A high fatigue-resistant recyclable epoxidized natural rubber based on a dual dynamic network and a preparation method thereof

Abstract

The application discloses a kind of high anti-fatigue recyclable epoxidized natural rubber based on double dynamic network and a preparation method thereof, belong to high polymer material and rubber modification technical field.The method first synthesizes precursor monomer containing end double bond and epoxy group, and then activates elemental sulfur to occur ring-opening reaction using activator, to prepare multifunctional crosslinking agent containing dynamic polysulfide bond, hydroxyl and end double bond;Subsequently, the crosslinking agent is mixed with epoxidized natural rubber and compounding agent, and a double dynamic network coordinated by dynamic polysulfide bond and reversible hydrogen bond is constructed in situ by high-temperature hot pressing.The application adopts filler-free strategy, and uses the macroscopic multiscale sacrificial network formed by hydrogen bond and polysulfide bond to achieve high strength and toughness, effectively passivate crack, and give the material extremely high fatigue resistance performance.Meanwhile, the material has excellent solid-state recyclable performance, the preparation route is simple, compatible with traditional rubber processing equipment, and has broad industrial application prospect.

Description

Technical Field

[0001] This invention relates to the field of polymer materials and rubber modification technology, and more specifically to a highly fatigue-resistant recyclable epoxidized natural rubber based on a dual dynamic network and its preparation method. Background Technology

[0002] Rubber elastomers, due to their high elasticity and large deformation recovery capabilities, play an indispensable role in modern industries and emerging fields such as heavy-duty tires, aerospace seals, vibration isolation, and flexible electronics. However, under complex dynamic service conditions, microscopic defects inevitably develop within the material. Driven by alternating stress, these defects undergo irreversible fatigue crack propagation, ultimately leading to brittle fracture.

[0003] In classical polymer network theory, the "strength-toughness paradox" is a recognized fundamental bottleneck: while increasing the density of covalent crosslinks can improve material strength, it severely restricts the mobility of polymer chains, leading to a sharp decline in ductility and fracture toughness. Furthermore, traditional pure rubber networks lack effective stress dissipation mechanisms, exhibiting significant notch sensitivity. Therefore, overcoming the strength-toughness paradox to achieve high strength and robust energy dissipation capabilities, thereby suppressing dynamic fatigue failure, remains a core challenge in this field.

[0004] Industrially, physical reinforcement typically relies on nanofillers (such as carbon black or silica). However, under high-frequency cyclic loading, this method induces internal friction and hysteresis heat generation (Payne effect). This not only increases energy loss but also accelerates thermo-oxidative aging and the initiation of early fatigue cracks due to heat accumulation. In recent years, while supramolecular chemistry-based toughening strategies (such as dual networks and multiple sacrificial bonds) have achieved theoretical breakthroughs, most of these strategies rely on solvent systems, making them incompatible with traditional solvent-free rubber processing techniques. In dry rubber systems, the thermodynamic incompatibility between rigid aggregates and flexible rubber matrices makes uniform blending difficult, easily leading to the formation of macroscopic defects in the matrix. These defects, in turn, can evolve into new crack initiation sites.

[0005] Therefore, developing a new type of elastomer material that is filler-free, compatible with traditional dry rubber processing, and simultaneously possesses ultra-high fatigue resistance and recyclability has significant industrial application value and scientific significance. Summary of the Invention

[0006] The purpose of this invention is to provide a filler-free epoxidized natural rubber with a dual dynamic network and a method for its preparation. By introducing a multifunctional crosslinking agent containing dynamic polysulfide bonds, a dual network of covalent polysulfide bonds and physical hydrogen bonds is constructed in situ.

[0007] To achieve the above objectives, the present invention adopts the following technical solution:

[0008] A method for preparing epoxidized natural rubber based on a dual dynamic network includes the following steps: S1. Synthesis of precursor monomers (VBGE) containing terminal double bonds and epoxy groups. In the presence of a catalyst, a haloaromatic derivative is etherified with an alcohol containing an epoxy group at a suitable temperature. After the reaction, the mixture is separated and purified to obtain the precursor monomer 4-vinylbenzyl glycidyl ether (VBGE).

[0009] S2. Synthesis of multifunctional crosslinking agents (S-VBGE) Elemental sulfur (S8) and an activator were mixed in an organic solvent and ultrasonically treated to activate the elemental sulfur; then, VBGE synthesized in step one was added to initiate a ring-opening reaction. After the reaction was completed, the mixture was quenched, extracted, and desolventized to obtain S-VBGE, a multifunctional crosslinking agent integrating polar hydroxyl groups, dynamic polysulfide bonds, and double bonds.

[0010] S3. Mixing and in-situ construction of a dual dynamic rubber network Epoxidized natural rubber (ENR), rubber additives, and the S-VBGE crosslinking agent synthesized in step two are mechanically mixed in rubber processing equipment (two-roll mill or internal mixer). After the uniformly mixed rubber compound is left to stand, it is cured at high temperature in a hot press. During the hot pressing process, the secondary hydroxyl groups of the crosslinking agent undergo etherification and ring-opening with the epoxy groups of the rubber backbone, while its terminal double bonds co-vulcanize with the rubber backbone, thus constructing a dual dynamic network in situ coupled with a covalent polysulfide bond network and a reversible hydrogen bond network.

[0011] Preferably, in step S1, the haloaromatic derivative is 4-vinylbenzyl chloride, the epoxy group-containing alcohol compound is glycidyl ether, and the catalyst is 1,5,7-triazidobicyclo[4.4.0]dec-5-ene; the molar ratio of the haloaromatic derivative, the epoxy group-containing alcohol compound and the catalyst is 1 : (1.5 ~ 2.5) : (0.01 ~ 0.05).

[0012] Preferably, in step S2, the activator is sodium sulfide nonahydrate, the organic solvent is tetrahydrofuran, and the molar ratio of elemental sulfur (based on sulfur molecules), activator and precursor monomer is (2.0 ~ 4.0): (0.2 ~ 0.6):1.

[0013] The mixing and activation method is ultrasonic treatment or mechanical stirring for 5 to 30 minutes; the ring-opening reaction conditions are: stirring reaction at 15 to 40 °C for 6 to 24 hours.

[0014] Preferably, in step S3, the compounding formula comprises, by mass parts: 100 parts of epoxidized natural rubber (epoxidation degree of 10-50 mol%, preferably 25 mol%); 5-25 parts of multifunctional crosslinking agent S-VBGE; and 5-15 parts of rubber compounding agents (including vulcanizing agent, accelerator, activator and antioxidant).

[0015] Preferably, in step S3, the conditions for high-temperature curing are: temperature 140 ~ 180 ℃, pressure 5 ~ 15 MPa, and time is the positive vulcanization time of the rubber compound.

[0016] The present invention also protects an epoxidized natural rubber material based on a dual dynamic network prepared by the above preparation method.

[0017] In the network structure of this material, dynamic covalent polysulfide bonds form a continuous macroscopic support framework; dense, reversible hydrogen bonds formed by intermolecular interactions of hydroxyl groups act as multi-scale sacrificial elements. Under mechanical stress, the hydrogen bonds preferentially undergo large-scale dissociation and recombination to dissipate energy, thereby effectively passivating the crack tip and comprehensively inhibiting crack propagation before the covalent backbone undergoes catastrophic fracture.

[0018] As can be seen from the above technical solution, compared with the prior art, the present invention has the following technical effects: 1. The crosslinking agent synthesis conditions in the preparation method of epoxidized natural rubber of the present invention are mild, and the mixing and vulcanization process is fully compatible with traditional solvent-free rubber equipment. The preparation route is simple and easy to industrialize.

[0019] 2. The epoxidized natural rubber of this invention does not require the addition of rigid nanofillers; it achieves a perfect combination of high strength and high toughness solely through the energy dissipation of a dual dynamic network.

[0020] 3. The epoxidized natural rubber of this invention contains a macroscopic sacrificial network composed of dynamic polysulfide bonds and reversible hydrogen bonds, which can effectively passivate cracks and has extremely high fatigue resistance.

[0021] 4. The epoxidized natural rubber of this invention contains dynamic polysulfide bonds and reversible hydrogen bonds, and has good solid-state remodeling properties. It can be directly recycled and reused by hot pressing without solvent. Attached Figure Description

[0022] To more clearly illustrate the technical solutions in the embodiments of the present invention 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 embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on the provided drawings without creative effort.

[0023] Figure 1This is a hydrogen nuclear magnetic resonance spectrum of the crosslinking agent VBGE and its raw materials in one embodiment of the present invention.

[0024] Figure 2 This is a hydrogen NMR spectrum of the crosslinking agent S-VBGE in one embodiment of the present invention.

[0025] Figure 3 These are the uniaxial tensile stress-strain curves of the elastomer under different amounts of crosslinking agent added according to the present invention.

[0026] Figure 4 This is a comparison chart of the fatigue threshold of embodiments of the present invention and pure covalent rubber, demonstrating the superior anti-fatigue effect.

[0027] Figure 5 This is a schematic diagram illustrating the principle of constructing a dual dynamic sacrificial network of "polysulfide covalent bonds-reversible hydrogen bonds" in situ according to the present invention. Detailed Implementation

[0028] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. 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.

[0029] Example 1: A method for synthesizing a multifunctional crosslinking agent S-VBGE, the specific steps of which are as follows: 7.63 g of 4-vinylbenzyl chloride, 7.41 g of glycidyl ether, and 0.15 g of 1,5,7-triazidobicyclo[4.4.0]dec-5-ene (TBD) were mixed and reacted at 25 °C for 8 h to prepare the precursor VBGE. Subsequently, 3.84 g of sulfur, 3.84 g of sodium sulfide nonahydrate, and 60 mL of tetrahydrofuran were mixed thoroughly and sonicated for 10 min. Then, 7.61 g of precursor VBGE was added, and the reaction was stirred at 25 °C for 12 h. After the reaction was complete, an appropriate amount of water was added to quench the reaction. The organic phase was extracted with dichloromethane and washed with water to remove the solvent, yielding the crosslinking agent S-VBGE.

[0030] Example 2: A method for preparing a fatigue-resistant recyclable dual dynamic elastomer (ENR-SV5) includes the following steps: 100 g of epoxidized natural rubber (ENR-25) was plasticized on a two-roll mill at 40 °C. 5 g of ZnO, 2 g of stearic acid, 1 g of sulfur, 0.75 g of accelerator CZ, 1 g of antioxidant 1010, and 1 g of antioxidant 168 were added sequentially and mixed thoroughly. Then, 5 g of the S-VBGE crosslinking agent prepared in Example 1 was added for thin-pass processing. After the compound was left to stand at room temperature for 24 hours, it was placed in a mold and hot-pressed at 160 °C and 8 MPa to obtain the dual dynamic elastomer ENR-SV5. The elastomer prepared in Example 2 was subjected to mechanical property testing, and the tensile strength was measured to be approximately 10.1 MPa, and the fracture toughness was approximately 61.6 MJ / m. 3 .

[0031] Example 3: A method for preparing a fatigue-resistant recyclable dual dynamic elastomer (ENR-SV10) includes the following steps: The preparation steps are the same as in Example 2, except that the amount of S-VBGE crosslinking agent added is 10 g.

[0032] The prepared elastomer was subjected to mechanical property testing, and its tensile strength was increased to approximately 12.0 MPa, and its fracture toughness was increased to approximately 70.3 MJ / m. 3 .

[0033] Example 4: A method for preparing a fatigue-resistant, recyclable dual dynamic elastomer (ENR-SV15) includes the following steps: The preparation steps are the same as in Example 2, except that the amount of S-VBGE crosslinking agent added is 15 g.

[0034] The prepared elastomer was subjected to mechanical testing, and the tensile strength was found to be 14.8 MPa, and the fracture toughness was found to be 85 MJ / m. 3 Pure shear fatigue testing shows that its intrinsic fatigue threshold is as high as approximately 318 J / m. 2 .

[0035] Comparative Example 1 (Blank Control without Crosslinking Agent): As a basic comparison, no S-VBGE multifunctional crosslinking agent was added; only pure covalent rubber (ENR-0) was used. Its tensile strength was measured to be only about 9.6 MPa, and its fracture toughness was about 65.8 MJ / m. 3 The fatigue threshold is only 40 J / m 2 about.

[0036] Comparative Example 2 (Conventional Pure Covalent Sulfide System as a Reference): The preparation steps are basically the same as in Example 4, except that S-VBGE crosslinking agent is not added. Instead, the crosslinking density of the rubber compound is kept consistent with that of Example 4 (ENR-SV15) by adjusting the amount of conventional elemental sulfur and accelerator in the formulation (specifically, 1.8 parts sulfur and 1.2 parts accelerator), thus forming a traditional pure covalent network rubber.

[0037] The prepared elastomer was subjected to mechanical testing, and its tensile strength was measured to be approximately 11.5 MPa, and its fracture toughness was approximately 60.2 MJ / m. 3 Pure shear fatigue testing shows that its intrinsic fatigue threshold is only about 52 J / m².

[0038] Comparative Example 3 (Single Dynamic Network Control): The preparation steps are basically the same as in Example 4, except that the S-VBGE crosslinking agent is replaced with an equimolar amount of a conventional bifunctional polysulfide crosslinking agent (such as bis(triethoxysilylpropyl)tetrasulfide, TESPT). This system contains only dynamic polysulfide bonds and lacks polar hydroxyl groups, thus it cannot form a large number of reversible hydrogen bonds as multi-scale sacrificial elements.

[0039] The prepared elastomer was subjected to mechanical testing, and its tensile strength was measured to be approximately 12.8 MPa, and its fracture toughness was approximately 72.5 MJ / m. 3 Pure shear fatigue testing showed that its fatigue threshold was approximately 135 J / m. 2 .

[0040] Comparison conclusion: Based on Example 4 and the comparative examples above, it can be seen that when faced with mechanical stress, the traditional pure covalent network (Comparative Example 2) is prone to irreversible fatigue crack propagation due to the lack of an effective stress dissipation mechanism; while the single dynamic polysulfide bond network (Comparative Example 3) can provide some energy dissipation, but there is a bottleneck in improving fatigue resistance. In contrast, Example 4 of this invention relies on the "dynamic polysulfide bond-reversible hydrogen bond" double sacrifice network constructed in situ by S-VBGE, which can preferentially dissipate energy through large-scale dissociation and recombination of hydrogen bonds, thereby effectively blunting the crack tip before the covalent main chain fractures. Its final fatigue threshold (318 J / m) 2 Compared to conventional pure covalent systems (52 J / m) 2 This represents a nearly 6-fold improvement over a single dynamic network (135 J / m). 2 The improvement was more than doubled, which fully demonstrates the irreplaceable nature of the synergistic effect of the multifunctional groups in the crosslinking agent of this invention and its extremely excellent anti-fatigue effect.

[0041] Example 5: A method for preparing a fatigue-resistant recyclable dual dynamic elastomer (ENR-SV20) includes the following steps: The preparation steps are the same as in Example 2, except that the amount of S-VBGE crosslinking agent added is 20 g.

[0042] Due to the excessively high crosslinking density, the measured tensile strength dropped to approximately 9.7 MPa, and the fracture toughness was approximately 62.5 MJ / m. 3 .

[0043] Example 6: The mechanical remodeling (solid-state recycling) method for dual dynamic elastomers comprises the following steps: The elastomer obtained in Example 4 and which fractured during testing was cut into small pieces and placed in a hot press for mechanical reshaping. The hot pressing conditions were set as follows: temperature 180 ℃, pressure 4 MPa, and time 1 h. After hot pressing, the samples fused into complete sheets, confirming that the dual dynamic elastomer of the present invention can be effectively recycled in solid state. The tensile strength and toughness retention rates after secondary recycling both exceeded 80%.

[0044] The various embodiments in this specification are described in a progressive manner, with each embodiment focusing on its differences from other embodiments. Similar or identical parts between embodiments can be referred to interchangeably. For the apparatus disclosed in the embodiments, since they correspond to the methods disclosed in the embodiments, the description is relatively simple; relevant parts can be referred to the method section.

[0045] The above description of the disclosed embodiments enables those skilled in the art to make or use the invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the invention. Therefore, the invention is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A method for preparing highly fatigue-resistant recyclable epoxidized natural rubber based on a dual dynamic network, characterized in that, Includes the following steps: S1. Synthesis of precursor monomers containing terminal double bonds and epoxy groups: Halogenated aromatic hydrocarbon derivatives and alcohols containing epoxy groups are reacted under the action of a catalyst to obtain precursor monomers; S2. Synthesis of multifunctional crosslinking agent: Elemental sulfur and activator are mixed and activated in an organic solvent, and then the precursor monomer described in step S1 is added to carry out a ring-opening reaction to prepare a multifunctional crosslinking agent; S3. Mixing and construction of dual dynamic networks: Epoxidized natural rubber, rubber compounding agent and the multifunctional crosslinking agent described in step S2 are mixed and then vulcanized in a hot pressing device to obtain the target product.

2. The preparation method according to claim 1, characterized in that, In step S1, the haloaromatic derivative is 4-vinylbenzyl chloride, the epoxide-containing alcohol compound is glycidyl ether, and the catalyst is 1,5,7-triazidobicyclo[4.4.0]dec-5-ene.

3. The preparation method according to claim 1, characterized in that, In step S1, the molar ratio of the haloaromatic derivative, the epoxide-containing alcohol compound, and the catalyst is 1:(1.5~2.5):(0.01~0.05).

4. The preparation method according to claim 1, characterized in that, In step S2, the activator is sodium sulfide nonahydrate, the organic solvent is tetrahydrofuran, and the molar ratio of elemental sulfur (based on sulfur molecules), activator and precursor monomer is (2.0 ~ 4.0): (0.2 ~ 0.6):

1.

5. The preparation method according to claim 1, characterized in that, In step S2: the mixing and activation method is ultrasonic treatment or mechanical stirring for 5 to 30 minutes; the conditions for the ring-opening reaction are: stirring reaction at 15 to 40 °C for 6 to 24 hours.

6. The preparation method according to claim 1, characterized in that, In step S3, the formulation components to be mixed, by mass parts, include: Epoxidized natural rubber: 100 parts; Multifunctional crosslinking agent: 5 ~ 25 parts; Rubber compounding agent: 5 to 15 parts.

7. The preparation method according to claim 5, characterized in that, The epoxy degree of the epoxidized natural rubber is 10~50 mol%; the rubber compounding agent is a composition of zinc oxide, stearic acid, sulfur, accelerator and antioxidant mixed in any proportion.

8. The preparation method according to claim 1, characterized in that, In step S3, the vulcanization molding conditions are: temperature 140 ~ 180℃, pressure 5 ~ 15 MPa, and time is the corresponding vulcanization time of the rubber compound.

9. A highly fatigue-resistant recyclable epoxidized natural rubber based on a dual dynamic network, characterized in that, It is prepared by any one of claims 1-8.

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