CN118390197A - Method for macro spinning of aramid nanofiber - Google Patents

Abstract

The invention discloses a method for mass spinning of aramid nanofibers, comprising the following steps: S1: adding aramid fibers to a potassium hydroxide solution, heating and stirring to obtain an ANF dispersion; S2: mixing the ANF dispersion obtained in step S1 with a PVA solution, heating and stirring evenly to obtain an ANF/PVA spinning fluid; S3: subjecting the ANF/PVA spinning fluid to wet spinning to obtain aramid nanofiber gel filaments; S4: drying the aramid nanofiber gel filaments to obtain aramid nanofiber filaments. The invention regulates the spinning fluid and the coagulation bath respectively to improve the strength and spinning speed of the gel fiber, and can solve the problems of the prior art in the large-scale spinning of aramid nanofibers, such as the difficulty in drafting and winding, and the unsatisfactory mechanical properties.

Description

A method for mass spinning of aramid nanofibers

Technical Field

The invention relates to the technical field of fiber spinning, in particular to a method for macro-spinning aramid nanofibers.

Background technique

The recycling of waste textiles is of great significance for green environmental protection, energy conservation and emission reduction, and is also an inevitable demand for the sustainable development of the textile industry. Aramid fiber is widely used in national defense, aerospace, special protection and other fields due to its light weight, high strength, high wear resistance and flame retardancy. However, a large amount of aramid fibers are treated by incineration and filling every year, resulting in a large waste of resources. At present, the macroscopic aramid filaments can be converted into nano-scale fibers by chemical splitting. Because of their higher specific surface area and better mechanical properties, they have important application value for improving the performance of composite materials, such as strength, stiffness and toughness. Nano-sizing aramid fibers and preparing regenerated aramid fibers by reorganization is one of the important ways to give aramid fibers a new life. Among them, the aramid nanofiber filaments prepared by wet spinning have similar morphology and properties to the original aramid fibers, and have the characteristics of high softness, excellent mechanical properties and flame retardancy. In addition, as a one-dimensional linear structure, aramid nanofibers can be compounded with other nanofunctional materials to prepare composite materials with multiple functions such as conductivity, antibacterial, thermal insulation, and energy storage. They have broad application prospects in all walks of life and have therefore received widespread attention from the scientific research community.

The wet spinning method for preparing aramid nanofiber filaments requires the preparation of aramid nanofiber spinning fluid first, and the squeezing of the spinning fluid into a coagulation bath to form aramid nanofiber gel filaments, which are then dried to obtain aramid nanofiber filaments. However, the transformation of aramid nanofiber spinning fluid into gel fiber is a slow process, and aramid nanogel fiber only has a single hydrogen bond network constructed by amide groups, and has poor mechanical properties, making it difficult to meet the requirements of rapid, continuous spinning and mass production.

Therefore, developing a method for large-scale spinning of aramid nanofibers, which can not only achieve the requirements of rapid spinning large-scale preparation, but also improve the mechanical properties of aramid nanofiber filaments, is an important research direction of current aramid nanofiber preparation technology.

Summary of the invention

In view of the above problems existing in the prior art, the present invention provides a method for large-scale spinning of aramid nanofibers. The present invention regulates the spinning fluid and the coagulation bath respectively to improve the strength and spinning speed of the gel fiber, and can solve the problems of the prior art in large-scale spinning of aramid nanofibers such as drafting, winding difficulties and unsatisfactory mechanical properties.

The technical solution of the present invention is as follows:

The object of the present invention is to provide a method for macro-spinning of aramid nanofibers, the method comprising the following steps:

S1: adding aramid fiber into potassium hydroxide solution, heating and stirring to obtain ANF dispersion;

S2: mixing the ANF dispersion obtained in step S1 with the PVA solution, heating and stirring to obtain an ANF/PVA spinning fluid;

S3: The ANF/PVA spinning fluid is wet-spinned to obtain aramid nanofiber gel filaments;

S4: Drying the aramid nanofiber gel filaments to obtain aramid nanofiber filaments.

In one embodiment of the present invention, in step S1, the potassium hydroxide solution consists of potassium hydroxide, water and dimethyl sulfoxide; the concentration of potassium hydroxide in the potassium hydroxide solution is 7.5-150 g/L; and the volume ratio of dimethyl sulfoxide to water in the potassium hydroxide solution is 25-100:1.

In one embodiment of the present invention, in step S1, the mass ratio of the aramid fiber to the potassium hydroxide in the potassium hydroxide solution is 1:0.5-1.5.

In one embodiment of the present invention, in step S1, the conditions for heating and stirring are: temperature of 65-95° C., time of 6-24 hours, and stirring speed of 500-1500 rpm.

In one embodiment of the present invention, in step S1, the concentration of the ANF dispersion is 0.5-10%.

In one embodiment of the present invention, in step S2, the concentration of the PVA solution is 0.5-15%; the volume ratio of the ANF dispersion to the PVA solution is 2:0.1-2.

When the concentration of ANF dispersion or PVA increases, the viscosity of the spinning solution increases. It is too viscous to be squeezed out of the spinneret hole smoothly, making it difficult to carry out continuous spinning.

In one embodiment of the present invention, in step S2, the temperature of heating and stirring is 60-95°C.

In one embodiment of the present invention, in step S3, during the wet spinning process, the spinning fluid is extruded by a propeller and then passes through a spinneret, a coagulation bath, and a winding drum in sequence.

The temperature of the spinning fluid is 20-80°C, and the temperature of the coagulation bath is 20-60°C.

In one embodiment of the present invention, the coagulation bath is an acidic coagulation bath, an alkaline coagulation bath or a deionized water coagulation bath.

In one embodiment of the present invention, the acid reagent in the acidic coagulation bath is one or more of sulfuric acid, hydrochloric acid, nitric acid, formic acid, acetic acid, sulfurous acid, phosphoric acid, lactic acid, benzoic acid, and acrylic acid.

In one embodiment of the present invention, the concentration of the acid reagent in the acid coagulation bath is 0.05-5 mol/L.

In one embodiment of the present invention, the alkaline agent in the alkaline coagulation bath is one or more of sodium hydroxide, sodium carbonate, sodium phosphate, sodium orthosilicate, potassium tert-butoxide, sodium tert-butoxide, potassium hydride, sodium hydride, potassium hydroxide, and ammonium hydroxide.

In one embodiment of the present invention, the concentration of the alkaline agent in the alkaline coagulation bath is 0.05-5 mol/L.

In one embodiment of the present invention, when the spinning fluid is extruded, the specification of the spinneret is 8-30G, the extrusion speed of the propeller is 0.3-30ml/min; the winding speed of the winding drum is 0.2-14m/min; by changing the winding speed of the winding drum, a draft of -0.8-1.5 times can be achieved.

In one embodiment of the present invention, in step S4, the drying process is freeze-drying or heat-drying.

In one embodiment of the present invention, the freeze-drying conditions are: temperature of -35°C, vacuum degree of 10-20Pa, and time of 12-24 hours; the heating drying conditions are: temperature of 80-150°C, and time of 6-12 hours.

The beneficial technical effects of the present invention are:

(1) In the present invention, polyvinyl alcohol solution is added to the ANF solution. During the deprotonation process of the aramid fiber, the polyvinyl alcohol is uniformly coated on the surface of the aramid nanofiber to construct a hydrogen bond cross-linking network, form a good interface interaction, and simultaneously improve the strength and toughness of the ANF/PVA gel fiber filaments, thereby effectively improving the spinning speed of the ANF gel fiber filaments.

(2) The coagulation bath in the present invention can regulate the sol-gel transition rate of aramid nanofibers. By changing the type and concentration of the proton donor, the fiber gelation rate is controlled, and then the gel fiber skin-core structure is regulated, which affects the orderly arrangement of the aramid nanofibers in the gel filaments. The internal microstructure of the gel fiber is regulated, and the resulting aramid nanofiber filaments have high orientation, mechanical strength, chemical corrosion resistance and high temperature resistance, and have broad application prospects in the field of preparing high-performance regenerated chemical fibers.

(3) By using the aramid nanofiber gel filaments provided by the present invention, different forms of aramid nanofiber filaments and aramid nanofiber aerogel filaments can be obtained by adopting different dry spinning methods. The aramid nanofiber filaments and aramid nanofiber aerogel filaments not only have high mechanical strength and orientation but can also be woven into various fabrics such as woven fabrics and knitted fabrics through textile processing methods.

(4) Compared with the preparation method of the prior art, the technical solution of the present invention has a simple process, low production cost and energy consumption, less environmental pollution, and the large-scale spinning industry can meet the requirements of large-scale production.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG1 is a schematic diagram of the equipment composition of wet spinning in the present invention;

FIG2 is an optical photograph of the ANF dispersion, PVA solution and ANF/PVA spinning fluid in Example 1 of the present invention;

FIG3 is an optical photograph of aramid nanofiber gel filaments in Example 2 of the present invention;

FIG4 is a scanning electron microscope photograph of aramid nanofiber filaments in Example 3 of the present invention;

FIG5 is an optical photograph of aramid nanofiber filaments in Example 4 of the present invention;

FIG6 is an optical photograph of the aramid nano-aerogel fiber in Example 8 of the present invention and a corresponding scanning electron microscope photograph;

FIG7 is a tensile stress-strain curve of aramid nanofiber gel filaments of Example 2 of the present invention and Comparative Example 1;

FIG8 is a tensile stress-strain curve of aramid nanofiber gel filaments of Examples 1-5 of the present invention;

FIG9 is a tensile stress-strain curve of aramid nanofiber filaments of Examples 1-5 of the present invention;

FIG10 is a tensile stress-strain curve of aramid nanofiber gel filaments obtained in different coagulation baths in Examples 2, 6 and 7 of the present invention;

FIG11 is a tensile stress-strain curve of aramid nanofiber filaments obtained in different coagulation baths in Examples 2, 6 and 7 of the present invention;

FIG12 is a schematic diagram of a method for calculating gelation time;

FIG13 is a graph showing the gelation time of different coagulation bath spinning fluids in Examples 2, 6 and 7 of the present invention;

FIG. 14 shows the fastest spinning take-up speeds of different coagulation bath spinning fluids in Examples 2, 6 and 7 of the present invention.

Detailed ways

The present invention is described in detail below in conjunction with the accompanying drawings and embodiments.

FIG1 is a schematic diagram of the wet spinning equipment used in the present invention, which is composed of a propeller, a spinneret, a coagulation bath and a winding drum.

Example 1

A method for macro-spinning aramid nanofibers, the method comprising the following steps:

(1) 1.5 g of aramid fiber was added to a potassium hydroxide solution (composed of 2.25 g of potassium hydroxide, 50 mL of dimethyl sulfoxide and 2 mL of deionized water), and stirred at 95° C. for 24 hours to obtain a 3 wt % dark red aramid nanofiber dispersion;

(2) adding 0.375 g of polyvinyl alcohol to 25 mL of dimethyl sulfoxide and stirring at 95° C. for 4 hours to obtain a 1.5 wt % transparent polyvinyl alcohol solution;

(3) mixing the 3 wt % aramid nanofiber dispersion prepared in step (1) and the 1.5 wt % transparent polyvinyl alcohol solution prepared in step (2) in a volume ratio of 2:1, stirring and mixing at 85° C. for 4 hours to obtain an ANF/PVA spinning fluid;

(4) passing the ANF/PVA spinning fluid obtained in step (3) through a propeller, through a 21G spinneret, into a coagulation bath (5 L deionized water) at a speed of 4 ml/min, solidifying the spinning fluid into aramid nanofiber gel filaments, and collecting the filaments on a winding drum at a speed of 6 m/min;

(5) The aramid nanofiber gel filaments obtained in step (4) are wound onto a yarn bobbin from a winding drum, and placed in an oven at 100° C. to dry for 8 hours to obtain aramid nanofiber filaments.

FIG2 is an optical photograph of the ANF dispersion, PVA solution and ANF/PVA spinning fluid in this embodiment. It can be seen from the figure that the spinning fluid is uniform and stable, and still has good dispersibility after storage for 180 days. The solution has no nanofiber deposition and can be used for wet spinning.

Example 2

A method for macro-spinning aramid nanofibers, the method comprising the following steps:

(1) 1.5 g of aramid fiber was added to a potassium hydroxide solution (composed of 2.25 g of potassium hydroxide, 50 mL of dimethyl sulfoxide and 2 mL of deionized water), and stirred at 95° C. for 24 hours to obtain a 3 wt % dark red aramid nanofiber dispersion;

(2) adding 0.75 g of polyvinyl alcohol to 25 mL of dimethyl sulfoxide and stirring at 95° C. for 4 hours to obtain a 3 wt % transparent polyvinyl alcohol solution;

(3) mixing the 3 wt % aramid nanofiber dispersion prepared in step (1) and the 3 wt % transparent polyvinyl alcohol solution prepared in step (2) in a volume ratio of 2:1, stirring and mixing at 85° C. for 4 hours to obtain an ANF/PVA spinning fluid;

(4) passing the ANF/PVA spinning fluid obtained in step (3) through a propeller, through a 21G spinneret, into a coagulation bath (5 L deionized water) at a speed of 4 ml/min, solidifying the spinning fluid into aramid nanofiber gel filaments, and collecting the filaments on a winding drum at a speed of 6 m/min;

(5) The aramid nanofiber gel filaments obtained in step (4) are wound onto a yarn bobbin from a winding drum, and placed in an oven at 100° C. to dry for 8 hours to obtain aramid nanofiber filaments.

Figure 3 is an optical photograph of the aramid nanofiber gel filaments in this embodiment. It can be seen from the figure that the gel filaments are obtained from the ANF/PVA spinning fluid, and a hydrogen bond cross-linking network is formed between the ANF and PVA molecules, which greatly enhances the structural mechanical properties of the gel filaments and can be smoothly and continuously wound into the yarn tube without breaking.

Example 3

A method for macro-spinning aramid nanofibers, the method comprising the following steps:

(1) 1.5 g of aramid fiber was added to a potassium hydroxide solution (composed of 2.25 g of potassium hydroxide, 50 mL of dimethyl sulfoxide and 2 mL of deionized water), and stirred at 95° C. for 24 hours to obtain a 3 wt % dark red aramid nanofiber dispersion;

(2) adding 1.5 g of polyvinyl alcohol to 25 mL of dimethyl sulfoxide and stirring at 95° C. for 4 hours to obtain a 6 wt % transparent polyvinyl alcohol solution;

(3) mixing the 3 wt % aramid nanofiber dispersion prepared in step (1) and the 6 wt % transparent polyvinyl alcohol solution prepared in step (2) in a volume ratio of 2:1, stirring and mixing at 85° C. for 4 hours to obtain an ANF/PVA spinning fluid;

(4) passing the ANF/PVA spinning fluid obtained in step (3) through a propeller, through a 21G spinneret, into a coagulation bath (5 L deionized water) at a speed of 4 ml/min, solidifying the spinning fluid into aramid nanofiber gel filaments, and collecting the filaments on a winding drum at a speed of 6 m/min;

(5) The aramid nanofiber gel filaments obtained in step (4) are wound onto a yarn bobbin from a winding drum, and placed in an oven at 100° C. to dry for 8 hours to obtain aramid nanofiber filaments.

FIG4 is a scanning electron microscope photograph of the aramid nanofiber filaments in this embodiment. As can be seen from the figure, the diameter of the prepared aramid nanofiber filaments is about 125 μm, and the surface is smooth and free of impurities.

Example 4

A method for macro-spinning aramid nanofibers, the method comprising the following steps:

(1) 1.5 g of aramid fiber was added to a potassium hydroxide solution (composed of 2.25 g of potassium hydroxide, 50 mL of dimethyl sulfoxide and 2 mL of deionized water), and stirred at 95° C. for 24 hours to obtain a 3 wt % dark red aramid nanofiber dispersion;

(2) adding 2.25 g of polyvinyl alcohol to 25 mL of dimethyl sulfoxide and stirring at 95° C. for 4 hours to obtain a 9 wt % transparent polyvinyl alcohol solution;

(3) mixing the 3 wt % aramid nanofiber dispersion prepared in step (1) and the 9 wt % transparent polyvinyl alcohol solution prepared in step (2) in a volume ratio of 2:1, stirring and mixing at 85° C. for 4 hours to obtain an ANF/PVA spinning fluid;

(4) passing the ANF/PVA spinning fluid obtained in step (3) through a propeller, through a 21G spinneret, into a coagulation bath (5 L deionized water) at a speed of 4 ml/min, solidifying the spinning fluid into aramid nanofiber gel filaments, and collecting the filaments on a winding drum at a speed of 6 m/min;

(5) The aramid nanofiber gel filaments obtained in step (4) are wound onto a yarn bobbin from a winding drum, and placed in an oven at 100° C. to dry for 8 hours to obtain aramid nanofiber filaments.

FIG5 is an optical photograph of the aramid nanofiber filaments in this embodiment. It can be seen from the figure that the prepared aramid nanofiber filaments are orange-yellow in color. Since the fibers have good flexibility and strength, they can be tightly and continuously wound into a yarn tube without breaking.

Example 5

A method for macro-spinning aramid nanofibers, the method comprising the following steps:

(1) 1.5 g of aramid fiber was added to a potassium hydroxide solution (composed of 2.25 g of potassium hydroxide, 50 mL of dimethyl sulfoxide and 2 mL of deionized water), and stirred at 95° C. for 24 hours to obtain a 3 wt % dark red aramid nanofiber dispersion;

(2) adding 3.75 g of polyvinyl alcohol to 25 mL of dimethyl sulfoxide and stirring at 95° C. for 4 hours to obtain a 9 wt % transparent polyvinyl alcohol solution;

(3) mixing the 3 wt % aramid nanofiber dispersion prepared in step (1) and the 12 wt % transparent polyvinyl alcohol solution prepared in step (2) in a volume ratio of 2:1, stirring and mixing at 85° C. for 4 hours to obtain an ANF/PVA spinning fluid;

(4) passing the ANF/PVA spinning fluid obtained in step (3) through a propeller, through a 21G spinneret, into a coagulation bath (5 L deionized water) at a speed of 4 ml/min, solidifying the spinning fluid into aramid nanofiber gel filaments, and collecting the filaments on a winding drum at a speed of 6 m/min;

(5) The aramid nanofiber gel filaments obtained in step (4) are wound onto a yarn bobbin from a winding drum, and placed in an oven at 100° C. to dry for 8 hours to obtain aramid nanofiber filaments.

Example 6

A method for macro-spinning aramid nanofibers, the method comprising the following steps:

(1) 1.5 g of aramid fiber was added to a potassium hydroxide solution (composed of 2.25 g of potassium hydroxide, 50 mL of dimethyl sulfoxide and 2 mL of deionized water), and stirred at 95° C. for 24 hours to obtain a 3 wt % dark red aramid nanofiber dispersion;

(2) adding 0.75 g of polyvinyl alcohol to 25 mL of dimethyl sulfoxide and stirring at 95° C. for 4 hours to obtain a 3 wt % transparent polyvinyl alcohol solution;

(3) mixing the 3 wt % aramid nanofiber dispersion prepared in step (1) and the 3 wt % transparent polyvinyl alcohol solution prepared in step (2) in a volume ratio of 2:1, stirring and mixing at 85° C. for 4 hours to obtain an ANF/PVA spinning fluid;

(4) passing the ANF/PVA spinning fluid obtained in step (3) through a propeller, through a 21G spinneret, into a coagulation bath (100 g of sodium hydroxide dissolved in 5 L of deionized water) at a speed of 4 ml/min, solidifying the spinning fluid into aramid nanofiber gel filaments, and collecting the spinning fluid on a winding drum at a speed of 6 m/min;

(5) The aramid nanofiber gel filaments obtained in step (4) are wound onto a yarn bobbin from a winding drum, and placed in an oven at 100° C. to dry for 8 hours to obtain aramid nanofiber filaments.

Example 7

A method for macro-spinning aramid nanofibers, the method comprising the following steps:

(1) 1.5 g of aramid fiber was added to a potassium hydroxide solution (composed of 2.25 g of potassium hydroxide, 50 mL of dimethyl sulfoxide and 2 mL of deionized water), and stirred at 95° C. for 24 hours to obtain a 3 wt % dark red aramid nanofiber dispersion;

(2) adding 0.75 g of polyvinyl alcohol to 25 mL of dimethyl sulfoxide and stirring at 95° C. for 4 hours to obtain a 3 wt % transparent polyvinyl alcohol solution;

(3) mixing the 3 wt % aramid nanofiber dispersion prepared in step (1) and the 3 wt % transparent polyvinyl alcohol solution prepared in step (2) in a volume ratio of 2:1, stirring and mixing at 85° C. for 4 hours to obtain an ANF/PVA spinning fluid;

(4) passing the ANF/PVA spinning fluid obtained in step (3) through a propeller, through a 21G spinneret, into a coagulation bath (420 mL of 37% concentrated hydrochloric acid dissolved in 4580 mL of deionized water) at a speed of 4 ml/min, solidifying the spinning fluid into aramid nanofiber gel filaments, and collecting the filaments on a winding drum at a speed of 6 m/min;

(5) The aramid nanofiber gel filaments obtained in step (4) are wound onto a yarn bobbin from a winding drum, and placed in an oven at 100° C. to dry for 8 hours to obtain aramid nanofiber filaments.

Example 8

A method for macro-spinning aramid nanofibers, the method comprising the following steps:

(1) 1.5 g of aramid fiber was added to a potassium hydroxide solution (composed of 2.25 g of potassium hydroxide, 50 mL of dimethyl sulfoxide and 2 mL of deionized water), and stirred at 95° C. for 24 hours to obtain a 3 wt % dark red aramid nanofiber dispersion;

(2) adding 0.75 g of polyvinyl alcohol to 25 mL of dimethyl sulfoxide and stirring at 95° C. for 4 hours to obtain a 3 wt % transparent polyvinyl alcohol solution;

(3) mixing the 3 wt % aramid nanofiber dispersion prepared in step (1) and the 3 wt % transparent polyvinyl alcohol solution prepared in step (2) in a volume ratio of 2:1, stirring and mixing at 85° C. for 4 hours to obtain an ANF/PVA spinning fluid;

(4) passing the ANF/PVA spinning fluid obtained in step (3) through a propeller, through a 21G spinneret, into a coagulation bath (5 L deionized water) at a speed of 4 ml/min, solidifying the spinning fluid into aramid nanofiber gel filaments, and collecting the filaments on a winding drum at a speed of 6 m/min;

(5) The aramid nanofiber gel filaments obtained in step (4) are wound onto a yarn bobbin from a winding drum, and freeze-dried at -40°C for 8 hours to obtain aramid nanofiber aerogel filaments.

FIG6 is an optical photograph of the aramid nano-aerogel filaments in this embodiment and a corresponding scanning electron microscope photograph. It can be seen from the figure that the prepared aramid nano-aerogel fibers are light yellow in color, have a rich porous structure inside, show obvious aerogel structural characteristics, and have the potential to be used in the field of thermal insulation.

Comparative Example 1

A method for preparing aramid nanofibers comprises the following steps:

(1) 1.5 g of aramid fiber was added to a potassium hydroxide solution (composed of 2.25 g of potassium hydroxide, 50 mL of dimethyl sulfoxide and 2 mL of deionized water), and stirred at 95° C. for 24 hours to obtain a 3 wt % dark red aramid nanofiber dispersion;

(2) mixing the 3 wt % aramid nanofiber dispersion prepared in step (1) with dimethyl sulfoxide in a volume ratio of 2:1, stirring and mixing at 85° C. for 4 hours to obtain an ANF spinning fluid;

(3) passing the ANF spinning fluid obtained in step (2) through a propeller, through a 21G spinneret, into a coagulation bath (5 L deionized water) at a speed of 4 ml/min, solidifying the spinning fluid into aramid nanofiber gel filaments, and collecting them on a winding drum at a speed of 6 m/min;

(4) The aramid nanofiber gel filaments obtained in step (3) are wound onto a yarn bobbin from a winding drum, and placed in an oven at 100° C. to dry for 8 hours to obtain aramid nanofiber filaments.

Test example:

(1) Mechanical properties

The fiber strength test method is carried out with reference to the national standard GB/T 14344-2022 chemical fiber filament tensile performance test method. The prepared fiber filament is cut into 300 mm and clamped in a fiber strength tester. The clamp distance is adjusted to 250 mm and the tensile speed is 250 mm/min. The mechanical properties test results of the aramid nanogel fiber filaments and aramid nanofiber filaments obtained in Examples 1-7 and Comparative Example 1 are shown in Tables 1 and 2 below, respectively.

Table 1 Mechanical properties of aramid nanogel fiber filaments

Table 2 Mechanical properties of aramid nanofiber filaments

sample strain(%) Stress(MPa) Example 1 5.0 314.76 Example 2 6.0 346.99 Example 3 7.8 297.15 Example 4 10.3 252.79 Example 5 13.2 208.33 Example 6 5.4 384.63 Example 7 6.9 333.54 Comparative Example 1 3.65 289.04

Figure 7 shows the tensile stress-strain curves of the aramid nanofiber gel filaments of Example 2 and Comparative Example 1 of the present invention. Since PVA is not added to Comparative Example 1, its maximum stress and strain are 0.03Mpa and 3.2%, respectively, while Example 2 contains PVA, which forms a hydrogen bond cross-linked network with ANF, wherein Example 2 has a stress of 0.16Mpa and a strain of 14.1%, and the mechanical properties are significantly improved, providing mechanical guarantee for rapid spinning.

FIG8 is a tensile stress-strain curve of the aramid nanofiber gel filaments of Examples 1-5 of the present invention. It can be seen from the figure that as the PVA concentration increases, the degree of crosslinking of the gel fiber increases, the mechanical properties of the gel fiber are enhanced, and increase with the increase of the PVA content.

Figure 9 is the tensile stress-strain curve of the aramid nanofiber filaments of Examples 1-5 of the present invention. It can be seen from the figure that the mechanical properties of the dried aramid nanofiber filaments are different from the change pattern of the mechanical properties of the gel fiber. The stress of the filaments first increases and then decreases. When the mass ratio of ANF to PVA is 2:1, it has the highest stress, which is about 325.6Mpa.

Figure 10 is the tensile stress-strain curve of the aramid nanofiber gel filaments obtained in different coagulation baths of Examples 2, 6 and 7 of the present invention. It can be seen from the figure that the mechanical properties of the aramid nanofiber gel filaments prepared by acid reagent are the best among the three, which indirectly verifies that the proton donor affects the arrangement of the aramid nanofibers, thereby affecting the mechanical properties of the gel fibers.

FIG11 is a tensile stress-strain curve of aramid nanofiber filaments obtained in different coagulation baths of Examples 2, 6 and 7 of the present invention. It can be seen from the figure that the stress of the aramid nanofiber filaments prepared by alkaline reagent is higher among the three, which indirectly verifies that the proton donor affects the arrangement of aramid nanofibers, thereby affecting the mechanical properties of the filaments.

(2) Gelation time

As shown in FIG12 , the spinning fluid extruded from the spinneret is dark yellow, and the color of the gradually gelled fiber changes to light yellow. The time required for the spinning fluid to change from dark yellow to light yellow is recorded as the gelation time.

Figure 13 shows the gelation time of the spinning fluids in different coagulation baths in Examples 2, 6 and 7 of the present invention, and the results are shown in Table 3. It can be seen from Figure 13 and Table 3 that since there are more proton donors in the acidic coagulation bath, the gelation time is the shortest at 5.23 s, while the gelation time in the alkaline coagulation bath is 13.2 s.

Table 3 Gel time under different coagulation baths

sample Average gelation time (s) Example 2 9.52 Example 6 13.2 Example 7 5.23

Figure 14 shows the fastest spinning winding speed of different coagulation bath spinning fluids in Examples 2, 6 and 7 of the present invention. The test method is to gradually increase the winding speed during the spinning process, and record the winding speed when the gel fiber breaks. It can be seen from the figure that the aramid nanogel filaments obtained in the acidic coagulation bath have the fastest winding speed of 12.4 m/min. This means that the aramid nanogel filaments obtained in the acidic coagulation bath have better mechanical properties and can withstand the centrifugal force generated by the faster winding speed.

The embodiments provided above are not intended to limit the scope of the present invention, and the steps described are not intended to limit the execution order thereof. Those skilled in the art may make obvious improvements to the present invention in combination with existing common knowledge, which also fall within the scope of protection defined by the claims of the present invention.

Claims (10)

1. A method for macro-spinning of aramid nanofibers, comprising the steps of:

s1: adding aramid fiber into potassium hydroxide solution, heating and stirring to obtain ANF dispersion;

s2: mixing the ANF dispersion liquid prepared in the step S1 with the PVA solution, and heating and stirring uniformly to prepare an ANF/PVA spinning fluid;

S3: carrying out wet spinning on the ANF/PVA spinning fluid to obtain aramid nanofiber gel filaments;

s4: and drying the aramid nanofiber gel filaments to obtain the aramid nanofiber filaments.

2. The method according to claim 1, wherein in step S1, the potassium hydroxide solution consists of potassium hydroxide, water and dimethyl sulfoxide; the concentration of potassium hydroxide in the potassium hydroxide solution is 7.5-150g/L; the volume ratio of dimethyl sulfoxide to water in the potassium hydroxide solution is 25-100:1.

3. The method according to claim 1, wherein in step S1, the mass ratio of the aramid fiber to potassium hydroxide in the potassium hydroxide solution is 1:0.5-1.5.

4. The method according to claim 1, wherein in step S1, the concentration of the ANF dispersion is 0.5-10%.

5. The method according to claim 1, wherein in step S2, the concentration of the PVA solution is 0.5 to 15%; the volume ratio of the ANF dispersion liquid to the PVA solution is 2:0.1-2.

6. The method according to claim 1, wherein in step S3, the spinning fluid is extruded by a propeller and then sequentially passed through a spinneret, a coagulation bath, and a winding drum during wet spinning.

7. The method of claim 6, wherein the coagulation bath is an acidic coagulation bath, an alkaline coagulation bath, or a deionized water coagulation bath;

The acid reagent in the acidic coagulating bath is one or more of sulfuric acid, hydrochloric acid, nitric acid, formic acid, acetic acid, sulfurous acid, phosphoric acid, lactic acid, benzoic acid and acrylic acid; the concentration of the acid reagent in the acid coagulation bath is 0.05-5mol/L;

The alkaline reagent in the alkaline coagulating bath is one or more of sodium hydroxide, sodium carbonate, sodium phosphate, sodium orthosilicate, potassium tert-butoxide, sodium tert-butoxide, potassium hydride, sodium hydride, potassium hydroxide and ammonium hydroxide; the concentration of the alkali reagent in the alkaline coagulating bath is 0.05-5mol/L.

8. The method according to claim 6, wherein the spinneret has a size of 8-30G and the propeller has an extrusion speed of 0.3-30ml/min when the spinning fluid is extruded; the winding speed of the winding drum is 0.2-14m/min.

9. The method according to claim 1, wherein in step S4, the drying treatment is freeze-drying or heat-drying.

10. The method according to claim 9, wherein the conditions of freeze-drying are: the temperature is-35 ℃, the vacuum degree is 10-20Pa, and the time is 12-24 hours; the conditions of the heating and drying are as follows: the temperature is 80-150 ℃ and the time is 6-12 hours.