High-temperature-resistant high-toughness polyurethane hot-pressing quick-drying adhesive and preparation method thereof

Abstract

The invention relates to a high-temperature-resistant high-toughness polyurethane hot-pressing quick-drying adhesive and a preparation method thereof, and the quick-drying adhesive is prepared from the following raw materials in parts by weight: 40 to 65 parts of solid polyester polyol, 15 to 40 parts of polyether polyol, 15 to 25 parts of diphenylmethane diisocyanate, 0.01 to 0.2 part of dimorpholinyl diethyl ether and 4 to 10 parts of functionalized carbon nanotubes. And 15-33 parts of a modified mica sheet-carbon dot compound. The polyurethane adhesive provided by the invention has excellent weather resistance and high temperature resistance, is high in curing rate, can better meet use requirements, and has a wide application prospect. According to the invention, through the construction of two composite systems of the functionalized carbon nanotubes and the modified mica sheet-carbon dot compound, the mechanical properties, the high temperature resistance, the weather resistance and the curing performance of the polyurethane adhesive can be comprehensively improved by virtue of the synergistic cooperation of the components in the functionalized carbon nanotubes and the modified mica sheet-carbon dot compound and the complementary enhancement between the functionalized carbon nanotubes and the modified mica sheet-carbon dot compound.

Description

Technical Field

[0001] This invention relates to the field of adhesive materials. In particular, it relates to a high-temperature resistant, high-toughness polyurethane hot-pressing fast-drying adhesive and its preparation method. Background Art Polyurethane adhesives (PU adhesives) are adhesives whose molecular chains contain urethane groups (-NHCOO-) and / or isocyanate groups (-NCO). Most common polyurethane adhesives are obtained by reacting isocyanates with hydroxyl-containing compounds such as polyester diols and polyether diols. Polyurethane adhesives have been widely used due to their excellent adhesion, elasticity, wear resistance, and low-temperature resistance, but they have the following shortcomings: (1) poor initial tack and long curing time; (2) poor high-temperature resistance and insufficient toughness, making it difficult to meet the needs of many application scenarios; (3) insufficient post-treatment performance, and the invasion of oxidizing substances such as oxygen (especially at high temperatures) leads to oxidative degradation of the molecular chains, causing polyurethane adhesives to age, yellow, and degrade. Traditional solutions typically improve weather resistance by adding antioxidants. For example, CN115404035B discloses a high thermal conductivity and weather-resistant polyurethane adhesive for automotive lithium batteries and its preparation method. However, during use, the migration, aggregation, or gradual deterioration of antioxidants can make it difficult to provide long-lasting antioxidant protection. Patent CN102827569A discloses a single-component, fast-drying, solvent-free polyurethane adhesive and its preparation method, which, through formulation optimization, can achieve a curing time of less than 45 minutes, but it does not improve high-temperature resistance or toughness. Patent CN117125922A discloses a triple-curing, fast-drying polyurethane-modified epoxy permeable pavement adhesive and its preparation method and application, which can achieve a surface drying time of less than 5 minutes and has good post-treatment properties, but it also does not improve high-temperature resistance. Patent CN117567976A discloses a fast-curing, high-toughness, low-shrinkage polyurethane structural adhesive and its preparation method, which has a short surface drying time and good toughness, but it does not optimize or improve the high-temperature resistance and post-curing properties. Patent CN115612435B discloses a high-temperature resistant polyurethane adhesive for sealing and its preparation method. This method utilizes the reaction of epoxy groups on a modified end-capping agent with isocyanate groups on a modified prepolymer to form an oxazolidinone, and includes the addition of mica powder, resulting in a polyurethane adhesive with good high-temperature resistance, but it does not improve weather resistance and curing rate.

[0002] In summary, the existing technologies described above have failed to comprehensively improve the curing performance, weather resistance, and high-temperature resistance of polyurethane adhesives. Summary of the Invention

[0003] The technical problem to be solved by the present invention is to provide a high-temperature resistant, high-toughness polyurethane hot-pressing quick-drying adhesive and its preparation method, addressing the shortcomings of the prior art.

[0004] To solve the above technical problems, the technical solution adopted by the present invention is: a high-temperature resistant and high-toughness polyurethane hot-pressing quick-drying adhesive, the raw materials for which are prepared by weight include: 40-65 parts of solid polyester polyol, 15-40 parts of polyether polyol, 15-25 parts of diphenylmethane diisocyanate, 0.01-0.2 parts of bismorpholino diethyl ether, 4-10 parts of functionalized carbon nanotubes, and 15-33 parts of modified mica sheet-carbon dot composite; The functionalized carbon nanotubes are carbon nanotubes modified with silane coupling agents and loaded with curing accelerators.

[0005] Preferably, the curing accelerator is at least one of zinc isooctanoate and bismuth isooctanoate; and the silane coupling agent is at least one of KH-550, KH-560, and KH-570.

[0006] Preferably, the functionalized carbon nanotubes are prepared by the following method: 1) Preparation of modified carbon nanotubes: 1-1) Carbon nanotubes were purified by treating them with nitric acid; 1-2) Take purified carbon nanotubes and deionized water, sonicate them in ethanol, add silane coupling agent, adjust the pH to acidic, stir the reaction, filter, wash, and dry to obtain modified carbon nanotubes. 2) Add modified carbon nanotubes and deionized water to ethanol, disperse by ultrasonication, adjust pH to acidic, add zinc isooctanoate, heat and stir to react, filter after reaction, wash, dry to obtain functionalized carbon nanotubes.

[0007] Preferably, the functionalized carbon nanotubes are prepared by the following method: 1) Preparation of modified carbon nanotubes: 1-1) Carbon nanotubes were added to 65wt% nitric acid, the solid content was controlled at 5%, and the mixture was sonicated at 70℃ for 6h. After filtration, the mixture was vacuum dried at 90℃ to constant weight to obtain purified carbon nanotubes. 1-2) Take 1g of purified carbon nanotubes and 15mL of deionized water and add them to 85mL of ethanol. Disperse by sonication for 45min. Then add 1.2g of silane coupling agent KH550, adjust the pH to 5 with glacial acetic acid, stir at 60℃ for 5h, filter, wash with deionized water and ethanol in sequence, and vacuum dry at 90℃ for 12h to obtain modified carbon nanotubes. 2) Take 1g of modified carbon nanotubes and 10mL of deionized water and add them to 50mL of ethanol. Disperse the mixture by sonication for 1h. Adjust the pH to 2 with 30wt% hydrochloric acid. Then, add 10mL of ethanol solution containing 0.1g of zinc isooctanoate dropwise while stirring. Stir at 50℃ for 8h, filter, wash with ethanol, and vacuum dry at 70℃ for 12h to obtain functionalized carbon nanotubes.

[0008] Preferably, the modified mica sheet-carbon dot composite is prepared by the following method: S1. Pretreated mica is obtained by drying mica powder and treating it with oxalic acid aqueous solution; the pretreated mica is added to a mixture of ethanol and deionized water and ultrasonically treated to obtain a mica sheet suspension. S2. Preparation of mica sheet-carbon dot composite: S1-2. N,N-dimethylformamide is mixed with deionized water. Glucose, dithiothreitol and urea are added to the resulting mixed solvent and stirred to obtain mixture 1. Copper butyrate is added to the mica sheet suspension and sonicated to obtain mixture 2. S1-2. Add mixture 1 to mixture 2, disperse by ultrasonication, transfer the resulting precursor mixture into a reaction vessel, react under heating, filter after the reaction is complete, wash, dry, and obtain mica sheet-carbon dot composite. S3, Pretreatment of mica sheet-carbon dot composite: Take mica flake-carbon dot composite and deionized water and add them to ethanol. Disperse by ultrasonication. Add hydroxyl silicone oil dropwise to the resulting suspension to adjust the pH to alkaline. Heat and stir the reaction. After the reaction is complete, filter, wash and dry to obtain pretreated mica flake-carbon dot composite. S4, Grafted Polymer: S4-1. The pretreated mica sheet-carbon dot composite was sonicated in ethanol to obtain a precursor suspension. S4-2. Hydroxypropyl acrylate, methyl acrylate, and acrylated castor oil are mixed in ethanol to obtain a monomer solution. S4-3. The monomer solution is added dropwise to the precursor suspension. After the addition is complete, nitrogen gas is passed through and the mixture is stirred and heated. A mixture containing hydroxypropyl acrylate, methyl acrylate and benzoyl peroxide is added dropwise. The mixture is heated and stirred to react. After the reaction is complete, the mixture is filtered, washed, and dried to obtain the modified mica sheet-carbon dot composite.

[0009] Preferably, acrylated castor oil is prepared by the following method: Castor oil and triethylamine were added to toluene and stirred. Acryloyl chloride was added dropwise to react. After the reaction was completed, deionized water was added dropwise to the product. The precipitate was filtered and discarded. The supernatant was added to an aqueous sodium bicarbonate solution. The oil phase was separated to obtain acrylated castor oil.

[0010] Preferably, the modified mica sheet-carbon dot composite is prepared by the following method: S1. Preparation of mica sheet suspension: Mica powder was dried at 160℃ for 12 hours, then added to a 15wt% oxalic acid aqueous solution, with the solid content controlled at 10%, stirred at 70℃ for 6 hours, filtered, and dried at 90℃ for 12 hours to obtain pretreated mica; 2g of pretreated mica was added to a mixture of 100mL ethanol and 50mL deionized water, and ultrasonically treated at 450W for 2 hours to obtain a mica sheet suspension. S2. Preparation of mica sheet-carbon dot composite: S1-2. Mix 50 mL of N,N-dimethylformamide with 70 mL of deionized water. Add 0.55 g of glucose, 0.3 g of dithiothreitol, and 0.2 g of urea to the resulting mixed solvent and stir for 10 min to obtain mixture 1. Add 0.357 g of copper butyrate to 75 mL of mica sheet suspension and sonicate for 30 min to obtain mixture 2. S1-2. Mixture 1 is added to mixture 2 under stirring and ultrasonically dispersed for 1 hour to obtain a precursor mixture. Then, it is transferred to a reaction vessel and reacted at 180°C for 9 hours. After cooling to room temperature, it is filtered, and the solid product is washed with deionized water and vacuum dried at 70°C for 12 hours to obtain a mica sheet-carbon dot composite. S3, Pretreatment of mica sheet-carbon dot composite: Take 1g of mica sheet-carbon dot composite and 25mL of deionized water and add them to 75mL of ethanol. Disperse by sonication for 1h. Add 0.45g of hydroxyl silicone oil dropwise to the resulting suspension. After sonication for 45min, adjust the pH to 9 with 0.5mol / L KOH solution. Stir and react for 4h at 85℃ and 1000rpm under nitrogen atmosphere. Filter, wash with ethanol, and vacuum dry at 80℃ for 12h to obtain the pretreated mica sheet-carbon dot composite. S4. Grafting polymers onto pretreated mica sheet-carbon dot composites: S4-1. Add 1g of pretreated mica sheet-carbon dot complex to 40mL of ethanol and ultrasonically disperse for 90min to obtain a precursor suspension. S4-2. Add 2,5-hydroxypropyl acrylate, 1 g methyl acrylate, and 0.6 g acrylated castor oil to 60 mL of ethanol and stir for 15 min to obtain a monomer solution. S4-3. The monomer solution was added dropwise to the precursor suspension under stirring, and the addition was completed within 60 min. Nitrogen gas was purged and stirred for 30 min. The mixture was heated to 70 °C, and then a mixture containing 0.5 g hydroxypropyl acrylate, 0.25 g methyl acrylate and 0.035 g benzoyl peroxide was added dropwise under stirring, and the addition was completed within 30 min. The mixture was heated to 80 °C and stirred for 5 h. The mixture was filtered, the solid product was washed with ethanol, and dried under vacuum at 70 °C for 24 h to obtain the modified mica sheet-carbon dot composite.

[0011] Preferably, acrylated castor oil is prepared by the following method: Take 6.9g castor oil and 4.1g triethylamine and add them to 100g toluene. Stir for 10min, add 3.62g acryloyl chloride dropwise at 0℃, react at 25℃ for 24h, add 30g deionized water dropwise to the product, filter and discard the precipitate, add the obtained supernatant to 100g of 5% sodium bicarbonate aqueous solution, separate the oil phase and obtain acrylated castor oil.

[0012] Preferably, the solid polyester polyol is at least one of polycaprolactone diol and polybutylene adipate; The polyether polyol is at least one of polyethylene glycol, polypropylene glycol, polybutylene glycol, and polyoxypropylene triol.

[0013] This invention also provides a method for preparing the high-temperature resistant, high-toughness polyurethane hot-pressing quick-drying adhesive as described above, comprising the following steps: Solid polyester polyol and polyether polyol are mixed and dried at 90-120℃ for 4-12 hours under N2 atmosphere. The mixture is then cooled to 50-70℃, and diphenylmethane diisocyanate and bismorpholino diethyl ether are added under stirring. The mixture is stirred for 30-90 minutes, and then functionalized carbon nanotubes and modified mica sheet-carbon dot composites are added. The mixture is stirred and reacted at 95-115℃ for 2-8 hours. The mixture is then cooled to room temperature to obtain the high-temperature resistant, high-toughness polyurethane hot-pressing quick-drying adhesive.

[0014] The beneficial effects of this invention are: The polyurethane adhesive provided by this invention has both excellent weather resistance and high temperature resistance, and a fast curing rate, which can better meet the application requirements and has broad application prospects.

[0015] This invention introduces functionalized carbon nanotubes into a polyurethane adhesive: carbon nanotubes modified with a silane coupling agent and loaded with a curing accelerator can significantly improve the curing rate and simultaneously enhance the mechanical strength and heat resistance of the polyurethane adhesive. Adding a modified mica sheet-carbon dot composite further improves the high-temperature resistance of the polyurethane adhesive. Furthermore, the long-lasting antioxidant capacity imparted by the carbon dots and the physical barrier effect and high stability of the mica sheets significantly improve the weather resistance of the polyurethane adhesive. Simultaneously, the mica sheets also improve the mechanical strength of the system. The synergistic effect of acrylated castor oil introduced into the modified mica sheet-carbon dot composite with the carbon nanotubes enhances the toughness of the polyurethane adhesive and balances its mechanical properties.

[0016] Zinc isooctanoate supported on functionalized carbon nanotubes can catalyze and promote curing. The large specific surface area, high aspect ratio, and porous structure of the carbon nanotube support enable uniform dispersion of zinc isooctanoate, preventing aggregation and exposing more active catalytic sites, thus significantly enhancing the catalytic effect of zinc isooctanoate. Simultaneously, the conductive network of the carbon nanotubes can regulate the electron density of zinc ions in zinc isooctanoate through electron transfer, optimizing its electrophilicity and accelerating the catalytic reaction.

[0017] In this invention, by constructing two composite systems—functionalized carbon nanotubes and modified mica sheet-carbon dot composites—the mechanical properties, high-temperature resistance, weather resistance, and curing properties of polyurethane adhesives can be comprehensively improved through the synergistic effect of the components in both systems and the complementary enhancement between them. Attached Figure Description

[0018] Figure 1 The infrared absorption spectrum of the mica sheet-carbon dot composite prepared in Example 1; Figure 2 The surface drying time test results are for the examples and comparative examples; Figure 3 The bonding strength test results are for the examples and comparative examples; Figure 4 The curing curve test results are for Example 1, Comparative Examples 1, 2, and 3; Figure 5 The results of the elongation at break test are for the examples and comparative examples; Figure 6 The results of high-temperature resistance tests are for the examples and comparative examples; Figure 7 The TGA curve of the polyurethane hot-pressed fast-drying adhesive in Example 1; Figure 8 The results of heat and oxygen aging resistance tests are for the examples and comparative examples; Figure 9 The results are the antioxidant performance test results of the mica sheet-carbon dot composite prepared in Example 1. Detailed Implementation

[0019] The following specific embodiments illustrate the implementation of the present invention. Those skilled in the art can easily understand other advantages and effects of the present invention from the content disclosed in this specification. Obviously, the described embodiments are only some, not all, of the embodiments of the present invention. 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.

[0020] Unless otherwise specified, the experimental methods used in the following examples are conventional methods. Unless otherwise specified, the materials and reagents used in the following examples are commercially available. For examples where specific conditions are not specified, conventional conditions or conditions recommended by the manufacturer are followed. For reagents or instruments whose manufacturers are not specified, they are all commercially available products.

[0021] This invention provides a high-temperature resistant, high-toughness polyurethane hot-pressing quick-drying adhesive, the raw materials of which, by weight, include: 40-65 parts of solid polyester polyol, 15-40 parts of polyether polyol, 15-25 parts of diphenylmethane diisocyanate, 0.01-0.2 parts of bismorpholino diethyl ether, 4-10 parts of functionalized carbon nanotubes, and 15-33 parts of modified mica sheet-carbon dot composite. Among them, functionalized carbon nanotubes are carbon nanotubes modified with silane coupling agents and loaded with curing accelerators.

[0022] In a preferred embodiment, the curing accelerator is at least one of zinc isooctanoate and bismuth isooctanoate; the silane coupling agent is at least one of KH-550, KH-560, and KH-570.

[0023] In a preferred embodiment, functionalized carbon nanotubes are prepared by the following method: 1) Preparation of modified carbon nanotubes: 1-1) Carbon nanotubes were purified by treating them with nitric acid; 1-2) Take purified carbon nanotubes and deionized water, sonicate them in ethanol, add silane coupling agent, adjust the pH to acidic, stir the reaction, filter, wash, and dry to obtain modified carbon nanotubes. 2) Add modified carbon nanotubes and deionized water to ethanol, disperse by ultrasonication, adjust pH to acidic, add zinc isooctanoate, heat and stir to react, filter after reaction, wash, dry to obtain functionalized carbon nanotubes.

[0024] In a preferred embodiment, functionalized carbon nanotubes are prepared by the following method: 1) Preparation of modified carbon nanotubes: 1-1) Carbon nanotubes were added to 65wt% nitric acid, sonicated, filtered, and dried to obtain purified carbon nanotubes. 1-2) Take purified carbon nanotubes and deionized water and add them to ethanol. Disperse them by ultrasonication. Add silane coupling agent KH550 and adjust the pH to 5 with glacial acetic acid. Stir at 60℃ for 5 hours, filter, wash and dry to obtain modified carbon nanotubes. 2) Add modified carbon nanotubes and deionized water to ethanol, disperse by ultrasonication, adjust the pH to 2 with 30wt% hydrochloric acid, and then add an ethanol solution containing zinc isooctanoate dropwise while stirring. Stir at 50℃ for 8 hours, filter, wash, and dry to obtain functionalized carbon nanotubes.

[0025] In a preferred embodiment, the modified mica sheet-carbon dot composite was prepared by the following method: S1. Pretreated mica is obtained by drying mica powder and treating it with oxalic acid aqueous solution; the pretreated mica is added to a mixture of ethanol and deionized water and ultrasonically treated to obtain a mica sheet suspension. S2. Preparation of mica sheet-carbon dot composite: S1-2. N,N-dimethylformamide is mixed with deionized water. Glucose, dithiothreitol and urea are added to the resulting mixed solvent and stirred to obtain mixture 1. Copper butyrate is added to the mica sheet suspension and sonicated to obtain mixture 2. S1-2. Add mixture 1 to mixture 2, disperse by ultrasonication, transfer the resulting precursor mixture into a reaction vessel, react under heating, filter after the reaction is complete, wash, dry, and obtain mica sheet-carbon dot composite. S3, Pretreatment of mica sheet-carbon dot composite: Take mica flake-carbon dot composite and deionized water and add them to ethanol. Disperse by ultrasonication. Add hydroxyl silicone oil dropwise to the resulting suspension to adjust the pH to alkaline. Heat and stir the reaction. After the reaction is complete, filter, wash and dry to obtain pretreated mica flake-carbon dot composite. S4, Grafted Polymer: S4-1. The pretreated mica sheet-carbon dot composite was sonicated in ethanol to obtain a precursor suspension. S4-2. Hydroxypropyl acrylate, methyl acrylate, and acrylated castor oil are mixed in ethanol to obtain a monomer solution. S4-3. The monomer solution is added dropwise to the precursor suspension. After the addition is complete, nitrogen gas is passed through and the mixture is stirred and heated. A mixture containing hydroxypropyl acrylate, methyl acrylate and benzoyl peroxide is added dropwise. The mixture is heated and stirred to react. After the reaction is complete, the mixture is filtered, washed, and dried to obtain the modified mica sheet-carbon dot composite.

[0026] In a preferred embodiment, the reaction temperature in steps S1-2 is 160-200°C, and the reaction time is 6-16 hours.

[0027] In a preferred embodiment, the modified mica sheet-carbon dot composite was prepared by the following method: S1. Preparation of mica sheet suspension: Mica powder was dried at 160℃, then added to a 15wt% oxalic acid aqueous solution, stirred at 70℃ for 6 hours, filtered, and dried to obtain pretreated mica; the pretreated mica was added to a mixture of ethanol and deionized water and ultrasonically treated at 450W for 2 hours to obtain a mica sheet suspension. S2. Preparation of mica sheet-carbon dot composite: S1-2. N,N-dimethylformamide is mixed with deionized water. Glucose, dithiothreitol and urea are added to the resulting mixed solvent and stirred to obtain mixture 1. Copper butyrate is added to the mica sheet suspension and sonicated to obtain mixture 2. S1-2. Mixture 1 is added to mixture 2 under stirring and ultrasonically dispersed for 1 hour to obtain a precursor mixture. Then, it is transferred to a reaction vessel and reacted at 180°C for 9 hours. After cooling, filtration, washing, and drying, mica sheet-carbon dot composite is obtained. S3, Pretreatment of mica sheet-carbon dot composite: Take mica flake-carbon dot composite and deionized water and add them to ethanol. Disperse by ultrasonication. Add hydroxyl silicone oil dropwise to the resulting suspension. After ultrasonication, adjust the pH to 9 with 0.5 mol / L KOH solution. Stir and react for 4 h at 85℃ and 1000 rpm under nitrogen atmosphere. Filter, wash and dry to obtain pretreated mica flake-carbon dot composite. S4. Grafting polymers onto pretreated mica sheet-carbon dot composites: S4-1. Add the pretreated mica sheet-carbon dot complex to ethanol and disperse it by ultrasonication to obtain a precursor suspension; S4-2. Hydroxypropyl acrylate, methyl acrylate, and acrylated castor oil are added to ethanol and stirred to obtain a monomer solution. S4-3. The monomer solution was added dropwise to the precursor suspension under stirring, nitrogen gas was passed through and the mixture was heated to 70°C. Then, a mixture containing hydroxypropyl acrylate, methyl acrylate and benzoyl peroxide was added dropwise under stirring. The addition was completed in 30 min. The temperature was raised to 80°C and the mixture was stirred for 5 h. The mixture was then filtered, washed and dried to obtain the modified mica sheet-carbon dot composite.

[0028] In a preferred embodiment, acrylated castor oil is prepared by the following method: Castor oil and triethylamine were added to toluene and stirred. Acryloyl chloride was added dropwise to react. After the reaction was completed, deionized water was added dropwise to the product. The precipitate was filtered and discarded. The supernatant was added to an aqueous sodium bicarbonate solution. The oil phase was separated to obtain acrylated castor oil.

[0029] In a preferred embodiment, acrylated castor oil is prepared by the following method: Castor oil and triethylamine were added to toluene and stirred for 10 min. Acryloyl chloride was added dropwise at 0 °C and reacted at 25 °C for 24 h. Deionized water was added dropwise to the product, the precipitate was filtered off, and the supernatant was added to a 5% sodium bicarbonate aqueous solution. The oil phase was separated to obtain acrylated castor oil.

[0030] In a preferred embodiment, the solid polyester polyol is at least one of polycaprolactone diol and polybutylene adipate.

[0031] In a preferred embodiment, the polyether polyol is at least one of polyethylene glycol, polypropylene glycol, polybutylene glycol, and polyoxypropylene triol.

[0032] In a preferred embodiment, the preparation method of the high-temperature resistant, high-toughness polyurethane hot-pressing quick-drying adhesive includes the following steps: Solid polyester polyol and polyether polyol are mixed and dried at 90-120℃ for 4-12 hours under N2 atmosphere. The mixture is then cooled to 50-70℃, and diphenylmethane diisocyanate and bismorpholino diethyl ether are added under stirring. The mixture is stirred for 30-90 minutes, and then functionalized carbon nanotubes and modified mica sheet-carbon dot composites are added. The mixture is stirred and reacted at 95-115℃ for 2-8 hours. After cooling to room temperature, a high-temperature resistant, high-toughness polyurethane hot-pressing quick-drying adhesive is obtained.

[0033] Invention Mechanism This invention utilizes functionalized carbon nanotubes added to polyurethane adhesives: carbon nanotubes modified with silane coupling agents and loaded with curing accelerators significantly improve the curing rate and simultaneously enhance the mechanical strength and heat resistance of the polyurethane adhesive. The addition of modified mica sheet-carbon dot composites further improves the high-temperature resistance of the polyurethane adhesive. Furthermore, the long-lasting antioxidant capacity imparted by carbon dots and the physical barrier effect and high stability of mica sheets significantly improve the weather resistance of the polyurethane adhesive. Simultaneously, mica sheets also improve the mechanical strength of the system. The synergistic effect of acrylated castor oil introduced into the modified mica sheet-carbon dot composite with the carbon nanotubes enhances the toughness of the polyurethane adhesive and balances its mechanical properties. The mechanisms of action of each component are further explained below.

[0034] 1. Functionalized carbon nanotubes In this invention, carbon nanotubes are first treated with concentrated nitric acid to enrich their surface carboxyl groups, then modified with silane coupling agent KH550 to obtain modified carbon nanotubes, and finally loaded with a curing accelerator to obtain functionalized carbon nanotubes. Taking zinc isooctanoate as an example of the curing accelerator, during the loading process, after zinc isooctanoate is mixed with uniformly dispersed modified carbon nanotubes, the adsorption effect of the carbon nanotube cavity structure and the coordination effect of zinc ions in zinc isooctanoate with functional groups such as carboxyl groups on the surface of modified carbon nanotubes enable a large amount of zinc isooctanoate to be loaded onto the carbon nanotubes, achieving uniform dispersion on a carbon nanotube carrier with a large specific surface area.

[0035] (1) In functionalized carbon nanotubes, the modification of silane coupling agent KH550 can improve the dispersion performance of carbon nanotubes in polyurethane system. At the same time, through the double bond in KH550 participating in the copolymerization reaction of polyurethane, chemical bonding with polyurethane system can be achieved, which can improve the interfacial connection strength and dispersion uniformity. Meanwhile, the silane groups in KH550 replace some of the original isocyanate groups (-NCO) in the wet curing reaction. During this process, the silane groups first react with water to generate silanols. These silanols are unstable and form hydrogen bonds or Si-O-R (where R is the adhesive) with hydroxyl groups on the adhesive surface. Thus, the silane exists chemically between the PUR hot melt adhesive and the adhesive, thereby increasing the strength of the cohesive points of the polyurethane hot melt adhesive, which macroscopically translates to improved adhesive strength. Simultaneously, the silanols condense to form a three-dimensional network structure, increasing the crosslinking degree of the polyurethane hot melt adhesive and ultimately effectively improving the adhesive strength and heat resistance of the polyurethane (Zhang Xu. Preparation and Performance Study of Novel Reactive Polyurethane (PUR) Hot Melt Adhesives [D]. Beijing University of Chemical Technology, 2020.) (2) Zinc isooctanoate loaded on functionalized carbon nanotubes is a commonly used curing accelerator for polyurethane. Its mechanism of action is mainly as follows: (1) Zinc ions (Zn²⁺) act as Lewis acids and coordinate with nitrogen or oxygen atoms in isocyanate groups (-NCO), thereby enhancing the positive charge of carbon atoms in isocyanate and making them more susceptible to nucleophilic attacks by hydroxyl groups (-OH) in polyols, thus reducing the activation energy of the reaction. (2) Coordination activation mechanism: Zinc isooctanoate can form intermediate complexes with reactants. Zinc ions coordinate with both isocyanate and polyol, making them spatially closer and promoting the orderly progress of the reaction. (3) Zinc isooctanoate is uniformly dispersed by the large specific surface area, high aspect ratio and porous structure of carbon nanotube carriers, which can prevent agglomeration and expose more active catalytic sites, thereby significantly improving the catalytic effect of zinc isooctanoate. At the same time, the conductive network of carbon nanotubes can adjust the electron density of zinc ions in zinc isooctanoate through electron transfer, optimize its electrophilicity and accelerate the catalytic reaction.

[0036] Therefore, loading with carbon nanotubes can greatly enhance the catalytic performance of zinc isooctanoate. Besides serving as a carrier, carbon nanotubes also play the following roles: They possess excellent thermal conductivity and mechanical strength. Uniformly dispersed carbon nanotubes in a polyurethane system form a cross-linked network structure. This network structure creates an effective heat conduction and stress transfer network, improving the bonding strength and mechanical properties of the polyurethane adhesive. Simultaneously, as a heat transfer medium, they promote heat dispersion, helping to reduce localized overheating. Combined with the excellent thermal stability of carbon nanotubes, the high-temperature resistance of polyurethane is significantly improved.

[0037] 2. Modified mica sheet-carbon dot composite The modified mica sheet-carbon dot composite of this invention is obtained by sequentially grafting carbon dots with antioxidant properties, modifying silicone oil, and grafting polymer onto mica sheets. The preparation process is as follows: First, mica powder is soaked in oxalic acid and then ultrasonically dispersed to obtain two-dimensional mica sheets. Then, using glucose, dithiothreitol, and urea as carbon sources, and adding copper butyrate as a dopant, carbon dots were synthesized in situ on two-dimensional mica sheets via a hydrothermal reaction, yielding a mica sheet-carbon dot composite. In this process, copper butyrate introduces copper ions and enriches carboxyl functional groups. Copper ions coordinate with hydroxyl groups on the mica sheet surface, and simultaneously coordinate with carboxyl, hydroxyl, amino, and thiol functional groups in the carbon source, thus acting as a consortium to promote the attachment of the carbon source to the two-dimensional mica sheet. Finally, under high-temperature and high-pressure hydrothermal reaction conditions, carbon dots are formed, facilitating the smooth synthesis and uniform dispersion of carbon dots on the mica sheet. These carbon dots inherit the reducing properties of dithiothreitol well, exhibiting excellent antioxidant effects. The doped copper butyrate enhances the reducing properties of the carbon dots by increasing the electron cloud density and introducing new active sites, and also introduces carboxyl groups.

[0038] Subsequently, hydroxyl silicone oil was modified onto the mica sheet-carbon dot composite to obtain a pretreated mica sheet-carbon dot composite. The hydroxyl silicone oil molecule contains a large number of Si-O-Si bonds, which are easily hydrolyzed into a large number of silanol groups under acidic and alkaline conditions. These silanol groups can condense with hydroxyl groups (Ma Zhiling, Hao Xuehui, He Jiayin, et al. Preparation of hydrophobic precipitated silica by in-situ modification of hydroxyl silicone oil [J]. Inorganic Salt Industry, 2011, 43(3):36.DOI:10.3969 / j.issn.1006-4990.2011.03.011.). The grafting of hydroxyl silicone oil onto the mica sheet-carbon dot composite is achieved through the above-mentioned interaction between the hydroxyl groups on the surface of the mica sheet and the Si-O-Si bonds of the hydroxyl silicone oil.

[0039] Finally, using hydroxypropyl acrylate, methyl acrylate, and acrylated castor oil as monomers, and benzoyl peroxide as an initiator, in-situ polymerization grafting was performed on the pretreated mica sheet-carbon dot composite to obtain the modified mica sheet-carbon dot composite. The hydroxyl groups in the hydroxyl silicone oil and the hydroxyl groups in the acrylic monomers can undergo a condensation reaction, thereby allowing the polymer to be chemically bonded to the modified mica sheet-carbon dot composite.

[0040] The roles of each component in the modified mica sheet-carbon dot composite are as follows: (1) Mica sheets Mica sheets possess excellent thermal stability and high strength. The physical barrier effect formed by the two-dimensional sheet structure of mica sheets can reduce the penetration of substances such as oxygen. In a polyurethane matrix, it can improve the high-temperature resistance and aging resistance of polyurethane adhesives. Through interfacial interaction, mica sheets and polyurethane matrix can effectively transfer and disperse stress, improve the tensile strength, abrasion resistance and tear resistance of polyurethane adhesives, thereby enhancing the durability and load-bearing capacity of polyurethane adhesives.

[0041] (2) Carbon dots The carbon dots in the modified mica sheet-carbon dot composite of this invention possess excellent antioxidant properties, capable of scavenging free radicals in the polyurethane adhesive system, inhibiting the oxidative degradation reaction of molecular chains, and delaying the aging of the polyurethane adhesive at high temperatures. Because the carbon dots are fixed and uniformly dispersed on the mica sheet, and the mica sheet is uniformly dispersed in the polyurethane system, the migration and aggregation of carbon dots are reduced, improving its stability and providing long-lasting antioxidant protection for the polyurethane system. Simultaneously, the spherical carbon dots uniformly distributed on the mica sheet also increase the filling density and act as physical connection nodes, thereby improving the interfacial bonding strength.

[0042] (3) Hydroxy silicone oil Grafting of hydroxyl silicone oil can improve the dispersibility of mica sheet-carbon dot composites and promote the grafting of polymers onto mica sheet-carbon dot composites. At the same time, hydroxyl silicone oil can introduce organosilicon functional groups into the molecular chains of polyurethane and polyacrylate, thereby improving the weather resistance and water resistance of polyurethane adhesives.

[0043] (4) Grafted polymers The polymer grafted onto the modified mica sheet-carbon dot composite is a polyacrylate doped with castor oil, which can significantly improve the uniform dispersion of mica sheets and carbon dots in the polyurethane system.

[0044] Polyacrylates possess excellent weather resistance, water resistance, and alkali resistance. The ester and hydroxyl functional groups in their molecules exhibit strong hydrogen bonds, which can enhance adhesive properties. The doping of polyacrylates into polyurethane adhesives can improve the weather resistance and bonding strength of hot melt adhesives (Zhang Xi, Liu Jiapei, Zhang Jun, et al. Synthesis of Weather-Resistant and Yellowing-Resistant Acrylic Acid-Modified Polyurethane Adhesives [J]. Adhesion, 2017, 38(10):3.DOI:10.3969 / j.issn.1001-5922.2017.10.010.). The hydroxyl groups on the hydroxypropyl acrylate monomers in the polymer can react with isocyanates to crosslink, improving water resistance and weather resistance, increasing reactivity, and enhancing the rigidity of the polyurethane adhesive.

[0045] Then, when polyacrylate-based polymers are added to a polyurethane system, the dilution effect leads to a lower curing rate and a longer curing time. However, in this invention, the curing-promoting effect of functionalized carbon nanotubes loaded with curing accelerators can effectively compensate for the aforementioned adverse effects of polyacrylate-based polymers.

[0046] Castor oil, a polymer monomer, contains hydroxyl groups, unsaturated carbon-carbon double bonds, ester bonds, and other active functional groups. The long fatty acid chains in its structure can improve toughness and water resistance. The long carbon chain structure of castor oil can prevent polyurethane from becoming brittle at low temperatures, maintaining the material's flexibility (Fang Tao, Yin Hong, Zhang Man, et al. Research progress on silicon-modified polyurethane high-temperature resistant coatings [J]. Journal of Putian University, 2024, 31(2):1-8.DOI:10.3969 / j.issn.1672-4143.2024.02.002.). Castor oil can also increase the crosslinking density of polyurethane, thereby improving tensile strength. However, the double bonds in castor oil are relatively weak and do not readily participate in reactions. Modification with acryloyl chloride introduces active double bonds into the molecular chain of castor oil, increasing its polymerization reactivity and thus fully leveraging its toughening and strengthening effects on polyurethane.

[0047] Adding mica sheets, as two-dimensional sheet-like rigid fillers, to polyurethane systems inevitably has a negative impact on the toughness of the polyurethane. However, the toughness loss caused by mica can be compensated by the improvement in toughness caused by acrylated castor oil. The high aspect ratio and high physical strength of carbon nanotubes, combined with the dispersion promotion and improved interfacial bonding strength brought about by the silane coupling agent modification on the carbon nanotube surface, and the effect of acrylated castor oil on improving the interfacial crosslinking strength between carbon nanotubes and the polyurethane system, significantly enhance the toughness of the polyurethane system. At the same time, the increased crosslinking density of acrylated castor oil can improve the interfacial bonding force between mica powder, carbon nanotube fillers and the polyurethane system, thereby balancing the comprehensive mechanical properties of polyurethane and giving it excellent toughness and mechanical strength. The heat resistance improvement effect of mica powder and carbon nanotubes can compensate for the lack of thermal stability of castor oil, thus improving its high-temperature resistance. Therefore, the synergistic effect of acrylated castor oil, mica powder and carbon nanotubes balances the mechanical properties of polyurethane while significantly improving its high-temperature resistance.

[0048] In this invention, by constructing two composite systems—functionalized carbon nanotubes and modified mica sheet-carbon dot composites—the mechanical properties, high-temperature resistance, weather resistance, and curing properties of polyurethane adhesives can be comprehensively improved through the synergistic effect of the components in both systems and the complementary enhancement between them.

[0049] The above is the general concept of the present invention. Based on this, detailed embodiments and comparative examples are provided below to further illustrate the present invention.

[0050] The main sources of raw materials involved in the following examples and comparative examples are as follows: Polycaprolactone diol, model PCL 2000, molecular weight 2000, hydroxyl value 56mgKOH / g, Xuzhou Yihuiyang New Material Co., Ltd.; Polypropylene triol, molecular weight 4000, Greenlink (Jining) Chemical Technology Co., Ltd. Polybutanediol, model PTMG1000, molecular weight 1000, Greenlink (Jining) Chemical Technology Co., Ltd. Diphenylmethane diisocyanate, Jiangsu Haolong Chemical Co., Ltd.; Bismorpholino diethyl ether, Nantong Shenglun Chemical Technology Co., Ltd.; Carbon nanotubes, multi-walled carbon nanotubes (MWCNTs), average diameter 20 nm, average length 5 μm, Guangzhou Hongwu Materials Technology Co., Ltd. Silane coupling agent KH550, Nanjing Dimont Chemical Co., Ltd.; Mica powder, 1250 mesh sericite, Suzhou Jiaoda New Material Technology Co., Ltd.; Hydroxysilicone oil, brand Alfa, molecular weight (MW) 4200, Shanghai Hans Chemical Co., Ltd. Hydroxypropyl acrylate, Rongsheng New Material Technology (Nantong, Jiangsu) Co., Ltd.; Methyl acrylate, Shanghai Aladdin Biochemical Technology Co., Ltd.; Castor oil, Shanghai Aladdin Biochemical Technology Co., Ltd.; Acryloyl chloride, Shanghai Aladdin Biochemical Technology Co., Ltd.; Triethylamine, Changzhou Hongyu Chemical Co., Ltd.

[0051] The acrylated castor oil used in the following examples and comparative examples was prepared according to the method in the literature "Zhao Dan. Study on preparation of impact-resistant polypropylene by suspension grafting method [D]. Beijing University of Chemical Technology, 2017. DOI:10.7666 / d.Y3220003." The specific steps are as follows: Take 6.9g castor oil and 4.1g triethylamine and add them to 100g toluene. Stir for 10min, add 3.62g acryloyl chloride dropwise at 0℃, react at 25℃ for 24h, add 30g deionized water dropwise to the product, filter and discard the precipitate, add the obtained supernatant to 100g of 5% sodium bicarbonate aqueous solution, separate the oil phase and obtain acrylated castor oil.

[0052] Example 1

[0053] A high-temperature resistant, high-toughness polyurethane hot-pressing quick-drying adhesive, the raw materials for which are prepared by weight include: 50 parts of solid polyester polyol, 20 parts of polyether polyol, 18 parts of diphenylmethane diisocyanate, 0.05 parts of bismorpholino diethyl ether, 6.5 parts of functionalized carbon nanotubes, and 24 parts of modified mica sheet-carbon dot composite.

[0054] Among them, the solid polyester polyol is polycaprolactone diol, and the polyether polyol is a mixture of polybutane glycol and polyoxypropylene triol in a mass ratio of 1:1.

[0055] Functionalized carbon nanotubes were prepared using the following methods: 1) Preparation of modified carbon nanotubes: 1-1) Carbon nanotubes were added to 65wt% nitric acid, the solid content was controlled at 5%, and the mixture was sonicated at 70℃ for 6h. After filtration, the mixture was vacuum dried at 90℃ to constant weight to obtain purified carbon nanotubes. 1-2) Take 1g of purified carbon nanotubes and 15mL of deionized water and add them to 85mL of ethanol. Disperse by sonication for 45min. Then add 1.2g of silane coupling agent KH550, adjust the pH to 5 with glacial acetic acid, stir at 60℃ for 5h, filter, wash with deionized water and ethanol in sequence, and vacuum dry at 90℃ for 12h to obtain modified carbon nanotubes. 2) Take 1g of modified carbon nanotubes and 10mL of deionized water and add them to 50mL of ethanol. Disperse the mixture by sonication for 1h. Adjust the pH to 2 with 30wt% hydrochloric acid. Then, add 10mL of ethanol solution containing 0.1g of zinc isooctanoate dropwise while stirring. Stir at 50℃ for 8h, filter, wash with ethanol, and vacuum dry at 70℃ for 12h to obtain functionalized carbon nanotubes.

[0056] The modified mica sheet-carbon dot composite was prepared by the following method: S1. Preparation of mica sheet suspension: Mica powder was dried at 160℃ for 12 hours, then added to a 15wt% oxalic acid aqueous solution, with the solid content controlled at 10%, stirred at 70℃ for 6 hours, filtered, and dried at 90℃ for 12 hours to obtain pretreated mica; 2g of pretreated mica was added to a mixture of 100mL ethanol and 50mL deionized water, and ultrasonically treated at 450W for 2 hours to obtain a mica sheet suspension. S2. Preparation of mica sheet-carbon dot composite: S1-2. Mix 50 mL of N,N-dimethylformamide with 70 mL of deionized water. Add 0.55 g of glucose, 0.3 g of dithiothreitol, and 0.2 g of urea to the resulting mixed solvent and stir for 10 min to obtain mixture 1. Add 0.357 g of copper butyrate to 75 mL of mica sheet suspension and sonicate for 30 min to obtain mixture 2. S1-2. Mixture 1 is added to mixture 2 under stirring, and ultrasonically dispersed for 1 hour to obtain the precursor mixture. This mixture is then transferred to a reaction vessel and reacted at 180°C for 9 hours. After cooling to room temperature, it is filtered, and the solid product is washed with deionized water and vacuum dried at 70°C for 12 hours to obtain the mica sheet-carbon dot composite. (Refer to...) Figure 1 The infrared absorption spectrum of the mica sheet-carbon dot composite prepared in this example demonstrates that carbon dots were successfully grafted onto the mica sheet in situ. S3, Pretreatment of mica sheet-carbon dot composite: Take 1g of mica sheet-carbon dot composite and 25mL of deionized water and add them to 75mL of ethanol. Disperse by sonication for 1h. Add 0.45g of hydroxyl silicone oil dropwise to the resulting suspension. After sonication for 45min, adjust the pH to 9 with 0.5mol / L KOH solution. Stir and react for 4h at 85℃ and 1000rpm under nitrogen atmosphere. Filter, wash with ethanol, and vacuum dry at 80℃ for 12h to obtain the pretreated mica sheet-carbon dot composite. S4. Grafting polymers onto pretreated mica sheet-carbon dot composites: S4-1. Add 1g of pretreated mica sheet-carbon dot complex to 40mL of ethanol and ultrasonically disperse for 90min to obtain a precursor suspension. S4-2. Add 2,5-hydroxypropyl acrylate, 1 g methyl acrylate, and 0.6 g acrylated castor oil to 60 mL of ethanol and stir for 15 min to obtain a monomer solution. S4-3. The monomer solution was added dropwise to the precursor suspension under stirring, and the addition was completed within 60 min. Nitrogen gas was purged and stirred for 30 min. The mixture was heated to 70 °C, and then a mixture containing 0.5 g hydroxypropyl acrylate, 0.25 g methyl acrylate and 0.035 g benzoyl peroxide was added dropwise under stirring, and the addition was completed within 30 min. The mixture was heated to 80 °C and stirred for 5 h. The mixture was filtered, the solid product was washed with ethanol, and dried under vacuum at 70 °C for 24 h to obtain the modified mica sheet-carbon dot composite. Example 2

[0057] A high-temperature resistant, high-toughness polyurethane hot-pressing quick-drying adhesive, the raw materials for which are prepared by weight include: 50 parts of solid polyester polyol, 20 parts of polyether polyol, 18 parts of diphenylmethane diisocyanate, 0.05 parts of bismorpholino diethyl ether, 5.5 parts of functionalized carbon nanotubes, and 24.5 parts of modified mica sheet-carbon dot composite.

[0058] Among them, the solid polyester polyol is polycaprolactone diol, and the polyether polyol is a mixture of polybutane glycol and polyoxypropylene triol in a mass ratio of 3:2.

[0059] The preparation method of functionalized carbon nanotubes and modified mica sheet-carbon dot composites is the same as in Example 1. Example 3

[0060] A high-temperature resistant, high-toughness polyurethane hot-pressing quick-drying adhesive, the raw materials for which are prepared by weight include: 50 parts of solid polyester polyol, 20 parts of polyether polyol, 18 parts of diphenylmethane diisocyanate, 0.05 parts of bismorpholino diethyl ether, 7.0 parts of functionalized carbon nanotubes, and 23 parts of modified mica sheet-carbon dot composite.

[0061] Among them, the solid polyester polyol is polycaprolactone diol, and the polyether polyol is a mixture of polybutane glycol and polyoxypropylene triol in a mass ratio of 1.5:1.

[0062] Comparative Example 1 The only difference between this example and Example 1 is that no functionalized carbon nanotubes are added to the raw materials used in its preparation.

[0063] Comparative Example 2 A high-temperature resistant, high-toughness polyurethane hot-pressing quick-drying adhesive, the raw materials for which are prepared by weight include: 50 parts of solid polyester polyol, 20 parts of polyether polyol, 18 parts of diphenylmethane diisocyanate, 0.05 parts of bismorpholino diethyl ether, 0.7 parts of zinc isooctanoate, and 24 parts of modified mica sheet-carbon dot composite.

[0064] Among them, the solid polyester polyol is polycaprolactone diol, and the polyether polyol is a mixture of polybutane glycol and polyoxypropylene triol in a mass ratio of 1:1.

[0065] The preparation method of the modified mica sheet-carbon dot composite is the same as in Example 1.

[0066] Comparative Example 3 A high-temperature resistant, high-toughness polyurethane hot-pressing quick-drying adhesive, the raw materials for which are prepared by weight include: 50 parts of solid polyester polyol, 20 parts of polyether polyol, 18 parts of diphenylmethane diisocyanate, 0.05 parts of bismorpholino diethyl ether, 3 parts of modified carbon nanotubes, 0.7 parts of zinc isooctanoate, and 24 parts of modified mica sheet-carbon dot composite.

[0067] Among them, the solid polyester polyol is polycaprolactone diol, and the polyether polyol is a mixture of polybutane glycol and polyoxypropylene triol in a mass ratio of 1:1.

[0068] The preparation methods for modified carbon nanotubes and modified mica sheet-carbon dot composites are the same as in Example 1.

[0069] Comparative Example 4 The only difference between this example and Example 1 is that the modified mica sheet-carbon dot composite is not added to the raw materials.

[0070] Comparative Example 5 The only difference between this example and Example 1 is that modified mica sheets are used instead of the modified mica sheet-carbon dot composite in Example 1. The modified mica sheets are prepared by the following method: S1. Prepare mica sheet suspension, using the same method as in Example 1; S2. Mica sheet pretreatment: The mica sheet suspension was centrifuged, and the solid product was vacuum dried at 70°C for 12 hours to obtain mica sheets. Take 1g of mica sheet and 25mL of deionized water and add them to 75mL of ethanol. Disperse the mixture by sonication for 1h. Add 0.45g of hydroxyl silicone oil to the resulting suspension. After sonication for 45min, adjust the pH to 9 with 0.5mol / L KOH solution. Stir the mixture under nitrogen atmosphere, 85℃ and 1000rpm for 4h. Filter the mixture, wash it with ethanol, and vacuum dry it at 80℃ for 12h to obtain the pretreated mica sheet. S3. Grafting polymers onto pretreated mica sheets: S3-1. Add 1g of pretreated mica sheet to 40mL of ethanol and ultrasonically disperse for 90min to obtain a precursor suspension. S3-2. Add 2,5-hydroxypropyl acrylate, 1 g methyl acrylate, and 0.6 g acrylated castor oil to 60 mL of ethanol and stir for 15 min to obtain a monomer solution. S3-3. The monomer solution was added dropwise to the precursor suspension under stirring, and the addition was completed within 60 min. Nitrogen gas was purged and stirred for 30 min. The mixture was heated to 70 °C, and then a mixture containing 0.5 g hydroxypropyl acrylate, 0.25 g methyl acrylate and 0.035 g benzoyl peroxide was added dropwise under stirring, and the addition was completed within 30 min. The mixture was heated to 80 °C and stirred for 5 h. The mixture was filtered, the solid product was washed with ethanol, and dried under vacuum at 70 °C for 24 h to obtain modified mica sheets.

[0071] Comparative Example 6 The only difference between this example and Example 1 is that acrylated castor oil is not added in step S4 of the preparation of the modified mica sheet-carbon dot composite, and the amount of methyl acrylate added is changed to 1.6g.

[0072] Comparative Example 7 The only difference between this example and Example 1 is that castor oil is used instead of acrylated castor oil in step S4 of the preparation of the modified mica sheet-carbon dot composite.

[0073] Comparative Example 8 A high-temperature resistant, high-toughness polyurethane hot-pressing quick-drying adhesive, the raw materials for which are prepared by weight include: 50 parts of solid polyester polyol, 20 parts of polyether polyol, 18 parts of diphenylmethane diisocyanate, 0.05 parts of bismorpholino diethyl ether, 6.5 parts of functionalized carbon nanotubes, and 4.8 parts of pretreated mica sheet-carbon dot composite.

[0074] Among them, the solid polyester polyol is polycaprolactone diol, and the polyether polyol is a mixture of polybutane glycol and polyoxypropylene triol in a mass ratio of 1:1.

[0075] The preparation method of the pretreated mica sheet-carbon dot composite is the same as in Example 1.

[0076] Performance testing 1. Drying time The prepared polyurethane hot-pressing quick-drying adhesive was uniformly applied to a substrate (aluminum / aluminum) (application amount 20 g / m2), and cured at RH=50% and T=25℃. The surface drying time was tested using the tack method in GB / T 7123.1-2015 "Determination of Workability Time of Multicomponent Adhesives". The test results are shown in Table 1 below. Figure 2 As shown: Table 1 Example 1 Example 2 Example 3 Comparative Example 1 Comparative Example 2 Comparative Example 3 Comparative Example 4 Comparative Example 5 Comparative Example 6 Comparative Example 7 Comparative Example 8 Surface drying time / s 190 215 200 755 440 365 185 190 195 190 195 The test results show that Examples 1-3 all achieved surface drying within 4 minutes. In Comparative Example 1, the surface drying time was significantly prolonged due to the absence of activated carbon nanotubes. In Comparative Example 2, although a curing accelerator was added to the polyurethane adhesive raw material, no carbon nanotubes were added, resulting in a significantly prolonged surface drying time. In Comparative Example 3, both a curing accelerator and carbon nanotubes were added to the polyurethane adhesive raw material, but the curing accelerator was not supported by a carbon nanotube structure, leading to a less effective curing process than in Example 1 and a longer surface drying time. The surface drying times of Comparative Examples 4-8 were not significantly different from those of Example 1.

[0077] 2. Bond strength The prepared polyurethane hot-pressing quick-drying adhesive was uniformly applied to the substrate (aluminum / aluminum) (application amount 20g / m²). 2 The sample was left to stand for 3 minutes at RH=50% and T=25℃, then hot-pressed (1.5MPa, 180s, 120℃) to obtain the test sample. It was then cured at RH=50% and T=25℃ (curing time was calculated from this point). Referring to standard GB / T 7124-2008 "Determination of Tensile Shear Strength of Adhesives (Rigid Material to Rigid Material)" for different curing times, the tensile shear strength after 5 minutes of curing was taken as the initial bond strength; the tensile shear strength after 24 hours of curing was taken as the final bond strength.

[0078] The initial and final tack strength test results of the examples and comparative examples are shown in Table 2 below. Figure 3 As shown: Table 2 Example 1 Example 2 Example 3 Comparative Example 1 Comparative Example 2 Comparative Example 3 Comparative Example 4 Comparative Example 5 Comparative Example 6 Comparative Example 7 Comparative Example 8 Initial Tack Strength / MPa 3.41 3.13 3.65 0.92 1.48 1.79 3.13 3.34 3.11 3.25 3.20 Final Tack Strength / MPa 10.2 9.40 9.82 6.30 7.51 8.03 8.82 9.76 9.06 9.47 8.94 The test results show that Examples 1-3 have relatively fast curing rates. In Comparative Example 1, the curing rate decreased, and the initial and final strengths were reduced due to the absence of activated carbon nanotubes. In Comparative Example 2, although a curing accelerator was added to the polyurethane adhesive raw material, no carbon nanotubes were added, resulting in a decreased curing rate and reduced initial and final strengths. In Comparative Example 3, both a curing accelerator and carbon nanotubes were added to the polyurethane adhesive raw material, but the curing accelerator was not supported by a carbon nanotube-loaded curing accelerator structure, leading to a worse curing effect than Example 1. Comparative Examples 5-8 showed varying degrees of decrease, indicating that the modified mica sheet-carbon dot composite can improve the bond strength to some extent. The results of Comparative Examples 6 and 7 show that acrylated castor oil can improve the bond strength.

[0079] The curing curves of Example 1, Comparative Examples 1, 2, and 3 are as follows: Figure 4 As shown, the curing rate of Example 1 is significantly faster than that of Comparative Examples 1-3.

[0080] 3. Elongation at break The tests were conducted according to the standard ASTM D 638, Standard Test Method for Tensile Properties of Plastics. The test results are shown in Table 3 below. Figure 5 As shown: Table 3 Example 1 Example 2 Example 3 Comparative Example 1 Comparative Example 2 Comparative Example 3 Comparative Example 4 Comparative Example 5 Comparative Example 6 Comparative Example 7 Comparative Example 8 Elongation at break / % 16.4 15.5 16.1 14.3 14.5 16.2 15.3 16.0 14.2 15.1 12.4 The test results show that Examples 1-3 have good toughness. The results of Comparative Examples 1-2 indicate that uniformly dispersed functionalized carbon nanotubes have a certain effect on improving toughness. The results of Comparative Examples 6 and 7 show that acrylated castor oil can improve the toughness of polyurethane adhesive. In Comparative Example 8, the polymer was not grafted onto the pretreated mica sheet-carbon dot composite, which affected its dispersibility. Furthermore, the negative impact of mica sheets on toughness could not be compensated by acrylated castor oil, resulting in a significant decrease in elongation at break.

[0081] 4. High temperature resistance (1) After preparing the test sample according to the same method as in 2 above, it was cured at RH=50% and T=25℃ for 24h. Then, the test sample was subjected to high-temperature treatment (held at 140℃ for 6h). The tensile shear strength after high-temperature treatment was then tested according to standard GB / T 7124-2008 "Determination of Tensile Shear Strength of Adhesives (Rigid Material to Rigid Material)". The high-temperature strength retention rate was calculated as: (Tensile shear strength before high-temperature treatment / Tensile shear strength after high-temperature treatment) × 100%. The test results are shown in Table 4 below. Figure 6 As shown: Table 4 Example 1 Example 2 Example 3 Comparative Example 1 Comparative Example 2 Comparative Example 3 Comparative Example 4 Comparative Example 5 Comparative Example 6 Comparative Example 7 Comparative Example 8 High-temperature strength retention rate / % 98.7 97.4 96.8 92.5 92.9 98.3 91.3 97.4 98.1 98.4 93.6 The test results show that Examples 1-3 have excellent high-temperature resistance. The results of Comparative Examples 1-2 indicate that functionalized carbon nanotubes can significantly improve the high-temperature resistance of polyurethane adhesives, while the results of Comparative Example 4 indicate that modified mica sheet-carbon dot composite can significantly improve the high-temperature resistance of polyurethane adhesives.

[0082] (2) TGA curve The polyurethane hot-pressing quick-drying adhesive prepared in Example 1 was prepared into test samples using the same method as in Example 2 above. These samples were then cured for 24 hours at RH=50% and T=25℃. The thermogravimetric analysis (TGA) curves were then measured using a thermogravimetric analyzer (nitrogen atmosphere, scanning range 30~600℃, heating rate 5℃ / min). The test results are as follows: Figure 7 As shown, its thermal decomposition initiation temperature is around 350℃, and its thermal stability is excellent, significantly stronger than that of conventional polyurethane adhesives.

[0083] 5. Resistance to heat and oxygen aging (1) After preparing the test sample according to the same method as in 2 above, cure it for 24 hours at RH=50% and T=25℃. Then, age the test sample for 720 hours in an air atmosphere at 85℃ and RH=85%. Test the tensile shear strength after aging according to the standard GB / T 7124-2008 "Determination of tensile shear strength of adhesives (rigid material to rigid material)" and calculate the aging strength retention rate: (tensile shear strength before aging / tensile shear strength after aging) × 100%. The test results are shown in Table 4 below: Table 5 Example 1 Example 2 Example 3 Comparative Example 1 Comparative Example 2 Comparative Example 3 Comparative Example 4 Comparative Example 5 Comparative Example 6 Comparative Example 7 Comparative Example 8 Aging strength retention rate / % 97.4 97.1 95.2 93.7 93.9 97.0 78.3 85.2 94.8 96.2 89.3 The test results show that Examples 1-3 have excellent aging resistance. The results of Comparative Examples 1-2 indicate that functionalized carbon nanotubes can significantly improve the aging resistance of polyurethane adhesives. The results of Comparative Example 4 indicate that modified mica sheet-carbon dot composite can significantly improve the aging resistance of polyurethane adhesives. The results of Comparative Example 5 indicate that carbon dots in the modified mica sheet-carbon dot composite play a crucial role in improving aging resistance. In Comparative Example 8, the improvement effect of the aging resistance of the mica sheet-carbon dot composite is greatly reduced due to poor dispersibility.

[0084] (2) Antioxidant properties of mica sheet-carbon dot composite The antioxidant properties of the mica sheet-carbon dot composite prepared in Example 1 were tested according to the following method: Mica sheet-carbon dot complexes were added to ethanol and ultrasonically dispersed for 1 hour to prepare dispersions of different concentrations (0 mg / mL, 0.25 mg / mL, 0.5 mg / mL, and 1 mg / mL). The antioxidant properties of each dispersion were tested using a nitrogen free radical (DPPH) scavenging ability test kit [Sangon Biotech (Shanghai) Co., Ltd.]. DPPH free radicals have unpaired electrons, and their alcoholic solution is purple with strong absorption at 515 nm. When an antioxidant is present, DPPH free radicals are scavenged, the solution color lightens, and the absorbance at 515 nm decreases. Within a certain range, the change in absorbance is directly proportional to the degree of free radical scavenging. That is, the lower the absorbance, the stronger the antioxidant performance.

[0085] Test results are as follows Figure 9 As shown, the absorbance gradually decreases with the increase of the concentration of the mica sheet-carbon dot composite dispersion, indicating that its antioxidant properties gradually increase. This test result, combined with the above results of heat and oxygen aging resistance, shows that the antioxidant properties of carbon dots are the key factor in improving the aging resistance of polyurethane adhesives.

[0086] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention in any way. Although the present invention has been disclosed above with reference to preferred embodiments, it is not intended to limit the present invention. Any person skilled in the art can make some modifications or alterations to the above-disclosed technical content to create equivalent embodiments without departing from the scope of the present invention. Any simple modifications, equivalent changes and alterations made to the above embodiments based on the technical essence of the present invention without departing from the scope of the present invention shall still fall within the scope of the present invention.

Claims

1. A high-temperature resistant, high-toughness polyurethane hot-pressing quick-drying adhesive, characterized in that, The raw materials for its preparation include, by weight: 40-65 parts of solid polyester polyol, 15-40 parts of polyether polyol, 15-25 parts of diphenylmethane diisocyanate, 0.01-0.2 parts of bismorpholino diethyl ether, 4-10 parts of functionalized carbon nanotubes, and 15-33 parts of modified mica sheet-carbon dot composite. The functionalized carbon nanotubes are carbon nanotubes modified with silane coupling agents and loaded with curing accelerators.

2. The high-temperature resistant, high-toughness polyurethane hot-pressing quick-drying adhesive according to claim 1, characterized in that, The curing accelerator is at least one of zinc isooctanoate and bismuth isooctanoate; the silane coupling agent is at least one of KH-550, KH-560 and KH-570.

3. The high-temperature resistant, high-toughness polyurethane hot-pressing quick-drying adhesive according to claim 2, characterized in that, The functionalized carbon nanotubes were prepared by the following method: 1) Preparation of modified carbon nanotubes: 1-1) Carbon nanotubes were purified by treating them with nitric acid; 1-2) Take purified carbon nanotubes and deionized water, sonicate them in ethanol, add silane coupling agent, adjust the pH to acidic, stir the reaction, filter, wash, and dry to obtain modified carbon nanotubes. 2) Add modified carbon nanotubes and deionized water to ethanol, disperse by ultrasonication, adjust pH to acidic, add zinc isooctanoate, heat and stir to react, filter after reaction, wash, dry to obtain functionalized carbon nanotubes.

4. The high-temperature resistant, high-toughness polyurethane hot-pressing quick-drying adhesive according to claim 3, characterized in that, The functionalized carbon nanotubes were prepared by the following method: 1) Preparation of modified carbon nanotubes: 1-1) Carbon nanotubes were added to 65wt% nitric acid, the solid content was controlled at 5%, and the mixture was sonicated at 70℃ for 6h. After filtration, the mixture was vacuum dried at 90℃ to constant weight to obtain purified carbon nanotubes. 1-2) Take 1g of purified carbon nanotubes and 15mL of deionized water and add them to 85mL of ethanol. Disperse by sonication for 45min. Then add 1.2g of silane coupling agent KH550, adjust the pH to 5 with glacial acetic acid, stir at 60℃ for 5h, filter, wash with deionized water and ethanol in sequence, and vacuum dry at 90℃ for 12h to obtain modified carbon nanotubes. 2) Take 1g of modified carbon nanotubes and 10mL of deionized water and add them to 50mL of ethanol. Disperse the mixture by sonication for 1h. Adjust the pH to 2 with 30wt% hydrochloric acid. Then, add 10mL of ethanol solution containing 0.1g of zinc isooctanoate dropwise while stirring. Stir at 50℃ for 8h, filter, wash with ethanol, and vacuum dry at 70℃ for 12h to obtain functionalized carbon nanotubes.

5. The high-temperature resistant, high-toughness polyurethane hot-pressing quick-drying adhesive according to claim 1, characterized in that, The modified mica sheet-carbon dot composite was prepared by the following method: S1. Pretreated mica is obtained by drying mica powder and treating it with oxalic acid aqueous solution; the pretreated mica is added to a mixture of ethanol and deionized water and ultrasonically treated to obtain a mica sheet suspension. S2. Preparation of mica sheet-carbon dot composite: S1-2. N,N-dimethylformamide is mixed with deionized water. Glucose, dithiothreitol and urea are added to the resulting mixed solvent and stirred to obtain mixture 1. Copper butyrate is added to the mica sheet suspension and sonicated to obtain mixture 2. S1-2. Add mixture 1 to mixture 2, disperse by ultrasonication, transfer the resulting precursor mixture into a reaction vessel, react under heating, filter after the reaction is complete, wash, dry, and obtain mica sheet-carbon dot composite. S3, Pretreatment of mica sheet-carbon dot composite: Take mica flake-carbon dot composite and deionized water and add them to ethanol. Disperse by ultrasonication. Add hydroxyl silicone oil dropwise to the resulting suspension to adjust the pH to alkaline. Heat and stir the reaction. After the reaction is complete, filter, wash and dry to obtain pretreated mica flake-carbon dot composite. S4, Grafted Polymer: S4-1. The pretreated mica sheet-carbon dot composite was sonicated in ethanol to obtain a precursor suspension. S4-2. Hydroxypropyl acrylate, methyl acrylate, and acrylated castor oil are mixed in ethanol to obtain a monomer solution. S4-3. The monomer solution is added dropwise to the precursor suspension. After the addition is complete, nitrogen gas is passed through and the mixture is stirred and heated. A mixture containing hydroxypropyl acrylate, methyl acrylate and benzoyl peroxide is added dropwise. The mixture is heated and stirred to react. After the reaction is complete, the mixture is filtered, washed, and dried to obtain the modified mica sheet-carbon dot composite.

6. The high-temperature resistant, high-toughness polyurethane hot-pressing quick-drying adhesive according to claim 5, characterized in that, Acrylate-esterified castor oil is prepared by the following method: Castor oil and triethylamine were added to toluene and stirred. Acryloyl chloride was added dropwise to react. After the reaction was completed, deionized water was added dropwise to the product. The precipitate was filtered and discarded. The supernatant was added to an aqueous sodium bicarbonate solution. The oil phase was separated to obtain acrylated castor oil.

7. The high-temperature resistant, high-toughness polyurethane hot-pressing quick-drying adhesive according to claim 6, characterized in that, The modified mica sheet-carbon dot composite was prepared by the following method: S1. Preparation of mica sheet suspension: Mica powder was dried at 160℃ for 12 hours, then added to a 15wt% oxalic acid aqueous solution, with the solid content controlled at 10%, stirred at 70℃ for 6 hours, filtered, and dried at 90℃ for 12 hours to obtain pretreated mica; 2g of pretreated mica was added to a mixture of 100mL ethanol and 50mL deionized water, and ultrasonically treated at 450W for 2 hours to obtain a mica sheet suspension. S2. Preparation of mica sheet-carbon dot composite: S1-2. Mix 50 mL of N,N-dimethylformamide with 70 mL of deionized water. Add 0.55 g of glucose, 0.3 g of dithiothreitol, and 0.2 g of urea to the resulting mixed solvent and stir for 10 min to obtain mixture 1. Add 0.357 g of copper butyrate to 75 mL of mica sheet suspension and sonicate for 30 min to obtain mixture 2. S1-2. Mixture 1 is added to mixture 2 under stirring and ultrasonically dispersed for 1 hour to obtain a precursor mixture. Then, it is transferred to a reaction vessel and reacted at 180°C for 9 hours. After cooling to room temperature, it is filtered, and the solid product is washed with deionized water and vacuum dried at 70°C for 12 hours to obtain a mica sheet-carbon dot composite. S3, Pretreatment of mica sheet-carbon dot composite: Take 1g of mica sheet-carbon dot composite and 25mL of deionized water and add them to 75mL of ethanol. Disperse by sonication for 1h. Add 0.45g of hydroxyl silicone oil dropwise to the resulting suspension. After sonication for 45min, adjust the pH to 9 with 0.5mol / L KOH solution. Stir and react for 4h at 85℃ and 1000rpm under nitrogen atmosphere. Filter, wash with ethanol, and vacuum dry at 80℃ for 12h to obtain the pretreated mica sheet-carbon dot composite. S4. Grafting polymers onto pretreated mica sheet-carbon dot composites: S4-1. Add 1g of pretreated mica sheet-carbon dot complex to 40mL of ethanol and ultrasonically disperse for 90min to obtain a precursor suspension. S4-2. Add 2,5-hydroxypropyl acrylate, 1 g methyl acrylate, and 0.6 g acrylated castor oil to 60 mL of ethanol and stir for 15 min to obtain a monomer solution. S4-3. The monomer solution was added dropwise to the precursor suspension under stirring, and the addition was completed within 60 min. Nitrogen gas was purged and stirred for 30 min. The mixture was heated to 70 °C, and then a mixture containing 0.5 g hydroxypropyl acrylate, 0.25 g methyl acrylate and 0.035 g benzoyl peroxide was added dropwise under stirring, and the addition was completed within 30 min. The mixture was heated to 80 °C and stirred for 5 h. The mixture was filtered, the solid product was washed with ethanol, and dried under vacuum at 70 °C for 24 h to obtain the modified mica sheet-carbon dot composite.

8. The high-temperature resistant, high-toughness polyurethane hot-pressing quick-drying adhesive according to claim 7, characterized in that, Acrylate-esterified castor oil is prepared by the following method: Take 6.9g castor oil and 4.1g triethylamine and add them to 100g toluene. Stir for 10min, add 3.62g acryloyl chloride dropwise at 0℃, react at 25℃ for 24h, add 30g deionized water dropwise to the product, filter and discard the precipitate, add the obtained supernatant to 100g of 5% sodium bicarbonate aqueous solution, separate the oil phase and obtain acrylated castor oil.

9. The high-temperature resistant, high-toughness polyurethane hot-pressing quick-drying adhesive according to claim 1, characterized in that, The solid polyester polyol is at least one of polycaprolactone diol and polybutylene adipate; The polyether polyol is at least one of polyethylene glycol, polypropylene glycol, polybutylene glycol, and polyoxypropylene triol.

10. A method for preparing a high-temperature resistant, high-toughness polyurethane hot-pressing quick-drying adhesive as described in any one of claims 1-9, characterized in that, Includes the following steps: Solid polyester polyol and polyether polyol are mixed and dried at 90-120℃ for 4-12 hours under N2 atmosphere. The mixture is then cooled to 50-70℃, and diphenylmethane diisocyanate and bismorpholino diethyl ether are added under stirring. The mixture is stirred for 30-90 minutes, and then functionalized carbon nanotubes and modified mica sheet-carbon dot composites are added. The mixture is stirred and reacted at 95-115℃ for 2-8 hours. The mixture is then cooled to room temperature to obtain the high-temperature resistant, high-toughness polyurethane hot-pressing quick-drying adhesive.

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