Fabrication, application and apparatus of fibers with aligned porous structure

Abstract

Provided is a method of manufacturing fiber with aligned porous structure, an apparatus, and applications of the fiber. The apparatus comprises: a fiber extrusion unit, a freezing unit, and a collection unit for collecting the frozen fibers, wherein fibers extruded from the fiber extrusion unit pass through the freezing unit. Continuous and large scale preparation of such fiber with aligned porous structure is achieved by combining directional freezing and solution spinning.

Claims

1. A method of fabricating a fiber which is thermal-insulating at high temperature and fire-retardant, comprising: (1) using a poly(amic acid) hydrogel for spinning, performing a directional freezing process during spinning, and collecting the frozen fiber, wherein the directional freezing process includes: the poly(amic acid) hydrogel passing through a freezing copper ring after being extruded from an extruder and water is frozen directionally in a direction of a temperature gradient under a temperature field; (2) freeze-drying the frozen fiber to remove ice crystal and then obtain a fiber with aligned porous structure; and (3) heating the fiber to realize a thermal imidization of poly(amic acid) into polyimide, wherein the fiber is a polyimide porous fiber with an aligned and continuous through-hole along an axial direction.

2. The method as claimed in claim 1, wherein a preparation of the poly(amic acid) hydrogel in step 1 comprises: dissolving 4,4′-diaminodiphenyl ether in N,N-dimethylacetamide with adding pyromellitic dianhydride and trimethylamine subsequently to obtain a poly(amic acid) solid, and mixing the poly(amic acid) solid with trimethylamine and water to obtain the poly(amic acid) hydrogel.

3. The method as claimed in claim 1, wherein a temperature of the freezing copper ring is any temperature below a freezing point of water.

4. The method as claimed in claim 1, wherein the thermal imidization in step 3 is through treating the fiber with three-stage heating and three-stage constant temperature processing, and the heating and the constant temperature processing are performed alternately.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 shows the schematic diagram of apparatus in Example 1.

(2) FIG. 2 shows the schematic diagram of apparatus in Example 2.

(3) FIG. 3 shows the schematic diagram of apparatus in Example 3.

(4) FIG. 4 shows the schematic diagram of freezing tank in Example 3.

(5) FIG. 5 shows the schematic diagram of apparatus in Example 4.

(6) FIG. 6 shows the schematic diagram of apparatus in Example 5.

(7) FIG. 7 shows the optical image of porous fiber fabricated in Example 6.

(8) FIG. 8 shows the X-ray micro computed tomography (Micro-CT) image of porous fiber fabricated in Example 6.

(9) FIG. 9 shows the SEM image of porous fiber fabricated in Example 7.

(10) FIG. 10 shows the SEM image of porous fiber fabricated in Example 8.

(11) FIG. 11 shows the optical image and SEM image of textile which is woven with porous fiber fabricated in Example 9.

(12) FIG. 12 shows the SEM image of porous fiber fabricated in Comparative Example 1.

(13) FIG. 13 shows the infrared images of thermal-insulating textile fabricated in Application Example 1 (see part (a)), and shows the statistics of absolute temperature difference (see part (b)).

(14) FIG. 14 shows the optical images of thermal-insulating textile used as thermal stealth material in Application Example 2 (see part (a)), and shows the corresponding infrared images (see part (b)).

(15) FIG. 15 shows the optical image and SEM images of porous textile doped with carbon nanotube in Application Example 3.

(16) FIG. 16 shows the infrared images of porous textile doped with carbon nanotube in Application Example 3.

(17) FIG. 17 shows the electrothermal property of porous textile doped with carbon nanotube under voltage in Application Example 3.

(18) FIG. 18 shows the SEM image of porous fiber fabricated in Example 13.

(19) FIG. 19 shows the SEM image of porous fiber fabricated in Example 14.

(20) FIG. 20 shows the SEM image of porous fiber fabricated in Example 15.

(21) FIG. 21 shows the SEM image of porous fiber fabricated in Example 16.

(22) FIG. 22 shows the optical image of textile which is woven with porous fiber fabricated in Example 17.

(23) FIG. 23 shows the infrared images of textile which is woven with porous fiber fabricated in Application Example 4.

(24) FIG. 24 shows the statistics of the temperature of the textile which is woven with porous fiber fabricated in Application Example 4 and the temperature of the hot stage.

(25) FIG. 25 shows the infrared images of burning the porous fiber in Application Example 5.

(26) FIG. 26 shows the optical images of burning the textile which is woven with porous fiber fabricated in Application Example 6.

(27) FIG. 27 shows the optical images of burning the polyester textile in Comparative Example 2.

DESCRIPTION OF THE EMBODIMENTS

(28) The invention will be further illustrated by means of the following examples.

Example 1: Apparatus

(29) An apparatus for fabricating fibers with aligned porous structure is shown in FIG. 1, including fiber extrusion unit, freezing unit and collection unit.

(30) The fiber extrusion unit comprises a syringe pump 5 and a syringe 4. The syringe 4 is mounted on the syringe pump 5 and controlled by the syringe pump 5 to extrude spinning solution. The syringe pump 5 may have a built-in control system or an external link control system (not shown in the figure) for controlling the flow rate. The syringe pump 5 controls the extrusion of the spinning solution by squeezing the piston of the syringe 4. The range of the syringe 4 is 20 ml, and the flow rate of the syringe pump 5 is selected to be 0.05 ml/min.

(31) The freezing unit comprises a freezing tank 1, a refrigerating fluid circulating pipe 8, a refrigerating system 9 and a freezing copper ring. The refrigerating system 9 is a low-temperature thermostat bath. The freezing tank 1 is made of red copper. The thermal conductivity is 386.4 W/(m.Math.K), which means the freezing tank has excellent thermal conductivity. The refrigerating system 9 connects to the freezing tank 1 through the refrigerating fluid circulating pipe 8. The refrigerating fluid circulates in the refrigerating system 9, the refrigerating fluid circulating pipe 8 and the freezing tank 1, which forms a closed circuit to maintain the low temperature environment in the freezing tank 1. The freezing copper ring comprises an annular freezing section 2 and a thermally conductive section 3. The thermally conductive section 3 is mounted on the wall of the freezing tank 1, such that the freezing copper ring is located above the refrigerating fluid and is not in direct contact with the refrigerating fluid. The freezing copper ring is made of red copper. And the temperature of the freezing copper ring may be any temperature below the freezing point of water, preferably −120 to −30° C., more preferably −100° C.

(32) The collection unit comprises a collecting roller 6 and a motor 7. The collecting roller 6 is driven by the motor 7 to rotate slowly and collect fibers continuously.

(33) The working process involves:

(34) The spinning solution is extruded from the syringe 4 which is controlled by the syringe pump 5 and then passes through the freezing section 2. There is temperature gradient in the direction perpendicular to the freezing section 2, which influences and controls the nucleation and growth of ice crystal to be oriented along the direction of temperature gradient. Meanwhile, due to the micro-phase separation of the system, the ingredient is squeezed and compressed in the gap between the ice crystals. The frozen fibers are collected by the collecting roller 6 and then freeze-dried to remove ice crystal. Thus, fibers with aligned porous structure using ice crystal as template are obtained.

Example 2: Apparatus

(35) As shown in FIG. 2, the difference with Example 1 is that the freezing tank 1 is made of thermal-insulating material Teflon. The thermally conductive section 3 of the copper ring is set on the bottom of the freezing tank 1 and contacts directly with the refrigerating fluid which controls the temperature of the copper ring directly.

Example 3: Apparatus

(36) As shown in FIG. 3 and FIG. 4, the difference with Example 1 is that the freezing tank 1 has interlayer structure which is composed of walls of the freezing tank 1. The refrigerating fluid is stored in the interlayer 10 to provide low temperature environment for cavity 11 in the freezing tank 1. The thermally conductive section 3 of the copper ring connects to the wall of the freezing tank 1, and the annular freezing section 2 is located in the cavity 11.

Example 4: Apparatus

(37) As shown in FIG. 5, the difference with Example 1 is that the syringe 4 and the syringe pump 5 are placed horizontally, while the copper ring is placed vertically. The thermally conductive section 3 of the copper ring connects to the wall of the freezing tank 1. And the fibers pass through the annular freezing section 2 horizontally. The whole freezing unit and collection unit are set at low temperature environment below 0° C. to avoid the ice crystal in fibers melting.

Example 5: Apparatus

(38) As shown in FIG. 6, the difference with Example 4 is that the syringe 4 connects to a multi-nozzle spinneret 12, and a corresponding number of copper rings are set side by side. The thermally conductive sections 3 of all the copper rings are mounted on the wall of the freezing tank 1. Multi strands of fibers pass through the annular freezing sections 2 and are collected by the collecting roller 6 simultaneously, realizing freezing and collection of multi strands of fibers.

Example 6: Fabrication of Porous Fibers

(39) The apparatus in Example 1 is selected to fabricate fibers with aligned porous structure. The detailed method comprises the following steps.

(40) (1) Shear 4.5 g of natural silk cocoons. Boil the cocoons in 1 wt % sodium carbonate solution and then dry them. Dissolve them in 20 ml of 9 mol/ml lithium bromide solution, and dialyze for 24 h to make a 0.225 g/ml silk fibroin solution.

(41) Dissolve 0.5 g of chitosan powder in 10 ml of 1 wt % acetic acid solution, and stir for 30 min for complete dissolving to form a 0.05 g/ml chitosan solution with the rotator being 800 rpm/min.

(42) Mix 20 ml of silk fibroin solution and 10 ml of chitosan solution, and centrifuge the mixture to get rid of bubbles to obtain a spinning solution. The mass ratio of silk fibroin and chitosan is 9:1.

(43) (2) Load the syringe with the spinning solution which is then extruded by the pump. The temperature of the copper ring is −100° C. The spinning solution passes through the copper ring, and the frozen fibers are collected by a motor.

(44) (3) Freeze-dry the fibers obtained in step 2 for 24 h to remove ice crystal and then obtain fibers with aligned porous structure. The optical image is shown in FIG. 7.

(45) (4) Characterize the porous fibers in the present example via Micro-CT. As shown in FIG. 8, the fiber has aligned porous structure.

Example 7: Fabrication of Porous Fibers

(46) The apparatus in Example 1 is selected to fabricate fibers with aligned porous structure. The detailed method comprises the following steps.

(47) (1) Shear 4.5 g of natural silk cocoons. Boil the cocoons in 1 wt % sodium carbonate solution and then dry them. Dissolve them in 20 ml of 9 mol/ml lithium bromide solution, and dialyze for 24 h to make a 0.225 g/ml silk fibroin solution.

(48) Dissolve 0.5 g of chitosan powder in 10 ml of 1 wt % acetic acid solution, and stir for 30 min for complete dissolving to form a 0.05 g/ml chitosan solution with the rotator being 800 rpm/min.

(49) Mix 20 ml of silk fibroin solution and 10 ml of chitosan solution, and centrifuge the mixture to get rid of bubbles to obtain a spinning solution. The mass ratio of silk fibroin and chitosan is 9:1.

(50) (2) Load the syringe with the spinning solution which is then extruded by the pump. The temperature of the copper ring is −40, −60, −80, −100° C., respectively. The spinning solution passes through the copper ring, and the frozen fibers are collected by a motor.

(51) (3) Freeze-dry the fibers obtained in step 2 for 24 h to remove ice crystal and then obtain fibers with aligned porous structure.

(52) (4) Characterize the porous fibers in the present example via scanning electron microscope (SEM). As shown in FIG. 9, the fibers have aligned porous structure.

Example 8: Fabrication of Porous Fibers

(53) The apparatus in Example 2 is selected to fabricate fibers with aligned porous structure. The detailed method comprises the following steps.

(54) (1) Shear 4.5 g of natural silk cocoons. Boil the cocoons in 1 wt % sodium carbonate solution and then dry them. Dissolve them in 20 ml of 9 mol/ml lithium bromide solution, and dialyze for 24 h to make a 0.225 g/ml silk fibroin solution.

(55) Dissolve 0.5 g of chitosan powder in 10 ml of 1 wt % acetic acid solution, and stir for 30 min for complete dissolving to form a 0.05 g/ml chitosan solution with the rotator being 800 rpm/min.

(56) Dissolve 0.01 g of carbon nanotube in 10 ml of 1 wt % sodium dodecylbenzene sulfonate solution. Mix 20 ml of silk fibroin solution, 10 ml of chitosan solution and 20 ml of carbon nanotube solution, and centrifuge the mixture to get rid of bubbles to obtain a spinning solution. The mass ratio of silk fibroin and chitosan is 9:1, and the mass ratio of silk fibroin and carbon nanotube is 225:1.

(57) (2) Load the syringe with the spinning solution which is then extruded by the pump. The temperature of the copper ring is −100° C. The spinning solution passes through the copper ring, and the frozen fibers are collected by a motor.

(58) (3) Freeze-dry the fibers obtained in step 2 for 24 h to remove ice crystal and then obtain fibers with aligned porous structure.

(59) (4) Characterize the porous fibers in the present example via SEM. As shown in FIG. 10, the fiber doped with carbon nanotube has aligned porous structure.

Example 9: Fabrication of Porous Fibers

(60) The apparatus in Example 3 is selected to fabricate fibers with aligned porous structure. The detailed method comprises the following steps.

(61) (1) Shear 4.5 g of natural silk cocoons. Boil the cocoons in 1 wt % sodium carbonate solution and then dry them. Dissolve them in 20 ml of 9 mol/ml lithium bromide solution, and dialyze for 24 h to make a 0.225 g/ml silk fibroin solution.

(62) Dissolve 0.5 g of chitosan powder in 10 ml of 1 wt % acetic acid solution, and stir for 30 min for complete dissolving to form a 0.05 g/ml chitosan solution with the rotator being 800 rpm/min.

(63) Mix 20 ml of silk fibroin solution and 10 ml of chitosan solution, and centrifuge the mixture to get rid of bubbles to obtain a spinning solution. The mass ratio of silk fibroin and chitosan is 9:1.

(64) (2) Load the syringe with the spinning solution which is then extruded by the pump. The temperature of the copper ring is −100° C. The spinning solution passes through the copper ring, and the frozen fibers are collected by a motor.

(65) (3) Freeze-dry the fibers obtained in step 2 for 24 h to remove ice crystal and then obtain fibers with aligned porous structure.

(66) (4) Weave the fibers obtained in step 3 into textile.

(67) (5) Characterize the textile in the present example via SEM. As shown in FIG. 11, the porous fibers can be woven into wearable textile for thermal insulation.

Comparative Example 1

(68) (1) Shear 4.5 g of natural silk cocoons. Boil the cocoons in 1 wt % sodium carbonate solution and then dry them. Dissolve them in 20 ml of 9 mol/ml lithium bromide solution, and dialyze for 24 h to make a 0.225 g/ml silk fibroin solution.

(69) Dissolve 0.5 g of chitosan powder in 10 ml of 1 wt % acetic acid solution, and stir for 30 min for complete dissolving to form a 0.05 g/ml chitosan solution with the rotator being 800 rpm/min.

(70) Mix 20 ml of silk fibroin solution and 10 ml of chitosan solution, and centrifuge the mixture to get rid of bubbles to obtain a spinning solution. The mass ratio of silk fibroin and chitosan is 9:1.

(71) (2) Load the syringe with spinning solution which is then extruded directly into liquid nitrogen (−196° C.).

(72) (3) Freeze-dry the fibers obtained in step 2 for 24 h to remove ice crystal and then obtain fibers with random porous structure.

(73) (4) Characterize the porous fibers in the present comparative example via SEM. As shown in FIG. 12, the fiber has random porous structure, mainly because the freezing is along multi-direction rather than a single direction.

Application Example 1

(74) Weave the porous fibers obtained in Example 9 into thermal-insulating textile. The porous structure and textile layers both have influence on the thermal-insulating property. Therefore, from left to right, single layer textiles with pore diameters of 85, 65, 45, 30 μm respectively, three layers textile with pore diameter of 30 μm, five layers textile with pore diameter of 30 μm are placed to test their thermal-insulating property (an area of 2×2 mm, and the thicknesses respectively are 0.4, 1.2 and 2 mm).

(75) These six textiles are placed on the same hot stage for comparison, as shown in part (a) of FIG. 13. When the hot stage is heated from −20 to 80° C., a series of infrared images are obtained. When the temperatures of the hot stage respectively are −20, 50, 80° C., there are three typical infrared images. The absolute temperature differences (|ΔT|) between textile surface and hot stage are counted in part (b) of FIG. 13. The temperature difference of textile woven with fibers having smaller pore diameter is greater, which means textile possesses better thermal-insulating property.

Application Example 2

(76) Weave the porous fibers obtained in Example 9 into thermal-insulating textile. Biomimetic textile with excellent thermal-insulating property can be good option for thermal stealth material.

(77) As shown in part (a) of FIG. 14, a rabbit wearing a single layer of biomimetic textile and a rabbit wearing commercial polyester textile are shown in optical and infrared images. The rabbit wearing commercial polyester textile can be detected by an infrared camera. However, when the rabbit wears the biomimetic textile, it can hardly be detected, because the surface temperature of textile is closely near the environment temperature. This phenomenon indicates that the biomimetic textile can be used as thermal stealth material.

(78) Similarly, as shown in part (b) of FIG. 14, the rabbit cannot be detected by infrared camera at different temperatures, indicating that the biomimetic textile can be used as thermal stealth material at a wide range of environment temperature from −10 to 40° C.

Application Example 3

(79) Weave the porous fibers in Example 8 into textile. Since the carbon nanotube is dispersed in silk fibroin solution, a conductive network forms in the textile inducing electrothermal property. The optical and SEM images in FIG. 15 shows the carbon nanotube is dispersed and embedded well in the polymer matrix without destroying the fiber's aligned porous structure.

(80) When the textile doped with carbon nanotube is connected to a circuit, as shown in FIG. 16, the surface temperature of textile increases rapidly from 20 to 36.1° C. in 45 seconds with a voltage of 5 V applied. As shown in FIG. 17, the temperature of the textile doped with carbon nanotube can be adjusted effectively by changing applied voltage.

Example 10: Preparation of the Poly(Amic Acid) Hydrogel

(81) (1) Dissolve 8.0096 g of 4,4′-diaminodiphenyl ether (ODA) in 95.57 g of N,N-dimethylacetamide (DMAc) with adding 8.8556 g of pyromellitic dianhydride (PMDA) and 4.0476 g of trimethylamine (TEA) subsequently. Stir for 4 hours to produce a viscous lightyyellow poly(amic acid) (PAA) solution. Pour the as-prepared solution slowly into water to replace the solvent, and then freeze-dry it to obtain lightyellow poly(amic acid) solid.

(82) (2) Mix 5 g of poly(amic acid) solid with 5 g of TEA and 90 g of deionized water. Stir for several hours and stand for 24 h to obtain 5 wt % poly(amic acid) hydrogel.

Example 11: Preparation of the Poly(Amic Acid) Hydrogel

(83) The preparation is carried out according to the Example 10. The difference is that mixing 10 g of poly(amic acid) solid with 5 g of TEA and 85 g of deionized water in step 2. Stir for several hours and stand for 24 h to obtain 10 wt % poly(amic acid) hydrogel.

Example 12: Preparation of the Poly(Amic Acid) Hydrogel

(84) The preparation is carried out according to the Example 10. The difference is that mixing 15 g of poly(amic acid) solid with 5 g of TEA and 80 g of deionized water in step 2. Stir for several hours and stand for 24 h to obtain 15 wt % poly(amic acid) hydrogel.

Example 13: Fabrication of the Polyimide Porous Fibers

(85) The apparatus in Example 1 is selected to fabricate polyimide porous fibers. The detailed method comprises the following steps.

(86) (1) Load the syringe with 5 wt % poly(amic acid) hydrogel in Example 10 which is then extruded by the pump. The temperature of the copper ring is −100° C. The hydrogel fibers pass through the copper ring, and the frozen fibers are collected by a motor.

(87) (2) Freeze-dry the fibers obtained in step 1 for 24 h to remove ice crystal and then obtain fibers with aligned porous structure.

(88) (3) Heat the as-prepared fibers to realize complete imidization of poly(amic acid) into polyimide. The thermal imidization specifically includes: heating to 100° C. at a rate of 2° C./min, maintaining 30 min; heating to 200° C. at a rate of 2° C./min, maintaining 30 min; heating to 300° C. at a rate of 2° C./min, maintaining 60 min.

(89) (4) Characterize the polyimide porous fibers in the present example via SEM. As shown in FIG. 18, the fiber has aligned porous structure, and the pore diameter is 50˜100 μm.

Example 14: Fabrication of the Polyimide Porous Fibers

(90) The apparatus in Example 1 is selected to fabricate polyimide porous fibers. The detailed method comprises the following steps.

(91) (1) Load the syringe with 10 wt % poly(amic acid) hydrogel in Example 11 which is then extruded by the pump. The temperature of the copper ring is −80° C. The hydrogel fibers pass through the copper ring, and the frozen fibers are collected by a motor.

(92) (2) Freeze-dry the fibers obtained in step 1 for 24 h to remove ice crystal and then obtain fibers with aligned porous structure.

(93) (3) Heat the as-prepared fibers to realize complete imidization of poly(amic acid) into polyimide. The thermal imidization specifically includes: heating to 100° C. at a rate of 2° C./min, maintaining 30 min; heating to 200° C. at a rate of 2° C./min, maintaining 30 min; heating to 300° C. at a rate of 2° C./min, maintaining 60 min.

(94) (4) Characterize the polyimide porous fibers in the present example via SEM. As shown in FIG. 19, the fiber has aligned porous structure.

Example 15: Fabrication of the Polyimide Porous Fibers

(95) The apparatus in Example 4 is selected to fabricate polyimide porous fibers. The detailed method comprises the following steps.

(96) (1) Load the syringe with 15 wt % poly(amic acid) hydrogel in Example 12 which is then extruded by the pump. The temperature of the copper ring is −60° C. The hydrogel fibers pass through the copper ring, and the frozen fibers are collected by a motor.

(97) (2) Freeze-dry the fibers obtained in step 1 for 24 h to remove ice crystal and then obtain fibers with aligned porous structure.

(98) (3) Heat the as-prepared fibers to realize complete imidization of poly(amic acid) into polyimide. The thermal imidization specifically includes: heating to 100° C. at a rate of 2° C./min, maintaining 30 min; heating to 200° C. at a rate of 2° C./min, maintaining 30 min; heating to 300° C. at a rate of 2° C./min, maintaining 60 min.

(99) (4) Characterize the polyimide porous fibers in the present example via SEM. As shown in FIG. 20, the fiber has aligned porous structure.

Example 16: Fabrication of the Polyimide Porous Fibers

(100) The apparatus in Example 5 is selected to fabricate polyimide porous fibers. The detailed method comprises the following steps.

(101) (1) Load the syringe with 5 wt % poly(amic acid) hydrogel in Example 10 which is then extruded by the pump. The temperature of the copper ring is −40° C. The hydrogel fibers pass through the copper ring, and the frozen fibers are collected by a motor.

(102) (2) Freeze-dry the fibers obtained in step 1 for 24 h to remove ice crystal and then obtain fibers with aligned porous structure.

(103) (3) Heat the as-prepared fibers to realize complete imidization of poly(amic acid) into polyimide. The thermal imidization specifically includes: heating to 100° C. at a rate of 2° C./min, maintaining 30 min; heating to 200° C. at a rate of 2° C./min, maintaining 30 min; heating to 300° C. at a rate of 2° C./min, maintaining 60 min.

(104) (4) Characterize the polyimide porous fibers in the present example via SEM. As shown in FIG. 21, the fiber has aligned porous structure.

Example 17: Fabrication of Thermal-Insulating at High Temperature and Fire-Retardant Textile

(105) Weave the polyimide porous fibers obtained in Example 13 into textile. The optical image is shown in FIG. 22.

Application Example 4

(106) Test the thermal-insulating property of textile in Example 17. The textile is placed on a hot stage. When the hot stage is heated from 50 to 220° C., a series of infrared images are obtained. When the temperatures of the hot stage respectively are 50, 100, 150, 200, 220° C., there are five typical infrared images, as shown in FIG. 23. The background temperature and the average surface temperature of the textile can be obtained through the infrared images and they are counted in FIG. 24. The textile possesses excellent thermal-insulating property even at high temperature.

Application Example 5

(107) Test the fire-retardant property of polyimide porous fiber in Example 13. The polyimide porous fiber is ignited by an alcohol lamp, and a series of infrared images are obtained, as shown in FIG. 25. The fiber is not be completely burned and the morphology remains essentially unchanged. And the fiber is self-extinguishing after being removed from the fire, indicating excellent fire-retardant property of the polyimide porous fiber.

Application Example 6

(108) Test the fire-retardant property of textile in Example 17. The polyimide textile is ignited by an alcohol lamp, and a series of optical images are obtained, as shown in FIG. 26. The textile is not be completely burned and the morphology remains essentially unchanged. And the textile is self-extinguishing after being removed from the fire, indicating excellent fire-retardant property of the polyimide textile.

Comparative Example 2

(109) Test the fire-retardant property of polyester textile. The polyester textile is ignited by an alcohol lamp, and a series of optical images are obtained, as shown in FIG. 27. The morphology of the polyester textile is instantly destroyed. And the flame on the textile is not extinguished after the textile being removed from the fire, indicating bad fire-retardant property of the polyester textile. As comparison, it further indicates the excellent fire-retardant property of the biomimetic polyimide textile.