A bio-based polyurethane adhesive and a method of making the same

Abstract

The application discloses a kind of bio-based polyurethane adhesive and preparation method thereof, belong to adhesive technical field.The adhesive includes A component and B component, by mass fraction, A component includes the following raw materials: modified castor oil 50-70 parts, rosin-based polyol 30-50 parts, catalyst 0.1-0.5 parts;By mass fraction, B component includes the following raw materials: bio-based aliphatic diisocyanate 60-80 parts, polyether polyol 5-10 parts, 2,5-furandicarboxylic acid 3-6 parts.Wherein, modified castor oil is castor oil by double bond and thiol grafting thiol-polyethylene glycol-amino, rosin-based polyol is the polyester polyol formed by polymerization reaction of rosin dimer and small molecule dihydric alcohol.The polyurethane adhesive is prepared by using bio-based polyol and isocyanate as raw materials, which can improve the heat resistance while ensuring flexibility, and the adhesive has high tensile shear strength and peel strength.

Description

Technical Field

[0001] This invention belongs to the field of adhesive technology, specifically relating to a bio-based polyurethane adhesive and its preparation method. Background Technology

[0002] Polyurethane adhesives are adhesives containing urethane or isocyanate groups in their molecular chains. By reacting these urethane or isocyanate groups with substances containing active hydrogen within or outside the system, polyurethane groups are generated, thereby greatly increasing the strength of the system and achieving the purpose of bonding.

[0003] Polyurethane adhesives possess properties such as strong adhesion, low-temperature resistance, and no formaldehyde release, making them widely used in various fields, including automobiles, wood, packaging, and construction. With increasing attention to issues such as petroleum resource shortages and ecological imbalances in the chemical industry, research on the synthesis and application of bio-based polyurethane adhesives based on renewable resources such as modified vegetable oils, polysaccharides, and lignin derivatives is constantly emerging.

[0004] Bio-based polyurethane adhesives are polyurethane adhesives made from bio-based materials. The main characteristic of this type of adhesive is that it uses renewable biomass as raw material, produced through specific chemical reactions and processing techniques. It possesses a certain degree of biodegradability, aligning with the industrial trend towards green and low-carbon development. However, the inherent poor heat resistance of polyurethane adhesives still limits its application in some fields. Summary of the Invention

[0005] The purpose of this invention is to provide a bio-based polyurethane adhesive and its preparation method, which can solve the problem of poor heat resistance of adhesives in the prior art.

[0006] The objective of this invention can be achieved through the following technical solutions:

[0007] A bio-based polyurethane adhesive, comprising component A and component B; component A comprises the following raw materials in parts by weight:

[0008] Modified castor oil 50-70 parts, rosin-based polyol 30-50 parts, catalyst 0.1-0.5 parts;

[0009] By mass fractions, component B comprises the following raw materials:

[0010] 60-80 parts of bio-based aliphatic diisocyanate, 5-10 parts of polyether polyol, and 3-6 parts of 2,5-furandicarboxylic acid;

[0011] The modified castor oil is castor oil grafted with thiol-polyethylene glycol-amino groups through a reaction between double bonds and thiol groups;

[0012] The rosin-based polyol is a polyester polyol formed by the polymerization reaction of rosin dimer and small molecule diol.

[0013] Replacing petroleum-based polyols with bio-based polyols reduces dependence on petroleum resources. Castor oil is a commonly used bio-based raw material for polyurethane preparation. Castor oil contains unsaturated double bonds. Using these double bonds as grafting sites, flexible polyethylene glycol (PEG) long chains are introduced into its molecular chain through a green technology double-bond-thiol click chemistry reaction. The terminal amino groups of the modified castor oil are highly reactive and can react with isocyanate groups, acting as chain extenders to promote adhesive curing. The highly reactive amino groups react with isocyanates to form urea bonds, which are more polar and can improve the adhesion of polyurethane adhesives. The terminal amino groups, through the entanglement of the long chains, fully contact other components in the system, enabling them to participate in the reaction. PEG segments are strongly hydrophilic, while the fatty acid chains of castor oil are hydrophobic. The grafting reaction makes the modified castor oil amphiphilic, resulting in better compatibility with other components in the polyurethane.

[0014] The simultaneous addition of rosin-based polyols with extremely rigid structures provides rigid nodes for the polyurethane network, improving heat resistance. By forming an interwoven network between the flexible long chains on modified castor oil and the rigid structure on the rosin-based polyols, stress concentration and premature cracking caused by excessively dense rigid groups are avoided, resulting in polyurethane adhesives with high tensile shear strength, good flexibility, and peel strength.

[0015] Bio-based aliphatic diisocyanate provides isocyanate groups to participate in the reaction. In component B, polyether polyol reacts with bio-based aliphatic diisocyanate to form a prepolymer. The introduction of long-chain molecules of polyether polyol gives the adhesive higher elongation at break, flexibility and impact toughness, ensuring that the adhesive can maintain good elasticity and will not become brittle in low-temperature environments.

[0016] Furthermore, the preparation steps of the modified castor oil are as follows:

[0017] S1. Mix castor oil, mercapto-polyethylene glycol-amino and photoinitiator, add to ethyl acetate and stir until homogeneous;

[0018] S2. Under ultraviolet light irradiation, the mixture is stirred and reacted for 30-40 minutes. The product is collected and the solvent is removed by rotary evaporation to obtain modified castor oil.

[0019] Thiol-olefin click chemistry is a simple and efficient method for synthesizing multifunctional materials. It features simple reaction conditions, high stereoselectivity, fast reaction rate, and excellent yield. Castor oil is a triol containing unsaturated double bonds. Under the action of a photoinitiator, a long polyethylene glycol chain is introduced into the side chain of the molecular chain through click chemistry, while simultaneously introducing amino groups.

[0020] Furthermore, the photoinitiator is benzoin dimethyl ether, and the photoinitiator is 3.5-5.5% of the total mass of mercapto-polyethylene glycol-amino.

[0021] Furthermore, the castor oil is mixed with mercapto-polyethylene glycol-amino at a molar ratio of carbon-carbon double bonds to mercapto groups of 2-3:1.

[0022] Furthermore, the preparation steps of the rosin-based polyol are as follows:

[0023] A1. Add rosin dimer, ethylene glycol, 1,4-butanediol and diethylene glycol to a reaction vessel, heat to 140-150℃ under nitrogen atmosphere, and after complete melting, start stirring and heat to 170-180℃ and continue stirring for 1-2 hours.

[0024] A2. Heat to 220-230℃ and evacuate the vacuum inside the vessel to a vacuum degree of 4500-5500Pa, and maintain for 10-20 minutes.

[0025] A3. After the reaction is complete, reduce the temperature of the reactor to 150-160℃ and the pressure inside the reactor to atmospheric pressure. Discharge the product to obtain rosin-based polyol.

[0026] Rosin dimer and small molecule diols form hydroxyl-terminated polyester polyols through a polymerization reaction.

[0027] Further, in step A1, the molar ratio of the rosin dimer to the alcohol is 1:1.1-1.2.

[0028] Furthermore, the molar ratio of ethylene glycol, 1,4-butanediol and diethylene glycol is 1:1:1-2.

[0029] Furthermore, the catalyst is at least one of dibutyltin dilaurate, stannous octoate, and dibutyltin diacetate.

[0030] Furthermore, the bio-based aliphatic diisocyanate is at least one of 1,5-pentanediisocyanate and L-lysine diisocyanate.

[0031] Furthermore, the polyether polyol is at least one of polytetrahydrofuran diol and polypropylene glycol.

[0032] This invention also provides a method for preparing a bio-based polyurethane adhesive, which includes the following preparation steps:

[0033] Step 1: Under a nitrogen atmosphere, mix the raw materials in component B in proportion, heat to 80-90℃ and stir for 3-5 hours, heat to 110-120℃ and dehydrate under reduced pressure, cool to 80-90℃ after dehydration, determine the NCO mass fraction to be 6-10%, cool to room temperature and discharge to obtain component B.

[0034] Step 2: Mix the modified castor oil and rosin-based polyol in component A, then add the catalyst and stir until homogeneous to obtain component A;

[0035] Step 3: Mix component A and component B at a molar ratio of OH in component A to NCO in component B of 1:1.05-1.10 to obtain the adhesive.

[0036] In component B, the bio-based diisocyanate first reacts with the polyether polyol to generate a prepolymer with -NCO end groups. Simultaneously, the carboxyl group (-COOH) of 2,5-furandicarboxylic acid also reacts with some of the -NCO groups to form amide bonds, introducing a rigid furan ring structure and amide groups, thereby improving the heat resistance of the polyurethane.

[0037] When components A and B are mixed, the large number of hydroxyl groups (-OH) contained in the modified castor oil and rosin-based polyol in component A undergoes rapid chain extension and cross-linking reactions with the -NCO groups in the prepolymer of component B, thus constructing a three-dimensional network structure that is both rigid and flexible and highly cross-linked.

[0038] The beneficial effects of this invention are:

[0039] (1) Using bio-based polyols and isocyanates as raw materials to prepare polyurethane adhesives reduces dependence on petroleum resources, improves the environmental friendliness of polyurethane adhesives, and conforms to the trend of sustainable development.

[0040] (2) Polyurethane is prepared by using polyols with flexible long chains and polyols with rigid structures. The flexible chains are spaced apart from the rigid structure to avoid cracking of the adhesive after curing due to excessive concentration of rigid structure. This improves heat resistance while ensuring flexibility.

[0041] (3) By grafting terminal amino-terminated polyethylene glycol long chains onto castor oil using green and energy-saving click chemistry technology, modified castor oil is efficiently obtained. This allows the modified castor oil to form an adhesive network system with higher crosslinking density with the diisocyanate in component B, resulting in better water resistance and adhesion. The introduced amino groups react with NCO to form urea bonds, which have very strong polarity and the ability to form hydrogen bonds, promoting the curing of polyurethane adhesives and shortening the curing time.

[0042] (4) Polyester polyols are formed by esterification polymerization with rosin dimer as the matrix. Rosin dimer has a rigid structure, which can improve the thermal stability of adhesives.

[0043] (5) In component B, bio-based aliphatic diisocyanate, polyether polyol and 2,5-furandicarboxylic acid form a prepolymer. The bio-based diisocyanate first reacts with the polyether polyol to generate a prepolymer with -NCO end group. The carboxyl group (-COOH) of 2,5-furandicarboxylic acid also reacts with some -NCO to generate amide bonds, introducing a furan ring structure to ensure the heat resistance of component B prepolymer. The polyurethane formed by mixing component B and component A achieves a good balance between strength and toughness, with high tensile shear strength, as well as good flexibility and peel strength. Detailed Implementation

[0044] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0045] Example 1

[0046] Preparation of modified castor oil:

[0047] S1. Weigh castor oil and mercapto-polyethylene glycol-amino (polyethylene glycol with a molecular weight of 2000) according to a carbon-carbon double bond and mercapto molar ratio of 2.5:1. Weigh benzoin dimethyl ether as a photoinitiator according to 4.0% of the total mass of mercapto-polyethylene glycol-amino. Mix the three together and add them to ethyl acetate at a mass concentration of 20% and stir until homogeneous.

[0048] S2. Place the thoroughly stirred reaction solution under ultraviolet light (wavelength 365nm) with an irradiation power of approximately 0.1W. cm -2 The mixture was stirred and reacted for 35 minutes. The product was collected and removed by rotary evaporation to obtain modified castor oil.

[0049] Preparation of rosin-based polyols:

[0050] A1. Prepare ethylene glycol, 1,4-butanediol and diethylene glycol in a molar ratio of 1:1:1.5. Prepare rosin dimer (polymerized rosin) in a molar ratio of rosin dimer to alcohol of 1:1.15. Add all of the rosin dimer and alcohol to the reaction vessel. Use nitrogen to replace the reaction vessel to form a nitrogen atmosphere. Raise the temperature inside the reaction vessel to 150°C. Once the reactants have completely melted, start stirring and raise the temperature to 175°C and continue stirring for 1.5 hours.

[0051] A2. Then raise the temperature of the reactor to 230°C and start vacuuming until the vacuum degree inside the reactor reaches 5000Pa, and maintain it for 15 minutes.

[0052] A3. After the reaction is complete, the temperature of the reactor is reduced to 150°C, and the pressure inside the reactor is brought up to atmospheric pressure. The product is then discharged to obtain rosin-based polyol.

[0053] Preparation of adhesives:

[0054] Step 1: Prepare 70 parts L-lysine diisocyanate, 8 parts polytetrahydrofurandiol, and 4 parts 2,5-furandicarboxylic acid by mass. Mix all ingredients thoroughly under a nitrogen atmosphere, heat to 80°C, start stirring and continue the reaction for 4 hours. Then heat to 115°C and dehydrate under reduced pressure (-0.09 MPa). After dehydration, cool to 80°C and determine that the NCO mass fraction is 8.4%. Cool to room temperature and discharge to obtain component B.

[0055] Step 2: Prepare 60 parts of modified castor oil, 40 parts of rosin-based polyol, and 0.3 parts of dibutyltin dilaurate according to the mass proportions. Mix the modified castor oil and rosin-based polyol, then add dibutyltin dilaurate and mix evenly to obtain component A.

[0056] Step 3: Mix component A and component B at a molar ratio of OH in component A to NCO in component B of 1:1.05 to obtain the adhesive.

[0057] Example 2

[0058] The only difference from Example 1 is that, in preparing the modified castor oil, the ratio of castor oil to mercapto-polyethylene glycol-amino is 2.0:1 according to the molar ratio of carbon-carbon double bond to mercapto group. The steps for preparing rosin-based polyol and preparing adhesive are the same as in Example 1.

[0059] Preparation of modified castor oil:

[0060] S1. Weigh castor oil and mercapto-polyethylene glycol-amino (polyethylene glycol with a molecular weight of 2000) according to a carbon-carbon double bond and mercapto molar ratio of 2.0:1. Weigh benzoin dimethyl ether as a photoinitiator according to 4.0% of the total mass of mercapto-polyethylene glycol-amino. Mix the three together and add them to ethyl acetate at a mass concentration of 20% and stir until homogeneous.

[0061] S2. Place the thoroughly stirred reaction solution under ultraviolet light (wavelength 365nm) with an irradiation power of approximately 0.1W. cm -2 The mixture was stirred and reacted for 35 minutes. The product was collected and removed by rotary evaporation to obtain modified castor oil.

[0062] Example 3

[0063] The only difference from Example 1 is that, in preparing the modified castor oil, the ratio of castor oil to mercapto-polyethylene glycol-amino is 3.0:1 according to the molar ratio of carbon-carbon double bond to mercapto group. The steps for preparing rosin-based polyol and preparing adhesive are the same as in Example 1.

[0064] Preparation of modified castor oil:

[0065] S1. Weigh castor oil and mercapto-polyethylene glycol-amino (polyethylene glycol with a molecular weight of 2000) according to a carbon-carbon double bond and mercapto molar ratio of 3.0:1. Weigh benzoin dimethyl ether as a photoinitiator according to 4.0% of the total mass of mercapto-polyethylene glycol-amino. Mix the three together and add them to ethyl acetate at a mass concentration of 20% and stir until homogeneous.

[0066] S2. Place the thoroughly stirred reaction solution under ultraviolet light (wavelength 365nm) with an irradiation power of approximately 0.1W. cm -2 The mixture was stirred and reacted for 35 minutes. The product was collected and removed by rotary evaporation to obtain modified castor oil.

[0067] Example 4

[0068] The only difference from Example 1 is that, when preparing the adhesive, the mass fraction of modified castor oil is adjusted to 70 parts and the mass fraction of rosin-based polyol is adjusted to 30 parts. The steps for preparing modified castor oil and rosin-based polyol are the same as in Example 1.

[0069] Preparation of adhesives:

[0070] Step 1: Prepare 70 parts L-lysine diisocyanate, 8 parts polytetrahydrofurandiol, and 4 parts 2,5-furandicarboxylic acid by mass. Mix all ingredients thoroughly under a nitrogen atmosphere, heat to 80°C, start stirring and continue the reaction for 4 hours. Then heat to 115°C and dehydrate under reduced pressure (-0.09 MPa). After dehydration, cool to 80°C and determine that the NCO mass fraction is 8.4%. Cool to room temperature and discharge to obtain component B.

[0071] Step 2: Prepare 70 parts modified castor oil, 30 parts rosin-based polyol, and 0.3 parts dibutyltin dilaurate by weight. Mix the modified castor oil and rosin-based polyol together, then add dibutyltin dilaurate and mix well to obtain component A.

[0072] Step 3: Mix component A and component B at a molar ratio of OH in component A to NCO in component B of 1:1.05 to obtain the adhesive.

[0073] Example 5

[0074] The only difference from Example 1 is that, when preparing the adhesive, the mass fraction of modified castor oil is adjusted to 50 parts and the mass fraction of rosin-based polyol is adjusted to 50 parts. The steps for preparing modified castor oil and rosin-based polyol are the same as in Example 1.

[0075] Preparation of adhesives:

[0076] Step 1: Prepare 70 parts L-lysine diisocyanate, 8 parts polytetrahydrofurandiol, and 4 parts 2,5-furandicarboxylic acid by mass. Mix all ingredients thoroughly under a nitrogen atmosphere, heat to 80°C, start stirring and continue the reaction for 4 hours. Then heat to 115°C and dehydrate under reduced pressure (-0.09 MPa). After dehydration, cool to 80°C and determine that the NCO mass fraction is 8.4%. Cool to room temperature and discharge to obtain component B.

[0077] Step 2: Prepare 50 parts modified castor oil, 50 parts rosin-based polyol, and 0.3 parts dibutyltin dilaurate by weight. Mix the modified castor oil and rosin-based polyol together, then add dibutyltin dilaurate and mix well to obtain component A.

[0078] Step 3: Mix component A and component B at a molar ratio of OH in component A to NCO in component B of 1:1.05 to obtain the adhesive.

[0079] Example 6

[0080] The only difference from Example 1 is that the mass fraction of 2,5-furandicarboxylic acid in component B is adjusted to 3 parts when preparing the adhesive. The steps for preparing the modified castor oil and the rosin-based polyol are the same as in Example 1.

[0081] Preparation of adhesives:

[0082] Step 1: Prepare 70 parts L-lysine diisocyanate, 8 parts polytetrahydrofurandiol, and 3 parts 2,5-furandicarboxylic acid by mass. Mix all ingredients thoroughly under a nitrogen atmosphere, heat to 80°C, start stirring and continue the reaction for 4 hours. Then heat to 115°C and dehydrate under reduced pressure (-0.09 MPa). After dehydration, cool to 80°C and determine that the NCO mass fraction is 8.8%. Cool to room temperature and discharge to obtain component B.

[0083] Step 2: Prepare 60 parts of modified castor oil, 40 parts of rosin-based polyol, and 0.3 parts of dibutyltin dilaurate according to the mass proportions. Mix the modified castor oil and rosin-based polyol, then add dibutyltin dilaurate and mix evenly to obtain component A.

[0084] Step 3: Mix component A and component B at a molar ratio of OH in component A to NCO in component B of 1:1.05 to obtain the adhesive.

[0085] Example 7

[0086] The only difference from Example 1 is that the mass fraction of 2,5-furandicarboxylic acid in component B was adjusted to 6 parts when preparing the adhesive. The steps for preparing the modified castor oil and the rosin-based polyol were the same as in Example 1.

[0087] Preparation of adhesives:

[0088] Step 1: Prepare 70 parts L-lysine diisocyanate, 8 parts polytetrahydrofurandiol, and 6 parts 2,5-furandicarboxylic acid by mass. Mix all ingredients thoroughly under a nitrogen atmosphere, heat to 80°C, start stirring and continue the reaction for 4 hours. Then heat to 115°C and dehydrate under reduced pressure (-0.09 MPa). After dehydration, cool to 80°C and determine that the NCO mass fraction is 8.1%. Cool to room temperature and discharge to obtain component B.

[0089] Step 2: Prepare 60 parts of modified castor oil, 40 parts of rosin-based polyol, and 0.3 parts of dibutyltin dilaurate according to the mass proportions. Mix the modified castor oil and rosin-based polyol, then add dibutyltin dilaurate and mix evenly to obtain component A.

[0090] Step 3: Mix component A and component B at a molar ratio of OH in component A to NCO in component B of 1:1.05 to obtain the adhesive.

[0091] Example 8

[0092] The only difference from Example 1 is that, in preparing the adhesive, the mass fraction of L-lysine diisocyanate in component B is adjusted to 60 parts, and the mass fraction of polyether polyol is adjusted to 10 parts. The steps for preparing the modified castor oil and the rosin-based polyol are the same as in Example 1.

[0093] Preparation of adhesives:

[0094] Step 1: Prepare 60 parts L-lysine diisocyanate, 10 parts polytetrahydrofurandiol, and 4 parts 2,5-furandicarboxylic acid by mass. Mix all ingredients thoroughly under a nitrogen atmosphere, heat to 80°C, start stirring and continue the reaction for 4 hours. Then heat to 115°C and dehydrate under reduced pressure (-0.09 MPa). After dehydration, cool to 80°C and determine that the NCO mass fraction is 7.6%. Cool to room temperature and discharge to obtain component B.

[0095] Step 2: Prepare 60 parts of modified castor oil, 40 parts of rosin-based polyol, and 0.3 parts of dibutyltin dilaurate according to the mass proportions. Mix the modified castor oil and rosin-based polyol, then add dibutyltin dilaurate and mix evenly to obtain component A.

[0096] Step 3: Mix component A and component B at a molar ratio of OH in component A to NCO in component B of 1:1.05 to obtain the adhesive.

[0097] Example 9

[0098] The only difference from Example 1 is that, when preparing the adhesive, the mass fraction of L-lysine diisocyanate in component B was adjusted to 80 parts and the mass fraction of polyether polyol was adjusted to 5 parts.

[0099] Preparation of adhesives:

[0100] Step 1: Prepare 80 parts L-lysine diisocyanate, 5 parts polytetrahydrofurandiol, and 4 parts 2,5-furandicarboxylic acid by mass. Mix all ingredients thoroughly under a nitrogen atmosphere, heat to 80°C, start stirring and continue the reaction for 4 hours. Then heat to 115°C and dehydrate under reduced pressure (-0.09 MPa). After dehydration, cool to 80°C and determine that the NCO mass fraction is 9.3%. Cool to room temperature and discharge to obtain component B.

[0101] Step 2: Prepare 60 parts of modified castor oil, 40 parts of rosin-based polyol, and 0.3 parts of dibutyltin dilaurate according to the mass proportions. Mix the modified castor oil and rosin-based polyol, then add dibutyltin dilaurate and mix evenly to obtain component A.

[0102] Step 3: Mix component A and component B at a molar ratio of OH in component A to NCO in component B of 1:1.05 to obtain the adhesive.

[0103] Comparative Example 1

[0104] The only difference from Example 1 is that castor oil and the like are directly used to replace the modified castor oil in this comparative example.

[0105] Preparation of rosin-based polyols:

[0106] A1. Prepare ethylene glycol, 1,4-butanediol and diethylene glycol in a molar ratio of 1:1:1.5. Prepare rosin dimer (polymerized rosin) in a molar ratio of rosin dimer to alcohol of 1:1.15. Add all of the rosin dimer and alcohol to the reaction vessel. Use nitrogen to replace the reaction vessel to form a nitrogen atmosphere. Raise the temperature inside the reaction vessel to 150°C. Once the reactants have completely melted, start stirring and raise the temperature to 175°C and continue stirring for 1.5 hours.

[0107] A2. Then raise the temperature of the reactor to 230°C and start vacuuming until the vacuum degree inside the reactor reaches 5000Pa, and maintain it for 15 minutes.

[0108] A3. After the reaction is complete, the temperature of the reactor is reduced to 150°C, and the pressure inside the reactor is brought up to atmospheric pressure. The product is then discharged to obtain rosin-based polyol.

[0109] Preparation of adhesives:

[0110] Step 1: Prepare 70 parts L-lysine diisocyanate, 8 parts polytetrahydrofurandiol, and 4 parts 2,5-furandicarboxylic acid by mass. Mix all ingredients thoroughly under a nitrogen atmosphere, heat to 80°C, start stirring and continue the reaction for 4 hours. Then heat to 115°C and dehydrate under reduced pressure (-0.09 MPa). After dehydration, cool to 80°C and determine that the NCO mass fraction is 8.4%. Cool to room temperature and discharge to obtain component B.

[0111] Step 2: Prepare 60 parts castor oil, 40 parts rosin-based polyol, and 0.3 parts dibutyltin dilaurate by weight. Mix the castor oil and rosin-based polyol together, then add the dibutyltin dilaurate and mix well to obtain component A.

[0112] Step 3: Mix component A and component B at a molar ratio of OH in component A to NCO in component B of 1:1.05 to obtain the adhesive.

[0113] Comparative Example 2

[0114] The only difference from Example 1 is that no rosin-based polyol is added to component A in this comparative example.

[0115] Preparation of modified castor oil:

[0116] S1. Weigh castor oil and mercapto-polyethylene glycol-amino (polyethylene glycol with a molecular weight of 2000) according to a carbon-carbon double bond and mercapto molar ratio of 2.5:1. Weigh benzoin dimethyl ether as a photoinitiator according to 4.0% of the total mass of mercapto-polyethylene glycol-amino. Mix the three together and add them to ethyl acetate at a mass concentration of 20% and stir until homogeneous.

[0117] S2. Place the thoroughly stirred reaction solution under ultraviolet light (wavelength 365nm) with an irradiation power of approximately 0.1W. cm -2 The mixture was stirred and reacted for 35 minutes. The product was collected and removed by rotary evaporation to obtain modified castor oil.

[0118] Preparation of adhesives:

[0119] Step 1: Prepare 70 parts L-lysine diisocyanate, 8 parts polytetrahydrofurandiol, and 4 parts 2,5-furandicarboxylic acid by mass. Mix all ingredients thoroughly under a nitrogen atmosphere, heat to 80°C, start stirring and continue the reaction for 4 hours. Then heat to 115°C and dehydrate under reduced pressure (-0.09 MPa). After dehydration, cool to 80°C and determine that the NCO mass fraction is 8.4%. Cool to room temperature and discharge to obtain component B.

[0120] Step 2: Prepare 100 parts of modified castor oil and 0.3 parts of dibutyltin dilaurate by mass. Stir the modified castor oil and dibutyltin dilaurate evenly to obtain component A.

[0121] Step 3: Mix component A and component B at a molar ratio of OH in component A to NCO in component B of 1:1.05 to obtain the adhesive.

[0122] Comparative Example 3

[0123] The only difference from Example 1 is that 2,5-furandicarboxylic acid is not added to component B in this comparative example. The steps for preparing the modified castor oil and the rosin-based polyol are the same as in Example 1.

[0124] Preparation of adhesives:

[0125] Step 1: Prepare 70 parts L-lysine diisocyanate and 8 parts polytetrahydrofuran diol by mass. Mix them thoroughly under a nitrogen atmosphere, heat to 80°C and stir continuously for 4 hours. Then heat to 115°C and dehydrate under reduced pressure (-0.09MPa). After dehydration, cool to 80°C and determine that the NCO mass fraction is 9.5%. Cool to room temperature and discharge to obtain component B.

[0126] Step 2: Prepare 60 parts of modified castor oil, 40 parts of rosin-based polyol, and 0.3 parts of dibutyltin dilaurate according to the mass proportions. Mix the modified castor oil and rosin-based polyol, then add dibutyltin dilaurate and mix evenly to obtain component A.

[0127] Step 3: Mix component A and component B at a molar ratio of OH in component A to NCO in component B of 1:1.05 to obtain the adhesive.

[0128] The adhesives prepared in Examples 1-9 and Comparative Examples 1-3 were subjected to performance tests, and the results are shown in Table 1.

[0129] Apply adhesive to the surface of the aluminum plate with a thickness of 0.25 mm and a coverage area of ​​25 × 10 mm. Overlap two aluminum plates coated with adhesive, with a bonding area of ​​25 × 10 mm, and cure at room temperature for 5 days.

[0130] The reference standard for tensile shear strength testing is GB / T 7124-2008.

[0131] The peel strength test reference standard is GB / T 15254-2014.

[0132] After the aluminum sheets were overlapped and cured, they were placed in an oven at 180°C for 24 hours. After being removed, the tensile shear strength was tested.

[0133] Table 1

[0134]

[0135] As shown in Table 1, all embodiments of the present invention maintain high tensile shear strength and peel strength, and possess excellent heat resistance, making them suitable for applications in high-temperature environments. Compared to Example 1, Comparative Example 1, due to the lack of side link branches, has fewer active groups when castor oil participates in the reaction, resulting in a lower density of the crosslinked network and a significant decrease in the mechanical properties and heat resistance of the adhesive. Compared to Example 1, Comparative Example 2 contains only modified castor oil as a single polyol in component A, resulting in a polyurethane adhesive with a higher content of flexible chains, and its heat resistance is far inferior to that of Example 1.

[0136] It should be noted that, in this document, relational terms such as "first" and "second" are used only to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such process, method, article, or apparatus.

[0137] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A bio-based polyurethane adhesive, characterized in that, The adhesive comprises component A and component B; By mass fractions, component A comprises the following raw materials: Modified castor oil 50-70 parts, rosin-based polyol 30-50 parts, catalyst 0.1-0.5 parts; By mass fractions, component B comprises the following raw materials: 60-80 parts of bio-based aliphatic diisocyanate, 5-10 parts of polyether polyol, and 3-6 parts of 2,5-furandicarboxylic acid; The modified castor oil is castor oil grafted with thiol-polyethylene glycol-amino groups through a reaction between double bonds and thiol groups; the castor oil and thiol-polyethylene glycol-amino groups are mixed at a molar ratio of carbon-carbon double bonds to thiol groups of 2-3:

1. The rosin-based polyol is a polyester polyol formed by the polymerization reaction of rosin dimer and small molecule diol; the small molecule diol is ethylene glycol, 1,4-butanediol and diethylene glycol. The molar ratio of the rosin dimer to the small molecule diol is 1:1.1-1.2; The molar ratio of ethylene glycol, 1,4-butanediol and diethylene glycol is 1:1:1-2.

2. The bio-based polyurethane adhesive according to claim 1, characterized in that, The preparation method of the modified castor oil includes the following steps: S1. Mix castor oil, mercapto-polyethylene glycol-amino and photoinitiator, add to ethyl acetate and stir until homogeneous; S2. Under ultraviolet light irradiation, the mixture is stirred and reacted for 30-40 minutes. The product is collected and the solvent is removed by rotary evaporation to obtain modified castor oil.

3. The bio-based polyurethane adhesive according to claim 2, characterized in that, The photoinitiator is benzoin dimethyl ether, and the photoinitiator is 3.5-5.5% of the total mass of mercapto-polyethylene glycol-amino.

4. The bio-based polyurethane adhesive according to claim 1, characterized in that, The preparation steps of the rosin-based polyol are as follows: A1. Add rosin dimer, ethylene glycol, 1,4-butanediol and diethylene glycol to a reaction vessel, heat to 140-150℃ under nitrogen atmosphere, and after complete melting, start stirring and heat to 170-180℃ and continue stirring for 1-2 hours. A2. Heat to 220-230℃ and evacuate the vacuum inside the vessel to a vacuum degree of 4500-5500Pa, and maintain for 10-20 minutes. A3. After the reaction is complete, reduce the temperature of the reactor to 150-160℃ and the pressure inside the reactor to atmospheric pressure. Discharge the product to obtain rosin-based polyol.

5. The bio-based polyurethane adhesive according to claim 1, characterized in that, The catalyst is at least one of dibutyltin dilaurate, stannous octoate, and dibutyltin diacetate.

6. The bio-based polyurethane adhesive according to claim 1, characterized in that, The bio-based aliphatic diisocyanate is at least one of 1,5-pentanediisocyanate and L-lysine diisocyanate.

7. The bio-based polyurethane adhesive according to claim 1, characterized in that, The polyether polyol is at least one of polytetrahydrofuran diol and polypropylene glycol.

8. A method for preparing a bio-based polyurethane adhesive, characterized in that, The preparation method for the bio-based polyurethane adhesive as described in any one of claims 1-7 comprises the following preparation steps: Step 1: Under a nitrogen atmosphere, mix the raw materials in component B in proportion, heat to 80-90℃ and stir for 3-5 hours, heat to 110-120℃ and dehydrate under reduced pressure, cool to 80-90℃ after dehydration, determine the NCO mass fraction to be 6-10%, cool to room temperature and discharge to obtain component B. Step 2: Mix the modified castor oil and rosin-based polyol in component A, then add the catalyst and stir until homogeneous to obtain component A; Step 3: Mix component A and component B at a molar ratio of OH in component A to NCO in component B of 1:1.05-1.10 to obtain the adhesive.

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