A synergistic toughening method of high temperature fast curing epoxy resin for prepreg

Abstract

The application discloses a synergistic toughening method of high-temperature rapid curing epoxy resin for prepreg, which uses high-temperature epoxy resin as a matrix, and adopts liquid rubber, polyetherimide and nano-silicon dioxide as three conventional toughening agents for synergistic toughening. The epoxy resin and the polyetherimide are heated and dissolved, then the liquid rubber and the nano-silicon dioxide are added in sequence and are high-speed dispersed by lowering temperature, finally, a curing agent and an accelerator are added and vacuum defoaming is carried out, so as to obtain a toughened high-temperature epoxy resin system. The three toughening agents are combined with rigidity and flexibility, and are synergized in multiple scales, which is different from simple physical blending and single toughening, and the toughness is significantly improved while the high heat resistance is maintained. The system can be rapidly cured at 150-180 DEG C for 30-60 min, has suitable viscosity, low resin loss rate and good storage stability.

Description

Technical Field

[0001] This invention relates to a synergistic toughening method for high-temperature rapid curing epoxy resins of liquid rubber, polyetherimide, and nano-silica prepregs, belonging to the field of composite material technology. Background Technology

[0002] High-temperature epoxy resins are an important matrix for prepregs in aerospace structural components due to their high crosslinking density and good heat resistance. However, their cured products are brittle, have poor impact resistance and crack propagation resistance, and toughening under rapid curing conditions requires both high heat resistance and high toughness.

[0003] Patent CN103374320A (published on October 30, 2013) discloses a method for toughening epoxy resin with liquid rubber. The liquid rubber content is relatively high, and the system is more biased towards adhesives and low-temperature toughness improvement. A large amount of rubber phase may reduce the modulus, heat resistance and dimensional stability of the cured resin, which is not conducive to maintaining high Tg and high rigidity of high-temperature structural resin.

[0004] Patent CN103154131A (published on June 12, 2013) discloses a method for toughening epoxy resin with low molecular weight polyethersulfone. Polyethersulfone needs to be fully dissolved at a high temperature, which can easily increase the energy consumption and process complexity of preparation. Toughening thermoplastic resin usually increases the viscosity of the system, which is not conducive to the phase structure control within the prepreg coating, fiber wetting and rapid curing window. Single toughening is difficult to simultaneously achieve high heat resistance, high toughness, low process viscosity and rapid curing compatibility. Summary of the Invention

[0005] The technical problem to be solved by the present invention is to overcome the defects of insufficient toughening or decreased heat resistance and modulus caused by single toughening, as well as the difficulty in adapting phase separation to rapid curing, and to provide a toughening method that uses conventional toughening agents in synergy and takes into account both high heat resistance and high toughness.

[0006] To address the above problems, this invention provides a synergistic toughening method for high-temperature rapid-curing epoxy resins used in prepregs, comprising the following steps:

[0007] Step 1): The epoxy resin and polyetherimide are mixed and stirred under heating conditions to dissolve them, thus obtaining a homogeneous resin solution; Step 2): After the homogeneous resin solution has cooled down, add the liquid rubber and stir to mix evenly; Step 3): Add nano-silica to the mixture obtained in Step 2), disperse it at high speed and uniformly, and promote the enrichment of nano-silica at the interface between the rubber phase and the thermoplastic phase; Step 4): After the mixture obtained in Step 3) has cooled down, add the curing agent and accelerator, stir evenly and degas under vacuum to obtain high-temperature rapid curing epoxy resin.

[0008] Preferably, the epoxy resin is any one or more of tetrafunctional epoxy resin, trifunctional epoxy resin, phenolic epoxy resin, and bisphenol A type epoxy resin.

[0009] Preferably, the liquid rubber is any one or more of carboxyl-terminated butadiene-acrylonitrile rubber, amino-terminated butadiene-acrylonitrile rubber, and epoxy-terminated butadiene-acrylonitrile rubber.

[0010] Preferably, the nano-silica is fumed nano-silica or nano-silica with a surface modified by a silane coupling agent, and the average particle size is 7~40nm.

[0011] Preferably, the curing agent is any one or more of 4,4'-diaminodiphenyl sulfone and 3,3'-diaminodiphenyl sulfone; the accelerator is any one or more of microencapsulated imidazole, modified imidazole, boron trifluoride monoethylamine complex, and urea accelerators.

[0012] Preferably, based on 100 parts by weight of the total epoxy resin, the amount of polyetherimide is 5-20 parts by weight, the amount of liquid rubber is 5-15 parts by weight, the amount of nano-silica is 2-10 parts by weight, the amount of curing agent is 30-50 parts by weight, and the amount of accelerator is 1-8 parts by weight.

[0013] Preferably, in step 1), the heating temperature is 130~140℃; in step 2), the temperature is reduced to 90~110℃; in step 3), the high-speed dispersion temperature is 70~90℃ and the high-speed dispersion time is 10~30min; in step 4), the temperature is reduced to 75~90℃ and the vacuum degree of vacuum degassing is not higher than -0.08MPa.

[0014] The present invention also provides a high-temperature rapid curing epoxy resin prepared by the synergistic toughening method of the above-mentioned high-temperature rapid curing epoxy resin for prepreg.

[0015] Preferably, during the curing process of the high-temperature rapid-curing epoxy resin, the liquid rubber, polyetherimide, and nano-silica work synergistically to form a multi-scale toughening structure in the epoxy crosslinking network, consisting of a micron-sized rubber phase, a submicron thermoplastic phase, and interface-enriched nano-silica. Specifically, the liquid rubber forms a micron-sized rubber phase to provide cavitation toughening, the polyetherimide forms a submicron thermoplastic phase to induce shear yielding, and the nano-silica, on the one hand, is enriched at the interface between the rubber and thermoplastic phases, inhibiting phase coarsening and refining the stable microphase structure during rapid curing; on the other hand, it acts as a rigid nanophase to compensate for the glass transition temperature and modulus.

[0016] Preferably, the curing conditions for the high-temperature rapid curing epoxy resin are: rapid curing can be completed by holding at 150~180℃ for 30~60 minutes.

[0017] Compared with the prior art, the beneficial effects of the present invention are as follows: (1) Good toughening can be achieved by using conventional and readily available toughening agents through co-design, and the process is simple and the cost is controllable.

[0018] (2) The interfacial stabilization effect of nano-silica makes toughening independent of slow phase separation and is suitable for high-temperature rapid curing.

[0019] (3) While significantly improving fracture toughness and strength, the glass transition temperature and modulus are basically maintained, and it has a process viscosity suitable for hot melt coating. It is also beneficial to reduce resin loss and improve storage stability, and is suitable for high-temperature rapid curing prepreg. Detailed Implementation

[0020] To make the present invention more apparent and understandable, preferred embodiments are described in detail below.

[0021] Example 1 A synergistic toughening method for prepregs using high-temperature rapid-curing epoxy resins: (1) By mass, 60 parts of tetrafunctional epoxy resin AG-80 and 40 parts of bisphenol A type epoxy resin E-51 were added to the reactor, heated to 140°C, and 12 parts of polyetherimide were added and stirred until dissolved.

[0022] (2) Cool down to 100℃ and add 10 parts of carboxyl-terminated butadiene-acrylonitrile rubber and stir evenly; cool down to 80℃ and add 5 parts of fumed nano silica and disperse at high speed for 25 min.

[0023] (3) Add 40 parts of micronized 4,4'-diaminodiphenyl sulfone and 2 parts of microencapsulated imidazole at 80℃, stir evenly, and degas under vacuum of -0.09MPa for 30min to obtain the toughening system. The resin is cured by preheating at 120℃ for 30min + 180℃ / 50min.

[0024] Example 2 A synergistic toughening method for prepregs using high-temperature rapid-curing epoxy resins: (1) By mass, add 60 parts of AG-80 and 40 parts of bisphenol A type epoxy resin E-51 to the reactor, heat to 140°C, and add 8 parts of polyetherimide and stir until dissolved.

[0025] (2) Cool down to 100℃, add 10 parts of carboxyl-terminated butadiene-acrylonitrile rubber and stir evenly. Cool down to 80℃, add 5 parts of fumed nano silica and disperse at high speed for 25 min.

[0026] (3) Cool down to 80°C, add 40 parts of 4,4'-diaminodiphenyl sulfone and 2 parts of microencapsulated imidazole, stir to remove bubbles, and solidify as in Example 1.

[0027] Comparative Example 1 A method for preparing an epoxy resin: The difference from Example 1 is that only 60 parts of AG-80 and 40 parts of E-51 are used as the matrix, and 40 parts of 4,4'-diaminodiphenyl sulfone and 2 parts of microencapsulated imidazole are added without any toughening agent. The rest is the same as in Example 1.

[0028] Comparative Example 2 A method for preparing an epoxy resin: The difference from Example 1 is that only 10 parts of carboxyl-terminated butadiene-acrylonitrile rubber, a toughening agent, are added to the matrix of Example 1, and polyetherimide and nano-silica are not added, while the rest is the same as in Example 1.

[0029] Performance testing The materials obtained in Examples 1-2 and Comparative Examples 1-2 were subjected to performance tests. The tensile strength and modulus were determined according to ASTM D638, the fracture toughness according to ASTM D5045, the gel time was measured on a hot plate at 180°C, and the Tg was determined using DMA. The results are shown in Table 1.

[0030] Table 1 Performance Test Results

[0031] This invention utilizes a multi-scale rigid-flexible synergy of three conventional toughening agents: liquid rubber, polyetherimide, and nano-silica. By leveraging the interfacial phase-stabilizing effect of nano-silica, toughening is made independent of slow phase separation. This approach effectively improves toughness while maintaining high heat resistance. Furthermore, the process is simple and cost-controllable, making it suitable for high-temperature rapid curing epoxy resin prepregs for carbon fiber and glass fiber.

Claims

1. A method for synergistic toughening of prepreg with high-temperature rapid-curing epoxy resin, characterized in that, Includes the following steps: Step 1): Mix and stir the epoxy resin and polyetherimide under heating conditions to obtain a homogeneous resin solution; Step 2): After the homogeneous resin solution has cooled down, add the liquid rubber and stir to mix evenly; Step 3): Add nano-silica to the mixture obtained in Step 2), disperse it at high speed and uniformly, and promote the enrichment of nano-silica at the interface between the rubber phase and the thermoplastic phase; Step 4): After the mixture obtained in Step 3) has cooled down, add the curing agent and accelerator, stir evenly and degas under vacuum to obtain high-temperature rapid curing epoxy resin.

2. The synergistic toughening method of high-temperature rapid-curing epoxy resin for prepreg as described in claim 1, characterized in that, The epoxy resin is any one or more of tetrafunctional epoxy resin, trifunctional epoxy resin, phenolic epoxy resin, and bisphenol A type epoxy resin.

3. The synergistic toughening method of high-temperature rapid-curing epoxy resin for prepreg as described in claim 1, characterized in that, The liquid rubber is any one or more of the following: carboxyl-terminated butadiene-acrylonitrile rubber, amino-terminated butadiene-acrylonitrile rubber, and epoxy-terminated butadiene-acrylonitrile rubber.

4. The synergistic toughening method of high-temperature rapid-curing epoxy resin for prepreg as described in claim 1, characterized in that, The nano-silica is fumed nano-silica or nano-silica with a surface modified by a silane coupling agent, and has an average particle size of 7~40nm.

5. The synergistic toughening method of high-temperature rapid-curing epoxy resin for prepreg as described in claim 1, characterized in that, The curing agent is any one or more of 4,4'-diaminodiphenyl sulfone and 3,3'-diaminodiphenyl sulfone; the accelerator is any one or more of microencapsulated imidazole, modified imidazole, boron trifluoride monoethylamine complex, and urea accelerators.

6. The synergistic toughening method of high-temperature rapid-curing epoxy resin for prepreg as described in claim 1, characterized in that, Based on 100 parts by mass of the total epoxy resin, the amount of polyetherimide is 5-20 parts by mass, the amount of liquid rubber is 5-15 parts by mass, the amount of nano silica is 2-10 parts by mass, the amount of curing agent is 30-50 parts by mass, and the amount of accelerator is 1-8 parts by mass.

7. The synergistic toughening method of high-temperature rapid-curing epoxy resin for prepreg as described in claim 1, characterized in that, In step 1), the heating temperature is 130~140℃; in step 2), the temperature is reduced to 90~110℃; in step 3), the high-speed dispersion temperature is 70~90℃ and the high-speed dispersion time is 10~30min; in step 4), the temperature is reduced to 75~90℃ and the vacuum degree of vacuum degassing is not higher than -0.08MPa.

8. A high-temperature rapid-curing epoxy resin prepared by the synergistic toughening method of the prepreg high-temperature rapid-curing epoxy resin according to any one of claims 1-7.

9. The high-temperature rapid-curing epoxy resin as described in claim 8, characterized in that, During the curing process of the high-temperature rapid-curing epoxy resin, liquid rubber, polyetherimide and nano-silica work synergistically to form a multi-scale toughened structure in the epoxy crosslinking network, consisting of a micron-scale rubber phase, a submicron thermoplastic phase and interface-enriched nano-silica.

10. The high-temperature rapid-curing epoxy resin as described in claim 8, characterized in that, The curing conditions for the high-temperature rapid-curing epoxy resin are: rapid curing can be completed by holding it at 150~180℃ for 30~60 minutes.

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