Enhancing Crystallinity and Orientation by Hot-Stretching to Improve the Mechanical Properties of Electrospun Partially Aligned Polyacrylonitrile (PAN) Nanocomposites

Abstract

Partially aligned polyacrylonitrile (PAN)-based nanofibers were electrospun from PAN and PAN/single-walled carbon nanotubes (SWNTs) in a solution of dimethylformamide (DMF) to make the nanofiber composites. The as-spun nanofibers were then hot-stretched in the oven to enhance its orientation and crystallinity. With the introduction of SWNTs and by the hot-stretched process, the mechanical properties will be enhanced correspondingly. Scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray scattering (XRD), differential scanning calorimetry (DSC), and the tensile test were used to characterize the microstructure and performances of the nanofibers. The orientation and crystallinity of the as-spun and hot-stretched nanofibers confirmed by X-ray have increased. Differential scanning calorimetry showed that the glass transition temperature of PAN increased about 3 °C by an addition of 0.75 wt% SWNTs indicating a strong interfacial interaction between PAN and SWNTs. The tensile strength and the modulus of the nanofibers increased revealing significant load transfer across the nanotube-matrix interface. For PAN nanofibers, the improved fiber alignment, orientation and crystallinity resulted in enhanced mechanical properties, such as the tensile strength and modulus of the nanofibers. It was concluded that the hot-stretched nanofiber and the PAN/SWNTs nanofibers can be used as a potential precursor to produce high-performance nanocomposites.

Production of polyacrylonitrile/boehmite nanofibrous composite tubular structures by opposite‐charge electrospinning with enhanced properties from a low‐concentration polymer solution

“…The average crystallite size can be evaluated using Scherer's relation according to Equation , where “ λ ” is the X‐ray wavelength, “ β ” is the full width at half the maximum of the diffraction peak, “ θ ” is the diffraction angle and “ K ” is the Scherer's constant of the order of unity for an average crystal . Moreover, λ = 1.54 Å and K = 0.90, and β = FWHM at a reflection intensity of 100% . The degree of orientation Π (%) can be estimated by using the fully corrected azimuthal intensity distribution diffracted from the 100 reflection at d‐spacing [Å].…”

“…Crystallinity is generally measured as a ratio of the diffraction portion from the crystalline part of the tubular structure sample, Ic , and the total diffraction from the same sample, I(c + b) . The values of Ic can be obtained after a suitable subtraction of the scattering portion from the background, Ib . where I total = I (c + b) . In the X'Pert Pro system, the calculation of crystallinity (%) was done by the user‐defined crystalline (peak region) and amorphous regions (background region) on a frame obtained from the analyzed material.…”

“…PAN nanofibers is a popular precursor of general carbon fibers. However, these applications of PAN nanofibers are limited by their poor strength, due to their small diameters and the low molecular orientation and crystallinity in the fibers . However, reinforcement of these nanofibers with organic or inorganic nanoparticles may lead to a tremendous improvement in fiber quality.…”

Polymer-based composites with improved energy density and dielectric constants by monoaxial hot-stretching for organic film capacitor applications

“…With increasing stretch ratio, more nanotubes were aligned and re-dispersed since the polymer start to orient during the hot-stretching process. Besides, former reports showed that the crystalline polymer tends to recrystallize during the hot-stretching process 31 .…”

Electrochemical hydrogen peroxide sensors based on electrospun La0.7Sr0.3Mn0.75Co0.25O3 nanofiber modified electrodes

“…21 With the development of nanotechnology, nanomaterials have become excellent substitutes for peroxidase. 28 Compared with these methods, electrospinning has proved to be a simple, low-cost and versatile way to mass fabricate uniform and continuous nanobers. 23,24 Many methods have been applied to synthesize nanobers, such as self-assembly, 25 template synthesis, 26 stretch method 27 and phase separation.…”