A detachable structure bonding hot melt adhesive based on multi-element synergistic self-repairing polyurethane and a synthesis method thereof

Abstract

The application belongs to the technical field of hot melt adhesives, and particularly relates to a detachable structure bonding hot melt adhesive based on a multi-element synergistic self-repairing polyurethane and a synthesis method thereof. The hot melt adhesive is synthesized according to the following molar ratio: 1:2 of polytetramethylene ether glycol or polytrimethylene ether glycol and isophorone diisocyanate or 4,4-diisocyanate dicyclohexyl methane, 1:10 of polytetramethylene ether glycol or polytrimethylene ether glycol and a catalyst ‑5 , 1:4 of 4,4'-diamino diphenyl disulfide or 2,2'-diamino diphenyl disulfide and a diluent, 1:1.2-2.0 of the prepolymer and 4,4'-diamino diphenyl disulfide or 2,2'-diamino diphenyl disulfide, and 1:0.4-2.0 of the prepolymer and 3,4-dihydroxybenzaldehyde. The hot melt adhesive has an aluminum-aluminum shear strength of 4.25-14.23 MPa at room temperature, a shear strength retention rate of 93.04% or more after repeated bonding for 6 times, and excellent mechanical properties at 0-55 DEG C and on various substrates. After being treated at 80 DEG C for 30 minutes, the self-healing efficiency of the tensile strength is 95% or more.

Description

Technical Field

[0001] This invention belongs to the field of hot melt adhesive technology, specifically relating to a detachable structural bonding hot melt adhesive based on multi-component synergistic self-healing polyurethane and its synthesis method. Background Technology

[0002] Adhesive materials are indispensable in modern life, ingeniously integrating complex structures such as buildings, electronic devices, industrial vehicles, and aircraft into a unified whole. With increasing demand for adhesive materials, their applications are becoming increasingly complex. Currently, adhesives on the market typically offer only either flexibility or rigidity, and achieving an effective balance between the two remains a challenge. Flexibility is common in most low-modulus materials, which possess weak molecular interactions and high chain mobility, enabling adhesives to withstand tensile and disperse mechanical stresses, effectively preventing sudden bond failure. However, the bond strength of these adhesives is generally low, making them vulnerable to significant external forces. Meanwhile, high bond strength relies on strong covalent bonds and a stable cross-linked network. While strong adhesives possess high cohesive strength and can withstand heavy loads, their embrittlement under stress can lead to sudden strength loss and breakage. An ideal adhesive should strike a balance between flexibility and strength, as these two properties often conflict. Therefore, developing an adhesive that combines removability, high flexibility, and high strength is a significant technical challenge for practical applications.

[0003] The adhesive strength of an adhesive is significantly influenced by two key factors: cohesive strength and adhesive strength. The cohesive strength of an adhesive is closely related to its mechanical properties and adhesive action. Crosslinking networks, involving the formation of covalent or non-covalent interactions between molecular chains, are one effective means of improving cohesive strength. Furthermore, traditional adhesives introduce non-covalent interactions as dynamic sacrificial bonds, including hydrogen bonds, host-guest interactions, and ionic dipole interactions, which effectively dissipate mechanical energy during bonding. However, these forces may gradually weaken over time and with changes in pH, leading to a decrease in adhesive strength. To address this issue, researchers have developed novel strong adhesives based on dynamic covalent networks; however, in most cases, they still fail to provide very strong adhesion. Adhesion refers to the bond strength formed between the adhesive and the adherend surface, influenced by the energy parameters of the adhesive on the substrate. This includes molecular-level adhesive forces, local chemical properties, microscopic surface roughness, and macroscopic mechanical properties. When adhesives are used in load-bearing applications, excessively high cohesive strength can lead to delamination, while excessively high adhesive strength can lead to internal breakage. Therefore, optimal adhesive strength depends on a balance between strong cohesive molecular interactions and strong adhesion to the substrate.

[0004] Based on this understanding, the present invention designs a series of detachable structural adhesive hot melt adhesives based on multi-component synergistic self-healing polyurethane. Summary of the Invention

[0005] The purpose of this invention is to overcome the shortcomings of the prior art and provide a detachable structural adhesive hot melt adhesive based on multi-component synergistic self-healing polyurethane and its synthesis method.

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

[0007] A method for synthesizing a removable structural adhesive hot melt adhesive based on multi-component synergistic self-healing polyurethane includes the following steps:

[0008] (1) Add polytetramethylene ether glycol (PTMEG) or polytrimethylene ether glycol (PO3G) to the reactor, heat to 120°C and dehydrate under vacuum for 1 hour, then lower the temperature to 80°C, add isophorone diisocyanate (IPDI) or 4,4-diisocyanate dicyclohexylmethane (HMDI) and stir for 1 hour under nitrogen atmosphere, and finally add the catalyst dibutyltin dilaurate (DBTDL) for prepolymerization for 3 hours to obtain the prepolymer;

[0009] (2) Add 4,4'-diaminodiphenyl disulfide or 2,2'-diaminodiphenyl disulfide (AD) dissolved in diluent to the reactor until the -NCO peak in FTIR disappears;

[0010] (3) Add 3,4-dihydroxybenzaldehyde (DBD), maintain the reaction at 80°C under a nitrogen atmosphere, pour the uniform viscous liquid into a polytetrafluoroethylene mold after 8 hours, maintain it at 80°C for 48 hours, and then vacuum dry for 12 hours to obtain a detachable structural adhesive hot melt adhesive (PU-PADx) based on multi-component synergistic self-healing polyurethane, where x represents the molar ratio of prepolymer to AD in the system.

[0011] Preferably, in step (1), the number-average molecular weight Mn of the polytetramethylene ether glycol (PTMEG) or polytrimethylene ether glycol (PO3G) is 850-1500 g / mol.

[0012] Preferably, in step (1), the molar ratio of polytetramethylene ether glycol (PTMEG) or polytrimethylene ether glycol (PO3G) to isophorone diisocyanate (IPDI) or 4,4-diisocyanate dicyclohexylmethane (HMDI) is 1:2.

[0013] Preferably, in step (1), the molar ratio of polytetramethylene ether glycol (PTMEG) or polytrimethylene ether glycol (PO3G) to the catalyst dibutyltin dilaurate (DBTDL) is 1:10. -5 .

[0014] Preferably, in step (2), the diluent is one or a mixture of N,N-dimethylformamide, cyclohexanone, N,N-dimethylacetamide, and N-methylpyrrolidone, and the mass ratio of 4,4'-diaminodiphenyl disulfide or 2,2'-diaminodiphenyl disulfide (AD) to the diluent is 1:4.

[0015] Preferably, in step (2), the molar ratio x of the prepolymer to 4,4'-diaminodiphenyl disulfide or 2,2'-diaminodiphenyl disulfide (AD) is 1:1.2 to 2.0, and most preferably 1:1.4.

[0016] Preferably, in step (3), the molar ratio of the prepolymer to 3,4-dihydroxybenzaldehyde (DBD) is 1:0.4 to 2.0, and most preferably 1:0.8.

[0017] Preferably, the hot melt adhesive synthesized by the above method has a room temperature aluminum-aluminum shear strength of 4.25–14.23 MPa, a shear strength retention rate of over 93.04% after 6 repeated bonding cycles, and exhibits excellent mechanical properties at 0–55°C and on various substrates, with a tensile strength of 11.4–24.5 MPa, an elongation at break of 234.3–743.3%, and a tensile toughness of 12.4–66.5 MJ / m. 3 When treated at 80℃ for 30 minutes, the self-healing efficiency of tensile strength reaches over 95%.

[0018] Compared with the prior art, the beneficial effects of the present invention are:

[0019] 1. The isophorone diisocyanate (IPDI) or 4,4-diisocyanate dicyclohexylmethane (HMDI)-terminated polytetramethylene ether glycol (PTMEG) or polytrimethylene ether glycol (PO3G) prepolymers are intentionally extended by different contents of 4,4'-diaminodiphenyl disulfide or 2,2'-diaminodiphenyl disulfide (AD) and then terminated by 3,4-dihydroxybenzaldehyde (DBD). This is intended to manipulate the subsequent chain length and aggregation state. By adjusting the ratio of the prepolymer to AD and DBD, the length of the molecular chain and the aggregation state are changed, thereby achieving an effective balance between cohesive energy and adhesive force.

[0020] 2. The hot melt adhesive synthesized in this invention possesses excellent shear strength, tensile strength, elongation at break, and tensile toughness, with tensile strength reaching 11.4–24.5 MPa, elongation at break reaching 234.3–743.3%, and tensile toughness reaching 12.4–66.5 MJ / m. 3These properties not only highlight its excellent adhesive performance in practical applications, but also provide a promising strategy for developing next-generation tougher materials and adhesives. With its outstanding toughness and high strength, PU-PADx hot melt adhesives offer innovative solutions for the environmentally friendly and high-precision processing industries.

[0021] 3. The hot melt adhesive synthesized in this invention not only has high bonding strength and re-bonding ability, but also exhibits excellent bonding performance on various metal substrates and wood panels, greatly expanding the application range of adhesives. The room temperature aluminum-aluminum shear strength of this hot melt adhesive is 4.25-14.23 MPa, and the shear strength retention rate after 6 repeated bonding is more than 93.04%. It exhibits excellent mechanical properties at 0-55°C and on a variety of substrates, which is superior to most reported reusable adhesives.

[0022] 4. The hot melt adhesive synthesized in this invention has a self-healing function, and its self-healing properties are particularly significant. After being heated at 80°C for 30 minutes, it can recover more than 95% of its tensile strength. Attached Figure Description

[0023] Figure 1 The GPC spectra of the PU-PADx hot melt adhesives in Examples 1 to 5 of this invention are shown. Detailed Implementation

[0024] To better illustrate the purpose, technical solution, and advantages of the present invention, the technical solution of the present invention will be clearly and completely described below in conjunction with specific embodiments. The following embodiments are used to illustrate the present invention, but are not intended to limit the scope of the present invention.

[0025] The raw materials used in the experiments of this invention are as follows, but are not limited to these raw materials. This invention only uses the following raw materials as specific examples to further illustrate the effect of the detachable structural adhesive hot melt adhesive based on multi-component synergistic self-healing polyurethane described in this invention:

[0026] Polytetramethylene ether glycol (PTMEG, Mn = 1000 g / mol), isophorone diisocyanate (IPDI), 4,4'-diaminodiphenyl disulfide (AD), dibutyltin dilaurate (DBTDL), 3,4-dihydroxybenzaldehyde (DBD), and N,N-dimethylformamide (DMF) were all purchased from Shanghai Adamas Reagent Co., Ltd. (a subsidiary of Shanghai Titan Technology Co., Ltd.).

[0027] The performance testing method in this embodiment of the invention is as follows:

[0028] Self-healing performance test: Samples were cut into dumbbell shapes for tensile testing. Similar to the lap shear test, the tensile test was conducted at a rate of 100 mm / min. At room temperature, a test strip was cut in the middle, and then the cut surfaces were assembled together. After the cut samples were allowed to heal for different periods at 80°C, the tensile test was performed again to calculate the self-healing rate. The formula is as follows:

[0029]

[0030] Where P represents elongation at break, tensile strength, or toughness.

[0031] This invention includes Examples 1-5, which synthesize a series of PU-PADx hot melt adhesives. The feed ratios are shown in Table 1.

[0032] Table 1

[0033]

[0034] Examples 1-5 were prepared according to the following process:

[0035] (1) Polytetramethylene ether glycol PTMEG (37.50 mmol, 37.50 g) was added to the reactor, heated to 120°C and vacuum dehydrated for 1 hour. Then the temperature was lowered to 80°C, and isophorone diisocyanate IPDI (75.00 mmol, 16.67 g) was added and stirred for 1 hour under a nitrogen atmosphere. Finally, the catalyst dibutyltin dilaurate DBTDL was added in the prescribed amount and prepolymerized for 3 hours to obtain the prepolymer.

[0036] (2) Add the amount of 4,4'-diaminodiphenyl disulfide AD dissolved in N,N-dimethylformamide DMF to the reactor until the -NCO peak in FTIR disappears;

[0037] (3) Add the formulation amount of 3,4-dihydroxybenzaldehyde DBD, maintain the reaction at 80°C under nitrogen atmosphere, pour the uniform viscous liquid into a polytetrafluoroethylene mold after 8 hours, maintain it at 80°C for 48 hours, and then vacuum dry for 12 hours to obtain PU-PADx hot melt adhesive, where x represents the molar ratio of prepolymer to AD in the system.

[0038] The GPC data of the PU-PADx hot melt adhesives of Examples 1 to 5 of this invention are shown in Table 2:

[0039] Table 2

[0040]

[0041] Note: * represents the dispersion index.

[0042] Depend on Figure 1As can be seen from the GPC data in Table 2, PU-PADx hot melt adhesive was successfully synthesized in Examples 1-5 of this invention.

[0043] The mechanical properties of the PU-PADx hot melt adhesives of Examples 1 to 5 of this invention were tested, and the results are shown in Table 3:

[0044] Table 3

[0045]

[0046]

[0047] As can be seen from the data in Table 3, the PU-PADx hot melt adhesives of Examples 1-5 of this invention have tensile strengths of 11.4-24.5 MPa, elongation at break of 234.3-743.3%, and tensile toughness of 12.4-66.5 MJ / m. 3 The PU-PADx hot melt adhesives of Examples 1 to 5 of this invention have excellent tensile strength, elongation at break and tensile toughness. These properties not only highlight their excellent adhesive performance in practical applications, but also provide a very promising strategy for developing next-generation tougher materials and adhesives.

[0048] The lap shear strength and debonding work of the PU-PADx hot melt adhesives of Examples 1-5 of this invention with aluminum substrates were tested, and the results are shown in Table 4:

[0049] Table 4

[0050]

[0051]

[0052] As can be seen from the data in Table 4, the lap shear strength of the PU-PADx hot melt adhesives of Examples 1-5 of the present invention with aluminum substrates reaches 4.25-14.23 MPa, and the debonding energy reaches 2.20-12.50 kN / m. That is, the PU-PADx hot melt adhesives of Examples 1-5 of the present invention have excellent shear strength and debonding energy with aluminum substrates. In particular, the PU-PAD1.4 hot melt adhesive of Example 2 has a shear strength with aluminum substrate as high as 14.23 MPa and a debonding energy as high as 12.50 kN / m, which is better than most adhesives reported on the market. The PU-PAD1.4 hot melt adhesive achieves the best balance between cohesion and adhesion, and exhibits the best performance.

[0053] The lap shear strength of the PU-PADx hot melt adhesive and aluminum substrate in Examples 1-5 of this invention was tested at different temperatures, and the results are shown in Table 5:

[0054] Table 5

[0055]

[0056] As can be seen from the data in Table 5, the PU-PADx hot melt adhesives of Examples 1 to 5 of the present invention exhibit excellent adhesion in the range of 0 to 55°C.

[0057] The PU-PADx hot melt adhesive of Examples 1-5 of this invention was subjected to lap shear tests by repeatedly using aluminum plates. The lap shear strength after cyclic bonding and debonding is shown in Table 6.

[0058] Table 6

[0059]

[0060] As can be seen from the data in Table 6, the room temperature aluminum-aluminum shear strength of the PU-PADx hot melt adhesive in Examples 1 to 5 of the present invention is 4.25 to 14.23 MPa, and the shear strength retention rate after 6 repeated bonding cycles is over 93.04%.

[0061] To evaluate the suitability of the PU-PADx hot melt adhesives in Examples 1-5, overlap shear tests were conducted on substrates of different materials, and the results are shown in Table 7:

[0062] Table 7

[0063]

[0064]

[0065] As can be seen from the data in Table 7, the PU-PADx hot melt adhesives of the present invention 1 to 5 exhibit significant strong adhesion to metal surfaces such as aluminum, steel, and iron, as well as wood boards. They can be tightly bonded to various metal materials and wood boards, have wide applicability, and greatly expand the application range of adhesives.

[0066] The self-healing ability of the PU-PADx hot melt adhesives of Examples 1-5 of the present invention was evaluated. The results, as shown by optical microscopy, showed that the scratches on the hot melt adhesives of Examples 1-5 were almost completely repaired within 30 minutes at 80°C, indicating that they have high self-healing performance. The self-healing efficiency of the tensile samples can be increased to more than 95% within 30 minutes of repair.

[0067] Therefore, this invention successfully prepared a series of detachable structural adhesive hot melt adhesives (PU-PADx) based on multi-component synergistic self-healing polyurethane. These adhesives are suitable for various substrates, greatly expanding the application range of adhesives. By adjusting the ratio of prepolymer to AD and DBD, the length and aggregation state of the molecular chains were changed, achieving an effective balance between cohesive energy and adhesive force. In Example 2, the hot melt adhesive exhibited an lap shear strength and debonding work of 14.23 MPa and 12.50 kN / m on aluminum plates, respectively. After six repeated bonding cycles, the strength remained as high as 13.24 MPa, superior to most reported reusable adhesives. Furthermore, PU-PAD1.4 hot melt adhesive showed significant strong adhesion to metal surfaces such as aluminum, steel, and iron, as well as wood panels. The excellent adhesion strength stemmed from metal chelation, hydrogen bonding, and electrostatic interactions. Moreover, at a tensile strength of 18.34 MPa, its elongation at break still reached 643.85%, and its self-healing rate was as high as 98.28%. These properties not only highlight its excellent adhesive performance in practical applications, but also provide a promising strategy for developing next-generation tougher materials and adhesives.

Claims

1. A method for synthesizing a detachable structural adhesive hot melt adhesive based on multi-component synergistic self-healing polyurethane, characterized in that, Includes the following steps: (1) Add polytetramethylene ether glycol or polytrimethylene ether glycol to the reactor, heat to 120°C and dehydrate under vacuum for 1 hour, then lower the temperature to 80°C, add isophorone diisocyanate or 4,4'-diisocyanate dicyclohexylmethane and stir for 1 hour under nitrogen atmosphere, and finally add the catalyst dibutyltin dilaurate for prepolymerization for 3 hours to obtain the prepolymer; (2) Add 4,4'-diaminodiphenyl disulfide or 2,2'-diaminodiphenyl disulfide dissolved in diluent to the reactor until the -NCO peak in the FTIR disappears; (3) Add 3,4-dihydroxybenzaldehyde, maintain the reaction at 80°C under nitrogen atmosphere, pour the uniform viscous liquid into a polytetrafluoroethylene mold after 8 hours, maintain it at 80°C for 48 hours, and then vacuum dry for 12 hours to obtain a detachable structural adhesive hot melt adhesive based on multi-component synergistic self-healing polyurethane. In step (1), the number average molecular weight Mn of the polytetramethylene ether glycol or polytrimethylene ether glycol is 850~1500 g / mol; in step (2), the molar ratio of the prepolymer to 4,4'-diaminodiphenyl disulfide or 2,2'-diaminodiphenyl disulfide is 1:1.2~2.0; in step (3), the molar ratio of the prepolymer to 3,4-dihydroxybenzaldehyde is 1:0.4~2.

0.

2. The method for synthesizing the detachable structural adhesive hot melt adhesive based on multi-component synergistic self-healing polyurethane as described in claim 1, characterized in that, In step (1), the molar ratio of polytetramethylene ether glycol or polytrimethylene ether glycol to isophorone diisocyanate or 4,4'-diisocyanate dicyclohexylmethane is 1:

2.

3. The method for synthesizing the detachable structural adhesive hot melt adhesive based on multi-component synergistic self-healing polyurethane as described in claim 1, characterized in that, In step (1), the molar ratio of polytetramethylene ether glycol or polytrimethylene ether glycol to the catalyst dibutyltin dilaurate is 1:

10. -5 .

4. The method for synthesizing the detachable structural adhesive hot melt adhesive based on multi-component synergistic self-healing polyurethane as described in claim 1, characterized in that, In step (2), the diluent is one or a mixture of N,N-dimethylformamide, cyclohexanone, N,N-dimethylacetamide, and N-methylpyrrolidone, and the mass ratio of 4,4'-diaminodiphenyl disulfide or 2,2'-diaminodiphenyl disulfide to the diluent is 1:

4.

5. A detachable structural adhesive hot melt adhesive based on multi-component synergistic self-healing polyurethane, characterized in that, The hot melt adhesive is prepared by the synthesis method according to any one of claims 1 to 4.

6. The detachable structural adhesive hot melt adhesive based on multi-component synergistic self-healing polyurethane as described in claim 5, characterized in that, The hot melt adhesive exhibits a room temperature aluminum-aluminum shear strength of 4.25–14.23 MPa, with a shear strength retention rate of over 93.04% after six repeated bonding cycles. It demonstrates excellent mechanical properties at 0–55°C and on various substrates, with a tensile strength of 11.4–24.5 MPa, an elongation at break of 234.3–743.3%, and a tensile toughness of 12.4–66.5 MJ / m. 3 When treated at 80℃ for 30 minutes, the self-healing efficiency of tensile strength reaches over 95%.

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