Formaldehyde-free cellulose composite bio-based rubber adhesive and preparation method thereof

Abstract

The invention discloses a formaldehyde-free cellulose composite bio-based rubber adhesive and a preparation method thereof, the formaldehyde-free cellulose composite bio-based rubber adhesive comprises the following raw material components by weight: 30-50 parts of composite tackifying resin; 10 to 20 parts of modified nano microcrystalline cellulose; 5 to 15 parts of a dibutyl itaconate-levulinic acid ester copolymer; 1-5 parts of a vulcanization active auxiliary agent; 0.5 to 3 parts of a bio-based antioxidant; 30 to 60 parts of a mixed solvent of D-limonene and ethyl acetate; the composite tackifying resin is prepared from dehydroabietic acid type rosin resin, epoxidized cardanol and a bio-based cross-linking agent through a reaction, and the bio-based cross-linking agent is furfural; the modified nano microcrystalline cellulose is obtained by performing esterification modification on the modified nano microcrystalline cellulose by dodecyl succinic anhydride; according to the invention, the common performance bottlenecks of low bonding strength, poor water resistance, easy aging, easy blooming and the like of a bio-based adhesive are solved.

Description

Technical Field

[0001] This invention relates to the field of rubber adhesive preparation technology, specifically to an aldehyde-free cellulose composite bio-based rubber adhesive and its preparation method. Background Technology

[0002] In the rubber industry, adhesives are key additives that ensure a strong bond between elastic rubber and reinforcing materials such as fibers or metals. Their performance directly affects the structural safety and service life of composite products such as tires and conveyor belts. With increasingly stringent global environmental regulations and the growing consensus on green and low-carbon development, the development of high-performance bio-based rubber adhesives that can replace traditional petroleum-based products has become an important direction for the industry. This is especially true for the new energy vehicle industry, which needs to meet low VOC and low odor requirements; such environmentally friendly materials have an urgent market demand.

[0003] In existing technologies, the bonding between rubber and reinforcing materials largely relies on petroleum-based adhesive systems, such as resorcinol-formaldehyde resin. While these systems offer good initial adhesion, they suffer from drawbacks including non-renewable raw materials, high volatile organic compound emissions during production, and the potential for residual formaldehyde and other toxic substances in the finished product. To address these issues, research has shifted towards developing adhesives using biomass such as natural rubber, vegetable oils, lignin, and starch as raw materials. Performance is being enhanced through methods such as nanofiller composites and bio-based additive formulations, aiming to improve the product's environmental compatibility while maintaining its adhesive properties.

[0004] However, existing bio-based adhesive technologies still face two key technical challenges that have not been adequately addressed. Firstly, due to their high polarity and dense structure, bio-based components exhibit poor compatibility with hydrophobic rubber matrices, resulting in weak interfacial bonding and difficulty maintaining sufficient adhesive strength and durability under humid heat aging or dynamic fatigue conditions. Secondly, small-molecule bio-based adhesive components are prone to migration and precipitation within rubber systems, leading not only to the loss of effective adhesive components and performance degradation but also to blooming on the product surface, affecting product appearance and subsequent processing, thus hindering their large-scale application in high-performance rubber products. Summary of the Invention

[0005] The existing technology has the following problems: existing bio-based rubber adhesives have low bonding strength, insufficient durability, and performance degradation and surface blooming caused by small molecule migration. In order to address the above technical problems, the present invention provides an aldehyde-free cellulose composite bio-based rubber adhesive and its preparation method.

[0006] The technical solution of this invention is: a formaldehyde-free cellulose composite bio-based rubber adhesive, wherein the raw material components, by weight, include: 30-50 parts of composite tackifying resin; 10-20 parts of modified nanocrystalline cellulose; 5-15 parts of dibutyl itaconic acid-levulinate copolymer; 1-5 parts of vulcanization activator; 0.5-3 parts of bio-based antioxidant; 30-60 parts of a mixed solvent of D-limonene and ethyl acetate; The composite tackifying resin is formed by reacting dehydroabsic acid type rosin resin, epoxidized cashew phenol, and a bio-based crosslinking agent, wherein the bio-based crosslinking agent is furfural; the modified nanocrystalline cellulose is obtained by esterification modification of dodecyl succinic anhydride. The preparation method of the itaconic acid dibutyl ester-levulinate copolymer is as follows: itaconic acid dibutyl ester and levulinate monomers are added at a molar ratio of 1:0.5-2, and azobisisobutyronitrile is used as the initiator. The amount of initiator is 0.5-1% of the total mass of the two monomers. Polymerization is carried out at 70-80℃ for 4-6 h. After precipitation and purification, a copolymer with a number average molecular weight of 3000-8000 is obtained.

[0007] Description: The composite tackifying resin serves as the adhesive matrix, providing high initial tack and cohesive strength; modified nanocrystalline cellulose acts as a reinforcing skeleton, significantly improving the mechanical properties and water resistance of the adhesive layer; dibutyl itaconic acid-acetylacetate copolymer, as a reactive compatibilizer, effectively improves the interfacial compatibility between the bio-based polar components and the rubber matrix; vulcanization activators ensure the synchronization of the adhesive and rubber vulcanization processes; the bio-based antioxidant compound provides long-lasting protection against heat and oxygen aging; and the mixed solvent of D-limonene and ethyl acetate further enhances the system's environmental friendliness while ensuring solubility. Through precise formulation and optimized processes, the synergistic effects of these components achieve a breakthrough in the overall performance of the adhesive.

[0008] Furthermore, in the composite tackifying resin, the weight ratio of dehydroabsic acid type rosin resin, epoxidized cashew phenol, and bio-based crosslinking agent is 1-2:1:0.05-0.1. The reaction of the dehydroabsic acid type rosin resin, epoxidized cashew phenol, and bio-based crosslinking agent is carried out in a microwave reactor, and a catalyst is added during the reaction. The catalyst is p-toluenesulfonic acid, and the amount of catalyst added is 0.1-0.3% of the total mass of dehydroabsic acid type rosin resin, epoxidized cashew phenol, and furfural. The microwave power is 300-500W, the reaction temperature is 140-160℃, and the reaction time is 1-2 h.

[0009] Note: The weight ratios described allow for precise control of the rigidity of dehydroabsic acid-type rosin resin, the flexibility of epoxidized cashew phenol, and the crosslinking density of furfural, resulting in a resin that combines high initial tack with toughness. The combination of p-toluenesulfonic acid catalysis and microwave reaction increases the polycondensation efficiency by over 40%, produces a more uniform molecular weight distribution, stabilizes the softening point at 80-100℃, and significantly enhances interfacial compatibility with rubber.

[0010] Further, the preparation method of the modified nanocrystalline cellulose is as follows: Microcrystalline cellulose and water are mixed at a mass ratio of 1:10-15, and cellulase is added at 0.5-1% of the mass of the microcrystalline cellulose. Enzymatic hydrolysis is performed at a microwave power of 200-400W and a temperature of 50-60℃ for 30-60 minutes. After the enzymatic hydrolysis reaction, the system is heated to 85-95℃ and kept at that temperature for 15-20 minutes to inactivate the cellulase at high temperature. After cooling to room temperature, the cellulose is then removed by filtration and centrifugation. The cellulose solid was separated and thoroughly washed with deionized water until the pH was neutral. It was then dried at 60-80℃ to constant weight to obtain pretreated microcrystalline cellulose. The pretreated microcrystalline cellulose was then dispersed in anhydrous pyridine at a mass ratio of 1:5-10. The temperature was then raised to 60-90℃, and dodecyl succinic anhydride was added dropwise with stirring at a weight ratio of 1:0.3-0.6. The reaction was maintained at this temperature for 1-3 hours. After the reaction, pyridine was removed by vacuum distillation, and the resulting solid product was redispersed in deionized water. The product was then subjected to nano-sizing using a high-pressure homogenizer at 800-1200 bar for 5-10 cycles to obtain a stable aqueous dispersion of nano-cellulose. This dispersion was then spray-dried to obtain powdered modified nanocrystalline cellulose. The final product, nanocrystalline cellulose, had a particle size distribution of 100-300 nanometers.

[0011] Note: An esterification ratio of 1:0.3-0.6 between microcrystalline cellulose and dodecyl succinic anhydride can introduce an appropriate amount of hydrophobic alkyl chains into the cellulose chain, increasing its contact angle from 40° to 110° and reducing the interfacial tension with rubber by 50%. Combined with high-pressure homogenization and nano-sizing, fibers with a particle size of 100-300 nanometers and a specific surface area of ​​200-400 m² can be obtained. 2 / g, forming a three-dimensional network structure in the rubber, which increases the bonding strength by 30-50%.

[0012] Furthermore, the spray dryer has an inlet temperature of 150-180℃, an outlet temperature of 70-90℃, a feed rate of 5-10 mL / min, and an atomization pressure of 0.3-0.5 MPa.

[0013] Note: The combination of an inlet temperature of 150-180℃ and an atomization pressure of 0.3-0.5 MPa allows the nanocellulose droplets to dry and solidify instantly, preventing the decomposition of heat-sensitive ester bonds.

[0014] Furthermore, in the itaconic acid dibutyl ester-acetylacetate copolymer, the molar ratio of itaconic acid dibutyl ester structural units to acetylacetate structural units is 1:0.5-2, and the number average molecular weight of the copolymer is 3000-8000.

[0015] Note: The molar ratio of dibutyl itaconic acid to acetylpropionate is 1:0.5-2, which can control the polarity and reactivity of the copolymer. Its number-average molecular weight of 3000-8000 allows it to penetrate fiber micropores while preventing migration and precipitation. Its carboxyl groups form ionic bonds with the rubber vulcanization system, resulting in a bond strength retention rate of ≥90% after 1000 hours of damp heat aging.

[0016] Furthermore, the vulcanization activator is a compound of zinc oxide, stearic acid and tetrabenzylthiuram disulfide, with a weight ratio of 2-3:1:0.5; the bio-based antioxidant is a compound of tea polyphenols, vitamin E and hydroxypropylated lignin, with a weight ratio of 1-2:1-2:0.5-1.

[0017] Note: Zinc oxide, stearic acid, and TBzTD are compounded in a ratio of 2-3:1:0.5 to form a ternary activation system of ZnO-zinc stearate-TBzTD, which increases the sulfidation rate by 20%; tea polyphenols, vitamin E, and hydroxypropylated lignin are compounded in a ratio of 1-2:1-2:0.5-1, which improves the product's weather resistance through the synergistic antioxidant effect of phenolic hydroxyl groups and quinone structures.

[0018] Furthermore, in the mixed solvent of D-limonene and ethyl acetate, the volume ratio of D-limonene to ethyl acetate is 1:1-3.

[0019] Note: The volume ratio of D-limonene to ethyl acetate is 1:1-3. By utilizing the strong permeability of limonene and the rapid volatility of ethyl acetate, the solvent residue is reduced to <50ppm and VOC emissions are reduced to below 40g / L.

[0020] A method for preparing an aldehyde-free cellulose composite bio-based rubber adhesive includes the following steps: S1. Crush the composite tackifying resin to a particle size of 1-5 mm and set aside. S2, Premixed: Add half of the formula amount of the mixed solvent of D-limonene and ethyl acetate to the dissolving vessel. While stirring, add the composite tackifying resin, dibutyl itaconic acid-acetylpropionate copolymer, vulcanization activator and bio-based antioxidant in sequence. Stir and dissolve at 40-60℃ for 0.5-1 h to obtain a uniform component A. Premix the modified nanocrystalline cellulose with the remaining half of the mixed solvent of D-limonene and ethyl acetate. First, disperse it with the assistance of microwave reactor at 200-300W for 5-10 min, and then disperse it with ultrasonic cell disruptor at a frequency of 25-35kHz and a power of 500-800W for 10-20 min to obtain a uniform component B dispersion. S3. Finished Product Preparation: At a high speed of 800-1200 rpm, the dispersion of component B obtained in S2 was slowly added to component A. After the addition was completed, the speed was increased to 1500-2000 rpm and high-speed dispersion was continued for 30-60 min until the system was uniform and stable. After filtration, formaldehyde-free cellulose composite bio-based rubber adhesive was obtained. The method of using the formaldehyde-free cellulose composite bio-based rubber adhesive is as follows: Apply the degassed formaldehyde-free cellulose composite bio-based rubber adhesive at a concentration of 150-250 g / m³. 2 Apply the coating evenly or impregnate it onto the surface of the material skeleton to be bonded. Then, treat it in an oven at 80-100℃ for 2-5 minutes to completely remove the mixed solvent of D-limonene and ethyl acetate, forming a dry adhesive pre-cured film. Precisely bond the treated material skeleton to the uncured raw rubber blank, such as natural rubber or styrene-butadiene rubber blank, in a mold. Then, place the entire composite in a vulcanizing machine and vulcanize it for 15-30 minutes at a high temperature of 140-160℃ and a pressure of 10-15 MPa to complete the bonding.

[0021] Description: This technical solution utilizes bio-based raw materials such as dehydroabsic acid rosin resin and epoxidized cashew phenol, along with a microwave-assisted synthesis process, combined with enzymatically hydrolyzed and esterified nanocellulose. This significantly improves the compatibility and interfacial bonding between the adhesive and the rubber matrix, resulting in bonding strength and resistance to damp heat aging that surpasses traditional petroleum-based products. Simultaneously, the fully bio-based formulation and formaldehyde-free design ensure VOC emissions ≤50g / L and a biodegradability rate ≥80%, fundamentally solving the high pollution and high toxicity problems of traditional adhesives and achieving a balance between high performance and environmental friendliness. This application method relies on the adhesive's built-in vulcanization active agent, designing an integrated process of low-temperature solvent desolventizing and film formation followed by a single vulcanization step. This eliminates the cumbersome traditional two-step vulcanization process involving additional curing agents, achieving simultaneous and deep bonding with rubber vulcanization. Combined with the reinforcing effect of nanocellulose, this simplifies the process, improves environmental friendliness, and overcomes the technical bottlenecks of low bonding strength and poor durability in traditional bio-based adhesives.

[0022] Furthermore, in S2, the stirring rate when dissolving component A is controlled at 300-500 rpm.

[0023] Note: A stirring rate of 300-500 rpm can produce a laminar and turbulent mixing effect, so that the adhesive with a viscosity of 5000-8000 cP can be uniformly dispersed within 10 minutes, avoiding pre-crosslinking caused by shear heating.

[0024] Further, after S3 is completed, the formaldehyde-free cellulose composite bio-based rubber adhesive is subjected to vacuum degassing treatment under the conditions of vacuum degree -0.08 to -0.095 MPa and degassing time 15-30 min.

[0025] Note: The synergistic effect of the vacuum degree of -0.08 to -0.095 MPa and the degassing time of 15-30 min effectively removes micron-sized air bubbles remaining inside the adhesive, keeping the system density deviation within ±0.02 g / cm³. 3 Within ±5%. This process eliminates interface defects caused by bubble expansion during vulcanization, narrowing the shear strength fluctuation range of the adhesive layer from ±15% to ±5%, while reducing solvent residue and preventing pinholes or fisheyes on the product surface, significantly improving appearance quality and service reliability.

[0026] The beneficial effects of this invention are: This invention fundamentally eliminates the dependence of traditional petroleum-based adhesives, such as resorcinol-formaldehyde systems, on non-renewable resources and the problems of high VOC emissions and toxic and harmful substances such as formaldehyde during their production and use. By using fully bio-based raw materials, such as dehydroabsic acid-type rosin resin, epoxidized cashew phenol, D-limonene solvent, and an optimized formaldehyde-free formula, the product complies with the strictest environmental regulations, significantly increases the bio-based content, has extremely low VOC emissions, and is biodegradable, achieving greening of the entire life cycle from raw materials to waste. Secondly, the solution successfully overcomes the performance bottlenecks of early bio-based adhesives, such as low bonding strength, poor water resistance, and easy aging. The key lies in the innovative microwave-assisted synthesis combined with enzymatic hydrolysis-esterification modification: the composite tackifying resin prepared by the microwave reactor exhibits higher reactivity and uniformity; while the enzymatic activation followed by hydrophobic modification of nanocellulose significantly improves its interfacial compatibility with the hydrophobic rubber matrix. Furthermore, itaconic acid copolymers serve as efficient molecular bridges, collectively constructing a robust resin-cellulose-rubber three-dimensional network structure, thereby endowing the adhesive with excellent bonding strength, superior resistance to damp heat aging, and durability. Finally, by macromolecularizing key functional components such as the tackifying resin, itaconic acid copolymer, and nano-modified cellulose, and employing a bio-based antioxidant compound system, the solution effectively inhibits small molecule migration and blooming phenomena, ensuring long-term product performance stability and appearance quality. This solution not only achieves a leap in environmental protection attributes, but also meets or even surpasses traditional petroleum-based products in key performance indicators, providing a practical solution for the green and low-carbon transformation of the rubber industry. Detailed Implementation

[0027] To further illustrate the methods and effects of this invention, the technical solution of this invention will be clearly and completely described below in conjunction with experiments.

[0028] Example 1: A formaldehyde-free cellulose composite bio-based rubber adhesive, comprising the following raw material components by weight: 40 parts of composite tackifying resin; 15 parts of modified nanocrystalline cellulose; 10 parts of dibutyl itaconic acid-levulinate copolymer; 3 parts of vulcanization activator; Two portions of bio-based antioxidants; 45 parts of a mixed solvent of D-limonene and ethyl acetate; The composite tackifying resin is formed by reacting dehydroabsic acid type rosin resin, epoxidized cashew phenol, and a bio-based crosslinking agent, wherein the bio-based crosslinking agent is furfural; the modified nanocrystalline cellulose is obtained by esterification modification of dodecyl succinic anhydride; in the composite tackifying resin, the weight ratio of dehydroabsic acid type rosin resin, epoxidized cashew phenol, and bio-based crosslinking agent is 1.5:1:0.07; the reaction of dehydroabsic acid type rosin resin, epoxidized cashew phenol, and bio-based crosslinking agent is carried out in a microwave reactor, and a catalyst is added during the reaction process, wherein the catalyst is p-toluenesulfonic acid, and the amount of catalyst added is 0.2% of the total mass of dehydroabsic acid type rosin resin, epoxidized cashew phenol, and furfural; the microwave power is 400W, the reaction temperature is 150℃, and the reaction time is 1.5 h; The modified nanocrystalline cellulose is prepared by a raw material in which the weight ratio of microcrystalline cellulose to dodecyl succinic anhydride is 1:0.45, and the final product, nanocrystalline cellulose, has a particle size distribution of 150-250 nm. In the itaconic acid dibutyl ester-levulinate copolymer, the molar ratio of itaconic acid dibutyl ester structural units to levulinate structural units is 1:1, and the number-average molecular weight of the copolymer is 5410. The vulcanization activator is a compound of zinc oxide, stearic acid, and tetrabenzyl thiuram disulfide, with a weight ratio of 2.5:1:0.5. The bio-based antioxidant is a compound of tea polyphenols, vitamin E, and hydroxypropylated lignin, with a weight ratio of 1.5:1.5:0.8. In the mixed solvent of D-limonene and ethyl acetate, the volume ratio of D-limonene to ethyl acetate is 1:2. The method for preparing the composite tackifying resin is as follows: the prescribed amount of dehydroabscisic acid type rosin resin is added to a microwave reactor and heated to a molten state at 125°C. Under nitrogen protection, epoxidized cashew phenol, bio-based crosslinking agent and p-toluenesulfonic acid catalyst are added. The microwave power is controlled at 400W, and the reaction is carried out at 150°C and a stirring rate of 300 rpm for 1.5 h to obtain the composite tackifying resin. The modified nanocellulose is prepared as follows: microcrystalline cellulose and water are mixed at a mass ratio of 1:12.5, and cellulase is added at a mass ratio of 0.8% of the microcrystalline cellulose. Enzymatic hydrolysis is performed at 55°C and 300W microwave power for 45 minutes. This step aims to gently disrupt the crystal structure of cellulose and expose more hydroxyl active sites. After the enzymatic hydrolysis reaction, the system is heated to 90°C and held for 18 minutes to inactivate the cellulase at high temperature. After cooling to room temperature, the cellulose solid is separated by filtration and centrifugation, and thoroughly washed with deionized water until the pH is neutral. Then, it is dried at 70°C to constant weight to obtain pretreated microcrystalline cellulose. The pretreated microcrystalline cellulose is then dispersed in anhydrous pyridine at a mass ratio of 1:8. The mixture is then heated to 75°C, and dodecyl succinic anhydride is added dropwise under stirring. The reaction is maintained at this temperature for 2 minutes. h; After the reaction was completed, pyridine was removed by vacuum distillation, and the resulting solid product was washed three times with anhydrous ethanol. It was then filtered until there was no pyridine odor, and the resulting solid product was redispersed in deionized water. It was then subjected to nano-sizing treatment at 1000 bar using a high-pressure homogenizer and cyclically repeated eight times to obtain a stable aqueous dispersion of nanocellulose. The dispersion was then spray-dried to obtain powdered modified nanocrystalline cellulose. The spray drying process had an inlet temperature of 160°C, an outlet temperature of 80°C, a feed rate of 8 mL / min, and an atomization pressure of 0.4 MPa.

[0029] Example 2: This example describes the preparation method of the formaldehyde-free cellulose composite bio-based rubber adhesive of Example 1, including the following steps: S1. Crush the composite tackifying resin to a particle size of 3-4 mm and set aside. S2, Premixed: Half of the formulated amount of a mixed solvent of D-limonene and ethyl acetate was added to a dissolving vessel. Then, under stirring, the composite tackifying resin, dibutyl itaconic acid-acetylpropionate copolymer, vulcanization activator, and bio-based antioxidant were added sequentially. The mixture was stirred and dissolved at 50°C for 0.8 h to obtain a uniform component A. Modified nanocrystalline cellulose was premixed with the remaining half of the D-limonene and ethyl acetate mixed solvent. The mixture was first dispersed using a microwave reactor with 250W assistance for 8 min, and then ultrasonically dispersed for 15 min using an ultrasonic cell disruptor at a frequency of 30kHz and a power of 650W to obtain a uniform component B dispersion. The stirring rate during the dissolution of component A was controlled at 400 rpm. The preparation method of the itaconic acid dibutyl ester-levulinate copolymer is as follows: itaconic acid dibutyl ester and levulinate monomers are added at a molar ratio of 1:1.8, and azobisisobutyronitrile is used as an initiator. The amount of initiator is 0.7% of the total mass of the two monomers. Polymerization is carried out at 75°C for 5 h. After precipitation and purification, itaconic acid dibutyl ester-levulinate copolymer is obtained. S3. Finished Product Preparation: At a high-speed disperser speed of 1000 rpm, the dispersion of component B obtained in S2 was slowly added to component A. After the addition was completed, the speed was increased to 1800 rpm, and high-speed dispersion was continued for 45 min until the system was homogeneous and stable. After filtration, the formaldehyde-free cellulose composite bio-based rubber adhesive was obtained. The formaldehyde-free cellulose composite bio-based rubber adhesive was subjected to vacuum degassing treatment under the conditions of vacuum degree -0.09 MPa and degassing time of 20 min.

[0030] Example 3: This example is basically the same as Example 1, except that, by weight, its raw material components include: 30 parts of composite tackifying resin; 10 parts of modified nanocrystalline cellulose; 5 parts of dibutyl itaconic acid-acetylacetate copolymer; One part of vulcanization activator; 0.5 parts of bio-based antioxidant; 30 parts of a mixed solvent of D-limonene and ethyl acetate; The composite tackifying resin is formed by reacting dehydroabsic acid type rosin resin, epoxidized cashew phenol, and a bio-based crosslinking agent, wherein the bio-based crosslinking agent is furfural; the modified nanocrystalline cellulose is obtained by esterification modification of dodecyl succinic anhydride; in the composite tackifying resin, the weight ratio of dehydroabsic acid type rosin resin, epoxidized cashew phenol, and bio-based crosslinking agent is 1:1:0.05; the reaction of dehydroabsic acid type rosin resin, epoxidized cashew phenol, and bio-based crosslinking agent is carried out in a microwave reactor, and a catalyst is added during the reaction process, wherein the catalyst is p-toluenesulfonic acid, and the amount of catalyst added is 0.1% of the total mass of dehydroabsic acid type rosin resin, epoxidized cashew phenol, and furfural; the microwave power is 300W, the reaction temperature is 140℃, and the reaction time is 1 h; The modified nanocrystalline cellulose is prepared by a raw material in which the weight ratio of microcrystalline cellulose to dodecyl succinic anhydride is 1:0.3, and the final product, nanocrystalline cellulose, has a particle size distribution of 100-200 nm. In the itaconic acid dibutyl ester-levulinate copolymer, the molar ratio of itaconic acid dibutyl ester structural units to levulinate structural units is 1:0.5, and the number-average molecular weight of the copolymer is 3008. The vulcanization activator is a compound of zinc oxide, stearic acid, and tetrabenzyl thiuram disulfide, with a weight ratio of 2:1:0.5. The bio-based antioxidant is a compound of tea polyphenols, vitamin E, and hydroxypropylated lignin, with a weight ratio of 1:1:0.5. In the mixed solvent of D-limonene and ethyl acetate, the volume ratio of D-limonene to ethyl acetate is 1:1. The preparation method of the composite tackifying resin is as follows: the prescribed amount of dehydroabscisic acid type rosin resin is put into a microwave reactor and heated to a molten state at 120°C. Under nitrogen protection, epoxidized cashew phenol, bio-based crosslinking agent and p-toluenesulfonic acid catalyst are added. The microwave power is controlled at 300W and the reaction is carried out at 140°C and a stirring rate of 200 rpm for 1 h to obtain the composite tackifying resin. The modified nanocellulose is prepared as follows: microcrystalline cellulose and water are mixed at a mass ratio of 1:10, and cellulase is added at a mass ratio of 0.5% of the microcrystalline cellulose. Enzymatic hydrolysis is then performed at a microwave power of 200W and a temperature of 50℃ for 30 min. This step aims to gently disrupt the crystal structure of cellulose and expose more hydroxyl active sites. After the enzymatic hydrolysis reaction is completed, the system is heated to 85℃ and held for 15 minutes. Cellulase was inactivated at high temperature for 1 minute. After cooling to room temperature, the cellulose solid was separated by filtration and centrifugation, and washed thoroughly with deionized water until the pH was neutral. Then, it was dried at 60°C to constant weight to obtain pretreated microcrystalline cellulose. The pretreated microcrystalline cellulose was then dispersed in anhydrous pyridine at a mass ratio of 1:5. The temperature was then raised to 60°C, and dodecyl succinic anhydride was added dropwise with stirring. The reaction was maintained at this temperature for 1 hour. After the reaction, pyridine was removed by vacuum distillation. The resulting solid product was washed three times with anhydrous ethanol and filtered until no pyridine odor was detected. The resulting solid product was redispersed in deionized water and nano-sized using a high-pressure homogenizer at 800 bar for 5 cycles to obtain a stable aqueous dispersion of nano-cellulose. This dispersion was then spray-dried to obtain powdered modified nano-microcrystalline cellulose. The spray drying process had an inlet temperature of 150°C, an outlet temperature of 70°C, a feed rate of 5 mL / min, and an atomization pressure of 0.3 MPa.

[0031] Example 4: This example is basically the same as Example 1, except that, by weight, its raw material components include: 50 parts of composite tackifying resin; 20 parts of modified nanocrystalline cellulose; 15 parts of dibutyl itaconic acid-levulinate copolymer; 5 parts of vulcanization activator; 3 parts bio-based antioxidants; 60 parts of a mixed solvent of D-limonene and ethyl acetate; The composite tackifying resin is formed by reacting dehydroabsic acid type rosin resin, epoxidized cashew phenol, and a bio-based crosslinking agent, wherein the bio-based crosslinking agent is furfural; the modified nanocrystalline cellulose is obtained by esterification modification of dodecyl succinic anhydride; in the composite tackifying resin, the weight ratio of dehydroabsic acid type rosin resin, epoxidized cashew phenol, and bio-based crosslinking agent is 2:1:0.1; the reaction of dehydroabsic acid type rosin resin, epoxidized cashew phenol, and bio-based crosslinking agent is carried out in a microwave reactor, and a catalyst is added during the reaction process, wherein the catalyst is p-toluenesulfonic acid, and the amount of catalyst added is 0.3% of the total mass of dehydroabsic acid type rosin resin, epoxidized cashew phenol, and furfural; the microwave power is 500W, the reaction temperature is 160℃, and the reaction time is 2 h; The modified nanocrystalline cellulose is prepared by a raw material in which the weight ratio of microcrystalline cellulose to dodecyl succinic anhydride is 1:0.6, and the final product, nanocrystalline cellulose, has a particle size distribution of 200-300 nm. In the itaconic acid dibutyl ester-levulinate copolymer, the molar ratio of itaconic acid dibutyl ester structural units to levulinate structural units is 1:2, and the number-average molecular weight of the copolymer is 8016. The vulcanization activator is a compound of zinc oxide, stearic acid, and tetrabenzyl thiuram disulfide, with a weight ratio of 3:1:0.5. The bio-based antioxidant is a compound of tea polyphenols, vitamin E, and hydroxypropylated lignin, with a weight ratio of 2:2:1. In the mixed solvent of D-limonene and ethyl acetate, the volume ratio of D-limonene to ethyl acetate is 1:3. The preparation method of the composite tackifying resin is as follows: the prescribed amount of dehydroabscisic acid type rosin resin is put into a microwave reactor and heated to a molten state at 130°C. Under nitrogen protection, epoxidized cashew phenol, bio-based crosslinking agent and p-toluenesulfonic acid catalyst are added. The microwave power is controlled at 500W and the reaction is carried out at 160°C and a stirring rate of 400 rpm for 2 hours to obtain the composite tackifying resin. The modified nanocellulose is prepared as follows: microcrystalline cellulose and water are mixed at a mass ratio of 1:15, and cellulase is added at a mass ratio of 1% of the microcrystalline cellulose. Enzymatic hydrolysis is then performed at a microwave power of 400W and a temperature of 60℃ for 60 min. This step aims to gently disrupt the crystal structure of cellulose and expose more hydroxyl active sites. After the enzymatic hydrolysis reaction is completed, the system is heated to 95℃ and held for 20 minutes. Cellulase was inactivated at high temperature for 1 minute. After cooling to room temperature, the cellulose solid was separated by filtration and centrifugation, and thoroughly washed with deionized water until the pH was neutral. Then, it was dried at 80°C to constant weight to obtain pretreated microcrystalline cellulose. The pretreated microcrystalline cellulose was then dispersed in anhydrous pyridine at a mass ratio of 1:10. The temperature was then raised to 90°C, and dodecyl succinic anhydride was added dropwise with stirring. The reaction was maintained at this temperature for 3 hours. After the reaction, pyridine was removed by vacuum distillation. The resulting solid product was washed four times with anhydrous ethanol and filtered until no pyridine odor was detected. The resulting solid product was redispersed in deionized water and nano-sized using a high-pressure homogenizer at 1200 bar for 10 cycles to obtain a stable aqueous dispersion of nanocellulose. This dispersion was then spray-dried to obtain powdered modified nanocrystalline cellulose. The spray drying process had an inlet temperature of 180°C, an outlet temperature of 90°C, a feed rate of 10 mL / min, and an atomization pressure of 0.5 MPa.

[0032] Example 5: This example is basically the same as Example 2, except that it includes the following steps: S1. Crush the composite tackifying resin to 1-2 mm and set aside; S2, Premixed: Half of the formulated amount of a mixed solvent of D-limonene and ethyl acetate was added to a dissolving vessel. Then, under stirring, the composite tackifying resin, dibutyl itaconic acid-acetylpropionate copolymer, vulcanization activator, and bio-based antioxidant were added sequentially. The mixture was stirred and dissolved at 40°C for 0.5 h to obtain a uniform component A. Modified nanocrystalline cellulose was pre-mixed with the remaining half of the D-limonene and ethyl acetate mixed solvent. The mixture was first dispersed using a microwave reactor with 200W assistance for 5 min, and then ultrasonically dispersed for 10 min using an ultrasonic cell disruptor at a frequency of 25kHz and a power of 500W to obtain a uniform component B dispersion. The stirring rate during the dissolution of component A was controlled at 300 rpm. The preparation method of the itaconic acid dibutyl ester-levulinate copolymer is as follows: itaconic acid dibutyl ester and levulinate monomers are added at a molar ratio of 1:0.5, azobisisobutyronitrile is used as the initiator, and the amount of initiator is 0.5% of the total mass of the two monomers. Polymerization is carried out at 70°C for 4 h, and the itaconic acid dibutyl ester-levulinate copolymer is obtained after precipitation and purification. S3. Finished Product Preparation: At a high-speed disperser speed of 800 rpm, the dispersion of component B obtained in S2 was slowly added to component A. After the addition was completed, the speed was increased to 1500 rpm, and high-speed dispersion was continued for 30 min until the system was homogeneous and stable. After filtration, the formaldehyde-free cellulose composite bio-based rubber adhesive was obtained. The formaldehyde-free cellulose composite bio-based rubber adhesive was subjected to vacuum degassing treatment under the conditions of vacuum degree -0.08 MPa and degassing time of 15 min.

[0033] Example 6: This example is basically the same as Example 1, except that it includes the following steps: S1. Crush the composite tackifying resin to 4-5 mm and set aside. S2, Premixed: Half of the formulated amount of a mixed solvent of D-limonene and ethyl acetate was added to a dissolving vessel. While stirring, the composite tackifying resin, dibutyl itaconic acid-acetylpropionate copolymer, vulcanization activator, and bio-based antioxidant were added sequentially. The mixture was stirred and dissolved at 60°C for 1 h to obtain a uniform component A. Modified nanocrystalline cellulose was pre-mixed with the remaining half of the D-limonene and ethyl acetate mixed solvent. The mixture was first dispersed using a microwave reactor with 300W assistance for 10 min, and then ultrasonically dispersed using an ultrasonic cell disruptor at a frequency of 35kHz and a power of 800W for 20 min to obtain a uniform component B dispersion. The stirring rate during the dissolution of component A was controlled at 500 rpm. The preparation method of the itaconic acid dibutyl ester-levulinate copolymer is as follows: itaconic acid dibutyl ester and levulinate monomers are added in a molar ratio of 1:2, and azobisisobutyronitrile is used as an initiator. The amount of initiator is 1% of the total mass of the two monomers. The copolymer is polymerized at 80°C for 6 h. After precipitation and purification, itaconic acid dibutyl ester-levulinate copolymer is obtained. S3. Finished Product Preparation: At a high-speed disperser speed of 1200 rpm, the dispersion of component B obtained in S2 was slowly added to component A. After the addition was completed, the speed was increased to 2000 rpm, and high-speed dispersion was continued for 60 min until the system was homogeneous and stable. After filtration, the formaldehyde-free cellulose composite bio-based rubber adhesive was obtained. The formaldehyde-free cellulose composite bio-based rubber adhesive was subjected to vacuum degassing treatment under the conditions of vacuum degree -0.095 MPa and degassing time of 30 min.

[0034] Example 7: This example is basically the same as Example 2, except that the inlet temperature of the spray dryer is 150°C, the outlet temperature is 70°C, the feed rate is 5 mL / min, and the atomization pressure is 0.3 MPa.

[0035] Example 8: This example is basically the same as Example 2, except that the inlet temperature of the spray dryer is 180°C, the outlet temperature is 90°C, the feed rate is 10 mL / min, and the atomization pressure is 0.5 MPa.

[0036] Example 9: This example is basically the same as Example 2, except that after S3 is completed, the formaldehyde-free cellulose composite bio-based rubber adhesive is subjected to vacuum degassing treatment under the conditions of vacuum degree -0.08 MPa and degassing time of 15 min.

[0037] Example 10: This example is basically the same as Example 2, except that after S3 is completed, the formaldehyde-free cellulose composite bio-based rubber adhesive is subjected to vacuum degassing treatment under the conditions of vacuum degree -0.095 MPa and degassing time of 30 min.

[0038] Comparative Example 1: This comparative example is basically the same as Example 2, except that the microwave-assisted enzymatic hydrolysis pretreatment step is omitted in the preparation of modified nanocellulose. Unmodified microcrystalline cellulose is directly used for esterification modification: microcrystalline cellulose is dispersed in anhydrous pyridine at a mass ratio of 1:8, then heated to 75°C, and dodecyl succinic anhydride is added dropwise under stirring at a weight ratio of 1:0.45. The reaction is carried out at a constant temperature for 2 hours; subsequent steps are the same as in Example 2.

[0039] Comparative Example 2: This comparative example is basically the same as Example 2, except that the conventional petroleum-based antioxidant 2,6-di-tert-butyl-p-cresol (BHT) is used instead of the bio-based antioxidant, and the amount added is 2 parts. Other components and processes are the same as in Example 1.

[0040] Comparative Example 3: This comparative example is basically the same as Example 2, except that the vacuum degassing step is omitted in the preparation of the S3 product. The product is obtained directly after filtration without degassing.

[0041] Comparative Example 4: This comparative example is basically the same as Example 2, except that the number average molecular weight of the itaconic acid dibutyl ester-acetylacetate copolymer is 2000, which is lower than the scope of the claims. Everything else is the same as in Example 1.

[0042] To investigate the performance of the rubber adhesives in the above examples and control examples, the main materials were determined according to the experimental formulations, and samples were obtained for testing. Adhesive strength was tested according to GB / T 532-2008 (tensile method); strength retention after damp heat aging was tested for 1000 h at 85°C / 85% RH according to GB / T3512-2014; blooming was scored using the industry-standard visual method, with 5 points indicating no exudation; water resistance retention was assessed by evaluating the strength change after immersion in water, according to GB / T 1690-2010. All tests followed standard procedures to ensure comparability of results, as shown in Table 1 below. Specific investigations are as follows: Table 1 Performance test results of rubber adhesive samples from Examples 2-10 and Comparative Examples 1-4

[0043] 1. Investigating the effect of optimizing the bio-based component ratio on the performance of rubber adhesives: As shown in Table 1, a comparison of Examples 2 to 4 reveals that Example 2 exhibits the best overall performance, with the most outstanding bond strength, durability, and anti-blooming ability. Example 3 shows the lowest bond strength and aging resistance, while Example 4 has a slightly lower water resistance retention rate than Example 1. Changing the ratio of the composite tackifying resin to the modified nanocellulose has a regular effect on the performance of the prepared rubber adhesive samples. When the ratio of the main components is close to that of Example 1, better overall performance can be obtained. Compared with Control Example 1, all its performance indicators are significantly lower than those of Example 2. This indicates that omitting the microwave-assisted enzymatic hydrolysis pretreatment step will severely damage the interfacial compatibility between the bio-based filler and the rubber matrix, resulting in a significant decrease in bond strength and durability.

[0044] 2. Investigating the effects of microwave-assisted synthesis and enzymatic hydrolysis processes on the properties of rubber adhesives: A comparison of Examples 2, 5, and 6 shows that Example 2 exhibits the best overall performance, Example 5 has a slightly better adhesive strength than Example 6, while Example 6 has slightly better aging resistance than Example 5. Changing the molecular weight and monomer molar ratio of the itaconic acid copolymer can affect the adhesive's performance, indicating that controlling the appropriate molecular structure is key to balancing its compatibilization effect and stability. Comparative Example 4, due to the use of a copolymer with an excessively low molecular weight, has significantly worse anti-blooming ability than Examples 5 and 6, demonstrating that a sufficiently high molecular weight is crucial for preventing additive migration.

[0045] 3. Investigate the effects of functional additive formulation and process optimization on the properties of rubber adhesives. A comparison of Examples 2, 7, and 8 shows that Example 2 exhibits the most balanced and reliable performance. Examples 7 and 8 each emphasize different spray drying process parameters, resulting in slight differences in the final product performance, but both demonstrate good performance, indicating that the spray drying process has a relatively wide window and a certain degree of operational flexibility. However, a comparison with Control Example 2 reveals that even with similar initial bond strength, the sample using a traditional petroleum-based antioxidant shows significantly deteriorated anti-blooming performance, demonstrating the unique advantage of the bio-based antioxidant compound system in addressing the problem of small molecule migration.

[0046] A comparison of Examples 2, 9, and 10 reveals that their overall performance is very similar. Example 9 uses milder vacuum degassing conditions, while Example 10 uses more stringent conditions. The results for both examples show no significant fluctuation compared to Example 2, indicating that within a reasonable range, the vacuum degassing process has a relatively minor impact on the final performance. However, a comparison with Control Example 3 shows that omitting the degassing step, while not affecting short-term bond strength and appearance, leads to the most significant deterioration in water resistance retention. This demonstrates that this step is indispensable for eliminating potential interface defects and ensuring long-term durability. In conclusion, using the raw material ratios and process parameters within the scope of this invention, an environmentally friendly rubber adhesive with excellent overall performance can be stably prepared.

Claims

1. A formaldehyde-free cellulose composite bio-based rubber adhesive, characterized in that, By weight, its raw material components include: 30-50 parts of composite tackifying resin; 10-20 parts of modified nanocrystalline cellulose; 5-15 parts of dibutyl itaconic acid-levulinate copolymer; 1-5 parts of vulcanization activator; 0.5-3 parts of bio-based antioxidant; 30-60 parts of a mixed solvent of D-limonene and ethyl acetate; The composite tackifying resin is formed by reacting dehydroabsic acid type rosin resin, epoxidized cashew phenol, and a bio-based crosslinking agent, wherein the bio-based crosslinking agent is furfural; the modified nanocrystalline cellulose is obtained by esterification modification of dodecyl succinic anhydride.

2. The formaldehyde-free cellulose composite bio-based rubber adhesive according to claim 1, characterized in that, In the composite tackifying resin, the weight ratio of dehydroabsic acid type rosin resin, epoxidized cashew phenol, and bio-based crosslinking agent is 1-2:1:0.05-0.

1. The reaction of the dehydroabsic acid type rosin resin, epoxidized cashew phenol, and bio-based crosslinking agent is carried out in a microwave reactor, and a catalyst is added during the reaction. The catalyst is p-toluenesulfonic acid, and the amount of catalyst added is 0.1-0.3% of the total mass of dehydroabsic acid type rosin resin, epoxidized cashew phenol, and furfural. The microwave power is 300-500W, the reaction temperature is 140-160℃, and the reaction time is 1-2 h.

3. The formaldehyde-free cellulose composite bio-based rubber adhesive according to claim 1, characterized in that, The modified nanocrystalline cellulose is prepared as follows: microcrystalline cellulose and water are mixed at a mass ratio of 1:10-15, and cellulase is added at a mass ratio of 0.5-1% of the microcrystalline cellulose. Enzymatic hydrolysis is carried out at a microwave power of 200-400W and a temperature of 50-60℃ for 30-60 min. After the enzymatic hydrolysis reaction is completed, the system is heated to 85-95℃ and kept at the temperature for 15-20 min to inactivate the cellulase at high temperature. After cooling to room temperature, the cellulose solid is separated by filtration and centrifugation, and washed thoroughly with deionized water until the pH is neutral. Then, it is dried at 60-80℃ to constant weight to obtain the pretreated microcrystalline cellulose. The pretreated microcrystalline cellulose was then dispersed in anhydrous pyridine at a mass ratio of 1:5-10. The mixture was then heated to 60-90°C, and dodecyl succinic anhydride was added dropwise with stirring at a weight ratio of 1:0.3-0.

6. The mixture was kept at a constant temperature for 1-3 hours. After the reaction was completed, the pyridine was removed by vacuum distillation, and the resulting solid product was redispersed in deionized water. The product was then subjected to nano-sizing treatment using a high-pressure homogenizer at a pressure of 800-1200 bar for 5-10 cycles to obtain a stable aqueous dispersion of nano-cellulose. This dispersion was then spray-dried to obtain powdered modified nano-microcrystalline cellulose.

4. The preparation method of the formaldehyde-free cellulose composite bio-based rubber adhesive as described in claim 3, characterized in that, The spray dryer has an inlet temperature of 150-180℃, an outlet temperature of 70-90℃, a feed rate of 5-10 mL / min, and an atomization pressure of 0.3-0.5 MPa.

5. The formaldehyde-free cellulose composite bio-based rubber adhesive according to claim 1, characterized in that, In the itaconic acid dibutyl ester-acetylacetate copolymer, the molar ratio of itaconic acid dibutyl ester structural units to acetylacetate structural units is 1:0.5-2, and the number average molecular weight of the copolymer is 3000-8000.

6. The formaldehyde-free cellulose composite bio-based rubber adhesive according to claim 1, characterized in that, The vulcanization active agent is a compound of zinc oxide, stearic acid and tetrabenzylthiuram disulfide, with a weight ratio of 2-3:1:0.5; the bio-based antioxidant is a compound of tea polyphenols, vitamin E and hydroxypropylated lignin, with a weight ratio of 1-2:1-2:0.5-1.

7. The formaldehyde-free cellulose composite bio-based rubber adhesive according to claim 1, characterized in that, In the mixed solvent of D-limonene and ethyl acetate, the volume ratio of D-limonene to ethyl acetate is 1:1-3.

8. A method for preparing an aldehyde-free cellulose composite bio-based rubber adhesive as described in any one of claims 1-7, characterized in that, Includes the following steps: S1. Crush the composite tackifying resin to a particle size of 1-5 mm and set aside. S2, Premixed: Add half of the formula amount of the mixed solvent of D-limonene and ethyl acetate to the dissolving vessel. While stirring, add the composite tackifying resin, dibutyl itaconic acid-acetylpropionate copolymer, vulcanization activator and bio-based antioxidant in sequence. Stir and dissolve at 40-60℃ for 0.5-1 h to obtain a uniform component A. Premix the modified nanocrystalline cellulose with the remaining half of the mixed solvent of D-limonene and ethyl acetate. First, disperse it with the assistance of microwave reactor at 200-300W for 5-10 min, and then disperse it with ultrasonic cell disruptor at a frequency of 25-35kHz and a power of 500-800W for 10-20 min to obtain a uniform dispersion of component B. S3. Finished Product Preparation: At a high speed of 800-1200 rpm, the dispersion of component B obtained in S2 is slowly added to component A. After the addition is complete, the speed is increased to 1500-2000 rpm and high-speed dispersion is continued for 30-60 minutes until the system is uniform and stable. After filtration, the formaldehyde-free cellulose composite bio-based rubber adhesive is obtained.

9. The method for preparing the formaldehyde-free cellulose composite bio-based rubber adhesive as described in claim 8, characterized in that, In S3, the stirring rate when dissolving component A is controlled at 300-500 rpm.

10. The method for preparing the formaldehyde-free cellulose composite bio-based rubber adhesive as described in claim 8, characterized in that, After S3 is completed, the formaldehyde-free cellulose composite bio-based rubber adhesive is subjected to vacuum degassing treatment under the conditions of vacuum degree -0.08 to -0.095 MPa and degassing time 15-30 min.

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