Melt electrospinning process

Abstract

Melt electrospinning processes, including: S1, Heating an inorganic material to a molten state to form a melt, and S2, Forming the melt into fibers by electrospinning, wherein the melt electrospinning is carried out at an ambient temperature of no more than 100 °C and normal pressure; wherein the inorganic material is silicon or tin, and wherein the melt flow rate during the electrospinning process is 2 to 10 µl / min; wherein the melt electrospinning is carried out under vacuum, an inert atmosphere or a reduction atmosphere, wherein the inert atmosphere is selected from nitrogen and / or argon, and wherein the reduction atmosphere comprises hydrogen; where the voltage for electrospinning is set to be between 10 and 50 kV.

Description

BACKREFERENCE

[0001] The present patent application claims priority over Chinese patent applications Nos. 201910267466.0 and 201910266659.4, filed on April 3, 2019, the entire contents of which are incorporated by reference into this patent specification. TECHNICAL AREA

[0002] The present disclosure relates to the field of electrospinning and in particular to a process for melt electrospinning. BACKGROUND

[0003] Electrospinning technologies are essentially divided into solution electrospinning and melt electrospinning. Solution electrospinning has developed rapidly in recent years, enabling the production of nanofibers. However, problems exist, such as low production efficiency, solvent recovery, and emissions. Melt electrospinning technologies, on the other hand, can to some extent compensate for the shortcomings of solution electrospinning, making it a new focus of interest.

[0004] Melt electrospinning uses a molten version of the target material directly as the starting material, without the need for an additional solvent. The higher viscosity of the melt compared to the solution overcomes the fiber's instability in an electrostatic field, resulting in fibers with improved orientation. Melt electrospinning has become a promising option for nanofiber production. However, current melt electrospinning technology and equipment are underdeveloped and largely based on in-house design and construction. Spinning technologies are mostly geared towards polymer materials, operate at temperatures only up to 200–300 °C, and are incapable of processing inorganic materials with melting points in the thousands.There are no technical facilities or related reports for the melt electrospinning of inorganic systems at ultra-high temperatures, so that a simple, efficient and cost-effective production of fibers cannot be achieved with existing spinning technologies and technical facilities.

[0005] A process for melt electrospinning is known from CN 1 05 734 695 A. In this process, an inorganic material is heated to a molten state to form a melt, and the melt is then electrospinned to form fibers. Melt electrospinning is carried out at an ambient temperature of no more than 100 °C and at normal pressure. Further processes are known from KR 10 2005 0 031 073 A, US 2004 / 0 137 225 A1, US 2011 / 0151 736 A1, CN 1 858 308 A, KR 101 479 759 B1 and CN 2 01 933 210 U. SUMMARY

[0006] The present disclosure provides for a device and a method not belonging to the invention, which are capable of performing fusion electrospinning using inorganic material as the starting material.

[0007] The present disclosure provides for a melt electrospinning apparatus not belonging to the invention. The melt electrospinning apparatus comprises a melting unit, a spinning unit, an electrostatic generation unit, a collecting unit, and a sealed cavity. A casing of the melting unit is made of a material having a melting point above 500 °C. The spinning unit is connected to the base of the melting unit and comprises a spinneret made of a conductive material having a melting point above 500 °C. The melt electrospinning process is carried out in the sealed cavity.

[0008] According to an exemplary arrangement of the disclosure, the lining of the melting unit is made of one or more materials selected from the group consisting of quartz, graphite, silicon nitride, silicon carbide, boron nitride, tungsten carbide, tungsten, molybdenum and titanium boride.

[0009] According to an exemplary arrangement of the disclosure, the spinneret is made of one or more materials selected from graphite, tungsten, molybdenum and titanium boride.

[0010] According to an exemplary arrangement of the disclosure, the spinning unit comprises one or more spinnerets.

[0011] According to an exemplary arrangement of the disclosure, an opening of the spinneret has a diameter of 0.5 to 3 mm, preferably 0.8 to 2.5 mm.

[0012] According to an exemplary arrangement of the disclosure, the static voltage of the electrostatic generating unit is in the range of 0 to 70 kV.

[0013] According to an exemplary arrangement of the disclosure, the distance from an opening of the spinneret to the collecting unit is 100 to 300 mm.

[0014] According to an exemplary arrangement of the disclosure, the sealed cavity is provided with an intermediate layer and the intermediate layer is supplied with circulating cooling water.

[0015] According to an exemplary arrangement of the disclosure, the device for melt electrospinning further comprises a powder feed unit consisting of a screw conveyor and a vacuum transition cavity.

[0016] According to an exemplary arrangement of the disclosure, the device for melt electrospinning further comprises a vacuum unit connected to the closed cavity, wherein the vacuum unit comprises a vacuum pump and the vacuum pump is selected from a diffusion pump or a molecular pump.

[0017] According to an exemplary arrangement of the disclosure, the device for melt electrospinning further comprises a temperature measuring and control unit.

[0018] According to an exemplary arrangement of the disclosure, the device for melt electrospinning further comprises a pressure measuring and control unit, wherein the pressure measuring and control unit is connected to the sealed cavity and the melting unit and comprises a pressure gauge and a gas intake system.

[0019] The invention relates to a method for melt electrospinning, comprising: S1, heating an inorganic material to a molten state to form a melt, and S2, forming the melt into fibers by electrospinning.

[0020] According to the invention, the inorganic material is silicon or tin.

[0021] According to a non-inventive embodiment, the inorganic material is selected from germanium and / or tin dioxide.

[0022] According to the invention, the voltage for electrospinning is set to be 10 to 50 kV, preferably 12 to 45 kV, particularly preferably 20 to 40 kV.

[0023] According to the invention, the flow rate of the melt during the electrospinning process is 2 to 10 µl / min, preferably 2 to 8 µl / min, particularly preferably 2.5 to 5 µl / min.

[0024] According to the invention, the melt is subjected to electrospinning under vacuum, an inert atmosphere, or a reduction atmosphere. The inert atmosphere is selected from nitrogen and / or argon. The reduction atmosphere comprises hydrogen.

[0025] According to the invention, electrofusion spinning is carried out at an ambient temperature of no more than 100 °C and a pressure corresponding to normal pressure.

[0026] According to an exemplary arrangement of the disclosure, electrofusion spinning is carried out through one or more spinnerets. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] The above and further features and advantages of the present disclosure will become more apparent from the detailed description of the exemplary arrangements. Fig. Figure 1 shows a constructive representation illustrating a device for electrofusion spinning according to an exemplary arrangement of the present disclosure. Fig. Figure 2 shows an enlarged constructive representation illustrating part of a device for electrofusion spinning according to an exemplary arrangement of the present disclosure. Fig. Figure 3 shows a flow chart illustrating a process for melt electrospinning according to an exemplary arrangement of the present disclosure. Reference symbols are as follows.

[0028] 1: Sealed cavity, 2: Temperature measuring and control unit, 3: Pressure measuring and control unit, 4: Melting unit, 41: Heating sleeve, 42: Casing, 5: Spinning unit, 6: Electrostatic generation unit, 7: Collecting unit, 8: Vacuum unit, 9: Melt, 10: Fiber. DETAILED DESCRIPTION

[0029] The present disclosure is described in detail below in connection with specific instructions.

[0030] As in Fig. As shown in Figure 1, the device for melt electrospinning of the present disclosure comprises a melting unit 4, a spinning unit 5, an electrostatic generation unit 6, a collecting unit 7 and a sealed cavity 1.

[0031] In particular, melting unit 4 is used to heat a starting material to form a melt. As in Fig. As shown in Figure 2, the melting unit 4 can comprise a heating sleeve 41 and a lining 42. The heating sleeve 41 can be, but is not limited to, a resistive graphite furnace or an induction furnace, wherein the heating power and heating temperature are controlled by an input current and an input voltage. The inner lining 42 is made of a heat-resistant material, preferably a material having a melting point above 500 °C. It is ensured that the lining does not melt or react with the pretreated inorganic material during the forming process, and those skilled in the art can select a suitable lining material according to the type and melting point of the inorganic material. Preferably, the melting point of the lining material is 200 °C higher than the melting point of the pretreated inorganic material.An alternative cladding material may be one or more materials selected from, but is not limited to, the group consisting of quartz, graphite, silicon nitride, silicon carbide, boron nitride, tungsten carbide, tungsten, molybdenum, and titanium boride. The starting material forms a melt 9 in melting unit 4 (as in ). Fig. 2). The upper end of the melting unit 4 can also be connected to a powder feed unit (not shown). The powder feed unit conveys the starting material to the melting unit 4. The powder feed unit can include a screw conveyor and a vacuum transition cavity. The starting material powder enters the vacuum transition cavity via the screw conveyor and is then conveyed to the melting unit 4. The melting unit 4 can also be connected to a temperature measurement and control unit 2 for measuring and controlling the temperature of the melting unit 4. The temperature of the melting unit can be measured using an infrared thermometer or a high-temperature thermocouple. An opening is provided at the bottom of the melting unit 4, with the melt flowing through the opening in the inner lining 42 into the spinning unit 5.

[0032] The spinning unit 5 comprises a spinneret made of a high-temperature-resistant and conductive material. The spinning unit 5 is connected to the base of the melting unit 4 and includes a spinneret made of a conductive material with a melting point above 500 °C. The high-temperature-resistant material can be, but is not limited to, graphite, tungsten, molybdenum, and / or titanium boride. The spinneret can be threaded to the base of the opening of the melting unit 4. The spinneret can be tapered, and the inner diameter of the opening is in the range of 0.5 to 3 mm, preferably 0.8 to 2.5 mm. The melting unit 4 can comprise a single spinneret or a plurality of spinnerets. The number of spinnerets can be determined according to the fiber production requirements.The melting unit 4 and the spinneret can be designed as a program-controlled three-dimensional movement.

[0033] The electrostatic generation unit 6 serves to provide an electric field for electrospinning and is connected to the spinneret of the spinning unit 5 or the collecting unit 7. The electrostatic generation unit 6 can be a commercially available high-voltage electrostatic generation device for solution electrospinning and has a static voltage in the range of 0 to 70 kV.

[0034] As in Fig. 1 and Fig. As shown in Figure 2, the collecting unit 7 is used to collect the product formed by electrospinning, i.e., the produced fiber 10. The collecting unit 7 can, in particular, be a collector. The collector can be a copper roller shaft coated with an insulating and heat-resistant material. The rotational speed, transmission speed, and displacement are controlled by a program. The distance from the spinneret opening to the collecting unit 7 is 100 to 300 mm. The collector can also be in the form of a flat plate or other shapes, and its operating mode can also be controlled by other programs. The operating mode of the collector interacts with the operating mode of the melting unit 4 and the spinneret to ensure that the collected fibers are formed in a predetermined orientation, such as when forming a fabric or the like.

[0035] The sealed cavity 1 serves to carry out the melt electrospinning process within it, preventing the high-temperature melt from being oxidized by oxygen during the spinning process. Therefore, the sealed cavity 1 is connected to the vacuum unit 8. The sealed cavity 1 is evacuated by the vacuum unit 8 and then filled with an inert gas, and the electrospinning process is carried out under the protection of an inert atmosphere. The vacuum unit 8 can consist of a vacuum pump, which may be a diffusion pump or a molecular pump. The sealed cavity 1 is also connected to a gas intake system (not shown). The intake system can be used in combination with the vacuum unit 8 or it can be used independently.When used in combination, the gas from the sealed cavity 1 is extracted by the vacuum unit 8, and the intake system blows an inert gas into the sealed cavity 1. When used individually, an inert gas is blown directly into the sealed cavity 1 through the intake system to displace oxygen. To prevent the materials from oxidizing during the electrospinning process, as shown in [reference], [further steps may be taken]. Fig. As shown in Figure 1, the melting unit 4, the spinning unit 5, and the electrostatic generation unit 6 are installed within the sealed cavity 1. Alternatively, the melting unit 4 and parts of the spinning unit 5 can be located outside the sealed cavity 1, with only the spinneret opening of the spinning unit 5, the electrostatic generation unit 6, and the collecting unit 1 located within the sealed cavity 1 to separate the materials from oxygen. The designs of the melting unit 1, the spinning unit 5, and the electrostatic generation unit 6 are not limited to the two configurations described above and can be designed differently, as long as the electrospinning process takes place within the sealed cavity 1. The sealed cavity 1 can also be provided with an intermediate layer through which cooling water circulates to regulate the temperature within the sealed cavity 1.

[0036] The electrospinning device of the present disclosure may further comprise a pressure measuring and control unit 3 which is connected to the sealed cavity 1 or the melting unit 4 in order to control an extrusion flow rate of the melt 9 in the melting unit 4 by independently controlling its pressure.

[0037] As in Fig. As shown in Figure 3, the melt electrospinning process of the present disclosure comprises: S1, heating an inorganic material to a molten state to form a melt, and S2, forming the melt into fibers by electrospinning.

[0038] The starting material powder is transported by the screw conveyor to the vacuum transition cavity, in which the oxygen is completely replaced by pre-evacuation and purging with inert or reducing gas, and is then conveyed to the melting unit 4 before step S1.

[0039] In step S1, the starting material is heated to a molten state in the melting unit 4 to form a melt 9.

[0040] In step S2, the melt 9 in the melting unit 4 is subjected to a specific pressure by a pressure control system in order to extrude the melt 9 from the spinneret at a specific flow rate, forming droplets at the opening. The voltage for electrospinning is set to 10 to 50 kV, preferably 12 to 45 kV, and particularly preferably 20 to 40 kV. The flow rate of the melt during electrospinning is 2 to 10 µl / min, preferably 2 to 8 µl / min, and particularly preferably 2.5 to 5 µl / min. In the sealed cavity 1 filled with an inert gas, the droplets of the melt form Taylor cones under the influence of high-voltage electrostatics and are further stretched to form beams whose diameter gradually decreases, eventually becoming nanofibers.The fibers gradually cool and solidify during formation, reaching the collecting unit 7, which can be a roller collector capable of rotating at a specific speed. During the electrospinning process, the ambient temperature in the sealed cavity 1 does not exceed 100 °C, and the pressure is normal. Spinning can be stopped by changing the extrusion pressure of the melt. If the extrusion pressure is reduced, the melt cannot flow spontaneously from the spinneret, indicating that the spinning process has ended.

[0041] The concept of the present revelation will be explained below in connection with specific instructions.

[0042] Using the in Fig. 1 and Fig.In the apparatus shown in Figure 2, silicon / tin fibers were produced from silicon powder (particle size 30 to 200 µm) and tin powder (30 to 150 µm), respectively. Product analysis revealed that the fiber diameter ranged from 50 nm to 1500 nm. Example 1, not according to the invention

[0043] All valves of the apparatus were closed, the vacuum pump was switched on, and the pressure in the cavity was released to below 4 Pa. The vacuum pump valve was switched off, the argon valve was switched on, and the pressure in the cavity was restored to normal. The emptying and argon purging were repeated twice. The cavity was maintained under an argon atmosphere and normal pressure. 10 g of silicon powder were added to the crucible via the feed system and heated to approximately 1420 °C to melt. The crucible pressure was adjusted to allow the melt to be extruded at a flow rate of 1 µl / min. The spinneret was positioned 150 mm from the collector, and spinning was carried out at a voltage of 10 kV. It was clearly visible to the naked eye that the fibrous substance extended from the opening to the collector.After collecting products for one hour, samples were taken and analyzed microscopically. The results showed that the diameter of the produced silicon nanofibers ranged from 1000 to 1500 nm. Example 2, according to the invention

[0044] All valves of the apparatus were closed, the vacuum pump was switched on, and the pressure in the cavity was released to below 4 Pa. The vacuum pump valve was switched off, the argon valve was switched on, and the pressure in the cavity was restored to normal. The emptying and argon purging were repeated twice. The cavity was maintained under an argon atmosphere and normal pressure. 10 g of silicon powder were added to the crucible via the feed system and heated to approximately 1420 °C to melt. The crucible pressure was adjusted to allow the melt to be extruded at a flow rate of 2 µl / min. The spinneret was positioned 150 mm from the collector, and spinning was carried out at a voltage of 12 kV. It was clearly visible to the naked eye that the fibrous substance extended from the opening to the collector.After collecting products for one hour, samples were taken and analyzed microscopically. The results showed that the diameter of the produced silicon nanofibers ranged from 500 to 800 nm. Example 3, according to the invention

[0045] All valves of the apparatus were closed, the vacuum pump was switched on, and the pressure in the cavity was released to below 4 Pa. The vacuum pump valve was switched off, the argon valve was switched on, and the pressure in the cavity was restored to normal. The emptying and argon purging were repeated twice. The cavity was maintained under an argon atmosphere and normal pressure. 10 g of silicon powder were added to the crucible via the feed system and heated to approximately 1420 °C to melt. The crucible pressure was adjusted to allow the melt to be extruded at a flow rate of 5 µl / min. The spinneret was positioned 150 mm from the collector, and spinning was carried out at a voltage of 20 kV. It was clearly visible to the naked eye that the fibrous substance extended from the opening to the collector.After collecting products for one hour, samples were taken and analyzed microscopically. The results showed that the diameter of the produced silicon nanofibers ranged from 200 to 400 nm. Example 4, according to the invention

[0046] All valves of the apparatus were closed, the vacuum pump was switched on, and the pressure in the cavity was released to below 4 Pa. The vacuum pump valve was switched off, the argon valve was switched on, and the pressure in the cavity was restored to normal. The emptying and argon purging were repeated twice. The cavity was maintained under an argon atmosphere and normal pressure. 10 g of silicon powder were added to the crucible via the feed system and heated to approximately 1510 °C to melt. The crucible pressure was adjusted to allow the melt to be extruded at a flow rate of 5 µl / min. The spinneret was positioned 150 mm from the collector, and spinning was carried out at a voltage of 20 kV. It was clearly visible to the naked eye that the fibrous substance extended from the opening to the collector.After collecting products for one hour, samples were taken and analyzed microscopically. The results showed that the diameter of the produced silicon nanofibers ranged from 150 to 350 nm. Example 5, according to the invention

[0047] All valves of the apparatus were closed, the vacuum pump was switched on, and the pressure in the cavity was released to below 4 Pa. The vacuum pump valve was switched off, the hydrogen valve was switched on, and the pressure in the cavity was restored to normal. The emptying and hydrogen purging process was repeated twice. The cavity was maintained under a hydrogen atmosphere and normal pressure. 10 g of silicon powder were added to the crucible via the feed system and heated to approximately 1510 °C to melt. The crucible pressure was adjusted to allow extrusion of the melt at a flow rate of 8 µl / min. The spinneret was positioned 150 mm from the collector, and spinning was carried out at a voltage of 30 kV. It was clearly visible to the naked eye that the fibrous substance extended from the opening to the collector.After collecting products for one hour, samples were taken and analyzed microscopically. The results showed that the diameter of the produced silicon nanofibers ranged from 100 to 400 nm. Example 6, according to the invention

[0048] All valves of the apparatus were closed, the vacuum pump was switched on, and the pressure in the cavity was released to below 4 Pa. The vacuum pump valve was switched off, the hydrogen valve was switched on, and the pressure in the cavity was restored to normal. The emptying and hydrogen purging process was repeated twice. The cavity was maintained under a hydrogen atmosphere and normal pressure. 10 g of silicon powder were added to the crucible via the feed system and heated to approximately 1510 °C to melt. The crucible pressure was adjusted to allow extrusion of the melt at a flow rate of 2.5 µl / min. The spinneret was positioned 150 mm from the collector, and spinning was carried out at a voltage of 40 kV. It was clearly visible to the naked eye that the fibrous substance extended from the opening to the collector.After collecting products for one hour, samples were taken and analyzed microscopically. The results showed that the diameter of the produced silicon nanofibers ranged from 50 to 200 nm. Example 7, according to the invention

[0049] All valves of the apparatus were closed, the vacuum pump was switched on, and the pressure in the cavity was released to below 4 Pa. The vacuum pump valve was switched off, the hydrogen valve was switched on, and the pressure in the cavity was restored to normal. The emptying and hydrogen purging process was repeated twice. The cavity was maintained under a hydrogen atmosphere and normal pressure. 10 g of silicon powder were added to the crucible via the feed system and heated to approximately 1510 °C to melt. The crucible pressure was adjusted to allow extrusion of the melt at a flow rate of 2.5 µl / min. The spinneret was positioned 150 mm from the collector, and spinning was carried out at a voltage of 45 kV. It was clearly visible to the naked eye that the fibrous substance extended from the opening to the collector.After collecting products for one hour, samples were taken and analyzed microscopically. The results showed that the diameter of the produced silicon nanofibers ranged from 50 to 150 nm. Example 8, according to the invention

[0050] All valves of the apparatus were closed, the vacuum pump was switched on, and the pressure in the cavity was released to below 4 Pa. The vacuum pump valve was switched off, the hydrogen valve was switched on, and the pressure in the cavity was restored to normal. The emptying and hydrogen purging process was repeated twice. The cavity was maintained under a hydrogen atmosphere and normal pressure. 10 g of silicon powder were added to the crucible via the feed system and heated to approximately 1510 °C to melt. The crucible pressure was adjusted to allow extrusion of the melt at a flow rate of 10 µl / min. The spinneret was positioned 150 mm from the collector, and spinning was carried out at a voltage of 50 kV. It was clearly visible to the naked eye that the fibrous substance extended from the opening to the collector.After collecting products for one hour, samples were taken and analyzed microscopically. The results showed that the diameter of the produced silicon nanofibers ranged from 100 to 250 nm. Example 9, according to the invention

[0051] All valves of the apparatus were closed, the vacuum pump was switched on, and the pressure in the cavity was released to below 4 Pa. The vacuum pump valve was switched off, the nitrogen valve was switched on, and the pressure in the cavity was restored to normal. The emptying and nitrogen purging were repeated twice. The cavity was maintained under a nitrogen atmosphere and normal pressure. 30 g of tin powder were added to the crucible via the feed system and heated to approximately 250 °C to melt. The crucible pressure was adjusted to allow the melt to be extruded at a flow rate of 5 µl / min. The spinneret was positioned 150 mm from the collector, and spinning was carried out at a voltage of 30 kV. It was clearly visible to the naked eye that the fibrous substance extended from the opening to the collector.After collecting products for one hour, samples were taken and analyzed microscopically. The results showed that the diameter of the produced tin nanofibers ranged from 130 to 300 nm.

[0052] The preferred arrangements of the revelation disclosed above are merely an illustration of the revelation. The preferred arrangements are not to be understood in all their details, and the revelation is not limited to the specific arrangements. In view of the teachings contained herein, many modifications and changes are obviously possible. The present revelation has been selected and described in detail to explain the arrangements of the revelation and the revelation itself. The revelation is limited only by the scope of the claims contained in the appendix and the claims contained therein.

Claims

[1] Melt electrospinning process, comprising: S1, Heating an inorganic material to a molten state to form a melt, and S2, Forming the melt into fibers by electrospinning, wherein the melt electrospinning is carried out at an ambient temperature of no more than 100 °C and normal pressure; wherein the inorganic material is silicon or tin, and wherein the melt flow rate during the electrospinning process is 2 to 10 µl / min; wherein the melt electrospinning is carried out under vacuum, an inert atmosphere or a reduction atmosphere, wherein the inert atmosphere is selected from nitrogen and / or argon, and wherein the reduction atmosphere comprises hydrogen; where the voltage for electrospinning is set to be between 10 and 50 kV. [2] Method for electrofusion spinning according to claim 1, wherein the voltage for electrofusion spinning is set to be 12 to 45 kV. [3] Method for melt electrospinning according to claim 1, wherein the flow rate of the melt during the electrospinning process is 2 to 8 µl / min. [4] Method for melt electrospinning according to claim 1, wherein the melt electrospinning is carried out through one or more spinnerets.

Images