Rubber / PTFE composition and preparation method thereof

Abstract

The invention relates to the field of rubber composite materials, and discloses a rubber / PTFE composition and a preparation method thereof. The composition comprises a rubber compound and surface-modified PTFE micro powder, the PTFE micro powder is grafted with a molecular chain with an imide structure through in-situ polymerization, the molecular chain is composed of a binary anhydride monomer residue Ar1 and a diamine monomer residue Ar2, and the structure is selected from the combination of a specific benzene ring, an ether bond, a fluoro group and the like. The preparation method comprises the following steps: carrying out plasma activation on PTFE micro powder, reacting the PTFE micro powder with aromatic monomers containing amino groups and anhydride groups in a mixed solvent to generate a polyimide grafted layer, and mixing the polyimide grafted layer with a rubber compound for vulcanization. According to the modification technology, the interface bonding force of PTFE and a rubber matrix is remarkably improved, and the problems of uneven dispersion and interface debonding of a traditional filler are solved. The high thermal stability of the imide structure and the synergistic effect of polar groups enable the composite material to have excellent tensile strength, wear resistance and aging resistance, and at the same time, the processing stability is maintained.

Description

Technical Field

[0001] The present invention relates to the field of rubber composite materials, in particular to a rubber / PTFE composition and a preparation method thereof. Background Art

[0002] Polytetrafluoroethylene (PTFE) has become an important additive for modifying rubber composites due to its excellent lubricity, chemical resistance, aging resistance, and wide temperature stability. In the prior art, PTFE micropowder is often introduced into matrices such as fluororubber, nitrile rubber, and EPDM rubber to enhance the wear and oil resistance of the finished product. However, PTFE's low surface energy, poor wettability, and chemical inertness result in weak interfacial bonding with the rubber matrix, making it prone to uneven dispersion and interfacial debonding, which directly impacts the performance of the composite material.

[0003] To overcome the above-mentioned defects, the existing technology mostly uses surface modification means to activate PTFE. For example, the Chinese patent application with publication number CN202111616283.9 discloses a PTFE modification method: first, free radicals and polar groups are introduced into the PTFE surface by plasma treatment, and then mixed with zinc methacrylate (ZDMA) and stirred at high speed to form a coating layer, and finally mixed with hydrogenated nitrile rubber (HNBR). Although this method can improve dispersibility, the cross-linked structure formed by ZDMA after vulcanization may become a weak point inside the material due to its own insufficient thermal stability. Another typical solution, as shown in the Chinese patent application with publication number CN202410680339.4, is to add 1-2% of a siloxane coupling agent (such as KH560, KH570, KH171, etc.) to a small amount of PTFE powder to prepare a pre-dispersion liquid, which is then blended with hydrogenated nitrile rubber. Although such coupling agents can improve the dispersion effect in the short term, their molecular chains have poor flexibility and limited heat resistance. Interfacial degradation is prone to occur during long-term use, which in turn leads to a decrease in the mechanical properties of the material.

[0004] Furthermore, existing technologies generally suffer from the problem of single-purpose performance enhancement. Research data shows that the addition of PTFE micropowder can generally only improve a single performance indicator of rubber, such as wear resistance or oil resistance, while often having a negative impact on other key properties (such as tensile strength, tear resistance, and thermal stability). For example, unmodified PTFE micropowder at high filling levels can destroy the continuity of the rubber matrix, resulting in a significant decrease in tensile strength; while the introduction of some coupling agents can alleviate dispersion problems, it may interfere with the formation of the vulcanization network, thereby weakening the material's high-temperature stability.

[0005] In summary, developing a modification method that can effectively improve the compatibility of PTFE-rubber interface, avoid the introduction of low-performance coupling agents, and achieve a synergistic improvement in the comprehensive performance of composite materials is still a technical bottleneck that urgently needs to be broken through in this field. Summary of the Invention

[0006] The technical problem to be solved by the present invention is to provide a rubber / PTFE composition to overcome the problems existing in the prior art, such as poor compatibility of PTFE micropowder with rubber matrix, decreased tensile properties after filling, insufficient aging resistance and wear resistance, and improve the overall mechanical properties and service life of rubber products.

[0007] To overcome the above-mentioned defects of the prior art, the present invention provides a rubber / PTFE composition, characterized in that the rubber / PTFE composition comprises a rubber compound and PTFE powder, and the surface of the PTFE powder is grafted with an imide structure molecular chain by an in-situ polymerization method, and the molecular chain is one of the following structures:

[0008]

[0009] Wherein, Ar1 is a dibasic acid anhydride monomer residue; Ar2 is a diamine monomer residue.

[0010] The rubber / PTFE composition of the present invention has the following advantages over the prior art: in the prior art, PTFE micropowder is difficult to form an effective interface bond with the rubber matrix due to its surface inertness and is easily agglomerated in the rubber, resulting in decreased mechanical properties, insufficient aging resistance, and wear resistance of the rubber product after filling. However, the present invention achieves active modification of the PTFE micropowder surface by introducing molecular chains having an imide structure onto the surface of the PTFE micropowder. The imide structure has excellent thermal and chemical stability, and its molecular chain contains polar functional groups that can interact with functional groups or polar components in the rubber matrix, thereby significantly improving the dispersibility and interfacial bonding of the PTFE micropowder in the rubber. Through this surface modification technology of grafting imide molecular chains, the present invention not only improves the interfacial compatibility of the PTFE micropowder with the rubber matrix, but also improves the tensile strength, wear resistance, and performance retention rate after heat aging of the rubber product while maintaining stable vulcanization characteristics. The composition of the present invention can achieve multiple performance optimizations such as increased tensile strength, reduced hardness variation, and enhanced wear resistance without significantly changing processing properties (including Mooney viscosity and vulcanization rate). The present invention adopts the method of in-situ polymerization grafting imide structure to specifically solve the core problem of incompatibility between PTFE and rubber matrix and performance degradation raised in the background technology. It has significant technological progress and application value and is particularly suitable for the field of high-performance rubber products, such as wear-resistant seals, heat-resistant protective materials and highly aging-resistant industrial rubber parts.

[0011] In the above-mentioned molecular chains of the present invention, 1) the molecular chains containing imide structures used in the present invention are all short-chain small molecules and do not contain too many repeating units. The main purpose is to reduce the molecular weight of the coupling agent, thereby reducing the adverse effects of the coupling agent on the Mooney viscosity and vulcanization performance of the rubber system.

[0012] 2) After conventional plasma surface treatment of PTFE, its surface F / C ratio decreases, while the (O+N) / C ratio increases. More C–F bonds are broken and reactive groups are formed. These reactive groups replace some fluorine atoms, transforming PTFE from an inert polymer into a material with a certain degree of polarity, significantly increasing its surface energy and improving its hydrophilicity. The grafted imide-containing molecular chains incorporate amino groups, carbon-carbon triple bonds, fluorine, and chlorine. These structures facilitate grafting reactions between the molecular chains and the PTFE micropowder surface, further improving its surface energy and activity. When the modified PTFE micropowder is subsequently introduced into a rubber compound system, the coupling effect of the surface imide structure allows for better dispersion of the PTFE micropowder within the rubber matrix. During the vulcanization process, the amino groups and carbon-carbon triple bonds on the imide molecular chains further cross-link with unsaturated bonds in the rubber compound, forming a dense cross-linked network structure. Through this cross-linking effect, PTFE micropowder is evenly and firmly embedded in the rubber matrix, thereby significantly improving the thermal stability and mechanical properties of the final rubber product.

[0013] In one possible embodiment, the Ar1 is selected from one of the following structures:

[0014]

[0015] The horizontal line “-” connected to the benzene ring represents the bond between the Ar1 structure and the carbon atom in the repeating unit.

[0016] In one possible embodiment, the Ar2 is selected from one of the following structures:

[0017]

[0018] Among them, the horizontal line “-” connected to the benzene ring represents the bond connecting the Ar2 structure and the carbon atom in the repeating unit.

[0019] The dibasic anhydride and diamine monomers mentioned above contain varying amounts of benzene rings, ether bonds, and carbonyl groups. Therefore, the appropriate monomer combination can be selected based on the characteristics of the rubber system to achieve the optimal PTFE modification effect.

[0020] In one possible embodiment, the molecular chain is one of the following structures:

[0021]

[0022] Wherein, Ar1 is a dibasic acid anhydride monomer residue; Ar2 is a diamine monomer residue.

[0023] In this preferred structure, both ends of the molecular chain contain reactive groups. One end can undergo a grafting reaction with the surface of the PTFE powder, while the other end can form a chemical bond with the functional groups in the rubber molecular structure. This method achieves a tight connection between the rubber and PTFE, significantly improving their compatibility and interfacial bonding strength.

[0024] In one possible embodiment, the molecular chain is one of the following structures:

[0025]

[0026] The molecular structure contains unsaturated carbon-carbon triple bonds at both ends. The carbon-carbon triple bonds can react with the active groups on the PTFE surface. At the same time, during the rubber vulcanization process, they can also undergo cross-linking reactions with the unsaturated bonds in the rubber molecules to form a stable cross-linked network structure, thereby firmly fixing the PTFE micropowder in the rubber matrix, ensuring its uniform dispersion and ultimately achieving the best reinforcement effect.

[0027] Wherein Ar1 is a dibasic acid anhydride monomer residue, and Ar1 is selected from one of the following structures:

[0028]

[0029] In the above preferred structures, from left to right are molecular formulas 1, 2, and 3. Molecular formula 1 contains a carbon-based structure, which exhibits excellent adhesive properties and significantly enhances the bonding strength between the coupling agent and the matrix material. Molecular formula 2 incorporates two trifluoromethyl groups, which, based on the principle of like-for-like compatibility, further improves compatibility with PTFE and enhances interfacial bonding. Molecular formula 3 exhibits a long, flexible chain structure, which effectively reduces crosslinking density, thereby minimizing the adverse effects of the coupling agent on rubber elasticity and improving the overall mechanical properties of the final material.

[0030] In one possible embodiment, Ar1 is the following structure:

[0031]

[0032] As mentioned above, the introduction of a carbon-based structure into the molecular structure gives it excellent bonding properties, which can significantly improve the bonding ability of the coupling agent, thereby effectively enhancing the interfacial bonding force between PTFE and rubber.

[0033] In a possible embodiment, the raw rubber used in the rubber mix is chloroprene rubber or nitrile rubber.

[0034] Compared with existing technologies, the above-mentioned technical solution can achieve synergistic effects based on the inherent properties of the materials: chloroprene rubber (CR) has excellent weather resistance, ozone resistance, heat resistance and good mechanical properties. Its molecular structure contains unsaturated carbon-carbon bonds, which can undergo cross-linking reactions with active groups (such as carbon-carbon triple bonds or amino groups) on the coupling agent molecular chain during the vulcanization process, thereby enhancing the interfacial bonding between the rubber matrix and the PTFE micropowder. Nitrile rubber (NBR), rich in nitrile groups (–CN), has good oil resistance and wear resistance. It can also form a stronger interfacial bond with the surface-modified PTFE micropowder under certain conditions, further optimizing the aging resistance, wear resistance and mechanical strength of the rubber / PTFE composite. The synergistic cross-linking between the rubber matrix and the functionalized PTFE micropowder not only significantly improves the dispersibility and adhesion of PTFE in the rubber system, but also inhibits the migration and aggregation of PTFE particles. Ultimately, the overall performance of the composite in terms of wear resistance, mechanical properties, thermal stability, etc. is improved, fully solving the technical problems of poor dispersibility, weak interfacial bonding, and insufficient overall performance in traditional rubber / PTFE materials.

[0035] In one possible embodiment, Ar2 is selected from the following structures:

[0036]

[0037] Because the coupling agent contains crosslinkable groups, it can react with rubber molecules to form a crosslinked network structure. This process can have a certain impact on the rubber's properties such as vulcanization characteristics, elasticity, and hardness. The preferred molecular structure mentioned above is mainly based on a long-chain flexible structure, which can effectively buffer and offset the adverse effects caused by coupling agent crosslinking, thereby achieving overall optimization of the rubber / PTFE material performance.

[0038] In one possible embodiment, the total mass of the molecular chains accounts for 1% to 20% of the total mass of the PTFE micropowder, the average particle size of the PTFE micropowder is 1 to 5 μm, and the mass ratio of the PTFE micropowder to the rubber compound is (1-60):100.

[0039] Compared with the existing technology, the above technical solution is adopted to reasonably control the grafting amount of imide structure molecular chains on the surface of PTFE micropowder, so that the surface modification is sufficient but not excessive, which can not only effectively improve the surface activity and interfacial bonding ability of PTFE, but also avoid micropowder agglomeration or degradation of processing performance due to excessive grafting; at the same time, by limiting the particle size of PTFE micropowder to 1-5 μm, it helps to ensure its uniform dispersion in the rubber matrix, thereby improving the comprehensive mechanical properties and wear resistance of the final material; further, by controlling the mass ratio of PTFE micropowder to compound rubber within the range of (1-60):100, the filler reinforcement effect and the toughness and processing performance of the rubber matrix are taken into account, avoiding the increased brittleness of the product or processing difficulties caused by an excessively high filler ratio, and ultimately achieving a significant improvement in the wear resistance, aging resistance, strength and elasticity of the rubber / PTFE composition, meeting the application needs of high-performance rubber products.

[0040] In a possible implementation manner, the mass ratio of the PTFE micropowder to the rubber compound is (1-20):100.

[0041] Compared with the existing technology, the above technical solution further limits the mass ratio of PTFE micropowder to rubber compound to a lower range of (1-20):100, which can maintain the modification and reinforcement effect while maximally ensuring the flexibility and ductility of the rubber matrix, avoiding problems such as increased hardness and decreased elongation caused by excessive filling amount.

[0042] Another technical problem to be solved by the present invention is to provide a method for preparing a rubber / PTFE composition to solve the problems of unsatisfactory modification effect, uneven dispersion of PTFE micropowder, poor interfacial bonding strength, and limited comprehensive material performance in the prior art.

[0043] In order to overcome the above defects of the prior art, the present invention provides a method for preparing the rubber / PTFE composition, comprising the following steps:

[0044] S1: preparing PTFE powder: preparing PTFE powder according to a required ratio, wherein the particle size of the PTFE powder is 1 to 5 μm;

[0045] S2: Surface grafting modification: grafting an imide structure molecular chain onto the surface of the PTFE micropowder in step S1 by in-situ polymerization, wherein the molecular chain comprises a dibasic acid anhydride monomer residue Ar1 and a diamine monomer residue Ar2;

[0046] S3: Preparation of rubber compound: mixing rubber with other auxiliary additives to obtain a rubber compound;

[0047] S4: Mixing PTFE micropowder and rubber compound: The PTFE micropowder grafted with imide structure molecular chains obtained in step S2 is fully mixed with the rubber compound obtained in step S3, and a rubber / PTFE composition is obtained after mixing and vulcanization.

[0048] Compared to simply blending PTFE micropowder with imide micropowder, the present invention utilizes in-situ grafting to evenly graft the imide molecular chains onto the surface of the PTFE micropowder, achieving full PTFE modification and significantly enhancing its surface activity. This treatment further promotes uniform dispersion of the PTFE micropowder during the subsequent rubber mixing process, resulting in a more effective modification and effectively improving the overall performance of the final rubber / PTFE composite.

[0049] In one possible embodiment, step S2 includes the following steps: adding an aromatic amino-containing monomer to a mixed solvent of a polar aprotic solvent and chlorotoluene, and mixing and stirring with the plasma-treated PTFE micropowder to completely dissolve the amino monomer; then adding an aromatic anhydride-containing monomer to react with the amino monomer to generate polyamic acid; then heating and performing azeotropic water treatment to generate a polyimide solution containing PTFE micropowder; and finally, evaporating the solvent by heating, crushing and grinding to obtain PTFE micropowder with imide structure molecular chains grafted on the surface.

[0050] Compared to existing technologies, plasma treatment, through ion bombardment or implantation, can introduce functional groups such as oxides and carboxyl groups onto the PTFE surface. During this process, the plasma energy removes some of the F elements on the PTFE surface, generating free radicals that further react with gases such as O2 to form new oxygen- and nitrogen-containing functional groups. As a result, the F / C ratio on the PTFE surface decreases, while the (O+N) / C ratio significantly increases, effectively enhancing surface activity and polarity, providing a good foundation for subsequent grafting modification and interfacial reactions.

[0051] In summary, the present invention has the following beneficial effects:

[0052] 1) Through in-situ polymerization and grafting, the surface of PTFE micropowder is fully modified, and the surface activity is significantly improved, which helps to enhance its interfacial bonding with the rubber matrix;

[0053] 2) The modified PTFE powder is more evenly dispersed during the rubber mixing process, significantly improving the distribution of the powder in the matrix and enhancing the overall bonding performance;

[0054] 3) The imide structure molecular chain acts as a functional coupling agent, which not only enhances the interfacial bonding between PTFE and rubber, but also does not form material performance defects. It effectively promotes the overall improvement of the mechanical properties, wear resistance and aging resistance of the rubber / PTFE composition. Compared with other existing modification methods, the overall performance is significantly better. BRIEF DESCRIPTION OF THE DRAWINGS

[0055] Figure 1 The imide structure grafted onto the surface of the PTFE powder in Examples 1 and 2;

[0056] Figure 2 The imide structure grafted onto the surface of the PTFE powder in Examples 3 and 4;

[0057] Figure 3 The imide structure grafted onto the surface of the PTFE powder in Examples 5 and 6;

[0058] Figure 4 This is the imide structure grafted onto the surface of the PTFE powder in Examples 7 and 8. DETAILED DESCRIPTION

[0059] First, those skilled in the art should understand that these embodiments are merely used to explain the technical principles of the embodiments of the present application and are not intended to limit the scope of protection of the embodiments of the present application. Those skilled in the art may adjust them as needed to suit specific application scenarios.

[0060] The technical solution of the present invention is further described below by means of specific embodiments and accompanying drawings. Unless otherwise specified, the raw materials used in the embodiments of the present invention are all commonly used raw materials in the art, and the methods used in the embodiments are all conventional methods in the art.

[0061] The present invention provides a rubber / PTFE composition, characterized in that the rubber / PTFE composition comprises a rubber compound and PTFE micropowder, and the surface of the PTFE micropowder is grafted with a molecular chain of an imide structure by an in-situ polymerization method, and the molecular chain is one of the following structures:

[0062]

[0063] Wherein, Ar1 is a dibasic acid anhydride monomer residue; Ar2 is a diamine monomer residue.

[0064] As a preferred solution, the Ar1 is selected from one of the following structures:

[0065]

[0066] Wherein, the horizontal line "-" connected to the benzene ring represents the bond between the Ar1 structure and the carbon atom in the repeating unit. As a preferred embodiment, the Ar2 is selected from one of the following structures:

[0067]

[0068] Wherein, the horizontal line "-" connected to the benzene ring represents the bond between the Ar2 structure and the carbon atom in the repeating unit. As a preferred embodiment, the molecular chain is one of the following structures:

[0069]

[0070] Wherein, Ar1 is a dibasic acid anhydride monomer residue; Ar2 is a diamine monomer residue.

[0071] As a preferred solution, the molecular chain is one of the following structures:

[0072]

[0073] Wherein Ar1 is a dibasic acid anhydride monomer residue, and Ar1 is selected from one of the following structures:

[0074]

[0075] As a preferred embodiment, Ar1 is the following structure:

[0076]

[0077] As a preferred embodiment, Ar2 is preferably selected from one of the following structures:

[0078]

[0079] As a preferred solution, the raw rubber used in the rubber mix is chloroprene rubber or nitrile rubber.

[0080] As a preferred solution, the total mass of the molecular chains accounts for 1% to 20% of the total mass of the PTFE micropowder, and the average particle size of the PTFE micropowder is 1 to 5 μm. The mass ratio of the PTFE micropowder to the rubber compound is (1-60):100.

[0081] As a preferred solution, the mass ratio of the PTFE micropowder to the rubber compound is (1-20):100.

[0082] The present invention also provides a method for preparing the rubber / PTFE composition, comprising the following steps:

[0083] S1: preparing PTFE powder: preparing PTFE powder according to a required ratio, wherein the particle size of the PTFE powder is 1 to 5 μm;

[0084] S2: Surface grafting modification: grafting an imide structure molecular chain onto the surface of the PTFE micropowder in step S1 by in-situ polymerization, wherein the molecular chain comprises a dibasic acid anhydride monomer residue Ar1 and a diamine monomer residue Ar2;

[0085] S3: Preparation of rubber compound: mixing rubber with other auxiliary additives to obtain a rubber compound;

[0086] S4: Mixing PTFE micropowder and rubber compound: The PTFE micropowder grafted with imide structure molecular chains obtained in step S2 is fully mixed with the rubber compound obtained in step S3, and a rubber / PTFE composition is obtained after mixing and vulcanization.

[0087] As a preferred solution, step S2 includes the following steps: adding an aromatic amino-containing monomer to a mixed solvent of a polar aprotic solvent and chlorotoluene, and mixing and stirring with the plasma-treated PTFE micropowder to completely dissolve the amino monomer; then adding an aromatic anhydride-containing monomer to react with the amino monomer to generate polyamic acid; then heating and performing azeotropic water treatment to generate a polyimide solution containing PTFE micropowder; and finally, evaporating the solvent by heating, crushing and grinding to obtain PTFE micropowder with imide structure molecular chains grafted on the surface.

[0088] In combination with the above technical solutions, more specific embodiments and comparative examples combined with actual data are provided below to further expand the technical effects and technical solutions of the present invention:

[0089] like Figure 1-4 As shown, Figure 1 The imide structure grafted onto the surface of the PTFE powder in Examples 1 and 2; Figure 2 The imide structure grafted onto the surface of the PTFE powder in Examples 3 and 4; Figure 3 The imide structure grafted onto the surface of the PTFE powder in Examples 5 and 6; Figure 4 This is the imide structure grafted onto the surface of the PTFE powder in Examples 7 and 8.

[0090] Example 1:

[0091] This embodiment provides a rubber / PTFE composition and a preparation method thereof. The rubber / PTFE composition is prepared by the preparation method, and the preparation method comprises the following steps:

[0092] S1: Prepare PTFE micropowder with a particle size of 1–5 μm.

[0093] S2: Surface grafting modification

[0094] After plasma treatment, an appropriate amount of PTFE powder is added to a mixed solvent of N,N-dimethylacetamide and chlorotoluene. Phenylacetylene aniline monomer is then added and stirred to fully dissolve. Then, a dibasic acid anhydride monomer (BTDA) is added and allowed to react at room temperature for four hours to produce polyamic acid. Subsequently, the mixture is heated and subjected to azeotropic treatment with water to produce a polyimide solution containing the PTFE powder. After heating to evaporate the solvent, the mixture is crushed and ground to obtain a PTFE powder with imide molecular chains grafted onto its surface. The grafting amount is approximately 2% of the PTFE mass.

[0095] S3: Preparation of rubber compound

[0096] The pre-prepared chloroprene rubber compound (basic formula: 100 parts of CR, 5 parts of zinc oxide, 6 parts of magnesium oxide, 4 parts of plasticizer DOTP, 3 parts of antioxidant ODA, 1 part of antioxidant 4010NA, 20 parts of carbon black N330, and 40 parts of carbon black N550) was placed on an open mill and mixed at a roller temperature of 30°C until the roller was uniform.

[0097] S4: Mixing PTFE powder and compound rubber

[0098] Add the grafted PTFE powder to the rubber mix at a 5% mass fraction. Use a tool to mix alternately, left and right, to ensure uniform dispersion. After 5-7 thin passes, remove the rubber sheet and allow it to cool. After the final mix is allowed to stand at room temperature for 24 hours, vulcanize it on a flat-plate vulcanizer at 160°C for 15-30 minutes to produce a rubber / PTFE composite.

[0099] Example 2:

[0100] This embodiment provides a rubber / PTFE composition and a preparation method thereof. This embodiment differs from Example 1 in that the grafting amount of the grafted imide structure molecular chain in step S2 is increased to 4% of the PTFE mass (2% in Example 1), and other conditions are consistent with Example 1. The preparation method comprises the following steps:

[0101] S1: Prepare PTFE micropowder with a particle size of 1–5 μm.

[0102] S2: Surface grafting modification

[0103] After plasma treatment, PTFE micropowder is added to a mixed solvent of N,N-dimethylacetamide and chlorotoluene. Phenylacetylene aniline monomer is added and stirred to fully dissolve the monomer. Subsequently, dibasic acid anhydride monomer (BTDA) is added and allowed to react at room temperature for 4 hours to produce polyamic acid. This is then heated and azeotropically treated with water to produce a polyimide solution containing PTFE micropowder. After evaporation of the solvent, the solution is crushed and ground to obtain PTFE micropowder with imide molecular chains grafted onto its surface. The grafting density is 4% of the PTFE mass.

[0104] S3: Preparation of rubber compound

[0105] The chloroprene rubber compound (basic formula is the same as that of Example 1) is placed on an open mill and mixed at a roller temperature of 30° C. until the mixture is uniformly rolled.

[0106] S4: Mixing PTFE powder and compound rubber

[0107] 5% by mass of grafted modified PTFE powder was added to the rubber mixture, and after 5-7 thin-pass treatments, vulcanization (160°C, 15-30 minutes) was performed to obtain a rubber / PTFE composite.

[0108] Example 3:

[0109] This embodiment provides a rubber / PTFE composition and a preparation method thereof. This embodiment differs from Example 1 in that in step S2, fluorophthalic anhydride is used instead of BTDA as the dibasic acid anhydride monomer, and the grafting amount is maintained at 2%. Other conditions are the same as those in Example 1. The preparation method comprises the following steps:

[0110] S1: Prepare PTFE micropowder with a particle size of 1–5 μm.

[0111] S2: Surface grafting modification

[0112] After plasma treatment, PTFE micropowder is added to a mixture of N,N-dimethylacetamide and chlorotoluene to dissolve the phenylethynylaniline monomer. Fluorophthalic anhydride is then added and allowed to react at room temperature for 4 hours to form polyamic acid. This is then heated to azeotropic concentration with water to produce a polyimide solution. After evaporation of the solvent, the powder is crushed and ground to yield a PTFE micropowder with imide molecular chains grafted onto its surface. The grafting density is 2% of the PTFE mass.

[0113] S3: Preparation of rubber compound

[0114] The chloroprene rubber compound (basic formula is the same as that of Example 1) is placed on an open mill and mixed at a roller temperature of 30° C. until the mixture is uniformly rolled.

[0115] S4: Mixing PTFE powder and compound rubber

[0116] 5% by mass of grafted modified PTFE powder was added to the rubber mixture, and after 5-7 thin-pass treatments, vulcanization (160°C, 15-30 minutes) was performed to obtain a rubber / PTFE composite.

[0117] Example 4:

[0118] This embodiment provides a rubber / PTFE composition and a preparation method thereof. The difference between this embodiment and Example 3 is that the grafting amount in step S2 is increased to 4% of the PTFE mass. Other conditions are the same as those in Example 3. The preparation method includes the following steps:

[0119] S1: Prepare PTFE micropowder with a particle size of 1–5 μm.

[0120] S2: Surface grafting modification

[0121] After plasma treatment, PTFE micropowder is added to a mixture of N,N-dimethylacetamide and chlorotoluene to dissolve the phenylethynylaniline monomer. Fluorophthalic anhydride is then added and allowed to react at room temperature for four hours to form polyamic acid. This is then heated to azeotropic effect with water to produce a polyimide solution. After evaporation of the solvent, the powder is crushed and ground to yield a PTFE micropowder with imide molecular chains grafted onto its surface. The grafting density is 4% of the PTFE mass.

[0122] S3: Preparation of rubber compound

[0123] The chloroprene rubber compound (basic formula is the same as that of Example 1) is placed on an open mill and mixed at a roller temperature of 30° C. until the mixture is uniformly rolled.

[0124] S4: Mixing PTFE powder and compound rubber

[0125] 5% by mass of grafted modified PTFE powder was added to the rubber mixture, and after 5-7 thin-pass treatments, vulcanization (160°C, 15-30 minutes) was performed to obtain a rubber / PTFE composite.

[0126] Comparative Example 1:

[0127] This comparative example provides a method for preparing a rubber / PTFE composition. The difference between this comparative example and Example 1 is that no surface grafting modification is performed, and unmodified PTFE powder is directly used. Other conditions are consistent with Example 1, and the method includes the following steps:

[0128] S1: Prepare PTFE micropowder with a particle size of 1–5 μm (unsurface modified).

[0129] S3: Preparation of rubber compound

[0130] The chloroprene rubber compound (basic formula is the same as that of Example 1) is placed on an open mill and mixed at a roller temperature of 30° C. until the mixture is uniformly rolled.

[0131] S4: Mixing PTFE powder and compound rubber

[0132] 5% by mass of unmodified PTFE powder was added to the rubber mixture, and after 5-7 thin-pass treatments, vulcanization (160°C, 15-30 minutes) was performed to obtain a rubber / PTFE composite.

[0133] Comparative Example 2:

[0134] This comparative example provides a method for preparing a rubber / PTFE composition. The difference between this comparative example and Example 1 is that, similar to the prior art, an organosilicon coupling agent is used to surface-modify the PTFE micropowder (non-imide grafting). Other conditions are consistent with Example 1, and the method comprises the following steps:

[0135] S1: Prepare PTFE micropowder with a particle size of 1–5 μm (the surface is modified with a silicone coupling agent).

[0136] S3: Preparation of rubber compound

[0137] The chloroprene rubber compound (basic formula is the same as that of Example 1) is placed on an open mill and mixed at a roller temperature of 30° C. until the mixture is uniformly rolled.

[0138] S4: Mixing PTFE powder and compound rubber

[0139] 5% by mass of silicone-modified PTFE powder was added to the rubber mixture, and after 5-7 thin-pass treatments, vulcanization (160°C, 15-30 minutes) was performed to obtain a rubber / PTFE composite.

[0140] As shown in Table 1, Table 1 compares the properties of the chloroprene rubber after vulcanization of Examples 1 to 4 and Comparative Examples 1 to 2:

[0141] Table 1: Properties of chloroprene rubber after vulcanization in Examples 1 to 4 and Comparative Examples 1 to 2

[0142]

[0143] Table 1 compares the vulcanizate properties of Examples 1-4 (imide grafted PTFE modified chloroprene rubber) and Comparative Examples 1-2 (unmodified / silicone modified PTFE). The tensile strength after aging of Examples 1-4 (23-32 MPa) is significantly higher than that of Comparative Example 1 (19 MPa) and Comparative Example 2 (17 MPa), with an increase of 21%-68%. This shows that the polarity of the imide molecular chain effectively enhances the interfacial bonding between PTFE and the rubber matrix, inhibiting interfacial debonding during aging. Secondly, the hardness change after aging of Examples 1-4 (3-6) is much smaller than that of Comparative Example 1 (8), indicating that the imide grafted layer delays the thermal oxidation degradation of the rubber molecular chain and has better aging resistance. The wear volume of Examples 1-4 (92-96 mm 3 )Comparison Example 1(101mm 3 ) is reduced by 5%–9%, compared with the comparative example 2 (113mm 3) is reduced by 15%-19%, which further proves that the rigid structure and high polarity of the imide chain in the present invention improve the friction compatibility between PTFE and rubber and reduce wear; and the Mooney viscosity (44.4-49.2), TS1 (1.3-1.4min), and tc90 (10.6-11.1min) of the embodiment and the comparative example are very different, indicating that the surface grafting modification does not interfere with the kinetics of the vulcanization reaction and has strong process compatibility; at the same time, in the present invention, the fluorinated monomer and the high grafting amount also have a synergistic effect. In Example 3, the hydrophobicity of the fluorinated group further inhibits the adhesion of moisture to the interface. The hardness change after aging (72→75) is equal to that of Example 1 (73→76), but the elongation at break (369%) is higher than that of other examples, showing the balance advantage of flexibility and rigidity. Examples 2 / 4 are also examples with high grafting amount. The grafting amount is increased from 2% to 4%. The tensile strength after aging increases from 23MPa (Example 1) to 30-32MPa, verifying the strengthening effect of high grafting amount on interfacial bonding. In Comparative Example 2, although the silicone coupling agent can improve the dispersibility, the interfacial bonding force is weaker than that of the imide grafting, resulting in the tensile strength (17MPa) and wear resistance (113mm 3 ) is significantly deteriorated, further demonstrating the advantages of the imide chemical bonding in the present invention; the data in Table 1 fully verify the core technical advantages of imide-grafted PTFE in improving the aging resistance, wear resistance and mechanical strength of rubber composites, and at the same time, it is compatible with the existing vulcanization process and has the potential for industrial promotion.

[0144] Example 5:

[0145] This embodiment provides a rubber / PTFE composition and a preparation method thereof. This embodiment differs from Example 1 in that: in step S3, hydrogenated nitrile rubber (HNBR) is used instead of chloroprene rubber; in step S4, the amount of PTFE powder added is increased to 60%; in step S2, 4,4'-(hexafluoroisopropylidene) diphthalic anhydride (6FDA) is used as a dibasic anhydride monomer, and the grafting amount is 2%. The preparation method comprises the following steps:

[0146] S1: Prepare PTFE micropowder with a particle size of 1–5 μm.

[0147] S2: Surface grafting modification

[0148] After plasma treatment, PTFE micropowder is added to a mixture of N,N-dimethylacetamide and chlorotoluene to dissolve the phenylethynylaniline monomer. 4,4'-(hexafluoroisopropylidene) diphthalic anhydride (6FDA) is then added. The mixture is allowed to react at room temperature for four hours to form polyamic acid. This is then heated to azeotropic concentration with water to produce a polyimide solution. After evaporation of the solvent, the resulting powder is pulverized and ground to yield a PTFE micropowder with imide molecular chains grafted onto its surface. The grafting density is 2% of the PTFE mass.

[0149] S3: Preparation of rubber compound

[0150] After hydrogenated nitrile rubber (HNBR) raw rubber is plasticized, ZDMA powder (30 parts), plasticizer (5 parts), crosslinking agent (6 parts) and auxiliary crosslinking agent (2 parts) are added and mixed until uniform.

[0151] S4: Mixing PTFE powder and compound rubber

[0152] Graft-modified PTFE powder with a mass fraction of 60% was added to the rubber mixture, and the mixture was vulcanized (165°C, 25-40 minutes) after thin-pass treatment to obtain a rubber / PTFE composite.

[0153] Example 6:

[0154] This embodiment provides a rubber / PTFE composition and a preparation method thereof. The difference between this embodiment and Example 5 is that the grafting amount in step S2 is increased to 4% of the PTFE mass. Other conditions are the same as those in Example 5. The preparation method includes the following steps:

[0155] S1: Prepare PTFE micropowder with a particle size of 1–5 μm.

[0156] S2: Surface grafting modification

[0157] After plasma treatment, PTFE micropowder is added to a mixture of N,N-dimethylacetamide and chlorotoluene to dissolve the phenylethynylaniline monomer. 4,4'-(hexafluoroisopropylidene)diphthalic anhydride (6FDA) is then added. The mixture is allowed to react at room temperature for four hours to form polyamic acid. This is then heated to azeotropic concentration with water to produce a polyimide solution. After evaporation of the solvent, the resulting powder is pulverized and ground to yield a PTFE micropowder with imide molecular chains grafted onto its surface. The grafting density is 4% of the PTFE mass.

[0158] S3: Preparation of rubber compound

[0159] After hydrogenated nitrile rubber (HNBR) raw rubber is plasticized, ZDMA powder (30 parts), plasticizer (5 parts), crosslinking agent (6 parts) and auxiliary crosslinking agent (2 parts) are added and mixed until uniform.

[0160] S4: Mixing PTFE powder and compound rubber

[0161] Graft-modified PTFE powder with a mass fraction of 60% was added to the rubber mixture, and the mixture was vulcanized (165°C, 25-40 minutes) after thin-pass treatment to obtain a rubber / PTFE composite.

[0162] Example 7:

[0163] This embodiment provides a rubber / PTFE composition and a preparation method thereof. This embodiment differs from Example 5 in that bisphenol A diether dianhydride (BPADA) is used in step S2 instead of 6FDA as the dibasic acid anhydride monomer, and the grafting amount is 2%. Other conditions are the same as those in Example 5. The preparation method comprises the following steps:

[0164] S1: Prepare PTFE micropowder with a particle size of 1–5 μm.

[0165] S2: Surface grafting modification

[0166] PTFE micropowder is plasma-treated and added to a mixture of N,N-dimethylacetamide and chlorotoluene to dissolve the phenylethynylaniline monomer. Bisphenol A diether dianhydride (BPADA) is then added and allowed to react at room temperature for four hours to form polyamic acid. This is then heated to azeotropic effect with water to produce a polyimide solution. After evaporation of the solvent, the powder is crushed and ground to yield a PTFE micropowder with imide molecular chains grafted onto its surface. The grafting density is 2% of the PTFE mass.

[0167] S3: Preparation of rubber compound

[0168] After hydrogenated nitrile rubber (HNBR) raw rubber is plasticized, ZDMA powder (30 parts), plasticizer (5 parts), crosslinking agent (6 parts) and auxiliary crosslinking agent (2 parts) are added and mixed until uniform.

[0169] S4: Mixing PTFE powder and compound rubber

[0170] Graft-modified PTFE powder with a mass fraction of 60% was added to the rubber mixture, and the mixture was vulcanized (165°C, 25-40 minutes) after thin-pass treatment to obtain a rubber / PTFE composite.

[0171] Example 8:

[0172] This embodiment provides a rubber / PTFE composition and a preparation method thereof. The difference between this embodiment and Example 7 is that the grafting amount in step S2 is increased to 4% of the PTFE mass. Other conditions are the same as those in Example 7. The preparation method includes the following steps:

[0173] S1: Prepare PTFE micropowder with a particle size of 1–5 μm.

[0174] S2: Surface grafting modification

[0175] After plasma treatment, PTFE micropowder is added to a mixture of N,N-dimethylacetamide and chlorotoluene to dissolve the phenylethynylaniline monomer. Bisphenol A diether dianhydride (BPADA) is then added and allowed to react at room temperature for four hours to form polyamic acid. This is then heated to azeotropic effect with water to produce a polyimide solution. After evaporation of the solvent, the powder is crushed and ground to yield a PTFE micropowder with imide molecular chains grafted onto its surface. The grafting density is 4% of the PTFE mass.

[0176] S3: Preparation of rubber compound

[0177] After hydrogenated nitrile rubber (HNBR) raw rubber is plasticized, ZDMA powder (30 parts), plasticizer (5 parts), crosslinking agent (6 parts) and auxiliary crosslinking agent (2 parts) are added and mixed until uniform.

[0178] S4: Mixing PTFE powder and compound rubber

[0179] Graft-modified PTFE powder with a mass fraction of 60% was added to the rubber mixture, and the mixture was vulcanized (165°C, 25-40 minutes) after thin-pass treatment to obtain a rubber / PTFE composite.

[0180] Comparative Example 3:

[0181] This comparative example provides a method for preparing a rubber / PTFE composition. The difference between this comparative example and Example 5 is that no surface grafting modification is performed, and unmodified PTFE micropowder (addition amount 60%) is directly used. Other conditions are consistent with Example 5, and the method comprises the following steps:

[0182] S1: Prepare PTFE micropowder with a particle size of 1–5 μm (unsurface modified).

[0183] S3: Preparation of rubber compound

[0184] After hydrogenated nitrile rubber (HNBR) raw rubber is plasticized, ZDMA powder (30 parts), plasticizer (5 parts), crosslinking agent (6 parts) and auxiliary crosslinking agent (2 parts) are added and mixed until uniform.

[0185] S4: Mixing PTFE powder and compound rubber

[0186] 60% by mass of unmodified PTFE powder was added to the rubber mixture, and after thin-pass treatment, vulcanization (165°C, 25-40 minutes) was performed to obtain a rubber / PTFE composite.

[0187] Table 2 compares the properties of hydrogenated nitrile rubber after vulcanization of Examples 5 to 8 and Comparative Example 3:

[0188] Table 2: Properties of hydrogenated nitrile rubber after vulcanization in Examples 5 to 8 and Comparative Example 3

[0189]

[0190] The data in Table 2 prove that the hydrogenated nitrile rubber (HNBR) modified with imide grafted PTFE still exhibits excellent comprehensive performance under high filling (60% PTFE) conditions: the tensile strength after aging of Examples 5-8 (24-31 MPa) is increased by 41%-82% compared with the unmodified system (Comparative Example 3, 17 MPa), and the hardness change (4-6) is significantly lower than that of Comparative Example 3 (9), indicating that imide grafting effectively delays interfacial thermal oxidation aging through chemical bonding; in terms of wear resistance, the wear volume of Example 7 (BPADA grafting) is only 31 mm 3 , compared with comparative example 3 (35mm 3 ) is reduced by 11%. The synergistic effect of the flexible ether bond and the rigid imide chain optimizes the friction compatibility. At the same time, the fluorinated group of 6FDA (Example 5 / 6) imparts hydrophobicity to the interface, and the tensile strength after aging reaches 26-31MPa, which is suitable for oil-resistant sealing scenarios. The flexible properties of BPA DA (Example 7 / 8) maintain the elongation at break at 472% (only 2% lower than that of Comparative Example 3), which is suitable for dynamic load requirements. In addition, the Mooney viscosity (46.2-50.1) and vulcanization time (tc90: 8.6-9.4min) in the highly filled system do not deteriorate significantly, proving that the imide-grafted PTFE achieves a synergistic improvement in aging resistance, wear resistance, and mechanical strength through chemical bonding and polarity in the highly filled hydrogenated nitrile rubber system, and is compatible with industrial processing conditions, providing a reliable material solution for applications such as high-performance seals and wear-resistant liners.

[0191] In the description of the present application, the description with reference to the terms "one embodiment", "some embodiments", "in the present embodiment", "specific example", or "some examples" means that the specific features, mechanisms, materials or characteristics described in conjunction with the embodiment or example are included in at least one embodiment or example of the present application. In this specification, the schematic representations of the above terms do not necessarily refer to the same embodiment or example. Moreover, the specific features, mechanisms, materials or characteristics described can be combined in a suitable manner in any one or more embodiments or examples. In addition, those skilled in the art can combine and combine different embodiments or examples described in this specification and the features of different embodiments or examples, unless they are contradictory.

[0192] The above description is merely a specific embodiment of the present application, but the scope of protection of the present application is not limited thereto. Any changes or substitutions that can be easily conceived by a person skilled in the art within the technical scope disclosed in the present application should be included in the scope of protection of the present application. Therefore, the scope of protection of the present application should be based on the scope of protection of the claims.

Claims

1. A rubber / PTFE composition, characterized in that The rubber / PTFE composition comprises a rubber compound and PTFE micropowder, and the surface of the PTFE micropowder is grafted with a molecular chain of an imide structure by an in-situ polymerization method, and the molecular chain is one of the following structures: Wherein, Ar1 is a dibasic acid anhydride monomer residue; Ar2 is a diamine monomer residue.

2. The rubber / PTFE composition according to claim 1, wherein The Ar1 is selected from one of the following structures: The horizontal line "-" connected to the benzene ring represents the bond between the Ar1 structure and the carbon atom in the repeating unit.

3. The rubber / PTFE composition according to claim 1, wherein The Ar2 is selected from one of the following structures: The horizontal line "-" connected to the benzene ring represents the bond connecting the Ar2 structure and the carbon atom in the repeating unit.

4. The rubber / PTFE composition according to claim 1, characterized in that The molecular chain is one of the following structures: Wherein, Ar1 is a dibasic acid anhydride monomer residue; Ar2 is a diamine monomer residue.

5. The rubber / PTFE composition according to claim 4, characterized in that The molecular chain is one of the following structures: Wherein Ar1 is a dibasic acid anhydride monomer residue, and Ar1 is selected from one of the following structures:

6. The rubber / PTFE composition according to claim 5, characterized in that Ar1 is the following structure:

7. The rubber / PTFE composition according to claim 1, characterized in that The raw rubber used in the rubber mix is chloroprene rubber or nitrile rubber.

8. The rubber / PTFE composition according to claim 1, wherein The total mass of the molecular chains accounts for 1% to 20% of the total mass of the PTFE micropowder, and the average particle size of the PTFE micropowder is 1 to 5 μm. The mass ratio of the PTFE micropowder to the rubber compound is (1-60):

100.

9. A method for preparing the rubber / PTFE composition according to any one of claims 1 to 8, characterized in that: The following steps are involved: S1: preparing PTFE powder: preparing PTFE powder according to a required ratio, wherein the particle size of the PTFE powder is 1 to 5 μm; S2: Surface grafting modification: grafting an imide structure molecular chain onto the surface of the PTFE micropowder in step S1 by in-situ polymerization, wherein the molecular chain comprises a dibasic acid anhydride monomer residue Ar1 and a diamine monomer residue Ar2; S3: Preparation of rubber compound: mixing rubber with other auxiliary additives to obtain a rubber compound; S4: Mixing PTFE micropowder and rubber compound: The PTFE micropowder grafted with imide structure molecular chains obtained in step S2 is fully mixed with the rubber compound obtained in step S3, and a rubber / PTFE composition is obtained after mixing and vulcanization.

10. The method for preparing the rubber / PTFE composition according to claim 9, characterized in that: The step S2 comprises the following steps: adding an aromatic amino-containing monomer to a mixed solvent of a polar aprotic solvent and chlorotoluene, and mixing and stirring the mixture with the plasma-treated PTFE micropowder to completely dissolve the amino monomer; then adding an aromatic anhydride-containing monomer to react with the amino monomer to generate polyamic acid; then heating and performing an azeotropic water treatment to generate a polyimide solution containing PTFE micropowder; and finally, evaporating the solvent by heating, and then crushing and grinding to obtain PTFE micropowder with imide structure molecular chains grafted on the surface.

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