High-strength interlaminar shear carbon fiber reinforced thermoplastic resin composite material and preparation method thereof
By fluorinating carbon fibers and inserting polypropylene resin, a covalent interface and a flexible intermediate layer are constructed, which solves the problems of interfacial bonding and wettability in carbon fiber reinforced thermoplastic resin composites, and improves mechanical properties and processing reliability.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- SICHUAN UNIV
- Filing Date
- 2026-02-05
- Publication Date
- 2026-05-19
AI Technical Summary
Existing carbon fiber reinforced thermoplastic resin composites have poor mechanical properties, especially weak interfacial bonding and poor resin wettability, which limits the performance of the composites.
Fluorinated carbon fibers are formed by fluorinating carbon fibers, and polypropylene resin is inserted as a flexible interlayer into the fluorinated carbon fibers and polyphenylene sulfide resin. The interfacial bonding is enhanced by the fluorinated layer and the free radical transfer reaction mechanism, thus constructing a covalent interface and a flexible interlayer.
It significantly improves the mechanical properties of composite materials, including flexural strength, flexural modulus and interlaminar shear strength, reduces porosity, enhances fiber-resin wettability, simplifies the preparation process and reduces costs.
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Figure CN122060193A_ABST
Abstract
Description
Technical Field
[0001] This invention belongs to the field of composite material technology, specifically relating to a high-strength, high-layer inter-shear carbon fiber reinforced thermoplastic resin composite material and its preparation method. Background Technology
[0002] Carbon fiber reinforced thermoplastic resin composites are characterized by their light weight, high specific strength and specific modulus, excellent corrosion resistance and thermal properties, and are therefore widely used in aerospace, rail transportation and wind power generation.
[0003] There are many factors that affect the performance of carbon fiber reinforced thermoplastic resin composites. In addition to the intrinsic properties of the fiber and the resin matrix, the two most important factors are: first, the poor surface polarity and low bonding energy of carbon fiber and thermoplastic resin make the interface between the two easily damaged, thus affecting the performance of the composite material; second, the high melt viscosity of thermoplastic resin makes it difficult to wet the carbon fiber during processing, thus forming pores in the composite material and affecting its performance.
[0004] In light of this, researchers have undertaken extensive work to address the aforementioned two issues. A commonly used method involves surface modification or alteration of both carbon fibers and resins to enhance their surface polarity and the melt flowability of the resin. However, this method is complex, time-consuming, and costly, and the resulting composite materials show limited improvement in mechanical properties.
[0005] Therefore, there is an urgent need to develop a new carbon fiber reinforced thermoplastic resin composite material with high mechanical strength and interlayer shear properties, thereby improving the reliability of processed structural components. Summary of the Invention
[0006] This invention provides a high-strength, high-layer interfacial shear carbon fiber reinforced thermoplastic resin composite material and its preparation method, aiming to solve the problem of poor mechanical properties in existing carbon fiber reinforced thermoplastic resin composite materials. This invention involves directly fluorinating carbon fibers to form fluorinated carbon fibers, then inserting polypropylene (PP) resin as a flexible interlayer into the fluorinated carbon fibers and polyphenylene sulfide (PPS) resin. Utilizing the characteristics of fluorine and the thermally activated free radical transfer reaction mechanism, the carbon fiber thermoplastic composite material is in-situ reinforced. After curing, a high-strength, high-layer interfacial shear carbon fiber reinforced thermoplastic resin composite material is obtained. The preparation method provided by this invention can increase the wettability of the fiber and resin while forming a covalent interface, enhancing the interfacial properties of the composite material. Simultaneously, the construction of the flexible interlayer also facilitates energy dissipation and stress transfer in the composite material.
[0007] To achieve the above objectives, the technical solution adopted by the present invention is as follows: On one hand, the present invention provides a method for preparing a high-strength interlayer shear carbon fiber reinforced thermoplastic resin composite material, comprising the following steps:
[0008] (1) Fluoride carbon fibers to form fluorinated carbon fibers;
[0009] (2) The fluorinated carbon fiber is composited with polypropylene resin to obtain polypropylene resin modified fluorinated carbon fiber.
[0010] (3) The polypropylene resin-modified fluorinated carbon fiber is combined with polyphenylene sulfide resin and cured to obtain the high-strength high-layer inter-shear carbon fiber reinforced thermoplastic resin composite material.
[0011] Further, the carbon fiber mentioned in step (1) includes at least one of the following: carbon fiber filament, carbon fiber staple filament, carbon fiber unidirectional tape, carbon fiber nonwoven fabric, carbon fiber felt, carbon fiber paper, carbon fiber fabric, carbon fiber filament with sizing agent on its surface, carbon fiber staple filament with sizing agent on its surface, carbon fiber unidirectional tape with sizing agent on its surface, carbon fiber nonwoven fabric with sizing agent on its surface, carbon fiber felt with sizing agent on its surface, carbon fiber paper with sizing agent on its surface, and carbon fiber fabric with sizing agent on its surface.
[0012] Furthermore, the carbon fiber fabric includes carbon fiber plain weave fabric, carbon fiber satin weave fabric, and carbon fiber twill weave fabric.
[0013] Furthermore, the sizing agent refers to a sizing agent containing active functional groups, including epoxy resin type sizing agents, polyamide type sizing agents, polyurethane type sizing agents, polyetheretherketone type sizing agents, etc.
[0014] Furthermore, the fluorination treatment method described in step (1) is either an independent fluorination treatment or a continuous fluorination treatment;
[0015] The independent fluorination process is as follows: a fluorinated mixture is mixed with the carbon fiber in a sealed metal cavity, and the fluorinated mixture is extracted after the mixing is completed to obtain the fluorinated carbon fiber.
[0016] The continuous fluorination process involves continuously drawing the carbon fibers at a constant speed through a well-sealed tunnel while simultaneously introducing a fluorinated mixture to ultimately obtain the fluorinated carbon fibers. The carbon fibers do not include short carbon fiber filaments and / or short carbon fiber filaments with a sizing agent on their surface.
[0017] Furthermore, the fluorinated mixture is a mixture of fluorine and an inert gas, wherein the volume percentage of fluorine in the fluorinated mixture is 1-20%, and the inert gas includes at least one of nitrogen, helium, argon, and xenon.
[0018] Furthermore, both the independent fluorination treatment and the continuous fluorination treatment are two-step fluorination processes, namely, sequential room temperature fluorination treatment and high temperature fluorination treatment.
[0019] Furthermore, in the independent fluorination treatment, the pressure of the fluorinated mixed gas in the room temperature fluorination treatment is 20~40 kPa, the reaction temperature is room temperature, and the reaction time is 120~180 min; the pressure of the fluorinated mixed gas in the high temperature fluorination treatment is 5~20 kPa, the reaction temperature is 70~300℃, and the reaction time is 30~120 min.
[0020] And / or, in the continuous fluorination treatment, the flow rate of the fluorinated mixed gas in the room temperature fluorination treatment is 5~10L / min, the temperature inside the tunnel is room temperature, and the residence time of the carbon fiber in the tunnel is 10~20min; the flow rate of the fluorinated mixed gas in the high temperature fluorination treatment is 1~5L / min, the temperature inside the tunnel is 70~300℃, and the residence time of the carbon fiber in the tunnel is 3~5min.
[0021] Furthermore, the independent fluorination treatment specifically includes:
[0022] The carbon fiber is placed in a sealed metal cavity, and the gas in the sealed metal cavity is replaced with an inert gas. The specific operation of the replacement is to evacuate the gas in the sealed metal cavity to form a vacuum, and then introduce an inert gas to atmospheric pressure. After replacing the gas in the sealed metal cavity 3 to 5 times, the vacuum inside the sealed metal cavity is maintained. At room temperature, an inert gas is introduced to a pressure of 1 to 3 kPa in the sealed metal cavity, and the pressure is stabilized for 3 to 5 minutes.
[0023] A fluorinated mixture is introduced into the sealed metal cavity for room temperature fluorination treatment, and then all gases are evacuated at room temperature to form a vacuum.
[0024] The sealed metal cavity is heated to the temperature for high-temperature fluorination treatment and held for 5-10 minutes. Then, a fluorinated mixed gas is introduced into the sealed metal cavity for high-temperature fluorination treatment. The temperature is then maintained at the high-temperature fluorination treatment temperature. The gas in the sealed metal cavity is evacuated to a vacuum. The gas in the sealed metal cavity is replaced with an inert gas 3-5 times. The vacuum inside the sealed metal cavity is maintained. An inert gas is introduced to atmospheric pressure, and the temperature is lowered to room temperature to obtain the fluorinated carbon fiber.
[0025] The inert gas includes at least one of nitrogen, helium, argon, and xenon.
[0026] Furthermore, the fluorine content on the surface of the fluorinated carbon fiber in step (1) is 10%~20% (this percentage is atomic percentage). At this fluorine content, the fiber surface has strong reactivity and high polarity, and the intrinsic structure of the fiber is not damaged, thus maintaining the mechanical properties of the fiber itself, which is more conducive to the mechanical properties of carbon fiber reinforced thermoplastic resin composites.
[0027] Further, the amount of polypropylene resin added in step (2) is 0.1-1% of the volume of the fluorinated carbon fiber;
[0028] And / or, the molding method described in step (2) includes at least one of injection molding, hot pressing, extrusion molding, and autoclave molding.
[0029] Furthermore, the injection pressure of the injection molding is 7~10MPa, the injection temperature is 200~250℃, and the mold temperature is 60~80℃.
[0030] Furthermore, the hot pressing pressure is 2~7MPa, the temperature is 180~220℃, the heating rate is 20~50℃ / min, the molding time is 15~30min, and the temperature is allowed to cool naturally to room temperature.
[0031] Furthermore, the extrusion die pressure is 2~5MPa, the extrusion temperature is 200~230℃, and the screw speed is 100~200rpm.
[0032] Furthermore, the pressure of the autoclave molding is 1~5MPa, the temperature is 200~240℃, the heating rate is 5~20℃ / min, the molding time is 30~60min, and it is naturally cooled to room temperature.
[0033] Further, in step (3), the volume ratio of the polypropylene resin-modified fluorinated carbon fiber and the polyphenylene sulfide resin is (0.1~1.2):1;
[0034] And / or, the curing method described in step (3) includes at least one of injection molding, hot pressing, extrusion molding, and autoclave molding.
[0035] Furthermore, the injection pressure of the injection molding is 7~12MPa, the injection temperature is 300~350℃, and the mold temperature is 100~120℃.
[0036] Furthermore, the hot pressing pressure is 2~7MPa, the temperature is 300~320℃, the heating rate is 5~20℃ / min, the molding time is 15~30min, and the cooling rate is 20~50℃ / min.
[0037] Furthermore, the die head pressure of the extrusion molding is 3~7MPa, the extrusion temperature is 300~330℃, and the screw speed is 100~200rpm.
[0038] Furthermore, the pressure of the autoclave molding is 1~5MPa, the temperature is 280~320℃, the heating rate is 5~20℃ / min, the molding time is 30~60min, and the cooling rate is 20~50℃ / min.
[0039] This invention involves subjecting carbon fibers to high and low temperature fluorination treatment, forming a fluorinated layer and generating a large number of free radicals on the carbon fiber surface. The strong reactivity of fluorine or carbon free radicals is used to activate the carbon fibers, enhancing the chemical reactivity of the carbon fiber surface and making it easier for the fibers to form covalent bonds with resins.
[0040] This invention forms a highly reactive fluorinated layer on the surface of carbon fibers. This fluorinated layer contains abundant free radicals, which are activated under heating conditions. These free radicals attack the tertiary carbon reaction sites in the polypropylene resin, causing the polypropylene resin molecular chains to break and forming covalent bonds with the carbon fiber surface. Furthermore, due to the unique free radical transfer mechanism of polypropylene resin, active free radicals are retained after the molecular chains break, leading to covalent cross-linking with polyphenylene sulfide resin. The addition of the polypropylene resin interlayer fills the tiny gaps between the carbon fibers, allowing for better wetting of the fibers and resin and reducing the porosity of the molded composite material. In addition, the intrinsic flexibility of the polypropylene resin molecular chains is high. After forming grafted covalent bonds with the carbon fibers, the movement of the polypropylene resin molecular chains is restricted, thereby reducing the crystallinity of the polypropylene resin molecular chains. This decrease in crystallinity further enhances the flexible behavior of the polypropylene resin. The polypropylene resin, as an interlayer, forms a flexible region between the carbon fibers and the polyphenylene sulfide resin, together forming a rigid-flexible-rigid composite material structure. The interlayer between the carbon fibers and the polyphenylene sulfide resin can delay stress transmission, dissipate impact energy, and resist shear stress.
[0041] This invention enhances the interfacial bonding between carbon fiber and resin through the synergistic effect of the above strategies, increases the wettability of the fiber and resin, constructs a flexible resin interlayer, and delays the stress transmission between the fiber and resin through the rigid-flexible composite material interface structure, hinders the expansion of stress or defects along the fiber-resin interface direction, and prevents the interface slippage or detachment between the fiber and resin, thereby obtaining a carbon fiber reinforced thermoplastic resin composite material with high strength and high interlayer shear.
[0042] On the other hand, the present invention provides a high-strength interlayer shear carbon fiber reinforced thermoplastic resin composite material, which is prepared by any of the preparation methods described above.
[0043] Furthermore, the high-strength interlayer shear carbon fiber reinforced thermoplastic resin composite material includes carbon fibers, a fluorinated layer on the surface of the carbon fibers, a polypropylene resin interlayer after the fluorinated layer reacts with polypropylene resin, and a polyphenylene sulfide resin matrix.
[0044] Furthermore, the thickness of the fluorinated layer is 1 nm to 1 μm, preferably 0.4 μm.
[0045] Furthermore, the thickness of the polypropylene resin intermediate layer is 1 nm to 1 μm, preferably 0.4 μm.
[0046] Those skilled in the art will understand that the numerical ranges in this invention should be understood to specifically disclose each intermediate value between the upper and lower limits of the range. Each smaller range between any stated value or intermediate value within a stated range, and any other stated value or intermediate value within said range, is also included in this invention. The upper and lower limits of these smaller ranges may be independently included or excluded from the range.
[0047] Compared with the prior art, the present invention has the following beneficial effects:
[0048] (1) The preparation method of the present invention involves a two-step fluorination treatment of carbon fibers using independent or continuous direct fluorination technology at high and low temperatures. The low-temperature fluorination stage initially activates the surface of the carbon fibers, while the high-temperature fluorination stage utilizes the high reactivity of fluorine to introduce active free radicals onto the surface of the carbon fibers without damaging their intrinsic structure, thereby enhancing the surface polarity of the carbon fibers. The two-step fluorination treatment at high and low temperatures can significantly increase the free radical content on the fiber surface and enhance the interfacial bonding between the carbon fibers and the thermoplastic resin. The fluorinated carbon fibers are first mixed with a trace amount of polypropylene resin. The free radicals on the fiber surface attack the tertiary carbon sites in the polypropylene resin, causing the polypropylene resin molecular chains to disintegrate. At the same time, the unique free radical transfer mechanism of the polypropylene resin molecules ensures that the free radicals remain stable after chain disintegration, thereby grafting the polypropylene resin molecules onto the carbon fiber surface through free radical coupling. Subsequently, the fluorinated carbon fibers grafted with polypropylene resin are composited with polyphenylene sulfide resin. Polyphenylene sulfide resin also exhibits a temperature-responsive phenomenon to free radicals. The polypropylene resin on the surface of the fluorinated carbon fibers forms covalent bonds with the polyphenylene sulfide resin, thereby enhancing the interface and mechanical properties of the composite material. The addition of polypropylene resin fills the tiny gaps between carbon fibers, enabling complete wetting at lower temperatures during subsequent lamination with polyphenylene sulfide (PPS) resin. As an intermediate phase between carbon fibers and PPS resin, polypropylene resin increases the compatibility and wettability of PPS resin with carbon fibers. Simultaneously, the free radicals remaining on the polypropylene resin molecular chains can undergo free radical cross-linking reactions with the CS on the PPS resin molecular chains, forming covalent bonds. This results in a fully covalently linked, tough interfacial phase, significantly improving the mechanical properties of carbon fiber reinforced thermoplastic resin composites. Furthermore, the inherent flexibility of the polypropylene resin molecular chains, after forming grafted covalent bonds with carbon fibers, further restricts the movement of the polypropylene resin molecular chains, thus reducing their crystallinity. This decrease in crystallinity further enhances the flexible behavior of the polypropylene resin as an intermediate layer, forming a rigid-flexible-rigid interfacial gradient transition layer with the carbon fibers and PPS resin. This layer helps to delay stress transmission, dissipate impact energy, and resist shear stress.
[0049] (2) The high-strength interlaminar shear carbon fiber reinforced thermoplastic resin composite material prepared by this invention has a maximum flexural strength of 1021.1 MPa, a maximum flexural modulus of 90.4 GPa, a maximum interlaminar shear strength of 101.7 MPa, and a maximum impact strength of 150.5 kJ / m. 2 The prepared composite material does not require grafting modification of the resin matrix; only simple fiber treatment is needed. The process is simple, low-cost, and conducive to industrial application. Attached Figure Description
[0050] To more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the accompanying drawings described below are only some embodiments recorded in the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.
[0051] Figure 1 This diagram illustrates the mechanism by which the reaction between fluorinated carbon fiber and polypropylene resin molecular chains leads to chain breakage in polypropylene resin.
[0052] Figure 2 Diagrams showing the mechanism of fully covalent bonding between polypropylene resin molecular chain segments containing free radicals and fluorinated carbon fiber and polyphenylene sulfide resin molecular chains, respectively.
[0053] Figure 3 In the figure, 'a' is a physical image of the high-strength interlayer shear carbon fiber reinforced thermoplastic resin composite material prepared in Example 1 of this invention. Figure 3 b in the figure is a metallographic microscope image of the cross section of the high-strength interlayer shear carbon fiber reinforced thermoplastic resin composite material prepared in Example 1;
[0054] Figure 4 The electron paramagnetic spectra of the carbon fibers after fluorination treatment in Example 1 and Comparative Example 3 of this invention are shown. Detailed Implementation
[0055] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of the present invention. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are within the scope of protection of the present invention.
[0056] While this invention describes only preferred methods and materials, any methods and materials similar to or equivalent to those described herein may be used in the implementation or testing of this invention.
[0057] The principle behind this invention, a high-strength, high-layer interfacial shear carbon fiber reinforced thermoplastic resin composite material, is based on the fact that fluorine has extremely strong electronegativity and reactivity, enabling it to activate the surface of inert carbon fibers, making them more readily react with the resin. A two-step fluorination process, using both high and low temperatures, is employed. The low-temperature fluorination stage initially activates the carbon fiber surface, while the high-temperature fluorination stage introduces active free radicals. The fluorinated layer formed on the carbon fiber surface attacks the active reaction sites in the resin, causing the polypropylene resin molecular chains to break, thereby reducing the melt viscosity of the thermoplastic resin and enhancing the wettability between the resin and the fiber. Due to the unique free radical transfer mechanism of polypropylene resin, even after the polypropylene resin molecular chains break, active free radicals remain on the molecular chains, which can covalently bond with the polyphenylene sulfide resin matrix, enhancing the interfacial bonding ability. The addition of polypropylene resin fills the tiny gaps between carbon fibers, enabling complete impregnation at lower temperatures during subsequent lamination with polyphenylene sulfide resin. Furthermore, the inherent flexibility of the polypropylene resin molecular chain, after forming grafted covalent bonds with carbon fibers, further restricts the movement of the polypropylene resin molecular chains, thereby reducing their crystallinity. This decrease in crystallinity further enhances the flexibility of the polypropylene resin as an interlayer. The polypropylene resin, acting as an interlayer, forms a flexible region between the carbon fibers and polyphenylene sulfide resin, together with the carbon fibers and polyphenylene sulfide resin to form a rigid-flexible-rigid composite material structure. This structure can delay stress transmission, dissipate impact energy, and resist shear stress. The mechanism of polypropylene resin chain scission caused by the reaction of fluorinated carbon fibers with polypropylene resin is shown in the diagram below. Figure 1 As shown in the diagram, the mechanism of the fully covalent bonding between polypropylene resin molecular chain segments containing free radicals and fluorinated carbon fiber and polyphenylene sulfide resin molecular chains is illustrated in the diagram. Figure 2 As shown.
[0058] The present invention will be further illustrated by the following examples.
[0059] Example 1
[0060] This embodiment provides a method for preparing a high-strength interlayer shear carbon fiber reinforced thermoplastic resin composite material, including:
[0061] S1, the carbon fiber plain weave fabric (purchased from Hexcel Corporation, USA, model HexForce) with sizing agent on its surface is treated to remove adsorbed water molecules, specifically including: drying the carbon fiber plain weave fabric in a 60℃ vacuum oven for 1 hour.
[0062] S2, the carbon fiber plain weave fabric after the removal of adsorbed water molecules is fluorinated using a fluorinated mixed gas. Specifically, this involves placing the treated carbon fiber plain weave fabric into a sealed stainless steel container, replacing the gas inside the container with nitrogen. The replacement process involves evacuating the gas from the stainless steel container to create a vacuum, then introducing nitrogen to atmospheric pressure. This gas replacement is repeated three times, maintaining the vacuum inside the container. Nitrogen is then introduced at room temperature until the pressure inside the stainless steel container reaches 1 kPa, and the pressure is stabilized for 5 minutes.
[0063] S3. A mixture of fluorine and nitrogen gas with a volume percentage of 5% (5% fluorine) is introduced into a stainless steel container until the pressure of the mixture reaches 20 kPa and the temperature is room temperature. This process is continued for 120 minutes. Subsequently, all gases are evacuated at room temperature to create a vacuum. The volume of the stainless steel container is 12 L.
[0064] S4. The inside of the stainless steel container is heated using a thermocouple at a rate of 10℃ / min. After reaching 150℃, the temperature is maintained for 10min. Then, a mixture of fluorine and nitrogen with a volume percentage of 5% is introduced into the stainless steel container. The pressure of the mixture of fluorine and nitrogen with a volume percentage of 5% is 20kPa. The pressure and internal temperature are maintained for 60min. Subsequently, the temperature is maintained at 150℃. The mixture inside the stainless steel container is evacuated to a vacuum. The replacement process in S2 is repeated using nitrogen. After replacement, nitrogen is introduced into the stainless steel container to atmospheric pressure, and the temperature is lowered at a rate of 10℃ / min. After cooling to room temperature, the stainless steel container is opened to obtain fluorinated carbon fiber plain weave fabric.
[0065] S5, fluorinated carbon fiber plain weave fabric and polypropylene resin film are hot-pressed together. The polypropylene resin film content is 0.5% of the volume of fluorinated carbon fiber plain weave fabric. The hot-pressing temperature is 200℃, the heating rate is 25℃ / min, the pressure is 5MPa, and after holding for 15min, it is naturally cooled to room temperature to obtain polypropylene resin modified fluorinated carbon fiber plain weave fabric.
[0066] S6. Fluorinated carbon fiber plain weave fabric modified with polypropylene resin (53% by volume) and polyphenylene sulfide resin film (47% by volume) are stacked in a mold and then autoclaved at 300°C for 30 min. The heating rate is 10°C / min, the cooling rate is 30°C / min, and the pressure is 5 MPa. Finally, a high-strength interlayer shear carbon fiber reinforced thermoplastic resin composite material is obtained.
[0067] Example 2
[0068] S1, the carbon fiber short filaments (purchased from Japan's DYAN Carbon Fiber Co., Ltd., model E300) containing sizing agent on the surface are treated to remove adsorbed water molecules. Specifically, the carbon fiber short filaments are placed in a vacuum oven at 60°C and dried for 1 hour.
[0069] S2, the carbon fiber short filaments after the adsorbed water molecule removal treatment are fluorinated using a fluorinated mixed gas. Specifically, the treated carbon fiber short filaments are placed in a sealed stainless steel container, and the gas inside the stainless steel container is replaced with nitrogen. The replacement operation involves evacuating the gas from the stainless steel container, creating a vacuum inside, and then introducing nitrogen to atmospheric pressure. After replacing the gas inside the stainless steel container three times, the vacuum inside the stainless steel container is maintained. Nitrogen is then introduced at room temperature until the pressure inside the stainless steel container reaches 1 kPa, and the pressure is stabilized for 5 minutes.
[0070] S3. A mixture of fluorine and nitrogen gas with a volume percentage of 5% (5% fluorine) is introduced into a stainless steel container until the pressure of the mixture reaches 20 kPa and the temperature is room temperature. This process is continued for 120 minutes. Subsequently, all gases are evacuated at room temperature to create a vacuum. The volume of the stainless steel container is 12 L.
[0071] S4. The inside of the stainless steel container is heated using a thermocouple at a rate of 10°C / min. After reaching 150°C, the temperature is maintained for 10 minutes. Then, a mixture of fluorine and nitrogen with a volume percentage of 5% is introduced into the stainless steel container. The pressure of the mixture of fluorine and nitrogen with a volume percentage of 5% is 20 kPa. The pressure and internal temperature are maintained for 60 minutes. Subsequently, the temperature is maintained at 150°C. The mixture inside the stainless steel container is then evacuated to a vacuum. The replacement process in S2 is repeated using nitrogen. After replacement, nitrogen is introduced into the stainless steel container to atmospheric pressure, and the temperature is lowered at a rate of 10°C / min. After cooling to room temperature, the stainless steel container is opened to obtain fluorinated carbon fiber short filaments.
[0072] S5 involves mixing fluorinated carbon fiber short filaments with polypropylene resin powder and then extruding and granulating them. The polypropylene resin powder content is 0.5% of the volume of the fluorinated carbon fiber short filaments. The extrusion temperature is 200℃, the die head pressure is 3MPa, and the screw speed is 100rpm. After extrusion, the fluorinated carbon fiber short filament particles modified with polypropylene resin are obtained by cutting them through a granulator.
[0073] S6. Fluorinated carbon fiber short filament particles modified with polypropylene resin with a volume fraction of 20% were mixed with polyphenylene sulfide resin powder with a volume fraction of 80% and then injection molded. The injection temperature was 320℃, the mold temperature was 100℃, and the injection pressure was 10MPa, finally obtaining a high-strength interlayer shear carbon fiber reinforced thermoplastic resin composite material.
[0074] Example 3
[0075] Other conditions are the same as in Example 1, except that S2, S3, and S4 are changed to: the carbon fiber plain weave fabric after the removal of adsorbed water molecules is fluorinated using a fluorinated mixed gas, specifically including: passing the continuous carbon fiber plain weave fabric through two airtight tunnels at a uniform speed.
[0076] The first airtight tunnel is filled with a mixture of fluorine and nitrogen with a fluorine volume percentage of 5%, and the flow rate of the fluorinated mixture is controlled at 10L / min. The temperature inside the tunnel is room temperature, and the fiber stays in the tunnel for 15 minutes. After passing through the tunnel, a room temperature fluorinated carbon fiber plain weave fabric is obtained.
[0077] The second airtight tunnel is filled with a mixture of fluorine and nitrogen with a fluorine volume percentage of 5%, and the flow rate of the fluorinated mixture is controlled at 3L / min. The temperature inside the tunnel is 150℃, and the fiber stays in the tunnel for 5 minutes. After passing through the tunnel, a high-temperature fluorinated carbon fiber plain weave fabric is obtained.
[0078] Example 4
[0079] Other conditions are the same as in Example 1, except that S1 is changed to: immersing the carbon fiber plain weave fabric (purchased from Hexcel Corporation, USA, model HexForce) with sizing agent on its surface in acetone solvent, extracting the carbon fiber plain weave fabric at 60°C for 24 hours using a Soxhlet extractor, washing with deionized water and ethanol, and drying to obtain desized carbon fiber plain weave fabric.
[0080] Example 5
[0081] The other conditions are the same as in Example 1, except that the carbon fiber plain weave fabric with sizing agent on the surface in S1 is replaced with carbon fiber unidirectional tape with sizing agent on the surface (purchased from Hexcel Corporation, USA, model HexForce).
[0082] Comparative Example 1
[0083] The difference between Comparative Example 1 and Example 1 is that steps S2, S3 and S4 were removed, and the carbon fiber plain weave fabric with sizing agent on the surface was not fluorinated. All other aspects are the same as in Example 1.
[0084] Comparative Example 2
[0085] The difference between Comparative Example 2 and Example 1 is that the pressure of the mixed gas of fluorine and nitrogen with a fluorine volume percentage of 5% in the stainless steel container in steps S3 and S4 is changed to 70 kPa, while the rest are the same as in Example 1.
[0086] Comparative Example 3
[0087] The difference between Comparative Example 3 and Example 1 is that step S3 was removed, and only the carbon fiber plain weave fabric with sizing agent on the surface was subjected to high-temperature fluorination treatment. All other aspects were the same as in Example 1.
[0088] Comparative Example 4
[0089] The difference between Comparative Example 4 and Example 1 is that in step S4, a mixture of fluorine and nitrogen with a fluorine volume percentage of 5% is introduced and continued for 30 minutes. Then, the temperature is lowered to room temperature, and the mixture in the stainless steel container is evacuated to a vacuum and the S2 replacement process is performed. The rest is the same as in Example 1.
[0090] Comparative Example 5
[0091] The difference between Comparative Example 5 and Example 1 is that step S5 is omitted, and fluorinated carbon fiber plain weave fabric is directly composited with polyphenylene sulfide resin film. All other aspects are the same as in Example 1.
[0092] Comparative Example 6
[0093] The difference between Comparative Example 6 and Example 1 is that in step S5, the polypropylene resin film content is 5% of the volume of the fluorinated carbon fiber plain weave fabric, and in step S6, the volume fraction of the polypropylene resin-modified fluorinated carbon fiber plain weave fabric is 40%, and the volume fraction of the polyphenylene sulfide resin film is 60%. The rest are the same as in Example 1.
[0094] The actual product of the high-strength interlayer shear carbon fiber reinforced thermoplastic resin composite material prepared in Example 1 is shown below. Figure 3 As shown in Figure a, its surface is smooth and without obvious defects; the metallographic microscope image of its cross-section is shown below. Figure 3 As shown in Figure b, the composite material is dense with few pores and no obvious voids. The resin and fiber have good wettability and no obvious delamination.
[0095] Electron paramagnetic resonance (EPR) tests were performed on the fluorinated carbon fiber plain weave fabrics of Example 1 and Comparative Example 3, and the obtained EPR spectra are shown below. Figure 4 As shown, after a two-step fluorination treatment at room temperature and high temperature, a more significant free radical signal appeared on the surface of the carbon fiber plain weave fabric.
[0096] The mechanical properties and XPS tests were performed on the carbon fiber reinforced thermoplastic resin composites prepared in Examples 1-5 and Comparative Examples 1-6. Flexural strength and flexural modulus were tested according to GB / T 1449-2005 "Test Method for Flexural Properties of Fiber Reinforced Plastics", interlaminar shear strength according to ASTM D2344 "Standard Test Method for Short Beam Strength of Polymer-Based Composites and Laminates", and impact strength according to GB / T 1451-2005 "Test Method for Impact Toughness of Simply Supported Beams of Fiber Reinforced Plastics". The fluorine content on the surface of the fluorinated carbon fibers was obtained through XPS analysis. The test results are shown in Table 1.
[0097] Table 1 Mechanical property data of carbon fiber reinforced thermoplastic resin composites
[0098]
[0099] As shown in Table 1, after the carbon fibers were subjected to high and low temperature fluorination treatment in Examples 1 to 5 of the present invention and then compounded with thermoplastic resin, the mechanical properties of the carbon fiber reinforced thermoplastic resin composite material without fluorination treatment in Comparative Example 1 were significantly improved. This proves that the high and low temperature fluorination treatment can significantly improve the mechanical properties of the carbon fiber reinforced thermoplastic resin composite material.
[0100] In Comparative Example 2, the pressure of the mixture of fluorine and nitrogen with a fluorine volume percentage of 5% was increased, which increased the fluorine content involved in the fluorination treatment. This resulted in an excessive amount of fluorine on the carbon fiber surface. Excessive fluorine would encapsulate the carbon atoms on the carbon fiber surface, which would hinder the covalent bonding between the carbon fiber and the resin. Therefore, the mechanical properties of the prepared composite material were reduced.
[0101] In Comparative Example 3, the original two-step fluorination process of room temperature and high temperature was changed to a high-temperature fluorination process only. This resulted in the carbon fiber not undergoing activation pretreatment. After high-temperature fluorination, the fluorine content on the carbon fiber surface was low, resulting in a low degree of binding between fluorine and the carbon fiber surface. The resulting free radicals were fewer and could not exist stably, which would hinder the subsequent composite with resin.
[0102] In Comparative Example 4, the operation of removing the fluorine and nitrogen mixture with a fluorine volume percentage of 5% from the stainless steel reactor at high temperature was changed to first cooling to room temperature before removing the mixture. This caused the free radicals that were originally active at high temperature to be quenched during the cooling process, reducing the active reaction sites of the fluorinated layer on the carbon fiber surface. As a result, the mechanical properties of the prepared composite material were reduced.
[0103] In Comparative Example 5, the step of modifying fluorinated carbon fiber plain weave fabric with polypropylene resin was omitted, and the fluorinated carbon fiber plain weave fabric was directly composited with polyphenylene sulfide resin. The melt viscosity of polyphenylene sulfide resin is relatively high, and without the induction of polypropylene as an intermediate layer, the wettability of polyphenylene sulfide resin and fluorinated carbon fiber plain weave fabric is poor, which leads to a decrease in the performance of composite material. In addition, the problem of modulus mismatch between fluorinated carbon fiber plain weave fabric and polyphenylene sulfide resin cannot be alleviated by polypropylene resin intermediate layer, resulting in a decrease in the overall mechanical properties of composite material.
[0104] In Comparative Example 6, the content ratio of fluorinated carbon fiber plain weave fabric to polypropylene resin and polyphenylene sulfide resin was adjusted. The increase in polypropylene resin content was not conducive to the complete free radical transfer mechanism, which prevented polypropylene resin from forming covalent crosslinks with polyphenylene sulfide resin and reduced the performance of composite materials. In addition, the decrease in the content of carbon fiber plain weave fabric in composite materials would lead to a reduction in the amount of carbon fiber that plays a reinforcing role in composite materials, resulting in a decrease in the mechanical properties of the prepared composite materials.
[0105] In summary, based on the performance results of Examples 1-5 and Comparative Examples 1-6, it can be found that the two-step fluorination of carbon fibers at room temperature and high temperature in this invention forms a highly reactive fluorinated layer on the surface of the carbon fibers. Subsequently, a small amount of polypropylene resin is used to graft and modify the fluorinated carbon fibers. The free radicals in the fluorinated layer undergo a molecular chain breaking and grafting process with the polypropylene resin. Then, it is compounded with polyphenylene sulfide resin. By utilizing the reaction characteristics of polyphenylene sulfide resin with free radicals, covalent bonds are formed between the polypropylene resin intermediate layer and the polyphenylene sulfide resin, which enhances the wettability and bonding degree between the carbon fibers and the polyphenylene sulfide resin, and can effectively improve the mechanical properties of carbon fiber reinforced thermoplastic resin composites.
[0106] Although the present invention has been described in detail in this specification with general description and specific embodiments, some modifications or improvements can be made to it, which will be obvious to those skilled in the art. Therefore, all such modifications or improvements made without departing from the spirit of the present invention are within the scope of protection claimed by the present invention.
Claims
1. A method for preparing a high-strength interlayer shear carbon fiber reinforced thermoplastic resin composite material, characterized in that, Includes the following steps: (1) Fluoride carbon fibers to form fluorinated carbon fibers; (2) The fluorinated carbon fiber is composited with polypropylene resin to obtain polypropylene resin modified fluorinated carbon fiber. (3) The polypropylene resin-modified fluorinated carbon fiber is combined with polyphenylene sulfide resin and cured to obtain the high-strength high-layer inter-shear carbon fiber reinforced thermoplastic resin composite material.
2. The preparation method according to claim 1, characterized in that, The carbon fiber mentioned in step (1) includes at least one of the following: carbon fiber filament, carbon fiber staple filament, carbon fiber unidirectional tape, carbon fiber nonwoven fabric, carbon fiber felt, carbon fiber paper, carbon fiber fabric, carbon fiber filament with sizing agent on its surface, carbon fiber staple filament with sizing agent on its surface, carbon fiber unidirectional tape with sizing agent on its surface, carbon fiber nonwoven fabric with sizing agent on its surface, carbon fiber felt with sizing agent on its surface, carbon fiber paper with sizing agent on its surface, and carbon fiber fabric with sizing agent on its surface.
3. The preparation method according to claim 2, characterized in that, The fluorination treatment method described in step (1) is either an independent fluorination treatment or a continuous fluorination treatment; The independent fluorination process is as follows: a fluorinated mixture is mixed with the carbon fiber in a sealed metal cavity, and the fluorinated mixture is extracted after the mixing is completed to obtain the fluorinated carbon fiber. The continuous fluorination process involves continuously drawing the carbon fibers at a constant speed through a well-sealed tunnel while simultaneously introducing a fluorinated mixture to ultimately obtain the fluorinated carbon fibers. The carbon fibers do not include short carbon fiber filaments and / or short carbon fiber filaments with a sizing agent on their surface.
4. The preparation method according to claim 3, characterized in that, The fluorinated mixture is a mixture of fluorine and an inert gas, wherein the volume percentage of fluorine in the fluorinated mixture is 1-20%, and the inert gas includes at least one of nitrogen, helium, argon, and xenon.
5. The preparation method according to claim 3, characterized in that, Both the independent fluorination treatment and the continuous fluorination treatment are two-step fluorination processes, namely, sequential room temperature fluorination treatment and high temperature fluorination treatment.
6. The preparation method according to claim 5, characterized in that, In the independent fluorination process, the pressure of the fluorinated mixed gas in the room temperature fluorination process is 20~40 kPa, the reaction temperature is room temperature, and the reaction time is 120~180 min; the pressure of the fluorinated mixed gas in the high temperature fluorination process is 5~20 kPa, the reaction temperature is 70~300℃, and the reaction time is 30~120 min. And / or, in the continuous fluorination treatment, the flow rate of the fluorinated mixed gas in the room temperature fluorination treatment is 5~10L / min, the temperature inside the tunnel is room temperature, and the residence time of the carbon fiber in the tunnel is 10~20min; the flow rate of the fluorinated mixed gas in the high temperature fluorination treatment is 1~5L / min, the temperature inside the tunnel is 70~300℃, and the residence time of the carbon fiber in the tunnel is 3~5min.
7. The preparation method according to claim 6, characterized in that, The independent fluorination treatment specifically refers to: The carbon fiber is placed in a sealed metal cavity, and the gas in the sealed metal cavity is replaced with an inert gas. The specific operation of the replacement is to evacuate the gas in the sealed metal cavity to form a vacuum, and then introduce an inert gas to atmospheric pressure. After replacing the gas in the sealed metal cavity 3 to 5 times, the vacuum inside the sealed metal cavity is maintained. At room temperature, an inert gas is introduced to a pressure of 1 to 3 kPa in the sealed metal cavity, and the pressure is stabilized for 3 to 5 minutes. A fluorinated mixture is introduced into the sealed metal cavity for room temperature fluorination treatment, and then all gases are evacuated at room temperature to form a vacuum. The sealed metal cavity is heated to the temperature for high-temperature fluorination treatment and held for 5-10 minutes. Then, a fluorinated mixed gas is introduced into the sealed metal cavity for high-temperature fluorination treatment. The temperature is then maintained at the high-temperature fluorination treatment temperature. The gas in the sealed metal cavity is evacuated to a vacuum. The gas in the sealed metal cavity is replaced with an inert gas 3-5 times. The vacuum inside the sealed metal cavity is maintained. An inert gas is introduced to atmospheric pressure, and the temperature is lowered to room temperature to obtain the fluorinated carbon fiber. The inert gas includes at least one of nitrogen, helium, argon, and xenon.
8. The preparation method according to claim 1, characterized in that, The amount of polypropylene resin added in step (2) is 0.1-1% of the volume of the fluorinated carbon fiber; And / or, the molding method described in step (2) includes at least one of injection molding, hot pressing, extrusion molding, and autoclave molding; preferably, the injection molding pressure is 7~10MPa, the injection temperature is 200~250℃, and the mold temperature is 60~80℃; preferably, the hot pressing pressure is 2~7MPa, the temperature is 180~220℃, the heating rate is 20~50℃ / min, the molding time is 15~30min, and the temperature is allowed to cool naturally to room temperature; preferably, the extrusion molding die head pressure is 2~5MPa, the extrusion temperature is 200~230℃, and the screw speed is 100~200rpm; preferably, the autoclave molding pressure is 1~5MPa, the temperature is 200~240℃, the heating rate is 5~20℃ / min, the molding time is 30~60min, and the temperature is allowed to cool naturally to room temperature.
9. The preparation method according to claim 1, characterized in that, The volume ratio of the polypropylene resin-modified fluorinated carbon fiber and the polyphenylene sulfide resin in step (3) is (0.1~1.2):1; And / or, the curing method described in step (3) includes at least one of injection molding, hot pressing, extrusion molding, and autoclave molding; preferably, the injection molding pressure is 7~12MPa, the injection temperature is 300~350℃, and the mold temperature is 100~120℃; the hot pressing pressure is 2~7MPa, the temperature is 300~320℃, the heating rate is 5~20℃ / min, the molding time is 15~30min, and the cooling rate is 20~50℃ / min; preferably, the extrusion molding die head pressure is 3~7MPa, the extrusion temperature is 300~330℃, and the screw speed is 100~200rpm; preferably, the autoclave molding pressure is 1~5MPa, the temperature is 280~320℃, the heating rate is 5~20℃ / min, the molding time is 30~60min, and the cooling rate is 20~50℃ / min.
10. A high-strength, high-layer interfacial shear carbon fiber reinforced thermoplastic resin composite material, characterized in that, It is prepared by any one of the preparation methods described in claims 1 to 9.