High-strength self-repairing waterborne polyurethane and preparation method thereof

Abstract

The invention relates to a waterborne polyurethane material, in particular to high-strength self-repairing waterborne polyurethane with excellent stability and a preparation method thereof. According to the invention, the waterborne polyurethane with high tensile strength is prepared by adjusting the process steps (changing the adding time of diisocyanate); the technical problem that the tensile strength of the prepared waterborne polyurethane is low in the existing process for preparing the waterborne polyurethane by adopting a pre-polymerization method is solved. According to the invention, polytetrahydrofuran glycol is further selected as a soft segment, (4-hydroxyphenyl) disulfide is used as a chain extender, and waterborne polyurethane with high tensile strength, good stability and good self-healing performance is prepared.

Description

Technical Field

[0001] The present invention relates to a waterborne polyurethane material, and more particularly to a high-strength, self-repairable and stable waterborne polyurethane and a preparation method thereof. Background Art

[0002] Polyurethane, a common polymer material, boasts high strength, excellent elasticity, and superior wear resistance, and is widely used in numerous fields. However, the most commonly used high-performance polyurethanes are solvent-based, which consume large amounts of solvent during use, posing a threat to the environment and personal safety. With growing environmental awareness, the use of solvent-based polyurethanes is increasingly restricted.

[0003] Waterborne polyurethane (also known as water-dispersible polyurethane, water-based polyurethane, or water-based polyurethane) is a novel polyurethane system that uses water as a dispersion medium instead of organic solvents. Using water as a solvent, waterborne polyurethane offers advantages such as being pollution-free, safe and reliable, possessing excellent mechanical properties, good compatibility, and ease of modification. Consequently, the development and research of waterborne polyurethane is becoming increasingly widespread both domestically and internationally. However, the tensile strength of waterborne polyurethanes prepared using existing technologies is relatively low, failing to meet demand. Summary of the Invention

[0004] In order to solve the technical problem of low tensile strength of waterborne polyurethane produced by the existing prepolymerization process, the present invention prepares a waterborne polyurethane with high tensile strength by adjusting the process steps (adjusting the timing of adding diisocyanate).

[0005] One of the purposes of the present invention is to provide a method for preparing waterborne polyurethane.

[0006] The preparation method of the waterborne polyurethane comprises the following steps:

[0007] (1) under catalyst action, polytetrahydrofuran diol (PTMG) and diisocyanate react;

[0008] (2) After step (1), 2,2-dihydroxymethylpropionic acid (DMPA) and an organic solvent are added to continue the reaction;

[0009] (3) After step (2), materials and catalyst are added to continue the reaction; wherein the materials are composed of diisocyanate, (4-hydroxyphenyl) disulfide (SS) and optionally 1,4-butanediol (BDO),

[0010] (4) After step (3), triethylamine (TEA) is added to continue the reaction to obtain the waterborne polyurethane;

[0011] Wherein, the diisocyanate in step (1) is the same as that in step (3).

[0012] The R value of waterborne polyurethane, or the molar ratio of diisocyanate groups to hydroxyl groups, significantly influences the mechanical properties (tensile strength) of the waterborne polyurethane. The present invention has discovered through experimental research that, while maintaining the R value (and the total amount of diisocyanate used) of the waterborne polyurethane, adjusting the timing of diisocyanate addition can significantly alter the mechanical properties of the resulting waterborne polyurethane. Specifically, the present invention achieves improved mechanical properties of the resulting waterborne polyurethane by regulating the R value of the reaction system during prepolymerization through the stepwise addition of diisocyanate.

[0013] Take the molar ratio of diisocyanate to polytetrahydrofuran diol as 3:1 and the amount of diisocyanate as 0.3 mol as an example. If the diisocyanate is added to the reaction system at once, the diisocyanate content in the reaction system is high, the R value of the reaction system during prepolymerization is as high as about 3, and the reaction system activity is high. If the reaction system is not completely dehydrated, it may cause a side reaction between water and isocyanate, or it may cause a violent polymerization reaction, resulting in poor mechanical properties of the waterborne polyurethane, difficulty in subsequent emulsification, and even failure of the experiment. If the diisocyanate is divided into two parts and added twice; the first part is 0.2 mol and added in step (1); the second part is 0.1 mol and added in step (2) or (3). After the first addition of diisocyanate (addition of 0.2 mol of diisocyanate), the R value of the reaction system during prepolymerization is about 2, the reaction system activity is low, the viscosity of the reaction system increases, the molecular weight of the prepolymer increases, which is conducive to the subsequent chain extension reaction, and ultimately improves the tensile strength of the prepared waterborne polyurethane. That is, compared with the existing process of adding all the diisocyanate at once in step (1), the process of adding the same amount of diisocyanate in two times can improve the tensile strength of the prepared waterborne polyurethane.

[0014] Through further experimental research, the present invention has found that under the premise of "dividing the required amount of diisocyanate into two parts and adding them in two times": compared with the process of "adding the second part of diisocyanate in step (2)", the tensile strength of the waterborne polyurethane prepared by the process of "adding the second part of diisocyanate in step (3)" is more significantly improved. Therefore, the present invention adopts the process of "dividing the diisocyanate into two parts and adding them in two times; the first part is added in step (1) and the second part is added in step (3)" to prepare the waterborne polyurethane.

[0015] In addition, the selection of soft segments and the type of chain extender have a significant impact on the properties of waterborne polyurethane (tensile strength, emulsion stability, and self-healing properties). The present invention, based on the process of "dividing the diisocyanate into two parts and adding them twice; the first part is added in step (1) and the second part is added in step (3)", selects polytetramethylene glycol as the soft segment, isophorone diisocyanate (IPDI) as the hard segment, and 2,2-dimethylolpropionic acid and (4-hydroxyphenyl) disulfide as chain extenders to prepare a waterborne polyurethane with high tensile strength, good stability, and good self-healing properties.

[0016] Furthermore, the choice of diisocyanate also has a significant impact on the mechanical properties of waterborne polyurethane. When the diisocyanate is isophorone diisocyanate, the improvement in the tensile strength of the waterborne polyurethane brought about by adding isophorone diisocyanate twice, in steps (1) and (3), is particularly significant; the tensile strength can be increased by 117%. Therefore, as a preferred embodiment, the diisocyanate used in the preparation method of the waterborne polyurethane is isophorone diisocyanate.

[0017] The preparation method of the waterborne polyurethane can refer to existing preparation methods for the molar ratio of raw materials, the selection and amount of organic solvent, catalyst and protective gas, reaction temperature and time. Specifically, the molar ratio of raw materials, the selection and amount of organic solvent, catalyst and protective gas, reaction temperature and time can be as follows:

[0018] In step (1), the molar ratio of polytetrahydrofuran diol to diisocyanate is 1:2±0.1.

[0019] The molar ratio of the 2,2-dihydroxymethylpropionic acid in step (2) to the polytetrahydrofuran diol in step (1) is 1±0.1:1.

[0020] The molar ratio of the diisocyanate in step (3) to the diisocyanate in step (1) is 0.5±0.1:1.

[0021] The molar ratio of the total amount of (4-hydroxyphenyl) disulfide and 1,4-butanediol in step (3) to the polytetrahydrofuran diol in step (1) is 1±0.1:1.

[0022] In step (3), the molar ratio of (4-hydroxyphenyl) disulfide to 1,4-butanediol is 0.25-4:1, preferably 1-2:1.

[0023] The number average molecular weight of polytetramethylene glycol (PTMG) is 1000±50.

[0024] The organic solvent is selected from one of tetrahydrofuran and N,N-dimethylformamide. In order to facilitate post-processing, tetrahydrofuran is preferably used as the organic solvent.

[0025] The catalyst is selected from one or more of dibutyltin dilaurate and 2-ethyltin acetate; preferably, the catalyst consists of dibutyltin dilaurate and 2-ethyltin acetate, and the volume ratio of dibutyltin dilaurate to 2-ethyltin acetate is 1-3:1.

[0026] The reaction temperature of step (1) is 70-80°C.

[0027] The reaction time of step (1) is 2-3h.

[0028] The reaction in step (1) is carried out in a protective gas atmosphere.

[0029] The reaction temperature of step (2) is 70-75°C.

[0030] The reaction time of step (2) is 4-5h.

[0031] The reaction in step (2) is carried out in a protective gas atmosphere.

[0032] The reaction temperature of step (3) is 65-75°C.

[0033] The reaction time of step (3) is 4-5h.

[0034] The reaction in step (3) is carried out in a protective gas atmosphere.

[0035] The reaction temperature of step (4) is 40-45°C.

[0036] The reaction time of step (4) is 1-1.5h.

[0037] The reaction in step (4) is carried out in a protective gas atmosphere.

[0038] Preferably, the protective gas in steps (1), (2), (3) and (4) is nitrogen.

[0039] The preparation method of the present invention can adjust the mechanical properties of the prepared waterborne polyurethane by adjusting the molar ratio of (4-hydroxyphenyl) disulfide to 1,4-butanediol (SS:BDO). Mechanical property testing of waterborne polyurethanes prepared with SS:BDO ratios of 1 / 4, 2 / 3, 3 / 2, 4 / 1, and 5 / 0 revealed that a 3:2 molar ratio of (4-hydroxyphenyl) disulfide to 1,4-butanediol (SS:BDO) resulted in the best mechanical properties (maximum tensile strength) and a self-healing efficiency of 83.38%. The possible reasons are: as the SS content increases, the hard segment content increases, and its disulfide bonds will form hydrogen bonds, which will increase the strength of the overall waterborne polyurethane; BDO has a regular structure and is easy to crystallize, so as the BDO content increases, the crystallinity of the waterborne polyurethane will increase, which will also increase its tensile strength; the changes in the contents of the two are in a competitive relationship with the enhancement of the tensile strength of the waterborne polyurethane elastomer; therefore, the molar ratio of 4-hydroxyphenyl) disulfide to 1,4-butanediol has an optimal value SS:BDO of 3:2.

[0040] Varying the molar ratio of (4-hydroxyphenyl) disulfide to 1,4-butanediol (SS:BDO) has little effect on the stability of aqueous polyurethane emulsions (prepared by adding deionized water and stirring). Zeta potential tests were conducted on aqueous polyurethane emulsions prepared with SS:BDO ratios of 1 / 4, 2 / 3, 3 / 2, 4 / 1, and 5 / 0 (a zeta potential greater than 50 indicates high stability). The results showed excellent stability for all five ratios.

[0041] In view that commercial polytetrahydrofuran diol contains moisture usually, therefore, polytetrahydrofuran diol vacuumizes and removes the process of moisture usually before use.For example, vacuumize 2 hours to remove moisture wherein at 120 ℃.

[0042] According to the embodiments disclosed in the present invention, a specific solution of the method for preparing the waterborne polyurethane is:

[0043] (1) Dehydrated polytetramethylene glycol (PTMG-1000), isophorone diisocyanate (IPDI) and dibutyltin dilaurate (DBTDL) are reacted in a nitrogen atmosphere at 70-80°C for 2-3 hours; the molar ratio of polytetramethylene glycol to isophorone diisocyanate is 0.5-1:1

[0044] (2) After step (1) is completed, 2,2-dihydroxymethylpropionic acid (DMPA) and tetrahydrofuran (THF) are added to the reaction system and reacted in a nitrogen atmosphere at 70-75° C. for 4-5 hours; the molar ratio of 2,2-dihydroxymethylpropionic acid to isophorone diisocyanate in step (1) is 0.5-1:1;

[0045] (3) After step (2) is completed, isophorone diisocyanate (IPDI), (4-hydroxyphenyl) disulfide (SS), 1,4-butanediol (BDO), dibutyltin dilaurate (DBTDL) and 2-ethyltin acetate are added to the reaction system and reacted at 65-75°C in a nitrogen atmosphere for 4-5 hours; wherein the molar ratio of the total amount of isophorone diisocyanate, (4-hydroxyphenyl) disulfide and 1,4-butanediol to the diisocyanate of step (1) is 1-2:1; the molar ratio of the total amount of (4-hydroxyphenyl) disulfide and 1,4-butanediol to isophorone diisocyanate is 0.5-1:1; the molar ratio of (4-hydroxyphenyl) disulfide to 1,4-butanediol is 0.25-4:1, preferably 1-2:1; the volume ratio of dibutyltin dilaurate to 2-ethyltin acetate is 1-3:1;

[0046] (4) After step (3) is completed, the temperature is lowered to 40-45°C, triethylamine (TEA) is added, and the reaction is carried out for 1-1.5 hours to obtain waterborne polyurethane.

[0047] A second object of the present invention is to provide a waterborne polyurethane prepared by the preparation method described in the first object of the invention.

[0048] The aqueous polyurethane is added with deionized water and stirred to obtain an aqueous polyurethane emulsion. The aqueous polyurethane emulsion is poured into a PTFE mold, shaped at room temperature, and then heated at 70-80°C to obtain an aqueous polyurethane elastomer.

[0049] Compared with the prior art, the present invention has the following beneficial effects:

[0050] The existing process for preparing waterborne polyurethane using the prepolymerization method involves adding all the isocyanate at once for reaction; this results in the waterborne polyurethane produced generally having low tensile strength, and failing to achieve high tensile strength, emulsion stability, and good self-healing properties. The present invention significantly improves the tensile strength of the waterborne polyurethane produced by adjusting the timing of adding the isocyanate and adopting the process of "adding the same amount of diisocyanate in two steps (adding them in steps (1) and (3) respectively)."

[0051] The present invention selects polytetramethylene glycol (PTMG) as a soft segment, isophorone diisocyanate (IPDI) as a hard segment, and (4-hydroxyphenyl) disulfide (SS) as a chain extender. By adjusting the process steps, a waterborne polyurethane with high tensile strength, toughness, self-healing efficiency and stable waterborne emulsion is prepared.

[0052] In the present invention, unless otherwise specified, the room temperature is 20-30°C. BRIEF DESCRIPTION OF THE DRAWINGS

[0053] Figure 1 The stress-strain curves of the waterborne polyurethane elastomer prepared in Example 3 and after cutting and self-healing are shown; the abscissa is strain, the ordinate is stress, original refers to the uncut waterborne polyurethane elastomer, and healed refers to the waterborne polyurethane elastomer that was cut and self-healed in a 60°C oven for 12 hours;

[0054] Figure 2 The incision appearance of the waterborne polyurethane elastomer prepared in Example 3 after cutting was observed using a polarizing microscope;

[0055] Figure 3 The incision appearance of the waterborne polyurethane elastomer prepared in Example 3 observed with a polarizing microscope after being cut and then oven-dried at 60°C for 12 hours;

[0056] Figure 4 This is the Zeta potential diagram of the aqueous polyurethane emulsion prepared in Examples 1, 2, 3, 4, and 5; wherein the ordinate is the absolute value of the Zeta potential. DETAILED DESCRIPTION

[0057] The present invention will be described in detail below with reference to specific drawings and embodiments. It is necessary to point out that the following embodiments are only used to further illustrate the present invention and cannot be understood as limiting the scope of protection of the present invention. Some non-essential improvements and adjustments made by those skilled in the art to the present invention based on the contents of the present invention still fall within the scope of protection of the present invention.

[0058] The reagents used in the following examples and comparative examples are all commercially available products.

[0059] Polytetrahydrofuran diol (PTMG, Mn = 1000) was purchased from Shanghai Aladdin Biochemical Technology Co., Ltd.;

[0060] Isophorone diisocyanate (IPDI) was purchased from Shanghai Aladdin Biochemical Technology Co., Ltd.;

[0061] Dibutyltin dilaurate (DBTDL, 97.5%) was from J&K Scientific Ltd;

[0062] Tetrahydrofuran (THF) was from J&K Scientific Ltd;

[0063] 2,2-Dihydroxymethylpropionic acid (DMPA) was purchased from Alfa Aesar;

[0064] 1,4-Butanediol (BDO) was purchased from Alfa Aesar;

[0065] Bis(4-hydroxyphenyl)disulfide (MSDS) was purchased from Alfa Aesar.

[0066] Example 1

[0067] (1) polytetrahydrofuran diol was vacuumized 2 hours at 120 ℃ to remove moisture wherein.

[0068] (2) Weigh 0.005 mol of polytetramethylene glycol (PTMG) and 0.01 mol of isophorone diisocyanate (IPDI) into a three-necked flask, then add 50 μl of dibutyltin dilaurate (DBTDL) and react at 80°C in a nitrogen atmosphere for 2 h.

[0069] (3) 0.005 mol of 2,2-dihydroxymethylpropionic acid (DMPA) and 10 ml of tetrahydrofuran (THF) as a solvent were added to a three-necked flask and reacted at 70°C in a nitrogen atmosphere for 4 h.

[0070] (4) 0.005 mol of isophorone diisocyanate (IPDI), 0.001 mol of (4-hydroxyphenyl) disulfide (SS), and 0.004 mol of 1,4-butanediol (BDO) were added to a three-necked flask. 50 μl of dibutyltin dilaurate (DBTDL) and 30 μl of 2-ethyltin acetate were also added as catalysts. The mixture was reacted at 70 °C in a nitrogen atmosphere for 4 h.

[0071] (5) Cooling to 45°C, adding 0.005 mol of triethylamine (TEA), and reacting for 1 h to obtain waterborne polyurethane.

[0072] (6) Add deionized water and stir at high speed to obtain a water-based polyurethane emulsion.

[0073] (7) Pour the water-based polyurethane emulsion into a PTFE mold, place it at room temperature for 6 days, and then place it in an 80°C oven for 1 day to obtain a water-based polyurethane elastomer.

[0074] Example 2

[0075] (1) polytetrahydrofuran diol was vacuumized 2 hours at 120 ℃ to remove moisture wherein.

[0076] (2) Weigh 0.005 mol of polytetramethylene glycol (PTMG) and 0.01 mol of isophorone diisocyanate (IPDI) into a three-necked flask, then add 50 μl of dibutyltin dilaurate (DBTDL) and react at 80°C in a nitrogen atmosphere for 2 h.

[0077] (3) 0.005 mol of 2,2-dihydroxymethylpropionic acid (DMPA) and 10 ml of tetrahydrofuran (THF) as a solvent were added to a three-necked flask and reacted at 70°C in a nitrogen atmosphere for 4 h.

[0078] (4) 0.005 mol of isophorone diisocyanate (IPDI), 0.002 mol of (4-hydroxyphenyl) disulfide (SS), and 0.003 mol of 1,4-butanediol (BDO) were added to a three-necked flask. 50 μl of dibutyltin dilaurate (DBTDL) and 30 μl of 2-ethyltin acetate were also added as catalysts. The mixture was reacted at 70 °C in a nitrogen atmosphere for 4 h.

[0079] (5) Cooling to 45°C, adding 0.005 mol of triethylamine (TEA), and reacting for 1 h to obtain waterborne polyurethane.

[0080] (6) Add deionized water and stir at high speed to obtain a water-based polyurethane emulsion.

[0081] (7) Pour the water-based polyurethane emulsion into a PTFE mold, place it at room temperature for 6 days, and then place it in an 80°C oven for 1 day to obtain a water-based polyurethane elastomer.

[0082] Example 3

[0083] (1) polytetrahydrofuran diol was vacuumized 2 hours at 120 ℃ to remove moisture wherein.

[0084] (2) Weigh 0.005 mol of polytetramethylene glycol (PTMG) and 0.01 mol of isophorone diisocyanate (IPDI) into a three-necked flask, then add 50 μl of dibutyltin dilaurate (DBTDL) and react at 80°C in a nitrogen atmosphere for 2 h.

[0085] (3) 0.005 mol of 2,2-dihydroxymethylpropionic acid (DMPA) and 10 ml of tetrahydrofuran (THF) as a solvent were added to a three-necked flask and reacted at 70°C in a nitrogen atmosphere for 4 h.

[0086] (4) 0.005 mol of isophorone diisocyanate (IPDI), 0.003 mol of (4-hydroxyphenyl) disulfide (SS), and 0.002 mol of 1,4-butanediol (BDO) were added to a three-necked flask. 50 μl of dibutyltin dilaurate (DBTDL) and 30 μl of 2-ethyltin acetate were also added as catalysts. The mixture was reacted at 70 °C in a nitrogen atmosphere for 4 h.

[0087] (5) Cooling to 45°C, adding 0.005 mol of triethylamine (TEA), and reacting for 1 h to obtain waterborne polyurethane.

[0088] (6) Add deionized water and stir at high speed to obtain a water-based polyurethane emulsion.

[0089] (7) Pour the water-based polyurethane emulsion into a PTFE mold, place it at room temperature for 6 days, and then place it in an 80°C oven for 1 day to obtain a water-based polyurethane elastomer.

[0090] Example 4

[0091] (1) polytetrahydrofuran diol was vacuumized 2 hours at 120 ℃ to remove moisture wherein.

[0092] (2) Weigh 0.005 mol of polytetramethylene glycol (PTMG) and 0.01 mol of isophorone diisocyanate (IPDI) into a three-necked flask, then add 50 μl of dibutyltin dilaurate (DBTDL) and react at 80°C in a nitrogen atmosphere for 2 h.

[0093] (3) 0.005 mol of 2,2-dihydroxymethylpropionic acid (DMPA) and 10 ml of tetrahydrofuran (THF) as a solvent were added to a three-necked flask and reacted at 70°C in a nitrogen atmosphere for 4 h.

[0094] (4) 0.005 mol of isophorone diisocyanate (IPDI), 0.004 mol of (4-hydroxyphenyl) disulfide (SS), and 0.001 mol of 1,4-butanediol (BDO) were added to a three-necked flask. 50 μl of dibutyltin dilaurate (DBTDL) and 30 μl of 2-ethyltin acetate were also added as catalysts. The mixture was reacted at 70°C in a nitrogen atmosphere for 4 h.

[0095] (5) Cooling to 45°C, adding 0.005 mol of triethylamine (TEA), and reacting for 1 h to obtain waterborne polyurethane.

[0096] (6) Add deionized water and stir at high speed to obtain a water-based polyurethane emulsion.

[0097] (7) Pour the water-based polyurethane emulsion into a PTFE mold, place it at room temperature for 6 days, and then place it in an 80°C oven for 1 day to obtain a water-based polyurethane elastomer.

[0098] Example 5

[0099] (1) polytetrahydrofuran diol was vacuumized 2 hours at 120 ℃ to remove moisture wherein.

[0100] (2) Weigh 0.005 mol of polytetramethylene glycol (PTMG) and 0.01 mol of isophorone diisocyanate (IPDI) into a three-necked flask, then add 50 μl of dibutyltin dilaurate (DBTDL) and react at 80°C in a nitrogen atmosphere for 2 h.

[0101] (3) 0.005 mol of 2,2-dihydroxymethylpropionic acid (DMPA) and 10 ml of tetrahydrofuran (THF) as a solvent were added to a three-necked flask and reacted at 70°C in a nitrogen atmosphere for 4 h.

[0102] (4) Add 0.005 mol of isophorone diisocyanate (IPDI) and 0.005 mol of (4-hydroxyphenyl) disulfide (SS) to a three-necked flask, and add 50 μl of dibutyltin dilaurate (DBTDL) and 30 μl of 2-ethyltin acetate as catalysts. React at 70°C in a nitrogen atmosphere for 4 h.

[0103] (5) Cooling to 45°C, adding 0.005 mol of triethylamine (TEA), and reacting for 1 h to obtain waterborne polyurethane.

[0104] (6) Add deionized water and stir at high speed to obtain a water-based polyurethane emulsion.

[0105] (7) Pour the water-based polyurethane emulsion into a PTFE mold, place it at room temperature for 6 days, and then place it in an 80°C oven for 1 day to obtain a water-based polyurethane elastomer.

[0106] Comparative Example 1

[0107] (1) polytetrahydrofuran diol was vacuumized 2 hours at 120 ℃ to remove moisture wherein.

[0108] (2) Weigh 0.005 mol of polytetramethylene glycol (PTMG) and 0.015 mol of isophorone diisocyanate (IPDI) into a three-necked flask, then add 50 μl of dibutyltin dilaurate (DBTDL) and react at 80°C in a nitrogen atmosphere for 2 h.

[0109] (3) 0.005 mol of 2,2-dihydroxymethylpropionic acid (DMPA) and 10 ml of tetrahydrofuran (THF) as a solvent were added to a three-necked flask and reacted at 70°C in a nitrogen atmosphere for 4 h.

[0110] (4) 0.003 mol of (4-hydroxyphenyl) disulfide (SS) and 0.002 mol of 1,4-butanediol (BDO) were added to a three-necked flask, and 50 μl of dibutyltin dilaurate (DBTDL) and 30 μl of 2-ethyltin acetate were added as catalysts. The mixture was reacted at 70°C in a nitrogen atmosphere for 4 h.

[0111] (5) Cooling to 45°C, adding 0.005 mol of triethylamine (TEA), and reacting for 1 h to obtain waterborne polyurethane.

[0112] (6) Add deionized water and stir at high speed to obtain a water-based polyurethane emulsion.

[0113] (7) Pour the water-based polyurethane emulsion into a PTFE mold, place it at room temperature for 6 days, and then place it in an 80°C oven for 1 day to obtain a water-based polyurethane elastomer.

[0114] Performance Testing

[0115] 1. Mechanical properties test

[0116] The mechanical properties of the waterborne polyurethane elastomers prepared in Examples 1-5 and Comparative Example 1 were tested. The tests were performed according to the national standard number: GB / T 528-2009, standard name: Determination of tensile stress-strain properties of vulcanized rubber or thermoplastic rubber. For mechanical property measurements, a CMT4104 electric tensile testing machine (SANS Testing Machine Co., Ltd., Shenzhen, China) was used at ambient temperature (25°C) to test a specimen with a width of 4 mm, a gauge length of 75 mm, and a thickness of 1 mm: tensile rate = 100 mm / min1, sample length between the jaws = 35 mm. Deformation was evaluated based on the crosshead displacement. At least three samples were tested under each test condition. The test results are shown in Table 1.

[0117] Table 1

[0118] Tensile strength (MPa) Example 1 13.2 Example 2 14.3 Example 3 26.9 Example 4 17.9 Example 5 14.9 Comparative Example 1 12.4

[0119] Compared to Examples 1, 2, 3, 4, and 5, only the molar ratio of SS to BDO changed. From Example 1 to Example 5, the SS content gradually increased while the BDO content gradually decreased. Within the SS to BDO molar ratio range of (1:4) to (5:0), the tensile strength of the prepared waterborne polyurethane elastomers first increased and then decreased with increasing SS content. When SS:BDO = 3:2 (Example 3), the prepared waterborne polyurethane elastomer achieved the highest tensile strength.

[0120] The only difference between Example 3 and Comparative Example 1 is the preparation process. In Example 3, isophorone diisocyanate was added in steps (1) and (3), respectively, while in Comparative Example 1, isophorone diisocyanate was added in step (1). Table 1 shows that the tensile strength of Example 3 is 26.9 MPa, while the tensile strength of Comparative Example 1 is 12.4 MPa. The tensile strength of Example 3 is 117% higher than that of Comparative Example 1. This indicates that, compared with existing processes, the preparation method of the present invention can significantly improve the tensile strength of waterborne polyurethane.

[0121] 2. Self-healing performance test

[0122] The self-healing performance test of the waterborne polyurethane elastomer prepared in Example 3 was carried out. Two standard specimens were made using the waterborne polyurethane elastomer prepared in Example 3. One of the specimens was used as a standard comparison specimen, i.e., the original, and the mechanical properties test was carried out directly; the other specimen was cut from the middle, and the cut ends of the damaged specimen were aligned and placed in a 60°C oven for 12 hours (i.e., healed), and then the mechanical properties test was carried out. The test method was based on GB / T 528-2009 Determination of tensile stress-strain properties of vulcanized rubber or thermoplastic rubber. The test results are shown in the figure. Figure 1The self-healing efficiency is obtained by integrating the stress-strain curves of the damaged and healed spline with the initial spline. Figure 1 It shows that the self-healing efficiency of the specimen reaches 83.38% after being placed in a 60℃ oven for 12h.

[0123] Polarized light microscope was used to observe the appearance of the incision before and after healing after the spline was cut from the middle. Figure 2 、 Figure 3 shown. Figure 2 This is the appearance of the cut after the spline is cut from the middle. Figure 3 The cut surface of the specimen after being cut in the middle, aligned, and placed in a 60°C oven for 12 hours. Figure 2-Figure 3 The middle part with a relatively dark color and vertical line is the incision. Figure 2-Figure 3 It can be seen that the incision has basically healed over time.

[0124] 3. Stability Test

[0125] The waterborne polyurethane emulsions prepared in Examples 1-5 were tested for Zeta potential. Zeta potential is a measure of the strength of mutual repulsion or attraction between particles. One of the Zeta potential tests involves testing the stability of waterborne polyurethane using electrophoresis. Using the principle of Doppler electrophoretic light scattering, the electrophoretic velocity of the particles is indirectly measured by measuring the change in the frequency or phase of light. The larger the absolute value obtained, the more stable the emulsion. The test results are shown in Figure 2. Figure 4 shown. Figure 4 When the absolute value of the Zeta potential (ordinate) is greater than 50, it proves that the emulsion is very stable. Figure 4 It shows that the aqueous polyurethane emulsions prepared in Examples 1-5 have excellent stability and can be stably stored for more than 6 months.

Claims

1. A method for preparing waterborne polyurethane, characterized in that: The preparation method comprises the following steps: (1) under catalyst action, polytetrahydrofuran diol and diisocyanate react; (2) After step (1), 2,2-dihydroxymethylpropionic acid and an organic solvent are added to continue the reaction; (3) After step (2), materials and catalyst are added to continue the reaction; wherein the materials are composed of diisocyanate, (4-hydroxyphenyl) disulfide and 1,4-butanediol. (4) After step (3), triethylamine is added to continue the reaction to obtain the waterborne polyurethane; Wherein, the diisocyanate in step (1) is the same as that in step (3).

2. The preparation method according to claim 1, wherein The diisocyanate is isophorone diisocyanate.

3. The preparation method according to claim 1, wherein In step (1), the molar ratio of polytetrahydrofuran diol to diisocyanate is 1:2±0.

1.

4. The preparation method according to claim 1, wherein The molar ratio of the 2,2-dihydroxymethylpropionic acid in step (2) to the polytetrahydrofuran diol in step (1) is 1±0.1:

1.

5. The preparation method according to claim 1, wherein The molar ratio of the diisocyanate in step (3) to the diisocyanate in step (1) is 0.5±0.1:

1.

6. The preparation method according to claim 1, wherein The molar ratio of the total amount of (4-hydroxyphenyl) disulfide and 1,4-butanediol in step (3) to the polytetrahydrofuran diol in step (1) is 1±0.1:

1.

7. The preparation method according to claim 1, wherein In step (3), the molar ratio of (4-hydroxyphenyl) disulfide to 1,4-butanediol is 0.25-4:1, preferably 1-2:

1.

8. The preparation method according to claim 1, wherein The number-average molecular weight of polytetrahydrofuran diol is 1000 ± 50; or / and, The organic solvent is selected from one or more of tetrahydrofuran and N,N-dimethylformamide; or / and, The catalyst is selected from one or more of dibutyltin dilaurate and 2-ethyltin acetate; preferably, the catalyst consists of dibutyltin dilaurate and 2-ethyltin acetate, and the volume ratio of dibutyltin dilaurate to 2-ethyltin acetate is 1-3:

1.

9. The preparation method according to claim 1, wherein The reaction temperature of step (1) is 70-80°C; or / and, The reaction time of step (1) is 2-3h; or / and, The reaction of step (1) is carried out in a protective gas atmosphere; or / and, The reaction temperature of step (2) is 70-75°C; or / and, The reaction time of step (2) is 4-5h; or / and, The reaction in step (2) is carried out in a protective gas atmosphere; or / and, The reaction temperature of step (3) is 65-75°C; or / and, The reaction time of step (3) is 4-5h; or / and, The reaction in step (3) is carried out in a protective gas atmosphere; or / and, The reaction temperature of step (4) is 40-45°C; or / and, The reaction time of step (4) is 1-1.5h; or / and, The reaction of step (4) is carried out in a protective gas atmosphere; or / and, Preferably, the protective gas is nitrogen.

10. A waterborne polyurethane, characterized in that The waterborne polyurethane is prepared by the preparation method according to any one of claims 1 to 9.

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