A polyurea adhesive with in-situ long-lasting adhesion in ultra-low temperature environment and its preparation method and application

Abstract

The present invention discloses a polyurea adhesive with in-situ persistent adhesion in an ultra-low temperature environment, and a preparation method and application thereof. The polyurea adhesive has the following structural formula, wherein n is 0 to 65, and m is 3-25. The preparation method comprises the following steps: step 1, causing aminopropyl-terminated polydimethylsiloxane to undergo a ring-opening reaction with ethylene carbonate to obtain a product PDMS-EC; step 2, blending the product PDMS-EC with the aminopropyl-terminated polydimethylsiloxane shown in formula I and a catalyst, and then performing pre-polycondensation, vacuuming to remove by-products until the reactants undergo Weissenberg effect to obtain a prepolymer. Step 3, melt-polycondensing the obtained prepolymer under a vacuum state to obtain the polyurea adhesive. The polyurea adhesive provided by the present invention has excellent low-temperature compliance, and can achieve in-situ reversible adhesion and strong and persistent adhesion on a variety of substrates in an ultra-low temperature environment.

Description

Technical Field

[0001] The present invention relates to the technical field of adhesives, and in particular to a polyurea adhesive with in-situ permanent adhesion in an ultra-low temperature environment, and a preparation method and application thereof. Background Art

[0002] Adhesive is a substance that can bond two interfaces together intact. It is widely used in many fields such as daily life, medical care, aerospace, electronic equipment, etc. However, existing adhesives generally have poor adhesion in ultra-low temperature environments. Although ultra-low temperatures are conducive to the formation of non-covalent bond structures of polymers, they often cause deformation of most polymer materials. Long-term exposure will make the materials brittle, thus causing adhesion failure. The ultra-low temperature resistance of adhesives is poor.

[0003] In addition, in extreme application scenarios such as orbital capture in outer space, safe transportation of biological tissues, and other ultra-low temperature capture operations, the adhesive is not only required to maintain good adhesion at ultra-low temperatures, but also to have in-situ adhesion capabilities. However, at ultra-low temperatures, the chain migration of the adhesive is highly restricted, which severely hinders the wetting of the adhesive on the substrate surface, making in-situ adhesion difficult. Therefore, despite the strong demand for adhesives used in ultra-low temperature environments, such adhesives have remained very rare until now.

[0004] Several low-temperature resistant adhesives have been reported in the prior art. For example, a low-temperature resistant high-strength adhesive disclosed in CN107513133A and a low-temperature resistant solvent-based polyurethane adhesive and a preparation method thereof disclosed in CN102634318A, the lowest test temperature of adhesion strength is higher than -50°C. An ionic reversible adhesive and a preparation method thereof disclosed in CN114231236A that are suitable for both ultra-low temperature and organic solvent environments, a combined supramolecular adhesive that is resistant to ultra-low temperatures and organic solvents disclosed in CN116285829A, and a preparation method of an adhesive that is both resistant to high temperatures and low temperatures disclosed in CN112341958A, the lowest test temperature of adhesion strength is about -196°C (in liquid nitrogen), and the adhesion strength is relatively high. However, there are no public reports of high-efficiency adhesives that combine ultra-low temperature resistant adhesion performance and ultra-low temperature in-situ adhesion performance. Summary of the invention

[0005] In order to solve the problem of poor adhesion of adhesives in ultra-low temperature environments, the present invention provides a polyurea adhesive containing polyurea and PDMS segments. The adhesive has excellent ultra-low temperature toughness and can achieve in-situ long-lasting strong adhesion in ultra-low temperature environments, providing a new technical solution for solving the limitations of adhesive application scenarios.

[0006] To achieve the above object, the technical solution adopted by the present invention is:

[0007] A polyurea adhesive with in-situ permanent adhesion in an ultra-low temperature environment, wherein the polyurea adhesive has the following structural formula:

[0008]

[0009] Among them, n is 0-65, and m is 3-25.

[0010] The polyurea adhesive designed in the present invention contains both a polydimethylsiloxane structure and a polyurea structure, combining the low-temperature compliance of the PDMS chain with the adhesion of the polyurea, and the alkyl chain containing a multi-carbon structure in the PDMS segment provides low-temperature compliance, and the polyurea structure content is low to avoid self-formation of a hard phase region. The polyurea adhesive achieves in-situ reversible adhesion on a variety of substrates in an ultra-low temperature environment (liquid nitrogen), and can maintain a high adhesion strength after long-term immersion in liquid nitrogen, and can act as a buffer material in an ultra-low temperature environment.

[0011] The present invention also provides a method for preparing the polyurea adhesive with in-situ permanent adhesion in an ultra-low temperature environment, comprising the steps of:

[0012] Step 1, allowing aminopropyl-terminated polydimethylsiloxane (A-PDMS) represented by formula I to undergo a ring-opening reaction with ethylene carbonate to obtain a product PDMS-EC represented by formula III; wherein n is 0 to 65;

[0013]

[0014]

[0015] Step 2: After the product PDMS-EC is mixed with the aminopropyl-terminated polydimethylsiloxane shown in formula I and a catalyst, a pre-condensation is performed, and the by-products are removed by vacuum until the reactants undergo Weissenberg effect to obtain a prepolymer.

[0016] The specific reaction formula is:

[0017]

[0018] Step 3, melt-polycondensing the obtained prepolymer under vacuum to obtain the polyurea adhesive.

[0019] In the process of synthesizing the polyurea adhesive, the present invention is based on a non-isocyanate route, does not use toxic isocyanates and solvents, does not produce any harmful substances, and has a simple preparation process, is green, environmentally friendly and sustainable.

[0020] The aminopropyl-terminated polydimethylsiloxane has a molecular weight of 248-5058 g / mol. The higher the molecular weight of the siloxane, the higher the content of siloxy groups in its structure. The corresponding polyurea adhesive has higher in-situ adhesion strength and better low-temperature resistant adhesion performance at low temperatures.

[0021] Preferably, the aminopropyl-terminated polydimethylsiloxane has a molecular weight of 1000-3000 g / mol;

[0022] The molecular weights of the aminopropyl-terminated polydimethylsiloxane used in step 1 and step 2 may be the same or different.

[0023] In step 1, the molar ratio of aminopropyl-terminated polydimethylsiloxane to ethylene carbonate is 1:1-2.

[0024] The ring-opening reaction temperature of step 1 is 50-100°C and the reaction time is 8-10h.

[0025] In step 2, the molar ratio of PDMS-EC to the aminopropyl-terminated polydimethylsiloxane shown in formula I is 1:0.5-1.

[0026] The molecular weight of the polyurea adhesive can be regulated by adjusting the content of ethylene carbonate in the reaction step 1 and the content of aminopropyl-terminated polydimethylsiloxane in the step 2, so that the interfacial adhesion energy and the cohesive energy are balanced. The higher the content of ethylene carbonate, the higher the molecular weight of the corresponding polyurea adhesive, the lower the content of terminal functional groups, the higher the interfacial adhesion strength and the lower the cohesive energy.

[0027] In step 2, the catalyst is one of dibutyltin oxide, anhydrous stannous chloride and dibutyltin dimethoxide, and its mass is 0.1-1% of the total mass of the reaction raw materials.

[0028] Preferably, the molar ratio of the aminopropyl-terminated polydimethylsiloxane to ethylene carbonate is 1:1-2, and more preferably the molar ratio is 1:1.8-2. The molar ratio of the product PDMS-EC to A-PDMS is 1:0.5-1, and more preferably the molar ratio is 1:0.9-1.

[0029] In step 2, the pre-polycondensation reaction temperature is 80-170° C., and the reaction time is 7-12 h.

[0030] In step 3, the melt polycondensation temperature is 170-200° C., and the curing time is 1-3 hours.

[0031] The present invention also provides the use of the polyurea adhesive with in-situ permanent adhesion in an ultra-low temperature environment in an ultra-low temperature environment, wherein the ultra-low temperature environment refers to an environment temperature below -50°C.

[0032] The polyurea adhesive of the present invention can exhibit excellent and durable in-situ adhesion performance in ultra-low temperature environments, such as at -80°C, -100°C, or liquid nitrogen (about -196°C).

[0033] The polyurea adhesive of the present invention can reversibly adhere to different substrates in situ in liquid nitrogen, including but not limited to hydrophilic surfaces such as glass, steel plate, nitrile rubber (NBR) and hydrophobic surfaces such as polytetrafluoroethylene (PTFE), polyethylene terephthalate (PET), polymethyl methacrylate (PMMA) and silicone rubber (SR).

[0034] In some embodiments, the in-situ adhesion strength of the polyurea adhesive to the steel plate in an ultra-low temperature environment is above 1.3 MPa, and the used polyurea adhesive can be effectively recycled by simple drying. Even after 10 times of recycling, the in-situ adhesion strength of the recycled polyurea adhesive is still comparable to that of the original adhesive, or even slightly higher than that of the original adhesive, and the effect is very excellent.

[0035] In some embodiments, the polyurea adhesive also exhibits a long-lasting and stable adhesion effect. For example, after being adhered to a steel plate and then immersed in liquid nitrogen for 60 days, the adhesion strength thereof is above 10 MPa and can be as high as 15.8 MPa.

[0036] Compared with the prior art, the present invention has the following beneficial effects:

[0037] (1) The polyurea adhesive provided by the present invention has a polydimethylsiloxane and polyurea structure. The polydimethylsiloxane portion gives it excellent low-temperature compliance, enabling it to wet on the surfaces of various substrates in an ultra-low temperature environment, providing conditions for the formation of interactions between the adhesive / substrate interface; in addition, since polyurea can form multiple interactions with various substrates, it can achieve in-situ reversible adhesion and strong and durable adhesion on various substrates in an ultra-low temperature environment.

[0038] (2) The polyurea adhesive disclosed in the present invention that has in-situ permanent adhesion in an ultra-low temperature environment has excellent ultra-low temperature toughness, can bend in liquid nitrogen and can act as a buffer material.

[0039] (3) The polyurea adhesive with in-situ persistent adhesion in an ultra-low temperature environment of the present invention has a simple preparation process, does not require solvents and toxic isocyanates, is green, environmentally friendly, sustainable, and has readily available raw materials, which is conducive to industrial production and promotion. BRIEF DESCRIPTION OF THE DRAWINGS

[0040] Figure 1 : is the Fourier transform infrared spectrum of PDMS-EC prepared in Examples 1, 3 and 4.

[0041] Figure 2 is the Fourier infrared spectrum of the polyurea adhesive prepared in Examples 1-5.

[0042] Figure 3 The following are actual pictures of the polyurea adhesive prepared in Example 3 being adhered to various substrates in situ in liquid nitrogen.

[0043] Figure 4 It is the in-situ adhesion strength of the polyurea adhesives prepared in Examples 1-3 on a steel plate in liquid nitrogen under cyclic in-situ adhesion.

[0044] Figure 5 The polyurea adhesives prepared in Examples 1-3 are tested for adhesion strength after being immersed in liquid nitrogen on steel plates for different time periods.

[0045] Figure 6 This is a physical picture of the polyurea adhesive prepared in Example 3 bending in liquid nitrogen.

[0046] Figure 7 This is a physical picture showing that the polyurea adhesive prepared in Example 4 becomes brittle in liquid nitrogen.

[0047] Figure 8 The ordered hydrogen bond association degree, disordered hydrogen bond association degree and total hydrogen bond association degree of the polyurea adhesive prepared in Example 3 within the range of -170 to 30°C. DETAILED DESCRIPTION

[0048] In order to make the purpose, technical scheme and advantages of the present invention clearer, the present invention is further described in detail below in conjunction with embodiment. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention. Those skilled in the art can make modifications or equivalent substitutions based on the understanding of the technical scheme of the present invention without departing from the spirit and scope of the technical scheme of the present invention, and all should be included in the protection scope of the present invention.

[0049] The raw materials used in the following specific embodiments are all purchased from the market.

[0050] Example 1

[0051] (1) Add aminopropyl-terminated polydimethylsiloxane (A-PDMS) and ethylene carbonate (EC) into a single-necked flask equipped with a magnetic stirrer for a ring-opening reaction. The reaction temperature is 60°C and the mixture is stirred thoroughly until the absorption peak of the carbonyl group in the cyclic carbonate disappears in the FTIR spectrum. The molecular weight of A-PDMS is 1000 g / mol, and the molar ratio of A-PDMS to EC is 1:2. After the reaction, a colorless, transparent, viscous liquid is obtained, i.e., the product PDMS-EC is obtained and is denoted as A1000-EC. The Fourier transform infrared spectrum of A1000-EC is shown in Figure 1 .

[0052] (2) Add A1000-EC, A-PDMS and catalyst obtained in the first step into a three-necked flask equipped with mechanical stirring and nitrogen inlet. First, stir at 80°C, 100°C and 130°C for 1 hour respectively under nitrogen atmosphere. Then remove the by-product ethylene glycol under high vacuum conditions at 150°C until the Weissenberg effect occurs to obtain a prepolymer. Among them, the molecular weight of A-PDMS is 1000g / mol, the molar ratio of A1000-EC and A-PDMS is 1:1, and the catalyst is anhydrous stannous chloride, the mass of which is 0.3% of the total mass of the reaction raw materials.

[0053] (3) The obtained prepolymer was poured into a polytetrafluoroethylene mold and further melt-polycondensed in a vacuum oven at 170°C to finally obtain a polyurea adhesive, which was recorded as P1. The number average molecular weight (Mn) of P1 was 2.1×10 4 g / mol, and the weight average molecular weight (Mw) is 4.6×10 4 g / mol, the polydispersity index (PDI) is 2.2, n in its molecular structure is about 10, and m is about 21. The molecular weight data are shown in Table 1.

[0054] The Fourier infrared spectrum of P1 is shown in Figure 2 The in-situ adhesion strength of cyclic in-situ adhesion on steel plate in liquid nitrogen (LN) is shown in Figure 4 The adhesion strength of the steel plate after being immersed in liquid nitrogen for different time periods is shown in Figure 5 .

[0055] Table 1 Molecular weight data of polyurea adhesives prepared in Examples 1-3 (PDI is dispersion index)

[0056]

[0057]

[0058] Example 2

[0059] The preparation process of Example 1 was followed, except that the molecular weight of A-PDMS in step 2 was 3000 g / mol, and the obtained polyurea adhesive was recorded as P2, as shown in Table 1, and its Mn was 1.0×10 4 g / mol, Mw is 2.7×10 4 g / mol, PDI is 2.6, n in the molecular structure is about 10 and 37, m is about 5, and the Fourier infrared spectrum is shown in Figure 2 The in-situ adhesion strength of cyclic in-situ adhesion on steel plate in liquid nitrogen is shown in Figure 4 The adhesion strength of the steel plate after being immersed in liquid nitrogen for different time periods is shown in Figure 5 .

[0060] Example 3

[0061] According to the preparation process of Example 1, the only difference is that the molecular weight of A-PDMS in step 1 is 3000 g / mol, and the product PDMS-EC is obtained, denoted as A3000-EC, and its Fourier transform infrared spectrum is shown in Figure 1 In step 2, the molecular weight of A-PDMS is 3000 g / mol, and the obtained polyurea adhesive is recorded as P3. As shown in Table 1, its Mn is 1.5×10 4 g / mol, Mw is 3.3×10 4 g / mol, PDI is 2.2, n is about 37, and m is about 5 in its molecular structure.

[0062] Fourier infrared spectrum of polyurea adhesive P3 is shown in Figure 2 , in situ adhesion of various substrates in liquid nitrogen Figure 3 The in-situ adhesion strength of the cyclic in-situ adhesion on the steel plate in liquid nitrogen is shown in Figure 4 The adhesion strength of the steel plate after being immersed in liquid nitrogen for different time periods is shown in Figure 5 , the actual picture before and after bending in liquid nitrogen is as follows Figure 6 shown.

[0063] Example 4

[0064] According to the preparation process of Example 1, the only difference is that the molecular weight of A-PDMS in step 1 is 248 g / mol, and the product PDMS-EC is obtained, denoted as A248-EC, and its Fourier transform infrared spectrum is shown in Figure 1 The molecular weight of A-PDMS in step 2 is 3000 g / mol, and the obtained polyurea adhesive is denoted as P4. In its molecular structure, n is approximately 0 and 37. The Fourier transform infrared spectrum is shown in FIG. Figure 2 .

[0065] Example 5

[0066] The preparation process of Example 1 is the same, except that the molecular weight of A-PDMS in step 1 is 248 g / mol, and the product PDMS-EC is obtained, which is recorded as A248-EC. The molecular weight of A-PDMS in step 2 is 248 g / mol, and the polyurea adhesive is obtained, which is recorded as P5. In its molecular structure, n is 0, and the Fourier infrared spectrum is shown in FIG. Figure 2 .

[0067] Performance testing and results analysis

[0068] The products prepared in the examples were characterized and tested for performance, and the test process was as follows:

[0069] 1. Fourier transform infrared spectroscopy

[0070] At room temperature and pressure, the PDMS-EC (A1000-EC, A3000-EC and A248-EC) and polyurea adhesives (P1, P2, P3 and P4) prepared in Examples 1-3 were tested using an attenuated total reflection Fourier transform infrared (Nicolet IS 50) produced by Thermo Scientific USA, and Fourier infrared spectroscopy data were obtained.

[0071] The infrared spectra of PDMS-EC of Examples 1, 3 and 4 are as follows: Figure 1 As shown, the absorption peak of the carbonyl group in ethylene carbonate disappears, and the characteristic peak of the carbamate group appears, indicating that the ring-opening reaction is completed.

[0072] The infrared spectra of the polyurea adhesives of Examples 1-5 are as follows: Figure 2 As shown, the characteristic peak of the urethane group basically disappears, and the characteristic peak of the urea group appears, indicating that the polyurea adhesive is successfully synthesized.

[0073] 2. Adhesion performance test

[0074] The adhesion strength was tested according to GB / T528-2009 on a universal material testing machine (CK-10KN) produced by Beijing Times Maker Technology Co., Ltd. Adhesion substrate size: 100 mm × 20 mm × 20 mm; adhesion area: 25 mm × 20 mm.

[0075] (1) In-situ adhesion strength test in liquid nitrogen

[0076] First, place a substrate with adhesive and a blank substrate in liquid nitrogen and wait for the temperature to reach equilibrium before taking them out. Then, immediately adhere the two substrates together and quickly clamp them with a folder, and then immediately place them in liquid nitrogen. After reaching the specified time of 15 minutes, take them out and immediately remove the folder to test the in-situ adhesion strength. Each adhesion test is performed using at least three independent samples.

[0077] In-situ adhesion strength on steel plate in liquid nitrogen Figure 4 As shown in the figure, the in-situ adhesion strengths of P1, P2 and P3 are as high as 1.3, 1.2 and 1.6 MPa respectively. The results show that polyurea adhesive has excellent ultra-low temperature in-situ adhesion performance. Figure 7 As shown in Figure 2, P4 and P5 become brittle and lose adhesion in liquid nitrogen. These results indicate that in the A-PDMS molecular structure, the larger the n, the higher the content of siloxy groups, which significantly affects the in-situ adhesion performance of polyurea adhesives at low temperatures within a certain range.

[0078] (2) Cyclic test of in-situ adhesion strength in liquid nitrogen

[0079] After the lap-shear test, the recovered polyurea adhesive was dried in a vacuum oven at 60°C, cooled to room temperature, and then subjected to the same adhesion process in liquid nitrogen.

[0080] The in-situ adhesion strength of cyclic in-situ adhesion on steel plate in liquid nitrogen is shown in Figure 4 As shown in the figure, even after 10 cycles, the in-situ adhesion strength of P1, P2 and P3 remained basically unchanged, or even slightly improved. The results show that polyurea adhesives have excellent recyclability, which is beneficial from both economic and environmental perspectives.

[0081] (3) Ultra-low temperature resistance adhesion test

[0082] The steel plates bonded at room temperature were immersed in liquid nitrogen for different time periods and then immediately taken out for adhesion strength testing.

[0083] The adhesion strength obtained after immersion in liquid nitrogen for different time periods is shown in Figure 2. Figure 5 As shown in the figure, after immersion in liquid nitrogen for 4 hours, the adhesion strengths of P1, P2 and P3 were 7.5, 9.3 and 20.6 MPa respectively. As the immersion time was extended to 60 days, their adhesion strengths did not decay significantly, and the adhesion strength of P3 was still as high as 15.8 MPa. The results show that polyurea adhesives exhibit excellent ultra-low temperature tolerance and can maintain strong and lasting adhesion in liquid nitrogen.

[0084] (4) Bending test

[0085] A rectangular P3 spline with a size of about 10×0.5cm and a thickness of about 0.27mm was placed in liquid nitrogen. After the temperature reached equilibrium, one end was fixed with tweezers and the other end was bent with tweezers. Figure 6 As shown, the P3 spline can be bent about 180° in liquid nitrogen without breaking, and after the external force is removed, the spline can almost return to its original shape.

[0086] (5) Variable Temperature Fourier Transform Infrared Spectroscopy

[0087] The Fourier transform infrared spectroscopy data of the polyurea adhesive P3 prepared in Example 3 was measured using a Thermo Scientific Nicolet 6700 in the temperature range of -170 to 30°C, with a temperature interval of 10°C, in transmission mode. The peak splitting method was used to analyze the evolution of hydrogen bonds as the temperature decreased. -1 The C=O absorption peak at 1622-1634 cm -1 Ordered hydrogen bonding at C=O, 1635-1654cm -1 The disordered hydrogen bonding of C=O and 1672-1678cm -1The total hydrogen bonding degree (DHA) can be calculated by the following formula.

[0088] DHA=(A ordered +A disordered ) / (A ordered +A disordered +A free )

[0089] Among them, A ordered ,A disordered ,and A free They represent the peak areas of ordered hydrogen bonding, disordered hydrogen bonding, and free C=O, respectively.

[0090] like Figure 8 As shown, up to the test limit of -170°C, the continuous transition between ordered hydrogen bond association and disordered hydrogen bond association C=O indicates that the polyurea adhesive P3 has excellent flexibility at extremely low temperatures, providing a basis for the in-situ adhesion ability.

Claims

1. A polyurea adhesive with in-situ permanent adhesion in an ultra-low temperature environment, characterized in that: The polyurea adhesive has the following structural formula: Among them, n is 10-65, and m is 3-25.

2. The method for preparing a polyurea adhesive with in-situ permanent adhesion in an ultra-low temperature environment according to claim 1, characterized in that: Includes steps: Step 1, allowing aminopropyl-terminated polydimethylsiloxane represented by formula I to undergo a ring-opening reaction with ethylene carbonate to obtain a product PDMS-EC represented by formula III; wherein n is 10 to 65; Step 2, after the product PDMS-EC is mixed with the aminopropyl-terminated polydimethylsiloxane shown in formula I and a catalyst, a pre-condensation is performed, and the by-products are removed by vacuum until the reactants undergo Weissenberg effect to obtain a prepolymer; Step 3, melt-polycondensing the obtained prepolymer under vacuum to obtain the polyurea adhesive.

3. The method for preparing a polyurea adhesive with in-situ permanent adhesion in an ultra-low temperature environment according to claim 2, characterized in that: The ring-opening reaction temperature of step 1 is 50-100°C and the reaction time is 8-10h.

4. The method for preparing a polyurea adhesive with in-situ permanent adhesion in an ultra-low temperature environment according to claim 2, characterized in that: In step 2, the molar ratio of PDMS-EC to the aminopropyl-terminated polydimethylsiloxane shown in formula I is 1:0.5-1.

5. The method for preparing a polyurea adhesive with in-situ permanent adhesion in an ultra-low temperature environment according to claim 2, characterized in that: In step 2, the catalyst is one of dibutyltin oxide, anhydrous stannous chloride and dibutyltin dimethoxide, and its mass is 0.1-1% of the total mass of the reaction raw materials.

6. The method for preparing a polyurea adhesive with in-situ permanent adhesion in an ultra-low temperature environment according to claim 2, characterized in that: In step 2, the pre-polycondensation reaction temperature is 80-170° C., and the reaction time is 7-12 h.

7. The method for preparing a polyurea adhesive with in-situ permanent adhesion in an ultra-low temperature environment according to claim 2, characterized in that: In step 3, the melt polycondensation temperature is 170-200° C., and the curing time is 1-3 hours.

8. The use of the polyurea adhesive with in-situ permanent adhesion in an ultra-low temperature environment according to claim 1 in an ultra-low temperature environment, characterized in that: The ultra-low temperature environment refers to an environment temperature below -50°C.

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