CN111748905A - A kind of reprocessing method of recycled carbon fiber - Google Patents

Abstract

The invention relates to a reprocessing method for recycled carbon fiber, comprising the following steps: (1) making recycled carbon fiber into a recycled carbon fiber felt body; (2) cleaning and drying the recycled carbon fiber felt body to remove surface impurities; (3) recycling Both ends of the carbon fiber felt body are connected with lead ears, connected to the power source through the lead ears, and subjected to high-voltage electrical treatment. Compared with the prior art, the present invention has a wide application range, and can be applied to carbon fiber products with different resin residues and recovered by different methods. At the same time, the processing time is short, which can ensure the improvement of carbon fiber performance at lower energy consumption.

Description

A kind of reprocessing method of recycled carbon fiber

technical field

The invention relates to the recycling of carbon fibers, in particular to a reprocessing method for the recycled carbon fibers.

Background technique

Resin-based carbon fiber composite materials (referred to as "composite materials") are based on thermosetting resins or thermoplastic resins, and are connected with carbon fibers and their fabrics (unidirectional fabrics, two-dimensional woven fabrics, three-dimensional woven preforms, etc.) or chopped dispersed fibers. Composite material for reinforcement. It has high specific strength, high specific stiffness, high corrosion resistance, excellent performance and structural design, and flexible formability. It has been widely used in the fields of national defense, aerospace, aviation, automobile, energy, construction, etc. One of the pillar materials in the field. With the expansion of the application field of composite components, the recycling of composite components and waste has become an important economic and environmental issue.

In view of the easy formability of composite materials, as well as the differences in application fields and functions, the shapes of composite materials are generally complex, and the material systems are also different, which makes the recycling of composite materials difficult to achieve through a single means, among which, Carbon fiber composite products have excellent performance and high cost. The recycling of high-cost carbon fiber and even high-performance resin matrix has important strategic value. At present, the mainstream composite recycling technologies mainly include pyrolysis method, solution dissolution method and supercritical dissolution method. Their basic idea is to remove the resin matrix and obtain carbon fibers. In the process of recycling, high temperature treatment or strong oxidant corrosion are often involved, which will destroy the shape of the carbon fiber tow and even cause damage to the carbon fiber tow itself. Therefore, when carbon fiber is reused, the recycled carbon fiber will be cut and screened. Due to the disordered shape and scattered properties of the fibers, it is difficult to ensure the stability of the quality after cutting, which limits the comprehensive performance of the composite material used as a reinforcement. In addition, the cutting of the fiber introduces additional operation steps, which is troublesome to implement. At the same time, the cut carbon fiber is not suitable for the processing method of the braided body, which greatly limits its application field. Therefore, a large number of researchers are studying how to deal with the recycled carbon fiber. , such as Chinese patent CN108586797A discloses a recycling preparation method of waste carbon fiber PA6 composite material, although this partial recycling method can maintain the integrity of carbon fiber tow to a certain extent, but the recycling process involves many steps, which is not conducive to large-scale recycling operation.

SUMMARY OF THE INVENTION

The purpose of the present invention is to provide a reprocessing method for recycling carbon fiber in order to overcome the defects of the above-mentioned prior art, which can effectively improve the performance of carbon fiber tow, improve the performance stability of carbon fiber felt, and improve the comprehensive performance of composite materials. .

The object of the present invention can be achieved through the following technical solutions: a reprocessing method for reclaiming carbon fiber, characterized in that, comprising the following steps:

(1) The recycled carbon fiber is made into a recycled carbon fiber felt;

(2) cleaning and drying the recovered carbon fiber felt to remove surface impurities;

(3) Connect the lugs at both ends of the recycled carbon fiber felt, connect the positive and negative poles of the regulated DC power supply through the lugs, and perform high-voltage electrical treatment. .

The recycled carbon fiber in step (1) is a mixture of one or more of chopped fiber, continuous carbon fiber, two-dimensional carbon fiber fabric or three-dimensional carbon fiber fabric recovered by pyrolysis, solution dissolution or supercritical dissolution.

Step (1) The method of recycling carbon fiber to make recycled carbon fiber felt is to cut the recycled carbon fiber (if the size and shape are suitable, it is not necessary to cut), and non-woven molding (using a molding method such as acupuncture) to make the recycled carbon fiber felt. body.

Step (2) Before cleaning, the recycled carbon fiber felt body is cut into rectangular felt sheets.

The cleaning agent used in step (2) and step (3) cleaning process is one or more of ethanol, acetone, dichloromethane, trichloroethylene, tetrachloroethylene, chloroform or carbon tetrachloride, for removing the Treat the grease and impurities on the surface of the recovered carbon fiber, and remove the residual adhesive and impurities on the surface of the recovered carbon fiber after the treatment.

In step (3), the lugs are copper foil, thin copper electrodes, thin graphite electrodes or combinations thereof.

In step (3), the lugs are bonded to both ends of the recycled carbon fiber felt body by an adhesive, and the adhesive is one or more of conductive silver paste, conductive adhesive IAC, and conductive adhesive ACA.

Step (3) The high voltage electric treatment is performed in a protective atmosphere, wherein the protective atmosphere is an argon atmosphere, a nitrogen atmosphere or a combination thereof.

Step (3) In the high-voltage electric treatment process, the applied voltage density is 1V/cm ² -5V/cm ² , and the treatment time is 10s - 300s. Further preferably, the voltage density ranges from 3V/cm ² to 4V/cm ² , and the processing time ranges from 60s to 120s.

Since carbon fiber is a good electric heating element, when a sufficient current is given, the carbon fiber body will rapidly rise to a very high temperature. In the carbon fiber felt body, due to the lack of bonding, the carbon fiber tow overlapped places have high resistance. During the process of electrification and heating, these overlapped places will become "hot spots", which emit higher heat than the carbon fiber tow body. Co-lattice is formed between carbon fiber tows, so as to realize "welding" between fibers and improve the uniformity and stability of the felt body. At the same time, the carbon fiber felt is in a high temperature state (>2000K) during the high-voltage electrical treatment, which is close to the graphitization temperature of the carbon material, so the graphitization degree of the carbon fiber tow is improved, and the cracks and defects on the carbon fiber can be effectively treated. Repair, to achieve the improvement of carbon fiber mechanical properties, electrical and thermal conductivity. In addition, the residual resin, surfactant and other impurities on the surface of the recycled carbon fiber can be further removed at high temperature, which can further improve the interface performance between the fiber and the resin matrix, and improve the comprehensive performance of the composite material.

The application mode of the regenerated carbon fiber obtained by electrification includes further sizing treatment, application as thermoplastic or thermosetting resin-based composite material; application as functional composite material such as electrical conductivity and thermal conductivity; application as functional material such as electric heating heater; Applications are functional materials such as electrocatalysis and energy storage.

Compared with the prior art, the present invention has the following beneficial effects:

1. The present invention is aimed at the problems of disordered shape, scattered performance and serious performance loss of recycled carbon fibers. By making a felt body again, and then applying high voltage at both ends, the carbon fiber filaments with different shapes and unstable performance are recovered. The rapid processing of the tow can effectively improve the performance of the carbon fiber tow, improve the performance stability of the carbon fiber felt, improve the comprehensive performance of the composite material, and expand the reuse field of recycled carbon fiber. Compared with the traditional recycling carbon fiber reprocessing method, the present invention can be applied to recycled carbon fibers with different surface residual resins and different treatment methods, has high versatility, and can significantly reduce the treatment time. The defects in the reprocessed recycled carbon fiber tow can be effectively repaired, which is manifested in the improvement of mechanical properties, electrical and thermal conductivity, and the lap joints in the fabric are effectively "welded", which shows that the performance of carbon fiber fabrics is stable and uniform, suitable for use as Reinforcements are used in the preparation of high-performance composite materials, which can strongly promote the reuse of recycled carbon fibers and expand their application fields.

2. The processing time required by the present invention is short, and the mechanical, electrical and thermal conductivity properties of recycled carbon fibers can be improved under lower energy consumption, and the interface properties between carbon fibers and resin matrix can be effectively improved. The recycled carbon fiber after reprocessing by electrification is suitable for use as a reinforcement or functional body, which can be re-prepared into a composite material for reuse. It has great application prospects as a mechanical component or an electrothermal heating functional component, which will effectively promote the high value-added reuse of recycled carbon fiber. development of technology.

3. The reprocessed carbon fiber fabric of the present invention is suitable for use as a mechanical reinforcement or an electrothermal functional body to prepare composite materials with integrated structure and function integration, which can effectively promote the development of high value-added recycling technology for recycling carbon fibers.

Description of drawings

Fig. 1 is the reprocessing device that reclaims carbon fiber of the present invention;

FIG. 2 is a schematic diagram of a reprocessing method for recycling carbon fiber according to the present invention.

Detailed ways

The present invention will be described in detail below with reference to specific embodiments. This embodiment is implemented on the premise of the technical solution of the present invention, and provides a detailed implementation manner and a specific operation process, but the protection scope of the present invention is not limited to the following embodiments.

In the following examples, if there is no special description of raw materials or processing techniques, it is indicated that they are all conventional commercially available raw materials or conventional processing techniques in the art.

As shown in Figure 1, the present invention firstly arranges the recycled carbon fibers to make a felt body, and then cuts it into a regular rectangular recycled carbon fiber felt body 1, and connects lugs 2 at both ends of the felt body and places it in a closed place. In the box, under the atmosphere of the protective gas 3, the two ends of the lead 2 are connected to the regulated DC power supply 4 through wires, and a high voltage is applied to both ends of the recovered carbon fiber felt 1. The principle of Joule heat is used to make the recovered carbon fiber felt 1 It reaches extremely high temperature (>1600K) in a short time. High temperature can further remove impurities such as residual resin and surfactant on the surface of recycled carbon fiber, and can improve the interface performance between carbon fiber and resin matrix. At the same time, this extremely high temperature is conducive to the graphitization of carbon, so this electrification treatment can repair the defects in the carbon fiber tow and realize the connection at the overlap of the carbon fiber tow. The schematic diagram is shown in Figure 2. From a macro perspective, the mechanical properties of the carbon fiber felt can be significantly improved; at the same time, the increase in the degree of graphitization can also effectively improve the electrical and thermal conductivity of the carbon fiber felt. In addition, due to the "welding" of the carbon fiber tows overlapping in the electrification process, the performance of the felt body becomes more uniform, and the performance stability of the felt body is effectively improved.

Example 1:

The bidirectional carbon fiber cloth recovered by pyrolysis was ultrasonically cleaned with ethanol, and the cleaning time was 1 h. Then, the cleaned carbon fiber cloth was placed in a vacuum oven at 60 °C and dried for 12 h. Then, the recycled carbon fiber cloth was non-woven and cut into rectangular pieces of 10cm×5cm for use. Using conductive silver paste, two copper electrodes with a size of 4 cm × 5 cm were bonded to both sides of the cut recycled carbon fiber cloth, placed in a vacuum oven at 70 °C, and dried for 3 h. The dried samples were transferred to a closed box with an argon protective atmosphere, and the positive and negative electrodes of the regulated DC power supply were connected to the copper electrodes. The carbon fiber cloth was electrified with a voltage of 150V, the voltage density was 3V/cm ² , and the electrification time was 1min. After electrification, take out the sample, remove the copper sheet electrode leads at both ends, use acetone to clean the carbon fiber after electrification treatment, remove the residual adhesive and impurities, and dry it in a vacuum oven at 60°C for 12h to obtain a solid sample.

The carbon fiber cloth before and after the electrification treatment was used as the reinforcement, and the thermosetting resin matrix composites were prepared respectively, using bisphenol A epoxy resin (E-51) as the resin matrix, methyl nadic anhydride as the curing agent, and tertiary amine salt as the resin matrix. The accelerator is mixed evenly at room temperature, and the mass ratio of resin, curing agent and accelerator is 100:98.5:4. The vacuum-assisted molding process is used for molding, and the curing system is 100 °C for 1 h + 130 °C for 4 h to obtain a carbon fiber reinforced composite material. After mechanical testing, the composite material with carbon fiber before treatment as reinforcement has a tensile strength of 377.4MPa and a flexural strength of 449.3MPa; while the composite material made of carbon fiber after electrification treatment has a tensile strength of 430.6MPa and a flexural strength of 430.6MPa. 503.9MPa, which shows that the electrification treatment effectively repairs the defects in the carbon fiber tow, and at the same time realizes the "welding" of the overlap of the carbon fiber fabric, which significantly improves the mechanical properties of the carbon fiber fabric.

Example 2:

Ultrasonic cleaning was performed on the carbon fiber precursors obtained by the supercritical dissolving thermosetting composite material method, and the cleaning time was 1 h. Then, the cleaned carbon fiber cloth was placed in a vacuum oven at 60 °C and dried for 12 h. Subsequently, the recycled carbon fiber cloth was non-woven and cut into rectangular pieces of 8cm×6cm for use. Two pieces of copper foil with a size of 6 cm × 5 cm were bonded to both sides of the cut recycled carbon fiber cloth sheet using conductive adhesive IAC, placed in a vacuum oven at 70 °C, and dried for 3 h. The dried samples were transferred to a closed box with an argon protective atmosphere, and the positive and negative electrodes of the regulated DC power supply were connected to the copper foil. The carbon fiber cloth was electrified with a voltage of 120V, the voltage density was 2.5V/cm ² , and the electrification time was 3min. After electrification, take out the sample, remove the copper foil leads at both ends, use acetone to clean the carbon fiber after electrification treatment, remove the residual adhesive and impurities, and dry it in a vacuum oven at 60°C for 12h to obtain a solid sample.

Using the carbon fiber cloth before and after the electrification treatment as the reinforcement, the thermosetting resin matrix composites were prepared respectively, using bisphenol A epoxy resin (E-48) as the resin matrix, triethylenetetramine as the curing agent, and tertiary amine salt as the accelerator , mixed evenly at room temperature, and the mass ratio of resin, curing agent and accelerator is 100:15:2. The vacuum-assisted molding process is used for molding, and the curing system is curing at room temperature for 24 hours to obtain a carbon fiber reinforced composite material. After mechanical testing, the composite material with carbon fiber before treatment as reinforcement has a tensile strength of 280.3 MPa and a flexural strength of 322.7 MPa; while the composite material made of carbon fiber after electrification treatment has a tensile strength of 348.6 MPa and a flexural strength of 348.6 MPa and 322.7 MPa. 385.5MPa, which indicates that the electrification treatment can significantly improve the mechanical properties of the composite material and improve the high value-added reuse value of recycled carbon fibers.

Example 3

During the high-voltage treatment, the applied voltage density was 1 V/cm ² , and the treatment time was 300 s. The rest are the same as in Example 1.

The carbon fiber cloth before and after the electrification treatment was used as the reinforcement, and the thermosetting resin matrix composites were prepared respectively, using bisphenol A epoxy resin (E-51) as the resin matrix, methyl nadic anhydride as the curing agent, and tertiary amine salt as the resin matrix. The accelerator is mixed evenly at room temperature, and the mass ratio of resin, curing agent and accelerator is 100:98.5:4. The vacuum-assisted molding process is used for molding, and the curing system is 100 °C for 1 h + 130 °C for 4 h to obtain a carbon fiber reinforced composite material. After mechanical testing, the composite material with carbon fiber before treatment as reinforcement has a tensile strength of 377.4 MPa and a flexural strength of 449.3 MPa; while the composite material made of carbon fiber after electrification treatment has a tensile strength of 440.3 MPa and a flexural strength of 440.3 MPa and 449.3 MPa. 510.5MPa, which indicates that the electrification treatment effectively repairs the defects in the carbon fiber tow, and at the same time realizes the "welding" of the overlap of the carbon fiber fabric, which significantly improves the mechanical properties of the carbon fiber fabric.

Example 4

During the high voltage treatment, the applied voltage density was 5V/cm ² and the treatment time was 10s. The rest are the same as in Example 1.

The carbon fiber cloth before and after the electrification treatment was used as the reinforcement, and the thermosetting resin matrix composites were prepared respectively, using bisphenol A epoxy resin (E-51) as the resin matrix, methyl nadic anhydride as the curing agent, and tertiary amine salt as the resin matrix. The accelerator is mixed evenly at room temperature, and the mass ratio of resin, curing agent and accelerator is 100:98.5:4. The vacuum-assisted molding process is used for molding, and the curing system is 100 °C for 1 h + 130 °C for 4 h to obtain a carbon fiber reinforced composite material. After mechanical testing, the composite material with carbon fiber before treatment as reinforcement has a tensile strength of 377.4MPa and a flexural strength of 449.3MPa; while the composite material made of carbon fiber after electrification treatment has a tensile strength of 436.7MPa and a flexural strength of 436.7MPa. 495.4MPa, which shows that the electrification treatment effectively repairs the defects in the carbon fiber tow, and at the same time realizes the "welding" of the overlap of the carbon fiber fabric, which significantly improves the mechanical properties of the carbon fiber fabric.

Claims (10)

1. A method of reprocessing a recycled carbon fiber, comprising the steps of:

(1) preparing the recycled carbon fibers into recycled carbon fiber felt bodies;

(2) cleaning and drying the recycled carbon fiber felt body to remove surface impurities;

(3) leading lugs are connected to two ends of the recovered carbon fiber felt body, high-voltage electric treatment is carried out by connecting the leading lugs with a power supply, the leading lugs are taken down after treatment, cleaning and drying are carried out, and then the process is finished.

2. The reprocessing method for recycling carbon fiber according to claim 1, wherein the recycled carbon fiber of step (1) is one or a mixture of more of pyrolysis, solution dissolution or supercritical dissolution recycled chopped fiber, continuous carbon fiber, two-dimensional carbon fiber fabric or three-dimensional carbon fiber fabric.

3. The reprocessing method of the recycled carbon fibers according to claim 1, wherein the recycled carbon fibers in the step (1) are formed into a recycled carbon fiber felt by slitting and non-woven molding the recycled carbon fibers.

4. The method of claim 1, wherein the recycled carbon fiber mat is cut into rectangular mats before the cleaning in step (2).

5. The method of claim 1, wherein the cleaning agent used in the cleaning process of the step (2) and the step (3) is one or more of ethanol, acetone, dichloromethane, trichloroethylene, tetrachloroethylene, chloroform or carbon tetrachloride.

6. The method of claim 1, wherein the tab of step (3) is a copper foil, a flake red copper electrode, a flake graphite electrode, or a combination thereof.

7. The method for reprocessing the recycled carbon fiber as claimed in claim 1, wherein the leading lugs in the step (3) are bonded to two ends of the recycled carbon fiber felt body through a bonding agent, wherein the bonding agent is one or more of conductive silver paste, conductive adhesive IAC and conductive adhesive ACA.

8. The method of claim 1, wherein the step (3) of high-voltage electrical treatment is performed in a protective atmosphere, wherein the protective atmosphere is an argon atmosphere, a nitrogen atmosphere, or a combination thereof.

9. The method for reprocessing a recycled carbon fiber according to claim 1, wherein the applied voltage density during the high voltage electric treatment of the step (3) is 1V/cm²～5V/cm²The treatment time is 10 s-300 s.

10. The method of claim 9, wherein the voltage density is 3V/cm²～4V/cm²The treatment time is 60 s-120 s.

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