Bio-based toughening agent, epoxy adhesive, and preparation method therefor

Abstract

The present invention relates to a bio-based toughening agent, an epoxy adhesive, and a preparation method therefor. The bio-based toughening agent is obtained by reacting a polyurethane prepolymer with cardanol; the polyurethane prepolymer is obtained by reacting castor oil with a polyisocyanate; the molar ratio of the isocyanate groups in the polyurethane prepolymer to the phenolic hydroxyl groups in the cardanol is 1:1-2; the molar ratio of the hydroxyl groups in the castor oil to the isocyanate groups in the polyisocyanate is 1:1-3. The epoxy adhesive prepared by applying the toughening agent of the present invention to an epoxy adhesive has high peel strength and impact absorption capacity, and good aging resistance.

Description

A bio-based toughening agent, an epoxy adhesive, and a method for preparing the same.

[0001] This invention claims priority to Chinese Patent Application No. 2024114465737, filed on October 16, 2024, entitled "A Bio-based Toughening Agent, Epoxy Adhesive and Preparation Method Thereof", the entire contents of which are incorporated herein by reference. Technical Field

[0002] This invention belongs to the field of adhesive technology, specifically relating to a bio-based toughening agent, an epoxy adhesive, and a method for preparing the same. Background Technology

[0003] With the rapid development of the new energy vehicle industry, the demands and requirements of related supporting industries are also constantly increasing. In terms of lightweighting of new energy vehicles, compared with traditional bolt and riveting processes, high-strength body structural adhesives can provide excellent bonding performance, replacing or assisting traditional connection processes, thereby achieving the goal of weight reduction and efficiency improvement.

[0004] Epoxy adhesives have a wide range of applications, commonly used for bonding devices and components, due to their high mechanical strength and good dielectric properties. In many industrial and everyday applications, epoxy adhesives are widely used for material bonding and repair. However, epoxy adhesives often exhibit drawbacks such as high brittleness and low peel strength. Since automobiles are frequently exposed to vibrations and occasionally experience extreme collisions, these drawbacks prevent epoxy adhesives from being used for joining automotive body structural components. To expand the application of epoxy adhesives in the new energy vehicle industry, it is necessary to improve their peel strength and impact resistance. Summary of the Invention

[0005] Therefore, the purpose of this invention is to improve the peel strength and impact resistance of epoxy adhesives.

[0006] To achieve the above-mentioned objectives, the present invention includes the following technical solutions.

[0007] In a first aspect, the present invention provides a bio-based toughening agent obtained by reacting a polyurethane prepolymer with cashew nut shell extract;

[0008] The polyurethane prepolymer was obtained by reacting castor oil with polyisocyanate;

[0009] The molar ratio of isocyanate groups in the polyurethane prepolymer to phenolic hydroxyl groups in the cashew phenol is 1:1-2.

[0010] The molar ratio of the hydroxyl groups in the castor oil to the isocyanate groups in the polyisocyanate is 1:1-3.

[0011] In some embodiments, the molar ratio of isocyanate groups in the polyurethane prepolymer to phenolic hydroxyl groups in the cashew phenol is 1:1.1-1.5; and the molar ratio of hydroxyl groups in the castor oil to isocyanate groups in the polyisocyanate is 1:1.2-2.5.

[0012] In some embodiments, the molar ratio of isocyanate groups in the polyurethane prepolymer to phenolic hydroxyl groups in the cashew phenol is 1:1.1-1.5; and the molar ratio of hydroxyl groups in the castor oil to isocyanate groups in the polyisocyanate is 1:1.8-2.2.

[0013] In some embodiments, the molar ratio of isocyanate groups in the polyurethane prepolymer to phenolic hydroxyl groups in the cashew phenol is 1:1.2-1.3; and the molar ratio of hydroxyl groups in the castor oil to isocyanate groups in the polyisocyanate is 1:1.8-2.2.

[0014] In some embodiments, the molar ratio of isocyanate groups in the polyurethane prepolymer to phenolic hydroxyl groups in the cashew phenol is 1:1.2; and the molar ratio of hydroxyl groups in the castor oil to isocyanate groups in the polyisocyanate is 1:2.

[0015] In some embodiments, the polyisocyanate is selected from one or more of toluene diisocyanate, diphenylmethane diisocyanate, dicyclohexylmethane diisocyanate, hexamethylene diisocyanate, and isophorone diisocyanate.

[0016] Secondly, the present invention provides a method for preparing the bio-based toughening agent, comprising the following steps:

[0017] (1) The castor oil and polyisocyanate are reacted at a temperature of 60℃-100℃ for 2-8 hours to obtain the polyurethane prepolymer;

[0018] (2) The polyurethane prepolymer and cashew phenol are reacted at a temperature of 50℃-80℃ for 2-8 hours to obtain the bio-based toughening agent.

[0019] In some embodiments, the method for preparing the bio-based toughening agent includes the following steps:

[0020] (1) The castor oil and polyisocyanate are reacted at a temperature of 70℃-80℃ for 5-7 hours to obtain the polyurethane prepolymer;

[0021] (2) The polyurethane prepolymer and cashew phenol are reacted at a temperature of 55℃-65℃ for 4-6 hours to obtain the bio-based toughening agent.

[0022] In some embodiments, the reaction is carried out with or without a solvent; the solvent is selected from one or more of acetone, butanone, dichloroethane, ethyl acetate, and butyl acetate.

[0023] In some embodiments, the reaction is carried out with the addition of a solvent, and the reaction of the polyurethane prepolymer and cashew phenol includes a step of removing the solvent.

[0024] In some embodiments, the solvent removal is achieved by vacuuming and stirring for 1-2 hours.

[0025] In some embodiments, the vacuuming is performed to a vacuum level of -0.08 MPa to -0.1 MPa.

[0026] Thirdly, the present invention also provides an epoxy adhesive having added a toughening agent, wherein the toughening agent comprises the bio-based toughening agent described in the present invention.

[0027] In some embodiments, the bio-based toughening agent comprises 5-25% by weight in the epoxy adhesive.

[0028] In some embodiments, the bio-based toughening agent accounts for 10-20% by weight in the epoxy adhesive.

[0029] In some embodiments, the bio-based toughening agent accounts for 13-20% by weight in the epoxy adhesive.

[0030] In some embodiments, the bio-based toughening agent accounts for 15-20% by weight in the epoxy adhesive.

[0031] In some embodiments, the bio-based toughening agent accounts for 14-16% by weight of the epoxy adhesive.

[0032] In some of these embodiments, the epoxy adhesive is prepared from raw materials comprising, by weight, the following components:

[0033] In some embodiments, the epoxy adhesive is prepared from raw materials comprising the following components, in parts by weight:

[0034] In some embodiments, the epoxy adhesive is prepared from raw materials comprising the following components, in parts by weight:

[0035] In some embodiments, the epoxy adhesive is prepared from raw materials comprising the following components, in parts by weight:

[0036] In some embodiments, the general toughening agent comprises 5-25% by weight in the epoxy adhesive.

[0037] In some embodiments, the general toughening agent comprises 10-25% by weight in the epoxy adhesive.

[0038] In some embodiments, the general toughening agent comprises 15-25% by weight in the epoxy adhesive.

[0039] In some embodiments, the general toughening agent comprises 20-25% by weight in the epoxy adhesive.

[0040] In some embodiments, the general toughening agent accounts for 18-20% by weight in the epoxy adhesive.

[0041] In some embodiments, the epoxy resin is one or more of glycidyl ether epoxy resin and glycidyl ester epoxy resin.

[0042] In some embodiments, the general toughening agent is one or more of CTBN toughening agent, core-shell rubber, and polyurethane-modified epoxy resin.

[0043] In some embodiments, the curing agent is one or more of imidazole, dicyandiamide, acid anhydride, and pyridine.

[0044] In some embodiments, the promoter is one or more of imidazole, pyridine, and organic urea (e.g., diuron, feuron).

[0045] Fourthly, the present invention also provides a method for preparing the epoxy adhesive, comprising the following steps: mixing the epoxy resin, bio-based toughening agent, general toughening agent, curing agent and accelerator uniformly at a temperature of 50°C-70°C, and cooling to room temperature to obtain the epoxy adhesive.

[0046] The present invention has the following beneficial effects:

[0047] This invention prepares a bio-based toughening agent by reacting castor oil, polyisocyanate, and cashew nut phenol in a specific ratio. When applied to epoxy adhesives, this toughening agent can significantly improve the peel strength and impact absorption capacity of epoxy adhesives, overcoming the defects of high brittleness and low peel strength of epoxy adhesives, thereby improving their performance and reliability in various applications.

[0048] Meanwhile, the toughening agent prepared by this invention contains unsaturated bonds, which can undergo addition reactions when free radicals are generated during thermo-oxidative aging, thereby slowing down the aging phenomenon and improving the anti-aging ability of epoxy adhesives.

[0049] Furthermore, this invention uses castor oil and cashew phenol as bio-based raw materials, which has significant advantages in the use of renewable raw materials and the reduction of carbon emissions. Attached Figure Description

[0050] Figure 1 is the infrared spectrum of the bio-based toughening agent prepared in Example 1. Detailed Implementation

[0051] To facilitate understanding of the present invention, a more complete description will be provided below. The present invention can be implemented in many different forms and is not limited to the embodiments described herein. Rather, these embodiments are provided to provide a thorough and complete understanding of the disclosure of the present invention.

[0052] Unless otherwise specified, experimental methods in the following examples are generally performed under standard conditions or as recommended by the manufacturer. All commonly used chemical reagents used in the examples are commercially available products.

[0053] Unless otherwise defined, all technical and scientific terms used in this invention have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. The terminology used in this specification is for the purpose of describing particular embodiments only and is not intended to limit the invention. The term "and / or" as used in this invention includes any and all combinations of one or more of the associated listed items.

[0054] Furthermore, as used herein, the term "or" is an inclusive "or" sign and is equivalent to the term "and / or" unless the context clearly specifies otherwise. The term "based on" is not exclusive and allows for basing on other factors not described unless the context clearly specifies otherwise. Additionally, throughout the specification, the meanings of "an," "a," and "the" include plural indicators. The meaning of "in" includes both "in" and "on."

[0055] In the following examples, the structural formula of castor oil is as follows:

[0056] The structural formula of diphenylmethane diisocyanate is as follows:

[0057] The structural formula of cashew phenol is as follows:

[0058] Where n is 0, 1, 2, or 3.

[0059] The reaction mechanism of castor oil, diphenylmethane diisocyanate, and cashew nut shell powder is as follows:

[0060] The epoxy resin used in the following examples and comparative examples is bisphenol A glycidyl ether, the curing agent is dicyandiamide, and the accelerator is diuron.

[0061] The following are specific examples.

[0062] Example 1

[0063] This embodiment provides a bio-based toughening agent, an epoxy adhesive, and a method for preparing the same.

[0064] (1) Prepare the bio-based toughening agent according to the following method:

[0065] Step 1: Weigh castor oil and diphenylmethane diisocyanate in a molar ratio of hydroxyl to isocyanate group = 1:1.2, and weigh 30% by mass of ethyl acetate (i.e., ethyl acetate accounts for 30% of the total mass, and castor oil + diphenylmethane diisocyanate accounts for 70% of the total mass).

[0066] Step 2: Add the above raw materials to a three-necked flask, reflux at 75°C, and stir for 6 hours to obtain polyurethane prepolymer.

[0067] Step 3: Weigh cashew phenol according to the molar ratio of isocyanate group to phenolic hydroxyl group in polyurethane prepolymer and cashew phenol = 1:1.5, add it to the three-necked flask in Step 2, stir at 60°C for 4 hours, then evacuate to -0.1 MPa, stir for 2 hours, and recover the solvent to obtain the bio-based toughening agent.

[0068] Its infrared spectrum is shown in Figure 1: 2250 cm⁻¹ -1 The NCO infrared peak is greatly reduced at 1560 cm⁻¹. -1 3500cm -1 The NH and OH peaks are enhanced at 2900 cm⁻¹. -1 The enhanced infrared peak at CH indicates that NCO reacts with the phenolic hydroxyl group to generate the bio-based toughening agent.

[0069] (2) Prepare epoxy adhesive according to the raw material composition in Table 1 and the following method:

[0070] Table 1. Components of the epoxy adhesive in Example 1

[0071] The preparation method of the epoxy adhesive is carried out according to the following steps: weigh each raw material according to the mass fraction of each raw material in Table 1, stir and mix them evenly at 60°C, and obtain the adhesive after cooling to room temperature.

[0072] Example 2

[0073] This embodiment provides a bio-based toughening agent, an epoxy adhesive, and a method for preparing the same.

[0074] (1) Prepare the bio-based toughening agent according to the following method:

[0075] Step 1: Weigh castor oil and diphenylmethane diisocyanate in a molar ratio of 1:2 (hydroxyl:isocyanate group = 1:2), and weigh 30% ethyl acetate.

[0076] Step 2: Add the above raw materials to a three-necked flask, reflux at 75°C, and stir for 6 hours to obtain polyurethane prepolymer.

[0077] Step 3: Weigh cashew phenol according to the molar ratio of isocyanate group to phenolic hydroxyl group in polyurethane prepolymer and cashew phenol = 1:1.2, add it to the three-necked flask in Step 2, stir at 60°C for 4 hours, then evacuate to -0.1 MPa, stir for 2 hours, and recover the solvent to obtain the bio-based toughening agent.

[0078] (2) Prepare epoxy adhesive according to the raw material composition in Table 2 and the preparation method in Example 1.

[0079] Table 2. Adhesive components in Example 2

[0080] Example 3

[0081] This embodiment provides a bio-based toughening agent, an epoxy adhesive, and a method for preparing the same.

[0082] (1) Prepare the bio-based toughening agent according to the following method:

[0083] Step 1: Weigh castor oil and diphenylmethane diisocyanate in a molar ratio of 1:2.5 (hydroxyl:isocyanate group = 1:2.5), and weigh 30% ethyl acetate at the same time.

[0084] Step 2: Add the above raw materials to a three-necked flask, reflux at 75°C, and stir for 6 hours to obtain polyurethane prepolymer.

[0085] Step 3: Weigh cashew phenol in the polyurethane prepolymer and cashew phenol in a molar ratio of isocyanate group:phenolic hydroxyl group = 1:1.1, add it to the three-necked flask of Step 2, stir at 60°C for 4 hours, then evacuate to -0.1 MPa and stir for 2 hours, recover the solvent, and obtain the bio-based toughening agent.

[0086] (2) Prepare epoxy adhesive according to the raw material composition in Table 3 and the preparation method in Example 1.

[0087] Table 3. Adhesive components in Example 3

[0088] Example 4

[0089] This embodiment provides an epoxy adhesive and its preparation method.

[0090] The epoxy adhesive was prepared according to the raw material composition in Table 4 and the preparation method in Example 1.

[0091] Table 4. Adhesive components in Example 4

[0092] The bio-based toughening agent used is the same as in Example 2.

[0093] Example 5

[0094] This embodiment provides an epoxy adhesive and its preparation method.

[0095] The epoxy adhesive was prepared according to the raw material composition in Table 5 and the preparation method in Example 1.

[0096] Table 5. Adhesive components in Example 5

[0097] The bio-based toughening agent used is the same as in Example 2.

[0098] Example 6

[0099] This embodiment provides an epoxy adhesive and its preparation method.

[0100] The epoxy adhesive was prepared according to the raw material composition in Table 6 and the preparation method in Example 1.

[0101] Table 6. Adhesive components in Example 6

[0102] The bio-based toughening agent used is the same as in Example 2.

[0103] Comparative Example 1

[0104] This comparative example provides an epoxy adhesive and its preparation method, which differs from Example 2 in that no bio-based toughening agent is added, i.e., CTBN toughening agent is used instead of bio-based toughening agent.

[0105] The epoxy adhesive was prepared according to the raw material composition in Table 7 and the preparation method in Example 1.

[0106] Table 7. Adhesive Components in Comparative Example 1

[0107] Comparative Example 2

[0108] This comparative example provides an epoxy adhesive and its preparation method, which differs from Example 2 in that the polyurethane prepolymer and cashew phenol do not react and are directly added to the adhesive components.

[0109] The epoxy adhesive was prepared according to the raw material composition in Table 8 and the preparation method in Example 1.

[0110] Table 8. Adhesive components in Comparative Example 2

[0111] The polyurethane prepolymer is the polyurethane prepolymer prepared in Example 2.

[0112] Comparative Example 3

[0113] This comparative example provides an epoxy adhesive and its preparation method, which differs from Example 2 in that an equal amount of polyurethane prepolymer is used to replace the bio-based toughening agent.

[0114] The epoxy adhesive was prepared according to the raw material composition in Table 9 and the preparation method in Example 1.

[0115] Table 9. Adhesive components in Comparative Example 3

[0116] The polyurethane prepolymer is the polyurethane prepolymer prepared in Example 2.

[0117] Comparative Example 4

[0118] This comparative example provides an epoxy adhesive and its preparation method, which differs from Example 2 in that an equal amount of polyurethane prepolymer is used to replace the bio-based toughening agent.

[0119] The epoxy adhesive was prepared according to the raw material composition in Table 10 and the preparation method in Example 1.

[0120] Table 10 Adhesive Components in Comparative Example 4

[0121] The preparation method of polyurethane prepolymer is as follows:

[0122] Step 1: Weigh out diphenylmethane diisocyanate and cashew phenol in a molar ratio of 1:1.2 (isocyanate group: phenolic hydroxyl group = 1:1.2) and weigh out ethyl acetate (30% by mass).

[0123] Step 2: Add the above raw materials to a three-necked flask, stir at 60°C for 4 hours, then evacuate to -0.1 MPa, stir for 2 hours, and recover the solvent to obtain the polyurethane prepolymer.

[0124] The epoxy adhesives prepared in Examples 1-6 and Comparative Examples 1-4 were subjected to the following performance tests:

[0125] Shear strength: Tested according to GB / T 7124 method.

[0126] Peel strength: Tested according to GB / T 2791 method.

[0127] Tensile strength: Tested according to GB / T 7124 method.

[0128] Impact toughness: Tested according to GB / T 1043 method.

[0129] Aging test: After alternating high and low temperatures (holding at -40℃ for 2 hours and at 95℃ for 2 hours), the test is carried out according to the above method.

[0130] The test results are shown in Table 11.

[0131] Table 11 Performance test results of epoxy adhesives

[0132] As shown in Table 1, the different raw material ratios used in Examples 1-3 resulted in variations in the peel strength and impact resistance of the epoxy adhesives. In Example 2, the bio-based toughening agent produced by reacting castor oil and diphenylmethane diisocyanate at a molar ratio of hydroxyl to isocyanate groups of 1:2, and by reacting polyurethane prepolymer and cashew nut shell phenol at a molar ratio of isocyanate to phenolic hydroxyl groups of 1:1.2, exhibited the best reinforcing effect on the epoxy adhesive.

[0133] Compared to Example 2, Examples 4-6 varied the amounts of bio-based toughening agent and CTBN toughening agent. As shown in Table 1, the amounts of both bio-based and CTBN toughening agents affected the peel strength and impact resistance of the resulting epoxy adhesives. The peel strength and impact resistance of the epoxy adhesives increased with increasing bio-based toughening agent dosage (Example 5), but when the dosage was too high, the performance improvement effect was limited or even decreased (Example 6); when the CTBN dosage was too high, the properties of the resulting epoxy adhesives significantly decreased (Example 4).

[0134] Compared with Example 2, Comparative Example 1 did not add a bio-based toughening agent. The peel strength and impact resistance of the resulting epoxy adhesive were significantly lower than those of Example 2. This shows that the bio-based toughening agent of the present invention can significantly improve the overall performance of epoxy adhesives, such as peel strength and impact resistance.

[0135] Compared to Example 2, in Comparative Example 2, the polyurethane prepolymer and cashew phenol were added directly to the adhesive components without reaction. The resulting epoxy adhesive exhibited lower peel strength and impact resistance compared to Example 2. In Comparative Examples 3 and 4, an equal amount of polyurethane prepolymer replaced the bio-based toughening agent in Example 2. The resulting epoxy adhesives showed significantly lower peel strength and impact resistance compared to Example 2, indicating that the bio-based toughening agent prepared by reacting castor oil, polyisocyanate, and cashew phenol in this invention can synergistically improve the peel strength and impact resistance of epoxy adhesives.

[0136] The embodiments described above are merely illustrative of several implementations of the present invention, and while the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the invention patent. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these all fall within the protection scope of the present invention. Therefore, the protection scope of this invention patent should be determined by the appended claims.

Claims

1. A bio-based toughening agent, characterized in that, It is obtained by reacting polyurethane prepolymer with cashew nut shell powder; The polyurethane prepolymer was obtained by reacting castor oil with polyisocyanate; The molar ratio of isocyanate groups in the polyurethane prepolymer to phenolic hydroxyl groups in the cashew phenol is 1:1-2. The molar ratio of the hydroxyl groups in the castor oil to the isocyanate groups in the polyisocyanate is 1:1-3.

2. The bio-based toughening agent according to claim 1, characterized in that, The molar ratio of isocyanate groups in the polyurethane prepolymer to phenolic hydroxyl groups in the cashew phenol is 1:1.1-1.5; the molar ratio of hydroxyl groups in the castor oil to isocyanate groups in the polyisocyanate is 1:1.2-2.

5.

3. The bio-based toughening agent according to claim 2, characterized in that, The molar ratio of isocyanate groups in the polyurethane prepolymer to phenolic hydroxyl groups in the cashew phenol is 1:1.2-1.3; the molar ratio of hydroxyl groups in the castor oil to isocyanate groups in the polyisocyanate is 1:1.8-2.

2.

4. The bio-based toughening agent according to claim 3, characterized in that, The molar ratio of isocyanate groups in the polyurethane prepolymer to phenolic hydroxyl groups in the cashew phenol is 1:1.2; the molar ratio of hydroxyl groups in the castor oil to isocyanate groups in the polyisocyanate is 1:

2.

5. The bio-based flexibilizer according to any one of claims 1 to 4, characterized in that, The polyisocyanate is selected from one or more of toluene diisocyanate, diphenylmethane diisocyanate, dicyclohexylmethane diisocyanate, hexamethylene diisocyanate, and isophorone diisocyanate.

6. A method for the preparation of the bio-based toughening agent according to any one of claims 1 to 5, characterized in that, Includes the following steps: (1) The castor oil and polyisocyanate are reacted at a temperature of 60℃-100℃ for 2-8 hours to obtain the polyurethane prepolymer; (2) The polyurethane prepolymer and cashew phenol are reacted at a temperature of 50℃-80℃ for 2-8 hours to obtain the bio-based toughening agent.

7. An epoxy adhesive, characterized by It contains a toughening agent, and the toughening agent includes the bio-based toughening agent according to any one of claims 1-5.

8. The epoxy adhesive of claim 7, wherein The bio-based toughening agent accounts for 5-25% of the weight of the epoxy adhesive.

9. The epoxy adhesive of claim 8, wherein The bio-based toughening agent accounts for 10-20% by weight in the epoxy adhesive.

10. The epoxy adhesive of claim 9, wherein The bio-based toughening agent accounts for 13-20% by weight in the epoxy adhesive.

11. The epoxy adhesive of claim 10, wherein The bio-based toughening agent accounts for 14-16% by weight in the epoxy adhesive.

12. The epoxy adhesive according to any one of claims 7 to 11, characterized in that, Prepared from raw materials comprising the following components in parts by weight:

13. The epoxy adhesive of claim 12, wherein, The epoxy adhesive is prepared from raw materials including the following components in parts by weight:

14. The epoxy adhesive of claim 13, wherein The epoxy adhesive is prepared from raw materials including the following components in parts by weight:

15. The epoxy adhesive of claim 14, wherein The epoxy adhesive is prepared from raw materials including the following components in parts by weight:

16. The epoxy adhesive according to any one of claims 11 to 15, wherein The epoxy resin is one or more of glycidyl ether epoxy resin and glycidyl ester epoxy resin; and / or The general toughening agent is one or more of CTBN toughening agent, core-shell rubber, and polyurethane-modified epoxy resin; and / or, The curing agent is one or more selected from imidazole, dicyandiamide, acid anhydride, and pyridine; and / or, The promoter is one or more of imidazole, pyridine, and organic urea.

17. A process for the preparation of the epoxy adhesive according to any one of claims 11 to 16, characterized in that, The process includes the following steps: mixing the epoxy resin, bio-based toughening agent, general toughening agent, curing agent and accelerator evenly at a temperature of 50℃-70℃, and then cooling to room temperature to obtain the epoxy adhesive.

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