Heat treatment device and method for treating chopped carbon fibers by using same

Abstract

The invention discloses a heat treatment device and a method for treating short carbon fibers by using the heat treatment device, and belongs to the technical field of carbon fiber preparation. The device comprises a gas mixing unit and a heat treatment furnace, the gas mixing unit comprises an inert gas pipeline, a reaction gas pipeline and a gas mixing tank for mixing the inert gas pipeline and the reaction gas pipeline; the heat treatment furnace comprises a gas inlet, a treatment cavity and a gas outlet which are sequentially connected; a microwave generator is arranged on the outer side of the treatment cavity, and an infrared heating element is further arranged in the microwave generator; the gas mixing tank is connected with the gas inlet through a gas inlet path, and a discontinuous gas inlet control element is arranged on the gas inlet path. According to the method, inert gas and reaction gas are mixed and then are discontinuously introduced into a heat treatment furnace filled with short carbon fibers, and heat treatment is carried out through infrared heating and microwave-assisted strengthening. According to the invention, a matched heat treatment device is designed, hydrothermal reaction and microwave-assisted strengthening are carried out, heat treatment at a relatively low temperature is carried out by controlling reaction conditions, and desizing and modification treatment on the surface of the short carbon fiber are realized.

Description

Technical Field

[0001] The invention belongs to the technical field of carbon fiber preparation, and in particular relates to a heat treatment device and a method for treating chopped carbon fibers using the same. Background Art

[0002] Carbon fiber is mainly composed of carbon elements, and has the characteristics of high temperature resistance, friction resistance, thermal conductivity and corrosion resistance. It is fibrous in appearance, soft, and can be processed into various fabrics. Because its graphite microcrystalline structure is preferentially oriented along the fiber axis, it has high strength and modulus along the fiber axis. Carbon fiber has a low density, so its specific strength and specific modulus are high. The main use of carbon fiber is as a reinforcing material combined with resin, metal, ceramic and carbon to manufacture advanced composite materials. Carbon fiber reinforced epoxy resin composite materials have the highest specific strength and specific modulus among existing engineering materials.

[0003] Carbon fiber is composed of tens of thousands of single filaments, so a layer of sizing agent is applied to the surface of the carbon fiber before it is rolled up. Its main function is to gather these single filaments into bundles to prevent them from fluffing and loosening, and to provide support for the production of carbon fiber cloth and three-dimensional woven bodies. In addition, carbon fiber will rub against multiple rollers during the production and weaving process. Without the protection of the sizing agent layer, the carbon fiber single filaments are very easy to break, resulting in a decrease in the overall strength of the fiber.

[0004] However, in the preparation process of non-oriented chopped carbon fiber composites, the highly clustered carbon fibers not only make it difficult for the resin to fully infiltrate the carbon fiber surface, but also easily cause obvious defects to form inside the composite material, reducing the non-oriented uniformity.

[0005] Currently, there are many common methods for removing sizing agents and surface modification of carbon fiber, including thermal decomposition, solvent method, mechanical method, chemical method, etc.

[0006] Among them, the pyrolysis method is to place the carbon fiber in a high-temperature furnace and pyrolyze the resin and sizing agent at high temperature (>600°C). This method is suitable for some relatively thermally stable resins and sizing agents. The solvent method is to soak the carbon fiber in an appropriate solvent and decompose the resin and sizing agent through chemical reactions. The mechanical method is to remove the sizing agent by physical force without damaging the carbon fiber. Common mechanical methods include wiping, sandblasting and ultrasonic methods. The chemical method is to dissolve or decompose the sizing agent in a specific chemical environment. Common chemical methods include oxidation, reduction, acid washing and alkali washing.

[0007] However, in the process of large-scale mass production, the above methods will have various disadvantages such as high energy consumption, difficulty in handling hazardous waste solvents, and inability to accurately control the degree of reaction. In addition, large-scale mass production process equipment is mainly used for continuous carbon fiber processing, and it is difficult to directly use existing technology for short-cut carbon fiber.

[0008] In view of this, this application is hereby filed. Summary of the invention

[0009] The object of the present invention is to provide a heat treatment device and a method for treating chopped carbon fibers using the same. By designing a matching heat treatment device, hydrothermal reaction and microwave-assisted strengthening are carried out using the device, and heat treatment is carried out at a relatively low temperature by controlling the reaction conditions, so as to achieve desizing and modification of the surface of the chopped carbon fibers.

[0010] In order to achieve the above objectives, the present invention particularly adopts the following technical solutions:

[0011] In the first aspect, the present invention provides a heat treatment device, comprising a gas mixing unit and a heat treatment furnace; the gas mixing unit comprises an inert gas pipeline and a reaction gas pipeline and a gas mixing tank for mixing the inert gas and the reaction gas pipeline; the heat treatment furnace comprises an air inlet, a processing chamber, and an air outlet connected in sequence; a microwave generator is provided outside the processing chamber, and an infrared heating element is also provided inside the microwave generator. The gas mixing tank and the air inlet are connected through an air inlet path, and a discontinuous air inlet control element is provided on the air inlet path.

[0012] In a second aspect, the present invention also provides a method for treating chopped carbon fibers using the heat treatment device: after the inert gas and the reaction gas are mixed, they are discontinuously introduced into a heat treatment furnace filled with chopped carbon fibers, the reaction temperature is controlled by infrared heating, and the heat treatment is performed using microwave-assisted intensification.

[0013] Compared with the prior art, the present invention has the following beneficial effects:

[0014] The present invention produces a similar effect to fluidized bed technology by designing the heat treatment device and the reaction process, and effectively improves the heat treatment efficiency by combining microwave-assisted strengthening and discontinuous periodic treatment, and can quickly complete batch processing, realize the removal of the sizing agent on the surface of the carbon fiber, improve the fiber opening of the carbon fiber, and help the resin matrix to infiltrate the fiber. At the same time, by introducing a certain proportion of reaction gas and regulating the reaction temperature, pressure and cycle and other factors, the short-cut carbon fiber can be effectively surface-modified, the oxygen-containing functional groups can be increased, the interface performance of the composite material can be improved, and thus the overall performance of the carbon fiber composite material can be improved; the surface modification effect and degree can also be controlled, the generation of macromolecular tar can be effectively reduced, and the fiber processing efficiency can be improved. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] In order to more clearly illustrate the technical solutions of the embodiments of the present application, the drawings required for use in the embodiments will be briefly introduced below. It should be understood that the following drawings only show certain embodiments of the present application and therefore should not be regarded as limiting the scope of the present application.

[0016] Figure 1It is a schematic structural diagram of the heat treatment device of the present invention;

[0017] Figure 2 This is a microscope photo of a composite material prepared from chopped carbon fibers treated in Example 1;

[0018] Figure 3 This is a microscope photograph of the composite material prepared from the chopped carbon fibers treated in Comparative Example 3.

[0019] Description of reference numerals:

[0020] 1-nitrogen tank; 2-heat exchanger; 3-gas mixing tank; 31-steam generator; 32-pulse valve; 4-heat treatment furnace; 41-air flow distributor; 42-lower filter; 43-upper filter; 44-discharge port; 45-processing chamber; 5-microwave generator, 51 infrared heating tube; 6-exhaust gas treatment device; 71-inlet gas path; 72-outlet gas path. DETAILED DESCRIPTION

[0021] The embodiments of the present invention will be described in detail below in conjunction with specific examples, but it will be appreciated by those skilled in the art that the following examples are only used to illustrate the present invention and should not be considered to limit the scope of the present invention. If specific conditions are not specified in the examples, they are carried out according to normal conditions or conditions recommended by the manufacturer. If the manufacturer is not specified for the reagents or instruments used, they are all conventional products that can be purchased commercially.

[0022] In the present invention, the term "and / or" describes the association relationship of associated objects, indicating that there may be three relationships. For example, A and / or B can represent: A exists alone, A and B exist at the same time, and B exists alone. A and B can be singular or plural. The character " / " generally indicates that the associated objects before and after are in an "or" relationship.

[0023] It should be noted that in the following examples or comparative examples, if there is a mixture, if there is no description of the ratio of each component, it can be any ratio. The solution concentration of the substance not specified is the conventional standard concentration or any concentration.

[0024] The embodiment of the present invention provides a heat treatment device, such as Figure 1 As shown, it includes a gas mixing unit and a heat treatment furnace 4; the gas mixing unit includes an inert gas pipeline and a reaction gas pipeline and a gas mixing tank 3 for mixing the inert gas and the reaction gas pipeline; the heat treatment furnace 4 includes an air inlet, a processing chamber 45, and an air outlet connected in sequence; a microwave generator 5 is provided outside the processing chamber 45, and an infrared heating element is also provided inside the microwave generator 5. The gas mixing tank 3 and the air inlet are connected through an air inlet path 71, and a discontinuous air inlet control element is provided on the air inlet path 71.

[0025] In an embodiment, the main structure of the processing chamber 45 is made of ceramic material.

[0026] In the embodiment, the infrared heating element is an infrared heating tube 51 .

[0027] In some preferred embodiments, the inert gas pipeline is a nitrogen pipeline connecting the nitrogen tank 1 and the gas mixing tank 3; the reaction gas pipeline is a steam pipeline connecting the steam generator 31 and the gas mixing tank 3; the discontinuous air intake control element is a pulse valve 32, which can control the instantaneous pressure of the reaction gas entering the heat treatment furnace 4.

[0028] In the embodiment, an air flow distributor 41, a lower filter screen 42 and an upper filter screen 43 are sequentially arranged inside the processing chamber 45 from the air inlet to the air outlet. A discharge port 44 is arranged on the processing chamber 45 for feeding the raw material chopped carbon fiber. Among them, the air flow distributor can ensure the stable output of the air flow, and the lower filter screen 42 and the upper filter screen 43 can be metal porous plates for isolating the chopped fibers.

[0029] In the embodiment, the outlet port is connected downstream to an outlet gas path 72, and the outlet gas path 72 is connected in sequence to a heat exchanger 2 and an exhaust gas processor 6, and the heat exchanger 2 is also connected to the inert gas pipeline.

[0030] An embodiment of the present invention also provides a method for treating chopped carbon fibers using the heat treatment device, wherein the inert gas and the reaction gas are mixed and then discontinuously introduced into a heat treatment furnace 4 filled with chopped carbon fibers, the reaction temperature is controlled by infrared heating, and microwave-assisted intensification is used for heat treatment to complete the removal of sizing agents and modification of the carbon fiber surface.

[0031] In the embodiment, the microwave operating frequency of the microwave generator 5 is 300M-3GHz, preferably 915M-2.45GHz; the microwave power density is 0.2-1mW / cm 2 The microwave-assisted power density mainly reflects the degree of reaction. The appropriate processing power density can not only reduce the molecular bond energy and achieve surface modification at a relatively low temperature, but also avoid damaging the carbon fiber matrix structure.

[0032] Microwave-assisted strengthening is used to achieve efficient processing, that is, under the Lorentz force of the microwave electromagnetic field, the polar molecules of the chopped carbon fibers undergo energy level transitions, from the ground state to the excited state, thereby reducing the activation energy of the reaction and increasing the reaction activity. Through microwave-assisted strengthening, the purpose of removing the sizing agent on the surface of the carbon fibers at low temperatures (<500°C) can be achieved, so that the chopped carbon fibers have good fiber opening properties, which is conducive to uniform dispersion in the composite material, is conducive to the isotropic performance, and reduces defective structures.

[0033] In some preferred embodiments, the reaction gas includes water vapor; in some preferred embodiments, the inert gas includes nitrogen.

[0034] The carbon-based organic matter in the sizing agent can be decomposed into small molecule gases, such as carbon monoxide, carbon dioxide, hydrogen, methane, etc.; and the carbon fiber structure, due to its good graphite-like structure, has a large interatomic bond energy and a stable structure, is not easy to participate in the carbon gasification reaction, and the turbostratic graphite structure is retained. This can not only remove the sizing agent on the surface of the carbon fiber, but also eliminate the tar produced after the sizing agent is condensed at the outlet due to incomplete decomposition. In addition, by introducing a certain proportion of reaction gas and regulating the reaction temperature, the surface of the carbon fiber can be effectively modified, the oxygen-containing functional groups can be increased, and the interface performance of the composite material can be improved, thereby improving the overall performance of the carbon fiber composite material.

[0035] The steam generator 31 converts water into saturated steam through electric heating as the input source of reaction gas; the high-pressure nitrogen is used as the load gas, and after being reduced in pressure, it enters the heat exchanger 2 for preheating first; the post-mixing tank 3 mixes the water vapor and the preheated nitrogen in a certain proportion and stabilizes the pressure.

[0036] In an embodiment, the volume ratio of the reaction gas to the mixed gas is 0.5-8%, and the pressure of the mixed gas is 0.2-0.6 MPa.

[0037] The amount of water vapor used as a reaction gas directly determines the degree of surface modification of the carbon fiber. If the amount of reaction gas used is too small, the oxygen-containing functional groups in the surface modification of the carbon fiber will be insufficient, resulting in a decrease in interfacial adhesion. If the amount of water vapor used is too large, it may cause irreversible damage to the carbon fiber matrix, such as etching, and will also affect the overall performance of the prepared composite material.

[0038] In an embodiment, the heat treatment temperature is 320-420°C.

[0039] In an embodiment, the ratio of the volume of the chopped carbon fibers to the volume of the processing chamber 45 is ≤ 1 / 2.

[0040] In an embodiment, the length of the chopped carbon fibers is 1-8 mm.

[0041] In an embodiment, the discontinuous introduction into the heat treatment furnace includes a treatment time and a stop time. In some preferred embodiments, the treatment time is 2-16S; the stop time is 1-8S. The discontinuous reaction gas flow mainly utilizes high-pressure load gas to disturb and fluidize the chopped fibers, and the chopped fibers are purged discontinuously to avoid problems such as insufficient contact between the reaction gas and the fibers, uneven residence time, and decreased reaction efficiency, thereby improving the reaction efficiency of the carbon fiber surface desizing and surface treatment.

[0042] In some preferred embodiments, the total treatment time is 3 min-20 min.

[0043] In the embodiment, the reacted gas is discharged from the gas outlet and passes through the heat exchanger to exchange heat with the gas inlet path. The gas heat exchange process is performed through the gas inlet path 71 and the gas outlet path 72, which can effectively utilize heat energy, reduce energy consumption, and improve equipment efficiency.

[0044] In the embodiment, the inert gas is used as the load gas, and after being decompressed, it enters the heat exchanger 2 for preheating first, and then mixes with the reaction gas. The outlet gas path 72 leads to the tail gas treatment device 6, and the tail gas treatment device 6 may be provided with an activated carbon adsorption device to adsorb small molecule gases before discharging.

[0045] The present invention is further described below by some embodiments:

[0046] Example 1

[0047] Put the chopped carbon fibers with a length of 6 mm to be treated into the treatment chamber 45 of the heat treatment furnace 4, the volume of the chopped carbon fibers accounts for 1 / 2 of the volume of the treatment chamber 45, and close the discharge port 44. Turn on the infrared heating tube 51 to heat the furnace body to a set temperature of 360°C. Turn on the steam generator 31 and the valve of the nitrogen tank 1, and turn on the mixing tank 3, and fully mix and pressurize the water vapor and nitrogen generated by the steam generator 31, wherein the volume ratio of water vapor to the mixed gas is 1.5%, and the pressure of the mixed gas is 0.4MPa.

[0048] Turn on the microwave generator 5, the microwave operating frequency is 1200MHz, and the microwave power density is 0.5mW / cm 2 At the same time, the pulse valve 32 is opened in a discontinuous manner, with an opening time of 10 seconds, a closing time of 5 seconds, a cycle of 15 seconds, and this reciprocating, and the total reaction time is 12 minutes. The treated fiber is then taken out.

[0049] The carbonyl content on the carbon fiber surface was determined by X-ray photoelectron spectroscopy (XPS). 65wt% of chopped carbon fiber and 35wt% of phenolic resin were mixed, molded, cured, and carbonized to form a carbon / carbon composite material. The tensile strength and flexural strength of the composite material were determined, and the morphology of the carbon fiber composite material was observed by microscopy. Figure 2 shown.

[0050] Embodiment 2-6

[0051] During the preparation process, the treatment temperature, the mixed gas pressure, the volume ratio of water vapor in the mixed gas, the microwave power density, the treatment cycle and the total treatment time were changed. Other conditions were treated according to the same conditions as in Example 1, as shown in Table 1. The performance characterization method was the same as in Example 1, and the results are shown in Table 2.

[0052] Comparative Example 1

[0053] The difference from Example 1 is that microwave-assisted strengthening is not used in the treatment process. The specific preparation conditions are shown in Table 1. The performance characterization method is the same as that of Example 1, and the results are shown in Table 2.

[0054] Comparative Example 2

[0055] The difference from Example 1 is that: no reaction gas, i.e., water vapor, is added during the treatment process. The specific preparation conditions are shown in Table 1. The performance characterization method is the same as that of Example 1, and the results are shown in Table 2.

[0056] Comparative Example 3

[0057] The difference from Example 1 is that: the discontinuous treatment method is not used in the treatment process, and the specific preparation conditions are shown in Table 1; the performance characterization method is the same as that of Example 1, and the results are shown in Table 2. The morphology of the composite material is as follows Figure 3 shown.

[0058] Table 1 Preparation conditions in Examples and Comparative Examples

[0059]

[0060] Table 2 Characterization of carbon fiber properties after heat treatment in the examples and comparative examples

[0061]

[0062]

[0063] As can be seen from Table 1 and Table 2, compared with Comparative Example 1, Example 1 adopts microwave-assisted strengthening, so that the fiber surface can not only thermally react and decompose the surface sizing agent at a relatively low temperature to achieve uniform distribution of the fiber in the composite material; but also introduces water vapor as a reaction gas to increase the effective functional groups on the fiber surface, wherein the carbonyl content reaches 7.91%, thereby enhancing the interface bonding of the composite material. However, since Comparative Example 1 does not adopt microwave-assisted strengthening, the molecular bonds in the sizing agent molecules are insufficient to be completely broken at low temperatures, resulting in insufficient wettability of the resin to the fiber in the composite material, obvious defects or uneven performance, and the mechanical properties of the composite material after preparation are significantly reduced compared with Example 1.

[0064] From the results, compared with Example 1 and Comparative Example 2, since water vapor was not used as the reaction gas in Comparative Example 2, only nitrogen was used to disturb and purge the carbon fiber, although the sizing agent on the fiber surface was completely thermally decomposed under the microwave-assisted function. However, due to the lack of hydrothermal reaction, the sizing agent in Comparative Example 2 was more likely to form a tar-like substance with a larger molecular weight after decomposition, which was easy to block the filter screen and the gas outlet after long-term use.

[0065] From the results, compared with Example 1 and Comparative Example 3, since Comparative Example 3 does not adopt a discontinuous treatment method, the fibers in the heat treatment furnace are always in a stable airflow disturbance state, and the fibers are in a "fluid-like" state, and some fibers may be in a dead corner of the reaction or an insufficient reaction area. Figure 3 It can be seen that some fibers are adhered to each other, the fibers are in a clustered state, the resin cannot infiltrate their surface, and the effective functional group reaction is not sufficient, resulting in an insignificant increase in the surface carbonyl content. Due to poor interface performance, the excellent performance of carbon fiber cannot be fully reflected in the composite material, and its tensile strength is only 37.5MPa and its bending strength is only 59.4MPa.

[0066] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or replace some or all of the technical features therein with equivalents. However, these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

[0067] In addition, those skilled in the art will appreciate that, although some embodiments herein include certain features included in other embodiments but not other features, the combination of features of different embodiments is meant to be within the scope of the present invention and to form different embodiments. For example, in the above claims, any one of the claimed embodiments may be used in any combination. The information disclosed in this background technology section is intended only to deepen the understanding of the overall background technology of the present invention and should not be regarded as an admission or in any form of implication that the information constitutes prior art known to those skilled in the art.

Claims

1. A heat treatment device, characterized in that: include: A gas mixing unit, including an inert gas pipeline and a reaction gas pipeline and a gas mixing tank for mixing the two; A heat treatment furnace comprises an air inlet, a processing chamber, and an air outlet connected in sequence; a microwave generator is arranged outside the processing chamber, and an infrared heating element is also arranged inside the microwave generator; The gas mixing tank and the air inlet are connected via an air inlet path, and a discontinuous air inlet control element is provided on the air inlet path.

2. The heat treatment device according to claim 1, characterized in that An air flow distributor, a lower filter screen and an upper filter screen are arranged in sequence inside the processing chamber from the air inlet to the air outlet.

3. The heat treatment device according to claim 1, characterized in that The downstream of the gas outlet is connected to a gas outlet gas path, and a heat exchanger and an exhaust gas processor are sequentially connected to the gas outlet gas path, and the heat exchanger is also connected to the inert gas pipeline.

4. A method for treating chopped carbon fibers using the heat treatment device according to any one of claims 1 to 3, characterized in that: After the inert gas and the reaction gas are mixed, they are discontinuously introduced into a heat treatment furnace filled with chopped carbon fibers, the reaction temperature is controlled by infrared heating, and the heat treatment is performed using microwave-assisted intensification.

5. The method according to claim 4, characterized in that The reaction gas includes water vapor; and / or, the inert gas comprises nitrogen; And / or, the volume ratio of the reaction gas to the mixed gas is 0.5-8%, and the pressure of the mixed gas is 0.2-0.6 MPa.

6. The method according to claim 4, characterized in that The microwave operating frequency of the microwave-assisted enhancement is 300M-3GHz; And / or, the microwave power density of the microwave-assisted enhancement is 0.2-1 mW / cm 2 .

7. The method according to claim 4, characterized in that The temperature of the heat treatment is 320-420°C.

8. The method according to claim 4, characterized in that The volume of the chopped carbon fibers accounts for a ratio of ≤1 / 2 of the volume of the processing chamber; And / or, the length of the chopped carbon fiber is 1-8 mm.

9. The method according to claim 4, characterized in that The discontinuous introduction into the heat treatment furnace includes treatment time and stop time; Preferably, the processing time is 2-16S; the stopping time is 1-8S; And / or, the total processing time is 3 min-20 min.

10. The method according to claim 4, characterized in that The gas after the reaction is discharged from the gas outlet, and passes through the heat exchanger to exchange heat with the gas inlet path; And / or, the inert gas is used as a load gas, and after being decompressed, enters the heat exchanger to be preheated first, and then is mixed with the reaction gas.

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