Preparation method of modified natural rubber, modified natural rubber, tire tread rubber and tire

Abstract

The invention provides a preparation method of modified natural rubber, the modified natural rubber, tire tread rubber and a tire, the preparation method of the modified natural rubber comprises the following steps: step (i), mixing choline chloride, glycerol and gallic acid to obtain a ternary eutectic solvent; (ii) adding the ternary eutectic solvent into the natural latex, uniformly mixing, and foaming and expanding to obtain a mixed emulsion; and (iii) drying the mixed emulsion to obtain the modified natural rubber. According to the present invention, it is possible to provide a modified natural rubber having excellent performance.

Description

Technical Field

[0001] This disclosure relates to the field of natural rubber processing technology, specifically to a method for preparing modified natural rubber, the modified natural rubber obtained by the preparation method, a tire tread compound prepared from the modified natural rubber as raw material, and a tire including the tire tread compound. Background Technology

[0002] Natural rubber, as an environmentally friendly and renewable biopolymer, not only possesses excellent resilience, mechanical strength, fatigue resistance, and low heat generation, but also belongs to the category of "negative carbon footprint" biomaterials, aligning with the current green and low-carbon development concept and holding irreplaceable value in key sectors of the national economy. Its unique properties make it a core material in high-end fields such as military and aerospace, directly impacting the reliability and safety of end-use equipment.

[0003] However, the traditional coagulation method for natural rubber uses an acid-based coagulation process, which has many inherent drawbacks: it not only easily corrodes production equipment and harms human health, but also causes serious environmental pollution, making it difficult to meet environmental protection production requirements. Furthermore, this process damages the properties of the rubber itself, resulting in suboptimal product performance and insufficient quality stability, making it difficult to meet the stringent standards for materials in high-end applications.

[0004] It should be noted that the information disclosed in the background section above is only used to enhance the understanding of the background of the present invention, and therefore may contain information that does not constitute prior art known to those skilled in the art. Summary of the Invention

[0005] In order to solve one or more of the above-mentioned problems in the prior art, the present invention aims to provide a method for preparing modified natural rubber, modified natural rubber obtained by the preparation method, tire tread compound prepared from the modified natural rubber as raw material, and tire including the tire tread compound.

[0006] The method for preparing the modified natural rubber of the present invention includes the following steps: Step (i): mixing choline chloride, glycerol and gallic acid to obtain a ternary eutectic solvent; Step (ii): adding the above ternary eutectic solvent to natural rubber latex, mixing evenly and foaming to obtain a mixed emulsion; Step (iii): drying the above mixed emulsion to obtain the above modified natural rubber.

[0007] According to one embodiment of the present invention, in step (iii) above, the mixed emulsion is dried by microwave irradiation.

[0008] According to one embodiment of the present invention, in step (iii) above, the mixed emulsion is dried by irradiating it with a microwave generator at a power of 50W to 800W for 1 to 10 minutes.

[0009] According to one embodiment of the present invention, in step (i) above, the molar ratio of choline chloride, glycerol and gallic acid is 1:1.5:(0.01~1).

[0010] According to an embodiment of the present invention, in step (i) above, choline chloride, glycerol and gallic acid are stirred and mixed at a temperature of 60°C to 130°C for 0.5 to 10 hours and at a stirring speed of 100 to 1300 r / min.

[0011] According to an embodiment of the present invention, in step (ii) above, the weight ratio of the ternary eutectic solvent to the dry rubber in the natural latex is (0.1~10):100.

[0012] According to one embodiment of the present invention, in step (ii) above, a high-shear emulsifier is used for mixing and foaming expansion, and the volume expansion rate of the above mixed emulsion after expansion is 10% to 80%.

[0013] According to another aspect of the present invention, a modified natural rubber is provided, wherein the modified natural rubber is prepared by the above-described method for preparing modified natural rubber.

[0014] According to another aspect of the present invention, a tire tread compound is provided, which is prepared from raw materials including the modified natural rubber described above.

[0015] According to another aspect of the present invention, a tire is provided, wherein the surface of the tire comprises the tire tread compound as described above.

[0016] Beneficial effects: According to the present invention, a modified natural rubber with excellent performance can be provided. Attached Figure Description

[0017] To more clearly illustrate the technical solutions in the embodiments of this specification or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments recorded in the embodiments of this specification. For those skilled in the art, other drawings can be obtained based on these drawings.

[0018] Figure 1 The infrared spectra of the raw materials choline chloride, glycerol, gallic acid, and the choline chloride-glycerol-gallic acid ternary eutectic solvent (CGG-DES) prepared from the three are shown.

[0019] Figure 2 The infrared spectra of raw rubber prepared by microwave irradiation micro-crosslinking technology with CGG-DES, fresh natural latex and concentrated natural latex are shown. Detailed Implementation

[0020] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the embodiments and accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. It should be noted that, unless otherwise specified, the implementation methods and features in the implementation methods of the present invention can be combined, separated, interchanged, and / or rearranged. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0021] Furthermore, when exemplary embodiments can be implemented differently, the specific process sequence can be performed in a different order than that described. For example, two consecutively described processes can be performed substantially simultaneously or in the reverse order of their description.

[0022] Furthermore, the terminology used herein is for the purpose of describing particular embodiments and is not intended to be limiting. As used herein, unless the context clearly indicates otherwise, the singular forms “a” and “the” are intended to include the plural forms as well. Additionally, when the terms “comprising” and / or “including” and variations thereof are used herein, it indicates the presence of the stated features, integrals, steps, operations, parts, components, and / or groups thereof, but does not exclude the presence or addition of one or more other features, integrals, steps, operations, parts, components, and / or groups thereof. It should also be noted that, as used herein, the terms “substantially,” “about,” and other similar terms are used as approximate terms rather than as terms of degree, thus explaining the inherent biases in measurements, calculated values, and / or provided values ​​that would be recognized by one of ordinary skill in the art.

[0023] The inventive concept of this invention is to add a novel ternary eutectic solvent (also known as a "bio-based ternary eutectic solvent") to natural rubber before drying. By utilizing the drying process of natural rubber, the solvent is pre-crosslinked with the natural rubber to form a natural rubber network with a large number of physical entanglement points and hydrogen bond interaction sites that are evenly distributed, thereby modifying the natural rubber.

[0024] The novel ternary eutectic solvent of this invention is composed of choline chloride, glycerol, and gallic acid. Choline chloride acts as a hydrogen bond acceptor in the ternary eutectic solvent, while glycerol and gallic acid act as hydrogen bond donors. The choline cations and chloride ions in the choline chloride (quaternary ammonium salt) molecule interact with the hydroxyl groups in glycerol and the hydroxyl and carboxyl groups in gallic acid molecules to form intermolecular hydrogen bonds, resulting in a stronger hydrogen bond network in the prepared ternary eutectic solvent. This, in turn, enhances the ternary eutectic solvent's effect on promoting the crosslinking of natural rubber.

[0025] It should be noted that, in this specification, deep eutectic solvents (DES) are eutectic systems composed of hydrogen bond donors (HBD) and hydrogen bond acceptors (HBA) in a stoichiometric ratio. The hydrogen bonding between the raw materials HBD and HBA is disrupted and replaced by a stronger hydrogen bond network, resulting in a melting point of the mixture (DES) that is much lower than that of either component (HBA and HBD). Therefore, it is called a deep eutectic solvent. Furthermore, in this specification, the "micro-crosslinked" structure is distinct from traditional sulfur crosslinking and includes a physical entanglement network, a hydrogen bond network, and a trace amount of chemical crosslinking.

[0026] The inventors discovered that by using a eutectic solvent made of choline chloride, glycerol, and gallic acid as a key modifying medium, after mixing with natural rubber, it uniformly penetrates into the rubber during the foaming and expansion process. Subsequently, during the drying process of the natural rubber, it forms a physical entanglement network, a hydrogen bonding network, and a trace chemical cross-linking network, thus reconstructing the natural raw rubber network. This unique "micro-cross-linking" structure can enhance the processability, resistance to thermo-oxidative aging, tensile strength, and reinforcing coefficient of natural rubber without impairing its inherent physicochemical properties. It avoids the problems of molecular chain breakage and poor aging resistance caused by traditional strong acid coagulation. Furthermore, gallic acid, as a natural polyphenol, can improve the thermo-oxidative aging resistance of the raw rubber. Based on this, the present invention was completed.

[0027] Specifically, the method for preparing the modified natural rubber of the present invention includes the following steps: Step (i): mixing choline chloride, glycerol and gallic acid to obtain a ternary eutectic solvent; Step (ii): adding the above ternary eutectic solvent to natural rubber latex, mixing evenly and foaming to obtain a mixed emulsion; Step (iii): drying the above mixed emulsion to obtain the above modified natural rubber.

[0028] In step (iii), the mixed emulsion can be dried using drying methods known in the art, such as hot air drying or flash drying, while simultaneously promoting micro-crosslinking between the natural rubber and the modifying medium. However, the present invention particularly prefers to use microwave irradiation for drying.

[0029] That is, another inventive point of the present invention is to use microwave irradiation to dry and micro-crosslink the mixed emulsion after foaming and expansion.

[0030] The inventors believe this is because traditional hot air drying and flash drying methods work by removing moisture from the surface of natural rubber before removing it from the inside. This results in incomplete drying of the rubber's interior, leaving residual moisture. Microwave drying, on the other hand, dries the rubber from the inside out, separating moisture in reverse. By leveraging the unique drying properties of microwaves, an innovative approach combining foaming technology with microwaves was developed. The foaming process pre-opens the pores, further promoting moisture separation from the inside out.

[0031] In step (i), the ternary eutectic solvent can be prepared into a colorless, transparent, homogeneous liquid by mixing predetermined amounts of choline chloride, glycerol, and gallic acid at a certain temperature and stirring speed. The mixing amount of choline chloride, glycerol, and gallic acid can be determined based on the relative molecular mass of the substances to achieve the ratio of hydrogen bond acceptors to hydrogen bond donors. Specifically, the molar ratio of choline chloride, glycerol, and gallic acid can be 1:1.5:(0.01~1). The reason for choosing the above molar ratio for gallic acid is that if the molar ratio is less than 0.01, the content of gallic acid is too low to provide more hydrogen bond network interaction for the ternary eutectic solvent, making it difficult for the ternary eutectic solvent to achieve the above function. If the molar ratio is greater than 1, there will be too many hydrogen bond donors, resulting in the inability of the three to form a homogeneous and transparent solution (i.e., the required DES cannot be formed). In an exemplary embodiment of the present invention, choline chloride, glycerol and gallic acid in a molar ratio of 1:1.5:(0.01~1) can be mixed and reacted at 60℃~130℃ and a stirring speed of 100~1300r / min for 0.5~10h to obtain the ternary eutectic solvent of the present invention.

[0032] Furthermore, the preferred weight ratio of the ternary eutectic solvent to the dry rubber in the natural latex in step (ii) is (0.1~10):100. The reason for the weight ratio of the ternary eutectic solvent (0.1~10) is that: if the amount of ternary eutectic solvent is too low relative to a certain amount of dry rubber in the natural latex, the modification will be insufficient, and a complete raw rubber network structure cannot be formed; if the amount of ternary eutectic solvent is too high, the plasticity of the natural rubber may be too high due to excessive entanglement and cross-linking of the raw rubber network, resulting in poor processability and affecting the quality and stability of the natural rubber. In an exemplary embodiment of the present invention, the ternary eutectic solvent and the dry rubber in the natural latex are mixed in a weight ratio of (0.1~10):100, and a mixture is obtained by foaming and expansion.

[0033] In a further exemplary embodiment of the present invention, a high-shear emulsifier can be used to expand and disperse the mixed emulsion of ternary eutectic solvent and natural rubber latex. The foaming power of the shear emulsification can be less than or equal to 150W, and the time can be maintained for 1 to 8 minutes, resulting in a volume expansion rate of 10% to 80% for the mixed emulsion. Here, "volume expansion rate of 10% to 80%" means that the volume of the final mixture is 1.1 to 1.8 times the total volume of the two components before mixing. However, the present invention is not limited to this; other emulsifiers can also be used to expand and disperse the mixed emulsion, as long as the volume expansion rate of the mixed emulsion reaches 10% to 80% in a short time. According to the embodiments of the present invention, if the volume expansion rate is less than 10%, the ternary eutectic solvent may not be able to fully penetrate into the interior of the latex, and a uniform raw rubber network may not be formed. If the volume expansion rate is greater than 80%, the foaming and expansion process may exert excessive mechanical force on the rubber molecular chains, damage the properties of the raw rubber itself, and cause unnecessary energy waste.

[0034] According to embodiments of the present invention, natural latex can be fresh natural latex or concentrated natural latex. That is, natural latex can be obtained directly from tapping natural rubber trees or obtained after centrifugal concentration technology, as long as the dry rubber content in the natural latex is 18% to 65%.

[0035] According to one embodiment of the present invention, in step (iii) above, the moisture content of the modified natural rubber after microwave irradiation micro-crosslinking drying is ≤0.8%. By controlling the moisture content of the modified natural rubber to below 0.8%, the quality and stability of the modified natural rubber obtained by the process of the present invention can be effectively guaranteed, and the moisture content can meet the national standard. According to one embodiment of the present invention, a microwave generator can be used to perform the irradiation micro-crosslinking process for 1 min to 10 min at a power of 50W to 800W to obtain modified natural rubber with a moisture content of less than or equal to 0.8%.

[0036] Furthermore, according to embodiments of the present invention, in step (iii) above, the modified natural rubber sheet after irradiation and micro-crosslinking can also undergo thin-passing and pressing, wherein the number of roll passes during thin-passing can be less than or equal to 5. According to an example embodiment, thin-passing and pressing can be performed using an open mill at room temperature, and the number of roll passes during thin-passing can be less than or equal to 5 to ensure that the initial properties of the raw rubber are not damaged. Preferably, the number of roll passes can be greater than or equal to 2 and less than or equal to 5.

[0037] The modified natural rubber of this invention can be used to produce tire tread compounds. Another aspect of this invention provides a tire that may include a tire tread compound prepared using raw materials including the modified natural rubber, which may be formed on the surface of the tire. However, this invention is not limited thereto. For example, the modified natural rubber provided by this invention can also be used in any prior art formulation using natural rubber to improve tire performance. For example, it can be applied to the preparation of: (Classification 1) TBR tires, OTR tires, PCR tires; (Classification 2) all-steel tires, semi-steel tires.

[0038] The inventors have demonstrated through experiments that the modified natural rubber preparation method of the present invention, by using a eutectic solvent made of choline chloride, glycerol, and gallic acid as the key modifying medium, and in conjunction with microwave irradiation micro-crosslinking technology, can enhance the processability, resistance to thermo-oxidative aging, tensile strength, and reinforcing coefficient of natural rubber without damaging its physicochemical properties, thus avoiding problems such as molecular chain breakage and poor aging resistance caused by traditional strong acid coagulation.

[0039] In addition, since the modified natural rubber preparation method of the present invention adopts acid-free and green preparation, it avoids the corrosion of equipment, the harm to the health of operators, and the generation of acidic wastewater and harmful waste gas during the strong acid coagulation process, thereby reducing the cost of "three wastes" treatment and environmental risks.

[0040] The present invention will be further described in detail below with reference to specific embodiments, but the present invention is not limited to the following embodiments. The implementation conditions used in the embodiments can be further adjusted according to different requirements of specific use, and the implementation conditions not specified are conventional conditions in this industry.

[0041] Example 1 Choline chloride, glycerol, and gallic acid were mixed in a molar ratio of 1:1.5:0.2 and stirred at 80°C for 2 hours at a speed of 325 r / min to prepare a ternary eutectic solvent CGG.

[0042] Take fresh natural latex with a dry rubber content of 28%, add 0.5 parts by weight of ternary eutectic solvent to 100 parts by weight of fresh natural latex with a dry rubber content (357g), and use a high-shear emulsifier at 150W power to perform emulsification, foaming and expansion treatment on the mixed emulsion for 3 minutes, so that the volume expansion rate of the mixed emulsion reaches 30%.

[0043] The mixture was then placed in a microwave generator, which was set to 800W, and subjected to microwave irradiation for micro-crosslinking drying for approximately 5 minutes to obtain natural rubber with a moisture content of less than or equal to 0.8%. This rubber was then passed through a two-roll mill twice to obtain modified natural rubber.

[0044] The modified natural rubber was conventionally compounded using formulation ACS1 (100.00 parts by weight of the modified natural rubber obtained above, 6.00 parts by weight of zinc oxide, 3.50 parts by weight of sulfur, 0.50 parts by weight of stearic acid, and 0.50 parts by weight of MBT) from the industry standard NY / T 1403-2007 "Evaluation Methods for Natural Rubber" and the corresponding mixing procedure in the industry standard. After the compound was allowed to stand for 12 hours, the positive vulcanization time t was measured using a rotorless rheometer. 90 Using a flat vulcanizing machine, the vulcanization time is 1.3 times the t. 90 The material is vulcanized and molded at a pressure of 10 MPa and a temperature of 150 °C.

[0045] Example 2 The preparation of the modified natural rubber in Example 2 is the same as in Example 1.

[0046] The difference between Example 2 and Example 1 is that 1.0 part by weight of ternary eutectic solvent was added to 100 parts by weight of fresh natural latex (357g) with dry rubber content; the volume expansion rate of the mixed emulsion was 40%.

[0047] The same mixing and vulcanization process as in Example 1 was used.

[0048] Example 3 The preparation of the modified natural rubber in Example 3 is the same as in Example 1.

[0049] The difference between Example 3 and Example 1 is that the natural latex used is concentrated natural latex with a dry rubber content of 60%; 0.5 parts by weight of ternary eutectic solvent are added to 100 parts by weight of concentrated natural latex with a dry rubber content (166.67g); and the volume expansion rate of the mixed emulsion is 50%.

[0050] The same mixing and vulcanization process as in Example 1 was used.

[0051] Comparative Example 1 Fresh natural latex with a dry rubber content of 28% was directly subjected to microwave irradiation for micro-crosslinking drying. The microwave generator power was 800W, and the time was 7 minutes. The obtained dry rubber was then passed through a two-roll mill twice to obtain natural rubber.

[0052] The same mixing and vulcanization process as in Example 1 was used.

[0053] Comparative Example 2 Concentrated natural rubber latex with a dry rubber content of 60% was directly subjected to microwave irradiation for micro-crosslinking drying. The microwave generator power was 800W, and the time was 5 minutes. The obtained dry rubber was then passed through a two-roll mill twice to obtain natural rubber.

[0054] The same mixing and vulcanization process as in Example 1 was used.

[0055] Comparative Example 3 Vietnamese 3L standard natural rubber SVR 3L was selected and the same conventional mixing and vulcanization process as in Example 1 was adopted. Specifically, the Vietnamese 3L standard natural rubber SVR 3L was obtained by adding strong acid to fresh natural latex for coagulation and then drying it with hot air.

[0056] The above materials were tested.

[0057] Performance Analysis (a) Infrared spectroscopy test Infrared spectroscopy was performed on the raw materials choline chloride, glycerol, gallic acid, and the ternary eutectic solvent CGG (choline chloride-glycerol-gallic acid) prepared from these three materials in Example 1. The results are shown in the figure. Figure 1 .

[0058] like Figure 1 As shown, in the infrared curve of CGG-DES, 1040 cm⁻¹ -1 The characteristic peak of the stretching vibration of CO in glycerol appeared at 1474 cm⁻¹. -1 (CH3)3N from choline chloride appeared at the location. + Characteristic absorption peak of the group; 1536 cm⁻¹ -1 Location, 1613 cm -1 The peak at 1695 cm⁻¹ represents the skeletal vibration of the benzene ring. -1 The peak at 3362 cm⁻¹ is a stretching vibration peak of C=O, which shows the characteristics of gallic acid; -1 The broad peak nearby is the stretching vibration peak of the hydroxyl group (-OH), which is larger than the hydroxyl peak at the same position in the infrared curve of glycerol. Based on the above results, it is indicated that there is a strong hydrogen bond interaction between HBA and HBD in CGG-DES, forming a more complete hydrogen bond network. This is beneficial for CGG-DES to promote the formation of physical entanglement networks, hydrogen bond networks, and trace chemical crosslinking networks in the natural rubber raw rubber network during the microwave drying process. Combined with the foaming expansion emulsification process, CGG-DES is evenly distributed in the natural rubber matrix, thus providing favorable conditions for CGG-DES to promote the degree and uniformity of crosslinking in the subsequent natural rubber compounding and vulcanization process.

[0059] Figure 2 Infrared spectra of raw rubber prepared by microwave irradiation microcrosslinking technology using CGG-DES, fresh natural latex, and concentrated natural latex (fresh latex corresponds to Example 1, concentrated latex corresponds to Example 2, fresh latex-0.5CGG and fresh latex-1CGG correspond to Examples 1 and 2 respectively, and concentrated latex-0.5CGG corresponds to Example 3). Figure 2As shown in (a), in the dry gel prepared from fresh latex (without added CGG-DES), 1035 cm -1 and 1545 cm -1 The characteristic peaks of CO and amide II bands appear at 3295 cm⁻¹, which is due to non-rubber components such as proteins and phospholipids contained in natural rubber. -1 The hydroxyl peaks nearby are stronger. When CGG-DES is added to fresh latex, the peak at 1035 cm⁻¹ is [missing value]. -1 1545 cm -1 The weakening of both the CO and amide bond peaks at 3295 cm⁻¹ is likely due to the hydrogen bond interactions between the hydrogen bond network in CGG-DES and proteins, which disrupts the structure and hydrogen bond network of some proteins in natural rubber, causing denaturation or dissolution of some proteins. Because CGG-DES perturbs the protein protective layer on the surface of rubber particles, more polyisoprene chains are exposed, leading to increased hydrophobicity. -1 The hydroxyl peak at that location is weakened. For example... Figure 2 As shown in (b), in the dry gel prepared from concentrated emulsion (without added CGG-DES), 1035 cm -1 The characteristic peak of CO is weaker at 1545 cm⁻¹. -1 The absence of a characteristic peak at this point is due to the reduction of non-gel components such as proteins in the concentrated latex obtained after centrifugation (this result can be verified by the total nitrogen content of Comparative Examples 1 and 2). After adding CGG-DES to the concentrated latex, the peak at 1035 cm⁻¹... -1 The peak enhancement at 1545 cm⁻¹ is due to the CO contained in the eutectic solvent itself. -1 The peak enhancement at 3295 cm⁻¹ is a characteristic peak of the benzene rings or carboxylate groups contained in the eutectic solvent itself. Because the content of non-gel components such as proteins in concentrated milk is low, the interaction between the eutectic solvent and these non-gel components is weak. Therefore, the strong hydrogen bond network carried by the eutectic solvent itself may lead to the peak enhancement at 3295 cm⁻¹. -1 The hydroxyl peak at that location is enhanced.

[0060] It should be noted that, for ease of observation, Figure 1 and Figure 2 This is a graph that has been shifted vertically, so the direction of the vertical axis does not represent a specific intensity value; it is only used to compare the relative position of the peaks and the size of the peak area.

[0061] (ii) Raw rubber performance testing of natural rubber (including the modified natural rubber of Examples 1-3) Total nitrogen content was determined by the Kjeldahl method. Number-average molecular weight (Mn), weight-average molecular weight (Mw), Z-average molecular weight (Mz), and polydispersity index (PDI) were determined by gel permeation chromatography. Density was determined according to national standard GB / T 21863-2008. P0 is the initial plasticity value of the modified natural rubber.30 It is the plasticity value of modified natural rubber after aging at 140℃ for 30 minutes. The plasticity retention rate PRI is P 30 The ratio of P0 to P0, P0 and P 30 Tested according to national standard GB / T 3517-2014.

[0062] The specific test results are shown in Table 1.

[0063] Table 1. Test results of performance parameters of the prepared raw rubber Basis: A higher PDI index indicates a wider molecular weight distribution and better processability of the raw rubber. A smaller PRI change rate indicates better resistance to thermo-oxidative aging of the raw rubber.

[0064] As described above regarding the embodiments, the raw materials for Examples 1, 2, and Comparative Example 1 were all fresh natural latex; the raw materials for Examples 3 and Comparative Example 2 were all concentrated natural latex; and Comparative Example 3 used Vietnamese 3L standard natural rubber SVR3L. Therefore, the measurement results for Examples 1, 2, and Comparative Example 1 will be compared; the measurement results for Examples 3 and Comparative Example 2 will be compared; and the results for Examples 1-3 and Comparative Example 3 will be compared.

[0065] As shown in Table 1, compared with Comparative Example 1, the total nitrogen content, Mn, Mw, Mz, PDI index, and P0 of Example 1 all increased, indicating that in the fresh natural latex test, the ternary eutectic solvent foaming-assisted microwave irradiation micro-crosslinking drying technology improved the nitrogen content, molecular weight, and processability of the raw rubber. The decrease in the rate of change of PRI indicates improved resistance to thermo-oxidative aging. In Example 2, due to the addition of 1 part of eutectic solvent, the crosslinking effect was stronger, resulting in a slight decrease in its PDI index (i.e., a slight decrease in processability). Compared with Comparative Example 2, the total nitrogen content and PDI index of Example 3 both increased, indicating that in the concentrated natural latex test, the ternary eutectic solvent foaming-assisted microwave irradiation micro-crosslinking drying technology could also improve the nitrogen content and processability of the raw rubber. The decrease in the rate of change of PRI indicates improved resistance to thermo-oxidative aging. Compared with Comparative Example 3, the modified natural rubber of Examples 1-3 showed significant improvements in nitrogen content, initial plasticity, and resistance to thermo-oxidative aging.

[0066] (III) Performance testing of natural rubber (including the modified natural rubber of Examples 1-3) compounds and vulcanizates Vulcanization characteristics (M) L M H t 10 t 90The hardness was measured by a rotorless rheometer according to GB / T 16584; the tensile properties (stress at a constant elongation, tensile strength, and elongation at break) were measured by a universal testing machine according to GB / T 528-2009; the aging coefficient was determined by aging the vulcanizate in a hot air aging chamber at 100℃ for 72 h, and the aging performance of the vulcanizate was determined according to GB / T 3512-2014.

[0067] The specific test results are shown in Table 2.

[0068] Table 2 shows the performance parameters of the compound rubbers and vulcanizates prepared from Examples 1-3 and Comparative Examples 1-3. Basis: t 10 It can characterize the scorch performance and processing safety of rubber compounds, t 10 The longer the scorching time, the better the processing safety of the rubber compound; t 90 M represents the positive vulcanization time of the rubber compound, indicating vulcanization efficiency. L It is the minimum torque, which characterizes the processing flow properties of the rubber compound, M L The smaller the value, the better the processing flow properties of the rubber compound; M H The maximum torque is usually related to hardness and tensile strength; the reinforcement coefficient is the ratio of 300% constant elongation stress to 100% constant elongation stress. The larger the reinforcement coefficient, the better the reinforcement effect; the tensile product is the product of tensile strength and elongation at break, which can characterize the comprehensive mechanical properties of vulcanizates; the aging coefficient is the ratio of the tensile product after aging to the tensile product before aging. The larger the aging coefficient, the better the aging resistance of vulcanizates.

[0069] As can be seen from the results in Table 1, compared with Comparative Example 1, the t values ​​of Examples 1 and 2 are... 10 Slightly shortened, M L The increase in physical entanglement networks, hydrogen bonding networks, and chemical micro-crosslinking networks in natural raw rubber prepared by microwave irradiation micro-crosslinking technology leads to premature crosslinking in the early stages of rotorless testing (early vulcanization), thus affecting the minimum torque M. LThe strength, tensile strength, tensile volume coefficient, and aging coefficient of the vulcanizate were significantly improved. In Example 1, these values ​​increased by 4%, 5%, 4%, and 15%, respectively, while in Example 2, they increased by 5%, 17%, 20%, and 18%, respectively. Compared to Comparative Example 2, the aging resistance of Example 3 was improved by 39%. Compared to Comparative Example 3, all Examples 1-3 showed significant improvements in processing fluidity, tensile strength, strength, and aging coefficient. Specifically, compared to Comparative Example 3, the strength, tensile strength, tensile volume coefficient, and aging coefficient of Example 2 increased by 22%, 46%, 38%, and 14%, respectively, indicating that the ternary eutectic solvent foaming-assisted microwave irradiation micro-crosslinking drying technology can effectively improve the strength and aging resistance of the vulcanizate.

[0070] It should also be noted that fresh natural latex and concentrated natural latex differ not only in moisture content but also in the content of non-rubber components (proteins, lipids, etc.). Fresh natural latex mainly consists of rubber hydrocarbons, water, and non-rubber components, with non-rubber components accounting for approximately 5%. Fresh natural latex is obtained directly from tapping natural rubber trees, while concentrated natural latex is obtained by centrifugation and concentration of fresh natural latex. During centrifugation and concentration, some non-rubber components, such as proteins, are ejected as byproducts (latex clear). Therefore, per unit dry weight of latex, concentrated natural latex contains less of these non-rubber components than fresh latex. In the foaming and expansion-assisted microwave irradiation micro-crosslinking technology provided in this invention, the ternary eutectic solvent interacts with the proteins in natural rubber through hydrogen bonds and ionic interactions, causing changes in the structure and state of the proteins, thereby achieving a micro-crosslinking effect. Therefore, although the performance trend of this invention is the same in both types of latex, the degree of improvement in certain properties will differ due to the different contents of non-rubber components such as proteins. For example, there are differences in total nitrogen content, molecular weight, and the degree of increase in tensile strength of vulcanized rubber.

[0071] In summary, the technical solution of the present invention mainly has the following technical effects: (1) A eutectic solvent made of choline chloride, glycerol, and gallic acid was used as the key modifying medium. During the foaming and expansion process, it uniformly penetrated into the latex. Subsequently, under microwave irradiation, it induced the formation of a physical entanglement network, a hydrogen bonding network, and a trace chemical cross-linking network, thus reconstructing the natural raw rubber network. This unique "micro-cross-linking" structure can enhance the processability, resistance to thermo-oxidative aging, tensile strength, and reinforcing coefficient of natural rubber without damaging its physicochemical properties, avoiding the problems of molecular chain breakage and poor aging resistance caused by traditional strong acid coagulation. Among them, gallic acid, as a natural polyphenol, significantly improves the thermo-oxidative aging resistance of raw rubber.

[0072] (2) This invention belongs to acid-free green preparation, avoiding the corrosion of equipment, the harm to the health of operators, and the generation of acidic wastewater and harmful exhaust gas during the strong acid coagulation process. It reduces the cost of "three wastes" treatment and environmental risks, and is a clean and safe green production method. At the same time, the combination of novel ternary eutectic solvent foaming and microwave irradiation micro-crosslinking technology not only realizes the rapid and uniform dehydration of the film and improves the drying efficiency, but also further consolidates the micro-crosslinking network structure of natural raw rubber, ensuring the uniformity and stability of product performance.

[0073] (3) The process steps of this invention are simple and controllable. The ternary eutectic solvent in the raw materials is biodegradable and inexpensive. The overall production cost is more competitive than the traditional method of relying on imported high-end rubber or treating acid pollution, which provides a solid foundation for promoting the high-quality development of the rubber industry.

[0074] The specific embodiments described above further illustrate the purpose, technical solution, and beneficial effects of the present invention. It should be understood that the above description is only a specific embodiment of the present invention and is not intended to limit the scope of protection of the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for preparing modified natural rubber, characterized in that, The method for preparing the modified natural rubber includes the following steps: Step (i): Choline chloride, glycerol and gallic acid are mixed to obtain a ternary eutectic solvent; Step (ii): Add the ternary eutectic solvent to the natural rubber latex, mix evenly and foam to obtain a mixed emulsion; Step (iii): Dry the mixed emulsion to obtain the modified natural rubber.

2. The method for preparing modified natural rubber according to claim 1, characterized in that, In step (iii), the mixed emulsion is dried by microwave irradiation.

3. The method for preparing modified natural rubber according to claim 2, characterized in that, In step (iii), the mixed emulsion is dried by irradiating it with a microwave generator at a power of 50W to 800W for 1 to 10 minutes.

4. The method for preparing modified natural rubber according to any one of claims 1 to 3, characterized in that, In step (i), the molar ratio of choline chloride, glycerol and gallic acid is 1:1.5:(0.01~1).

5. The method for preparing modified natural rubber according to claim 4, characterized in that, In step (i), choline chloride, glycerol and gallic acid are mixed and stirred at a temperature of 60℃ to 130℃ for 0.5 to 10 hours and at a stirring speed of 100 to 1300 r / min.

6. The method for preparing modified natural rubber according to claim 5, wherein in step (ii), the weight ratio of the ternary eutectic solvent to the dry rubber in the natural latex is (0.1~10):

100.

7. The method for preparing modified natural rubber according to claim 6, characterized in that, In step (ii), a high-shear emulsifier is used for mixing and foaming expansion, and the volume expansion rate of the expanded mixed emulsion is 10% to 80%.

8. A modified natural rubber, characterized in that, The modified natural rubber is prepared by any one of the modified natural rubber preparation methods according to claims 1 to 7.

9. A tire tread compound, characterized in that, The tire tread compound is made from raw materials including the modified natural rubber described in claim 8.

10. A tire, characterized in that, The surface of the tire includes the tire tread compound as described in claim 9.

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