Preparation method of underwater polyurethane adhesive based on dopamine grafting and waste PET chain extension

Abstract

The invention discloses a preparation method of an underwater polyurethane adhesive based on dopamine grafting and waste PET chain extension. The preparation method specifically comprises the following steps: carrying out purification treatment on a GLP degradation solution through silica gel column chromatography; the preparation method comprises the following steps: carrying out a reaction on PPG and IPDI to prepare an NCO-terminated polyurethane prepolymer; and under a water bath condition, adding the GLP degradation liquid after chromatography into the polyurethane prepolymer, stirring, adding a dopamine hydrochloride solution, stirring, pouring into a preheated polytetrafluoroethylene mold, storing at room temperature, and curing to obtain the underwater polyurethane adhesive. According to the preparation method disclosed by the invention, the polyurethane material is endowed with underwater self-adaptive adhesion capacity through the reversible oxidation-metal chelation effect of a dopamine catechol group. Hydroxyl and amino in dopamine can easily form hydrogen bonds with water molecules, so that the interaction force between molecules is increased, and the adhesiveness is improved. Meanwhile, water molecules can promote oxidation reaction of dopamine, so that chemical adsorption is generated between formation of polydopamine and the surface of an adhered object.

Description

Technical Field

[0001] This invention belongs to the field of adhesive preparation technology, specifically relating to a method for preparing underwater polyurethane adhesives based on dopamine grafting and chain extension of waste PET. Background Technology

[0002] GLP (Glyco-Liquid Polyethylene Terephthalate) was prepared from waste packaging plastic polyethylene terephthalate (PET) via alcoholysis. This GLP was used as a chain extender in the synthesis of polyurethane adhesive materials. Simultaneously, a rational design of the soft and hard segment structures was implemented during the material synthesis stage to achieve effective adhesion of the polyurethane adhesive material to various substrates. However, the development of polyurethane adhesive materials using GLP requires addressing the following issues: removal of macromolecular impurities from PET alcoholysis products; synergistic design of soft and hard segments in the polyurethane molecular chain; adhesion stability at various substrate interfaces; and adhesion stability in aqueous environments.

[0003] Polyurethane adhesives (PUAs) possess excellent bonding properties, particularly exceptional toughness, good solvent resistance, high cohesive strength, abrasion resistance, and impact resistance. They can bond to a wide range of substrates, including metals, plastics, composites, wood, and textiles, making them widely used in manufacturing, construction, automotive, and aerospace industries. The flexibility and high load-bearing capacity of PUAs make them suitable for bonding materials with different coefficients of thermal expansion, thereby improving performance and structural integrity. The polyurethane molecular chain contains highly polar isocyanate and urethane groups. When in contact with substrates containing active hydrogen, polyurethane adhesives can form hydrogen bonds, thereby strengthening interfacial forces and enhancing adhesion, thus exhibiting high polarity and reactivity. More importantly, polyurethane possesses highly designable molecular structures; by precisely controlling the type and ratio of soft and hard segments, its flexibility, hardness, abrasion resistance, and other properties can be adjusted. Therefore, polyurethane adhesives can adapt to the diverse needs of different fields.

[0004] Traditional adhesives, such as acrylates, epoxy resins, and polyurethanes, often have stringent environmental requirements for adhesion, typically requiring clean and dry surfaces to achieve good bonding. This limitation significantly restricts their application in complex environments, especially humid or underwater ones. The presence of moisture interferes with the interaction between the adhesive and the adherend surface, leading to a significant decrease in adhesion or even complete failure. This is primarily due to moisture's ability to disrupt the adhesive's curing process, weaken chemical bonds, or prevent the formation of effective contact interfaces. On the curing process side, moisture can penetrate the adhesive system, disrupting the originally ordered curing reaction. This prevents the adhesive from completing cross-linking and polymerization steps according to the expected chemical pathway, ultimately resulting in a failure to form a sufficiently strong cohesive structure and a significant decrease in adhesion. On the other hand, at the chemical bonding level, the hydrogen-oxygen bonds in water are highly reactive and can compete with the chemical bonds formed by adhesive molecules and atoms on the surface of the adhered object. Through displacement, hydrolysis, and other mechanisms, water gradually weakens or even completely destroys the chemical bonds that originally maintained adhesion, causing the adhesive to lose its effective adhesion to the adhered object. From the perspective of the contact interface, water forms a thin water film between the adhesive and the surface of the adhered object. This water film acts like a barrier, preventing the smooth formation of an effective contact interface between the two, reducing effective bonding sites, further reducing adhesive force, and in severe cases, directly causing complete adhesion failure. Summary of the Invention

[0005] The purpose of this invention is to provide a method for preparing an underwater polyurethane adhesive based on dopamine grafting and waste PET chain extension, which solves the problem of low adhesion of existing polyurethane adhesives in humid or underwater environments.

[0006] The technical solution adopted in this invention is a method for preparing underwater polyurethane adhesive based on dopamine grafting and chain extension of waste PET, specifically implemented according to the following steps: Step 1: Prepare GLP degradation solution; Step 2: The GLP degradation solution obtained in Step 1 is purified by silica gel column chromatography. Step 3: Prepare NCO-terminated polyurethane prepolymer by reacting PPG and IPDI; Step 4: Under water bath conditions, add the chromatographically purified GLP degradation solution to the polyurethane prepolymer obtained in Step 3, stir, then add the hydrochloric acid dopamine solution and stir, then pour it into a preheated polytetrafluoroethylene mold, store at room temperature and cure to obtain underwater polyurethane adhesive.

[0007] The invention is further characterized in that, Step 1 specifically involves: Step 1.1: Pre-treat the waste PET plastic: Waste PET plastic is cut into fragments, soaked in HCl solution and stirred for 10-15 minutes, then filtered out and rinsed with deionized water 3-4 times; then soaked in NaOH solution and stirred for 10-15 minutes, filtered out and rinsed with deionized water 3-4 times; finally, it is placed in a forced-air drying oven and dried at 50-55℃ to obtain pretreated waste PET fragments. Step 1.2: Mix the pretreated waste PET fragments, NPG, and DPG, stir at 238-251 rpm, and perform alcoholysis reaction at an oil bath temperature of 158-160℃ for 0.9-1 h. Then add the catalyst tetrabutyl titanate, raise the temperature to 178-180℃, and mechanically stir at 398-400 rpm for 3.4-3.5 h. Finally, filter out the undegraded solid residue with a filter screen and collect the GLP degradation liquid.

[0008] In step 1.2, the mass ratio of waste PET fragments, NPG and DPG is 1:1:0.95~1.01; the mass of the catalyst tetrabutyl titanate added is 0.48~0.5% of the total mass of the three.

[0009] Step 2 specifically involves: Dissolve the GLP degradation solution in the mobile phase solvent and stir for 5-10 minutes to mix it evenly. Then slowly add it to the chromatographic column packed with SiO2 gel. Collect the chromatographic solution and perform vacuum rotary evaporation to remove excess solvent. Finally, collect the chromatographically purified GLP degradation solution.

[0010] The solvent is petroleum ether or a chloroform-methanol blend; the concentration of the GLP degradation solution in the mobile phase solvent is 29–30 mg / mL. -1 Maintain a flow rate of 1.5–2.1 mL / min. -1 .

[0011] Step 3 specifically involves: PPG and IPDI were vacuum dried in a vacuum drying oven at 108~110℃ for 2 hours, and then refluxed and stirred in a water bath. Then, dibutyltin dilaurate catalyst was added and the reaction was continued for 2-2.5 hours to generate polyurethane prepolymer from PPG and IPDI.

[0012] The stirring reaction temperature is 80-85℃, the stirring reaction time is 1-1.5h, and the stirring speed is 250-255r / min; the mass ratio of PPG, IPDI, and dibutyltin dilaurate is 20-21:5.5-5.6:0.1-0.12.

[0013] In step 4, the room temperature storage time is 24~26h, the curing temperature is 60~65℃, and the curing time is 2~3 days; the polytetrafluoroethylene mold is preheated in a forced-air oven at 110~120℃ for 2~3h; after adding the dopamine hydrochloride solution, the stirring time is 2~2.1h, and the stirring speed is 395~400 rpm.

[0014] In step 4, the dopamine hydrochloride solution is a mixture of dopamine hydrochloride and N,N-dimethylformamide; the amount of dopamine hydrochloride added accounts for 4.8~20% of the mass fraction of N,N-dimethylformamide; the volume ratio of the GLP degradation solution after chromatography to the dopamine hydrochloride solution is 0.35-0.4:1-1.5.

[0015] The beneficial effects of this invention are: The dopamine-grafted polyurethane adhesive of this invention exhibits excellent repeatable adhesion in an aqueous environment. This is because the catechol structure in dopamine combines with the urethane groups of the polyurethane hard segments, achieving oxidative crosslinking and metal chelation through conformational changes in catechol molecules, thus improving the adhesive's cohesive strength and bonding properties. Furthermore, the hydroxyl and amino groups in dopamine readily form hydrogen bonds with water molecules, increasing intermolecular interactions and thus enhancing adhesion. Simultaneously, water molecules can promote the oxidation reaction of dopamine, causing the polydopamine to form and chemically adsorb onto the surface of the adherend. Attached Figure Description

[0016] Figure 1 These are photographs and transmission electron microscope images of the unpurified degradation solution N-GLP (original degradation solution); Figure 2 These are photographs and transmission electron microscope images of the degradation solution after E-GLP (ethanol) mobile phase silica gel column chromatography. Figure 3 These are photographs and transmission electron microscope images of the degradation solution after C-GLP (chloroform and methanol) mobile phase silica gel column chromatography. Figure 4 These are photographs and transmission electron microscope images of the degradation solution after P-GLP (petroleum ether) mobile phase silica gel column chromatography. Figure 5 These are Fourier transform infrared (FTIR) spectra of the degradation solutions N-GLP, C-GLP, P-GLP, and E-GLP after silica gel column chromatography with different mobile phases. Figure 6 This is a matrix-assisted laser desorption / ionization time-of-flight mass spectrometry (MALDI-TOF MS) analysis of the N-GLP degradation solution. Figure 7 This is a matrix-assisted laser desorption / ionization time-of-flight mass spectrometry (MALDI-TOF MS) analysis of the degradation solution C-GLP. Figure 8This is a gas chromatography-mass spectrometry (GC-MS) analysis chromatogram of the degradation solution C-GLP; Figure 9a This is a field emission scanning electron microscope image (I) of C-GPUA polyurethane adhesive that does not contain dopamine hydrochloride. Figure 9b This is a field emission scanning electron microscope image (II) of C-GPUA polyurethane adhesive that does not contain dopamine hydrochloride. Figure 10a This is a field emission scanning electron microscope image (I) of C-GPUD5 polyurethane adhesive with a dopamine hydrochloride mass fraction of 5%. Figure 10b This is a field emission scanning electron microscope image (II) of C-GPUD5 polyurethane adhesive with a dopamine hydrochloride mass fraction of 5%. Figure 11a It is C-GPUD with a dopamine hydrochloride mass fraction of 10%. 10 Field emission scanning electron microscope image of polyurethane adhesive (I); Figure 11b It is C-GPUD with a dopamine hydrochloride mass fraction of 10%. 10 Field emission scanning electron microscope image of polyurethane adhesive (II); Figure 12a It is C-GPUD with a dopamine hydrochloride mass fraction of 15%. 15 Field emission scanning electron microscope image of polyurethane adhesive (I); Figure 12b It is C-GPUD with a dopamine hydrochloride mass fraction of 15%. 15 Field emission scanning electron microscope image of polyurethane adhesive (II); Figure 13a It is C-GPUD with a dopamine hydrochloride mass fraction of 20%. 20 Field emission scanning electron microscope image of polyurethane adhesive (I); Figure 13b It is C-GPUD with a dopamine hydrochloride mass fraction of 20%. 20 Field emission scanning electron microscope image of polyurethane adhesive (II); Figure 14 It is C-GPUD 10 of 1 H nuclear magnetic resonance spectroscopy ( 1 H-NMR spectrum; Figure 15 It is C-GPUA, C-GPUD5, C-GPUD 10 C-GPUD 15 C-GPUD 20 Water contact angle (WCA) diagram for polyurethane adhesives; Figure 16 C-GPUD on a stainless steel substrate with different curing times 10 Overlap shear strength diagram; Figure 17 C-GPUD on a stainless steel substrate in air and underwater environments 10 Analysis diagram of cyclic adhesion-peel test; Figure 18 It is C-GPUA, C-GPUD5, and C-GPUD at 25 ℃ 10 C-GPUD 15 C-GPUD 20 The storage modulus (G′) and loss modulus (G′′) of polyurethane adhesives vary with frequency. Detailed Implementation

[0017] The following detailed description is provided in conjunction with the accompanying drawings and specific embodiments.

[0018] This invention relates to a method for preparing an underwater polyurethane adhesive based on dopamine grafting and chain extension of waste PET, specifically implemented according to the following steps: Step 1, prepare the GLP degradation solution, specifically as follows: Step 1.1 involves pre-treating the waste PET plastic, specifically as follows: Cut waste PET plastic into The PET plastic fragments were soaked in HCl solution and stirred for 10-15 minutes. Then the PET plastic fragments were filtered out and rinsed with deionized water 3-4 times. Then the PET plastic fragments were soaked in NaOH solution and stirred for 10-15 minutes. The PET plastic fragments were filtered out and rinsed with deionized water 3-4 times. Finally, the fragments were dried in a forced-air drying oven at 50-55℃ to obtain pretreated waste PET fragments. Step 1.2: Mix the pretreated waste PET fragments, NPG (neopentyl glycol), and DPG (dipropylene glycol), stir at 238-251 rpm, and perform alcoholysis reaction at an oil bath temperature of 158-160℃ for 0.9-1 h. Then add the catalyst tetrabutyl titanate, raise the temperature to 178-180℃, and mechanically stir at 398-400 rpm for 3.4-3.5 h. Finally, filter out the undegraded solid residue with a filter screen and collect the GLP degradation liquid. The mass ratio of waste PET fragments, NPG and DPG is 1:1:0.95~1.01; the mass of the catalyst tetrabutyl titanate added is 0.48~0.5% of the total mass of the three. In the preparation method of this invention, the purpose of pretreatment of waste PET fragments is to cut plastic bottles into 1×1cm pieces. 2The uniform fragments are used to increase the specific surface area, and the inorganic and organic pollutants are removed by alternating cleaning with hydrochloric acid and sodium hydroxide. Then, the product is washed with deionized water and dried with low-temperature blower to accelerate the evaporation rate of water, making the drying more uniform and efficient.

[0019] Step 2: The GLP degradation solution obtained in Step 1 is purified by silica gel column chromatography, specifically as follows: Dissolve the GLP degradation solution in the mobile phase solvent and stir for 5-10 minutes to mix it evenly. Then slowly add it to the chromatographic column packed with SiO2 gel. Collect the chromatographic solution and perform vacuum rotary evaporation to remove excess solvent. Finally, collect the chromatographically purified GLP degradation solution. The solvent is petroleum ether or a chloroform-methanol mixture; The concentration of the GLP degradation solution in the mobile phase solvent is 29–30 mg·mL. -1 Maintain a flow rate of 1.5–2.1 mL / min. -1 . During the column packing process, the SiO2 gel is slowly loaded into the chromatography column through a funnel, and the side of the column is tapped repeatedly with a rubber hammer to ensure that the silica gel is tightly packed without any gaps.

[0020] Before the mobile phase enters the silica gel column, open the stopcock at the bottom of the column and pour in the eluent to completely wet the silica gel column and remove air from the column.

[0021] In the preparation method of this invention, the PET degradation solution GLP is purified by silica gel column chromatography because GLP has a complex composition. Silica gel column chromatography is used to purify GLP by utilizing the adsorption capacity of silica gel. After chromatography, the final product is a mixture of various oligomers with terminal hydroxyl groups, which has a relatively low degree of polymerization, a narrower size distribution, and significantly improved stability.

[0022] Step 3: Prepare NCO-terminated polyurethane prepolymer by reacting polypropylene glycol 2000 (PPG) and isophorone diisocyanate (IPDI); PPG and IPDI were vacuum dried in a vacuum drying oven at 108~110℃ for 2 hours, and then refluxed and stirred in a water bath. Then, dibutyltin dilaurate catalyst was added and the reaction was continued for 2-2.5 hours to generate polyurethane prepolymer from PPG and IPDI. The stirring reaction temperature is 80-85℃, the stirring reaction time is 1-1.5h, and the stirring speed is 250-255r / min; The mass ratio of PPG, IPDI, and dibutyltin dilaurate is 20-21:5.5-5.6:0.1-0.12; Step 4: Under a water bath temperature of 60℃, add the chromatographically purified GLP degradation solution to the polyurethane prepolymer obtained in Step 3 and stir at 300 rpm for 2 hours. Then add the hydrochloric acid dopamine solution and stir at 395~400 rpm for 2~2.1 hours. Pour the mixture into a preheated polytetrafluoroethylene mold. After that, store the sample at room temperature for 24~26 hours and then cure it in an oven at 60~65℃ for 2~3 days to obtain the underwater polyurethane adhesive C-GPUD. The dopamine hydrochloride solution is prepared by mixing dopamine hydrochloride and N,N-dimethylformamide; the amount of dopamine hydrochloride added is 4.8% to 20% of the mass fraction of N,N-dimethylformamide. Preheat the polytetrafluoroethylene mold in a forced-air drying oven at 110~120℃ for 2~3 hours; The volume ratio of the GLP degradation solution after chromatography to the dopamine hydrochloride solution was 0.35-0.4:1-1.5.

[0023] In the preparation method of this invention, PPG and IPDI are used to form an NCO-terminated prepolymer, and then waste PET degradation product GLP is introduced to carry out a chain extension reaction, achieving rapid crosslinking and expansion of PU segments. This method develops a solvent-free in-situ chain extension technology. By controlling the gradient reaction kinetics between the hydroxyl groups in GLP and the IPDI prepolymer, the synergistic toughening of the micro-crosslinked network and linear segments is achieved, solving the VOC emission problem of traditional solvent-based polyurethane adhesives.

[0024] Example 1 The underwater polyurethane adhesive based on dopamine grafting and waste PET chain extension of the present invention was tested, and the results are as follows: The GLP degradation solution obtained from alcoholysis in step 1 was purified by silica gel column chromatography using three different solvents as mobile phases. GLP was dissolved in different solvents and stirred with a glass rod for 5-10 minutes until homogeneous. The mixture was then slowly added to a chromatographic column packed with SiO2 gel. The chromatographic solution was collected and subjected to vacuum rotary evaporation to remove excess solvent. The final chromatographically purified degradation solutions were named C-GLP (chloroform and methanol), P-GLP (petroleum ether), and E-GLP (ethanol) according to the mobile phase.

[0025] from Figures 1-4It can be seen that the TEM microstructure of GLP treated by silica gel column chromatography with different mobile phases shows that the unchromatographically purified N-GLP contains a large number of polar ester groups, forming a network structure through hydrogen bonding and van der Waals forces. When the mobile phase is chloroform-methanol, the chromatographically purified C-GLP exhibits small plate-like and spherical structures, with no excess impurities and molecular sizes reaching the nanoscale, classifying it as a homogeneous system. When petroleum ether is used as the mobile phase, the morphology of P-GLP is mainly composed of small particles. The comparison shows that chloroform and petroleum ether, with their moderate polarity and excellent diffusion properties, can efficiently remove large molecular impurities remaining from PET degradation, obtaining nanoscale homogeneous GLP.

[0026] from Figures 5-8 As can be seen from FTIR, MALDI-TOF, and GC-MS data, the molecular structure of the PET alcoholysis product GLP mainly comprises: BHET, oligomeric polyols, PET chain fragments, and residual alcoholysis agent. The hydroxyl-containing segment -CH2OOCC6H4COOCH2- is similar in structure to the main structure of BHET; both contain hydroxyl functional groups and can act as chain extenders in the synthesis of polyurethane. After silica column chromatography, large PET fragment segments are adsorbed onto the silica column; therefore, the chromatographically derived GLP contains hydroxyl-terminated oligomers and a small amount of residual alcoholysis agent.

[0027] Example 2 Different mass fractions of dopamine hydrochloride were dissolved in N,N-dimethylformamide and added to the reaction system. The mixture was stirred at 395 rpm for 2 h and then poured into a preheated polytetrafluoroethylene mold. The sample was then stored at room temperature for 24 h and cured in an oven at 65 °C for 2 days, thus successfully synthesizing C-GPUD.

[0028] The amounts of dopamine hydrochloride added as a percentage of N,N-dimethylformamide were 0%, 5%, 10%, 15%, and 20%, respectively, and the samples were named C-GPUA, C-GPUD5, and C-GPUD, respectively. 10 C-GPUD 15 C-GPUD 20 .

[0029] Figure 9a and Figure 9b This is a field emission scanning electron microscope image of C-GPUA polyurethane adhesive. Figure 10a and Figure 10b This is a field emission scanning electron microscope image of C-GPUD5 polyurethane adhesive. Figure 11a and Figure 11b It is C-GPUD 10 Field emission scanning electron microscope image of polyurethane adhesive. Figure 12a and Figure 12b It is C-GPUD 15 Field emission scanning electron microscope image of polyurethane adhesive. Figure 13a and Figure 13b It is C-GPUD 20 Field emission scanning electron microscopy (FESEM) images of the polyurethane adhesive show that, as the dopamine content increases to 10%, the surface smoothness of the adhesive layer significantly improves, and some of the white, fibrous structures exhibit adhesion, indicating that the introduction of dopamine induces the formation of microphase separation structures. Subsequently, with further increases in dopamine content, the white aggregates on the adhesive layer surface gradually decrease, while the adhesion of the fibrous structures gradually increases, forming large, clustered structures.

[0030] Example 3 from Figure 14 C-GPUD 10 of 1 The H-NMR spectrum and chemical structure show that the multiple peaks at δ=7.00-6.49 ppm correspond to the benzene ring hydrogen on the dopamine side chain. By grafting dopamine onto the polyurethane side chain through an acylation reaction, a mussel-inspired polyurethane adhesive was prepared.

[0031] from Figure 15 As can be seen, the introduction of dopamine gives the polyurethane adhesive surface good hydrophobicity. With the increase of dopamine content, the water contact angle of the adhesive layer surface continuously increases. When the dopamine content is 10%, the surface water contact angle is 93.7°, indicating that the adhesive layer exhibits good hydrophobicity.

[0032] from Figure 16 As can be seen from the data, the adhesive strength of C-GPUD after repeated tearing is 1.03 MPa after the first curing. Repeated tearing experiments show that the adhesive strength of the material significantly increases with the extension of curing time. (C-GPUD) 10 The lap shear strength gradually increased. Among them, after the sixth repeated test, the adhesive strength of the sample cured for 60 min recovered to 0.93 MPa, and the adhesive effect reached 90.29% of the initial strength.

[0033] Example 4 from Figure 17It can be seen that the repeatability of polyurethane adhesive bonding in air and underwater environments was thoroughly studied through cyclic adhesion-peel tests, proving that it can meet the requirements for multiple adhesion uses. The adhesion performance under room temperature air curing conditions is generally better than that under underwater conditions. This is because the hydration layer weakens the non-covalent interaction at the interface between the adhesive layer and the substrate, resulting in lower adhesion strength underwater than in air. Data from repeated underwater tear tests show that with increasing repetitions, the lap shear strength increases at the third peel test, reaching a peak adhesion strength of 0.47 MPa. From the fourth tear onwards, the strength begins to decrease, ranging from 0.23 to 0.32 MPa. After the tenth tear, the strength drops to 0.21 MPa, but the adhesion effect still reaches 45.65% of the initial adhesion strength. These results indicate that C-GPUD… 10 It exhibits relatively stable adhesion strength in both air and underwater environments.

[0034] from Figure 18 Rheological measurements analyzed the curves of G′ and G′′ as a function of frequency. It can be seen that G′ and G′′ for all samples remain relatively stable within the test frequency range, and G′′ is consistently higher than G′. This characteristic indicates that the material primarily exhibits viscous rheological behavior at room temperature. Furthermore, when the dopamine content is 10%, C-GPUD... 10 The storage modulus and loss modulus of this sample are both higher than those of other samples. The catechol groups in the dopamine molecule form a stable physical cross-linking network with the polyurethane matrix, which enhances the interaction between molecular chains and improves the overall mechanical properties of the material.

[0035] Example 5 This invention relates to a method for preparing an underwater polyurethane adhesive based on dopamine grafting and chain extension of waste PET, specifically implemented according to the following steps: Step 1, prepare the GLP degradation solution, specifically as follows: Step 1.1 involves pre-treating the waste PET plastic, specifically as follows: Cut waste PET plastic into The PET plastic fragments were soaked in HCl solution and stirred for 10 minutes. Then the PET plastic fragments were filtered out and rinsed three times with deionized water. Next, the PET plastic fragments were soaked in NaOH solution and stirred for 10 minutes. The PET plastic fragments were filtered out and rinsed four times with deionized water. Finally, they were placed in a forced-air drying oven and dried at 50°C to obtain pretreated waste PET fragments. Step 1.2: Pretreated waste PET fragments, NPG (neopentyl glycol), and DPG (dipropylene glycol) are mixed and stirred at 245 rpm. The mixture is then subjected to alcoholysis at 158°C in an oil bath for 1 hour. Next, tetrabutyl titanate catalyst is added, and the temperature is raised to 180°C. The mixture is then mechanically stirred at 400 rpm for 3.5 hours. Finally, the undegraded solid residue is filtered out using a filter screen, and the GLP degradation liquid is collected. The mass ratio of waste PET fragments, NPG, and DPG is 1:1:0.95; the mass of the catalyst tetrabutyl titanate added is 0.48% of the total mass of the three. Step 2: The GLP degradation solution obtained in Step 1 is purified by silica gel column chromatography, specifically as follows: The GLP degradation solution was dissolved in the mobile phase solvent and stirred for 10 min to make it evenly mixed. Then it was slowly added to the chromatographic column packed with SiO2 gel. The chromatographic solution was collected and vacuum rotary evaporated to remove excess solvent. Finally, the chromatographically purified GLP degradation solution was collected. The solvent is petroleum ether; the concentration of the GLP degradation solution in the mobile phase solvent is 30 mg·mL. -1 ; maintain a flow rate of 1.5 mL / min -1 . Step 3: Place PPG and IPDI in a vacuum drying oven at 110℃ and dry for 2 hours. Then place them in a water bath for condensation, reflux and stirring reaction. Then add the catalyst dibutyltin dilaurate and continue the reaction for 2 hours to generate polyurethane prepolymer from PPG and IPDI. The stirring reaction temperature was 80℃, the stirring reaction time was 1 hour, and the stirring speed was 250 r / min; The mass ratio of PPG, IPDI, and dibutyltin dilaurate is 20:5.5:0.1; Step 4: Under the condition of water bath temperature of 60℃, add the GLP degradation solution obtained by chromatography to the polyurethane prepolymer obtained in step 3, and stir at 300 rpm for 2 hours. Then add the hydrochloric acid dopamine solution and stir at 395 rpm for 2 hours. Then pour it into a preheated polytetrafluoroethylene mold. After that, store the sample at room temperature for 24 hours, and then cure it in an oven at 60℃ for 2 days to obtain underwater polyurethane adhesive C-GPUD. The dopamine hydrochloride solution is composed of a mixture of dopamine hydrochloride and N,N-dimethylformamide; the amount of dopamine hydrochloride added accounts for 10% of the mass fraction of N,N-dimethylformamide. The polytetrafluoroethylene mold was preheated in a 110℃ forced-air drying oven for 2 hours. The volume ratio of the GLP degradation solution after chromatography to the dopamine hydrochloride solution was 0.35:1.

[0036] Example 6 This invention relates to a method for preparing an underwater polyurethane adhesive based on dopamine grafting and chain extension of waste PET, specifically implemented according to the following steps: Step 1, prepare the GLP degradation solution, specifically as follows: Step 1.1 involves pre-treating the waste PET plastic, specifically as follows: Cut waste PET plastic into The PET plastic fragments were soaked in HCl solution and stirred for 15 minutes. Then the PET plastic fragments were filtered out and rinsed three times with deionized water. Next, the PET plastic fragments were soaked in NaOH solution and stirred for 10 minutes. The PET plastic fragments were filtered out and rinsed four times with deionized water. Finally, they were placed in a forced-air drying oven and dried at 55°C to obtain pretreated waste PET fragments. Step 1.2: The pretreated waste PET fragments, NPG (neopentyl glycol), and DPG (dipropylene glycol) are mixed and stirred at 250 rpm. The mixture is then subjected to alcoholysis at an oil bath temperature of 160°C for 1 hour. Next, tetrabutyl titanate catalyst is added, and the temperature is raised to 180°C. The mixture is then mechanically stirred at 400 rpm for 3.5 hours. Finally, the undegraded solid residue is filtered out using a filter screen, and the GLP degradation liquid is collected. The mass ratio of waste PET fragments, NPG, and DPG is 1:1:1; the mass of the catalyst tetrabutyl titanate added is 0.5% of the total mass of the three. Step 2: The GLP degradation solution obtained in Step 1 is purified by silica gel column chromatography, specifically as follows: The GLP degradation solution was dissolved in the mobile phase solvent and stirred for 5 minutes to mix it evenly. Then it was slowly added to the chromatographic column packed with SiO2 gel. The chromatographic solution was collected and vacuum rotary evaporated to remove excess solvent. Finally, the chromatographically purified GLP degradation solution was collected. The solvent was a chloroform-methanol blend; the concentration of the GLP degradation solution in the mobile phase solvent was 30 mg·mL. -1 Maintain a flow rate of 2 mL / min. -1 . Step 3: Place PPG and IPDI in a vacuum drying oven at 110℃ and dry for 2 hours. Then place them in a water bath for condensation, reflux and stirring reaction. Then add the catalyst dibutyltin dilaurate and continue the reaction for 2.5 hours to generate polyurethane prepolymer from PPG and IPDI. The stirring reaction temperature was 85℃, the stirring reaction time was 1.5h, and the stirring speed was 255r / min; The mass ratio of PPG, IPDI, and dibutyltin dilaurate is 20:5.5:0.12; Step 4: Under a water bath temperature of 60℃, add the chromatographically purified GLP degradation solution to the polyurethane prepolymer obtained in Step 3 and stir at 300 rpm for 2 hours. Then add the hydrochloric acid dopamine solution and stir at 400 rpm for 2.1 hours. Pour the mixture into a preheated polytetrafluoroethylene mold. After that, store the sample at room temperature for 26 hours and then cure it in a 65℃ oven for 3 days to obtain the underwater polyurethane adhesive C-GPUD. The dopamine hydrochloride solution is composed of a mixture of dopamine hydrochloride and N,N-dimethylformamide; the amount of dopamine hydrochloride added accounts for 5% of the mass fraction of N,N-dimethylformamide. The polytetrafluoroethylene mold was preheated in a 120℃ forced-air drying oven for 3 hours. The volume ratio of the GLP degradation solution after chromatography to the dopamine hydrochloride solution was 0.4:1.5.

[0037] In the preparation method of this invention, the reason for introducing dopamine hydrochloride into the side chain structure of polyurethane via grafting is that the reversible oxidation-metal chelation of the catechol groups of dopamine endows the polyurethane material with underwater adaptive adhesion. The hydroxyl and amino groups in dopamine readily form hydrogen bonds with water molecules, increasing intermolecular forces and thus improving adhesion. Simultaneously, water molecules can promote the oxidation reaction of dopamine, causing the polydopamine to form and chemically adsorb onto the surface of the adherend.

Claims

1. A method for preparing an underwater polyurethane adhesive based on dopamine grafting and chain extension of waste PET, characterized in that, The specific steps are as follows: Step 1: Prepare GLP degradation solution; Step 2: The GLP degradation solution obtained in Step 1 is purified by silica gel column chromatography. Step 3: Prepare NCO-terminated polyurethane prepolymer by reacting PPG and IPDI; Step 4: Under water bath conditions, add the chromatographically purified GLP degradation solution to the polyurethane prepolymer obtained in Step 3, stir, then add the hydrochloric acid dopamine solution and stir, then pour it into a preheated polytetrafluoroethylene mold, store at room temperature and cure to obtain underwater polyurethane adhesive.

2. The preparation method of the underwater polyurethane adhesive based on dopamine grafting and waste PET chain extension as described in claim 1, characterized in that, In step 1, specifically: Step 1.1: Pre-treat the waste PET plastic: Waste PET plastic is cut into fragments, soaked in HCl solution and stirred for 10-15 minutes, then filtered out and rinsed with deionized water 3-4 times; then soaked in NaOH solution and stirred for 10-15 minutes, filtered out and rinsed with deionized water 3-4 times; finally, it is placed in a forced-air drying oven and dried at 50-55℃ to obtain pretreated waste PET fragments. Step 1.2: Mix the pretreated waste PET fragments, NPG and DPG, stir at 238~251 rpm, and perform alcoholysis reaction at 158~160℃ in an oil bath for 0.9~1h. Then add the catalyst tetrabutyl titanate, raise the temperature to 178~180℃, and mechanically stir at 398~400 rpm for 3.4~3.5h. Finally, filter out the undegraded solid residue with a filter screen and collect the GLP degradation liquid.

3. The preparation method of the underwater polyurethane adhesive based on dopamine grafting and waste PET chain extension as described in claim 2, characterized in that, In step 1.2, the mass ratio of waste PET fragments, NPG and DPG is 1:1:0.95~1.01; the mass of the catalyst tetrabutyl titanate added is 0.48~0.5% of the total mass of the three.

4. The preparation method of the underwater polyurethane adhesive based on dopamine grafting and waste PET chain extension as described in claim 1, characterized in that, Step 2 specifically involves: Dissolve the GLP degradation solution in the mobile phase solvent and stir for 5-10 minutes to mix it evenly. Then slowly add it to the chromatographic column packed with SiO2 gel. Collect the chromatographic solution and perform vacuum rotary evaporation to remove excess solvent. Finally, collect the chromatographically purified GLP degradation solution.

5. The preparation method of the underwater polyurethane adhesive based on dopamine grafting and waste PET chain extension as described in claim 4, wherein the solvent is petroleum ether or a chloroform-methanol blend; and the concentration of the GLP degradation solution in the mobile phase solvent is 29-30 mg / mL. -1 Maintain a flow rate of 1.5–2.1 mL / min. -1 .

6. The preparation method of the underwater polyurethane adhesive based on dopamine grafting and waste PET chain extension as described in claim 1, characterized in that, Step 3 specifically involves: PPG and IPDI were vacuum dried in a vacuum drying oven at 108~110℃ for 2 hours, and then refluxed and stirred in a water bath. Then, dibutyltin dilaurate catalyst was added and the reaction was continued for 2-2.5 hours to generate polyurethane prepolymer from PPG and IPDI.

7. The preparation method of the underwater polyurethane adhesive based on dopamine grafting and waste PET chain extension as described in claim 6, characterized in that, The stirring reaction temperature is 80-85℃, the stirring reaction time is 1-1.5h, and the stirring speed is 250-255r / min; the mass ratio of PPG, IPDI, and dibutyltin dilaurate is 20-21:5.5-5.6:0.1-0.

12.

8. The preparation method of the underwater polyurethane adhesive based on dopamine grafting and waste PET chain extension as described in claim 1, characterized in that, In step 4, the room temperature storage time is 24-26 hours, the curing temperature is 60-65℃, and the curing time is 2-3 days; the polytetrafluoroethylene mold is preheated in a forced-air oven at 110-120℃ for 2-3 hours; after adding the dopamine hydrochloride solution, the stirring time is 2-2.1 hours, and the stirring speed is 395-400 rpm.

9. The preparation method of the underwater polyurethane adhesive based on dopamine grafting and waste PET chain extension as described in claim 1, characterized in that, In step 4, the dopamine hydrochloride solution is a mixture of dopamine hydrochloride and N,N-dimethylformamide; the amount of dopamine hydrochloride added accounts for 4.8-20% of the mass fraction of N,N-dimethylformamide; the volume ratio of the GLP degradation solution after chromatography to the dopamine hydrochloride solution is 0.35-0.4:1-1.

5.

10. The underwater polyurethane adhesive prepared by the method for preparing underwater polyurethane adhesive based on dopamine grafting and waste PET chain extension as described in claims 1-9.

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