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Quantitative explanation on the improved mechanical properties of aligned electrospun polyimide (PI) nanofibers as the increased imidization temperatures is highly required. In this work, polarized FT-IR spectroscopy is applied to solve this problem. Based on the polarized FT-IR spectroscopy and the molecular model in the fibers, the length of the repeat unit of PI molecule, the angle between the fiber axis and the symmetric stretching direction of carbonyl group on the imide ring, and the angle between the PI molecular axis and fiber axis are all investigated. The Mark-Howink equation is used to calculate the number-average molar mass of PI molecules. The orientation states of PI molecules in the electrospun nanofibers are studied from the number-average molar mass of PI molecules and the average fiber diameter. Quantitative analysis of the orientation factor of PI molecules in the electrospun nanofibers is performed by polarized FT-IR spectroscopy. [ABSTRACT FROM AUTHOR]

Mechanical properties of polyimide (PI) electrospun nanofibers could be improved by increasing imidization temperatures. However, the intrinsic mechanism on this phenomenon is highly required, which is helpful to improve mechanical properties of electrospun nanofibers by external thermal treatment. In this work, single electrospun PI nanofibers (SNF-PI) with different imidization temperatures were prepared. The nanofiber morphology was studied by SEM and AFM and the mechanical properties were measured by single fiber micro-tensile test. Polarized Raman Spectroscopy was applied to determine the PI molecular orientation in SNF-PI. The molecular orientation factor provides directly explanation on the effect of imidization temperatures on the mechanical properties of SNF-PI. [ABSTRACT FROM AUTHOR]

High mechanical performance materials at high temperature are highly desired for the materials used in high temperature industries. This study reports the aligned electrospun polyimide nanofiber belt (A-PI-NFB) fabricated from the electrospinning followed with imidization. The A-PI-NFB showed increased mechanical and thermal mechanical properties as increasing the imidization temperature. At room temperature, the A-PI-NFB imidized at 450 °C (A-PI-NFB-450) had the highest tensile strength (689 MPa) and E modulus (13.2 GPa). The thermomechanical analysis (TMA) and dynamic mechanical analysis (DMA) showed that A-PI-NFB-450 possessed 80% tensile strength and 90% modulus when heated at 300 and 350 °C in N 2 , respectively. These excellent properties made A-PI-NFB good candidates for use in high temperature filtration, protective clothes etc. [ABSTRACT FROM AUTHOR]

Highlights: [•] Heat-resistant electrospun PBO nanofibers were prepared from precursor OH-PAA. [•] The obtained PBO nanofibers are thermally stable up to 643°C. [•] The obtained PBO nanofibers have excellent mechanical properties. [•] PBO nanofibers have retention of tensile strength and modulus over 80% at 350°C. [•] Such heat-resistant PBO nanofibers could be used in high temperature fields. [ABSTRACT FROM AUTHOR]

Abstract: This work highlights the usage of short electrospun fibers for the first time for the preparation of homogeneous polymer nanofiber/polymer composites and the improvement in mechanical properties by an order to magnitude compared to as-electrospun long and continuous nanofibers. Dispersions of short electrospun nanofibers can be processed by liquid processing techniques resulting in nanofiber nonwovens similar to electrospun nonwovens but is independent from the demands of the electrospinning process is one of the emphasis of this work. The re-formation of electrospun fiber nonwovens by dispersion casting of short electrospun polyimide (PI) nanofibers and the preparation of homogeneous polymer/polymer nanofiber composite films were selected as representative examples for showing the versatility of short electrospun fibers. The self-reinforced PI/PI-short nanofiber composite films were obtained from mixtures of short electrospun PI nanofibers and polyamic acid after imidization. Significant improvement of 53% and 87% in mechanical properties like tensile strength and modulus, respectively in comparison to the neat PI film was observed by using just 2wt% of short fibers. Parallel experiments were also carried out with long and continuous electrospun PI fibers and amazingly a huge difference was observed. The amount of continuously long fibers required for achieving almost the same strength was much higher i.e. 38wt% in comparison to the 2wt% required of short fibers. [Copyright &y& Elsevier]

Abstract: The use of small amounts (<5wt%) of short nylon-6 nanofibers (diameter less than 200nm) for reinforcing mechanical properties of TPU without losing its optical properties is highlighted in this work. The interaction of H-bonding type between the reinforcing fibers and the matrix polymer could provide a homogenous distribution of fibers and a strong interface leading to significant enhancement in mechanical properties (185% increase in E modulus) as shown by comparative use of TPU and PMMA as matrix polymers. The reinforcing effect of short fibers was attained without sacrificing transparency (>90% transparency in 400–800nm range) of TPU. The effective use of short nylon-6 fibers in comparison to the long and continuous fibers is also discussed. [Copyright &y& Elsevier]

Tantalum carbide has been widely used as an excellent refractory material. However, there are no reports regarding the continuous tantalum carbide-carbon nanofibers (TaC/CNFs) and their mechanical and electrical properties. In this work, TaC/CNFs were prepared by electrospinning. The morphology and structures of the nanofibers and the distribution of TaC in the nanofibers were investigated by SEM, EDX, TEM, XRD, XPS and Raman spectroscopy. The TaC/CNFs showed excellent thermal stability, mechanical flexibility and conductivity even after folding for 180 cycles. These flexible, refractory and conductive TaC/CNFs could be found potential applications for flexible electronic devices and refractory materials. [ABSTRACT FROM AUTHOR]

Flexible materials with high mechanical strength and good dielectric properties are highly desired for modern electronics. In this research, all-organic PVDF/PI nanofiber-reinforced composites were fabricated by layer-by-layer hot-pressing the random PVDF nanofibers and aligned co-PI nanofibers. Dielectric and mechanical properties of the PVDF/PI composites were investigated. Results showed that the mechanical properties were highly enhanced by the aligned co-PI nanofibers and the dielectric permittivity was inherited from the intrinsic good dielectric properties of PVDF. These all-organic PVDF/PI composites with excellent mechanical strength and good tunable permittivity can be used for flexible embedded capacitors and can be further employed as the polymer matrix for preparing high dielectric polymer–matrix composites. [ABSTRACT FROM AUTHOR]

High performance epoxy composites are highly required in many applications. In this work, polyimide electrospun nanofibers (PIENFs) with excellent thermal and mechanical properties were used to reinforce the epoxy matrix by a vacuum-assisted hot-pressing procedure. The morphologies of PIENFs and PI/epoxy composites were investigated by scanning electron microscopy (SEM). Thermogravimetric analyses (TGA) was used to characterize the thermal properties of PI/epoxy composites and calculated the actual weight amount of PIENFs in the composites. The effects of nanofiber amount and the degree of fiber alignment on the mechanical properties of PI/epoxy composites have been studied. Owing to the superior mechanical performance of PIENFs and the strong interfacial adhesion, the PI/epoxy composites presented significantly mechanical improvement as compared to the pure epoxy. Image 1 [ABSTRACT FROM AUTHOR]

[Display omitted] • Ultra-light carbon nanofiber aerogels assisted by bimetal-organic frameworks. • Enhanced microwave absorption of −66.57 dB and super-wide absorption bandwidth. • Long-term thermal stability with super-fast Joule heating (cooling) rate. Lightweight carbon-based aerogels with fast heat dissipation capability are promising electromagnetic wave absorber materials for developing integrated electronics, artificial intelligence, and human-interaction equipment under harsh thermal environments. Herein, the bimetallic (cobalt (Co) and nickel (Ni)) metal–organic frameworks (CoNi-MOFs), cellulose nanofibrils (CNFs), and aramid nanofibers (ANFs) were assembled into a conductive and magnetic CoNi@carbon/ANF/CNF carbon composite aerogel (CoNi@C/ACA) with an ultra-low density of 6.15 mg/cm3 using freeze-drying and subsequent carbonization treatment. Owing to the synergistic effects of multiple reflections inside the three-dimensional interconnected structures, abundant interfacial/dipolar polarizations, and coordinated dielectric and magnetic losses, the CoNi@C/ACA achieved a fascinating minimum reflection loss value of −66.57 dB and broad effective absorption bandwidth up to 6.3 GHz, which were characterized with an ultra-low loading of 1.8 wt%. In addition, it displayed good thermal stability with a super-fast Joule heating (cooling) rate at low driving voltages. These unique characteristics of the ultra-light CoNi@C/ACA make it a promising material for demanding applications, e.g. , electromagnetic pollution elimination and thermal management. [ABSTRACT FROM AUTHOR]

Electrospinning is a common method for preparing nanomaterials. Among many electrospinning materials, electrospun carbon nanofibers (CNFs) have become one of the hot research directions for advanced functional materials owing to their good mechanical properties, high surface area, excellent flexibility, physical and chemical stability. Particularly, significant progress has been made in the engineering advancement of electrospinning, electrospun CNFs and their derived reinforced composites to fulfill various applications. This review aims to afford a comprehensive overview of electrospun CNF reinforced composites. Firstly, the different precursors, the correlative properties, and surface modification strategies (e.g. , physical modification and chemical modification) of electrospun CNFs are introduced. Secondly, the preparation methods of reinforced composites based on electrospun CNFs are described in detail. Then, the functional applications of electrospun CNF reinforced composites are discussed. Finally, the challenges and future solutions of electrospun CNF reinforced composites are also prospected. This review is expected to offer a basic but deep understanding of modification strategies to heighten the surface performances of CNFs for the future development of high-performance electrospun CNF reinforced composites in the composite industry, defense, and aerospace applications. [Display omitted] • Electrospun CNF reinforced composites are widly used in engineering materials. • The precursors and modification strategies of electrospun CNFs are detailly reviewed. • Diverse preparation and application of CNF reinforced composites are summarized. • The current challenges of electrospun CNF reinforced composites are discussed. • The future prospects of CNF-based composites in advanced engineering are proposed. [ABSTRACT FROM AUTHOR]

Polyaniline/polyimide (PANI/PI) composites with hierarchical 3D micro/nano-architecture have been prepared via electrospinning and in-situ polymerization. The PANI/PI composite prepared from 0.2 M aniline (PANI/PI-2) exhibited a small average pore size (1.730 μm) and a narrow pore size distribution (1.552–1.882 μm). Compared to the commercial polyolefin separators, the PANI/PI composite separator possesses a much better thermal stability up to 180 °C, a higher porosity (84%), a larger liquid electrolyte uptake (619%) and a higher ionic conductivity (2.33 mS cm −1 ). The cell with PANI/PI-2 composite separator showed a low interfacial resistance, an enhanced capacity (133 mAh g −1 at 0.2C), a better rate capability (41.4% at 10C) and cyclability (89.3% retention after 500 charge/discharge cycles at 0.2C). The PANI/PI composite with a superior thermal stability and high electrochemical performances is a promising candidate for uses in high perform LIBs. [ABSTRACT FROM AUTHOR]

[Display omitted] • The recent progress of electrospun nanofibers as electrocatalysts for flexible metal-air batteries has been reviewed. • The fundamental principles of electrospinning technique have been introduced. • The importance of bifunctional electrocatalysts for oxygen reduction and oxygen evolution in metal-air batteries has been highlighted. • Future perspectives of novel electrospun nanofibers composite for flexible metal-air batteries have been proposed. Rechargeable metal-air (O 2) batteries have been regarded as the promising candidates for wearable and flexible energy devices owing to their outstanding energy density, low cost, and high safety. Generally, the electrocatalyst at air cathode plays a significant role in various metal-air (O 2) batteries. As a versatile and efficient technique, electrospinning has been considered as a powerful method to fabricate nanofibers, which hold great potential as bifunctional electrocatalysts for such batteries. Although great progresses have been achieved in improving the electrochemical performance of catalysts in recent years, some critical challenges still maintain. In this review, the advanced electrospun carbon nanofiber-based electrocatalysts for flexible metal-air batteries have been summarized. Then, additional discussions have been included focusing on the advantages and characteristics of different nanofibers and some special requirements for various flexible metal-air batteries. Moreover, some current challenges and future prospects in the development of electrospun carbon nanomaterials for flexible metal-air cathode catalysts have been rationally analyzed. [ABSTRACT FROM AUTHOR]