Modified PTFE composite material and preparation method thereof

Abstract

The invention relates to the technical field of high polymer materials, in particular to a modified PTFE composite material and a preparation method thereof.The modified PTFE composite material comprises polytetrafluoroethylene resin and an MXene material, and the MXene material accounts for 5%-15% of the total mass of the modified PTFE composite material. According to the modified PTFE composite material provided by the invention, a specific amount of MXene material is added into polytetrafluoroethylene resin, so that the wear resistance of the modified PTFE composite material is effectively improved, and the mechanical property, thermal stability and other properties of the modified PTFE composite material can be improved, thereby improving the overall performance of the modified PTFE composite material. Therefore, the method has a wider application range.

Description

Technical Field

[0001] The invention relates to the technical field of polymer materials, and in particular to a modified PTFE composite material and a preparation method thereof. Background Art

[0002] Polytetrafluoroethylene (PTFE) is widely used in aerospace, military, petrochemical and other fields due to its excellent chemical stability, high and low temperature resistance, corrosion resistance, excellent self-lubrication and electrical insulation. However, the main disadvantages of PTFE are poor mechanical properties, poor wear resistance, poor thermal conductivity, poor creep resistance, large linear expansion coefficient, etc., which limit the application of PTFE to a certain extent. In order to improve these properties, a common method is to prepare PTFE composite materials by adding various fillers or reinforcements. However, these prepared PTFE composite materials may have problems such as poor mechanical properties and poor wear resistance. Summary of the invention

[0003] The present invention provides a modified PTFE composite material and a preparation method thereof, which are used to solve the problems of poor mechanical properties and poor wear resistance of existing PTFE composite materials, and improve the wear resistance and overall performance of the PTFE composite material.

[0004] According to a first aspect of the present invention, the present invention provides a modified PTFE composite material, comprising a polytetrafluoroethylene resin and a MXene material, wherein the mass percentage of the MXene material in the total mass of the modified PTFE composite material is 5% to 15%.

[0005] Optionally, the mass percentage of the MXene material in the total mass of the modified PTFE composite material can be 5%, 6%, 7%, 8%, 9%, 10%, 11%, 12%, 13%, 14% or 15%, etc., and of course it can also be other values ​​within the above range, which is not limited here.

[0006] In the above scheme, the chemical formula of MXene material is M n+1 AX n, where (n=1~3), M represents early transition metals, such as Sc, Ti, Zr, V, Nb, Cr or Mo; A usually represents the third and fourth main group elements; X represents C or N elements. MXene, as a rising star in the 2D material family, is a type of metal carbide and metal nitride material with a two-dimensional layered structure. The excellent mechanical properties of MXene can preferentially improve the mechanical properties of polymers, and the interlayer force of MXene is weak, and adjacent layers are easily peeled off, which makes MXene materials have excellent self-lubricating properties. Compared with traditional lubricating fillers (carbon nanotubes, graphite, graphene, etc.), MXene also has strong interface coupling characteristics, which can form a firm self-lubricating transfer film on the friction contact surface, thereby significantly reducing the friction coefficient and wear rate. Based on the above characteristics, MXene has broad application prospects in friction and lubrication. The modified PTFE composite material of the present invention adds a specific amount of MXene material to the polytetrafluoroethylene resin, which effectively improves the wear resistance of the modified PTFE composite material while also improving the mechanical properties and thermal stability of the modified PTFE composite material, thereby improving the overall performance of the modified PTFE composite material and making it have a wider range of applications.

[0007] Furthermore, the mass percentage of the MXene material in the modified PTFE composite material is 7.5% to 12.5%.

[0008] Furthermore, the MXene material is a single-layer Ti3C2T obtained by etching the MAX phase Ti3AlC2 with HF generated in situ by HCl and LiF. x powder.

[0009] It should be noted that Ti3C2T x The "T" in represents the surface groups, which usually include -O, -OH, -F, etc. The presence of these functional groups has an important influence on the chemical properties, hydrophilicity, conductivity, etc. of the material. Different functional group combinations can lead to significant differences in material properties. "x" represents the number of surface groups that may exist on the surface of the material. "x" can change, indicating the diversity and number of surface groups.

[0010] In the above scheme, the single-layer Ti3C2T x The powder has better mechanical properties and better interface coupling characteristics, and can more effectively improve the overall performance of modified PTFE composite materials.

[0011] In addition, the surface of MXene materials can be functionalized to improve their compatibility with polymer matrices and give new functions to composite materials. For example, MXene can be surface modified by organic, inorganic or organic-inorganic hybrid modification methods to improve its application effect in PTFE composite materials.

[0012] Furthermore, the particle size of the MXene material is 300-500 mesh.

[0013] Furthermore, the polytetrafluoroethylene resin is a polytetrafluoroethylene suspension resin with an average particle size of 15 to 45 μm.

[0014] In the above scheme, the polytetrafluoroethylene suspension resin is a special form of PTFE, which exists in the form of a suspension during the production process and is usually used to make PTFE powder. This powder can be used for further processing, such as making various PTFE products through processes such as extrusion, molding or sintering. The suspension resin provides better uniformity and more precise control during the processing, thereby producing high-quality PTFE products with consistent performance. By selecting a polytetrafluoroethylene resin with a suitable particle size and morphology, it is more conducive to the preparation of modified PTFE composite materials with excellent performance and high quality.

[0015] Furthermore, the modified PTFE composite material has a hardness of 55-65 HD, a compression modulus of 135-200 MPa, a compression yield strength of 20-45 MPa, and a friction coefficient of 0.06-0.15. The modified PTFE composite material with these properties can be widely used in the manufacture of key seals for high-end equipment such as aviation, aerospace, and marine heavy industry.

[0016] According to a second aspect of the present invention, the present invention also provides a method for preparing the above-mentioned modified PTFE composite material, comprising the following steps: Step (1): preparing MXene materials; Step (2): uniformly mixing the prepared MXene material and the dried polytetrafluoroethylene resin, and pressing and molding to obtain a PTFE-based composite material precursor; Step (3): sintering the obtained PTFE-based composite material precursor at high temperature to obtain a modified PTFE composite material.

[0017] In the above scheme, the preparation method of the modified PTFE composite material of the present invention first prepares the MXene material, then mixes it with the dried polytetrafluoroethylene resin and presses it into shape, and then performs high-temperature sintering. The preparation method is simple and suitable for a wide range of applications. During the molding process, the MXene material can withstand high-temperature sintering and does not chemically react with PTFE, which helps to improve the multiple physical and chemical properties of PTFE.

[0018] Furthermore, the polytetrafluoroethylene resin is generally dried at 60-80° C. for 12-36 hours.

[0019] Furthermore, before pressing and molding, the MXene material and the dried polytetrafluoroethylene resin were dried by wet mixing and drying, specifically, the two powders were placed in anhydrous ethanol and mixed with an electric magnetic stirrer at a stirring rate of 1000-1400r / min. Subsequently, the alcohol was filtered off, and the sample was placed in an oven at a temperature of 50-70°C for 12-36h.

[0020] Furthermore, in step (2), the pressing molding is performed by cold pressing; preferably, the pressure of the cold pressing is 20-30 MPa, and the holding time is 1-2 min.

[0021] During the molding process, the amount of material for each pressed part should be evenly sprinkled into the mold cavity. Vibration or knocking methods should not be used to fill the material to avoid segregation caused by different filler weights. At the same time, it is not allowed to add materials in batches to prevent the product from being delaminated. The unit pressure should be appropriate during molding to ensure that the pressed parts are dense and pore-free, with high yield strength and wear resistance. The size of the unit pressure is related to the type, performance and content of the filler. During the molding process, the pressure should be applied slowly, and impact pressure should not be used. At the same time, 2 to 4 pressure relief and venting are required to discharge the air in the sample in time. By limiting the pressure, it helps to ensure that the green body has sufficient strength and density after molding. By limiting the holding time, the pressure can be evenly transmitted, and then the pressure can be slowly reduced. Finally, the upper and lower molds of the mold are slowly removed using a demolding frame, and the molded product is removed from the mold cavity using appropriate tools.

[0022] Furthermore, in step (3), the high temperature sintering is performed by heating the temperature to 350-400°C at a heating rate of 0.5-1.5°C / min, and keeping the temperature at 350-400°C for 1-3 hours; the cooling is performed by cooling the temperature to 300-340°C at a cooling rate of 0.5-1.5°C / min, keeping the temperature at 300-340°C for 1-3 hours, and then cooling to room temperature. It should be noted that room temperature generally refers to 20-30°C.

[0023] In the above scheme, by reasonably limiting the heating rate, it is possible to ensure that PTFE maintains a small internal and external temperature difference during the heating process, and prevent the PTFE product from expanding inconsistently inside and outside and causing cracking. Insulation is to keep the preformed product that has reached the sintering and curing temperature at this temperature for a period of time. As the temperature rises, the PTFE macromolecular chain begins to entangle irregularly. The insulation temperature and time determine the compactness of the molecular entanglement. If the temperature is lower than 350-400°C or the insulation time is lower than 1h, or even 50min, the PTFE molecular chain activity is poor and the product compactness is poor. If the sintering temperature is too long, it will cause excessive decomposition of PTFE, causing the product to blister. During the insulation process, the molecular motion of PTFE intensifies, the interface between particles disappears, and it becomes a dense and continuous whole. Therefore, the present invention has made special limitations on the insulation temperature and time of high-temperature sintering. Cooling is the process of cooling the preformed product that has been sintered from the insulation temperature to room temperature. In this process, the PTFE resin changes from an amorphous phase to a crystalline phase, and the product volume shrinks. The present invention stipulates that during the cooling process, the temperature is first lowered to 300-340°C at a cooling rate of 0.5-1.5°C / min, and kept at 300-340°C for 1-3 hours, so that the internal and external temperatures of the PTFE are reduced to the recrystallization temperature, which is beneficial to the cooling and shrinkage of the PTFE to improve the performance, and then cooled to room temperature with the furnace.

[0024] Furthermore, in step (3), the high temperature sintering is carried out under an inert gas, and the pressure is in a positive pressure state. Optionally, the inert gas includes nitrogen, argon, etc. Using an inert gas for high temperature sintering can improve product quality, protect the material from oxidation and other harmful reactions, and ensure the stability and controllability of the sintering process.

[0025] Furthermore, N2 atmosphere protection is used for high-temperature sintering. Before heating, the air in the furnace is repeatedly replaced with N2 until all the air is replaced by N2. Thereafter, N2 is replenished at regular intervals to keep the pressure in the furnace in a positive pressure state.

[0026] The present invention provides a modified PTFE composite material. By adding a specific amount of MXene material to polytetrafluoroethylene resin, the wear resistance of the modified PTFE composite material can be effectively improved while the mechanical properties and thermal stability of the modified PTFE composite material can be improved, thereby improving the overall performance of the modified PTFE composite material and making it have a wider range of applications. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] In order to more clearly illustrate the technical solutions in the present invention or the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0028] Figure 1 This is a thermal sintering process parameter diagram of the modified PTFE composite materials of Examples 1 to 5 of the present invention and the PTFE material of Comparative Example 1.

[0029] Figure 2 It is a compression performance test curve chart of the modified PTFE composite materials of Examples 1 to 5 of the present invention and the PTFE material of Comparative Example 1.

[0030] Figure 3 This is a test chart of the friction coefficient of the modified PTFE composite materials of Examples 1 to 5 of the present invention and the PTFE material of Comparative Example 1.

[0031] Figure 4 TG curves of the modified PTFE composite material of Example 4 and the pure PTFE of Comparative Example 1 during the thermogravimetric test. DETAILED DESCRIPTION

[0032] In order to make the purpose, technical solution and advantages of the present invention clearer, the technical solution of the present invention will be clearly and completely described below in conjunction with the drawings of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0033] The test methods used in the following examples and comparative examples are: 1. Mechanical properties test

[0034] Hardness is tested according to JB / T 6148-2017. The same sample is 6 mm apart, and 5 hardness testers are measured and the average value is calculated; The compression performance was tested according to GB / T1041-2008, the compression rate was 20 mm / min, and the final result was the average value of 5 parallel samples.

[0035] 2. Friction performance test: The test was carried out using the reciprocating module of the MFT-4000 multifunctional material surface properties tester.

[0036] Specifically: the test load is 20 N, the reciprocating frequency is 1 Hz, the time is 30 min, the grinding distance is 5 mm, the grinding ball is an alumina ceramic ball with a diameter of 5 mm, the experimental sample size is 10 mm×10 mm×4 mm, and the friction coefficient of the composite material is recorded during the experiment. Each sample is repeated 5 times and the average value is taken.

[0037] 3. Thermogravimetric analysis test: The test was carried out using a thermogravimetric analysis tester (TG 2009 F3-Tarsus).

[0038] Specifically: The test was carried out under N2 protective atmosphere, with N2 flow rate of 40 mL / min, purge gas flow rate of 60 mL / min, temperature test range of 20~750 ℃, heating rate of 20 ℃ / min, and cooling rate of 10 ℃ / min.

[0039] Sources of raw materials used in the embodiments and comparative examples: PTFE: specification 45 μm, brand M-18F, purchased from Daikin Industries, Ltd., Japan; Ti3AlC2 powder: particle size 400 mesh, purchased from Jilin Yiyi Technology Co., Ltd.

[0040] Examples 1 to 5, Comparative Example 1

[0041] This embodiment provides a method for preparing a modified PTFE composite material, comprising the following steps: Step (1) Using HF generated in situ by HCl and LiF to etch Ti3AlC2-MAX to obtain a single layer of Ti3C2T x Obtain MXene materials.

[0042] HF generated in situ by HCl and LiF was used to etch away the Ti-Al bond in Ti3AlC2-MAX to obtain the Ti-C bond. 2 gLiF and 30 mL of 9 mol / L HCl solution were placed in a reactor, and in a constant temperature water bath, the temperature was adjusted to 35 °C, the speed was 500-800 r, and stirred for 5 min. Then, 2 g Ti3AlC2 was added during the stirring process, 0.1-0.2 g each time (after each addition, the bubbles disappeared completely before the next addition), and then reacted for 48 h. After the reaction was completed, the reaction product was poured into a centrifuge tube, divided equally into two centrifuge tubes, and water was added to 45 mL respectively. The mass difference between the two centrifuge tubes was within 0.05 g by weighing, and the two centrifuge tubes were shaken evenly. Centrifuged at 3500 r / min for 5 min, the upper clear liquid was taken out and poured into the waste liquid bottle, and 45 mL of water was added. Repeat the experiment several times. When the supernatant cannot be separated, the centrifugation is finished, and the liquid in the centrifuge tube is poured into a beaker after shaking, and then placed in an ultrasonic machine for ice bath ultrasonication for 1 h. After the ultrasonication is finished, the supernatant is poured into two centrifuge tubes, and then balanced, centrifuged at 3500 r / min for 1 h, and then placed in a refrigerator for freezing, and then placed in a freeze dryer for drying for 48 h to obtain the desired powdered single-layer Ti3C2T x .

[0043] Step (2) Preparation of PTFE-based composite material precursor: Dry PTFE at 70°C for 24 hours to obtain dried PTFE. After drying, a wet mixing drying method is used to place the MXene material with a particle size of 400 mesh and the dried PTFE in anhydrous ethanol according to the mass ratio shown in Table 1, and mix them with an electric magnetic stirrer at a stirring rate of 1200 r / min. Subsequently, the alcohol is filtered off, and the sample is placed in an oven at a temperature of 60°C for 24 hours.

[0044] After drying, transfer 10~11g of the dried mixture to a special mold at room temperature, apply 25MPa pressure, and hold the pressure for 1 min to form. During the molding process, the amount of material for each pressed piece should be evenly sprinkled into the mold cavity, and the material should not be filled by vibration or knocking to avoid segregation due to different filler weights. At the same time, it is not allowed to add materials in batches to prevent the product from stratification. The unit pressure should be appropriate during molding to ensure that the pressed pieces are dense and pore-free, with high yield strength and wear resistance. The size of the unit pressure is related to the type, performance and content of the filler. During the molding process, the pressure should be applied slowly, and impact pressure should not be used. At the same time, 2~4 pressure relief and deflation are required to discharge the air in the sample in time. Hold the pressure for 1 min to ensure that the pressure is evenly transmitted, and then slowly reduce the pressure. Finally, use the demolding frame to slowly remove the upper and lower molds of the mold, and use appropriate tools to remove the molded product from the mold cavity.

[0045] Step (3) sintering the PTFE-based composite material precursor at high temperature and cooling to obtain a PTFE composite material filled with multiple inorganic materials. The high temperature sintering and cooling process parameters are as follows: Figure 1 shown.

[0046] During the heating stage, the sintering heating rate is controlled within 370 °C at 1 °C / min to ensure that the PTFE maintains a small internal and external temperature difference during the heating process to prevent the PTFE product from cracking due to inconsistent internal and external expansion. The temperature is kept at 370 °C for 2 h.

[0047] Insulation is to keep the preformed product that has reached the sintering and curing temperature at this temperature for a period of time. As the temperature rises, the PTFE macromolecular chains begin to entangle irregularly. The insulation temperature and time determine the density of the molecular entanglement. When the temperature is lower than 370 ℃ or the insulation time is lower than 50 min, the PTFE molecular chain activity is poor and the product density is poor. If the sintering temperature is too long, PTFE will decompose too much and cause the product to blister. During the insulation process, the molecular movement of PTFE intensifies and the interface between particles disappears. It becomes a dense and continuous whole. Therefore, the sintering temperature of 370 ℃ was used for 2 h in the experiment.

[0048] Cooling is the process of cooling the sintered preformed product from the holding temperature to room temperature. In this process, the PTFE resin changes from amorphous to crystalline phase, and the product volume shrinks. In the temperature range of 320~370℃, the cooling rate is controlled at 1℃ / min, and the temperature is kept at 320℃ for 2 hours, so that the temperature inside and outside of PTFE drops to the recrystallization temperature, which is conducive to the cooling and shrinkage of PTFE to improve its performance, and then it is cooled to room temperature with the furnace.

[0049] Comparative Example 2

[0050] This comparative example provides a method for preparing a modified PTFE composite material, which is different from Example 4 in that an equal amount of alkali-free glass fiber is used to replace the MXene material.

[0051] Next, the performance tests of the materials of Examples 1 to 5 and Comparative Examples 1 to 2 were carried out respectively. The density test standard was carried out in accordance with the national standard GT / T1463-2005 "Fiber reinforced plastic density and relative density test". The hardness test standard was carried out in accordance with the national standard GB / T2411-2008 "Plastics and hard rubber using a hardness tester to measure the indentation hardness (Shore hardness)". The compression performance test standard was carried out in accordance with GB / T1041-2008 "Plastics-Determination of compression properties". The friction coefficient test standard was carried out in accordance with the national standard GB / T 10006-2021 "Determination of the coefficient of friction of plastic films and sheets". The thermogravimetric analysis test was carried out in accordance with the national standard GB / T27761-2011 "Test method for weight loss and residual amount of thermogravimetric analyzer". The test results are shown in Table 1 below. The stress-strain curves of PTFE filled with different contents of MXene during compression are shown in Table 1. Figure 2 The friction coefficient changes during the experiment as shown in Figure 3 Example 4 and comparative example 1 were selected for thermogravimetric analysis, and the mass change during the weight loss process was recorded. The TG curve is shown as follows: Figure 4 shown.

[0052] Table 1

[0053] According to the experimental results in Table 1, combined with Figure 2-4It can be seen that the modified PTFE composite material obtained by modifying the MXene material in the present invention has excellent mechanical properties, hardness of 59.8~63.8HD, compression modulus of 136.99~199.85Mpa, compression yield strength of 21~42Mpa, maximum compression modulus and compression strength of 199.85 MPa and 42 MPa, respectively, which are 37.4% and 152.7% higher than pure PTFE (compression modulus and compression strength are 145.44 MPa and 16.62 MPa, respectively). The modified PTFE composite material of the present invention has friction resistance, a friction coefficient of 0.061~0.112, and a minimum friction coefficient of 0.061, which is only 0.03 higher than pure PTFE (friction coefficient of 0.031), and still maintains good friction performance. It can be seen from the comparison results of Example 4 and Comparative Example 2 that compared with other modified materials (glass fiber of Comparative Example 2), the modified PTFE composite material obtained by modifying the MXene material in the present invention has lower density, better mechanical properties, and higher friction coefficient. The modified PTFE composite material of the present invention maintains the good thermal stability of PTFE. After adding MXene, the decomposition rate of PTFE is increased, but the decomposition temperature remains unchanged.

[0054] 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 make equivalent replacements for some of the technical features therein. However, these modifications or replacements do not deviate the essence of the corresponding technical solutions from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A modified PTFE composite material, characterized in that: It includes polytetrafluoroethylene resin and MXene material, and the mass percentage of the MXene material in the total mass of the modified PTFE composite material is 5% to 15%.

2. The modified PTFE composite material according to claim 1, characterized in that The mass percentage of the MXene material in the modified PTFE composite material is 7.5% to 12.5%.

3. The modified PTFE composite material according to claim 1, characterized in that The MXene material is a single-layer Ti3C2T obtained by etching the MAX phase Ti3AlC2 with HF generated in situ by HCl and LiF. x powder.

4. The modified PTFE composite material according to claim 1 or 3, characterized in that: The particle size of the MXene material is 300-500 mesh.

5. The modified PTFE composite material according to claim 1, characterized in that The polytetrafluoroethylene resin is a polytetrafluoroethylene suspension resin with an average particle size of 15 to 45 μm.

6. The modified PTFE composite material according to any one of claims 1 to 5, characterized in that: The modified PTFE composite material has a hardness of 55-65 HD, a compression modulus of 135-200 MPa, a compression yield strength of 20-45 MPa, and a friction coefficient of 0.06-0.

15.

7. The method for preparing the modified PTFE composite material according to any one of claims 1 to 6, characterized in that: The steps include: Step (1): preparing MXene materials; Step (2): uniformly mixing the prepared MXene material and the dried polytetrafluoroethylene resin, and pressing and molding to obtain a PTFE-based composite material precursor; Step (3): sintering the obtained PTFE-based composite material precursor at high temperature and cooling it to obtain a modified PTFE composite material.

8. The preparation method according to claim 7, characterized in that: In step (2), the pressing molding is cold pressing; preferably, the pressure of cold pressing is 20-30 MPa, and the holding time is 1-2 min.

9. The preparation method according to claim 7, characterized in that: In step (3), the high temperature sintering is performed by heating the temperature to 350-400°C at a heating rate of 0.5-1.5°C / min, and keeping the temperature at 350-400°C for 1-3 hours; the cooling is performed by cooling the temperature to 300-340°C at a cooling rate of 0.5-1.5°C / min, keeping the temperature at 300-340°C for 1-3 hours, and then cooling to room temperature.

10. The preparation method according to claim 7, characterized in that: In step (3), the high temperature sintering is carried out under an inert gas and the pressure is in a positive pressure state.

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