A high-bio-based adhesive resin based on one-pot method, and a preparation method and application thereof

Abstract

The application discloses a kind of high bio-based adhesive resin based on one-pot method and its preparation method and application.The resin is lignin as raw material, under sulfuric acid-hydrobromic acid synergistic catalytic system, demethylation phenolization modification is carried out again with formaldehyde polycondensation and is obtained;Phenolic agent is selected from any one or two compound of phenol, o-dihydroxybenzene, m-cresol, cashew nut shell oil, tannin.This application adopts one-pot method process, without intermediate product separation and purification, simple operation, low production cost.The obtained resin does not contain resorcinol at all, and the bio-based content can be up to 60% or more, which can replace traditional resorcinol-formaldehyde resin in equal mass parts.According to GB / T16586-2014 standard test, the steel wire cord static pull-out force is not less than resorcinol-formaldehyde resin, and the adhesion retention rate after 100℃×96h thermal oxidative aging is better than or not less than traditional resin, especially suitable for tire, conveyor belt, steel wire reinforced rubber hose and other rubber products framework material bonding.

Description

Technical Field

[0001] This invention belongs to the field of rubber processing aids and polymer materials technology, specifically relating to a highly bio-based adhesive resin based on a one-pot process, its preparation method, and its application. Background Technology

[0002] In reinforcing rubber products such as tires, conveyor belts, and steel wire reinforced hoses, the steel wire cord serves as the skeleton support structure, and its adhesion performance to the rubber directly determines the product's service life and safety. Industrially, the resorcinol-formaldehyde-fumed silica (rh-formaldehyde-fumed silica) adhesive reinforcement system is widely used. In this system, resorcinol-formaldehyde resin acts as a methylene acceptor, undergoing in-situ condensation with formaldehyde released from the decomposition of the methylene donor during vulcanization. This forms a dense three-dimensional network structure, achieving a strong bond between the rubber and the steel wire.

[0003] However, traditional resorcinol has significant drawbacks: first, it is highly toxic and easily volatilizes during high-temperature rubber mixing, producing irritating and toxic fumes that seriously endanger the health of operators; second, it relies on petrochemical raw materials and has zero bio-based content, which does not meet the requirements of dual-carbon development; and third, it has low adhesion retention after thermo-oxidative aging, making it difficult to meet the long-term use requirements of high-end rubber products.

[0004] Lignin is the second most abundant natural aromatic polymer in the world, with wide availability and low price, and has great potential to replace phenol in the synthesis of phenolic resins. However, the natural lignin molecule contains a large number of methoxy groups, resulting in large steric hindrance and few reactive sites. When used directly in resin synthesis, it has low cross-linking density and poor adhesive properties. In existing technologies, the phenolic modification of lignin usually requires high temperature and pressure, strong acids and bases, or expensive ionic liquid catalysis. Furthermore, the modified lignin needs to undergo complex separation and purification before it can be used in subsequent polycondensation reactions. The process is cumbersome, costly, and difficult to industrialize.

[0005] Cashew nut shell oil is a renewable natural phenolic compound. The long aliphatic hydrocarbon side chains in its molecular structure can significantly improve the compatibility of resins with non-polar rubbers, but it has low reactivity and insufficient initial adhesive strength when used alone. Current technology has not systematically studied the synergistic modification effect of lignin and different phenols, nor has it developed a bio-based adhesive resin that can simultaneously meet the requirements of environmental protection, adhesive performance, and industrialization. Summary of the Invention

[0006] The first technical problem to be solved by the present invention is to provide a high bio-based adhesive resin based on one-pot process, so as to solve the defects of the existing technology, such as the high toxicity of traditional resorcinol-formaldehyde resin, dependence on petrochemical resources and low adhesion retention rate after aging, and the harsh conditions, complicated separation and inability to perform one-pot in-situ polycondensation of existing lignin phenolic modification process.

[0007] The second technical problem to be solved by the present invention is to provide a method for preparing the above-mentioned highly bio-based adhesive resin.

[0008] The third technical problem to be solved by the present invention is to provide the application of the above-mentioned highly bio-based adhesive resin.

[0009] To solve the above-mentioned technical problems, the present invention adopts the following technical solution:

[0010] A method for preparing a highly bio-based adhesive resin based on a one-pot process includes the following steps: (1) Lignin and phenolic agent are subjected to demethylation and phenolization reaction under the action of acid catalyst to obtain modified lignin; (2) Formaldehyde is added to the modified lignin obtained in step (1) to carry out a condensation reaction. After the reaction is completed, it is post-treated to obtain the final product.

[0011] In some embodiments, in step (1), the lignin is any one or a combination of enzymatically hydrolyzed lignin, sulfate lignin, alkali lignin, or lignin sulfonate; and / or, the phenolic agent is any one or a combination of two of phenol, catechol, m-cresol, cashew nut shell oil, or tannin.

[0012] In some embodiments, in step (1), the acidic catalyst is a combination of sulfuric acid and hydrobromic acid; and / or, the concentration of the sulfuric acid is 40-55 wt%; and / or, the sulfuric acid accounts for 1.0-1.4 wt% of the phenolic agent; and / or, the hydrobromic acid accounts for 25-32 wt% of the lignin; and / or, the mass ratio of the lignin to the phenolic agent is 1-3:13, preferably 3:13; and / or, the demethylation phenolization reaction is carried out at a temperature of 95-105°C for a time of 3.5-4.5 h.

[0013] In some embodiments, in step (2), the formaldehyde is an aqueous formaldehyde solution with a concentration of 37-40 wt%; and / or, the mass ratio of the phenolic agent to the formaldehyde is 2-3:1; and / or, the polycondensation reaction is carried out at a temperature of 85-95°C for 2.5-3.5 h; and / or, the post-treatment is to heat to 155-165°C for dehydration for 0.5-1.5 h, followed by vacuum distillation at 155-165°C and -0.08-0.095 MPa for 1.5-2.5 h.

[0014] The highly bio-based adhesive resin prepared by the above method is also within the scope of protection of this invention.

[0015] This invention also protects the use of the above-mentioned highly bio-based adhesive resin in the preparation of rubber products.

[0016] In some embodiments, the rubber product is a tire, a conveyor belt, or a steel wire reinforced hose.

[0017] A rubber composition comprising the following components in parts by weight: 100 parts of rubber component, 1.5 to 5 parts of the high bio-based adhesive resin of claim 5, and 3 to 10 parts of vulcanizing agent.

[0018] In some embodiments, the rubber composition further includes 3-10 parts of methylene donor, 40-70 parts of reinforcing agent, 0.5-1.5 parts of adhesion promoter, 1-5 parts of antioxidant, 5-12 parts of vulcanization activator, and 0.5-2 parts of vulcanization accelerator.

[0019] In some embodiments, the rubber component is selected from at least one of natural rubber and synthetic rubber; and / or, the vulcanizing agent is insoluble sulfur; and / or, the methylene donor is any one of hexamethylenetetramine, hexamethoxymethylmelamine, or hexamethoxymethylmelamine; and / or, the reinforcing agent is carbon black; and / or, the adhesion promoter is cobalt borylate; and / or, the antioxidant is a combination of antioxidant 4020 and antioxidant RD; and / or, the vulcanization activator is zinc oxide; and / or, the vulcanization accelerator is N,N-dicyclohexyl-2-benzothiazole sulfenamide.

[0020] The core principle of this invention lies in the following: sulfuric acid catalyzes the phenolic modification and phenolic condensation reaction of lignin, and hydrobromic acid specifically breaks the methoxy groups in the lignin molecule. The synergistic effect of the two can efficiently activate lignin at 100°C and normal pressure, exposing more phenolic hydroxyl reaction sites. At the same time, the combination of different phenols can achieve structural complementarity: the long side chain of cashew nut shell oil improves the compatibility of resin and rubber, the bisphenol hydroxyl group of catechol increases the initial adhesive strength, the methyl side chain of m-cresol optimizes the processing fluidity, and the polyphenolic structure of tannin enhances thermal stability.

[0021] Beneficial effects:

[0022] (1) Excellent environmental performance: It does not use toxic resorcinol at all, eliminating the problem of toxic fumes in the rubber refining process; it uses a large amount of lignin and cashew nut shell oil, two bio-based raw materials, and the bio-based content of the resin can reach more than 60%, which meets the requirements of green chemical industry and dual carbon development.

[0023] (2) Simple and efficient process: The one-pot process is adopted to complete the demethylation and phenolation of lignin and the condensation of formaldehyde in the same reactor. There is no need to separate and purify intermediate products. The operation is simple, the production efficiency is high, the production cost is low, and it is suitable for large-scale industrial production.

[0024] (3) Excellent performance: The obtained resin can directly replace the traditional resorcinol formaldehyde resin in equal parts by mass. The initial wire pull-out force is comparable to that of the traditional resin. The adhesion retention rate after thermo-oxidative aging is significantly better than that of the traditional resin, which can effectively extend the service life of rubber products.

[0025] (4) Wide applicability: By selecting different combinations and ratios of phenolic agents, the softening point, processing fluidity and adhesive properties of the resin can be flexibly controlled to meet the needs of different rubber products. Attached Figure Description

[0027] The present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments, and the advantages of the present invention in the above and / or other aspects will become clearer.

[0028] Figure 1 This invention relates to the hydrobromic acid-sulfuric acid catalyzed lignin phenolation reaction mechanism;

[0029] Figure 2 The images show the infrared spectra (FT-IR) of the synthetic resins used in the embodiments and comparative examples of this invention. Detailed Implementation

[0031] The present invention can be better understood from the following embodiments. However, those skilled in the art will readily understand that the descriptions in the embodiments are for illustrative purposes only and should not, and will not, limit the invention as detailed in the claims.

[0032] Unless otherwise specified, the experimental methods described in the following examples are conventional methods; unless otherwise specified, the reagents and materials are commercially available.

[0033] All examples used uniform baseline process parameters: demethylation reaction temperature 100℃, time 4h; polycondensation reaction temperature 90℃, time 3h; atmospheric pressure dehydration temperature 160℃, time 1h; vacuum distillation temperature 160℃, vacuum degree -0.09MPa, time 2h; catalyst dosage: 50wt% sulfuric acid was 1.2wt% of the total mass of the phenolic agent, and hydrobromic acid was 28.75wt% of the lignin content. All examples and comparative examples used uniform rubber formulations and mixing processes for performance testing.

[0034] Example 1

[0035] In a reactor equipped with a mechanical stirrer, temperature control device, reflux condenser, and constant-pressure dropping funnel, 30g of lignin (from Longli Biotechnology Co., Ltd., using enzymatic hydrolysis of corn stalks), 65g of phenol, and 65g of cashew nut shell oil (1 mol cashew nut shell oil equals 1 mol phenolic hydroxyl groups) were added sequentially. Then, the catalyst (sulfuric acid and hydrobromic acid) in the above-mentioned formulation was slowly added dropwise, and the temperature was raised to 100℃ and maintained for 4 hours to carry out the demethylation reaction. Next, the temperature was lowered to 90℃, and 51.54g of 37wt% formaldehyde aqueous solution was added dropwise, and the reaction was maintained for 3 hours to carry out the polycondensation reaction. After the reaction was completed, the temperature was raised to 160℃ and dehydrated under normal pressure for 1 hour, followed by vacuum distillation for 2 hours. Finally, the product was cooled and discharged to obtain bio-based phenolic lignin resin.

[0036] Example 2

[0037] Formula: 30g lignin, 65g catechol, 65g cashew nut shell oil. The synthesis process is exactly the same as in Example 1.

[0038] Example 3

[0039] Formula: 30g lignin, 65g m-cresol, 65g cashew nut shell oil. The synthesis process is exactly the same as in Example 1.

[0040] Example 4

[0041] Formula: 30g lignin, 65g tannin, 65g cashew nut shell oil. The synthesis process is exactly the same as in Example 1.

[0042] Example 5

[0043] Formula: 30g lignin, 65g phenol, 65g catechol. The synthesis process is exactly the same as in Example 1.

[0044] Example 6

[0045] Formula: 30g lignin, 65g phenol, 65g m-cresol. The synthesis process is exactly the same as in Example 1.

[0046] Example 7

[0047] Formula: 30g lignin, 65g phenol, 65g tannin. The synthesis process is exactly the same as in Example 1.

[0048] Example 8

[0049] Formula: 30g lignin, 65g catechol, 65g m-cresol. The synthesis process is exactly the same as in Example 1.

[0050] Example 9

[0051] Formula: 30g lignin, 65g catechol, 65g tannin. The synthesis process is exactly the same as in Example 1.

[0052] Example 10

[0053] Formula: 30g lignin, 65g m-cresol, 65g tannin. The synthesis process is exactly the same as in Example 1.

[0054] Example 11

[0055] Formula: 30g lignin, 75g phenol, 55g cashew nut shell oil. The synthesis process is exactly the same as in Example 1.

[0056] Example 12

[0057] Formula: 30g lignin, 55g phenol, 75g cashew nut shell oil. The synthesis process is exactly the same as in Example 1.

[0058] Example 13

[0059] Formula: 15g lignin, 65g phenol, 65g cashew nut shell oil. The synthesis process is exactly the same as in Example 1.

[0060] Example 14

[0061] Formula: 25g lignin, 65g phenol, 65g cashew nut shell oil. The synthesis process is exactly the same as in Example 1.

[0062] Example 15

[0063] Formula: 30g sulfate lignin (Shandong Sun Paper Industry, hardwood sulfate lignin), 65g phenol, 65g cashew nut shell oil. The synthesis process is exactly the same as in Example 1.

[0064] Comparative Example 1

[0065] Formula: 130g phenol, 30g lignin. The synthesis process is exactly the same as in Example 1.

[0066] Comparative Example 2

[0067] Preparation of demethylated lignin: Add 50g of lignin to a reaction vessel, add 100mL of pure water, and add 14.38g of hydrobromic acid (40%) (28.75% of the lignin content). React at 90℃ for 4h. Filter and wash the lignin filter cake with water until the pH of the filtrate is neutral. Dry under vacuum at 50℃ for later use.

[0068] Formula: 30g demethylated lignin, 65g phenol, 65g cashew nut shell oil. The synthesis process is exactly the same as in Example 1.

[0069] Comparative Example 3

[0070] Commercially available resorcinol formaldehyde resin, purchased from Shandong Yanggu Huatai Chemical Co., Ltd., product number: ML-RF-30.

[0071] Performance testing

[0072] Figure 1 This is a schematic diagram of the phenolation and demethylation mechanism. Under acidic conditions, the α-OH group of lignin dehydrates and leaves, forming a carbocation. This structure forms an enol ether structure and the β-O-4 group breaks the γ-OH group to form a Hibber ketone structure. Phenols then undergo nucleophilic substitution or nucleophilic addition reactions (phenolation) with this generated structure. During this process, the lignin methoxy group undergoes demethylation under the action of hydrobromic acid to form a phenolic hydroxyl group.

[0073] Figure 2 The infrared spectra of the synthetic resins in Example 1 and Comparative Example 1 are shown. Cashew nut shell oil contains long-chain alkyl side chains (C15 unsaturated hydrocarbon chains), which are retained during the polycondensation reaction, providing a large number of methylene and methyl groups, thus exhibiting high activity at 2800-3000 cm⁻¹. -1 The region exhibits strong absorption. The red line is at 1600 cm. -1 The strong and sharp absorption in the vicinity indicates that the cashew nut shell oil system retains a significant portion of its aromatic structure. (1200 cm) -1 Region: The absorption of the CO stretching vibration (phenolic hydroxyl group) red line is stronger, further confirming that the cashew nut shell oil system has a high content of phenolic hydroxyl groups.

[0074] (2) The physicochemical properties, softening point and free phenol content of the resin samples prepared in Examples 1-15 and Comparative Examples 1-3 were determined according to relevant standards (Table 1). The softening point and free phenol content of the resins are in line with industry standards.

[0075] Table 1. Physicochemical properties of synthetic resins from the examples and comparative examples.

[0076]

[0077] (3) Application test of synthetic resin in tire rubber products

[0078] Tire steel wire bonding rubber test pieces were prepared according to the following rubber compounding formula (Table 2) and mixing process (Table 3), and the practical application performance of the bonding resins of Examples 1-15 and Comparative Examples 1-3 was evaluated.

[0079] Table 2: Rubber Mixture Formula for Tire Steel Wire Adhesive

[0080]

[0081] Table 3: Two-stage mixing process and method using an internal mixer

[0082]

[0083] The vulcanization characteristics were determined using a high-speed iron vulcanization apparatus (150℃). Subsequently, vulcanization was performed to prepare samples, and wire pull-out tests (including before and after aging) were conducted according to GB / T16586-2014 standard. The data of the modified vulcanized rubber composition are shown in Table 4.

[0084] Table 4: Comparison of Mechanical and Adhesive Properties of Rubber Compounds

[0085]

[0086] (1) All pairwise combinations meet industrial requirements: The resins prepared by pairwise combinations of 15 phenols have a steel wire rubber coverage of 100%, an initial pull-out force of not less than 627N, and an adhesion retention rate of not less than 69.1%, which fully meet the adhesion performance requirements of the rubber industry.

[0087] (2) Bio-based combinations have outstanding aging resistance: The four bio-based combinations containing cashew shell oil (Examples 1-4) all have an adhesion retention rate of over 70%, with Example 4 (tannin + cashew shell oil) reaching 76.8%, which is 6.9% higher than Comparative Example 1. This proves that the long hydrophobic side chains of cashew shell oil can effectively block the penetration of water and oxygen, and significantly improve the thermo-oxidative stability of the resin.

[0088] (3) The performance of different combinations is significantly different: the combination containing catechol (Examples 2, 5, 8, 9) has the highest initial adhesive strength and the shortest positive vulcanization time; the combination containing m-cresol (Examples 3, 6, 8, 10) has the longest scorch time and the best processing safety; the combination containing tannin (Examples 4, 7, 9, 10) has the best aging resistance and can be flexibly selected according to different application scenarios.

[0089] (4) The ratio and lignin content can be flexibly adjusted: As the proportion of cashew shell oil increases (Example 11→1→12), the resin bio-based content and adhesion retention rate gradually increase; As the amount of lignin added increases (Example 13→14→1), the bio-based content increases synchronously, and the performance does not decrease significantly.

[0090] (5) Compared with Comparative Example 2 (stepwise method), the resin synthesized by the one-pot method in Example 1 has no effect on the rubber properties and has an advantage in adhesion.

[0091] (6) Compared with Comparative Example 3, the resin obtained in Example 1 of the present invention can directly replace the traditional resorcinol formaldehyde resin in equal parts by mass. The initial wire pull-out force is comparable to that of the traditional resin, but the adhesion retention rate after thermo-oxidative aging is significantly better than that of the traditional resin, indicating that it has better resistance to thermo-oxidative aging and can effectively extend the service life of rubber products.

[0092] This invention employs a sulfuric acid-hydrobromic acid synergistic catalytic system to achieve efficient demethylation and phenolization of lignin under mild conditions, followed by one-pot polycondensation with formaldehyde. It is completely free of resorcinol, has a high bio-based content, and can directly replace traditional resorcinol-formaldehyde resin. Furthermore, it exhibits excellent adhesion and aging resistance.

[0093] This invention provides a one-pot method for preparing and applying a highly bio-based adhesive resin. Many methods and approaches exist for implementing this technical solution; the above description is merely a preferred embodiment. It should be noted that those skilled in the art can make various improvements and modifications without departing from the principles of this invention, and these improvements and modifications should also be considered within the scope of protection of this invention. All components not explicitly stated in this embodiment can be implemented using existing technologies.

Claims

1. A method for preparing a highly bio-based adhesive resin based on a one-pot process, characterized in that, Includes the following steps: (1) Lignin and phenolic agent are subjected to demethylation and phenolization reaction under the action of acid catalyst to obtain modified lignin; (2) Formaldehyde is added to the modified lignin obtained in step (1) to carry out a polycondensation reaction. After the reaction is completed, it is post-treated to obtain the final product.

2. The preparation method according to claim 1, characterized in that, In step (1), the lignin is any one or a combination of enzymatically hydrolyzed lignin, sulfate lignin, alkali lignin, or lignin sulfonate; and / or, the phenolic agent is any one or a combination of two of phenol, catechol, m-cresol, cashew nut shell oil, or tannin.

3. The preparation method according to claim 1, characterized in that, In step (1), the acidic catalyst is a combination of sulfuric acid and hydrobromic acid; and / or, the concentration of the sulfuric acid is 40~55wt%; and / or, the sulfuric acid accounts for 1.0~1.4wt% of the phenolic agent; and / or, the hydrobromic acid accounts for 25~32wt% of the lignin; and / or, the mass ratio of the lignin to the phenolic agent is 1~3:13; and / or, the demethylation phenolization reaction is carried out at a temperature of 95~105℃ for a time of 3.5~4.5h.

4. The preparation method according to claim 1, characterized in that, In step (2), the formaldehyde is an aqueous solution of formaldehyde with a concentration of 37-40 wt%; and / or, the mass ratio of the phenolic agent to the formaldehyde is 2-3:1; and / or, the polycondensation reaction is carried out at a temperature of 85-95℃ for 2.5-3.5 hours; and / or, the post-treatment is to heat to 155-165℃ for dehydration for 0.5-1.5 hours, followed by vacuum distillation at 155-165℃ and -0.08-0.095 MPa for 1.5-2.5 hours.

5. The highly bio-based adhesive resin prepared by any one of the preparation methods of claims 1 to 4.

6. The use of the highly bio-based adhesive resin according to claim 5 in the preparation of rubber products.

7. The application according to claim 6, characterized in that, The rubber products are tires, conveyor belts, or steel wire reinforced rubber hoses.

8. A rubber composition, characterized in that, The product comprises the following components in parts by weight: 100 parts of rubber component, 1.5 to 5 parts of the high bio-based adhesive resin as described in claim 5, and 3 to 10 parts of vulcanizing agent.

9. The rubber composition according to claim 8, characterized in that, It also includes 3-10 parts of methylene donor, 40-70 parts of reinforcing agent, 0.5-1.5 parts of adhesion promoter, 1-5 parts of antioxidant, 5-12 parts of vulcanization activator, and 0.5-2 parts of vulcanization accelerator.

10. The rubber composition according to claim 8, characterized in that, The rubber component is selected from at least one of natural rubber and synthetic rubber; and / or, the vulcanizing agent is insoluble sulfur; and / or, the methylene donor is any one of hexamethylenetetramine, hexamethoxymethylmelamine, or hexamethoxymethylmelamine; and / or, the reinforcing agent is carbon black; and / or, the adhesion promoter is cobalt borate; and / or, the antioxidant is a combination of antioxidant 4020 and antioxidant RD; and / or, the vulcanization activator is zinc oxide; and / or, the vulcanization accelerator is N,N-dicyclohexyl-2-benzothiazole sulfenamide.

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