Polyurethane toughened epoxy resin as well as preparation method and application thereof

Abstract

The invention provides polyurethane toughened epoxy resin as well as a preparation method and application thereof, and relates to the technical field of high polymer materials, the preparation method comprises the following steps: carrying out grafting reaction on epoxy resin and a polyurethane black material, and then curing to obtain the polyurethane toughened epoxy resin. Through two-step quantitative reaction control, complete grafting of a soft segment and a hard segment of polyurethane can be directly realized on an epoxy resin molecular chain, and meanwhile, the strength and toughness of the resin can be regulated and controlled by adjusting the molecular weight of the soft segment, so that a polymer with an interpenetrating network structure is obtained; therefore, the tensile strength and the impact strength of the epoxy resin are synergistically improved on the basis that the content of polyurethane chain segments is relatively low. According to the invention, the technical problems of complex synthetic reaction steps, uncontrollable grafting reaction degree, large polyurethane addition amount and poor two-phase synergism of polyurethane toughened modified epoxy resin are solved.

Description

Technical Field

[0001] This invention relates to the technical field of polymer materials, and in particular to a polyurethane toughened epoxy resin, its preparation method, and its application. Background Technology

[0002] Epoxy resins possess excellent mechanical properties, adhesive properties, chemical stability, and electrical insulation properties, leading to their widespread application in coatings, adhesives, electronic packaging, and composite materials. However, the high crosslinking density of cured epoxy resins results in inherent defects such as brittleness and poor impact resistance. Under dynamic loads or extreme environments, they are prone to brittle fracture, leading to instantaneous material failure. This severely restricts their application in demanding applications such as wind turbine blades, high-speed rail brake pads, and bulletproof materials. To address this issue, toughening modification has become a core research direction for epoxy resins. The fundamental goal is to introduce toughening phases to regulate the microstructure of the material, achieving a synergistic effect of "crack deflection-energy dissipation-toughness enhancement," while maintaining or optimizing key properties such as strength and heat resistance.

[0003] Currently, progress has been made in the toughening modification of epoxy resins using rubber elastomers, thermoplastic resins, and nanoparticles. However, challenges remain regarding the balance between toughness and strength, processability, and cost. Polyurethane possesses a designable alternating structure of soft segments (polyether / polyester) and hard segments (urethane), combining the flexibility of elastomers with the rigidity of plastics. The polar groups in its molecular chains can form hydrogen bonds or chemical bonds with epoxy resins, achieving efficient toughening while improving compatibility. Polyurethane toughening modification of epoxy resins mainly includes prepolymer methods, in-situ polymerization methods, and interpenetrating network structure methods. Achieving a synergistic reinforcement of "rigid skeleton-flexible toughening" by forming an interpenetrating network structure of polyurethane / epoxy resin through specific preparation processes is a research hotspot.

[0004] Existing technologies disclose the preparation of isocyanate-terminated polyurethane prepolymers, followed by the stepwise preparation of grafted and ungrafted epoxy resin E54 / polyurethane interpenetrating network polymers, and the study of the effects of different ratios on the mechanical and thermal properties of the materials. Existing technologies also disclose the preparation of polyurethane prepolymers with long flexible segments using castor oil, followed by grafting the prepolymers with epoxy resin 128 to obtain modified resins containing a large number of flexible segments. Adding 5% of the modified resin to epoxy resin 128 during curing forms a polymer with a soft and hard segment interpenetrating network structure. Furthermore, existing technologies disclose the mechanical properties of interpenetrating network polymers formed after curing mixtures of different amounts of polyurethane prepolymers with epoxy resin E44.

[0005] The prior art CN114773610A discloses a method for preparing polyurethane toughened epoxy resin, which uses ferrocene-modified polyisocyanate and polypropylene glycol to synthesize piperazine-modified polyurethane prepolymer, and mixes and cures the piperazine-modified polyurethane prepolymer with epoxy resin, curing agent and other substances to prepare polyurethane toughened epoxy resin.

[0006] The prior art CN119899492B discloses a method for preparing modified polyurethane toughened epoxy resin. In view of the requirements for the flame retardant performance of epoxy resin in high-temperature environments, the polyurethane prepolymer is first modified with borate siloxane chain extender, and then the modified polyurethane prepolymer is mixed with epoxy resin, curing agent and reactive diluent for curing reaction, thereby improving the toughness and flame retardancy of epoxy resin.

[0007] The prior art CN120192635B discloses a mechanically interlocked epoxy resin polymer, its preparation method, and its application. A columnar aromatic hydrocarbon daisy chain polyurethane prepolymer is prepared by a complex synthesis step. The epoxy resin, crosslinking agent, and columnar aromatic hydrocarbon daisy chain polyurethane form a mechanically interlocked network structure containing daisy chain supramolecular polymer through ring-opening polymerization. Due to the host-guest recognition effect between columnar aromatic hydrocarbon and triazole, the epoxy resin polymer has dynamic properties, which can improve the mechanical properties and energy dissipation of the epoxy resin.

[0008] The prior art CN110305466B discloses a polyurethane / epoxy resin blend with shape memory, self-healing and recyclable functions and its preparation method. The method involves homogeneously mixing a linear polyurethane material containing disulfide bonds on the main chain and an epoxy resin prepolymer containing furan rings on the side groups in an organic solvent and then directly drying it, or cooling it to room temperature, adding a curing agent, and drying and curing it to obtain the blend. The use of small-molecule epoxy as a plasticizer improves the flowability of polyurethane, thereby improving the self-healing and recyclability of the material.

[0009] Existing technology CN116284655B discloses a method for preparing graphene-organosilicon synergistically reinforced polyurethane graft-modified epoxy resin. First, graphene oxide modified with diisocyanate and isocyanate-terminated polyurethane prepolymers are prepared separately. Then, these two substances, along with a polyhydroxysilane and a catalyst, are reacted in a butanone solvent to obtain a graphene-organosilicon synergistically reinforced polyurethane prepolymer. Next, the graphene-organosilicon synergistically reinforced polyurethane prepolymer is added to a mixture of liquid and solid epoxy resins for grafting, followed by the addition of a curing agent and an accelerator for curing. By functionalizing graphene with isocyanate, the compatibility between graphene and the polyurethane prepolymer is improved, and Si-O bonds are embedded in the graphene nanoparticles, thereby improving the toughness and heat resistance of the epoxy resin while maintaining its strength.

[0010] The prior art CN118373964A discloses a polyurethane prepolymer modified epoxy resin, its preparation method and application. Polypropylene glycol of different molecular weights and toluene diisocyanate react to generate a polyurethane prepolymer, which is then added to epoxy resin and a catalyst and reacted with a curing agent and an accelerator to form a polyurethane prepolymer modified epoxy resin. By adjusting the ratio of soft and hard segments in the polyurethane prepolymer with different molecular weights of polypropylene glycol, the toughness of the epoxy resin is improved. It can be used for road paving in low-temperature areas or areas with large temperature differences.

[0011] The prior art CN120329514B discloses a polyurethane epoxy polymer network, its preparation method and application. Polyurethane is obtained by reacting polyol, small molecule chain extender, diisocyanate and tridentate ligand, then coordinated with divalent palladium compound and monodentate ligand, and finally mixed with epoxy resin and curing agent, and cured after solvent removal to obtain a woven polymer network with topological structure. The overall toughness and strength of the polymer are improved by utilizing the effects of molecular entanglement and metal coordination.

[0012] The prior art CN115057989A discloses a grafted polyether toughened epoxy resin composite material, its preparation method and application. First, epoxy resin is pre-reacted with an imidazole curing agent to obtain an epoxy resin-imidazole preproduct. Then, isocyanate is reacted with polyether or polyester to prepare a polyurethane prepolymer. The two preproducts are then mixed, cross-linked and cured to obtain a toughened epoxy resin-imidazole-isocyanate-polyester material. This resin material is then used in conductive silver paste materials.

[0013] The prior art CN108976425B discloses a method for preparing a polyurethane-epoxy resin block copolymer waterborne resin emulsion. A polyurethane prepolymer is prepared by reacting a diol oligomer with a diisocyanate. Then, epoxy resin, piperazine and a water-soluble solvent are added. Deionized water is added to the mixture obtained from the reaction, and the mixture is stirred evenly. The polymer is allowed to precipitate by standing. After washing with water, a precursor resin is obtained. Then, an organic acid and deionized water are added to the precursor resin, and the mixture is stirred and emulsified to obtain a polyurethane-epoxy resin block copolymer waterborne resin.

[0014] However, while the aforementioned existing technologies have achieved a certain degree of toughening effect on epoxy resin, the resin synthesis steps are too complex and the reaction conditions are quite harsh. At the same time, due to the high viscosity of the synthesized polyurethane prepolymer, organic solvents are usually required as diluents, and the solvents need to be removed before the resin is cured. In addition, the degree of grafting reaction is uncontrollable during the mixing and reaction of polyurethane prepolymer and epoxy resin, resulting in poor synergy between the two phases. Usually, a large amount of polyurethane is required to achieve the ideal toughening effect.

[0015] In view of this, the present invention is hereby proposed. Summary of the Invention

[0016] One of the objectives of this invention is to provide a method for preparing polyurethane-toughened epoxy resin, which solves the technical problems of complex synthesis reaction steps, uncontrollable grafting reaction degree, large amount of polyurethane added, and poor synergy between the two phases in polyurethane-toughened modified epoxy resin.

[0017] The second objective of this invention is to provide a polyurethane-toughened epoxy resin that achieves a synergistic improvement in tensile strength and impact resistance of the epoxy resin while maintaining a low polyurethane segment content.

[0018] The third objective of this invention is to provide an application of polyurethane toughened epoxy resin that can achieve outstanding application results.

[0019] In order to achieve the above-mentioned objectives of the present invention, the following technical solution is adopted: In a first aspect, a method for preparing a polyurethane-toughened epoxy resin includes the following steps: After grafting epoxy resin and polyurethane black material, the polyurethane toughened epoxy resin is obtained by curing.

[0020] Furthermore, the preparation method includes the following steps: (a) Grafting reaction of epoxy resin and polyurethane black material to obtain polyurethane segment graft modified epoxy resin matrix. Preferably, the grafting reaction further includes the step of adding polyols and / or polyether polyols to carry out the reaction; Preferably, the modified epoxy resin matrix comprises a hydroxyl-terminated modified epoxy resin matrix; (b) The modified epoxy resin matrix is ​​cured to obtain the polyurethane toughened epoxy resin.

[0021] Furthermore, the epoxy resin includes bisphenol A type epoxy resin; Preferably, the epoxy resin includes at least one of epoxy resin E-51, epoxy resin E-44, and epoxy resin E-54; Preferably, the polyurethane black material comprises diphenylmethane diisocyanate and polyphenylmethylene polyisocyanate; Preferably, the isocyanate groups in the polyurethane black material account for 30% to 32% by mass; Preferably, the polyurethane black material has a viscosity of 100 mPa·s to 250 mPa·s at 25°C and an average functionality of 2.3 to 2.7. Preferably, the molar ratio of the hydroxyl groups of the epoxy resin to the isocyanate groups of the polyurethane black is 1:1.2~2.0.

[0022] Furthermore, the polyol includes at least one of 1,4-butanediol, 1,5-pentanediol, and 1,6-hexanediol; Preferably, the polyether polyol has an average functionality of 2 and a molecular weight of 200-1000; Preferably, the polyether polyol includes at least one of polyethylene glycol, polypropylene glycol, and polytetrahydrofuran glycol.

[0023] Furthermore, the catalyst used in the grafting reaction includes at least one of stannous octoate, dibutyltin dilaurate, and stannous oleate.

[0024] Furthermore, the grafting reaction is carried out at a temperature of 65°C to 75°C for a duration of 1 hour to 3 hours.

[0025] Furthermore, the curing agent used in the curing process includes an acid anhydride curing agent; Preferably, the anhydride curing agent includes at least one of methyltetrahydrophthalic anhydride, methylhexahydrophthalic anhydride, and methylnadic anhydride; Preferably, the curing accelerator used includes imidazole accelerators; Preferably, the imidazole accelerator includes at least one of 2-methylimidazole, 2-ethyl-4-methylimidazole, 2-phenylimidazole, and 1-benzyl-2-methylimidazole; Preferably, the mass ratio of the modified epoxy resin matrix, curing agent and accelerator is 100:(80~90):(1~3).

[0026] Furthermore, the curing method includes the following steps: First, cure at 100℃~110℃ for 0.5h~1.5h, then raise the temperature to 125℃~130℃ for 1.5h~2.5h, and then raise the temperature to 135℃~140℃ for 0.5h~1.5h. Preferably, the process further includes a step of vacuum degassing the system prior to curing.

[0027] Secondly, a polyurethane toughened epoxy resin is prepared by any of the preparation methods described above.

[0028] Thirdly, the application of the aforementioned polyurethane toughened epoxy resin in wind turbine blades, high-speed rail brake pads, and bulletproof materials.

[0029] Compared with the prior art, the present invention has at least the following beneficial effects: The present invention provides a method for preparing polyurethane toughened epoxy resin. Using polyurethane black material (commercially available industrial crude MDI) as raw material, a simple two-step quantitative reaction control method is used to directly achieve complete grafting of polyurethane soft and hard segments onto the epoxy resin molecular chain, forming a modified epoxy resin matrix with good flowability and stability. After curing, a polymer with an interpenetrating network structure is obtained. This achieves a synergistic improvement in the tensile strength and impact strength of the epoxy resin while maintaining a low polyurethane segment content. The strength and toughness of the resin can also be controlled by adjusting the molecular weight of the soft segments. The preparation method of the present invention is simple and easy to operate, suitable for daily large-scale formulation and use, and can meet the application requirements of fiber composite material molding and processing.

[0030] The polyurethane toughened epoxy resin provided by this invention achieves a synergistic improvement in tensile strength and impact resistance of epoxy resin with a low polyurethane segment content.

[0031] The application of the polyurethane toughened epoxy resin provided by this invention can achieve outstanding application results. Detailed Implementation

[0032] The technical solution of the present invention will be clearly and completely described below with reference to the embodiments. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0033] According to a first aspect of the present invention, a method for preparing a polyurethane toughened epoxy resin is provided, comprising the following steps: After grafting epoxy resin and polyurethane black material, and then curing, polyurethane toughened epoxy resin is obtained.

[0034] This invention uses polyurethane black material (commercially available industrial crude MDI) as raw material and achieves complete grafting of polyurethane soft and hard segments directly onto the epoxy resin molecular chain through a simple two-step quantitative reaction control method. This forms a modified epoxy resin matrix with good flowability and stability. After curing, a polymer with an interpenetrating network structure is obtained. This achieves a synergistic improvement in the tensile strength and impact strength of epoxy resin with a low polyurethane segment content. The strength and toughness of the resin can also be controlled by adjusting the molecular weight of the soft segments.

[0035] In a preferred embodiment, the preparation method of the present invention includes the following steps: (a) Grafting reaction of epoxy resin and polyurethane black material to obtain polyurethane segment graft modified epoxy resin matrix. The grafting reaction also includes the step of adding polyols and / or polyether polyols to carry out the reaction; Modified epoxy resin matrices include epoxy resin matrices with terminal hydroxyl groups; (b) The modified epoxy resin matrix is ​​cured to obtain polyurethane toughened epoxy resin.

[0036] In a preferred embodiment, the epoxy resin includes, but is not limited to, bisphenol A type epoxy resin.

[0037] In a preferred embodiment, the epoxy resin includes, but is not limited to, at least one of epoxy resin E-51, epoxy resin E-44, and epoxy resin E-54.

[0038] In a preferred embodiment, the polyurethane black material can be a mixture of diphenylmethane diisocyanate (MDI) and a certain amount of polyphenyl polymethylene polyisocyanate (PAPI) with higher functionality.

[0039] In this invention, the mass percentage of isocyanate groups (-NCO) in the polyurethane black material can be 30% to 32%; at the same time, the viscosity of the polyurethane black material at 25°C can be 100 mPa·s to 250 mPa·s, and the average functionality can be 2.3 to 2.7.

[0040] In a preferred embodiment, the molar ratio of the hydroxyl groups of the epoxy resin to the isocyanate groups of the polyurethane black material can be 1:1.2 to 2.0, for example, 1:1.2, 1:1.4, 1:1.6, 1:1.8, or 1:2.0, but is not limited thereto, which is more conducive to improving the grafting reaction effect.

[0041] In a preferred embodiment, the polyol includes, but is not limited to, at least one of 1,4-butanediol, 1,5-pentanediol, and 1,6-hexanediol, which have active hydroxyl groups at both ends.

[0042] In a preferred embodiment, the polyether polyol may have an average functionality of 2 and a molecular weight of 200-1000; the polyether polyol may include, but is not limited to, at least one of polyethylene glycol, polypropylene glycol and polytetrahydrofuran glycol.

[0043] In this invention, the molar ratio of the remaining unreacted isocyanate group (-NCO) to the -OH group in the polyol and / or polyether polyol can be 1:1.2 to 2.0, for example, 1:1.2, 1:1.4, 1:1.6, 1:1.8, 1:2.0, but is not limited thereto.

[0044] In a preferred embodiment, the catalyst used in the grafting reaction includes, but is not limited to, at least one of stannous octoate, dibutyltin dilaurate, and stannous oleate.

[0045] In a preferred embodiment, the grafting reaction temperature can be 65°C to 75°C, with typical but non-limiting temperatures such as 65°C, 70°C, and 75°C, and the grafting reaction time can be 1h to 3h, with typical but non-limiting times such as 1h, 2h, and 3h, which is more conducive to fully carrying out the grafting reaction.

[0046] A typical preparation method for a polyurethane toughened epoxy resin includes the following steps: (a) Add crude MDI to epoxy resin, stir and mix evenly, add catalyst, and react under nitrogen atmosphere. After the hydroxyl groups are completely reacted by infrared spectroscopy, add polyol and / or polyether polyol to continue the reaction. After the isocyanate is completely reacted by infrared spectroscopy, the epoxy resin matrix with hydroxyl-terminated polyurethane segments is obtained. (b) At room temperature, the modified epoxy resin matrix obtained in step (a) is added to a curing agent and an accelerator. After the mixture is thoroughly stirred, it is placed in a vacuum drying oven for degassing. The resin is then poured into a mold coated with a release agent using a casting method for curing to obtain a polyurethane toughened epoxy resin.

[0047] In this invention, the curing agent used for curing includes, but is not limited to, acid anhydride curing agents.

[0048] In a preferred embodiment, the anhydride curing agent includes, but is not limited to, at least one of methyltetrahydrophthalic anhydride, methylhexahydrophthalic anhydride, and methylnadic anhydride.

[0049] In this invention, the curing accelerators used include, but are not limited to, imidazole accelerators.

[0050] In a preferred embodiment, the imidazole accelerator includes, but is not limited to, at least one of 2-methylimidazole, 2-ethyl-4-methylimidazole, 2-phenylimidazole, and 1-benzyl-2-methylimidazole.

[0051] In this invention, the mass ratio of the modified epoxy resin matrix, curing agent, and accelerator can be 100:(80~90):(1~3), and typical but non-limiting mass ratios are, for example, 100:80:3, 100:85:3, 100:90:3, 100:80:2, 100:85:2, 100:90:2, 100:80:1, 100:85:1, and 100:90:1.

[0052] In a preferred embodiment, the curing method includes the following steps: First, cure at 100℃~110℃ for 0.5h~1.5h, then raise the temperature to 125℃~130℃ for 1.5h~2.5h, and then raise the temperature to 135℃~140℃ for 0.5h~1.5h.

[0053] In a preferred embodiment, the system is further subjected to vacuum degassing before curing, which is more conducive to improving the subsequent curing effect.

[0054] According to a second aspect of the present invention, a polyurethane toughened epoxy resin is provided, which is prepared by any of the preparation methods described above.

[0055] The polyurethane toughened epoxy resin provided by this invention achieves a synergistic improvement in tensile strength and impact resistance of epoxy resin with a low polyurethane segment content.

[0056] According to a third aspect of the present invention, an application of polyurethane toughened epoxy resin is provided, which can achieve outstanding application effects.

[0057] The present invention will be further illustrated by the following examples. Unless otherwise specified, the materials in the examples are prepared according to existing methods or purchased directly from the market.

[0058] Example 1 A method for preparing a polyurethane toughened epoxy resin includes the following steps: (a) Add 9.10g of crude MDI (polyurethane black material) to 50.87g of epoxy resin E-44, add 1-2 drops of stannous octoate as a catalyst, and react at 70°C under nitrogen protection for 1h. Observe the 3470cm² value using infrared spectroscopy. -1 After the nearby hydroxyl groups had completely reacted, 3.46 g of PEG200 was added, and the reaction was continued for 2 hours at 70°C under nitrogen protection. The 2270 cm⁻¹ was observed by infrared spectroscopy. -1 After the nearby -NCO (isocyanate group) reacts completely, a fully grafted epoxy resin matrix with hydroxyl-terminated polyurethane segments is obtained. (b) Cool the modified epoxy resin matrix obtained in step (a) to about 40°C, add 37.0g of methylhexahydrophthalic anhydride curing agent and 1.5g of 2-ethyl-4-methylimidazolium accelerator and mix them. After stirring for 30 minutes, place it in a vacuum drying oven at 40°C for 2 hours to degas. Then, pour the resin into a mold coated with release agent using the casting method. First, cure it at 105°C for 1 hour, then raise the temperature to 125°C for 2 hours, and then raise the temperature to 138°C for 1 hour to obtain polyurethane toughened epoxy resin.

[0059] Example 2 A method for preparing polyurethane toughened epoxy resin includes the following steps: (a) Add 5.02g of crude MDI (polyurethane black material) to 50.62g of epoxy resin E-51, add 1-2 drops of stannous octoate as a catalyst, and react at 70℃ under nitrogen protection for 1h. Observe the 3470cm² value using infrared spectroscopy. -1 After the nearby hydroxyl groups had completely reacted, 3.82 g of PEG400 was added, and the reaction was continued for 2 hours at 70°C under nitrogen protection. The 2270 cm⁻¹ chromatogram was observed by infrared spectroscopy. -1 After the nearby -NCO (isocyanate group) reacts completely, a fully grafted epoxy resin matrix with hydroxyl-terminated polyurethane segments is obtained. (b) Cool the modified epoxy resin matrix obtained in step (a) to about 40°C, add 42.40g of methyltetrahydrophthalic anhydride curing agent and 1.5g of 2-methylimidazolium accelerator and mix. After stirring thoroughly for 30 minutes, place it in a vacuum drying oven at 40°C for 2 hours to degas. Then, pour the resin into a mold coated with release agent using the casting method. First, cure at 107°C for 1 hour, then raise the temperature to 125°C for 2 hours, and then raise the temperature to 137°C for 1 hour to obtain polyurethane toughened epoxy resin.

[0060] Example 3 A method for preparing polyurethane toughened epoxy resin includes the following steps: (a) 4.39 g of crude MDI (polyurethane black material) was added to 50.38 g of epoxy resin E-54, along with 2 drops of stannous octoate as a catalyst. The reaction was carried out at 75 °C under nitrogen protection for 1 h. The 3470 cm⁻¹ was observed by infrared spectroscopy. -1 After the nearby hydroxyl groups had completely reacted, 7.29 g of PPG 600 was added, and the reaction was continued for 3 hours at 75°C under nitrogen protection. The 2270 cm⁻¹ was observed by infrared spectroscopy. -1 After the nearby -NCO (isocyanate group) reacts completely, a fully grafted epoxy resin matrix with hydroxyl-terminated polyurethane segments is obtained. (b) Cool the modified epoxy resin matrix obtained in step (a) to about 40°C, add 48.11g of methyl nadic anhydride curing agent and 2g of 1-phenylmethyl-2-methylimidazolium accelerator and mix. After stirring for 30 minutes, place it in a vacuum drying oven at 40°C for 2 hours to degas. Then, pour the resin into a mold coated with release agent using the casting method. First, cure at 110°C for 1 hour, then raise the temperature to 130°C for 2 hours, and then raise the temperature to 140°C for 1 hour to obtain polyurethane toughened epoxy resin.

[0061] Example 4 A method for preparing polyurethane toughened epoxy resin includes the following steps: (a) Add 5.05g of crude MDI (polyurethane black material) to 50.25g of epoxy resin E-51, add 1-2 drops of stannous octoate as a catalyst, and react at 70℃ under nitrogen protection for 1h. Observe the 3470cm² value using infrared spectroscopy. -1 After the nearby hydroxyl groups had completely reacted, 0.86 g of 1,4-butanediol was added, and the reaction was continued for 2 hours at 70 °C under nitrogen protection. The 2270 cm⁻¹ was observed by infrared spectroscopy. -1 After the nearby -NCO (isocyanate group) reacts completely, a fully grafted epoxy resin matrix with hydroxyl-terminated polyurethane segments is obtained. (b) Cool the modified epoxy resin matrix obtained in step (a) to about 40°C, add 42.40g of methyltetrahydrophthalic anhydride curing agent and 1.5g of 2-phenylimidazolium accelerator and mix them. After stirring for 30 minutes, place it in a vacuum drying oven at 40°C for 2 hours to degas. Then, pour the resin into a mold coated with release agent using the casting method. First, cure it at 105°C for 1 hour, then raise the temperature to 125°C for 2 hours, and then raise the temperature to 135°C for 1 hour to obtain polyurethane toughened epoxy resin.

[0062] Example 5 A method for preparing polyurethane toughened epoxy resin includes the following steps: (a) 7.28 g of crude MDI (polyurethane black material) was added to 50.58 g of epoxy resin E-44, along with 2 drops of stannous octoate as a catalyst. The reaction was carried out at 70 °C under nitrogen protection for 1 h. The 3470 cm⁻¹ was observed by infrared spectroscopy. -1 After the nearby hydroxyl groups had completely reacted, 0.66 g of 1,6-hexanediol was added, and the reaction was continued for 2 hours at 70 °C under nitrogen protection. The 2270 cm⁻¹ was observed by infrared spectroscopy. -1 After the nearby -NCO (isocyanate group) reacts completely, a fully grafted epoxy resin matrix with hydroxyl-terminated polyurethane segments is obtained. (b) Cool the modified epoxy resin matrix obtained in step (a) to about 40°C, add 37.0g of methylhexahydrophthalic anhydride curing agent and 2g of 2-ethyl-4-methylimidazolium accelerator and mix. After stirring thoroughly for 30 minutes, place it in a vacuum drying oven at 40°C for 2 hours to degas. Then, pour the resin into a mold coated with release agent using the casting method. First, cure at 105°C for 1 hour, then raise the temperature to 125°C for 2 hours, and then raise the temperature to 138°C for 1 hour to obtain polyurethane toughened epoxy resin.

[0063] Example 6 A method for preparing polyurethane toughened epoxy resin includes the following steps: (a) 3.29 g of crude MDI (polyurethane black material) was added to 50.42 g of epoxy resin E-54, along with 2 drops of stannous octoate as a catalyst. The reaction was carried out at 75 °C under nitrogen protection for 1 h. The 3470 cm⁻¹ was observed by infrared spectroscopy. -1 After the nearby hydroxyl groups had completely reacted, 6.08 g of PPG1000 was added, and the reaction was continued for 3 hours at 75°C under nitrogen protection. The 2270 cm⁻¹ was observed by infrared spectroscopy. -1 After the nearby -NCO (isocyanate group) reacts completely, a fully grafted epoxy resin matrix with hydroxyl-terminated polyurethane segments is obtained. (b) Cool the modified epoxy resin matrix obtained in step (a) to about 40°C, add 45.41g of methylhexahydrophthalic anhydride curing agent and 2g of 2-ethyl-4-methylimidazolium accelerator and mix. After stirring thoroughly for 30 minutes, place it in a vacuum drying oven at 40°C for 2 hours to degas. Then, pour the resin into a mold coated with release agent using the casting method. First, cure at 105°C for 1 hour, then raise the temperature to 125°C for 2 hours, and then raise the temperature to 135°C for 1 hour to obtain polyurethane toughened epoxy resin.

[0064] Comparative Example 1 A method for curing epoxy resin, comprising the following steps: Add 37.0g of methylhexahydrophthalic anhydride curing agent and 1.5g of 2-ethyl-4-methylimidazolium accelerator to 50.08g of epoxy resin E-44 and mix thoroughly for 30 minutes. Then place it in a vacuum drying oven at 40℃ for 2 hours to degas. Next, pour the resin into a mold coated with release agent using the casting method. First, cure at 105℃ for 1 hour, then raise the temperature to 125℃ for 2 hours, and then raise the temperature to 138℃ for 1 hour to obtain the cured epoxy resin.

[0065] Comparative Example 2 A method for curing epoxy resin, comprising the following steps: Add 42.40g of methyltetrahydrophthalic anhydride curing agent and 1.5g of 2-methylimidazole accelerator to 50.35g of epoxy resin E-51 and mix thoroughly for 30 minutes. Then place it in a vacuum drying oven at 40°C for 2 hours to degas. Then pour the resin into a mold coated with release agent using the casting method. First, cure at 107°C for 1 hour, then raise the temperature to 125°C for 2 hours, and then raise the temperature to 137°C for 1 hour to obtain the cured epoxy resin.

[0066] Comparative Example 3 A method for curing epoxy resin, comprising the following steps: Add 48.11g of methyl nadic anhydride curing agent and 2g of 1-benzyl-2-methylimidazolium accelerator to 50.28g of epoxy resin E-54 and mix thoroughly for 30 minutes. Then place it in a vacuum drying oven at 40°C for 2 hours to degas. Next, pour the resin into a mold coated with a release agent using the casting method. First, cure at 110°C for 1 hour, then raise the temperature to 130°C for 2 hours, and then raise the temperature to 140°C for 1 hour to obtain the cured epoxy resin.

[0067] Comparative Example 4 The only difference between this comparative example and Example 1 is that, in step (a), the polyurethane black material is replaced with an equal amount of TDI. The remaining steps are the same as in Example 1.

[0068] Compared with Example 1, the drawback of this comparative example is that TDI is a monobenzene ring diisocyanate with short hard segments and low functionality in its grafted segments, and low crosslinking degree of polyurethane segments and epoxy resin, resulting in lower tensile strength and impact strength of the cured resin.

[0069] Comparative Example 5 The only difference between this comparative example and Example 1 is that, in step (a), the polyurethane black material is replaced with an equal amount of MDI. The remaining steps are the same as in Example 1.

[0070] Compared with Example 1, the drawback of this comparative example is that MDI is a diisocyanate with a double benzene ring, which has low functionality and low crosslinking degree of polyurethane segments and epoxy resin, resulting in lower tensile strength of the cured resin.

[0071] Comparative Example 6 The only difference between this comparative example and Example 1 is that, in step (b), curing was not performed; The remaining steps are the same as in Example 1.

[0072] Compared with Example 1, the drawback of this comparative example is that the resin can also be cured after being left at room temperature for 24 hours, but the mechanical properties of the resin are poor.

[0073] Test case The mechanical properties of the products in the examples and comparative examples were tested, and the test results are shown in Table 1.

[0074] Tensile property test: The tensile strength of the resin casting was tested according to GB / T 2567-2021 standard.

[0075] Impact performance test: The impact strength of the resin casting was tested according to GB / T 2567-2021 standard.

[0076] The test results show that, compared with the cured resins of Comparative Examples 1-3, the cured resins of Examples 1-6 of this invention exhibit significantly improved tensile strength and impact strength at room temperature. This indicates that after toughening and modifying the epoxy resin using the method of this invention, the resin possesses good mechanical strength and fracture toughness. The principle lies in utilizing the active hydroxyl groups on the epoxy resin chain segments to graft low molecular weight polyurethane hard and soft segments onto the epoxy resin chain. Complete grafting is achieved through quantitative reaction control. During the curing process, an interpenetrating polymer network of epoxy resin and polyurethane chain segments is formed, with good compatibility between the two phases. Thus, a synergistic improvement in the strength and toughness of the epoxy resin is achieved with a relatively low polyurethane content.

[0077] The preparation method of this invention is simple and easy to operate, suitable for mass production and can be applied to the field of fiber-reinforced composite material preparation and molding.

[0078] Table 1 Mechanical performance test results

[0079] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for preparing a polyurethane-toughened epoxy resin, characterized in that, Includes the following steps: After grafting epoxy resin and polyurethane black material, the polyurethane toughened epoxy resin is obtained by curing.

2. The preparation method according to claim 1, characterized in that, The preparation method includes the following steps: (a) Grafting reaction of epoxy resin and polyurethane black material to obtain polyurethane segment graft modified epoxy resin matrix. Preferably, the grafting reaction further includes the step of adding polyols and / or polyether polyols to carry out the reaction; Preferably, the modified epoxy resin matrix comprises a hydroxyl-terminated modified epoxy resin matrix; (b) The modified epoxy resin matrix is ​​cured to obtain the polyurethane toughened epoxy resin.

3. The preparation method according to claim 2, characterized in that, The epoxy resin includes bisphenol A type epoxy resin; Preferably, the epoxy resin includes at least one of epoxy resin E-51, epoxy resin E-44, and epoxy resin E-54; Preferably, the polyurethane black material comprises diphenylmethane diisocyanate and polyphenylmethylene polyisocyanate; Preferably, the isocyanate groups in the polyurethane black material account for 30% to 32% by mass; Preferably, the polyurethane black material has a viscosity of 100 mPa·s to 250 mPa·s at 25°C and an average functionality of 2.3 to 2.

7. Preferably, the molar ratio of the hydroxyl groups of the epoxy resin to the isocyanate groups of the polyurethane black is 1:1.2~2.

0.

4. The preparation method according to claim 2, characterized in that, The polyol includes at least one selected from 1,4-butanediol, 1,5-pentanediol, and 1,6-hexanediol; Preferably, the polyether polyol has an average functionality of 2 and a molecular weight of 200-1000; Preferably, the polyether polyol includes at least one of polyethylene glycol, polypropylene glycol, and polytetrahydrofuran glycol.

5. The preparation method according to any one of claims 1-4, characterized in that, The catalyst used in the grafting reaction includes at least one of stannous octoate, dibutyltin dilaurate, and stannous oleate.

6. The preparation method according to claim 5, characterized in that, The grafting reaction is carried out at a temperature of 65℃~75℃ for 1h~3h.

7. The preparation method according to any one of claims 1-4, characterized in that, The curing agent used in the curing process includes an acid anhydride curing agent; Preferably, the anhydride curing agent includes at least one of methyltetrahydrophthalic anhydride, methylhexahydrophthalic anhydride, and methylnadic anhydride; Preferably, the curing accelerator used includes imidazole accelerators; Preferably, the imidazole accelerator includes at least one of 2-methylimidazole, 2-ethyl-4-methylimidazole, 2-phenylimidazole, and 1-benzyl-2-methylimidazole; Preferably, the mass ratio of the modified epoxy resin matrix, curing agent and accelerator is 100:(80~90):(1~3).

8. The preparation method according to claim 7, characterized in that, The curing method includes the following steps: First, cure at 100℃~110℃ for 0.5h~1.5h, then raise the temperature to 125℃~130℃ for 1.5h~2.5h, and then raise the temperature to 135℃~140℃ for 0.5h~1.5h. Preferably, the process further includes a step of vacuum degassing the system prior to curing.

9. A polyurethane-toughened epoxy resin, characterized in that, It is prepared by the preparation method described in any one of claims 1-8.

10. The application of the polyurethane toughened epoxy resin according to claim 9 in wind turbine blades, high-speed rail brake pads, and bulletproof materials.

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