Sulfur-containing polyurethane microspheres, and a method for preparing a sulfur-containing polyurethane microsphere-toughened epoxy resin composite

Abstract

The application discloses a kind of sulfur-containing polyurethane microspheres, the preparation method of sulfur-containing polyurethane microspheres toughened epoxy resin composite.The sulfur-containing polyurethane microspheres powder is dispersed in organic solvent, then epoxy resin is added, to prepare sulfur-containing polyurethane microspheres / epoxy resin dispersion;Epoxy resin and curing agent are added again, mixed, poured and cured, to obtain sulfur-containing polyurethane microspheres / epoxy resin composite;The toughness and strength of the obtained epoxy resin composite are improved compared with pure epoxy resin.Sulfur-containing polyurethane microspheres are polythiourethane microspheres or polyurethane / polythiourethane core-shell microspheres.Polyurethane / polythiourethane core-shell microspheres synthesized by precipitation polymerization, with polyurethane as core and polythiourethane as shell, are size-controllable;Sulfur-containing polythiourethane microspheres with polyurethane as "soft core" and polythiourethane as shell can effectively toughen epoxy resin.

Description

Technical Field

[0001] This invention belongs to the field of epoxy resin toughening technology, and specifically relates to a method for preparing sulfur-containing polyurethane microspheres and sulfur-containing polyurethane microsphere-toughened epoxy resin composite materials. Background Technology

[0002] Epoxy resin is a high-molecular-weight polymer containing polar groups such as epoxy groups, hydroxyl groups, and ether bonds in its molecular structure. It possesses high strength and excellent insulation, mechanical properties, and heat resistance, making it widely used in electronic components, aerospace, civil engineering, and sporting goods, among other fields. However, unmodified epoxy resin exhibits high crosslinking density after curing, resulting in lower toughness and impact resistance. Furthermore, its poor weather resistance hinders its further application.

[0003] Toughening is an important method to improve the strength and toughness of epoxy resins. Currently, the main methods for toughening epoxy resins include thermoplastic resin toughening, interpenetrating network toughening, hyperbranched resin toughening, and nanofiller toughening. These toughening methods also have some drawbacks. For example, while thermoplastic resin toughening can effectively improve the toughness of epoxy resins, the poor solubility of thermoplastic resins themselves increases the viscosity of the system, which is detrimental to actual production and operation. Interpenetrating network toughening can improve the toughness of epoxy resins, but it suffers from poor interpenetration. Hyperbranched resin toughening of epoxy resins, while improving the flexibility of epoxy resins, can lead to phase separation and longer curing time. Nanofiller toughening of epoxy resins suffers from poor compatibility and uneven dispersion, thus affecting the toughening effect.

[0004] Core-shell microspheres are a novel composite material consisting of a core and an outer shell covering its surface. Core-shell microspheres can be broadly classified into inorganic and organic types. Organic core-shell microspheres can be further divided into soft-core / hard-shell structures and hard-core / soft-shell structures, with applications varying according to their structural differences. Core-shell microspheres used to toughen epoxy resins generally employ a soft-core / hard-shell structure. The soft core absorbs energy, while the hard shell enhances the composite's strength, resulting in excellent toughening. Common core-shell particles used for toughening epoxy resins are polyacrylates. The core is typically made of polybutylene acrylate (PB), while the shell is usually made of polymethyl methacrylate (PMMA). Polyacrylate core-shell particle toughening of epoxy resins can significantly improve the toughness of epoxy resins without much decrease in tensile strength, making it an effective method for toughening epoxy resins. However, when using polyacrylate core-shell particles to toughen epoxy resins, although PB exhibits good flexibility at room temperature, its elasticity decreases at lower temperatures, exhibiting a "hot-sticky, cold-brittle" phenomenon, reducing its toughening effect on epoxy resins. On the other hand, since the glass transition temperature of polymethyl methacrylate is around 100°C, using it as a shell will reduce the heat resistance of epoxy resin. Summary of the Invention

[0005] Based on the technical problems pointed out in the background, the present invention provides a method for preparing a sulfur-containing polyurethane microsphere-toughened epoxy resin composite material.

[0006] To achieve the above-mentioned objectives, the technical solution adopted by this invention is as follows: A method for preparing a sulfur-containing polyurethane microsphere-toughened epoxy resin composite material, the specific steps of which are as follows: (1) Disperse sulfur-containing polyurethane microsphere powder in an organic solvent, then weigh an appropriate amount of epoxy resin and add it to a three-necked flask. Heat and stir at 65°C for 0.5-5 h. After the reaction is completed, cool down and discharge the material. Remove the solvent by rotary evaporation to obtain sulfur-containing polyurethane microsphere / epoxy resin dispersion; wherein, the sulfur-containing polyurethane microsphere is polyurethane microsphere or polyurethane / polyurethane core-shell microsphere. (2) Mix the above sulfur-containing polyurethane microspheres / epoxy resin dispersion, epoxy resin and curing agent, stir evenly, remove air bubbles by vacuuming, and then pour evenly onto the template and cure at a certain temperature to obtain core-shell microspheres / epoxy resin composite material.

[0007] Furthermore, the organic solvent is any one or more of ethanol, acetone, propylene glycol methyl ether, ethylene glycol methyl ether, ethyl acetate, and toluene.

[0008] The epoxy resin is any one or more of E51, E54, E44, and E20.

[0009] Furthermore, the amount of organic solvent used is 1 to 10 times the mass of sulfur-containing polyurethane microsphere powder; the amount of epoxy resin used is 100:1 to 30 by mass ratio to the amount of sulfur-containing polyurethane microspheres; the reaction temperature is 20 to 80°C, and the reaction time is 0.5 to 8 h.

[0010] Furthermore, the epoxy resin curing agent is any one or more of 2-methylimidazole, 2,4-dimethylimidazole, 2-ethyl-4-methylimidazole, the adduct of 2-methylimidazole and butyl glycidyl ether (704 curing agent), the adduct of 2-methylimidazole and 2-ethylhexyl glycidyl ether (705 curing agent), and polythiol and isocyanate modified imidazole.

[0011] Furthermore, the amount of epoxy resin curing agent used is 1% to 60% of the total mass of epoxy resin used; the stirring temperature is in the range of 40 to 60°C, the stirring time is 5 to 10 min; the curing temperature is 20 to 180°C, and the curing time is 0.5 to 5 h.

[0012] The polyurethane / polysulfuric acid ester core-shell microspheres of this invention are prepared by the following method: a hydrophilic monomer is added to a reaction vessel, and after dehydration, a polyisocyanate is added. The reaction is carried out at 25-90°C for 2-4 h to obtain a hydrophilic polyisocyanate. The hydrophilic polyisocyanate and thiol monomer are dissolved in an organic solvent, and the polyurethane microsphere powder is dispersed in the organic solvent. A catalyst is added, and the reaction is carried out at room temperature for 2-4 h to obtain a polyurethane / polysulfuric acid ester microsphere dispersion. The polyurethane / polysulfuric acid ester core-shell microsphere dispersion is filtered and dried to obtain a polyurethane / polysulfuric acid ester core-shell microsphere solid powder.

[0013] Furthermore, the hydrophilic monomer is one or more of dimethylolpropionic acid, dimethylolbutyric acid, polyethylene glycol, polyethylene glycol monomethyl ether (MPEG), and polyethylene glycol-polypropylene glycol block copolymer. The molecular weight is 600-2000.

[0014] The polyisocyanate monomer is any one or more of polymethylene polyphenyl isocyanate (PAPI), toluene diisocyanate trimer (TDI trimer), and diphenylmethane diisocyanate (MDI).

[0015] The thiol monomer is any one or more of trimethylolpropane tris(3-mercaptopropionate) (TMMP), pentaerythritol tetra(3-mercaptopropionate), 1,2-ethylenedithiol (EDT), 1,6-hexanedithiol (DMH), and polyethylene glycol dithiol.

[0016] The solvent is any one or more of anhydrous ethanol, acetonitrile, acetone, butanone, and tetrahydrofuran.

[0017] The catalyst is any one or more of potassium hydroxide, sodium hydroxide, triethylamine, trimethylamine, and ammonia.

[0018] Furthermore, the thiol monomer and hydrophilic polyisocyanate are fed in a molar ratio of NCO:SH = 1: (0.1~3). The weight ratio of the polyurethane microsphere powder to the total mass of the hydrophilic polyisocyanate and thiol monomer is (0~2):1.

[0019] Furthermore, the hydrophilic monomer is 1% to 20% of the total mass of the polyisocyanate; even further, the catalyst content is 0.1% to 3% of the total mass of the reactants; the solvent content is added according to the solid content of the system being 10%; the reaction temperature is room temperature (25°C); and the reaction time is 1 to 8 hours.

[0020] Furthermore, the polyurethane microsphere powder was prepared according to the preparation method of polyurethane microspheres disclosed in CN116655886A. The preparation method is as follows: a small molecule diol, a large molecule polyol, and a hydrophilic monomer were added to a reaction vessel, and after removing water, diisocyanate was added. The reaction was carried out at 25~120℃ for 4~8 h, followed by the addition of polyisocyanate. During the process, a solvent was added to reduce the viscosity of the reaction system. The system was cooled to 25~50℃, a neutralizing agent was added, and the mixture was stirred evenly. Water was added to emulsify the mixture to obtain a polyurethane prepolymer dispersion. Polyamine was added to extend the chain, and the mixture was reacted at room temperature to obtain a polyurethane microsphere emulsion. The polyurethane microsphere emulsion was demulsified with dilute hydrochloric acid, filtered, and dried to obtain polyurethane microsphere powder.

[0021] This method first employs an aqueous polyurethane synthesis process to prepare polyurethane microspheres; secondly, it uses precipitation polymerization to synthesize polyurethane / polysulfurethane core-shell microspheres with a polyurethane core and a polysulfurethane shell. Next, the polyurethane / polysulfurethane core-shell microspheres are mixed with epoxy resin to obtain a core-shell microsphere / epoxy resin dispersion; finally, a curing agent is added to prepare a polyurethane / polysulfurethane core-shell microsphere-toughened epoxy resin composite material.

[0022] The method for preparing core-shell microspheres in this invention is simple and the size of the microspheres can be controlled; the polyurethane / polysulfuric acid ester core-shell microspheres have good dispersibility in epoxy resin; using polyurethane with excellent low-temperature performance as a "soft core" can effectively toughen the epoxy resin; the toughness and strength of the resulting epoxy resin composite material are improved compared with pure epoxy resin.

[0023] This invention provides a method for preparing polyurethane microsphere-toughened epoxy resin composites, as well as a method for preparing polyurethane / polyurethane core-shell microspheres and polyurethane / polyurethane core-shell microsphere epoxy resin composites. The preparation method is simple, and the prepared polyurethane / polyurethane core-shell microspheres have uniform particle size. The obtained polyurethane / polyurethane core-shell microspheres have good compatibility with epoxy resin. The polyurethane / polyurethane core-shell microsphere epoxy resin composites can improve the toughness and strength of epoxy resin. Attached Figure Description

[0024] Figure 1 This is a scanning electron microscope image of the polyurethane / polythiourethane core-shell microspheres synthesized in Example 1 of the present invention.

[0025] Figure 2 The diagram shows the mechanical properties of polyurethane / polythiourethane core-shell microsphere epoxy resin composites with different core-shell ratios synthesized in Example 1 of this invention.

[0026] Figure 3 Figures showing the mechanical properties of epoxy resin composites toughened with polyurethane microspheres at different dosages. Detailed Implementation

[0027] Preferred embodiments of the present invention will now be described in detail with reference to specific examples. Example 1

[0028] (1) Synthesis of polyurethane microspheres Prepared according to method CN116655886A.

[0029] Weigh 1.50 g (0.022 mol) of dihydroxypropionic acid (DMPA), 3.50 g (0.007 mol) of polyether polyol (N210), and 0.315 g (0.007 mol) of 1,4-butanediol (BDO) into a three-necked flask, stir until homogeneous, and dehydrate at 160℃ for 7-8 min. Cool to 90℃, and add 10 g (0.090 mol) of isophorone diisocyanate (IPDI) dropwise. React for 4 h to obtain a polyurethane prepolymer. Then add 1.8 g (0.009 mol) of HDI trimer. During this process, the viscosity of the system increases; add 5 g of butanone to reduce the viscosity. After the system temperature drops to room temperature, add 0.94 g (0.009 mol) of triethylamine (TEA), stir at high speed until homogeneous, and then add 41 g of deionized water. Stir to disperse and obtain a polyurethane prepolymer dispersion.

[0030] 1.85 g of diethylenetriamine (DETA) was dissolved in 5.56 g of deionized water and added dropwise to the dispersion. The mixture was stirred for 5 h to obtain a polyurethane microsphere emulsion.

[0031] The emulsion was added dropwise to 5% dilute hydrochloric acid to break the emulsion, filtered, washed, and dried to obtain polyurethane microsphere powder. The particle size of the microspheres was measured to be 311 nm.

[0032] (2) Synthesis of polyurethane / polythiourethane core-shell microspheres 0.3 g (0.00015 mol) of polyethylene glycol monomethyl ether (MPEG-2000) was weighed and added to a three-necked flask. The mixture was stirred and dehydrated at 160 °C for 7–8 min. The temperature was then lowered to 90 °C, and 3 g (0.0214 mol) of polymethylene polyphenyl isocyanate (PAPI) was added dropwise. The reaction was allowed to proceed for 4 h to obtain a polyurethane prepolymer. 3.3 g of the above polyurethane prepolymer and 2.823 g (0.02125 mol) of trimethylolpropane tris(3-mercaptopropionate) (TMMP) were weighed and dispersed in 10.36 g of acetonitrile solution. 0.77 g of polyurethane microsphere powder was dispersed in 10 g of anhydrous ethanol and added dropwise to the above acetonitrile solution. One drop of triethylamine (TEA) was then added as a catalyst, and the reaction was carried out at room temperature for 2.5 h to obtain a polyurethane / polysulfuric acid core-shell microsphere dispersion. The polyurethane / polysulfuric acid core-shell microsphere emulsion was filtered and dried to obtain a polyurethane / polysulfuric acid core-shell microsphere solid powder. The mass ratio of polyurethane microspheres to polysulfuric acid was 1:8. Its scanning electron microscope image is shown below. Figure 1 As shown.

[0033] (3) Preparation of core-shell microspheres and epoxy resin dispersion Weigh 2g of polyurethane / polysulfuric acid core-shell microsphere powder and dissolve it in 20g of anhydrous ethanol. Then weigh 10g of E-51 type epoxy resin and add it to a three-necked flask. React at 65℃ for 5 h, cool down and discharge the material, remove the solvent by rotary evaporation to obtain the core-shell microsphere / epoxy resin dispersion.

[0034] (4) Polyurethane / polysulfuric acid ester core-shell microsphere epoxy resin composite material 12 g of core-shell microsphere / epoxy resin dispersion, 15 g of E-51 type epoxy resin, and 1.25 g of 2-ethyl-4-methylimidazole were weighed, mixed and stirred evenly, and the mixture was vacuumed to remove air bubbles. The mixture was then poured into a mold and cured at 60℃ for 2 h and then at 120℃ for 2 h to obtain a polyurethane / polysulfuric acid ester core-shell microsphere epoxy resin composite material. The microsphere content was 8% of the weight of the epoxy resin.

[0035] Following the same experimental procedures, the ratio of polyurethane microspheres to polyurethane sulfide was adjusted to obtain polyurethane / polyurethane core-shell microspheres with ratios of 1:1, 1:2, 1:5, and 1:10. Polyurethane / polyurethane core-shell microsphere epoxy resin composites were then prepared, and their properties were determined. Figure 2 . Example 2

[0036] (1) Synthesis of polyurethane microspheres Same as Example 1.

[0037] (2) Synthesis of polyurethane / polythiourethane core-shell microspheres 0.3 g (0.0045 mol) of dimethylolpropionic acid (DMPA) was weighed and added to a three-necked flask. The mixture was stirred and dehydrated at 160 °C for 7–8 min. The temperature was lowered to 90 °C, and 3 g (0.0214 mol) of polymethylene polyphenyl isocyanate (PAPI) was added dropwise. The reaction was allowed to proceed for 4 h to obtain a polyurethane prepolymer. 3.3 g of the above polyurethane prepolymer and 2.245 g (0.0169 mol) of trimethylolpropane tris(3-mercaptopropionate) (TMMP) were weighed and dispersed in 10.36 g of acetone solution. 0.69 g of polyurethane microsphere powder from step (1) was dispersed in 10 g of anhydrous ethanol and added dropwise to the above acetone solution. Then, 1 drop of triethylamine (TEA) was added as a catalyst, and the mixture was reacted at room temperature for 4 h to obtain a polyurethane / polysulfuric acid core-shell microsphere dispersion. The polyurethane / polysulfuric acid core-shell microsphere emulsion was filtered and dried to obtain polyurethane / polysulfuric acid core-shell microsphere solid powder.

[0038] (3) Preparation of core-shell microspheres and epoxy resin dispersion Weigh 2g of polyurethane / polysulfuric acid core-shell microsphere powder and dissolve it in 20g of ethyl acetate. Then weigh 10g of E-51 type epoxy resin and add it to a three-necked flask. React at 70℃ for 4h, cool down and discharge the material, remove the solvent by rotary evaporation to obtain the core-shell microsphere / epoxy resin dispersion.

[0039] (4) Polyurethane / polysulfuric acid ester core-shell microsphere epoxy resin composite material Weigh 12 g of core-shell microsphere / epoxy resin dispersion, 15 g of E-51 type epoxy resin, and 1.25 g of 2-methylimidazole, mix and stir evenly, remove air bubbles by vacuuming, pour into a mold, and cure at 100℃ for 4 h to obtain polyurethane / polysulfuric acid core-shell microsphere epoxy resin composite material. The microsphere content is 8% of the weight of epoxy resin. Example 3

[0040] (1) Synthesis of polyurethane microspheres Same as Example 1.

[0041] (2) Synthesis of polyurethane / polythiourethane core-shell microspheres 0.3 g (0.00015 mol) of polyethylene glycol monomethyl ether (MPEG-2000) was weighed and added to a three-necked flask. The mixture was stirred and dehydrated at 160 °C for 7–8 min. The temperature was then lowered to 65 °C, and 3 g (0.024 mol) of diphenylmethane diisocyanate (MDI) was added dropwise. The reaction was allowed to proceed for 6 h to obtain a polyurethane prepolymer. 3.3 g of the polyurethane prepolymer and 1.123 g (0.02385 mol) of 1,2-ethylenedithiol (EDT) were weighed and dispersed in 7.904 g of acetonitrile solution. 0.553 g of polyurethane microsphere powder from step (1) was dispersed in 8 g of tetrahydrofuran and added dropwise to the above acetonitrile solution. Then, 1 drop of trimethylamine was added as a catalyst, and the reaction was carried out at room temperature for 3 h to obtain a polyurethane / polysulfuric acid core-shell microsphere dispersion. The polyurethane / polysulfuric acid core-shell microsphere emulsion was filtered and dried to obtain polyurethane / polysulfuric acid core-shell microsphere solid powder.

[0042] (3) Preparation of core-shell microspheres and epoxy resin dispersion Weigh 2g of polyurethane / polysulfuric acid core-shell microsphere powder and dissolve it in 20g of anhydrous ethanol. Then weigh 10g of E-54 type epoxy resin and add it to a three-necked flask. React at 45℃ for 8h, cool down and discharge the material, remove the solvent by rotary evaporation to obtain the core-shell microsphere / epoxy resin dispersion.

[0043] (4) Polyurethane / polysulfuric acid ester core-shell microsphere epoxy resin composite material Weigh 12 g of core-shell microsphere / epoxy resin dispersion, 15 g of E-54 type epoxy resin, and 1.25 g of 2-ethyl-4-methylimidazole, mix and stir evenly, remove air bubbles by vacuuming, pour into a mold, and cure at 60℃ for 2 h, then at 120℃ for 2 h to obtain a polyurethane / polysulfuric acid ester core-shell microsphere epoxy resin composite material. The microsphere content is 8% of the weight of epoxy resin. Example 4

[0044] (1) Synthesis of polyurethane microspheres Same as Example 1.

[0045] (2) Synthesis of polyurethane / polythiourethane core-shell microspheres 0.3 g (0.00015 mol) of polyethylene glycol monomethyl ether (MPEG-2000) was weighed and added to a three-necked flask. The mixture was stirred and dehydrated at 160 °C for 7–8 min. The temperature was then lowered to 80 °C, and 3 g (0.0214 mol) of polymethylene polyphenyl isocyanate (PAPI) was added dropwise. The reaction was allowed to proceed for 5 h to obtain a polyurethane prepolymer. 3.3 g of the above polyurethane prepolymer and 5.2 g (0.02125 mol) of pentaerythritol tetra(3-mercaptopropionate) were weighed and dispersed in 28.25 g of acetonitrile solution. 1.0625 g of polyurethane microsphere powder from step (1) was dispersed in 10 g of anhydrous ethanol and added dropwise to the above acetonitrile solution. Then, 1 drop of ammonia was added as a catalyst, and the reaction was carried out at room temperature for 2.5 h to obtain a polyurethane / polysulfuric acid core-shell microsphere dispersion. The polyurethane / polysulfuric acid core-shell microsphere emulsion was filtered and dried to obtain polyurethane / polysulfuric acid core-shell microsphere solid powder.

[0046] (3) Preparation of core-shell microspheres and epoxy resin dispersion Weigh 2g of polyurethane / polysulfuric acid core-shell microsphere powder and dissolve it in 20g of anhydrous ethanol. Then weigh 10g of E-51 type epoxy resin and add it to a three-necked flask. React at 65℃ for 5 h, cool down and discharge the material, remove the solvent by rotary evaporation to obtain the core-shell microsphere / epoxy resin dispersion.

[0047] (4) Polyurethane / polysulfuric acid ester core-shell microsphere toughened epoxy resin Weigh 12 g of core-shell microsphere / epoxy resin dispersion, 15 g of E-51 type epoxy resin, and 1.25 g of the adduct of 2-methylimidazole and 2-ethylhexyl glycidyl ether (705 curing agent). Mix and stir evenly, remove air bubbles by vacuuming, pour into a mold, and cure at 60℃ for 2 h and then at 120℃ for 2 h to obtain a polyurethane / polysulfuric acid ester core-shell microsphere toughened epoxy resin composite material. The microsphere content is 8% of the weight of epoxy resin. Example 5

[0048] (1) Synthesis of polyurethane microspheres Same as Example 1.

[0049] (2) Synthesis of polyurethane / polythiourethane core-shell microspheres 0.3 g (0.0003 mol) of polyethylene glycol (PEG-2000) was weighed and added to a three-necked flask. The mixture was stirred and dehydrated at 120 °C for 7–8 min. The temperature was then lowered to 90 °C, and 3 g (0.0345 mol) of toluene diisocyanate (TDI) was added dropwise. The reaction was allowed to proceed for 4 h to obtain a polyurethane prepolymer. 3.3 g of the polyurethane prepolymer and 2.567 g (0.03415 mol) of 1,6-hexanedithiol (DMH) were weighed and dispersed in 16.402 g of anhydrous ethanol solution. 0.733 g of polyurethane microsphere powder from step (1) was dispersed in 10 g of acetonitrile and added dropwise to the above anhydrous ethanol solution. Then, 1 drop of triethylamine (TEA) was added as a catalyst, and the reaction was carried out at room temperature for 2.5 h to obtain a polyurethane / polysulfuric acid core-shell microsphere dispersion. The polyurethane / polysulfuric acid core-shell microsphere emulsion was filtered and dried to obtain polyurethane / polysulfuric acid core-shell microsphere solid powder.

[0050] (3) Preparation of core-shell microspheres and epoxy resin dispersion Weigh 2g of polyurethane / polysulfuric acid core-shell microsphere powder and dissolve it in 20g of anhydrous ethanol. Then weigh 10g of E-51 type epoxy resin and add it to a three-necked flask. React at 70℃ for 4h, cool down and discharge the material, remove the solvent by rotary evaporation to obtain the core-shell microsphere / epoxy resin dispersion.

[0051] (4) Polyurethane / polysulfuric acid ester core-shell microsphere toughened epoxy resin Weigh 12 g of core-shell microsphere / epoxy resin dispersion, 15 g of E-51 type epoxy resin, and 1.25 g of the adduct of 2-methylimidazole and butyl glycidyl ether (704 curing agent). Mix and stir evenly, remove air bubbles under vacuum, pour into a mold, and cure at 60℃ for 2 h and 70℃ for 4 h to obtain a polyurethane / polysulfuric acid ester core-shell microsphere toughened epoxy resin composite material. The microsphere content is 8% of the epoxy resin weight. Example 6

[0052] (1) Synthesis of polyurethane microspheres Same as Example 1.

[0053] (2) Synthesis of polyurethane / polythiourethane core-shell microspheres 0.3 g (0.00015 mol) of polyethylene glycol monomethyl ether (MPEG-2000) was weighed and added to a three-necked flask. The mixture was stirred and dehydrated at 160 °C for 7–8 min. The temperature was then lowered to 75 °C, and 3 g (0.0214 mol) of polymethylene polyphenyl isocyanate (PAPI) was added dropwise. The reaction was allowed to proceed for 5 h to obtain a polyurethane prepolymer. 3.3 g of the above polyurethane prepolymer and 2.823 g (0.02125 mol) of trimethylolpropane tris(3-mercaptopropionate) (TMMP) were weighed and dispersed in 10.36 g of acetonitrile solution. 0.77 g of polyurethane microsphere powder from step (1) was dispersed in 10 g of tetrahydrofuran and added dropwise to the above acetonitrile solution. Then, 1 drop of sodium hydroxide (NaOH) was added as a catalyst, and the reaction was carried out at room temperature for 3 h to obtain a polyurethane / polysulfuric acid core-shell microsphere dispersion. The polyurethane / polysulfuric acid core-shell microsphere emulsion was filtered and dried to obtain polyurethane / polysulfuric acid core-shell microsphere solid powder.

[0054] (3) Preparation of core-shell microspheres and epoxy resin dispersion Weigh 2g of polyurethane / polysulfuric acid core-shell microsphere powder and dissolve it in 20g of anhydrous ethanol. Then weigh 10g of E-44 type epoxy resin and add it to a three-necked flask. React at 60℃ for 6 h, cool down and discharge the material, remove the solvent by rotary evaporation to obtain the core-shell microsphere / epoxy resin dispersion.

[0055] (4) Polyurethane / polysulfuric acid ester core-shell microsphere epoxy resin composite material Weigh 12 g of core-shell polyurethane microspheres / epoxy resin dispersion, 15 g of E-44 type epoxy resin, and 1.25 g of 2-ethyl-4-methylimidazole, mix and stir evenly, remove air bubbles under vacuum, pour into a mold, and cure at 60℃ for 2 h and 70℃ for 4 h to obtain polyurethane / polysulfuric acid ester core-shell microsphere toughened epoxy resin composite material. The microsphere content is 8% of the epoxy resin weight. Example 7

[0056] (1) Synthesis of polyurethane microspheres 0.3 g (0.00015 mol) of polyethylene glycol monomethyl ether (MPEG-2000) was weighed and added to a three-necked flask. The mixture was stirred and dehydrated at 160 °C for 7–8 min. The temperature was lowered to 90 °C, and 3 g (0.0214 mol) of polymethylene polyphenyl isocyanate (PAPI) was added dropwise. The reaction was allowed to proceed for 4 h to obtain a polyurethane prepolymer. 3.3 g of the polyurethane prepolymer and 2.823 g (0.02125 mol) of trimethylolpropane tris(3-mercaptopropionate) (TMMP) were weighed and dispersed in 10.36 g of acetonitrile solution. One drop of triethylamine (TEA) was added as a catalyst, and the reaction was allowed to proceed for 2.5 h at room temperature to obtain a polysulfuric acid urethane microsphere dispersion. The polysulfuric acid urethane microsphere emulsion was filtered and dried to obtain a solid powder of polysulfuric acid urethane microspheres.

[0057] (2) Preparation of polyurethane microspheres and epoxy resin dispersion Weigh 2g of polyurethane microsphere powder and dissolve it in 20g of anhydrous ethanol. Then weigh 10g of E-51 type epoxy resin and add it to a three-necked flask. React at 65℃ for 5 h, cool down and discharge the material, remove the solvent by rotary evaporation to obtain polyurethane microsphere / epoxy resin dispersion.

[0058] (3) Polyurethane microsphere epoxy resin composite material Weigh 12 g of polyurethane microspheres / epoxy resin dispersion, 15 g of E-51 type epoxy resin, and 1.25 g of 2-ethyl-4-methylimidazole, mix and stir evenly, remove air bubbles by vacuuming, pour into a mold, and cure at 60℃ for 2 h, then at 120℃ for 2 h to obtain polyurethane microsphere epoxy resin composite material. The microsphere content is 8% of the weight of epoxy resin.

[0059] Following the same experimental procedure, the ratio of polyurethane microspheres to epoxy resin was adjusted to obtain epoxy resin composites with polyurethane microsphere contents of 2%, 5%, and 10%, respectively. Their properties were then measured. Figure 3 .

[0060] The properties of the polyurethane microsphere / epoxy resin composites prepared in Examples 1-7 were tested according to the following methods: Tensile property testing: The tensile properties of the specimens were tested using a TY8000 universal tensile testing machine according to GB / T 2567-2008 standard. The specimen dimensions were specified as 4 mm × 2 mm, the gauge length was 20 mm, the tensile speed was selected as 10 mm / min, and the test was conducted at room temperature. Five specimens were selected for testing for each formulation, and the average value was taken.

[0061] Impact performance testing: The impact performance of the specimens was tested using an XJU-2.75 cantilever beam impact testing machine according to GB / T 1843-2008 standard. The specimen dimensions were specified as 100 mm × 10 mm × 4 mm, and the test was conducted at room temperature. Seven specimens were selected for testing for each formulation, and the average value was taken.

[0062] Table 1. Tensile strength and impact strength data for each embodiment.

[0063] The preferred embodiments of the present invention have been described in detail above. However, the present invention is not limited to the specific details in the above embodiments. Within the scope of the technical concept of the present invention, various simple modifications can be made to the technical solution of the present invention, and these simple modifications all fall within the protection scope of the present invention.

Claims

1. A method for preparing a sulfur-containing polyurethane microsphere-toughened epoxy resin composite material, characterized in that, The specific steps include: dispersing sulfur-containing polyurethane microsphere powder in a first organic solvent, then adding epoxy resin, heating and stirring at 20-80℃ for 0.5-8 h, cooling and discharging after the reaction, removing the solvent by rotary evaporation to obtain a sulfur-containing polyurethane microsphere / epoxy resin dispersion; mixing the sulfur-containing polyurethane microsphere / epoxy resin dispersion, epoxy resin and curing agent, stirring evenly at 40-60℃, removing air bubbles by vacuuming, and then pouring for curing at a curing temperature of 20-180℃ for 0.5-5 h to obtain a sulfur-containing polyurethane microsphere / epoxy resin composite material; wherein the sulfur-containing polyurethane microspheres are polyurethane microspheres or polyurethane / polyurethane core-shell microspheres; The preparation method of the sulfur-containing polyurethane microspheres includes the following specific steps: adding a hydrophilic monomer to a reaction vessel, removing water, adding a polyisocyanate, and reacting at 25~90℃ for 2~4 h to obtain a hydrophilic polyisocyanate; dissolving the hydrophilic polyisocyanate and thiol monomer in a second organic solvent, dispersing the polyurethane microsphere powder in the second organic solvent, adding a catalyst, and reacting at room temperature for 2~4 h to obtain a sulfur-containing polyurethane microsphere dispersion; filtering and drying the sulfur-containing polyurethane microsphere dispersion to obtain a sulfur-containing polyurethane microsphere solid powder; the weight ratio of the polyurethane microsphere powder to the total mass of the hydrophilic polyisocyanate and thiol monomer is (0~2):

1.

2. The method for preparing the sulfur-containing polyurethane microsphere-toughened epoxy resin composite material according to claim 1, characterized in that, The amount of the first organic solvent is 1 to 10 times the mass of the sulfur-containing polyurethane microsphere powder; the first organic solvent is any one or more of ethanol, acetone, propylene glycol methyl ether, ethylene glycol methyl ether, ethyl acetate, and toluene.

3. The method for preparing the sulfur-containing polyurethane microsphere-toughened epoxy resin composite material according to claim 1, characterized in that, The curing agent is used in an amount of 1% to 60% of the total mass of the epoxy resin used; the curing agent is any one or more of 2-methylimidazole, 2,4-dimethylimidazole, 2-ethyl-4-methylimidazole, adduct of 2-methylimidazole and butyl glycidyl ether, adduct of 2-methylimidazole and 2-ethylhexyl glycidyl ether, and polythiol and isocyanate modified imidazole.

4. The method for preparing the sulfur-containing polyurethane microsphere-toughened epoxy resin composite material according to claim 1, characterized in that, The mass ratio of epoxy resin to sulfur-containing polyurethane microspheres is 100:1~30; the epoxy resin is any one or more of E51, E54, E44, and E20.

5. The method for preparing the sulfur-containing polyurethane microsphere-toughened epoxy resin composite material according to claim 1, characterized in that, In the preparation method of the sulfur-containing polyurethane microspheres, the hydrophilic monomer is 1% to 20% of the total mass of the polyisocyanate; the thiol monomer and the hydrophilic polyisocyanate are fed in a molar ratio of NCO:SH = 1: (0.1 to 3).

6. The method for preparing the sulfur-containing polyurethane microsphere-toughened epoxy resin composite material according to claim 1, characterized in that, In the preparation method of the sulfur-containing polyurethane microspheres, the content of the catalyst is 0.1% to 3% of the total mass of the reactants; the content of the second organic solvent is added according to the solid content of the system being 10%.

7. The method for preparing the sulfur-containing polyurethane microsphere-toughened epoxy resin composite material according to claim 1, characterized in that, The method for preparing sulfur-containing polyurethane microspheres includes the following steps for synthesizing polyurethane microsphere powder: Small molecule diols, macromolecule polyols, and hydrophilic monomers are added to a reaction vessel. After dehydration, diisocyanate is added, and the reaction is carried out at 25-120°C for 4-8 hours. Then, polyisocyanate is added, with a third solvent added during the process to reduce the viscosity of the reaction system. The system is cooled to 25-50°C, a neutralizing agent is added, and the mixture is stirred until homogeneous. Water is added to emulsify the mixture to obtain a polyurethane prepolymer dispersion. Polyamine is added for chain extension, and the mixture is reacted at room temperature to obtain a polyurethane microsphere emulsion. The polyurethane microsphere emulsion is demulsified with dilute hydrochloric acid, filtered, and dried to obtain polyurethane microsphere powder.

8. The method for preparing the sulfur-containing polyurethane microsphere-toughened epoxy resin composite material according to claim 1, characterized in that, In the preparation method of the sulfur-containing polyurethane microspheres, the hydrophilic monomer is one or more of dimethylolpropionic acid, dimethylolbutyric acid, polyethylene glycol, polyethylene glycol monomethyl ether, and polyethylene glycol-polypropylene glycol block copolymer, with a molecular weight of 600-2000; the polyisocyanate monomer is any one or more of polymethylene polyphenyl isocyanate, toluene diisocyanate trimer, and diphenylmethane diisocyanate; the thiol monomer is any one or more of trimethylolpropane tris(3-mercaptopropionate), pentaerythritol tetra(3-mercaptopropionate), 1,2-ethanedithiol, 1,6-hexanedithiol, and polyethylene glycol dithiol; the second organic solvent is any one or more of anhydrous ethanol, acetonitrile, acetone, butanone, and tetrahydrofuran; and the catalyst is any one or more of potassium hydroxide, sodium hydroxide, triethylamine, trimethylamine, and ammonia.

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