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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]

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]

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]