An ultra-high molecular weight polyethylene-based lubricious composite material and a method of making the same

Abstract

The application relates to the technical field of lubricating composite materials, in particular to an ultrahigh molecular weight polyethylene-based lubricating composite material and a preparation method thereof, wherein the ultrahigh molecular weight polyethylene-based lubricating composite material comprises, in terms of weight parts, 82-88 parts of ultrahigh molecular weight polyethylene, 8-12 parts of carbon fibers and 2-8 parts of whisker carbon nanotubes with surfaces grafted by alkyl triethoxysilane. The whisker carbon nanotubes with surfaces grafted by alkyl triethoxysilane are introduced into the carbon fiber and ultrahigh molecular weight polyethylene system, a micro-nano multi-scale reinforcing network is constructed by utilizing the good compatibility of the whisker carbon nanotubes with the ultrahigh molecular weight polyethylene matrix and the ultrahigh strength of the whisker carbon nanotubes, the problems of poor interface bonding between the carbon fibers and the matrix, easy pulling out under heavy load and high wear rate are effectively solved, and the obtained composite material has extremely low friction coefficient and wear rate under water lubrication conditions, and is excellent in mechanical properties.

Description

Technical Field

[0001] This invention relates to the field of lubricating composite materials technology, specifically to an ultra-high molecular weight polyethylene-based lubricating composite material and its preparation method. Background Technology

[0002] Ultra-high molecular weight polyethylene (UHMWPE) is a linear thermoplastic engineering plastic with excellent chemical resistance, extremely low water swelling, good self-lubricating properties, and biocompatibility, making it an ideal water-lubricating material widely used in water-lubricated bearings, artificial joints, and water-lubricated guide rails. However, pure UHMWPE materials suffer from insufficient load-bearing capacity, relatively poor wear resistance, and susceptibility to adhesive wear and plastic deformation under heavy loads, limiting their application in harsh working conditions.

[0003] To improve the mechanical and tribological properties of UHMWPE, researchers have explored various reinforcement methods, with fiber reinforcement being one of the most effective. Carbon fiber (CF) possesses advantages such as high specific strength, high specific modulus, high temperature resistance, and self-lubrication, making it an ideal filler for reinforcing UHMWPE. Studies have shown that the addition of carbon fiber can improve the load-bearing capacity and wear resistance of UHMWPE to a certain extent. However, there is a significant interfacial compatibility problem between carbon fiber and the UHMWPE matrix. The surface of carbon fiber is chemically inert with low surface energy, while the molecular chain of UHMWPE is non-polar. The interfacial bonding force between the two is mainly weak van der Waals forces, lacking effective chemical bonding or strong physical entanglement. This leads to the inability of carbon fiber to effectively transfer the load to the matrix during friction and wear, especially under heavy load conditions, resulting in stress concentration. When the stress exceeds the interfacial bonding strength, carbon fiber is easily pulled out of the matrix, forming abrasive particles and exacerbating wear. At the same time, the pores and cracks left after fiber pull-out become crack initiation points, leading to the destruction of the overall material structure and ultimately causing the friction device to fail.

[0004] To improve the interfacial compatibility between fillers and the matrix, researchers have explored various methods, such as surface oxidation of carbon fibers, plasma treatment, and polymer grafting. While these methods have improved interfacial bonding strength to some extent, their effects are limited and the processes are complex. In recent years, nanomaterials, due to their unique size and surface effects, have been widely used to construct multi-scale reinforced composite materials. By introducing nanoscale fillers into micron-scale carbon fiber / UHMWPE systems, micro-nano multi-scale co-reinforcement networks can be constructed. The nanofillers can fill the interfacial region between the fiber and the matrix, acting as a bridge, dispersing stress, and inhibiting crack propagation.

[0005] Whisker carbon nanotubes (Wh-CNTs) are carbon nanomaterials with a unique morphology. Unlike traditional hollow tubular carbon nanotubes, whisker carbon nanotubes exhibit a solid, fibrous single-crystal structure with extremely high crystallinity and very few internal defects. This unique structure endows them with excellent mechanical properties (such as ultra-high elastic modulus and tensile strength) and better dispersibility in polymer matrices. However, unmodified whisker carbon nanotubes also face the problem of poor compatibility with UHMWPE matrices, are prone to aggregation, and cannot fully realize their reinforcing potential.

[0006] Effectively addressing the interfacial compatibility issues between carbon fibers, whisker carbon nanotubes, and UHMWPE matrices to construct uniform, stable, and multi-scale composite materials with excellent mechanical and tribological properties remains a pressing technical challenge in this field. Therefore, existing technologies require further improvement and development. Summary of the Invention

[0007] In view of the shortcomings of the prior art, the purpose of this invention is to provide an ultra-high molecular weight polyethylene-based lubricating composite material and its preparation method, aiming to solve the technical problems of poor interfacial bonding force, easy pull-out of carbon fibers under heavy load, high wear rate, and unstable friction performance of carbon fiber reinforced ultra-high molecular weight polyethylene composite materials in the prior art.

[0008] To achieve the above objectives, the present invention adopts the following technical solution:

[0009] An ultra-high molecular weight polyethylene-based lubricating composite material, wherein, by weight, the ultra-high molecular weight polyethylene-based lubricating composite material comprises: 82-88 parts of ultra-high molecular weight polyethylene, 8-12 parts of carbon fiber, and 2-8 parts of whisker carbon nanotubes whose surface has been grafted and modified with alkyltriethoxysilane.

[0010] The ultra-high molecular weight polyethylene-based lubricating composite material, wherein the surface of the whisker carbon nanotubes modified by alkyltriethoxysilane grafting has alkyl carbon atoms grafted on it having a number of C5-C12.

[0011] The ultra-high molecular weight polyethylene-based lubricating composite material, wherein the alkyltriethoxysilane is selected from one or more of pentyltriethoxysilane, octyltriethoxysilane, and dodecyltriethoxysilane.

[0012] The ultra-high molecular weight polyethylene-based lubricating composite material, wherein the carbon fiber is one or more of PAN-based carbon fiber, pitch-based carbon fiber, and viscose-based carbon fiber.

[0013] The ultra-high molecular weight polyethylene-based lubricating composite material, by weight, comprises: 88 parts ultra-high molecular weight polyethylene, 10 parts carbon fiber, and 2 parts whisker carbon nanotubes with surface grafted with alkyltriethoxysilane.

[0014] The ultra-high molecular weight polyethylene-based lubricating composite material, by weight, comprises: 86 parts ultra-high molecular weight polyethylene, 10 parts carbon fiber, and 4 parts whisker carbon nanotubes with surface grafted with alkyltriethoxysilane.

[0015] The ultra-high molecular weight polyethylene-based lubricating composite material, by weight, comprises: 82 parts ultra-high molecular weight polyethylene, 10 parts carbon fiber, and 8 parts whisker carbon nanotubes with surface grafted with alkyltriethoxysilane.

[0016] A method for preparing an ultra-high molecular weight polyethylene-based lubricating composite material as described in this invention, comprising the steps of:

[0017] Ultra-high molecular weight polyethylene, carbon fiber, and whisker carbon nanotubes with surface grafted with alkyltriethoxysilane were mixed to obtain a mixed powder.

[0018] The mixed powder is placed in a mold and hot-pressed to obtain the ultra-high molecular weight polyethylene-based lubricating composite material. The hot-pressing process parameters are as follows: the temperature is raised from room temperature to 160-180°C in 1-3 hours, then cooled to 110-120°C at a rate of 2-3°C / min, and held at 110-120°C for 1-3 hours. The hot-pressing pressure is 15-20 MPa, and finally the temperature is cooled to 30-50°C for demolding.

[0019] The preparation method of the ultra-high molecular weight polyethylene-based lubricating composite material, wherein the preparation of the alkyltriethoxysilane-grafted modified whisker carbon nanotubes includes the following steps:

[0020] Whiskered carbon nanotubes were dispersed in water, and ferrous sulfate heptahydrate and hydrogen peroxide were added to carry out a hydroxylation reaction to obtain hydroxylated whiskered carbon nanotubes.

[0021] The hydroxylated whisker carbon nanotubes were grafted with alkyltriethoxysilane in an organic solvent to obtain the whisker carbon nanotubes with alkyltriethoxysilane graft modification on the surface.

[0022] The preparation method of the ultra-high molecular weight polyethylene-based lubricating composite material includes hot pressing sintering carried out under inert gas protection, wherein the inert gas is nitrogen or argon.

[0023] Beneficial Effects: This invention is the first to introduce carbon fibers (micrometer-scale) and surface-modified alkyltriethoxysilane-grafted whisker carbon nanotubes (nanoscale) into a UHMWPE matrix, constructing a micro-nano multi-scale reinforcement network. The carbon fibers provide the main load-bearing skeleton, while the modified whisker carbon nanotubes act as nano-connectors and stress dispersants, filling the interfacial region and bridging the carbon fibers and the matrix, thus achieving uniform load transfer. This invention also solves the core technical problem of poor interfacial bonding between nanofillers and the non-polar UHMWPE matrix by grafting non-polar long-chain silane coupling agents onto the surface of the whisker carbon nanotubes. The grafted non-polar alkyl long chains have good compatibility with the UHMWPE molecular chains, forming a dual bonding mode of chemical anchoring and physical entanglement, resulting in an order-of-magnitude improvement in interfacial bonding strength. This significantly improves the overall mechanical properties and wear resistance of the composite material. This synergistic effect cannot be achieved by single fillers or simple physical blending. Attached Figure Description

[0024] Figure 1 The present invention provides a flowchart of a method for preparing an ultra-high molecular weight polyethylene-based lubricating composite material.

[0025] Figure 2 This is a scanning electron microscope (SEM) image of the surface morphology of octyltriethoxysilane-modified whisker carbon nanotubes prepared in Example 1 of this invention.

[0026] Figure 3 The image shows the Fourier transform infrared (FTIR) spectra of the whisker carbon nanotubes before and after modification in Example 1 of this invention.

[0027] Figure 4 The X-ray photoelectron spectroscopy (XPS) spectra of the whisker carbon nanotubes before and after modification in Example 1 of this invention are shown. Detailed Implementation

[0028] This invention provides an ultra-high molecular weight polyethylene-based lubricating composite material and its preparation method. To make the objectives, technical solutions, and effects of this invention clearer and more explicit, the invention is further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only for explaining the invention and are not intended to limit the invention.

[0029] This invention provides an ultra-high molecular weight polyethylene-based lubricating composite material, wherein, by weight, the ultra-high molecular weight polyethylene-based lubricating composite material comprises: 82-88 parts of ultra-high molecular weight polyethylene, 8-12 parts of carbon fiber, and 2-8 parts of whisker carbon nanotubes with surface grafted with alkyltriethoxysilane.

[0030] In this invention, ultra-high molecular weight polyethylene (UHMWPE) serves as the main matrix of the composite material, providing self-lubricating properties, corrosion resistance, and flexibility. Its ultra-long molecular chains can undergo orientation and partial transfer during friction, forming a transfer film that reduces the coefficient of friction. In the formulation of this invention, the UHMWPE content is 82-88 parts, ensuring the overall lubrication characteristics and processing performance of the material.

[0031] The carbon fiber (CF), as a micron-sized reinforcing phase, primarily bears the load, improving the rigidity and load-bearing capacity of the composite material. The high modulus of the carbon fiber effectively limits the large deformation of the UHMWPE matrix, resisting external loads. This invention controls the carbon fiber content to 8-12 parts. Below 8 parts, the reinforcing effect is not significant; above 12 parts, the carbon fiber easily agglomerates in the matrix, disrupting the continuity of the UHMWPE matrix, leading to material brittleness and an increased coefficient of friction.

[0032] The core improvement of this invention is the alkyltriethoxysilane-grafted crystalline carbon nanotubes (m-Wh-CNTs). These crystalline carbon nanotubes possess extremely high strength and a unique whisker-like single-crystal structure, enabling them to act as nanoscale reinforcing agents, bridging and pinning the carbon fibers and the UHMWPE matrix. More importantly, this invention grafts a nonpolar long-chain silane coupling agent, namely alkyltriethoxysilane, onto their surface. The purpose and mechanism of this grafting modification are as follows: the UHMWPE molecular chain is composed of numerous methylene (-CH2-) groups, exhibiting high nonpolarity; the hydrolysis products of alkyltriethoxysilane can react with the hydroxyl (-OH) groups on the surface of the crystalline carbon nanotubes to form strong Si-OC covalent bonds, thereby grafting nonpolar long-chain alkyl groups (such as pentyl, octyl, and dodecyl) onto the surface of the crystalline carbon nanotubes. These nonpolar alkyl long chains have excellent thermodynamic compatibility with the UHMWPE matrix and can be tightly bound to the UHMWPE macromolecular chains through inter-chain entanglement, van der Waals forces, and other interactions.

[0033] Furthermore, when m-Wh-CNTs are added to the CF / UHMWPE system, a ternary multi-scale composite structure is formed, consisting of a UHMWPE matrix, a CF micron-reinforcing phase, and an m-Wh-CNTs nanon-reinforcing phase. On one hand, the grafted nonpolar alkyl long chains act as anchors, firmly anchoring the m-Wh-CNTs within the UHMWPE matrix, thus solving the problems of poor dispersion and interfacial bonding of nanofillers. On the other hand, these uniformly dispersed and well-bonded m-Wh-CNTs can tightly encapsulate the CF or fill the interfacial gaps between the CF and UHMWPE. When the composite is subjected to external loads (especially shear forces during friction), the load is first transferred through the UHMWPE matrix to the m-Wh-CNTs network, and then through the m-Wh-CNTs to the CF. This gradient stress transfer mechanism effectively avoids direct stress concentration on the CF; simultaneously, the ultra-high strength of the m-Wh-CNTs can suppress the generation and propagation of microcracks, preventing premature pull-out of the CF.

[0034] The inventors also discovered that there is an optimal window for the content of m-Wh-CNTs in relation to the performance of the composite material. If the content is too low (<2 parts), an effective nano-reinforcing network cannot be formed, and the reinforcing effect is not obvious. If the content is too high (>8 parts), the nanoparticles will undergo severe agglomeration. These agglomerates become defects and stress concentration points in the composite material, and during friction, they will become abrasive particles, leading to increased wear and decreased performance. A moderate content (2-8 parts) can construct a perfect bridging structure, and the composite material exhibits a low coefficient of friction and wear rate, as well as high tensile strength.

[0035] In some embodiments, the whisker carbon nanotubes with surfaces grafted with alkyltriethoxysilane have alkyl carbon atoms with a number of C5-C12.

[0036] Specifically, because the UHMWPE molecular chain is composed of a large number of methylene (-CH2-) repeating units, it exhibits high nonpolarity. The alkyl chains (C5-C12) are also nonpolar. According to the principle of "like dissolves like," the alkyl chains grafted onto the surface of the whisker carbon nanotubes can generate strong van der Waals forces and molecular chain entanglement with the UHMWPE molecular chain, thus significantly improving the interfacial compatibility between the filler and the matrix. If the alkyl chain is too short (e.g., C1-C4), its interaction with UHMWPE is insufficient, and the interfacial reinforcement effect is limited; if the alkyl chain is too long (e.g., above C12), it will excessively insert itself between the UHMWPE molecular chains, interfering with the normal crystallization and molecular chain entanglement of the matrix, thereby degrading the material properties.

[0037] In some specific embodiments, the alkyltriethoxysilane is selected from one or more of pentyltriethoxysilane, octyltriethoxysilane, and dodecyltriethoxysilane, but is not limited thereto. When pentyltriethoxysilane (C5, short chain) is used, the modification effect is limited and the improvement in interfacial compatibility is insufficient; when dodecyltriethoxysilane (C12, long chain) is used, although the compatibility is very good, the excessively long flexible chain may excessively insert into the molecular chains of UHMWPE, interfering with its normal crystallization and molecular chain entanglement, thus reducing the mechanical strength of the matrix; while octyltriethoxysilane (C8, medium chain) reaches an optimal balance point, its chain length is sufficient to provide good compatibility and entanglement with the UHMWPE matrix, while not excessively destroying the original structure of UHMWPE, thereby obtaining the best comprehensive performance.

[0038] In some embodiments, the carbon fiber is one or more of PAN-based carbon fiber, pitch-based carbon fiber, and viscose-based carbon fiber, but is not limited thereto.

[0039] In some embodiments, a method for preparing ultra-high molecular weight polyethylene-based lubricating composite materials as described in this invention is also provided, such as... Figure 1 As shown, it includes the following steps:

[0040] S10. Mix ultra-high molecular weight polyethylene, carbon fiber and whisker carbon nanotubes whose surface has been modified by alkyltriethoxysilane grafting to obtain a mixed powder.

[0041] S20. The mixed powder is placed in a mold and hot-pressed to obtain the ultra-high molecular weight polyethylene-based lubricating composite material; wherein the hot-pressing process parameters are as follows: the temperature is raised from room temperature to 160-180℃ in 1-3 hours, then cooled to 110-120℃ at a rate of 2-3℃ / min, and held at 110-120℃ for 1-3 hours; the hot-pressing pressure is 15-20 MPa; and finally, the temperature is cooled to 30-50℃ for demolding.

[0042] In this invention, the mixing process in step S10 aims to achieve uniform dispersion of the components. Since UHMWPE, CF, and m-Wh-CNTs are all solid powders with significant differences in density and particle size, thorough mixing (e.g., using high-speed mechanical stirring, ball milling, etc.) is crucial to ensuring the uniformity of the final material properties. The hot-pressing sintering process in step S20 is a commonly used method for molding UHMWPE composite materials, but the parameter selection in this invention has specific considerations. The heating rate and temperature (160-180℃) are set to ensure that UHMWPE can fully melt (UHMWPE melting point is approximately 135-138℃, at which temperature it has good fluidity), while avoiding excessively high temperatures that could lead to polymer degradation. The subsequent cooling process (cooling to 110-120℃ at 2-3℃ / min and holding at that temperature) is key to controlling the crystallization behavior of UHMWPE. A slow cooling rate and appropriate holding allow sufficient time for the UHMWPE molecular chains to align in an orderly manner, forming a more complete crystalline structure, thereby improving the mechanical properties of the material. In addition, this process also helps to release residual stress within the material. Maintaining a temperature of 110-120℃ (between the melting point and the glass transition temperature) is beneficial for crystal growth; pressure (15-20 MPa) ensures that the powder can be compacted in the molten state, reducing internal porosity and increasing the density of the material.

[0043] Preferably, the hot pressing sintering in step S20 is performed under inert gas protection, wherein the inert gas is nitrogen or argon. Inert gas protection can prevent UHMWPE from undergoing oxidative degradation at high temperatures, thus ensuring the intrinsic properties of the material.

[0044] Further, the preparation of the surface-modified alkyltriethoxysilane-grafted whisker carbon nanotubes includes the following steps: S1, dispersing the whisker carbon nanotubes in water, adding ferrous sulfate heptahydrate and hydrogen peroxide to carry out a hydroxylation reaction, obtaining hydroxylated whisker carbon nanotubes; S2, carrying out a grafting reaction between the hydroxylated whisker carbon nanotubes and alkyltriethoxysilane in an organic solvent, obtaining the surface-modified alkyltriethoxysilane-grafted whisker carbon nanotubes.

[0045] The mechanism of this preparation method lies in the fact that step S1 utilizes Fenton's reagent (Fe... 2+ The strong oxidizing hydroxyl radicals (·OH) generated by H₂O₂ introduce hydroxyl (-OH) active functional groups onto the surface of the whisker carbon nanotubes, providing reaction sites for subsequent grafting reactions. In step S2, the alkoxy group (-OCH₂CH₃) of the alkyltriethoxysilane first hydrolyzes to generate silanol (Si-OH), which then undergoes a dehydration condensation reaction with the hydroxyl groups on the surface of the whisker carbon nanotubes to form stable Si-OC covalent bonds, thereby chemically grafting nonpolar long chains onto the surface of the whisker carbon nanotubes. Compared to physical blending, this chemical grafting method is more stable and has a more lasting modification effect.

[0046] The present invention will be further described in detail below with reference to embodiments and comparative examples. The following embodiments are for illustrative purposes only and are not intended to limit the scope of the invention.

[0047] The raw materials for this embodiment and comparative example are as follows:

[0048] Ultra-high molecular weight polyethylene (UHMWPE): molecular weight 2 million;

[0049] Carbon fiber (CF): PAN-based carbon fiber, 50-100 micrometers in length;

[0050] Whisker carbon nanotubes (Wh-CNTs): diameter 50-150 nm, length 5-20 μm;

[0051] Pentyltriethoxysilane, Octyltriethoxysilane, Dodecyltriethoxysilane: Shanghai Aladdin Biochemical Technology Co., Ltd.;

[0052] Ferrous sulfate heptahydrate, hydrogen peroxide: Sinopharm Chemical Reagent Co., Ltd.;

[0053] Anhydrous ethanol and n-hexane: analytical grade, Sinopharm Chemical Reagent Co., Ltd.

[0054] I. Preparation of surface-modified alkyltriethoxysilane-grafted whisker carbon nanotubes (m-Wh-CNTs)

[0055] The following uses octyltriethoxysilane modification as an example to illustrate the general preparation method of m-Wh-CNTs. The preparation methods for other modifiers are the same, only the type of silane coupling agent is changed.

[0056] Example 1

[0057] The preparation of octyltriethoxysilane modified whisker carbon nanotubes includes the following steps:

[0058] (1) Hydroxylation: 0.3 g of whisker carbon nanotubes were added to 90 mL of deionized water in a 500 mL beaker and ultrasonically dispersed for 30 minutes. Then, 0.15 g of FeSO4·7H2O and 30 mL of H2O2 (30%) were added, and the mixture was magnetically stirred at room temperature for 2 hours. After the reaction was completed, the mixture was filtered through a 0.22 μm filter membrane. The filter cake was washed three times each with deionized water and anhydrous ethanol, and then vacuum dried at 60 °C for 12 hours to obtain hydroxylated whisker carbon nanotubes (Wh-CNTs-OH).

[0059] (2) Grafting modification: All Wh-CNTs-OH obtained in step (1) were dispersed in 150 mL of anhydrous ethanol and sonicated for 30 minutes. Then, 0.5 mL of octyltriethoxysilane was added, and the reaction was continued to be magnetically stirred at room temperature for 1 hour. After the reaction was completed, the mixture was filtered, and the filter cake was washed three times with anhydrous ethanol and n-hexane to remove unreacted silane coupling agent. Finally, the mixture was vacuum dried at 60 °C for 12 hours to obtain octyltriethoxysilane-modified whisker carbon nanotubes (denoted as C8-m-Wh-CNTs).

[0060] Similarly, pentyltriethoxysilane-modified whisker carbon nanotubes (C5-m-Wh-CNTs) and dodecyltriethoxysilane-modified whisker carbon nanotubes (C12-m-Wh-CNTs) were prepared using pentyltriethoxysilane and dodecyltriethoxysilane, respectively. Unmodified whisker carbon nanotubes are denoted as p-Wh-CNTs.

[0061] II. Preparation of Ultra-High Molecular Weight Polyethylene-Based Lubricating Composite Materials

[0062] Example 2

[0063] 88 parts of ultra-high molecular weight polyethylene, 10 parts of carbon fiber and 2 parts of pentyltriethoxysilane modified whisker carbon nanotubes were thoroughly mixed. The uniformly mixed powder was then transferred to a cylindrical mold with a diameter of 30 mm for hot pressing and sintering. The room temperature was raised to 170°C in 2 hours, and then cooled at a rate of 2.5°C / min. The temperature was then maintained at 115°C for 2 hours. The hot pressing pressure was set to 18 MPa. After cooling to 40°C, the product was demolded and polished to obtain an ultra-high molecular weight polyethylene-based lubricating composite material.

[0064] Example 3

[0065] 88 parts of ultra-high molecular weight polyethylene, 10 parts of carbon fiber and 2 parts of octyltriethoxysilane modified whisker carbon nanotubes were thoroughly mixed. The uniformly mixed powder was then transferred to a cylindrical mold with a diameter of 30 mm for hot pressing and sintering. The room temperature was raised to 170°C in 2 hours, and then cooled at a rate of 2.5°C / min. The temperature was then maintained at 115°C for 2 hours. The hot pressing pressure was set to 18 MPa. After cooling to 40°C, the product was demolded and polished to obtain an ultra-high molecular weight polyethylene-based lubricating composite material.

[0066] Example 4

[0067] 88 parts of ultra-high molecular weight polyethylene, 10 parts of carbon fiber and 2 parts of dodecyltriethoxysilane modified whisker carbon nanotubes were thoroughly mixed. The uniformly mixed powder was then transferred to a cylindrical mold with a diameter of 30 mm for hot pressing and sintering. The room temperature was raised to 170°C in 2 hours, and then cooled at a rate of 2.5°C / min. The temperature was then maintained at 115°C for 2 hours. The hot pressing pressure was set to 18 MPa. After cooling to 40°C, the product was demolded and polished to obtain an ultra-high molecular weight polyethylene-based lubricating composite material.

[0068] Example 5

[0069] 86 parts of ultra-high molecular weight polyethylene, 10 parts of carbon fiber and 4 parts of octyltriethoxysilane modified whisker carbon nanotubes were thoroughly mixed. The uniformly mixed powder was then transferred to a cylindrical mold with a diameter of 30 mm for hot pressing and sintering. The room temperature was raised to 160°C in 1 hour, and then cooled at a rate of 2°C / min. The temperature was then maintained at 110°C for 1 hour. The hot pressing pressure was set to 15 MPa. After cooling to 30°C, the product was demolded and polished to obtain an ultra-high molecular weight polyethylene-based lubricating composite material.

[0070] Example 6

[0071] 84 parts of ultra-high molecular weight polyethylene, 10 parts of carbon fiber and 6 parts of octyltriethoxysilane modified whisker carbon nanotubes were thoroughly mixed. The uniformly mixed powder was then transferred to a cylindrical mold with a diameter of 30 mm for hot pressing and sintering. The room temperature was raised to 170°C in 2 hours, and then cooled at a rate of 2.5°C / min. The temperature was then maintained at 115°C for 2 hours. The hot pressing pressure was set to 18 MPa. After cooling to 40°C, the product was demolded and polished to obtain an ultra-high molecular weight polyethylene-based lubricating composite material.

[0072] Example 7

[0073] 82 parts of ultra-high molecular weight polyethylene, 10 parts of carbon fiber and 8 parts of octyltriethoxysilane modified whisker carbon nanotubes were thoroughly mixed. The uniformly mixed powder was then transferred to a cylindrical mold with a diameter of 30 mm for hot pressing and sintering. The room temperature was raised to 180°C in 3 hours, and then cooled at a rate of 3°C / min. The temperature was then maintained at 120°C for 3 hours. The hot pressing pressure was set to 20 MPa. After cooling to 50°C, the product was demolded and polished to obtain an ultra-high molecular weight polyethylene-based lubricating composite material.

[0074] Comparative Example 1

[0075] 100 parts of ultra-high molecular weight polyethylene were transferred into a cylindrical mold with a diameter of 30 mm and hot-pressed for sintering. The room temperature was raised to 170°C in 2 hours, and then cooled at a rate of 2.5°C / min. The temperature was then maintained at 115°C for 2 hours. The hot pressing pressure was set to 18 MPa. After cooling to 40°C, the material was demolded and polished to obtain ultra-high molecular weight polyethylene material.

[0076] Comparative Example 2

[0077] 95 parts of ultra-high molecular weight polyethylene and 10 parts of carbon fiber were thoroughly mixed. The uniformly mixed powder was then transferred to a cylindrical mold with a diameter of 30 mm for hot pressing and sintering. The room temperature was raised to 170°C in 2 hours, and then cooled at a rate of 2.5°C / min. The temperature was then maintained at 115°C for 2 hours. The hot pressing pressure was set to 18 MPa. After cooling to 40°C, the material was demolded and polished to obtain ultra-high molecular weight polyethylene material.

[0078] Comparative Example 3

[0079] 88 parts of ultra-high molecular weight polyethylene, 10 parts of carbon fiber and 2 parts of unmodified whisker carbon nanotubes were thoroughly mixed. The uniformly mixed powder was then transferred to a cylindrical mold with a diameter of 30 mm for hot pressing and sintering. The room temperature was raised to 170°C in 2 hours, and then cooled at a rate of 2.5°C / min. The temperature was then maintained at 115°C for 2 hours. The hot pressing pressure was set to 18 MPa. After cooling to 40°C, the material was demolded and polished to obtain ultra-high molecular weight polyethylene material.

[0080] Comparative Example 4

[0081] 94 parts of ultra-high molecular weight polyethylene and 6 parts of octyltriethoxysilane modified whisker carbon nanotubes were thoroughly mixed. The uniformly mixed powder was then transferred to a cylindrical mold with a diameter of 30 mm for hot pressing and sintering. The room temperature was raised to 170°C in 2 hours, and then cooled at a rate of 2.5°C / min. The temperature was then maintained at 115°C for 2 hours. The hot pressing pressure was set to 18 MPa. After cooling to 40°C, the product was demolded and polished to obtain an ultra-high molecular weight polyethylene-based lubricating composite material.

[0082] III. Material Characterization and Performance Comparison

[0083] Among them, the testing and characterization methods are:

[0084] Friction and wear performance: Tested using an RTEC reciprocating friction and wear testing machine. Test conditions: The wear pair consisted of 10mm diameter GCr-15 steel balls, a linear velocity of 0.06 m / s, a load of 15 N, a 3% NaCl aqueous solution as the lubricant, and a test time of 1 hour. The coefficient of friction was directly recorded by the software. The wear rate was calculated by measuring the three-dimensional morphology of the wear track using a white light interferometer (Bruker, ContourGT-K), calculating the wear volume, and then using the formula: Wear rate = Wear volume / (Load × Sliding distance).

[0085] Surface hardness: Tested using an LX-D type Shore hardness tester according to GB / T 2411-2008 standard.

[0086] Tensile strength: Tested using a universal testing machine (Instron 5967) according to GB / T 1040.2-2006 standard, with a tensile rate of 50 mm / min.

[0087] Microstructure: The fracture morphology of the modified whisker carbon nanotubes and composite materials was observed using a scanning electron microscope (SEM, Zeiss Sigma 500).

[0088] Chemical structure: The chemical structure changes of whisker carbon nanotubes before and after modification were characterized using Fourier transform infrared spectroscopy (FTIR, Thermo Nicolet iS10) and X-ray photoelectron spectroscopy (XPS, Thermo Fisher ESCALAB 250Xi).

[0089] Figure 2 This is a SEM image of the C8-m-Wh-CNTs prepared in Example 1 of this invention. It can be clearly seen from the image that after hydroxylation and grafting modification, the whisker carbon nanotubes still maintain their unique fibrous structure without significant breakage or morphological damage. This high aspect ratio fibrous structure is the basis for its ability to play a bridging and reinforcing role in composite materials.

[0090] Figure 3 The images show the FTIR spectra of whisker carbon nanotubes before and after modification. In the figures, the black curve represents unmodified p-Wh-CNTs, and the light blue curve represents C8-m-Wh-CNTs. Within the black curve, the peak value is located at approximately 3200 cm⁻¹. - The broad and strong absorption peak at ¹ is attributed to the stretching vibrations of a small number of hydroxyl groups (-OH) on the surface of the whisker carbon nanotubes or the OH stretching vibrations of adsorbed water; located at approximately 1600 cm⁻¹ - The absorption peak at ¹ is attributed to the C=C stretching vibration of the whisker carbon nanotube graphite framework. In the light blue curve, in addition to the aforementioned characteristic peaks, two new absorption peaks appear: one at approximately 2900 cm⁻¹. - The absorption peak at ¹ is attributed to the stretching vibrations of the CH bonds in the grafted octyl chain (including -CH2- and -CH3); it is located at approximately 1100 cm⁻¹. - The strong and broad absorption peak at ¹ is attributed to the characteristic stretching vibration of the Si-OC bond. The appearance of these new peaks directly proves that octyltriethoxysilane has been successfully grafted onto the surface of whisker carbon nanotubes through a chemical reaction.

[0091] Figure 4The XPS full spectra of p-Wh-CNTs and C8-m-Wh-CNTs are shown. The figures clearly show that, in addition to the characteristic peaks of carbon (C1s, approximately 284 eV) and oxygen (O1s, approximately 532 eV), two new characteristic peaks appear in C8-m-Wh-CNTs: peaks at approximately 150 eV and 103 eV, corresponding to the Si2s and Si2p orbitals of silicon, respectively. XPS is a surface-sensitive analytical technique, and the presence of Si strongly confirms that octyltriethoxysilane molecules were successfully grafted onto the surface of the whisker carbon nanotubes, since the original whisker carbon nanotubes do not contain silicon.

[0092] The above characterization results collectively confirm that the present invention successfully prepared modified whisker carbon nanotubes with surface grafted nonpolar long chains.

[0093] The tribological properties of the ultra-high molecular weight polyethylene-based lubricating composite materials prepared in Examples 2-7 and the ultra-high molecular weight polyethylene materials in Comparative Examples 1-3 were tested, and the results are shown in Table 1.

[0094] Table 1. Tribological and mechanical properties of the materials

[0095]

[0096] Comparing the data in Table 1, we can see that:

[0097] 1. Performance of pure UHMWPE (Comparative Example 1): The coefficient of friction of pure UHMWPE under water lubrication is 0.060, reflecting its intrinsic self-lubricating properties. Its wear rate is 5.80 × 10⁻⁶. -6 mm 3 The hardness is 64.0 HD and the tensile strength is 31.5 MPa. These data are used as the benchmark for subsequent comparisons.

[0098] 2. Reinforcing and Degrading Effects of Carbon Fiber (Comparative Example 2 vs. Comparative Example 1): After adding 10 parts of carbon fiber, the coefficient of friction of the composite material significantly decreased to 0.041, and the hardness also slightly increased to 66.3 HD. This indicates that carbon fiber, as a rigid filler, improves the shear resistance of the material and helps reduce friction. However, surprisingly, the wear rate increased from 5.80 to 6.14, and the tensile strength decreased from 31.5 MPa to 27.9 MPa. This precisely confirms the interfacial bonding problem mentioned in the background section; there is a lack of effective chemical bonding between the carbon fiber and the UHMWPE matrix, resulting in weak interfacial strength. Under the shear stress of reciprocating friction, the stress concentrates at the ends of the carbon fiber, causing the carbon fiber to be pulled out from the surrounding matrix. The pulled-out carbon fiber forms abrasive grains, exacerbating abrasive wear and thus increasing the wear rate. At the same time, as a stress concentration point, the carbon fiber can induce microcracks in the tensile test, leading to premature material fracture and a decrease in tensile strength. This shows that simple physical blending cannot realize the reinforcing potential of carbon fiber and may even introduce defects.

[0099] 3. Effect of unmodified whisker carbon nanotubes (Comparative Example 3 vs. Comparative Example 2): After adding 2 parts of unmodified p-Wh-CNTs, the coefficient of friction (0.045) actually increased compared to Comparative Example 2 (0.041), the wear rate (5.64) decreased slightly, and the tensile strength (28.5) increased slightly. This indicates that the unmodified p-Wh-CNTs themselves have very poor compatibility with UHMWPE and are prone to agglomeration. In the early stages of friction, the agglomerated p-Wh-CNTs may peel off from the matrix, forming abrasive grains with higher hardness, leading to an increase in the coefficient of friction (abrasive wear). Although its high strength and whisker structure inhibit crack propagation to some extent, improving the wear rate and tensile strength, the improvement is limited and the advantage of the coefficient of friction is sacrificed.

[0100] 4. No carbon fiber added, only modified whisker carbon nanotubes added (Comparative Example 4 vs Example 6): Due to the lack of micron-scale skeleton support from carbon fiber, the wear resistance (wear rate) and friction coefficient of the material are not as good as those of Example 6, which adds both CF and m-Wh-CNTs. This proves that there is a clear synergistic enhancement effect between carbon fiber and modified whisker carbon nanotubes, and neither can be omitted.

[0101] 5. Effect of different chain length modifiers (Examples 2-4 vs. Comparative Examples 2-3):

[0102] C5-m-Wh-CNTs (Example 2): Compared to Comparative Example 3, the coefficient of friction decreased from 0.045 to 0.042, the wear rate decreased from 5.64 to 5.03, and the tensile strength increased from 28.5 MPa to 30.2 MPa. This indicates that the grafting of pentyl (C5) improves the compatibility of Wh-CNTs with UHMWPE, reducing agglomeration and abrasive wear. However, the C5 chain is relatively short, and its entanglement with the UHMWPE molecular chain is limited, resulting in insufficient interfacial reinforcement.

[0103] C8-m-Wh-CNTs (Example 3): Performance was further improved, with the coefficient of friction reduced to 0.038, the wear rate reduced to 4.32, and the tensile strength reaching 31.7 MPa, approaching the strength level of pure UHMWPE. This indicates that the octyl (C8) chain length is moderate, enabling it to form effective physical entanglement with the UHMWPE molecular chain without excessively interfering with the matrix. The modified Wh-CNTs exhibit better dispersion in the matrix and stronger interfacial bonding, effectively bearing and transferring stress and inhibiting CF pull-out.

[0104] C12-m-Wh-CNTs (Example 4): Performance declined compared to Example 3. The coefficient of friction (0.040) and wear rate (4.92) were higher than those of the C8 modified form, while the tensile strength (29.3) was lower. This indicates that the dodecyl (C12) chain is too long. Although the ultra-long nonpolar chain has excellent compatibility with UHMWPE, the excessively long flexible chain segments act like a lubricant, excessively intercalating between the molecular chains of UHMWPE, weakening the van der Waals forces between the molecular chains, and reducing the crystallinity and molecular chain entanglement density of UHMWPE itself. This leads to the deterioration of the mechanical properties of the matrix itself, thus affecting the overall performance. The comparison also shows that octyltriethoxysilane (C8) is the optimal chain length selected through creative labor in this invention, achieving the best balance between improved compatibility and maintained matrix performance.

[0105] 6. Effect of different modified whisker carbon nanotube contents (Examples 3, 5-7):

[0106] Content 2 parts (Example 3): The performance was improved to some extent, but the enhancement effect was not fully realized;

[0107] Content 4 parts (Example 5): Performance was significantly improved, the coefficient of friction was reduced to 0.031, the wear rate was reduced to 3.88, and the tensile strength jumped to 38.3 MPa.

[0108] Content 6 parts (Example 6, optimal example): Performance reaches peak. The coefficient of friction is as low as 0.025 (only 41.7% of that of pure UHMWPE), and the wear rate is as low as 3.36 × 10⁻⁶. -6 mm 3The C8-m-Wh-CNTs content (42.1% lower than pure UHMWPE) and tensile strength of 41.1 MPa (30.5% higher than pure UHMWPE) indicate that a complete, continuous, and interconnected nanonetwork structure can be formed around the CF and within the UHMWPE matrix when the C8-m-Wh-CNTs content reaches 6 parts. This network efficiently transfers stress from the UHMWPE matrix to the CF through bridging, significantly suppressing CF pull-out and microcrack formation. Furthermore, the high-density nano-reinforcing phase itself possesses extremely high strength and modulus, directly improving the overall hardness and tensile strength of the composite material. Simultaneously, the uniformly dispersed nanoparticles can bear most of the load during friction and promote the formation of a uniform and dense transfer film, thereby achieving extremely low friction and wear.

[0109] Content 8 parts (Example 7): Performance began to decline, the coefficient of friction rebounded to 0.030, the wear rate increased to 4.43, and the tensile strength decreased to 33.4 MPa. This indicates that when the content of nanofillers exceeds the critical value (percolation threshold), excess C8-m-Wh-CNTs will agglomerate. These agglomerates become new stress concentration points and structural defects, easily inducing cracks under stress. During friction, the agglomerated hard particles detach and become three-body abrasive particles, exacerbating wear and causing the coefficient of friction and wear rate to rebound. This also explains why the hardness continued to increase (69.1 HD), but the tensile strength decreased significantly, because hardness mainly reflects local resistance to indentation, while tensile strength is more sensitive to internal defects.

[0110] It is understood that those skilled in the art can make equivalent substitutions or modifications to the technical solution and inventive concept of the present invention, and all such substitutions or modifications should fall within the protection scope of the appended claims.

Claims

1. A high molecular weight polyethylene-based lubricating composite material, characterized in that, The ultra-high molecular weight polyethylene-based lubricating composite material comprises, by weight, 82-88 parts of ultra-high molecular weight polyethylene, 8-12 parts of carbon fiber, and 2-8 parts of alkyltriethoxysilane-grafted modified whisker carbon nanotubes; the alkyltriethoxysilane-grafted modified whisker carbon nanotubes have alkyl carbon atoms grafted onto their surface having a number of C5-C12; the preparation of the alkyltriethoxysilane-grafted modified whisker carbon nanotubes includes the following steps: dispersing the whisker carbon nanotubes in water, adding ferrous sulfate heptahydrate and hydrogen peroxide to perform a hydroxylation reaction to obtain hydroxylated whisker carbon nanotubes; and performing a grafting reaction between the hydroxylated whisker carbon nanotubes and alkyltriethoxysilane in an organic solvent to obtain the alkyltriethoxysilane-grafted modified whisker carbon nanotubes.

2. The ultra-high molecular weight polyethylene-based lubricating composite material according to claim 1, characterized in that, The alkyltriethoxysilane is selected from one or more of pentyltriethoxysilane, octyltriethoxysilane, and dodecyltriethoxysilane.

3. The ultra-high molecular weight polyethylene-based lubricating composite material according to claim 1, characterized in that, The carbon fiber is one or more of PAN-based carbon fiber, pitch-based carbon fiber, and viscose-based carbon fiber.

4. The ultra-high molecular weight polyethylene-based lubricating composite material according to claim 1, characterized in that, By weight, the ultra-high molecular weight polyethylene-based lubricating composite material comprises: 88 parts of ultra-high molecular weight polyethylene, 10 parts of carbon fiber, and 2 parts of whisker carbon nanotubes with surface grafted with alkyltriethoxysilane.

5. The ultra-high molecular weight polyethylene-based lubricating composite material according to claim 1, characterized in that, By weight, the ultra-high molecular weight polyethylene-based lubricating composite material comprises: 86 parts ultra-high molecular weight polyethylene, 10 parts carbon fiber, and 4 parts whisker carbon nanotubes with surface grafted with alkyltriethoxysilane.

6. The ultra-high molecular weight polyethylene-based lubricating composite material according to claim 1, characterized in that, By weight, the ultra-high molecular weight polyethylene-based lubricating composite material comprises: 82 parts of ultra-high molecular weight polyethylene, 10 parts of carbon fiber, and 8 parts of whisker carbon nanotubes with surface grafted with alkyltriethoxysilane.

7. A method for preparing an ultra-high molecular weight polyethylene-based lubricating composite material as described in any one of claims 1-6, characterized in that, Including the following steps: Ultra-high molecular weight polyethylene, carbon fiber, and whisker carbon nanotubes with surface grafted with alkyltriethoxysilane were mixed to obtain a mixed powder. The mixed powder is placed in a mold and hot-pressed to obtain the ultra-high molecular weight polyethylene-based lubricating composite material. The hot-pressing process parameters are as follows: the temperature is raised from room temperature to 160-180°C in 1-3 hours, then cooled to 110-120°C at a rate of 2-3°C / min, and held at 110-120°C for 1-3 hours. The hot-pressing pressure is 15-20 MPa, and finally the temperature is cooled to 30-50°C for demolding.

8. The method for preparing the ultra-high molecular weight polyethylene-based lubricating composite material according to claim 7, characterized in that, Hot pressing sintering is carried out under the protection of an inert gas, namely nitrogen or argon.

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