Preparation and properties of PVA nanofibers with spiral ordered internal structure

The spinning solution of PVA(polyvinyl alcohol) was chosen as the spiral spinning research object. With enough needle length, the macromolecules were straightened and aligned under laminar flow theory. The spiral spinning needle controlled the spiral twisting of the straightened macromolecules. The motion trajectory of titanium dioxide(nanoparticles) in nanofibers was photographed by TEM(transmission electron microscope) under the action of spiral centripetal force, which directly verified the feasibility of the spiral spinning principle. The greater the number of spiral spinning needles, the tighter the spiral arrangement inside the nanofibers and the greater the crystallinity of the nanofibers. The SEM(scanning electron microscope) observation revealed that the diameter of nanofibers had a relationship with the number of spiral spinning needles. When the spiral number of spinning needle was 13, the tensile and bursting properties of the nanofiber membrane were optimal, but when the spiral number of spinning needle was 19, the pore structure, electrical resistance, and antibacterial properties of the nanofiber membrane were optimal.


Introduction
Because of the rapid advancement of electrospinning technology, electrospun nanofiber membranes as filter materials, electronic materials, biomedical engineering materials, and electrical materials have gained increasing attention from researchers both at home and abroad [1][2][3][4]. There are numerous methods for producing and processing nanofibers at the moment. Electrospinning can be divided into two types based on the state of the polymers used to make nanofiber membranes: solution electrospinning and melt electrospinning, the latter is also known as solvent-free electrospinning [5,6]. The most common solution electrospinning or single nozzle electrospinning device is relatively simple, but low productivity and the residue of organic/toxic solvents in nanofibers is the main challenges at present [2]. The advancement of needleless electrospinning and multineedle electrospinning research demonstrates the benefits of rapid and large-scale production of electrospun membranes, laying the groundwork for their expanded application. Because melt electrospinning uses fewer toxic solvents, it is considered more environmentally friendly than solvent electrospinning [4,5].
At present, domestic and foreign scholars have developed various functional nanofiber materials using the above spinning methods. Ng et al [7] created poly (caprolactone) (PCL), poly (lactic acid) (PLA), and poly (vinyl alcohol) (PVA) nanofiber mats using a rotating disc electrospinning system. Compared to the traditional singlenozzle electrospinning, this needleless electrospinning method has higher productivity, and it has been demonstrated that it is easier to operate but has no blockage, and it can form nanofiber mats at relatively low Any further distribution of this work must maintain attribution to the author(s) and the title of the work, journal citation and DOI.
voltage. Liu et al [8][9][10][11] used linear multi-needles or circular multi-pillows, while Yu et al [12] developed an electrostatic spinning device with stepped pyramid spinnerets to solve the problem of uneven electric field at the needle tip to prepare functional nanofibers. In 2006, He et al [13] was the first to propose bubble spinning technology for the preparation of nanofibers. After the formation of bubbles by spinning solution, droplets were drawn into nanofibers by the action of a high-voltage electrostatic field [14]. He et al pointed out that after several generations of improvement in bubble electrostatic spinning technology, the mature and stable bubble electrostatic spinning technology can realize mass production of nanofibers [15,16], and bubble electrostatic spinning technology successfully prepared PAN, PVA, and multi-component composite nanofibers (films) [17,18]. Zakaria et al [19] invented melt electrospinning and used the CO 2 laser melting device to create fine polypropylene (pp) nanofibers of polyvinyl butyral (PVB). The main focus of the existing electrostatic spinning devices is on yield and efficiency, and the nanofiber membrane still has obvious mechanical weaknesses.
At present, domestic and foreign scholars have developed various functional nanofiber materials using the aforementioned spinning methods, so many domestic and international researchers are currently studying spider silk. The primary reason is its numerous benefits, which include light weight, good elasticity, ultraviolet resistance, biodegradability, and excellent biocompatibility. However, no other material can match its outstanding mechanical properties [20,21]. The spider's long tube spinning is infinitely close in this study, and spiral spinning control technology is used to control the spiral arrangement structure of macromolecules in nanofibers. The laminar flow and spiral twisting principles are combined to control the spiral orientation arrangement of macromolecules in nanofibers, and the structure and properties of spiral orderly spun nanofibers (membranes) are discussed [22]. Spiral spinning technology, which is based on long needle spinning technology [10], is a type of macromolecule spinning control technology. When a macromolecule is straightened, its molecular chain is twisted by a spiral needle under the influence of a spiral magnetic field, which increases the transverse pressure between macromolecules and improves the sliding resistance between macromolecules [3,4], thereby improving the physical and mechanical properties of a single nanofiber filament. A complete set of selfassembled spiral spinning equipment was built to test the theoretical feasibility of spiral spinning. The selfassembled spiral spinning equipment(as shown in figure 1) contains a single-push injection pump, a highvoltage electrostatic generator with a maximum adjustment of 50 kV, a 10 ml syringe, a stainless steel bending flexible needle with a length of 300 mm, a 9 V battery, the adjustable resistor from 0 ohms to 20 ohms, a stable conductive wire, and an injection tube. The pre-prepared spinning solution is pumped into the syringe during spiral spinning, the injection tube is attached to the single-push injection pump, and the sample injection speed of spinning solution is set. The stainless steel bending flexible needle's pin is tightly connected to the syringe's nipple, and the front 150 mm of the stainless steel flexible needle (near the nipple) is straight, while the rear 150 mm of the stainless steel flexible needle (near pinhead) is wound into different spiral numbers. A closed loop circuit is formed by the battery, the conductive wire, the adjustable resistor, and the spiral part of the stainless steel bending flexible needle. When a small current is generated in the circuit and the polymer spinning solution passes through the spiral part of the stainless steel bending needle, a spiral centripetal force is generated on the polymer macromolecular chains under the action of a magnetic field, resulting in a twisting effect among the polymer macromolecular chains. The polymer spinning solution is now sprayed out of the stainless steel bending needle, which is connected to the positive pole of a high-voltage electrostatic generator. The cathode of that high-voltage electrostatic generator is connected to the collecting end of nanofiber (flat aluminum foil paper), and when the high-voltage electrostatic generator generates high-voltage static electricity, the polymeric spinning solution is drawn into nanofiber and uniformly collected on the aluminum foil paper.

Materials and methods
2.1. Raw materials and reagents PVA2488 (polyvinyl alcohol, molecular weight of 120000, analytical purity) was supplied by Sinopharm Chemical Reagent Co., Ltd Deionized water (analytical pure) is provided by Nanjing Jinghao Water Treatment Technology Co., Ltd. TiO 2 (analytical purity, average diameter 50-60 nm) was supplied by Beijing Wan Yun Hua Rui Chemical Co.,Ltd Staphylococcus aureus, ATCC6638; SCDLP liquid culture medium, counting culture medium (EA) (provided by Nanwei Yueda Fiber Technology Co., Ltd).

Preparation of spiral ordered nanofibers with internal structure
The polyvinyl alcohol (PVA) was used for long-needle spiral electrostatic spinning. A mass fraction of 8.5% spinning solution with PVA as the solute and deionized water as the solvent prior to spinning. To prevent the solvent from volatilizing during the stirring process, the mixture was sealed in a small-capacity glass container and stirred for 4-5 h on a heat-collecting constant-temperature magnetic stirrer. The magnetic stirrer's water bath temperature was set to 85 ure magnetic stirrer. The magnetic stirrere was sealed in a small-capacity glass mPwa) was injected into a 10 ml needle tube which was attached to an injection pump. In the spinning experiment, different numbers of long needle spirals were used. The needle diameter was 0.7 mm, and the needle configuration was as follows: 150 mm long needle + x number of spirals (x is 0, 4, 7, 10, 13, 16, 19 respectively). The injection speed of electrostatic spinning is set to 1.1 ml h −1 , the vertical distance between the needle and the receiving plate (covered with aluminum foil) is 18 cm, the front section of the spiral needle is connected to the anode of the high-voltage electrostatic generator, the receiving plate is connected to the cathode of the highvoltage electrostatic generator, and the voltage is set to 20 kV, resulting in the formation of a nanofiber film on the aluminum foil after spinning. During the spinning process, the temperature is 28 re is 28 m, the front section of th We prepared the PVA solution containing TiO 2 for spinning and then scanned PVA/TiO 2 composite nanofibers with a transmission electron microscope to observe the distribution and arrangement of TiO 2 nanoparticles in nanofibers to verify the role of spiral. We prepare PVA aqueous solution with mass fraction of 8.5% according to the above method, and add TiO 2 nanoparticles with mass fraction of 1.5% (the diameter of TiO 2 nanoparticles is 50∼60 nm), then seal the PVA aqueous solution with TiO 2 completely, put it on a highspeed disperser, stir it for 1 h, and use an ultrasonic cleaning machine to uniformly disperse TiO 2 nanoparticles in PVA aqueous solution. Add the dispersed spinning solution into the syringe and fix it on the injection pump. The needle used in spinning is the same as that used in spinning pure PVA nanofibers.

Characterization of nanofiber membranes 2.3.1. Testing of microscopic morphology
The appearance of the nanofiber membrane was assessed using a scanning electron microscope (Japan Electronics Co., Ltd), and the diameter of a single nanofiber was measured using imagJ software (National Institute of Mental Health, USA), with 150 nanofibers chosen for measurement and the average value was taken.

Testing of tensile and bursting performance
The tensile properties of nanofiber membranes were evaluated using a universal testing machine (INSTRON-3365, American instron Company), with each sample tested five times. After testing, the average value was calculated [19,20]. The thickness of nanofiber membranes was measured with a micrometer at ten different locations, and the average value was calculated. The following formula was used to calculate the tensile breaking strength and breaking elongation of nanofiber membranes: The bursting performance of the nanofiber membranes were also evaluated using a universal testing machine (INSTRON-3365, American instron Company), with the average value obtained after five times of testing. The distribution of nano-sized titanium dioxide in nanofibers was tested and analyzed using a TEM transmission electron microscope (Talos L120C, OuB tong optical technology Co., Ltd).

Testing of pore structure
An automatic pore tester (POROMETER 3G, Anton Paar (Shanghai)TRADING Co., Ltd) is used to test the pores of the nanofiber membrane. Before the testing, a circular nanofiber membrane with a uniform thickness and a diameter of 2.5 cm is taken, and the circular nanofiber membrane was fully immersed in the porofil solution before being placed in the instrument tank for characterization. The testing must determine the pore distribution in both the dry and wet states. Gravimetric analysis was used to determine porosity. First, the 3 cm long nanofiber membrane was dried to a constant weight and then weighed. The dried nanofiber membrane was then completely soaked in alcohol, and the weight of residual alcohol on the surface was removed, as well as the quality of the completely soaked nanofiber membrane, which was measured. As a result, the porosity was determined by the volume of alcohol in the nanofiber membrane sample and was calculated as follows: In the above formula, w 1 and w 2 represent the weight (g) of the nanofiber membrane before and after soaking in alcohol, respectively, D e represents the density of alcohol, and D p represents the density of the nanofiber membrane polymer.

Testing of crystallinity
The crystallinity of nanofibers was characterized by x-ray diffraction pattern analysis using an instrument called X'Pert Powder (Panaco, Netherlands). The dried nanofiber film was cut into small pieces and placed in a sample tank. The radiation source is a Cu target, with a tube voltage of 40 kV and a current of 40 mA. The diffraction angle range is set to 10°∼90°, and the scanning speed is 2°/min.

Testing of electrical performance
The resistance of the nanofiber membrane was characterized by a resistance tester (FT-400AHXM, Ningbo Ruike Weiye Instrument Co., Ltd), and the calculation formulas of the resistivity ρ and conductivity σ of the nanofiber membrane were as follows: In the above formula, R refers to the measured nanofiber membrane resistance (Ω); S refers to the measured area of nanofiber membrane (m 2 ); L refers to the measured thickness of nanofiber membrane (m).

Testing of antibacterial performance
The antibacterial properties of composite nanofiber membrane were tested according to the standard of industry standard FZ/T73023-2006 =Antibacterial Knitwear? with Staphylococcus aureus as the representative of bacteria. After cutting the nanofiber membrane sample into fragments, weigh (0.75 ± 0. 05) g and pack separately. Sterilize at 103 kPa and 125°C for 15 min for backup. Place the sample into a 10 ml test tube and add 0 Prepare 2 ml of culture medium bacterial suspension, then fix the test tube on the test tube rack. Incubate at 20-25°C for 24 h before sampling. Then, pipette 1 ml of the solution into SCDLP liquid culture medium, dilute it by 10 times, shake well, and add 1 ml to a sterilized plate. Pour and count about 15 ml of culture medium (EA), solidify at room temperature, invert the plate, and incubate at 37°C for 24 h before sampling and testing its antibacterial performance.
The evaluation indexes were bacterial number(G), bacteriostatic value(B) and bacteriostatic rate(H), and the detailed calculation formula is as follows: In the above formula: G-the number of bacteria tested with the nanofiber membrane; K-the average number of colonies (CFU) in two Petri dishes; L-dilution ratio; 15-Eluent concentration per milliliter; B-Bacteriostatic value; X n -the average number of bacteria counted after inoculating and cultureing two nanofiber membrane test samples for 1824 h; H-bacteriostatic rate as a percentage; P n -the viable bacteria concentration of a standard blank nanofiber membrane sample. Q i -the concentration of viable bacteria in a nanofiber membrane sample.  figure 2, and the diameter and thickness testing results of PVA nanofiber(membranes) were shown in table 1.The thickness of the nanofiber membrane was relatively uniform, controlled within 95-97 microns. Figure 2 and table 1 showed that as the number of spirals increases, the diameter of the nanofiber goes through two stages. When the number of spirals was increased from 0 to 7, the diameter of the nanofiber tends to increase, with the average diameter increasing from 113 nm to 162 nm. The diameter of nanofibers gradually decreased as the number of spirals increased from 7 to 22. The decreasing trend of nanofibers became gentle when the number of spirals exceeded 19, and the average diameter of nanofibers only decreased from 162 nm to 77 nm. PVA macromolecules were fully stretched after the spinning liquid was polymerized by PVA to move along the long needle when the number of spirals was small, and the spiral centripetal force (twisting force) generated by the spiral part of the needle was small, and the PVA macromolecular chains did not form efficient twisting. Straight macromolecular chains cannot rely on centripetal force to bring them close enough to each other to form a twisting effect; Instead, the transverse projection area of the originally tightly arranged macromolecular chains expands, and the macromolecular chain structure loosen. When the number of spirals gradually increased to 7, the spiral centripetal force (twisting force) generated by the spiral part of the spinning needle continued to increase, and PVA macromolecular chains form effective twisting among themselves, bringing the macromolecular structure inside the spun nanofibers closer together and reducing the fiber diameter significantly. Although the spiral centripetal force generated by the spiral part of the spinning needle continued to increase, because the pores formed between PVA macromolecular chains were getting smaller and smaller, further twisting PVA macromolecular chains was impossible, so the diameter change of nanofibers tended to be stable [23][24][25][26]. Figure 3 showed that the surface of PVA nanofibers prepared by needles with varying numbers of spirals were all very smooth, and it was also clear that as the number of spirals increased, the diameter of a single nanofiber first increased and then gradually decreased. It can also be seen from table 1 that when the number of spirals changed from 0 to 7, the average diameter of a single nanofiber increased and its uniformity also decreased; The average diameter of a single nanofiber was gradually decreasing as the number of spirals increased, and its uniformity was improving.

Results and discussion
3.2. Testing and analysis of crystallinity of nanofibers with internal ordered structure XRD pattern of PVA nanofibers was showed in figure 4. We can see from figure 4 that all nanofibers have strong peaks at 2θ (20°) corresponding to PVA crystal planes, and the calculated crystallinity was shown in table 2. Table 2 showed that as the number of spirals increased, the crystallinity of PVA nanofibers decreased at first and then gradually increased, indicating that when the number of spirals was less than 7, regular spiral orderly  arrangement had not formed inside PVA nanofibers. The spiral arrangement effect of macromolecules inside PVA nanofibers became more apparent as the number of spirals of spinning needles increased; that is, the more orderly the arrangement, the maximum crystallinity of nanofibers. This demonstrated that spiral needles can be used to control the spiral arrangement of macromolecules in a spinning solution. The more spiral needles there are, the more regular the spiral arrangement of macromolecules.

Mechanical properties of spiral ordered nanofiber membrane with internal structure
The tensile stress-strain curves of PVA nanofiber membrane were showed in figure 5, the bursting stress-strain curves of PVA nanofiber membrane were showed in figure 6. As shown in figure 5, the tensile stress-strain behavior of the PVA nanofiber membrane had changed clearly as the number of spirals increased. When the number of spirals was increased from 0 to 13, the breaking strength and elongation of the PVA nanofiber membrane were greatly improved; The breaking strength decreased from 6.565 MPa to 5.413 MPa by the fracture stress decreased by 17.55%, the fracture strain decreased from 1.23% to 0.9% by the fracture strain decreased by 26.83%. The tensile stress and fracture strain of PVA nanofiber membrane decreased gradually as the number of spirals increased from 13 to 22, with the tensile stress decreasing from 6.565 MPa to 5.413 MPa, the tensile stress decreasing by 17.55%, the tensile strain decreasing from 1.23% to 0.9%, and the tensile strain decreasing by 26.83%. As shown in figure 6, the bursting stress-strain behavior of PVA nanofiber membrane changed noticeably as the number of spirals increased. When the number of spirals increased from 0 to 13, it followed the tensile stressstrain trend. The bursting displacement and bursting stress of PVA nanofiber membranes showed an increasing trend, with the bursting stress rising from 7.37 MPa to 10   Theoretically, the changes in the above mechanical properties were analyzed as follows: as the number of needle spirals increased, the straightened PVA macromolecules were twisted by the spiral centripetal force of the magnetic field.
On the one hand, the deepening of the twist increased the transverse pressure of macromolecules, which increased the friction resistance between macromolecules, so that the macromolecules did not easily slip when the nano single fiber was stretched, and the breaking strength of the single fiber was improved. When subjected to external force, the nanofiber membrane was difficult to break. If the macromolecular chains were subjected to lateral pressure, the proximity of the macromolecular chains increased the Van Der Waals force and covalent bonding force between them, which improved the mechanical properties of nanofibers to some extent. When the number of spirals was increased beyond 13, the inclination degree of macromolecular chains increased, and the contribution to the strength of nanofibers was shown as a negative factor, that is, the effective decomposition force of nanofiber macromolecules in the longitudinal direction was less than that in the transverse direction, and the decrease of this effective decomposition force cannot compensate for the small increase in friction resistance.
As depicted in figure 7, an increase in the number of spiral needles resulted in an increase of the spiral twist angle (α), i.e., α 1 <α 2 <α 3 , leading to the greater spiral extrusion between macromolecular chains, and the resulting centripetal pressure will also increase, that is, F n1 <F n2 <F n3 . When macromolecular chains were subjected to external tensile force, the frictional resistance caused by macromolecular chain sliding will also increased, that is, f 1 <f 2 <f 3 . It can be assumed that the tensile tension(F 1 , F 2 , F 3) of polymer macromolecular chains were basically the same, and the decomposition force along the axial direction of nanofibers were  F 1 * Cosα 1 , F 2 * Cosα 2 , F 3 * Cosα 3 , respectively. Since α 1 <α 2 <α 3 , therefore, F 1 * Cosα 1 >F 2 * Cosα 2 >F 3 * Cosα 3 .
When the helix twist angle was changed from α 1 to α 2 , The tensile tension decomposition force along the fiber axis and the sliding resistance of macromolecular chains in the nanofibers after resisting external forces during the drawing process also increase, that is, α 2 can be used as a critical twist angle, but when the spiral twist angle exceed α 2 and increases to α 3 , the tensile tension decomposition force and macromolecular chain decreasd all the time after resisting the sliding resistance caused by external force during the stretching process, that is, the mechanical force generated by the whole nanofiber membrane will be reduced [27][28][29][30].
3.4. Pore structure analysis of spiral ordered nanofiber membrane with internal structure Table 3 showed testing result of the pore size for PVA nanofiber membranes, and figure 8 showed the pore distribution of PVA nanofiber membranes. It was clear that as the spiral number of spinning needle gradually increased from 0 to 22, the average pore diameter of the nanofiber membrane increased first and then decreased continuously, whereas the pore diameter and porosity increased first and then decreased. Figure 8 also showed that as the spiral number of spinning needle increased, the pore size distribution of PVA nanofiber membrane widened first and then narrowed, which was also related to the change in fiber diameter on PVA nanofiber membrane, that is, the larger the diameter of PVA nanofiber, the wider the pore size distribution, and the smaller the diameter of PVA nanofiber, the narrower the pore size distribution.
The main reason for the above result was that the diameter of the nanofiber inside itself influenced the pore size of the nanofiber membrane. The greater the pore size, the smaller the diameter of the nanofiber, the smaller the specific surface area of the nanofiber, and the smaller the pore size formed after uniform accumulation of Figure 7. Schematic diagram of the principle of helical twisting of macromolecular chains inside PVA nanofibers(F 1 , F 2 , F 3 -The tensile tension of the polymer macromolecular chain itself;∅, α 1 , α 2 , α 3 -Helical twist angle of polymer macromolecular chain;MF-IH-ideal helical macromolecular chain;F n1 , F n2 , F n3 -Centripetal pressure due to helical twisting;f 1 , f 2 , f 3 -Frictional resistance due to slippage of macromolecular chains).  nanofiber. According to some studies, the pore size of the nanofiber membrane was positively related to the diameter of the nanofiber inside, while the pore size of the nanofiber membrane was negatively related to the diameter of the nanofiber inside [23]. Its theory is simply consistent with the research on this topic and proves it to be so.

3.5.
Testing and analysis of resistance performance of spiral ordered nanofiber membrane with internal structure Table 4 displayed the resistivity testing result of the PVA nanofiber membrane. Table 4 showed that as the spiral number of spinning needle increased, the resistivity of the PVA nanofiber membrane increased and then decreased, whereas the conductivity decreased and then increased. The reason for this was that the macromolecular mechanism of nanofibers had a strong correlation, and the conductivity of the material increased as crystallinity increased. PVA macromolecules entered the spiral twisting stage after they had been fully straightened. When the spiral number was low, the centripetal spiral force generated by the magnetic field was insufficient; Instead, the original straightened macromolecules were disrupted and cannot form an orderly arrangement. When the spiral number increased to a certain point, the centripetal spiral force generated by the magnetic field produced an effective twisting effect, causing macromolecule twisting to become regular and macromolecule arrangement to gradually become orderly. The flow of electron in macromolecules will also become smoother at this time, resulting in a corresponding increase in the conductivity of nanofiber membranes. That is, after a certain number of needles is increased, the orderly arrangement of nanofibers will be more regular, and the resistivity of the obtained nanofiber membranes will also decrease [31][32][33].
3.6. Testing and analysis of antibacterial performance of spiral ordered nanofiber membrane with internal structure Table 5 displayed the antibacterial testing result of the PVA/TiO 2 nanofiber membrane. Figure 9 depicted the number of colonies tested by the PVA/TiO 2 nanofiber membrane. As shown in table 5, the bacteriostatic rate and value of the PVA/TiO 2 composite nanofiber membrane changed noticeably as the spiral number of spinning needles increased. The bacteriostatic rate of PVA/TiO 2 composite nanofiber membrane decreased from 85.98% to 81.36% as the spiral number of spinning needles increased from 0 to 7, and the bacteriostatic value decreased from 0.7848 to 0.6603. These three PVA/TiO 2 composite nanofiber membranes used the same raw materials. And except for the spiral number of spinning needles, the parameters of high-pressure electrostatic spinning were the same. This proved that the spiral design of the spinning needles influenced the distribution of TiO 2 on PVA nanofibers. When the spiral number of spinning needles was zero, the distribution of TiO 2 along the axial direction of PVA nanofibers was relatively uniform, and it was not necessarily fixed in the radial direction, according to the long-needle spinning principle of Tian Dan and others (that is, both inside and outside) [34]. When the spiral number increased to four, the distribution of TiO 2 along the axis of PVA nanofibers was relatively uniform, resulting in a chaotic distribution of TiO 2 on PVA nanofibers, i.e., the distribution of TiO 2 was irregular, so the distribution of TiO 2 on PVA nanofiber membrane was not very uniform, resulting in a decrease in the antibacterial property of PVA/TiO 2 composite nanofiber membrane. The bacteriostatic rate of PVA/TiO 2 nanofiber membrane increased obviously as the spiral number of spinning needle increased from 7 to 22, but the increasing range became smaller and smaller. The bacteriostatic rate of PVA/TiO 2 nanofiber membrane increased from 81.36% to 98.19%, and the bacteriostatic value increased from 0.6603 to 1.7538. The reason for this was that the spiral force generated once the needle spirals reach a certain level was sufficient. It can spiral TiO 2 along the axial direction of PVA nanofibers and distribute TiO 2 as much as possible on the outer layer of PVA nanofibers. However, once a certain number of spinning needles was reached, the spiral effect became large enough, and the spiral arrangement of TiO 2 along the axial direction of PVA nanofibers reached an extreme, and the antibacterial property of the PVA/TiO 2 nanofiber membrane can no longer be greatly improved. Furthermore, figure 8 clearly showed that the number of colonies on the PVA/TiO 2 nanofiber membrane prepared with different screw numbers differed each other. When the spiral number of spinning needle was 7, the number of colonies on the PVA/TiO 2 nanofiber membrane was the greatest, indicating that its antibacterial property was the worst at this time, whereas when the spiral number of spinning needle was 19 or 12, there were virtually no colonies, indicating that this sample had the best antibacterial property.
3.7. Verification research of spiral ordered nanofiber membrane with internal structure Figure 10 depicted a transmission electron microscope diagram of PVA/TiO 2 . Figure 10 showed that when the spiral number of spinning needle was zero, the twisting effect produced by the spiral needle tube was not visible. The transmission electron microscope testing revealed that TiO 2 nano-particles were arranged in a straight line, which was consistent with the findings of Tian Dan [34] and others. When the spiral number of spinning needle changed to 4, 7, 10, 13, and 16, the spiral distribution of nano-TiO 2 particles in PVA nanofibers was becoming more apparent because of the spiral centripetal force; that is, the inclination of TiO 2 nano-particles along the length direction of nanofibers changed to some extent. The inclination of TiO 2 nano-particles along the length direction of nanofibers increased as the number of spirals increased, indicating that the spiral spinning process did play a role in spiral twisting of macromolecular chains inside PVA nanofibers.

Conclusion
In this study we are fully close to the spider's long tube spinning, and integrate with the physical principle of spiral magnetic field. Based on the laminar flow theory, we straighten and orient the macromolecular chains under the condition of sufficient needle length, and rely on the spiral spinning needle to twist the straightened macromolecular chains. Under the effect of the spiral centripetal force, the spiral twisting will occur between the macromolecules. When the number of needle spiral spinning reached a certain value, adequate spiral ordered twisting can be obtained between stretched macromolecular chains; Composite nanofibers were prepared by spiral spinning a spinning solution mixed with nano TiO 2 particles, and the motion trajectory of the nanoparticles in the nanofibers was captured using transmission electron microscopy, which intuitively verified the feasibility of the spiral spinning principle; The spiral arrangement of macromolecules inside the nanofibers was characterized by calculating the crystallinity of the nanofibers. The more needles spiral spun, the closer the spiral arrangement inside the nanofibers; Through scanning electron microscopy observation, the appearance of the nanofiber membrane has undergone certain changes under spiral physics technology; The analysis of the tensile and bursting properties of nanofiber membranes proves that the nanofiber structure after spiral spinning has a significant impact on the membrane performance; At the optimal helix number of spinning needles, the nanofiber membrane achieved the optimal values in pore structure, electrical resistance, and antibacterial properties.