Preparation method of self-repairing recyclable creep-resistant polyurethane elastomer

Abstract

The invention discloses a self-repairing recoverable creep-resistant polyurethane elastomer and a preparation method thereof.The polyurethane elastomer is obtained by polymerizing a chain extender, diisocyanate, macromolecule dihydric alcohol / amine and a cross-linking agent according to the mass ratio of (2-15): (4-30): (30-90): (2-15), the obtained self-repairing recoverable creep-resistant polyurethane elastomer is cut into small blocks, the small blocks are subjected to heat preservation at the temperature of 180 DEG C and the temperature of 80 DEG C, and the self-repairing recoverable creep-resistant polyurethane elastomer is obtained. And carrying out hot press molding again under the condition of 30 MPa, so that 65% of mechanical properties of the obtained polyurethane can be recovered. A urea group in the dynamic polyurethane can be subjected to an exchange reaction at a high temperature, and the polyurethane elastomer containing the urea group can be recycled at the high temperature by utilizing the characteristic of the urea group. The chiral cyclic diamine used in the invention has a single spatial configuration, provides a hard chain segment for the polyurethane elastomer, and improves the mechanical properties and high-temperature creep resistance of the polyurethane elastomer.

Description

Technical Field

[0001] The invention relates to the technical field of polyurethane materials, and in particular to a method for preparing a self-repairing, recyclable, creep-resistant polyurethane elastomer. Background Art

[0002] Traditional polymers are divided into two categories: thermosetting and thermoplastic. Thermosetting materials have excellent mechanical properties, creep resistance, solvent resistance, wear resistance, thermal stability and dimensional stability due to their covalent cross-linking structure. However, due to the restriction of molecular chain movement by the cross-linking structure, thermosetting materials are insoluble and infusible after curing, lose processability, and usually need to be cured in a mold. This leads to difficulties in repair and recycling, and brings environmental and energy problems. On the contrary, thermoplastic materials have good processability and recyclability, but are relatively poor in creep resistance, heat resistance, solvent resistance, dimensional stability, etc. Among them, polyurethane elastomers are also divided into two categories, one is thermosetting polyurethane elastomer; the other is thermoplastic polyurethane elastomer, which also have the above characteristics respectively. In order to solve the above problems, scientists introduced dynamic covalent bonds into the network to form a dynamic covalent cross-linked polymer with a "covalently adaptable network" structure, which fully combines the advantages of thermoplastic materials and thermosetting materials.

[0003] Many dynamic covalent bonds have been designed and used to prepare high-performance, recyclable polyurethane elastomers. A dynamic covalent bond is a special chemical bond that can undergo reversible breakage-recombination. The dynamic process may be spontaneous and continuous, or it may require special conditions such as temperature, catalyst, and light. Types of dynamic covalent bonds include disulfide bonds, Diels-Alder reactions, oxime-formate bonds, Schiff bases, photocycloaddition reactions, ester exchanges, boric acid esters, etc. They have high bond energies and require external stimuli to show dynamic properties, otherwise they show covalent bond characteristics.

[0004] Polyurethane elastomer is a comprehensive material composed of thermodynamically incompatible soft segments and hard segments, with excellent properties such as high strength, high toughness, and high elasticity. Polyurethane elastomer can be prepared into a variety of products such as pipes, films, and complex molded bodies through a variety of melt processing methods (such as injection molding and extrusion, etc.), and is suitable for all walks of life. In some special fields, it replaces engineering plastics and is used as some structural parts. The parts are required to have a longer service life, and the creep resistance of polyurethane elastomer materials is required to be higher. However, due to the soft and hard segment microphase separation structure formed by the material, under the action of long-term fatigue stress, the material is prone to creep, resulting in deformation of parts and even high-risk failure. Therefore, one of the important directions for studying the preparation of creep-resistant polyurethane elastomers is to study the preparation of creep-resistant polyurethane elastomers.

[0005] CN114230485A uses a multifunctional azine derivative as a chain extender or crosslinker to prepare a polyurethane elastomer. As the temperature rises, the tensile strain of the spline gradually increases. Below 100°C, after the tensile stress is removed, the spline can return to its initial state. Above 120°C, after the tensile stress is removed, the spline cannot return and there is still a large residual strain. This shows that the sample has good creep resistance at 100°C. However, after exceeding 100°C, the creep resistance of the spline decreases. CN114015015A uses a diol containing a quaternary ammonium-furan structure or a diamine containing a quaternary ammonium-furan structure and a diol containing a quaternary ammonium-maleimide structure or a diamine containing a quaternary ammonium-maleimide structure as a chain extender, and adds diisocyanate and a high molecular diol to polymerize to obtain a polyurethane material with a DA bond. The furan and maleimide groups carried by the material will not affect the synthesis and processing of polyurethane at higher temperatures, and can then undergo cross-linking reactions again at lower temperatures, achieving post-heating cross-linking treatment between polyurethane hard segments and enhancing the creep resistance of the material. However, the double bonds in the DA system have the risk of self-polymerization and oxidation at high temperatures. Summary of the invention

[0006] Based on the current status of the above-mentioned polyurethane materials, the technical problem to be solved by the present invention is to provide a method for preparing a creep-resistant dynamic polyurethane containing chiral diamine by adding a chiral cyclic diamine small molecule as a chain extender to polyurethane. The polyurethane is more resistant to creep at high temperatures and has a longer service life.

[0007] The present invention is achieved by the following technical means:

[0008] The present invention first discloses a self-repairing, recyclable, creep-resistant polyurethane elastomer, which is obtained by polymerizing a chain extender, a diisocyanate, a high molecular weight diol / amine and a cross-linking agent; wherein:

[0009] The chain extender is a chain extender containing a chiral cyclic diamine, and its structural formula is selected from any one of the following:

[0010]

[0011] m is an integer of 1-5, n is an integer of 0-3, and o is an integer of 1-2.

[0012] Furthermore, the structural formula of the chiral cyclic diamine is selected from any one of the following:

[0013]

[0014] Furthermore, the diisocyanate is selected from: the diisocyanate is at least one of aliphatic, alicyclic and aromatic diisocyanates.

[0015] Further, the diisocyanate is selected from at least one of 4,4'-diphenylmethane diisocyanate, 2,4-toluene diisocyanate, isophorone diisocyanate, meta-xylyl diisocyanate, 1,6-hexane diisocyanate, 4,4'-dicyclohexylmethane diisocyanate, 1,5-naphthalene diisocyanate and 1,4-cyclohexyl diisocyanate.

[0016] Furthermore, the polymer diol / amine is selected from at least one of polyester diol, polyether diol, polysiloxane diol, polyether siloxane diol, polyester diamine, polyether diamine, polycarbonate diamine, polysiloxane diamine and polyether siloxane diamine; and the weight average molecular weight of the polymer diol / amine is 400 to 8000 g / mol.

[0017] Furthermore, the cross-linking agent is selected from at least one of hexamethylene diisocyanate trimer, toluene diisocyanate trimer and isophorone diisocyanate trimer.

[0018] Furthermore, the mass ratio of the chain extender, diisocyanate, polymer diol / amine and cross-linking agent is (2-15):(4-30):(30-90):(2-15).

[0019] The present invention also discloses a method for preparing any of the above self-repairing recyclable creep-resistant polyurethane elastomers, comprising:

[0020] (1) weighing diisocyanate and high molecular weight diol / amine in proportion, heating and stirring to obtain a bulk prepolymer;

[0021] (2) If the viscosity of the bulk prepolymer is too high, an appropriate amount of N,N-dimethylformamide can be added to reduce the viscosity, and then a chain extender can be added to extend the chain to obtain a chain extension reactant;

[0022] (3) adding a cross-linking agent to the chain extension reactant for cross-linking, pouring the obtained polymer into a mold, and then putting it into an oven to remove the solvent. After the solvent is completely removed, taking it out from the mold, thus obtaining a self-repairing, recyclable, creep-resistant polyurethane elastomer.

[0023] Furthermore, the heating and stirring conditions in step (1) are: stirring the reaction at 90° C. for 5 to 10 hours.

[0024] Furthermore, in step (2), when the viscosity of the bulk prepolymer is 15000 mPa·s, N,N-dimethylformamide is added.

[0025] Furthermore, the chain extension reaction time in step (2) is 0.5 h.

[0026] The present invention is also applicable to the compound use of the chiral chain extender and other diols or diamine chain extenders, wherein the proportion of the chiral diamine chain extender is greater than or equal to 50%.

[0027] The present invention is also applicable to linear materials without adding a cross-linking agent, and can also obtain a better creep resistance material.

[0028] The beneficial effects of the present invention are:

[0029] 1. The urea groups in the dynamic polyurethane of the present invention can undergo exchange reactions at high temperatures. By utilizing this characteristic of the urea groups, the polyurethane elastomer containing urea groups can be recycled and reused at high temperatures.

[0030] 2. The chiral cyclic diamine used in the present invention has a single stereo configuration, provides a hard segment for the polyurethane elastomer, and improves the mechanical properties and high-temperature creep resistance of the polyurethane elastomer.

[0031] 3. The self-repairing, recyclable, creep-resistant polyurethane elastomer obtained by the present invention is cut into small pieces and hot-pressed again under the conditions of 180° C. and 30 MPa. The obtained polyurethane can recover 65% of its mechanical properties. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] Figure 1 The infrared spectra of the polyurethane elastomers prepared in Examples 1 and 2 of the present invention are shown in FIG.

[0033] Figure 2 The following are the recovery test results of the sample of Example 2 of the present invention.

[0034] Figure 3 This is a test curve of the tensile properties of the sample in Example 2 of the present invention after recovery.

[0035] Figure 4 This is the creep resistance test curve of the sample in Example 1 of the present invention.

[0036] Figure 5 This is the creep resistance test curve of the sample in Example 2 of the present invention.

[0037] Figure 6 The following are photos of the product of Example 1 being cut through a microscope and placed in an oven at 180°C for different periods of time for self-repair. DETAILED DESCRIPTION

[0038] The following will be combined with the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0039] Embodiment 1:

[0040] The raw materials for preparing the self-repairing recyclable creep-resistant polyurethane elastomer include, based on 100 parts by total weight:

[0041] Diisocyanate: 2,4-toluene diisocyanate, 13 parts;

[0042] Polycaprolactone diol PCL2000: 75 parts;

[0043] Chain extender: chiral cyclic diamine (Formula 1-4), 6 parts;

[0044] Crosslinking agent: hexamethylene diisocyanate trimer, 6 parts.

[0045] The preparation method thereof comprises the following steps:

[0046] 75 parts by weight of polycaprolactone diol PCL2000 and 13 parts by weight of 2,4-toluene diisocyanate were added to a reactor, heated to 90°C, and mechanically stirred for 5 hours under a nitrogen atmosphere to obtain a colorless viscous prepolymer. After obtaining the prepolymer, an appropriate amount of N,N-dimethylformamide was added to the reactor to reduce its viscosity, and a chain extender (Formula 1-4) dissolved in N,N-dimethylformamide was added to the reactor, and mechanically stirred for 0.5 hours under a nitrogen atmosphere to obtain a linear dynamic polyurethane solution containing chiral diamines. Finally, hexamethylene diisocyanate trimer dissolved in N,N-dimethylformamide was added to the reactor, and mechanically stirred for 0.5 hours. The reaction solution was poured into a polytetrafluoroethylene mold and placed in a vacuum oven at 100°C to remove the residual solvent to obtain a yellow transparent film of dynamic covalent polyurethane, namely the polyurethane. The obtained polyurethane was subjected to infrared spectroscopy detection, and the test results are as follows: Figure 1 shown.

[0047] Example 2

[0048] The raw materials for preparing the self-repairing recyclable creep-resistant polyurethane elastomer include, based on 100 parts by total weight:

[0049] Diisocyanate: 2,4-toluene diisocyanate, 13 parts;

[0050] Polycaprolactone diol PCL2000: 75 parts;

[0051] Chain extender: chiral cyclic diamine (Formula 4-4), 6 parts;

[0052] Crosslinking agent: hexamethylene diisocyanate trimer, 6 parts.

[0053] The preparation method thereof comprises the following steps:

[0054] 75 parts by weight of polycaprolactone diol PCL2000 and 13 parts by weight of 2,4-toluene diisocyanate were added to a reactor, heated to 90°C, and mechanically stirred for 5 hours under a nitrogen atmosphere to obtain a colorless viscous prepolymer. After obtaining the prepolymer, an appropriate amount of N,N-dimethylformamide was added to the reactor to reduce its viscosity, and a chain extender (Formula 4-4) dissolved in N,N-dimethylformamide was added to the reactor, and mechanically stirred for 0.5 hours under a nitrogen atmosphere to obtain a linear dynamic polyurethane solution containing chiral diamine. Finally, hexamethylene diisocyanate trimer dissolved in N,N-dimethylformamide was added to the reactor, and mechanically stirred for 0.5 hours. The reaction solution was poured into a polytetrafluoroethylene mold and placed in a vacuum oven at 100°C to remove the residual solvent to obtain a yellow transparent film of dynamic covalent polyurethane, namely the polyurethane elastomer. The obtained polyurethane was subjected to infrared spectroscopy detection, and the test results are as follows: Figure 1 shown.

[0055] Test Example 1

[0056] (1) Recovery experiment:

[0057] The sample was cut into small pieces, and hot pressed for 5 minutes at 180°C and 30 MPa pressure using a hot press, and then cooled to room temperature. Figure 2 As shown, after the sample is cut into small pieces and hot-pressed at 180°C, 30 MPa for 5 minutes, the urea groups in the polyurethane undergo an exchange reaction and the sample can be recycled.

[0058] (2) Tensile properties:

[0059] According to GB / T 528-2009 standard, the mechanical properties test results of the dynamic covalent polyurethane obtained in Example 1 and Example 2 are as follows: Figure 3 As shown. Figure 3 It can be seen that the tensile strengths of the polyurethanes containing urea groups in Examples 1 and 2 of the present application are 58.8 MPa and 57 MPa, respectively, and the elongations at break are 1056% and 1021%, respectively. This may be due to the stereo configuration structure of the chiral cyclic diamine, which gives the elastomer excellent mechanical properties. Figure 3 This is the tensile property of the sample in Example 2 after recycling. It can be seen that the tensile strength can still be maintained above 35 MPa, and it has good mechanical properties.

[0060] (3) Creep resistance test:

[0061] The DMA Q800 dynamic thermal mechanical analyzer was used to test. A sample with a size of about 20 mm (length) x 5 mm (width) x 0.5 mm (thickness) was installed on the fixture, and the tensile stress was set to 0.1 MPa. When the temperature was raised to the test temperature, it was kept constant for 5 minutes, and then stretched at 0.1 MPa stress for 20 minutes, and then the stress was removed and maintained for 40 minutes. Example 1 Creep resistance test of the product Figure 4 As shown by Figure 4 It can be seen that as the temperature increases, the tensile strain of the sample gradually increases. At 130°C, the tensile strain is only less than 1%, and at 150°C, the tensile strain is about 1.4%, indicating that this sample has good creep resistance at 150°C. Figure 5 As shown by Figure 5 It can be seen that as the temperature increases, the tensile strain of the spline gradually increases. At 130°C, the tensile strain is about 1%, and at 150°C, the tensile strain is 1.4%. This shows that this sample has good creep resistance at 150°C. When the temperature is raised to 170°C, it also has good creep resistance.

[0062] (4) Self-repair experiment:

[0063] Figure 6 The following are photos of the product of Example 1 being cut through a microscope and placed in an oven at 180°C for different periods of time for self-repair.

[0064] The above is a detailed description of the present invention in combination with the embodiments, but the implementation methods of the present invention are not limited to the above embodiments, and any other changes, replacements, combination simplifications, etc. made under the core guiding idea of ​​the patent of the present invention are included in the protection scope of the patent of the present invention.

Claims

1. A self-repairing, recyclable, creep-resistant polyurethane elastomer obtained by polymerization of a chain extender, a diisocyanate, a polymer diol / amine and a crosslinking agent; wherein: The chain extender is a chain extender containing a chiral cyclic diamine, and its structural formula is selected from any one of the following: m is an integer of 1-5, n is an integer of 0-3, and o is an integer of 1-2.

2. The self-repairing, recyclable, creep-resistant polyurethane elastomer according to claim 1, wherein: The structural formula of the chiral cyclic diamine is selected from any one of the following:

3. The self-repairing, recyclable, creep-resistant polyurethane elastomer according to claim 1, wherein: The diisocyanate is selected from at least one of 4,4'-diphenylmethane diisocyanate, 2,4-toluene diisocyanate, isophorone diisocyanate, meta-xylyl diisocyanate, 1,6-hexane diisocyanate, 4,4'-dicyclohexylmethane diisocyanate, 1,5-naphthalene diisocyanate and 1,4-cyclohexyl diisocyanate.

4. The self-repairing, recyclable, creep-resistant polyurethane elastomer according to claim 1, wherein: The polymer diol / amine is selected from at least one of polyester diol, polyether diol, polysiloxane diol, polyether siloxane diol, polyester diamine, polyether diamine, polycarbonate diamine, polysiloxane diamine and polyether siloxane diamine; The weight average molecular weight of the polymer diol / amine is 400 to 8000 g / mol.

5. The self-repairing, recyclable, creep-resistant polyurethane elastomer according to claim 1, wherein: The cross-linking agent is selected from at least one of hexamethylene diisocyanate trimer, toluene diisocyanate trimer and isophorone diisocyanate trimer.

6. The self-repairing, recyclable, creep-resistant polyurethane elastomer according to claim 1, wherein: The mass ratio of the chain extender, diisocyanate, high molecular weight diol / amine and crosslinking agent is (2-15):(4-30):(30-90):(2-15).

7. A method for preparing the self-repairing, recyclable, creep-resistant polyurethane elastomer according to any one of claims 1 to 6, comprising: (1) weighing diisocyanate and high molecular weight diol / amine in proportion, heating and stirring to obtain a bulk prepolymer; (2) If the viscosity of the bulk prepolymer is too high, first add an appropriate amount of N,N-dimethylformamide to reduce the viscosity, and then add a chain extender to extend the chain to obtain a chain extension reactant; (3) adding a cross-linking agent to the chain extension reactant for cross-linking, pouring the obtained polymer into a mold, and then putting it into an oven to remove the solvent. After the solvent is completely removed, taking it out from the mold, thus obtaining a self-repairing, recyclable, creep-resistant polyurethane elastomer.

8. The preparation method according to claim 7, wherein: The heating and stirring conditions of step (1) are: stirring the reaction at 90° C. for 5 to 10 hours.

9. The preparation method according to claim 7, wherein: In step (2), when the viscosity of the bulk prepolymer is 15000 mPa·s, N,N-dimethylformamide is added.

10. The preparation method according to claim 7, wherein: The chain extension reaction time in step (2) is 0.5h.

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