A polyimide composite material filled with a polyimide fiber-carbon nanotube fiber hybrid and a preparation method thereof

Abstract

The present invention provides a polyimide composite filled with a polyimide fiber-carbon nanotube fiber hybrid and a preparation method thereof, relating to the technical field of polyimide material modification. In the present invention, PIF-MWCNTs are used as fillers and filled into a thermoplastic polyimide matrix. Since PIF-MWCNTs contain polyimide fibers, they have good compatibility with the thermoplastic polyimide matrix. As a physical barrier, PIF-MWCNTs reduce the transport rate during the decomposition of volatile products in the thermal decomposition process of the thermoplastic polyimide, so that the composite material filled with it requires more heat to promote the movement of its molecular chains during the thermal decomposition process, and thus has good thermal stability. In addition, the polyimide fibers in PIF-MWCNTs can play a role in sharing the load during the friction process, which can reduce the wear rate of the composite material; the carbon nanotubes in PIF-MWCNTs can improve the lubricity.

Description

Technical Field

[0001] The present invention relates to the technical field of polyimide material modification, and particularly to a polyimide composite material filled with a polyimide fiber-carbon nanotube fiber hybrid and a preparation method thereof. Background Art

[0002] As a special engineering material, polyimide has been widely used in the fields of aviation, aerospace, microelectronics, nanotechnology, liquid crystal, separation membrane, laser, etc. In the 1960s, countries all included the research, development and utilization of polyimide among the most promising engineering plastics in the 21st century. Polyimide, due to its outstanding characteristics in performance and synthesis, whether as a structural material or as a functional material, its huge application prospects have been fully recognized, and it is called the "problem solver".

[0003] Polyimide is divided into thermoplastic polyimide and thermosetting polyimide according to its thermal properties. Thermoplastic polyimide (TPI) is one of the special engineering plastics with good thermoplastic processing performance developed on the basis of traditional thermosetting polyimide (PI). It can not only be formed by all the processing methods of thermosetting PI, but also by the methods of extrusion and injection molding suitable for thermoplastic plastics. Therefore, it is particularly suitable for forming products with complex structures in one step without secondary processing, solving the problems of difficult forming and processing and single product form of traditional thermosetting PI.

[0004] At present, the highest thermal decomposition temperature of TPI can reach 600°C, and it has good thermal stability, but its tribological properties are poor. If the tribological properties of TPI can be improved and its thermal stability can be further improved, it will be beneficial to further expand the application range of TPI. Summary of the Invention

[0005] The purpose of the present invention is to provide a polyimide composite material filled with a polyimide fiber-carbon nanotube fiber hybrid and a preparation method thereof. The polyimide composite material provided by the present invention has good thermal stability and tribological properties.

[0006] In order to achieve the above invention purpose, the present invention provides the following technical solutions:

[0007] The present invention provides a polyimide composite material filled with a polyimide fiber-carbon nanotube fiber hybrid, including a thermoplastic polyimide matrix and a polyimide fiber-carbon nanotube fiber hybrid filled in the thermoplastic polyimide matrix;

[0008] The mass ratio of the thermoplastic polyimide matrix to the polyimide fiber-carbon nanotube fiber hybrid is 90:10;

[0009] The polyimide fiber-carbon nanotube fiber hybrid includes polyimide fibers and carbon nanotubes coated on the surface of the polyimide fibers; the polyimide fibers and the carbon nanotubes are connected by polydopamine.

[0010] Preferably, the carbon nanotubes are multi-walled carbon nanotubes.

[0011] The present invention provides a method for preparing a polyimide composite filled with the polyimide fiber-carbon nanotube fiber hybrid described in the above solution, including the following steps:

[0012] Disperse polyimide fibers, carbon nanotubes, and dopamine into a Tris-HCl buffer solution and carry out a modification reaction to obtain a polyimide fiber-carbon nanotube fiber hybrid;

[0013] Mix the polyimide fiber-carbon nanotube fiber hybrid with thermoplastic polyimide matrix powder and carry out hot pressing and sintering to obtain a polyimide composite filled with the polyimide fiber-carbon nanotube fiber hybrid; the mass ratio of the thermoplastic polyimide matrix powder to the polyimide fiber-carbon nanotube fiber hybrid is 90:10.

[0014] Preferably, the pH value of the Tris-HCl buffer solution is 8.4.

[0015] Preferably, the mass ratio of the carbon nanotubes to the polydopamine is 1:1.

[0016] Preferably, the mass ratio of the carbon nanotubes to the polyimide fibers is 1:1.

[0017] Preferably, the length of the polyimide fibers is below 50 mm.

[0018] Preferably, the time of the modification reaction is 12 hours.

[0019] Preferably, the temperature of the hot pressing and sintering is 370-380 °C, the heat preservation time is 110-130 min, and the pressure is 17-23 MPa.

[0020] Preferably, after the modification reaction, it further includes filtering the obtained modified suspension and washing the obtained filter cake.

[0021] The present invention provides a polyimide composite filled with a polyimide fiber-carbon nanotube fiber hybrid, comprising a thermoplastic polyimide matrix and a polyimide fiber-carbon nanotube fiber hybrid (abbreviated as PIF-MWCNTs) filled in the thermoplastic polyimide matrix; the mass ratio of the thermoplastic polyimide matrix to the polyimide fiber-carbon nanotube fiber hybrid is 90:10; the polyimide fiber-carbon nanotube fiber hybrid comprises polyimide fibers and carbon nanotubes coated on the surfaces of the polyimide fibers; the polyimide fibers and the carbon nanotubes are connected by polydopamine.

[0022] In the present invention, PIF-MWCNTs are used as fillers and filled into the thermoplastic polyimide matrix. Since PIF-MWCNTs contain polyimide fibers, they have good compatibility with the thermoplastic polyimide matrix. As a physical barrier, PIF-MWCNTs reduce the transport rate during the decomposition of volatile products in the thermal decomposition process of the thermoplastic polyimide, which enables the composite material filled with it to require more heat to promote the movement of its molecular chains during the thermal decomposition process, and thus has good thermal stability. In addition, the polyimide fibers in PIF-MWCNTs can play a role in sharing the load during the friction process, which can reduce the wear rate of the composite material; the carbon nanotubes in PIF-MWCNTs can improve the lubricity and reduce the friction coefficient of the composite material. Description of the Drawings

[0023] Figure 1 Photographs of the physical objects and SEM images of the polyimide fibers before and after modification;

[0024] Figure 2 AFM images of the polyimide fibers before and after modification;

[0025] Figure 3 TGA curves of the polyimide materials prepared in the examples and comparative examples under argon;

[0026] Figure 4 Friction property diagrams of the polyimide materials prepared in the examples and comparative examples. Detailed Embodiments

[0027] The present invention provides a polyimide composite filled with a polyimide fiber-carbon nanotube fiber hybrid, comprising a thermoplastic polyimide matrix and a polyimide fiber-carbon nanotube fiber hybrid filled in the thermoplastic polyimide matrix;

[0028] The mass ratio of the thermoplastic polyimide matrix to the polyimide fiber-carbon nanotube fiber hybrid is 90:10;

[0029] The polyimide fiber-carbon nanotube fiber hybrid includes polyimide fibers and carbon nanotubes coated on the surface of the polyimide fibers; the polyimide fibers and the carbon nanotubes are connected by polydopamine.

[0030] In the present invention, the carbon nanotubes are preferably multi-walled carbon nanotubes.

[0031] The present invention controls the mass ratio of the matrix to the filler to be 90:10 to ensure a better modification effect.

[0032] In the present invention, PIF-MWCNTs are used as fillers and filled into a thermoplastic polyimide matrix. PIF-MWCNTs have good compatibility with the thermoplastic polyimide matrix due to the presence of polyimide fibers. PIF-MWCNTs act as a physical barrier to reduce the transport rate during the decomposition of volatile products in the thermal decomposition process of the thermoplastic polyimide. This makes the composite material filled with it require more heat to promote the movement of its molecular chains during the thermal decomposition process, and thus has good thermal stability. In addition, the polyimide fibers in PIF-MWCNTs can play a role in sharing the load during the friction process, which can reduce the wear rate of the composite material; the carbon nanotubes in PIF-MWCNTs can improve lubricity and reduce the friction coefficient of the composite material.

[0033] The present invention provides a method for preparing a polyimide composite material filled with the polyimide fiber-carbon nanotube fiber hybrid described in the above solution, including the following steps:

[0034] Disperse polyimide fibers, carbon nanotubes and dopamine into a Tris-HCl buffer solution, and carry out a modification reaction to obtain a polyimide fiber-carbon nanotube fiber hybrid;

[0035] Mix the polyimide fiber-carbon nanotube fiber hybrid with the thermoplastic polyimide matrix powder, and carry out hot pressing and sintering to obtain a polyimide composite material filled with the polyimide fiber-carbon nanotube fiber hybrid; the mass ratio of the thermoplastic polyimide matrix powder to the polyimide fiber-carbon nanotube fiber hybrid is 90:10.

[0036] In the present invention, unless otherwise specified, the raw materials used are all commercially available products well-known in the art.

[0037] The present invention disperses polyimide fibers, carbon nanotubes and dopamine into a Tris-HCl buffer solution, and carries out a modification reaction to obtain a polyimide fiber-carbon nanotube fiber hybrid.

[0038] In the present invention, the length of the polyimide fiber is preferably below 50 mm; the carbon nanotubes are preferably multi-walled carbon nanotubes; the pH value of the Tris-HCl buffer solution is preferably 8.4. In the present invention, the mass ratio of dopamine to carbon nanotubes is preferably 1:1; the mass ratio of carbon nanotubes to polyimide fibers is preferably 1:1. The present invention has no special requirements for the dosage of the Tris-HCl buffer solution, as long as the polyimide fibers, dopamine, and carbon nanotubes can be evenly dispersed.

[0039] In the present invention, dispersing the polyimide fiber, carbon nanotubes, and dopamine into the Tris-HCl buffer solution preferably includes: dispersing the polyimide fiber into the Tris-HCl buffer solution, and then adding dopamine and carbon nanotubes to the dispersion under magnetic stirring conditions.

[0040] In the present invention, the modification reaction is preferably carried out at room temperature, and the time of the modification reaction is preferably 12 hours. During the modification reaction of the present invention, dopamine polymerizes, and carbon nanotubes are grafted onto the polyimide fiber to form a polyimide fiber-carbon nanotube fiber hybrid (PIF-MWCNTs).

[0041] In the present invention, after the modification reaction, it preferably further includes filtering the obtained modified suspension and washing the obtained filter cake. The present invention has no special requirements for the filtering method, and any well-known filtering method in the art can be used. In the present invention, the washing is preferably carried out with distilled water.

[0042] After obtaining the polyimide fiber-carbon nanotube fiber hybrid, the present invention mixes the polyimide fiber-carbon nanotube fiber hybrid with the thermoplastic polyimide matrix powder and conducts hot pressing and sintering to obtain a polyimide composite filled with the polyimide fiber-carbon nanotube fiber hybrid.

[0043] In the present invention, the mixing is preferably carried out under mechanical stirring conditions; the mixing time is preferably 10 - 20 min. In the present invention, the mass ratio of the thermoplastic polyimide matrix powder to the polyimide fiber-carbon nanotube fiber hybrid is 90:10.

[0044] In the present invention, the hot pressing and sintering is preferably carried out in a mold. The temperature of the hot pressing and sintering is preferably 370 - 380 °C, more preferably 372 - 378 °C; the heat preservation time is preferably 110 - 130 min, more preferably 115 - 125 min; the pressure of the hot pressing and sintering is preferably 17 - 23 MPa, more preferably 19 - 21 MPa.

[0045] During the hot pressing and sintering process of the present invention, the polyimide fiber crosslinks with the polyimide matrix, improving the compatibility with the matrix.

[0046] After hot pressing and sintering, the present invention preferably further includes: naturally cooling to room temperature, demolding, to obtain the polyimide composite material filled with the polyimide fiber-carbon nanotube fiber hybrid.

[0047] The following is a detailed description of the polyimide composite material filled with the polyimide fiber-carbon nanotube fiber hybrid and its preparation method provided by the present invention in conjunction with the embodiments, but they should not be construed as limiting the protection scope of the present invention.

[0048] Example 1

[0049] First, cut short polyimide fibers are dispersed in a Tris-HCl buffer solution with a pH value of 8.4, and then dopamine (DA) and multi-walled carbon nanotubes (MWCNTs) with a mass ratio of 1:1 are added to the solution under magnetic stirring. The mass ratio of polyimide fibers to MWCNTs is 1:1. The reaction is maintained at room temperature for 12 hours, and then the suspension is filtered and washed with distilled water to obtain the polyimide fiber-carbon nanotube fiber hybrid, denoted as PIF-MWCNTs;

[0050] PIF-MWCNTs and polyimide matrix powder are mechanically stirred and mixed at a ratio of 10% to 90% by mass for 15 min, and then the mixture is filled into a mold and sintered at a temperature of 370 °C and a pressure of 20 MPa for 120 min. After naturally cooling to room temperature, demolding can obtain the polyimide composite material filled with the polyimide fiber-carbon nanotube fiber hybrid, denoted as TPI / PIF-MWCNTs.

[0051] Comparative Example 1

[0052] The difference from Example 1 is only that no filling is carried out, and all are prepared with polyimide matrix powder, and the obtained material is denoted as TPI.

[0053] Comparative Example 2

[0054] The difference from Example 1 is only that PIF-MWCNTs is replaced with an equal amount of polyimide fibers (PIF), and the obtained composite material is denoted as TPI / PIF.

[0055] The detailed formulation compositions of Example 1 and Comparative Examples 1-2 are shown in Table 1.

[0056] Table 1 Compositions of materials in examples and comparative examples (wt.%)

[0057]

[0058] Structure and property characterization:

[0059] (1) Microscopic morphology

[0060] The morphology of the polyimide fibers before and after modification was observed. Figure 1 As shown, Figure 1 In the figure, (a) untreated PIF fiber photo, (b-c) untreated PIF fiber SEM photos, (d) PIF-NWCNTs photo, (e-f) PIF-NWCNTs SEM photos. Figure 1 It can be seen that the original polyimide fiber surface is relatively smooth, with only some shallow lines and micro-convex points. The treated fiber is darker in color than the untreated one, and the direction of the fiber becomes disordered. The photo taken by a high-resolution scanning electron microscope with a magnification of 10,000 times can clearly show that the originally smooth fiber surface is covered with multi-walled carbon nanotubes after treatment. The inventor tried to control the amount of grafting on the fiber by changing the added mass of DA and NWCNTs, but the experimental results showed that the amount of grafting would not change due to changes in the concentration of the suspension.

[0061] The surface roughness (Ra) of the material was studied by atomic force microscopy (AFM). Figure 2 As shown, (a) AFM photo of untreated PIF fiber, (b) AFM photo of PIF-NWCNT. Figure 2 It can be seen that the surface roughness of the untreated polyimide fiber is relatively small, with an Ra value of 117, while the surface roughness of the fiber covered with NWCNTs suddenly increases (Ra=136), which creates more anchor points on the fiber surface and makes it more likely to have a stronger interface bond with the matrix.

[0062] (2) Thermal properties of composite materials

[0063] The size and dispersion of the filler, the crystallinity of the composite material, and the interfacial bonding between the matrix and the filler will affect the thermal stability of the composite material. In this experiment, the thermal stability of several composite materials in an argon atmosphere was analyzed using a thermogravimetric analyzer. The results are as follows: Figure 3 As shown in the figure, the corresponding parameters are listed in Table 2. As can be seen from the figure, the PIF-NWCNT fiber hybrid acts as a physical barrier to reduce the transport rate of volatile products during the thermal decomposition of the composite material, which makes the composite filled with it require more heat to promote the movement of its molecular chains during the thermal decomposition process. Compared with the pure polyimide matrix, the T5 and R w The temperature increased by 14.5℃ and 7.3% respectively. Compared with the single polyimide fiber (PIF) filling, the heat resistance is significantly improved.

[0064] Table 2 Thermal properties of composite materials

[0065]

[0066] (T5: Temperature at which the material mass loss is 5%; R w : Residual mass fraction of the material at 750 °C)

[0067] (3) High-temperature tribological properties of the composite material

[0068] The tribological properties of the composite material are as Figure 4 shown, where (a) friction coefficients of the composite material at room temperature and 300 °C, (b) wear rates of the composite material at room temperature and 300 °C. The corresponding specific data are shown in Tables 3 - 4. From Figure 4 and Tables 3 - 4, it can be seen that for the wear resistance of the material, compared with the pure polyimide matrix, the wear rate of the composite material decreases after adding PIF fibers and PIF-NWCNTs. This is mainly because the fibers play a role in sharing the load during the friction process, and the change trend at high temperature is the same as that at room temperature. The friction coefficient of the material slightly decreases due to the lubricity of MWCNTs, but the number of MWCNTs grafted on the fiber hybrid is small, so the lubrication effect is not obvious.

[0069] Table 3 Friction coefficients of the composite material

[0070] Coefficient of friction (room temperature) Error Coefficient of friction (300 °C) Error TPI 0.301 0.0294 0.407 0.0332 TPI / PIF 0.321 0.0303 0.424 0.0198 TPI / PIF - NWCNTs 0.297 0.0243 0.399 0.0329

[0071] Table 4 Wear rates of the composite material

[0072] Wear rate (room temperature) Error Wear rate (300 °C) Error TPI 6.93 0.53 23.92 2.13 TPI / PIF 4.87 0.48 16.72 2.11 TPI / PIF - NWCNTs 3.92 0.55 15.66 1.87

[0073] The above are only the preferred embodiments of the present invention. It should be noted that for those of ordinary skill in the art, without departing from the principle of the present invention, several improvements and refinements can be made, and these improvements and refinements should also be regarded as the protection scope of the present invention.

Claims

1. A polyimide composite filled with a polyimide fiber-carbon nanotube fiber hybrid, comprising a thermoplastic polyimide matrix and a polyimide fiber-carbon nanotube fiber hybrid filled in the thermoplastic polyimide matrix; The mass ratio of the thermoplastic polyimide matrix to the polyimide fiber-carbon nanotube fiber hybrid is 90:10; The polyimide fiber-carbon nanotube fiber hybrid includes polyimide fibers and carbon nanotubes coated on the surface of the polyimide fibers; the polyimide fibers and the carbon nanotubes are connected by polydopamine.

2. The polyimide composite filled with a polyimide fiber-carbon nanotube fiber hybrid according to claim 1, wherein, The carbon nanotubes are multi-walled carbon nanotubes.

3. A method for preparing the polyimide composite filled with a polyimide fiber-carbon nanotube fiber hybrid according to claim 1 or 2, wherein, It includes the following steps: Disperse polyimide fibers, carbon nanotubes and dopamine into a Tris-HCl buffer solution for a modification reaction to obtain a polyimide fiber-carbon nanotube fiber hybrid; Mix the polyimide fiber-carbon nanotube fiber hybrid with thermoplastic polyimide matrix powder and conduct hot pressing and sintering to obtain a polyimide composite filled with the polyimide fiber-carbon nanotube fiber hybrid; the mass ratio of the thermoplastic polyimide matrix powder to the polyimide fiber-carbon nanotube fiber hybrid is 90:

10.

4. The preparation method according to claim 3, wherein, The pH value of the Tris-HCl buffer solution is 8.

4.

5. The preparation method according to claim 3, wherein, The mass ratio of the carbon nanotubes to polydopamine is 1:

1.

6. The preparation method according to claim 3 or 5, wherein, The mass ratio of the carbon nanotubes to polyimide fibers is 1:

1.

7. The preparation method according to claim 3, wherein, The length of the polyimide fibers is below 50 mm.

8. The preparation method according to claim 3, 4, 5 or 7, wherein, The time of the modification reaction is 12 hours.

9. The preparation method according to claim 3, wherein, The temperature of the hot pressing and sintering is 370-380 °C, the heat preservation time is 110-130 min, and the pressure is 17-23 MPa.

10. The preparation method according to any one of claims 3, 4, 5 or 7, wherein, After the modification reaction, it further includes filtering the obtained modified suspension and washing the obtained filter cake.

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