Preparation method of recyclable light-controlled reversible crosslinking polyacrylonitrile fiber

Abstract

The application discloses a preparation method of a recyclable light-controlled reversible cross-linking polyacrylonitrile fiber, and the method comprises the following steps: fully dissolving polyacrylonitrile and a light-controlled reversible coordination cross-linking agent, i.e., a ruthenium complex, in N,N-dimethylformamide to prepare a spinning solution; and collecting the spinning solution under high voltage through a collecting device to obtain the polyacrylonitrile fiber containing the ruthenium complex. Different from the preparation of a traditional electrospun fiber, the prepared light-controlled reversible cross-linking polyacrylonitrile fiber is fully reacted with the cross-linking agent, i.e., the ruthenium complex, and the polyacrylonitrile macromolecule in a post-processing process to form a cyano-ruthenium coordination bond, i.e., to complete coordination cross-linking, and further improve the mechanical property of the fiber. In the solvent environment of N,N-dimethylformamide, the fiber is de-cross-linked under visible light irradiation to re-form a mixed solution of the polyacrylonitrile and the light-controlled reversible ruthenium complex, and the mixed solution can be used for preparing the light-controlled reversible cross-linking polyacrylonitrile fiber again through concentration and recycling.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of photoresponsive polymer materials and the field of electrospinning, and particularly relates to a preparation method of photo-controlled reversible crosslinking polyacrylonitrile fiber which can be recycled. BACKGROUND

[0002] Building a green low-carbon circular economy system is the goal of modern social development, and producing and using recyclable materials is of great significance. Polymer materials have many advantages such as easy availability of raw materials, controllable performance, wide application range, and certain recyclability, and therefore are highly concerned. At present, the recycling of linear polymers has become mature, but crosslinked polymers with excellent performance cannot be recycled due to their insoluble and infusible characteristics.

[0003] To this end, people have developed adaptive networks and glass-like polymers by studying reversible crosslinked polymers. However, these polymers often need special chemical design from their molecular structure, and therefore are difficult to be practically applied in industrial production. How to recycle low-cost polymer materials that have been put into industrial production still faces challenges.

[0004] Plastics, synthetic fibers and synthetic rubber are three major synthetic materials, and are essential raw materials in industrial production. Polyacrylonitrile, as a common synthetic fiber material, has good corrosion resistance and flame retardance, and can be produced and prepared by electrospinning. However, acrylic fiber often has the disadvantage of low mechanical strength, which can be enhanced by crosslinking design, but how to realize the recycling of crosslinked fibers is still a technical problem to be solved. SUMMARY

[0005] The present application provides a production and recycling method of photo-controlled reversible crosslinking polyacrylonitrile fiber prepared by electrospinning technology to solve the problems in the prior art. The reversible crosslinking polyacrylonitrile fiber prepared by the present application has good recyclability and mechanical strength. Unlike traditional electrospun fibers, the crosslinking process occurs only in the presence of solvent and light, and the material can be recycled. The present application provides a reference for solving the recycling problem of industrial polymer production.

[0006] The preparation method of the photo-controlled reversible crosslinking polyacrylonitrile fiber of the present application comprises the following steps:

[0007] The photo-controlled reversible coordination crosslinking agent ruthenium complex and polyacrylonitrile are fully dissolved in N,N-dimethylformamide to obtain a mixed solution; the obtained mixed solution is spun under high voltage, and vacuum annealing drying is carried out at 120 DEG C to obtain reversible crosslinking polyacrylonitrile fiber.

[0008] The total mass fraction of polyacrylonitrile in the spinning solution is 10-15%; the addition amount of the light-controlled reversible coordination crosslinking agent ruthenium complex is not strictly limited, and in the examples, the mass fraction is 10% (the mass ratio of polyacrylonitrile), and the range can be appropriately expanded or reduced on this basis. The voltage selected for electrospinning needs to be adjusted according to the actual situation to form a Taylor cone and stabilize the silk.

[0009] The light-controlled reversible coordination crosslinking agent ruthenium complex in the application includes but is not limited to the following compounds, the structural formula of which is as shown in the following formula:

[0010]

[0011] The light-controlled reversible crosslinking polyacrylonitrile fiber is prepared by the method comprising the following steps:

[0012] a) Dissolve polyacrylonitrile in N,N-dimethylformamide solvent, to ensure sufficient dissolution, continuously stir at 60°C in a water bath for 4h, until the solution is clear and transparent;

[0013] b) Continue to stir after the solution is cooled to room temperature, and add a light-controlled reversible crosslinking agent ruthenium complex, to ensure sufficient dissolution, continuously stir at room temperature for more than 3h;

[0014] c) After the solution is prepared, it is drawn into a 10mL syringe, air bubbles are avoided as much as possible, and the syringe is fixed to a syringe pump, a 19G stainless steel needle (inner diameter of 0.72mm, total length of 50mm) is installed, the needle is connected to the positive electrode of a high-voltage power supply, the receiving drum is connected to the ground wire, and aluminum foil paper is attached; the receiving distance is set to 10-20cm, the voltage is +15kV, the syringe pump specification is 10mL, the extrusion flow rate is 0.02mL / min, the drum rotation speed is 250r / min, and electrospinning is carried out at a temperature of 35°C and a relative humidity of 35-55%;

[0015] d) The fibers collected on the aluminum foil paper are removed and placed in a vacuum oven and heated to 120°C for annealing and drying until the solvent is completely volatilized.

[0016] Further:

[0017] In step a), the molecular weight of the polyacrylonitrile is 15kDa.

[0018] In step b), the reversible crosslinking agent ruthenium complex should be prepared and used immediately, and air contact should be avoided as much as possible during preparation.

[0019] In step c), the spinning solution should be drawn into the syringe to avoid air bubbles, and the spinning solution is easily oxidized by air, so it needs to be prepared and used immediately. The voltage should ensure that a Taylor cone can be formed and the spinning can be stabilized, the selected receiving device can be a drum or a flat plate, and the wrapping material should have good conductivity.

[0020] In step c), the electrospinning voltage is +15kV, and too high or too low voltage will make the fiber unable to form or difficult to collect.

[0021] In step d), to ensure that the prepared fiber can be removed, the spun fiber membrane should have a certain thickness, and the vacuum should be maintained during the annealing and drying process to ensure the sufficient volatilization of N,N-dimethylformamide solvent.

[0022] On this basis, the application also prepares nanofiber yarn with recyclable function by adding a twisting device and a negative electrode, and the preparation process is as follows:

[0023] a) Dissolve polyacrylonitrile in N,N-dimethylformamide solvent, to ensure sufficient dissolution, continuously stir for 4h at 60℃ in water bath until the solution is clear and transparent;

[0024] b) Continue stirring after the solution is cooled to room temperature, and add a light-controlled reversible crosslinking agent ruthenium complex, to ensure sufficient dissolution, continuously stir for more than 3h at room temperature;

[0025] c) After the solution is prepared, it is drawn into two 10mL syringes, bubbles are avoided as much as possible, and the syringes are fixed to the syringe pump, a 19G stainless steel needle (inner diameter of 0.72mm, total length of 50mm) is installed, the needle is connected to the positive and negative electrodes of the high-voltage power supply, and according to the experiment, the positive and negative voltage is set to ±10kV, and the prepared yarn has higher mechanical strength;

[0026] d) Control the relative humidity of the box to be 35-55%, adjust the spinning temperature to be 35℃, and the extrusion flow rate of the syringe to be 0.02mL / min;

[0027] e) The collection device adopts a collection roller, and the rotation speed is adjusted to be 100r / min, and the rotation speed of the twisting horn is set to be 1200r / min;

[0028] f) To ensure that the crosslinking is completed, the yarn after spinning should also be annealed and dried at 120℃ until the solvent is completely volatilized.

[0029] The recycling method of the reversible crosslinking polyacrylonitrile fiber prepared by the application is that the crosslinking polyacrylonitrile fiber is irradiated under an LED light source in the presence of N,N-dimethylformamide to obtain a de-crosslinking mixed solution; the de-crosslinking mixed solution is reduced and concentrated, and then electrospun and annealed and dried at 120℃ to obtain the recovered crosslinking polyacrylonitrile fiber. The above steps are repeated to realize the recycling of the crosslinking polyacrylonitrile fiber.

[0030] Unlike traditional electrospun fiber preparation, electrospun fibers undergo a post-treatment process where the crosslinking agent ruthenium complex and polyacrylonitrile polymer react fully to form cyano-ruthenium coordination bonds, thus completing coordination crosslinking and further enhancing their mechanical properties.

[0031] The light source used for recycling must include a wavelength of 470nm.

[0032] Compared with existing technologies, this invention provides a method for preparing and recycling light-controlled reversible cross-linked fibers. This invention can improve the mechanical properties of industrially mass-producible polyacrylonitrile fibers through cross-linking. The cross-linking agent used is a light-controlled reversible coordination cross-linking agent, ruthenium complex, and the prepared reversible cross-linked fibers can be recycled. Attached Figure Description

[0033] Figure 1 The 1H NMR spectrum of the photo-controlled reversible crosslinking agent is shown.

[0034] Figure 2 A schematic diagram of a model of electrospun, light-controlled, reversibly crosslinked polyacrylonitrile fiber is shown.

[0035] Figure 3 A schematic diagram of a model of electrospun, light-controlled, reversibly cross-linked polyacrylonitrile fiber yarn is shown.

[0036] Figure 4 The images show actual photos of reversibly cross-linked polyacrylonitrile fibers before and after annealing.

[0037] Figure 5 The study showed that the change in UV-Vis diffuse reflectance was monitored at different annealing times using solvent annealing. The crosslinking effect was optimal when the annealing time was around 1.5 h.

[0038] Figure 6 The study showed that the reflectance changes of the UV-Vis diffuse reflectance spectrum at different annealing times were monitored using vacuum annealing. Extending the annealing time had little effect on the crosslinking effect.

[0039] Figure 7 A scanning electron microscope image of reversibly cross-linked polyacrylonitrile fibers after annealing is shown.

[0040] Figure 8 The solvent resistance of reversibly cross-linked polyacrylonitrile fibers after annealing in a good solvent (N,N-dimethylformamide) is demonstrated. From Figure 8 As can be seen, the amount of dissolved material increased with the increase in storage time, but there were still polyacrylonitrile fibers with a mass fraction of over 85% that did not dissolve after six days.

[0041] Figure 9The tensile curves of the fiber yarns prepared at different voltages are shown at a stretching rate of 10 mm / min.

[0042] Figure 10 The recycling flow chart of the light-controlled reversible crosslinking polyacrylonitrile fiber is shown. From the Figure 10 It can be seen that the sheared crosslinked fiber is decrosslinked to form a solution by supplementing N,N-dimethylformamide solvent and irradiating under a 470 nm wavelength LED lamp, and the recovered spinning solution is obtained by concentration under reduced pressure, and the recovered crosslinked fiber is obtained by the steps of electrospinning and annealing drying.

[0043] Figure 11 The UV-Vis diffuse reflectance spectra of the light-controlled reversible crosslinking polyacrylonitrile fiber before and after annealing and after recycling are shown.

[0044] Figure 12 The stress-strain curves of the light-controlled reversible crosslinking polyacrylonitrile fiber before and after recycling and the uncrosslinked fiber are shown, and the stretching rate is 10 mm / min. Figure 11 It can be seen from the above that the reversible coordination crosslinking agent ruthenium complex makes the mechanical strength of the polyacrylonitrile fiber slightly improved. DETAILED DESCRIPTION

[0045] In order to further illustrate the present application, the preparation and recycling method of the light-controlled reversible crosslinking polyacrylonitrile fiber provided by the present application are described in detail below in combination with examples. However, it should be understood that these descriptions are only for further illustrating the features and advantages of the present application, and are not limitations on the claims of the present application.

[0046] The light-controlled reversible crosslinking agent ruthenium complex used in the following examples is a self-made crosslinking agent, and the raw materials 2,2'-dipyridyl, ruthenium trichloride trihydrate, lithium chloride, N,N-dimethylformamide, silver hexafluorophosphate, and ammonium hexafluorophosphate are purchased from Anjieji Chemical, and ethanol and acetone are purchased from National Pharmaceutical Group Chemical Reagent Co., Ltd.

[0047] The polyacrylonitrile used is an industrial variety (Du Pont, model: R60), and the molecular weight is 15 kDa.

[0048] The electrospinning uses a multifunctional full-automatic integrated nanofiber experimental device (Beijing Xinrui Bainana Technology Co., Ltd., model: TEADFS-700).

[0049] The LED lamp used for recycling is a 470 nm wavelength lamp (Mightex, model: LCS-0470-15-22).

[0050] Example 1: Preparation of Spinning Solution

[0051] a) 3 g of polyacrylonitrile powder was dissolved in 22 g of dehydrated and deoxygenated N,N-dimethylformamide, and continuously stirred in a water bath at 60°C for about 4 h until the solution was clear and transparent without insoluble substances, obtaining a polyacrylonitrile solution with a mass fraction of about 12%;

[0052] b) The solution was continuously stirred and cooled to room temperature, 0.3 g of the light-controlled reversible coordination crosslinking agent ruthenium complex was added, and stirred at room temperature for 3 h until the solution was a uniform reddish-brown solution without gel appearing, and was configured into a spinning solution.

[0053] Example 2: Preparation of reversible crosslinked polyacrylonitrile fibers by electrospinning

[0054] a) The prepared spinning solution was drawn into a 10 mL syringe, and air bubbles should be avoided as much as possible during the process, and if air bubbles were present, the air bubbles should be extruded by pushing and pulling the plunger;

[0055] b) The syringe in step a) was fixed on the upper part of the electrospinning machine push pump, and the position of the injection pump was adjusted to just extrude the spinning solution;

[0056] c) The collection device used a roller, the surface of which was pasted with aluminum foil to ensure its conductivity, and the roller was grounded, and a 19G needle was used at the front end of the electrospinning machine with a voltage of +15 kV;

[0057] d) The relative humidity of the box was controlled to be 35-55%, the spinning temperature was adjusted to be 35°C, and the receiving distance was adjusted to be at an appropriate position of 10-20 cm, the injection syringe extrusion flow rate was 0.02 mL / min, and the roller rotation speed was 250 r / min, and electrospinning was carried out;

[0058] e) In order to ensure that the crosslinking is completed, the fiber after spinning should be annealed and dried in an oven at 120°C until the solvent is completely volatilized.

[0059] Example 3: Preparation of reversible crosslinked polyacrylonitrile fiber yarn

[0060] a) The spinning solution was prepared according to Example 1 and drawn into two 10 mL syringes, and air bubbles should be avoided as much as possible during the process, and if air bubbles were present, the air bubbles should be extruded by pushing and pulling the plunger;

[0061] b) The two syringes in step a) were fixed on the upper part of the electrospinning machine push pump, the position of the injection pump was adjusted to just extrude the spinning solution, and +10 kV and -10 kV voltages were applied at both ends, respectively;

[0062] c) The relative humidity of the box was controlled to be 35-55%, the spinning temperature was adjusted to be 35°C, and the injection syringe extrusion flow rate was 0.02 mL / min;

[0063] d) The collection device uses a collection roller to collect, and its rotation speed is adjusted to 100 r / min, and the rotation speed of the twisting horn is set to 1200 r / min;

[0064] e) To ensure that the crosslinking is completed, the fiber yarn after spinning should be annealed and dried at 120°C until the solvent is completely volatilized.

[0065] Example 4: Recycling method of reversibly crosslinked polyacrylonitrile fibers

[0066] About 50 mg of reversibly crosslinked polyacrylonitrile fibers were cut and placed in a 50 mL round-bottom flask, and then 5 mL of N,N-dimethylformamide was added;

[0067] b) The mixture in step a) was irradiated under stirring under an LED lamp (470 nm, 30 mW cm -2 , 3 h) until a uniform reddish-brown solution was formed;

[0068] c) The mixture in step b) was concentrated by an oil pump under reduced pressure until the mass of the solution was about 0.42 g, and no gel was formed, obtaining the recovered spinning solution;

[0069] d) The recovered spinning solution was re-pumped into the syringe pump for electrospinning, and the prepared fibers were placed in a vacuum oven at 120°C for drying and annealing for more than half an hour until the solvent was completely volatilized.

[0070] Repeating steps a), b), c), and d) can realize the recycling of crosslinked polyacrylonitrile fibers.

[0071] Example 5: Effect of different annealing conditions on fiber crosslinking

[0072] Taking the fibers prepared with bipyridine crosslinking agent as an example, the fibers were annealed in the following two ways, and the coordination crosslinking was characterized by UV-Vis diffuse reflectance spectroscopy:

[0073] a) The solvent annealing method was used to promote fiber crosslinking, and the selected solvent was N,N-dimethylformamide, and the annealing temperature was selected as 120°C. The changes of UV-Vis diffuse reflectance spectra of the fibers with different annealing times were monitored, as shown in Figure 5 .

[0074] b) The vacuum drying method was used to promote fiber crosslinking, and a vacuum oven was used for annealing at 120°C. The changes of UV-Vis diffuse reflectance spectra of the fibers with different annealing times were also monitored, as shown in Figure 6 .

[0075] Example 6: Effect of different voltages on the mechanical properties of fiber yarns

[0076] Take the preparation of fiber yarn with bipyridine crosslinking agent as an example, different voltages are used for electrospinning preparation, and the mechanical strength is characterized by a universal tensile tester:

[0077] As shown in Figure 9 , the preparation of fiber yarn is carried out with 10 kV and 12 kV voltages respectively, and the stretching is carried out at a stretching rate of 10 mm / min. The experiment shows that the yarn prepared by 10 kV voltage has higher tensile strength.

[0078] Example 7: Preparation of light-controlled reversible crosslinking agent

[0079] a) Stir and dissolve ruthenium trichloride trihydrate (0.44 g, 1.6 mmol), 2,2'-bipyridine (0.52 g, 3.4 mmol) and lithium chloride (0.52 g, 12.2 mmol) in 10 mL of N,N-dimethylformamide, heat under reflux for 8 h under nitrogen atmosphere; after the reaction is cooled to room temperature, 15 mL of acetone is added to the flask to produce a precipitate; then the precipitate is filtered, washed with water and dried to obtain a black solid;

[0080] b) Add 20 mL of a mixed solution of ethanol and water (volume ratio 1:1) to the black solid (0.14 g, 0.29 mmol) and silver hexafluorophosphate (0.15 g, 0.6 mmol); heat under reflux for 12 h under nitrogen atmosphere; filter the mixture, concentrate the filtrate to about 5 mL by reduced pressure distillation, then add a saturated ammonium hexafluorophosphate solution, cool in the refrigerator to crystallize, then filter, wash with water and dry to obtain the light-controlled reversible crosslinking agent.

[0081] The above examples are only used to help understand the method of the present application and its core idea. It should be noted that for those skilled in the art, without departing from the principles of the present application, the present application can be improved and modified in several ways, and these improvements and modifications also fall within the scope of the claims of the present application. Therefore, the present application will not be limited to the examples shown herein, but will conform to the widest scope consistent with the principles and novel features disclosed herein.

Claims

1.A method for preparing a recyclable light-controlled reversibly crosslinked polyacrylonitrile fiber, characterized in that: a light-controlled reversible coordination crosslinking agent ruthenium complex and polyacrylonitrile are fully dissolved in N, N-dimethylformamide to obtain a mixed solution; the obtained mixed solution is electrospun and vacuum annealed and dried to obtain reversibly crosslinked polyacrylonitrile fiber, comprising the following steps: a) dissolving polyacrylonitrile in N, N-dimethylformamide solvent, continuously stirring at 60℃ in a water bath until the solution is clear and transparent; b) continuing to stir after the solution is cooled to room temperature, adding a light-controlled reversible crosslinking agent ruthenium complex, continuously stirring at room temperature for more than 3h, the mass fraction of polyacrylonitrile in the mixed solution is 10-15%, and the addition amount of the light-controlled reversible coordination crosslinking agent is 8-10% of the mass of polyacrylonitrile; c) drawing the mixed solution obtained in step b) into a 10 mL syringe to avoid air bubbles, fixing the syringe on a syringe pump, installing a stainless steel needle, connecting the needle to the positive electrode of a high-voltage power supply, connecting the receiving drum to the ground wire, and pasting aluminum foil paper, and then electrospinning; the inner diameter of the stainless steel needle is 0.72 mm, the total length is 50 mm, and the electrospinning parameters are set as follows: receiving distance is 10-20 cm, pressure voltage is + 15 kV, extrusion flow rate is 0.02 mL / min, and drum rotation speed is 250 r / min, electrospinning is carried out at a temperature of 35℃ and a relative humidity of 35-55%; d) removing the fiber collected on the aluminum foil paper and placing it in a vacuum oven for annealing at 120℃ for 1.5h; the structure of the light-controlled reversible coordination crosslinking agent is as follows: in step a), the molecular weight of the polyacrylonitrile is 15 kDa. 2.A reversibly crosslinked polyacrylonitrile fiber prepared by the method according to claim 1. 3.A recycling method for the reversibly crosslinked polyacrylonitrile fiber according to claim 2, characterized in that: the reversibly crosslinked polyacrylonitrile fiber is irradiated under an LED light source in the presence of N, N-dimethylformamide to obtain a decrosslinked mixed solution; the decrosslinked mixed solution is concentrated under reduced pressure, then electrospun again, and dried by annealing at 120℃ to obtain a crosslinked polyacrylonitrile fiber after recycling; and the above steps are repeated to realize the recycling of the crosslinked polyacrylonitrile fiber. ​ ​ ​ ​ ； ​ ​ ​ ​ ​

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