A fluorosilane interfacial modified foamed metal-polytetrafluoroethylene interpenetrating phase composite and a method of making the same

Abstract

The application provides a fluorosilane interfacial modification foam metal-polytetrafluoroethylene interpenetrating phase composite material and a preparation method thereof, which is prepared by fluorosilane interfacial modification, polytetrafluoroethylene emulsion impregnation and high-temperature free sintering, and takes polytetrafluoroethylene emulsion as a main matrix material, takes three-dimensional continuous open-cell foam metal as a reinforcing framework, and takes fluorosilane coupling agent as an interfacial modification material. The foam metal is modified by the fluorosilane coupling agent through reaction condition regulation and fluorosilane type selection, and the interface combination between the foam metal and the polytetrafluoroethylene matrix is improved. In addition, the structure parameters of the foam metal and the regulation of the composite material preparation process are combined, and the thermal conductivity, mechanical strength and wear resistance of the foam metal-polytetrafluoroethylene interpenetrating phase composite material are further improved.

Description

TECHNICAL FIELD

[0001] The application relates to the technical field of lubricating materials, and in particular to a fluorosilane modified interfacial modified foam metal-polytetrafluoroethylene interpenetrating phase composite material and a preparation method thereof. BACKGROUND

[0002] An interpenetrating phase composite material is a material formed by two or more constituent phases connected to each other in a three-dimensional structure. The interpenetrating phase composite material has the advantages of low density, excellent thermal conductivity, good acoustic conductivity and the like, and is widely applied to the fields of thermal management, electric conductors, electromagnetic shielding and the like. Among them, the interpenetrating metal-polymer composite material taking foam metal as a skeleton and taking polymer as a matrix has been widely concerned due to the comprehensive advantages of metal and polymer. In recent years, the interpenetrating phase composite material based on the interpenetrating metal-polymer has been developed for the field of friction and wear. In the interpenetrating metal-polymer, the open-cell metal foam is introduced into the design of the lubricating material due to the advantages of light weight, high thermal conductivity and large specific surface area; and as for the polymer matrix, most of the researches use thermosetting resins which are easy to solidify as the interpenetrating matrix. Due to the difficulty in controlling the preparation process, the foam metal-polymer interpenetrating phase composite material is less at present.

[0003] Polytetrafluoroethylene is widely applied to various friction components due to its excellent self-lubricating performance, but the polytetrafluoroethylene itself has low thermal conductivity, low mechanical strength and poor wear resistance, and is often lubricated to fail in the friction process due to a large amount of wear, friction heat deformation and load deformation. In the previous research, the polytetrafluoroethylene is usually modified by compounding with functional fillers of different dimensions to improve the thermal conductivity, wear resistance and mechanical strength of the polytetrafluoroethylene. However, the functional fillers with low content in the method are often insufficient to form a continuous phase, and the reinforcing effect on the polytetrafluoroethylene is limited by the interface scale, and it is difficult to greatly improve the performance of the polytetrafluoroethylene. In combination with the above reasons, the three-dimensional connected foam metal is compounded with the polytetrafluoroethylene to construct the interpenetrating composite material, so as to comprehensively improve the comprehensive performance of the composite material and apply it to the field of solid lubrication. In the research on the interpenetrating polytetrafluoroethylene-foam metal, the thermoplastic polytetrafluoroethylene needs to be sintered at high temperature, and the mismatch of the intrinsic thermal expansion coefficients of the metal and the polymer will cause the separation of the interface between the two at the high-temperature sintering process, thereby causing the decline of the performance of the material.

[0004] Based on this, the application provides a fluorosilane interface modified foam metal-polytetrafluoroethylene interpenetrating phase composite material and a preparation method thereof. On the basis of a foam metal-polytetrafluoroethylene interpenetrating phase composite system, a foam metal skeleton is modified by using a fluorosilane coupling agent to improve the combination of the three-dimensional continuous interface of the foam metal-polytetrafluoroethylene interpenetrating phase composite material. In addition, by combining the regulation of the structural parameters of the foam metal and the preparation process of the composite material, the thermal conductivity, mechanical strength and wear resistance of the foam metal-polytetrafluoroethylene interpenetrating phase composite material are further improved. The foam metal-polytetrafluoroethylene interpenetrating phase composite material modified by the fluorosilane has good interface combination, high mechanical strength, high thermal conductivity and high wear resistance. SUMMARY

[0005] The purpose of the application is to solve the problem that the comprehensive performance of the traditional composite modified polytetrafluoroethylene lubricating material is not ideal, and provide a fluorosilane interface modified foam metal-polytetrafluoroethylene interpenetrating phase composite material and a preparation method thereof. By introducing a three-dimensional continuous foam metal skeleton and regulating its structural parameters, the mechanical strength and thermal conductivity of the polytetrafluoroethylene composite material are greatly improved. The three-dimensional continuous interface combination of the interpenetrating phase composite material is improved by modifying the fluorosilane coupling agent, and the comprehensive performance of the composite material is further improved.

[0006] I. Preparation of a fluorosilane interface modified foam metal-polytetrafluoroethylene interpenetrating phase composite material

[0007] A preparation method of a fluorosilane interface modified foam metal-polytetrafluoroethylene interpenetrating phase composite material, comprising the following steps:

[0008] 1) Interface modification: first add the fluorosilane coupling agent to the ethanol aqueous solution, adjust the pH value to 2-6 using acetic acid to obtain a fluorosilane hydrolysis solution; then add the foam metal to the fluorosilane hydrolysis solution, and stir at room temperature-110 DEG C for 12-24 h; after the reaction is completed, the foam metal is taken out, washed with anhydrous ethanol until it is neutral, and finally dried at 50-80 DEG C;

[0009] 2) Polytetrafluoroethylene matrix impregnation: under the condition of a vacuum degree of-0.03 to-0.10 MPa, the foam metal modified by the fluorosilane in step 1) is impregnated in a polytetrafluoroethylene emulsion for 10-30 min, and then taken out after the bubbles are eliminated, and dried at 90-130 DEG C for 60-120 min to remove the solvent; the above impregnation-drying steps are repeated several times;

[0010] 3) Sintering: the foam metal-polytetrafluoroethylene interpenetrating phase composite material modified in step 2) is placed in a polytetrafluoroethylene sintering furnace and sintered at 350-390 DEG C for 100-400 min.

[0011] In step 1), the fluorosilane coupling agent is one or more of trifluoropropyltrimethoxysilane, perfluorooctyltriethoxysilane, perfluorodecyltrimethoxysilane and perfluorodecyltriethoxysilane; the foamed metal is one or more of foamed nickel, foamed copper and foamed iron, the number of openings per inch is 10-100, and the porosity is 70%-98%. The content of the fluorosilane coupling agent is 10-60% of the mass fraction of the modified foamed metal.

[0012] In step 2), the mass concentration of the polytetrafluoroethylene emulsion is 30%-65%, and the particle size of the polytetrafluoroethylene in the emulsion is 80-500 nm.

[0013] II. Structure characterization of the fluorosilane interfacial modification foamed metal-polytetrafluoroethylene interpenetrating phase composite

[0014] The interfacial modification of the fluorosilane and the interfacial bonding of the foamed metal-polytetrafluoroethylene interpenetrating phase composite prepared are analyzed by contact angle measurement, scanning electron microscopy and X-ray energy spectrum analysis. Figures 1-3 The results are shown in the accompanying drawings.

[0015] Figure 1 The foamed metal skeleton morphology and energy spectrum diagram of the fluorosilane interfacial modification of the present application are shown. As can be seen from the figure, after the fluorosilane interfacial modification, there is a layer of fluorosilane on the surface of the metal skeleton, which proves the successful modification of the fluorosilane on the surface of the metal skeleton.

[0016] Figure 2 The contact angle test of the foamed metal skeleton before and after the fluorosilane interfacial modification is shown. As can be seen from the figure, after the fluorosilane interfacial modification, the foamed metal skeleton changes from hydrophilic to hydrophobic, which further illustrates the successful modification of the fluorosilane on the surface of the metal skeleton, and on the other hand, the hydrophobic metal skeleton is more easily combined with the hydrophobic polytetrafluoroethylene, which improves the bonding degree of the three-dimensional continuous interface of the interpenetrating phase composite.

[0017] Figure 3 The structure comparison of the fluorosilane interfacial modification foamed metal-polytetrafluoroethylene interpenetrating phase composite and the foamed metal-polytetrafluoroethylene interpenetrating phase composite without interfacial modification is shown. As can be seen from the figure, without interfacial modification, due to the difference of more than one order of magnitude between the linear expansion coefficients of the metal and the polymer, the high-temperature sintering process of the polytetrafluoroethylene causes an interface separation with a size of more than 60 μm, which blocks the effective transmission of stress and heat energy from the hard and high-heat-conducting metal to the polytetrafluoroethylene. After the interfacial modification, the foamed metal and the polytetrafluoroethylene are closely combined, and the interface spacing is only a few microns, so that the normal load, shear stress and environmental heat can be effectively transmitted from the foamed metal to the polytetrafluoroethylene substrate through the three-dimensional continuous interface, thereby greatly improving the thermal conductivity, strength and friction and wear properties of the composite.

[0018] III. Performance evaluation of fluorosilane interfacial modified foam metal-polytetrafluoroethylene interpenetrating phase composite

[0019] 1. Tensile strength test

[0020] The sample was processed into a standard size for mechanical property testing on a universal testing machine, and the test standard was GB / T1040.2-2006, and the tensile rate was 1 mm / min.

[0021] 2. Thermal conductivity test

[0022] The sample prepared in Example 1-3 was mechanically processed into a square sheet of 20 mm x 20 mm x 4 mm, and was tested on a thermal conductivity tester according to ISO 22007-2. The data are listed in Table 1.

[0023] 3. Friction and wear performance

[0024] The sample prepared in Example 1-3 was mechanically processed into a rectangular sheet of 40 mm long, 15 mm wide and 2 mm thick, and its friction and wear performance was tested using a UMT friction and wear tester, and the test environment temperature was 23±5℃. The upper test piece was a 4.7 mm diameter Al2O3 ceramic flat pin. Reciprocating motion was performed under a load of 50 N and a frequency of 5 Hz, with a single stroke of 5 mm and a total stroke of 200 m. The test data are listed in Table 1.

[0025] Table 1 Performance of foam metal-polytetrafluoroethylene interpenetrating phase composite prepared in Example 1-3

[0026]

[0027] As can be seen from Table 1, the thermal conductivity of the fluorosilane interfacial modified foam metal-polytetrafluoroethylene interpenetrating phase composite prepared in the application is 2.8-16.0 W / (m·K), the friction coefficient is 0.09-0.16, and the wear rate is (0.04-6.3) x 10 -5 mm 3 / Nm. As can be seen, the fluorosilane interfacial modified foam metal-polytetrafluoroethylene interpenetrating phase composite has excellent thermal conductivity, mechanical properties and friction and wear properties. In Comparative Example 1, the foam metal was not subjected to fluorosilane interfacial modification, resulting in a lack of strong bonding between the polytetrafluoroethylene and the foam metal, limiting the effective transfer of stress and heat energy, resulting in a significant decrease in thermal conductivity to 0.7 W / (m·K), a slight decrease in tensile strength to 20 MPa, and a sharp increase in wear rate to 8.1 x 10 -5 mm 3 / Nm.

[0028] Based on the above excellent performance, the material is expected to be applied to the moving and bearing parts in the fields of aerospace, marine engineering, automobile industry, etc., so as to obtain the comprehensive advantages of lightweight, high strength, friction reduction and wear resistance. BRIEF DESCRIPTION OF DRAWINGS

[0029] Figure 1 The morphology and energy spectrum of the foam metal skeleton modified by the fluorosilane interfacial modification of the application are shown.

[0030] Figure 2 The contact angle test of the foam metal skeleton before and after the modification by the fluorosilane interfacial modification of the application is shown.

[0031] Figure 3 The structure comparison of the foam metal-polytetrafluoroethylene interpenetrating phase composite material modified by the fluorosilane interfacial modification of the application and the foam metal-polytetrafluoroethylene interpenetrating phase composite material without interfacial modification is shown. DETAILED DESCRIPTION

[0032] The application will be further explained and described below in combination with specific embodiments.

[0033] Embodiment 1

[0034] Take 6 g of foam nickel (porosity 95%, number of openings per inch 60) and 300 g of excess polytetrafluoroethylene emulsion (polytetrafluoroethylene particle size 90 nm, mass percentage 55%).

[0035] 1) Interfacial modification

[0036] Prepare 50 g of anhydrous ethanol, 5 g of deionized water and 2.4 g of trifluoropropyltrimethoxysilane into a fluorosilane hydrolysis solution; use acetic acid to adjust the pH value to 5.0; add the foam metal into the fluorosilane hydrolysis solution, and mechanically stir the hydrolysis reaction at room temperature for 12 h; after the reaction is completed, take out the foam metal, wash it with anhydrous ethanol until it is neutral, and finally dry it at 50℃;

[0037] 2) Polytetrafluoroethylene emulsion matrix impregnation

[0038] Under the condition of vacuum degree-0.10 MPa, the foam metal modified in 1) is immersed in the polytetrafluoroethylene emulsion for 10 min after the bubbles are eliminated, and then dried at 90℃ for 50 min to remove the solvent; repeat the above impregnation-drying steps 2 times;

[0039] 3) Composite sintering forming

[0040] Place the foam metal-polytetrafluoroethylene interpenetrating phase composite material modified in step 2) in a polytetrafluoroethylene special sintering furnace, and sinter at a temperature of 370℃ for 180 min. The performance is shown in Table 1.

[0041] Embodiment 2

[0042] Take 10 g of foamed nickel (porosity 85%, 100 pores per inch) and 360 g of excess polytetrafluoroethylene emulsion (polytetrafluoroethylene particle size 100 nm, mass percentage 45%).

[0043] 1) Interface assembly

[0044] 80 g of anhydrous ethanol, 8 g of deionized water and 3 g of perfluorodecyltrimethoxysilane were configured into a fluorosilane hydrolysis solution; acetic acid was used to adjust the pH value to 3.0; the foamed metal was added to the fluorosilane hydrolysis solution, and the hydrolysis reaction was carried out at 110°C for 24 h under the condition of constant stirring; after the reaction was completed, the foamed metal was taken out, washed with anhydrous ethanol until neutral, and finally dried at 60°C;

[0045] 2) Polytetrafluoroethylene emulsion matrix impregnation

[0046] Under the condition of vacuum degree-0.06 MPa, the interface modified foamed metal in 1) was immersed in the polytetrafluoroethylene emulsion for 15 min after the bubbles were eliminated, and then dried at 100°C for 60 min to remove the solvent; the above-mentioned impregnation-drying steps were repeated 4 times;

[0047] 3) Sintering of composite material

[0048] The interface modified foamed metal-polytetrafluoroethylene interpenetrating phase composite material obtained in step 2) was placed in a polytetrafluoroethylene special sintering furnace and sintered at a temperature of 380°C for 260 min. The performance is shown in Table 1, and the structure characterization is shown in Figures 1-3 .

[0049] Example 3

[0050] Take 20 g of foamed nickel (porosity 80%, 80 pores per inch) and 500 g of excess polytetrafluoroethylene emulsion (polytetrafluoroethylene particle size 180 nm, mass percentage 50%).

[0051] 1) Interface assembly

[0052] 120 g of anhydrous ethanol, 12 g of deionized water and 4 g of perfluorodecyltriethoxysilane were configured into a fluorosilane hydrolysis solution; acetic acid was used to adjust the pH value to 2.0; the foamed metal was added to the fluorosilane hydrolysis solution, and the hydrolysis reaction was carried out at 110°C for 24 h under the condition of constant stirring; after the reaction was completed, the foamed metal was taken out, washed with anhydrous ethanol until neutral, and finally dried at 80°C;

[0053] 2) Polytetrafluoroethylene emulsion matrix impregnation

[0054] The interface modified foam metal in 1) was immersed in the polytetrafluoroethylene emulsion for 20 min under a vacuum of -0.08 MPa, taken out after the bubbles were eliminated, and dried at 110°C for 80 min to remove the solvent; the above-mentioned immersion-drying steps were repeated 6 times.

[0055] 3) Sintering of the composite

[0056] The interface modified foam metal-polytetrafluoroethylene interpenetrating phase composite obtained in step 2) was placed in a polytetrafluoroethylene special sintering furnace and sintered at a temperature of 375°C for 360 min. The properties thereof are shown in Table 1, and the structural characterization thereof is shown in Figures 1-3 .

[0057] Comparative Example 1

[0058] Foam nickel 6 g (porosity 95%, number of openings per inch 60) and excess polytetrafluoroethylene emulsion 300 g (polytetrafluoroethylene particle size 90 nm, mass percentage 55%) were taken.

[0059] 1) Polytetrafluoroethylene emulsion matrix immersion

[0060] The foam metal was immersed in the polytetrafluoroethylene emulsion for 10 min under a vacuum of -0.10 MPa, taken out after the bubbles were eliminated, and dried at 90°C for 50 min to remove the solvent; the above-mentioned immersion-drying steps were repeated 2 times.

[0061] 2) Sintering of the composite

[0062] The interface modified foam metal-polytetrafluoroethylene interpenetrating phase composite obtained in step 2) was placed in a polytetrafluoroethylene special sintering furnace and sintered at a temperature of 370°C for 180 min. The properties thereof are shown in Table 1.

Claims

1. A method for the preparation of fluorosilane interfacially modified metal- polytetrafluoroethylene interpenetrating phase composites, characterized by, The method comprises the following steps: 1) interface modification: first, add fluorosilane coupling agent to an aqueous ethanol solution, adjust the pH value to 2-6 using acetic acid to obtain a fluorosilane hydrolysis solution; then add the foamed metal to the fluorosilane hydrolysis solution, and incubate and stir at room temperature-110℃ for 12-24 h; after the reaction is completed, take out the foamed metal, wash it with anhydrous ethanol until it is neutral, and finally dry it at 50-80℃; 2) polytetrafluoroethylene matrix immersion: under a vacuum degree of-0.03 to-0.10 Mpa, immerse the foamed metal modified by the fluorosilane in step 1) in a polytetrafluoroethylene emulsion for 10-30 min, take it out after the bubbles are eliminated, and dry it at 90-130℃ for 60-120 min to remove the solvent; repeat the above immersion-drying steps several times; 3) sintering: place the foamed metal-polytetrafluoroethylene interpenetrating phase composite material obtained in step 2) in a polytetrafluoroethylene sintering furnace, and sinter it at 350-390℃ for 100-400 min; The fluorosilane coupling agent is one or more of trifluoropropyltrimethoxysilane, perfluorooctyltriethoxysilane, perfluorodecyltrimethoxysilane, and perfluorodecyltriethoxysilane; the foamed metal is one or more of foamed nickel, foamed copper, and foamed iron, with a number of openings per inch of 10-100 and a porosity of 70%-98%; The content of the fluorosilane coupling agent is 10-60% of the mass fraction of the modified foamed metal; The mass concentration of the polytetrafluoroethylene emulsion is 30%-65%, and the particle size of the polytetrafluoroethylene in the emulsion is 80-500 nm.

2. A fluorosilane interface-modified foamed metal-polytetrafluoroethylene interpenetrating phase composite material prepared by the method of claim 1.

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