Mechanical characterization of single high-strength electrospun polyimide nanofibres

Abstract

Ultimate tensile strength and axial tensile modulus of single high-strength electrospun polyimide [poly(p-phenylene biphenyltetracarboximide), BPDA/PPA] nanofibres have been characterized by introducing a novel micro tensile testing method. The polyimide nanofibres with diameters of around 300 nm were produced by annealing their precursor (polyamic acid) nanofibres that were fabricated by the electrospinning technique. Experimental results of the micro tension tests show that polyimide nanofibres had an average ultimate tensile strength of 1.7 ± 0.12 GPa, axial tensile modulus of 76 ± 12 GPa and ultimate strain of ∼3%. The ultimate tensile strength and axial tensile modulus of the electrospun polyimide nanofibres in this study are among the highest ones reported in the literature to date. The precursor nanofibres with similar diameters and molecular weights had an average ultimate tensile strength of 766 ± 41 MPa, axial tensile modulus of 13 ± 0.4 GPa and ultimate strain of ∼43%. The experimental stress-strain curves obtained in this study indicate that under axial tension, the precursor (polyamic acid) nanofibres behave as linearly strain-hardening ductile material without obvious softening at final failure, while the polyimide nanofibres behave simply as brittle material with very high tensile strength and axial tensile modulus. Furthermore, by using a transmission electron microscope, detailed fractographical analysis was performed to examine the tensile failure mechanisms of the polyimide nanofibres, which include chain scission, pull-out, chain bundle breakage, etc. X-ray diffraction analysis of the highly aligned polyimide nanofibres shows the high chain alignment along the nanofibre axis that was formed in the electrospinning process and responsible for the high tensile strength and axial tensile stiffness.

Development of an electrospinning method for the tensile testing of single nanofibers

“…For PLLA nanofibers, tensile strength was reported as 204 ± 86 MPa [8], which is close to our result. The stress-strain curve in Fig.9 consists of two linear stages, which is similar to that of the case of polyimide nanofibers [9]. After elastic deformation, large plastic deformation was observed.…”

High-performance electrospun co-polyimide nanofibers

“…4b, revealing preferred crystal orientation along the fiber axis in these materials. Herman's orientation factor, f, was introduced here to quantify the orientation of crystals before and after imidization and was determined from the fully corrected azimuthal intensity distribution diffracted from the (110) reflection [23] at d = 3.03 Å. where I(ϕ) is the intensity distribution of the (110) reflection at that angle ϕ which is the azimuthal angle between the axis of the crystal plane and the fiber. For a given crystallographic axis, <cos 2 ϕ> assumes values of 1 for perfect alignment, 1/3 for random orientations, and 0 for precise perpendicularly, which corresponds to a Herman's orientation factor with respective values of 1, 0 and -1/2 [21].…”

“…Polymer. 76:105-112, 2015 [23] ~22 [23] BPDA/BPA/ODA co-polyimide Nonwoven UD nanofiber mat ~120 [20] Spider silk Single nanofiber 160 (MA silk) [26] 150 (Viscid silk) [26] 221 (Nephila edulis silk) […”

“…A second method involved the use of a high resolution nano-tensile tester that allows for the testing of single nanofibers. This method has been used by Tan et al, Leong et al and Chen et al [23,29,30]. For the testing of single nanofibers two main challenges have to be faced.…”

Rotary jet spinning review – a potential high yield future for polymer nanofibers

“…The bundle data were evaluated using Daniels' theory 183 based on Weibull statistics in order to calculate individual fiber strengths. Figure 16 shows the testing procedure of a single nanofiber using the framing method as proposed by Chen et al 184 In their paper they discussed the mechanical properties of single electrospun polyimide nanofibers with a diameter of ~250 nm and reported a record high tensile modulus of 89 GPa.…”