Cellulose nanocrystal in-situ anchored microcapsule enhanced self-lubricating composite material

Abstract

The application discloses a kind of cellulose nanocrystal in situ anchoring microcapsule enhanced self-lubricating composite material, belong to high polymer composite lubricating material technical field.The composite material is made of resin matrix, epoxy group modified cellulose nanocrystal, microcapsule and curing agent.The preparation method is: resin matrix, epoxy group modified cellulose nanocrystal, microcapsule and curing agent are mixed uniformly, then temperature is cured, and self-lubricating composite material is obtained.Microcapsule has shell-core structure, and shell layer is composed of engineering plastic and amino-modified cellulose nanocrystal;core is lubricating medium, and lubricating medium is encapsulated in shell layer inside.The application not only effectively solves the uneven distribution of lubricant in prior art, weak interface bonding, lubricant early leakage and other problems, but also can give full play to the advantage of casting forming technology, meet the demand of long service life, high reliability and friction reduction and wear resistance of high-end equipment in precision moving parts.

Description

Technical Field

[0001] This invention relates to the field of polymer composite lubricating materials technology, and in particular to a self-lubricating composite material reinforced with in-situ anchored microcapsules of cellulose nanocrystals. Background Technology

[0002] Self-lubricating bulk materials can achieve more stable mechanical and tribological properties and longer service life through overall material optimization and structural design, demonstrating irreplaceable advantages in high-end fields such as aerospace and precision instruments. Early mainstream self-lubricating bulk materials, such as porous oil-containing polymers, were mostly manufactured by cold-pressing / hot-pressing sintering or foaming processes to create internal pores and then vacuum-impregnating with lubricating oil. While these methods can achieve self-lubrication, the manufacturing process is complex, and the pore structure and oil content are still difficult to control precisely. Furthermore, the presence of numerous pores inevitably severely compromises the mechanical strength of the matrix. In recent years, 3D printing technology has provided a new approach for manufacturing complex-shaped self-lubricating parts. By blending lubricating components with photosensitive resins or thermoplastic polymer filaments, customized structures can be printed layer by layer. However, this technological path also faces serious challenges: firstly, it is highly dependent on specialized equipment, and the cost of such equipment and specialized materials is high; secondly, the printing process parameters are extremely sensitive, requiring extremely high levels of process control; and thirdly, insufficient interlayer bonding strength can easily lead to interlayer delamination under frictional stress, affecting the overall stability of mechanical and tribological properties.

[0003] Self-lubricating composite materials based on microcapsules containing lubricating media are produced by encapsulating liquid lubricants in microcapsules, mixing them as solid powder with a resin matrix, and typically curing them using processes such as casting. Casting is considered an ideal process for creating irregularly shaped self-lubricating parts due to its simple equipment and suitability for manufacturing complex configurations, offering a high degree of molding freedom. However, this highly promising technological approach has faced significant challenges in practical applications due to the following three core technological bottlenecks:

[0004] First, there are compatibility and dispersibility issues. The surface chemical properties of the microcapsule shell differ significantly from those of the resin matrix, making it difficult to wet in liquid resin and prone to agglomeration. These agglomerates become stress concentration points after curing, severely degrading the mechanical properties of the material and causing uneven lubrication film formation during friction. Second, there is the issue of microcapsule sedimentation. In the cast liquid resin, there is a density difference between the microcapsules and the resin matrix. During the long curing period, the microcapsules settle or float under gravity, resulting in a gradient distribution of the lubricating phase inside the cured bulk material. This leads to inconsistent tribological properties at different locations of the component, compromising stability and reliability. Finally, there is the risk of premature leakage due to insufficient shell strength. The stirring, mixing, and vacuum degassing processes necessary for casting molding exert continuous shear and pressure on the microcapsule shell. If the shell's mechanical strength is insufficient, premature breakage will occur, causing the lubricant to leak into the resin matrix before friction occurs. This could not only pollute the environment and interfere with resin curing, but also cause the ideal on-demand release mechanism to fail, significantly shortening the effective lubrication life of the material.

[0005] In existing technologies, to improve the thermal stability and mechanical strength of polysulfone microcapsule shells, some researchers have used methods such as depositing nickel layers to prepare nickel-polysulfone bilayer microcapsules to reinforce the shell structure; using silica solutions as Pickering emulsifiers to prepare reinforced polysulfone shell microcapsules; and using surface modifiers such as dopamine to strengthen the shell. However, these methods generally suffer from problems such as cumbersome steps, high costs, complex processes, and poor lubrication effects.

[0006] In summary, although the fabrication of self-lubricating materials containing lubricating medium microcapsules based on casting molding technology shows great promise, the three major bottlenecks of "poor compatibility," "poor dispersibility," and "premature leakage" result in generally poor mechanical properties and unstable lubrication performance in the prepared self-lubricating bulk materials, rendering their design freedom and performance advantages meaningless. Therefore, developing a novel self-lubricating composite material and its preparation method that can solve the above problems from the material design stage has become an urgent goal pursued by those skilled in the art. The present invention is proposed precisely to overcome these long-standing technical bottlenecks. Summary of the Invention

[0007] To address the technical challenges of poor compatibility, poor dispersibility, and premature leakage of microencapsulated lubricants in self-lubricating composite materials, this invention provides a self-lubricating composite material reinforced with in-situ anchored microcapsules of cellulose nanocrystals. This composite material is a self-lubricating composite material with excellent mechanical and tribological properties and high molding freedom, reinforced by in-situ anchored cellulose microcapsules containing lubricating media.

[0008] The self-lubricating composite material reinforced by in-situ anchored microcapsules of cellulose nanocrystals provided by the present invention is made of a resin matrix, epoxy-modified cellulose nanocrystals, microcapsules and curing agent.

[0009] The microcapsule has a core-shell structure, with the shell composed of engineering plastics and amino-modified cellulose nanocrystals; the core is a lubricating medium, which is encapsulated inside the shell.

[0010] The self-lubricating composite material is prepared by mixing the resin matrix, the epoxy-modified cellulose nanocrystals, the microcapsules and the curing agent evenly, and then heating and curing to obtain the self-lubricating composite material.

[0011] The advantages of this invention are:

[0012] (1) This invention modifies cellulose nanocrystals with two different surface modifications, enabling them to play a dual role in composite materials: on the one hand, as a three-dimensional network support for epoxy resin matrix reinforcement; on the other hand, as part of microcapsules, synergistically enhancing the bonding force between the microcapsule shell and the matrix. The combined use of the two modified cellulose nanocrystals creates a strong bridge between the microcapsules and the matrix, resulting in composite materials with excellent mechanical properties, less susceptibility to interfacial debonding, and facilitated effective stress transfer from the resin matrix to the reinforcing phase. This improves tribological properties while maintaining or even enhancing the mechanical properties of the composite material.

[0013] (2) This invention constructs a stable three-dimensional network structure in an epoxy resin matrix by modifying cellulose nanocrystals. Through physical-chemical interaction, the microcapsules are formed with spatial steric hindrance and anchoring effect, which effectively inhibits the floating or settling of microcapsules caused by density differences. This achieves uniform and stable dispersion of microcapsules in three-dimensional space and ensures the consistency of the tribological properties of the material.

[0014] (3) This invention utilizes amino-modified cellulose nanocrystals (CNC) to enter the microcapsule shell in a one-step process, forming an organic-inorganic composite reinforced shell structure. This directly enhances the mechanical strength and density of the microcapsule shell, while simultaneously improving the dispersibility of the microcapsules in the resin matrix. In addition to avoiding the agglomeration of microcapsules in the resin, this composite shell can also withstand the shear and pressure during the processing of the composite material, effectively preventing premature leakage of the lubricant and enabling the lubricant to be released only on demand under frictional stress, significantly extending the lubrication life of the material.

[0015] (4) Modified cellulose nanocrystals provide excellent dispersibility and stability during the casting process, enabling the composite material to maintain excellent uniformity during the molding process, thereby overcoming the common bubble problem and stress concentration phenomenon in traditional casting.

[0016] (5) The excellent interfacial interaction of the composite material of the present invention ensures the degree of freedom of the composite material in molding. It can not only be molded into a coating to achieve surface protection, but also into a lubricating block of various shapes to achieve friction reduction and wear resistance under specific conditions; it can also be molded into precision parts of various complex shapes according to actual application needs to meet the urgent needs of high-end equipment for irregular self-lubricating parts.

[0017] In summary, this invention integrates four functions—emulsification, shell reinforcement, three-dimensional anchoring, and interfacial compatibility—through modified cellulose nanocrystals. By precisely controlling the functional roles of modified nanocrystalline cellulose at different stages, it achieves controllable structural construction from the nanoscale to the macroscale, representing a typical multi-scale, integrated structural-functional design. This design paradigm simplifies the preparation process, avoids compatibility issues arising from the introduction of multiple components, and enables the composite material to maintain high toughness and strength while stably reducing the coefficient of friction to below 0.15, significantly lowering the wear rate. It not only effectively addresses the requirements of long lifespan, high reliability, and friction reduction and wear resistance for precision moving parts in high-end equipment (such as aerospace bearings and precision guide rails), but also has broad application prospects, especially offering unique advantages in the customized needs of irregularly shaped self-lubricating parts. Attached Figure Description

[0018] Figure 1 This is a scanning electron microscope image of the polysulfone-encapsulated lubricating oil microcapsule powder prepared in Example 1.

[0019] Figure 2 These are Fourier transform infrared spectra of unmodified cellulose nanocrystals, epoxy-modified cellulose nanocrystals, and amino-modified cellulose nanocrystals.

[0020] Figure 3 This is a schematic diagram illustrating the preparation principle of a self-lubricating composite material according to some embodiments of the present invention.

[0021] Figure 4 These are self-lubricating block materials of different shapes prepared based on different molds, as shown in some embodiments of the present invention.

[0022] Figure 5 This is a cross-sectional morphology diagram of the self-lubricating block material prepared in Example 4.

[0023] Figure 6 This is a graph showing the change in the friction coefficient of the self-lubricating block material of Example 4 over time.

[0024] Figure 7 These are the three-dimensional morphology and two-dimensional contour diagram of the wear marks of the self-lubricating block material in Example 4.

[0025] Figure 8 This is a surface morphology diagram of the self-lubricating coating prepared in Example 5.

[0026] Figure 9 This is a cross-sectional morphology diagram of the self-lubricating coating prepared in Example 5.

[0027] Figure 10 This is a graph showing the change in the friction coefficient of the self-lubricating coating prepared in Example 6 over time.

[0028] Figure 11 These are the three-dimensional morphology and two-dimensional contour diagram of the wear marks of the self-lubricating coating prepared in Example 6.

[0029] Figure 12 This is a cross-sectional morphology diagram of the epoxy coating prepared in Comparative Example 1.

[0030] Figure 13 This is a graph showing the change in the friction coefficient of the epoxy coating prepared in Comparative Example 1 over time.

[0031] Figure 14 The figures show the three-dimensional morphology and two-dimensional contour of the wear marks on the epoxy resin bulk material in Comparative Example 2.

[0032] Figure 15 This is a microscopic morphology diagram of microcapsules containing amino-modified cellulose nanocrystals.

[0033] Figure 16 This is a graph showing the change in the friction coefficient of the bulk material prepared in Comparative Example 4 over time.

[0034] Figure 17 The figures show the three-dimensional morphology and two-dimensional contour of the wear marks on the bulk material prepared in Comparative Example 4.

[0035] Figure 18 This is a surface morphology diagram of the bulk material prepared in Comparative Example 5. Detailed Implementation

[0036] To further illustrate the present invention, the following detailed description of the invention is provided in conjunction with embodiments. However, it should be understood that these embodiments are implemented based on the technical solution of the present invention, and provide detailed implementation methods and specific operation processes. They are only for further illustrating the features and advantages of the present invention, and are not intended to limit the scope of the claims of the present invention. The protection scope of the present invention is not limited to the following embodiments.

[0037] The advantages, objectives and features of the present invention will be apparent in part from the following description, and in part from the understanding of those skilled in the art through study and practice of the invention.

[0038] To address the technical challenges of poor compatibility, poor dispersibility, and premature leakage of microencapsulated lubricants in self-lubricating composite materials, this invention provides a self-lubricating composite material reinforced with in-situ anchored microcapsules of cellulose nanocrystals. This self-lubricating composite material is reinforced with microcapsules containing a lubricating medium anchored in situ by cellulose, exhibiting excellent mechanical and tribological properties and high degree of molding freedom.

[0039] The self-lubricating composite material reinforced by in-situ anchored microcapsules of cellulose nanocrystals is made of a resin matrix, epoxy-modified cellulose nanocrystals, microcapsules, and a curing agent. The microcapsules have a core-shell structure comprising a shell and a core. The shell is composed of engineering plastics and amino-modified cellulose nanocrystals, and the core is a lubricating medium encapsulated within the shell. The self-lubricating composite material is prepared by uniformly mixing the resin matrix, the epoxy-modified cellulose nanocrystals, the microcapsules, and the curing agent, followed by heating and curing to obtain the self-lubricating composite material.

[0040] The resin matrix refers to the thermosetting polymer material that constitutes the continuous phase of the self-lubricating composite material. As the structural framework and continuous phase of the composite material, the resin matrix is ​​responsible for bearing and transferring loads, firmly binding together reinforcing phases and functional phases such as epoxy-modified cellulose nanocrystals and microcapsules. In some embodiments, the resin matrix is ​​selected from at least one of epoxy resin, phenolic resin, and polyimide resin. In some embodiments, the epoxy value of the resin matrix can be 0.48-0.54 eq / 100g. In some embodiments, the viscosity can be 600-800 mPa·s (25°C). In some embodiments, the epoxy value and viscosity of the resin matrix can be adjusted according to the performance requirements of the product.

[0041] Epoxy-modified cellulose nanocrystals refer to functionalized nanomaterials in which epoxy groups (-CH(O)CH2) are grafted onto the surface of cellulose nanocrystals using chemical methods. The preparation of epoxy-modified cellulose nanocrystals includes silane coupling agent grafting, direct esterification / etherification, and click chemistry. Silane coupling agent grafting refers to the method of grafting epoxy groups (-CH(O)CH2) onto the surface of cellulose nanocrystals using silane coupling agents. Direct esterification / etherification involves using small molecules such as epoxy-containing acid anhydrides (e.g., epoxy derivatives of maleic anhydride) or epichlorohydrin to directly react with the hydroxyl groups on the surface of cellulose nanocrystals under alkaline or acidic catalysis. Click chemistry involves first converting the hydroxyl groups on the surface of cellulose nanocrystals to azide or alkynyl groups through steps such as bromination and amination, and then performing a click chemical reaction (e.g., CuAAC reaction) with epoxy functional molecules containing complementary reactive groups (e.g., alkynyl or azido groups).

[0042] In some embodiments, the epoxy-modified cellulose nanocrystals are prepared as follows:

[0043] (a1) Cellulose nanocrystals (CNC) were ultrasonically dispersed in deionized water, and the pH was adjusted to 4.5-5.0 to obtain dispersion A1;

[0044] (a2) Dissolve silane coupling agent KH560 in a mixed solution of ethanol and water, and stir to hydrolyze the silane coupling agent to obtain solution B1;

[0045] (a3) Slowly add solution B1 to dispersion A1, heat to 50-60℃ and stir for 2-3 hours. After centrifugation and washing, the wet precipitate of the epoxy-modified cellulose nanocrystals is obtained.

[0046] CNC is modified by silane coupling agent to introduce epoxy groups, which form a three-dimensional network structure in the resin matrix. The interfacial bonding force is enhanced by the ring-opening reaction between the epoxy groups and the curing agent, providing mechanical reinforcement.

[0047] In some embodiments, the cellulose nanocrystals in step (a1) have a diameter of 10-30 nm and a length of 200-500 nm.

[0048] The silane coupling agent KH560 is γ-glycidoxypropyltrimethoxysilane. In some embodiments, the silane coupling agent KH560 can be replaced by γ-glycidoxypropyltriethoxysilane or the like.

[0049] In some embodiments, the pH in step (a1) can be adjusted to 4.0-6.5. In some embodiments, the pH in step (a1) can be adjusted to 4.5-6.0. In some embodiments, the pH in step (a1) can be adjusted to 4.5-5.0. The pH range is determined so as not to affect the dispersion state of CNC and the final modification effect.

[0050] In some embodiments, in step (a2), ethanol can be replaced by isopropanol, methanol, acetone, etc. In some embodiments, in step (a2), the volume ratio of ethanol to water can be 70-90:30-10. In some embodiments, in step (a2), the volume ratio of ethanol to water can be 80-85:20-15.

[0051] In some embodiments, the slow addition in step (a3) ​​refers to "drop by drop" or even slower continuous addition. Slow addition can be performed using a micro-injection pump, a peristaltic pump, or by using a constant-pressure separatory funnel or manually adding drop by drop with a syringe.

[0052] In some embodiments, the reaction temperature in step (a3) ​​can be 40-70°C. In some embodiments, the reaction temperature in step (a3) ​​can be 45-65°C. In some embodiments, the reaction temperature in step (a3) ​​can be 50-60°C. In some embodiments, the reaction time in step (a3) ​​can be 1-6 hours. In some embodiments, the reaction time in step (a3) ​​can be 2-5 hours. In some embodiments, the reaction time in step (a3) ​​can be 2-4 hours. In some embodiments, the reaction time in step (a3) ​​can be 2-3 hours. The higher the reaction temperature, the shorter the required reaction time. The reaction temperature and reaction time should be determined so as not to affect the final modification effect of CNC.

[0053] In some embodiments, the washing in step (a3) ​​can be ethanol washing, deionized water washing, or alternating washing with ethanol and deionized water.

[0054] Microcapsules are tiny containers with a "core-shell" structure. Microcapsules encapsulate and seal an internal liquid core substance through a solid, semi-permeable, or hermetically sealed outer shell (shell layer), forming independent tiny particles. The structure of microcapsules allows the core substance to be released in a controlled manner when needed (e.g., under external stimuli such as pressure, heating, friction, or pH changes). The shell layer of a microcapsule is the continuous solid membrane that forms the outer barrier of the microcapsule. The core of the capsule refers to the encapsulated substance inside the microcapsule, also known as the core material, capsule core, or inner phase, and is the source of the microcapsule's functionality. Microcapsules can be prepared using chemical methods, emulsion-based phase separation methods, and other methods. Chemical methods involve dissolving two reactive monomers separately in immiscible core materials and dispersed phases, where they meet at the droplet interface and rapidly polymerize to form a polymer shell. Emulsion-based phase separation methods are explained below.

[0055] In some embodiments, the shell is composed of engineering plastics and amino-modified cellulose nanocrystals, and the core is a lubricating medium. The lubricating medium is encapsulated inside the shell.

[0056] Engineering plastics are high-performance polymers with excellent mechanical properties, heat resistance, chemical resistance, and long-term stability, and are typically used as structural materials. In some embodiments, the engineering plastic is selected from at least one of polysulfone, polyethersulfone, polyphenylene ether, and polycarbonate.

[0057] Amino-modified cellulose nanocrystals refer to functionalized nanomaterials with amino groups (-NH2) grafted onto the surface of cellulose nanocrystals. Preparation methods for amino-modified cellulose nanocrystals include silane coupling agent grafting and amidation reactions. Silane coupling agent grafting is the mainstream method, and its principle is similar to that of KH560-modified CNC, the core of which is the condensation of the hydrolysis products of silane coupling agents (such as KH550) with the hydroxyl groups on the CNC surface. Amidation reaction: CNC is reacted with amino-containing carboxylic acids or acyl chlorides (such as N-(2-aminoethyl)-3-aminopropyltrimethoxysilane).

[0058] Lubricating media refers to fluid or semi-fluid substances encapsulated within microcapsules that reduce friction and wear. During friction, the microcapsule shell ruptures, releasing the lubricating media to the friction interface, forming a lubricating film, thereby reducing friction and wear. In some embodiments, the lubricating media is at least one of mineral oil, synthetic oil, and vegetable oil. In some embodiments, the lubricating media is selected from at least one of polyalphaolefin oil, ester oil, silicone oil, and perfluoropolyether oil.

[0059] The microcapsule is prepared by the self-assembly of amino-modified cellulose nanocrystals at the oil-water interface to form a stable emulsion template, followed by the deposition of the shell material at the interface induced by the evaporation of organic solvent.

[0060] In some embodiments, the microcapsules are prepared as follows:

[0061] (b1) Cellulose nanocrystals were ultrasonically dispersed in anhydrous ethanol, and the pH was adjusted to 4.5-5.0 to obtain dispersion A2; silane coupling agent KH550 was dissolved in a mixed solution of ethanol and water, and the mixture was stirred to hydrolyze the silane coupling agent to obtain solution B2; solution B2 was slowly added dropwise to dispersion A2, and the mixture was stirred and reacted under reflux at 70-80℃ for 3-4 hours, centrifuged, washed, and dried to obtain amino-modified cellulose nanocrystals.

[0062] (b2) Disperse amino-modified cellulose nanocrystals in deionized water and add electrolyte NaCl to form an aqueous phase.

[0063] (b3) Dissolve the engineering plastic in an organic solvent, add a lubricating medium, and mix evenly to form an oil phase.

[0064] (b4) The oil phase is added to the aqueous phase under high-speed shearing and subjected to pulsed ultrasonic treatment to form a Pickering emulsion; nitrogen gas is bubbled through for 2-3 hours, and then the organic solvent is removed by vacuum distillation, allowing engineering plastics to deposit at the emulsion interface to form a shell. Finally, the microcapsules are obtained by centrifugation, washing, and freeze-drying. In some embodiments, the cellulose nanocrystals in step (b1) have a diameter of 10-30 nm and a length of 200-500 nm.

[0065] In some embodiments, the mass ratio of amino-modified cellulose nanocrystals in step (b2) to engineering plastics in step (b3) is 10:(3-6). In some embodiments, the mass ratio of amino-modified cellulose nanocrystals in step (b2) to engineering plastics in step (b3) is 10:(4-5).

[0066] In some embodiments, in step (b4), the rotational speed of the high-speed shearing is 5000-8000 rpm, the amplitude of the pulsed ultrasound is 20%-30%, and the evaporation temperature of the organic solvent is 35-40℃.

[0067] In some embodiments, the silane coupling agent KH550 in step (b1) is γ-aminopropyltriethoxysilane. In some embodiments, the silane coupling agent KH550 in step (b1) can be replaced by N-(β-aminoethyl)-γ-aminopropyltrimethoxysilane, γ-aminopropyltrimethoxysilane, (aminoethylaminomethyl)phenethyltrimethoxysilane, etc.

[0068] The pH, slow addition, ethanol and water mixture, and washing in step (b1) are similar to those in step (a1), and will not be repeated here. The washing in step (b4) is similar to that in step (a1), and will not be repeated here.

[0069] In some embodiments, the reaction time in step (b1) can be 2-8 hours. In some embodiments, the reaction time in step (b1) can be 2-6 hours. In some embodiments, the reaction time in step (b1) can be 2-4 hours. In some embodiments, the reaction time in step (b1) can be 3-4 hours.

[0070] In some embodiments, the electrolyte NaCl in step (b2) can be replaced by potassium chloride, sodium sulfate, sodium nitrate, sodium acetate, etc.

[0071] CNC was modified with silane coupling agent KH550 to introduce amino groups, which act as a Pickering emulsifier to stabilize the oil / water interface during microcapsule preparation. During the curing process, the amino groups react with the epoxy groups to further anchor the microcapsules firmly into the composite material.

[0072] These microcapsules not only release lubricating media on demand during friction, but also chemically react with the epoxy resin matrix through amino groups grafted onto the CNC surface, ensuring the stability and durability of the microcapsules in the composite material. The curing process of the composite material involves the microcapsules being anchored in a three-dimensional network constructed from modified cellulose nanocrystals, and forming a strong interfacial bond with the resin matrix through chemical bonding.

[0073] A curing agent is a chemical substance that can chemically react with a thermosetting resin matrix (such as epoxy resin), initiating and promoting the cross-linking of its molecular chains to form an insoluble and infusible three-dimensional network structure. The type and amount of curing agent directly determine the curing speed, cross-linking density, and final properties of the cured product (such as hardness, strength, toughness, and heat resistance). Curing agents include, but are not limited to, aliphatic amine curing agents, such as ethylenediamine and diethylenetriamine; polyamide curing agents, which are formed by the condensation of dimer acids and polyamines; and acid anhydride curing agents, such as phthalic anhydride and methyltetrahydrophthalic anhydride. In some embodiments, the curing agent is a modified polyetheramine curing agent.

[0074] In some embodiments, based on the mass of the resin matrix, the wet precipitation of epoxy-modified cellulose nanocrystals accounts for 2-5% of the mass of the resin matrix, the amount of microcapsules accounts for 3-10% of the mass of the resin matrix, and the amount of curing agent accounts for 30-35% of the mass of the resin matrix.

[0075] The amount of wet precipitation of the above-mentioned epoxy-modified cellulose nanocrystals can enable CNC to form an effective three-dimensional network or uniformly dispersed reinforcing points in the resin matrix. The amount of the above-mentioned microcapsules can enable the microcapsules to be uniformly dispersed and encapsulate a sufficient amount of lubricant for lubrication. The amount of the above-mentioned curing agent can enable the epoxy groups in the resin matrix to fully react with the curing agent and achieve high cross-linking, thereby enabling the composite material to obtain the optimal mechanical properties (strength, hardness, toughness), thermal stability and chemical stability required by the design.

[0076] The self-lubricating composite material is prepared by mixing a resin matrix, epoxy-modified cellulose nanocrystals, microcapsules, and a curing agent evenly, followed by heating and curing to obtain the self-lubricating composite material. In some embodiments, the curing process is a stepped temperature curing or a single-temperature curing. The curing process may include, but is not limited to, holding at 60°C for 3 hours → holding at 90°C for 5 hours → holding at 120°C for 1 hour, holding at 50°C for 3 hours → holding at 100°C for 2 hours → holding at 140°C for 30 minutes, or holding at 100°C for 8 hours. In some embodiments, the resin matrix and epoxy-modified cellulose nanocrystals may be mixed evenly first, and then the microcapsules and curing agent may be added and mixed evenly.

[0077] The self-lubricating composite material of the present invention can be used as a coating material to prepare a coating. In some embodiments, the preparation of the coating includes: mixing a resin matrix and epoxy-modified cellulose nanocrystals wet precipitate evenly, vacuum dehydrating the system until there are no bubbles to obtain a premix; adding microcapsules and a curing agent to the premix, mixing evenly to obtain a coating solution; spraying the coating solution onto the surface of a substrate, heating and curing to obtain a self-lubricating protective coating.

[0078] The self-lubricating composite material of the present invention can also be made into self-lubricating blocks. In some embodiments, the preparation of self-lubricating blocks includes: uniformly mixing a resin matrix and epoxy-modified cellulose nanocrystals in a wet precipitate, vacuum dehydrating the system until no bubbles are present, obtaining a premix; adding microcapsules and a curing agent to the premix, mixing uniformly to obtain a casting liquid; pouring the casting liquid into a mold after vacuum degassing, and curing by heating to obtain a self-lubricating block. The thickness of the self-lubricating block can be controlled by the mold size, and the thickness can be in the range of 5-10 mm. Depending on the mold used, self-lubricating blocks of various shapes can be made.

[0079] The self-lubricating composite material of the present invention can be used for lubrication and protection of precision moving parts. The precision moving parts are any mechanical components requiring lubrication, including but not limited to bearings, guide rails, gears, and sliders. Before using the self-lubricating composite material for lubrication, the precision moving parts need to undergo surface pretreatment. Pretreatment includes: sandblasting, grinding, or chemical treatment of the component surface to achieve a roughness Ra∈[0.8,1.6], followed by cleaning with anhydrous ethanol and wiping clean with a lint-free cloth to obtain the pretreated component surface.

[0080] The preferred embodiments of the present invention will be described below with reference to the accompanying drawings. It should be understood that the preferred embodiments described herein are for illustration and explanation only and are not intended to limit the present invention.

[0081] Example 1

[0082] A self-lubricating bulk material reinforced with in-situ anchored microcapsules of cellulose nanocrystals, with the following amounts of each component:

[0083] 10 g of epoxy resin, 0.2 g of wet precipitate of epoxy-modified cellulose nanocrystals, 0.5 g of microcapsules, and 3.33 g of curing agent.

[0084] The epoxy resin is a bisphenol A type epoxy resin with an epoxy value of 0.48-0.54 eq / 100g and a viscosity of 600-800 mPa·s. The curing agent is a modified polyether amine curing agent with an amine value of 200-250 mg KOH / g.

[0085] Preparation method of epoxy-modified cellulose nanocrystals: 2.5g of cellulose nanocrystals were dispersed in 10g of water to obtain an aqueous dispersion. The pH of the aqueous dispersion was adjusted to 4.5-5.0 with 0.1mol / L hydrochloric acid solution. 2.5g of silane coupling agent KH560 was dissolved in 10mL of ethanol / water mixed solution and hydrolyzed by magnetic stirring at room temperature for 30min. The hydrolyzed silane coupling agent KH560 solution was slowly added dropwise to the aqueous dispersion, and the reaction was carried out at 50℃ for 3 hours. After centrifugation and washing, a wet precipitate of epoxy-modified cellulose nanocrystals was obtained.

[0086] The preparation method of microcapsules is as follows:

[0087] (1) 2.5 g of cellulose nanocrystals were dispersed in 10 g of water to obtain an aqueous dispersion. The pH of the aqueous dispersion was adjusted to 4.5-5.0 with 0.1 mol / L hydrochloric acid solution. 2.5 g of silane coupling agent KH550 was dissolved in 10 mL of ethanol / water mixed solution and hydrolyzed by magnetic stirring at room temperature for 30 min. The hydrolyzed silane coupling agent KH550 solution was slowly added dropwise to the aqueous dispersion and reacted at 70 °C for 4 hours. After the reaction was completed, the nanocrystals were centrifuged, washed, and dried to obtain amino-modified cellulose nanocrystals.

[0088] (2) Disperse 2g of amino-modified cellulose nanocrystals in 200ml of deionized water and add 0.5g of electrolyte NaCl to form an aqueous phase.

[0089] (3) Dissolve 0.9g of polysulfone in 40mL of dichloromethane. After complete dissolution, add 0.6g of PAO40 lubricating oil and mix well to form the oil phase.

[0090] (4) Under high-speed shear (5000-8000rpm), the oil phase is added to the aqueous phase, emulsified for 5min, and then transferred to an ice-water bath for pulsed ultrasonic treatment (pulse ultrasonic amplitude is 20%-30%) to form a Pickering emulsion; nitrogen gas is bubbled for 2-3h, and then the organic solvent is removed by vacuum distillation at 40℃, so that polysulfone is deposited at the Pickering emulsion interface to form a shell layer. Finally, after centrifugation, washing and freeze drying, polysulfone-encapsulated lubricating oil microcapsule powder is obtained.

[0091] Preparation method of self-lubricating bulk material: Weigh 10 g of epoxy resin and 0.2 g of epoxy-modified cellulose nanocrystals into a wet precipitate and mix. Shear the mixture at 5000 rpm for 5 min, then ultrasonically disperse for 15 min. Dehydrate the mixture under vacuum at 60℃ and -0.09 MPa until no bubbles remain, obtaining a premix. Weigh 0.5 g of microcapsules and 3.33 g of curing agent and add them to the premix. Stir at 150-200 rpm for 10 min to ensure uniform mixing. After vacuum degassing, pour the mixture into a mold of a specific shape and cure according to a set program. The curing program is: 60℃ for 3 h → 90℃ for 5 h → 120℃ for 1 h. After natural cooling, demold to obtain the self-lubricating bulk material.

[0092] Figure 1 This is a scanning electron microscope image of polysulfone-encapsulated lubricating oil microcapsule powder. It can be observed that the surface of the microcapsules containing the lubricating medium is successfully and uniformly loaded with amino-modified cellulose nanocrystals, exhibiting a regular spherical structure, which is beneficial for the encapsulation of the lubricating medium.

[0093] Figure 2These are Fourier transform infrared spectra of unmodified CNC, epoxy-modified cellulose nanocrystals (E-CNC), and amino-modified cellulose nanocrystals (A-CNC). Figure 2 As shown, at 3500cm -1 A strong OH stretching vibration peak appears nearby, which is a characteristic peak of the numerous hydroxyl groups (-OH) on the surface of cellulose nanocrystals; 1000~1200 cm⁻¹ -1 The CO, COC, and CH peaks in the region are characteristic peaks of the cellulose sugar ring structure. Unmodified CNC peaks are at 3500-3200 cm⁻¹. -1 The strong hydroxyl stretching vibration peak at [value missing] was significantly weakened in both modified products, indicating that the hydroxyl groups on the CNC surface underwent a silanization reaction with the alkoxy groups of the silane coupling agent; simultaneously, the peaks at ~2900 cm⁻¹ in A-CNC and E-CNC were [value missing]. -1 A new propyl CH stretching vibration peak was added at 1050-1100 cm⁻¹. -1 The Si-OC characteristic peak is significantly enhanced, confirming that the silane molecule was successfully grafted and formed a covalent bond, and the A-CNC peak is at ~3300 cm⁻¹. -1 The characteristic amino peak of KH550 appears at ~910 cm⁻¹. E-CNC shows a peak at ~910 cm⁻¹. -1 The presence of a characteristic epoxy group peak unique to KH560 further confirms the effective binding of the specific silane coupling agent with CNC.

[0094] The dispersion stability of the epoxy-modified cellulose nanocrystals in the epoxy resin matrix is ​​significantly increased, mainly due to two reasons: First, epoxy modification endows the cellulose surface with similar chemical properties and polarity to the epoxy resin matrix; the epoxy resin molecular chain ends contain epoxy groups, and the modified cellulose surface is also grafted with epoxy groups, which makes the surface energies of the two closer and significantly reduces the interfacial tension. Second, the epoxy modification process usually introduces molecular chain segments into the cellulose surface, and the steric hindrance effect of these molecular chain segments hinders the aggregation of cellulose.

[0095] The lubricating microcapsules anchor onto epoxy-modified cellulose nanocrystals during the subsequent curing process, thus overcoming the challenge of uniform and stable dispersion of lubricating microcapsules in the resin matrix. The core of this process lies in the direct, rapid, and irreversible chemical reaction between the aminated microcapsules and the epoxy-modified cellulose nanocrystals during resin curing, forming covalent bridges. The specific process is as follows... Figure 3 As shown:

[0096] (1) The initial state is transformed into the pre-assembled state.

[0097] In the uncured epoxy resin slurry, the surface of the aminated microcapsules tends to be positively charged, while the surface of the epoxy-based cellulose nanocrystals is slightly negatively charged due to the polarity of the epoxy groups and the negative charge of cellulose itself. An electrostatic attraction exists between the two, causing the epoxy-based cellulose nanocrystals to spontaneously adsorb onto the microcapsule surface in the initial mixing stage, forming a preliminary, uniform pre-assembled structure. This creates excellent close-range contact conditions for subsequent chemical reactions.

[0098] (2) Curing anchoring: curing triggering and direct interface reaction

[0099] When the curing agent (polyamine) of the epoxy resin is added, the system undergoes cross-linking. The amino groups on the surface of the microcapsules and the epoxy groups on the surface of the cellulose nanocrystals are themselves a pair of highly reactive functional groups. While the curing agent diffuses and initiates the curing of the resin bulk, the amino groups on the surface of the microcapsules preferentially undergo ring-opening addition with the epoxy groups on the surface of the nearest cellulose nanocrystals. This reaction does not require a curing agent molecule as an intermediate bridge, but occurs directly at the target interface, reaching the "soldering point" directly, resulting in a more direct bonding.

[0100] (3) Network integration and three-dimensional locking

[0101] The remaining epoxy groups on the surface of cellulose nanocrystals will undergo a curing reaction with the epoxy resin bulk and the diffused curing agent molecules. That is, each fiber bundle becomes a cross-linking hub, with one end anchored to the aminated microcapsule by covalent bonds, and the other end and side chain integrated into the three-dimensional cross-linking network of epoxy resin by chemical bonds. The microcapsule thus achieves uniform dispersion and stability at the molecular level.

[0102] Example 2

[0103] A self-lubricating bulk material reinforced with in-situ anchored microcapsules of cellulose nanocrystals, with the following amounts of each component:

[0104] 10 g of epoxy resin, 0.3 g of wet precipitate of epoxy-modified cellulose nanocrystals, 0.7 g of microcapsules, and 3.33 g of curing agent.

[0105] The types of epoxy resin and curing agent are the same as in Example 1.

[0106] The methods for preparing the wet precipitation of epoxy-modified cellulose nanocrystals, the preparation of microcapsules, and the preparation of self-lubricating bulk materials are all the same as those in Example 1.

[0107] Example 3

[0108] A self-lubricating bulk material reinforced with in-situ anchored microcapsules of cellulose nanocrystals, with the following amounts of each component:

[0109] 10 g of epoxy resin, 0.3 g of wet precipitate of epoxy-modified cellulose nanocrystals, 0.7 g of microcapsules, and 3.33 g of curing agent.

[0110] The types of epoxy resin and curing agent are the same as in Example 1.

[0111] The method for preparing the wet precipitation of epoxy-modified cellulose nanocrystals is the same as in Example 1.

[0112] The preparation method of the microcapsules is the same as in Example 1, except that the lubricating oil used is replaced with G2825 lubricating oil.

[0113] The preparation method of the self-lubricating bulk material is the same as in Example 1.

[0114] Example 4

[0115] A self-lubricating bulk material reinforced with in-situ anchored microcapsules of cellulose nanocrystals, with the following amounts of each component:

[0116] 10 g of epoxy resin, 0.2 g of wet precipitate of epoxy-modified cellulose nanocrystals, 0.5 g of microcapsules, and 3.33 g of curing agent.

[0117] The types of epoxy resin and curing agent are the same as in Example 1.

[0118] The preparation methods for wet precipitation of epoxy-modified cellulose nanocrystals and microcapsules are the same as in Example 1.

[0119] The preparation method of the self-lubricating block material is the same as in Example 1, except that the curing process is: heat preservation at 50°C for 3 hours → heat preservation at 100°C for 2 hours → heat preservation at 140°C for 30 minutes.

[0120] Figure 4 The examples demonstrate self-lubricating block materials of different shapes prepared using different molds in the above embodiments. For example... Figure 4 As shown, the self-lubricating material of the present invention has extremely high molding freedom and can be used as a precursor to achieve efficient molding of block and complex irregular engineering components.

[0121] Figure 5 This is a cross-sectional morphology diagram of the self-lubricating bulk material prepared in Example 4. (See diagram for reference.) Figure 5 As shown, the microcapsules exhibit a spatially uniform and ordered distribution within the resin matrix.

[0122] Friction experiments were conducted on the self-lubricating bulk material prepared in Example 4 using a UMT3 general-purpose micro-tribometer in a ball-and-disc configuration. Φ10mm GCr45 bearing steel balls were used, and the balls were thoroughly cleaned with alcohol before each test. The reciprocating friction stroke was 5mm, and the test was conducted under a normal load of 3N, with an average sliding speed of 10mm / s. Subsequent friction coefficient measurements were performed using the same parameters. Test results are shown below. Figure 6 . Figure 6 This is a graph showing the change in the friction coefficient of the self-lubricating block material of Example 4 over time (also known as a friction curve). Figure 6 As shown in the friction curve, after the test begins, the microcapsules rupture under the action of frictional force and frictional heat, releasing the lubricating medium and forming an effective liquid lubricating film that separates the two contact surfaces, thereby greatly reducing frictional resistance. Simultaneously, the uniform distribution of the microcapsules allows for a continuous and stable supply of the lubricating medium, resulting in a uniform and continuous lubricating film. The friction process is very stable, without stick-slip or other abnormal fluctuations. The coefficient of friction remains stable at around 0.1 over a long period.

[0123] Figure 7 These are the three-dimensional morphology and two-dimensional contour images of the wear tracks of the self-lubricating block material in Example 4. It can be seen that after adding the lubricating oil-containing microcapsules, the wear surface width, depth, and deep cross-sectional area are smaller, resulting in excellent wear resistance. The three-dimensional morphology shows a shallow U-shaped groove. The wear volume is 0.003 mm. 3 The calculated wear rate is 0.28 × 10⁻⁶. -4 mm 3 / N·m. The reasons for this are twofold. First, during friction, the introduced microcapsules containing lubricating media rupture at the friction interface to form a lubricating film. This film transforms the direct solid contact between the friction pairs into oil film shearing, eliminating adhesive wear and severe ploughing wear to some extent, thus significantly reducing the wear rate. Second, the epoxidized cellulose nanocrystals form a network within the epoxy resin, greatly improving the composite material and reducing the possibility of material being peeled off in fragments during friction, directly reducing the impact of abrasive wear and fatigue wear. Finally, the chemical anchoring effect between the lubricating media-containing microcapsules and the epoxidized cellulose nanocrystals ensures that even if the microcapsules rupture after friction, their shell fragments are chemically bonded and bound near the matrix surface, making them less likely to detach and become free, hard three-body abrasive particles, thereby reducing wear.

[0124] Example 5

[0125] A self-lubricating coating reinforced with in-situ anchored microcapsules of cellulose nanocrystals, wherein the amounts of each component are as follows:

[0126] 10 g of epoxy resin, 0.2 g of wet precipitate of epoxy-modified cellulose nanocrystals, 0.5 g of microcapsules, and 3.33 g of curing agent.

[0127] The types of epoxy resin and curing agent are the same as in Example 1.

[0128] The preparation methods for wet precipitation of epoxy-modified cellulose nanocrystals and microcapsules are the same as in Example 1.

[0129] Preparation method of self-lubricating coating: Weigh 10 g of epoxy resin and 0.2 g of epoxy-modified cellulose nanocrystals into a wet precipitate and mix. Shear the mixture at 5000 rpm for 5 min, then ultrasonically disperse for 15 min. Dehydrate the mixture under vacuum at 60℃ and -0.09 MPa until no bubbles remain, obtaining a premix. Weigh 0.5 g of microcapsules and 3.33 g of curing agent and add them to the premix. Stir at 150-200 rpm for 10 min to ensure uniform mixing, obtaining a coating solution. Transfer the coating solution into a spray gun and spray it onto the surface of a titanium alloy substrate. The thickness of the self-lubricating coating (10~300 μm) can be adjusted by controlling the spray flow rate and number of sprays. After curing, allow it to cool naturally before demolding to obtain the finished self-lubricating coating. The curing procedure is: 60℃ for 3 h → 90℃ for 5 h → 120℃ for 1 h.

[0130] Figure 8 This is a surface morphology diagram of the self-lubricating coating prepared in Example 5. For example... Figure 8 As shown, the coating surface is flat and smooth.

[0131] Figure 9 This is a cross-sectional morphology diagram of the self-lubricating coating prepared in Example 5. For example... Figure 9 As shown, the microcapsules in the self-lubricating coating exhibit a uniform and orderly distribution.

[0132] Example 6

[0133] A self-lubricating coating reinforced with in-situ anchored microcapsules of cellulose nanocrystals, wherein the amounts of each component are as follows:

[0134] 10 g of epoxy resin, 0.2 g of wet precipitate of epoxy-modified cellulose nanocrystals, 0.5 g of microcapsules, and 3.33 g of curing agent.

[0135] The types of epoxy resin and curing agent are the same as in Example 1.

[0136] The preparation methods for wet precipitation of epoxy-modified cellulose nanocrystals and microcapsules are the same as in Example 1.

[0137] The preparation method of the self-lubricating coating is the same as in Example 5, except that the curing process is to keep it at 100°C for 8 hours.

[0138] Figure 10This is a graph showing the change in the coefficient of friction of the self-lubricating coating prepared in Example 6 over time. The method for testing the coefficient of friction is the same as in Example 4, and the coefficient of friction was found to be stable at around 0.1. The self-lubricating coating exhibits the same excellent lubrication performance as the self-lubricating block.

[0139] Figure 11 These are the three-dimensional morphology and two-dimensional contour images of the wear tracks of the self-lubricating coating prepared in Example 6. It can be seen that after adding microcapsules containing lubricating oil to the coating, the wear surface width, depth, and deep cross-sectional area are smaller, resulting in excellent wear resistance. The three-dimensional morphology shows that the U-shaped grooves are relatively shallow. The wear volume is 0.007 mm. 3 The calculated wear rate is 0.65 × 10⁻⁶. -4 mm 3 / N·m. The self-lubricating coating exhibited a higher wear volume and wear rate compared to the self-lubricating block. This is because the coating contains a limited number of oil-containing microcapsules, which leads to a slight increase in the subsequent coefficient of friction, as reflected in the friction curve. The increase in the coefficient of friction resulted in more severe wear.

[0140] Comparative Example 1

[0141] An epoxy resin coating is made from 10 g of epoxy resin and 3.33 g of curing agent. The types of epoxy resin and curing agent are the same as in Example 1.

[0142] Preparation method: Weigh 10g of epoxy resin and 3.33g of curing agent, stir at 150-200 rpm for 10 min to make the system uniformly mixed, transfer the system into the spray gun, spray it on the surface of the aluminum alloy substrate to obtain a self-lubricating coating, heat and cure, the curing program is to keep at 100℃ for 8h to obtain the finished epoxy coating.

[0143] Figure 12 This is a cross-sectional morphology diagram of the epoxy coating prepared in Comparative Example 1.

[0144] Figure 13 This is a graph showing the change in the friction coefficient of the epoxy coating prepared in Comparative Example 1 over time. Figure 13 As shown, pure epoxy resin has an extremely high coefficient of friction, with an overall coefficient of friction of around 0.67. This is because the pure resin coating has poor tribological properties due to the material's inherent characteristics and internal defects.

[0145] Comparative Example 2

[0146] An epoxy resin bulk material is prepared from 10 g of epoxy resin and 3.33 g of curing agent. The types of epoxy resin and curing agent are the same as in Example 1.

[0147] Preparation method: Weigh 10g of epoxy resin and 3.33g of curing agent, stir at 150-200rpm for 10min to make the system uniformly mixed, pour into a mold of a specific shape after vacuum degassing, heat and cure, the curing program is 50℃ for 3h → 100℃ for 2h → 140℃ for 30min, demold after natural cooling to obtain the epoxy resin block material.

[0148] Figure 14 The figures show the three-dimensional morphology and two-dimensional contour of the wear marks on the epoxy resin bulk material in Comparative Example 2. Figure 14 As shown, the wear volume of the pure epoxy resin block is 0.021 mm. 3 The wear rate is 1.94 × 10⁻⁶. -4 mm 3 / N·m, which is much higher than that of self-lubricating bulk materials and self-lubricating coatings containing lubricating oil microcapsules, also shows that pure resin bulk materials do have poor wear resistance due to the material's own characteristics and internal defects.

[0149] Comparative Example 3

[0150] An epoxy resin-based bulk material is made of 10 g of epoxy resin, 3.33 g of curing agent and 0.5 g of microcapsules without amino-modified cellulose nanocrystals.

[0151] The types of epoxy resin and curing agent are the same as in Example 1.

[0152] The preparation method of microcapsules without amino-modified cellulose nanocrystals is as follows:

[0153] (1) Add 0.5g of electrolyte NaCl to 200ml of deionized water to form an aqueous phase.

[0154] (2) Dissolve 0.9g of polysulfone in 40mL of dichloromethane. After complete dissolution, add 0.6g of PAO40 lubricating oil and mix well to form the oil phase.

[0155] (3) The oil phase was added to the aqueous phase under high-speed shearing, and after emulsification for 5 min, it was transferred to an ice-water bath and subjected to pulsed ultrasonic treatment to form a Pickering emulsion. Nitrogen gas was bubbled in for 2-3 h, and the organic solvent was removed by vacuum distillation at 40 °C, so that polysulfone was deposited at the Pickering emulsion interface to form a shell layer. Finally, after centrifugation, washing and freeze drying, microcapsule powder was obtained.

[0156] Preparation method of bulk material: Weigh 10g of epoxy resin, 0.5g of microcapsules without amino-modified cellulose nanocrystals, and 3.33g of curing agent, and stir at 150-200rpm for 10min to ensure uniform mixing. After vacuum degassing, pour into a mold of a specific shape, and heat to cure. The curing procedure is: hold at 50℃ for 3h → hold at 100℃ for 2h → hold at 140℃ for 30min. After natural cooling, demold to obtain the epoxy resin-based bulk material.

[0157] Figure 15 This is a microscopic morphology image of microcapsules containing amino-modified cellulose nanocrystals. For example... Figure 15 As shown, the surface of the microcapsules was not loaded with cellulose nanocrystals.

[0158] Comparative Example 4

[0159] An epoxy resin-based bulk material is prepared by wet precipitation of 10 g epoxy resin, 3.33 g curing agent and 0.2 g epoxy-modified cellulose nanocrystals.

[0160] The types of epoxy resin and curing agent are the same as in Example 1.

[0161] The method for preparing the wet precipitation of epoxy-modified cellulose nanocrystals is the same as in Example 1.

[0162] Preparation method of bulk material: Weigh 10 g of epoxy resin and 0.2 g of epoxy-modified cellulose nanocrystals into a wet precipitate and mix. Shear the mixture at 5000 rpm for 5 min, then ultrasonically disperse for 15 min. Dehydrate the mixture under vacuum at 60℃ and -0.09 MPa until no bubbles remain, thus obtaining a premix. Weigh 3.33 g of curing agent and add it to the premix. Stir at 150-200 rpm for 10 min to ensure uniform mixing. After vacuum degassing, pour the mixture into a mold of a specific shape and cure it according to a set program: 60℃ for 3 h → 90℃ for 5 h → 120℃ for 1 h. After natural cooling, demold to obtain the bulk material.

[0163] Figure 16 This is a graph showing the change in the friction coefficient of the bulk material prepared in Comparative Example 4 over time. Figure 17 The figures show the three-dimensional morphology and two-dimensional contour of the wear tracks on the bulk material prepared in Comparative Example 4. Due to the introduction of epoxy-modified CNC, the friction coefficient of the bulk material changed from adhesive wear to abrasive wear, resulting in an increased coefficient of friction of approximately 0.73. However, the calculated wear volume, based on the three-dimensional morphology and two-dimensional contour of the wear tracks obtained from white light testing, is 0.015 mm. 3 The wear rate reached 1.39 × 10⁻⁶. -4 mm 3 / N·m, which shows that the introduction of epoxidized cellulose can reduce the wear rate and wear volume of self-lubricating bulk materials, improve wear resistance, and thus enable them to have a longer friction life.

[0164] Comparative Example 5

[0165] An epoxy resin-based bulk material is made of 10 g of epoxy resin, 3.33 g of curing agent and 7 g of PAO40.

[0166] The types of epoxy resin and curing agent are the same as in Example 1.

[0167] Preparation method of bulk material: Weigh 10 g of epoxy resin and 7 g of PAO40 and mix them. Shear the mixture at 5000 rpm for 5 min, then ultrasonically disperse it for 15 min. Vacuum dehydrate the mixture at 60℃ and -0.09 MPa until no bubbles remain, thus obtaining the premix. Weigh 3.33 g of curing agent and add it to the premix. Stir at 150-200 rpm for 10 min to ensure uniform mixing. After vacuum degassing, pour the mixture into a mold of a specific shape and cure it according to a set program: 60℃ for 3 h → 90℃ for 5 h → 120℃ for 1 h. After natural cooling, demold to obtain the bulk material.

[0168] Figure 18 This is a surface morphology image of the bulk material prepared in Comparative Example 5. (Example: ...) Figure 18 As shown, the surface of the block material is sticky, soft, and has extremely low strength, and it is in a state where it cannot be completely cured.

[0169] In summary, this invention provides a method for preparing a self-lubricating composite material. The material is cured in a mold to obtain a self-lubricating material composed of an epoxy resin matrix, a three-dimensional cellulose nanocrystal network, and uniformly dispersed microcapsules. In this self-lubricating composite material, the epoxy resin is the continuous phase, while the epoxidized cellulose nanocrystals simultaneously act as emulsifiers, shell reinforcements, microcapsule anchoring points, and interfacial compatibilizers. The microcapsules serve as lubricant reservoirs. The synergistic effect of these multiple components enables the material to maintain excellent mechanical properties while possessing durable and stable self-lubricating characteristics. By effectively utilizing the high strength, large specific surface area, and modifiability of cellulose nanocrystals, as well as the on-demand release characteristics of the microcapsules, the coefficient of friction of the composite material is reduced to below 0.15, resulting in a lower wear rate and significantly improved service life and reliability of moving parts.

[0170] Technical effects of this application

[0171] The advantages of this invention are:

[0172] (1) This invention modifies cellulose nanocrystals in two different ways to enable them to play a dual role in composite materials: on the one hand, as a three-dimensional network support for epoxy resin matrix reinforcement; on the other hand, as a Pickering emulsifier in microcapsule preparation, synergistically enhancing the bonding force between the microcapsule shell and the matrix. The combined use of the two modified cellulose nanocrystals in this invention forms a strong bridge between the microcapsules and the matrix, resulting in composite materials with excellent mechanical properties, less susceptibility to interfacial debonding, and facilitated effective stress transfer from the resin matrix to the reinforcing phase. Thus, while improving tribological properties, the mechanical properties of the composite material are maintained or even enhanced.

[0173] (2) This invention utilizes modified cellulose nanocrystals to construct a stable three-dimensional network structure in an epoxy resin matrix. Through physical-chemical interactions, the microcapsules are spatially anchored by steric hindrance, effectively suppressing the floating or settling of microcapsules caused by density differences. This achieves uniform and stable dispersion of microcapsules in three-dimensional space, ensuring the consistency of the tribological properties of the material.

[0174] (3) This invention utilizes amino-modified cellulose nanocrystals as a Pickering emulsifier and incorporates them into the microcapsule shell in a one-step process, forming an organic-inorganic composite reinforced shell structure. This directly enhances the mechanical strength and density of the microcapsule shell, while simultaneously improving the dispersibility of the microcapsules in the resin matrix. In addition to avoiding the agglomeration of microcapsules in the resin, this composite shell can also withstand the shear and pressure during the processing of the composite material, effectively preventing premature leakage of the lubricant and enabling the lubricant to be released only on demand under frictional stress, significantly extending the lubrication life of the material.

[0175] (4) Modified cellulose nanocrystals provide excellent dispersibility and stability during the casting process, enabling the composite material to maintain excellent uniformity during the molding process, thereby overcoming the common bubble problem and stress concentration phenomenon in traditional casting.

[0176] (5) The excellent interfacial interaction of the composite material of the present invention ensures the degree of freedom of the composite material in molding. It can not only be molded into a coating to achieve surface protection, but also into a lubricating block of various shapes to achieve friction reduction and wear resistance under specific conditions; it can also be molded into precision parts of various complex shapes according to actual application needs to meet the urgent needs of high-end equipment for irregular self-lubricating parts.

[0177] In summary, this invention integrates four functions—emulsification, shell reinforcement, three-dimensional anchoring, and interfacial compatibility—through modified cellulose nanocrystals. By precisely controlling the functional roles of modified cellulose nanocrystals at different stages, controllable structural construction from the nanoscale to the macroscale is achieved, representing a typical multi-scale, integrated structural-functional design. This design paradigm simplifies the fabrication process, avoids compatibility issues arising from the introduction of multiple components, and enables the composite material to maintain high toughness and strength while stably reducing the coefficient of friction to below 0.15, significantly lowering the wear rate. It not only effectively addresses the requirements for long lifespan, high reliability, and friction reduction and wear resistance in precision moving parts of high-end equipment (such as aerospace bearings and precision guide rails), but also has broad application prospects, especially offering unique advantages in the customized needs of irregularly shaped self-lubricating parts.

[0178] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention in any way. Although the present invention has been disclosed above with reference to preferred embodiments, it is not intended to limit the present invention. Any person skilled in the art can make modifications or alterations to the above-disclosed technical content to create equivalent embodiments without departing from the scope of the present invention. Any modifications, equivalent changes, and alterations made to the above embodiments based on the technical essence of the present invention without departing from the scope of the present invention shall still fall within the scope of the present invention.

Claims

1. A self-lubricating composite material reinforced with in-situ anchored microcapsules of cellulose nanocrystals, characterized in that, It is made of resin matrix, epoxy-modified cellulose nanocrystals, microcapsules and curing agent; The microcapsule has a shell-core structure comprising a shell and a core. The shell is composed of engineering plastics and amino-modified cellulose nanocrystals, and the core is a lubricating medium encapsulated inside the shell. The self-lubricating composite material is prepared by mixing the resin matrix, the epoxy-modified cellulose nanocrystals, the microcapsules and the curing agent evenly, and then heating and curing to obtain the self-lubricating composite material.

2. The self-lubricating composite material reinforced with in-situ anchored microcapsules of cellulose nanocrystals as described in claim 1, characterized in that, The preparation method of the epoxy-modified cellulose nanocrystals is as follows: (a1) Cellulose nanocrystals were ultrasonically dispersed in deionized water, and the pH was adjusted to 4.5-5.0 to obtain dispersion A1; (a2) Dissolve silane coupling agent KH560 in a mixed solution of ethanol and water, and stir to hydrolyze the silane coupling agent KH560 to obtain solution B1; (a3) The solution B1 is slowly added dropwise to the dispersion A1, the temperature is raised to 50-60℃, the mixture is stirred for 2-3 hours, and after centrifugation and washing, a wet precipitate containing the epoxy-modified cellulose nanocrystals is obtained.

3. The self-lubricating composite material reinforced with in-situ anchored microcapsules of cellulose nanocrystals as described in claim 1, characterized in that, The microcapsules are prepared as follows: (b1) Cellulose nanocrystals were ultrasonically dispersed in anhydrous ethanol, and the pH was adjusted to 4.5-5.0 to obtain dispersion A2; silane coupling agent KH550 was dissolved in a mixed solution of ethanol and water, and the mixture was stirred to hydrolyze the silane coupling agent KH550 to obtain solution B2. The solution B2 was slowly added dropwise to the dispersion A2, and the mixture was stirred and reacted under reflux at 70-80℃ for 3-4 hours. After centrifugation, washing, and drying, the amino-modified cellulose nanocrystals were obtained. (b2) The amino-modified cellulose nanocrystals are dispersed in deionized water, and the electrolyte NaCl is added to form an aqueous phase; (b3) Dissolve the engineering plastic in an organic solvent, add the lubricating medium, and mix evenly to form an oil phase; (b4) The oil phase is added to the aqueous phase under high-speed shearing and ultrasonic treatment is performed to form a Pickering emulsion; nitrogen gas is bubbled for 2-3 hours and the organic solvent is removed by vacuum distillation, so that the engineering plastic is deposited at the interface of the Pickering emulsion to form the shell layer. The microcapsules are obtained by centrifugation, washing and freeze drying.

4. The self-lubricating composite material reinforced with in-situ anchored microcapsules of cellulose nanocrystals as described in claim 3, characterized in that, The engineering plastic is selected from at least one of polysulfone, polyethersulfone, polyphenylene ether, and polycarbonate.

5. The self-lubricating composite material reinforced with in-situ anchored microcapsules of cellulose nanocrystals as described in claim 3, characterized in that, The lubricating medium is at least one of mineral oil, synthetic oil, and vegetable oil.

6. The self-lubricating composite material reinforced with in-situ anchored microcapsules of cellulose nanocrystals as described in claim 3, characterized in that, The mass ratio of the amino-modified cellulose nanocrystals to the engineering plastic is 10:(4-5).

7. The self-lubricating composite material reinforced with in-situ anchored microcapsules of cellulose nanocrystals as described in claim 1, characterized in that, The resin matrix is ​​selected from at least one of epoxy resin, phenolic resin, and polyimide resin.

8. The self-lubricating composite material reinforced with in-situ anchored microcapsules of cellulose nanocrystals as described in claim 2, characterized in that, Based on the mass of the resin matrix, the amount of the wet precipitate of the epoxy-modified cellulose nanocrystals accounts for 2-5% of the mass of the resin matrix, the amount of the microcapsules accounts for 3-10% of the mass of the resin matrix, and the amount of the curing agent accounts for 30-35% of the mass of the resin matrix.

9. The self-lubricating composite material reinforced with in-situ anchored microcapsules of cellulose nanocrystals as described in claim 8, characterized in that, The resin matrix and the wet precipitate of the epoxy-modified cellulose nanocrystals are mixed evenly and then vacuum dehydrated until the system is free of bubbles to obtain a premixed solution. The microcapsules and the curing agent are added to the premixed liquid and mixed evenly to obtain a coating solution; the coating solution is sprayed onto the surface of the substrate and cured by heating to obtain a self-lubricating protective coating.

10. The self-lubricating composite material reinforced with in-situ anchored microcapsules of cellulose nanocrystals as described in claim 8, characterized in that, The resin matrix and the epoxy-modified cellulose nanocrystals are mixed evenly and then vacuum dehydrated until the system is free of bubbles to obtain a premixed liquid. The microcapsules and the curing agent are added to the premixed liquid and mixed evenly to obtain a casting liquid. The casting liquid is vacuum degassed and then poured into a mold, and then heated and cured to obtain a self-lubricating block.

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