Polyurethane adhesive and method of production

Abstract

The application discloses a polyurethane adhesive and a production method. The polyurethane adhesive is obtained by preparing an isocyanate end group prepolymer, then obtaining a water-based polyurethane molecular chain through small molecule chain extension, and finally introducing a copper ion crosslinked sodium alginate gel component to obtain a water-based polyurethane adhesive with interpenetrating polyurethane molecular chains and sodium alginate gel. The water-based polyurethane molecular chain is modified by dimethylol propionic acid, and Cu in CuO is released slowly in the subsequent preparation process 2+ , so that Cu 2+ is crosslinked with G units on the sodium alginate to obtain an ion crosslinked sodium alginate gel component. Since Cu 2+ forms a dynamic covalent bond with the G units, the bond can be reformed after being pulled apart by an external force, thus endowing the water-based polyurethane adhesive with self-repairing ability. The molar ratio of dimethylol propionic acid, CuO and triethylamine is required to be 2:1:1 to control the content of carboxyl groups in the polyurethane, so that the polyurethane adhesive obtained by self-emulsification has good hydrophilicity, and the system as a whole is neutral, thus expanding the application range of the water-based polyurethane adhesive.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of adhesives, and in particular to the field of waterborne polyurethane adhesives. BACKGROUND

[0002] Waterborne polyurethane is generally polymerized from soft and hard segments, and the low molecular weight prepolymer is connected together by chain extender to increase the chain length, so as to improve the molecular weight of the polymer and obtain a polyurethane material with good performance. In addition, waterborne polyurethane has lower toxicity than traditional solvent-based polyurethane, and the preparation process is more environmentally friendly, so it is widely used in the fields of coatings, waterproofing, adhesives, etc. In the field of waterborne adhesives, there are still problems such as low initial adhesion, poor wettability on non-polar substrates, and low solid content. Therefore, researchers have proposed various improvement measures to improve the performance of waterborne polyurethane adhesives to expand their application range. For example, Lu Gang et al. formed a dense winding structure and a network crosslinking material by crosslinking reaction between undecylenamide and pentaerythritol tetramercaptoacetate, which promoted strain-induced crystallization to obtain better initial adhesion and mechanical properties (CN 113549421B); Xu Hongmei et al. used the synergistic effect of polyether polyol and polyester polyol to improve the wettability of waterborne polyurethane adhesive on PVC substrate, and the obtained adhesive had good bonding strength and water resistance (CN112341983B); Zhang Bo et al. introduced castor oil on a large scale to improve the high solid content of waterborne polyurethane emulsion and improve its storage stability (CN113583207B). Although the previous researchers have improved the performance of waterborne polyurethane adhesives in various ways, they may be affected by temperature changes, rainwater erosion, wind and sand erosion, etc. during service, so it is necessary to endow waterborne polyurethane adhesives with self-repairing properties. The most common way is to introduce disulfide bonds to construct dynamic hydrogen bonds to help the self-repairing process, but this type of application scenario is generally for polyurethane elastomers, so there are few reports on self-repairing waterborne polyurethane adhesives. SUMMARY

[0003] The purpose of the present application is to introduce sodium alginate polymer chains into waterborne polyurethane to obtain interpenetrating polymer networks, and then rely on the ionic crosslinking effect of copper ions on sodium alginate to improve the mechanical properties of the adhesive, and realize the self-repairing process through the dynamic crosslinking of ions during the service of the adhesive, so as to solve the problems of low initial adhesion, poor wettability, and low environmental tolerance of existing waterborne polyurethane adhesives.

[0004] To achieve the above purpose, the present application provides the following technical solution: a polyurethane adhesive and a production method, comprising the following preparation steps:

[0005] S1: Connect a three-necked flask to a nitrogen atmosphere. Weigh 40g of poly(1,4-butanediol adipate) and place it into the flask. Stir at 80°C for 0.5h. Then add 25g of liquid tetramethylphenyl dimethyl diisocyanate and continue stirring for 1h. After thorough mixing, add 3-4g of dibutyltin dilaurate dropwise. Maintain the temperature at 80°C and stir for 1h to obtain the isocyanate-terminated prepolymer. Acetone can be added appropriately during the reaction to reduce the viscosity of the system. Wherein, poly(1,4-butanediol adipate) and tetramethylphenyl dimethyl diisocyanate are the soft and hard segments of polyurethane, respectively, and dibutyltin dilaurate is the initiator for the polymerization of both soft and hard segments.

[0006] S2: Add 2.48 g of ethylene glycol to a three-necked flask to induce a chain extension reaction in the isocyanate-terminated prepolymer. The reaction time is 2 hours, and the temperature is maintained at 80°C. Acetone can be added appropriately during the reaction to reduce the viscosity of the system. The ethylene glycol contains active hydroxyl groups at both ends, and therefore can be used as a small molecule chain extender.

[0007] S3: Weigh 4.5g of dimethylolpropionic acid and dissolve it in 50mL of water. Add the solution to a three-necked flask, maintain a constant temperature of 80℃ and a nitrogen atmosphere, stir for 1 hour, and then cool to room temperature. Waterborne polyurethanes generally require hydrophilic additives to improve their dispersibility in water. Dimethylolpropionic acid, containing carboxyl groups, acts as a hydrophilic additive. Furthermore, dimethylolpropionic acid also contains hydroxyl groups, allowing it to polymerize with the isocyanate end groups in the prepolymer and embed into the rigid segments of the polyurethane.

[0008] S4: Weigh 24.75-29.78g of sodium alginate and pour it into a beaker containing 200mL of water. Stir for 3 hours until completely dissolved. Then add 1.25-1.5g of CuO powder. Sodium alginate is a water-soluble linear polymer with good viscosity, which can stably disperse the CuO powder. After the CuO powder is evenly dispersed in the sodium alginate solution, pour it into a three-necked flask. Continue stirring the mixture in the three-necked flask for 10 minutes. During stirring, the sodium alginate polymer chains and polyurethane molecular chains form an interpenetrating structure, which improves the viscosity and structural toughness of the system. In addition, sodium alginate has a large number of polar functional groups, which is beneficial to improving the initial adhesion of polyurethane. Most importantly, the carboxyl groups of dimethylolpropionic acid in the system can release H+. + These H + In situ, it reacts with CuO to slowly release Cu 2+ These Cu 2+ Further Na on the carboxylate group of sodium alginate + The exchange process ultimately yields a copper ion-crosslinked sodium alginate gel component with uniform properties, which forms an interpenetrating structure with polyurethane.

[0009] S5: 2.06-1.84g of triethylamine is weighed and dissolved in 150ml of water, and then poured into the three-necked flask and stirred for 10 minutes. The triethylamine is alkaline, and can neutralize the excess carboxyl groups on the dimethylol propionic acid, so that the pH of the system is neutral, and the hydrophilicity of the system is improved.

[0010] S6: The nitrogen atmosphere is removed, and the temperature is raised to 60°C again. The three-necked flask is connected to a reduced pressure distillation device to remove the acetone in the system, and a pre-emulsion is obtained. The pre-emulsion is subjected to mechanical stirring at a speed of 3000r / min. The shear force generated by the mechanical stirring causes the pre-emulsion to self-emulsify, and a final polyurethane adhesive is obtained.

[0011] In fact, the cyanate group has strong activity and is easy to react with water to form polyurea. Therefore, the raw materials and containers must be treated to remove water before the preparation begins. Preferably, a certain amount of poly(1,4-butanediol adipate) diol, ethylene glycol, a stirrer and a three-necked flask are subjected to reduced pressure heating treatment for 2h to remove water.

[0012] The length of the soft segment in the polyurethane has a great influence on the mechanical properties and viscosity of the material. In order to ensure the normal progress of the post-treatment of the isocyanate-terminated prepolymer, a soft segment with a suitable molecular length must be selected. Preferably, the number average molecular weight Mn of the poly(1,4-butanediol adipate) diol is 2000.

[0013] In fact, sodium alginate is a block polymer of G units and M units in its internal structure. The G unit and the M unit are isomers. Therefore, sodium alginate with different G / M ratios has performance differences. Preferably, the molar ratio of the G unit to the M unit in the internal structure of the sodium alginate is 1:1.

[0014] In fact, Cu 2+ is released by exchanging Na + on two G units of sodium alginate and forming Cu 2+ crosslinked gel, so that Cu 2+ is released from the G unit. The molar ratio of CuO to the G unit has a major influence on the performance of the gel. Preferably, the molar ratio of CuO to the G unit of sodium alginate is 0.25:1.

[0015] In fact, Cu 2+ is released by exchanging Na + on two G units of sodium alginate and forming Cu 2+ crosslinked gel, so that Cu 2+ is released from the G unit. The molar ratio of CuO to the G unit has a major influence on the performance of the gel. Preferably, the molar ratio of CuO to the G unit of sodium alginate is 0.25:1.

[0016] Compared with the prior art, the present application has the following beneficial effects:

[0017] 1. The waterborne polyurethane adhesive with high strength and high wettability is obtained by forming interpenetrating network through polyurethane prepolymer molecular chain and sodium alginate molecular chain. The sodium alginate is a linear biomass polymer, has the characteristics of environmental protection and low cost, and the rich hydroxyl groups contained in the sodium alginate can be micro-polymerized with the isocyanate end groups of the prepolymer, so that the adhesive with uniform texture is obtained, and the rich carboxyl groups contained in the sodium alginate also enhance the water solubility of the system.

[0018] 2. The carboxyl groups on the dimethylol propionic acid are used to slow release Cu in CuO 2+ , so that Cu 2+ is in-situ crosslinked with the G units on the sodium alginate to obtain an ionically crosslinked sodium alginate gel component, which is interpenetrated with the polyurethane. Since the Cu 2+ forms a dynamic covalent bond with the G units, the bond can be broken by external force and then self-formed again, so that the waterborne polyurethane adhesive has self-repairing ability.

[0019] 3. The molar ratio of dimethylol propionic acid, CuO and triethylamine is 2:1:1, so that the content of carboxyl groups in the polyurethane is accurately controlled, the self-emulsified polyurethane adhesive further has good hydrophilicity, and the system as a whole is neutral, so that the use range of the waterborne polyurethane adhesive is expanded. BRIEF DESCRIPTION OF DRAWINGS

[0020] Figure 1 The scanning electron microscope graph of the present application;

[0021] Figure 2 The self-healing process graph of the present application;

[0022] Figure 3 The loss factor graph of the present application. DETAILED DESCRIPTION

[0023] The technical solutions in the embodiments of the present application will be described clearly and completely below in combination with the drawings in the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative labor fall within the scope of protection of the present application.

[0024] Example 1

[0025] Raw material water removal: a certain amount of polybutylene adipate glycol, ethylene glycol, a stirring rod and a three-necked flask are heated in a vacuum drying oven under reduced pressure, and the treatment time is 2 h to remove the water in the raw materials and the vessel.

[0026] Prepolymerization: the three-necked flask is connected to a nitrogen atmosphere, and the flow rate of nitrogen is 60 cm 3 / min, and 40 g of polybutylene adipate glycol was weighed into the three-necked flask, and the polybutylene adipate glycol was completely melted by heating in the 80°C constant-temperature oil bath for 0.5 h. Then, 25 g of tetramethylxylylene diisocyanate liquid was slowly added, and stirring was continued for 1 h. After the two were fully mixed and uniform, 3 g of dibutyltin dilaurate was added dropwise, and stirring was continued at 80°C for 1 h. The dibutyltin dilaurate catalyzed the reaction of the polybutylene adipate glycol and the tetramethylxylylene diisocyanate, and an isocyanate-terminated prepolymer was obtained. During the reaction, acetone could be appropriately added to reduce the viscosity of the system.

[0027] Small molecule chain extension: 2.48 g of ethylene glycol liquid was added to the three-necked flask to cause chain extension of the isocyanate-terminated prepolymer. The reaction time was 2 h, and the oil bath was kept at 80°C. During the reaction, acetone could be appropriately added to reduce the viscosity of the system.

[0028] Introduction of hydrophilic groups: 4.5 g of dimethylolpropionic acid was dissolved in 50 mL of water, and then added to the three-necked flask. The constant temperature was kept at 80°C, and the nitrogen atmosphere was maintained. Stirring was continued for 1 h, and then the temperature was lowered to room temperature.

[0029] Construction of interpenetrating networks: 24.75 g of sodium alginate was poured into a beaker containing 200 mL of water, and magnetic stirring was continued for 3 h. After complete dissolution, 1.25 g of CuO powder was added, and the mixture was subjected to ultrasonic treatment using a cell disrupter. The purpose was to uniformly disperse the CuO in the SA solution, and stirring could be appropriately increased during the dispersion process. After 10 min of ultrasonic treatment and stirring, the liquid in the beaker was poured into the three-necked flask, and stirring was continued in the three-necked flask for 10 min.

[0030] Neutralization reaction: 2.06 g of triethylamine liquid was dissolved in 150 mL of water, and then poured into the three-necked flask and stirred for 10 min.

[0031] Self-emulsification: The nitrogen atmosphere of the three-necked flask was removed, the oil bath was again heated to 60°C, and the three-necked flask was connected to a reduced-pressure distillation device with a pressure slightly lower than atmospheric pressure to remove acetone from the system. A pre-emulsion was obtained, which was transferred from the three-necked flask to a clean beaker and subjected to mechanical stirring at a speed of 3000 r / min. The high-speed shearing force of mechanical stirring caused the pre-emulsion to self-emulsify, and finally an aqueous polyurethane adhesive was obtained.

[0032] Example 2

[0033] Water removal from raw materials: The polybutylene adipate glycol, ethylene glycol, stirrer, and three-necked flask were heated under reduced pressure in a vacuum drying oven for 2 h to remove water from the raw materials and the vessel.

[0034] Pre-polymerization: The three-necked flask was connected to a nitrogen atmosphere with a flow rate of 60 cm 3 / min, and 40 g of polybutylene adipate glycol was weighed into the three-necked flask along with a stir bar. The polybutylene adipate glycol was completely melted by heating in an 80°C constant temperature oil bath for 0.5 h. Then 30 g of tetramethylxylylenediisocyanate liquid was slowly added, and stirring was continued for 1 h. After the two were fully mixed and uniform, 4 g of dibutyltin dilaurate was added dropwise, and stirring was continued at 80°C for 1 h. The dibutyltin dilaurate catalyzed the reaction of the polybutylene adipate glycol and the tetramethylxylylenediisocyanate, and an isocyanate-terminated prepolymer was obtained. During the reaction, acetone could be appropriately added to reduce the viscosity of the system.

[0035] Small molecule chain extension: 2.48 g of ethylene glycol liquid was added to the three-necked flask to cause chain extension of the isocyanate-terminated prepolymer. The reaction time was 2 h, and the oil bath was kept at 80°C. During the reaction, acetone could be appropriately added to reduce the viscosity of the system.

[0036] Introduction of hydrophilic groups: 5.0 g of dimethylolpropionic acid was dissolved in 50 mL of water, and then added together to the three-necked flask. The temperature was kept at 80°C and a nitrogen atmosphere was maintained, and stirring was continued for 1 h. Then the temperature was lowered to room temperature.

[0037] Construction of interpenetrating networks: 29.78 g of sodium alginate was poured into a beaker containing 200 mL of water, and magnetic stirring was continued for 3 h. After complete dissolution, 1.5 g of CuO powder was added, and the mixture was subjected to ultrasonic treatment using a cell disrupter. The purpose was to uniformly disperse the CuO in the SA solution, and stirring could be appropriately increased during the dispersion process. After 10 min of ultrasonic treatment and stirring, the liquid in the beaker was poured into the three-necked flask, and stirring was continued in the three-necked flask for 10 min.

[0038] Neutralization reaction: 1.84 g of triethylamine liquid was dissolved in 150 mL of water, and after mixing, the solution was poured into the three-necked flask and stirred for 10 min.

[0039] Self-emulsification: The nitrogen atmosphere of the three-necked flask was removed, the oil bath was again heated to 60°C, and the three-necked flask was connected to a reduced pressure distillation device with a pressure slightly lower than atmospheric pressure to remove acetone from the system. A pre-emulsion was obtained, which was transferred from the three-necked flask to a clean beaker and subjected to mechanical stirring at a speed of 3000 r / min. The high-speed shear force of mechanical stirring caused the pre-emulsion to self-emulsify, and finally an aqueous polyurethane adhesive was obtained.

[0040] The samples obtained in the examples were subjected to relevant tests. Figure 1The surface scanning electron microscope image of the film obtained after the sample of Example 1 was coated on a copper foil and cured, from which it can be seen that the surface of the film is dense and relatively flat as a whole, indicating that the obtained waterborne polyurethane has film-forming property and uniformity. The elastomer prepared from the waterborne polyurethane adhesive of Example 1 was scored with a craft knife, and then observed under an optical microscope, and the change in the morphology of the score was as shown in Figure 2 The score was found to be substantially healed after 4h, indicating that the obtained material has good self-healing ability. The materials obtained in Example 1 and Example 2 were coated on a PVC plate to perform T-type peel strength testing and shear strength testing, and the test results showed that the peel strength of the material obtained in Example 1 was 2.22 N / mm, and the shear strength was 1.114 MPa, while the peel strength of the material obtained in Example 2 was 2.53 N / mm, and the shear strength was 1.257 MPa, indicating that as the content of isocyanate groups increases, the material exhibits stronger bonding performance. The waterborne polyurethane materials of Example 1 and Example 2 were made into rectangular adhesive films, and the storage modulus and loss modulus of the adhesive films were tested under vibration mode using a dynamic mechanical property analyzer, and the relationship curve between temperature and loss factor was obtained, as shown in Figure 3 The size of the loss factor is a direct reflection of the viscoelastic properties of the material, and as the initial isocyanate group content increases, the loss factor of the waterborne polyurethane adhesive film first increases and then decreases, and the curve moves to high temperature. This is because as the content of isocyanate groups in the system increases, more urethane is generated, improving the viscoelasticity of the material, but excessive isocyanate groups will react with water to generate more urea groups, which have strong polarity and are easy to form hydrogen bonds. As the number of urea groups increases, the hydrogen bond force becomes larger, which limits the movement of the molecular chain and reduces the viscoelasticity of the material, so the loss factor first increases and then decreases.

[0041] Although embodiments of the present application have been shown and described, it will be understood by those of ordinary skill in the art that various changes, modifications, substitutions and alterations can be made thereto without departing from the principles and spirit of the present application, and the scope of the present application is defined by the appended claims and their equivalents.

Claims

1. A polyurethane adhesive, characterized in that, It is prepared by the following steps: S1: Connect a three-necked flask to a nitrogen atmosphere, weigh 40 g of poly(1,4-butanediol adipate) into the three-necked flask, stir at 80 °C for 0.5 h, then add 25 g of tetramethylphenyl dimethyl diisocyanate liquid, continue stirring for 1 h, and after it is fully mixed, add 3 g of dibutyltin dilaurate dropwise, keep warm at 80 °C and stir for 1 h to obtain isocyanate end-group prepolymer. During the reaction, acetone can be added appropriately to reduce the viscosity of the system. S2: Add 2.48 g of ethylene glycol to a three-necked flask to induce chain extension of the isocyanate end-group prepolymer. The reaction time is 2 h, and the temperature is maintained at 80 ℃. During the reaction, acetone can be added appropriately to reduce the viscosity of the system. S3: Weigh 4.5 g of dimethylolpropionic acid and dissolve it in 50 mL of water. Then add it to a three-necked flask, maintain a constant temperature of 80 °C and a nitrogen atmosphere, stir for 1 h, and then cool to room temperature. S4: Weigh 24.75-29.78 g of sodium alginate and pour it into a beaker containing 200 mL of water. Stir for 3 h and after it is completely dissolved, add 1.25-1.5 g of CuO powder. After the CuO powder is evenly dispersed in the sodium alginate solution, pour it into a three-necked flask. Continue to stir the mixture in the three-necked flask for 10 min. S5: Weigh 2.06-1.84 g of triethylamine, dissolve it in 150 mL of water, and then pour it into a three-necked flask and stir for 10 min; S6: Remove the nitrogen atmosphere, heat up to 60 °C again, connect the three-necked flask to the vacuum distillation apparatus to remove acetone from the system, and obtain the pre-emulsion. Mechanically stir the pre-emulsion at 3000 r / min to obtain the self-emulsifying polyurethane adhesive. The molar ratio of dimethylolpropionic acid, CuO, and triethylamine is 2:1:

1.

2. The polyurethane adhesive according to claim 1, characterized in that: Before preparation, the poly(1,4-butanediol adipate), ethylene glycol, and three-necked flask must be subjected to reduced pressure heating to remove moisture.

3. The polyurethane adhesive according to claim 1, characterized in that: The number-average molecular weight (Mn) of the poly(1,4-butanediol adipate) is 2000.

4. The polyurethane adhesive according to claim 1, characterized in that: The molar ratio of G units to M units within the sodium alginate molecule is 1:

1.

5. The polyurethane adhesive according to claim 1, characterized in that: The molar ratio of CuO to sodium alginate G unit is 0.25:1.

Images