Polyurethane synthetic leather capable of being repeatedly shaped and preparation method thereof

Abstract

According to the polyurethane synthetic leather capable of being shaped repeatedly and the preparation method thereof, dynamic covalent bonds are introduced into the molecular structure design of polyurethane resin, the dynamic covalent bonds are reversibly exchanged under external stimulation, a network cross-linked structure is rearranged, and reshaping and fixing of the shape of thermosetting polyurethane are achieved. According to the polyurethane synthetic leather capable of being repeatedly shaped, the problem that the surface of the thermosetting polyurethane synthetic leather is difficult to stamp for multiple times or the shape is difficult to fix again is solved, the shaping conditions are reduced, and the shaping efficiency is improved; the preparation cost is low, the synthesis process is simple and easy to operate, and the universality is realized.

Description

Technical Field

[0001] The invention relates to the technical field of polymer materials and synthetic leather manufacturing, and in particular to a method for preparing repeatedly reshapeable polyurethane synthetic leather. Background Art

[0002] Polyurethane synthetic leather is a man-made composite material with a look and feel similar to genuine leather. Due to its excellent properties such as wear resistance, chemical resistance, and breathability, it has found widespread application in footwear, luggage, furniture, and other categories. Currently, the resin used in most polyurethane synthetic leather production is thermosetting cross-linked polyurethane. Due to the insoluble and infusible nature of thermoset materials, their shape remains fixed after curing, making them difficult to reshape. In practical applications, polyurethane synthetic leather requires multiple shaping processes (such as embossing 3D logos or patterns, or fixing the three-dimensional shape). During the product design and production process, adjustments or modifications to the synthetic leather's shape require re-production, which not only increases production costs but also results in material waste. Furthermore, with increasing consumer demand for personalized products, synthetic leather that can be reshaped repeatedly will have a broader market prospect.

[0003] Dynamic covalent bonds are a new type of covalent bond that can reversibly break and reform under specific external stimuli (such as heat, light, pH, and specific chemicals). Unlike traditional permanent covalent bonds, dynamic covalent bonds endow materials with unique properties, such as self-healing, reshapeability, and recyclability. Their essence lies in the fact that under specific conditions, the bond breaking rate is significantly accelerated, and new bonds can be quickly reformed, thereby achieving a reorganization of the material's macroscopic network structure, thereby relaxing internal stress and achieving solid-state reshaping. However, the urethane bonds in polyurethane have low dynamic activity, and effectively introducing other more active dynamic covalent bonds into the resin matrix of polyurethane synthetic leather to enable convenient, controllable, and repeatable shaping while maintaining the synthetic leather's original excellent properties remains a challenge.

[0004] Therefore, it is of great significance to develop a polyurethane synthetic leather based on dynamic covalent bonds and reusable shaping and its preparation method. Summary of the Invention

[0005] In response to the shortcomings of the existing technology, the present invention aims to provide a polyurethane synthetic leather that can be repeatedly reshaped. The present invention is designed around the molecular structure of a cross-linked polyurethane resin, introduces dynamic covalent bonds, and after molding, the shape is programmed under the action of an external force. Stress relaxation occurs after the dynamic covalent bond exchange, thereby achieving multiple solid-state repeated shaping of a permanent shape.

[0006] To achieve the above objectives, the present invention proposes the following technical solutions:

[0007] A polyurethane synthetic leather capable of being repeatedly reshaped comprises a base layer and a dynamically cross-linked polyurethane layer composited on the base layer;

[0008] The preparation method of the dynamically cross-linked polyurethane layer is as follows:

[0009] Step 1: stirring and dissolving polyol, diisocyanate and catalyst to prepare polyurethane prepolymer;

[0010] Step 2: adding a chain extender and a cross-linking agent to the polyurethane prepolymer in sequence to obtain a dynamically cross-linked polyurethane, that is, obtaining the dynamically cross-linked polyurethane layer;

[0011] The chain extender is a chain extender containing a dynamic covalent bond, or a chain extender that can generate a dynamic covalent bond after being added to the polyurethane prepolymer. Preferably, the chain extender is a chain extender containing a dynamic covalent bond. More preferably, the dynamic covalent bond is a borate bond, more preferably a mercaptophenyl ring borate compound, and its reaction equation is as follows: Figure 1 shown.

[0012] Furthermore, the polyol in step 1 is one or more of polycarbonate diol, polycaprolactone diol, polylactide diol, and polytetramethylene glycol, and the molecular weight of the polyol is 100-20000 g / mol.

[0013] Furthermore, the isocyanate in step 1 is one or more of hexamethylene diisocyanate, isophorone diisocyanate and dicyclohexylmethane diisocyanate.

[0014] Furthermore, the polyurethane prepolymer in step 1 is an isocyanate-terminated polyurethane or a hydroxyl-terminated polyurethane.

[0015] Furthermore, in step 1, the functional group molar ratio of the polyol, diisocyanate, chain extender, and crosslinker is (3-6):(7-13):(3-6):1; and in step 2, the crosslinker contains a thiol, an amine, a hydroxyl group, or a monomer containing an isocyanate functional group, and the functionality of the crosslinker is ≥ 3. Monomers containing thiol, amine, or hydroxyl groups can be crosslinked with isocyanate-terminated prepolymers, or isocyanate monomers containing isocyanate functional groups can be crosslinked with hydroxyl-terminated prepolymers.

[0016] Furthermore, the dynamic covalent bond in step 2 is one or more of a borate bond, a hindered urea bond, a thiourethane bond, an acylhydrazone bond, an imine bond, and an ester bond.

[0017] Furthermore, a filler is added to the polyurethane prepolymer in step 2, wherein the filler is modified cellulose nanofiber, and the filler accounts for 0.05%-0.5% of the total mass of the raw material.

[0018] Furthermore, the method for preparing the re-shaping polyurethane synthetic leather comprises the following steps:

[0019] S1. Slurry preparation

[0020] The polyol, diisocyanate and catalyst are mixed uniformly and heated to 60-120°C, and stirred at 300-500 rpm for 1-5 hours to obtain a polyurethane prepolymer with an isocyanate or hydroxyl terminal group; a dynamic covalent bond chain extender, a crosslinking agent and a filler are added to the polyurethane prepolymer and mixed uniformly to obtain a polyurethane slurry that can be repeatedly molded;

[0021] S2, coating

[0022] The re-shaping polyurethane slurry described in step S1 is evenly coated on the base layer by scraping or spraying, and the coating thickness is controlled to be 0.2-1.0 mm;

[0023] S3, drying and curing

[0024] The coated synthetic leather is dried at 80-140° C. for 0.2-5 hours to obtain polyurethane synthetic leather that can be repeatedly reshaped.

[0025] Furthermore, the catalyst is a tin catalyst, and the amount of the catalyst added is 0.1-3wt% of the total mass of the reactants.

[0026] Furthermore, the shaping temperature of the polyurethane synthetic leather is 80-200°C.

[0027] Furthermore, the base fabric includes but is not limited to non-woven fabric, knitted fabric, and woven fabric.

[0028] The present invention discloses a reshapeable polyurethane synthetic leather and its preparation method. Dynamic covalent bonds are introduced into the molecular structure of the polyurethane resin. Under external stimulation, the dynamic covalent bonds are reversibly exchanged, and the network cross-linking structure is rearranged, achieving permanent shape reshaping and fixation. Compared with the existing technology, the present invention has the following advantages:

[0029] (1) The present invention modifies thermosetting cross-linked polyurethane to synthesize a polyurethane resin containing dynamic covalent bonds, which can be reshaped multiple times according to temperature changes and maintain the desired shape;

[0030] (2) To a certain extent, it solves the operational difficulties of multiple logo imprinting or shape fixing on thermosetting polyurethane synthetic leather, reduces the shaping conditions, and improves the shaping efficiency;

[0031] (3) The preparation cost is low, the synthesis process is simple and easy to operate, and it has universal applicability.

[0032] It should be appreciated that all combinations of the foregoing concepts, as well as additional concepts described in greater detail below, to the extent such concepts are not mutually inconsistent, can be considered to be part of the present subject matter disclosure.

[0033] The foregoing and other aspects, embodiments and features of the present invention will be more fully understood from the following description. Other additional aspects of the present invention, such as the features and / or beneficial effects of the exemplary embodiments, will become apparent from the following description or will be learned from the practice of the specific embodiments according to the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] In order to more clearly illustrate the technical solutions in the embodiments of the present disclosure, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are only some embodiments of the present disclosure. For ordinary technicians in this field, other drawings can be obtained based on these drawings without any creative work.

[0035] Figure 1 This is a schematic diagram showing the principle of preparing the mercaptophenyl ring borate compound of the present invention;

[0036] Figure 2 This is a schematic diagram and mechanism diagram of the shape reshaping operation of the present invention;

[0037] Figure 3 2 are stress relaxation curves of polyurethane films of different embodiments and comparative examples;

[0038] Figure 4 It is the initial shape of the polyurethane film after curing;

[0039] Figure 5 This is the folded corner shape of the polyurethane film after plasticization in Comparative Example 1;

[0040] Figure 6 The folded corner shapes of the polyurethane films after plasticization according to different embodiments of the present invention;

[0041] Figure 7 This is a comparison diagram of the TAPU-3 polyurethane film before and after plasticization and embossing in Example 3 of the present invention. DETAILED DESCRIPTION

[0042] In order to enable those skilled in the art to better understand the technical solutions of the present invention, preferred embodiments of the present invention are described below in conjunction with specific examples, but this should not be construed as limiting this patent.

[0043] Unless otherwise specified, the experimental methods or test methods described in the following examples / comparative examples are conventional methods; the reagents and materials described are obtained from conventional commercial channels or prepared by conventional methods unless otherwise specified.

[0044] A re-shapeable polyurethane synthetic leather comprises a base layer and a dynamically cross-linked polyurethane layer composited on the base layer; the dynamically cross-linked polyurethane layer is prepared as follows:

[0045] Step 1: stirring and dissolving polyol, diisocyanate and catalyst to prepare polyurethane prepolymer;

[0046] Step 2: adding a chain extender and a cross-linking agent to the polyurethane prepolymer in sequence to obtain a dynamically cross-linked polyurethane, that is, obtaining the dynamically cross-linked polyurethane layer;

[0047] The chain extender is a chain extender containing a dynamic covalent bond, or a chain extender that can generate a dynamic covalent bond after reacting with the polyurethane prepolymer after being added.

[0048] Furthermore, the polyol in step 1 is one or more of polycarbonate diol, polycaprolactone diol, polylactide diol, and polytetramethylene glycol, and the molecular weight of the polyol is 100-20000 g / mol.

[0049] Furthermore, the isocyanate in step 1 is one or more of hexamethylene diisocyanate, isophorone diisocyanate and dicyclohexylmethane diisocyanate.

[0050] Furthermore, the polyurethane prepolymer in step 1 is an isocyanate-terminated polyurethane or a hydroxyl-terminated polyurethane.

[0051] Furthermore, the crosslinking agent in step 2 contains a thiol, amine, hydroxyl, or isocyanate-functional monomer, and the functionality of the crosslinking agent is ≥ 3. Monomers containing thiol, amine, or hydroxyl groups can be crosslinked with isocyanate-terminated prepolymers, or isocyanate monomers containing isocyanate functional groups can be crosslinked with hydroxyl-terminated prepolymers.

[0052] Furthermore, the chain extender containing a dynamic covalent bond in step 2 may be one or more of a borate bond, a hindered urea bond, a thiourethane bond, an acylhydrazone bond, an imine bond, and an ester bond.

[0053] Furthermore, the chain extender is a mercaptophenyl ring borate compound.

[0054] Furthermore, a filler is added to the polyurethane prepolymer in step 2, wherein the filler is modified cellulose nanofiber, and the filler accounts for 0.05%-0.5% of the total mass of the raw material.

[0055] Furthermore, the method for preparing the re-shaping polyurethane synthetic leather comprises the following steps:

[0056] S1. Slurry preparation

[0057] The polyol, diisocyanate and catalyst are mixed uniformly and heated to 60-120°C, and stirred at 300-500 rpm for 1-5 hours to obtain a polyurethane prepolymer with an isocyanate or hydroxyl terminal group; a dynamic covalent bond chain extender, a crosslinking agent and a filler are added to the polyurethane prepolymer and mixed uniformly to obtain a polyurethane slurry that can be repeatedly molded;

[0058] S2, coating

[0059] The re-shaping polyurethane slurry described in step S1 is evenly coated on the base layer by scraping or spraying, and the coating thickness is controlled to be 0.2-1.0 mm;

[0060] S3, drying and curing

[0061] The coated synthetic leather is dried at 80-140° C. for 0.2-5 hours to obtain polyurethane synthetic leather that can be repeatedly reshaped.

[0062] Furthermore, the catalyst is a tin catalyst, and the amount of the catalyst added is 0.1-3wt% of the total mass of the reactants.

[0063] Furthermore, the shaping temperature of the polyurethane synthetic leather is 80-200°C.

[0064] Furthermore, the base fabric includes but is not limited to non-woven fabric, knitted fabric, and woven fabric.

[0065] Example 1

[0066] A polyurethane synthetic leather capable of being repeatedly reshaped comprises a base layer and a dynamically cross-linked polyurethane layer composited on the base layer. In this embodiment, the base layer is a non-woven fabric, and the polyurethane synthetic leather is prepared as follows:

[0067] A1. Preparation of chain extender

[0068] The chain extender of this embodiment is a mercaptophenyl ring borate compound, which is obtained by dehydrating 1-thioglycerol and 1,4-phenylenediboronic acid. Specifically, 4.14g of 1,4-phenylenediboronic acid is dissolved in 12g of tetrahydrofuran, 5.41g of 1-thioglycerol is added and mixed for 5 minutes. After clarification, 5g of anhydrous magnesium sulfate is added, and the reactants are stirred at 25°C for 24 hours. The precipitate and solvent are removed by vacuum filtration and reduced pressure distillation respectively to obtain a mercaptophenyl ring borate compound, and its reaction equation is as follows: Figure 1 As shown;

[0069] A2. Preparation of polyurethane prepolymer

[0070] Under a nitrogen atmosphere, 20 g of polycarbonate diol (molecular weight 2000), 2.52 g of hexamethylene diisocyanate and 0.3 g of dibutyltin dilaurate were stirred and dissolved in 50 g of tetrahydrofuran, and the mixture was stirred and reacted at 60° C. and 500 rpm for 4 h to obtain a polyurethane prepolymer solution.

[0071] A3. Solution mixing

[0072] 0.77 g of the mercaptophenyl ring borate compound obtained in step A1 was dissolved in the polyurethane prepolymer solution in step A2, the temperature was raised to 80° C., and the solution was stirred for 10 minutes to obtain a mixed solution.

[0073] A4. Preparation of re-shaping polyurethane slurry

[0074] The mixed solution obtained in step A3 was cooled to 30° C., 0.22 g of crosslinking agent trimethylolpropane was added, and the mixture was stirred at 200 rpm for 5 minutes to obtain a clear solution, i.e., a polyurethane slurry that can be repeatedly molded;

[0075] A5. Coating and drying

[0076] The re-shaping polyurethane slurry in step A4 is evenly coated on a non-woven fabric, and then cured and dried at a high temperature of 120° C. to obtain TAPU-1 polyurethane synthetic leather.

[0077] Furthermore, the re-shapeable polyurethane slurry of step A4 was poured into an aluminum pan, heated and cured at 120°C for 2 h, and vacuum dried at 80°C for 10 h to obtain a thermo-adaptive polyurethane, denoted as TAPU-1. The plasticizing properties of the polyurethane film at 100°C were characterized by the fold angle, as shown in FIG. Figure 6 (a) shown.

[0078] Example 2

[0079] The difference from the above embodiment 3 is that:

[0080] In step A2, under a nitrogen atmosphere, 20 g of polycarbonate diol (molecular weight 2000), 3.36 g of hexamethylene diisocyanate, and 0.3 g of dibutyltin dilaurate were stirred and dissolved in 50 g of tetrahydrofuran, and the mixture was stirred at 500 rpm and 60° C. for 4 h to obtain a polyurethane prepolymer solution.

[0081] In step A3, 2.32 g of the mercaptophenyl ring borate compound obtained in step A1 is dissolved in the polyurethane prepolymer solution in step A2, the temperature is raised to 80° C., and the solution is stirred for 10 minutes to obtain a mixed solution.

[0082] For other steps, refer to Example 3.

[0083] Furthermore, the re-shapeable polyurethane slurry of step A4 was poured into an aluminum pan, heated and cured at 120°C for 2 h, and vacuum dried at 80°C for 10 h to obtain a thermo-adaptive polyurethane, denoted as TAPU-2. The plasticizing properties of the polyurethane film at 100°C were characterized by the fold angle, as shown in FIG. Figure 6 (b)

[0084] Example 3

[0085] The difference from the above embodiment 3 is that:

[0086] In step A2, under a nitrogen atmosphere, 20 g of polycarbonate diol (molecular weight 2000), 4.63 g of hexamethylene diisocyanate, and 0.3 g of dibutyltin dilaurate were stirred and dissolved in 50 g of tetrahydrofuran, and the mixture was stirred at 500 rpm and 60° C. for 4 h to obtain a polyurethane prepolymer solution.

[0087] In step A3, 4.64 g of the mercaptophenyl ring borate compound obtained in step A1 is dissolved in the polyurethane prepolymer solution in step A2, the temperature is raised to 80° C., and the solution is stirred for 10 minutes to obtain a mixed solution.

[0088] For other steps, refer to Example 3.

[0089] Furthermore, the re-shapeable polyurethane slurry of step A4 was poured into an aluminum pan, heated and cured at 120°C for 2 h, and vacuum dried at 80°C for 10 h to obtain a thermo-adaptive polyurethane, designated as TAPU-3. The plasticizing properties of the polyurethane film at 100°C were characterized by the fold angle, as shown in FIG. Figure 6 (c) shown.

[0090] Comparative Example 1

[0091] Unlike Example 3, this comparative example used trimethylolpropane as the chain extender, replacing the mercaptophenyl ring borate compound in Example 3. Due to the change in chain extender, the amount of diisocyanate was also adaptively adjusted based on the total functional group content of trimethylolpropane; other factors remained unchanged. Specifically, the polyurethane synthetic leather preparation method in this comparative example was as follows:

[0092] A1. Preparation of polyurethane prepolymer

[0093] Under a nitrogen atmosphere, 20 g of polycarbonate diol (molecular weight 2000), 2.1 g of hexamethylene diisocyanate and 0.3 g of dibutyltin dilaurate were stirred and dissolved in 50 g of tetrahydrofuran, and the mixture was stirred and reacted at 60°C and 500 r / min for 4 h to obtain a polyurethane prepolymer solution.

[0094] A2. Preparation of polyurethane slurry

[0095] The polyurethane prepolymer solution obtained in step A1 was cooled to 25° C., 0.22 g of crosslinking agent trimethylolpropane was dissolved in the polyurethane prepolymer solution, and the mixture was stirred at 200 rpm for 5 minutes to obtain a polyurethane slurry.

[0096] A3. Coating and drying

[0097] The polyurethane slurry in step A2 is evenly coated on a non-woven fabric, and then cured and dried at 120°C to obtain TSPU polyurethane synthetic leather.

[0098] Furthermore, the polyurethane slurry in step A2 was poured into an aluminum pan, heated and cured at 120°C for 2 h, and vacuum dried at 80°C for 10 h to obtain a thermosetting polyurethane, which was denoted as TSPU. The plasticizing properties of the polyurethane film at 100°C were characterized by the angle of folding, as shown in FIG. Figure 5 shown.

[0099] The rest is the same as Example 3.

[0100] Example 4

[0101] Unlike Example 3 above, in this embodiment, a dynamic bond is generated by the reaction after adding a chain extender, and the dynamic bond is a hindered urea bond. Correspondingly, the amount of polyol, diisocyanate, and catalyst used is also adaptively adjusted according to the total functional group content involved in the reaction, and the others do not change. Specifically, the chain extender used in this comparative example is N, N'-di-tert-butylethylenediamine, which replaces the mercaptophenyl ring borate compound in Example 1, and the dynamic covalent bond formed after the reaction is a hindered urea bond.

[0102] In this comparative example, the preparation method of polyurethane synthetic leather is as follows:

[0103] A1. Preparation of polyurethane prepolymer

[0104] Under a nitrogen atmosphere, 20 g of polytetramethylene glycol (molecular weight 4000), 2.98 g of dicyclohexylmethane diisocyanate and 0.05 g of 1,8-diazabicycloundec-7-ene (DBU) were dissolved in 30 g of tetrahydrofuran, and the mixture was stirred at 500 rpm at 80° C. for 3 h to obtain a polyurethane prepolymer solution.

[0105] A2. Solution mixing

[0106] 1.29 g of N,N'-di-tert-butylethylenediamine was dissolved in the polyurethane prepolymer solution prepared in step A1, the temperature was raised to 80°C, and the solution was stirred and dissolved for 10 minutes to obtain a mixed solution.

[0107] A3. Preparation of re-shaping polyurethane slurry

[0108] The mixed solution obtained in step A3 was cooled to 30° C., 0.38 g of a crosslinking agent, hexamethylene diisocyanate isocyanurate trimer, was added, and stirred at 200 rpm for 5 minutes to obtain a clear solution, i.e., a polyurethane slurry that can be repeatedly molded;

[0109] A4. Coating and drying

[0110] The re-shaping polyurethane slurry in step A3 is evenly coated on a non-woven fabric, and cured and dried at 100°C to obtain a polyurethane synthetic leather containing dynamically hindered urea bonds.

[0111] The re-shapeable polyurethane slurry was poured into an aluminum pan, cured at 100°C for 3 hours, and then vacuum-dried at 80°C for 10 hours to obtain a thermoplastic polyurethane, designated TAPU-4. The plasticizing properties of the polyurethane film were then tested at 80°C, described by the shape plasticization rate.

[0112] The rest is the same as Example 3.

[0113] Example 5

[0114] Unlike Example 3 above, in this example, a dynamic bond is generated by the reaction after adding a chain extender, and the dynamic covalent bond is a dynamic thiurethane bond. Correspondingly, the amounts of polyol, diisocyanate, and catalyst used are also adaptively adjusted according to the total functional group content involved in the reaction, and other factors remain unchanged. Specifically, the chain extender used in this comparative example is 3,6-dioxo-1,8-octanedithiol, which replaces the mercaptophenyl ring borate compound in Example 1. The dynamic covalent bond formed after the reaction is a thiurethane bond.

[0115] In this comparative example, the preparation method of the polyurethane synthetic leather is as follows:

[0116] A1. Preparation of polyurethane prepolymer

[0117] Under nitrogen atmosphere, 20 g of polycaprolactone diol (molecular weight 5000), 2.45 g of isophorone diisocyanate and 0.2 g of triethylamine were dissolved in 30 g of tetrahydrofuran, and the mixture was stirred at 500 rpm at 80° C. for 3 h to obtain a polyurethane prepolymer solution.

[0118] A2. Solution mixing

[0119] 1.10 g of 3,6-dioxo-1,8-octanedithiol was dissolved in the polyurethane prepolymer solution prepared in step A2, the temperature was raised to 80° C., and the mixture was stirred and dissolved for 10 minutes to obtain a mixed solution.

[0120] A3. Preparation of re-shaping polyurethane slurry

[0121] The mixed solution obtained in step A3 was cooled to 30° C., 0.09 g of crosslinking agent trimethylolpropane was added, and the mixture was stirred at 200 rpm for 5 minutes to obtain a clear solution, i.e., a polyurethane slurry that can be repeatedly molded;

[0122] A4. Coating and drying

[0123] The re-shaping polyurethane slurry in step A3 is evenly coated on a non-woven fabric, and cured and dried at 130°C to obtain a polyurethane synthetic leather containing dynamic thiol-urethane bonds.

[0124] The reshapeable polyurethane slurry from step A3 was poured into an aluminum pan, cured at 130°C for 1 hour, and vacuum-dried at 80°C for 10 hours to obtain a thermoplastic polyurethane, designated TAPU-5. The plasticizing properties of the polyurethane film were tested at 150°C, using the shape plasticization rate as the indicator.

[0125] The rest is the same as Example 3.

[0126] Performance Testing

[0127] The plasticizing effect test methods include stress relaxation test and shape plasticizing rate determination.

[0128] Determination of shape plasticization rate

[0129] Taking angle plasticization as an example, polyurethane film or polyurethane synthetic leather is cut into 15mm*5mm strips, and the initial angle θ0 of the material is 180°. The strip is folded in half with an external force at high temperature and fixed for 1 hour. At this time, the angle θ1 fixed by the external force during plasticization is 0°. Then, the external force is removed at 100° and the folded angle θ2 is maintained. The shape plasticization rate (η) is calculated as follows:

[0130]

[0131] Stress relaxation test

[0132] To further investigate the effects of varying borate ester bond content on the viscoelasticity and internal molecular segment motion of polyurethane synthetic leather, stress relaxation tests were conducted on the samples. Specifically, the tests were performed using a rotational rheometer in oscillation mode, which provides a visual indicator of the rate and extent of dynamic covalent bond exchange.

[0133] According to the different examples and comparative examples, the performance test methods were used to test the plasticization rates. The comparison results are shown in the following table:

[0134] Table 1 Comparison of plasticization rates of different polyurethanes

[0135] Figure 6 It is the angle shape of the polyurethane film after plasticization in different embodiments of the present invention. In Examples 1-3, a mercaptophenyl ring borate compound is used as a chain extender, and the chain extender contains a borate dynamic covalent bond and a thiocarbamate dynamic covalent bond, and as the usage increases from low to high, the trend of the influence of different borate bond introduction contents on the polyurethane synthetic leather is as follows: the usage increases continuously, and the plasticization rate also increases synchronously. No dynamic covalent bonds are introduced into the network formed in Comparative Example 1. Examples 4 and 5 use chain extenders that can generate different dynamic covalent bonds, thereby proving two problems: 1. The plasticization effect of introducing dynamic covalent bonds is better; 2. The dynamic covalent bonds introduced into the system can not only use borate bonds, but also other dynamic covalent bonds. Moreover, the inventor unexpectedly found that the plasticization rate of the polyurethane synthetic leather prepared using a mercaptophenyl ring borate compound as a chain extender, as well as the stress relaxation rate and degree of the system are optimal.

[0136] Specifically, as the amount of mercaptophenyl ring borate compound used increases from Example 1 to Example 3, the angle of the polyurethane film after plasticization also varies significantly. Combined with the test results in the table above, it can be seen that as the amount of borate bond introduced increases, the plasticization rate also increases. Specifically, thermosetting TSPU, which does not contain dynamic borate bonds, has a plasticization rate of only 19.4% after reshaping, due to the exchange of dynamic urethane bonds. However, as the borate bond content increases, the plasticization rate of TAPU-3 reaches 83.3%. Figure 3 The stress relaxation curve at 100°C shown also verifies this result. With the increase in the dynamic covalent bond content, the stress relaxation speed and degree of the system are further improved, and the plasticizing effect is simultaneously improved.

[0137] In Comparative Example 1, no mercaptophenyl ring borate compound was added. Due to the lack of chain extender, isocyanate supplementation was required, resulting in a greater amount of crosslinking agent than in Example 1. The stress relaxation rate and degree of the polyurethane film in the comparative example were inferior to those in Examples 1-3. Figure 5 This is also confirmed by the corner shape of the polyurethane film after plasticization.

[0138] It should be noted that TAPU-4 has good plasticizing properties and can maintain the folded shape after plasticizing at 80°C for 1 hour. TAPU-5 has good plasticizing properties and can maintain the folded shape after plasticizing at 150°C for 1 hour.

[0139] The polyurethane synthetic leather disclosed in the present invention introduces dynamic covalent bonds into the molecular structure design of the polyurethane resin. Under external stimulation, the dynamic covalent bonds are reversibly exchanged, the network cross-linking structure is rearranged, and the permanent shape is reshaped and fixed, which has important reference significance for actual production.

[0140] Furthermore, polyurethane synthetic leather is subject to collision and friction from various objects during use, which reduces its service life. To further investigate the wear resistance and other mechanical properties of re-shapeable polyurethane synthetic leather, we studied the effect of adding fillers on re-shapeable polyurethane synthetic leather while ensuring re-shapeability.

[0141] The filler described in this application is modified cellulose nanofiber (modified CNF), specifically cellulose nanofiber modified with Mxene, thereby affecting the tensile strength, elongation, strain range and wear resistance of polyurethane.

[0142] Example 6

[0143] The difference from Example 3 is that a filler is further added to the polyurethane prepolymer in step 2. The filler is modified CNF, and the filler accounts for 0.05% of the total mass of the raw materials.

[0144] Furthermore, the modified CNF includes raw material processing, preparation of layered solution, and CNF modification, and the preparation method thereof is as follows:

[0145] 1. Raw material processing

[0146] First, LiF was prepared into a LiF / HCl solution with a concentration of 3M. Subsequently, 400-mesh Ti3AlC2 powder was slowly added to the LiF / HCl solution. After stirring for 24 hours, it was washed with deionized water and centrifuged at 8000 rpm until the pH value of the supernatant reached above 6. The precipitate was collected and then redissolved in deionized water to prepare a 0.5 wt% precipitate solution.

[0147] 2. Preparation of Layered Solutions

[0148] The precipitate solution was sonicated in an ice bath for 1 hour, and the layers were separated. During sonication, 0.25 mL of bis-[3-(triethoxysilyl)propyl]-tetrasulfide was added every 25 minutes. Finally, the solution was centrifuged at 3500 rpm for 1 hour, and the dark green supernatant, i.e., the layered solution, was collected.

[0149] 3. CNF modification

[0150] A 50 M suspension of CNF was prepared. The layered solution was then added to the CNF suspension at a rate of 1 mL / min. After addition, the mixture was stirred continuously for at least 30 minutes. After mixing thoroughly, the mixture was dried in an oven to obtain the modified CNF. The calculated mass ratio of the cellulose nanofibers to the Ti3AlC2 material was 10:3.

[0151] It should be further explained that Ti3AlC2 (400 mesh) was purchased from Jilin Yiyi Technology Co., Ltd., LiF (99%) and hydrochloric acid (HCl, 36%) were purchased from Shanghai Aladdin Biochemical Technology Co., Ltd., and cellulose nanofiber aqueous solution (6 wt.%) was purchased from Shanghai Hu's Laboratory Equipment Co., Ltd.

[0152] For other steps, refer to Example 3.

[0153] Example 7

[0154] The difference from Example 6 is that a filler is further added to the polyurethane prepolymer solution in step 2. The filler is modified CNF, and the filler accounts for 0.25% of the total mass of the raw materials.

[0155] The rest is the same as Example 6.

[0156] Example 8

[0157] The difference from Example 6 is that a filler is further added to the polyurethane prepolymer solution in step 2. The filler is modified CNF, and the filler accounts for 0.5% of the total mass of the raw materials.

[0158] The rest is the same as Example 6.

[0159] Comparative Example 2

[0160] The difference from Example 6 is that the filler-modified CNF is replaced by Ti3AlC2 powder of equal mass, and the rest is the same as Example 6.

[0161] Comparative Example 3

[0162] The difference from Example 6 is that the filler-modified CNF is replaced with cellulose nanofiber CNF of equal mass. Other steps are the same as those in Example 6.

[0163] Comparative Example 4

[0164] Unlike Example 6, the filler-modified CNF was replaced with a mixed powder of equal weights of Ti3AlC2 powder and cellulose nanofiber CNF. After simple mixing, the mixture was added directly to the polyurethane prepolymer solution. The mass ratio of Ti3AlC2 powder to cellulose nanofiber CNF was 1:1. All other conditions were the same as in Example 6.

[0165] Performance Testing

[0166] Mechanical properties testing

[0167] The thermoadaptive polyurethane samples of Example 3, Examples 6-8, and Comparative Examples 2-4 were cut into dumbbell shapes with a length of 35 mm, a narrow portion width of 2 mm, and a sample thickness of 1 mm. The tensile strength was tested in accordance with the national standard GBT 528-2009, and performance tests were performed. The test results are shown in Table 2.

[0168] Wear resistance test

[0169] According to ASTM D4060, the CS-17 was rotated 5000 times and the mass loss was measured to evaluate the wear resistance. The test results are shown in Table 2.

[0170] Table 2 Performance test analysis table sample Tensile strength (MPa) Elongation at break (%) Strain range (%) Mass loss (mg) Example 6 22.9 732 11.20 58 Example 7 23.1 798 11.63 51 Example 8 23.5 850 11.96 42 Comparative Example 2 20.0 523 9.65 61 Comparative Example 3 19.5 411 9.31 69 Comparative Example 4 22.0 694 10.35 68 Example 3 15.3 187 8.03 88

[0171] According to the comparative data analysis in Table 2, the re-shapeable polyurethane synthetic leather disclosed in the present invention has high breaking strength, large elongation at break, good mechanical properties, and good comprehensive shape plasticization performance. The specific analysis is as follows:

[0172] No filler CNF was added in Example 3, and the fillers in Examples 6-8 were modified CNF in different usage amounts, and the usage amounts were from low to high; in Comparative Examples 2-4, there was a lack of modifying elements or the materials were simply added directly; Examples 6-8, Example 3 and Comparative Examples 2-4, which prove two problems: 1. The use of modified CNF has mechanical synergy and improves wear resistance; 2. There are two elements in the modified CNF, and the use of modified CNF is better than a single element, and better than the simple superposition of two elements.

[0173] Although the polyurethane leather in Example 3 has a good repeatable shaping effect, its wear resistance is not as good as that of Example 8. The use of fillers, the modified CNF is first pre-treated by exfoliation of the material Ti3AlC2, and then activated with bis-[3-(triethoxysilyl)propyl]-tetrasulfide, and finally the material is added to CNF to form a material with excellent compatibility. The modified CNF utilizes the excellent mechanical strength and wear resistance of Ti3AlC2. CNF has the advantages of light weight and high strength. The modified CNF formed by the combination has good interface bonding performance with the polyurethane matrix, which improves the mechanical weather resistance of the material while achieving repeatable shaping.

[0174] In Comparative Examples 2 and 3, using either Ti3AlC2 or CNF alone resulted in the Ti3AlC2 material easily agglomerating, while the CNF material easily floated on the surface of the system, leading to stress concentration and poor mechanical properties during stress loading. In Comparative Example 4, using either material alone resulted in system instability and weak interfacial bonding, resulting in a far less effective performance than using modified CNF.

[0175] In summary, the use of modified CNF will not affect the overall shape plasticizing effect, and the addition of fillers has a positive effect on tensile strength and elongation, and also helps the strain range of thermoadaptive polyurethane, which is helpful for repeated shaping of the overall synthetic leather.

[0176] While the present invention has been disclosed above with reference to preferred embodiments, this is not intended to limit the present invention. Persons skilled in the art will readily appreciate that various modifications and variations can be made without departing from the spirit and scope of the present invention. Therefore, the scope of protection of the present invention shall be determined by the claims.

Claims

1. A polyurethane synthetic leather that can be repeatedly reshaped, characterized in that: include: A base layer, and a dynamically cross-linked polyurethane layer composited on the base layer; The preparation method of the dynamically cross-linked polyurethane layer is as follows: Step 1: stirring and dissolving polyol, diisocyanate and catalyst to prepare polyurethane prepolymer; Step 2: adding a chain extender and a cross-linking agent to the polyurethane prepolymer in sequence to obtain a dynamically cross-linked polyurethane, that is, obtaining the dynamically cross-linked polyurethane layer; The chain extender is a chain extender containing a dynamic covalent bond, or a chain extender that can generate a dynamic covalent bond after reacting with the polyurethane prepolymer after being added.

2. The re-shapeable polyurethane synthetic leather according to claim 1, characterized in that: The polyol in step 1 is one or more of polycarbonate diol, polycaprolactone diol, polylactide diol, and polytetramethylene glycol, and the molecular weight of the polyol is 100-20000 g / mol; the diisocyanate in step 1 is one or more of hexamethylene diisocyanate, isophorone diisocyanate, and dicyclohexylmethane diisocyanate.

3. The re-shapeable polyurethane synthetic leather according to claim 1, characterized in that: The polyurethane prepolymer in step 1 is an isocyanate-terminated polyurethane or a hydroxyl-terminated polyurethane.

4. The re-shapeable polyurethane synthetic leather according to claim 1, characterized in that: The cross-linking agent in step 2 contains a thiol, an amine, a hydroxyl or a monomer containing an isocyanate functional group, and the functionality of the cross-linking agent is ≥3.

5. The re-shapeable polyurethane synthetic leather according to claim 1, characterized in that: The chain extender containing a dynamic covalent bond in step 2 may be one or more of a borate bond, a hindered urea bond, a thiourethane bond, an acylhydrazone bond, an imine bond, and an ester bond.

6. The re-shapeable polyurethane synthetic leather according to claim 5, characterized in that: The chain extender in step 2 is a chain extender containing a borate bond.

7. The re-shapeable polyurethane synthetic leather according to claim 6, characterized in that: The chain extender is a mercaptophenyl ring borate compound.

8. The re-shapeable polyurethane synthetic leather according to claim 1, characterized in that: In step 2, a filler is further added to the polyurethane prepolymer, wherein the filler is modified cellulose nanofiber, and the filler accounts for 0.05% to 0.5% of the total mass of the raw material.

9. A method for preparing the re-shapeable polyurethane synthetic leather according to any one of claims 1 to 8, characterized in that: The following steps are involved: S1. Slurry preparation The polyol, diisocyanate and catalyst are mixed uniformly and heated to 60-120°C, and stirred at 300-500 rpm for 1-5 hours to obtain a polyurethane prepolymer with an isocyanate or hydroxyl terminal group; a dynamic covalent bond chain extender, a crosslinking agent and a filler are added to the polyurethane prepolymer and mixed uniformly to obtain a polyurethane slurry that can be repeatedly molded; S2, coating The re-shaping polyurethane slurry described in step S1 is evenly coated on the base layer by scraping or spraying, and the coating thickness is controlled to be 0.2-1.0 mm; S3, drying and curing The coated synthetic leather is dried at 80-140° C. for 0.2-5 hours to obtain polyurethane synthetic leather that can be repeatedly reshaped.

10. The re-shapeable polyurethane synthetic leather and the preparation method thereof according to claim 9, characterized in that: The shaping temperature of the polyurethane synthetic leather is 80-200°C.

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