A polyglutamic acid / epoxy soybean oil-based adhesive and a preparation method thereof

Abstract

This invention provides a polyglutamic acid / epoxidized soybean oil-based adhesive and its preparation method, comprising the following raw materials in parts by weight: polyglutamic acid: 10-65 parts, epoxidized soybean oil: 20-50 parts, and tannic acid: 0-30 parts; the polyglutamic acid has a relative molecular weight of 100,000-2,000,000 g / mol, and includes glutamic acid units and monosodium glutamate units, with the glutamic acid units comprising 30-60% by mass. The adhesive of this invention is prepared from fully biologically derived polyglutamic acid, epoxidized soybean oil, and tannic acid. The polyglutamic acid / epoxidized soybean oil-based epoxy resin adhesive obtained by this invention utilizes the reaction between epoxy groups and polycarboxyl groups, while using tannic acid to increase adhesion. It does not use bisphenol A, which is toxic to humans, and achieves a bonding strength of up to 10 MPa, making it suitable for various applications such as wood and steel adhesives.

Description

Technical Field

[0001] This invention belongs to the field of adhesive technology, and particularly relates to a polyglutamic acid / epoxidized soybean oil-based adhesive and its preparation method. Background Technology

[0002] Commercial adhesives currently used in industries such as timber often contain toxic gases such as formaldehyde, which harm human health. There is a need to develop a VOC-free, environmentally friendly adhesive. Furthermore, current commercial adhesives are often not fully biodegradable after use, generating large amounts of polymeric waste and impacting the environment. Therefore, there is a need to develop a fully bio-based and biodegradable adhesive. However, current biomass raw materials are often expensive, necessitating the selection of readily available, mass-producible biomass raw materials to prepare inexpensive bio-based crosslinking agents. Epoxy resin is a widely used adhesive, but current epoxy resins are mainly prepared by reacting epoxy groups with bisphenol A (BPA). BPA poses health risks to humans, including endocrine system disruption, reproductive system impact, and increased cancer risk. Therefore, there is a need to develop a more environmentally friendly epoxy resin adhesive. Summary of the Invention

[0003] The purpose of this invention is to provide a polyglutamic acid / epoxidized soybean oil-based adhesive and its preparation method. The polyglutamic acid / epoxidized soybean oil-based adhesive of this invention does not use bisphenol A, which is toxic to the human body, and is beneficial to human health. Moreover, the adhesive provided by this invention can achieve a bonding strength of 10 MPa and can be used in various applications such as wood and steel adhesives.

[0004] This invention provides a polyglutamic acid / epoxidized soybean oil-based adhesive, comprising the following raw materials in parts by weight:

[0005] Polyglutamic acid: 10-65 parts, epoxidized soybean oil: 20-50 parts, tannic acid: 0-30 parts;

[0006] The polyglutamic acid has a relative molecular weight of 100,000 to 2,000,000 g / mol, and includes glutamic acid units and monosodium glutamate units, with the glutamic acid units accounting for 30 to 60% of the total mass.

[0007] Preferably, the epoxy value of the epoxidized soybean oil is >0.6 mol / 100g.

[0008] Preferably, the mass percentage of the glutamic acid unit is 40-60%.

[0009] Preferably, the polyglutamic acid is present in a weight ratio of 30 to 65 parts.

[0010] Preferably, the tannin content is 0 to 20 parts by weight.

[0011] Preferably, the molar ratio of the carboxyl group in the polyglutamic acid to the epoxy group in the epoxidized soybean oil is 1:(0.9~1.1).

[0012] This invention provides a method for preparing the polyglutamic acid / epoxidized soybean oil-based adhesive as described above, comprising the following steps:

[0013] A) Mix polyglutamic acid, epoxidized soybean oil, and tannic acid to form a prepolymer;

[0014] B) The prepolymer is coated onto the surface of the material to be bonded and cured to obtain the cured polyglutamic acid / epoxy soybean oil-based adhesive.

[0015] Preferably, the mixing temperature in step A) is 60~100℃, and the mixing time in step A) is 1~24 hours.

[0016] Preferably, the curing temperature in step B) is 150~180℃, and the curing time in step B) is 1~8 hours.

[0017] This invention provides a polyglutamic acid / epoxidized soybean oil-based adhesive, comprising the following raw materials in parts by weight: polyglutamic acid: 10-65 parts, epoxidized soybean oil: 20-50 parts, and tannic acid: 0-30 parts; the polyglutamic acid has a relative molecular weight of 100,000-2,000,000 g / mol, and includes glutamic acid units and monosodium glutamate units, with the glutamic acid units comprising 30-60% by mass. The polyglutamic acid / epoxidized soybean oil-based adhesive prepared by this invention is derived from fully biologically sourced polyglutamic acid, epoxidized soybean oil, and tannic acid. The polyglutamic acid / epoxidized soybean oil-based epoxy resin adhesive prepared by this invention utilizes the reaction between epoxy groups and polycarboxyl groups, while using tannic acid to increase its effectiveness. It does not use bisphenol A, which is toxic to humans, thus being beneficial to human health. The adhesive provided by this invention has a bonding strength of up to 10 MPa and can be used in various applications such as wood and steel adhesives. Attached Figure Description

[0018] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on the provided drawings without creative effort.

[0019] Figure 1 Image of the prepolymer of the polyglutamic acid / epoxidized soybean oil-based / tannic acid adhesive in Example 1 of this invention;

[0020] Figure 2The original shear strength curves of five parallel samples of the adhesive bonded to steel sheets in Example 1 of this invention were tested by a tensile testing machine after curing. Detailed Implementation

[0021] This invention provides a polyglutamic acid / epoxidized soybean oil-based adhesive, comprising the following raw materials in parts by weight:

[0022] Polyglutamic acid: 10-65 parts, epoxidized soybean oil: 20-50 parts, tannic acid: 0-30 parts;

[0023] The polyglutamic acid has a relative molecular weight of 100,000 to 2,000,000 g / mol, and includes glutamic acid units and monosodium glutamate units, with the glutamic acid units accounting for 30 to 60% of the total mass.

[0024] In this invention, the polyglutamic acid is preferably 10 to 65 parts by weight, more preferably 15 to 60 parts, such as 10 parts, 15 parts, 20 parts, 25 parts, 30 parts, 35 parts, 40 parts, 45 parts, 50 parts, 55 parts, 60 parts, 65 parts, and preferably a range of values ​​with any of the above values ​​as the upper or lower limit.

[0025] In this invention, the weight of the epoxidized soybean oil is preferably 20 to 50 parts, more preferably 25 to 45 parts, such as 20 parts, 25 parts, 30 parts, 35 parts, 40 parts, 45 parts, 50 parts, and preferably any of the above values ​​as the upper or lower limit.

[0026] In this invention, the weight of the tannic acid is preferably 0 to 30 parts, more preferably 5 to 25 parts, such as 0 parts, 5 parts, 10 parts, 15 parts, 20 parts, 25 parts, 30 parts, and preferably a range of values ​​with the above values ​​as the upper or lower limit.

[0027] When the total weight parts of the polyglutamic acid, epoxidized soybean oil and tannic acid are 100 parts by weight, the weight parts of the polyglutamic acid, epoxidized soybean oil and tannic acid mentioned above can be equivalent to mass percentages.

[0028] In this invention, when the polyglutamic acid content in the adhesive is less than 10 wt%, the content of carboxyl functional groups in the adhesive is low, affecting the adhesive strength. When the polyglutamic acid content in the adhesive is greater than 50 wt%, the high viscosity of polyglutamic acid itself leads to a high viscosity of the prepolymer, making it difficult to flow and affecting the coating of the adhesive. In this invention, the epoxy groups in epoxidized soybean oil react with the carboxyl groups in polyglutamic acid to form crosslinking points. To effectively form the crosslinking reaction, the molar ratio of carboxyl groups in polyglutamic acid to epoxy groups in epoxidized soybean oil is controlled to be approximately 1:1. Therefore, the mass fraction of epoxidized soybean oil in this invention is related to the carboxyl group content in the added polyglutamic acid. Tannic acid contains multiple phenolic hydroxyl groups and can self-oxidize and crosslink to form a crosslinked network structure, which is used in this invention to increase the adhesive strength. However, when the tannic acid content in polyglutamic acid / epoxidized soybean oil-based / tannic acid exceeds 30 wt%, the fracture strain of the cured adhesive is small, thus affecting the bonding performance.

[0029] In this invention, the relative molecular weight of the polyglutamic acid is preferably 100,000-2,000,000 g / mol, more preferably 200,000-1,000,000 g / mol. The polyglutamic acid includes glutamic acid units and monosodium glutamate units, wherein the mass percentage of the glutamic acid units is preferably 30-60%, more preferably 40-60%, such as 30%, 35%, 40%, 45%, 50%, 55%, 60%, preferably within the range of any of the above values ​​as the upper or lower limit.

[0030] In this invention, when the molecular weight of polyglutamic acid is below 100,000 g / mol, the shear strength is low due to the low physical entanglement of polyglutamic acid itself. When the molecular weight of polyglutamic acid in this invention is above 2,000,000 g / mol, the viscosity of polyglutamic acid itself is very high, making it difficult to stir during the prepolymerization stage and thus difficult to form a uniform reaction system.

[0031] Commercially available polyglutamic acid typically contains glutamate units and monosodium glutamate (MSG) units. This invention utilizes a conventional inductively coupled plasma atomic emission spectrometry (ICP-AES) method to determine the sodium content in polyglutamic acid, allowing for the calculation of the molar percentages of glutamate and MSG units. The specific calculation is as follows: Assuming the sodium content in polyglutamic acid measured by ICP-AES is m1 (ppm), and given that the molar masses of sodium, glutamate, and MSG units are 23 g / mol, 129 g / mol, and 151 g / mol respectively, the formula for calculating the molar percentage (F) of glutamate units in polyglutamic acid is:

[0032] (1)

[0033] In this invention, when the proportion of glutamic acid units in polyglutamic acid is less than 30%, the adhesive performance is poor due to the low content of reactive carboxyl groups on each polyglutamic acid side chain. When the proportion of glutamic acid units in polyglutamic acid is higher than 60%, during the prepolymer formation stage, a large number of carboxyl groups react with epoxy groups to form a non-adhesive blocky material, which is not conducive to coating during subsequent curing.

[0034] In this invention, the epoxy value of the epoxidized soybean oil is preferably >0.6 mol / 100g. Typically, the maximum epoxy value of commercially available epoxidized soybean oil is 0.616 mol / 100g. In order to control the content of epoxy groups per unit mass of epoxidized soybean oil to improve the adhesive performance, the epoxy value of the epoxidized soybean oil used in this invention is required to be greater than 0.6 mol / 100g.

[0035] This invention also provides a method for preparing a polyglutamic acid / epoxidized soybean oil-based adhesive, comprising the following steps:

[0036] A) Mix polyglutamic acid, epoxidized soybean oil, and tannic acid to form a prepolymer;

[0037] B) The prepolymer is coated onto the surface of the material to be bonded and cured to obtain the cured polyglutamic acid / epoxy soybean oil-based adhesive.

[0038] In this invention, the physical properties and dosages of polyglutamic acid, epoxidized soybean oil, and tannic acid are consistent with those described above, and will not be repeated here.

[0039] In this invention, the mixing to form the prepolymer is preferably carried out at a lower temperature, preferably 60~100℃, more preferably 70~90℃, such as 60℃, 65℃, 70℃, 75℃, 80℃, 85℃, 90℃, 95℃, 100℃, preferably a range of values ​​with any of the above as the upper or lower limit; the mixing to form the prepolymer is preferably 1~24 hours, more preferably 5~20 hours.

[0040] In this invention, when the prepolymer reaction temperature is below 60°C and the reaction time is greater than 24 hours, production efficiency is affected. At lower temperatures such as room temperature, the reaction degree is very low, causing the adhesive to flow easily and making it difficult to coat. In this invention, when the prepolymer reaction temperature is above 100°C, the reaction time can be less than 1 hour. If the prepolymer reaction temperature is even higher, the reaction rate is very fast, the reaction degree is difficult to control, and a non-stick solid is easily formed. When the prepolymer reaction temperature is 100°C and the reaction time can be greater than 1 hour, the reaction degree in the prepolymerization stage is too high, making it difficult to coat.

[0041] In this invention, the curing reaction is preferably carried out at a relatively high temperature, preferably 150~180℃, more preferably 160~170℃, such as 150℃, 155℃, 160℃, 165℃, 170℃, 175℃, 180℃, preferably a range of values ​​with any of the above values ​​as the upper or lower limit; the curing reaction time is preferably 1~8 hours, more preferably 3~5 hours.

[0042] In this invention, when the curing temperature is below 150°C, the prepolymer reaction time is greater than 8 hours, affecting production efficiency. In this invention, when the prepolymer reaction temperature is above 180°C, the curing reaction time can be less than 1 hour. Higher curing temperatures may lead to high-temperature decomposition of the adhesive, affecting bonding performance. When the prepolymer reaction temperature is 180°C and the curing reaction time can be greater than 1 hour, it can also easily lead to over-crosslinking, resulting in an adhesive with low fracture strain.

[0043] This invention provides a polyglutamic acid / epoxidized soybean oil-based adhesive, comprising the following raw materials in parts by weight: polyglutamic acid: 10-65 parts, epoxidized soybean oil: 20-50 parts, and tannic acid: 0-30 parts; the polyglutamic acid has a relative molecular weight of 100,000-2,000,000 g / mol, and includes glutamic acid units and monosodium glutamate units, with the glutamic acid units comprising 30-60% by mass. The polyglutamic acid / epoxidized soybean oil-based adhesive prepared by this invention is derived from fully biologically sourced polyglutamic acid, epoxidized soybean oil, and tannic acid. The polyglutamic acid / epoxidized soybean oil-based epoxy resin adhesive prepared by this invention utilizes the reaction between epoxy groups and polycarboxyl groups, while using tannic acid to increase its effectiveness. It does not use bisphenol A, which is toxic to humans, thus being beneficial to human health. The adhesive provided by this invention has a bonding strength of up to 10 MPa and can be used in various applications such as wood and steel adhesives.

[0044] To further illustrate the present invention, the following detailed description of a polyglutamic acid / epoxidized soybean oil-based adhesive and its preparation method provided by the present invention is provided in conjunction with embodiments, but it should not be construed as limiting the scope of protection of the present invention.

[0045] Example 1

[0046] Formula components: 59.2 parts of polyglutamic acid with a glutamic acid unit ratio of 40% and a molecular weight of 100,000 g / mol, 27 parts of epoxidized soybean oil, and 13.8 parts of tannic acid.

[0047] The mass ratio of polyglutamic acid and epoxidized soybean oil is calculated as follows: Based on the molar masses of glutamic acid units and monosodium glutamate units being 129 g / mol and 151 g / mol respectively, the average molecular weight of repeating units in polyglutamic acid with a glutamic acid unit content of 40% is: 129 × 40% + 151 × 60% = 142.3 g / mol. Assuming there are 10 g of epoxidized soybean oil with an epoxy value of 0.616 mol / 100g (molecular weight of 974 g / mol), the mass m2 of polyglutamic acid with an equivalent carboxyl group content after all epoxy groups have reacted is calculated as follows:

[0048] (10 × 6) / 974 = (m2 / 142.3) × 40%

[0049] The calculated mass ratio of m2 = 21.9 g is 2.19:1, meaning the mass ratio of polyglutamic acid to epoxidized soybean oil is 2.19:1. In the subsequent examples and comparative examples, if the molar ratio of the carboxyl groups in the designed polyglutamic acid to the epoxy groups in the epoxidized soybean oil is also 1:1, the mass ratio will be calculated using the same method as above.

[0050] Prepolymer preparation method: Polyglutamic acid, epoxidized soybean oil, and tannic acid are stirred and reacted at 70℃ for 6 hours to form a prepolymer, such as... Figure 1 As shown.

[0051] Steel sheet bonding experiment: Five pairs of stainless steel sheets, each 10 cm long and 1 cm wide, were butt-welded with a prepolymer coating. The coating bonding area was 1 × 1 cm. 2 After securing the bonding area with dovetail clips, place it at 180℃ for 1 hour to cure. Then allow it to cool naturally at room temperature.

[0052] Adhesive shear strength test: The five pairs of steel sheets cured with the adhesive were tested using a tensile testing machine to measure the load (N) as a function of mechanical elongation (mm), as shown in the figure. Figure 2 As shown. The bond strength (MPa) was obtained by dividing the maximum load by the bond area, and the average bond strength of the five samples was 2.13 MPa.

[0053] Example 2

[0054] Formula components: 53.5 parts of polyglutamic acid with a glutamic acid unit content of 50% and a molecular weight of 1,000,000 g / mol, 31.1 parts of epoxidized soybean oil, and 15.4 parts of tannic acid.

[0055] The mass ratio of polyglutamic acid and epoxidized soybean oil is calculated as follows: Given that the molar masses of glutamic acid units and monosodium glutamate units are 129 g / mol and 151 g / mol respectively, the average molecular weight of repeating units in polyglutamic acid with a glutamic acid unit content of 50% is: 129 × 50% + 151 × 50% = 140 g / mol. Assuming there are 10 g of epoxidized soybean oil with an epoxy value of 0.616 mol / 100 g (molecular weight of 974 g / mol), the mass m2 of polyglutamic acid with an equivalent carboxyl group content after all epoxy groups have reacted is calculated as follows:

[0056] (10 × 6) / 974 = (m2 / 140) × 50%

[0057] The calculated mass ratio of m2 to 17.2 g indicates that the mass ratio of polyglutamic acid to epoxidized soybean oil is 1.72:1. In the subsequent examples and comparative examples, if the molar ratio of the carboxyl groups in the designed polyglutamic acid to the epoxy groups in the epoxidized soybean oil is also 1:1, the mass ratio should be calculated using the same method described above. Detailed calculation processes will not be provided in the subsequent examples and comparative examples; please refer to Examples 1 and 2 for calculations.

[0058] Prepolymer preparation method: Polyglutamic acid, epoxidized soybean oil and tannic acid are stirred and reacted at 70℃ for 24h to form a prepolymer.

[0059] Steel sheet bonding experiment: Five pairs of stainless steel sheets, each 10 cm long and 1 cm wide, were butt-welded with a prepolymer coating. The coating bonding area was 1 × 1 cm. 2 After securing the bonding area with dovetail clips, place it at 160℃ for 6 hours to cure. Then allow it to cool naturally at room temperature.

[0060] Adhesive shear strength test: The load (N) versus mechanical elongation (mm) curves of the five pairs of steel sheets cured with the above adhesive were tested using a tensile testing machine. The bond strength (MPa) was obtained by dividing the maximum load by the bonded area. The average bond strength of the five samples was 10.68 MPa.

[0061] Example 3

[0062] Formula components: 53.5 parts of polyglutamic acid with a glutamic acid unit content of 50% and a molecular weight of 1,000,000 g / mol, 31 parts of epoxidized soybean oil, and 15.5 parts of tannic acid.

[0063] Prepolymer preparation method: Polyglutamic acid, epoxidized soybean oil and tannic acid are stirred and reacted at 70℃ for 24h to form a prepolymer.

[0064] Wood board bonding experiment: Five pairs of birch wood boards, each 10 cm long, 2 cm wide, and 1 cm thick, were butted together using a prepolymer coating. The coating bonding area was 1 × 1 cm. 2 After securing the bonding area with dovetail clips, place it at 150 ℃ for 1 hour to cure. Then allow it to cool naturally at room temperature.

[0065] Adhesive shear strength test: The load (N) versus mechanical elongation (mm) curves of the five pairs of wood boards cured with the above adhesive were tested using a tensile testing machine. The bond strength (MPa) was obtained by dividing the maximum load by the bonded area. The average bond strength of the five samples was taken as 2.54 MPa.

[0066] Example 4

[0067] Formula components: 59.2 parts of polyglutamic acid with a glutamic acid unit content of 40% and a molecular weight of 20,000,000 g / mol, 27.2 parts of epoxidized soybean oil, and 13.6 parts of tannic acid.

[0068] Prepolymer preparation method: Polyglutamic acid, epoxidized soybean oil and tannic acid are stirred and reacted at 70°C for 1 hour to form a prepolymer.

[0069] Steel sheet bonding experiment: Five pairs of stainless steel sheets, each 10 cm long and 1 cm wide, were butt-welded with a prepolymer coating. The coating bonding area was 1 × 1 cm. 2 After securing the bonding area with dovetail clips, place it at 150℃ for 6 hours to cure. Then allow it to cool naturally at room temperature.

[0070] Adhesive shear strength test: The load (N) versus mechanical elongation (mm) curves of the five pairs of steel sheets cured with the above adhesive were tested using a tensile testing machine. The bond strength (MPa) was obtained by dividing the maximum load by the bonded area. The average bond strength of the five samples was 9.73 MPa.

[0071] Example 5

[0072] Formula components: 48.5 parts of polyglutamic acid with a glutamic acid unit content of 60% and a molecular weight of 1,000,000 g / mol, 34.4 parts of epoxidized soybean oil, and 17.1 parts of tannic acid.

[0073] Prepolymer preparation method: Polyglutamic acid, epoxidized soybean oil and tannic acid are stirred and reacted at 80℃ for 5h to form a prepolymer.

[0074] Steel sheet bonding experiment: Five pairs of stainless steel sheets, each 10 cm long and 1 cm wide, were butt-welded with a prepolymer coating. The coating bonding area was 1 × 1 cm. 2After securing the bonding area with dovetail clips, place it at 170℃ for 3 hours to cure. Then allow it to cool naturally at room temperature.

[0075] Adhesive shear strength test: The load (N) versus mechanical elongation (mm) curves of the five pairs of steel sheets cured with the above adhesive were tested using a tensile testing machine. The bond strength (MPa) was obtained by dividing the maximum load by the bonded area, and the average bond strength of the five samples was taken as 8.57 MPa.

[0076] Example 6

[0077] Formula components: 63.2 parts of polyglutamic acid with a glutamic acid unit content of 50% and a molecular weight of 1,000,000 g / mol, and 36.8 parts of epoxidized soybean oil.

[0078] Prepolymer preparation method: Polyglutamic acid and epoxidized soybean oil are stirred and reacted at 70°C for 24 hours to form a prepolymer.

[0079] Steel sheet bonding experiment: Five pairs of stainless steel sheets, each 10 cm long and 1 cm wide, were butt-welded with a prepolymer coating. The coating bonding area was 1 × 1 cm. 2 After securing the bonding area with dovetail clips, place it at 160℃ for 6 hours to cure. Then allow it to cool naturally at room temperature.

[0080] Adhesive shear strength test: The load (N) versus mechanical elongation (mm) curves of the five pairs of steel sheets cured with the above adhesive were tested using a tensile testing machine. The bond strength (MPa) was obtained by dividing the maximum load by the bonded area, and the average bond strength of the five samples was taken as 4.85 MPa.

[0081] Comparative Example 1

[0082] The adhesive was prepared according to the method of Example 1, except that the mass ratio of polyglutamic acid in Comparative Example 1 was 68 wt%.

[0083] Formula components: 68 parts of polyglutamic acid with a glutamic acid unit content of 40% and a molecular weight of 100,000 g / mol, 31 parts of epoxidized soybean oil, and 1 part of tannic acid.

[0084] Prepolymer preparation method: Polyglutamic acid, epoxidized soybean oil and tannic acid are stirred and reacted at 70°C for 6 hours to form a prepolymer.

[0085] The resulting prepolymer is highly reactive, clumps together, and cannot be evenly coated for subsequent bonding. Therefore, subsequent bonding and bond strength testing are impossible.

[0086] Comparative Example 2

[0087] The adhesive was prepared according to the method of Example 1, except that the mass ratio of polyglutamic acid was 8 wt%.

[0088] Formula components: 8 parts of polyglutamic acid with a glutamic acid unit content of 40% and a molecular weight of 100,000 g / mol, 3.6 parts of epoxidized soybean oil, and 88.4 parts of tannic acid.

[0089] Prepolymer preparation method: Polyglutamic acid, epoxidized soybean oil and tannic acid are stirred and reacted at 70°C for 6 hours to form a prepolymer.

[0090] Steel sheet bonding experiment: Five pairs of stainless steel sheets, each 10 cm long and 1 cm wide, were butt-welded with a prepolymer coating. The coating bonding area was 1 × 1 cm. 2 After securing the bonding area with dovetail clips, place it at 180℃ for 1 hour to cure. Then allow it to cool naturally at room temperature.

[0091] Adhesive shear strength test: The load (N) versus mechanical elongation (mm) curves of the five pairs of steel sheets cured with the above adhesive were tested using a tensile testing machine. The bond strength (MPa) was obtained by dividing the maximum load by the bonded area, and the average bond strength of the five samples was taken as 0.84 MPa.

[0092] Comparative Example 3

[0093] The adhesive was prepared according to the method of Example 2, except that the molecular weight of polyglutamic acid was less than 1,000,000 g / mol.

[0094] Formula components: 53.5 parts of polyglutamic acid with a glutamic acid unit content of 50% and a molecular weight of 1000 g / mol, 31.1 parts of epoxidized soybean oil, and 15.4 parts of tannic acid.

[0095] Prepolymer preparation method: Polyglutamic acid, epoxidized soybean oil and tannic acid are stirred and reacted at 70℃ for 24h to form a prepolymer.

[0096] Steel sheet bonding experiment: Five pairs of stainless steel sheets, each 10 cm long and 1 cm wide, were butt-welded with a prepolymer coating. The coating bonding area was 1 × 1 cm. 2 After securing the bonding area with dovetail clips, place it at 160℃ for 6 hours to cure. Then allow it to cool naturally at room temperature.

[0097] Adhesive shear strength test: The load (N) versus mechanical elongation (mm) curves of the five pairs of steel sheets cured with the above adhesive were tested using a tensile testing machine. The bond strength (MPa) was obtained by dividing the maximum load by the bonded area, and the average bond strength of the five samples was taken as 0.95 MPa.

[0098] Comparative Example 4

[0099] The adhesive was prepared according to the method of Example 2, except that the molecular weight of polyglutamic acid was greater than 2,000,000 g / mol.

[0100] Formula components: 53.5 parts of polyglutamic acid with a glutamic acid unit content of 50% and a molecular weight of 3,000,000 g / mol, 31.1 parts of epoxidized soybean oil, and 15.4 parts of tannic acid.

[0101] Prepolymer preparation method: Polyglutamic acid, epoxidized soybean oil and tannic acid are stirred and reacted at 70℃ for 24h to form a prepolymer.

[0102] The resulting prepolymer is highly reactive, clumps together, and cannot be evenly coated for subsequent bonding. Therefore, subsequent bonding and bond strength testing are impossible.

[0103] Comparative Example 5

[0104] The adhesive was prepared according to the method of Example 2, except that polyglutamic acid with a molecular weight of 1,000,000 g / mol was used, but the proportion of glutamic acid units was less than 40%.

[0105] Formula components: 53.5 parts of polyglutamic acid with a glutamic acid unit ratio of 30% and a molecular weight of 1,000,000 g / mol, 18.1 parts of epoxidized soybean oil, and 28.4 parts of tannic acid.

[0106] Prepolymer preparation method: Polyglutamic acid, epoxidized soybean oil and tannic acid are stirred and reacted at 70℃ for 24h to form a prepolymer.

[0107] Steel sheet bonding experiment: Five pairs of stainless steel sheets, each 10 cm long and 1 cm wide, were butt-welded with a prepolymer coating. The coating bonding area was 1 × 1 cm. 2 After securing the bonding area with dovetail clips, place it at 160℃ for 6 hours to cure. Then allow it to cool naturally at room temperature.

[0108] Adhesive shear strength test: The load (N) versus mechanical elongation (mm) curves of the five pairs of steel sheets cured with the above adhesive were tested using a tensile testing machine. The bond strength (MPa) was obtained by dividing the maximum load by the bonded area, and the average bond strength of the five samples was taken as 1.15 MPa.

[0109] Comparative Example 6

[0110] The adhesive was prepared according to the method of Example 2, except that polyglutamic acid with a molecular weight of 1,000,000 g / mol was used, but the proportion of glutamic acid units was greater than 60%.

[0111] Formula components: 53.5 parts of polyglutamic acid with a glutamic acid unit content of 70% and a molecular weight of 1,000,000 g / mol, 45 parts of epoxidized soybean oil, and 1.5 parts of tannic acid.

[0112] Prepolymer preparation method: Polyglutamic acid, epoxidized soybean oil and tannic acid are stirred and reacted at 70 ℃ for 24 h to form a prepolymer.

[0113] The resulting prepolymer is highly reactive, clumps together, and cannot be evenly coated for subsequent bonding. Therefore, subsequent bonding and bond strength testing are impossible.

[0114] Comparative Example 7

[0115] The adhesive was prepared according to the method of Example 2, except that the prepolymerization temperature was lower than 60°C.

[0116] Formula components: 53.5 parts of polyglutamic acid with a glutamic acid unit content of 50% and a molecular weight of 1,000,000 g / mol, 31.1 parts of epoxidized soybean oil, and 15.4 parts of tannic acid.

[0117] Prepolymer preparation method: Polyglutamic acid, epoxidized soybean oil and tannic acid are stirred and reacted at 50°C for 24 hours to form a prepolymer.

[0118] The resulting prepolymer has a very low viscosity; when bonding steel sheets, it basically flows out when fixed with dovetail clips, requiring very little adhesive. It is placed in a 160°C container. o After curing at C temperature for 6 hours, and then cooling to room temperature and stretching, it broke immediately upon stretching. The reason may be that the amount of adhesive applied was too small.

[0119] Comparative Example 8

[0120] The adhesive was prepared according to the method of Example 2, except that the prepolymerization temperature was higher than 100°C.

[0121] Formula components: 53.5 parts of polyglutamic acid with a glutamic acid unit content of 50% and a molecular weight of 1,000,000 g / mol, 31.1 parts of epoxidized soybean oil, and 15.4 parts of tannic acid.

[0122] Prepolymer preparation method: Polyglutamic acid, epoxidized soybean oil and tannic acid are stirred and reacted at 110℃ for 1 hour to form a prepolymer.

[0123] The prepolymer forms a non-sticky solid, making it difficult to coat.

[0124] Comparative Example 9

[0125] The adhesive was prepared according to the method of Example 2, except that the curing temperature of the adhesive was lower than 150°C. o C.

[0126] Formula components: 53.5 parts of polyglutamic acid with a glutamic acid unit content of 50% and a molecular weight of 1,000,000 g / mol, 31.1 parts of epoxidized soybean oil, and 15.4 parts of tannic acid.

[0127] Prepolymer preparation method: Polyglutamic acid, epoxidized soybean oil and tannic acid are stirred and reacted at 70℃ for 24h to form a prepolymer.

[0128] Steel sheet bonding experiment: Five pairs of stainless steel sheets, each 10 cm long and 1 cm wide, were butt-welded with a prepolymer coating. The coating bonding area was 1 × 1 cm. 2 After securing the bonding area with dovetail clips, place it at 140 ℃ for 8 hours to cure. Then allow it to cool naturally at room temperature.

[0129] Adhesive shear strength test: The load (N) versus mechanical elongation (mm) curves of the five pairs of steel sheets cured with the above adhesive were tested using a tensile testing machine. The bond strength (MPa) was obtained by dividing the maximum load by the bonded area, and the average bond strength of the five samples was taken as 1.35 MPa.

[0130] Comparative Example 10

[0131] The adhesive was prepared according to the method of Example 2, except that the curing temperature of the adhesive was higher than 180°C. o C.

[0132] Formula components: 53.5 parts of polyglutamic acid with a glutamic acid unit content of 50% and a molecular weight of 1,000,000 g / mol, 31.1 parts of epoxidized soybean oil, and 15.4 parts of tannic acid.

[0133] Prepolymer preparation method: Polyglutamic acid, epoxidized soybean oil and tannic acid are stirred and reacted at 70℃ for 24h to form a prepolymer.

[0134] Steel sheet bonding experiment: Five pairs of stainless steel sheets, each 10 cm long and 1 cm wide, were butt-welded with a prepolymer coating. The coating bonding area was 1 × 1 cm. 2 After securing the bonding area with dovetail clips, place it at 190℃ for 1 hour to cure. Then allow it to cool naturally at room temperature.

[0135] Adhesive shear strength test: The load (N) versus mechanical elongation (mm) curves of the five pairs of steel sheets cured with the above adhesive were tested using a tensile testing machine. The bond strength (MPa) was obtained by dividing the maximum load by the bonded area, and the average bond strength of the five samples was taken as 1.67 MPa.

[0136] As can be seen from the above embodiments and comparative examples, the preparation method of the polyglutamic acid / epoxidized soybean oil-based / tannic acid adhesive of the present invention requires controlling the appropriate content of each reactant (polyglutamic acid, epoxidized soybean oil-based, and tannic acid), selecting the appropriate molecular weight and glutamic acid content of polyglutamic acid, and adjusting the prepolymerization temperature and time, curing temperature and time, in order to prepare an adhesive with high bonding strength (greater than 2 MPa), which may be applied in multiple fields.

[0137] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A polyglutamic acid / epoxidized soybean oil-based adhesive, comprising the following raw materials in parts by weight: Polyglutamic acid: 10-65 parts, epoxidized soybean oil: 20-50 parts, tannic acid: 0-20 parts; The polyglutamic acid has a relative molecular weight of 100,000 to 2,000,000 g / mol, and includes glutamic acid units and monosodium glutamate units, with the glutamic acid units accounting for 40% to 60% by mass. The polyglutamic acid / epoxidized soybean oil-based adhesive is prepared according to the following steps: A) Mix polyglutamic acid, epoxidized soybean oil, and tannic acid to form a prepolymer; The mixing temperature in step A) is 60~100℃, and the mixing time in step A) is 1~24 hours; B) The prepolymer is coated onto the surface of the material to be bonded and cured to obtain the cured polyglutamic acid / epoxy soybean oil-based adhesive; The curing temperature in step B) is 150~180℃, and the curing time in step B) is 1~8 hours.

2. The polyglutamic acid / epoxidized soybean oil-based adhesive according to claim 1, characterized in that, The epoxy value of the epoxidized soybean oil is >0.6 mol / 100g.

3. The polyglutamic acid / epoxidized soybean oil-based adhesive according to claim 1, characterized in that, The weight fraction of polyglutamic acid is 30 to 65 parts.

4. The polyglutamic acid / epoxidized soybean oil-based adhesive according to claim 1, characterized in that, The molar ratio of the carboxyl group in the polyglutamic acid to the epoxy group in the epoxidized soybean oil is 1:(0.9~1.1).

5. The preparation method of the polyglutamic acid / epoxidized soybean oil-based adhesive as described in claim 1, comprising the following steps: A) Mix polyglutamic acid, epoxidized soybean oil, and tannic acid to form a prepolymer; B) The prepolymer is coated onto the surface of the material to be bonded and cured to obtain the cured polyglutamic acid / epoxy soybean oil-based adhesive.

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