Preparation method of modified attapulgite-polytetrafluoroethylene composite material

Abstract

The invention discloses a preparation method of a modified attapulgite-polytetrafluoroethylene composite material. The LDHs are loaded on the surface of ATP through a coprecipitation method, and a PTFE matrix is synergistically enhanced through the hydrogen-bond interaction of the LDHs and the fiber structure of ATP. The tensile strength of the obtained composite material reaches 35.2 MPa, the friction coefficient is as low as 0.174, the wear rate is only 1 / 116 of that of pure PTFE, and the composite material is suitable for the high-wear-resistance fields of mechanical sealing, aerospace and the like. The method is simple in process and low in cost, and has remarkable industrial value.

Description

Technical Field

[0001] The present invention relates to the technical field of polymer composites, and particularly relates to a method for preparing a high-performance polytetrafluoroethylene composite material by modifying attapulgite with layered double hydroxide. Background Art

[0002] Polytetrafluoroethylene (PTFE) is a typical polymer-based self-lubricating material. Due to its excellent chemical inertness, low friction coefficient, excellent self-lubricating performance, and broad temperature application range, it is widely used as stable components in air bearings, seal assemblies, and other industrial sectors. However, the application of PTFE in high-performance requirement fields is restricted due to its poor mechanical properties and wear resistance. Therefore, in actual industrial applications, it is required to modify PTFE, aiming to further expand its application scope in various fields while retaining its unique properties.

[0003] Attapulgite (ATP) is an aquiferous banded magnesium-aluminum silicate clay mineral with a fibrous morphology. Due to the relatively simple pretreatment technology, natural abundance, and simplicity of the refining process of ATP, the cost of ATP is very low. ATP has attracted attention in tribology research due to its large specific surface area (the internal specific surface area is as high as 300 - 400 m 2 / g), special pore structure, excellent thermal properties, and mechanical properties, etc. ATP can be a promising anti-wear nano-filler for PTFE-based composites. However, the low surface roughness and poor dispersibility of ATP in the polymer matrix usually lead to weak interfacial bonding, which is an important reason affecting the performance of the composite material. Therefore, how to improve the interfacial bonding between ATP and the polymer matrix is a problem worthy of more attention.

[0004] The present invention uses the co-precipitation method to prepare a layered double hydroxide (LDHs)-loaded modified ATP-based hybrid ATP@LDHs, and enhances the friction performance of the polytetrafluoroethylene composite material through ATP@LDHs. The filling modification can maximize its friction performance and prepare a high-wear-resistant polytetrafluoroethylene composite material. Moreover, the process of the present invention has the advantages of simple process, low cost, suitability for mass production, etc., which is conducive to industrialization promotion. Summary of the Invention

[0005] The object of the present invention is to provide a preparation method of a modified attapulgite-polytetrafluoroethylene composite material. The preparation method of the modified attapulgite-polytetrafluoroethylene composite material of the present invention is to load layered double hydroxides (LDHs) on the surface of attapulgite by a coprecipitation method for layered double hydroxide modification, and then use the hydrogen bond action of LDHs and the fibrous structure of attapulgite to fill and modify polytetrafluoroethylene, which is applicable to high wear-resistant fields such as mechanical seals and aerospace. The process of the present invention is simple, has low cost, is suitable for mass production and other advantages, and is conducive to industrialization promotion.

[0006] In order to achieve the above object, the technical solution of the present invention is as follows: A preparation method of a modified attapulgite-polytetrafluoroethylene composite material, wherein the preparation method of the modified attapulgite-polytetrafluoroethylene composite material is to load layered double hydroxides on the surface of attapulgite by a coprecipitation method for layered double hydroxide modification, and then use the hydrogen bond action of LDHs and the fibrous structure of attapulgite to fill and modify polytetrafluoroethylene.

[0007] The foregoing preparation method is carried out according to the following steps:

[0008] (1) Preparation of metal salt solution: Weigh 2.434 - 7.301 g of calcium chloride hexahydrate and 1.338 - 4.016 g of aluminum chloride hexahydrate, add them to 100 - 300 mL of deionized water, stir and dissolve at room temperature to obtain a metal salt solution for standby;

[0009] (2) Preparation of alkali solution: Disperse 2.664 - 7.992 g of NaOH and 1.5 - 4.5 g of attapulgite powder in 100 - 300 mL of deionized water to obtain an alkali solution for standby;

[0010] (3) Modification of attapulgite: Drop 100 - 300 mL of the metal salt solution into 100 - 300 mL of the alkali solution under magnetic stirring to obtain an ATP@LDHs suspension; Seal and place it in an oven at 70 - 90 °C for aging for 9 - 12 hours, filter, dry at 60 - 80 °C for 10 - 14 h, pulverize and pass through a 400 - 600 mesh sieve to obtain ATP@LDHs for standby;

[0011] (4) Modification of polytetrafluoroethylene: Freeze the polytetrafluoroethylene powder at -2 - -4 °C for 7 - 9 h, then mix the polytetrafluoroethylene powder and ATP@LDHs for 15 - 25 min, and the mixing speed is 1000 - 1500 r / min to obtain an ATP@LDHs-PTFE mixed powder;

[0012] (5) Compression molding: Pour the ATP@LDHs-PTFE mixed powder into a cold pressing mold, and keep the pressure at 40-60 MPa for 12-18 minutes at room temperature; After demolding, trim and remove burrs to make it smooth and flat, and obtain a compression-molded composite material plate;

[0013] (6) Sintering treatment: Put the compression-molded composite material plate into a sintering furnace for sintering. The furnace temperature rises to 320-330 °C at a rate of 0.8-1.2 °C / min and keeps warm for 50-70 minutes; Then rise to 365-385 °C and keep warm for 80-100 minutes; Cool down to 320-330 °C and keep warm for 50-70 minutes; Naturally cool to room temperature; Then cut and process the sintered composite material plate to obtain the ATP@LDHs / PTFE composite material.

[0014] In the aforementioned step (1), preparation of the metal salt solution: Weigh 4.867 g of calcium chloride hexahydrate and 2.677 g of aluminum chloride hexahydrate, add them to 200 mL of deionized water, stir and dissolve at room temperature to obtain the metal salt solution for standby.

[0015] In the aforementioned step (2), preparation of the alkali solution: Disperse 5.328 g of NaOH and 3 g of attapulgite powder in 200 mL of deionized water to obtain the alkali solution for standby.

[0016] In the aforementioned step (3), modification of attapulgite: Drop 200 mL of the metal salt solution into 200 mL of the alkali solution under magnetic stirring to obtain an ATP@LDHs suspension; Seal it and place it in an 80 °C oven for aging for 10 hours, filter, dry at 70 °C for 12 h, and crush and pass through a 500-mesh sieve to obtain ATP@LDHs for standby.

[0017] In the aforementioned step (4), modification of polytetrafluoroethylene: Freeze the polytetrafluoroethylene powder at -3 °C for 8 h, then mix the polytetrafluoroethylene powder and ATP@LDHs for 20 min, and the mixing speed is 1200 r / min; Obtain the ATP@LDHs-PTFE mixed powder.

[0018] In the aforementioned step (4), the modified attapulgite accounts for 4-20 wt% of the total weight of polytetrafluoroethylene.

[0019] Specifically, in the aforementioned step (4), the modified attapulgite accounts for 4-16 wt% of the total weight of polytetrafluoroethylene.

[0020] In the aforementioned step (5), compression molding: Pour the ATP@LDHs-PTFE mixed powder into a cold pressing mold, and keep the pressure at 50 MPa for 15 minutes at room temperature; After demolding, trim and remove burrs to make it smooth and flat, and obtain a compression-molded composite material plate.

[0021] In the aforementioned step (6), sintering treatment: put the pressed composite material plate into a sintering furnace for sintering. The furnace temperature is raised to 327 °C at a rate of 1 °C / min and held for 60 minutes; then it is raised to 375 °C and held for 90 minutes; then it is lowered to 327 °C and held for 60 minutes; and then it is naturally cooled to room temperature. Then, the sintered composite material plate is cut and processed to obtain the ATP@LDHs / PTFE composite material.

[0022] Compared with the prior art, the present invention has the following beneficial effects:

[0023] 1. The present invention uses LDHs to load and modify ATP, which not only retains the original structure of ATP, but also improves its surface roughness and compatibility in the matrix. And ATP@LDHs has an excellent enhancing effect on the anti-friction and wear resistance performance of the PTFE matrix. The wear rate of the polytetrafluoroethylene composite material filled with ATP@LDHs is only 1 / 100 - 1 / 200 of that of pure polytetrafluoroethylene. At the same time, the modified polytetrafluoroethylene composite material filled with ATP@LDHs has a lower friction coefficient, and the lowest friction coefficient reaches 0.174, and the lowest wear rate is only 0.142×10 -13 m 3 / Nm.

[0024] 2. LDHs is a two-dimensional layered structure with a large specific surface area and exchangeable interlayer anions. At the same time, it can form hydrogen bond interactions with the PTFE molecular chain, and LDHs has good dispersibility and compatibility in the PTFE matrix. Therefore, preparing the ATP hybrid loaded with LDHs not only retains the original structure of ATP, but also improves its surface roughness and the ability to anchor with the polymer matrix. Therefore, the modified polytetrafluoroethylene composite material filled with ATP@LDHs in the present invention can maintain the excellent mechanical properties of polytetrafluoroethylene, and its tensile strength exceeds 20 MPa.

[0025] 3. The present invention uses the method of filling and modification to enhance the wear resistance of polytetrafluoroethylene, which is applicable to high-wear fields such as mechanical seals and aerospace. The production process is simple and can realize industrial large-scale production. Description of the Drawings

[0026] Figure 1 : Tensile strength of LDHs / PTFE, ATP / PTFE and ATP@LDHs / PTFE composite materials;

[0027] Figure 2 : Friction coefficients of LDHs / PTFE, ATP / PTFE and ATP@LDHs / PTFE composite materials;

[0028] Figure 3: Wear rates of LDHs / PTFE, ATP / PTFE, and ATP@LDHs / PTFE composites;

[0029] Figure 4 : Friction coefficient change curves of LDHs / PTFE, ATP / PTFE, and ATP@LDHs / PTFE composites with different contents of LDHs, ATP, and ATP@LDHs (a is 4 wt% content; b is 8 wt% content; c is 12 wt% content; d is 16 wt% content);

[0030] Figure 5 : Finished product diagrams of pure polytetrafluoroethylene and polytetrafluoroethylene composites (a is pure polytetrafluoroethylene; b is polytetrafluoroethylene composite after adding 4 wt% ATP@LDHs). Detailed implementation mode

[0031] The present invention will be specifically described below through examples. It is necessary to point out that the following examples are only used to further illustrate the present invention and should not be construed as limiting the protection scope of the present invention.

[0032] Example 1

[0033] Preparation method of modified attapulgite-polytetrafluoroethylene composite (ATP@LDHs / PTFE):

[0034] (1) Preparation of metal salt solution: Weigh 4.867 g of calcium chloride hexahydrate and 2.677 g of aluminum chloride hexahydrate (Ca 2+ :Al 3+ The molar ratio is 2:1), add it to 200 mL of deionized water, stir and dissolve at room temperature to obtain a metal salt solution for standby.

[0035] (2) Preparation of alkali solution: Disperse 5.328 g of NaOH and 3 g of attapulgite powder in 200 mL of deionized water to obtain an alkali solution for standby.

[0036] (3) Modification of attapulgite: Drop 200 mL of the metal salt solution into 200 mL of the alkali solution under magnetic stirring to obtain an ATP@LDHs suspension; seal it and place it in an oven at 80 °C for 10 hours of aging, filter, dry at 70 °C for 12 h, and pulverize through a 500-mesh sieve to obtain ATP@LDHs for standby.

[0037] (4) Modification of polytetrafluoroethylene: Freeze the polytetrafluoroethylene powder at -3 °C for 8 h, then mix the polytetrafluoroethylene powder and ATP@LDHs for 20 min. The modified attapulgite accounts for 4 wt% of the total weight of polytetrafluoroethylene, and the mixing speed is 1200 r / min; obtain ATP@LDHs-PTFE mixed powder.

[0038] (5) Compression molding: Pour the ATP@LDHs-PTFE mixed powder into a cold pressing mold, and keep the pressure at 50 MPa for 15 min at room temperature; after demolding, trim and remove the burrs to make it smooth and flat, thus obtaining the compression-molded composite material plate.

[0039] (6) Sintering treatment: Put the compression-molded composite material plate into a sintering furnace for sintering. The furnace temperature is raised to 327 °C at a rate of 1 °C / min and kept for 60 minutes; then it is raised to 375 °C and kept for 90 minutes; then it is lowered to 327 °C and kept for 60 minutes; it is naturally cooled to room temperature; then the sintered composite material plate is cut and processed to obtain the ATP@LDHs / PTFE composite material.

[0040] Example 2

[0041] Preparation method of modified attapulgite-polytetrafluoroethylene composite material (ATP@LDHs / PTFE):

[0042] (1) Preparation of metal salt solution: Weigh 4.867 g of calcium chloride hexahydrate and 2.677 g of aluminum chloride hexahydrate (Ca 2+ :Al 3+ with a molar ratio of 2:1), add them to 200 mL of deionized water, stir and dissolve at room temperature to obtain the metal salt solution for standby.

[0043] (2) Preparation of alkali solution: Disperse 5.328 g of NaOH and 3 g of attapulgite powder in 200 mL of deionized water to obtain the alkali solution for standby.

[0044] (3) Modification of attapulgite: Drop 200 mL of the metal salt solution into 200 mL of the alkali solution under magnetic stirring to obtain the ATP@LDHs suspension; seal it and place it in an 80 °C oven for aging for 10 hours, filter, dry at 70 °C for 12 h, and pulverize and pass through a 500-mesh sieve to obtain ATP@LDHs for standby.

[0045] (4) Modification of polytetrafluoroethylene: Freeze the polytetrafluoroethylene powder at -3 °C for 8 h, then mix the polytetrafluoroethylene powder and ATP@LDHs for 20 min. The modified attapulgite accounts for 8 wt% of the total weight of polytetrafluoroethylene, and the mixing speed is 1200 r / min; obtain the ATP@LDHs-PTFE mixed powder.

[0046] (5) Compression molding: Pour the ATP@LDHs-PTFE mixed powder into a cold pressing mold, and keep the pressure at 50 MPa for 15 min at room temperature; after demolding, trim and remove the burrs to make it smooth and flat, thus obtaining the compression-molded composite material plate.

[0047] (6) Sintering treatment: Put the pressed composite material plate into a sintering furnace for sintering. The furnace temperature is raised to 327 °C at a rate of 1 °C / min and held for 60 minutes; then it is raised to 375 °C and held for 90 minutes; then it is lowered to 327 °C and held for 60 minutes; and then it is naturally cooled to room temperature; then the sintered composite material plate is cut and processed to obtain the ATP@LDHs / PTFE composite material.

[0048] Example 3

[0049] Preparation method of modified attapulgite-polytetrafluoroethylene composite material (ATP@LDHs / PTFE):

[0050] (1) Preparation of metal salt solution: Weigh 4.867 g of calcium chloride hexahydrate and 2.677 g of aluminum chloride hexahydrate (Ca 2+ :Al 3+ The molar ratio is 2:1), add 200 mL of deionized water, stir and dissolve at room temperature to obtain a metal salt solution for standby.

[0051] (2) Preparation of alkali solution: Disperse 5.328 g of NaOH and 3 g of attapulgite powder in 200 mL of deionized water to obtain an alkali solution for standby.

[0052] (3) Modification of attapulgite: Drop 200 mL of the metal salt solution into 200 mL of the alkali solution under magnetic stirring to obtain an ATP@LDHs suspension; seal it and place it in an 80 °C oven for aging for 10 hours, filter, dry at 70 °C for 12 h, and crush and pass through a 500-mesh sieve to obtain ATP@LDHs for standby.

[0053] (4) Modification of polytetrafluoroethylene: Freeze the polytetrafluoroethylene powder at -3 °C for 8 h, then mix the polytetrafluoroethylene powder and ATP@LDHs for 20 min. The modified attapulgite accounts for 12 wt% of the total weight of polytetrafluoroethylene, and the mixing speed is 1200 r / min; obtain the ATP@LDHs-PTFE mixed powder.

[0054] (5) Compression molding: Pour the ATP@LDHs-PTFE mixed powder into a cold pressing mold, and keep the pressure at 50 MPa for 15 min at room temperature; after demolding, trim and remove the burrs to make it smooth and flat, and obtain the pressed composite material plate.

[0055] (6) Sintering treatment: Put the pressed composite material plate into a sintering furnace for sintering. The furnace temperature is raised to 327 °C at a rate of 1 °C / min and held for 60 minutes; then it is raised to 375 °C and held for 90 minutes; then it is lowered to 327 °C and held for 60 minutes; and then it is naturally cooled to room temperature; then the sintered composite material plate is cut and processed to obtain the ATP@LDHs / PTFE composite material.

[0056] Example 4

[0057] Preparation method of modified attapulgite-polytetrafluoroethylene composite material (ATP@LDHs / PTFE):

[0058] (1) Preparation of metal salt solution: Weigh 4.867 g of calcium chloride hexahydrate and 2.677 g of aluminum chloride hexahydrate (Ca 2+ :Al 3+ The molar ratio is 2:1), add it to 200 mL of deionized water, stir and dissolve at room temperature to obtain a metal salt solution for standby.

[0059] (2) Preparation of alkali solution: Disperse 5.328 g of NaOH and 3 g of attapulgite powder in 200 mL of deionized water to obtain an alkali solution for standby.

[0060] (3) Modification of attapulgite: Drop 200 mL of the metal salt solution into 200 mL of the alkali solution under magnetic stirring to obtain an ATP@LDHs suspension; seal it and place it in an oven at 80 °C for aging for 10 hours, filter, dry at 70 °C for 12 h, crush and pass through a 500-mesh sieve to obtain ATP@LDHs for standby.

[0061] (4) Modification of polytetrafluoroethylene: After freezing the polytetrafluoroethylene powder at -3 °C for 8 h, mix the polytetrafluoroethylene powder and ATP@LDHs for 20 min. The modified attapulgite accounts for 16 wt% of the total weight of polytetrafluoroethylene, and the mixing speed is 1200 r / min; obtain ATP@LDHs-PTFE mixed powder.

[0062] (5) Compression molding: Pour the ATP@LDHs-PTFE mixed powder into a cold pressing mold, and keep the pressure at 50 MPa for 15 min at room temperature; after demolding, trim and remove burrs to make it smooth and flat, and obtain a compression-molded composite material plate.

[0063] (6) Sintering treatment: Put the compression-molded composite material plate into a sintering furnace for sintering. The furnace temperature rises to 327 °C at a rate of 1 °C / min and keeps warm for 60 minutes; then rises to 375 °C and keeps warm for 90 minutes; drops to 327 °C and keeps warm for 60 minutes; naturally cools to room temperature; then cut and process the sintered composite material plate to obtain ATP@LDHs / PTFE composite material.

[0064] Example 5

[0065] Preparation method of modified attapulgite-polytetrafluoroethylene composite material (ATP@LDHs / PTFE):

[0066] (1) Preparation of metal salt solution: Weigh 4.867 g of calcium chloride hexahydrate and 2.677 g of aluminum chloride hexahydrate (Ca2+ :Al 3+ (with a molar ratio of 2:1), add it to 200 mL of deionized water, stir and dissolve at room temperature to obtain a metal salt solution for standby.

[0067] (2) Preparation of alkali solution: Disperse 5.328 g of NaOH and 3 g of attapulgite powder in 200 mL of deionized water to obtain an alkali solution for standby.

[0068] (3) Modification of attapulgite: Drop 200 mL of the metal salt solution into 200 mL of the alkali solution under magnetic stirring to obtain an ATP@LDHs suspension; seal it and place it in an oven at 80 °C for 10 hours of aging, filter, dry at 75 °C for 13 h, pulverize and pass through a 500-mesh sieve to obtain ATP@LDHs for standby.

[0069] (4) Modification of polytetrafluoroethylene: Freeze the polytetrafluoroethylene powder at -3 °C for 8 h, then mix the polytetrafluoroethylene powder and ATP@LDHs for 20 min. The modified attapulgite accounts for 20 wt% of the total weight of polytetrafluoroethylene, and the mixing speed is 1200 r / min; obtain an ATP@LDHs-PTFE mixed powder.

[0070] (5) Compression molding: Pour the ATP@LDHs-PTFE mixed powder into a cold pressing mold, and keep the pressure at 50 MPa for 15 min at room temperature; after demolding, trim and remove burrs to make it smooth and flat, and obtain a compression-molded composite material plate.

[0071] (6) Sintering treatment: Put the compression-molded composite material plate into a sintering furnace for sintering. The furnace temperature rises to 327 °C at a rate of 1 °C / min and holds for 60 minutes; then rises to 375 °C and holds for 90 minutes; drops to 327 °C and holds for 60 minutes; naturally cools to room temperature; then cut and process the sintered composite material plate to obtain an ATP@LDHs / PTFE composite material.

[0072] Example 6

[0073] (1) Preparation of metal salt solution: Weigh 2.434 g of calcium chloride hexahydrate and 4.016 g of aluminum chloride hexahydrate, add them to 300 mL of deionized water, stir and dissolve at room temperature to obtain a metal salt solution for standby;

[0074] (2) Preparation of alkali solution: Disperse 7.992 g of NaOH and 1.5 g of attapulgite powder in 300 mL of deionized water to obtain an alkali solution for standby;

[0075] (3) Attapulgite modification: 300 mL of metal salt solution was added dropwise to 300 mL of lye under magnetic stirring to obtain an ATP@LDHs suspension; after sealing, it was placed in an oven at 70 °C for aging for 12 hours, filtered, dried at 60 °C for 14 h, pulverized through 600 meshes, and ATP@LDHs was obtained for standby;

[0076] (4) Polytetrafluoroethylene modification: After the polytetrafluoroethylene powder was frozen at -2 °C for 9 h, the polytetrafluoroethylene powder and ATP@LDHs were mixed for 15 min. The modified attapulgite accounted for 8 wt% of the total weight of polytetrafluoroethylene, and the mixing speed was 1000 r / min to obtain an ATP@LDHs-PTFE mixed powder;

[0077] (5) Compression molding: The ATP@LDHs-PTFE mixed powder was poured into a cold pressing mold, and the pressure was kept at 40 MPa for 18 min at room temperature; after demolding, the burrs were trimmed and removed to make it smooth and flat, and a compression-molded composite material plate was prepared;

[0078] (6) Sintering treatment: The compression-molded composite material plate was put into a sintering furnace for sintering. The furnace temperature was raised to 330 °C at a rate of 0.8 °C / min and held for 70 minutes; then it was raised to 385 °C and held for 100 minutes; then it was lowered to 330 °C and held for 50 minutes; and it was naturally cooled to room temperature; then the sintered composite material plate was cut and processed to obtain an ATP@LDHs / PTFE composite material.

[0079] Example 7

[0080] (1) Preparation of metal salt solution: Weigh 7.301 g of calcium chloride hexahydrate and 1.338 g of aluminum chloride hexahydrate, add them to 100 mL of deionized water, stir and dissolve at room temperature to obtain a metal salt solution for standby;

[0081] (2) Preparation of lye: Disperse 2.664 g of NaOH and 4.5 g of attapulgite powder in 100 mL of deionized water to obtain lye for standby;

[0082] (3) Attapulgite modification: 100 mL of metal salt solution was added dropwise to 100 mL of lye under magnetic stirring to obtain an ATP@LDHs suspension; after sealing, it was placed in an oven at 90 °C for aging for 9 hours, filtered, dried at 80 °C for 10 h, pulverized through 400 meshes, and ATP@LDHs was obtained for standby;

[0083] (4) Polytetrafluoroethylene modification: After the polytetrafluoroethylene powder was frozen at -4 °C for 7 h, the polytetrafluoroethylene powder and ATP@LDHs were mixed for 25 min. The modified attapulgite accounted for 12 wt% of the total weight of polytetrafluoroethylene, and the mixing speed was 1500 r / min to obtain an ATP@LDHs-PTFE mixed powder;

[0084] (5) Compression molding: Pour the ATP@LDHs-PTFE mixed powder into a cold pressing mold, and keep the pressure at 60 MPa for 12 min at room temperature; after demolding, trim and remove the burrs to make it smooth and flat, and obtain the compression-molded composite material plate.

[0085] (6) Sintering treatment: Put the compression-molded composite material plate into a sintering furnace for sintering. The furnace temperature is raised to 320 °C at a rate of 1.2 °C / min and kept warm for 50 minutes; then it is raised to 365 °C and kept warm for 80 minutes; then it is lowered to 320 °C and kept warm for 70 minutes; it is naturally cooled to room temperature; then the sintered composite material plate is cut and processed to obtain the ATP@LDHs / PTFE composite material.

[0086] Comparative Example 1:

[0087] Preparation method of LDHs:

[0088] (1) Preparation of metal salt solution: Weigh 4.867 g of calcium chloride hexahydrate and 2.677 g of aluminum chloride hexahydrate, add them to 200 mL of deionized water, stir and dissolve at room temperature to obtain the metal salt solution for standby.

[0089] (2) Preparation of alkali solution: Disperse 5.328 g of NaOH in 200 mL of deionized water to obtain the alkali solution for standby.

[0090] (3) Drop 200 mL of the metal salt solution into 200 mL of the alkali solution under magnetic stirring to obtain the LDHs suspension; seal it and place it in an oven at 80 °C for aging for 10 hours, filter, dry at 70 °C for 12 h, and pulverize through a 500-mesh sieve to obtain LDHs.

[0091] Comparative Example 2

[0092] Preparation method of LDHs / PTFE:

[0093] (1) Preparation of metal salt solution: Weigh 4.867 g of calcium chloride hexahydrate and 2.677 g of aluminum chloride hexahydrate, add them to 200 mL of deionized water, stir and dissolve at room temperature to obtain the metal salt solution for standby.

[0094] (2) Preparation of alkali solution: Disperse 5.328 g of NaOH in 200 mL of deionized water to obtain the alkali solution for standby.

[0095] (3) Drop 200 mL of the metal salt solution into 200 mL of the alkali solution under magnetic stirring to obtain the LDHs suspension; seal it and place it in an oven at 80 °C for aging for 10 hours, filter, dry at 70 °C for 12 h, and pulverize through a 500-mesh sieve to obtain LDHs for standby.

[0096] (4) Polytetrafluoroethylene modification: After freezing polytetrafluoroethylene powder at -3°C for 8 hours, the polytetrafluoroethylene powder and LDHs are mixed for 20 minutes at a mixing speed of 1200 r / min. The LDHs account for 4 wt%, 8 wt%, 12 wt%, and 16 wt% of the total weight of polytetrafluoroethylene, obtaining four groups of LDHs / PTFE powders with different ratios.

[0097] (5) Compression molding: Pour the four groups of LDHs / PTFE mixed powders with different ratios into cold pressing molds respectively, and keep the pressure at 50 MPa for 15 minutes at room temperature; after demolding, trim and remove burrs to make it smooth and flat, obtaining four groups of compression-molded composite material plates.

[0098] (6) Sintering treatment: Put the four groups of compression-molded composite material plates into a sintering furnace for sintering. The furnace temperature is raised to 327°C at a rate of 1°C / min and kept warm for 60 minutes; then it is raised to 375°C and kept warm for 90 minutes; then it is lowered to 327°C and kept warm for 60 minutes; naturally cooled to room temperature; then the sintered composite material plates are cut and processed to obtain four groups of LDHs / PTFE composites with filler contents of 4 wt%, 8 wt%, 12 wt%, and 16 wt% respectively.

[0099] Comparative Example 3

[0100] Preparation method of ATP / PTFE:

[0101] (1) Polytetrafluoroethylene modification: After freezing polytetrafluoroethylene powder at -3°C for 8 hours, the polytetrafluoroethylene powder and ATP powder are mixed for 20 minutes at a mixing speed of 1200 r / min. Attapulgite accounts for 4 wt%, 8 wt%, 12 wt%, and 16 wt% of the total weight of polytetrafluoroethylene, obtaining four groups of ATP / PTFE mixed powders with different ratios.

[0102] (2) Compression molding: Pour the four groups of ATP / PTFE mixed powders with different ratios into cold pressing molds respectively, and keep the pressure at 50 MPa for 15 minutes at room temperature; after demolding, trim and remove burrs to make it smooth and flat, obtaining four groups of compression-molded composite material plates.

[0103] (3) Sintering treatment: Put the four groups of compression-molded composite material plates into a sintering furnace for sintering. The furnace temperature is raised to 327°C at a rate of 1°C / min and kept warm for 60 minutes; then it is raised to 375°C and kept warm for 90 minutes; then it is lowered to 327°C and kept warm for 60 minutes; naturally cooled to room temperature; then the sintered composite material plates are cut and processed to obtain four groups of ATP / PTFE composites with filler contents accounting for 4 wt%, 8 wt%, 12 wt%, and 16 wt% respectively.

[0104] Comparative Example 4

[0105] Preparation method of pure PTFE:

[0106] Pour the polytetrafluoroethylene powder into a cold pressing mold, and keep the pressure at 50 MPa for 15 min at room temperature; after demolding, trim and remove the burrs to make it smooth and flat to obtain a pure PTFE plate. Put the pure PTFE into a sintering furnace for sintering. The furnace temperature is raised to 327 °C at a rate of 1 °C / min and kept warm for 60 minutes; then it is raised to 375 °C and kept warm for 90 minutes; then it is lowered to 327 °C and kept warm for 60 minutes; it is naturally cooled to room temperature; then the sintered pure PTFE is cut and processed to obtain pure PTFE.

[0107] In this invention, various composite materials prepared by the methods of Examples 1-4 and Comparative Examples 1-4 were subjected to mechanical property tests and friction and wear property tests. The following are the results of the experimental research of this invention:

[0108] 1. Mechanical property tests

[0109] On a TSE104B type microcomputer-controlled electronic universal testing machine, according to the GB / T10402-2006 standard, the sample was stretched to fracture at a stretching rate of 50 mm / min to measure its tensile strength. The final result of each test group was the average value of 5 tests.

[0110] The tensile properties of LDHs / PTFE, ATP / PTFE and ATP@LDHs / PTFE composite materials and pure PTFE are as Figure 1 shown. It can be seen from Figure 1 that as the contents of LDHs, ATP and ATP@LDHs increase, the tensile strength of LDHs / PTFE, ATP / PTFE and ATP@LDHs / PTFE composite materials first increases and then decreases. The tensile strength of the pure PTFE material is 18.39 MPa. When the filler content is 4 wt%, the tensile strength of the PTFE composite material reaches the highest. Under the same conditions, the ATP@LDHs / PTFE composite material has a higher tensile strength than the ATP / PTFE composite material. This is because ATP has high rigidity and strength, can effectively transfer stress, and can limit the slip of PTFE molecular chains, further improving the tensile strength of the material. Therefore, compared with pure PTFE, the tensile strength of the ATP / PTFE composite material will increase. However, the surface roughness of ATP in the PTFE matrix is low and the dispersion is poor, which usually leads to weak interfacial bonding. When LDHs are loaded on the surface of ATP, its dispersion and interfacial bonding in the PTFE matrix can be improved. Therefore, the ATP@LDHs / PTFE composite material has a higher tensile strength than the ATP / PTFE composite material. When the content of ATP@LDHs reaches 4 wt%, the highest tensile strength can reach 35.2 MPa

[0111] 2. Friction and Wear Performance Test

[0112] According to the national standard GB / T3960 - 2016, the tribological properties of PTFE composites were tested using an M - 200A friction and wear testing machine, such as Figure 2 and Figure 3 shown. The material of the test ring is generally 45# steel, and its outer dimensions are: the outer diameter is (40 ± 0.5) mm, the inner diameter is 16 mm, the width is 10 mm, the outer circle needs to be chamfered, and the chamfer is 0.5×45°. The specimen size is 20 mm×10 mm×4 mm. Before the test, the specimen and the test ring were ground with 500 - mesh sandpaper, washed with ethanol and dried, weighed with an electronic balance and the data was recorded. Each group of test specimens was not less than 3. During the test, the specimen remained stationary, the rotation speed of the test ring was 200 r / min, that is, the sliding speed was 0.42 m / s, the load was 196 N, and it lasted for 2 h.

[0113] After dry sliding friction test, the tribological properties of pure PTFE and LDHs / PTFE, ATP / PTFE and ATP@LDHs / PTFE composites with different contents of LDHs, ATP and ATP@LDHs added respectively are as Figure 2 shown. It can be seen from Figure 2 that the friction coefficient (μ) of pure PTFE is 0.183. When 4 wt% of LDHs, ATP or ATP@LDHs are added to PTFE respectively, all three can reduce the friction coefficient (pure PTFE is 0.183), among which 4 wt% ATP has the best effect (μ = 0.167); but when the addition amount increases to 8 wt% and above, the friction coefficient begins to rise and even exceeds that of pure PTFE (such as when 8 wt%, LDHs = 0.179, ATP = 0.186, ATP@LDHs = 0.183), and the negative impact of ATP is the most significant (up to 0.224 at 16 wt%); while ATP@LDHs formed by compounding ATP and LDHs can significantly alleviate the increase of the friction coefficient at high contents (such as when 16 wt%, ATP@LDHs = 0.203, significantly lower than 0.224 of pure ATP), and its performance is similar to that of LDHs.

[0114] Figure 3 shows the wear rates of PTFE composites with different contents of LDHs, ATP and ATP@LDHs added. The wear rate (k) of pure PTFE is 16.517×10 -13 m 3 / Nm, the wear rate of PTFE composites decreases significantly after adding LDHs, ATP, and ATP@LDHs as anti-wear fillers. When the contents of LDHs, ATP, and ATP@LDHs reach 16 wt% respectively, the wear rates of PTFE composites decrease to 0.307×10 -13 m 3 / Nm, 0.246×10 -13 m 3 / Nm, and 0.142×10 -13 m 3 / Nm, which are 57.2, 67.1, and 116.3 times lower than that of pure PTFE respectively. Under the same wear conditions, the wear rate of PTFE composites filled with ATP@LDHs as anti-wear fillers is lower than that of PTFE composites filled with LDHs and ATP as anti-wear fillers. Therefore, ATP modified by LDHs loading can endow PTFE-based composites with better anti-wear and abrasion resistance performance.

[0115] To deeply analyze the friction process of LDHs / PTFE, ATP / PTFE, and ATP@LDHs / PTFE composites, the evolution process of the friction coefficient of PTFE-based composites. As Figure 4 shown, different from the friction coefficient of pure PTFE showing a gradually decreasing trend during the whole sliding friction process, the friction coefficients of PTFE composites filled with different contents of LDHs, ATP, and ATP@LDHs show a trend of first decreasing, then increasing, and finally stabilizing during the whole sliding friction process.

[0116] Among them, the PTFE-based composites with the contents of LDHs, ATP, and ATP@LDHs being 4 wt% did not reach the stable stage of the friction coefficient in the first 2 h of wear, and the friction coefficient was lower than that of pure PTFE for most of the time. Therefore, when the filler content is low, the PTFE-based composites exhibit a lower friction coefficient. However, as the agglomeration of the filler on the worn surface and the temperature of the worn surface increase, the PTFE matrix softens, and the friction coefficient also increases. When the friction reaches about 5900 s, the friction coefficient exceeds that of pure PTFE. The PTFE-based composites with the contents of LDHs, ATP, and ATP@LDHs being 8 wt% had a friction coefficient lower than that of pure PTFE for only about half of the time at 2 h of wear. When the addition amount of various fillers was 8 wt%, the friction coefficient of the composite was higher than that with an addition amount of 4 wt%. The PTFE-based composites with the contents of LDHs, ATP, and ATP@LDHs being 12 wt% reached the stable stage of the friction coefficient at about 5000 s of wear, and the friction coefficient was higher than that of pure PTFE for most of the time. The PTFE-based composites with the contents of LDHs, ATP, and ATP@LDHs being 16 wt% reached the stable stage of the friction coefficient the fastest. Therefore, as the contents of LDHs, ATP, and ATP@LDHs increase, the PTFE-based composites can enter the stable wear stage faster during the friction and wear process, and the wear rate is lower. It should be noted that under the same conditions, when ATP@LDHs is added, compared with the addition of LDHs and ATP, the PTFE-based composites will enter the stable wear stage slightly faster, and the friction coefficient is lower after entering the stable wear stage. This indicates that the ATP@LDHs / PTFE composites exhibit more excellent anti-friction and wear resistance during the entire wear process.

Claims

1. A preparation method of a modified attapulgite-polytetrafluoroethylene composite material, characterized in that: The preparation method of the modified attapulgite-polytetrafluoroethylene composite material is to load layered double hydroxides on the surface of attapulgite by coprecipitation method for layered double hydroxide modification, and then fill and modify polytetrafluoroethylene by the hydrogen bond action of LDHs and the fiber structure of attapulgite.

2. The preparation method of the modified attapulgite-polytetrafluoroethylene composite material according to claim 1, wherein: The preparation method is carried out according to the following steps: (1) Preparation of metal salt solution: Weigh 2.434 - 7.301 g of calcium chloride hexahydrate and 1.338 - 4.016 g of aluminum chloride hexahydrate, add them to 100 - 300 mL of deionized water, stir and dissolve at room temperature to obtain a metal salt solution for standby. (2) Preparation of alkali solution: Disperse 2.664 - 7.992 g of NaOH and 1.5 - 4.5 g of attapulgite powder in 100 - 300 mL of deionized water to obtain an alkali solution for standby. (3) Modification of attapulgite: Drop 100 - 300 mL of the metal salt solution into 100 - 300 mL of the alkali solution under magnetic stirring to obtain an ATP@LDHs suspension; seal it and place it in an oven at 70 - 90 °C for aging for 9 - 12 hours, filter, dry at 60 - 80 °C for 10 - 14 h, pulverize and pass through a 400 - 600 mesh sieve to obtain ATP@LDHs for standby. (4) Modification of polytetrafluoroethylene: Freeze the polytetrafluoroethylene powder at -2 - -4 °C for 7 - 9 h, then mix the polytetrafluoroethylene powder and ATP@LDHs for 15 - 25 min at a mixing speed of 1000 - 1500 r / min to obtain an ATP@LDHs-PTFE mixed powder. (5) Compression molding: Pour the ATP@LDHs-PTFE mixed powder into a cold pressing mold, keep the pressure at 40 - 60 MPa for 12 - 18 min at room temperature; after demolding, trim and remove burrs to make it smooth and flat to obtain a compression-molded composite material plate. (6) Sintering treatment: Put the compression-molded composite material plate into a sintering furnace for sintering. Raise the furnace temperature from 0.8 - 1.2 °C / min to 320 - 330 °C, keep it warm for 50 - 70 minutes; then raise it to 365 - 385 °C, keep it warm for 80 - 100 minutes; lower it to 320 - 330 °C, keep it warm for 50 - 70 minutes; cool it naturally to room temperature; then cut and process the sintered composite material plate to obtain an ATP@LDHs / PTFE composite material.

3. The preparation method of the modified attapulgite-polytetrafluoroethylene composite material according to claim 2, characterized in that: In the step (1), for the preparation of the metal salt solution: Weigh 4.867 g of calcium chloride hexahydrate and 2.677 g of aluminum chloride hexahydrate, add them to 200 mL of deionized water, stir and dissolve at room temperature to obtain a metal salt solution for standby.

4. The preparation method of the modified attapulgite-polytetrafluoroethylene composite material according to claim 2, characterized in that: In the step (2), for the preparation of the alkali solution: Disperse 5.328 g of NaOH and 3 g of attapulgite powder in 200 mL of deionized water to obtain an alkali solution for standby.

5. The preparation method of the modified attapulgite-polytetrafluoroethylene composite material according to claim 2, characterized in that: In the step (3), modification of attapulgite: 200 mL of metal salt solution was added dropwise to 200 mL of alkali solution under magnetic stirring to obtain an ATP@LDHs suspension; after sealing, it was placed in an oven at 80 °C for aging for 10 hours, filtered, dried at 70 °C for 12 h, pulverized and passed through a 500-mesh sieve to obtain ATP@LDHs for standby.

6. The preparation method of the modified attapulgite-polytetrafluoroethylene composite material according to claim 2, characterized in that: In the step (4), modification of polytetrafluoroethylene: The polytetrafluoroethylene powder was frozen at -3 °C for 8 h, and then the polytetrafluoroethylene powder and ATP@LDHs were mixed for 20 min at a mixing speed of 1200 r / min; an ATP@LDHs-PTFE mixed powder was obtained.

7. The preparation method of the modified attapulgite-polytetrafluoroethylene composite material according to claim 2 or 6, characterized in that: In the step (4), the modified attapulgite accounts for 4-20 wt% of the total weight of polytetrafluoroethylene.

8. The preparation method of the modified attapulgite-polytetrafluoroethylene composite material according to claim 7, characterized in that: In the step (4), the modified attapulgite accounts for 4-16 wt% of the total weight of polytetrafluoroethylene.

9. The preparation method of the modified attapulgite-polytetrafluoroethylene composite material according to claim 2, wherein: In the step (5), press molding: The ATP@LDHs-PTFE mixed powder was poured into a cold pressing mold, and the pressure was kept at 50 MPa for 15 min at room temperature; after demolding, the burrs were trimmed and removed to make it smooth and flat, and a press-molded composite material plate was prepared.

10. The preparation method of the modified attapulgite-polytetrafluoroethylene composite material according to claim 2, characterized in that: In the step (6), sintering treatment: The press-molded composite material plate was put into a sintering furnace for sintering. The furnace temperature was raised to 327 °C at a rate of 1 °C / min and held for 60 minutes; then it was raised to 375 °C and held for 90 minutes; then it was lowered to 327 °C and held for 60 minutes; and it was naturally cooled to room temperature; then the sintered composite material plate was cut and processed to obtain an ATP@LDHs / PTFE composite material.

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