Optically Reversible Cross-Linked Polyester Aerogel Fibers and Their Preparation and Recycling Methods

Abstract

The present invention relates to a photo-reversibly crosslinked polyester aerogel fiber, a preparation method thereof and a recycling method thereof. The preparation method is as follows: after dissolving a photo-reversibly crosslinked polyester containing a coumarin group to obtain a spinning solution, extruding it, and successively passing through ultraviolet light irradiation curing with a wavelength ≥260 nm, collecting, solvent replacement and supercritical drying to obtain a photo-reversibly crosslinked polyester aerogel fiber. The ultraviolet light irradiation curing is carried out in a coagulation bath, and the coagulation bath contains 0.1-10 wt% of coumarin; the breaking strength of the photo-reversibly crosslinked polyester aerogel fiber is 5-20 MPa, and the porosity is 80-90%; the recycling method is as follows: placing the photo-reversibly crosslinked polyester aerogel fiber in a solvent and irradiating and dissolving it with ultraviolet light with a wavelength <260 nm to obtain a spinning solution. The present invention prepares a new material of a photo-reversibly crosslinked polyester aerogel fiber, realizes the rapid shaping and reversible recycling of the aerogel fiber, and meets the strategic requirements of sustainable development.

Description

Technical Field

[0001] The present invention belongs to the technical field of aerogels, and relates to a photo-reversibly cross-linked polyester aerogel fiber, a preparation method thereof, and a recycling method thereof. Background Art

[0002] Light weight, high performance, low cost, and sustainability have always been the most important driving forces in the design of structural materials. Among them, organic aerogels are porous materials containing enclosed air molecules, which have the characteristics of small pore size, extremely low density, high porosity, and high specific surface area, and have been widely used in heat insulation, energy storage, and chemical absorption. However, organic aerogels are usually made based on fossil raw materials, and in order to construct a porous structure, a chemical cross-linked structure is inevitably introduced into the polymer network, resulting in the difficulty of recycling and reusing the aerogel material after the structure is damaged, which does not meet the strategic requirements of sustainable development.

[0003] Currently, researchers have proposed a new idea of introducing dynamic reversible cross-linked bonds into organic aerogels to achieve the closed-loop recycling of organic aerogels. For example, in Document 1 (10.1002 / adma.202209003), different primary amines and cyclophosphazene derivatives made from bio-based raw materials (vanillin and 4-hydroxybenzaldehyde) are used to prepare a closed-loop recyclable high-performance polyimine aerogel. The reversible imine bonds introduced into the aerogel network can be hydrolyzed under acidic conditions to realize the recycling and reuse of raw materials; in Document 2 (10.1093 / nsr / nwac012), phthalaldehyde and diethylenetriamine are used as monomers, and tris(2-aminoethyl)amine is used as a cross-linking agent to form a high-strength gel network through a mild Schiff base reaction. A polyimine aerogel is prepared by solvent replacement and drying. Adding an excessive amount of amine to the polyimine aerogel can break the imine bonds and degrade them into monomers or oligomers.

[0004] The recyclable aerogels reported above form a reversible imine bond to construct an aerogel network by adding an amine cross-linking agent to the precursor solution, and further change the pH of the gel to break the cross-linking bond to achieve the recyclability of the aerogel. However, the conversion of monomers to wet gels through polycondensation and cross-linking reactions is a long-term static sol-gel transformation in a mold. However, it is not feasible to construct recyclable aerogel fibers through the above ideas. This is because the static sol-gel and slow gel kinetics processes are contradictory to the dynamic sol-gel spinning process of aerogel fibers. The key to constructing recyclable aerogel fibers lies in: (1) the formed cross-linking bonds are reversible and can be broken under certain conditions; (2) the process of forming cross-linking bonds is fast and controllable, and can match the dynamic process of spinning. Summary of the Invention

[0005] The object of the present invention is to solve the problems existing in the prior art and provide a photo-reversibly crosslinked polyester aerogel fiber, a preparation method thereof, and a recovery method thereof.

[0006] A preparation method of a photo-reversibly crosslinked polyester aerogel fiber. After dissolving the photo-reversibly crosslinked polyester to obtain a spinning solution, it is extruded through an injection pump, and successively undergoes ultraviolet light irradiation curing with a wavelength ≥ 260 nm, collection, solvent replacement, and supercritical drying to obtain the photo-reversibly crosslinked polyester aerogel fiber. Among them, the molecular structural formula of the photo-reversibly crosslinked polyester is as follows:

[0007]

[0008] In the formula, n is 50 or 40, and m is 50 or 60; n and m represent the degree of polymerization, and the values of n and m are determined by the molar ratio and the feeding amount of N,N-bis(2-hydroxyethyl)-4-((4-methyl-2-oxo-2H-chromen-7-yl)-oxy)butyramide and N,N-bis(2-hydroxyethyl)soybean amide; the values of n and m are related to the crosslinking degree of the final product, and the crosslinking degree of the product obtained when n is 50 is less than that of the product when n is 40;

[0009] The ultraviolet light irradiation curing is carried out in a coagulation bath, which is beneficial to forming. Because when gelling in the coagulation bath, the requirement for the viscosity of the spinning solution is lower, and the coagulation bath contains 0.1 - 10 wt% of coumarin.

[0010] The photo-reversibly crosslinked polyester of the present invention contains coumarin groups, that is, the present invention realizes reversible crosslinking based on coumarin. After the photo-reversibly crosslinked polyester is extruded through a spinneret, under an ultraviolet light source (λ ≥ 260 nm), the coumarin groups are induced to undergo a [2+2] cycloaddition reaction to form crosslinking bonds, thereby causing the spinning solution to undergo a sol-gel transition to form a polyester wet gel fiber with a stable structure, providing conditions for constructing an aerogel material. However, it is difficult to construct an aerogel fiber based on the reversible crosslinking of coumarin because the crosslinking reaction of coumarin is relatively slow, so it is impossible to construct an aerogel fiber. In the present invention, a certain amount of coumarin is added to the spinning coagulation bath. In the crosslinking reaction, the crosslinkable groups on the molecular chain have weak motility and cannot quickly capture the crosslinkable groups for crosslinking. While adding coumarin in the coagulation bath, its motility is not restricted and it can diffuse to the crosslinking sites on the polyester molecular chain to form crosslinking points, thereby increasing the rate of the crosslinking reaction. Therefore, the formation of polyester aerogel fibers can be realized. The content of coumarin in the coagulation bath is 0.1 - 10 wt%. Too low a content of coumarin has an insignificant effect on improving the gelation rate, while too high a content will reduce the gelation rate (because it may cause coumarin to undergo self-crosslinking under ultraviolet light and cannot react with polyester).

[0011] As a preferred technical solution:

[0012] A preparation method of a photo-reversibly crosslinked polyester aerogel fiber as described above. The preparation method of the photo-reversibly crosslinked polyester is as follows: Under stirring conditions, N,N'-diisopropylcarbodiimide is added to a reaction solution at a temperature of 0 - 5 °C and stirred continuously for 20 - 30 min. Then, the temperature is raised to 25 - 30 °C and stirred continuously for 30 - 36 h. After post-treatment (methanol precipitation), the photo-reversibly crosslinked polyester is obtained.

[0013] The reaction solution is composed of N,N-bis(2-hydroxyethyl)-4-((4-methyl-2-oxo-2H-chromen-7-yl)-oxy)butyramide, N,N-bis(2-hydroxyethyl)soybean amide, oxalic acid, 4-(dimethylamino)pyridinium 4-toluenesulfonate, and dichloromethane.

[0014] The molecular structural formula of N,N-bis(2-hydroxyethyl)-4-((4-methyl-2-oxo-2H-chromen-7-yl)-oxy)butyramide is as follows:

[0015]

[0016] The molecular structural formula of N,N-bis(2-hydroxyethyl)soybean amide is as follows:

[0017]

[0018] The chemical reaction equation for the whole process is as follows:

[0019]

[0020] A preparation method of a photo-reversibly crosslinked polyester aerogel fiber as described above. The molar ratio of N,N-bis(2-hydroxyethyl)-4-((4-methyl-2-oxo-2H-chromen-7-yl)-oxy)butyramide to N,N-bis(2-hydroxyethyl)soybean amide is 1:1 or 2:3.

[0021] The molar amount ratio of oxalic acid to the total molar amount of N,N-bis(2-hydroxyethyl)-4-((4-methyl-2-oxo-2H-chromen-7-yl)-oxy)butyramide and N,N-bis(2-hydroxyethyl)soybean amide is 1 - 1.1:1.

[0022] The molar amount of N,N'-diisopropylcarbodiimide is 2.5 - 5 times the molar amount of oxalic acid.

[0023] The molar volume ratio of oxalic acid to dichloromethane is 0.5 - 1 mol:1 L.

[0024] The molar volume ratio of 4-(dimethylamino)pyridinium 4-toluenesulfonate to dichloromethane is 0.3 - 0.5 mol:1 L.

[0025] A method for preparing a photo-reversibly crosslinked polyester aerogel fiber as described above, wherein the solvent in the spinning solution is hexafluoroisopropanol, and the concentration of the spinning solution is 5-20 wt%. A concentration within this range can avoid both the inability to spin due to too low a concentration and the too large product density due to too high a concentration.

[0026] A method for preparing a photo-reversibly crosslinked polyester aerogel fiber as described above, wherein the extrusion speed of the syringe pump is 10-100 μL min -1 , which can ensure complete gelation of the spinning solution. The needle diameter is 60-500 μm, which can ensure the uniformity of the gel.

[0027] A method for preparing a photo-reversibly crosslinked polyester aerogel fiber as described above, wherein the coagulation bath is an ethanol solution of coumarin. Ethanol is selected as the solvent in the coagulation bath because the subsequent fibers need to be supercritically dried, and ethanol is a commonly used medium for supercritical drying.

[0028] A method for preparing a photo-reversibly crosslinked polyester aerogel fiber as described above, wherein the power of ultraviolet light irradiation curing is 0.3-10 W cm -2 , and the time is 1-3 min, which can match the extrusion speed to ensure gelation. Generally, an ultraviolet lamp has two fixed wavelengths, one is 254 nm and the other is 365 nm. Therefore, a wavelength of 365 nm can be specifically selected during spinning.

[0029] A method for preparing a photo-reversibly crosslinked polyester aerogel fiber as described above, wherein the collection speed is 0.3-15 m min -1 ; the time for solvent replacement is 24-76 h, and the solvent used is ethanol.

[0030] The present invention also provides a photo-reversibly crosslinked polyester aerogel fiber prepared by using the method for preparing a photo-reversibly crosslinked polyester aerogel fiber described in any one of the above. The breaking strength of the photo-reversibly crosslinked polyester aerogel fiber is 5-20 MPa, and the porosity is 80-90%.

[0031] The present invention also provides a method for recycling the photo-reversibly crosslinked polyester aerogel fiber as described above. The photo-reversibly crosslinked polyester aerogel fiber is placed in a solvent (hexafluoroisopropanol) and irradiated with ultraviolet light with a wavelength <260 nm to be dissolved to obtain a spinning solution; the crosslinking bonds of the polyester aerogel fiber will break under ultraviolet light irradiation (λ <260 nm), so as to obtain non-crosslinked polyester. The recovered non-crosslinked polyester can be extruded through a spinneret and can be crosslinked again under the induction of ultraviolet light (λ ≥ 260 nm) to obtain a photo-reversibly crosslinked polyester aerogel fiber.

[0032] Beneficial effects:

[0033] (1) The present invention prepares a recyclable polyester aerogel fiber, realizing the closed-loop recycling of the polyester aerogel fiber and effectively improving the utilization rate of polyester materials;

[0034] (2) After extrusion, polyester undergoes [2+2] cycloaddition cross-linking of coumarin induced by ultraviolet light in a coagulation bath, and the formed cross-linking bonds are photoreversible, so they can reversibly break at a certain wavelength; this photoreversible cross-linking bond can, on the one hand, meet the requirements of the dynamic sol-gel transition in the formation of aerogel fibers, and on the other hand, can also realize the recyclability of polyester aerogel fibers. Specific embodiments

[0035] The present invention will be further described below in conjunction with specific embodiments. It should be understood that these embodiments are only used to illustrate the present invention and not to limit the scope of the present invention. In addition, it should be understood that after reading the content taught by the present invention, those skilled in the art can make various changes or modifications to the present invention, and these equivalent forms also fall within the scope defined by the appended claims of this application.

[0036] In the following embodiments:

[0037] The molecular structural formula of N,N-bis(2-hydroxyethyl)-4-((4-methyl-2-oxo-2H-chromen-7-yl)-oxy)butyramide is as follows:

[0038]

[0039] The molecular structural formula of N,N-bis(2-hydroxyethyl)soybean amide is as follows:

[0040]

[0041] The preparation steps of N,N-bis(2-hydroxyethyl)-4-((4-methyl-2-oxo-2H-chromen-7-yl)-oxy)butyramide and N,N-bis(2-hydroxyethyl)soybean amide are as follows:

[0042] (1) Under stirring conditions, a solution composed of 4-methylumbelliferone, methyl 4-bromobutyrate, 18-crown(ether), potassium carbonate and dimethylformamide is reacted at 50 °C under the organic layer for 24 h, and after post-treatment (diluted with deionized water, extracted with dichloromethane, combined, dried with anhydrous potassium carbonate, filtered, and rotary evaporated), methyl 4-((4-methyl-2-oxo-2H-chromen-7-yl)oxy)butyrate is obtained;

[0043] (2) Under stirring conditions, methyl 4-((4-methyl-2-oxo-2H-chromen-7-yl)oxy)butyrate was mixed with diethanolamine and then reacted at 80 °C for 8 h to obtain N,N-bis(2-hydroxyethyl)-4-((4-methyl-2-oxo-2H-chromen-7-yl)oxy)butyramide;

[0044] (3) Sodium methoxide and diethanolamine were added to N,N-bis(2-hydroxyethyl)-4-((4-methyl-2-oxo-2H-chromen-7-yl)oxy)butyramide. After stirring until sodium methoxide was completely dissolved, soybean oil was added, and then the reaction was carried out at 110 °C for 1 h under vacuum conditions. After cooling to room temperature, N,N-bis(2-hydroxyethyl)soyamide was obtained;

[0045] The molecular structural formula of the photo-reversibly crosslinked polyester is as follows:

[0046]

[0047] The test methods for the relevant performance indicators in the following examples are as follows:

[0048] Porosity of the photo-reversibly crosslinked polyester aerogel fiber: Porosity = 1 - ρ0 / ρ, where ρ0 is the density of the polyester aerogel fiber and ρ is the intrinsic density of the obtained photo-reversibly crosslinked polyester material.

[0049] Tensile strength of the photo-reversibly crosslinked polyester aerogel fiber: The tensile strength of the aerogel fiber was measured by a universal testing machine (UTM2102, Suns Technology Stock Co., Ltd). The fiber length during testing was 2 cm, and the tensile speed was 5 mm / min -1 .

[0050] Example 1

[0051] A preparation method of a photo-reversibly crosslinked polyester aerogel fiber, the steps are as follows:

[0052] (1) Prepare the reaction solution:

[0053] Reaction solution: It consists of N,N-bis(2-hydroxyethyl)-4-((4-methyl-2-oxo-2H-chromen-7-yl)oxy)butyramide, N,N-bis(2-hydroxyethyl)soyamide, oxalic acid, 4-(dimethylamino)pyridinium 4-toluenesulfonate, and dichloromethane;

[0054] The molar ratio of N,N-bis(2-hydroxyethyl)-4-((4-methyl-2-oxo-2H-chromen-7-yl)oxy)butyramide to N,N-bis(2-hydroxyethyl)soyamide is 1:1;

[0055] The molar ratio of oxalic acid to the total molar amount of N,N-bis(2-hydroxyethyl)-4-((4-methyl-2-oxo-2H-chromen-7-yl)-oxy)butyramide and N,N-bis(2-hydroxyethyl)soybean amide is 1:1;

[0056] The molar volume ratio of oxalic acid to dichloromethane is 0.5 mol:1 L;

[0057] The molar volume ratio of 4-(dimethylamino)pyridinium 4-toluenesulfonate to dichloromethane is 0.3 mol:1 L;

[0058] (2) Under stirring conditions, N,N'-diisopropylcarbodiimide is added to the reaction solution at 0 °C and stirring is continued for 20 min, then the temperature is raised to 25 °C and stirring is continued for 30 h. After post-treatment, a photo-reversibly cross-linked polyester is obtained; the molar amount of N,N'-diisopropylcarbodiimide is 2.5 times the molar amount of oxalic acid; in the molecular structural formula of the photo-reversibly cross-linked polyester, n is 50 and m is 50;

[0059] (3) After dissolving the photo-reversibly cross-linked polyester in hexafluoroisopropanol to prepare a spinning solution with a concentration of 5 wt%, it is extruded through an injection pump with a needle diameter of 60 μm at a speed of 10 μL min -1 and first irradiated and cured with ultraviolet light at a wavelength of 365 nm and a power of 0.3 W cm -2 in an ethanol solution of coumarin with a concentration of 0.1 wt% for 3 min, then collected at a speed of 0.3 m min -1 and then replaced with ethanol for 24 h, and finally supercritically dried to obtain photo-reversibly cross-linked polyester aerogel fibers.

[0060] The finally prepared photo-reversibly cross-linked polyester aerogel fibers have a breaking strength of 5 MPa and a porosity of 80%.

[0061] The method for recycling the above photo-reversibly cross-linked polyester aerogel fibers is as follows: The photo-reversibly cross-linked polyester aerogel fibers are placed in hexafluoroisopropanol and irradiated and dissolved with ultraviolet light at a wavelength of 254 nm to obtain a spinning solution.

[0062] Comparative Example 1

[0063] A method for preparing photo-reversibly cross-linked polyester aerogel fibers is basically the same as in Example 1, except that the concentration of the ethanol solution of coumarin in step (3) is 0.01 wt%.

[0064] When the fiber is extruded into the ethanol solution containing coumarin, since the content of coumarin in the coagulation bath is small and cannot diffuse into the fiber interior, the gelation rate is slow, resulting in the rapid diffusion of polyester into the coagulation bath and the inability to form continuous and stable polyester gel fibers, thus polyester aerogel fibers cannot be obtained.

[0065] Comparative Example 2

[0066] A preparation method of a photo-reversibly crosslinked polyester aerogel fiber is basically the same as that of Example 1, except that the concentration of the ethanol solution of coumarin in step (3) is 12 wt%.

[0067] When the fiber is extruded into the ethanol solution containing coumarin, since the content of coumarin in the coagulation bath is too high, the coumarin in the coagulation bath preferentially undergoes self-crosslinking and cannot diffuse into the fiber to react with the coumarin groups on the polyester side chain, thus continuous gel fibers cannot be formed, and finally continuous and stable polyester aerogel fibers cannot be prepared.

[0068] Example 2

[0069] A preparation method of a photo-reversibly crosslinked polyester aerogel fiber comprises the following steps:

[0070] (1) Prepare the reaction solution:

[0071] The reaction solution consists of N,N-bis(2-hydroxyethyl)-4-((4-methyl-2-oxo-2H-chromen-7-yl)-oxy)butanamide, N,N-bis(2-hydroxyethyl)soybean amide, oxalic acid, 4-(dimethylamino)pyridinium 4-toluenesulfonate, and dichloromethane;

[0072] The molar ratio of N,N-bis(2-hydroxyethyl)-4-((4-methyl-2-oxo-2H-chromen-7-yl)-oxy)butanamide to N,N-bis(2-hydroxyethyl)soybean amide is 1:1;

[0073] The molar amount of oxalic acid to the total molar amount of N,N-bis(2-hydroxyethyl)-4-((4-methyl-2-oxo-2H-chromen-7-yl)-oxy)butanamide and N,N-bis(2-hydroxyethyl)soybean amide is 1:1;

[0074] The molar volume ratio of oxalic acid to dichloromethane is 0.75 mol:1 L;

[0075] The molar volume ratio of 4-(dimethylamino)pyridinium 4-toluenesulfonate to dichloromethane is 0.4 mol:1 L;

[0076] (2) Under stirring conditions, N,N′-diisopropylcarbodiimide was added to the reaction solution at 3 °C and stirring was continued for 25 min. Then the temperature was raised to 28 °C and stirring was continued for 32 h. After post-treatment, a photo-reversibly cross-linked polyester was obtained; the molar amount of N,N′-diisopropylcarbodiimide was 3 times the molar amount of oxalic acid; in the molecular structural formula of the photo-reversibly cross-linked polyester, n was 50 and m was 50;

[0077] (3) After dissolving the photo-reversibly cross-linked polyester in hexafluoroisopropanol to prepare a spinning solution with a concentration of 15 wt%, it was extruded through an injection pump with a needle diameter of 300 μm at a speed of 80 μL min -1 and first irradiated and cured with ultraviolet light with a wavelength of 365 nm and a power of 8 W cm -2 in an ethanol solution of coumarin with a concentration of 5 wt% for 2 min, then collected at a speed of 1 m min -1 , then replaced with ethanol for 48 h, and finally supercritically dried to obtain photo-reversibly cross-linked polyester aerogel fibers.

[0078] The finally obtained photo-reversibly cross-linked polyester aerogel fibers had a breaking strength of 8 MPa and a porosity of 90%.

[0079] The method for recycling the above photo-reversibly cross-linked polyester aerogel fibers was as follows: The photo-reversibly cross-linked polyester aerogel fibers were placed in hexafluoroisopropanol and irradiated and dissolved with ultraviolet light with a wavelength of 254 nm to obtain a spinning solution.

[0080] Example 3

[0081] A method for preparing photo-reversibly cross-linked polyester aerogel fibers, the steps are as follows:

[0082] (1) Prepare a reaction solution:

[0083] The reaction solution: It consisted of N,N-bis(2-hydroxyethyl)-4-((4-methyl-2-oxo-2H-chromen-7-yl)-oxy)butyramide, N,N-bis(2-hydroxyethyl)soybean amide, oxalic acid, 4-(dimethylamino)pyridinium 4-toluenesulfonate, and dichloromethane;

[0084] The molar ratio of N,N-bis(2-hydroxyethyl)-4-((4-methyl-2-oxo-2H-chromen-7-yl)-oxy)butyramide to N,N-bis(2-hydroxyethyl)soybean amide was 1:1;

[0085] The molar amount ratio of oxalic acid to the total molar amount of N,N-bis(2-hydroxyethyl)-4-((4-methyl-2-oxo-2H-chromen-7-yl)-oxy)butyramide and N,N-bis(2-hydroxyethyl)soybean amide was 1.1:1;

[0086] The molar volume ratio of oxalic acid to dichloromethane is 1 mol: 1 L;

[0087] The molar volume ratio of 4-(dimethylamino)pyridinium 4-toluenesulfonate to dichloromethane is 0.5 mol: 1 L;

[0088] (2) Under stirring conditions, N,N'-diisopropylcarbodiimide is added to the reaction solution at 0 °C and stirring is continued for 30 min. Then the temperature is raised to 28 °C and stirring is continued for 36 h. After post-treatment, a photo-reversibly cross-linked polyester is obtained; the molar amount of N,N'-diisopropylcarbodiimide is 4 times the molar amount of oxalic acid; in the molecular structural formula of the photo-reversibly cross-linked polyester, n is 50 and m is 50;

[0089] (3) After dissolving the photo-reversibly cross-linked polyester in hexafluoroisopropanol to prepare a spinning solution with a concentration of 20 wt%, it is extruded through an injection pump with a needle diameter of 500 μm at a rate of 100 μL min -1 and first irradiated and cured with ultraviolet light at a wavelength of 365 nm and a power of 10 W cm -2 in an ethanol solution of coumarin with a concentration of 10 wt% for 1 min, then collected at a rate of 15 m min -1 and then replaced with ethanol for 76 h, and finally supercritically dried to obtain photo-reversibly cross-linked polyester aerogel fibers.

[0090] The finally prepared photo-reversibly cross-linked polyester aerogel fibers have a breaking strength of 16 MPa and a porosity of 89%.

[0091] The method for recycling the above photo-reversibly cross-linked polyester aerogel fibers is as follows: The photo-reversibly cross-linked polyester aerogel fibers are placed in hexafluoroisopropanol and irradiated and dissolved with ultraviolet light at a wavelength of 254 nm to obtain a spinning solution.

[0092] Example 4

[0093] A method for preparing photo-reversibly cross-linked polyester aerogel fibers, the steps are as follows:

[0094] (1) Prepare a reaction solution:

[0095] The reaction solution: It is composed of N,N-bis(2-hydroxyethyl)-4-((4-methyl-2-oxo-2H-chromen-7-yl)-oxy)butyramide, N,N-bis(2-hydroxyethyl)soybean amide, oxalic acid, 4-(dimethylamino)pyridinium 4-toluenesulfonate and dichloromethane;

[0096] The molar ratio of N,N-bis(2-hydroxyethyl)-4-((4-methyl-2-oxo-2H-chromen-7-yl)oxy)butanamide to N,N-bis(2-hydroxyethyl)soyamide is 2:3;

[0097] The molar amount of oxalic acid to the total molar amount of N,N-bis(2-hydroxyethyl)-4-((4-methyl-2-oxo-2H-chromen-7-yl)oxy)butanamide and N,N-bis(2-hydroxyethyl)soyamide is 1:1;

[0098] The molar volume ratio of oxalic acid to dichloromethane is 0.5 mol:1 L;

[0099] The molar volume ratio of 4-(dimethylamino)pyridinium 4-toluenesulfonate to dichloromethane is 0.3 mol:1 L;

[0100] (2) Under stirring conditions, N,N'-diisopropylcarbodiimide is added to the reaction solution at 5 °C and stirring is continued for 20 min. Then the temperature is raised to 30 °C and stirring is continued for 30 h. After post-treatment, a photo-reversibly crosslinked polyester is obtained; the molar amount of N,N'-diisopropylcarbodiimide is 3 times the molar amount of oxalic acid; in the molecular structural formula of the photo-reversibly crosslinked polyester, n is 40 and m is 60;

[0101] (3) After dissolving the photo-reversibly crosslinked polyester in hexafluoroisopropanol to prepare a spinning solution with a concentration of 5 wt%, it is extruded through an injection pump with a needle diameter of 60 μm at a speed of 10 μL min -1 and first irradiated and cured with ultraviolet light at a wavelength of 365 nm and a power of 0.3 W cm in an ethanol solution of coumarin with a concentration of 0.1 wt% for 3 min, then collected at a speed of 0.3 m min -2 and then ethanol is used for replacement for 24 h, and finally supercritical drying is carried out to obtain photo-reversibly crosslinked polyester aerogel fibers. -1 (4) The finally prepared photo-reversibly crosslinked polyester aerogel fibers have a breaking strength of 6 MPa and a porosity of 82%.

[0102] (5) The method for recycling the above photo-reversibly crosslinked polyester aerogel fibers is as follows: the photo-reversibly crosslinked polyester aerogel fibers are placed in hexafluoroisopropanol and irradiated and dissolved with ultraviolet light at a wavelength of 254 nm to obtain a spinning solution.

[0103] Example 5

[0104] A method for preparing photo-reversibly crosslinked polyester aerogel fibers, the steps are as follows:

[0105] (1) Prepare a reaction solution:

[0106] (1) Prepare a reaction solution:

[0107] Reaction solution: It is composed of N,N-bis(2-hydroxyethyl)-4-((4-methyl-2-oxo-2H-chromen-7-yl)-oxy)butyramide, N,N-bis(2-hydroxyethyl)soybean amide, oxalic acid, 4-(dimethylamino)pyridinium 4-toluenesulfonate, and dichloromethane;

[0108] The molar ratio of N,N-bis(2-hydroxyethyl)-4-((4-methyl-2-oxo-2H-chromen-7-yl)-oxy)butyramide to N,N-bis(2-hydroxyethyl)soybean amide is 2:3;

[0109] The molar amount ratio of oxalic acid to the total molar amount of N,N-bis(2-hydroxyethyl)-4-((4-methyl-2-oxo-2H-chromen-7-yl)-oxy)butyramide and N,N-bis(2-hydroxyethyl)soybean amide is 1:1;

[0110] The molar volume ratio of oxalic acid to dichloromethane is 0.75 mol:1 L;

[0111] The molar volume ratio of 4-(dimethylamino)pyridinium 4-toluenesulfonate to dichloromethane is 0.4 mol:1 L;

[0112] (2) Under stirring conditions, N,N'-diisopropylcarbodiimide is added to the reaction solution at 3 °C and stirred continuously for 25 min. Then, the temperature is raised to 30 °C and stirred continuously for 36 h. After post-treatment, a photo-reversibly crosslinked polyester is obtained; the molar amount of N,N'-diisopropylcarbodiimide is 2.5 times the molar amount of oxalic acid; in the molecular structural formula of the photo-reversibly crosslinked polyester, n is 40 and m is 60;

[0113] (3) After dissolving the photo-reversibly crosslinked polyester in hexafluoroisopropanol to prepare a spinning solution with a concentration of 15 wt%, it is extruded through an injection pump with a needle diameter of 300 μm at a speed of 80 μL min -1 and first irradiated and cured with ultraviolet light with a wavelength of 365 nm and a power of 8 W cm -2 in an ethanol solution of coumarin with a concentration of 5 wt% for 2 min, then collected at a speed of 1 m min -1 , then replaced with ethanol for 48 h, and finally supercritically dried to obtain photo-reversibly crosslinked polyester aerogel fibers.

[0114] The finally prepared photo-reversibly crosslinked polyester aerogel fibers have a breaking strength of 8.5 MPa and a porosity of 85%.

[0115] The method for recycling the above photo-reversibly crosslinked polyester aerogel fibers is: placing the photo-reversibly crosslinked polyester aerogel fibers in hexafluoroisopropanol and irradiating and dissolving them with ultraviolet light with a wavelength of 254 nm to obtain a spinning solution.

[0116] Example 6

[0117] A preparation method of a photo-reversibly crosslinked polyester aerogel fiber, the steps are as follows:

[0118] (1) Prepare the reaction solution:

[0119] The reaction solution: It is composed of N,N-bis(2-hydroxyethyl)-4-((4-methyl-2-oxo-2H-chromen-7-yl)-oxy)butyramide, N,N-bis(2-hydroxyethyl)soybean amide, oxalic acid, 4-(dimethylamino)pyridinium 4-toluenesulfonate and dichloromethane;

[0120] The molar ratio of N,N-bis(2-hydroxyethyl)-4-((4-methyl-2-oxo-2H-chromen-7-yl)-oxy)butyramide to N,N-bis(2-hydroxyethyl)soybean amide is 2:3;

[0121] The molar amount ratio of oxalic acid to the total molar amount of N,N-bis(2-hydroxyethyl)-4-((4-methyl-2-oxo-2H-chromen-7-yl)-oxy)butyramide and N,N-bis(2-hydroxyethyl)soybean amide is 1.1:1;

[0122] The molar volume ratio of oxalic acid to dichloromethane is 1mol:1L;

[0123] The molar volume ratio of 4-(dimethylamino)pyridinium 4-toluenesulfonate to dichloromethane is 0.5mol:1L;

[0124] (2) Under stirring conditions, add N,N′-diisopropylcarbodiimide to the reaction solution at 0 °C and continue stirring for 30 min, then raise the temperature to 30 °C and continue stirring for 36 h, and obtain photo-reversibly crosslinked polyester after post-treatment; the molar amount of N,N′-diisopropylcarbodiimide is 5 times the molar amount of oxalic acid; in the molecular structural formula of the photo-reversibly crosslinked polyester, n is 40 and m is 60;

[0125] (3) After dissolving the photo-reversibly crosslinked polyester in hexafluoroisopropanol to prepare a spinning solution with a concentration of 20 wt%, extrude it through an injection pump with a needle diameter of 500 μm at a speed of 100 μL min -1 , first irradiate and cure it with ultraviolet light with a wavelength of 365 nm and a power of 10 W cm -2 in an ethanol solution of coumarin with a concentration of 10 wt% for 1 min, then collect it at a speed of 15 m min -1 , then replace it with ethanol for 76 h, and finally perform supercritical drying to obtain the photo-reversibly crosslinked polyester aerogel fiber.

[0126] The breaking strength of the finally obtained photo-reversibly crosslinked polyester aerogel fiber is 20 MPa, and the porosity is 87%.

[0127] The method for recycling the photo-reversibly crosslinked polyester aerogel fiber is as follows: placing the photo-reversibly crosslinked polyester aerogel fiber in hexafluoroisopropanol and irradiating it with ultraviolet light with a wavelength of 254 nm for dissolution to obtain a spinning solution.

Claims

1. A preparation method of a photo-reversibly cross-linked polyester aerogel fiber, characterized in that, After dissolving the photo-reversibly crosslinked polyester to prepare a spinning solution, it is extruded and successively irradiated and cured with ultraviolet light with a wavelength ≥ 260 nm, collected, solvent-exchanged, and supercritically dried to obtain photo-reversibly crosslinked polyester aerogel fibers. Among them, the molecular structural formula of the photo-reversibly crosslinked polyester is as follows: In the formula, n is 50 or 40, and m is 50 or 60; The ultraviolet light irradiation curing is carried out in a coagulation bath, and the coagulation bath contains 0.1 - 10 wt% of coumarin.

2. The preparation method of a photo-reversibly crosslinked polyester aerogel fiber according to claim 1, characterized in that, The preparation method of the photo-reversibly crosslinked polyester is as follows: under stirring conditions, N,N'-diisopropylcarbodiimide is added to a reaction solution at a temperature of 0 - 5 °C and continuously stirred for 20 - 30 min. Then, the temperature is raised to 25 - 30 °C and continuously stirred for 30 - 36 h. After post-treatment, the photo-reversibly crosslinked polyester is obtained; The reaction solution is composed of N,N-bis(2-hydroxyethyl)-4-((4-methyl-2-oxo-2H-chromen-7-yl)-oxy)butanamide, N,N-bis(2-hydroxyethyl)soybean amide, adipic acid, 4-(dimethylamino)pyridinium 4-toluenesulfonate, and dichloromethane; The molecular structural formula of N,N-bis(2-hydroxyethyl)-4-((4-methyl-2-oxo-2H-chromen-7-yl)-oxy)butanamide is as follows: The molecular structural formula of N,N-bis(2-hydroxyethyl)soybean amide is as follows:

3. The preparation method of a photo-reversibly crosslinked polyester aerogel fiber according to claim 2, characterized in that, The molar ratio of N,N-bis(2-hydroxyethyl)-4-((4-methyl-2-oxo-2H-chromen-7-yl)-oxy)butanamide to N,N-bis(2-hydroxyethyl)soybean amide is 1:1 or 2:3; The molar amount ratio of adipic acid to the total molar amount of N,N-bis(2-hydroxyethyl)-4-((4-methyl-2-oxo-2H-chromen-7-yl)-oxy)butanamide and N,N-bis(2-hydroxyethyl)soybean amide is 1 - 1.1:1; The molar amount of N,N'-diisopropylcarbodiimide is 2.5 - 5 times the molar amount of adipic acid; The molar volume ratio of adipic acid to dichloromethane is 0.5 - 1 mol:1 L; The molar volume ratio of 4-(dimethylamino)pyridinium 4-toluenesulfonate to dichloromethane is 0.3 - 0.5 mol:1 L.

4. The preparation method of a photo-reversibly cross-linked polyester aerogel fiber according to claim 1, characterized in that, The concentration of the spinning solution is 5 - 20 wt%.

5. The preparation method of a photo-reversibly crosslinked polyester aerogel fiber according to claim 1, characterized in that, The coagulation bath is an ethanol solution of coumarin.

6. The preparation method of a photo-reversibly crosslinked polyester aerogel fiber according to claim 1, wherein, The power of ultraviolet radiation curing is 0.3 - 10 W / cm -2 , and the time is 1 - 3 min.

7. The preparation method of a photo-reversibly crosslinked polyester aerogel fiber according to claim 1, wherein, The collection speed is 0.3 to 15 m / min -1 ; the solvent replacement time is 24 to 76 h, and the solvent used is ethanol.

8. A photo-reversibly crosslinked polyester aerogel fiber prepared by the method for preparing a photo-reversibly crosslinked polyester aerogel fiber according to any one of claims 1 to 7, characterized in that, The breaking strength of the photo-reversibly crosslinked polyester aerogel fibers is 5 - 20 MPa, and the porosity is 80 - 90%.

9. A method for recovering the photo-reversibly crosslinked polyester aerogel fiber as claimed in claim 8, characterized in that, The photo-reversibly crosslinked polyester aerogel fibers are placed in a solvent and irradiated with ultraviolet light with a wavelength < 260 nm to be dissolved to obtain a spinning solution.

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