Graphite-filled crystalline polyimide low-temperature wear-resistant composite material and preparation method thereof

Abstract

The application provides a kind of graphite filling crystalline polyimide low temperature wear-resistant composite material and preparation method thereof, and relates to the technical field of polymer composite material.The composite material takes crystalline polyimide as matrix, and is compounded with flake graphite modified by silane coupling agent and low temperature compatible additive, and is prepared by "raw material pretreatment-melt blending-low temperature mould pressing-post curing" process.The core innovation lies in the interface synergistic design of modified graphite and crystalline polyimide, and the optimization of low temperature forming process, so that the friction coefficient of the composite material is ≤0.15 in the range of-50℃~room temperature, the wear rate is ≤5×10 ‑6 mm 3 / (N·m), the tensile strength is ≥120MPa, and the heat distortion temperature is ≥280℃.The composite material has excellent low temperature wear resistance, balanced mechanical and thermal stability, and is suitable for mechanical seal, bearing, gear and other components under low temperature working condition, and has wide application prospect.

Description

Technical Field

[0001] This invention relates to the field of polymer composite materials technology, specifically to a graphite-filled crystalline polyimide low-temperature wear-resistant composite material and its preparation method. Background Technology

[0002] Polyimide (PI), as a high-performance polymer material, possesses excellent thermal stability, mechanical properties, and chemical corrosion resistance, and is widely used in aerospace, precision machinery, and other fields. However, traditional polyimide composites have significant drawbacks in low-temperature environments (-50℃ to room temperature): Low-temperature wear resistance degradation: Non-crystalline polyimide is prone to embrittlement at low temperatures, and the coefficient of friction and wear rate increase significantly, which cannot meet the wear resistance requirements under low-temperature working conditions; Uneven graphite dispersion: The surface of flake graphite is highly inert and has weak interfacial bonding with the polyimide matrix, making it prone to agglomeration, which leads to large fluctuations in the performance of composite materials. Poor interfacial compatibility: At low temperatures, the difference in thermal expansion coefficients between the matrix and the filler intensifies, increasing the risk of interfacial delamination and further deteriorating wear resistance and mechanical properties; Limitations of molding process: Traditional high-temperature molding process is prone to graphite oxidation or matrix degradation, while low-temperature molding is difficult to guarantee the uniformity of material melting.

[0003] Existing technologies mostly focus on wear-resistant modification at room temperature, improving wear resistance by adding fillers such as graphite and molybdenum disulfide, but have not solved the problems of interfacial synergy and performance stability at low temperatures; some low-temperature modification schemes use non-crystalline matrices, which improve toughness, but lack thermal stability and wear resistance.

[0004] Therefore, developing a crystalline polyimide composite material with uniform graphite dispersion, strong interfacial bonding, and balanced wear resistance and mechanical properties at low temperatures has become an urgent need in the field of special working condition materials. Summary of the Invention

[0005] (a) Technical problems to be solved To address the shortcomings of existing technologies, this invention provides a graphite-filled crystalline polyimide low-temperature wear-resistant composite material and its preparation method. This composite material exhibits excellent low-temperature wear resistance and a balanced mechanical and thermal stability, making it suitable for mechanical seals, bearings, gears, and other components operating under low-temperature conditions, with broad application prospects. This invention solves the problem that existing technologies often focus on wear-resistant modification at room temperature by adding fillers such as graphite and molybdenum disulfide to improve wear resistance, but fail to address the issues of interfacial synergy and performance stability at low temperatures. Furthermore, some low-temperature modification schemes use amorphous matrices, which, while improving toughness, suffer from insufficient thermal stability and wear resistance.

[0006] (II) Technical Solution To achieve the above objectives, the present invention provides the following technical solution: A graphite-filled crystalline polyimide low-temperature wear-resistant composite material and its preparation method are disclosed. The composite material is composed of the following components by mass fraction: 70%~90% crystalline polyimide, 8%~25% modified flake graphite, and 1%~5% low-temperature compatibility additive. The preparation method includes the following steps: Step 1: Raw material pretreatment Flake graphite was modified with a silane coupling agent and dried for later use; crystalline polyimide resin was vacuum dried at 120~150℃ for 4~6h to remove moisture. Step 2: Melt blending Pretreated crystalline polyimide, modified flake graphite, and low-temperature compatibility additives are added to a twin-screw extruder and melt-blended at 320~380℃ and screw speed of 30~60r / min. The resulting composite masterbatch is then extruded and granulated. Step 3: Low-temperature molding The composite masterbatch is added to the mold and kept at 280~320℃ and 15~30MPa for 1~3 hours. Then, it is cooled to below 80℃ at a rate of 5~10℃ / min and demolded to obtain the initial blank. Step 4: Post-curing treatment The blank was placed in a vacuum oven and cured in a stepwise manner at 150℃ / 2h, 200℃ / 2h, and 250℃ / 1h. After cooling to room temperature, a graphite-filled crystalline polyimide low-temperature wear-resistant composite material was obtained.

[0007] Furthermore, the crystalline polyimide is a homophenyl, biphenyl, or ether anhydride-type crystalline polyimide with a number average molecular weight of 5 × 10⁻⁶. 4 ~2×10 5 Crystallinity ≥35%, glass transition temperature Tg ≥250℃, ensuring structural stability at low temperatures.

[0008] Furthermore, the flake graphite has a particle size of 1~50μm and a purity of ≥99%. It is modified with a silane coupling agent (KH550, KH560 or KH570) at a modification temperature of 80~100℃ for 2~4h. After modification, the hydroxyl content on the graphite surface is ≥0.8mmol / g, which improves the interfacial bonding force with the matrix.

[0009] Furthermore, the low-temperature compatibility aid is one or more of polyethersulfone (PES), polyetheretherketone (PEEK), or fluorinated polyimide, with a glass transition temperature ≤ -30℃ and a compatibility parameter δ difference with crystalline polyimide ≤ 1.5 (J / cm²). 3 ) 1 / 2 .

[0010] Furthermore, in step two, the temperature zones of the twin-screw extruder are set as follows: feeding zone 280~300℃, melting zone 320~360℃, homogenization zone 340~380℃, and die head zone 330~360℃, to ensure that the material is fully melted and does not degrade.

[0011] Furthermore, the cooling process of the low-temperature molding in step three is divided into two stages: a cooling rate of 5℃ / min in the 320~150℃ stage and a cooling rate of 10℃ / min in the 150~80℃ stage, to avoid excessive cooling leading to internal stress concentration.

[0012] Furthermore, the performance indicators of the composite material in the range of -50℃ to room temperature are as follows: coefficient of friction (dry friction conditions, mating parts are GCr15 steel) 0.08~0.15, wear rate 3×10 -6 ~5×10 -6 mm 3 / (N・m), tensile strength 120~160MPa, elongation at break 5%~12%, heat distortion temperature at 1.82MPa 280~320℃.

[0013] Furthermore, the graphite-filled crystalline polyimide low-temperature wear-resistant composite material is suitable for wear-resistant components such as mechanical seal rings, sliding bearings, gears, and valve cores at temperatures ranging from -50°C to room temperature, and can be applied in aerospace, cryogenic equipment, and precision machinery fields.

[0014] (III) Beneficial Effects This invention provides a graphite-filled crystalline polyimide low-temperature wear-resistant composite material and its preparation method. It possesses the following beneficial effects: 1. This invention provides a graphite-filled crystalline polyimide low-temperature wear-resistant composite material and its preparation method. It uses a silane coupling agent to modify flake graphite, introduces active groups to form chemical bonds with the crystalline polyimide matrix, solves the problems of uneven graphite dispersion and weak interfacial bonding, reduces the interfacial peeling rate by more than 60% at low temperatures, and selects a high-crystallinity polyimide as the crystalline matrix with a crystallinity ≥35%. Its regular crystal structure improves the structural stability at low temperatures and avoids the embrittlement phenomenon of amorphous matrix.

[0015] 2. This invention provides a graphite-filled crystalline polyimide low-temperature wear-resistant composite material and its preparation method. By adding a low Tg compatibility additive, the difference in thermal expansion coefficients between the matrix and the filler is adjusted, which alleviates the internal stress at low temperatures and improves the low-temperature toughness and wear resistance of the composite material. The "melt blending + stepped cooling molding + post-curing" process ensures that the materials are fully mixed and avoids internal stress and performance degradation caused by excessively rapid cooling, thus balancing molding efficiency and product quality.

[0016] 3. This invention provides a graphite-filled crystalline polyimide low-temperature wear-resistant composite material and its preparation method. All components are free of toxic and harmful substances, and the production process produces no waste gas or waste liquid, meeting environmental protection requirements. It is suitable for aerospace low-temperature mechanical parts, cold chain equipment wear-resistant parts, precision instrument seals, etc., filling the market gap of low-temperature wear-resistant polyimide composite materials. Detailed Implementation

[0017] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0018] Example 1: This invention provides a graphite-filled crystalline polyimide low-temperature wear-resistant composite material, which is composed of the following components by mass fraction: 70%~90% crystalline polyimide, 8%~25% modified flake graphite, and 1%~5% low-temperature compatibility additive; The crystalline polyimide selected is a homophenyl, biphenyl, or ether anhydride type crystalline polyimide with a number average molecular weight of 5 × 10⁻⁶. 4 ~2×10 5 It has a crystallinity of 35%~50%, a Tg ≥ 250℃, and a heat distortion temperature ≥ 280℃. As a matrix, it provides excellent thermal stability, mechanical properties, and low-temperature structural support. Its crystalline structure can reduce the degree of restriction on molecular chain activity at low temperatures and reduce embrittlement.

[0019] The modified flake graphite has a particle size of 1~50μm and a purity of ≥99%. It is modified by a silane coupling agent (KH550, KH560 or KH570). The modification process is as follows: Add graphite to an ethanol-water solution (ethanol:water = 3:1, volume ratio), add 1% to 3% of the graphite mass as silane coupling agent, stir at 80 to 100°C for 2 to 4 hours, filter, and dry at 120°C for 3 hours.

[0020] After modification, active groups such as amino and epoxy groups are introduced into the surface of graphite, which form interfacial chemical bonds with the polyimide matrix, improving dispersibility and bonding strength. At the same time, the self-lubricating effect of graphite is exerted, reducing the friction coefficient and wear rate of the composite material.

[0021] The low-temperature compatibility additives selected are polyethersulfone (PES), polyetheretherketone (PEEK), or fluorinated polyimide, with a Tg ≤ -30℃ and a compatibility parameter δ difference with crystalline polyimide ≤ 1.5 (J / cm). 3 ) 1 / 2Its function is to adjust the interfacial tension between the matrix and graphite, alleviate the internal stress caused by the difference in their thermal expansion coefficients at low temperatures, improve the low-temperature toughness of the composite material, and prevent interfacial delamination.

[0022] The preparation method includes the following steps: Step 1: Raw material pretreatment Graphite modification: Modify flake graphite with silane coupling agent according to the above modification process, dry it and set it aside, and ensure that the hydroxyl content on the surface of the modified graphite is ≥0.8mmol / g; Matrix drying: The crystalline polyimide resin is placed in a vacuum oven and dried at 120~150℃ for 4~6 hours to remove moisture. The moisture content is ≤0.1% to avoid the generation of bubbles during the molding process. Additive pretreatment: Low-temperature compatible additives are vacuum dried at 80~100℃ for 2~3h to remove adsorbed moisture.

[0023] Step 2: Melt blending Feeding sequence: First, add the dried crystalline polyimide to the feeding section of the twin-screw extruder. After it is completely melted, add the modified flake graphite and low-temperature compatibility additive through the side feed port. Process parameters: The extruder temperature zones are: feeding zone 280~300℃, melting zone 320~360℃, homogenization zone 340~380℃, die head zone 330~360℃, screw speed 30~60r / min, and material residence time in the barrel 3~5min; Granulation: The extruded material is cooled with water and granulated to obtain composite masterbatch with a diameter of 2~3mm, which is then placed in a vacuum dryer at 120℃ for 2 hours for later use.

[0024] Step 3: Low-temperature molding Mold loading: The composite masterbatch is evenly spread into the mold preheated to 80°C. The mold cavity corresponds to the shape of the target product, such as a sealing ring or bearing sleeve. Molding parameters: Send the mold into the flat vulcanizing machine, heat it to 280~320℃, apply pressure of 15~30MPa, keep it at the temperature and pressure for 1~3 hours to ensure that the material is fully melted and flows and fills the cavity; Step cooling: First, cool down to 150℃ at a rate of 5℃ / min, then cool down to below 80℃ at a rate of 10℃ / min, and demold to obtain the initial blank. This avoids excessive cooling that could lead to stress concentration.

[0025] Step 4: Post-curing treatment The preform is placed in a vacuum oven and subjected to step-by-step post-curing: 150℃ for 2 hours, 200℃ for 2 hours, and 250℃ for 1 hour, with a vacuum degree ≥-0.09MPa. After cooling to room temperature, the final composite material product is obtained.

[0026] Post-curing can further improve the crystallinity of the matrix and the interfacial bonding force, thus stabilizing product performance.

[0027] Implementation Case: Composite Material Preparation Composition: 80% BPDA-BAPP type biphenyl crystalline polyimide with 40% crystallinity and Tg=265℃, 15% KH560 modified flake graphite with a particle size of 5~20μm and a purity of 99.5%, and 5% PES polyethersulfone with Tg=-40℃.

[0028] The preparation steps are as follows: Step 1: Raw material pretreatment Graphite was modified with 2% KH560 by mass, stirred at 90℃ for 3 hours, and dried at 120℃ for 3 hours; polyimide was vacuum dried at 140℃ for 5 hours; and PES was vacuum dried at 90℃ for 2 hours. Step 2: Melt blending The twin-screw extruder temperature is set to 290℃ in the feeding section, 340℃ in the melting section, 360℃ in the homogenization section, and 350℃ in the die head section. The screw speed is 45r / min. Graphite and PES are added by side feeding, and the extrusion is granulated. Step 3: Low-temperature molding Preheat the mold to 80℃, after loading the material, raise the temperature to 300℃, press 25MPa, and hold for 2 hours; then cool down to 80℃ in stages to demold. Step 4: Post-curing 150℃ / 2h→200℃ / 2h→250℃ / 1h, vacuum degree -0.095MPa, cool to room temperature.

[0029] The performance test results are shown in Table 1 below: Table 1. Performance test results of the composite materials of the present invention. Test Project Test conditions Test Results coefficient of friction Dry friction, mating parts GCr15 steel, -50℃ 0.12 Wear rate Dry friction, mating parts GCr15 steel, -50℃ <![CDATA[3.8×10 -6 mm 3 / (N·m)]]> Tensile strength Room temperature, stretching rate 5 mm / min 145MPa Elongation at break Room temperature, stretching rate 5 mm / min 8.5% Heat distortion temperature 1.82MPa 305℃ Low-temperature impact strength (unnotched) -50℃ <![CDATA[12.8kJ / m 2 ]]> The composite material of the present invention was compared with the unmodified graphite-filled amorphous polyimide composite material, and the results are shown in Table 2 below; Table 2 Comparison of the composite material of the present invention with the unmodified graphite-filled amorphous polyimide composite material

[0030] The above comparison results show that the composite material of the present invention is significantly superior to the traditional composite material in terms of low-temperature wear resistance, mechanical properties and stability.

[0031] The following points should be noted in this article: 1. The embodiments disclosed herein only relate to the structures involved in the embodiments disclosed herein; other structures may refer to general designs.

[0032] 2. Where there is no conflict, the embodiments of this disclosure and the features in the embodiments can be combined with each other to obtain new embodiments.

[0033] Although embodiments of the present invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions, and variations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without inventive effort are within the scope of protection of the present invention.

Claims

1. A graphite-filled crystalline polyimide low-temperature wear-resistant composite material and its preparation method, characterized in that, The composite material is composed of the following components by mass fraction: 70%~90% crystalline polyimide, 8%~25% modified flake graphite, and 1%~5% low-temperature compatibility agent; The preparation method includes the following steps: Step 1: Raw material pretreatment Flake graphite was modified with a silane coupling agent and dried for later use; crystalline polyimide resin was vacuum dried at 120~150℃ for 4~6h to remove moisture. Step 2: Melt blending Pretreated crystalline polyimide, modified flake graphite, and low-temperature compatibility additives are added to a twin-screw extruder and melt-blended at 320~380℃ and screw speed of 30~60r / min. The resulting composite masterbatch is then extruded and granulated. Step 3: Low-temperature molding The composite masterbatch is added to the mold and kept at 280~320℃ and 15~30MPa for 1~3 hours. Then, it is cooled to below 80℃ at a rate of 5~10℃ / min and demolded to obtain the initial blank. Step 4: Post-curing treatment The blank was placed in a vacuum oven and cured in a stepwise manner at 150℃ / 2h, 200℃ / 2h, and 250℃ / 1h. After cooling to room temperature, a graphite-filled crystalline polyimide low-temperature wear-resistant composite material was obtained.

2. The graphite-filled crystalline polyimide low-temperature wear-resistant composite material and its preparation method according to claim 1, characterized in that, The crystalline polyimide is a homophenyl, biphenyl, or ether anhydride-type crystalline polyimide with a number average molecular weight of 5 × 10⁻⁶. 4 ~2×10 5 Crystallinity ≥35%, glass transition temperature Tg ≥250℃, ensuring structural stability at low temperatures.

3. The graphite-filled crystalline polyimide low-temperature wear-resistant composite material and its preparation method according to claim 1, characterized in that, The flake graphite has a particle size of 1~50μm and a purity of ≥99%. It is modified with a silane coupling agent at a modification temperature of 80~100℃ for 2~4h. After modification, the hydroxyl content on the graphite surface is ≥0.8mmol / g, which improves the interfacial bonding force with the matrix.

4. The graphite-filled crystalline polyimide low-temperature wear-resistant composite material and its preparation method according to claim 1, characterized in that, The low-temperature compatibility aid is one or more of polyethersulfone (PES), polyetheretherketone (PEEK), or fluorinated polyimide, with a glass transition temperature ≤ -30℃ and a compatibility parameter δ difference with crystalline polyimide ≤ 1.5 (J / cm). 3 ) 1 / 2 .

5. The graphite-filled crystalline polyimide low-temperature wear-resistant composite material and its preparation method according to claim 1, characterized in that, In step two, the temperature zones of the twin-screw extruder are set as follows: feeding zone 280~300℃, melting zone 320~360℃, homogenization zone 340~380℃, and die head zone 330~360℃, to ensure that the material is fully melted and does not degrade.

6. The graphite-filled crystalline polyimide low-temperature wear-resistant composite material and its preparation method according to claim 1, characterized in that, The cooling process of the low-temperature molding in step three is divided into two stages: a cooling rate of 5℃ / min in the 320~150℃ stage and a cooling rate of 10℃ / min in the 150~80℃ stage, to avoid excessive cooling that could lead to stress concentration.

7. The graphite-filled crystalline polyimide low-temperature wear-resistant composite material and its preparation method according to claim 1, characterized in that, The performance indicators of the composite material in the range of -50℃ to room temperature are: coefficient of friction 0.08~0.15, wear rate 3×10 -6 ~5×10 -6 mm 3 / (N・m), tensile strength 120~160MPa, elongation at break 5%~12%, heat distortion temperature at 1.82MPa 280~320℃.

8. The application of the graphite-filled crystalline polyimide low-temperature wear-resistant composite material according to claims 1-7, characterized in that, The composite material is suitable for mechanical seal rings, sliding bearings, gears, and wear-resistant valve core components at temperatures ranging from -50℃ to room temperature, and can be applied in aerospace, cryogenic equipment, and precision machinery fields.

Images