Graphene-modified natural rubber that is simultaneously reinforced and toughened based on strong interface action of free radical annihilation reaction

Abstract

The present invention belongs to the field of graphene and functional rubber composites thereof, and particularly relates to a graphene-modified natural rubber that is simultaneously reinforced and toughened based on a strong interface action of a free radical annihilation reaction. A free radical adsorbent is loaded on the surface of reduced graphene oxide during the process of reducing graphene oxide, and a reduced graphene oxide-modified natural rubber composite is then prepared by using a water-phase synergistic coagulation process and a mechanical blending method. During the mechanical blending process, the free radical adsorbent, which is loaded on the surface of the reduced graphene oxide, can be subjected to an annihilation reaction with free radicals, which are generated when rubber macromolecules are subjected to the action of heat and / or force, and the reinforcing effect thereof on the interaction of a two-phase interface is greater than that of a hydrogen bond, such that the content of bound rubber of the natural rubber can be increased, the cross-linking density of the natural rubber vulcanized rubber is increased, the cross-linked network is better improved, and a simultaneously reinforced and toughened graphene-modified natural rubber composite is finally obtained. The preparation process of the present invention is simple and environmentally friendly, and does not have any harsh requirements.

Description

Graphene-modified natural rubber with strong interfacial interaction and simultaneous toughening and enhancement based on free radical annihilation reaction

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS

[0002] This application claims priority to the Chinese patent application with application number 202311659208.X filed with the China Patent Office on December 6, 2023, entitled “Graphene-modified natural rubber with strong interfacial action and enhanced toughness based on free radical annihilation reaction”, the entire contents of which are incorporated by reference into this application. Technical Field

[0003] The invention belongs to the field of graphene and functional rubber composite materials thereof, and specifically relates to a graphene-modified natural rubber which is enhanced and toughened simultaneously based on a strong interface action of a free radical annihilation reaction. Background Art

[0004] As a vital component of transportation, rubber composites are playing an increasingly significant role with the rapid development of modern three-dimensional transportation. Natural rubber (NR), with its excellent mechanical properties, tear resistance, and elasticity, is widely used in defense and civilian applications such as tires, wires, and cables. However, extending its service life and improving operational stability remain significant challenges.

[0005] In addition, NR has no usable strength, and only reinforced NR can be applied to various products. Adding nanofillers is one of the most common reinforcement methods, which can obtain good strength and application flexibility. Therefore, in order to improve the performance of NR, nanoparticles such as ceramic particles, nanodiamonds, carbon nanotubes and graphene (GE) have become ideal fillers for reinforcing rubber matrices due to their small size and large specific surface area. Among them, GE and its derivatives are considered to be the most ideal fillers for NR composites and are often used to improve mechanical, electrical, thermal and chemical properties. As an important representative of GE derivatives, graphene oxide (GO) is increasingly being studied and applied because the surface is rich in oxygen-containing groups such as hydroxyl, epoxy, carboxyl and carbonyl groups, which can give it excellent dispersibility in the matrix. This has laid an important foundation for improving the performance of polymer composites.

[0006] The performance of nanofiller-reinforced rubber composites is influenced by two key factors: filler dispersion and the interfacial interaction between the filler and the rubber matrix. The interfacial interaction between the nanofiller and the polymer matrix is ​​a key factor influencing rubber performance and significantly influences particle dispersion. Strong interfacial interactions facilitate good dispersion of nanoparticles and significantly enhance composite performance. Therefore, establishing strong interfacial interactions between the matrix and filler is crucial for the successful application of polymer composites.

[0007] While filler-based methods significantly improve the mechanical properties of rubber composites, practical applications often require dozens or even hundreds of fillers, which presents additional challenges in dispersion and interface regulation. Furthermore, the introduction of large amounts of fillers reduces the elasticity of the rubber and increases energy consumption during processing. Therefore, finding novel and effective methods to prepare high-strength and high-toughness rubber composites remains a crucial yet challenging task.

[0008] Excellent mechanical properties can prevent wear and breakage, reduce the replacement frequency of NR products, and thus reduce production costs. Mechanical properties are a direct reflection of the construction of the rubber cross-linking network and the dispersion of fillers. Enhancing the interfacial interaction between fillers and the matrix can increase the bound rubber content, thereby increasing the cross-linking density. In addition, during long-term use, rubber will produce free radicals under the action of heat or force, which will cause aging and performance degradation. Improving aging resistance can extend the service life of rubber. In order to extend the service life of rubber and improve the quality stability of rubber products, the application of free radical adsorbents is of great significance. Free radical adsorbents can react with free radicals in rubber, thereby stabilizing the chemical structure of the rubber and delaying its aging. Therefore, loading free radical adsorbents on the surface of GO while reducing it can not only prevent aging caused by free radicals, but also enhance the interfacial interaction between fillers and rubber, thereby effectively improving the strength, toughness and aging resistance of rubber composites.

[0009] Summary of the Invention

[0010] In order to improve the strength, toughness and aging resistance of NR, thereby expanding its application field and extending the service life of corresponding products, the present invention provides a graphene-modified natural rubber that is strengthened and toughened simultaneously by a strong interfacial action based on a free radical annihilation reaction.

[0011] The present invention is achieved through the following technical solution: based on the strong interfacial effect of free radical annihilation reaction, a graphene-modified natural rubber is simultaneously strengthened and toughened. First, during the process of reducing graphene oxide, a free radical adsorbent is loaded on the surface of the reduced graphene oxide. Then, a water-phase cooperative coagulation process and a mechanical blending method are used to prepare the reduced graphene oxide-modified natural rubber composite material. During the mechanical blending process, the free radical adsorbent loaded on the surface of the reduced graphene oxide can undergo an annihilation reaction with free radicals generated when rubber macromolecules are subjected to heat and / or force. The free radical adsorbent has a greater effect on the interaction between the two phases than hydrogen bonds, thereby increasing the bound rubber content of the natural rubber, increasing the crosslinking density of the natural rubber vulcanizate, and improving the crosslinking network. Finally, the graphene-modified natural rubber composite material that is simultaneously strengthened and toughened is obtained.

[0012] The present invention further provides a preparation process for graphene-modified natural rubber with strong interfacial action and enhanced toughness based on free radical annihilation reaction, comprising the following steps:

[0013] ① Add the free radical adsorbent to water, fully dissolve it, then add a certain concentration of graphene oxide aqueous dispersion, react at a certain temperature for a certain time, and obtain a reduced graphene oxide aqueous dispersion with the free radical adsorbent loaded on the surface;

[0014] ② adding deionized water to natural rubber latex, and then adding the reduced graphene oxide aqueous dispersion with a surface-loaded free radical adsorbent prepared in step ①, and fully stirring and mixing to obtain a uniformly dispersed mixed emulsion, wherein the reduced graphene oxide particles with a surface-loaded free radical adsorbent will form bound particles with the rubber particles due to the positive ion electrostatic attraction of the protein-phospholipid membrane on the surface of the rubber particles and remain stable; after adding a flocculant, flocculation occurs due to the reduction of the negative charge repulsion between the particles that keeps the rubber latex stable, and the rubber particles with the damaged protective layer and the reduced graphene oxide particles will further adsorb each other through π-π forces, and the bound particles and rubber particles will gather in an orderly manner in the aqueous phase and precipitate out cooperatively; washing the obtained raw rubber with water, dehydrating, and drying to obtain a natural rubber masterbatch modified with reduced graphene oxide with a surface-loaded free radical adsorbent;

[0015] ③ Add rubber additives and reinforcing fillers to the reduced graphene oxide modified natural rubber masterbatch with a surface-loaded free radical adsorbent prepared in step ② in sequence, mix them, and evenly disperse them to obtain a rubber mix; start mixing the rubber mix, add a vulcanizing agent, mix them evenly, and thinly pass them until there are no bubbles in the rubber mix. After standing for a certain period of time, place them in a mold, and vulcanize them at a certain temperature and pressure for a certain period of time to obtain a graphene-modified natural rubber that is strengthened and toughened by a strong interfacial effect based on the free radical annihilation reaction.

[0016] As a further improvement of the preparation process technical scheme of the present invention, in step ①, the free radical adsorbent is one or a mixture of two or more of ascorbic acid, citric acid, sodium alginate, acrylic acid and sodium lignin sulfonate; the reaction temperature in step ① is 60-120°C, and the reaction time is 2-6h.

[0017] As a further improvement to the preparation process of the present invention, in step ②, deionized water is added to natural rubber latex to achieve a natural rubber latex emulsion concentration of 10-40 wt.%; the concentration of reduced graphene oxide particles in the surface-loaded free radical adsorbent-supported reduced graphene oxide aqueous dispersion is 0.5-5 mg / mL; and the flocculant is at least one of calcium chloride solution, sodium chloride solution, potassium chloride solution, sodium sulfate solution, hydrochloric acid solution, and formic acid solution, or a mixture of two or more thereof.

[0018] As a further improvement of the preparation process technical solution of the present invention, in step ③, the added amounts of each raw material are: 100 parts by mass of reduced graphene oxide modified natural rubber masterbatch, 30-90 parts by mass of reinforcing filler, and 10-20 parts by mass of rubber additive.

[0019] As a further improvement of the preparation process technical solution of the present invention, in step ③, the rubber additives include an antioxidant, an antioxidant, an activator, a softener, and a vulcanization accelerator, and the mass ratio of the antioxidant to the antioxidant, activator, softener, vulcanization accelerator, and vulcanizing agent is 2:2:5:2:2:2.

[0020] As a further improvement of the preparation process technical scheme of the present invention, in step ③, the antioxidant is 2,6-di-tert-butyl-4-methylphenol, 2,2,4-trimethyl-1,2-dihydroquinoline polymer or 2-thiol benzoimidazole; the antioxidant is N-(1-methylisopentyl)-N'-phenyl-p-phenylenediamine, p-phenylaniline or dilauryl dipropionate sulfide; the activator is zinc gluconate, zinc oxide or magnesium oxide; the softener is stearic acid, dibutyl titanate or dioctyl adipate; the reinforcing filler is carbon black, silica or clay; the vulcanization accelerator is N-tert-butyl-2-benzothiazole sulfenamide, N-cyclohexyl-2-benzothiazole sulfenamide or N-(diethylene oxide)-2-benzothiazole sulfenamide; and the vulcanizing agent is sulfur or sulfur monochloride.

[0021] As a further improvement of the preparation process technical scheme of the present invention, in step ③, the reduced graphene oxide modified natural rubber masterbatch with a surface-loaded free radical adsorbent is added to an internal mixer at a mixing temperature of 105-120°C, and each mixing time is 3-5 minutes; the open mixing temperature is 50-70°C, and the open mixing time is 8-12 minutes.

[0022] As a further improvement of the preparation process technical solution of the present invention, in step ③, the storage time of the mixed rubber is 18-36 hours; the vulcanization temperature is 135-170°C, the vulcanization pressure is 10-30 MPa, and the vulcanization time is 3-25 minutes.

[0023] Compared with the prior art, the present invention has the following beneficial effects:

[0024] (1) The present invention utilizes a streamlined process that is easy to industrialize to load a free radical adsorbent on the surface of reduced graphene oxide (rGO) sheets. The loaded free radical adsorbent can undergo an annihilation reaction with free radicals generated by rubber macromolecules due to force and / or oxygen during processing. The free radical annihilation reaction can enhance the interfacial interaction between the rubber matrix and rGO, thereby increasing the bound rubber content of natural rubber, increasing the cross-linking density of natural rubber vulcanizates and making the cross-linking network more complete, and ultimately obtaining a graphene-modified natural rubber composite material with improved strength and toughness.

[0025] (2) The present invention utilizes the annihilation reaction between the free radical adsorbent loaded on the rGO surface and the free radicals generated when the NR macromolecule is subjected to heat and / or force. On the one hand, it stabilizes the performance of NR and prevents its aging reaction from proceeding. On the other hand, it can also solve the problem of easy migration and volatility of antioxidants, thereby effectively improving the aging resistance of the prepared and toughened graphene-modified natural rubber composite material.

[0026] (3) The preparation process of the present invention is simple and environmentally friendly, without any stringent requirements, and involves conventional equipment, so it is easy to industrialize and has important significance for promoting the application of graphene in the field of high-performance rubber. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate embodiments consistent with the invention and, together with the description, serve to explain the principles of the invention.

[0028] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, for ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative labor.

[0029] FIG1 is a DSC curve of the reduced graphene oxide modified natural rubber composite material prepared in Examples 1-3 and Comparative Example 1.

[0030] FIG2 is an optical photograph and UV-vis spectrum of 2,2-diphenyl-1-picrylhydrazyl (DPPH) solution of reduced graphene oxide prepared in Examples 1-3 and Comparative Example 1.

[0031] FIG3 shows the binding rubber content of the reduced graphene oxide modified natural rubber composite materials prepared in Examples 1-3 and Comparative Example 1.

[0032] FIG4 shows the crosslinking density of the reduced graphene oxide modified natural rubber composite materials prepared in Examples 1-3 and Comparative Example 1.

[0033] Figure 1 shows the DSC curves of the prepared natural rubber composites. DSC testing can determine the interaction between the natural rubber matrix and the rGO filler, as the presence of the filler typically causes a change in the rubber's glass transition temperature. Compared to Comparative Example 1, the rubber composites prepared in Examples 1-3 exhibit increased glass transition temperatures due to increased interactions between the filler and the natural rubber macromolecular chains and the increased crosslinking network density, which restricts the movement of the rubber segments.

[0034] DPPH is a stable free radical at ambient temperature. Due to its special color change before and after deactivation, it is often selected as an indicator of free radical annihilation reaction. Figure 2 (a) shows that the color of the DPPH solution of the GO added to NR in Comparative Example 1 does not change, indicating that it does not have the ability to adsorb free radicals. The rGO of the surface-loaded free radical adsorbent added to NR in Example 1-3 is added to the DPPH solution. It can be seen that the color of the DPPH solution is significantly lighter, and as the amount of ascorbic acid added as a reducing agent increases during the generation of rGO, the color of the DPPH solution becomes lighter, from the initial dark purple to light purple, and finally to light brown, indicating that the free radicals in the DPPH solution are completely annihilated by the system. Therefore, it can be concluded that the rGO with the largest amount of ascorbic acid added has the strongest adsorption capacity for free radicals. The UV-vis spectrum of Figure 2 (b) shows that the DPPH solution has adsorption at 532nm-1, which is derived from the delocalization of unpaired electrons in its aromatic molecules. The intensity of this peak decreases with increasing amounts of ascorbic acid added during the reduction process, indicating an increase in the amount of adsorbed free radicals. This further demonstrates that rGO, reduced with ascorbic acid, can adsorb free radicals from NR. It is well known that during processing, rubber macromolecules are activated by heat and / or force, triggering chain scission and subsequently generating macromolecular free radicals. By loading ascorbic acid, rGO can adsorb free radicals generated by rubber and thus bond with it, generating interfacial interactions stronger than hydrogen bonds.

[0035] The formation of a cross-linked network structure depends largely on the bound rubber content, which in turn depends on the interaction between the matrix and filler in the composite rubber. Figure 3 shows the bound rubber content of the prepared graphene-modified natural rubber composites. Compared to Comparative Example 1, the bound rubber content of the composites prepared in Examples 1-3 was significantly increased. Furthermore, as the free radical adsorbent content increased, the interfacial interaction between the surface filler and the rubber was enhanced.

[0036] Figure 4 shows the crosslink density of the prepared graphene-modified natural rubber composites. Compared to Comparative Example 1, the crosslink density of the composites prepared in Examples 1-3 was significantly improved. Furthermore, as the free radical adsorbent content increased, the crosslink density of the rubber composites increased, and the crosslinked network became more complete. DETAILED DESCRIPTION

[0037] In order to more clearly understand the above-mentioned objects, features and advantages of the present invention, the solutions of the present invention will be further described below. It should be noted that, in the absence of conflict, the embodiments of the present invention and the features therein can be combined with each other.

[0038] In the following description, many specific details are set forth to facilitate a full understanding of the present invention, but the present invention may also be implemented in other ways different from those described herein; it is obvious that the embodiments in the specification are only part of the embodiments of the present invention, rather than all the embodiments.

[0039] The present invention provides a specific embodiment of a graphene-modified natural rubber that is simultaneously strengthened and toughened based on a strong interfacial effect of a free radical annihilation reaction. First, during the process of reducing graphene oxide, a free radical adsorbent is loaded on the surface of the reduced graphene oxide. Then, a water-phase collaborative coagulation process and a mechanical blending method are used to prepare a reduced graphene oxide-modified natural rubber composite material. During the mechanical blending process, the free radical adsorbent loaded on the surface of the reduced graphene oxide can undergo an annihilation reaction with free radicals generated when rubber macromolecules are subjected to heat and / or force. The free radical adsorbent has a greater effect on enhancing the interaction between the two phases than hydrogen bonds, thereby increasing the bound rubber content of the natural rubber, increasing the crosslinking density of the natural rubber vulcanizate, and improving the crosslinking network. Ultimately, a graphene-modified natural rubber composite material that is simultaneously strengthened and toughened is obtained.

[0040] The present invention further provides a preparation process for graphene-modified natural rubber with strong interfacial action and enhanced toughness based on free radical annihilation reaction, comprising the following steps:

[0041] ① Add the free radical adsorbent to water, fully dissolve it, then add a certain concentration of graphene oxide aqueous dispersion, react at a certain temperature for a certain time, and obtain a reduced graphene oxide aqueous dispersion with the free radical adsorbent loaded on the surface;

[0042] ② adding deionized water to natural rubber latex, and then adding the reduced graphene oxide aqueous dispersion with a surface-loaded free radical adsorbent prepared in step ①, and fully stirring and mixing to obtain a uniformly dispersed mixed emulsion, wherein the reduced graphene oxide particles with a surface-loaded free radical adsorbent will form bound particles with the rubber particles due to the positive ion electrostatic attraction of the protein-phospholipid membrane on the surface of the rubber particles and remain stable; after adding a flocculant, flocculation occurs due to the reduction of the negative charge repulsion between the particles that keeps the rubber latex stable, and the rubber particles with the damaged protective layer and the reduced graphene oxide particles will further adsorb each other through π-π forces, and the bound particles and rubber particles will gather in an orderly manner in the aqueous phase and precipitate out cooperatively; washing the obtained raw rubber with water, dehydrating, and drying to obtain a natural rubber masterbatch modified with reduced graphene oxide with a surface-loaded free radical adsorbent;

[0043] ③ Add rubber additives and reinforcing fillers to the reduced graphene oxide modified natural rubber masterbatch with a surface-loaded free radical adsorbent prepared in step ② in sequence, mix them, and evenly disperse them to obtain a rubber mix; start mixing the rubber mix, add a vulcanizing agent, mix them evenly, and thinly pass them until there are no bubbles in the rubber mix. After standing for a certain period of time, place them in a mold, and vulcanize them at a certain temperature and pressure for a certain period of time to obtain a graphene-modified natural rubber that is strengthened and toughened by a strong interfacial effect based on the free radical annihilation reaction.

[0044] In one embodiment of the preparation process provided by the present invention, in step ①, the free radical adsorbent is one or a mixture of two or more of ascorbic acid, citric acid, sodium alginate, acrylic acid and sodium lignin sulfonate; the reaction temperature in step ① is 60-120°C, and the reaction time is 2-6h.

[0045] In another embodiment of the preparation process provided by the present invention, in step ②, deionized water is added to natural rubber latex to make the concentration of the natural rubber latex emulsion be 10-40 wt.%; the concentration of the reduced graphene oxide particles in the surface-supported free radical adsorbent reduced graphene oxide aqueous dispersion is 0.5-5

[0046] mg / mL; the flocculant is at least one of calcium chloride solution, sodium chloride solution, potassium chloride solution, sodium sulfate solution, hydrochloric acid solution and formic acid solution, or a mixture of two or more thereof.

[0047] In one embodiment of the preparation process provided by the present invention, in step ③, the added amounts of the raw materials are: 100 parts by mass of reduced graphene oxide modified natural rubber masterbatch, 30-90 parts by mass of reinforcing filler, and 10-20 parts by mass of rubber additive.

[0048] In another embodiment of the preparation process provided by the present invention, in step ③, the rubber additives include an antioxidant, an antioxidant, an activator, a softener, and a vulcanization accelerator, and the mass ratio of the antioxidant to the antioxidant, activator, softener, vulcanization accelerator, and vulcanizing agent is 2:2:5:2:2:2.

[0049] In one embodiment of the preparation process provided by the present invention, in step ③, the antioxidant is 2,6-di-tert-butyl-4-methylphenol, 2,2,4-trimethyl-1,2-dihydroquinoline polymer or 2-mercaptobenzoimidazole; the antioxidant is N-(1-methylisopentyl)-N'-phenyl-p-phenylenediamine, p-phenylaniline or dilauryl dipropionate sulfide; the activator is zinc gluconate, zinc oxide or magnesium oxide; the softener is stearic acid, dibutyl titanate or dioctyl adipate; the reinforcing filler is carbon black, silica or clay; the vulcanization accelerator is N-tert-butyl-2-benzothiazole sulfenamide, N-cyclohexyl-2-benzothiazole sulfenamide or N-(diethylene oxide)-2-benzothiazole sulfenamide; and the vulcanizing agent is sulfur or sulfur monochloride.

[0050] In another embodiment of the preparation process provided by the present invention, in step ③, the reduced graphene oxide modified natural rubber masterbatch with a surface-loaded free radical adsorbent is added to an internal mixer at a mixing temperature of 105-120°C, with each mixing time of 3-5 minutes; the open mixing temperature is 50-70°C, and the open mixing time is 8-12 minutes.

[0051] In one embodiment of the preparation process provided by the present invention, in step ③, the storage time of the rubber mix is ​​18-36 hours; the vulcanization temperature is 135-170° C., the vulcanization pressure is 10-30 MPa, and the vulcanization time is 3-25 minutes.

[0052] The specific embodiments of the present invention are described in detail below.

[0053] Example 1

[0054] A graphene-modified natural rubber that is simultaneously strengthened and toughened is obtained based on the strong interfacial effect of a free radical annihilation reaction. The preparation process comprises the following steps:

[0055] ① Add 1 g of free radical adsorbent ascorbic acid to water and stir for 10 minutes to fully dissolve it. Then add the graphene oxide aqueous dispersion to prepare a dispersion with a graphene oxide particle concentration of 2.5 mg / mL. Stir and react at 95°C for 3 hours to obtain a reduced graphene oxide aqueous dispersion with a surface-loaded free radical adsorbent.

[0056] ② Add a certain amount of deionized water to natural rubber latex and stir until uniform to obtain a natural rubber latex emulsion with a concentration of 20 wt.%, then add the reduced graphene oxide aqueous dispersion with a surface-loaded free radical adsorbent having a reduced graphene oxide particle concentration of 2.5 mg / mL prepared in step ①, and stir and mix thoroughly to obtain a uniformly dispersed mixed emulsion; add 10 wt.% of a flocculant CaCl2 solution, so that the reduced graphene oxide particles and rubber particles are orderly aggregated and co-precipitated in the aqueous phase; wash the obtained raw rubber with water, dehydrate, and dry it in an oven at 50° C. to constant weight to obtain a natural rubber masterbatch modified with a surface-loaded free radical adsorbent, wherein the content of the reduced graphene oxide particles in the surface-loaded free radical adsorbent reduced graphene oxide is 0.5 wt.%;

[0057] ③ 100g of the surface-loaded free radical adsorbent-modified reduced graphene oxide natural rubber masterbatch prepared in step ② was placed in an internal mixer and mixed at 110°C and 40rpm for 4min. Then, 2g of vulcanization accelerator N-(diethylene oxide)-2-benzothiazolesulfonamide, 2g of antioxidant N-(1-methylisopentyl)-N'-phenyl-p-phenylenediamine and 2g of antioxidant 2,2,4-trimethyl-1,2-dihydroquinoline polymer were added and mixed for 4min. Then, 5g of activator zinc oxide and 2g of softener stearic acid were added and mixed for 4min. 60 g reinforcing filler carbon black was added and then mixed for 4 minutes, and the rubber was discharged; after the rubber was cooled to room temperature, it was transferred to an open mill for mixing at 60°C, and after uniform dispersion, 2g of sulfur was added and mixed evenly, and the rubber was thinly passed until there were no bubbles in the rubber, and the total mixing time was 10 minutes; after stopping the mixing for 24 hours, the mixed rubber was placed in a mold and vulcanized at 150°C*15MPa for a certain time (tc90) (5min), thereby obtaining a graphene-modified natural rubber composite material with strong interfacial phase transformation based on free radical annihilation reaction and enhanced toughness, wherein tc90 was measured by a rubber processing analyzer (RPA).

[0058] Example 2:

[0059] The process is exactly the same as that of Example 1, except that the amount of free radical adsorbent added in step ① is 2 g.

[0060] Example 3:

[0061] The process is exactly the same as that of Example 1, except that the amount of free radical adsorbent added in step ① is 3 g.

[0062] Comparative Example 1:

[0063] A graphene oxide modified natural rubber composite material, the preparation process of which comprises the following steps:

[0064] ① Add deionized water to graphene oxide and disperse it evenly to obtain a graphene oxide dispersion with a concentration of 2.5 mg / mL;

[0065] ② The same as step ② of Example 1, except that the reduced graphene oxide aqueous dispersion with a surface-loaded free radical adsorbent in step ② of Example 1 is replaced with a graphene oxide dispersion.

[0066] ③Same as step ③ of Example 1.

[0067] The natural rubber composite materials obtained in Examples 1-3 and Comparative Example 1 were subjected to performance tests. The tensile properties were tested according to ISO 37-2005, at a tensile rate of 500 mm / min. The tear properties were tested according to GB / T 529-2008. For aging resistance, the rubber was aged at 100°C for 1 day, with the tensile strength retention rate used as the indicator. The hardness was tested according to GB / T 531.1-2008. The heat generation performance was tested according to GB / T 1687.1-2016. The abrasion performance was tested according to GB / T 9867-2008.

[0068] Table 1 shows the test results of tensile strength, tearing strength, aging resistance, hardness, heat generation and wear resistance of the natural rubber composite materials prepared in Examples 1 to 3 and Comparative Example 1.

[0069] Table 1 Mechanical properties of Examples 1 to 3 and Comparative Example 1

[0070] As can be seen from Table 1, the tensile strength, tear strength, aging resistance (assessed by tensile strength retention), dynamic compression heat generation performance and wear resistance of the graphene-modified natural rubber of the present invention, which is simultaneously enhanced and toughened based on the strong interfacial effect of the free radical annihilation reaction, are significantly improved compared with the graphene oxide-modified natural rubber composite material of Comparative Example 1, and the high tensile strength and high tear strength of NR are achieved (i.e., simultaneous enhancement and toughening).

[0071] The above description is merely a specific embodiment of the present invention, which enables those skilled in the art to understand or implement the present invention. Although detailed descriptions have been made with reference to the aforementioned embodiments, those skilled in the art should understand that they may still modify the technical solutions described in the aforementioned embodiments, or replace some or all of the technical features therein with equivalents; and such modifications or replacements do not deviate from the essence of the corresponding technical solutions within the scope of the technical solutions of the embodiments, and they should all be included in the scope of protection of the claims.

Claims

1. Graphene-modified natural rubber with enhanced interfacial interaction and simultaneous reinforcement and toughening based on radical annihilation reaction, characterized in that, firstly, during the reduction of graphene oxide, a radical adsorbent is loaded on the surface of reduced graphene oxide, and then a reduced graphene oxide-modified natural rubber composite is prepared by an aqueous-phase co-precipitation process and a mechanical blending method; during the mechanical blending process, the radical adsorbent loaded on the surface of reduced graphene oxide can undergo an annihilation reaction with the radicals generated when rubber macromolecules are subjected to heat and / or force, and its enhancement effect on the interfacial interaction between the two phases is greater than that of hydrogen bonds, thereby increasing the bound rubber content of natural rubber, increasing the crosslink density of natural rubber vulcanizate and making the crosslink network more perfect, and finally obtaining a graphene-modified natural rubber composite with simultaneous reinforcement and toughening.

2. The preparation process of a graphene-modified natural rubber with enhanced interfacial interaction and simultaneous reinforcement and toughening based on radical annihilation reaction as described in claim 1, characterized in that, it comprises the following steps: ① Add a radical adsorbent to water, fully dissolve it, then add a certain concentration of graphene oxide aqueous dispersion, and react at a certain temperature for a certain time to obtain a reduced graphene oxide aqueous dispersion with a radical adsorbent loaded on its surface; ② Add deionized water to natural latex, then add the reduced graphene oxide aqueous dispersion with a radical adsorbent loaded on its surface prepared in step ①, fully stir and mix to obtain a uniformly dispersed mixed emulsion, in which the reduced graphene oxide particles with a radical adsorbent loaded on their surface will form bound particles with the rubber particles due to the positive ion electrostatic attraction of the protein-phospholipid membrane on the surface of the rubber particles and remain stable; after adding a flocculant, flocculation occurs due to the reduction of the negative charge repulsion between the particles that keep the rubber emulsion stable, and the rubber particles with damaged protective layers and the reduced graphene oxide particles will further adsorb each other by π-π interaction, and the bound particles and rubber particles will orderly aggregate and co-precipitate in the aqueous phase; wash, dewater and dry the obtained raw rubber, then a reduced graphene oxide-modified natural rubber masterbatch is obtained; ③ Add rubber additives and reinforcing fillers to the reduced graphene oxide-modified natural rubber masterbatch with a radical adsorbent loaded on its surface prepared in step ② in sequence, carry out internal mixing, and obtain a mixed rubber after uniform dispersion; open mill the mixed rubber, add a vulcanizing agent, mix evenly, then thin pass until there are no bubbles in the rubber compound, let it stand for a certain time and then place it in a mold, and vulcanize it at a certain temperature and a certain pressure for a certain time, then a graphene-modified natural rubber with enhanced interfacial interaction and simultaneous reinforcement and toughening based on radical annihilation reaction is obtained.

3. The preparation process of a graphene-modified natural rubber with enhanced interfacial interaction and simultaneous reinforcement and toughening based on radical annihilation reaction as described in claim 2, characterized in that, in step ①, the radical adsorbent is one or a mixture of two or more of ascorbic acid, citric acid, sodium alginate, acrylic acid and sodium lignosulfonate; the reaction temperature in step ① is 60 - 120 °C, and the reaction time is 2 - 6 h.

4. The preparation process of graphene-modified natural rubber with simultaneously enhanced strengthening and toughening based on radical annihilation reaction according to claim 2, characterized in that in step ②, deionized water is added to natural latex to make the concentration of the natural latex emulsion 10-40 wt.%; the concentration of reduced graphene oxide particles in the aqueous dispersion of reduced graphene oxide with surface-loaded radical adsorbent is 0.5-5 mg / mL; the flocculant is at least one or a mixture of two or more of calcium chloride solution, sodium chloride solution, potassium chloride solution, sodium sulfate solution, hydrochloric acid solution and formic acid solution.

5. The preparation process of graphene-modified natural rubber with simultaneously enhanced strengthening and toughening based on radical annihilation reaction according to claim 2, characterized in that in step ③, the addition amounts of each raw material are as follows: 100 parts by mass of reduced graphene oxide-modified natural rubber masterbatch, 30-90 parts by mass of reinforcing filler, and 10-20 parts by mass of rubber additives.

6. The preparation process of graphene-modified natural rubber with simultaneously enhanced strengthening and toughening based on radical annihilation reaction according to claim 5, characterized in that in step ③, the rubber additives include anti-aging agent, antioxidant, activator, softener, vulcanization accelerator, and the mass ratio of the anti-aging agent to the antioxidant, activator, softener, vulcanization accelerator and vulcanizing agent is 2:2:5:2:2:

2.

7. The preparation process of graphene-modified natural rubber with simultaneously enhanced strengthening and toughening based on radical annihilation reaction according to claim 6, characterized in that in step ③, the anti-aging agent is 2,6-di-tert-butyl-4-methylphenol, 2,2,4-trimethyl-1,2-dihydroquinoline polymer or 2-mercaptobenzothiazole; the antioxidant is N-(1-methylisoamyl)-N'-phenyl-p-phenylenediamine, p-phenylenediamine or dilauryl thiodipropionate; the activator is zinc gluconate, zinc oxide or magnesium oxide; the softener is stearic acid, dibutyl titanate or dioctyl adipate; the reinforcing filler is carbon black, silica or clay; the vulcanization accelerator is N-tert-butyl-2-benzothiazole sulfenamide, N-cyclohexyl-2-benzothiazole sulfenamide or N-(diethyleneglycol)-2-benzothiazole sulfenamide; the vulcanizing agent is sulfur or sulfur monochloride.

8. The preparation process of graphene-modified natural rubber with simultaneously enhanced strengthening and toughening based on radical annihilation reaction according to claim 2, characterized in that in step ③, the reduced graphene oxide-modified natural rubber masterbatch with surface-loaded radical adsorbent is added to the internal mixer at a mixing temperature of 105-120 °C, and the mixing time for each time is 3-5 min; the open mill temperature is 50-70 °C, and the open mill time is 8-12 min.

9. The preparation process of graphene-modified natural rubber with simultaneously enhanced interfacial interaction and toughening based on radical annihilation reaction according to claim 2, characterized in that in step ③, the standing time of the mixed rubber is 18 - 36 h; the vulcanization temperature is 135 - 170 °C, the vulcanization pressure is 10 - 30 MPa, and the vulcanization time is 3 - 25 min.

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