CN109485912B

CN109485912B - Electro-promotion heterogeneous catalytic device for recycling CFRP (carbon fiber reinforced plastics) and control method thereof

Info

Publication number: CN109485912B
Application number: CN201811333195.6A
Authority: CN
Inventors: 朱继华
Original assignee: Shenzhen University
Current assignee: Shenzhen University
Priority date: 2018-11-09
Filing date: 2018-11-09
Publication date: 2019-12-24
Anticipated expiration: 2038-11-09
Also published as: WO2020093503A1; CN109485912A

Abstract

The invention discloses an electro-promotion heterogeneous catalysis device for recycling CFRP (carbon fiber reinforced plastics) and a control method thereof, wherein the device comprises an external power supply, an electrolytic cell filled with electrolyte, a CFRP sample with one end inserted into the electrolyte and a metal sheet, wherein the electrolyte contains an organic solvent and ammonium acetate; the other end of the CFRP sample is connected with the anode of an external power supply, and the other end of the metal sheet is connected with the cathode of the external power supply. The heterogeneous catalysis recovery device provided by the invention has the advantages of simple structure and low cost, and the carbon fiber yarns with better performance can be efficiently recovered from the CFRP material by optimizing the current parameters and the ammonium acetate concentration.

Description

Electro-promotion heterogeneous catalytic device for recycling CFRP (carbon fiber reinforced plastics) and control method thereof

Technical Field

The invention relates to the field of CFRP material recovery, in particular to an electro-promotion heterogeneous catalytic device for recovering CFRP and a control method thereof.

Background

Carbon fiber (CF for short) is a microcrystalline graphite fiber material with a carbon content of 95% or more. As a novel high-performance fiber material, the carbon fiber has the advantages of high tensile strength (2 to 7GPa), high modulus (200 to 700GPa) and low density (1.5 to 2.0 g/cm)²) Small linear expansion coefficient, conductivity, excellent electromagnetic shielding performance and the like, and chemical advantage of acid-base and organic solvent corrosion resistance. In addition, carbon fiber has the advantages of high softness and plasticity, high ultrahigh temperature resistance, fatigue resistance and the like, so that the carbon fiber is unique in the field of new materials.

In order to utilize the characteristics of light weight and high strength of Carbon Fiber filament, Carbon Fiber is often combined with ceramic, resin, metal, etc. to form a Carbon Fiber Reinforced Composite (CFRP) material to complement the defects of the rest of materials in mechanical properties and fatigue resistance. Originally, CFRP was used in the field of defense and military, such as weight reduction of a fighter plane fuselage; with the development of science and technology, many excellent properties such as high toughness and corrosion resistance and light weight of CFRP have been developed and are gaining favor in the industrial and production fields such as aerospace, automobile materials, civil engineering and construction, sporting goods and the like. With the increasing application of CFRP materials, the enhancement of environmental awareness of all social circles and the sustainable development of economy, the CFRP waste materials are required to be recycled.

For carbon fiber reinforced resin based composites, high value carbon fibers are the main subject of recycling. The existing method for recovering the carbon fiber raw material mainly comprises two categories of physical recovery and chemical recovery.

Physical recycling mainly relies on machinery for recycling: scrap recycling is accomplished by reducing the composite size by disintegration, crushing, grinding or other similar mechanical means. The mechanical method is low in cost and simple, but the method usually needs to crush the size of the raw material to 5-10mm or even shorter, the length of the carbon fiber is seriously shortened, the performance of the recycled fiber is seriously reduced, the recycling value is greatly reduced, and the method can only be used in low-value fields such as fillers or resin reinforcements.

The chemical recovery is mainly divided into two recovery directions of heat treatment and a chemical solvent method: among them, the heat treatment is a method for converting wastes into one or more recyclable materials at a high temperature, is the only CFRP recycling method currently in the world for commercial operation, and mainly includes a vacuum pyrolysis method, a microwave pyrolysis method, a fluidized bed method, an aerobic pyrolysis method, and the like. The vacuum cracking method generally requires a vacuum condition of about 500 ℃, but the surface of the obtained carbon fiber has resin residue. The microwave pyrolysis method of Edward Lester, etc. requires strict nitrogen conditions, the reaction is completed within 8s at high temperature, and the violent reaction conditions can damage the recovered carbon fibers, so that the mechanical properties of the carbon fibers are reduced. The fluidized bed method has advantages in that carbon fibers having clean surfaces can be obtained, and it has a wide range of applications, and can treat contaminated waste, but also reduces the size of CFRP, and seriously loses the strength (25% -50%) of the recovered carbon fibers, and resin decomposition products cannot be recovered. The aerobic pyrolysis method combines oxygen and control of proper high temperature to achieve aerobic high-efficiency pyrolysis, does not need chemical reagents, but has very strict control on experimental conditions, can cause oxidation of carbon fiber yarns due to slight improper control to form carbon deposit and carbon residue, influences the surface and mechanical properties, and can emit toxic gases.

The chemical solvent rule is that the carbon fiber is separated by breaking the C-N or C-O linkage chemical bond of the resin matrix through the synergistic effect of the chemical solvent and high-temperature heat (and high pressure). The supercritical/subcritical fluid decomposition method, the normal pressure solvent method and the like may be classified according to the reaction conditions and the reagents used. The supercritical fluid has the comprehensive characteristics of liquid and gas, and has the density and solubility of liquid and the viscosity of gasAnd the subcritical fluid also has super strong diffusivity and solubility, and the two fluids can directly dissolve the resin curing material, have small influence on the performance of the carbon fiber, and can still partially oxidize the carbon fiber. The atmospheric pressure solvent method is an atmospheric pressure chemical solvent method for decomposing a resin matrix in CFRP with a chemical solvent under atmospheric pressure conditions, and there are many cases, for example, Maekawa and the like in K₃PO₄As a catalyst, benzyl alcohol is used as a solvent to react at 200 ℃ for 10 hours to decompose epoxy resin in the tennis racket and recover carbon fibers; yang et al used a polyethylene glycol (PEG)/NaOH system to dissolve the epoxy resin in the anhydride cured CFRP by processing at 180 ℃ for 50 min.

In summary, the heat treatment methods all require high temperature conditions, generally require high pressure conditions, have high equipment requirements and high energy consumption, and have a great adverse effect on the performance of the recovered product. The chemical solvent method is efficient and convenient, has little influence on the performance of the carbon fiber yarn compared with the thermal hydrolysis method, but relates to the influence of solvent use on the environment and the safety problem, is mainly used as a means for exploring material properties at the present stage, and is not easy to be made into large-scale industry. In addition, in the above recovery method, measures for reducing the size of CFRP are often required for the needs of instruments and other conditions, and although the raw material is not crushed as in physical recovery, the length of the recovered carbon fiber yarn is greatly reduced, and the use value thereof is greatly reduced.

Accordingly, the prior art is yet to be improved and developed.

Disclosure of Invention

In view of the above-mentioned deficiencies of the prior art, the present invention aims to provide an electro-promoted heterogeneous catalytic device for recovering CFRP and a control method thereof, which aims to solve the problems of high cost, harsh reaction conditions, high equipment requirements, poor performance, short length and greatly reduced utilization value of the recovered carbon fiber in the existing technology for recovering carbon fiber from CFRP materials.

The technical scheme of the invention is as follows:

an electrically-promoted heterogeneous catalytic device for recycling CFRP comprises an external power supply, an electrolytic cell filled with electrolyte, a CFRP sample and a metal sheet, wherein one end of the CFRP sample is inserted into the electrolyte, and the electrolyte contains an organic solvent and ammonium acetate; the other end of the CFRP sample is connected with the anode of an external power supply, and the other end of the metal sheet is connected with the cathode of the external power supply.

The electro-promoted heterogeneous catalysis device for recovering the CFRP is characterized in that the organic solvent is dimethyl sulfoxide.

The control method of the electro-promoted heterogeneous catalytic device for recovering the CFRP comprises the following steps:

inserting one end of a CFRP sample and one end of a metal sheet into electrolyte of an electrolytic cell, and respectively connecting the other end of the CFRP sample and the other end of the metal sheet with a positive electrode and a negative electrode of an external power supply, wherein the concentration of ammonium acetate in the electrolyte is 0.52-2.08 mol/L;

the external power supply is started and controlled to enable the current density passing through the CFRP sample to be 14842.3-37105.8mA/m²And calculating the current density according to the surface area of the CFRP sample exposed to the electrolyte, and recovering the carbon fiber yarns from the CFRP sample after the electrolytic reaction is carried out for a preset time.

The control method of the electro-promoted heterogeneous catalysis device for recycling the CFRP is characterized in that the concentration of ammonium acetate in the electrolyte is 0.52 mol/L.

The control method of the electro-promoted heterogeneous catalysis device for recovering the CFRP is characterized in that the current density of the CFRP sample is 29684.6mA/m²。

The control method of the electro-promoted heterogeneous catalysis device for recycling the CFRP is characterized in that the metal sheet is a stainless steel sheet.

The control method of the electro-promoted heterogeneous catalytic device for recovering CFRP is characterized in that the electrolytic reaction time is 4 days.

The control method of the electro-promoted heterogeneous catalysis device for recovering the CFRP comprises the steps of insulating the middle area of the CFRP sample in advance, and dividing the CFRP sample into a power-on area, an insulating area and a reaction area.

Has the advantages that: the invention provides an electro-promotion heterogeneous catalysis device for recycling CFRP (carbon fiber reinforced plastics), which comprises an external power supply, an electrolytic cell filled with electrolyte, a CFRP sample with one end inserted into the electrolyte and a metal sheet, wherein the electrolyte contains an organic solvent and ammonium acetate; and the other ends of the CFRP sample and the metal sheet are respectively connected with the anode and the cathode of an external power supply. The invention can efficiently recover carbon fiber yarns with better performance from the CFRP material by connecting the CFRP sample to the circuit and setting the adaptive parameters.

Drawings

FIG. 1 is a schematic structural diagram of a preferred embodiment of an electrically-promoted heterogeneous catalyst device for recovering CFRP according to the present invention.

FIG. 2 is a flow chart of a preferred embodiment of the method for controlling an electrically promoted heterogeneous catalyst device for CFRP recovery according to the present invention.

FIG. 3 is a schematic structural diagram of a CFRP sample according to an embodiment of the invention.

FIG. 4 is a graph showing the results of the degumming rate of the CFRP sample according to the present invention under different current conditions.

FIG. 5 is a graph showing the tensile strength results of the recovered carbon fiber filaments of the CFRP sample of the invention under different current conditions.

FIG. 6 is a graph showing the results of the shear strength of the carbon fiber filaments recovered from the CFRP sample of the present invention under different concentrations of ammonium acetate.

FIG. 7 is a graph showing the results of shear strength of the recovered carbon fiber filaments of the CFRP sample of the invention under different current conditions.

FIG. 8a is a drawing of the invention D₁₀₀A_x1I₁Electron microscopy of the sample scans the image.

FIG. 8b is a drawing of the invention D₁₀₀A_x2I₁Electron microscopy of the sample scans the image.

FIG. 8c is a drawing of the invention D₁₀₀A_x3I₁Electron microscopy of the sample scans the image.

FIG. 8D is a drawing of the invention D₁₀₀A_x4I₁Electron microscopy of the sample scans the image.

FIG. 9a shows the present invention D₁₀₀A_x1I₃Electron microscopy of the sample scans the image.

FIG. 9b shows a schematic view of the present invention D₁₀₀A_x2I₃Electron microscopy of the sample scans the image.

FIG. 9c is a drawing of the invention D₁₀₀A_x3I₃Electron microscopy of the sample scans the image.

FIG. 9D is a drawing of the invention D₁₀₀A_x4I₃Electron microscopy of the sample scans the image.

FIG. 10a shows the present invention D₁₀₀A_x1I₁Electron microscopy of the sample scans the image.

FIG. 10b shows a view of the present invention D₁₀₀A_x1I₂Electron microscopy of the sample scans the image.

FIG. 10c is a drawing of the invention D₁₀₀A_x1I₃Electron microscopy of the sample scans the image.

FIG. 10D is a drawing of the invention D₁₀₀A_x1I₄Electron microscopy of the sample scans the image.

FIG. 11 shows the present invention D₁₀₀A_x1I₃And (3) a two-dimensional topography of the sample under an atomic force microscope.

FIG. 12 shows the present invention D₁₀₀A_x1I₃And (3) three-dimensional topography of the sample under an atomic force microscope.

Detailed Description

The invention provides an electro-promoted heterogeneous catalytic device for recycling CFRP and a control method thereof, and the invention is further described in detail below in order to make the purpose, technical scheme and effect of the invention clearer and clearer. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention.

The existing technology for recycling the CFRP material has the following defects that firstly, the length of the recycled carbon fiber is reduced greatly or even crushed compared with the length of the original CFRP, the performance of the recycled carbon fiber is obviously reduced, and the recycling value of the recycled carbon fiber is greatly reduced; secondly, in the prior art, most recovery processes need high-temperature and even high-pressure treatment, the reaction conditions are harsh, the equipment requirements are high, and the cost investment is large.

Based on the problems in the prior art, the invention provides an electrically-promoted heterogeneous catalysis device for recycling CFRP, as shown in FIG. 1, the device comprises an external power supply 100, an electrolytic cell 300 filled with an electrolyte 200, a CFRP sample 400 with one end inserted into the electrolyte 300, and a metal sheet 500, wherein the electrolyte 300 comprises an organic solvent and ammonium acetate; the other end of the CFRP sample 400 is connected to the positive electrode of the external power supply 100, and the other end of the metal sheet 500 is connected to the negative electrode of the external power supply 100.

In the present invention, the CFRP sample is a CFRP plate formed by using carbon fibers as a reinforcement, epoxy resin as a matrix, and an amine as a curing agent, the epoxy resin is generally a kind of organic polymer having epoxy groups at both ends, a carbon-nitrogen bond is generated by a reaction with the curing agent, the epoxy groups at both ends of the epoxy resin are opened to serve as connection points, so that epoxy resin molecules gradually form a whole to form a three-dimensional network structure. The electro-promotion heterogeneous catalysis device for recycling the CFRP is simple in structure and low in cost, can remove epoxy resin in a CFRP material in a short time, and accordingly recycles carbon fiber yarns with good performance, and the implementation principle of the electro-promotion heterogeneous catalysis device is as follows:

when the external power supply is electrified, the electrolyte reacts as follows:wherein, near the CFRP sample (i.e., anode side), the ammonium ions lose electrons to form NH₂OH (hydroxylamine), a small portion of which can continue to be oxidized to NO as the concentration increases, and which is unstable and readily decomposed to form N₂O、NH₃Or N₂. The NH₂OH is used as a nucleophilic reagent to perform redox reaction with a space cross-linking bond-carbon-nitrogen bond (C-N) in amine epoxy resin, so that the original space three-dimensional structure of the epoxy resin is damaged to lose bonding property and degrade the epoxy resin into a macromolecular product; furthermore, NH₂Ethers formed by ring opening of OH with epoxy groupsThe bonds react to further decompose the macromolecular products into small molecular products.

Specifically, in the early stage of the electrolytic reaction, the main reaction at the anode side is NH₄ ⁺Is oxidized into NH₂And (5) OH. At this stage, the epoxy resin is degraded into macromolecular organic matter, and at this time, the macromolecular organic matter still mainly covers the surface of the carbon fiber, so that the system resistance is not smooth and tends to be reduced. With NH₂The continuous increase of OH concentration can degrade the outer epoxy resin into macromolecular organic matter to cover the surface of epoxy resin and prevent the ring-opening reaction, and at this time, part of NH₂OH begins to lose electrons and is oxidized into NO, and NO and NH with strong reducibility₂OH reacts with carbon-nitrogen bonds and ether bonds to further decompose macromolecular degradation products on the surface layer of the epoxy resin into micromolecular products, so that the degradation of the epoxy resin is accelerated, and finally the carbon fibers are exposed in the electrolyte. The electro-promotion heterogeneous catalysis device for recycling the CFRP can efficiently recycle carbon fiber yarns with better performance from amine CFRP materials.

In a preferred embodiment, the organic solvent in the electrolyte is dimethyl sulfoxide (DMSO), which is an aprotic polar solvent, has better conductivity, better solubility characteristics for ammonium acetate and a specific solvent effect for many chemical reactions, and these characteristics can accelerate the reaction rate and promote complete ionization of ammonium acetate.

Based on the electro-promoted heterogeneous catalyst device for recovering CFRP, the invention also provides a control method of the electro-promoted heterogeneous catalyst device for recovering CFRP, wherein the control method comprises the following steps as shown in FIG. 2:

s100, inserting one end of a CFRP sample and one end of a metal sheet into electrolyte of an electrolytic cell, and respectively connecting the other end of the CFRP sample and the other end of the metal sheet with a positive electrode and a negative electrode of an external power supply, wherein the concentration of ammonium acetate in the electrolyte is 0.52-2.08 mol/L;

s200, starting and controlling the external power supply to enable the current density passing through the CFRP sample to be 14842.3-37105.8mA/m²The magnitude of the current density is according to the CFRP sample exposureAnd calculating the surface area of the electrolyte, and recovering the carbon fiber filaments from the CFRP sample after the electrolytic reaction is carried out for a preset time.

In a preferred embodiment, as shown in fig. 3, the CFRP sample is in a rectangular shape of 75mm by 25mm, and the middle region of the CFRP sample is insulated to divide the CFRP sample into a conducting region 410, an insulating region 420, and a reaction region 430, wherein the reaction region has an area of 25mm by 25 mm; the width of the insulating layer is 25mm, the insulating layer comprises a Kaffet silicon rubber layer, an insulating tape layer and an epoxy sealing adhesive layer from inside to outside, and the preparation process of the insulating layer comprises the following steps: firstly, coating a layer of uniform Kafft silicon rubber with the thickness of about 1.5mm on the surface of an insulating layer area of a clean and dry CFRP sample, and carrying out air drying for 24 hours under the condition of drying and ventilation in a laboratory; then wrapping the surface of the silicon rubber by using an insulating tape, wherein the width of the tape is the width of the insulating layer; and then, using epoxy sealant for sealing, and placing the sealed glass tube in a laboratory for air drying for 24 hours under the dry and ventilated conditions. The insulating layer mainly functions to control the reaction area of the CFRP sample and isolate the electrolyte from the part of the non-reaction area. The remaining 25mm width is the powered area of the CFRP sample for holding circuit components to connect the CFRP sample in series with the entire circuit.

Preferably, when the concentration of ammonium acetate in the electrolyte is 0.52-2.08mol/L, and the current density of the CFRP sample is controlled to be 14842.3-37105.8mA/m by an external power supply²And after 4 days of electrolytic reaction, the glue removing rate in the CFRP sample reaches more than 90 percent, namely, the matrix epoxy resin matrix in the CFRP sample is almost completely degraded, and the clean carbon fiber yarns with better performance can be recovered.

In this embodiment, the magnitude of the current density is calculated based on the amount of surface area of the CFRP sample exposed to the electrolyte. The calculation formula of the current density is I ═ I/S, wherein S is the reaction area of the CFRP sample, and I is the current magnitude.

The control method of the electrically promoted heterogeneous catalyst apparatus for recovery of CFRP according to the present invention is explained by experiments as follows:

for the purpose of illustration as shown in FIG. 3For comprehensive consideration of the performance and efficiency of the recycled carbon fiber, the experiment designs four current densities and four ammonium acetate concentrations as research parameters, and sets 16 groups of experiments in total, wherein the specific parameters are shown in table 1, and D₁₀₀Represents DMSO, A represents ammonium acetate, I represents the current density, e.g. "D₁₀₀A_x1I₁"represents the solvent is pure DMSO, the concentration of ammonium acetate is x1, and the current density is 14842.3mA/m²。

TABLE 1 test parameters table

After the experimental device is assembled, the recovery process can be started by electrifying, and the whole electrifying process lasts for 4 days. And (4) after the recovery process is finished, using tweezers and scissors to remove the soft carbon fiber yarns in the reaction area in the CFRP sample. Subsequently, the carbon fiber filaments are subjected to ultrasonic cleaning, and the ultrasonic cleaning comprises the following steps: the temperature is kept at 50 ℃, deionized water is used for 8 minutes, and absolute ethyl alcohol is used for 8 minutes, and the circulation is carried out for three times; after ultrasonic cleaning, the carbon fiber yarns are dried in a drying oven for 24 hours at 60 ℃ to obtain carbon fiber yarns which are smooth in texture, very good in flexibility and similar to the reaction zone in length (25 mm). TGA (gel removal rate) analysis was performed after the carbon fiber filaments obtained in this experiment were washed and dried, and data shown in table 2 were obtained.

TABLE 2 degumming rate of recycled carbon fibers

FIG. 4 is a graph showing the gel removal rate at different ammonium acetate concentrations, as shown by the graph, wherein the ammonium acetate concentration is A_x1The epoxy resin is decomposed basically completely and has little residue; at other ammonium acetate concentrations, the gel removal rate increases and then decreases with increasing current density, and at a current density of I₂The maximum value is obtained. In addition, the lower the ammonium acetate concentration, the higher the gel removal rate under the same current density condition.

The curve in fig. 4 trends upward and then downward because: when the current density is low, the reaction speed of the system is low, and the epoxy resin on the surface of the carbon fiber is not completely degraded in the whole experiment time; when current density is too big, the uneven epoxy resin layer thickness on carbon fiber surface can lead to epoxy degradation rate inhomogeneous, and the carbon fiber surface that partial cover epoxy resin thickness is little is exposed in electrolyte at first, because carbon fiber conductivity is better for carbon fiber surface becomes the active place of anodic reaction, at this moment NH₂The redox reaction of OH and carbon fiber surface active carbon becomes a main reaction, and the degradation reaction of epoxy resin becomes a secondary reaction, so that the epoxy resin is not completely decomposed in a short recovery period, and the carbon fiber is seriously degraded due to too strong oxidation and etching reaction of the carbon fiber.

The glue removing rate of the experimental groups in the table 2 is more than 90%, wherein the concentration of ammonium acetate is A_x1The glue removing rate of the series exceeds 98 percent. Therefore, under the conditions of proper current density and ammonium acetate concentration, the CFRP matrix in the reaction system taking DMSO as the solution can be almost completely degraded, so that clean carbon fiber yarns can be recovered. The result of gel removal rate analysis shows that the gel removal rate can be greatly improved by adding a small amount (0.52mol/L) of ammonium acetate into DMSO. Low ammonium acetate concentrations favor epoxy degradation, while lower or higher current densities can adversely affect epoxy degradation.

In a preferred embodiment, the recovered carbon fibers are analyzed for tensile strength of the filaments to yield the data shown in Table 3. The carbon fiber diameter was slightly reduced for each parameter set compared to 7 μm for the carbon fiber precursor diameter. Because the protofilament is wrapped by the epoxy resin sizing agent, under the condition of electrifying reaction, the epoxy resin matrix is firstly degraded, and then the epoxy resin sizing agent on the carbon fiber filament is gradually degraded by oxidation under the continuous action of current and electrolyte. In addition, since the carbon fiber precursor inevitably generates grooves in the production process, after the epoxy resin and the sizing agent are successively degraded, a current spike effect occurs on the surface of the carbon fiber precursor, which causes the oxidation reaction to proceed mainly along the upper edges of the grooves. It is speculated that the tip effect of the current etches the upper edge of the trench, making the surface of the carbon fiber smoother, resulting in a slight decrease in the diameter of the carbon fiber. The current cusp effect is more pronounced for the set of parameters with higher current densities.

TABLE 3 tensile Strength data sheet for recycled carbon fiber monofilaments

As can be seen from Table 3, the recovered carbon fiber filaments of each group had a reduced tensile strength relative to the tensile strength of the precursor, with a maximum reduction of 30.16%, with a maximum retention of tensile strength of 93.55% (D)₁₀₀A_x1I₃). According to the data in table 3, a relationship diagram of the tensile strength and the current density of the recycled carbon fiber monofilament shown in fig. 5 is obtained. As shown in the figure, when the concentration of ammonium acetate is x1(0.52mol/L), the tensile strength of the carbon fiber monofilament is increased and then decreased along with the increase of the current density, and the tensile strength is increased and decreased along with the increase of the current density at the current density of I3(29684.6 mA/m)²) The maximum value was 3602.48MPa, which was 93.55% of the tensile strength of the strand.

When the ammonium acetate concentration was x2, x3, x4, no significant tendency was observed for the tensile strength of the monofilaments, but fluctuations were observed, ranging from ± 300 MPa. It is presumed that when the concentration of ammonium acetate is greater than x1(0.52mol/L), the concentration of ions or molecules in the electrolyte reaches a critical value and becomes a decisive factor, i.e., the concentration of ammonium acetate is too high and the oxidation etching effect on the surface of the carbon fiber reaches a certain degree.

Therefore, in this embodiment, in order to ensure that the carbon fiber with better tensile strength can be recovered, it is preferable that the concentration of ammonium acetate in the electrolyte is 0.52mol/L, and the current density of the CFRP sample is 29684.6mA/m²。

In a preferred embodiment, in order to reflect the bonding performance of the carbon fiber and the epoxy resin, the present example will perform a droplet embedding experiment on each sample to determine the interfacial shear strength. To avoid excessive interfacial shear strength leading to carbon fiber breakage and to ensure data validity, the droplet diameters tested were in the range of 70-120 μm. The interfacial shear strength of the carbon fiber precursor (VCF) was 28.47MPa, and the interfacial shear strength of the remaining recovered carbon fibers was as shown in table 4.

TABLE 4 recycled carbon fiber interface shear strength data sheet

As shown in Table 4, unlike recycled carbon fibers, which all have different decreases in tensile strength of the filaments, the interfacial shear strength of the recycled carbon fibers generally increases in small increments, with the highest D₁₀₀A_x2I₄The interfacial shear strength of the recycled carbon fiber reaches 131.24 percent of protofilament. The minimum interface shear strength is 24.83MPa, which is only 87.23% of the interface shear strength of the carbon fiber precursor. The interfacial failure modes of recycled carbon fibers are mainly divided into two categories: the first is peel failure (DB) of the epoxy resin layer, and the second is peel failure (CB) of the interface between the carbon fiber and the epoxy resin. The interface failure mode of the carbon fiber precursor is the peeling failure of the epoxy resin layer, the bonding performance of the epoxy resin and the carbon fiber is good in the failure mode, and the shearing failure occurs in the epoxy resin layer when the resin balls and the carbon fiber are sheared. Under the peeling failure mode of the carbon fiber and epoxy resin interface, the epoxy resin ball and the carbon fiber have poor bonding performance, and the shear interface weak layer is the carbon fiber and epoxy resin interface, so the interface shear strength is lower in the failure mode. In this experiment, the failure mode of the recovered carbon fibers of most of the parameter sets was DB, and the failure mode of the recovered carbon fibers of only two parameter sets was CB. The CB failure mode occurs under the conditions of high ammonium acetate concentration and low current density, which means that the interface shear strength of the carbon fiber is damaged under the conditions of high ammonium acetate concentration and low current density, and the bonding property between the epoxy resin and the carbon fiber is not improved.

The interfacial shear strength of the recovered carbon fiber filaments at different ammonium acetate concentrations as shown in fig. 6 can be obtained from the data shown in table 4, and as shown in fig. 6, the change of the interfacial shear strength of the recovered carbon fibers is in a state of approximately increasing to decreasing with the increase of the ammonium acetate concentration, and it is estimated that the interfacial shear strength has a maximum value in the range of ammonium acetate concentration of 1.04 to 1.56 mol/L. According to the data shown in table 4, a schematic view of the interfacial shear strength of the recycled carbon fiber filament at different current densities can be obtained as shown in fig. 7, and the trend of the change of the interfacial shear strength of the recycled carbon fiber filament is approximately slowly increased along with the increase of the current density under the same ammonium acetate concentration condition. It is clearly noted that the interface shear strength increases from the lowest 87.23% to 122.41% at an ammonium acetate concentration of Ax4(2.08 mol/L). It is presumed that the current density is advantageous for improving the interfacial shear strength of the recycled carbon fiber. The interfacial shear strength of the recycled carbon fiber is mainly related to the surface roughness of the recycled carbon fiber and the type and the number of the surface functional groups.

Further, the surface morphology of the recycled carbon fiber sample can be imaged in two dimensions on a micron scale through an SEM (scanning electron microscope), and the quality of the carbon fiber can be simply and intuitively reflected as a result. FIGS. 8 a-8 d show the current density I₁SEM images of four samples, observed and divided by D₁₀₀A_x1I₁The upper surface was clean, and the remaining samples showed blurry portions with whitish colors, which means that the epoxy resin was not removed, and the current density was such that the surface of the carbon fiber was slightly etched and no peeling of the surface layer occurred. FIGS. 9a to 9d show the current density I₃SEM images of the four samples of (1), observed to be D₁₀₀A_x1I₃The surface is clean, grooves with different depths appear, and the depth and the width of a small number of grooves are large; d₁₀₀A_x2I₃In a sample, peeling with small areas appears at a plurality of positions on the surface of the rightmost carbon fiber, a deep and wide groove with longer length is observed on the surface of the carbon fiber, in addition, a small part of the carbon fiber is blurred, and the part is guessed to be covered with the epoxy resin or the degradation product thereof which is not fallen off; d₁₀₀A_x3I₃Depth and width of the grooves on the surface of the sample and D₁₀₀A_x2I₃The sample surface was similar, but D was observed₁₀₀A_x3I₃The deep trench length of the sample is largerD₁₀₀A_x2I₃The length of the sample is greater; d₁₀₀A_x4I₃The surface of the sample is in a plurality of positions with the phenomenon of carbon fiber surface layer shedding, and the sample has more deep and wide grooves and longer length. The research shows that^[14,15]And the surface of the carbon fiber is oxidized and etched under the electrochemical environment by anodic oxidation, so that the physical appearance of the surface is changed. The SEM analysis results show that in a certain range, the increase of the concentration of ammonium acetate can aggravate the oxidation suffered by the surface of the carbon fiber yarn, form a longitudinal crack-shaped groove and a groove structure with deep depth and large width, and even cause the surface of the carbon fiber yarn to be loose and the surface of the carbon fiber yarn to be peeled off.

Same current density (I)₃) SEM images of four groups of samples below, D₁₀₀A_x1I₃And D₁₀₀A_x2I₃The surfaces of the two groups of samples are clean and clear, and have no peeling or stripping condition, so that the two groups of samples have better surface oxidation etching condition intuitively. And D₁₀₀A_x3I₃And D₁₀₀A_x4I₃In two groups of samples, D₁₀₀A_x3I₃The surface of which appears epoxy resin fuzzy areas and small-area peeling, D₁₀₀A_x4I₃The surface layer was peeled off more seriously without the blurred portion on the surface. The SEM analysis result is not in direct proportion to the interface shear strength result, and it is likely that the surface oxidation etching condition of the recycled carbon fiber is not the only factor affecting the interface shear strength of the carbon fiber, and the interface shear strength is also affected by the type and the number of the functional groups on the surface of the carbon fiber.

10 a-10 d are SEM images of four samples with an ammonium acetate concentration of Ax1, showing that none of the surfaces of the four samples had epoxy residue, which is consistent with the results of gel removal rate, i.e., almost complete degradation of the epoxy on the carbon fiber surface at an ammonium acetate concentration of Ax 1. SEM image shows that the carbon fiber surface oxidation etching condition is good under the concentration, deep and wide grooves or cracks do not appear, and graphite layer shedding phenomenon does not exist. Therefore, when the concentration of the ammonium acetate in the electrolyte is 0.52mol/L, the recovery efficiency of the carbon fiber can be greatly improved, and the quality performance of the carbon fiber is better.

Further, the surface morphology of the recovered carbon fiber sample is analyzed by AFM (atomic force microscope) to obtain the current density I₃The average roughness data of the recycled carbon fibers are shown in table 5.

TABLE 5 average roughness of recycled carbon fiber filaments

FIG. 11 is a view taken from D₁₀₀A_x1I₃A two-dimensional topography map of 1 micron multiplied by 1 micron on the surface of the carbon fiber yarn recovered from the sample; FIG. 12 is a view taken from D₁₀₀A_x1I₃And (3) a three-dimensional topography of 1 micron multiplied by 1 micron on the surface of the carbon fiber filaments recovered from the sample. As can be seen from table 5 and fig. 11 and 12, the surface of the recovered carbon fiber filament is similar to the surface of the precursor filament, and the groove structure is obvious and complete. The reason is that the reaction conditions are mild, the exposure time of the carbon fiber to the electrolyte is short, and the oxidation of the reaction system is not so strong. As the ammonium acetate concentration increased, D₁₀₀A_x2I₃、D₁₀₀A_x3I₃、D₁₀₀A_x4I₃The average roughness of the sample is gradually reduced, and the surface roughness of the carbon fiber is reduced, so that the mechanical occlusion effect between the carbon fiber and the epoxy resin is weak.

The main acting force between carbon atom sheet layers on the surface layer of the carbon fiber is Van der Waals force, and the acting force can be weakened by the reduction of the area of the carbon atom sheet layers or the increase of the distance between the carbon atom sheet layers. In addition, the oxide etch effect is greatly attenuated to destroy the force. On the one hand, the carbon fiber is exposed to the electrolyte and is subjected to continuous oxidation etching, so that carbon chains are broken, and partial active carbon atoms are oxidized into CO₂Causing the carbon atom sheet to peel off and even peel off from the surface. On the other hand, CO produced₂The distance between the layers of the carbon atom sheets is increased by gas filled in the carbon atom sheets, the peeling of the carbon atom sheets also reduces the area of the sheets, and the van der Waals force is weakened in the two conditions, so that the surface layer of the carbon fiber surface layer is peeled off, and the carbon fiber is smootherThe effective diameter of the carbon fiber is also reduced. It is believed that the reduction in the effective diameter of the carbon fiber directly reduces the tensile strength of the filaments of the carbon fiber.

Combined current density of I₃In SEM and AFM analysis of four samples, the oxidation etching degree of the carbon fiber surface is increased, firstly, the grooves on the carbon fiber surface are exposed, and then the tip effect of the current is gradually obvious, so that the carbon fiber surface tends to be flat. In addition, the oxidation action is intensified, and the graphite layer on the surface of the carbon fiber falls off in a blocky manner, so that the average roughness of the carbon fiber is reduced.

Furthermore, after the epoxy resin matrix and the epoxy resin sizing agent on the surface of the carbon fiber are degraded successively, the carbon fiber is exposed in the electrolyte and is subjected to the actions of oxidation corrosion and the like, more oxygen or nitrogen is introduced to increase oxygen-containing functional groups and nitrogen-containing functional groups on the surface, and the surface activity of the carbon fiber is changed. In order to explore the relationship between the types and the quantity of functional groups on the surface of the carbon fiber and the mechanical strength of the recovered carbon fiber, a sample with high monofilament tensile strength and interface shear strength is selected to perform (X-ray photoelectron spectroscopy) XPS analysis, and the change of the surface of the carbon fiber under an organic electrochemical system is explored. The four samples are obtained under different current densities of ammonium acetate with the concentration of Ax1, XPS analysis is carried out on the surfaces of the carbon fibers of the four samples to obtain a scanning full spectrum and a C1s high-resolution narrow spectrum, and a plurality of fitting peaks are found by deconvoluting C1s peaks in the four samples, which indicates that a large number of different oxygen-containing functional groups or nitrogen-containing functional groups are introduced into the surfaces of the carbon fibers, so that the surface activity of the carbon fibers can be improved, the wettability of the carbon fibers and epoxy resin is increased, and the bonding performance of the carbon fibers and the epoxy resin is enhanced.

Table 6 shows the results of semi-quantitative analysis of carbon fiber filaments obtained at different current densities with the ammonium acetate concentration Ax1, and as shown in table 6, the carbon content of all four samples decreased, which is a result of the increased degree of oxidation. While the oxygen content rises, except for D₁₀₀A_x1I₂Besides, the content of the rest oxygen is over 22 percent. The highest oxygen to carbon ratio of the four samples was 30.64. The nitrogen content tends to rise first and then fall, at D₁₀₀A_x1I₄The nitrogen content in the sample decreased. Combining the shock peak appearing at the C1s peak with the judgment of the great increase of the oxygen content of the sample, due to the continuous action of the large current density, the nitrogen-containing functional group on the surface of the carbon fiber is oxidized into the oxygen-containing functional group, and more unsaturated structures are formed; in addition, according to the surface morphology analysis results of SEM and AFM, the oxidation etching of the carbon fiber surface is aggravated by the large current density, which may cause the peeling of the surface layer carbon, and the oxidation reaction is concentrated along the upper edge of the trench due to the current tip effect, so that it is likely to cause the detachment of the nitrogen-containing functional group along with the surface layer carbon, and finally, the content of the nitrogen-containing functional group is reduced.

TABLE 6 semi-quantitative analysis results data

Combining the tensile strength and nitrogen content analyses of these four samples, it was found that the higher the nitrogen content, the higher the monofilament tensile strength. This means that the more nitrogen-containing functional groups, the easier it is to maintain the monofilament tensile strength of the recovered carbon fiber filaments.

It is generally believed that the higher the ratio (N1s + O1s)/C1s, the better the surface activity of the carbon fiber. The interfacial shear strength data for the four samples show that, although the ratios (N1s + O1s)/C1s differ by 8%, the interfacial shear strength differs by less than 1%. Therefore, the relative amounts of the various types of functional groups are also required to comprehensively analyze the wettability of the carbon fiber and the epoxy resin. Table 7 shows the surface functional group content of each sample.

TABLE 7 data table of the content of functional groups on the surface of the sample

As can be seen from Table 7, the proportion of C-C single bonds is gradually decreased and the proportion of oxygen-containing functional groups is gradually increased, which is consistent with the results of semi-quantitative analysis, i.e., the degree of oxidation increases with increasing current density. With the increase of the oxidation degree, the C-C single bond on the surface of the carbon fiber is firstly oxidized into hydroxyl, and then the hydroxyl is continuously oxidized into carbonyl and carboxyl. Slave watch3.9 it can be seen that the relative content of carboxyl groups is not stable. The reason is that: the carboxyl is easy to combine with the hydroxyl on the adjacent C atom to generate CO₂Resulting in instability of the carboxyl group content.

D₁₀₀A_x1I₁The recycled carbon fiber has the largest content of C-C bonds on the surface, D₁₀₀A_x1I₄The recovered carbon fiber has the least C-C bond content on the surface, and the C-C bond content decreases with the increase of the current density, which indicates that the carbon fiber has a higher oxidation degree and thus a higher content of oxygen-containing functional groups as the current density on the surface is higher.

Among the oxygen-containing functional groups, the hydroxyl content is the highest and is relatively stable, and the sum of the contents of the carbonyl group and the hydroxyl group is close to or less than the content of the carboxyl group. The main reason is that the enthalpy of formation of hydroxyl groups is low, and therefore the chemical equilibrium shifts in the direction of formation of hydroxyl groups, and hydroxyl groups are first formed when activated carbon is oxidized. As the oxidation reaction proceeds, the hydroxyl group is oxidized into a carboxyl group, and the ketone group on the surface of the carbon fiber is also oxidized into a carboxyl group.

The nitrogen-containing functional groups on the surface of the carbon fiber are mainly pyridine type, nitrogen oxide type, pyrrole type and the like. Wherein the pyridine type and pyrrole type nitrogen-containing functional groups have higher stability, and generally substitute carbon atoms to form a heterocyclic ring structure. The increase of the nitrogen-containing functional groups can improve the affinity between the carbon fibers and the epoxy resin, so that the epoxy resin can be more easily infiltrated into small gaps or grooves on the surfaces of the carbon fibers, and the infiltration of the carbon fibers and the epoxy resin is improved. The nitrogen-containing functional groups on the surface of the carbon fiber are except NH₂NH in electrolyte, into which OH is introduced by reaction with activated carbon₄ ⁺It is also introduced by reacting with an oxygen-containing functional group such as-COOH.

Comparing the semi-quantitative analysis and the relative content data of the functional groups, in combination with the fact that the interfacial shear strength of the four samples exceeds that of the precursor, it is considered herein that both the oxygen-containing functional groups and the nitrogen-containing functional groups greatly improve the activity of the carbon fiber surface. The interface shear strength of the sample with few oxygen-containing and nitrogen-containing functional groups is small.

Estimated from the XPS analysis result, NH₂OH reacts with activated carbon on the surface of carbon fiber to generate-ONH₂or-NHOH, moietyAnd N is substituted for C in the graphite ring to form a nitrogen-oxygen type nitrogen-containing functional group. -ONH₂Is a functional group with high activity and easy oxidation, and is oxidized into-OH. NH since the reaction to form hydroxyl groups occurs more readily₂More OH reacts to form-ONH₂Therefore, the number of oxygen-containing functional groups is larger. At the same time, hydroxyl groups can be oxidized to keto groups and carboxyl groups, and this reaction of oxidizing hydroxyl groups also promotes the formation of hydroxyl groups. In general, the number of oxygen-containing functional groups on the surface of the carbon fiber is more, which is consistent with the semi-quantitative analysis result.

In summary, the present invention provides an electrically-promoted heterogeneous catalyst device for recovering CFRP and a control method thereof, wherein carbon fiber filaments with retained fibril length can be recovered from CFRP material by an electrically-promoted heterogeneous catalytic reaction recovery method, both current density and ammonium acetate concentration have obvious influence on the quality of the recovered carbon fibers, and the current density is 29684.6mA/m²When the concentration of ammonium acetate is 0.52mol/L, the carbon fiber filament with the best mechanical property can be obtained by recycling, the monofilament tensile strength of the recycled carbon fiber can reach 93.55 percent of the protofilament, the interface shear strength reaches 118.76 percent of the protofilament, and the degumming rate reaches 99.2 percent; SEM and AFM analysis of the recycled single fiber shows that under the condition of the same current density, the combined action of oxidation etching and the tip effect of current can cause the grooves and the shedding on the surface of the carbon fiber, so that the average roughness of the surface of the carbon fiber is reduced; XPS analysis of the recycled carbon fiber filament shows that oxygen-containing functional groups and nitrogen-containing functional groups on the surface of the recycled carbon fiber are increased, active sites on the surface of the carbon fiber are increased, and the interface shear strength of the recycled carbon fiber is improved.

It is to be understood that the invention is not limited to the examples described above, but that modifications and variations may be effected thereto by those of ordinary skill in the art in light of the foregoing description, and that all such modifications and variations are intended to be within the scope of the invention as defined by the appended claims.

Claims

1. An electrically-promoted heterogeneous catalytic device for recycling CFRP is characterized by comprising an external power supply, an electrolytic cell filled with electrolyte, a CFRP sample with one end inserted into the electrolyte and a metal sheet, wherein the electrolyte contains an organic solvent and ammonium acetate; the other end of the CFRP sample is connected with the anode of an external power supply, and the other end of the metal sheet is connected with the cathode of the external power supply, wherein the CFRP sample is a carbon fiber reinforced composite material formed by taking carbon fibers as a reinforcement, epoxy resin as a matrix and amine substances as a curing agent.

2. The electro-promoted heterogeneous catalyst device for recovery of CFRP according to claim 1, wherein the organic solvent is dimethyl sulfoxide.

3. A method for controlling an electrically promoted heterogeneous catalyst device for the recovery of CFRP as claimed in any one of claims 1 to 2, comprising the steps of:

the external power supply is started and controlled to enable the current density of the CFRP sample to be 14842.3-37105.8mA/m²And calculating the current density according to the surface area of the CFRP sample exposed to the electrolyte, and recovering the carbon fiber yarns from the CFRP sample after the electrolytic reaction is carried out for a preset time.

4. The method for controlling an electrically promoted heterogeneous catalyst device for CFRP recovery according to claim 3, wherein the concentration of ammonium acetate in said electrolyte is 0.52 mol/L.

5. The method for controlling an electrically-promoted heterogeneous catalyst device for recovery of CFRP according to claim 4, wherein the current density of the CFRP sample is 29684.6mA/m²。

6. The method for controlling an electrically promoted heterogeneous catalyst device for the recovery of CFRP according to claim 3 wherein said metal sheet is a stainless steel sheet.

7. The method for controlling an electrically promoted heterogeneous catalyst device for recovery of CFRP according to claim 3 wherein the electrolysis reaction time is 4 days.

8. The method for controlling an electrically promoted heterogeneous catalyst device for recovery of CFRP according to claim 3, wherein the middle region of the CFRP sample is subjected to an insulation treatment in advance, and the CFRP sample is divided into an electrifying region, an insulating region and a reaction region.