxygen plasma treatment on interfacial properties of poly(p‐phenylene benzobisoxazole) fiber‐reinforced poly(phthalazinone ether sulfone ketone) composite

The influence of oxygen plasma treatment on both surface properties of poly(p‐phenylene benzobisoxazole) (PBO) fibers and interfacial properties of PBO fiber reinforced poly(phthalazinone ether sulfone ketone) (PPESK) composite were investigated. Surface chemical composition, surface roughness, and surface morphologies of PBO fibers were analyzed by X‐ray photoelectron spectroscopy (XPS), Atomic force microscopy (AFM), and scanning electron microscopy (SEM), respectively. Surface free energy of the fibers was characterized by dynamic contact angle analysis (DCAA). The interlaminar shear strength (ILSS) and water absorption of PBO fiber‐reinforced PPESK composite were measured. Fracture mechanisms of the composite were examined by SEM. The results indicated that oxygen plasma treatment significantly improved the interfacial adhesion of PBO fiber‐reinforced PPESK composite by introducing some polar or oxygen‐containing groups to PBO fiber surfaces and by fiber surface roughening. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

X‐ray scattering study on the damage in fibers used in soft body armor after folding

The goals of the research effort described in this article are to develop a framework to evaluate improvements in next‐generation fibers used in soft body armor and to anticipate long‐term performance and potential fiber deterioration. This effort to date has included the effect of folding on the fibers and exploring the interaction between the specific fiber strain energy and their sound velocity. Previous work in this lab noted a severe drop‐off of tensile strength and strain‐to‐failure in poly(p‐phenylene benzobisoxazole) (PBO) fibers when subjected to repeated folding. Subsequent work on poly(p‐phenylene terephthalamide) (PPTA) fibers showed at most a slight drop‐off in these mechanical properties. Results from wide angle X‐ray diffraction indicated that both PPTA and PBO fibers showed no significant changes in the d‐spacing and the apparent crystal size. However, with small angle X‐ray scattering, it was found that the void and fibril sizes within PBO fibers may decrease after folding. Environmental scanning electron microscopy showed no damage to the fiber surfaces upon folding, and confocal microscopy revealed extensive internal damage to the PBO fibers that tracks well with the SAXS and mechanical testing results. POLYM. COMPOS., 2012. © 2012 Society of Plastics Engineers     

聚对苯撑苯并二噁唑溶液单孔纺丝条件的研究

由4,6-二氨基间苯二酚盐酸盐(DAR)和对苯二甲酸(TA)在多聚磷酸(PPA)中进行缩聚反应制得聚对苯撑苯并二噁唑(PBO)聚合物溶液,然后在液晶状态下采用干喷湿纺技术得到PBO纤维。为了提高PBO纤维的力学性能,用灰色关联法研究了单孔纺丝时各种纺丝条件对PBO纤维力学性能影响的关联序,深入研究了纺丝温度、纺丝压力、气隙段长度、纺丝速度对纤维力学性能的影响,探讨了各因素的影响机理。     

Influence of the monomer feeding sequence on the structure and properties of thermotropic liquid‐crystalline poly(ester imide)s

A series of poly(ester imide)s mainly derived from N,N′‐hexane‐1,6‐diylbistrimellitimides, 4,4′‐dihydroxybenzophenone, and p‐hydroxybenzoic acid were synthesized by a direct polycondensation method in benzenesulfonyl chloride, N,N′‐dimethylformamide, and pyridine with different monomer feeding sequences. The molecular structures and properties of the resultant poly(ester imide)s were characterized with NMR, IR spectrometry, polarized light microscopy, wide‐angle X‐ray diffraction, differential scanning calorimetry, and thermogravimetric analysis. The results showed that the monomer feeding sequences had a great effect on the sequential structure of the molecular chains of the copolymers and consequently on their liquid‐crystalline (LC) properties, fiber‐forming capability, and other properties. Thus, it is probable that one could obtain an LC poly(ester imide) with given properties by controlling the monomer feeding sequence during the polycondensation process. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Synthesis and melt spinning of fully aromatic thermotropic liquid crystalline copolyesters containing m‐hydroxybenzoic acid units

Fibers of fully aromatic thermotropic copolyesters based on p‐acetoxybenzoic acid (p‐ABA), hydroquinone diacetate (HQDA), terephthalic acid (TPA), and m‐acetoxybenzoic acid (m‐ABA) were prepared by a high‐temperature melt‐spinning technique. Two types of the copolyesters were prepared by a high‐temperature melt polycondensation reaction using 33 mol % of kink (m‐ABA) and 67 mol % linear monomer units (p‐ABA, TPA, HQDA), and characterized by differential scanning calorimetry (DSC), polarized optical microscopy, wide‐angle X‐ray diffraction (WAXD), and intrinsic viscosity measurements. The mechanical properties and the morphology of the fibers were also determined by tensile tester, WAXD, and scanning electron microscopy (SEM). The copolyesters exhibited phase‐separated nematic liquid crystalline morphology within a broad temperature range in an isotropic matrix. DSC analysis of the copolyesters revealed broad endotherms associated with the nematic phases. The melting and spinning temperatures were in a processable region. Fibers exhibit well‐developed fibrillar structure parallel to the fiber axis. The highly oriented morphology of the fibrils is slightly dependent on the type of the linear monomer. The strength and modulus values determined for the fibers that contain equal molar composition of the linear p‐ABA, HQDA/TPA units are comparable to other reported rigid systems containing fully aromatic species. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 85: 2580–2587, 2002     

Environmental effects on poly‐p‐phenylenebenzobisoxazole fibers. II. Attempts at stabilization

Approaches to alleviate the environmental degradation of as‐spun poly‐p‐phenylenebenzobisoxazole (PBO AS) fibers by moisture, acidic conditions, and UV–visible radiation were implemented and tested for efficacy. The general approaches tested include: extraction and neutralization of residual phosphoric acid using supercritical carbon dioxide; the use of UV–visible light blocking coatings of exfoliated graphite, carbon black, and glassy titanium dioxide; and improvement of initial fiber properties by the application of forces tending to compact the fiber microstructure. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102: 3819–3829, 2006     

Rigid‐rod polymeric fibers

This paper traces the historical development of high temperature resistant rigid‐rod polymers. Synthesis, fiber processing, structure, properties, and applications of poly(p‐phenylene benzobisoxazole) (PBO) fibers have been discussed. After nearly 20 years of development in the United States and Japan, PBO fiber was commercialized with the trade name Zylon® in 1998. Properties of this fiber have been compared with the properties of poly(ethylene terephthalate) (PET), thermotropic polyester (Vectran®), extended chain polyethylene (Spectra®), p‐aramid (Kevlar®), m‐aramid (Nomex®), aramid copolymer (Technora®), polyimide (PBI), steel, and the experimental high compressive strength rigid‐rod polymeric fiber (PIPD, M5). PBO is currently the highest tensile modulus, highest tensile strength, and most thermally stable commercial polymeric fiber. However, PBO has low axial compressive strength and poor resistance to ultraviolet and visible radiation. The fiber also looses tensile strength in hot and humid environment. In the coming decades, further improvements in tensile strength (10–20 GPa range), compressive strength, and radiation resistance are expected in polymeric fibers. Incorporation of carbon nanotubes is expected to result in the development of next generation high performance polymeric fibers. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 100: 791–802, 2006     

Theoretical investigations on some rigid-rod polymers used as high-performance materials

This review focuses on a new type of para-catenated aromatic polymer being used in the preparation of high-performance films and fibers of exceptional strength, thermal stability, and environmental resistance, including inertness to essentially all common solvents. Polymers of this type include cis and transpoly(p-phenylene benzobisoxazole) (PBO), and the cis and trans forms of the corresponding poly(p-phenylene benzobis-thiazole)(PBT). The purpose of this paper is to summarize the authors' theoretical work on the structures, conformational energies, intermolecular interactions, and electronic properties of PBO and PBT chains, including the protonated forms known to exist in strong acids. The emphasis is on how such studies provide a molecular understanding of the unusual properties and processing characteristics of this new class of materials.     

Improvement of interfacial adhesion between PBO fibers and cyanate ester matrix

Poly(p‐phenylene benzobisoxazole) (PBO) fibers were activated by the horseradish peroxidases (HRP) and then treated by 3‐Glycidoxypropyltrimethoxysilane (KH‐560) to improve the wettability and the interfacial adhesion between PBO fibers and cyanate ester matrix. The chemical compositions of PBO fibers were characterized and analyzed by FTIR and XPS. Surface morphologies of PBO fibers were examined by SEM. The wettability of PBO fibers was evaluated by the dynamic contact angle analysis test. The mechanical properties were evaluated by tensile strength and interfacial shear strength, respectively. The results demonstrated that hydroxyl groups and epoxy groups were introduced onto the surface of PBO fibers during the treatments. These treatments can effectively improve the wettability and adhesion of PBO fibers. The surface free energy of PBO fibers was increased from 31.1 mN/m to 55.2 mN/m, and the interfacial adhesion between PBO fiber and cyanate ester resin was improved to 10.77 MPa. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 40204.     

Competitive interaction of polyanions and anionic dye with bovine serum albumin

The binding of anionic dye, p-(2-amino-6-sulfonyl-8-naphthylazo)benzene sulfonic acid disodium salt (ASANA) to bovine serum albumin (BSA) at pH 7.5 has been studied by spectrophotometric techniques. The values of the dissociation constants were obtained with the use of the Benesi-Hildebrand equation for ASANA. Competitive binding of polyanions, sodium poly(styrene sulfonate) (PSSNa), potassium poly(vinyl sulfonate) (PVSK), poly(acrylic acid) (PAA), and poly(methacrylic acid) (PMAA) and anionic dye to BSA was evaluated through the variations in the different spectra of BSA-dye-polymer systems.     

Study on photoaging of poly(p‐phenylene benzobisoxazole) fiber

As a kind of rig‐rod‐like polymer, poly(p‐phenylene benzobisoxazole) (PBO) has received great interest because of its excellent mechanical properties and good thermal stability. The use of PBO fibers, however, is limited due to its low sunlight stability. In this work, the photoaging of PBO fibers, as well as the effects of oxygen and moisture on their photoaging, is investigated by tensile strength measurements, infrared spectroscopy, molecular mass determination, and scanning electron microscopy. It is first time to find that the photoaging of PBO fibers includes two development stages. The physical aging is the dominate factor at the first stage of photoaging relative to the second stage, in which the chemical aging is the dominate factor. In the first degradation stage, long defects appear and develop parallel to the fiber axis. Little chemical change occurs in this stage. In the second degradation stage, the molecular mass of PBO decreases and chemical degradation occurs. Oxygen accelerates the occurrence of chemical degradation. It is also found PBO fibers are more stable for photoaging when moisture and oxygen are isolated. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Improvement of the interfacial adhesion between PBO fibers and PPESK matrices using plasma‐induced coating

This work deals with the plasma‐induced coating process on the surface of PBO fibers to obtain a strong interfacial adhesion between the poly(p‐phenylene benzobisoxazole) (PBO) fibers and the poly(phthalazinone ether sulfone ketone) (PPESK) matrices. The process consisted of four steps: (a) plasma preactivation of PBO fibers; (b) immersion in an epoxy resin solution; (c) drying and then soaking with the PPESK solution; (d) shaped by compression molding technique. The orthogonal experiments used in this study enable the determination of the significant experimental parameters that influence efficiency of the process by comparing the values of ILSS. The order of their influences was the concentration > power > treating time > treating pressure. The results of the interlaminar shear strength (ILSS) and water absorption showed that the ILSS of the composite increased by 56.5% after coating, meanwhile the water absorption declined to 0.32%. The changes of the surface chemical composition, the surface morphology, and the surface free energy of fibers were studied by FTIR spectroscopy, atomic force microscope (AFM), and dynamic contact angle analysis (DCAA), respectively. Fracture mechanism of the composite was examined by scanning electron microscope (SEM). The results indicated that plasma‐induced coating process was an efficient method to enhance the interfacial adhesion of PBO fibers and PPESK matrices. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Effect of MWCNTs irradiation grafting treatment on the surface properties of PBO fiber

The aim of this article is improved the surface properties of Poly[p‐phenylenebenzobisoxazole] (PBO) fiber with epichlorohydrin hybridized carboxylic multi walled carbon nanotubes (MWCNTs‐Ecp) grafting by using γ‐ray irradiation technology. The surface chemical properties, the surface morphology, the amount of the grafted MWCNTs on PBO fiber and the surface free energy of PBO fibers have been analyzed. The results show that MWCNTs‐Ecp have been grafted on the surface of PBO fiber by γ‐ray irradiation treatment. The surface chemical inertness and the surface smoothness of PBO fiber are significantly improved by grafting MWCNTs‐Ecp chains, the amount of the grafted MWCNTs on PBO fiber is about 11.9%, and the surface free energy of PBO fiber has an increase of 42.6% by generating some active groups such as ? COOH, ? OH, and ? C? Cl on the surface of PBO fiber. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Enhanced thermal conductivity of semi‐aliphatic liquid crystalline polybenzoxazoles using magnetic orientation

Polybenzoxazole (PBO) model compounds consisting of benzoxazole mesogenic units linked with long alkyl chains via ether or ester groups were prepared from flexible dicarboxylic acids with two kinds of bis(o‐aminophenol)s, i.e. 4,4′‐diamino‐3,3′‐dihydroxybiphenyl (p‐HAB) and 3,3′‐diamino‐4,4′‐dihydroxybiphenyl (m‐HAB). The results revealed that the use of p‐HAB completely erased the thermotropic liquid crystallinity and that the m‐HAB‐based ether‐linked model compound was much more advantageous for the formation of a stable liquid crystal phase than the corresponding ester‐linked one. However, the relevant high‐molecular‐weight PBOs showed quite opposite results. Only the m‐HAB‐based ester‐linked C₁₀ PBO system showed a liquid crystal‐like texture among various semi‐aliphatic PBO systems examined. A very high thermal conductivity of 1.79 W m^?1 K^?1 along the thickness direction for the m‐HAB‐based ester‐linked C₁₀ PBO film was achieved by heat treatment in the liquid crystalline state under a strong magnetic field of 10 T. Copyright © 2011 Society of Chemical Industry     

In situ polymerization and photophysical properties of poly(p‐phenylene benzobisoxazole)/multiwalled carbon nanotubes composites

Poly(p‐phenylene benzobisoxazole)/multiwalled carbon nanotubes (PBO‐MWCNT) composites with different MWCNT compositions were prepared through in situ polymerization of PBO in the presence of carboxylated MWCNTs. The nanocomposite's structure, thermal and photophysical properties were investigated and compared with their blend counterparts (PBO/MWCNT) using Fourier transform infrared spectra, Raman spectra, Wide‐angle X‐ray diffraction, thermogravimetric analysis, UV‐vis absorption, and photoluminescence. The results showed that MWCNTs had a strong interaction with PBO through covalent bonding. The incorporation of MWCNTs increased the distance between two neighboring PBO chains and also improved the thermal resistance of PBO. The investigation of UV‐vis absorption and fluorescence emission spectra exhibited that in situ PBO‐MWCNT composites had a stronger absorbance and obvious trend of red‐shift compared with blend PBO/MWCNT composites for all compositions. This behavior can be attributed to the efficient energy transfer through forming conjugated bonding interactions in the PBO‐MWCNT composites. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011