An epoxy resin composite material based on flexible chain segments and rigid fiber particles and a preparation method thereof

Abstract

The invention relates to the technical field of composite materials, and discloses an epoxy resin composite material based on flexible segments and rigid fiber particles and a preparation method thereof, comprising the following steps: step 1: adding thionyl chloride SOCl2 to a cellulose nanofiber CNF solution, mixing thoroughly and reacting to obtain a chlorinated cellulose nanofiber CNF-Cl solution; step 2: fully mixing the CNF-Cl solution and an aramid nanofiber ANF solution, adding a silane coupling agent, mixing thoroughly and reacting, and removing the solvent to obtain aramid nanofiber fANF@CNF modified with silane functionalized cellulose nanofiber; step 3: adding fANF@CNF to an epoxy resin EP matrix containing epoxy functionalized polydimethylsiloxane E-PDMS, mixing thoroughly, adding a curing agent and a accelerator, vacuum degassing, and curing to obtain a desired composite material; the composite material obtained by the invention realizes the synergistic improvement of the strength, toughness and thermal properties of epoxy composite dielectrics.

Description

Technical Field

[0001] The invention relates to the technical field of composite materials, and in particular to an epoxy resin composite material based on flexible segments and rigid fiber particles and a preparation method thereof. Background Art

[0002] With the development of UHV transmission and large power grids, electrical equipment is gradually transforming towards high voltage, high power and integration. Gas-insulated metal-enclosed switchgear GIS has been widely used due to its advantages of high reliability, long maintenance cycle and small footprint. As a key component of GIS circuit breakers and disconnectors, insulating rods play the role of support, stress transmission, breaking contacts and insulation. During the operation of GIS, they are subjected to electrical and mechanical stress for a long time and are the weak link of the GIS insulation system. In order to maintain the reliability and stability of the power system, high requirements are put forward for the insulation performance, mechanical properties, chemical resistance and weather resistance of GIS insulating rods. Traditional GIS insulating rods are made of epoxy as adhesive and fiber fabric or powder as reinforcing material. Epoxy resin has the advantages of high mechanical strength, excellent insulation performance, thermal stability and good chemical resistance. However, the cured epoxy resin has problems such as low toughness and poor impact resistance, and the strength and toughness of epoxy resin are contradictory factors.

[0003] At present, epoxy resin toughening modification can be divided into homogeneous toughening and heterogeneous toughening. Heterogeneous toughening adds dispersed phase or constructs interpenetrating / semi-interpenetrating polymer networks; homogeneous toughening system introduces bio-based materials, flexible segments and hyperbranched polymers. While the toughness increases, there is a problem of decreased strength and glass transition temperature Tg. Rubber toughening is one of the common methods for epoxy resin toughening. Liquid rubber is dissolved in epoxy resin. As the crosslinking density increases, the matrix solubility decreases and phase separation occurs, and the rubber particle phase is precipitated. The cavitation effect generated by the particle phase can significantly improve the toughness of epoxy resin. However, while the toughness increases, the plasticization effect of rubber will also lead to a decrease in the strength, storage modulus and glass transition temperature Tg of the composite material. The deterioration of mechanical properties and thermal properties will idle the application of composite materials in actual working conditions. How to overcome the contradiction between strength and toughness of thermosetting epoxy resin and increase its strength and thermal properties while achieving effective toughening of epoxy resin is an urgent problem to be solved. Summary of the invention

[0004] In view of the problems existing in the prior art, the present invention provides an epoxy resin composite material based on flexible chain segments and rigid fiber particles and a preparation method thereof.

[0005] The technical solution adopted by the present invention is: a method for preparing an epoxy resin composite material based on flexible chain segments and rigid fiber particles, comprising the following steps:

[0006] Step 1: Disperse cellulose nanofibers CNF in a solvent to obtain a cellulose nanofiber solution, add thionyl chloride SOCl2, mix thoroughly and react to obtain a chlorinated cellulose nanofiber CNF-Cl solution;

[0007] Step 2: After the CNF-Cl solution obtained in step 1 and the aramid nanofiber ANF solution are fully mixed, a silane coupling agent is added to fully mix and react, and the solvent is removed to obtain aramid nanofiber fANF@CNF modified with silane functionalized cellulose nanofibers;

[0008] Step 3: Add the fANF@CNF obtained in step 2 to the epoxy resin EP matrix containing epoxy functionalized polydimethylsiloxane E-PDMS, mix thoroughly, add curing agent and accelerator, vacuum degas, and obtain the desired composite material after curing.

[0009] Furthermore, in step 1, the mass ratio of CNF to SOCl2 is 1:4, and the reaction temperature is 80°C.

[0010] Furthermore, in step 2, the mass ratio of CNF-Cl to ANF is 1:1; and the reaction temperature is 80°C.

[0011] Furthermore, the silane coupling agent is one of 3-aminopropyltriethoxysilane and 3-glycidoxypropyltrimethoxysilane; the solvent is removed by vacuum-assisted filtration, and then washed.

[0012] Furthermore, in the step 3, the mass ratio of E-PDMS to EP in the matrix is ​​4.5-18:90-110; the mass ratio of fANF@CNF to EP in the matrix is ​​0.9-3.6:90-110.

[0013] Furthermore, the temperature of the mixing process in step 3 is 60°C, and the curing agent and the accelerator are added at room temperature; the vacuum degassing temperature in step 3 is 60°C, and the time is 1 h.

[0014] Furthermore, the temperature rise and curing process in step 3 is as follows:

[0015] First, cure at 120 °C for 2 h, then at 130 °C for 2 h, and finally at 140 °C for 1 h.

[0016] Furthermore, in step 3, the mass ratio of the curing agent, the accelerator and the EP in the matrix is ​​72-88:1.4-1.8:90-110.

[0017] Furthermore, the curing agent is one of phthalic anhydride and maleic anhydride; the accelerator is one of 2,4,6-tris(dimethylaminomethyl)phenol, triethylamine, triethanol, and o-hydroxybenzyldimethylamine.

[0018] A high toughness, high strength epoxy resin composite material.

[0019] The beneficial effects of the present invention are:

[0020] (1) The present invention introduces polydimethylsiloxane as a flexible chain segment into an epoxy resin matrix and introduces a rigid nanofiber filler to form a ternary composite structure epoxy dielectric; the problem of reduced strength and glass transition temperature Tg in the toughening process of traditional thermosetting resins is overcome, and the synergistic improvement of strength, toughness and thermal properties of epoxy composite dielectrics is achieved;

[0021] (2) The present invention introduces epoxy-functionalized polydimethylsiloxane E-PDMS as a toughening flexible segment, which has good compatibility and interfacial bonding strength with the epoxy matrix, can effectively improve phase separation and increase crosslinking density; the sufficient crosslinking structure enables the PDMS flexible segment to deform when the composite material is subjected to external force and fully absorb and disperse impact energy, further improving the toughening effect; the rigid epoxy group on the PDMS segment can improve the strength of the composite material to a certain extent; the increase in crosslinking density will delay the relaxation process of the epoxy molecular chain, and since the amorphous segment has a higher energy storage capacity, the Tg will also increase;

[0022] (3) The present invention introduces aramid nanofibers modified with silane-functionalized cellulose nanofibers fANF@CNF as rigid nanofiber fillers. The CNF functionalized sites on ANF can achieve mechanical interlocking between nanofillers and epoxy matrix through a branched network structure. Silane functionalization can effectively improve the interaction between nanofillers and epoxy matrix. Under the combined effect of the two effects, the strength of the composite material is significantly improved. At the same time, the covalent bond interaction between fANF@CNF and epoxy matrix can enhance crack bridging and improve the toughness of the composite material; the mechanical interlocking and covalent bond interaction between nanofillers and epoxy matrix can limit the movement of epoxy molecular chains and effectively improve Tg. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 The figure is a schematic diagram of the preparation process of the composite material of the present invention.

[0024] Figure 2 It is a schematic diagram of the test results of Young's modulus of the composite materials obtained in Examples 1 to 5 of the present invention and Comparative Examples 1 to 4.

[0025] Figure 3It is a schematic diagram of the tensile strength test results of the composite materials obtained in Examples 1 to 5 of the present invention and Comparative Examples 1 to 4.

[0026] Figure 4 It is a schematic diagram of the average critical strength factor results of the composite materials obtained in Examples 1, 2, 6, 7, 8 of the present invention and Comparative Examples 4, 5, 6.

[0027] Figure 5 It is a schematic diagram of the impact strength results of the composite materials obtained in Examples 1, 2, 6, 7, 8 of the present invention and Comparative Examples 4, 5, 6.

[0028] Figure 6 Schematic diagram of glass transition temperature results of composite materials obtained in Example 1 of the present invention and Comparative Examples 1, 4, 6, and 7. DETAILED DESCRIPTION

[0029] The present invention will be further described below in conjunction with the accompanying drawings and specific embodiments.

[0030] A method for preparing an epoxy resin composite material based on flexible segments and rigid fiber particles comprises the following steps: Figure 1 As shown:

[0031] Step 1: Disperse cellulose nanofibers CNF in N,N-dimethylformamide DNF, and stir for 8 h in an oil bath at 80 °C to obtain a cellulose nanofiber solution; add sulfenamide SOCl2 to CNF / DMF, and stir for 24 h in an oil bath at 80 °C to obtain a chlorinated cellulose nanofiber CNF-Cl solution. The mass ratio of CNF to SOCl2 is 1:4, and the mass ratio of CNF to DNF is 1:20.

[0032] Step 2: The CNF-Cl solution obtained in step 1 and the DMSO solution of aramid nanofiber ANF were mixed and stirred in an oil bath at 80 °C for 24 h. Silane coupling agent was added to the mixed solution and stirred in an oil bath at 80 °C for 24 h to prepare fANF@CNF. The mixed solution was vacuum-filtered and fANF@CNF was washed with deionized water and acetone in sequence to obtain fANF@CNF / acetone dispersion.

[0033] The silane coupling agent is one of 3-aminopropyltriethoxysilane and 3-glycidoxypropyltrimethoxysilane; the mass ratio of CNF-Cl to ANF is 1:1.

[0034] Step 3: Add the fANF@CNF / acetone dispersion obtained in step 2 to the E-PDMS / EP mixture and stir in a 60°C oil bath until the acetone is completely removed; keep stirring, and after returning to room temperature, add the curing agent and accelerator and continue stirring for 20 min, and vacuum degas at 60°C for 1 h; cure at 120°C for 2 h, 130°C for 2 h, and 140°C for 1 h.

[0035] The mass ratio of E-PDMS to EP in the matrix is ​​4.5-18:90-110; the mass ratio of fANF@CNF to EP in the matrix is ​​0.9-3.6:90-110; the mass ratio of the curing agent, the accelerator and the EP in the matrix is ​​72-88:1.4-1.8:90-110; the curing agent is one of phthalic anhydride and maleic anhydride; the accelerator is one of 2,4,6-tris(dimethylaminomethyl)phenol, triethylamine, triethanol, and o-hydroxybenzyldimethylamine.

[0036] Example 1

[0037] A method for preparing an epoxy resin composite material based on flexible chain segments and rigid fiber particles comprises the following steps:

[0038] Step 1: Disperse 1 g of cellulose nanofiber CNF in 20 g of N,N-dimethylformamide DNF and stir at 400 rpm for 8 h in an 80 °C oil bath to obtain a cellulose nanofiber solution.

[0039] 4 g of sulfinamide SOCl2 was added to CNF / DMF and stirred at 400 rpm for 24 h in an 80 °C oil bath to obtain a chlorinated cellulose nanofiber CNF-Cl / DMF solution with a mass concentration of 4 wt.%.

[0040] Step 2: 3.5 g of the CNF-Cl / DMF solution obtained in step 1 and 35 g of a DMSO solution of aramid nanofibers ANF (ANF / DMSO) with a mass concentration of 0.4 wt.% were mixed and stirred at 400 rpm for 24 h in an oil bath at 80 °C. Due to the effect of covalent bonds, cellulose nanofiber-modified aramid nanofibers ANF@CNF were obtained.

[0041] 5.7 mg of 3-glycidoxypropyltrimethoxysilane (GPTMS) was added to the mixed solution for silane functionalization, and the mixture was stirred at 400 rpm for 24 h in an oil bath at 80 °C to prepare fANF@CNF. The mixed solution was vacuum-assisted filtered, and fANF@CNF was washed four times with deionized water and acetone to obtain fANF@CNF / acetone dispersion.

[0042] The preparation process of ANF DMSO solution is as follows:

[0043] Kevlar fibers cut into small pieces of 1 to 1.5 cm were placed in acetone and ultrasonicated at 200 W for 12 h. After the end, the Kevlar fibers were filtered and dried under vacuum at 60 °C for 3 days. 1 g of the dried Kevlar fibers, 1.5 g of KOH and 250 mL of dimethyl sulfoxide (DMSO) were placed in a beaker and stirred at 600 rpm for 14 days at room temperature to obtain a 0.4 wt.% ANF / DMSO solution by deprotonation stripping.

[0044] Step 3: Mix 0.9 g of epoxy-functionalized polydimethylsiloxane E-PDMS and 10 g of bisphenol A epoxy resin EP, and stir at 300 rpm for 2 h in an oil bath at 60 °C to obtain a matrix consisting of an E-PDMS / EP mixture.

[0045] The fANF@CNF / acetone dispersion was added to the E-PDMS / EP mixture and stirred at 300 rpm in an oil bath at 60 °C until the acetone was completely removed. The mixture was stirred continuously until the room temperature was restored. Then, 8 g of curing agent phthalic anhydride and 0.16 g of accelerator 2,4,6-tris(dimethylaminomethyl)phenol were added and stirring was continued for 20 min. The mixture was vacuum degassed at 60 °C for 1 h. The mixture was cured at 120 °C for 2 h, 130 °C for 2 h, and 140 °C for 1 h.

[0046] Example 2

[0047] The other steps of this embodiment are the same as those of embodiment 1, except that the silane coupling agent in step 2 is 3-aminopropyltriethoxysilane APTES.

[0048] Example 3

[0049] The other steps of this example are the same as those of Example 1, except that in step 2, the amount of ANF / DMSO solution is 11.7 g, the amount of CNF-Cl / DMF solution is 1.17 g, and the amount of GPTMS is 1.9 mg.

[0050] Example 4

[0051] The other steps of this example are the same as those of Example 1, except that in step 2, the amount of ANF / DMSO solution is 23.4 g, the amount of CNF-Cl / DMF solution is 2.34 g, and the amount of GPTMS is 3.8 mg.

[0052] Example 5

[0053] The other steps of this example are the same as those of Example 1, except that in step 2, the amount of ANF / DMSO solution is 46.8 g, the amount of CNF-Cl / DMF solution is 4.68 g, and the amount of GPTMS is 7.6 mg.

[0054] Example 6

[0055] The other steps of this example are the same as those of Example 1, except that in step 3, the amount of E-PDMS is 0.45 g.

[0056] Example 7

[0057] The other steps of this example are the same as those of Example 1, except that in step 3, the amount of E-PDMS is 1.35 g.

[0058] Example 8

[0059] The other steps of this example are the same as those of Example 1, except that in step 3, the amount of E-PDMS is 1.8 g.

[0060] Comparative Example 1

[0061] An epoxy resin composite material,

[0062] The other steps of this comparative example are the same as those of Example 1, except that step 1 is not included and a CNF / DMF solution is used in step 2.

[0063] The preparation process of CNF / DMF solution is as follows:

[0064] 1 g of cellulose nanofiber CNF was dispersed in 24 g of N,N-dimethylformamide DMF and stirred at 400 rpm for 8 h in an 80 °C oil bath to obtain a CNF / DMF solution with a mass concentration of 4 wt.%.

[0065] Comparative Example 2

[0066] An epoxy resin composite material, the preparation process is as follows:

[0067] Step 1: Take 70 g of DMSO solution of aramid nanofiber ANF with a mass concentration of 0.4 wt.% (ANF / DMSO), add 5.7 mg of 3-glycidoxypropyltrimethoxysilane GPTMS to the solution for silane functionalization, stir at 400 rpm for 24 h in an 80 °C oil bath to prepare fANF. The mixed solution is vacuum-assisted filtered, and the fANF is washed 4 times with deionized water and acetone in sequence to obtain a fANF / acetone dispersion.

[0068] The preparation process of ANF DMSO solution is as follows:

[0069] Kevlar fibers cut into small pieces of 1 to 1.5 cm were placed in acetone and ultrasonicated at 200 W for 12 h. After the end, the Kevlar fibers were filtered and dried under 60 vacuum conditions for 3 days. 1 g of the dried Kevlar fibers, 1.5 g of KOH and 250 mL of dimethyl sulfoxide (DMSO) were placed in a beaker and stirred at 600 rpm for 14 days at room temperature to obtain a 0.4 wt.% ANF / DMSO solution by deprotonation stripping.

[0070] Step 2: Mix 0.9 g of epoxy-functionalized polydimethylsiloxane E-PDMS and 10 g of bisphenol A epoxy resin EP, and stir at 300 rpm for 2 h in an oil bath at 60 °C to obtain a matrix consisting of an E-PDMS / EP mixture.

[0071] Add the fANF / acetone dispersion to the E-PDMS / EP mixture and stir at 300 rpm in a 60 °C oil bath until the acetone is completely removed; keep stirring, and after returning to room temperature, add 8 g of curing agent phthalic anhydride and 0.16 g of accelerator 2,4,6-tris(dimethylaminomethyl)phenol and continue stirring for 20 min, and degas under vacuum at 60 °C for 1 h; cure at 120 °C for 2 h, 130 °C for 2 h, and 140 °C for 1 h.

[0072] Comparative Example 3

[0073] An epoxy resin composite material, the preparation process is as follows:

[0074] Step 1: Disperse 1 g of cellulose nanofiber CNF in 20 g of N,N-dimethylformamide DNF and stir at 400 rpm for 8 h in an 80 °C oil bath to obtain a cellulose nanofiber solution (CNF / DMF) with a mass concentration of 4 wt.%.

[0075] Step 2: Take 7 g of the CNF / DMF solution obtained in step 1, add 5.7 mg of 3-glycidoxypropyltrimethoxysilane GPTMS for silane functionalization, stir at 400 rpm for 24 h in an 80 °C oil bath to prepare fCNF. The mixed solution was vacuum-filtered, and the fCNF was washed four times with deionized water and acetone in sequence to obtain an fCNF / acetone dispersion.

[0076] Step 3: Mix 0.9 g of epoxy-functionalized polydimethylsiloxane E-PDMS and 10 g of bisphenol A epoxy resin EP, and stir at 300 rpm for 2 h in an oil bath at 60 °C to obtain a matrix consisting of an E-PDMS / EP mixture.

[0077] The fCNF / acetone dispersion was added to the E-PDMS / EP mixture and stirred at 300 rpm in a 60 °C oil bath until the acetone was completely removed. The mixture was stirred until the room temperature was restored. Then, 8 g of curing agent phthalic anhydride and 0.16 g of accelerator 2,4,6-tris(dimethylaminomethyl)phenol were added and stirring was continued for 20 min. The mixture was vacuum degassed at 60 °C for 1 h. The mixture was cured at 120 °C for 2 h, 130 °C for 2 h, and 140 °C for 1 h.

[0078] Comparative Example 4

[0079] An epoxy resin composite material, the preparation process is as follows:

[0080] 0.9 g epoxy-functionalized polydimethylsiloxane E-PDMS and 10 g bisphenol A epoxy resin EP were mixed and stirred in an oil bath at 300 rpm at 60 °C for 2 h; stirring was continued, and after returning to room temperature, curing agent phthalic anhydride and accelerator 2,4,6-tris(dimethylaminomethyl)phenol were added and stirring was continued for 20 min; after stirring, vacuum degassing was performed at 60 °C for 1 h; curing was performed at 120 °C for 2 h, at 130 °C for 2 h, and at 140 °C for 1 h.

[0081] Comparative Example 5

[0082] An epoxy resin composite material, the preparation process is as follows:

[0083] Step 1: Disperse 1 g of cellulose nanofiber CNF in 20 g of N,N-dimethylformamide DNF and stir at 400 rpm for 8 h in an 80 °C oil bath to obtain a cellulose nanofiber solution.

[0084] 4 g of sulfinamide SOCl2 was added to CNF / DMF and stirred at 400 rpm for 24 h in an 80 °C oil bath to obtain a chlorinated cellulose nanofiber CNF-Cl / DMF solution with a mass concentration of 4 wt.%.

[0085] Step 2: 3.5 g of the CNF-Cl / DMF solution obtained in step 1 and 35 g of a DMSO solution of aramid nanofibers ANF (ANF / DMSO) with a mass concentration of 0.4 wt.% were mixed and stirred at 400 rpm for 24 h in an oil bath at 80 °C. Due to the effect of covalent bonds, cellulose nanofiber-modified aramid nanofibers ANF@CNF were obtained.

[0086] 5.7 mg of 3-glycidoxypropyltrimethoxysilane (GPTMS) was added to the mixed solution for silane functionalization, and the mixture was stirred at 400 rpm for 24 h in an oil bath at 80 °C to prepare fANF@CNF. The mixed solution was vacuum-assisted filtered, and fANF@CNF was washed four times with deionized water and acetone to obtain fANF@CNF / acetone dispersion.

[0087] The preparation process of ANF DMSO solution is as follows:

[0088] Kevlar fibers cut into small pieces of 1 to 1.5 cm were placed in acetone and ultrasonicated at 200 W for 12 h. After the end, the Kevlar fibers were filtered and dried under 60 vacuum conditions for 3 days. 1 g of the dried Kevlar fibers, 1.5 g of KOH and 250 mL of dimethyl sulfoxide (DMSO) were placed in a beaker and stirred at 600 rpm for 14 days at room temperature to obtain a 0.4 wt.% ANF / DMSO solution by deprotonation stripping.

[0089] Step 3: Mix 0.9 g of polydimethylsiloxane PDMS and 10 g of bisphenol A epoxy resin EP, and stir at 300 rpm for 2 h in a 60 °C oil bath to obtain a matrix composed of a PDMS / EP mixture.

[0090] The fANF@CNF / acetone dispersion was added to the PDMS / EP mixture and stirred at 300 rpm in an oil bath at 60 °C until the acetone was completely removed. The mixture was stirred until the room temperature was restored. Then, 8 g of curing agent phthalic anhydride and 0.16 g of accelerator 2,4,6-tris(dimethylaminomethyl)phenol were added and stirring was continued for 20 min. The mixture was vacuum degassed at 60 °C for 1 h. The mixture was cured at 120 °C for 2 h, 130 °C for 2 h, and 140 °C for 1 h.

[0091] Comparative Example 6

[0092] An epoxy composite material, the preparation process is as follows:

[0093] Step 1: Disperse 1 g of cellulose nanofiber CNF in 20 g of N,N-dimethylformamide DNF and stir at 400 rpm for 8 h in an 80 °C oil bath to obtain a cellulose nanofiber solution.

[0094] 4 g of sulfinamide SOCl2 was added to CNF / DMF and stirred at 400 rpm for 24 h in an 80 °C oil bath to obtain a chlorinated cellulose nanofiber CNF-Cl / DMF solution with a mass concentration of 4 wt.%.

[0095] Step 2: 3.5 g of the CNF-Cl / DMF solution obtained in step 1 and 35 g of a DMSO solution of aramid nanofibers ANF (ANF / DMSO) with a mass concentration of 0.4 wt.% were mixed and stirred at 400 rpm for 24 h in an oil bath at 80 °C. Due to the effect of covalent bonds, cellulose nanofiber-modified aramid nanofibers ANF@CNF were obtained.

[0096] 5.7 mg of 3-glycidoxypropyltrimethoxysilane (GPTMS) was added to the mixed solution for silane functionalization, and the mixture was stirred at 400 rpm for 24 h in an oil bath at 80 °C to prepare fANF@CNF. The mixed solution was vacuum-assisted filtered, and fANF@CNF was washed four times with deionized water and acetone to obtain fANF@CNF / acetone dispersion.

[0097] The preparation process of ANF DMSO solution is as follows:

[0098] Kevlar fibers cut into small pieces of 1 to 1.5 cm were placed in acetone and ultrasonicated at 200 W for 12 h. After the end, the Kevlar fibers were filtered and dried under 60 vacuum conditions for 3 days. 1 g of the dried Kevlar fibers, 1.5 g of KOH and 250 mL of dimethyl sulfoxide (DMSO) were placed in a beaker and stirred at 600 rpm for 14 days at room temperature to obtain a 0.4 wt.% ANF / DMSO solution by deprotonation stripping.

[0099] Step 3: Add the fANF@CNF / acetone dispersion to the bisphenol A epoxy resin EP, stir at 300 rpm in a 60 °C oil bath until the acetone is completely removed; keep stirring, and after returning to room temperature, add 8 g of curing agent phthalic anhydride and 0.16 g of accelerator 2,4,6-tris(dimethylaminomethyl)phenol and continue stirring for 20 min, and vacuum degas at 60 °C for 1 h; cure at 120 °C for 2 h, 130 °C for 2 h, and 140 °C for 1 h.

[0100] Comparative Example 7

[0101] An epoxy resin composite material, the preparation process is as follows:

[0102] Step 1: Disperse 1 g of cellulose nanofiber CNF in 20 g of N,N-dimethylformamide DNF and stir at 400 rpm for 8 h in an 80 °C oil bath to obtain a cellulose nanofiber solution.

[0103] 4 g of sulfinamide SOCl2 was added to CNF / DMF and stirred at 400 rpm for 24 h in an 80 °C oil bath to obtain a chlorinated cellulose nanofiber CNF-Cl / DMF solution with a mass concentration of 4 wt.%.

[0104] Step 2: Take 3.5 g of the CNF-Cl / DMF solution obtained in step 1 and 35 g of a DMSO solution of aramid nanofiber ANF (ANF / DMSO) with a mass concentration of 0.4 wt.%, and stir at 400 rpm for 24 h in an oil bath at 80 °C. Due to the effect of covalent bonds, cellulose nanofiber-modified aramid nanofiber ANF@CNF is obtained. The mixed solution is vacuum-assisted filtered, and the ANF@CNF is washed four times with deionized water and acetone to obtain an ANF@CNF / acetone dispersion.

[0105] The preparation process of ANF DMSO solution is as follows:

[0106] Kevlar fibers cut into small pieces of 1 to 1.5 cm were placed in acetone and ultrasonicated at 200 W for 12 h. After the end, the Kevlar fibers were filtered and dried under 60 vacuum conditions for 3 days. 1 g of the dried Kevlar fibers, 1.5 g of KOH and 250 mL of dimethyl sulfoxide (DMSO) were placed in a beaker and stirred at 600 rpm for 14 days at room temperature to obtain a 0.4 wt.% ANF / DMSO solution by deprotonation stripping.

[0107] Step 3: Mix 0.9 g of epoxy-functionalized polydimethylsiloxane E-PDMS and 10 g of bisphenol A epoxy resin EP, and stir at 300 rpm for 2 h in an oil bath at 60 °C to obtain a matrix consisting of an E-PDMS / EP mixture.

[0108] The ANF@CNF / acetone dispersion was added to the E-PDMS / EP mixture and stirred at 300 rpm in an oil bath at 60 °C until the acetone was completely removed. The mixture was stirred until the room temperature was restored. Then, 8 g of curing agent phthalic anhydride and 0.16 g of accelerator 2,4,6-tris(dimethylaminomethyl)phenol were added and stirring was continued for 20 min. The mixture was vacuum degassed at 60 °C for 1 h. The mixture was cured at 120 °C for 2 h, 130 °C for 2 h, and 140 °C for 1 h.

[0109] Figure 2 Schematic diagram of the Young's modulus results of Examples 1 to 5 of the present invention and Comparative Examples 1 to 4, Figure 3 It is a schematic diagram of the tensile strength results of Examples 1 to 5 of the present invention and Comparative Examples 1 to 4.

[0110] from Figure 2 and Figure 3 It can be seen that the strength improvement effect of the composite material treated with silane functionalization of nanofiber fillers using 3-glycidoxypropyltrimethoxysilane (GPTMS) is better than that of 3-aminopropyltriethoxysilane (APTES). fANF@CNF has the best mechanical strength when the content is 1.5 wt%. The improvement effect of fCNF, fANF / CNF, fANF, and fANF@CNF on the mechanical strength of the composite material increases in turn. The reason is that after chlorination, ANF and CNF form a covalent bond connection, and the CNF functionalization sites on ANF can achieve mechanical interlocking between nanofillers and epoxy matrix through a branched network structure, thereby significantly improving the strength of the composite material; when there is no covalent bond connection between ANF and CNF, the two nanofibers do not have a synergistic effect on the mechanical reinforcement of the composite material.

[0111] Figure 4 This is a schematic diagram of the average critical force intensity factor results of Examples 1, 2, 6, 7, 8 of the present invention and Comparative Examples 4, 5, 6, Figure 5 It is a schematic diagram of the impact strength results of Examples 1, 2, 6, 7, 8 of the present invention and Comparative Examples 4, 5, and 6. It can be seen from the figure that by comparing the average critical force intensity factor and impact strength results of Examples 1 and 2, it can be seen that the toughness improvement effect of the composite material using 3-glycidoxypropyltrimethoxysilane (GPTMS) as a silane coupling agent is better than that of 3-aminopropyltriethoxysilane (APTES). GPTMS can epoxy-functionalize the nanofiller, so that fANF@CNF forms an effective covalent bond interaction with the epoxy matrix, enhances crack bridging, and further improves the toughness of the composite material. By comparing the average critical force intensity factor and impact strength results of Examples 1, 6, 7, and 8, it can be seen that the E-PDMS content has the best toughness at 5 wt%, and the toughness shows a trend of first increasing and then decreasing with increasing filling content. By comparing the average critical force intensity factor and impact strength results of Example 1 and Comparative Examples 1 and 4, it can be seen that the addition of nanofibers can improve the toughness of the composite material. Comparing the average critical force intensity factor and impact strength results of Example 1 and Comparative Examples 5 and 6, it can be seen that the introduction of polydimethylsiloxane flexible segments can significantly improve the toughness of the composite material, and epoxy functionalization can further improve its modification effect. This is because E-PDMS has better compatibility and interfacial bonding strength with the epoxy matrix, and the more fully cross-linked structure makes the PDMS flexible segments deform when the composite material is subjected to external force and fully absorb and disperse the impact energy, further improving the toughening effect of the composite material.

[0112] Figure 6Schematic diagram of the glass transition temperature results of Example 1 of the present invention and Comparative Examples 1, 4, 6, and 7. As can be seen from the figure, the Tg of the composite material is increased after the addition of nanofibers, and the effect of fANF@CNF on the improvement of Tg is the most obvious. On the one hand, this is because the CNF functionalization sites on the ANF can achieve mechanical interlocking between the nanofiller and the epoxy matrix through the branched network structure, and on the other hand, it is because the silane functionalization can effectively improve the interaction between the nanofiller and the epoxy matrix to form a covalent bond. Under the joint action of mechanical interlocking and covalent bond connection, the movement of the epoxy molecular chain is restricted. Since Tg represents the chain mobility of the polymer matrix in the composite material, Tg is improved. Comparing the glass transition temperatures of Example 1 and Comparative Example 6, it can be seen that the addition of E-PDMS increases the Tg of the composite material, because the increase in crosslinking density will delay the relaxation process of the epoxy molecular chain.

[0113] The present invention introduces epoxy-functionalized polydimethylsiloxane E-PDMS as a toughening flexible segment into an epoxy resin matrix, and introduces aramid nanofiber fANF@CNF modified by silane-functionalized cellulose nanofibers as a rigid nanofiber filler to form a ternary composite structure epoxy dielectric, thereby significantly improving the comprehensive performance of epoxy composite materials. With the increase of crosslinking density, the matrix solubility decreases and phase separation occurs. The cavitation effect produced by the rubber particle phase achieves a significant improvement in the toughness of the epoxy resin; the rigid nanofiber filler has a high aspect ratio, a high specific surface area and excellent mechanical properties. Its addition improves the strength of the composite dielectric, while creating more obstacles to the expansion of cracks, reducing the mobility of the epoxy molecular chain, and further improving the toughness and Tg. The ternary composite structure overcomes the problem of reduced strength and glass transition temperature Tg in the toughening process of traditional thermosetting resins, and achieves a synergistic improvement in the strength, toughness and thermal properties of epoxy composite dielectrics.

[0114] The CNF functionalized sites on fANF@CNF can achieve mechanical interlocking between nanofillers and epoxy matrix through branched network structure, and silane functionalization can effectively improve the interaction between nanofillers and epoxy matrix. Under the combined effect of the two effects, the strength of the composite material is significantly improved; at the same time, the rigid epoxy groups on the E-PDMS chain segments can also improve the strength of the composite material to a certain extent. E-PDMS has good compatibility and interfacial adhesion strength with the epoxy matrix, which can effectively improve phase separation, increase crosslinking density, and achieve significant toughening; the covalent bond interaction between fANF@CNF and epoxy matrix can enhance crack bridging and further improve the toughness of the composite material. The tight crosslinking of E-PDMS and epoxy matrix can delay the relaxation process of epoxy molecular chains; the mechanical interlocking and covalent bond interaction between nanofillers and epoxy matrix can also limit the movement of epoxy molecular chains, and the chain mobility of the polymer matrix in the composite material is reduced, which effectively improves the Tg of the composite material.

[0115] The present invention introduces functionalized PDMS flexible segments into the rigid epoxy resin matrix to improve interface compatibility and bonding strength, effectively reduce phase separation, construct an energy dissipation network, and significantly improve toughness; rigid fiber particles fANF@CNF with good bonding performance with the epoxy matrix are introduced into the E-PDMS / EP binary system as the third phase, and the synergistic effect between the three phases achieves a synergistic improvement in toughness, strength and glass transition temperature.

Claims

1. A method for preparing an epoxy resin composite material based on flexible chain segments and rigid fiber particles, characterized in that: The following steps are involved: Step 1: Disperse cellulose nanofibers CNF in a solvent to obtain a cellulose nanofiber solution, add thionyl chloride SOCl2, mix thoroughly and react to obtain a chlorinated cellulose nanofiber CNF-Cl solution; Step 2: After the CNF-Cl solution obtained in step 1 and the aramid nanofiber ANF solution are fully mixed, a silane coupling agent is added to fully mix and react, and the solvent is removed to obtain aramid nanofiber fANF@CNF modified with silane functionalized cellulose nanofibers; Step 3: Add the fANF@CNF obtained in step 2 to the epoxy resin EP matrix containing epoxy functionalized polydimethylsiloxane E-PDMS, mix thoroughly, add curing agent and accelerator, vacuum degas, and obtain the desired composite material after curing.

2. The method for preparing an epoxy resin composite material based on flexible segments and rigid fiber particles according to claim 1, characterized in that: In the step 1, the mass ratio of CNF to SOCl2 is 1:4, and the reaction temperature is 80°C.

3. The method for preparing an epoxy resin composite material based on flexible segments and rigid fiber particles according to claim 1, characterized in that: In the step 2, the mass ratio of CNF-Cl to ANF is 1:1; and the reaction temperature is 80°C.

4. The method for preparing an epoxy resin composite material based on flexible segments and rigid fiber particles according to claim 1, characterized in that: The silane coupling agent is one of 3-aminopropyltriethoxysilane and 3-glycidoxypropyltrimethoxysilane; the solvent is removed by vacuum-assisted filtration, and then washed.

5. The method for preparing an epoxy resin composite material based on flexible segments and rigid fiber particles according to claim 1, characterized in that: In the step 3, the mass ratio of E-PDMS to EP in the matrix is ​​4.5-18:90-110; the mass ratio of fANF@CNF to EP in the matrix is ​​0.9-3.6:90-110.

6. The method for preparing an epoxy resin composite material based on flexible segments and rigid fiber particles according to claim 1, characterized in that: The temperature of the mixing process in step 3 is 60°C, and the curing agent and the accelerator are added at room temperature; the vacuum degassing temperature in step 3 is 60°C, and the time is 1 h.

7. The method for preparing an epoxy resin composite material based on flexible segments and rigid fiber particles according to claim 1, characterized in that: The heating and curing process in step 3 is as follows: First, cure at 120 °C for 2 h, then at 130 °C for 2 h, and finally at 140 °C for 1 h.

8. The method for preparing an epoxy resin composite material based on flexible segments and rigid fiber particles according to claim 1, characterized in that: In the step 3, the mass ratio of the curing agent, the accelerator and the EP in the matrix is ​​72-88:1.4-1.8:90-110.

9. The method for preparing an epoxy resin composite material based on flexible segments and rigid fiber particles according to claim 1, characterized in that: The curing agent is one of phthalic anhydride and maleic anhydride; the accelerator is one of 2,4,6-tris(dimethylaminomethyl)phenol, triethylamine, triethanol and o-hydroxybenzyldimethylamine.

10. An epoxy resin composite material based on flexible segments and rigid fiber particles obtained by any one of the preparation methods of claims 1 to 9.

Images