Ultralow-temperature-resistant bio-based polyurea-polyurethane adhesive and preparation method thereof

Abstract

The invention provides an ultralow-temperature-resistant bio-based polyurea-polyurethane adhesive and a preparation method of the ultralow-temperature-resistant bio-based polyurea-polyurethane adhesive. The adhesive is prepared from the following raw materials in molar ratio: 0.5 of polyhydric alcohol; 1.0 part of isocyanate; 1.6 to 1.8 parts of hydrazide; and 0.6 to 0.8 part of vanillin dimer. The adhesive prepared by the invention has a very good bonding effect on 304 stainless steel, and can be used at an ultralow temperature. A polymer network contains rich polar groups such as carbamate and urea bonds, and the polar groups can form hydrogen bonds or other chemical bonds with substances such as oxides on the surface of metal, so that the adhesive has relatively high adhesive capacity on various base materials. According to the invention, the cheap and environment-friendly bio-based chain extender is used as a raw material, and a flexible polymer chain is used as a soft segment, so that the adhesive is endowed with the use performance at ultralow temperature while the high shear strength of the adhesive is ensured.

Description

Technical Field

[0001] The present invention relates to the technical field of adhesives, and more specifically, to a bio-based polyurea-polyurethane adhesive resistant to ultra-low temperature and a preparation method thereof. Background Art

[0002] Thermoplastic polyurethane adhesives usually exhibit excellent adhesion strength and can meet the adhesion requirements of substrates with different coefficients of thermal expansion, so they are widely used in fields such as the automotive, packaging, and construction industries. However, the post-treatment of a large number of waste polyurethane adhesive products cannot be underestimated. At present, common methods for treating waste polyurethane adhesives (including chemical methods such as pyrolysis, ammonolysis, alcoholysis, and alkali hydrolysis, and physical methods such as incineration and burial) are difficult to achieve their efficient recycling. Using cheap biomass resources to replace traditional petroleum resources to develop polyurethane adhesives with low VOC content and low or no environmental pollution is a very effective solution. However, the low-temperature resistance of bio-based polyurethane adhesives still has deficiencies. For example, a degradable bio-based polyurethane adhesive composition and its preparation method disclosed in Chinese invention patent CN 114989770 B, an environmentally friendly bio-based polyurethane adhesive and its preparation method disclosed in Chinese invention patent CN 115305041 B, and a bio-based polyurethane adhesive for bonding aluminum and its preparation method and application disclosed in Chinese invention patent CN 118185549 A do not evaluate their performance at low temperatures. Some low-temperature resistant polyurethane adhesives have been reported in the prior art. For example, a high and low temperature resistant polyurethane adhesive and its preparation method and application disclosed in Chinese invention patent CN 118325556 A still have a relatively high minimum test temperature (higher than -50°C). A polyurea adhesive with in-situ persistent adhesion at ultra-low temperature and its preparation method and application disclosed in Chinese invention patent CN 118308059 A can maintain a relatively high adhesion strength at the liquid nitrogen temperature (about -196°C), but its adhesion strength is still relatively low. Therefore, there are few reports in the prior art on bio-based polyurethane adhesives that can still have a relatively high adhesion strength (exceeding 10 MPa) at ultra-low temperature (about -196°C). Summary of the Invention

[0003] The problem to be solved by the present invention is to provide a bio-based polyurea-polyurethane adhesive resistant to ultra-low temperature and a preparation method thereof. By using dihydrazide and vanillin dimer as chain extenders to react with a linear diisocyanate prepolymer to prepare the bio-based polyurea-polyurethane adhesive, a bio-based polyurethane adhesive with high adhesion strength at ultra-low temperature can be obtained.

[0004] To achieve the above object, the present invention provides the following technical solution: A bio-based polyurea-polyurethane adhesive resistant to ultra-low temperature and a preparation method thereof, characterized by comprising the following steps:

[0005] Bio-based polyurea-polyurethane adhesive resistant to ultra-low temperatures, characterized by the following steps:

[0006] (1) React polyol with diisocyanate at 60°C to 80°C for 2h to 4h to obtain a diisocyanate-terminated prepolymer;

[0007] (2) Drop this prepolymer solution into the dihydrazide solution and react at 40°C to 80°C for 4 to 8h;

[0008] (3) Add vanillin dimer solution to the above prepolymer solution, stir evenly at 80°C to 100°C, pour it into a silica gel mold, and remove the solvent at 80°C to 120°C to obtain the bio-based polyurea-polyurethane adhesive.

[0009] Preferably, the polyol is at least one of polypropylene glycol (M n ~1000, 2000, 5000), polytetrahydrofuran (M n ~1000, 2000), polycaprolactone diol (M n ~1000, 2000) and polydimethylsiloxane diol (M n ~2000, 3000, 5000).

[0010] Preferably, the hydrazide is at least one of adipic dihydrazide, sebacic dihydrazide, carbohydrazide, isophthalic dihydrazide.

[0011] Preferably, the isocyanate is at least one of isophorone diisocyanate, diphenylmethane diisocyanate, toluene diisocyanate, hexamethylene diisocyanate, benzodimethylenet diisocyanate, tetramethyl-m-xylylene diisocyanate, dicyclohexylmethane-4,4'-diisocyanate.

[0012] Preferably, the molar ratio of the isocyanate, hydrazide, and vanillin dimer is 1.6 to 1.8:1.0:0.6 to 0.8.

[0013] Preferably, in step (3), the specific operations of polymerization and drying include: drying at 80°C to 100°C for 48h to 72h to remove most of the solvent, and then further drying at 80°C to 120°C for 48h to 72h to obtain the final polyurea-polyurethane adhesive.

[0014] The main technical advantages of the present invention are:

[0015] 1. The present invention uses polyols, diisocyanates, dihydrazides, and vanillin dimers as raw materials. First, the polyols react with the diisocyanates to obtain isocyanate-terminated polyurethane prepolymers. Subsequently, the dihydrazides are used as chain extenders to react with the above prepolymers to obtain hydrazide-terminated polyurea-polyurethanes. Finally, the vanillin dimers react with the remaining hydrazides to obtain polyurea-polyurethanes containing acylhydrazone bonds, and ultimately a thermoplastic polyurea-polyurethane adhesive containing hydrogen bonds and acylhydrazone bonds is obtained. As a chain extender, the dihydrazide can provide a large number of hydrogen bond interaction sites in the material. The acylhydrazone bonds formed by its reaction with vanillin dimers also contain hydrogen bond sites. Combining with the aromatic skeleton structure of vanillin dimers itself, the obtained polyurea-polyurethane adhesive exhibits very good mechanical properties. Further, by adjusting the ratio of the chain extender, the physical cross-linking structure inside the polymer can be regulated, so as to achieve the purpose of regulating the mechanical properties of the material. In addition, the flexible polyols will improve the flexibility of the material, enabling the flexible long-chain structure to still maintain sufficient motility at low temperatures, so that the material will not become brittle at low temperatures. At the same time, a large number of hydrogen bonds in the material, as well as the hydrogen bonds and van der Waals forces existing between the aromatic structures of vanillin dimers, can maintain the stability of the adhesive at low temperatures, enabling it to be used at ultra-low temperatures.

[0016] 2. The present invention uses inexpensive biomass raw materials as chain extenders to prepare bio-based polyurea-polyurethane adhesives, and the obtained materials are more economical and more environmentally friendly.

[0017] 3. By adjusting the ratio of the isocyanate and the hydrazide, the physical structure of the polymer material is regulated, so as to achieve the purpose of regulating the bonding strength of the material.

[0018] 4. The urea bonds, acylhydrazone bonds, and urethane bonds in the structure are all dynamically reversible interactions. Based on the rapid response of the urea bonds and acylhydrazone bonds to high temperatures, they can rapidly relax under high-temperature conditions, which is more conducive to the rapid bonding of the material.

[0019] 5. The structure contains a large number of dynamic hydrogen bond interaction sites, enabling it to have good bonding strength to a variety of substrates and a wider range of applications. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] In order to more clearly illustrate the technical solutions in the embodiments of the present invention, the following will briefly introduce the drawings required for the description of the embodiments. Obviously, the following-described drawings are only some example drawings of the present invention. For those of ordinary skill in the art, without creative efforts, other drawings can also be obtained based on these drawings.

[0021] Figure 1 is the infrared spectrum diagram of the polyurea-polyurethane adhesive;

[0022] Figure 2Statistics of the shear strength of the polyurea-polyurethane adhesive bonding 304 stainless steel under the treatment conditions of 150 °C and 5 min and different heat treatment pressures;

[0023] Figure 3 Statistics of the shear strength of the polyurea-polyurethane adhesive bonding 304 stainless steel under the treatment conditions of 150 °C, 3 MPa and different heat treatment times;

[0024] Figure 4 Statistics of the shear strength of the polyurea-polyurethane adhesive bonding 304 stainless steel under the heat treatment pressure of 3 MPa for 5 min and different heat treatment temperatures;

[0025] Figure 5 Statistics of the shear strength of the polyurea-polyurethane adhesive bonding 304 stainless steel in liquid nitrogen at -196 °C and stored in liquid nitrogen for different times under the treatment conditions of 150 °C, 3 MPa and 5 min.

[0026] Figure 6 Shear strength of the polyurea-polyurethane adhesive prepared by the present invention in different substrates. Detailed Description of the Invention

[0027] Now, various exemplary embodiments of the present invention will be described in detail. This detailed description should not be considered as a limitation of the present invention, but rather as a more detailed description of certain aspects, characteristics and implementation manners of the present invention. It should be understood that the terms described in the present invention are only used to describe specific embodiments and are not used to limit the present invention.

[0028] In addition, for the numerical ranges in the present invention, it should be understood that each intermediate value between the upper and lower limits of the range is also specifically disclosed. Each intermediate value within any stated value or stated range, as well as each smaller range between any other stated value or intermediate value within the stated range, is also included in the present invention. The upper and lower limits of these smaller ranges can be independently included or excluded from the range.

[0029] Unless otherwise specified, all technical and scientific terms used herein have the same meaning as commonly understood by those of ordinary skill in the art to which the present invention pertains. Although the present invention only describes preferred methods and materials, any methods and materials similar or equivalent to those described herein can also be used in the implementation or testing of the present invention.

[0030] Regarding the terms "comprising", "including", "having", "containing", etc. used herein, they are all open-ended terms, meaning including but not limited to.

[0031] Example 1

[0032] (1) Dissolve 1.33 mmol of polypropylene glycol, 2.66 mmol of tolylene-2,4-diisocyanate and dibutyltin dilaurate (15 μl) in 15 ml of N,N-dimethylacetamide (DMAC), and react at 70 °C for 2 h to prepare an isocyanate prepolymer;

[0033] (2) Dissolve 2.13 mmol of sebacohydrazide in 15 ml of DMAC, and then dropwise add the isocyanate prepolymer solution in step 1 to the sebacohydrazide solution at 40 °C and react for 3 h to obtain a hydrazide-terminated prepolymer solution;

[0034] (3) Dissolve 0.8 mmol of vanillin dimer in 20 ml of DMAC, then add the vanillin dimer solution to the above prepolymer solution at 80 °C, stir evenly, react for 6 h, pour it into a silica gel mold, volatilize the solvent at 80 °C, and then further dry it under vacuum at 80 °C to finally obtain a polyurea-polyurethane adhesive.

[0035] Example 2

[0036] (1) Dissolve 1.33 mmol of polytetrahydrofuran glycol, 2.66 mmol of isophorone diisocyanate and dibutyltin dilaurate (15 μl) in 15 ml of N,N-dimethylacetamide (DMAC), and react at 70 °C for 2 h to prepare an isocyanate prepolymer;

[0037] (2) Dissolve 2.13 mmol of carbohydrazide in 15 ml of DMAC, and then dropwise add the isocyanate prepolymer solution in step 1 to the carbohydrazide solution at 40 °C and react for 3 h to obtain a hydrazide-terminated prepolymer solution;

[0038] (3) Dissolve 0.93 mmol of vanillin dimer in 20 ml of DMAC, then add the vanillin dimer solution to the above prepolymer solution at 80 °C, stir evenly, react for 6 h, pour it into a silica gel mold, volatilize the solvent at 80 °C, and then further dry it under vacuum at 80 °C to finally obtain a polyurea-polyurethane adhesive.

[0039] Example 3

[0040] (1) Dissolve 1.33 mmol of polypropylene glycol, 2.66 mmol of isophorone diisocyanate and dibutyltin dilaurate (15 μl) in 15 ml of N,N-dimethylacetamide (DMAC), and react at 70 °C for 2 h to prepare an isocyanate prepolymer;

[0041] (2) Dissolve 2.4 mmol of sebacohydrazide in 15 ml of DMAC, and then dropwise add the isocyanate prepolymer solution from step 1 to the sebacohydrazide solution at 40 °C and react for 3 h to obtain a hydrazide-terminated prepolymer solution;

[0042] (3) Dissolve 1.07 mmol of vanillin dimer in 20 ml of DMAC, and then add the vanillin dimer solution to the above prepolymer solution at 80 °C, stir evenly, pour into a silica gel mold after reacting for 6 h, volatilize the solvent at 80 °C, and then further dry under vacuum at 80 °C to finally obtain a polyurea-polyurethane adhesive.

[0043] Example 4:

[0044] (1) Dissolve 1.33 mmol of polycaprolactone diol, 2.66 mmol of hexamethylene diisocyanate and dibutyltin dilaurate (15 μl) in 15 ml of N,N-dimethylacetamide (DMAC), and react at 70 °C for 2 h to prepare an isocyanate prepolymer;

[0045] (2) Dissolve 2.4 mmol of adipic dihydrazide in 15 ml of DMAC, and then dropwise add the isocyanate prepolymer solution from step 1 to the adipic dihydrazide solution at 40 °C and react for 3 h to obtain a hydrazide-terminated prepolymer solution;

[0046] (3) Dissolve 1.07 mmol of vanillin dimer in 20 ml of DMAC, and then add the vanillin dimer solution to the above prepolymer solution at 80 °C, stir evenly, pour into a silica gel mold after reacting for 6 h, volatilize the solvent at 80 °C, and then further dry under vacuum at 80 °C to finally obtain a polyurea-polyurethane adhesive.

[0047] Example 5

[0048] (1) Dissolve 1.33 mmol of polydimethylsiloxane diol, 2.66 mmol of dicyclohexylmethane-4,4'-diisocyanate and dibutyltin dilaurate (15 μl) in 15 ml of N,N-dimethylacetamide (DMAC), and react at 70 °C for 2 h to prepare an isocyanate prepolymer;

[0049] (2) Dissolve 2.4 mmol of isophthalohydrazide in 15 ml of DMAC, and then dropwise add the isocyanate prepolymer solution from step 1 to the isophthalohydrazide solution at 40 °C and react for 3 h to obtain a hydrazide-terminated prepolymer solution;

[0050] (3) Dissolve 1.07 mmol of vanillin dimer in 20 ml of DMAC. Then, add the vanillin dimer solution to the above prepolymer solution at 80 °C, stir evenly, pour the mixture into a silica gel mold after reacting for 6 h, volatilize the solvent at 80 °C, and then further dry it under vacuum at 80 °C to finally obtain the polyurea-polyurethane adhesive.

[0051] Adhesive performance test

[0052] Taking the adhesion of 304 stainless steel as an example, the performance of the adhesive was evaluated by testing the shear strength under uniaxial tensile strain. This example was tested on an instrument UTM4103 Tension Instrument (Shenzhen SUNS Technology Co., Ltd., China). The test method was as follows: the size of 304 stainless steel was 60 mm × 10 mm, the bonding area was 10 mm × 10 mm, and the tensile rate was 50 mm / min. -1 . Suppose a longitudinal tensile test was carried out with a certain force F1. F1 was the shear force, and the shear strength in the test was defined as: σ1 = F1 / A1. Note that the shear strength σ1 defined here was the shear force F1 divided by the bonding area A1.

[0053] Taking Example 1 as an example, the structural accuracy of the prepared polyurea-polyurethane adhesive was confirmed by infrared spectroscopy ( Figure 1 ), where the wave number at 3275 cm -1 was the characteristic peak of -OH in the vanillin dimer, and the absorption peak at the wave number of 1712 cm -1 was attributed to the carbonyl characteristic peak in urethane and urea bonds, and the absorption peak at 1646 cm -1 was attributed to the characteristic peak of the acylhydrazone bond.

[0054] Taking Example 3 as an example, when the adhesive bonded 304 stainless steel under the treatment conditions of 150 °C and 5 min, different heat treatment pressures would affect the shear strength. As Figure 2 shown, when the heat treatment pressure was 1 MPa, the shear strength could reach 10.9 ± 0.23 MPa. When the heat treatment pressure was increased to 3 MPa, the shear strength could reach 15.5 ± 0.6 MPa, showing a significant increase. However, when the heat treatment pressure was further increased to 5 MPa, the effect on the shear strength was not significant (15.0 ± 0.3 MPa). It was proved that under this condition, a heat treatment pressure of 3 MPa was sufficient to fully exert the bonding performance of the adhesive.

[0055] Taking Example 3 as an example, when the adhesive bonds 304 stainless steel under the treatment conditions of 150°C and 3 MPa, the shear strength after heat treatment for 1 min can reach 8.4 ± 0.87 MPa. However, the heat treatment time has a great influence on the shear strength of the bond. The adhesive performance can be basically fully exerted after heat treatment for 5 min, and its shear strength can reach 15.5 ± 0.6 MPa.

[0056] Taking Example 3 as an example, when the adhesive bonds 304 stainless steel under the heat treatment pressure of 3 MPa for 5 min, the heat treatment temperature has a decisive influence on the shear strength of the bond. As Figure 4 shown, when the heat treatment temperature is 120°C, the shear strength is only 6.1 ± 0.3 MPa. As the temperature increases, the shear strength can be increased to 15.5 ± 0.6 MPa at 150°C. The adhesive performance of the adhesive is more easily exerted at a heat treatment temperature of 150°C.

[0057] Thanks to the molecular chains of the flexible structure, the flexible long chains can still move under low-temperature conditions. The adhesive will not become hard and brittle under low-temperature conditions, enabling the adhesive to be used under the ultra-low temperature condition of -196°C, and the shear strength can still reach 13.2 ± 1.1 MPa after storage for 30 days ( Figure 5 ).

[0058] Since the polymer network contains abundant physically crosslinked hydrogen bonds, polar groups such as urethane groups and urea groups in the molten polymer structure form hydrogen bonds or other chemical bonds with substances such as metal surface oxides, enabling the adhesive to have bonding ability to a variety of substrates. Taking Example 3 as an example, as Figure 6 shown, the adhesive shows high bonding strength to substrates such as aluminum, copper, and wood after hot pressing at 150°C and 3 MPa for 5 min and standing at room temperature for 24 h.

[0059] Although the present invention is disclosed as above, the protection scope of the present invention is not limited thereto. Those skilled in the art can make various changes and modifications without departing from the spirit and scope of the present invention, and these changes and modifications will all fall within the protection scope of the present invention.

Claims

1. A bio-based polyurea-polyurethane adhesive resistant to ultra-low temperature and a preparation method thereof, characterized in that: The raw materials include the following molar ratios: polyol: 0.5; Isocyanate: 1.0; Hydrazide: 1.6~1.8; Vanillin dimer: 0.6~0.

8.

2. The adhesive according to claim 1, characterized in that The polyol is polypropylene glycol (M n ~1000, 2000, 5000), polytetrahydrofuran (M n ~1000, 2000), polycaprolactone diol (M n ~1000, 2000) and polydimethylsiloxane diol (M n At least one of ~2000, 3000, 5000).

3. The adhesive according to claim 1, characterized in that The isocyanate is at least one of isophorone diisocyanate, diphenylmethane diisocyanate, toluene diisocyanate, hexamethylene diisocyanate, xylylene diisocyanate, tetramethyl metaxylylene diisocyanate and dicyclohexylmethane-4,4'-diisocyanate.

4. The adhesive according to claim 1, characterized in that The hydrazide is at least one of adipic dihydrazide, sebacic dihydrazide, carbohydrazide and isophthalic dihydrazide.

5. The method for preparing the bio-based polyurea adhesive set according to any one of claims 1 to 4, comprising: Step 1, prepolymerizing polyol and isocyanate at a molar ratio of 0.5:1 to obtain a polyurethane prepolymer; Step 2, reacting the isocyanate prepolymer obtained in step 1 with hydrazide molecules at a molar ratio of isocyanate to hydrazide of 1.0:1.6-1.8 to prepare a hydrazide-terminated prepolymer; Step 3, adding vanillin dimer to the hydrazide-terminated prepolymer prepared in step 2 to carry out chain extension until the reaction is completed, wherein the molar ratio of the hydrazide to the dehydrovanillin dimer is 1.6:0.6 to 1.8:0.8; Step 4: After the reaction is completed, the reaction system is poured into a silica gel mold for drying to obtain the final polyurea adhesive.

6. The method for preparing a polyurea adhesive according to claim 5, characterized in that: In step 1, the reaction temperature is 60° C. to 80° C., and the reaction time is 2 h to 4 h.

7. The method for preparing a polyurea adhesive according to claim 5, characterized in that: In step 2, the reaction temperature is 40° C. to 80° C., and the reaction time is 4 h to 8 h.

8. The method for preparing a polyurea adhesive according to claim 5, characterized in that: In step 3, the reaction temperature is 80° C. to 100° C., and the reaction time is 6 h to 8 h.

9. The method for preparing a polyurea adhesive according to claim 5, characterized in that: In step 4, the drying temperature is 80° C. to 120° C., and the drying time is 48 h to 72 h.

Images