Polymer-based composites containing multistage MOFs stress-dissipating layers, methods of making and applications thereof

Abstract

The application provides a polymer-based composite material containing a multistage MOFs stress dissipation layer and a preparation method and application thereof, and belongs to the technical field of lubricating materials.The application mixes nanocellulose, MXene, Ni-BDC and water, carries out a self-assembly reaction under the condition of standing, and obtains a first mixed slurry; ZIF-8 nanoparticles, a PVA aqueous solution and the first mixed slurry are mixed, a partial hydrolysis reaction is carried out under the condition of stirring, and a second mixed slurry is obtained; the second mixed slurry is placed in a mold for drying treatment, and a polymer-based composite material containing a multistage MOFs stress dissipation layer is obtained.The application can introduce the MOFs materials of MXene and Ni-BDC and ZIF-8 into a polymer matrix, and significantly improve the friction-reducing and wear-resisting performance, toughness and durability of the composite material by constructing a multistage friction stress dissipation layer.

Description

Technical Field

[0001] This invention relates to the field of lubrication materials technology, specifically to a polymer-based composite material containing a multi-level MOF stress dissipation layer, its preparation method, and its application. Background Technology

[0002] With the continuous development of materials science and engineering technology, polymer-based composite materials play an increasingly important role in industrial applications. However, common polymer-based composite materials still face the following problems: (1) Low toughness and easy wear: Traditional polymer-based composite materials usually have the disadvantages of insufficient toughness and easy wear. Especially in the long-term use, friction and wear will cause damage to the material surface, thereby affecting its service life and stability; (2) Uneven stress distribution: The dispersion of fillers in the polymer matrix has an important impact on the tribological and mechanical properties of the material. Uneven filler distribution will lead to local stress concentration, which will accelerate wear; (3) Insufficiency of traditional fillers: Common tribological performance reinforcing materials (such as graphite, carbon nanotubes, inorganic fillers, etc.) may not be able to effectively provide excellent friction reduction effect or have low wear resistance in some cases.

[0003] In the field of tribology, metal-organic frameworks (MOFs) can regulate the interaction between the friction interface and the lubricating medium through their unique pore structure and surface functional groups, thereby reducing the coefficient of friction and wear rate. Furthermore, MOFs can improve the mechanical properties of composite materials through crosslinking reactions, enhancing toughness and wear resistance. However, traditional MOFs exhibit poor dispersion in polymer matrices and are prone to agglomeration. This not only affects the effective utilization of MOFs but may also lead to a decline in the mechanical properties of the polymer matrix. Existing stress dissipation mechanisms often rely on a single material or structure, lacking multi-level structural design. This prevents materials from fully utilizing stress dispersion and energy dissipation in complex frictional environments. Therefore, achieving efficient dispersion and stability of MOFs in polymer matrices through structural design, and improving the tribological properties of composite materials through the design of multi-level stress dissipation layers, are key issues that urgently need to be addressed. Summary of the Invention

[0004] In view of this, the purpose of this invention is to provide a polymer-based composite material containing a multi-level MOF stress dissipation layer, its preparation method, and its application. This invention enables the introduction of MOF materials such as MXene, Ni-BDC, and ZIF-8 into a polymer matrix, and significantly improves the friction-reducing, wear-resistant, toughness, and durability of the composite material by constructing a multi-level friction stress dissipation layer.

[0005] To achieve the above-mentioned objectives, the present invention provides the following technical solution:

[0006] This invention provides a method for preparing a polymer-based composite material containing a multi-level MOF stress dissipation layer, comprising the following steps:

[0007] Nanocellulose, MXene, Ni-BDC and water were mixed and subjected to a self-assembly reaction under static conditions to obtain the first mixed slurry.

[0008] ZIF-8 nanoparticles and PVA aqueous solution were mixed with the first mixed slurry, and a partial hydrolysis reaction was carried out under stirring to obtain a second mixed slurry.

[0009] The second mixed slurry was placed in a mold and dried to obtain a polymer-based composite material containing a multi-level MOF stress dissipation layer.

[0010] Preferably, the amount of nanocellulose used is 75-100 parts by mass, the amount of MXene used is 10-25 parts, the amount of Ni-BDC used is 10-20 parts, and the amount of water used is 4000-5000 parts.

[0011] Preferably, the mixing is one or more of ultrasonic treatment, ball milling treatment, homogenization treatment and mechanical stirring.

[0012] Preferably, the self-assembly reaction takes 24 to 48 hours.

[0013] Preferably, the method for preparing Ni-BDC includes the following steps:

[0014] NiCl2, 1,4-phthalic acid and N,N-dimethylformamide were mixed and subjected to a solvothermal reaction to obtain Ni-BDC;

[0015] The solvothermal reaction is carried out at a temperature of 100–120°C for a duration of 16–24 hours.

[0016] Preferably, based on the mass fraction of the nanocellulose, the amount of ZIF-8 nanoparticles is 10-20 parts, the amount of the PVA aqueous solution is 3000-4000 parts, and the concentration of the PVA aqueous solution is 5-7 wt.%.

[0017] Preferably, the partial hydrolysis reaction takes 60 to 180 minutes.

[0018] Preferably, the drying process is carried out at a temperature of 50–70°C for 14–16 hours.

[0019] This invention provides a polymer-based composite material containing a multi-level MOF stress dissipation layer prepared by the above preparation method.

[0020] This invention provides the application of the above-mentioned polymer-based composite material containing a multi-level MOF stress dissipation layer as a self-lubricating material.

[0021] This invention provides a polymer-based composite material containing a multi-level MOF stress dissipation layer, comprising the following steps: mixing nanocellulose, MXene, Ni-BDC and water, and performing a self-assembly reaction under static conditions to obtain a first mixed slurry; mixing ZIF-8 nanoparticles and PVA aqueous solution with the first mixed slurry, and performing a partial hydrolysis reaction under stirring conditions to obtain a second mixed slurry; and placing the second mixed slurry in a mold for drying to obtain the polymer-based composite material containing a multi-level MOF stress dissipation layer.

[0022] Compared with the prior art, the present invention has the following beneficial effects:

[0023] (1) Construction of a multi-level friction stress dissipation layer: This invention forms a large-sized hybrid interwoven layer by self-assembling Ni-BDC and MXene with cellulose, and further hydrolyzes ZIF-8 nanoparticles to form an uneven surface with a volcano-like structure. This multi-level stress dissipation layer can effectively disperse the stress generated during friction, reduce the accumulation of frictional heat, and thus significantly reduce the wear rate;

[0024] (2) Highly efficient MOF dispersion and stability: This invention confines Ni-BDC and MXene within the cellulose framework through a self-assembly process, greatly improving the dispersion and stability of MOFs in the polymer matrix. This structure not only increases the loading capacity of MOFs but also improves the interfacial bonding between MOFs and the matrix;

[0025] (3) Combination of hydrolysis reaction and cross-linking: This invention promotes the hydrolysis reaction of ZIF-8 during stirring to generate zinc hydroxide, imidazole acid and its derivatives, thereby filling the gaps between the composite matrix, promoting the cross-linking reaction between the stacked layers, and further improving the toughness, wear resistance and long-term stability of the composite material.

[0026] (4) Excellent friction-reducing and wear-resistant properties: The polymer-based composite material prepared in this invention exhibits excellent self-lubricating ability and extremely low wear rate by constructing multi-level friction stress dissipation layers on the surface and inside. This enables the material to maintain stable tribological properties during long-term use and extends its service life.

[0027] The results of the examples show that the lowest coefficient of friction of the polymer-based composite material containing a multi-level MOF stress dissipation layer prepared by the present invention is 0.015 to 0.037. Attached Figure Description

[0028] Figure 1 The surface morphology of the polymer-based composite material prepared in Example 1 is shown in the image.

[0029] Figure 2 The surface morphology image is shown for the polymer-based composite material prepared in Example 2.

[0030] Figure 3 The friction coefficient curve of the polymer-based composite material prepared in Example 1 is shown.

[0031] Figure 4 The friction coefficient curve of the polymer-based composite material prepared in Example 2 is shown.

[0032] Figure 5 This is a graph showing the friction coefficient of the polymer-based composite material prepared in Example 3;

[0033] Figure 6 The friction coefficient curves are for the control group samples prepared in Comparative Examples 1 and 2. Detailed Implementation

[0034] This invention provides a method for preparing a polymer-based composite material containing a multi-level MOF stress dissipation layer, comprising the following steps:

[0035] Nanocellulose, MXene, Ni-BDC and water were mixed and subjected to a self-assembly reaction under static conditions to obtain the first mixed slurry.

[0036] ZIF-8 nanoparticles and PVA aqueous solution were mixed with the first mixed slurry, and a partial hydrolysis reaction was carried out under stirring to obtain a second mixed slurry.

[0037] The second mixed slurry was placed in a mold and dried to obtain a polymer-based composite material containing a multi-level MOF stress dissipation layer.

[0038] Unless otherwise specified, the raw materials used in this invention are commercially available.

[0039] This invention involves mixing nanocellulose, MXene, Ni-BDC, and water, and then subjecting the mixture to a self-assembly reaction under static conditions to obtain a first mixed slurry. In this invention, the preparation method of the Ni-BDC preferably includes the following steps:

[0040] NiCl2, 1,4-phthalic acid and N,N-dimethylformamide were mixed and subjected to a solvothermal reaction to obtain Ni-BDC.

[0041] The amount of NiCl2 is preferably 40-50 parts by mass, specifically 40, 45 or 50 parts; the amount of 1,4-phthalic acid is preferably 7.5-12 parts, specifically 7.5, 10 or 12 parts; and the amount of N,N-dimethylformamide is preferably 1000-1300 parts, specifically 1000, 1200 or 1300 parts.

[0042] This invention does not impose any special requirements on the mixing method; any mixing method well-known in the art can be used. In this invention, the solvothermal reaction is preferably carried out in a PTFE reactor, and the hydrothermal reaction temperature is preferably 100–120°C, specifically 100°C, 110°C, or 120°C. The hydrothermal reaction time is preferably 16–24 hours, specifically 16 hours, 18 hours, 20 hours, or 24 hours. After the hydrothermal reaction, this invention preferably filters and washes the obtained hydrothermal reaction product to obtain Ni-BDC. In this invention, the Ni-BDC has a layered structure, preferably with a size of 10–30 μm.

[0043] In this invention, the amount of nanocellulose used is preferably 75 to 100 parts by weight, specifically 75, 80, 85, 90, 95, or 100 parts. In this invention, the length of the nanocellulose is preferably 500 to 1000 μm, and the diameter is preferably 20 to 100 nm.

[0044] Based on the mass fraction of the nanocellulose, the amount of MXene is preferably 10 to 25 parts, specifically 10, 15, 20, or 25 parts. In this invention, the MXene is preferably multilayer MXene; the lateral dimension of the MXene is preferably 5 to 30 μm, and the thickness is preferably 5 to 10 μm.

[0045] Based on the mass fraction of the nanocellulose, the amount of Ni-BDC is preferably 10 to 20 parts, specifically 10 parts, 15 parts or 20 parts.

[0046] Based on the mass fraction of the nanocellulose, the amount of water used is preferably 4000-5000 parts, specifically 4000 parts, 4500 parts, or 5000 parts. In this invention, the water is preferably distilled water.

[0047] In this invention, the mixing is preferably vigorous mixing; the mixing is preferably one or more of ultrasonic treatment, ball milling, homogenization, and mechanical stirring. In this invention, the ultrasonic treatment is preferably cell disruptor ultrasonic treatment, with a power of 800-1000W and a time of 60-120 min; in this invention, the ball milling speed is preferably 300-400 rpm and the time is preferably 6-10 h; in this invention, the homogenization rate is preferably 7000-8000 rpm and the time is preferably 20-30 min; in this invention, the mechanical stirring rate is preferably 800-1200 rpm and the time is preferably 18-24 h.

[0048] This invention involves a self-assembly reaction under static conditions. Preferably, the temperature of the self-assembly reaction is room temperature, and the reaction time is 24–48 hours. In specific embodiments, the reaction time is 24 hours, 36 hours, or 48 hours. During the static process, Ni-BDC and MXene self-assemble with cellulose to form a large-sized hybrid interwoven layer, confining Ni-BDC and MXene within the cellulose framework. This significantly improves the dispersibility and stability of MOFs in the polymer matrix.

[0049] After obtaining the first mixed slurry, the present invention mixes ZIF-8 nanoparticles and PVA aqueous solution with the first mixed slurry, and performs a partial hydrolysis reaction under stirring to obtain a second mixed slurry. In this invention, based on the mass fraction of the nanocellulose, the amount of ZIF-8 nanoparticles is preferably 10-20 parts, specifically 10 parts, 15 parts, or 20 parts. In this invention, the particle size of the ZIF-8 nanoparticles is preferably 100-200 nm.

[0050] In this invention, the molecular weight of the PVA is M. W Preferably, the concentration is 50,000 to 150,000, more preferably 82,000. In this invention, the concentration of the PVA aqueous solution is 5 to 7 wt.%, specifically 5 wt.%, 6 wt.%, or 7 wt.%. Based on the mass fraction of the nanocellulose, the amount of the PVA aqueous solution is preferably 3,000 to 4,000 parts, specifically 3,000 parts, 3,500 parts, or 4,000 parts. In this invention, the preparation method of the PVA aqueous solution preferably includes the following steps:

[0051] PVA particles are heated and mixed with water to obtain a transparent PVA aqueous solution. In this invention, the water is preferably distilled water. In this invention, the heating treatment temperature is preferably 96°C, and the heating time is preferably 6–9 hours.

[0052] This invention involves a partial hydrolysis reaction under stirring conditions. The stirring rate is preferably 800–1200 rpm. The temperature of the partial hydrolysis reaction is preferably room temperature, and the time is preferably 60–180 min, specifically 60 min, 90 min, 120 min, 150 min, or 180 min. In this invention, stirring promotes the hydrolysis of ZIF-8, generating zinc hydroxide, imidazolic acid and its derivatives, as well as active species (such as Zn). 2+ Zinc hydroxide (Zn(OH)2) can fill the gaps between composite matrix layers, promote cross-linking reactions between stacked layers, and further improve the toughness, wear resistance, and long-term stability of the composite material. Specifically, zinc ions can promote cross-linking by interacting with hydroxyl groups in PVA, and can also affect the interaction between PVA and nanocellulose. Zinc hydroxide (Zn(OH)2) may play a more significant role in the cross-linking process of PVA and cellulose. Cellulose molecules have multiple hydroxyl groups, which may interact with Zn... 2+ Ions form coordination bonds, thereby promoting the cross-linking reaction between PVA and cellulose molecules. Zn 2+ Ions can act as crosslinking agents, linking PVA and cellulose molecules through hydrogen bonds or coordination bonds to form a crosslinked network structure. Furthermore, imidazole compounds such as imidazole acids primarily enhance the mechanical and frictional stability of polymer-based composites by improving solubility or strengthening intermolecular interactions through hydrogen bonding.

[0053] After obtaining the second mixed slurry, the present invention places the second mixed slurry in a mold for drying treatment to obtain a polymer-based composite material containing a multi-level MOF stress dissipation layer. In the present invention, the drying treatment temperature is preferably 50-70°C, more preferably 60°C, and the drying time is preferably 14-16 hours, specifically 14 hours, 15 hours, or 16 hours. In the present invention, the drying treatment can promote the cross-linking effect of hydrolysis products on nano-components and the evaporation of water, while promoting the hydrolysis of ZIF-8 on the polymer surface and obtaining a polymer-based composite material with a volcano-like structure surface. This volcano-like structure can effectively store the hydrolysis products of ZIF-8 and allow them to participate in the formation of a lubrication transfer film and rapidly dissipate frictional energy during friction. In the present invention, when the drying temperature exceeds 70°C, the performance of the polymer-based composite material will decrease sharply.

[0054] This invention provides a polymer-based composite material containing a multi-level MOF stress dissipation layer prepared by the above-described method. In this invention, the polymer-based composite material comprises a polymer matrix and a multi-level MOF stress dissipation layer dispersed on and within the polymer matrix. In this invention, the polymer matrix is ​​PVA, and the multi-level MOF stress dissipation layer comprises a hybrid interwoven layer formed by the self-assembly of Ni-BDC, MXene, and cellulose, and partially hydrolyzed ZIF-8 nanoparticles, wherein the ZIF-8 nanoparticles fill the gaps between the hybrid interwoven layer and the polymer matrix.

[0055] This invention provides the application of the above-mentioned polymer-based composite material containing a multi-level MOF stress dissipation layer as a self-lubricating material.

[0056] The following detailed description, in conjunction with embodiments, illustrates the polymer-based composite material containing a multi-level MOF stress dissipation layer provided by the present invention, its preparation method, and its application. However, these descriptions should not be construed as limiting the scope of protection of the present invention.

[0057] In the following embodiments, the method for preparing the PVA aqueous solution is to use a polymer with a molecular weight of M... W PVA particles with a mass of 82000 were added to distilled water and heated at 96°C until a transparent solution was obtained, ultimately yielding a PVA aqueous solution with a mass fraction of 5–7 wt.%.

[0058] In the following examples, the length of the nanocellulose is 500–1000 μm;

[0059] The lateral dimensions of MXene are 5–30 μm;

[0060] The ZIF-8 nanoparticles have a particle size of 100–200 nm.

[0061] Example 1

[0062] A method for preparing a polymer-based composite material containing a multi-level MOF stress dissipation layer comprises the following steps:

[0063] Step 1: Mix 40 parts NiCl2·6H2O, 7.5 parts 1,4-phthalic acid and 1000 parts N,N-dimethylformamide evenly, transfer it to a PTFE reactor and react at 100℃ for 24 hours. Then wash it three times with distilled water and ethanol alternately to obtain Ni-BDC.

[0064] Step 2: Disperse 75 parts of nanocellulose in 4000 parts of distilled water and add 10 parts of MXene and 10 parts of Ni-BDC prepared in Step 1. Mix them uniformly by mechanical homogenization (8000 rpm, 20 min) and let the mixture stand for 24 hours to promote the self-assembly process of the structure to obtain the first mixed slurry.

[0065] Step 3: Add 10 parts of ZIF-8 to the first mixed slurry prepared in Step 2, and simultaneously add 3000 parts of 5 wt.% PVA aqueous solution. During continuous stirring at room temperature, promote the hydrolysis reaction of part of ZIF-8. The stirring rate is 800 rpm and the time is 180 min to obtain the second mixed slurry.

[0066] Step 4: Place the well-stirred second slurry in a mold and dry it at 60°C for 14 hours to promote the cross-linking of the hydrolysis products on the nano-components and the evaporation of water, while promoting the hydrolysis of the ZIF-8 polymer surface layer and obtaining a polymer-based composite material with a volcano-like structure surface.

[0067] Example 2

[0068] A method for preparing a polymer-based composite material containing a multi-level MOF stress dissipation layer comprises the following steps:

[0069] Step 1: Mix 50 parts NiCl2·6H2O, 12 parts 1,4-phthalic acid and 1300 parts N,N-dimethylformamide evenly, transfer it to a PTFE reactor and react at 120°C for 16 hours. Then wash three times with distilled water and ethanol alternately to obtain Ni-BDC.

[0070] Step 2: Disperse 100 parts of nanocellulose in 5000 parts of distilled water and add 25 parts of MXene and 20 parts of Ni-BDC prepared in Step 1. Mix the mixture uniformly by mechanical homogenization (7000 rpm, 30 min) and let the mixture stand for 48 hours to promote the self-assembly process of the structure to obtain the first mixed slurry.

[0071] Step 3: Add 20 parts of ZIF-8 to the first mixed slurry prepared in Step 2, and simultaneously add 4000 parts of 7wt.% PVA aqueous solution. During continuous stirring at room temperature, promote the hydrolysis reaction of part of ZIF-8. The stirring rate is 1000 rpm and the time is 150 min to obtain the second mixed slurry.

[0072] Step 4: Place the well-stirred second slurry in a mold and dry it at 60°C for 16 hours to promote the cross-linking of the hydrolysis products on the nano-components and the evaporation of water, while promoting the hydrolysis of the ZIF-8 polymer surface layer and obtaining a polymer-based composite material with a volcano-like structure surface.

[0073] Example 3

[0074] A method for preparing a polymer-based composite material containing a multi-level MOF stress dissipation layer comprises the following steps:

[0075] Step 1: Mix 45 parts NiCl2·6H2O, 10 parts 1,4-phthalic acid and 1200 parts N,N-dimethylformamide evenly, transfer it to a PTFE reactor and react at 110℃ for 24 hours. Then wash it three times with distilled water and ethanol alternately to obtain Ni-BDC.

[0076] Step 2: Disperse 90 parts of nanocellulose in 4500 parts of distilled water and add 15 parts of MXene and 15 parts of Ni-BDC prepared in Step 1. Mix the mixture uniformly by mechanical homogenization (8000 rpm, 30 min) and let the mixture stand for 36 hours to promote the self-assembly process of the structure to obtain the first mixed slurry.

[0077] Step 3: Add 15 parts of ZIF-8 to the first mixed slurry prepared in Step 2, and simultaneously add 3500 parts of 6wt.% PVA aqueous solution. During continuous stirring at room temperature, promote the hydrolysis reaction of part of ZIF-8. The stirring rate is 1200 rpm and the time is 120 min to obtain the second mixed slurry.

[0078] Step 4: Place the well-stirred second slurry in a mold and dry it at 60°C for 12 hours to promote the cross-linking of the hydrolysis products on the nano-components and the evaporation of water, while promoting the hydrolysis of the ZIF-8 polymer surface layer and obtaining a polymer-based composite material with a volcano-like structure surface.

[0079] Example 4

[0080] A method for preparing a polymer-based composite material containing a multi-level MOF stress dissipation layer comprises the following steps:

[0081] Step 1: Mix 40 parts NiCl2·6H2O, 12 parts 1,4-phthalic acid and 1200 parts N,N-dimethylformamide evenly, transfer it to a PTFE reactor and react at 120℃ for 18 hours. Then wash three times with distilled water and ethanol alternately to obtain Ni-BDC.

[0082] Step 2: Disperse 100 parts of nanocellulose in 4000 parts of distilled water and add 10 parts of MXene and 20 parts of Ni-BDC prepared in Step 1. Mix the mixture uniformly by mechanical homogenization (8000 rpm, 30 min) and let the mixture stand for 48 hours to promote the self-assembly process of the structure to obtain the first mixed slurry.

[0083] Step 3: Add 20 parts of ZIF-8 to the first mixed slurry prepared in Step 2, and simultaneously add 4000 parts of 6wt.% PVA aqueous solution. During continuous stirring at room temperature, promote the hydrolysis reaction of part of ZIF-8. The stirring rate is 1000 rpm and the time is 90 min to obtain the second mixed slurry.

[0084] Step 4: Place the well-stirred second slurry in a mold and dry it at 60°C for 14 hours to promote the cross-linking of the hydrolysis products on the nano-components and the evaporation of water, while promoting the hydrolysis of the ZIF-8 polymer surface layer and obtaining a polymer-based composite material with a volcano-like structure surface.

[0085] Comparative Example 1

[0086] Step 1: Mix 50 parts NiCl2·6H2O, 12 parts 1,4-phthalic acid and 1200 parts N,N-dimethylformamide evenly, transfer it to a PTFE reactor and react at 120°C for 18 hours. Then wash three times with distilled water and ethanol alternately to obtain Ni-BDC.

[0087] Step 2: Disperse 100 parts of nanocellulose in 5000 parts of distilled water and add 10 parts of Ni-BDC prepared in Step 1. Mix the mixture uniformly by mechanical homogenization (8000 rpm, 30 min) and let the mixture stand for 48 hours to promote the self-assembly process of the structure to obtain the first mixed slurry.

[0088] Step 3: Add 10 parts of ZIF-8 to the first mixed slurry prepared in Step 2, and simultaneously add 4000 parts of 6wt.% PVA aqueous solution. During continuous stirring, promote the hydrolysis reaction of part of ZIF-8. The stirring rate is 1000 rpm and the time is 60 min to obtain the second mixed slurry.

[0089] Step 4: Place the well-stirred second slurry in a mold and dry it at 60°C for 14 hours to promote the cross-linking of the hydrolysis products on the nano-components and the evaporation of water, while promoting the hydrolysis of ZIF-8 on the polymer surface and obtaining a polymer-based composite material, which is designated as control sample 1.

[0090] Comparative Example 2

[0091] Step 1: Mix 50 parts NiCl2·6H2O, 12 parts 1,4-phthalic acid and 1200 parts N,N-dimethylformamide evenly, transfer it to a PTFE reactor and react at 120°C for 18 hours. Then wash three times with distilled water and ethanol alternately to obtain Ni-BDC.

[0092] Step 2: Disperse 100 parts of nanocellulose in 5000 parts of distilled water and add 10 parts of Ni-BDC prepared in Step 1. Mix the mixture uniformly by mechanical homogenization (8000 rpm, 30 min) and let the mixture stand for 48 hours to promote the self-assembly process of the structure to obtain the first mixed slurry.

[0093] Step 3: Add 4000 parts of 6wt.% PVA aqueous solution to the first mixed slurry prepared in Step 2, and continuously stir at a rate of 1000 rpm for 120 min to obtain the second mixed slurry;

[0094] Step 4: Place the well-stirred second slurry into a mold and dry it at 60°C for 14 hours to promote the cross-linking of the hydrolysis products with the nano-components and the evaporation of water to polymerize the composite material, which is designated as control sample 2.

[0095] Structural characterization

[0096] (1) The surface morphology of the polymer-based composite material prepared in Example 1 is shown in the figure. Figure 1 As shown, it exhibits a continuous arrangement of alternating peaks and valleys in a concave-convex morphology, which effectively reduces the actual contact area between friction pairs and enhances the friction-reducing and wear-resistant properties of the polymer-based composite material during friction. The formation of this peak-like structure is mainly attributed to the hydrolysis reaction of ZIF-8 and its cross-linking effect on nano-components. Zinc hydrates (such as Zn(H2O)6) 2+ It itself does not usually have strong cross-linking ability, but it may generate some active species (such as Zn) during hydrolysis. 2+ These active substances can participate in the cross-linking reaction. Zinc ions can promote cross-linking by interacting with hydroxyl groups in PVA, and can also affect the interaction between PVA and nanocellulose. Zinc hydroxide (Zn(OH)₂) may play a more significant role in the cross-linking process of PVA and cellulose. Cellulose molecules have multiple hydroxyl groups, which may interact with Zn... 2+ Ions form coordination bonds, thereby promoting the cross-linking reaction between PVA and cellulose molecules. Zn 2+Ions can act as crosslinking agents, linking PVA and cellulose molecules through hydrogen bonds or coordination bonds to form a crosslinked network structure. Furthermore, imidazole compounds such as imidazole acids primarily enhance the mechanical and frictional stability of polymer-based composites by improving solubility or strengthening intermolecular interactions through hydrogen bonding.

[0097] (2) Surface morphology image (partial magnified area) of the polymer-based composite material prepared in Example 2. Figure 2 As shown, it exhibits a crater-like, peak-shaped structure with inwardly concave features. This structure is mainly attributed to the hydrolysis of ZIF-8 during water evaporation, resulting in pit-like morphology left by the decomposition of particles in the peak region. This structure effectively stores the hydrolysis products of ZIF-8 and allows them to participate in the formation of a lubricating transfer film during friction, rapidly dissipating frictional energy. This is mainly manifested in the formation of a lubricating film at the friction interface by zinc hydroxide, reducing the coefficient of friction and wear, and the potential influence of imidazole acid (or its derivatives) on lubrication performance. Imidazole acid and its derivatives form a highly adhesive film or coating on the friction surface, significantly improving the slippage of the friction pair at the raised parts and promoting the stability of the coefficient of friction and the reduction of wear rate.

[0098] Performance testing

[0099] (1) The friction coefficient curve of the polymer-based composite material prepared in Example 1 is shown in the figure below. Figure 3 As shown, the material exhibits a consistently stable friction coefficient curve during the extended testing period, with almost no break-in period, ultimately achieving a friction coefficient as low as 0.037. This value is extremely low for solid self-lubricating materials, indicating that the construction of the multi-level MOF stress dissipation layer can quickly transfer or move the frictional stress and energy on the surface of the composite material to the matrix, effectively reducing the friction coefficient of the composite material.

[0100] (2) The friction coefficient curve of the polymer-based composite material prepared in Example 2 is shown in the figure. Figure 4 As shown, the average friction coefficient is further reduced to an ultra-low value of 0.015, indicating that the multi-level MOFs structure in the polymer matrix enhances the energy transfer of frictional stress at high sliding speeds, enabling the frictional energy at the friction interface to be transferred to the matrix interior at an extremely high speed, demonstrating excellent frictional energy dissipation capability.

[0101] (3) The friction coefficient curve of the polymer-based composite material prepared in Example 3 is shown in the figure. Figure 5 As shown, the lowest coefficient of friction reaches 0.023, indicating that changes in the raw material ratio have a certain impact on the friction performance of the composite material, but the fluctuation range of its value is small.

[0102] In summary, the polymer-based composite material containing a multi-level MOF stress dissipation layer of the present invention exhibits excellent tribological properties: (1) The surface of Ni-BDC may exhibit certain low-friction characteristics, and due to its metal center (nickel), it can form a certain chemical adsorption with the friction surface, which helps to reduce the friction coefficient; (2) The nanostructure and layered characteristics of MXene enable it to form a thin lubricating film at the friction interface, which helps to reduce the friction coefficient. Its sheet structure can slide during friction, thereby forming a "lubricating sheet" and further reducing friction; (3) The highly porous structure of ZIF-8 allows it to undergo flexible crystal deformation during friction, and significantly improves the dissipation of frictional stress through synergistic effects with other materials, greatly reducing the friction coefficient and wear rate of the polymer-based composite material.

[0103] The friction coefficient curves of the control group samples prepared in Comparative Examples 1 and 2 are shown in the figure. Figure 6 As shown, the control samples prepared in Comparative Examples 1 and 2 exhibited high coefficients of friction during the friction performance test, reaching 0.081 and 0.082 respectively, significantly higher than the composite material with a stress dissipation layer structure prepared in Example 2 of this invention. In contrast, the coefficient of friction of the control sample without a stress dissipation layer was 446.67% higher than that of the sample in Example 2, indicating that the construction of a multi-level MOF stress dissipation layer can significantly improve the friction reduction performance of the composite material.

[0104] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A method of preparing a polymer-based composite containing a multi-stage MOFs stress dissipating layer, characterized in that, The preparation method comprises the following steps: mixing nanocellulose, MXene, Ni-BDC and water, and performing a self-assembly reaction under static conditions to obtain a first mixed slurry; mixing ZIF-8 nanoparticles and a PVA aqueous solution with the first mixed slurry, and performing a partial hydrolysis reaction under stirring to obtain a second mixed slurry; placing the second mixed slurry in a mold and performing a drying treatment to obtain a polymer-based composite material containing a multi-level MOFs stress dissipation layer; the amount of the nanocellulose is 75-100 parts, the amount of the MXene is 10-25 parts, the amount of the Ni-BDC is 10-20 parts, and the amount of the water is 4000-5000 parts; based on the mass fraction of the nanocellulose, the amount of the ZIF-8 nanoparticles is 10-20 parts, and the amount of the PVA aqueous solution is 3000-4000 parts, and the concentration of the PVA aqueous solution is 5-7 wt.%.

2. The production method according to claim 1, characterized by, When the nanocellulose, the MXene, the Ni-BDC and the water are mixed, the mixing is one or several of ultrasonic treatment, ball milling treatment, homogenization treatment and mechanical stirring.

3. The preparation method according to claim 1, characterized in that, The self-assembly reaction is performed for 24-48 h.

4. The method of claim 1, wherein, The preparation method of the Ni-BDC comprises the following steps: mixing NiCl2, 1,4-benzenedicarboxylic acid and N,N-dimethylformamide, and performing a solvothermal reaction to obtain the Ni-BDC; the solvothermal reaction is performed at a temperature of 100-120 ℃ for 16-24 h.

5. The preparation method according to claim 1, characterized in that, The partial hydrolysis reaction is performed for 60-180 min.

6. The method of claim 1, wherein, The drying treatment is performed at a temperature of 50-70 ℃ for 14-16 h.

7. The polymer-based composite material containing a multi-level MOFs stress dissipation layer prepared by the preparation method of any one of claims 1-6.

8. Application of the polymer-based composite material containing a multi-level MOFs stress dissipation layer of claim 7 as a self-lubricating material.

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