Production line for composite yarns with

a nanofibrous envelope using high throughput AC

needleless and collectorless electrospinning

A composite yarn with a nanofibrous envelope

Production line for composite yarn is based on two inventions. • The nanofibres are generated by a highly productive method of collectorless as well as needleless AC electrospinning. An important feature of AC spinning is that it creates a plume of nanofibres resembling a sleeve of interconnected nanofibres. These are transported by the electric wind in the direction of the axis of the rod-like spinning electrode.

• The plume of nanofibres produced by AC electrospinning is collected by the axially rotating and ballooning classic yarn. This we call the core yarn. The axial rotation and ballooning is ensured by a set of two twirling devices. These devices have the capacity for virtually uninhibited axial rotation and ballooning of the yarn.

This method of producing a massive nanofibrous envelope around the yarn core can be implemented with cores of a linear density ranging from tens up to thousands of dtex. Nanofibrous composite yarns can be further processed by standard textile technologies opening up the possibility to produce textiles with unique added properties. This approach may well lead to the widespread production and use of composite nanofibrous yarns on an industrial scale.

The method of AC electrospinning, composite yarn production and special spinning electrodes design are covered by International Applications WO2014094694 A1, WO2017108012 A1, WO2016192697 A3 and WO2019047990 A1 respectively.

TECHNICAL PARAMETERS

GENERAL

Total external dimensions (w × h × d) 4750 × 2496 × 1180 mm

Total weight 400 kg

Power source 230V / 50 Hz

Maximum consumption 3.6 kW

DRIVES

Yarn ballooning Spindle(s) RPMs 0 – 18 000 RPMs

Yarn winding Speed 0 – 50 m/min

Stroke 0 – 150 mm

Twisting yarn spindle RPMs 0 – 25 000 RPMs

HV SOURCEVoltage range 0 – ±36 kV

Current range 0 – ±1.8 mA

A composite yarn cross section with a polyester (PES) multifilament core with a nanofibrous envelope made with polyamide 6 (PA6)

Environmental and social impact brought about by the innovation after its deployment

With the rapid developments in nanoscience and nanotechnology, yarns composed of nanofibres may open up a whole range of new possibilities. One application of these materials is the production of a porous artificial proboscis, which could be used to collect tiny liquid samples. Nanofibrous yarns are also the basic material element for the development of nanofibrous structures, such as woven and knitted fabrics, macramé and laces, whose mechanical, sorption and filtration properties will significantly differ from those of conventional textiles. Nanofibrous textiles may also have great potential uses in the field of medicine. Materials for biomedicine are by no means harmful to the environment or human health.

Composite yarns produced by our technology have better sorption and filtration properties than classic ones, and will therefore have better properties to capture harmful substances like filters. They can be applied for instance as valuable industrial, agricultural and domestic water purification devices, which can positively affect the environmental purity. That is an example of the positive social impact of this new technology.

Thanks to the high production rate of nanofibrous composite yarns by out method, these linear flexible materials will be quite cheap and therefore well accessible for wide social groups in the form of filters, sorption membranes, sutures, etc. For instance, implementation of sutures based on our nanofibrous composite yarns containing antibacterial agents should reduce postoperative complications. Commercialization of nanofibre composite yarns and equipment for their production can help address critical global environmental and health pollution issues.

The plume of nanofibres resembles fine smoke emerging from the AC electrospinning electrode

Impact of the innovation to workforce welfare and the effective developments for best practicesThe responsible development of electrospinning nanotechnology is a goal of many organizations worldwide. We are convinced that our nanotechnology will contribute to significant improvements of many technological and industrial sectors dealing with processing of linear flexible and highly functional materials accompanied, which will result in creation of new job opportunities.

Regarding the workforce welfare, we can point out that by operating our line for the production of composite nanofibre threads by the AC electrospinning method, there is no risk of injury to the operator by residual voltage after it is switched off, as is the case of the direct current (DC) electrospinning technology. The absence of an electrically charged collector reduces the area of electrically charged parts of the device, thereby reducing the risk of electric shock.

A SEM microphotograph of fabric made with a composite nanofibrous yarn

Excellence in design, technical development and efficient deployment of the innovationNanofibrous materials are essential components for a range of applications, particularly in the fields of medicine and material engineering. These include protective materials, sensors, cosmetics, and filtration and energy storage products. The most widely used and researched technology in these fields is electrospinning. This method of producing fibres yields highly promising results thanks to its versatility and simplicity. Electrospinning is employed in multiple forms, among which needle and needleless direct current (DC) variants are the most distinctive. The former is based on the generation of just one single jet from a nozzle; hence this fabrication process is not very productive. The latter uses the destabilization of free liquid surfaces by means of an electric field, which enhances the throughput since it produces numerous jets, emitted from the surfaces of rollers, spheres, strings and spirals. However, although some progress in total producibility has been achieved, the efficiency of the DC method still remains relatively low. A further drawback of DC electrospinning is that both variants need a collector, which makes it difficult to combine DC electrospinning easily with other technologies due to the presence of the high field strength within the entire spinning zone.

The excellence in design and technical development emerging from of our invention is that alternating current (AC) electrospinning based on a needleless spinning-electrode provides a highly productive smoke-like aerogel composed of nanofibres. This aerogel rises rapidly from the electrode like a thin plume of smoke, without any need for a collector. AC electrospinning combined with an appropriately-shaped, needleless spinning-electrode is highly efficient at generating a dense plume of nanofibres. The efficiency of this method is achieved by means of the virtual counter-electrode. This virtual counter-electrode formed by a cloud of nanofibres is recreated periodically in each half-wave of the AC cycle. The recombined pieces of newly-formed nanofibres are then moved by the electric wind to create the nanofibrous plume.

The AC needleless electrospinning method work has the potential to be linked to existing technologies. There are two significant reasons for this. Firstly, there is no obstacle, such as a collector, along the spinning line. AC electrospinning can therefore be used for the mass production of nanofibres thanks to its remarkable throughput. In addition, the immediate product of AC electrospinning is a compact aerogel (i.e. the plume of nanofibres), which can be readily manipulated for further processing.

The efficient deployment of the aforementioned invention is realised in the promising application of the nanofibrous plume for the production of nanofibrous yarns.

The unique technology for production of nanofibrous composite yarns is based on the extraordinary feature of AC electrospinning that does not require the presence of a counter-electrode, the so-called collector. In our production line, the yarn core is fed horizontally into a spinning space at a distance of 150 mm above the spinning electrode, or set of spinning electrodes. The yarn core axis and the axis of the nanofibrous plume emitted from the spinning electrode are almost perpendicular to one another. The preloaded core of the yarn unwind from the master bobbin, passes through the hole of the first disc, and then twists and loops into the shape of a balloon. Thanks to the local twisting and ballooning of the core yarn, the core is tightly enveloped by nanofibres at the area of contact of the core with the plume of nanofibres. Even when several plumes of nanofibres are wound up from a set of AC spinning units, the two co-rotating twirling devices ensure almost uninhibited rotation and ballooning of the yarn. The rotation and ballooning of the yarn depends on seven factors: the mechanical properties; linear density; diameter of the core yarn; the tension in the yarn; its winding speed; the angular speed of both twirling devices; and the eccentricity of their holes. The plume is formed by nanofibres which were originally electrically opposite. As a result of these attraction forces, a mechanically compact plume is formed. This enables almost 100% of the nanofibre mass to be entrapped by the spinning and ballooning yarn core. Lastly, the resulting composite yarn is wound onto the output bobbin.

The process whereby the nanofibrous envelope is formed is complex. High-speed camera recordings show that the plume of nanofibres is not entirely plastic, but that it also exhibits a partially elastic behaviour that helps „tighten“ the nanofibrous envelope around the core. This elasticity is a result of the structure of the plume, which consists of a network of mutually interconnected nanofibrous sections. Both in its elasticity and in structure, the plume resembles a fibrous web created by drum carders from staple fibres.

Technical solutions of AC electrospinning and production of nanofibrous composite yarns are protected by four Czech patents (CZ 304137, CZ 306428, CZ 306772 and CZ 307745). All four national patents are assigned with international applications and the first two have already passed the national phases in Europe, Japan, the USA, China and Russia:• WO2014094694 A1, Method for the production of polymeric nanofibres by spinning

of a solution or polymer melt in a field, and a linear formation from polymeric nanofibres prepared by this method. Transition to the national phase in Europe, Japan, the USA, China and Russia.

• WO2017108012 A1, A method for producing polymeric nanofibres by electrospinning and a polymer solution or a melt, and spinning electrodes for the production

of polymeric nanofibres equipped with at least one such spinning electrode.• WO2016192697 A3, Linear fibrous formation with a coating of polymeric nanofibres

enveloping and supporting linear formation constituting a core, a method and a device for producing it.

• WO2019047990 A1, Method for producing polymeric nanofibers by electric or electrostatic spinning of a polymer solution or melt, a spinning electrode for the method, and a device for production of polymeric nanofibers equipped with at least one such spinning electrode.

The International Application WO2014094694 A1 has already been granted in the USA as US10041189B2, in China as CN105008600B, in Japan as JP6360492B2 and in Russia as RU2672630C2. The International Application WO2017108012 A1 has already been granted in the USA as US 505245015.

References• Lukas, D, et al., Effective AC needleless and collectorless electrospinning for yarn production, PHYSICAL

CHEMISTRY CHEMICAL PHYSICS, 16 (48), pp. 26816-26822, 2014.

• Valtera, J, et al., Fabrication of dual-functional composite yarns with a nanofibrous envelope using high throughput AC needleless and collectorless electrospinning, Scientific Reports, 9 (1), Article number 1801, 2019

A SEM microphotograph of knitwear made with a composite nanofibrous yarn

Commercial impact resulting from the use of innovation and the integration of sustainability policies into the business strategy.The production line for nanofibrous composite yarns opens a new area of nanofibre technology based on alternating current (AC) electrospinning. The line allows subsequent development steps toward the production of new nanofibrous materials for applications in healthcare, pharmaceuticals, filtration, food packaging materials, etc. Furthermore, it elevates production of nanofibrous linear flexible materials to an industrial level thanks its efficiency and satisfying productivity. The acceptable production costs of this technology will allow expansion of these yarns to areas, where the use of nanofibrous materials is still limited, because it is still too expensive.

Commercial impact resulting from the use of the exhibited technology is given by the state of art of the industry related to the production of nanofibrous materials and devices. Nanofibrous materials are currently being used in some industrial applications such as air filtration and wastewater treatment. On the other hand, intensive development of nanofibrous materials is recently taking place in the areas of healthcare. More extensive use of nanofibrous materials is mainly prevented by their high production costs and market prices, which is due to the low productivity of the current industrial methods based on direct current (DC) electrospinning. The new AC electrospinning technology invented by us makes nanofibre production more efficient and will further increase its production rate.

In our research and development work leading to the production of nanofibre composite yarns, we have respected the concept of responsible nanotechnology development. The generally accepted criteria for assessing such development are to avoid damage to human health and the environment. We are aware of the fact that workers are the first people exposed to the potential risks of any new nanotechnology. We are also aware that workers often have the highest exposure that can occur at the beginning of technology development if risks are uncertain. For these reasons, health and safety at work has been a cornerstone of responsible development and implementation of our nanotechnology. Therefore, harmless polymers, i.e. bio-inert, biodegradable and biocompatible, and so called “green” solvents, for instance water, ethanol or natural carboxylic acids, have been of our primarily interest to be manufactured during the development of our nanofibrous composite yarns.

To our knowledge, a competing device producing linear flexible material containing nanofibres by electrospinning method or any other kind of nanotechnology is not available on the market today. Therefore the commercial impact resulting from the use of our innovation should be enormous as well as sustainable for a relatively long time period.

Production line for composite yarns with a nanofibrous envelope using high throughput AC needleless and collectorless electrospinning

The yarn core axis and the axis of the nanofibrous plume emitted from the spinning electrode are almost perpendicular to one another.

Confocal microscopy of PCL nanofibers on polyamide yarns seeded with Saos2 osteosarcoma cell line three days after seeding. Nuclei are stained in red (Propidium Iodide) and cell membranes are stained in green (DiOC(3)). Left: Magnification 20×, scale 100 µm, Right: Magnification 10×, scale 200 µm. (Courtesy of M. Rampichova group, IEM CAS).

Confocal microscopy of PCL nanofibres on PLA yarns seeded with Saos2 osteosarcoma cell line six days after seeding. Nuclei are stained in red (Propidium Iodide) and cell membranes are stained in green (DiOC(3)). Magnification 10×, scale 200 µm. (Courtesy of M. Rampichova group, IEM CAS).

www.kts.tul.cz/en/ac-electrospinning

Technical University of LiberecStudentská 2 | 461 17 Liberec 1

Czech Republic

Contact person: David Lukáš | david.lukas@tul.cz

Jaroslav Beran | jaroslav.beran@tul.cz