Polyurethane microspheres, polyurethane microsphere toughened epoxy resin composite material and preparation method thereof

Abstract

The application belongs to the technical field of materials, and particularly relates to a polyurethane microsphere, a polyurethane microsphere toughened epoxy resin composite material and a preparation method thereof. The method first prepares the polyurethane microsphere by using a water-based polyurethane synthesis process, then mixes the polyurethane microsphere and the epoxy resin to react at high temperature to obtain a polyurethane microsphere / epoxy resin dispersion, and finally adds a curing agent to prepare the polyurethane microsphere toughened epoxy resin composite material. The method for preparing the microsphere is simple, environment-friendly and controllable in size; the polyurethane microsphere has good dispersibility in the epoxy resin; and the mechanical properties of the obtained composite material are improved, and the toughness and strength are both improved.

Description

Technical Field

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

[0002] Epoxy resin is a thermosetting resin containing two or more epoxy groups in its molecule. Epoxy resins possess excellent thermal stability, chemical stability, corrosion resistance, electrical insulation, and good adhesion, and are widely used in coatings, adhesives, and aerospace applications. However, due to the high crosslinking density and the presence of numerous rigid groups in its molecular structure, epoxy resins exhibit drawbacks such as high brittleness, poor impact resistance, and susceptibility to cracking after curing, thus limiting their application range.

[0003] While conventional methods for toughening epoxy resins can improve their toughness, they also lead to a decrease in heat resistance, making it difficult to meet the demands of more demanding applications. Rubber elastomers, such as amine-terminated nitrile butadiene rubber (NBR), epoxy-terminated NBR, polysulfide rubber, and silicone rubber, can enhance the toughness of epoxy resins. By modifying and dispersing NBR and styrene-butadiene rubber into epoxy resins, the modified rubber particles help to induce cracks and voids in the blend, thereby improving the toughness of the epoxy resin. However, this method leads to a decrease in the glass transition temperature of the epoxy resin system, resulting in reduced heat resistance. Commonly used thermoplastic resins include polycarbonate and polyetherketone. Adding them to epoxy resins can effectively improve their toughness without affecting the mechanical properties of the epoxy resin itself. However, thermoplastic resins have poor solubility and flowability, and when added to epoxy resins, they tend to agglomerate, thus affecting the toughening effect.

[0004] Polyurethane, a thermoplastic polymer, is commonly used as a toughening agent for epoxy resins. Polyurethane possesses high impact strength and good compatibility with epoxy resins. There are two main methods for toughening epoxy resins with polyurethane: physical blending and copolymerization modification. In physical blending, a suitable amount of polyurethane dispersed in the epoxy resin provides good toughening; however, the size of the polyurethane domains is difficult to control, leading to a weakened toughening effect. Summary of the Invention

[0005] Based on the technical problems identified in the background section, this invention provides a method for preparing polyurethane microspheres and a polyurethane microsphere-toughened epoxy resin composite material, as well as the method for preparing the same. The method first employs an aqueous polyurethane synthesis process to prepare polyurethane microspheres, a simple and environmentally friendly preparation method that allows for controllable microsphere structure. Then, the polyurethane microspheres are mixed with epoxy resin to obtain a polyurethane microsphere / epoxy resin dispersion. Finally, a curing agent is added to prepare the polyurethane microsphere-toughened epoxy resin composite material. This invention provides a simple and environmentally friendly method for preparing microspheres, allowing for controllable microsphere size; the polyurethane microspheres exhibit good dispersibility in epoxy resin; and the resulting composite material demonstrates improved mechanical properties, with enhanced toughness and strength.

[0006] To achieve the above objectives, the present invention is implemented through the following technical solution:

[0007] A method for synthesizing polyurethane microspheres, the specific steps of which are as follows:

[0008] a1. Add small molecule diol, macromolecule polyol, and hydrophilic monomer to a reaction vessel, remove water, add diisocyanate, react at 60-120℃ for 4-5 hours, then add polyisocyanate. During the process, add solvent to reduce the viscosity of the reaction system; cool the system to 25-50℃, add neutralizing agent, and stir evenly; emulsify with water to obtain a polyurethane prepolymer dispersion.

[0009] The molar ratio of macromolecular polyols to small molecule diols is 1:0 to 7.

[0010] The hydrophilic monomer accounts for 1% to 50% of the total mass of the reactants; preferably, the hydrophilic monomer accounts for 5% to 15% of the total mass of the reactants.

[0011] Diisocyanate is added according to the molar ratio of NCO:OH in the reaction system being 1.2 to 2.5:1;

[0012] The polyisocyanate accounts for 0% to 50% of the total mass of the reactants, preferably 10% to 20% of the total mass of the reactants;

[0013] The amount of water added should be based on a solid content of 25% in the system;

[0014] a2. Add a polyamine aqueous solution to the above dispersion for chain extension, and add a trace amount of dibutyltin dilaurate (DBTDL) catalyst dropwise. React at room temperature for 1 to 8 hours to obtain a polyurethane microsphere emulsion. The amount of polyamine used is 0.5 to 10 times the number of unreacted isocyanate groups in the system.

[0015] a3. Demulsification, filtration, washing, and drying are performed to obtain polyurethane microsphere powder with a particle size of 50 nm to 2 μm.

[0016] Furthermore, the small molecule diol is any one or more of butanediol, ethylene glycol, pentanediol, isopentanediol, neopentanediol propylene glycol, 1,4-butanediol, diethylene glycol, and octanediol;

[0017] The macromolecular polyol is any one or more of polycaprolactone diol, polybutylene adipate diol, polytetrahydrofuran diol, polypropylene oxide diol, polycarbonate diol, and polyether polyol, with a molecular weight of 500-4000.

[0018] 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;

[0019] The diisocyanate mentioned is any one or more of diphenylmethane diisocyanate (MDI), toluene diisocyanate (TDI), isophorone diisocyanate (IPDI), 1,6-hexyl diisocyanate (HDI), and dicyclohexylmethane diisocyanate (HMDI).

[0020] The polyisocyanate is: 1,6-hexyl diisocyanate (HDI) trimer, toluene diisocyanate (TDI) trimer, isophorone diisocyanate (IPDI) trimer; the solvent is any one or more of acetone, butanone, 1-methyl-2-pyrrolidone (NMP), and N,N-dimethylformamide (DY-8);

[0021] The neutralizing agent is any one or more of triethylamine, triethanolamine, N-methyldiethanolamine, trimethylamine, and ammonia; the polyamine is any one or more of ethylenediamine, diethylenetriamine, triethylenetetramine, isophorone diamine, and hydrazine hydrate.

[0022] This invention also provides a polyurethane microsphere-toughened epoxy resin composite material, mainly composed of polyurethane microspheres and epoxy resin, wherein the particle size of the polyurethane microspheres is between 50 nm and 2 μm, and the weight ratio of epoxy resin to polyurethane microspheres is 100:(1-10); preferably, the weight ratio of epoxy resin to polyurethane microspheres is 100:(5-8). The epoxy resin selected in this invention is any one or more of E51, E54, E44, and E20.

[0023] This invention also provides a method for preparing the above-mentioned polyurethane microsphere-toughened epoxy resin composite material, specifically including the following steps:

[0024] (1) Disperse polyurethane microsphere powder with a particle size of 50nm~2μm in an organic solvent, add amine to adjust the pH value to 7~9, then weigh epoxy resin and add it to a three-necked flask, heat and stir at 20℃~80℃ for 0.5~5h, cool down and discharge the material after the reaction is completed, remove the solvent by rotary evaporation, and obtain polyurethane microsphere / epoxy resin dispersion;

[0025] (2) Mix the polyurethane microspheres / epoxy resin dispersion, epoxy resin and curing agent, stir evenly, remove air bubbles by vacuuming, and then pour evenly onto the template for curing to obtain polyurethane microspheres / epoxy resin composite material.

[0026] Furthermore, in step (1), the mass ratio of epoxy resin to polyurethane microspheres is 5 to 10:1, preferably 5:1;

[0027] Further, the amount of organic solvent used in step (1) is 1 to 10 times the mass of polyurethane microsphere powder; preferably 10 times; the organic solvent is any one or more of ethanol, acetone, propylene glycol methyl ether, ethylene glycol methyl ether, ethyl acetate, and toluene.

[0028] Further, the amine mentioned in step (1) is any one or more of trimethylamine, triethylamine, tetramethylammonium hydroxide, and tetraethylammonium hydroxide.

[0029] Further, the amount of epoxy resin curing agent used in step (2) is 1% to 10% of the total mass of epoxy resin used;

[0030] Furthermore, the stirring temperature in step (2) is 40–60°C, and the stirring time is 5–10 min;

[0031] Further, the curing temperature in step (2) is 20-180℃ and the curing time is 0.5-5h; specifically, the curing in step (2) is to first cure at 60℃ for 2-4h and then at 70-120℃ for 2-4h.

[0032] Further, the epoxy resin curing agent mentioned in step (2) 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.

[0033] Compared with existing technologies, the beneficial effects of this invention are as follows: This invention provides a polyurethane microsphere-toughened epoxy resin composite material and its preparation method. A polyurethane microsphere emulsion is synthesized by interfacial polymerization of diisocyanate monomers with small-molecule diols, large-molecule polyols, hydrophilic monomers, and polyamines for chain extension. This preparation method is simple, and the prepared polyurethane microspheres have a small particle size and good compatibility with epoxy resin. This invention disperses the microspheres in anhydrous ethanol solvent and adds triethylamine to make the dispersion weakly alkaline, which allows for better dispersion in the epoxy resin matrix, forming a uniformly dispersed and stable toughened epoxy resin system. The polyurethane microsphere-toughened epoxy resin composite material prepared by this invention improves the toughness and strength of the epoxy resin composite material. Attached image description:

[0034] Figure 1 This is a scanning electron microscope image of the polyurethane microspheres synthesized in Example 1 of the present invention;

[0035] Figure 2 The polyurethane microspheres synthesized in Example 1 of this invention are used to toughen the mechanical properties of epoxy resin. Detailed Implementation

[0036] Preferred embodiments of the present invention will now be described in detail with reference to specific examples.

[0037] In the specific implementation method, the polyurethane microsphere / epoxy resin composite material spline casting mold conforms to the national standard GB / T2567-2008 (tensile spline) or GB / T1843-2008 (impact spline).

[0038] Specific implementation of the mechanical property testing of polyurethane microsphere / epoxy resin composite material specimens:

[0039] Tensile property testing: The tensile properties of the specimens were tested using a TY8000 universal tensile testing machine according to GB / T2567-2008 standard. The specimen dimensions were specified as 4mm × 2mm, the gauge length was 20mm, the tensile speed was selected as 10mm / min, and the test was conducted at room temperature. Five specimens were selected for testing for each formulation, and the average value was taken.

[0040] Impact performance testing: The impact performance of the specimens was tested using an XJU-2.75 cantilever beam impact testing machine according to GB / T1843-2008 standard. The specimen dimensions were specified as 100mm × 10mm × 4mm, and the test was conducted at room temperature. Five specimens were selected for testing for each formulation, and the average value was taken.

[0041] Example 1

[0042] (1) Synthesis of polyurethane microspheres

[0043] 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) and add them to a three-necked flask. Stir well and dehydrate at 160 °C for 7–8 min. Cool to 90 °C and add 10 g (0.090 mol) of isophorone diisocyanate (IPDI). React for 4 h to obtain polyurethane prepolymer. During the process, the viscosity of the system increases. Add 5 g of butanone to reduce the viscosity of the system. After the system temperature cooled to room temperature, 0.94 g (0.009 mol) of triethylamine (TEA) was added and stirred at high speed until homogeneous. Then, 41 g of deionized water was added and stirred to disperse the mixture, yielding a polyurethane prepolymer dispersion. 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 hours to obtain a polyurethane microsphere emulsion. The emulsion was then added dropwise to 5% dilute hydrochloric acid to break the emulsion. The emulsion was filtered, washed, and dried to obtain polyurethane microsphere powder. The average particle size of the microspheres was measured to be 350 nm, and the yield was 95%.

[0044] (2) Preparation of polyurethane microspheres and epoxy resin dispersion

[0045] Weigh 2g of polyurethane microsphere powder and dissolve it in 20g of anhydrous ethanol. Add 0.15g of triethylamine (TEA) dropwise until the solution is weakly alkaline. Then weigh 10g of E-51 type epoxy resin and add it to a three-necked flask. React at 65℃ for 5h. Cool down and discharge the material. Remove the solvent by rotary evaporation to obtain a polyurethane microsphere / epoxy resin dispersion.

[0046] (3) Polyurethane microsphere-toughened epoxy resin

[0047] Weigh 12g of polyurethane microspheres / epoxy resin dispersion, 90g of E-51 type epoxy resin and 5g of 2-ethyl-4-methylimidazole, mix and stir evenly, remove air bubbles by vacuuming, pour into a mold, cure at 60℃ for 2h and at 70℃ for 4h to obtain polyurethane microsphere toughened epoxy resin composite material.

[0048] Example 2

[0049] (1) Synthesis of polyurethane microspheres

[0050] Weigh 1.50 g (0.022 mol) of dihydroxypropionic acid (DMPA) and 20 g (0.02 mol) of polyether polyol (N220) into a three-necked flask, stir until homogeneous, and dehydrate at 160 °C for 7–8 min. Cool to 80 °C, and add 8.483 g (0.076 mol) of isophorone diisocyanate (IPDI) dropwise. React for 5 h to obtain a polyurethane prepolymer. During the process, the viscosity of the system increases; therefore, 5 g of butanone is added to reduce the viscosity. After the system temperature drops to room temperature, add 0.962 g (0.009 mol) of 85% triethylamine (TEA), stir at high speed until homogeneous, and continue to add 85.708 g of deionized water. Stir to disperse and obtain a polyurethane prepolymer dispersion. Dissolve 1.165 g of diethylenetriamine (DETA) in 3.32 g of deionized water and add it dropwise to the dispersion. Stir for 5 h to obtain a polyurethane preemulsion. The emulsion was added dropwise to 5% dilute hydrochloric acid to break the emulsion, then filtered, washed, and dried to obtain polyurethane microsphere powder. The average particle size of the microspheres was measured to be 370 nm, and the yield was 98%.

[0051] (2) Preparation of polyurethane microspheres and epoxy resin dispersion

[0052] Weigh 3g of polyurethane microsphere powder and dissolve it in 30g of anhydrous ethanol. Add 0.25g of triethylamine (TEA) dropwise until the solution is weakly alkaline. Then weigh 15g of E-51 type epoxy resin and add it to a three-necked flask. React at 65℃ for 5h, cool down and discharge the material. Remove the solvent by rotary evaporation to obtain a polyurethane microsphere / epoxy resin dispersion.

[0053] (3) Polyurethane microsphere-toughened epoxy resin

[0054] Weigh 12g of polyurethane microspheres / epoxy resin dispersion, 90g of E-51 type epoxy resin and 5g of 2-ethyl-4-methylimidazole, mix and stir evenly, remove air bubbles by vacuuming, pour into a mold, cure at 60℃ for 2h and at 100℃ for 2h to obtain polyurethane microsphere toughened epoxy resin composite material.

[0055] Example 3

[0056] (1) Synthesis of polyurethane microspheres

[0057] 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) and add them to a three-necked flask. Stir well and dehydrate at 160 °C for 7–8 min. Cool to 75 °C and add 10 g (0.090 mol) of 1,6-hexyl diisocyanate (HDI) dropwise. React for 5 h to obtain polyurethane prepolymer. During the process, the viscosity of the system increases. Add 5 g of butanone to reduce the viscosity of the system. After the system temperature cooled to room temperature, 0.94 g (0.009 mol) of triethylamine (TEA) was added and stirred at high speed until homogeneous. Then, 41 g of deionized water was added and stirred to disperse the mixture, yielding a polyurethane prepolymer dispersion. 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 hours to obtain a polyurethane microsphere emulsion. The emulsion was then added dropwise to 5% dilute hydrochloric acid to break the emulsion. The emulsion was filtered, washed, and dried to obtain polyurethane microsphere powder. The average particle size of the microspheres was measured to be 500 nm, and the yield was 92%.

[0058] (2) Preparation of polyurethane microspheres and epoxy resin dispersion

[0059] Weigh 2g of polyurethane microsphere powder and dissolve it in 20g of anhydrous ethanol. Add 0.15g of triethylamine (TEA) dropwise until the solution is weakly alkaline. Then weigh 10g of E-51 type epoxy resin and add it to a three-necked flask. React at 70℃ for 5h. Cool down and discharge the material. Remove the solvent by rotary evaporation to obtain a polyurethane microsphere / epoxy resin dispersion.

[0060] (3) Polyurethane microsphere-toughened epoxy resin

[0061] Weigh 12g of polyurethane microspheres / epoxy resin dispersion, 90g of E-51 type epoxy resin and 5g of 2-ethyl-4-methylimidazole, mix and stir evenly, remove air bubbles by vacuuming, pour into a mold, cure at 60℃ for 2h and at 120℃ for 2h to obtain polyurethane microsphere toughened epoxy resin composite material.

[0062] Example 4

[0063] (1) Synthesis of polyurethane microspheres

[0064] Weigh 1.20 g (0.0179 mol) of dihydroxypropionic acid (DMPA), 1.35 g (0.000675 mol) of polyethylene glycol monomethyl ether (MPEG-2000), 0.2025 g (0.002025 mol) of polyether polyol (N3O3), and 0.693 g (0.0154 mol) of 1,4-butanediol (BDO) and add them to a three-necked flask. Stir well and dehydrate at 160 °C for 7–8 min. Cool to 90 °C and add 10 g (0.090 mol) of isophorone diisocyanate (IPDI). React for 5 h to obtain polyurethane prepolymer. During the process, the viscosity of the system increases. Add 5 g of butanone to reduce the viscosity of the system. After the system temperature cooled to room temperature, 0.94 g (0.009 mol) of triethylamine (TEA) was added and stirred at high speed until homogeneous. Then, 41 g of deionized water was added and stirred to disperse the mixture, yielding a polyurethane prepolymer dispersion. 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 hours to obtain a polyurethane preemulsion. The emulsion was then added dropwise to 5% dilute hydrochloric acid to break the emulsion. The emulsion was filtered, washed, and dried to obtain polyurethane microsphere powder. The average particle size of the microspheres was measured to be 290 nm, with a yield of 99%.

[0065] (2) Preparation of polyurethane microspheres and epoxy resin dispersion

[0066] Weigh 2g of polyurethane microsphere powder and dissolve it in 20g of anhydrous ethanol. Add 0.15g of triethylamine (TEA) dropwise until the solution is weakly alkaline. Then weigh 10g of E-51 type epoxy resin and add it to a three-necked flask. React at 80℃ for 5h. Cool down and discharge the material. Remove the solvent by rotary evaporation to obtain a polyurethane microsphere / epoxy resin dispersion.

[0067] (3) Polyurethane microsphere-toughened epoxy resin

[0068] Weigh 12g of polyurethane microspheres / epoxy resin dispersion, 90g of E-51 type epoxy resin and 5g of 2,4-dimethylimidazole, mix and stir evenly, remove air bubbles by vacuuming, pour into a mold, cure at 60℃ for 2h and at 120℃ for 2h to obtain polyurethane microsphere toughened epoxy resin composite material.

[0069] Example 5

[0070] (1) Synthesis of polyurethane microspheres

[0071] Weigh 1.50 g (0.022 mol) of dihydroxypropionic acid (DMPA), 4 g (0.004 mol) of polycarbonate diol (PCDL), and 0.45 g (0.01 mol) of 1,4-butanediol (BDO) and add them to a three-necked flask. Stir well and dehydrate at 160 °C for 7–8 min. Cool to 80 °C and add 10 g (0.090 mol) of isophorone diisocyanate (IPDI) dropwise. React for 5 h to obtain a polyurethane prepolymer. During the process, the viscosity of the system increases. Add 5 g of butanone to reduce the viscosity of the system. After the system temperature cooled to room temperature, 0.94 g (0.009 mol) of triethylamine (TEA) was added and stirred at high speed until homogeneous. Then, 42.85 g of deionized water was added and stirred to disperse the mixture, yielding a polyurethane prepolymer dispersion. 1.62 g of ethylenediamine (EDA) was dissolved in 6.48 g of deionized water and added dropwise to the dispersion. The mixture was stirred for 5 hours to obtain a polyurethane microsphere emulsion. The emulsion was then added dropwise to 5% dilute hydrochloric acid to break the emulsion. The emulsion was filtered, washed, and dried to obtain polyurethane microsphere powder. The microsphere particle size was measured to be 1050 nm, and the yield was 97%.

[0072] (2) Preparation of polyurethane microspheres and epoxy resin dispersion

[0073] Weigh 2g of polyurethane microsphere powder and dissolve it in 20g of anhydrous ethanol. Add 0.15g of triethylamine (TEA) dropwise until the solution is weakly alkaline. Then weigh 10g of E-54 type epoxy resin and add it to a three-necked flask. React at 65℃ for 5h. Cool down and discharge the material. Remove the solvent by rotary evaporation to obtain a polyurethane microsphere / epoxy resin dispersion.

[0074] (3) Polyurethane microsphere-toughened epoxy resin

[0075] Weigh 12g of polyurethane microspheres / epoxy resin dispersion, 90g of E-54 type epoxy resin and 5g of 2-ethyl-4-methylimidazole, mix and stir evenly, remove air bubbles by vacuuming, pour into a mold, cure at 60℃ for 4h and at 100℃ for 2h to obtain polyurethane microsphere toughened epoxy resin composite material.

[0076] Example 6

[0077] (1) Synthesis of polyurethane microspheres

[0078] Weigh 1.50 g (0.021 mol) of dimethylolbutyric acid (DMBA), 3.75 g (0.0075 mol) of polyether polyol (N210), and 0.3375 g (0.007 mol) of 1,4-butanediol (BDO) and add them to a three-necked flask. Stir well and dehydrate at 160 °C for 7–8 min. Cool to 90 °C and add 10 g (0.090 mol) of isophorone diisocyanate (IPDI). React for 4 h to obtain polyurethane prepolymer. During the process, the viscosity of the system increases. Add 5 g of acetone to reduce the viscosity of the system. After the system temperature cooled to room temperature, 0.94 g (0.009 mol) of triethylamine (TEA) was added and stirred at high speed until homogeneous. Then, 41.76 g of deionized water was added and stirred to disperse the mixture, yielding a polyurethane prepolymer dispersion. 1.62 g of ethylenediamine (EDA) was dissolved in 6.48 g of deionized water and added dropwise to the dispersion. The mixture was stirred for 5 hours to obtain a polyurethane microsphere emulsion. The emulsion was then added dropwise to 5% dilute hydrochloric acid to break the emulsion. The emulsion was filtered, washed, and dried to obtain polyurethane microsphere powder. The average particle size of the microspheres was measured to be 800 nm, and the yield was 98%.

[0079] (2) Preparation of polyurethane microspheres and epoxy resin dispersion

[0080] Weigh 2g of polyurethane microsphere powder and dissolve it in 20g of anhydrous ethanol. Add 0.15g of triethylamine (TEA) dropwise until the solution is weakly alkaline. Then weigh 10g of E-44 type epoxy resin and add it to a three-necked flask. React at 60℃ for 6h, cool down and discharge the material. Remove the solvent by rotary evaporation to obtain a polyurethane microsphere / epoxy resin dispersion.

[0081] (3) Polyurethane microsphere-toughened epoxy resin

[0082] Weigh 12g of polyurethane microspheres / epoxy resin dispersion, 90g of E-44 type epoxy resin and 5g of 2-ethyl-4-methylimidazole, mix and stir evenly, remove air bubbles by vacuuming, pour into a mold, cure at 60℃ for 2h and at 70℃ for 4h to obtain polyurethane microsphere toughened epoxy resin composite material.

[0083] Example 7

[0084] (1) Synthesis of polyurethane microspheres

[0085] 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) and add them to a three-necked flask. Stir well and dehydrate at 160 °C for 7–8 min. Cool to 90 °C and add 10 g (0.090 mol) of isophorone diisocyanate (IPDI). React for 4 h to obtain polyurethane prepolymer. During the process, the viscosity of the system increases. Add 5 g of butanone to reduce the viscosity of the system. After the system temperature cooled to room temperature, 0.94 g (0.009 mol) of triethylamine (TEA) was added and stirred at high speed until homogeneous. Then, 41 g of deionized water was added and stirred to disperse the mixture, yielding a polyurethane prepolymer dispersion. 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 hours to obtain a polyurethane microsphere emulsion. The emulsion was then added dropwise to 5% dilute hydrochloric acid to break the emulsion. The emulsion was filtered, washed, and dried to obtain polyurethane microsphere powder. The average particle size of the microspheres was measured to be 350 nm, and the yield was 96%.

[0086] (2) Preparation of polyurethane microspheres and epoxy resin dispersion

[0087] Weigh 2g of polyurethane microsphere powder and dissolve it in 20g of anhydrous ethanol. Add 0.15g of tetraethylamine hydroxide until the solution is weakly alkaline. Then weigh 10g of E-51 type epoxy resin and add it to a three-necked flask. React at 65℃ for 5h. Cool down and discharge the material. Remove the solvent by rotary evaporation to obtain a polyurethane microsphere / epoxy resin dispersion.

[0088] (3) Polyurethane microsphere-toughened epoxy resin

[0089] Weigh 12g of polyurethane microspheres / epoxy resin dispersion, 90g of E-51 type epoxy resin and 5g of 2-methylimidazole and butyl glycidyl ether adduct (704 curing agent), mix and stir evenly, remove air bubbles by vacuuming, pour into a mold, cure at 60℃ for 2h and at 70℃ for 4h to obtain polyurethane microsphere toughened epoxy resin composite material.

[0090] Example 8

[0091] (1) Synthesis of polyurethane microspheres

[0092] Weigh 1.50 g (0.022 mol) of dihydroxypropionic acid (DMPA), 6.50 g (0.013 mol) of polyether polyol (N210), and 0.585 g (0.013 mol) of 1,4-butanediol (BDO) and add them to a three-necked flask. Stir well and dehydrate at 160 °C for 7–8 min. Cool to 90 °C and add 6.4 g (0.058 mol) of isophorone diisocyanate (IPDI). React for 4 h to obtain a polyurethane prepolymer. Then add 1.9 g (0.0094 mol) of HDI trimer and add one drop of dibutyltin dilaurate (DBTDL). During the process, the viscosity of the system increases. Add 5 g of butanone to reduce the viscosity of the system. After the system temperature cooled to room temperature, 0.94 g (0.009 mol) of triethylamine (TEA) was added and stirred at high speed until homogeneous. Then, 51.82 g of deionized water was added and stirred to disperse the mixture, yielding a polyurethane prepolymer dispersion. 0.656 g of diethylenetriamine (DETA) was dissolved in 1.935 g of deionized water and added dropwise to the dispersion. The mixture was stirred for 5 hours to obtain a polyurethane microsphere emulsion. The emulsion was then added dropwise to 5% dilute hydrochloric acid to break the emulsion. The emulsion was filtered, washed, and dried to obtain polyurethane microsphere powder. The microsphere particle size was measured to be 220 nm, and the yield was 98%.

[0093] (2) Preparation of polyurethane microspheres and epoxy resin dispersion

[0094] Weigh 3.5g of polyurethane microsphere powder and dissolve it in 35g of anhydrous ethanol. Add 0.32g of triethylamine (TEA) dropwise until the solution is weakly alkaline. Then weigh 17.5g of E-51 type epoxy resin and add it to a three-necked flask. React at 65℃ for 5h. Cool down and discharge the material. Remove the solvent by rotary evaporation to obtain a polyurethane microsphere / epoxy resin dispersion.

[0095] (3) Polyurethane microsphere-toughened epoxy resin

[0096] Weigh 21g of polyurethane microspheres / epoxy resin dispersion, 26.25g of E-51 type epoxy resin and 2.19g of 2-ethyl-4-methylimidazole, mix and stir evenly, remove air bubbles by vacuuming, pour into a mold, cure at 60℃ for 2h and at 120℃ for 2h to obtain polyurethane microsphere toughened epoxy resin composite material.

[0097] Comparative Example 1

[0098] (1) Synthesis of linear polyurethane: 1.50 g (0.022 mol) of dihydroxypropionic acid (DMPA), 7.175 g (0.01435 mol) of polyether polyol (N210), and 0.646 g (0.01435 mol) of 1,4-butanediol (BDO) were weighed and added to a three-necked flask. The mixture was stirred until homogeneous and then stirred at 160 °C for 7–8 min to remove water. The temperature was then lowered to 90 °C, and 6.11 g (0.055 mol) of isophorone diisocyanate (IPDI) was added dropwise. The reaction was allowed to proceed for 4 h to obtain a polyurethane prepolymer. During the reaction, the viscosity of the system increased, and 5 g of butanone was added to reduce the viscosity. After the system temperature dropped to room temperature, 0.962 g (0.0095 mol) of triethylamine (TEA) was added and stirred at high speed until homogeneous. Then, 41.29 g of butanone was added and the mixture was stirred for 5 h to obtain a linear polyurethane emulsion. The average particle size of the emulsion was measured to be 180 nm, and the yield was 99%.

[0099] (2) Preparation of polyurethane and epoxy resin dispersion: Weigh 18g of linear polyurethane emulsion and 22.5g of E-51 type epoxy resin and add them to a three-necked flask. React at 65℃ for 5h, cool down and discharge the material, remove the solvent by rotary evaporation to obtain polyurethane / epoxy resin dispersion.

[0100] (3) Polyurethane toughened epoxy resin

[0101] Weigh 27g of polyurethane / epoxy resin dispersion, 33.75g of E-51 type epoxy resin and 2.813g of 2-ethyl-4-methylimidazole, mix and stir evenly, remove air bubbles by vacuuming, pour into a mold, cure at 60℃ for 2h and at 120℃ for 2h to obtain polyurethane toughened epoxy resin composite material.

[0102] Comparative Example 2

[0103] (1) The synthesis of polyurethane microspheres is the same as in Example 1.

[0104] (2) Preparation of polyurethane microspheres and epoxy resin dispersion: Weigh 2g of polyurethane microsphere powder and 10g of E-51 type epoxy resin and add them to a three-necked flask, stir and mix.

[0105] (3) Polyurethane microsphere toughened epoxy resin: Weigh 12g of polyurethane microsphere / epoxy resin dispersion, 90g of E-51 type epoxy resin and 5g of 2-ethyl-4-methylimidazole, mix and stir evenly, remove air bubbles by vacuuming, pour into a mold, cure at 60℃ for 2h and at 70℃ for 4h to obtain polyurethane microsphere toughened epoxy resin composite material.

[0106] The scanning electron microscope image of the polyurethane microspheres prepared in Example 1 is shown below. Figure 1 As shown.

[0107] The polyurethane microsphere-toughened epoxy resin composites prepared in Examples 1-8 and Comparative Examples 1 and 2 were subjected to tensile and impact tests. The results are shown in Table 1.

[0108] Table 1 Tensile strength and impact strength of each embodiment and comparative example

[0109]

[0110] The polyurethane microspheres prepared according to Example 1 were used to toughen epoxy resin. By changing the content of microspheres added in step 3 of Example 1, the mass ratio of microspheres to epoxy resin was made to be (0-10):100. Then, tensile and impact tests were conducted, and the results are as follows. Figure 2 As shown in Table 2, the mechanical performance test data are presented.

[0111] Table 2 Effect of polyurethane microsphere addition on the mechanical properties of epoxy resin

[0112]

[0113] As shown in Table 2, when the amount of polyurethane microspheres added is 5% to 8%, the impact strength of epoxy resin is significantly improved.

[0114] 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 polyurethane microsphere-toughened epoxy resin composite material, characterized in that, Includes the following steps: (1) Disperse polyurethane microsphere powder with a particle size of 50 nm to 2 µm in an organic solvent, add amine to adjust the pH value to 7 to 9, then weigh epoxy resin and add it to a three-necked flask. Heat and stir at 20℃ to 80℃ for 0.5 to 5 h. After the reaction is completed, cool down and discharge the material. Remove the solvent by rotary evaporation to obtain polyurethane microsphere / epoxy resin dispersion. (2) Mix the polyurethane microspheres / epoxy resin dispersion, epoxy resin and curing agent, stir evenly, remove air bubbles by vacuuming, and then pour evenly onto the template for curing to obtain polyurethane microspheres / epoxy resin composite material. The method for preparing the polyurethane microspheres includes the following steps: a1. Add a small molecule diol, a large molecule polyol, and a hydrophilic monomer to a reaction vessel. After removing water, add diisocyanate and react at 60-120℃ for 4-5 h. Then add polyisocyanate, adding solvent during the process to reduce the viscosity of the reaction system. Cool the system to 25-50℃, add a neutralizing agent, and stir until homogeneous. Emulsify with water to obtain a polyurethane prepolymer dispersion. The molecular weight of the large molecule polyol is 500-4000, and the polyisocyanate is any one of 1,6-hexyl diisocyanate trimer, toluene diisocyanate trimer, and isophorone diisocyanate trimer. a2. Add an aqueous solution of polyamine to the above dispersion for chain extension, and add dibutyltin dilaurate as a catalyst. React at room temperature for 1-8 h to obtain a polyurethane microsphere emulsion. The amount of polyamine used is 0.5-10 times the number of unreacted isocyanate groups in the system. a3. Demulsification, filtration, washing, and drying are performed to obtain polyurethane microsphere powder.

2. The method for preparing the polyurethane microsphere-toughened epoxy resin composite material according to claim 1, characterized in that, In step a1, the molar ratio of macromolecular polyol to small molecule diol is 1:0~7; the hydrophilic monomer is 1%~50% of the total mass of the reactants; the diisocyanate is added according to the molar ratio of NCO:OH in the reaction system of 1.2~2.5:1; the polyisocyanate is 0%~50% of the total mass of the reactants; and the amount of water is added according to the solid content of the system being 25%.

3. The method for preparing the polyurethane microsphere-toughened epoxy resin composite material according to claim 2, characterized in that, In step a1, the hydrophilic monomer accounts for 5% to 15% of the total mass of the reactants; the polyisocyanate accounts for 10% to 20% of the total mass of the reactants.

4. The method for preparing the polyurethane microsphere-toughened epoxy resin composite material according to claim 1, characterized in that, The small molecule diols mentioned are any one or more of butanediol, ethylene glycol, pentanediol, isopentanediol, neopentanediol, propylene glycol, 1,4-butanediol, diethylene glycol, and octanediol; The macromolecular polyols mentioned are any one or more of polycaprolactone diol, polybutylene adipate diol, polytetrahydrofuran diol, polypropylene oxide diol, and polycarbonate diol. The hydrophilic monomer is one or more of dimethylolpropionic acid and dimethylolbutyric acid; The diisocyanate mentioned is any one or more of diphenylmethane diisocyanate, toluene diisocyanate, isophorone diisocyanate, 1,6-hexyl diisocyanate, and dicyclohexylmethane diisocyanate; The solvent is any one or more of acetone, butanone, 1-methyl-2-pyrrolidone, and N,N-dimethylformamide; The neutralizing agent is any one or more of triethylamine, triethanolamine, N-methyldiethanolamine, trimethylamine, and ammonia. The polyamine is any one or more of ethylenediamine, diethylenetriamine, triethylenetetramine, isophorone diamine, and hydrazine hydrate.

5. The method for preparing the polyurethane microsphere-toughened epoxy resin composite material according to claim 1, characterized in that, The epoxy resin is any one or more of E51, E54, E44, and E20.

6. The method for preparing the polyurethane microsphere-toughened epoxy resin composite material according to claim 1, characterized in that, In step (1), the mass ratio of epoxy resin to polyurethane microspheres is 5-10:1; the amount of organic solvent is 1-10 times the mass of polyurethane microsphere powder; and the amount of curing agent in step (2) is 1%-10% of the total mass of epoxy resin used.

7. The method for preparing the polyurethane microsphere-toughened epoxy resin composite material according to claim 1, characterized in that, In step (2), the stirring temperature is 40~60℃ and the stirring time is 5~10 min; the curing temperature is 20~180℃ and the curing time is 0.5~5 h.

8. The method for preparing the polyurethane microsphere-toughened epoxy resin composite material according to claim 1, characterized in that, The organic solvent mentioned in step (1) is any one or more of ethanol, acetone, propylene glycol methyl ether, ethylene glycol methyl ether, ethyl acetate, and toluene; The amine mentioned in step (1) is any one or more of trimethylamine, triethylamine, tetramethylammonium hydroxide, and tetraethylammonium hydroxide; The curing agent mentioned in step (2) is any one or more of 2-methylimidazole, 2,4-dimethylimidazole, 2-ethyl-4-methylimidazole, 2-methylimidazole and butyl glycidyl ether adduct, 2-methylimidazole and 2-ethylhexyl glycidyl ether adduct, polythiol, and isocyanate-modified imidazole.

9. A polyurethane microsphere-toughened epoxy resin composite material, characterized in that, Prepared using the method described in any one of claims 1-8.

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