Preparation method and application of a near-infrared in-situ self-healing polyurea resin

Abstract

The present invention discloses a preparation method and application of a near-infrared in-situ self-healing polyurea resin, which comprises the following steps: mixing a hydroxyl-terminated polydimethylsiloxane with a 2,4-diisocyanate solution, adding dibutyltin dilaurate as a catalyst, heating, and reacting to obtain a prepolymer 1; slowly decreasing the temperature of the system, then adding isophorone diamine as a chain extender to the system, and reacting to obtain a prepolymer 2; dissolving a hexamethylene diisocyanate trimer in a solvent, adding it to the prepolymer 2, and continuing the reaction until the isocyanate is completely consumed, and then adding a dispersion liquid dispersed with photothermal conversion nanoparticles to obtain a polyurea resin liquid. The preparation process of the present invention is simple and low in cost, can achieve in-situ self-healing under near-infrared conditions by means of the photothermal conversion effect of photothermal conversion nanoparticles, has ultra-high barrier properties and mechanical properties, and can be used as a protective coating for outdoor textiles to extend the service life of fabric products.

Description

Technical Field

[0001] The present invention relates to a preparation method and application of a resin for textile coating, and particularly to a preparation method and application of a near-infrared in-situ self-healing polyurea resin. Background Art

[0002] Polyurea resins are polymer macromolecular materials with a -NH-CO-NH- repeating structural unit in the molecular main chain, mainly formed by the polycondensation of polyisocyanate groups and amino compounds. Compared with ordinary polyurethanes, polyurea resins have many advantages such as excellent mechanical properties, good dimensional stability, and chemical stability. The formed polyurea coatings have good flexibility and resilience. Due to the regular arrangement of the internal molecular chain structure, they can form a dense and continuous coating, which has good barrier properties to air and moisture. Therefore, they are very suitable as protective coatings for outdoor textiles, thereby extending the service life of textiles in outdoor environments.

[0003] During the outdoor application of textiles, the materials are inevitably affected by the external environment, such as mechanical forces, light, humidity, etc., which may cause the degradation of textiles and lead to a decline in performance. In particular, whether used in harsh environments or during long-term storage, the damage of polymer materials is inevitable. However, most current materials can only achieve micro / nano scratch self-repair of the materials. If the materials are severely damaged, they cannot fully restore their original form. Therefore, it is crucial to prepare a polyurea protective coating that can self-heal in-situ and achieve macroscopic damage repair by means of gravity and entropy driving force for the application of outdoor textiles. Summary of the Invention

[0004] Object of the Invention: The object of the present invention is to provide a preparation method of a near-infrared in-situ self-healing polyurea resin with excellent mechanical properties;

[0005] The second object of the present invention is to provide the application of the near-infrared in-situ self-healing polyurea resin prepared by the above method in a protective coating for outdoor textiles.

[0006] Technical Solution: The preparation method of the near-infrared in-situ self-healing polyurea resin described in the present invention includes the following steps:

[0007] (1) Mix hydroxyl-terminated polydimethylsiloxane with a 2,4-diisocyanate solution, add dibutyltin dilaurate as a catalyst, heat, and react to obtain prepolymer 1;

[0008] (2) Slowly lower the temperature of the system in step (1), then add isophorone diamine as a chain extender to the system, and react to obtain prepolymer 2;

[0009] (3) Dissolve hexamethylene diisocyanate trimer in a solvent, then add it to prepolymer 2, and continue the reaction until the isocyanate is completely consumed. Subsequently, add the dispersion liquid containing the photothermal conversion nanoparticles to obtain a polyurea resin liquid. After evaporating the solvent in the polyurea resin liquid, a polyurea resin is obtained.

[0010] Among them, in step (1), the device used is a three-necked flask equipped with a condenser; the reaction is carried out under oil bath heating and stirring conditions, and the stirring rate is 400 - 600 rpm; the addition amount of dibutyltin dilaurate is 0.1% - 0.3% of the total mass of the terminal hydroxyl poly(dimethylsiloxane) and 2,4-diisocyanate in the prepolymer. If the addition amount is too small, the prepolymerization time of the system will be too long, and it cannot ensure that all the terminal hydroxyl groups in the soft segment participate in the prepolymerization. If the addition amount is too large, the molecular chain reaction will intensify, affecting the storage stability of the resin liquid and the light transmittance of the resin film formation.

[0011] Among them, before step (1), the hydroxyl-terminated poly(dimethylsiloxane) and isophorone diamine are vacuum-dried; the temperature of the vacuum drying is 70 - 85 °C, and the time is 8 - 12 h.

[0012] Among them, the photothermal conversion nanoparticles are dispersed in 30 - 50 mL of a solvent, and after ultrasonic treatment for 20 - 50 min, they are ready for use; the photothermal conversion nanoparticles are one of polydopamine, wrinkled graphene, carbon nanotubes, and MXenes nanosheets; the particle size of the photothermal conversion nanoparticles is controlled within 160 - 200 nm, and the added mass of the photothermal conversion nanoparticles is 15 - 25 mg. The particle size of the photothermal conversion nanoparticles has a great influence on the photothermal conversion efficiency of the polymer. To ensure that the polyurea resin has a high light absorption rate to ensure a high photothermal conversion efficiency, the photothermal conversion nanoparticles need to have a small size. However, if the particle size is too small, the light stability and thermal stability of the photothermal nanoparticles are not high. Although a large particle size can improve the stability, a large particle size will increase the light scattering of the material and reduce the photothermal conversion efficiency. Therefore, the particle size of the photothermal conversion nanoparticles needs to be controlled within an effective range; if the addition amount of the photothermal conversion nanoparticles is too small, the photothermal conversion efficiency of the material cannot be effectively guaranteed, resulting in that after the damaged network of the polymer is irradiated by NIR light, the molecular chains in the network cannot be effectively thermally activated for migration, resulting in a weakening of the conformational change efficiency of the molecular chains in the damaged area and a decrease in the molecular network rearrangement rate, and a decrease in the dissociation efficiency of the dynamic urea bond by photothermal conversion, thus leading to a significant decrease in the self-healing efficiency of the polymer. If the addition amount of the photothermal conversion nanoparticles is too large, it is easy to cause restrictions on the chain migration in the polymer molecular network, and the molecular chains cannot effectively dissipate energy during the stretching process, resulting in a decrease in the tensile strain of the target product, an increase in the modulus, and a decrease in the overall toughness of the material.

[0013] Among them, the type of the solvent is one of acetone, N, N-dimethylformamide, tetrahydrofuran, dimethylacetamide, and dimethyl sulfoxide; preferably, the following treatment is performed on the solvent: after heating and activating 4A molecular sieve at 400-600 °C, it is put into the solvent to adsorb moisture and used after treatment for 3-6 days.

[0014] Among them, in step (1), the heating temperature is 70-80 °C, and the reaction time is 2-4 h; the heating temperature of 70-80 °C belongs to the reaction activation temperature of -NCO and -OH. In the case of adding a catalyst, the reaction is carried out for 2-4 h to ensure that the terminal hydroxyl groups fully participate in the reaction and the successful synthesis of the prepolymer;

[0015] The molecular weight of the hydroxyl-terminated polydimethylsiloxane is 800-1000 g / mol; if the molecular weight of the used OH-PDMS-OH is too low, the content of the hard segment in the synthesized cross-linked molecular network will be too high, resulting in an increase in the rigidity of the resin and being not suitable for practical use as a protective coating. If the molecular weight is too high, the proportion of the hard segment content of the polymer will decrease, the crystallization tendency of the soft segment will increase, the degree of microphase separation will increase, and the film-forming property of the resin will be poor;

[0016] The molar ratio of the 2,4-diisocyanate to the hydroxyl-terminated polydimethylsiloxane is 20:4-10; reasonably controlling the composition content of the resin soft segment in the synthesis system can effectively adjust the mechanical properties of the resin. The presence of side groups on the main chain can effectively adjust the molecular chain spacing in the polymer network and improve the ductility of the molecular chain, thereby enhancing the molecular chain mobility. As a soft segment component of the system, if the molar ratio content of the hydroxyl-terminated polydimethylsiloxane is too low, it will lead to an increase in the rigidity of the resin, and if the content is too high, it will lead to an increase in the viscosity of the resin. Therefore, it is necessary to reasonably control the ratio of the two to meet the excellent mechanical properties required for the synthesized resin to be used as a protective coating for outdoor textiles.

[0017] Among them, in step (2), the temperature of the system is slowly cooled to 40-55 °C; preferably, the cooling rate is 2-5 °C / min; if the temperature is too high, it is likely to cause explosive polymerization of the system, and if the temperature is too low, the maximum reaction activation temperature of the amine chain extender cannot be reached, resulting in too long a reaction system time;

[0018] The dropping rate of isophorone diamine is controlled at 5-10 mL / min; if the dropping rate of isophorone diamine is too fast, it is likely to cause rapid entanglement of the molecular chains in the system and explosive polymerization;

[0019] The isophorone diamine is added through a constant pressure funnel; the reaction is carried out under stirring conditions, and the stirring rate is 200 - 350 rpm; the molar ratio of the 2,4 - diisocyanate to the isophorone diamine is 20:17.33 - 20; the isophorone diamine is synthesized into the target product as a component of the hard segment, and an appropriate molar ratio range is ensured to make the molecular chain of prepolymer 2 have terminal amino groups to ensure the smooth progress of the cross - linking process with the molecular chain of hexamethylene diisocyanate trimer (THDI) in step (3).

[0020] Among them, in step (3), the temperature for continuous reaction is the same as that in step (2); the stirring rate is the same as that in step (2); the reaction continues for 4 - 5 h, and the reaction process is monitored using the dibutylamine chemical titration method until the isocyanate is completely consumed. Keeping the reaction temperature and rate in step (3) the same as those in step (2) is for two reasons. Firstly, it ensures the same thermal process of resin synthesis to ensure a lower degree of microphase separation in the molecular network. Secondly, it prevents the system from undergoing explosive polymerization due to the too high reaction activity of -NCO and -NH2; reacting for 4 - 5 h, a sufficient reaction time ensures that -NCO in the system fully participates in the reaction, thus ensuring the maximum cross - linking degree in the polymer molecular network.

[0021] Among them, in step (3), after adding the dispersion liquid containing the photothermal conversion nanoparticles, stir at a rate of 400 - 600 rpm for 2 - 3 h until it is uniformly mixed.

[0022] Among them, the molar ratio of the 2,4 - diisocyanate to the hexamethylene diisocyanate trimer is 20:0.95 - 6.67. The hexamethylene diisocyanate trimer is introduced into the polymer molecular network as a cross - linker. If the molar ratio is too high, the synthesized resin will be too hard to be used as a protective coating; if the molar ratio is too low, the cross - linking degree of the resin will decrease, and the elasticity and recovery of the resin will decline.

[0023] Among them, the R value of the system for synthesizing the polyurea resin is controlled between 1 and 1.2. The R value of the synthesis system has a great influence on the properties of the resin. If the R value is too low, the synthesized resin system is difficult to form a film; if the R value is too high, the content of the hard phase in the system is too high, resulting in increased rigidity and modulus of the resin, and it is not easy to be used as a protective coating for outdoor textiles.

[0024] Application of the near - infrared in - situ self - healing polyurea resin prepared by the above method in the protective coating of outdoor textiles.

[0025] The specific process is as follows: Immerse the fabric in the polyurea resin precursor solution, and obtain the fabric with a polyurea resin coating after drying and hot pressing and curing; the fabric is preferably nylon 6, polyester fiber, or polyamide fiber; the immersion time is 5 - 10 min, dry in an oven at 70 - 85 °C for 10 - 20 min, the hot pressing pressure is 2 - 5 MPa, and the curing time is 8 - 12 min. Preferably, the solid content of the polyurea resin solution is 40 - 60%; preferably, the rotary evaporation method is used to increase the solid content of the polyurea resin solution to 40 - 60%; if the solid content is too low, the formed resin film will be too thin, and if the solid content is too high, it will cause the viscosity of the resin precursor solution to be too large, which is not conducive to the film-forming process and affects its storage stability.

[0026] Principle of the invention: The photothermal conversion nanomaterials, as the filling materials of the resin, provide two properties: (1) acting as nano-fillers to toughen the resin material; (2) acting as photothermal materials to have high photothermal conversion efficiency under near-infrared irradiation, which can ensure the dynamic dissociation of urea bonds into amine and isocyanate groups, and simultaneously complete the solid-liquid phase transition. At the same time, the fast kinetics of the reaction of the already free amine and isocyanate groups at room temperature can induce the resin to regenerate urea bonds and cure into a protective layer after removing the near-infrared light irradiation. In terms of monomer selection, the chain extender is selected as isophorone diamine containing more side-chain methyl groups to react and extend the chain with toluene 2,4-diisocyanate, which can provide an effective loose packing structure for the molecular chain network. The molecular soft segment is selected as the thermosetting elastomer polydimethylsiloxane containing diol on both sides, which can make up for the defect that the thermosetting elastomer cannot be recycled. Hexamethylene diisocyanate is used as the crosslinking agent, which can provide a dense and ordered molecular network structure and excellent mechanical properties for the resin.

[0027] Isophorone diamine containing multiple side-chain methyl groups and an asymmetric structure provides a loose packing structure for the synthesis of the molecular network, which is beneficial to the dynamic dissociation and recombination of urea bonds in the molecular network.

[0028] Advantages: Compared with the prior art, the present invention has the following remarkable effects:

[0029] (1) The preparation process of the present invention is simple and the cost is low. Under near-infrared conditions, it can promote the dissociation of urea bonds and hydrogen bonds in the synthesized polyurea resin by means of the photothermal conversion effect of photothermal conversion nanoparticles, promote the flow of molecular chains, achieve in-situ self-healing, and the polymer molecular chains are arranged regularly in a network, with ultra-high barrier properties and mechanical properties, and can be used as a protective coating for outdoor textiles to extend the service life of fabric products.

[0030] (2) The present invention is based on a simple step-growth polyaddition reaction between an isocyanate prepolymer and isophorone diamine. The prepared polyurea resin has excellent mechanical properties and reprocessing performance; the mechanical strength of the prepared polyurea resin film containing a photothermal conversion material can reach more than 30 MPa, and the elongation at break is close to 1000%.

[0031] (3) Since nanoparticles such as polydopamine have a high photothermal conversion efficiency, the film can complete in-situ self-healing within 20 minutes under near-infrared irradiation. After cooling to room temperature, the free amine and isocyanate continue to react to regenerate dynamic urea bonds, and the healing efficiency of the repaired sample can reach more than 90%.

[0032] (4) The presence of the crosslinking agent hexamethylene diisocyanate makes the molecular network of the prepared polyurea arranged neatly. The presence of nano-fillers makes the path of air penetrating the film tortuous. The air permeability of the film is as low as 0.222 mm·s, lower than that of most commercially available packaging materials, and has a good air barrier rate. After hot pressing, it can provide a fabric with a highly efficient self-healing and high-barrier protective layer, providing a new preparation method for extending the service life of outdoor textiles such as tents and parachutes. Description of the Drawings

[0033] Figure 1 Stress-strain curves of Example 2 HTPU2 before and after healing;

[0034] Figure 2 Stress-strain curves of Comparative Example 1 before and after healing;

[0035] Figure 3 Stress-strain curves of Comparative Example 3 before and after healing;

[0036] Figure 4 Near-infrared in-situ healing process of Example 2;

[0037] Figure 5 Comparison chart of barrier properties between Example 2 and Comparative Example 1 and commercial packaging materials. Detailed Description of the Invention

[0038] The present invention will be further described in detail below.

[0039] Example 1

[0040] (1) Put 800 of hydroxyl-terminated polydimethylsiloxane with a molecular weight of 800 and isophorone diamine into a vacuum drying oven and heat at 70 °C for 10 h to remove the moisture in the reaction raw materials; use a vacuum tube high-temperature sintering furnace to heat 4A molecular sieve at 600 °C for 2 h for activation treatment, then put it into tetrahydrofuran to adsorb moisture, and use it after one week of treatment; where isophorone diamine is denoted as IDA;

[0041] (2) Disperse 18 mg of wrinkled graphene nanosheets with a particle size of 160 nm into 30 mL of tetrahydrofuran, and ultrasonically treat it for 50 min at a power of 300 W for later use;

[0042] (3) Set up a reaction device by using an oil bath for heating and mechanical stirring. Add 10 mmol of hydroxyl-terminated polydimethylsiloxane and 20 mmol of toluene 2,4-diisocyanate into a three-necked flask equipped with a condenser, and conduct oil bath and mechanical stirring at a stirring rate of 400 rpm. After the system is heated to 75 °C, add 50 μL of the catalyst DBTDL dropwise and react for 2 h to obtain prepolymer 1; among them, toluene 2,4-diisocyanate is denoted as 2,4-TDI;

[0043] (4) Cool the system to 40 °C at a cooling rate of 2 °C / min, reduce the stirring rate to 200 rpm, dissolve 20 mmol of dried IDA in tetrahydrofuran, and slowly add the IDA solution to prepolymer 1 through a constant-pressure funnel at a dropping rate of 5 mL / min, and continue to react for 5 h to obtain prepolymer 2;

[0044] (5) Completely dissolve 6.67 mmol of hexamethylene diisocyanate trimer in a tetrahydrofuran solution, and slowly add it to prepolymer 2 through a constant-pressure funnel at a dropping rate of 5 mL / min. Keep the system temperature and stirring rate unchanged, and continue to react for 5 h. Use di-n-butylamine chemical titration method to monitor the reaction process until the isocyanate groups in the system are completely consumed; then add the tetrahydrofuran dispersion of polydopamine dispersed in step (2) to the reaction system and continue to stir for 2 h to obtain a grayish-black near-infrared type polyurea resin solution; among them, hexamethylene diisocyanate trimer is denoted as tri-HDI;

[0045] (6) Rotate and evaporate the synthesized near-infrared self-healing polyurea resin solution to remove the unreacted substances and the solvent tetrahydrofuran in the system to obtain a polyurea resin solution with a solid content of 40%;

[0046] Immerse the nylon 6 fabric in the polyurea resin solution at 30 g / L for finishing for 5 min, then roll press it with a liquor pickup rate of 70%, dry it in an oven at 70 °C for 20 min, and then use a hot press to hot press the fabric at a hot press pressure of 2 MPa and a hot press time of 12 min to obtain a nylon 6 fabric containing a self-healing polyurea resin protective coating.

[0047] Example 2

[0048] (1) Put hydroxyl-terminated polydimethylsiloxane with a molecular weight of 900 and IDA into a vacuum drying oven and heat at 75 °C for 8 h to remove the moisture in the reaction raw materials; use a vacuum tube high-temperature sintering furnace to heat 4A molecular sieve at 450 °C for 3 h for activation treatment, then put it into acetone to adsorb moisture, and use it after treating for one week;

[0049] (2) Disperse 15 mg of polydopamine nanoparticles with a particle size of 180 nm into 40 mL of tetrahydrofuran, and ultrasonically treat it for 40 min at a power of 400 W for later use; among them, polydopamine is denoted as PDA.

[0050] (3) Set up a reaction device by using oil bath heating and mechanical stirring. Add 8 mmol of hydroxyl-terminated polydimethylsiloxane and 20 mmol of 2,4-TDI into a three-necked flask equipped with a condenser, and conduct oil bath and mechanical stirring. The stirring rate is 450 rpm. After the system is heated to 78 °C, add 100 μL of catalyst DBTDL dropwise, and react for 2.5 h to obtain prepolymer 1.

[0051] (4) Cool the system to 45 °C at a cooling rate of 3 °C / min, reduce the stirring rate to 250 rpm, dissolve 18 mmol of dried IDA in tetrahydrofuran, and slowly add the IDA solution to prepolymer 1 through a constant pressure funnel. Set the dropping rate to 6 mL / min, and continue to react for 4 h to obtain prepolymer 2.

[0052] (5) Completely dissolve 4 mmol of tri-HDI in a tetrahydrofuran solution, and slowly add it to prepolymer 2 through a constant pressure funnel. Set the dropping rate to 6 mL / min, keep the system temperature and stirring rate unchanged, and continue to react for 4.8 h. Use dibutylamine chemical titration to monitor the reaction process until the isocyanate groups in the system are completely consumed; then add the tetrahydrofuran dispersion of polydopamine dispersed in step (2) to the reaction system, and continue to stir for 2.5 h to obtain a gray-black polyurea resin solution.

[0053] (6) Rotavaporize the synthesized near-infrared self-healing polyurea resin solution to remove the unreacted substances and the solvent tetrahydrofuran in the system, and obtain a polyurea resin solution with a solid content of 50%.

[0054] Immerse the nylon 6 fabric in the polyurea resin solution at 30 g / L for 6 min, then roll it, with a liquor pickup rate of 70%, dry it in an oven at 75 °C for 18 min, and then use a hot press to hot press the fabric at a hot press pressure of 3 MPa and a hot press time of 10 min to obtain a nylon 6 fabric with a self-healing polyurea resin protective coating.

[0055] Example 3

[0056] (1) Put hydroxyl-terminated polydimethylsiloxane with a molecular weight of 850 and IDA into a vacuum drying oven and heat at 80 °C for 9 h to remove the moisture in the reaction raw materials. Activate 4A molecular sieve by heating it at 500 °C for 4 h using a vacuum tube high-temperature sintering furnace, then put it into dimethyl sulfoxide to adsorb moisture, and use it after treating for one week.

[0057] (2) Disperse 20 mg of carbon nanotubes with a particle size of 190 nm into 35 mL of tetrahydrofuran, and ultrasonically treat it for 35 min at a power of 500 W for later use.

[0058] (3) Set up a reaction device by using an oil bath heating and mechanical stirring method. Add 6 mmol of hydroxyl-terminated polydimethylsiloxane and 20 mmol of 2,4-TDI into a three-necked flask equipped with a condenser, and conduct oil bath and mechanical stirring at a stirring rate of 500 rpm. After the system is heated to 70 °C, add 120 μL of catalyst DBTDL dropwise, and react for 3.5 h to obtain prepolymer 1.

[0059] (4) Cool the system to 50 °C at a cooling rate of 4 °C / min, reduce the stirring rate to 300 rpm, dissolve 17.33 mmol of dried IDA in tetrahydrofuran, and slowly add the IDA solution to prepolymer 1 through a constant-pressure funnel at a dropping rate of 8 mL / min, and continue to react for 3 h to obtain prepolymer 2.

[0060] (5) Completely dissolve 2.22 mmol of tri-HDI in a tetrahydrofuran solution, and slowly add it to prepolymer 2 through a constant-pressure funnel at a dropping rate of 8 mL / min. Keep the system temperature and stirring rate unchanged, and continue to react for 4.5 h. Use the dibutylamine chemical titration method to monitor the reaction process until the isocyanate groups in the system are completely consumed; then add the tetrahydrofuran dispersion of the wrinkled graphene dispersed in step (2) to the reaction system, and continue to stir for 2.8 h to obtain a grayish-black near-infrared self-healing polyurea resin solution.

[0061] (6) Rotavaporize the synthesized near-infrared self-healing polyurea resin solution to remove the unreacted substances and the solvent tetrahydrofuran in the system to obtain a polyurea resin solution with a solid content of 55%.

[0062] Immerse the nylon 6 fabric in the polyurea resin solution at 30 g / L for finishing for 8 min, then roll press it with a liquor pickup rate of 70%, dry it in an oven at 80 °C for 15 min, and then use a hot press to hot press the fabric at a hot press pressure of 4 MPa and a hot press time of 9 min to obtain a nylon 6 fabric with a self-healing polyurea resin protective coating.

[0063] Example 4

[0064] (1) Put hydroxyl-terminated polydimethylsiloxane with a molecular weight of 1000 and IDA into a vacuum drying oven and heat at 85 °C for 12 h to remove the moisture in the reaction raw materials. Heat 4A molecular sieve at 400 °C for 5 h for activation treatment by using a vacuum tube high-temperature sintering furnace, and then put it into N,N-dimethylformamide to adsorb moisture, and use it after treating for one week.

[0065] (2) Disperse 25 mg of MXene nanosheets with a particle size of 200 nm into 50 mL of N,N-dimethylformamide, and ultrasonically treat it for 20 min at a power of 600 W for later use;

[0066] (3) Set up a reaction device by means of oil bath heating and mechanical stirring. Add 4 mmol of hydroxyl-terminated polydimethylsiloxane and 20 mmol of 2,4-TDI to a three-necked flask equipped with a condenser, and conduct oil bath and mechanical stirring at a stirring rate of 600 rpm. After the system is heated to 80 °C, add 150 μL of catalyst DBTDL dropwise and react for 4 h to obtain prepolymer 1;

[0067] (4) Cool the system to 55 °C at a cooling rate of 5 °C / min, reduce the stirring rate to 350 rpm, dissolve 17.43 mmol of dried IDA in N,N-dimethylformamide, and slowly add the IDA solution to prepolymer 1 through a constant-pressure funnel at a dropping rate of 10 mL / min, and continue to react for 2 h to obtain prepolymer 2;

[0068] (5) Completely dissolve 0.95 mmol of tri-HDI in N,N-dimethylformamide solution, and slowly add it to prepolymer 2 through a constant-pressure funnel at a dropping rate of 10 mL / min. Keep the system temperature and stirring rate unchanged and continue to react for 4 h. Use di-n-butylamine chemical titration method to monitor the reaction process until the isocyanate groups in the system are completely consumed; then add the N,N-dimethylformamide dispersion of polydopamine dispersed in step (2) to the reaction system and continue to stir for 3 h to obtain a gray-black near-infrared self-healing polyurea resin solution;

[0069] (6) Rotate and evaporate the synthesized near-infrared self-healing polyurea resin solution to remove unreacted substances and solvent N,N-dimethylformamide in the system to obtain a polyurea resin solution with a solid content of 60%.

[0070] Immerse the nylon 6 fabric in the polyurea resin solution at 30 g / L for finishing for 10 min, then roll press it with a liquor pickup rate of 70%, dry it in an oven at 85 °C for 10 min, and then use a hot press to hot press the fabric at a hot press pressure of 5 MPa and a hot press time of 8 min to obtain a nylon 6 fabric with a self-healing polyurea resin protective coating.

[0071] Comparative Example 1

[0072] (1) Put hydroxyl-terminated polydimethylsiloxane with a molecular weight of 900 and IDA into a vacuum drying oven and heat at 75 °C for 8 h to remove moisture in the reaction raw materials. Activate 4A molecular sieve by heating it in a vacuum tube high-temperature sintering furnace at 450 °C for 3 h, then put it into acetone to adsorb moisture, and use it after treating for one week;

[0073] (2) Set up the reaction apparatus by using oil bath heating and mechanical stirring. Add 8 mmol of hydroxyl-terminated polydimethylsiloxane and 20 mmol of 2,4-TDI into a three-necked flask equipped with a condenser, and conduct oil bath heating and mechanical stirring at a stirring rate of 450 rpm. After the system is heated to 78 °C, add 100 μL of catalyst DBTDL dropwise, and react for 2.5 h to obtain prepolymer 1;

[0074] (3) Cool the system to 45 °C at a cooling rate of 2 °C / min, reduce the stirring rate to 250 rpm. Dissolve 18 mmol of dried IDA in tetrahydrofuran, and slowly add the IDA solution to prepolymer 1 through a constant pressure funnel at a dropping rate of 6 mL / min, and continue to react for 4 h to obtain prepolymer 2;

[0075] (4) Completely dissolve 4 mmol of tri-HDI in a tetrahydrofuran solution, and slowly add it to prepolymer 2 through a constant pressure funnel at a dropping rate of 6 mL / min. Keep the system temperature and stirring rate unchanged, and continue to react for 4.8 h. Use di-n-butylamine chemical titration method to monitor the reaction process until the isocyanate groups in the system are completely consumed to obtain a milky yellow polyurea resin solution;

[0076] (5) Rotavaporize the synthesized polyurea resin solution to remove the unreacted substances and the solvent tetrahydrofuran in the system to obtain a polyurea resin solution with a solid content of 50%.

[0077] Immerse the nylon 6 fabric in the polyurea resin solution at 30 g / L for 6 min, then roll press it with a liquor pickup rate of 70%, dry it in an oven at 75 °C for 18 min, and then use a hot press to hot press the fabric at a hot press pressure of 3 MPa and a hot press time of 10 min to obtain a nylon 6 fabric with a polyurea resin protective coating.

[0078] Comparative Example 2

[0079] (1) Put the hydroxyl-terminated polydimethylsiloxane with a molecular weight of 900 and IDA into a vacuum drying oven and heat at 75 °C for 8 h to remove the moisture in the reaction raw materials. Activate the 4A molecular sieve by heating it at 450 °C for 3 h using a vacuum tube high-temperature sintering furnace, then put it into acetone to adsorb moisture, and use it after treating for one week;

[0080] (2) Set up the reaction apparatus by using oil bath heating and mechanical stirring. Add 8 mmol of hydroxyl-terminated polydimethylsiloxane and 20 mmol of 2,4-TDI into a three-necked flask equipped with a condenser, and conduct oil bath heating and mechanical stirring at a stirring rate of 450 rpm. After the system is heated to 78 °C, add 100 μL of catalyst DBTDL dropwise, and react for 2.5 h to obtain prepolymer 1;

[0081] (3) Cool down the system to 60 °C at a cooling rate of 2 °C / min, reduce the stirring rate to 250 rpm, dissolve 18 mmol of dried IDA in tetrahydrofuran, and slowly add the IDA solution to prepolymer 1 through a constant pressure funnel at a dropping rate of 15 mL / min. Continue the reaction for 4 h to obtain prepolymer 2;

[0082] (4) Completely dissolve 4 mmol of tri-HDI in a tetrahydrofuran solution, and slowly add it to prepolymer 2 through a constant pressure funnel at a dropping rate of 15 mL / min. Keep the system temperature and stirring rate unchanged, and continue the reaction for 4.8 h. Monitor the reaction process using the dibutylamine chemical titration method until the isocyanate groups in the system are completely consumed to obtain a milky yellow polyurea resin solution;

[0083] (5) Rotavaporize the synthesized polyurea resin solution to remove the unreacted substances and the solvent tetrahydrofuran in the system to obtain a polyurea resin solution with a solid content of 50%.

[0084] Immerse the nylon 6 fabric in a 30 g / L polyurea resin solution for 6 min, then roll it, with a liquor pickup rate of 70%. Dry it in an oven at 75 °C for 18 min, and then use a hot press to hot press the fabric at a hot press pressure of 3 MPa for 10 min to obtain a nylon 6 fabric with a polyurea resin protective coating.

[0085] Comparative Example 3

[0086] (1) Put the hydroxyl-terminated polydimethylsiloxane with a molecular weight of 900 and p-phenylenediamine into a vacuum drying oven and heat at 75 °C for 8 h to remove the moisture in the reaction raw materials; activate the 4A molecular sieve by heating it in a vacuum tube high-temperature sintering furnace at 450 °C for 3 h, then put it into acetone to adsorb moisture, and use it after one week of treatment; p-phenylenediamine is denoted as PPDA;

[0087] (2) Set up a reaction device using an oil bath heating and mechanical stirring method. Add 8 mmol of hydroxyl-terminated polydimethylsiloxane and 20 mmol of 2,4-TDI to a three-necked flask equipped with a condenser, and perform oil bath and mechanical stirring at a stirring rate of 450 rpm. After the system is heated to 78 °C, add 100 μL of the catalyst DBTDL and react for 2.5 h to obtain prepolymer 1;

[0088] (3) Cool down the system to 45 °C at a cooling rate of 2 °C / min, reduce the stirring rate to 250 rpm, dissolve 18 mmol of dried p-phenylenediamine in tetrahydrofuran, and slowly add the PDA solution to prepolymer 1 through a constant pressure funnel at a dropping rate of 6 mL / min. Continue the reaction for 4 h to obtain prepolymer 2;

[0089] (4) Dissolve 4 mmol of tri-HDI completely in a tetrahydrofuran solution, and slowly drop it into prepolymer 2 through a constant-pressure funnel. Set the dropping rate at 6 mL / min, keep the system temperature and stirring rate unchanged, and continue the reaction for 4.8 h. Monitor the reaction process using the dibutylamine chemical titration method until the isocyanate groups in the system are completely consumed to obtain a milky yellow polyurea resin solution;

[0090] (5) Rotavaporize the synthesized polyurea resin solution to remove the unreacted substances and the solvent tetrahydrofuran in the system to obtain a polyurea resin solution with a solid content of 50%.

[0091] Immerse the nylon 6 fabric in the polyurea resin solution at 30 g / L for finishing for 6 min, then roll press it with a liquor pickup rate of 70%, dry it in an oven at 75 °C for 18 min, and then use a hot press to hot press the fabric with a hot pressing pressure of 3 MPa and a hot pressing time of 10 min to obtain a nylon 6 fabric with a polyurea resin protective coating.

[0092] In the above three comparative examples of the present invention, Comparative Example 1 mainly focuses on the role of the photothermal conversion nanoparticles, Comparative Example 2 mainly focuses on the reaction temperature of the system and the addition rate of the chain extender during the synthesis process, and Comparative Example 3 mainly focuses on the influence of the type of chain extender on the molecular chain structure and properties during the polyurea resin synthesis process.

[0093] Taking the reaction monomer ratio in the system of Example 2 as a reference, replace the chain extender in Comparative Example 3 with p-phenylenediamine to illustrate the influence relationship between the molecular chain structure design during the polyurea resin synthesis process and the mechanical properties and self-healing performance of the synthesized resin. Neither Comparative Example 1 nor 3 involves the addition of photothermal conversion nanomaterials.

[0094] As Figure 3 shown, the mechanical strength of the polyurea resin synthesized in Comparative Example 3 is <25 MPa, the strain is <1000%, the elastic modulus is higher than that of Comparative Example 1, and the mechanical strength, elongation at break, and healing efficiency are all lower than those of the polyurea resin synthesized in the system of Comparative Example 1. In terms of molecular structure, since the soft segments and other components in the two systems are the same, the type of chain extender is an important factor leading to the differentiation of the properties of the synthesized polymers. The benzene ring in p-phenylenediamine is introduced as a rigid group into the hard segment region, resulting in a higher elastic modulus of the synthesized polyurea resin than that of Comparative Example 1, but the mechanical strength and elongation at break are both lower than those of Comparative Example 1. The isophorone diamine molecule has an asymmetric alicyclic structure, and the molecular network of the synthesized polyurea resin is loosely packed, which is conducive to the dissociation and rearrangement of the broken molecular chains.

[0095] Compared with Comparative Example 3, the molecular chains in the polyurea resin network in Comparative Example 1 have a higher mobility, which is beneficial to higher energy dissipation during the strain stretching process. The entangled soft-segment polydimethylsiloxane molecular chain segments will release the hidden strength and gradually form orientation during the stretching process. Therefore, there is a strain hardening stage in the polyurea resin in Comparative Example 1, and its mechanical strength and elongation at break are higher than those in Comparative Example 3. The healing efficiency in Comparative Example 1, that is, the degree of toughness recovery, is significantly lower than that in Comparative Example 3. This is because the molecular network formed by p-phenylenediamine is closely packed, seriously hindering the dynamic migration of the molecular network in the polyurea resin, resulting in a much lower self-healing efficiency than that in Comparative Example 3 under the same healing conditions.

[0096] Taking Example 2 as a reference, it can be seen from Figure 1 that the prepared polyurea resin has excellent mechanical properties, with a mechanical strength of up to 32.8 MPa and an elongation at break close to 1000%. After the sample is cut into pieces and filled into a mold for shaping, under the condition of NIR irradiation, the polydopamine nanoparticles in Example 2 absorb the near-infrared light energy to reach the required temperature for the dissociation of urea bonds in the system. The material undergoes a solid-liquid phase transition. During the process of the system cooling to room temperature, the dissociated amines react with isocyanate groups again to form dynamic urea bonds, achieving in-situ self-healing ( Figure 4 ). The breaking strength of the healed sample can reach 30 MPa, and the elongation at break can reach more than 900%. The healing efficiency of the sample is close to 93.7%. Among them, the healing efficiency is calculated according to the ratio of the breaking strength of the healed sample to that of the initial sample.

[0097] In the process of the polyurea resin system prepared in the present invention, the system temperature and the chain extension process are extremely important during the addition polymerization reaction, and the conditions need to be strictly controlled. Taking Comparative Example 2 as an example, both too high system temperature and too fast dropping rate will cause explosive polymerization during the synthesis process, resulting in the failure of the synthesis.

[0098] The types of monomers and the molar ratio of the reaction system in Comparative Example 1 are the same as those in Example 2, except that the latter introduces a polydopamine photothermal conversion material. The dimensions of the film-forming sample and the dumbbell-shaped sample in Example 2 are kept the same, width: 4 mm; length: 16 mm; thickness: 2 mm. From Figure 2It can be seen that the tensile strength of the sample made of the polyurea resin without the addition of the photothermal conversion material can reach 25.2 MPa after film formation, the strain exceeds 1000%, and the healing efficiency of the sample after healing under the same conditions is only 57.5%, which is much lower than the healing efficiency and tensile strength of Example 2. On the one hand, polydopamine is added as a nanofiller to the polyurea resin system to play a toughening effect. However, at the same time, the addition of the nanofiller will limit the migration of the molecular chains in the polyurea resin. Therefore, the elongation at break of the film in the comparative example is slightly higher than that of Example 2. On the other hand, the relatively high photothermal conversion efficiency of polydopamine can promote the dissociation of the dynamic urea bonds at the fracture interface of the film in Example 2 under the action of near-infrared light, improving the ductility of the molecular chains during the healing process of the material.

[0099] In Comparative Example 1, there is no photothermal conversion effect. After the contact at the fracture interface of the sample, it is only combined by the intermolecular hydrogen bond forces between the urea-urea, urea-carbamate, and carbamate-carbamate groups in the molecular chain. Therefore, it is much lower than the healing efficiency of the film in Example 2. From Figure 5 It can be seen that the air permeability of the initial nylon 6 fabric is 1.064 mm·s. After being coated with the polyurea resin prepared in Example 2, the air permeability decreases significantly, and the lowest can reach 0.222 mm·s. The air permeability of the healed sample is 0.232 mm·s, which is lower than that of most commercial sealing materials, such as balloons, shopping bags, food wraps, and sealed sample bags. This shows that the coating fills into the warp and weft structures on the fabric surface, forming a dense molecular network structure, greatly improving the barrier performance of the fabric surface. After treating the fabric with the polyurea resin of the comparative example, the air permeability can reach 0.278 mm·s, and the air permeability of the healed sample is 0.352 mm·s, slightly lower than that of Example 2. The addition of the polydopamine nanofiller can play a certain barrier role in the system, making the path of gas passing through the film tortuous, thereby improving the air barrier efficiency of the film.

Claims

1. A preparation method of a near-infrared in-situ self-healing polyurea resin, characterized in that, It includes the following steps: (1) Mix the hydroxyl-terminated polydimethylsiloxane with the 2,4-diisocyanate solution, add dibutyltin dilaurate as a catalyst, heat, and react to obtain prepolymer 1; (2) Slowly cool the temperature of the system in step (1) to 40-55 °C; then add isophorone diamine as a chain extender to the system, control the dropping rate of isophorone diamine at 5-10 mL / min, and react to obtain prepolymer 2; (3) Dissolve the hexamethylene diisocyanate trimer in a solvent, then add it to prepolymer 2, continue to react until the isocyanate is completely consumed, and then add a dispersion liquid dispersed with photothermal conversion nanoparticles to obtain a polyurea resin liquid. After evaporating the solvent in the polyurea resin liquid, a polyurea resin is obtained.

2. The preparation method of the near-infrared in-situ self-healing polyurea resin according to claim 1, characterized in that, In step (1), the heating temperature is 70-80 °C, and the reaction time is 2-4 h.

3. The preparation method of the near-infrared in-situ self-healing polyurea resin according to claim 1, wherein, In step (3), the temperature of the continued reaction is the same as the reaction temperature in step (2).

4. The preparation method of the near-infrared in-situ self-healing polyurea resin according to claim 1, characterized in that, The molar ratio of 2,4-diisocyanate to hydroxyl-terminated polydimethylsiloxane is 20:4-10; the molar ratio of 2,4-diisocyanate to isophorone diamine is 20:17.33-20; the molar ratio of 2,4-diisocyanate to hexamethylene diisocyanate trimer is 20:0.95-6.

67.

5. The preparation method of the near-infrared in-situ self-healing polyurea resin according to claim 1, wherein, In the said step (3), the R value of the system for synthesizing the polyurea resin is 1-1.

2.

6. The preparation method of the near-infrared in-situ self-healing polyurea resin according to claim 1, wherein, In step (3), the photothermal conversion nanoparticles are one of polydopamine, wrinkled graphene, carbon nanotubes, and MXenes nanosheets.

7. Application of the near-infrared in-situ self-healing polyurea resin prepared by the method according to claim 1 in an outdoor textile protection coating.

8. Use of the near-infrared in-situ self-healing polyurea resin according to claim 7 in an outdoor textile protective coating, characterized in that, Immerse the fabric in the polyurea resin liquid with a solid content of 40-60%, and after drying and hot pressing curing, a polyurea resin coating is prepared on the fabric surface.

Images