PBO Fiber Research Articles

Surface adhesive properties of continuous PBO fiber after air-plasma-grafting-epoxy treatment

It was found that air dielectric barrier discharge (DBD) plasma contributed to the grafting of epoxy resin onto continuous PBO fiber surface. This air-plasma-grafting-epoxy method yielded a noticeable enhancement in the interfacial adhesion between PBO fiber and thermoplastic matrix resin, with the interlaminar shear strength of the resulting composites increased by 66.7%. DSC and FTIR analyses were then used to study the curing behavior of epoxy coating on PBO fiber surface, deduce the possible grafting reactions and investigate the grafting mechanism. More importantly, TGA measurement showed that the grafting of epoxy onto PBO fiber had almost no effect on the composite heat resistance, and there was more thermoplastic matrix resin adhering to the fiber surface; the latter could also be clearly found in the SEM photos. Thereby, the air-plasma-grafting-epoxy treatment was proved to be an effective method for the improvement of continuous PBO fiber surface adhesive properties.

Influence of the Anchorage of PBO-FRCM Composites on the Effectiveness of Behaviour of Shearing Beams

The shear capacity of reinforced concrete beams strengthened with cement based composite materials (FRCM system) was investigated in this paper. The analysis refers to PBO-FRCM system made by PBO fibres (p-Phenylene Benzobis Oxazole) and cement based mortar. The use of cement mortar is connected with the slip phenomenon that occurs between the matrix layer and the fibres. This phenomenon leads to premature debonding of the ends of the composite and the loss of the shear capacity. To prevent this, designed end-anchorage systems is needed. Therefore, the laboratory tests on reinforced concrete beams strengthened in a shear with PBO-FRCM system were conducted. At this aim tests on three strengthened RC beams with different end-anchorages systems have been preformed and obtained results discussed. The experimental results revealed that the use of FRCM composites increased the shear capacity and construction of end-anchorage of composite had an impact on shear capacity.

Significant enhancement in compressive strength of poly(p-phenylenebenzobisoxazole) fibers by incorporation of carbon nanofibers

Poly(p-phenylenebenzobisoxazole) (PBO) composite fibers containing small amounts (~2 wt.%) of carbon nanofibers (CNFs) were successfully prepared by in-situ polymerization and dry-jet wet spinning. Polarized optical microscopy images displayed a lyotropic liquid-crystalline phase in the as-polymerized dopes. Solution viscosity measurements revealed that the molecular weights of the composite fibers were in the range from 1.81×104 gmol-1 to 2.2×104 gmol-1. Field emission scanning electron microscopy images of the composite fibers etched by UV irradiation showed that CNFs embedded in the PBO matrix were individually dispersed, and well oriented along the fiber direction. Tensile tests indicated that the tensile moduli of the PBO/CNF composite fibers were higher than those of the pristine PBO fibers, whereas the tensile strengths were lower or similar to those of the pristine PBO fibers. The elastic loop test was carried out to measure the compressive strength of the fibers. The compressive strength of the pristine PBO fiber was 0.3 GPa, whereas that of a PBO composite fiber containing 1.0 wt.% CNF increased to 0.92 GPa, which is about twice the compressive strength of Zylon (0.43 GPa). Moreover, a heat-treated PBO composite fiber containing 2.0 wt.% CNFs exhibited the high compressive strength of 1.17 GPa, which is the second highest value among all reported values for organic polymers.

A Facile Route to Synthesize Nanographene Reinforced PBO Composites Fiber via in Situ Polymerization.

The polymer matrix with introduced carbon-based nanofiber displays fascinating properties. They have inspired extensive research on the synthesis of polymer composites, which have been applied in catalysis, electronics, and energy storage. In this report, we reported a facile and efficient method to prepare poly(p-phenylene benzobisoxazole) (PBO)/nanographene (PNG) composites fibers via in-situ polymerization, accompanied by the reduction from (nanographene oxide) NGO to (nanographene) NG. By tuning the ratio of feeding PBO monomer to NGO, various composites fibers with 0.1–1 wt % contents of NG were obtained. The efficient PBO chains grafting made NG uniformly disperse in the PBO matrix, and it also increased the uniformity of the packing orientation of PBO chains. Consequently, the tensile strength, tensile modulus, and thermal stability of the obtained PNG composites fibers had been improved significantly. In addition, the composites fibers with 0.5 wt % NG exhibited a 25% increment in tensile strength, and a 41% enhancement in tensile modulus compared with neat PBO fibers. It reveals an excellent reinforcement to PBO composites fibers with NG.

Hierarchical poly(p-phenylene benzobisoxazole)/graphene oxide reinforcement with multifunctional and biomimic middle layer

A new hierarchical reinforcement developed by coating biomimic polydopamine (PDA) on the surface of poly(p-phenylene benzobisoxazole) (PBO) fibers, which served as a platform for the graphene oxide (GO) grafting, using branched polyethyleneimine (b-PEI) as a bridging agent. The surface morphologies and chemical structures of PBO fibers were characterized for confirming the formation of covalent bond between GO and PBO fibers. The surface roughness (Ra) and wettability of the obtained fibers, denoted as PBO@PDA-PEI-GO, were obviously increased in comparison with those of untreated one. The reinforcement offered a 68.8% enhancement in the interfacial shear strength (IFSS) without degrading the base fiber. The PDA layer on the PBO fiber surface led to improved UV resistance. The hydrothermal aging resistance of PBO/epoxy composite was also greatly improved. This biomimic surface modification approach is facile to prepare, highly efficient to enhance interface, adaptable to all high-performance fibers, and meaningful in multifunctional applications.

Thermal Conductivity in the Radial Direction of Deformed Polymer Fibers.

Thermal conductivity of polymer fibers in the axial direction has been extensively studied while thermal conductivity in the radial direction Λ remains unknown. In this work, polymer fibers with different molecular arrangements (crystalline, liquid crystalline, and amorphous) were plastically deformed. Λ was measured at engineering strains ε = 0.2-2.3 using time-domain thermoreflectance. Λ decreases with increasing strains for polyethylene (PE) and poly(p-phenylene-2,6-benzobisoxazole) (PBO) fibers and is independent of strain for poly(methyl methacrylate) (PMMA) fibers. The extrapolated thermal conductivity at zero strain is Λ0 ≈ 0.27 Wm-1 K-1 for crystalline PE, Λ0 ≈ 0.29 Wm-1 K-1 for liquid crystalline PBO, and Λ0 ≈ 0.18 Wm-1 K-1 for amorphous PMMA. Λ of PE drops to Λ ≈ 0.14 Wm-1 K-1 at ε = 1.9; Λ of PBO drops to Λ ≈ 0.12 Wm-1 K-1 at ε = 2.1. We attribute the decrease of Λ with ε in crystalline and liquid crystalline fibers to structural disorder induced by plastic deformation. The combination of structural disorder and phonon focusing effects produces a thermal conductivity in deformed PE and PBO fibers that is lower than amorphous PMMA.

Facile fabrication of hierarchically structured PBO-Ni(OH)2/NiOOH fibers for enhancing interfacial strength in PBO fiber/epoxy resin composites

A new hierarchical reinforcement was fabricated by depositing honeycomb-like Ni(OH)2/NiOOH coating onto poly(p-phenylene benzobisoxazole) (PBO) fibers using a facile chemical bath deposition (CBD) method. The crystal structure of Ni(OH)2/NiOOH deposited PBO fiber, denoted as PBO-Ni(OH)2/NiOOH, was characterized by X-ray diffractometer (XRD). Scanning electron microscopy (SEM) was employed to characterize the surface morphologies of PBO fibers and the de-bonding surface morphologies of their composites. Atomic force microscopy (AFM) and contact angle (CA) testing results demonstrated that the surface roughness (Ra) and wettability of PBO fibers increased obviously after Ni(OH)2/NiOOH deposition due to the unique honeycomb structure of the coating. Monofilament pull-out tests showed that the interfacial shear strength (IFSS) of PBO/epoxy composite increased by 46.3%. Moreover, the possible interfacial property enhancing reasons were explored. Thermogravimetric analysis (TGA) and hydrothermal aging tests revealed that PBO-Ni(OH)2/NiOOH had excellent thermal stability and hydrothermal aging resistance. Notably, the Ni(OH)2/NiOOH coating on the fiber surface can be easily reduced to Ni, resulting in a highly conductive PBO fiber. Our design starts from simple chemistry and inexpensive materials, and may offer a versatile and scalable method for fabricating hierarchical reinforcements.

Electrospun nanofiber-reinforced polypropylene composites: Nucleating ability of nanofibers

Electrospun nanofibers of 10 semi-crystalline polymers were obtained. The nucleating abilities of these nanofibers toward isotactic polypropylene (iPP) were investigated. Conventional PTFE and PBO fibers were also examined for comparison. The tested fibers were embedded in the iPP matrix to induce the transcrystalline layer and their nucleating abilities were characterized by optical microscopy. However, due to the limitation of optical resolution the increasing number of iPP nuclei on the tiny electrospun fibers was too difficult to trace for determining the surface nucleating rate. To address this problem, the variation of depolarized light intensity under a constant cooling rate was monitored. The induction temperature (Ti) for fiber-surface nucleation was determined to characterize the nucleating ability of fibers; that is, the higher the Ti, the better the nucleating ability of the fibers. Our results indicated that the nucleating ability of fibers can be classified into four categories: strong for the PBT and PTFE fibers; medium for the PTT, PET, iPS, PVA, PA6 and PBO fibers; weak for the sPS fiber; and inactive for the PA46, and PMP fibers. All active fibers induced the α-form of iPP crystals except the iPS fibers, which induced the β crystals through the α-to-β growth transition mechanism.

Mechanical reinforcement of PBO fibers by dicarboxylic acid functionalized carbon nanotubes through in situ copolymerization

An optimized interfacial interaction in CNTs & PBO copolymer fibers was put into effect via dicarboxylic acids functionalized CNTs, which results in well dispersed, high reactivity and efficient load transfer between CNTs fillers and PBO matrix.

キンク損傷がPBO繊維の疲労破壊挙動に及ぼす影響

キンク損傷がPBO繊維の疲労破壊挙動に及ぼす影響

Tensile Strength of Poly-p- Phenylene Benzobisoxazole (PBO) Fiber with Kinking Damage

In this study, tensile strength of PBO fiber with kink band was investigated in single fiber (monofilament) tensile tests. The kink band was introduced by the wrapping fiber bundle to the steel bars with several diameters. Weibull analysis on the obtained tensile strength was carried out to discuss the strength in the on region of kink band. It was found that the tensile strength of PBO fiber decreases with the increase in kink band density. Kink bands act as defects that degrade the tensile strength. A Weibull analysis demonstrated that the concept of effective volume explains the tensile strength of PBO fiber. The reduction of tensile strength at low bar diameters from the appearance of kink bands is not due to changes in strength near the kink bands but rather to the increase in kink band density.

キンク損傷がPBO繊維の引張強度特性に及ぼす影響

キンク損傷がPBO繊維の引張強度特性に及ぼす影響

폴리히드록시아미드/CNT 나노복합체 섬유에 대한 연구

Polyhydroxyamide (PHA) was synthesized by low-temperature solution polymer- ization of 3,3'-dihydroxybenzidine and terephthaloyl chloride. Then, pure PHA and PHA nanocomposite fibers, including multi-walled carbon nanotube (MWNT), were prepared by a wet-spinning process. The structural characteristics, thermal properties, and mechani- cal performances, such as tensile strength, initial modulus, and compressive strength, of the PHA fibers were investigated using FT-IR, TGA, and a tensile testing machine. The TGA results show that the PHA fiber has excellent thermal stability at high temperatures and can undergo thermal cyclization to yield PBO fiber. The tensile mechanical properties of PHA nanocomposite fibers were better than those of pure PHA fiber, and they were improved on increasing the MWNT content. The highly improved mechanical properties of the nanocomposite fibers are thought to be related to the strong interfacial interactions between the PHA matrix and MWNT.

Mechanical properties of FRCM using carbon fabrics with different coating treatments

The use of composite materials for repair and retrofit of structures has become a common use among the engineering community. Fabric Reinforced Cementitious Matrix (FRCM) is a composite material specifically designed for masonry and concrete rehabilitation and is becoming a viable alternative to FRP, whenever the project conditions do not allow the use of organic polymer based composites. FRCM is usually constituted by one or multiple plies of dry fabrics (carbon, glass, aramid, basalt or PBO fibers) embedded into an inorganic matrix. If a polymer is used to either cover or bond the fabric strands, such polymer does not fully penetrate and impregnate the fibers as it would for FRP. The purpose of this research work is to study how different types and amounts of organic coatings applied to a carbon fabric could affect the bond behavior between fabric and mortar. The effectiveness of coating treatments was studied by means of direct tensile, pull-off and shear-bond double-lap tests. Experimentation was carried out on different combinations of fabrics and mortars, by varying the levels of pre-impregnation of the fabric during its manufacturing. In addition, the use of a quartz sand layer applied to the fabric after impregnation was investigated. Experimental evidence shows a promising enhancement of the bond between fabric and matrix and, therefore, of the entire system even with the use of low percentages of resin, depending on the type of mortar used.

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.

Comparison of effects on PBO fiber by air and oxygen dielectric barrier discharge plasma

Poly(p-phenylene-2,6-benzobisoxazole) (or PBO) fibers were treated with dielectric barrier discharge plasma (DBD) using air and oxygen gas, respectively. The treatment time was set as 12s, plasma power density of air-DBD plasma was used as 10 W/cm3, 20 W/cm3, 30 W/cm3, 40 W/cm3 and 50 W/cm3. The interlaminar shear strength (ILSS) between PBO fiber and bismaleimide (BMI) resin was improved by air-DBD plasma treatment and reached its highest value 57.1 MPa at 12s, 30 W/cm3. Meanwhile, the ILSS of PBO/BMI composites treated by oxy-DBD plasma at the same condition was only 51.2 MPa. The chemical and physical changes of PBO fiber caused by plasma were studied by X-ray photoelectron spectroscopy (XPS) and atomic force microscopy (AFM), respectively. The surface polarity and reactivity of PBO fiber were enhanced by plasma treatment, the surface was roughened as well. Otherwise, the single fiber tensile strength of PBO fibers were studied, proper parameters by plasma would not decline the mechanical property evidently. These phenomena were considered as the reason of the improved ILSS. Furthermore, the water absorption of PBO/BMI composites was tested, the composites showed good humid resistance and the plasma treatment declined the water absorption of PBO/BMI composites.

New disperse dyeing method of poly(p-phenylene benzobisoxazole) fiber pretreated with polyphosphoric acid

Poly(p-phenylene benzobisoxazole) fiber is considered as a high-performance fiber because of its high strength and excellent thermal and chemical stability. It has been used in industrial reinforcement, body armor and military camouflage. But the application of poly(p-phenylene benzobisoxazole) fiber used for protective clothing is limited because it is difficult to dye with conventional dyeing processes. In this work, a carrier dyeing method with disperse dyes was first used to dye the fiber after a pretreatment with polyphosphoric acid. The effects of the carrier structure and dyeing conditions on the color strength of dyed samples were investigated. In addition, the crystallinity and orientation degree of the poly(p-phenylene benzobisoxazole) fibers before and after pretreatment with phthalimide and benzyl benzoate were measured by X-ray diffraction and velocity-oriented test, respectively. The results suggested phthalimide and benzyl benzoate, as carrier, could effectively promote disperse dyeing of the PBO fiber pretreated with polyphosphoric acid. Meanwhile, the optimal conditions for the carrier dyeing were obtained, that is, concentration of carrier 4%, dyeing temperature 150 °C and time 120 min. By way of the carrier dyeing, the K/S value of dyed sample and the percentage of dye exhaustion were greatly improved, while the crystalline structure and orientation degree of the pretreated samples hardly changed. Furthermore, the decreases of the tensile strength and the limiting oxygen index of dyed poly(p-phenylene benzobisoxazole) sample were very little, and the color fastness was also satisfactory.

Chemical and physical modification of poly(p-phenylene benzobisoxazole) polymers for improving properties of the PBO fibers. I. Ultraviolet-ageing resistance of PBO fibers with naphthalene moiety in polymer chain

In purpose of improving the poor ultraviolet-ageing resistance of poly(p-phenylene benzobisoxazole) (PBO) fiber, a series of modified PBO were synthesized in poly(phosphoric acid) (PPA) by introducing 2,6-naphthalene groups into PBO molecules. 2,6-naphthalenedicarboxylic acid (NDCA) was selected as a comonomer. It was found that there was little effect of NDCA on the molecular weight of PBO. PBO and PBO-NDCA fibers were prepared through dry-jet wet spinning. The PBO-NDCA fibers exhibited much improved UV-ageing resistance by showing less reduction in tensile strength after same amount of UV exposure, and the UV-ageing resistance increased with increasing of NDCA content. It was notable that the fiber diameter was significantly decreased in proportion to UV exposure time, which implies a kind of etching was occurred on the surface of the fibers by UV irradiation. It was also found that the degree of UV etching in fibers decreased with increasing of NDCA content. Surface morphology of the fibers before and after UV irradiation was observed using FE-SEM and AFM.

Preparation of polybenzoxazole nanofibers by a downsizing process

Poly(p-phenylene benzobisoxazole) (PBO) nanofibers were prepared from commercially available PBO fiber by a simple downsizing process for the first time.

Preparation of graphene/poly(p-phenylenebenzobisoxazole) composite fibers based on simultaneous zwitterion coating and chemical reduction of graphene oxide at room temperature

Graphene reinforced PBO fibers were fabricated based on zwitterion-coated rGO sheets, and a widely applicable mechanism for the acid-catalyzed reduction of GO was proposed.