Fabrication of dual-functional composite yarns with a nanofibrous envelope using high throughput AC needleless and collectorless electrospinning

Abstract

Nanotechnologies allow the production of yarns containing nanofibres for use in composites, membranes and biomedical materials. Composite yarns with a conventional thread core for mechanical strength and a nanofibrous envelope for functionality, e.g. biological, catalytic, have many advantages. Until now, the production of such yarns has been technologically difficult. Here, we show an approach to composite yarn production whereby a plume of nanofibers generated by high throughput AC needleless and collectorless electrospinning is wound around a classic thread. In the resulting yarn, nanofibres can form up to 80% of its weight. Our yarn production speed was 10 m/min; testing showed this can be increased to 60 m/min. After the yarn was embedded into knitwear, scanning electron microscope images revealed an intact nanofibrous envelope of the composite yarn. Our results indicate that this production method could lead to the widespread production and use of composite nanofibrous yarns on an industrial scale.

Figure 1

(a) The immediate product of AC electrospinning is a compact plume of nanofibres, which can be readily manipulated for further processing. The ability to grab and manipulate the plume by hand demonstrates that this method works without any electrically active collector. (b) The plume of nanofibres resembles fine smoke emerging from the AC electrospinning electrode. The spinning head of the electrode can be composed of three discs.

Figure 2

(a) A simplified schematic of the device: the AC spinning electrodes (1), the plumes of nanofibres (2), the core yarn being rewound from left to right (3), the first twirling device (4), the second twirling device (5), a storage coil with the core yarn coil (6), the output coil with the composite yarn (7). The yarn core is fed horizontally into the spinning space above the two vertically-oriented rod spinning-electrodes and is coated with nanofibres. (b) A simplified schematic of both twirling devices. The top image shows the first twirling device, which is comprised of a rotor (4) with a yarn chamber with an eccentric hole positioned with offset e from the axis of rotation, the static frame of the device (8), and the yarn (3) passing through the device. The bottom image shows a simplified schematic of the second twirling device (5). (c) The yarn core axis and the axis of the nanofibrous plume emitted from the spinning electrode are almost perpendicular to one another. (d) Two screw pumps integrated with the spinning electrode with disc like heads (1) and the polymer reservoir emitting nanofibrous plumes (2) which wrap around the ballooning yarn core (3).

Figure 3

(a) The maximum radius of the balloon depending on the tension of the yarn. (b) The shape of the ballooning yarn in the axial view. (c) The shape of the ballooning yarn between two twirling devices 4.5 m apart, under a constant yarn stress of 33 cN. (d) A section of the ballooning yarn inside the spinning space. The distance between two nodes in the balloon is 0.57 m. (e) When the ballooning yarn is weighed down with the plume of nanofibres, the balloon nodes cease to be clearly visible.

Figure 4

(a) A composite yarn with almost zero twist and a bare core yarn. (b) The nanofibre envelope with a twist value of about 10³ m⁻¹. (c) A cross section of a composite yarn with a polyester (PES) multifilament core with a linear weight of 330 dtex, and a nanofibrous envelope made with polyamide 6 (PA6). (d) A detailed view of the structure of a nanofibre envelope showing belts, beads and inter-twined fibers. Fibres are tortuous (inter-twined) due to the mechanism of their creation, in which positively and negatively charged jet segments are mutually attracted.

Figure 5

(a) A Constant Tension Tester. The composite yarn is wrapped around two ceramic rods with a total wrapping angle of 180°. (b) A comparison of the friction coefficients of the six composite yarn samples (grey bars) and six samples of their bare yarn cores (black bars), with standard deviations. For each uncoated and coated sample 50 measurements were carried out. Samples No. 1–3 have a polyester (PES) core and a polyvinylbutyral (PVB) envelope. Samples No. 4–6 have a polyamide 6,6 (PA 6,6) core and a polyamide 6 (PA6) envelope. (c) The typical friction coefficient values of a series of successive sections of a composite yarn for samples No. 2 and No. 4. For each sample 50 measurements were carried out. All samples were 50 m long. (d) The linear density fractions of the core and envelope fibres in composite yarn samples. The linear density values of the core and envelope fibres are introduced inside the bars in dtex.

Figure 6

(a) A diagram of the device measuring the envelope-core adhesion. (Inset) A photograph of the composite yarn (sample No. 1) at the moment when the envelope was damaged: (1) a spring, (2) the yarn to be tested, (3) a ceramic wire, (4) a tension sensor, (5) the shaft of the winding device. (b) The measuring device at the moment when the nanofibre envelope was detached from the yarn core (sample No. 1). (c) The force values and standard deviation bars at which the nanofibre envelope was detached from the core yarn. Ten measurements were carried out for each of the samples No. 1–6. (d) A SEM microphotograph of knitwear made with a composite nanofibrous yarn indentical to sample No. 4.