Search

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]

Single electrospun copolyimide nanofiber and aligned co-PI nanofiber belts with high strength and high modulus were prepared from copolyamic acid containing pyrimidine units. The chemical structures of copolyamic acid and copolyimide were characterized by 1H-NMR and FT-IR spectra. The morphology of the electrospun nanofibers was investigated by SEM and AFM. The mechanical properties of the single electrospun nanofiber and aligned nanofiber belts were measured by the single fiber micro-tensile test and the uniaxial tensile test, respectively. The thermal properties of the co-PI nanofiber belts were evaluated on TGA and DMA machines. The results indicated that the incorporation of rigid pyrimidine units, the molar ratio of pyrimidine/4,4′-oxydianiline and the imidization temperature played an important role in the mechanical properties of electrospun copolyamic acid and copolyimide nanofibers while the thermal properties were influenced by the molar ratio of rigid and soft components in the copolyimide main chains. [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]

Electrospun polyimide (PI) nanofibers possessed high tensile strength (δ), but the breaking load (BL) is very small. It is also a challenge to prepare electrospun PI microfibers from the PAA precursor in high boiling point solvents. In this work, PI microfibers with diameter more than 2 μm were prepared from their PAA-salt in water mixed with low boiling point solvent, such as ethanol. The single electrospun PI microfiber (S-EPIMF) showed excellent mechanical properties with BL, δ, modulus and tensile strain of 4872 μN, 1064 MPa, 5.6 GPa and 15.7%, respectively. The high BL allows a single electrospun PI microfiber even be able to hold a 0.5 g metal ring. The superior mechanical properties of the electrospun PI microfibers could be attributed to the high molecular orientation and crystallinity in the fibers, and the high BL is due to the large diameter of the electrospun PI microfibers. [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]

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]

Materials with outstanding mechanical properties and excellent dielectric properties are increasingly favored in the microelectronics industry. The application of polyimide (PI) in the field of microelectronics is limited because of the fact that PI with excellent mechanical properties does not have special features in the dielectric properties. In this work, PI composite films with high dielectric properties and excellent mechanical properties are fabricated by in-situ reduction of fluorinated graphene (FG) in polyamide acid (PAA) composites. The dielectric permittivity of pure PI is 3.47 and the maximum energy storage density is 0.664 J/cm3 at 100 Hz, while the dielectric permittivity of the PI composite films reaches 235.74 under the same conditions, a 68-times increase compared to the pure PI, and the maximum energy storage density is 5.651, a 9-times increase compared to the pure PI films. This method not only solves the problem of the aggregation of the filler particles in the PI matrix and maintains the intrinsic excellent mechanical properties of the PI, but also significantly improves the dielectric properties of the PI. [ABSTRACT FROM AUTHOR]

High dielectric permittivity, good mechanical properties, and excellent thermal stability are highly desired for the dielectric materials used in the embedded capacitors and energy-storage devices. This study reports polyimide (PI)/barium titanate (BaTiO3) nanocomposites fabricated from electrospun PI/BaTiO3 hybrid nanofibers. The PI/BaTiO3 nanocomposites were investigated using Fourier transform infrared spectroscopy, scanning electron microscope, transmission electron microscope, thermal gravimetric analysis, an electromechanical testing machine, a LCR meter and an electric breakdown strength tester. The results showed that BaTiO3 fillers were uniformly dispersed up to 50 vol% in PI matrix. The dielectric permittivity of the composite (50 vol% BaTiO3) was 29.66 with a dielectric loss of 0.009 at 1 kHz and room temperature. The dielectric permittivity showed a very small dependence on temperature (up to 150°C) and frequency (100 Hz-100 kHz). The nanocomposites also showed high thermal stability and good mechanical properties. The PI/BaTiO3 nanocomposites will be a promising candidate for uses in embedded capacitors, especially in high temperature circumstance. POLYM. COMPOS., 37:794-801, 2016. © 2014 Society of Plastics Engineers [ABSTRACT FROM AUTHOR]

A three-phase nanocomposite with outstanding dielectric properties was prepared via electrospinning and hot-pressing, by which multi-walled carbon nanotubes (MWCNTs) were homogeneously dispersed in polyimide (PI) matrix and separated by the BaTiO 3 particles (BTPs). The fairly enhanced dielectric properties were due to synergistic enhancing of the ferroelectric ceramic filler BTPs and conductive filler MWCNTs. The investigation shows that the dielectric permittivity of the as-fabricated three-phase nanocomposites with 40 vol% BTPs and 10 vol% MWCNTs loads is as high as 1061.98 at 100 Hz with a lower dielectric loss of 0.23, and the corresponding energy storage density is 4.773 J/cm 3 , 11 times that of the pure polyimide. The three-phase nanocomposites with enhanced dielectric properties also show excellent thermal properties and will be attractive in application in modern microelectronics. [ABSTRACT FROM AUTHOR]

[Display omitted] Designing intertwined porous structure is highly desirable to improve the electrochemical performance of carbon materials for supercapacitor. In this contribution, three-dimensional (3D) carbonized polyimide/cellulose (CPC) composite is fabricated via a facile "one-step" carbonization, in which cellulose as cross-linked agent is capable of modulating the molecular structure of polyamic acid, thus ensuring the formation of intertwined porous networks in the obtained carbon skeleton. Benefitting from the high specific surface area (951 m2 g−1) and uniformly distributed pores, the optimized CPC-5 electrode exhibits an outstanding specific capacitance of 300F g−1 in 6.0 M KOH electrolyte. More impressively, the CPC-5 based symmetrical supercapacitor affords a high energy density of 22.6 Wh kg−1 at power density of 800 W kg−1, as well as an exceptional capacitance retention of 91.4% after 10,000 cycles. This work affords an effective strategy to yield a promising polyimide derived carbon material for high-performance supercapacitors. [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]

Graphical abstract The preparation of superhydrophobic and superoleophilic PI-based nanofibrous membrane for oil-water separation. Abstract Marine pollution and industrial wastewater have caused serious environmental pollution, thereby resulting into an alarming damage to public health in the past decades, hence the high demand for, cost effective, energy-efficient oil-water separation technologies for the removal of oil contaminants from such water. Herein, we report a facile method to fabricate superhydrophobic/superoleophilic membrane by immersing a polyimide (PI)-based nanofibrous membrane into a water/ethanol/ammonia/dopamine mixture, followed by modification with 1H, 1H, 2H, 2H-perfluorodecanethiol (PFDT). The PI-based membrane exhibited water contact angle (WCA) above 153°, while the oil contact angle (OCA) approached 0°, thereby promoting an outstanding chemical stability which sustained its superhydrophobicity when immersed in aqueous solutions at different pH values. Additionally, the PI-based membrane possesses ultrahigh flux, high separation efficiency and good reusability in oil-water separation. The aforementioned properties, as well as the easily scale-up preparation process ensure that this promising as-fabricated membrane can be applied for practical environmental applications including treatment of oily wastewater and oil spillage clean-up. [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]

Short carbon nanofibers (SCNFs) were prepared by electrospinning followed with grinding and ultrasonic breaking and employed as fillers to prepare polyimide (PI) composites. The dielectric and mechanical properties of SCNFs/PI composites were investigated. Results showed that the SCNFs have significant improvement in mechanical properties and are good conductive filler for preparing high dielectric composites. Compared to the neat PI, the SCNFs/PI composite with 1 wt% SCNFs showed 39.43% improvement in tensile strength. The SCNFs/PI composites showed a low percolation threshold of 4 wt% for the dielectric permittivity (60.79 @100 Hz). These electrospun SCNFs reinforced PI composites can be good candidate for making high performance dielectric materials for modern electronic applications. [ABSTRACT FROM AUTHOR]