Polyimide Fibers Research Articles

Optical fiber multiparameter sensor for real‐time monitoring of thermoplastic composites during in situ consolidation process

AbstractTemperature and strain are important parameters in the in situ consolidation process of thermoplastic composites and have been monitored based on optical fiber Bragg gratings. A special polyimide fiber grating (PFBG) is used in this article. PFBG can monitor temperatures up to 400°C and strains up to 40,000 με. The wavelengths of the PFBGs are obtained by wavelength demodulation system and fast digital signal processing with field programmable gate array. Temperature and strain in auto fiber placement process of thermoplastic composites are monitored accurately according to wavelengths. During the whole consolidation process, temperatures have been monitored with the accuracy of 0.1°C in the range of 100–250°C and strains have been monitored with the accuracy of 1 με in the range of −250 to 500 με. The validity and correctness of the results have been validated by the thermocouple and the strain gauge.

Effect of waterborne epoxy resin sizing on the surface and properties of high‐strength‐high‐modulus polyimide fibers

AbstractTo improve the interface adhesion between high‐strength‐high‐modulus polyimide (PI) fibers and epoxy resin (EP) matrix, waterborne epoxy resin (WEP) sizing agents are used to modify the surface of PI fibers. The sizing treatment of PI fibers was carried out by the self‐made sizing machine, and the effect of WEP sizing concentrations on the structure and properties of PI fibers were discussed in detail. The surface roughness, activated carbon percentage, and surface energy of WEP‐sized PI fibers increased with increasing WEP sizing agent contents. While, the mechanical and thermal properties of WEP‐sized PI fibers decreased slightly with the increment of WEP sizing agent concentrations. The optimum WEP sizing concentration was recognized to be 2 wt%. The interfacial shear strength and the interlinear shear strength values of PI fibers and epoxy resin (PI/EP) composites were improved by 175.22 and 25.31%, respectively. Moreover, the mechanism of surface characteristic improvement with WEP sizing treatment were proposed, contributing to the enhancement of mechanical interlocking and chemical interaction between fibers and matrix.

Enhanced Impact Properties of Hybrid Composites Reinforced by Carbon Fiber and Polyimide Fiber.

A series of hybrid fiber-reinforced composites were prepared with polyimide fiber and carbon fiber as the reinforcement and epoxy resin as the matrix. The influence of stacking sequence on the Charpy impact and flexural properties of the composites as well as the failure modes were studied. The results showed that hybrid fiber-reinforced composites yielded nearly 50% increment in Charpy impact strength compared with the ones reinforced by carbon fiber. The flexural performance was significantly improved compared with those reinforced solely by polyimide fibers and was greatly affected by the stacking sequence. The specimens with compressive sides distributed with carbon fiber possessed higher flexural strength, while those holding a sandwich-like structure with carbon fiber filling between the outer layers displayed a higher flexural modulus.

Hollow Fiber Polyimide Membranes Prepared in a Triple Orifice Spinneret: Effect of a Reduced Water Activity in the Bore Fluid on the Gas Separation Performance.

Polyimide-based hollow fibers were spun using a triple orifice spinneret in order to apply them in gas separation. The membrane structure was tailored producing a porous external layer and a thin internal skin layer, that controlled the gas transport. The measurement of gas permeation rates and the morphological analysis were combined to obtain information on the performance of the membranes. The aim was to tune the inner top layer and investigate the role of the bore fluid on the gas permeation properties of the membranes. The bore fluid composition was explored by using water mixtures containing the solvent used for preparing the dope solution or a salt in order to reduce the water activity in the inner coagulant, but also a low amount of a crosslinker for improving the gas selectivity. The change of the dope flow-rate was also analyzed. At moderate dope flow-rates, the use of a saline water solution as bore fluid is more effective in enhancing the membrane gas selectivity with respect to a bore fluid containing certain amounts of solvent. This option represents a green approach for the preparation of the membrane. The behavior of the prepared hollow fibers over time (physical aging) in gas permeation was discussed.

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.

Influences of different imidization conditions on polyimide fiber properties and structure

AbstractIn the present work we prepared co‐polyimide (PI) fibers with excellent mechanical and dielectric properties by the wet‐spinning method. The co‐PI fiber exhibited high mechanical property with a tensile strength of 2.61 GPa and modulus of 86.7 Gpa as well as a low dielectric constant and a dielectric loss factor of 2.7463 and 0.00793 at 10 GHz, respectively. The relationship between the properties and the microstructure of co‐PI fibers after heat‐drawing was investigated. The results revealed that the hydrogen‐bond associations and the microvoids structure were highly affected by imidization conditions. Both the formations of the hydrogen‐bond associations and the evolution of microvoids were attributed to the change in tensile strength. Furthermore, the fibers prepared at proper conditions possessed fewer surface defects as well as homogeneous inner structure. Our work demonstrates the structure–property relationship in annealed PI fibers, which may provides a new avenue to access high‐performance PI fibers.

Performances of novel poly(diaryloxyphosphazene) based heat shielding materials with various fibrous reinforcements

AbstractElastomeric heat shielding materials (EHSMs) are necessary to protect combustion chambers of solid rocket motors during their working. Poly(diaryloxyphosphazene) (PDPP) elastomers own inherent thermal stability and flame retardancy because the backbone of alternating phosphorus and nitrogen atoms can be a novel promising polymer matrix toward EHSMs. The present study deals with the development of a novel PDPP based EHSMs with several different fibrous reinforcements, including Kevlar, polyimide, and carbon short fibers. It is found that PDPP/Kevlar composites show outstanding tensile strength and ablation resistance because of their strong interfacial bonding between matrix and fibers which benefits from the possible network of intermolecular hydrogen bonds. PDPP/carbon composites produce a compact charred layer due to their high char yields of carbon fibers. These results improve the understanding of the role of polyphosphazenes with different kinds of fibers on ablation mechanisms, which enable the possibility to exploit intrinsic properties of polyphosphazenes.

Structure‐Property Relationship of Polyimide Fibers with High Tensile Strength and Low Dielectric Constant by Introducing Benzimidazole and Trifluoromethyl Units

AbstractCopolyimide (co‐PI) fibers with high strength and low dielectric constant are synthesized and prepared by introducing 2,2′‐bis(trifluoromethyl)‐4,4′‐diaminobiphenyl (TFMB) and 2‐(4‐aminophenyl)‐5‐aminobenzimidazole (BIA) diamines into the rigid backbones. The resultant fibers not only exhibited excellent mechanical properties with a tensile strength of 2.627 GPa and an initial modulus of 96.786 GPa, but also possessed a dielectric constant as low as 2.433 at 10 GHz. The existence of intermolecular hydrogen‐bonding interaction is confirmed by Fourier transform infrared spectroscopy, which has been considered as the leading factor responsible for the significantly improved mechanical properties of the co‐PI fibers. 2D wide‐angle X‐ray diffraction (2D WAXD) is adopted to investigate the variation on the aggregation structure of PI fibers after the incorporation of fluorine group. The fibers with more TMFB content possessed a higher orientation degree together with a larger free volume fracture due to the combined effects of enhanced flexibility and the volume effect of trifluoromethyl groups. Meanwhile, the prepared PI fibers exhibit a 5% weight loss temperature ranging from 543 to 533 °C in the nitrogen atmosphere and a glass transition temperature ranging from 334 to 317 °C, revealing high thermal stability of co‐PI fibers.

Interlaminar Fracture Behavior of Carbon Fiber/Polyimide Composites Toughened by Interleaving Thermoplastic Polyimide Fiber Veils

Carbon fiber reinforced thermosetting polyimide (CF/TSPI) composites were interleaved with thermally stable thermoplastic polyimide (TPPI) fiber veils in order to improve the interlaminar fracture toughness without sacrificing the heat resistance. Both of the mode I and mode II interlaminar fracture toughness (GIC and GIIC) for the untoughened laminate and TPPI fiber veils interleaved laminates were characterized by the double cantilever beam (DCB) test and end notch flexure (ENF) test, respectively. It is found that the TPPI fiber veils interleaved laminates exhibit extremely increased fracture toughness than the untoughened one. Moreover, the areal density of TPPI greatly affected the fracture toughness of laminates. A maximum improvement up to 179% and 132% on GIC and GIIC is obtained for 15 gsm fiber veils interleaved laminate, which contributes to the existence of bicontinuous TPPI/TSPI structure in the interlayer according to the fractography analysis. The interlaminar fracture behavior at elevated temperatures for 15 gsm fiber veils interleaved laminate were also investigated. The results indicated that the introduction of thermally stable TPPI fiber veils could enhance the fracture toughness of CF/TSPI composites by exceeding 200% as compared to the untoughened one even as tested at 250 °C.

Biocompatibility of Polyimide Fibers with Human Gastric Cells In Vitro

Biocompatibility of Polyimide Fibers with Human Gastric Cells In Vitro

Cure kinetics of a nadic methyl anhydride cured tertiary epoxy mixture

Cure kinetics of a methyl nadic anhydride cured tertiary epoxy (i.e., Diglycidyl ether of bisphenol A, a tetrafunctional epoxy and a fluorine-containing diepoxy), which is potential matrix for a polyimide fiber reinforced composites, were studied using dynamic and isothermal differential scanning calorimeter scans. Results showed that addition of the tetrafunctional epoxy and fluorine-containing diepoxy has negligible effects on the underlying cure mechanisms. Variation of glass transition temperature with extent of cure can be fitted using DiBenedetto equation. The Kamal model coupled with an empirical diffusion factor can adequately model the isothermal cure data. The Kamal model can model the reaction data well before vitrification. However, after vitrification, obvious deviation from Kamal model was observed, which have to be corrected using a diffusion factor. The apparent activation energy obtained from the Kamal model using isothermal data, agrees with that from the advanced isoconversional method, which utilizes the dynamic cure data.

Electrospun polyimide fiber membranes for separation of oil-in-water emulsions

• Fouling is a persistent problem in microfiltration of oil/water emulsions. • Electrospun P84 polyimide membranes separate oil/water emulsions efficiently. • Resistance to fouling is due to the oleophobic character of P84. • Membrane performance is completely regenerated by thermal treatment. The separation of emulsified oils from water represents a significant challenge for water reclamation and clean-up, because such droplets remain suspended for long periods of time. Membrane technology offers a solution to such separations, but its major drawback is the requirement for frequent cleaning to remove foulants, which reduces membrane lifetime and incurs additional economic and environmental costs. To address this shortcoming, we examine the separation performance of fibrous membranes of P84 polyimide, a copolymer known for its thermal stability and chemical resistance, fabricated by electrospinning technology. The P84 membranes were challenged by surfactant-stabilized emulsions of dodecane or motor oil in a constant pressure dead-end configuration. The P84 membranes exhibited moderate oil rejections between 85 and 90%, while subsequent foulant removal by heat treatment restored permeate fluxes to essentially 100% of their original values. A comparison of P84 membranes to other common membrane polymers with respect to robustness against fouling shows that the P84 membranes have some advantages, which we attribute to the oleophobic nature of the P84 membrane, as well as the ease of membrane regeneration. These results indicate that the electrospun P84 membrane is a promising candidate for microfiltration of water contaminated by emulsified oil.

Enhanced high‐temperature tribological performance of PTFE/PI fabric composites by simultaneously introducing PDA/SiO2 hybrid coating and aramid product reinforcements

AbstractSurface modification with polydopamine (PDA)‐based coating is widely used to obtain high performance and build special functions for modified surfaces. Herein, a mussel‐inspired nanohybrid coating (PDA/SiO2) was first co‐deposited onto the polytetrafluoroethylene (PTFE)/polyimide (PI) fabric surfaces via simultaneous polymerization of dopamine and hydrolysis of the tetraethoxysilane (TEOS) in a simple one‐pot method. This nanohybrid coating could afford the hybrid‐fabric sufficient active groups, improved surface roughness, and wettability without compromising fiber intrinsic strength. As a result, the interfacial bonding strength between fabric and PI resin matrix presented a significant increase as measured by the peeling tests. In addition, aramid pulp and aramid fiber powder were incorporated into the fabric composites to construct synergistic enhancement effects with PI fibers on bearing capacity and wear resistance. Results showed that the fabric@PDA‐TEOS/micro‐powder composites presented the best high‐temperature anti‐wear property resulting from the improved interfacial adhesion strength and carrying capacity of lubricant films.

High-Performance Fibres – A Review of Properties and IR-Spectra

High-performance fibres are fibre materials that exhibit at least one extraordinary property compared to conventional fibre materials. That extraordinary property is frequently related to excellent fibre stability against certain influences such as fire, heat, chemicals or light. Also, a high mechanical strength is often a property of high-performance fibres. Nevertheless, it should be noted that high-performance fibres exhibit certain weaknesses in addition to their advantages. This review presents a broad overview of the most important high-performance fibres, with a special emphasis on their chemical structure and related infrared spectra (IR-spectra). The categorization of the fibres according to chemical substance classes was performed to make it easy for the reader to find a fibre of interest. The main categories are polyethylene (PE) fibres, polyacrylonitrile (PAN) fibres, polyvinylalcohol (PVAL) fibres, polyester-based fibres, polyamide-based fibres, polyetheretherketone (PEEK) fibres, polyimide (PI) fibres, halogen-containing fibres, polyphenylene sulfide (PPS fibres), resin-based fibres and finally inorganic fibres. Competing materials are also discussed, and structural related materials can be easily identified. In addition to discussing fibre properties and selected applications, one of the main aims is to present a various number of IR-spectra as a tool for structural understanding and to help identify unknown fibres. Here, beside the IR-spectra of high-performance fibres, the reference IR-spectra of common fibres are presented for comparison.

Preparation and properties of high-performance polyimide copolymer fibers containing rigid pyrimidine and benzoxazole moieties with hydrogen bonding

The utilization of 5-amino-2-(2′-hydroxy-4′-aminophenyl)-benzoxazole (HBOA) as third monomer was beneficial for the introduction of OH-type H-bonding into polyimide (PI) matrix through the copolymerization with 2,5-bis(4-aminophenyl)pyrimidine (PRM) and 3,3′,4,4′-biphenyltetracarboxylic dianhydride (BPDA). And high-performance PI fibers were successfully fabricated via the dry-jet wet spinning process. The FTIR spectra confirmed that the strong interactions of intramolecular and intermolecular H-bonding existed simultaneously in PI fibers. Moreover, the glass transition temperatures (Tg) of all fibers were within 276–318 °C, and the temperatures at 5% weight loss (T5%) ranged from 574 °C to 604 °C, revealing the remarkable thermal stability of PI fibers. The two-dimensional wide-angle X-ray diffraction (2D WAXD) results illustrated a U-shaped change in the crystallinity (from 32.1% to 12.2% until 33.4%) of PI fibers with increasing HBOA content, which was also reflected in the density variation of fibers. The two-dimensional small-angle X-ray scattering (2D SAXS) patterns demonstrated that the micro-defects in all co-PI fibers profitably decreased in comparison with those in homo-PI fibers. Furthermore, the orientation factor of fibers presented an improvement from 0.843 to 0.899 after incorporating HBOA moiety. When the molar ratio of PRM/HBOA was 7/3, the co-PI fiber exhibited optimum mechanical properties with tensile strength and modulus as high as 4.15 GPa and 125.93 GPa, respectively. Interestingly, the variation in fiber orientation was in line with the same trend as that of mechanical properties of PI fibers, indicating orientation was also a crucial factor to improve the mechanical properties. The relationship between structure and mechanical property was also investigated.

Freestanding polyimide fiber network as thermally safer separator for high-performance Li metal batteries

A stable and high-performance polyimide (PI) fiber mat was prepared via a facile two-step procedure, electrospinning deposition followed by an imidization process. The PI fiber separator presents higher thermal stability (>300 °C) than the commercial polypropylene (PP) separator (<160 °C). In Li/Cu half-cell configuration, PI fiber separator shows long cycle life performance with a coulombic efficiency of 82% at 0.5 mA cm–2 after 100 cycles and an impedance of 29 Ω. It also showed suppression of sharp Li dendrite growth. While the commercial PP separator delivers a poor coulombic efficiency of 24% after 100 cycles and an impedance of 99 Ω because of the formation of dendritic Li. Moreover, the Li/LiFePO4 full cell with a PI fiber separator exhibits a lower polarization and charge transfer impedance than the commercial PP separator. The PI fibers enhanced the electrochemical cycle performance and stability of the full cells that deliver a charge capacity of 118 mAh g−1 at a C-rate of 0.5 C with a capacity retention of 86% and a coulombic efficiency of > 99% after 200 cycles. Additionally, the multimode calorimetry (MMC) studies under in-situ mode revealed that the freestanding PI fiber separator presents high thermal stability in Li/LiFePO4 full cells.

Green Fabrication of Polyimide Fibers with Phosphate Monoester Network to Reinforce Carbon Nanotube Polymer Composites: Simultaneously improving the Mechanical Properties and Flame Retardancy

To further enhance the reinforcing effect of polyimide (PI) fibers on carbon nanotube polymer composites, in this work, networks of long chains of phosphate monoester (PMOEs) were grown on the surface of PI fibers, and silanized multiwalled carbon nanotubes (Si-MWCNTs) were dispersed into the phenolic resin (PR) matrix. Subsequently, these two interpenetrating networks were entangled tightly at the PI-PMOEs fiber paper/PR matrix by vacuum-assisted wet papermaking technology and impregnation and vacuum curing technology. A novel type of PI-PMOEs fiber-reinforced carbon nanotube polymer composite was prepared. Structural observation and analysis revealed that the fiber surface activity and roughness were improved, resulting in enhanced interfacial adhesion. The Si-MWCNTs at the interface play an anchoring role, which leads to a strong mechanical interlock between the PI-PMOEs fibers and the matrix. Therefore, the generation and propagation of cracks encountered greater resistance, and the mechanical properties of the composites were improved. Compared with the Si-MWCNTs/PR composite with tensile strength of 20.29 MPa and elongation at break of 0.1%, the tensile strength and elongation at break of 80PI-PMOEs/Si-MWCNTs/PR (the basis weight of paper is 40 wt.%) composite are increased to 91.22 MPa and 2.0%, respectively. In addition, a tightly connected fiber "large skeleton" was provided by the PI-PMOEs fiber paper with a uniform pore size distribution. The Si-MWCNTs network and the thermally degraded carbides of the matrix formed a "small skeleton" based on the "large skeleton", resulting in a complete and dense protective barrier layer. The volatilization of pyrolysis products (CO, small-molecule hydrocarbons, aromatic compounds, etc.) was restricted, and heat and mass transfer were suppressed. Finally, the composites exhibited excellent flame retardancy.

Multiple hydrogen bonding self-assembly tailored electrospun polyimide hybrid filter for efficient air pollution control

Air pollutions are extremely serious threats to human health and the functional hybrid filter is able to remove complicated pollutants with great potential. However, the stable structure design of hybrid filter to provide efficient filtration and adsorption performance for high temperature applications still remains a challenge. In this study, electrospun polyimide (PI) based hybrid filter was fabricated via multiple hydrogen bonding self-assembly for high-temperature air purification. In particular, Octa(amino-propylsilsesquioxane) (POSS-NH2) was utilized as “bridge” for the surface activation of PI fiber, and then amino-functionalized Zeolitic Imidazolate Framework-8 (NH2-ZIF-8) nanocrystals were anchored on the fiber surface through hydrogen bonding. On account of the synergistic effect of the interception effect of fibers and the electrostatic interaction of NH2-ZIF-8 nanocrystals, the as-obtained PI-POSS@ZIF hybrid filter possessed excellent filtration performance with a high PM0.3 removal efficiency of 99.28% and a low pressure drop of 49.21 Pa at high temperature of 280 °C. Moreover, due to the massive micropore structure, rich open metal sites and functional groups of NH2-ZIF-8, the hybrid filter exhibited prominent VOCs adsorption performance with adsorption capability of 89.95 mg/g for formaldehyde.

Understanding the self-polymerization mechanism of dopamine by molecular simulation and applying dopamine surface modification to improve the interfacial adhesion of polyimide fibers with epoxy resin matrix

The object of this paper is to interpret the self-polymerization mechanism of dopamine by molecular simulation and use dopamine polymerization to modify the surface properties of polyimide fibers for improving its interfacial adhesion strength with the epoxy resin matrix. Theoretically, the molecular simulation results of calculated energy band gaps and infrared spectrum of the intermediate products generated in the dopamine self-polymerization process confirmed that the spontaneity of self-polymerization of dopamine and the occurrence of intramolecular cyclization and intermolecular polymerization in the self-polymerization process of dopamine. Moreover, the interaction between polyimide and poly(dopamine) was simulated, and the calculated results showed that the interaction between them depended on hydrogen bonding and was verified by ultrasound treatment. Experimentally, the effect of dopamine treatment concentration on the surface properties of polyimide fibers was investigated. Obviously, after a relatively high dopamine concentration treatment, the surface roughness and surface energy of polyimide fibers were largely improved and the number of active groups on polyimide fibers surface were increased, which were altogether conducive to enhance the adhesion strength of polyimide fibers with the epoxy resin matrix.

ОРГАНОПЛАСТИКИ НА ОСНОВЕ ТЕРМОСТОЙКИХ ПОЛИМЕРНЫХ ВОЛОКОН И МАТРИЦ

The properties of heat-resistant polymer fibers (Arimid, PFBT) and samples of organoplastics based on them have been investigated. It has been established that polyimide and polybenzazole fibers can be used as a reinforcing filler to create organoplastics at operating temperatures up to 350‒400 °C. The level of retention of the elastic modulus in bending of organoplastics based on PFBT fiber and IP-5 heterocyclic binder is 90 %. Heat-resistant organoplastics are promising for use in the aerospace industry and mechanical engineering.