CN116200881A

CN116200881A - Heterocyclic aramid nanofiber membrane and preparation method thereof

Info

Publication number: CN116200881A
Application number: CN202310305614.XA
Authority: CN
Inventors: 刘向阳; 高可雄; 罗龙波; 刘洋; 王旭; 刘昌莉
Original assignee: Sichuan University
Current assignee: Sichuan University
Priority date: 2023-03-27
Filing date: 2023-03-27
Publication date: 2023-06-02

Abstract

A heterocyclic aramid nanofiber membrane and a preparation method thereof, wherein the preparation method comprises the following steps: adding aromatic heterocyclic diamine monomer containing benzimidazole or benzoxazole, aromatic diamine monomer and aromatic diacid chloride monomer into solvent to react to obtain heterocyclic aramid solution; adding a micromolecular physical cross-linking agent into the heterocyclic aramid fiber solution, and uniformly mixing to obtain spinning glue solution; the spinning glue solution is subjected to an electrostatic spinning process to obtain a nascent heterocyclic aramid nanofiber membrane oriented along the rotation direction of a roller; soaking the nascent heterocyclic aramid nanofiber membrane in alkali solution and distilled water respectively, taking out, drying or freeze drying under normal pressure, and annealing to obtain the pure heterocyclic aramid nanofiber membrane. The high-performance heterocyclic aramid nanofiber membrane successfully prepared by using the electrostatic spinning technology has good appearance, excellent mechanical strength and thermal stability, and good hydrophobicity, and can be used in the fields of high-temperature resistant diaphragms of lithium ion batteries and the like.

Description

Heterocyclic aramid nanofiber membrane and preparation method thereof

Technical Field

The invention relates to the field of high-performance fiber materials, in particular to a heterocyclic aramid nanofiber membrane and a preparation method thereof.

Background

With the development of nano material preparation technology, traditional poly (paraphenylene terephthamide) (PPTA) fiber (Kevlar) can be prepared into para-aramid nanofiber dispersion by a deprotonation etching method. ANFs are widely used to prepare high performance and functionalized materials due to their unique one-dimensional structure and retention of the excellent mechanical properties and heat resistance of Kevlar fibers. Compared with the deprotonation etching method, the electrostatic spinning technology is a widely used continuous nanofiber preparation method and has the potential of industrialized mass production. However, PPTA is only soluble in strong protonic acids such as concentrated sulfuric acid, methanesulfonic acid, and chlorosulfonic acid due to rigid molecular chain conformation and strong inter-chain hydrogen bonding. Limited by the harsh dissolution conditions of PPTA, it is difficult to directly prepare para-aramid nanofibers by electrospinning. In order to realize electrostatic spinnability of para-aramid, a flexible structure is generally introduced to modify PPTA by adopting a copolymerization or covalent grafting mode. Although these methods can obtain para-aramid fibers having good electrostatic spinnability by improving the solubility, the mechanical properties thereof are severely reduced as compared with PPTA. The Chinese patent with application number 202111496668.6 discloses a high-strength para-aramid nanofiber membrane and a preparation method thereof, wherein the electrospun membrane is prepared by adding a spinning aid into a deprotonated PPTA nanofiber dispersion liquid. As the spinning aid adopts flexible chain polymers (such as polyethylene oxide, polyvinylpyrrolidone and the like), the heat resistance and the thermal stability of the finally obtained para-aramid nanofiber membrane are seriously reduced. Based on the above results, it is very challenging to develop an electrospun aramid nanofiber membrane with excellent mechanical properties and heat resistance.

The heterocycle aramid fiber which is typically represented by introducing benzimidazole units or benzoxazole units on the basis of PPTA molecular chains has good solubility and excellent mechanical properties. This makes both a potential ideal material for preparing high performance electrospun aramid nanofiber membranes. Nevertheless, the rigid nature of the molecular chains of these two classes of heterocyclic aramids makes them lacking the effective topological entanglement required for electrospinning in solution, thus exhibiting poor electrostatic spinnability.

Up to now, there has been no report on the preparation of benzimidazole-type or benzoxazole-type heterocyclic aramid nanofiber membranes by electrospinning technology. How to improve the electrostatic spinnability of the two types of heterocyclic aramid fiber solutions and obtain the heterocyclic aramid fiber nanofiber material with reliable performance by a solution property regulation method is still an important subject of current research.

Disclosure of Invention

Based on the method, the invention provides the heterocyclic aramid nanofiber membrane and the preparation method thereof, so as to solve the problem of electrostatic spinnability of benzimidazole-type or benzoxazole-type heterocyclic aramid nanofiber solution.

In order to achieve the above object, the present invention provides a preparation method of a heterocyclic aramid nanofiber membrane, comprising the following steps:

(1) Dissolving aromatic heterocyclic diamine monomer containing benzimidazole or benzoxazole and aromatic diamine monomer in a solvent; and adding an aromatic diacid chloride monomer, and reacting to obtain a heterocyclic aramid fiber solution, wherein the molar ratio of the total amount of aromatic heterocyclic diamine monomer and aromatic diamine monomer to the aromatic diacid chloride monomer is 1: (0.9-1.1), wherein the molar ratio of the aromatic diamine monomer in the total amount of the aromatic heterocyclic diamine monomer and the aromatic diamine monomer is 0-60%, namely the aromatic heterocyclic diamine is mainly arranged, and the aromatic diamine is introduced as a comonomer;

(2) Adding inorganic polybasic acid or organic polybasic acid serving as a small molecular physical cross-linking agent into the heterocyclic aramid solution according to the mass concentration of 2% -6%, and uniformly mixing to obtain spinning glue solution with the mass concentration of 1% -3.0% and the kinetic viscosity of 1-20 Pa.s;

(3) The spinning glue solution is subjected to an electrostatic spinning process, and a roller receiving device is used for collecting spinning fibers at the rotating speed of 300-1000 rpm, so that a nascent heterocyclic aramid nanofiber membrane oriented along the rotating direction of the roller is obtained;

(4) Soaking the nascent heterocyclic aramid nanofiber membrane in alkali solution and distilled water respectively, taking out, drying or freeze-drying under normal pressure, and annealing to obtain the pure heterocyclic aramid nanofiber membrane with the diameter of 120-400 nm.

In the step (4), the porosity of the heterocyclic aramid nanofiber membrane obtained by normal pressure drying is 20% -40%, the tensile strength in the orientation direction is 400-600 MPa, and the tensile strength in the vertical orientation direction is 40-60 MPa; the porosity of the heterocyclic aramid nanofiber membrane obtained by freeze drying is 80% -95%, the water contact angle is 105-120 degrees, the tensile strength in the orientation direction is 80-150 MPa, and the tensile strength in the vertical orientation direction is 10-20 MPa.

As a further preferable technical scheme of the invention, in the step (1), the solvent is a composite solvent prepared from a polar aprotic organic solvent and an inorganic salt cosolvent, and the mass concentration of the inorganic salt cosolvent in the polar aprotic organic solvent is 1% -9%; the polar aprotic organic solvent includes: one or more of N, N-dimethylacetamide (DMAc), N-Dimethylformamide (DMF), dimethylsulfoxide (DMSO) and N-methylpyrrolidone (NMP), wherein the inorganic salt cosolvent comprises: lithium chloride (LiCl), calcium chloride (CaCl) ₂ ) Lithium bromide (LiBr), calcium bromide (CaBr) ₂ ) One or more of them.

As a further preferable technical scheme of the invention, the reaction in the step (1) is carried out under the protection of inert gas, wherein in the reaction process, aromatic heterocyclic diamine monomer containing benzimidazole or benzoxazole and aromatic diamine monomer are added into a solvent, and then aromatic diacid chloride monomer is added for reaction in two stages: in the first stage, 70% -90% of the aromatic diacid chloride monomer is added and reacted for 20-40 min at 0-5 ℃; and in the second stage, adding the rest aromatic diacid chloride monomer, and reacting for 1-2 hours at 20-40 ℃, wherein the mass concentration of the prepared heterocyclic aramid fiber solution is 3-7%, the kinetic viscosity at room temperature is 300-1200 Pa.s, and the intrinsic viscosity is 10-20 dL/g. After the diamine monomer is dissolved, the water content in the solution is controlled to be less than or equal to 100ppm so as to prevent the diacid chloride monomer from being deactivated by reaction with water, so that the characteristic viscosity number of the heterocyclic aramid fiber is too low.

As a further preferable technical scheme of the invention, the heterocyclic aramid fiber polymerized in the step (1) has good solubility in the composite solvent, and the appearance of the polymerized heterocyclic aramid fiber solution is uniform and isotropic. The phenomenon that the solution of the heterocyclic aramid is gelled or precipitates and precipitates due to poor solubility of the heterocyclic aramid cannot occur. Based on the consideration of the solubility of the heterocyclic aramid, in the step (1):

the aromatic heterocyclic diamine monomer is selected from the group consisting of: one or more of 2- (4-aminophenyl) -5-aminobenzoxazole (PBOA), 2- (3-aminophenyl) -5-aminobenzoxazole (MBOA), 2- (4-aminophenyl) -5-aminobenzimidazole (PABZ), 2- (3-aminophenyl) -5-aminobenzimidazole (MABZ) and 2-2' -p-phenyl-bisbenzimidazole diamine (BPABZ), wherein the structural formula of each monomer is shown in the table 1.

TABLE 1

The aromatic diamine monomer is selected from: (1) phenyl type: p-Phenylenediamine (PDA), 2-chloro-4-aminoaniline (PDA-Cl); (2) biphenyl: 4,4' -biphenyldiamine (HPA), 2' -bis (trifluoromethyl) diaminobiphenyl (TFMB), 4' -diamino-2, 2' -dimethyl-1, 1' -biphenyl (THMB); (3) phenyl spacer: one or more of 4,4' -diaminobenzil anilide (DABA), 4' -diaminodiphenyl ether (4, 4' -ODA) and para-aminobenzoic acid para-aminophenyl ester (APAB), wherein the structural formula of each monomer is shown in the table 2.

TABLE 2

The aromatic diacid chloride monomer is selected from the group consisting of: one or more of terephthaloyl chloride (TPC), isophthaloyl chloride (IPC), 4 '-benzil chloride (BPC) and 4,4' -diacyl chloride Diphenyl Ether (DEDC), wherein the structural formula of each monomer is shown in the table 3.

TABLE 3 Table 3

As a further preferable technical scheme of the invention, the small molecule physical cross-linking agent is a polybasic organic acid or an inorganic acid such as sulfuric acid, oxalic acid, phosphoric acid, polyphosphoric acid and the like. The spinning glue solution obtained in the step (2) contains the heterocyclic aramid polymer with the mass concentration of 1% -3.0%, and the dynamic viscosity range of the spinning glue solution is 1-20 Pa.s. In practical production, the viscosity of the spinning glue solution is too large or too small, which is not beneficial to the stability and continuity of the formation and electrospinning process of the heterocyclic aramid nanofiber.

As a further preferable technical scheme of the invention, the electrospinning process conditions in the step (3) are as follows: the voltage is 18-30 kV, the spinning speed is 0.1-3 mL/h, the distance between the needle head and the roller receiving device is 5-30 cm, the temperature is 20-50 ℃, and the relative humidity is 30-50%. The heterocyclic aramid nanofiber membrane oriented in the rotation direction of the drum can be obtained using the drum receiving means at a rotation speed of 300 to 1000rpm, and if the nanofibers are vertically erected on the plate receiving means when the plate receiving means is used, the heterocyclic aramid nanofiber membrane cannot be obtained.

As a further preferable technical scheme of the invention, in the step (4), the alkali solution is an aqueous solution of an alkaline substance, the alkaline substance is an organic alkali or an inorganic alkali, and the pH value of the alkali solution is 8-11; the soaking temperature is 20-80 ℃ and the soaking time is 1-24 h; the temperature of normal pressure drying is 50-100 ℃ and the time is 1-5 h; the annealing treatment temperature is 360-410 ℃ and the annealing treatment time is 0.5-1 h.

According to another aspect of the present invention, the present invention also provides a heterocyclic aramid nanofiber membrane manufactured by the method for manufacturing a heterocyclic aramid nanofiber membrane according to any one of the above.

The heterocyclic aramid nanofiber membrane and the preparation method thereof can achieve the following by adopting the technical scheme

The beneficial effects are that:

1. the invention realizes the preparation of the continuous heterocyclic aramid nanofiber membrane by using the electrostatic spinning technology for the first time. The molecular chain topology entanglement required by the equivalent electrospinning is realized by adding a small molecular physical crosslinking agent to construct a hydrogen bond crosslinking network among rigid heterocyclic aramid molecular chains, and the small molecular physical crosslinking agent can be removed by washing with alkali solution and distilled water after the nanofiber is formed, so that the pure heterocyclic aramid nanofiber membrane is obtained.

2. The nascent heterocyclic aramid nanofiber membrane provided by the invention has good hydrophilicity due to the fact that a large amount of inorganic salt cosolvent and micromolecular physical cross-linking agent are contained, so that the nascent heterocyclic aramid nanofiber membrane is converted into the heterocyclic aramid nanofiber hydrogel in the process of soaking in alkali solution and distilled water, and the heterocyclic aramid nanofiber membrane with high porosity is further prepared through a freeze drying or supercritical drying technology.

3. The spinning glue solution prepared by the invention does not need a special receiving device in the electrostatic spinning process, and the heterocyclic aramid nanofiber membrane with high orientation along the rotating direction of the roller can be obtained only by the roller receiving device at a lower rotating speed (300 rpm).

4. The water contact angle of the heterocyclic aramid nanofiber membrane provided by the invention is 105-120 degrees, and the heterocyclic aramid nanofiber membrane has good hydrophobicity; the heat stability is excellent, and meanwhile, the high tensile strength is realized due to the high orientation of the heterocyclic aramid nanofiber, so that the high-temperature-resistant polymer can be used in the fields of high-temperature-resistant diaphragms of lithium ion batteries and the like.

5. The preparation process of the heterocyclic aramid nanofiber membrane adopts a synthesis preparation strategy from bottom to top, is simple and easy to operate, and is suitable for industrial mass production.

Drawings

The invention will be described in further detail with reference to the drawings and the detailed description.

FIG. 1 is a heterocyclic aramid nanofiber membrane prepared in example 1.

Fig. 2 is a drawing curve of the heterocyclic aramid nanofiber membrane prepared in example 1 in a direction parallel to the orientation direction and perpendicular to the orientation direction.

Fig. 3 is an SEM surface and cross-sectional morphology of the heterocycle aramid nanofiber hydrogel prepared in example 2 after lyophilization.

Fig. 4 is a graph showing water contact angle measurement of the heterocyclic aramid nanofiber membrane prepared in example 2.

FIG. 5 is a graph showing N in the case of the heterocyclic aramid nanofiber membrane prepared in example 3 ₂ Thermal weight loss curve under atmosphere.

FIG. 6 is a SEM image of the surface and cross section of a heterocyclic aramid nanofiber membrane prepared in example 4.

Fig. 7 is a drawing curve of the heterocyclic aramid nanofiber membrane prepared in example 4 in a direction parallel to the orientation direction and perpendicular to the orientation direction.

Fig. 8 is a graph showing water contact angle measurement of the heterocyclic aramid nanofiber membrane prepared in example 4.

FIG. 9 is a graph showing the morphology of nanofibers collected from a solution of a heterocyclic aramid spinning dope without a small molecular physical cross-linking agent added to comparative example 1 after electrospinning.

The achievement of the objects, functional features and advantages of the present invention will be further described with reference to the accompanying drawings, in conjunction with the embodiments.

Detailed Description

The following describes specific embodiments of the present invention in detail with reference to the drawings. It should be understood that the detailed description and specific examples, while indicating and illustrating the invention, are not intended to limit the invention.

Unless defined otherwise, technical terms used in the following examples have the same meaning as commonly understood by one of ordinary skill in the art to which the inventive concepts pertain. The test reagents used in the following examples, unless otherwise specified, are all conventional biochemical reagents; the experimental methods are conventional methods unless otherwise specified.

The invention has the premise that the heterocyclic aramid obtained by polymerization has good solubility in the listed composite solvent, and can form uniform isotropic heterocyclic aramid solution. If gelation or precipitation and other phenomena occur during the polymerization process, which are caused by poor solubility of the heterocyclic aramid fiber, the preparation of the heterocyclic aramid fiber nanofiber membrane by the electrostatic spinning technology is not facilitated. Based on the method, the electrostatic spinnability of the uniform isotropic heterocyclic aramid solution can be remarkably improved by adding the small molecular physical cross-linking agent with the mass concentration of 2-6 percent. The five aromatic heterocyclic diamine monomers listed in table 1 can be reacted with three aromatic diacid chloride monomers listed in table 3, respectively, to produce a heterocyclic aramid fiber having good solubility. On the basis, one or more of the phenyl type, biphenyl type or phenyl interval type aromatic diamine monomers are introduced in a copolymerization mode, and the mole ratio of the aromatic heterocyclic diamine monomers to the total amount of the aromatic heterocyclic diamine monomers is controlled to be 0-60%, so that the uniform isotropic heterocyclic aramid solution can be obtained through polymerization.

Example 1

(1) Using BPABZ and TPC as raw materials, at N ₂ 6.61g of BPABZ was dissolved in 200g of DMAc/LiCl complex solvent (LiCl mass concentration 4%) at room temperature under an atmosphere. After the diamine monomer was dissolved, the temperature was reduced to 2℃and the water content 80ppm. 3.92g TPC was then added in two portions, at 30min intervals. The molar ratio of diamine to diacid chloride is 1:1. after the TPC is added for the last time, the temperature is raised to 35 ℃ and stirring is continued for 1 hour, and finally the heterocyclic aramid fiber solution with the mass concentration of 4.33% and the intrinsic viscosity of 15.4dL/g is obtained.

(2) 242.9g DMAc and 14.3g concentrated sulfuric acid were mixed well under an ice water bath, and then slowly added to 100g of the heterocyclic aramid dope using a constant pressure funnel. And (3) continuously stirring for 1h under the cooling condition of ice water bath to obtain the uniform spinning glue solution with the mass content of 1.21% and the sulfuric acid content of 4.0% of the heterocyclic aramid fiber.

(3) And adding a proper amount of the spinning glue solution into a 5mL syringe with the diameter of 12.5mm, and carrying out electrostatic spinning by adopting a 23G flat-head needle. The parameters were set as follows: the voltage is 23kV, the spinning speed is 3.0mL/h, the distance between the needle head and the roller receiving device is 8cm, the roller rotating speed is 300rpm, the temperature is 30 ℃, and the relative humidity is 42%. Setting the spinning time to be 4 hours, and finally obtaining the nascent heterocyclic aramid nanofiber membrane oriented along the rotation direction of the roller.

(4) The obtained nascent heterocyclic aramid nanofiber is soaked in an ammonia water solution with the mass concentration of 2.5% for 6 hours at room temperature. Then transferring the mixture into distilled water for soaking for 24 hours, and changing water for three times in the middle to obtain the heterocyclic aramid nanofiber hydrogel.

(5) The resulting heterocyclic aramid nanofiber hydrogel was dried in a forced air oven at 80 ℃ for 10 hours. Finally, the dried film is thermally annealed at 380 ℃ for 0.5h to obtain the heterocyclic aramid nanofiber film.

FIG. 1 shows the resulting pale yellow semitransparent heterocyclic aramid nanofiber membrane having a thickness of about 10 μm and a porosity of 26%. Fig. 2 (a) and (b) are respectively drawing curves of the parallel orientation direction and the perpendicular orientation direction of the heterocyclic aramid nanofiber after thermal annealing. The tensile strength in the direction parallel to the orientation direction is up to 576MPa. Although the tensile strength perpendicular to the orientation direction is only 45.4MPa, it is still higher than most electrospun films. The difference of mechanical properties of the heterocyclic aramid nanofiber membrane in different directions also indicates that the heterocyclic aramid nanofibers are oriented and arranged along the rotation direction of the roller.

Example 2

(1) PABZ and TPC are used as raw materials, and the raw materials are shown in N ₂ 13.8g of PABZ was dissolved in 500g of DMAc/LiCl complex solvent (LiCl mass concentration 3.5%) at room temperature under an atmosphere. After the diamine monomer was dissolved, the temperature was reduced to 2℃and the water content 80ppm. 12.4g TPC was then added in two portions, at 20min intervals. The molar ratio of diamine to diacid chloride is 1:0.99. after the TPC is added for the last time, the temperature is raised to 35 ℃ and stirring is continued for 1 hour, and finally the heterocyclic aramid fiber solution with the mass concentration of 4.15% and the intrinsic viscosity of 13.1dL/g is obtained.

(2) 29.2g DMAc and 4.17g concentrated sulfuric acid were mixed well under an ice-water bath, and then slowly added to 50g of the heterocyclic aramid dope using a constant pressure funnel. And (3) continuously stirring for 1h under the cooling condition of ice water bath to obtain the uniform spinning glue solution with the mass content of the heterocyclic aramid fiber being 2.5% and the sulfuric acid content being 5.0%.

(3) And adding a proper amount of the spinning glue solution into a 5mL syringe with the diameter of 12.5mm, and carrying out electrostatic spinning by adopting a 23G flat-head needle. The parameters were set as follows: the voltage is 25kV, the spinning speed is 1.5mL/h, the distance between the needle head and the roller receiving device is 10cm, the roller rotating speed is 500rpm, the temperature is 28 ℃, and the relative humidity is 40%. Setting the spinning time to be 6h, and finally obtaining the nascent heterocyclic aramid nanofiber membrane oriented along the rotation direction of the roller.

(4) The obtained nascent heterocyclic aramid nanofiber is soaked in an ammonia water solution with the mass concentration of 3% for 6 hours at room temperature. Then transferring the mixture into distilled water for soaking for 24 hours, and changing water for three times in the middle to obtain the heterocyclic aramid nanofiber hydrogel.

(5) And freeze-drying the obtained heterocyclic aramid nanofiber hydrogel. Finally, the dried film is thermally annealed at 380 ℃ for 0.5h to obtain the heterocyclic aramid nanofiber film with the porosity of 94%.

FIG. 3 is a SEM image of the surface and cross section of a freeze-dried aramid nanofiber hydrogel. The high porosity and loose cross-section morphology indicate that the heterocyclic aramid nanofiber hydrogel is obtained after alkali washing and water washing. Fig. 4 is a water contact angle test result of the obtained heterocyclic aramid nanofiber membrane, and it can be seen that it exhibits hydrophobicity, and the water contact angle is about 114 °.

Example 3

(1) Using PBOA, PDA and TPC as raw materials, in N ₂ 2.92g of PBOA and 1.40g of PDA were dissolved, under an atmosphere, in 150g of DMAc/LiCl complex solvent at room temperature (LiCl mass concentration 3.5%, diamine monomer molar ratio BOA: PDA=1:1). After the diamine monomer was dissolved, the temperature was reduced to 3℃and the water content was 100ppm. 5.26g TPC was then added in two portions, at 30min intervals, with a molar ratio of diamine to diacid chloride of 1:1. after the TPC is added for the last time, the temperature is raised to 30 ℃ and stirring is continued for 1 hour, and finally the heterocyclic aramid fiber solution with the mass concentration of 4.81% and the intrinsic viscosity of 13.5dL/g is obtained.

(2) 62.3g DMAc and 3.43g concentrated sulfuric acid were mixed well under an ice-water bath, and then slowly added to 20g of the heterocyclic aramid dope using a constant pressure funnel. Continuously stirring for 1.0h under the cooling condition of ice water bath to obtain the uniform spinning glue solution with the mass content of 1.12% and the sulfuric acid content of 4% of the heterocycle aramid.

(3) And adding a proper amount of the spinning glue solution into a 5mL syringe with the diameter of 12.5mm, and carrying out electrostatic spinning by adopting a 25G flat-head needle. The parameters were set as follows: the voltage is 23kV, the spinning speed is 2.0mL/h, the distance between the needle head and the roller receiving device is 8cm, the roller rotating speed is 500rpm, the temperature is 32 ℃, and the relative humidity is 45%. Setting the spinning time to be 5h, and finally obtaining the nascent heterocyclic aramid nanofiber membrane oriented along the rotation direction of the roller.

(4) The obtained nascent heterocyclic aramid nanofiber is soaked in KOH aqueous solution with the mass concentration of 1.5% for 6 hours at room temperature. Then transferring the mixture into distilled water for soaking for 24 hours, and changing water for three times in the middle to obtain the heterocyclic aramid nanofiber hydrogel.

(5) The resulting heterocyclic aramid nanofiber hydrogel was dried in a forced air oven at 80 ℃ for 10 hours. Finally, the dried film is thermally annealed for 0.5h at 360 ℃ to obtain the heterocyclic aramid nanofiber film with the porosity of 31.5%.

Fig. 5 is a thermal weight loss curve of the obtained heterocyclic aramid nanofiber membrane, and the thermal weight loss does not occur until 505 ℃, which indicates that the heterocyclic aramid nanofiber membrane has good thermal stability.

Example 4

(1) PABZ, PDA and TPC are taken as raw materials, and the raw materials are shown in N ₂ 3.20g of PABZ and 1.54g of PDA were dissolved at room temperature in 200g of DMAc/LiCl complex solvent (LiCl mass concentration 3.5%, diamine monomer molar ratio PABZ: PDA=1:1) under an atmosphere. After the diamine monomer was dissolved, the temperature was reduced to 5℃and the water content was 50ppm. 5.78g TPC was then added in two portions, at 20min intervals. The molar ratio of diamine to diacid chloride is 1:0.998. after the TPC is added for the last time, the temperature is raised to 35 ℃ and stirring is continued for 1 hour, and finally the heterocyclic aramid fiber solution with the mass concentration of 4.01% and the intrinsic viscosity of 15.2dl/g is obtained.

(2) 73.4g DMAc and 3.75g concentrated sulfuric acid were mixed well under an ice-water bath and then slowly added to 30g of the heterocyclic aramid dope using a constant pressure funnel. And (3) continuously stirring for 1h under the cooling condition of ice water bath to obtain the uniform spinning glue solution with the mass content of the heterocyclic aramid fiber of 1.12% and the sulfuric acid content of 3.5%.

(3) And adding a proper amount of the spinning glue solution into a 5mL syringe with the diameter of 12.5mm, and carrying out electrostatic spinning by adopting a 25G flat-head needle. The parameters were set as follows: the voltage is 22kV, the spinning speed is 1.0mL/h, the distance between the needle head and the roller receiving device is 10cm, the roller rotating speed is 300rpm, the temperature is 30 ℃, and the relative humidity is 45%. Setting the spinning time to be 10 hours, and finally obtaining the nascent heterocyclic aramid nanofiber membrane oriented along the rotation direction of the roller.

(4) The obtained nascent heterocyclic aramid nanofiber is soaked in NaOH aqueous solution with the mass concentration of 1.5% for 6 hours at room temperature. Then transferring the mixture into distilled water for soaking for 24 hours, and changing water for three times in the middle to obtain the heterocyclic aramid nanofiber hydrogel.

(5) The resulting heterocyclic aramid nanofiber hydrogel was dried in a forced air oven at 80 ℃ for 10 hours. Finally, the dried film is thermally annealed for 0.5h at 360 ℃ to obtain the heterocyclic aramid nanofiber film with the porosity of 31 percent.

FIGS. 6 (a) and (b) are SEM images of the surface and cross-section, respectively, of a heterocyclic aramid nanofiber membrane collected with a drum in example 2. The appearance of the heterocyclic aramid nanofiber is smooth, and the diameter distribution is uniform. And it can be seen from fig. 6 (a) that the heterocyclic aramid nanofibers have a significant orientation. Fig. 7 (a) and (b) are respectively drawing curves of the parallel orientation direction and the perpendicular orientation direction of the heterocyclic aramid nanofiber after thermal annealing. The tensile strength in the direction parallel to the orientation direction is up to 510MPa. Although the tensile strength perpendicular to the orientation direction is only 50MPa, it is still higher than most electrospun films. Fig. 8 is a water contact angle test result of the obtained heterocyclic aramid nanofiber membrane, and it can be seen that it exhibits hydrophobicity, and the water contact angle is about 106 °.

Example 5

(1) Using PABZ, TFMB and TPC as raw materials, 3.47g of PABZ and 4.96g of TFMB were dissolved in 280g of DMAc/LiCl complex solvent (LiCl mass concentration: 3.0% and diamine monomer molar ratio PABZ: TFMB=1:1) under argon atmosphere. After the diamine monomer was dissolved, the temperature was reduced to 0℃and the water content was 95ppm. Then 6.30g TPC was added in two portions, at 40min intervals. The molar ratio of diamine to diacid chloride is 1:1. after the TPC is added for the last time, the temperature is raised to 40 ℃ and stirring is continued for 2 hours, and finally the heterocyclic aramid fiber solution with the mass concentration of 4.23% and the intrinsic viscosity of 14.1dL/g is obtained.

(2) 52.7DMAc and 6.88g of concentrated sulfuric acid were mixed well under an ice-water bath, and then slowly added to 55g of the heterocyclic aramid dope using a constant pressure funnel. Continuously stirring for 2 hours under the cooling condition of ice water bath to obtain the uniform spinning glue solution with the mass content of the heterocyclic aramid fiber of 2.0 percent and the sulfuric acid content of 6.0 percent.

(3) And adding a proper amount of the spinning glue solution into a 5mL syringe with the diameter of 12.5mm, and carrying out electrostatic spinning by adopting a 22G flat-head needle. The parameters were set as follows: the voltage is 28kV, the spinning speed is 0.5mL/h, the distance between the needle head and the roller receiving device is 12cm, the roller rotating speed is 400rpm, the temperature is 29 ℃, and the relative humidity is 43%. And setting the spinning time to be 20h, and finally obtaining the nascent heterocyclic aramid nanofiber membrane oriented along the rotation direction of the roller.

(4) The obtained nascent heterocyclic aramid nanofiber is soaked in Na2CO3 aqueous solution with the mass concentration of 5% for 12 hours at room temperature. Then transferring the mixture into distilled water for soaking for 24 hours, and changing water for three times in the middle to obtain the heterocyclic aramid nanofiber hydrogel.

(5) The resulting heterocyclic aramid nanofiber hydrogel was dried in a forced air oven at 80 ℃ for 10 hours. Finally, the dried film is thermally annealed for 0.5h at 360 ℃ to obtain the heterocyclic aramid nanofiber film with the porosity of 32 percent.

Example 6

(1) Using MBOA, HPA and DEDC as raw materials, in N ₂ 2.02g of MBOA and 1.65g of HPA were dissolved at room temperature in 170g of DMAc/LiCl complex solvent (LiCl mass concentration 3.5%) under an atmosphere. After the diamine monomer had been dissolved, the temperature was lowered to 3℃and the water content 40ppm. Then 5.26g DEDC was added in two portions for a period of 30 minutes. The molar ratio of diamine to diacid chloride is 1:0.995. after the TPC is added for the last time, the temperature is raised to 35 ℃ and stirring is continued for 1 hour, and finally the heterocyclic aramid fiber solution with the mass concentration of 4.27% and the intrinsic viscosity of 16.1dL/g is obtained.

(2) 104.3g DMAc and 8.51g concentrated sulfuric acid were mixed well under an ice-water bath and then slowly added to 100g of the heterocyclic aramid dope using a constant pressure funnel. And (3) continuously stirring for 1h under the cooling condition of ice water bath to obtain the uniform spinning glue solution with the mass content of the heterocyclic aramid fiber of 2.0% and the sulfuric acid content of 4%.

(3) And adding a proper amount of the spinning glue solution into a 5mL syringe with the diameter of 12.5mm, and carrying out electrostatic spinning by adopting a 25G flat-head needle. The parameters were set as follows: the voltage is 22kV, the spinning speed is 1.0mL/h, the distance between the needle head and the roller receiving device is 10cm, the roller rotating speed is 300rpm, the temperature is 28 ℃, and the relative humidity is 32%. Setting the spinning time to be 10 hours, and finally obtaining the nascent heterocyclic aramid nanofiber membrane oriented along the rotation direction of the roller.

(5) The resulting heterocyclic aramid nanofiber hydrogel was dried in a forced air oven at 80 ℃ for 10 hours. Finally, the dried film is thermally annealed for 1.0h at 390 ℃ to obtain the heterocyclic aramid nanofiber film with the porosity of 28.5 percent.

Example 7

(1) Using BPABZ, 4' -ODA and BPC as raw materials, 2.66g of BPABZ and 3.63g of 4,4' -ODA were dissolved in 325g of DMAc/LiCl complex solvent (LiCl mass concentration 4.0%, diamine monomer mole ratio 4,4' -ODA: bpabz=7:3) at room temperature under argon atmosphere. After the diamine monomer was dissolved, the temperature was reduced to 0℃and the water content was 30ppm. 7.24g BPC was then added in two portions, at 45min intervals. The molar ratio of diamine to diacid chloride is 1:1. after the last time of adding BPC, heating to 40 ℃ and continuing stirring for 1h, and finally obtaining the heterocyclic aramid fiber solution with the mass concentration of 3.44% and the characteristic viscosity of 18.6 dL/g.

(2) 142.8DMAc and 4.14g polyphosphoric acid were mixed well under an ice water bath and then slowly added to 60g of the heterocyclic aramid dope using a constant pressure funnel. And (3) continuously stirring for 2 hours under the cooling condition of ice water bath to obtain the uniform spinning glue solution with the mass content of the heterocyclic aramid fiber of 1.0% and the polyphosphoric acid content of 2.0%.

(3) And adding a proper amount of the spinning glue solution into a 5mL syringe with the diameter of 12.5mm, and carrying out electrostatic spinning by adopting a 25G flat-head needle. The parameters were set as follows: the voltage is 28kV, the spinning speed is 1.5mL/h, the distance between the needle head and the roller receiving device is 10cm, the roller rotating speed is 400rpm, the temperature is 27.5 ℃, and the relative humidity is 46%. Setting the spinning time to 8h, and finally obtaining the nascent heterocyclic aramid nanofiber membrane oriented along the rotation direction of the roller.

(4) The obtained nascent heterocyclic aramid nanofiber is soaked in LiOH aqueous solution with the mass concentration of 1.5% for 6 hours at room temperature. Then transferring the mixture into distilled water for soaking for 24 hours, and changing water for three times in the middle to obtain the heterocyclic aramid nanofiber hydrogel.

(5) The resulting heterocyclic aramid nanofiber hydrogel was dried in a forced air oven at 80 ℃ for 10 hours. Finally, the dried film is thermally annealed for 0.5h at 360 ℃ to obtain the heterocyclic aramid nanofiber film with the porosity of 30.8 percent.

Example 8

(1) MABZ, DABA and TPC are used as raw materials, and the raw materials are shown in N ₂ 2.75g of MABZ and 2.79g of DABA were dissolved at room temperature in 200g of DMAc/LiCl complex solvent (LiCl mass concentration 3.5%, diamine monomer molar ratio DABA: MABZ=1:1) under an atmosphere. After the diamine monomer was dissolved, the temperature was reduced to 5℃and the water content was 100ppm. 4.95g TPC was then added in two portions, at 50min intervals. The molar ratio of diamine to diacid chloride is 1:0.992. after the TPC is added for the last time, the temperature is raised to 35 ℃ and stirring is continued for 1 hour, and finally the heterocyclic aramid fiber solution with the mass concentration of 4.15% and the intrinsic viscosity of 12.5dL/g is obtained.

(2) 115.0g DMAc and 5.0g anhydrous oxalic acid were mixed well and then slowly added to 80g of the heterocychc aramid gum solution using a constant pressure funnel. And (3) continuously stirring for 2 hours under the cooling condition of ice water bath to obtain the uniform spinning glue solution with the mass content of the heterocyclic aramid fiber of 1.66% and the oxalic acid content of 2.5%.

(3) And adding a proper amount of the spinning glue solution into a 5mL syringe with the diameter of 12.5mm, and carrying out electrostatic spinning by adopting a 25G flat-head needle. The parameters were set as follows: the voltage is 25kV, the spinning speed is 2.0mL/h, the distance between the needle head and the roller receiving device is 8cm, the roller rotating speed is 500rpm, the temperature is 32 ℃, and the relative humidity is 46%. Setting the spinning time to be 5h, and finally obtaining the nascent heterocyclic aramid nanofiber membrane oriented along the rotation direction of the roller.

(5) The resulting heterocyclic aramid nanofiber hydrogel was dried in a forced air oven at 80 ℃ for 10 hours. Finally, the dried film is thermally annealed for 0.5h at 400 ℃ to obtain the heterocyclic aramid nanofiber film with the porosity of 36 percent.

Example 9

The same process parameters and method as in example 1 were used to prepare the heterocyclic aramid nanofiber membrane, with the only differences:

in the step (1), PBOA and TPC are used as raw materials, the mass concentration of the solution of the heterocyclic aramid obtained by polymerization is 4.15%, and the intrinsic viscosity is 15.2dL/g. The thickness of the finally obtained heterocyclic aramid nanofiber is about 10 mu m, the porosity is 28.5%, the tensile strength in the direction parallel to the orientation direction is as high as 465MPa, and the tensile strength in the direction perpendicular to the orientation direction is 45.4MPa.

Example 10

The same process parameters and method as in example 1 were used to prepare the heterocyclic aramid nanofiber membrane with the following differences:

in the step (1), BPABZ and DEDC are used as raw materials, the mass concentration of the solution of the heterocyclic aramid obtained by polymerization is 4.43 percent, and the intrinsic viscosity is 14.5dL/g. The thickness of the finally obtained heterocyclic aramid nanofiber is about 10 mu m, the porosity is 35%, the tensile strength in the direction parallel to the orientation direction is up to 420MPa, and the tensile strength in the direction perpendicular to the orientation direction is 40.4MPa.

Example 11

The same process parameters and method as in example 3 were used to prepare the heterocyclic aramid nanofiber membrane with the following differences:

in the step (1), PBOA, 4' -ODA and TPC are used as raw materials, the mass concentration of the solution of the heterocyclic aramid obtained by polymerization is 4.95 percent, and the intrinsic viscosity is 14.9dL/g. The thermal decomposition temperature of the finally obtained heterocyclic aramid nanofiber membrane is 495 ℃.

Example 12

The same process parameters and method as in example 4 were used to prepare the heterocyclic aramid nanofiber membrane with the following differences:

and (5) freeze-drying the obtained heterocyclic aramid nanofiber hydrogel. Finally, the heterocyclic aramid nanofiber membrane with the porosity of 95% and the water contact angle of 114 DEG is obtained.

Example 13

The same process parameters and method as in example 5 were used to prepare the heterocyclic aramid nanofiber membrane with the following differences:

and (5) freeze-drying the obtained heterocyclic aramid nanofiber hydrogel. Finally, the heterocyclic aramid nanofiber membrane with the porosity of 93.8% and the water contact angle of 120 DEG is obtained.

Comparative example 1 (comparative experiment as example 3, no small molecule physical crosslinker was added)

A heterocyclic aramid solution was prepared by the method of example 3. The difference is that:

in step (2), 164.3g DMAc was slowly added to 50g of the heterocyclic aramid dope using a constant pressure funnel. And continuously stirring for 2 hours to obtain the uniform spinning glue solution which contains 1.12% of the mass content of the heterocyclic aramid fiber and does not contain the micromolecular physical cross-linking agent.

Then, electrospinning was performed under the same conditions as in example 3.

FIG. 9 is a graph showing the morphology of nanofibers collected from a heterocychc aramid spinning dope without added small molecule physical cross-linker after electrospinning. It can be seen that the above electrospinning process is discontinuous and unstable, and accompanied by dripping of the spinning dope.

Comparative example 2 (comparative experiment as example 4, mismatch in the addition amount of small molecule physical crosslinking agent resulted in excessive viscosity of spinning dope)

A heterocyclic aramid solution was prepared by the method of example 4. The difference is that:

125.9g DMAc and 2.68g concentrated sulfuric acid were mixed uniformly under an ice-water bath in (2), and then slowly added to 50g of the heterocyclic aramid dope using a constant pressure funnel. And continuously stirring for 1h to obtain the uniform spinning glue solution with the mass content of the heterocyclic aramid fiber being 1.12% and the sulfuric acid content being 1.5%. At this time, the apparent viscosity of the spinning dope was as high as 96.0pa·s, the fluidity was poor, and the electrospinning could not be performed under the same conditions as in example 4.

Comparative example 3 (comparative experiment as example 2)

A heterocyclic aramid solution was prepared by the method of example 2. The difference is that:

the step (1) is not carried out under the protection of inert gas, the water content after the diamine is dissolved is 500ppm, and the intrinsic viscosity of the obtained hybrid aramid fiber is 8.2dL/g.

A uniform spinning dope having a mass content of 2.5% and a sulfuric acid content of 5.0% was prepared in the same manner as in example 2.

Then, electrospinning was performed using the same parameters as in example 2. However, the molecular weight of the heterocyclic aramid fiber is low, the electrostatic spinning process is discontinuous and unstable, and the situation of dripping of spinning glue solution is accompanied, so that the heterocyclic aramid fiber nanofiber membrane with good morphology and structure cannot be obtained.

While particular embodiments of the present invention have been described above, it will be appreciated by those skilled in the art that these are merely illustrative, and that many variations or modifications may be made to the embodiments without departing from the principles and spirit of the invention, the scope of which is defined only by the appended claims.

Claims

1. The preparation method of the heterocyclic aramid nanofiber membrane is characterized by comprising the following steps of:

(1) Dissolving aromatic heterocyclic diamine monomer containing benzimidazole or benzoxazole and aromatic diamine monomer in a solvent, and adding aromatic diacid chloride monomer to react to obtain heterocyclic aramid fiber solution; wherein the molar ratio of the total amount of aromatic heterocyclic diamine monomer and aromatic diamine monomer to aromatic diacid chloride monomer is 1: (0.9 to 1.1), and the molar ratio of the aromatic diamine monomer in the total amount of the aromatic heterocyclic diamine monomer and the aromatic diamine monomer is 0 to 60 percent;

(4) Soaking the nascent heterocyclic aramid nanofiber membrane in alkali solution and distilled water respectively, taking out, drying or freeze drying under normal pressure, and annealing to obtain the pure heterocyclic aramid nanofiber membrane.

2. The method for preparing a heterocyclic aramid nanofiber membrane according to claim 1, wherein in the step (1), the solvent is a composite solvent prepared from a polar aprotic organic solvent and an inorganic salt cosolvent, and the mass concentration of the inorganic salt cosolvent in the polar aprotic organic solvent is 1% -9%;

the polar aprotic organic solvent includes: one or more of N, N-dimethylacetamide, N-dimethylformamide, dimethyl sulfoxide and N-methylpyrrolidone;

the inorganic salt cosolvent comprises: one or more of lithium chloride, calcium chloride, lithium bromide and calcium bromide.

3. The method for preparing a heterocyclic aramid nanofiber membrane according to claim 1, wherein the reaction in the step (1) is performed under the protection of inert gas, aromatic heterocyclic diamine monomer containing benzimidazole or benzoxazole and aromatic diamine monomer are added into a solvent, and the water content of the obtained solution is less than or equal to 100ppm; then adding aromatic diacid chloride monomer to react in two stages: in the first stage, 70% -90% of the aromatic diacid chloride monomer is added and reacted for 20-40 min at 0-5 ℃; and in the second stage, adding the rest aromatic diacid chloride monomer, and reacting for 1-2 hours at 20-40 ℃, wherein the mass concentration of the prepared heterocyclic aramid fiber solution is 3-7%, the kinetic viscosity at room temperature is 300-1200 Pa.s, and the intrinsic viscosity is 10-20 dL/g.

4. The method for producing a heterocyclic aramid nanofiber membrane according to claim 1, wherein in the step (1):

the aromatic heterocyclic diamine monomer containing benzimidazole or benzoxazole is selected from the group consisting of: one or more of 2- (4-aminophenyl) -5-aminobenzoxazole, 2- (3-aminophenyl) -5-aminobenzoxazole, 2- (4-aminophenyl) -5-aminobenzimidazole, 2- (3-aminophenyl) -5-aminobenzimidazole, 2-2' -p-phenyl-bisbenzimidazole diamine;

the aromatic diamine monomer is selected from: one or more of p-phenylenediamine, 2-chloro-4-aminoaniline, 4' -biphenyldiamine, 2' -di (trifluoromethyl) diaminobiphenyl, 4' -diamino-2, 2' -dimethyl-1, 1' -biphenyl, 4' -diaminoanilide, 4' -diaminodiphenyl ether and p-aminophenyl p-aminobenzoate;

the aromatic diacid chloride monomer is selected from the group consisting of: one or more of terephthaloyl chloride, isophthaloyl chloride, 4 '-benzil chloride and 4,4' -diacyl chloride diphenyl ether.

5. The method for preparing a heterocyclic aramid nanofiber membrane according to claim 1, wherein the small molecule physical crosslinking agent is sulfuric acid, oxalic acid, phosphoric acid or polyphosphoric acid.

6. The method for preparing a heterocyclic aramid nanofiber membrane according to claim 1, wherein the electrospinning process conditions in the step (3) are as follows: the voltage is 18-30 kV, the spinning speed is 0.1-3 mL/h, the distance between the needle head and the roller receiving device is 5-30 cm, the temperature is 20-50 ℃, and the relative humidity is 30-50%.

7. The method for preparing a heterocyclic aramid nanofiber membrane according to claim 1, wherein in the step (4), the alkaline solution is an aqueous solution of an alkaline substance, the alkaline substance is an organic or inorganic base, and the pH value of the alkaline solution is 8-11; the soaking temperature is 20-80 ℃ and the soaking time is 1-24 h; the temperature of normal pressure drying is 50-100 ℃ and the time is 1-5 h; the annealing treatment temperature is 360-410 ℃ and the annealing treatment time is 0.5-1 h.

8. The method for preparing a heterocyclic aramid nanofiber membrane according to claim 1, wherein the diameter of the nanofiber in the heterocyclic aramid nanofiber membrane obtained in the step (4) is 120-400 nm.

9. A heterocyclic aramid nanofiber membrane prepared by the method of any one of claims 1-8.