Poly P-phenylene Benzobisoxazole Research Articles

Ablation properties of SiC-reinforced PBI resin matrix composites under high-energy continuous laser ablation

In this work, poly-p-phenylene benzobisoxazole (PBO) fibers reinforced polybenzimidazole (PBI) resin-based laser ablation composites (thickness = 5 mm) with different SiC contents were prepared. SiC/PBI/PBO composites exhibited good mechanical properties, excellent thermal stability and laser ablation properties. The laser ablation properties and ablation mechanism of the composites were investigated using a high-energy continuous-wave laser (30 MW·m−2). Increasing the SiC content led to increase in composites density, while decreasing the bending performance of the composites. However, it improves the mass and linear ablation rates, resulting in an overall improvement in ablation properties. At a SiC content of 70 %, the composite exhibited a mass loss of 8.2 %, a mass ablation rate of 9.2 mg·s−1, and a linear ablation rate of 0.11 mm·s−1. The ablation process of SiC/PBI/PBO composites was delineated into pre-ablation and post-ablation stages, with the ablated composites divided into the ablation center, transition region, and outer region based on morphological characteristics. After ablation, numerous white hollow SiO2 spheres and SiO2 protective layers were formed in the ablation centers, the transition regions were deformed and cracked, while the outer region remained unscathed.

Analysis Model for Damage of PBO Composite Laminate Target by High-Velocity Projectile Penetration

Poly-p-phenylene benzobisoxazole (PBO) fiber is a new fiber with high ballistic performance, such as excellent heat and flame resistance and super mechanical properties. Consequently, increasing attention has been paid to its applications in the field of ballistic resistance. To identify the damage mechanism of PBO composite target caused by the high-velocity penetration of cylindrical projectiles and the energy conversion mode involved in the penetration process, this paper constructs a target damage engineering analysis model using the energy method in combination with stress wave propagation and projectile motion analysis. The residual velocity of the steel cylindrical projectile after perforating a PBO composite laminate is measured through ballistic tests, and it is compared with the value predicted by the analysis model. Comparison results show that the predicted value by the model is in good agreement with the measurement, with an error of less than 2.6%, thereby proving the validity of the constructed analysis model.

Thermal conductivity enhancement of carbon fiber/epoxy composites via constructing three-dimensionally aligned hybrid thermal conductive structures on fiber surfaces

Owing to high graphitization degree, polyacrylonitrile (PAN)-based high modulus carbon fiber (HMCF) can not only be used as the general structural reinforcement for advanced composites, but also be applied to improve the thermal conductivities (TC) of polymer composites. However, the enhancement of through-thickness TC of composites remains extremely challenging due to fiber anisotropy and the lack of continuous thermal conductive path among CFs. In the present work, three-dimensional (3D) hybrid thermal conductive structures were constructed onto PAN-CF surfaces to prepare HMCF/epoxy composites with high through-thickness TC. In details, crosslinked high thermal conductive Ni/CNT hybrid network was firstly electrodeposited onto HMCF surfaces, which also provided abundant channels for the impregnation of easily graphitized poly-p-phenylene benzobisoxazole (PBO)/graphene oxide (GO). The freeze-drying assisted grafting of 3D-oriented PBO/GO and high-temperature heat treatments were further conducted to create the 3D graphite structures onto CFs. The interconnected Ni/CNT networks with 500 nm thickness and 3D aligned PBO-graphite bridging structures with an average thickness of 1 μm contributed to the formation of efficient heat conduction pathways along the through-thickness direction. Additionally, high-temperature treatment had been proven critical to effective heat conductions. Especially, PAN-CF with the 3D hybrid thermal conductive structures treated at 2100 °C (named CNC@PG-2100) exhibited superior TC, and the maximum TC value of CNC@PG-2100 reinforced composites reached 5.39 W/(m‧K) at the CF loading of 55%, which improved by 573% compared to that of composites reinforced by untreated PAN-CFs (0.94 W/(m‧K)).

Radiation effect on stability and interfacial property of PBO fibers through high energy electron beam

Poly-p-phenylene benzobisoxazole (PBO) fibers have been studied and applied in many extreme environments owing to their excellent physical, mechanical properties and great chemical inertness. Here, radiation effect on PBO fibers is investigated through high energy electron beam with a high adsorbed dose up to 100 MGy. Changes of structure, mechanical strength, molecular weight and interfacial property are investigated in detail. It can be found that the structure and mechanical strength do not change obviously. Results of XPS and relative viscosity retention rate show a high radiation resistance of PBO fibers at below 10 MGy. Though PBO fibers can be degraded under over 50 MGy in a certain degree, the relative viscosity retention rate is still over 85% even at the absorbed dose of 100 MGy. Results of optical contact angle and interfacial shear strength of fiber/epoxy composite indicate the interfacial reaction activity decreases under 100 MGy. Therefore, it can be inferred that PBO fibers show a high radiation stability and an increasing trend of the interfacial inertness with the increase of absorbed dose. Through this work, it can provide references for PBO fibers application in the extreme environment.

Pressure-bearing performance of sliding poly-p-phenylene benzobisoxazole-rope-reinforced spherical composite envelope structures

Stratospheric airships require a lightweight envelope to contain lighter-than-air (LTA) buoyancy gas, making the lightweight design and pressure-bearing performance of the envelope structure a key research issue. This paper proposes a structural design scheme for a sliding poly-p-phenylene benzobisoxazole (PBO) fiber-rope-reinforced spherical envelope. The aims were to reduce envelope weight and improve pressure-bearing performance while solving the challenges of envelope structural strength. Two types of spherical envelope structures were constructed from Vectran fabric with PBO rope placed in various positions for reinforcement, and subjected to inflatable burst tests. Strain in the seam tape and envelope gores were measured by digital image correlation. A refined envelope structure model was established to simulate the bursting process with consideration of the cutting pattern effect and the mechanical properties of the weld seams. Comparison of the simulation and test results, combined with observations of the tear textures of damaged envelopes, enabled the determination of failure positions. The envelope material at the failure point was disassembled and the micromorphology and microstructure of the bearing layer were observed by scanning electron microscopy (SEM). The process and characteristics of damage origination, propagation, and collection in the envelope material are explained, and the stress behavior and state of the damage positions are analyzed. Based on the study of the mechanical behavior at the failure position, design suggestions for PBO-rope-reinforced spherical envelopes are provided. A strength criterion to incorporate tensile–shear coupling is proposed, which bridges the gap between the uniaxial tensile strength (UTS) and biaxial tensile mechanical properties of the envelope structure.

Covalently modified and hierarchically structured corn-like BNNs@BT/benzoxazole composites with enhanced dielectric properties over an ultra-wide temperature range

Polymer dielectric material is widely used in pulsed power technology and high-energy weapon systems. However, enhanced dielectric constant of polymer is accompanied by suppressed breakdown strength with the addition of dielectric ceramic. Herein, we report an efficient method to prepare functional corn-like hybrids which consist of BaTiO3 nanowires (BT) and BNNs nanosheets based on surface modification and high temperature ceramization. It is demonstrated that the outer BNNs not only optimizes the intrinsic dielectric difference matching, but also effectively suppress the loss caused by carrier migration. Especially, an increasement for operating temperature is achieved with the help of the poly-p-phenylene benzobisoxazole (PBO). Under 4 wt% filling, the composites have the highest discharged energy density (Ud = 2.24 J cm−3). Meanwhile, it also has high charge and discharge efficiency (η = 85 %) and an ultra-wide temperature dielectric stability (25 ℃-200 ℃). This work provides a promising dielectric nanocomposite candidate for high temperatures applications.

Dynamic Mechanical Properties of Several High-Performance Single Fibers.

High-performance fiber-reinforced composites (FRCs) are widely used in bulletproof structures, in which the mechanical properties of the single fibers play a crucial role in ballistic resistance. In this paper, the quasi-static and dynamic mechanical properties of three commonly used fibers, single aramid III, polyimide (PI), and poly-p-phenylenebenzobisoxazole (PBO) fibers are measured by a small-scale tensile testing machine and mini-split Hopkinson tension bar (mini-SHTB), respectively. The results show that the PBO fiber is superior to the other two fibers in terms of strength and elongation. Both the PBO and aramid III fibers exhibit an obvious strain-rate strengthening effect, while the tensile strength of the PI fiber increases initially, then decreases with the increase in strain rate. In addition, the PBO and aramid III fibers show ductile-to-brittle transition with increasing strain rate, and the PI fiber possesses plasticity in the employed strain rate range. Under a high strain rate, a noticeable radial splitting and fibrillation is observed for the PBO fiber, which can explain the strain-rate strengthening effect. Moreover, the large dispersion of the strength at the same strain rate is observed for all the single fibers, and it increases with increasing strain rate, which can be ascribed to the defects in the fibers. Considering the effect of strain rate, only the PBO fiber follows the Weibull distribution, suggesting that the hypothesis of Weibull distribution for single fibers needs to be revisited.

Analytical Approach and Numerical Simulation of Reinforced Concrete Beams Strengthened with Different FRCM Systems.

Fabric-reinforced cementitious matrices (FRCMs) are a novel composite material for strengthening structures. Fabric contributes to tying cross-sections under tensile stress. The complexity of the interfaces between the fabric and the matrix does not allow having a simple and accurate model that enables practitioners to perform feasible calculations. This work developed an analytical approach and a numerical simulation based on the reduction of FRCMs’ strength capabilities under tensile stress states. The concept of effective strength was estimated for different types of fabrics (basalt, carbon, glass, poly p-phenylene benzobisoxazole (PBO), and steel) from experimental evidence. The proposed models calculate the ultimate bending moment for reinforced concrete (RC) structures strengthened with FRCMs. The numerical models performed simulations that reproduced the moment–deflection curves of the different tested beams. Steel fabric showed the highest contribution to strength (78%), while PBO performed the worst (6%). Basalt and carbon showed irregular contributions.

Flexural and Tribological Properties of Polyimide Composites Reinforced by Poly-p-Phenylenebenzobisoxazole Fibers with Different Content

In this paper, the tribological property of polyimide (PI) resin was improved by adding poly-p-phenylenebenzobisoxazole (PBO) fibers. The effects of PBO fiber volume fraction were studied by mechanics and tribology tests. The fracture and wear surfaces of PBO/PI composites were investigated by using scanning electron microscopy (SEM). The measurement showed that the flexural properties of composites reinforced by 10 vol% PBO fibers were lower than pure PI resin. With the increase of PBO fiber content, the flexural strength was first increase and then decrease. The frictional coefficient and wear rate of the PBO/PI composites varied with the variety of fiber content, and the optimum parameter was obtained at 20 vol%. The dominant wear mechanism and friction process were discussed on the basis of microscopic morphology analysis of wear surface of PBO/PI composite and the counterpart.

Corrosion degradation behavior of PBO fibers under strong inorganic acid

Known as the super fiber of the twenty-first century, poly-p-phenylenebenzobisoxazole (PBO) fibers exhibit outstanding strength and modulus, fire and heat resistance, which are superior to those of poly-p-phenylene terephthalamide fiber. However, the poor resistance of acid corrosion is regarded as a fatal weakness, which restricts its application in complicated chemical environment. In present work, PBO fibers were exposed in strong acid solutions under different conditions, and then, surface morphology was observed by optical microscopy and scanning electron microscopy. Substantial changes in functional groups were investigated by Fourier-transform infrared (FTIR) spectroscopy, as well as changes in crystalline structure using differential scanning calorimetry (DSC) and thermal stability using thermogravimetric analysis (TGA). After treatment by H2SO4 and HNO3 solution, the strength of the fibers declines typically, while the modulus increases. It is attributed to the formation of N–H bonds in the vicinity of 3410.0 cm−1 confirmed by FTIR spectra. Hydrogen bonds, derived from N–H bonds, increase the thermal degradation temperature from 716.4 °C (untreated) to 725.6 °C (treated by H2SO4), shown in TGA curves. HNO3 treatment is more destructive than that of H2SO4. There exist longitudinal corrosion cracks after treatment by HNO3 solution. Furthermore, HNO3 solution penetrates into crystalline region and destroys the ordered crystal structure of PBO fibers demonstrated by DSC results.

Probabilistic model for structural mechanics of fiber bundle and its application to PBO fiber

The stress-strain relationship of single fiber and fiber bundle based on the different strain distribution functions of single fiber, including rectangular distribution, normal distribution and Weibull distribution, was studied. Strain distribution of Poly-p-phenylene benzobisoxazole (PBO) single fiber was measured, and the stress-strain curve of PBO fiber bundle can be deduced from the different strain distribution functions of single fiber. The results showed that normal distribution was closer to the measured strain distribution of PBO single fiber than rectangular distribution, and the stress and strain values of PBO fiber bundle estimated by the normal distribution were closer to the measured stress and strain values of PBO fiber bundle. In addition, the stress and strain values of PBO fiber bundle estimated by Weibull distribution were between those of rectangular distribution and normal distribution. In a word, the normal distribution can be effectively used to predict the fracture process of PBO fiber bundle.

Pull-off adhesion strength of poly-p-phenylene benzobisoxazole (PBO) – reinforced timber

Pull-off adhesion strength of poly-p-phenylene benzobisoxazole (PBO) – reinforced timber

Friction and Wear Behavior of Polyimide Composites Reinforced by Surface-Modified Poly-p-Phenylenebenzobisoxazole (PBO) Fibers in High Ambient Temperatures.

(1) In order to improve the properties of antifriction and wear resistance of polyimide (PI) composite under high temperature conditions, (2) 3-Aminopropyltriethoxysilane (APTES) and Lanthanum (La) salt modifications were employed to manufacture poly-p-phenylenebenzobisoxazole (PBO)/PI composites with different interface properties. The representative ambient temperatures of 130 and 260 °C were chosen to study the friction and wear behavior of composites with different interface properties. (3) Results revealed that while both modification methods can improve the chemical activity of the surface of PBO fibers, the La salt modification is more effective. The friction coefficient of all composites decreases with the increase of sliding velocity and load at two temperatures, and the specific wear rate is increases. Contrary to the situation in the 130 °C environment, the wear resistance of the unmodified composite in the 260 °C environment is greatly affected by the sliding velocity and load, while the modified composites are less affected. Under the same test parameters, the PBO–La/PI composite has the lowest specific wear rate and friction coefficient, and (4) La salt modification is a more effective approach to improve the properties of antifriction and wear resistance of PI composite than APTES modification in high ambient temperatures.

Interfacially enhancement of PBO/epoxy composites by grafting MWCNTs onto PBO surface through melamine as molecular bridge

Melamine and multi-walled carbon nanotubes (MWCNTs) were grafted onto Poly-p-phenylene benzobisoxazole (PBO) fiber surface effectively via layer-by-layer method. Both of them have been chemically bonded as fourier transform infrared spectroscopy (FTIR) confirmed. Grafting melamine overcame the inertness of PBO surface. Ammoniation was processed on PBO surface through grafting melamine so that the MWCNTs could be grafted onto PBO surface. Scanning electron microscopy (SEM) images indicated that melamine used as molecular bridge could increase MWCNTs’ quantity on PBO surface. X-ray photoelectron spectroscopy (XPS) results revealed the variation of chemical composition of PBO surface. Test of interfacial shear strength (IFSS) and tensile strength indicated the great mechanical properties of modified PBO fibers when combining with epoxy resin. Furthermore, whole reaction was processed under a simple condition. Results in this research also promised a potential method to modify PBO surface.

Investigation of reactivity and biocompatibility poly-p-phenylene benzobisoxazole fiber grafted hyperbranched polysiloxane

Abstract Hyperbranched polymer was synthesized via Michael addition. The biocompatible peptide was incorporated into hyperbranched polymer. As a result, they are promising candidates for cell adhesive molecular. Herein, we developed a strategy for synthetic hyperbranched polymer based on polysiloxane. A poly-p-phenylene benzobisoxazole (PBO) fiber as substrate, polyhedral oligomericsilsesquioxane (POSS) as core, prepared hyperbranched polymer was grafted to surface of PBO fiber. Experiment results show that hyperbranched polysiloxane was uniformly grafted onto the PBO fiber and significantly increase the surface activity. In addition, the functional PBO fiber as substrate presents biocompatible based on activity peptide. Hela cell selectively adhered on surface functional PBO fiber with activated peptide spots. Thus, the results of this study further extend the application of engineered polymer materials to cell biology.

Preparation of poly-p-phenylenebenzobisoxazole (PBO) fibrillated pulp and dielectric properties of carbon fiber/PBO wet-laid nonwoven fabric

A method to prepare a kind of wet-laid nonwoven fabric that can be used in microwave absorbing honeycomb is proposed. It was prepared through a papermaking process with carbon fiber (CF) and poly-p-phenylenebenzobisoxazole (PBO) fibrillated pulp. Fibrillated PBO pulp has a large surface area and lots of micro-fibrils which is beneficial for the uniformity and mechanical strength of the wet-laid nonwoven fabric. The electromagnetic properties and absorbing performances of the wet-laid nonwoven fabric with different content of CF were compared. The results showed that the complex permittivity increased when the content of the CF increased, and then decreased when the content was higher than 10 wt%. The resistivity measured by four probe testers decreased with the increase of the content of CF. Calculated by the measured complex permittivity and permeability, the CF/PBO wet-laid nonwoven fabric had a lowest reflection loss of -27.60 dB at a content of 20 wt%, with an optimum thickness of 1.72 mm.

キンク損傷を有するPBO繊維の疲労強度特性

In this study, fatigue strength properties of PBO (Poly-p-Phenylene Benzobisoxazole) fiber with kinking damage were investigated in monofilament fatigue tests. Two types of the PBO fibers were used in the experiment. One was the conventional type (AS fiber). The other was high-modulus type (HM fiber) with a higher crystal orientation than AS fiber. Kinking damages was created on surface of virgin fiber by winding bundle fibers to steel rod set to 0.625 mm. Load-controlled fatigue tests were carried out using a sinusoidal load with frequency 10 Hz and stress ratio of R = 0.5, and the load cell capacity was 10 N. It was found that fatigue strength with kinking damage was lower than that without kinking damage in neither AS fiber and HM fiber. Fatigue strength decrease of AS fiber and HM fiber with kinking damage in a low cycle area was larger than that in a high cycle area. The fatigue fracture of PBO fiber with kinking damage presented the different aspect at a high cycle area and a low cycle area in neither AS fiber and HM fiber.

Novel Fine Structures in poly-p-phenylenebenzobisoxazole (PBO) Fibers Induced by Water Vapor, Hot Water, and Nonaqueous Coagulation III. Random and Radial Preferential Orientations of the Crystal b-Axis

ABSTRACTThe preferential orientation of the crystal b-axis in PBO fibers was estimated from the diffraction intensities of micro-focus X-ray diffraction patterns. The observed X-ray diffraction intensities were compared with the calculated scattering volume in the fiber, with the crystal planes of the (010) and () giving coherent X-ray diffraction intensities on the detector. The calculation for the scattering volume was carried out based on an extended method of a previously-proposed two-phase model, which was utilized to predict the scattering volume by searching for the suitable crystal planes in the fiber according to Bragg's Law. Agreement was achieved between the predicted and measured intensity profiles for the (200) and () diffraction intensity profiles.

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

ABSTRACTAs 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.

An experimental study on the influence of composite materials used to reinforce masonry ring beams

For historic masonry constructions the out-of-plane wall behavior is critical to seismic performance. Because the main cause of out-of-plane collapses is the wall-to-wall level of connection, the application of a reinforced concrete (RC) ring beam at the eaves level of historic masonry buildings is an effective method to prevent an out-of-plane mechanism of a wall panel. However this effective reinforcing method presents some drawbacks. In order to address this, this paper describes the problems associated with this “traditional” reinforcing method and introduces a new retrofitting technique for historic masonry buildings by realizing a new type of ring beam made of recycled old stones or bricks reinforced at the bed joints with glass-fiber sheets, GFRP (Glass Fiber Reinforced Polymer) grids or/and PBO (polybenzoxazole: poly-p-phenylene benzobisoxazole) cords. An experimental investigation has been carried out on 10 full-scale rubble-stone or brickwork masonry ring beams. The testing included the use of composite materials inserted into the mortar joints during the fabrication phase of the beams and pinned end conditions (four-point bending configuration). Beams were reinforced with different composite layouts.