Ptfc short cut fiber with intrinsic core-shell structure, and preparation method and application thereof

Abstract

The application relates to the technical field of solid lubrication, and discloses PTFE short-cut fibers with an inherent core-shell structure, a preparation method and application. The preparation method of the PTFE short-cut fibers with the inherent core-shell structure comprises the following steps: (1) preparing PTFE concentrated solution with a core-shell structure; (2) preparing PTFE primary fibers with an inherent core-shell structure; and (3) preparing PTFE short-cut fibers with an inherent core-shell structure. The PTFE short-cut fibers with the inherent core-shell structure have the characteristics of small size and good dispersibility. In the friction and wear running-in stage, the inherent core-shell structure can quickly release PTFE particles below microns, which is beneficial to the rapid generation of a friction and wear transfer film of a friction pair and reduces the friction and wear.

Description

TECHNICAL FIELD

[0001] The application relates to the technical field of solid lubrication, and particularly relates to a PTFE short-cut fiber with an internal core-shell structure, a preparation method and application. BACKGROUND

[0002] In the field of self-lubrication, common products with a core-shell structure such as organic shell oil-containing microcapsules, inorganic shell oil-containing silica microcapsules and carbon sphere oil-containing microcapsules can provide good lubricity, but after the shell material is damaged to release the internal lubricating oil, the shell material forms a hollow structure, and even a small amount of oil-containing microcapsules as lubricating materials can cause a large decrease in the mechanical properties of the composite self-lubricating material.

[0003] In the field of high-load lubricating composite materials, polytetrafluoroethylene (PTFE) particles, PTFE short-cut fibers and PTFE compositions are often used as solid lubricating additives due to their good lubricating properties. However, when PTFE particles are used as lubricating fillers, the PTFE particles are prone to agglomeration and difficult to uniformly disperse in the matrix, resulting in a large decrease in the mechanical properties of the matrix; when PTFE short-cut fibers are used as lubricating fillers, the friction coefficient is high in the early stage of friction, the friction torque is large, and the heat generation is fast, resulting in a fast wear rate in the early stage, and the PTFE short-cut fibers are difficult to apply in the field with limited starting torque.

[0004] Therefore, the prior art still needs to be improved and developed. SUMMARY

[0005] In view of the deficiencies of the prior art, the purpose of the application is to provide a PTFE short-cut fiber with an internal core-shell structure, a preparation method and application, and to solve the problems of the existing PTFE short-cut fiber.

[0006] The technical scheme of the application is as follows:

[0007] A preparation method of a PTFE short-cut fiber with an internal core-shell structure, wherein the method comprises the following steps:

[0008] (1) preparing a PTFE concentrated solution with a core-shell structure:

[0009] diluting the PTFE concentrated dispersion solution with deionized water to obtain a PTFE dispersion solution;

[0010] adding methyl acrylamide to the PTFE dispersion solution under a nitrogen environment, then adding methyl methacrylate dropwise, and heating to 70-80 DEG C in a water bath after the dropwise addition is completed to obtain a first mixed solution;

[0011] adding a potassium persulfate solution dropwise in the first mixed solution, and reacting for at least 8 hours after the dropwise addition is completed to obtain a reaction solution;

[0012] The reaction solution is sieved and distilled under reduced pressure to obtain the PTFE concentrated solution with core-shell structure;

[0013] (2) Preparation of PTFE primary fiber with inherent core-shell structure:

[0014] Sodium alginate is dissolved in water to obtain a sodium alginate carrier solution;

[0015] The PTFE concentrated solution with core-shell structure is added to the sodium alginate carrier solution to obtain a second mixed solution, and a silicone defoaming agent is added dropwise to remove bubbles to obtain a spinning solution;

[0016] The spinning solution is spun, passed through a coagulation bath of CaCl2 solution, washed in an ethanol solution, and wound up to obtain the PTFE primary fiber with inherent core-shell structure;

[0017] (3) Preparation of PTFE chopped fiber with inherent core-shell structure:

[0018] The PTFE primary fiber with inherent core-shell structure is subjected to first sintering at a sintering temperature of 280-325°C for 5-15 min, and is cut to obtain mm-level chopped fiber;

[0019] The mm-level chopped fiber is subjected to second sintering at a sintering temperature of 300-325°C for 20-30 min, and is ground to obtain the PTFE chopped fiber with inherent core-shell structure.

[0020] The preparation method of the PTFE chopped fiber with inherent core-shell structure, wherein the amount of the PTFE concentrated dispersion solution is 50 parts by mass, the amount of the methacrylamide is 20-30 parts, and the amount of the methyl methacrylate is 120-130 parts;

[0021] The concentration of the PTFE concentrated dispersion solution is 60 wt%.

[0022] The preparation method of the PTFE chopped fiber with inherent core-shell structure, wherein the preparation method of the potassium persulfate solution is dissolving potassium persulfate in 20 parts of deionized water;

[0023] The amount of potassium persulfate added is 0.05 g per 100 g of the first mixed solution.

[0024] The preparation method of the PTFE chopped fiber with inherent core-shell structure, wherein the process of diluting the PTFE concentrated dispersion solution with deionized water is diluting the PTFE concentrated dispersion solution with 500-700 parts of the deionized water;

[0025] The reduced pressure distillation is reduced pressure distillation of the reaction solution to 250-350 parts.

[0026] The preparation method of the PTFE short-cut fiber with inherent core-shell structure, wherein the process of dissolving sodium alginate in water to obtain a sodium alginate carrier solution comprises the following steps:

[0027] According to the mass fraction, 600 parts of distilled water are placed in a container, stirring is started, and heating is started to 75℃, the speed is 200 RPM, 30 parts of the sodium alginate is weighed and added to the container in batches, after complete addition, the speed is increased to 400 RPM, stirring for at least 3h, defoaming, to obtain the sodium alginate carrier solution.

[0028] The preparation method of the PTFE short-cut fiber with inherent core-shell structure, wherein, for every 30 parts of the sodium alginate, 400-600 parts of the PTFE concentrated solution with core-shell structure is added;

[0029] 0.05 g of silicone defoaming agent is added per 100 g of the second mixed solution.

[0030] The preparation method of the PTFE short-cut fiber with inherent core-shell structure, wherein, in the spinning process, the diameter of the spinneret is set to 40-60 μm;

[0031] The mass concentration of the CaCl2 solution is 1-4%, and the mass concentration of the ethanol solution is 50%;

[0032] In step (3), during the cutting process, the cutter speed is 2 times / s, and the grinding time is at least 15 min;

[0033] The size of the PTFE short-cut fiber with inherent core-shell structure is 50-300 μm.

[0034] A PTFE short-cut fiber with inherent core-shell structure, wherein the PTFE short-cut fiber with inherent core-shell structure is prepared by the preparation method of the PTFE short-cut fiber with inherent core-shell structure as described above.

[0035] The application of the PTFE short-cut fiber with inherent core-shell structure as described above, wherein the PTFE short-cut fiber with inherent core-shell structure is used to prepare a self-lubricating composite material.

[0036] The application of the PTFE short-cut fiber with inherent core-shell structure, wherein the preparation method of the self-lubricating composite material comprises the following steps:

[0037] The PTFE short-cut fiber with the inherent core-shell structure is added into the liquid heat-curable resin, and the mixture is fully stirred at room temperature, then the resin curing component is added, and the system is continuously stirred to be uniform; after vacuum degassing, curing treatment is carried out to obtain the self-lubricating composite material.

[0038] The total amount of the PTFE short-cut fiber with the inherent core-shell structure and the liquid heat-curable resin is 100% by mass fraction, wherein the PTFE short-cut fiber with the inherent core-shell structure accounts for 5-40%, and the balance is the liquid heat-curable resin.

[0039] The liquid heat-curable resin is a liquid vinyl resin, a liquid epoxy resin or a liquid polyurethane resin.

[0040] Beneficial effects: The PTFE short-cut fiber with the inherent core-shell structure has the characteristics of small size and good dispersibility. During the friction and wear running-in stage, the inherent core-shell structure can quickly release PTFE particles below microns, which is beneficial to the rapid generation of the lubrication transfer film of the friction pair and reduces the friction and wear. At the same time, the rod-like structure of the PTFE short-cut fiber with the inherent core-shell structure has less effect on the mechanical strength of the self-lubricating composite material than the spherical structure of the powder, so that the self-lubricating composite material containing the PTFE short-cut fiber with the inherent core-shell structure has advantages in both mechanical and friction properties. BRIEF DESCRIPTION OF DRAWINGS

[0041] Figure 1 It is a scanning electron microscope result graph of the PTFE concentrated solution with the core-shell structure in Example 1 of the present application.

[0042] Figure 2 It is a scanning electron microscope result graph of the PTFE short-cut fiber with the inherent core-shell structure in Example 1 of the present application.

[0043] Figure 3 It is a friction coefficient test result graph in Example 1 of the present application.

[0044] Figure 4 It is a compression strength test and wear rate measurement result graph in Example 1 of the present application. DETAILED DESCRIPTION

[0045] The present application provides a PTFE short-cut fiber with an inherent core-shell structure, a preparation method and an application. In order to make the purpose, technical scheme and effects of the present application more clear and explicit, the present application is further described in detail below. It should be understood that the specific embodiments described herein are only used to explain the present application and do not limit the present application.

[0046] The application provides a preparation method of PTFE short-cut fibers with intrinsic core-shell structure, comprising the following steps:

[0047] (1) preparing a PTFE concentrated solution with core-shell structure:

[0048] Dilute the PTFE concentrated dispersion solution with deionized water (DI water) to obtain a diluted PTFE dispersion solution: take 50 parts of 60wt% PTFE concentrated dispersion solution and 500-700 parts of deionized water (DI water) according to the mass fraction, and add them into a four-necked flask in turn, start stirring at room temperature, and uniformly stir at 400-600 RPM to obtain a diluted PTFE dispersion solution;

[0049] Take 20-30 parts of methacrylamide (MAM) and add it into a four-necked flask with nitrogen, then slowly drop 120-130 parts of methyl methacrylate (MMA) into the four-necked flask, start water bath heating after the dropping is completed, heat to 70-80℃ to obtain a first mixed solution;

[0050] Dissolve an appropriate amount of potassium persulfate (0.05 g per 100 g of the first mixed solution) in 20 parts of DI water to obtain a potassium persulfate solution, slowly drop the potassium persulfate solution into the first mixed solution, and react for at least 8 hours after the dropping is completed to obtain a reaction solution;

[0051] Filter the reaction solution with a 50-mesh screen to remove a small amount of agglomerated precipitated substances, and then place it in a rotary evaporator for reduced pressure distillation to 250-350 parts to obtain a PTFE concentrated solution with core-shell structure ((MMA-MAM)@PTFE) that can be used for carrier spinning.

[0052] In the scheme, MAM and MMA are used as shell layer reaction monomers of the (MMA-MAM)@PTFE core-shell structure, and a free radical polymerization reaction occurs on the surface of the PTFE particles to form a core-shell structure of (MMA-MAM) coated PTFE. By introducing MAM, the thermal stability of the MAM-MMA copolymer can be improved, so that the shell material has both high heat resistance and good thermal stability, and can prevent the core-shell structure from being damaged by heat in the subsequent sintering process. When the MAM / MMA ratio is 20:130-30:120, the heat resistance is best.

[0053] In this step, after the reaction solution is prepared, the content of the PTFE concentrated solution with core-shell structure in the spinning solution can be increased by reducing pressure distillation to 250-350 parts.

[0054] (2) preparing PTFE primary fibers with intrinsic core-shell structure:

[0055] Sodium alginate is dissolved in water to obtain a sodium alginate carrier solution: 600 parts of distilled water is placed in a three-necked flask, stirring is started, and heating is started to 75°C at a rotation speed of 200 RPM. 30 parts of sodium alginate is added in small batches to the three-necked flask, and after complete addition, the rotation speed is increased to 400 RPM. Stirring is continued for at least 3 hours, and defoaming is performed to obtain the sodium alginate carrier solution;

[0056] 400-600 parts of the PTFE concentrated solution with the core-shell structure is added to the sodium alginate carrier solution to obtain a second mixed solution. A small amount of silicone defoaming agent is added dropwise (0.05 g per 100 g of the second mixed solution), and stirring is continued for at least 8 hours. Defoaming is performed to obtain the spinning solution.

[0057] The spinning solution is poured into a spinning machine solution tank, and a metering pump is started. The spinneret diameter is 40-60 μm. The nascent PTFE fiber with the internal core-shell structure is obtained by manually pulling through a coagulation bath of a CaCl2 solution with a mass concentration of 1-4%, a 50% ethanol solution, and winding.

[0058] In the present application, the spinneret diameter is set to 40-60 μm. If it is lower than 40 μm, the yarn drawing process is prone to yarn breakage. If it is higher than 60 μm, the mechanical properties of the product will be reduced.

[0059] (3) Preparation of the PTFE short-cut fiber with the internal core-shell structure:

[0060] The nascent PTFE fiber with the internal core-shell structure is sintered in a muffle furnace at 280-325°C for 5-15 min to obtain a light brown fiber. Subsequently, the fiber is cut by using a fiber cutting machine at a feeding speed of 5-10 mm / min and a cutter speed of 2 times / s to obtain a mm-level short-cut fiber.

[0061] The mm-level short-cut fiber is sintered in a muffle furnace at 300-325°C for 20-30 min to obtain a light brown short-cut fiber. Subsequently, the fiber is ground by using a fiber grinder for at least 15 min to obtain a PTFE short-cut fiber with the internal core-shell structure with a size of 50-300 μm.

[0062] In the present application, the first short-time sintering can obtain a fiber with insufficient carrier sintering. At this time, the fiber has poor toughness and is prone to cutting, and is suitable for cutting processing. The second sintering can obtain a fiber with sufficient carrier sintering, increase the content of PTFE in the fiber, and further improve the self-lubricating performance of the fiber. The present application is first cut to mm, which is beneficial to subsequent grinding processing to achieve the required size and uniformity.

[0063] The application further provides the PTFE short fiber with the intrinsic core-shell structure, which is prepared by the preparation method of the PTFE short fiber with the intrinsic core-shell structure.

[0064] The PTFE short fiber with the intrinsic core-shell structure has the characteristics of small size and good dispersibility. During the friction and wear running-in stage, the intrinsic core-shell structure can quickly release the PTFE particles below microns, which is beneficial to the rapid generation of the transfer film of the friction pair and the reduction of the friction and wear. Meanwhile, the rod-shaped structure of the PTFE short fiber with the intrinsic core-shell structure has little influence on the mechanical strength of the self-lubricating composite material compared with the spherical structure of the powder, so that the self-lubricating composite material containing the PTFE short fiber with the intrinsic core-shell structure has the advantages in the mechanical and friction properties.

[0065] The application further provides an application of the PTFE short fiber with the intrinsic core-shell structure, which is used for preparing the self-lubricating composite material.

[0066] Further, the preparation method of the self-lubricating composite material comprises the following steps.

[0067] The PTFE short fiber with the intrinsic core-shell structure is added into the liquid heat-curable resin in a certain mass fraction, and is fully stirred and mixed at room temperature. Then, the resin curing component is added, and the system is continuously stirred to be uniform. After vacuum degassing, the curing treatment is performed to obtain the self-lubricating composite material containing the PTFE short fiber with the intrinsic core-shell structure.

[0068] According to the mass fraction, the total amount of the PTFE short fiber with the intrinsic core-shell structure and the liquid heat-curable resin is 100%, wherein the PTFE short fiber with the intrinsic core-shell structure accounts for 5-40%, and the balance is the liquid heat-curable resin.

[0069] Further, the liquid heat-curable resin can be a liquid vinyl resin, a liquid epoxy resin, a liquid polyurethane resin and the like.

[0070] The dispersibility of the lubricating filler can be generally judged by observing the dispersion of the lubricating filler in the resin matrix after the lubricating filler is added into the resin matrix. For example, the PTFE powder (Mcln) often presents the lump above mm in the resin matrix. However, the PTFE short fiber with the intrinsic core-shell structure of the application is not aggregated itself and is uniformly dispersed in the resin matrix after being added into the resin matrix, and has good dispersibility.

[0071] The self-lubricating composite material containing the PTFE chopped fibers with an inherent core-shell structure of the present application achieves low friction, short running-in time, stable friction coefficient, and low wear over a long period of time, and can be used in aerospace, heavy machinery and other fields. In the embodiment of the present application, the self-lubricating composite material containing the PTFE chopped fibers with an inherent core-shell structure of the present application has a bearing strength of 95 MPa, a friction coefficient of 0.11, and a wear rate of 6.7*10 -6 mm 3 / Nm, it is an excellent high-load self-lubricating material.

[0072] The present application is further described below through specific examples.

[0073] Example 1

[0074] (1) Preparation of PTFE concentrate with core-shell structure, the specific operation is as follows:

[0075] 1. Take 50 g of 60wt% PTFE concentrated dispersion (McLean reagent) and 600 g of DI water, add them into a four-necked flask in sequence, start stirring at 500 RPM at room temperature, and stir thoroughly for 30 minutes to obtain a diluted PTFE dispersion.

[0076] 2. Take 20 g of methacrylamide (MAM) and add it to a four-necked flask filled with nitrogen. Then take 130 g of methyl methacrylate (MMA) and slowly add it dropwise to the four-necked flask. After the addition is completed, turn on the water bath and heat it to 75°C.

[0077] 3. Take 0.4g potassium persulfate and dissolve it in 20g DI water. Slowly add it dropwise to the mixed solution prepared in step 2. After the addition is complete, ensure the reaction for 8 hours.

[0078] 4. The reaction solution prepared in step 3 above was filtered through a 50-mesh sieve to remove a small amount of agglomerated precipitate, and then distilled on a rotary evaporator under reduced pressure to 300 g to obtain a PTFE concentrate with a core-shell structure ((MMA-MAM)@PTFE) that can be used for carrier spinning.

[0079] (2) Preparation of PTFE primary fibers with an intrinsic core-shell structure. The specific operations are as follows:

[0080] 1. Place 600 g of distilled water in a three-necked flask, start stirring, heat to 75°C, rotate at 200 RPM, weigh 30 g of sodium alginate and add it to the three-necked flask in small batches. After complete addition, increase the speed to 400 RPM, stir for 3 h, and degas to obtain a sodium alginate carrier solution.

[0081] 2. Add 400 g of PTFE concentrate with core-shell structure to the above sodium alginate carrier solution, add 0.5 g of silicone antifoaming agent dropwise, fully stir for 8 h, and defoam to obtain a spinning solution.

[0082] 3. Pour the above spinning solution into a spinning machine solution tank, start the metering pump, use a spinneret with a diameter of 40 μm, manually pull through a coagulation bath of a 2% CaCl2 solution, then through a 50% ethanol solution, and wind up to obtain PTFE nascent fibers with intrinsic core-shell structure.

[0083] (3) Preparation of PTFE short fibers with intrinsic core-shell structure, the specific operation is as follows:

[0084] 1. Sinter the PTFE nascent fibers with intrinsic core-shell structure at 300°C for 10 min using a muffle furnace to obtain light brown fibers, then use a fiber cutting machine for cutting treatment, set the feeding speed to 5 mm / min and the cutting knife speed to 2 times / s to obtain mm-level short fibers;

[0085] 2. Sinter the above mm-level short fibers at 300°C for 30 min using a muffle furnace to obtain light brown short fibers, then use a fiber grinder for grinding treatment for 15 min to obtain PTFE short fibers with intrinsic core-shell structure.

[0086] (4) Preparation of a vinyl resin composite containing PTFE short fibers with intrinsic core-shell structure, the specific operation is as follows:

[0087] According to the mass fraction, add 30% of PTFE short fibers with intrinsic core-shell structure to 70% of liquid vinyl resin (901 vinyl resin), mix thoroughly at room temperature, then add 0.5% of dibenzoyl peroxide (BPO) and 0.5% of cobalt naphthenate based on the mass of the liquid vinyl resin, and continue to stir to make the system uniform. After vacuum defoaming, heat from room temperature to 60°C at a rate of 1°C / min and keep the temperature for 6 h for curing to obtain a vinyl resin composite containing PTFE short fibers with intrinsic core-shell structure.

[0088] The PTFE concentrate with core-shell structure in this embodiment was tested using a scanning electron microscope, and the results are shown in Figure 1 The structure of the PTFE with core-shell structure presents a spherical shape with a size of 300-500 nm.

[0089] The PTFE short fibers with intrinsic core-shell structure in this embodiment were tested using a scanning electron microscope, and the results are shown in Figure 2 The PTFE short fibers with intrinsic core-shell structure have a fiber diameter of about 50 μm and a length of about 100 μm, and the core-shell structure components can be seen inside the fibers.

[0090] Compression strength test, friction coefficient test and wear rate measurement were performed using a universal testing machine, a Bruker UMT tribometer and a Bruker white light interferometer, respectively.

[0091] Test conditions: the universal testing machine test conditions were 1 mm / min loading speed; the Bruker UMT tribometer used a reciprocating drive module with a load of 20 N, a frequency of 5 HZ and a stroke of 3 mm, and the counterform sample was a 10 mm diameter steel ball; the Bruker white light interferometer was used to analyze the wear rate of the wear track after UMT testing.

[0092] The vinyl resin composite material containing 30%wt of the PTFE short-cut fiber with the intrinsic core-shell structure prepared in the present example was taken as the test object, and the comparative samples were pure vinyl resin (901 resin), vinyl resin composite material containing 30%wt of PTFE powder (Maklin) and vinyl resin composite material containing 30%wt of PTFE short-cut fiber (Dow Teflon™ PTFE Fibers). The preparation methods of the comparative samples and the vinyl resin composite material containing 30%wt of the PTFE short-cut fiber with the intrinsic core-shell structure of the present example were the same, and the only difference was that different lubricating fillers were used.

[0093] In the preparation of the vinyl resin composite material containing 30%wt of PTFE powder (Maklin), the dispersion of the PTFE powder in the liquid vinyl resin was observed after the PTFE powder was added to the vinyl resin, and the PTFE powder presented lumps of more than mm in the liquid vinyl resin; while the PTFE short-cut fiber with the intrinsic core-shell structure was added to the liquid vinyl resin in the present example, the PTFE short-cut fiber with the intrinsic core-shell structure did not agglomerate by itself and was uniformly dispersed in the liquid vinyl resin, which proved that the PTFE short-cut fiber with the intrinsic core-shell structure of the present example had good dispersibility.

[0094] (1) Friction coefficient test results

[0095] The test results are shown in Table 1. Figure 3 As shown in Table 1, the COF test results showed that the COF of the vinyl resin composite material containing 30%wt of the PTFE short-cut fiber with the intrinsic core-shell structure (corresponding to the “PTFE short-cut fiber composite resin with intrinsic core-shell structure” in Table 1) rapidly decreased and stabilized at about 0.11 as the friction and wear proceeded. The initial COF of the vinyl resin composite material containing 30%wt of PTFE short-cut fiber (corresponding to the “PTFE short-cut fiber composite resin” in Table 1) was relatively high, and stabilized at about 0.12 as the friction continued. The initial COF of the vinyl resin composite material containing 30%wt of PTFE powder (Maklin) (corresponding to the “PTFE powder composite resin” in Table 1) was relatively high, and stabilized at about 0.12 as the friction continued. Figure 3 Figure 3 Figure 3 ​​The initial COF of the “PTFE powder composite resin” is low, but the COF coefficient is unstable, which is related to its uneven distribution.

[0096] (2) Compression strength test and wear rate measurement results

[0097] like Figure 4 As shown in the mechanical test results, the vinyl resin composite material containing 30%wt PTFE powder (McLean) (corresponding to Figure 4 The strength of the "PTFE powder composite resin" in the above formula is the lowest. PTFE powder will cause the bearing strength of vinyl resin to drop significantly. The vinyl resin composite material containing 30%wt of PTFE chopped fibers with an internal core-shell structure (corresponding to Figure 4 The “PTFE chopped fiber composite resin with an internal core-shell structure”) and the vinyl resin composite material containing 30%wt PTFE chopped fibers (corresponding to Figure 4 The wear rate measurement results show that the vinyl resin composite material containing 30%wt of PTFE chopped fibers with an internal core-shell structure (corresponding to Figure 4 The wear rate of the “PTFE chopped fiber composite resin with an internal core-shell structure” was the lowest, and the vinyl resin composite material containing 30%wt PTFE powder (McLean) (corresponding to Figure 4 The wear rate of "PTFE powder composite resin" is the highest.

[0098] In summary, the vinyl resin composite material containing 30%wt of PTFE chopped fibers with an internal core-shell structure prepared in Example 1 has a bearing strength of 95 MPa, a friction coefficient of 0.11, and a wear rate of 6.7*10 -6 mm 3 / Nm, with good mechanical and tribological properties.

[0099] Example 2

[0100] (1) Preparation of PTFE concentrate with core-shell structure. The specific operation is as follows:

[0101] 1. Take 50 g of 60wt% PTFE concentrated dispersion (McLean reagent) and 600 g of DI water, add them into a four-necked flask in sequence, start stirring at 500 RPM at room temperature, and stir thoroughly for 30 minutes to obtain a diluted PTFE dispersion.

[0102] 2. Take 30 g of methacrylamide (MAM) and add it to a four-necked flask filled with nitrogen. Then take 120 g of methyl methacrylate (MMA) and slowly add it dropwise to the four-necked flask. After the addition is completed, turn on the water bath and heat it to 75°C.

[0103] 3. Take 0.4 g of potassium persulfate and dissolve it in 20 g of DI water, slowly add it to the mixed solution prepared in step 2, and ensure that the reaction is carried out for 8 h after the addition is completed.

[0104] 4. The reaction solution prepared in the above step 3 is filtered with a 50 mesh sieve to remove a small amount of agglomerated precipitated material, and is subjected to reduced pressure distillation on a rotary evaporator to 300 g to obtain a PTFE concentrate with a core-shell structure ((MMA-MAM)@PTFE) that can be used for carrier spinning.

[0105] (2) Preparation of PTFE nascent fiber with intrinsic core-shell structure, the specific operation is as follows:

[0106] 1. Take 600 g of distilled water and place it in a three-necked flask, start stirring, heat to 75℃, rotate at 200 RPM, take 30 g of sodium alginate and add it to the three-necked flask in small batches, after complete addition, increase the rotation speed to 400 RPM, stir for 3 h, and degas to obtain a sodium alginate carrier solution.

[0107] 2. Add 600 g of PTFE concentrate with a core-shell structure to the above sodium alginate carrier solution, add 0.6 g of silicone defoaming agent, stir thoroughly for 8 h, and degas to obtain a spinning solution.

[0108] 3. Pour the above spinning solution into the spinning machine solution tank, start the metering pump, the spinneret diameter is 60 μm, manually pull through the coagulation bath of 4% CaCl2 solution, and then through the 50% ethanol solution bath, and then wind up to obtain PTFE nascent fiber with intrinsic core-shell structure.

[0109] (3) Preparation of PTFE short-cut fiber with intrinsic core-shell structure, the specific operation is as follows:

[0110] 1. Sinter the PTFE nascent fiber with intrinsic core-shell structure in a muffle furnace at 280℃ for 10 minutes to obtain a light brown fiber, then use a fiber cutting machine for cutting treatment, set the feeding speed to 10 mm / min, and the cutter speed to 2 times / s to obtain mm-level short-cut fiber.

[0111] 2. Sinter the above mm-level short-cut fiber in a muffle furnace at 310℃ for 30 minutes to obtain a light brown short-cut fiber, then use a fiber grinder for grinding treatment for 15 min to obtain PTFE short-cut fiber with intrinsic core-shell structure.

[0112] (4) Epoxy resin composite material containing PTFE short-cut fiber with intrinsic core-shell structure, the specific operation is as follows:

[0113] 35% by weight of PTFE chopped fibers with an intrinsic core-shell structure were added to 65% of liquid epoxy resin (E51 epoxy resin) and thoroughly stirred at room temperature. Subsequently, a resin curing agent (isophorone diamine (IPDA)) was added at a mass ratio of 5:1 (liquid epoxy resin:curing agent). Stirring was continued until the mixture was homogenized. After vacuum degassing, the mixture was heated from room temperature to 80°C at a rate of 1°C / min and maintained at this temperature for 6 hours for curing. This yielded an epoxy resin composite containing PTFE chopped fibers with an intrinsic core-shell structure.

[0114] The epoxy resin composite material containing PTFE chopped fibers with an internal core-shell structure prepared in Example 2 has a bearing strength of 78 MPa, a friction coefficient of 0.103, and a wear rate of 5.9*10 -6 mm 3 / Nm, with good mechanical and tribological properties.

[0115] Example 3

[0116] (1) Preparation of PTFE concentrate with core-shell structure, the specific operation is as follows:

[0117] 1. Take 50 g of 60wt% PTFE concentrated dispersion (McLean reagent) and 600 g of DI water, add them into a four-necked flask in sequence, start stirring at 500 RPM at room temperature, and stir thoroughly for 30 minutes to obtain a diluted PTFE dispersion.

[0118] 2. Take 30g of methacrylamide (MAM) and add it to a four-necked flask filled with nitrogen. Then take 120g of methyl methacrylate (MMA) and slowly add it dropwise to the four-necked flask. After the addition is completed, turn on the water bath and heat it to 75℃.

[0119] 3. Take 0.4 g of potassium persulfate and dissolve it in 20 g of DI water. Slowly add it dropwise to the mixed solution prepared in step 2. After the addition is complete, ensure that the reaction is carried out for 8 hours.

[0120] 4. The reaction solution prepared in step 3 above was filtered through a 50-mesh sieve to remove a small amount of agglomerated precipitate and then distilled on a rotary evaporator under reduced pressure to 300 g to obtain a PTFE concentrate with a core-shell structure ((MMA-MAM)@PTFE) suitable for carrier spinning.

[0121] (2) Preparation of PTFE primary fibers with an intrinsic core-shell structure. The specific operations are as follows:

[0122] 1. Take 600 g distilled water into a three-necked flask, open the stirring, heat to 75℃, the speed of 200 RPM, take 30 g sodium alginate into the three-necked flask in small batches, after complete addition, the speed is increased to 400 RPM, stirring for 3 h, defoaming, to get sodium alginate carrier solution.

[0123] 2. Add 550 g PTFE concentrated solution with core-shell structure to the above sodium alginate carrier solution, add 0.55 g silicone defoaming agent dropwise, stir for 8 h, defoam, to get spinning solution.

[0124] 3. Pour the above spinning solution into the spinning machine solution tank, open the metering pump, the spinneret diameter is 60 μm, manually pull through the coagulation bath of 3% CaCl2 solution, through the 50% ethanol solution bath, and wind up. Get PTFE primary fiber with internal core-shell structure.

[0125] (3) Preparation of PTFE short fiber with internal core-shell structure, the specific operation is as follows:

[0126] 1. Sinter the PTFE primary fiber with internal core-shell structure in the muffle furnace at 325℃ for 10 minutes to get light brown fiber, then use the fiber cutting machine for cutting treatment, the feeding speed is set to 10 mm / min, the cutter speed is 2 times / s, to get mm-level short fiber.

[0127] 2. Sinter the above mm-level short fiber in the muffle furnace at 325℃ for 30 minutes to get light brown short fiber, then use the fiber grinder for grinding treatment for 15 min to get PTFE short fiber with internal core-shell structure.

[0128] (4) Preparation of polyurethane resin composite containing PTFE short fiber with internal core-shell structure, the specific operation is as follows:

[0129] According to the mass fraction, 35% PTFE short fiber with internal core-shell structure is added to 65% liquid polyurethane resin component A (liquid MDI), and stirred at room temperature, then 55:45 mass ratio of component A: component B is added to polyurethane component B containing resin catalyst (containing 0.2% dibutyltin dilaurate polyether polyol PPG-400), and the system is uniformly stirred. After vacuum defoaming, heat from room temperature to 65℃ at 1℃ / min and keep for 6 h for curing, to get polyurethane resin composite containing PTFE short fiber with internal core-shell structure.

[0130] The polyurethane resin composite containing PTFE short fiber with internal core-shell structure prepared in Example 3 has a bearing strength of 63 MPa, a friction coefficient of 0.87, and a wear rate of 4.8*10-6 mm 3 / Nm, with good mechanical and tribological properties.

[0131] It should be understood that the application is not limited to the examples described above, which can be modified or adapted by a person of ordinary skill in the art in the light of the above description, all such modifications and adaptations being intended to fall within the scope of the application.

Claims

1. A method for preparing PTFE chopped fibers with an intrinsic core-shell structure, characterized in that: The following steps are involved: (1) Preparation of PTFE concentrate with core-shell structure: diluting the PTFE concentrated dispersion with deionized water to obtain a PTFE dispersion; Under a nitrogen environment, adding methacrylamide to the PTFE dispersion, and then adding methyl methacrylate dropwise, and heating in a water bath to 70-80° C. after the addition is complete to obtain a first mixed solution; adding a potassium persulfate solution dropwise to the first mixed solution, and reacting for at least 8 hours after the addition is complete to obtain a reaction solution; The reaction solution is sieved and distilled under reduced pressure to obtain the PTFE concentrate having a core-shell structure; the methacrylamide and the methyl methacrylate are shell reaction monomers, and the methacrylamide and the methyl methacrylate undergo free radical polymerization on the surface of the PTFE particles to form a core-shell structure in which the copolymer of the methacrylamide and the methyl methacrylate encapsulates the PTFE; (2) Preparation of PTFE primary fibers with intrinsic core-shell structure: dissolving sodium alginate in water to obtain a sodium alginate carrier solution; adding the PTFE concentrate having a core-shell structure to the sodium alginate carrier solution to obtain a second mixed solution, adding a silicone defoamer dropwise thereto for degassing to obtain a spinning solution; The spinning solution is spun, passed through a coagulation bath of a CaCl2 solution, washed through an ethanol solution, and rolled up to obtain the PTFE nascent fiber with an intrinsic core-shell structure; (3) Preparation of PTFE chopped fibers with an intrinsic core-shell structure: The PTFE as-spun fibers with an intrinsic core-shell structure are subjected to a first sintering process at a temperature of 280-325° C. for a time of 5-15 minutes, and then cut to obtain millimeter-sized chopped fibers. The millimeter-sized chopped fibers are subjected to a second sintering process at a sintering temperature of 300-325° C. for a sintering time of 20-30 minutes, and then ground to obtain the PTFE chopped fibers with an intrinsic core-shell structure.

2. The method for preparing PTFE chopped fibers with an intrinsic core-shell structure according to claim 1, characterized in that: By mass, the amount of the PTFE concentrated dispersion is 50 parts, the amount of the methacrylamide is 20-30 parts, and the amount of the methyl methacrylate is 120-130 parts; The concentration of the PTFE concentrated dispersion is 60 wt %.

3. The method for preparing PTFE chopped fibers with an intrinsic core-shell structure according to claim 2, characterized in that: The potassium persulfate solution is prepared by dissolving potassium persulfate in 20 parts of deionized water; The amount of potassium persulfate added is 0.05 g per 100 g of the first mixed solution.

4. The method for preparing PTFE chopped fibers with an intrinsic core-shell structure according to claim 3, characterized in that: The process of diluting the PTFE concentrated dispersion with deionized water is to dilute the PTFE concentrated dispersion with 500-700 parts of the deionized water; The reduced pressure distillation is to distill the reaction solution under reduced pressure to 250-350 parts.

5. The method for preparing PTFE chopped fibers with an intrinsic core-shell structure according to claim 4, characterized in that: The process of dissolving sodium alginate in water to obtain a sodium alginate carrier solution specifically comprises the following steps: 600 parts of distilled water were placed in a container, stirred, heated to 75°C, and rotated at 200 RPM. 30 parts of sodium alginate were weighed and added to the container in batches. After complete addition, the speed was increased to 400 RPM, stirred for at least 3 hours, and degassed to obtain the sodium alginate carrier solution.

6. The method for preparing PTFE chopped fibers with an intrinsic core-shell structure according to claim 5, characterized in that: For every 30 parts of the sodium alginate, 400 to 600 parts of the PTFE concentrate with a core-shell structure are added; 0.05 g of organosilicon defoamer was added per 100 g of the second mixed solution.

7. The method for preparing PTFE chopped fibers with an intrinsic core-shell structure according to claim 1, characterized in that: During the spinning process, the spinneret diameter is set to 40-60 μm; The mass concentration of the CaCl2 solution is 1-4%, and the mass concentration of the ethanol solution is 50%; In step (3), during the cutting process, the cutting speed is 2 times / s, and the grinding process time is at least 15 minutes; The size of the PTFE chopped fibers with an internal core-shell structure is 50-300 μm.

8. A PTFE chopped fiber with an intrinsic core-shell structure, characterized in that: The PTFE chopped fibers with an intrinsic core-shell structure are prepared by the method for preparing PTFE chopped fibers with an intrinsic core-shell structure according to any one of claims 1 to 7.

9. A use of the PTFE chopped fibers with an intrinsic core-shell structure as claimed in claim 8, characterized in that: The PTFE chopped fibers with an intrinsic core-shell structure are used to prepare self-lubricating composite materials.

10. The use of the PTFE chopped fibers with an intrinsic core-shell structure according to claim 9, characterized in that: The preparation method of the self-lubricating composite material comprises the following steps: The PTFE chopped fibers with an intrinsic core-shell structure are added to a liquid heat-curable resin, and the mixture is thoroughly stirred at room temperature. The resin curing component is then added, and the stirring is continued to make the system uniform; vacuum degassing is performed and the curing treatment is performed to obtain the self-lubricating composite material; Calculated by mass fraction, the total amount of the PTFE chopped fibers with an intrinsic core-shell structure and the liquid heat-curable resin is 100%, wherein the PTFE chopped fibers with an intrinsic core-shell structure account for 5 to 40%, and the balance is the liquid heat-curable resin; The liquid heat-curable resin is liquid vinyl resin, liquid epoxy resin or liquid polyurethane resin.

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