CN110757908A - Method for synergistically toughening carbon fiber epoxy composite material by using porous nanofiber membrane - Google Patents

Abstract

The invention discloses a method for synergistically toughening carbon fiber epoxy composite materials with porous nanofiber membranes. The method steps include: 1. preparing nylon 66 nanofiber membranes by electrospinning technology; 2. acidizing carbon nanotubes Obtain the carboxylated carbon nanotubes; 3. Put the carboxylated carbon nanotubes into deionized water for ultrasonic treatment to make it disperse uniformly; 4. Put the nylon 66 nanofiber membrane into the uniform carboxylated carbon nanotube solution for ultrasonic treatment A nylon 66/carbon nanotube porous nanofiber membrane is obtained; 5. Apply epoxy resin on the carbon fiber cloth, and at the same time place the nylon 66/carbon nanotube porous nanofiber membrane in the middle layer, and solidify to obtain a carbon fiber epoxy composite laminate . The nylon 66/carbon nanotube porous nanofiber membrane prepared by the invention not only reduces the cost, but also realizes the interlayer toughening of the composite material and improves the interlaminar fracture of the composite material while maintaining the original form of the composite material. toughness.

Description

A method for synergistically toughening carbon fiber epoxy composites with porous nanofiber membranes

technical field

The invention belongs to the technical field of toughening and strengthening of composite materials, in particular to a method for synergistically toughening carbon fiber epoxy composite materials of nylon 66 (PA66)/carbon nanotube (CNTs) porous nanofiber membranes.

Background technique

Carbon fiber/epoxy composites have been widely used in aerospace and other fields due to their light weight, excellent mechanical properties, and thermal stability. However, the highly cross-linked network structure of epoxy resin and the weak ability of layered carbon fiber/epoxy composites to resist the load in the thickness direction make such composites prone to "delamination", that is, the phenomenon of interlayer debonding or cracking, which seriously limits the Applications of this high-performance composite material in the engineering field. Therefore, how to effectively suppress the delamination damage of composite materials and improve the interlaminar fracture toughness is the key problem to be solved urgently in the development and application of laminate composite materials.

At present, a lot of research work at home and abroad has been devoted to improving the interlaminar fracture toughness of carbon fiber/epoxy composites and reducing delamination damage. The main methods are Z-direction toughening, matrix toughening, fiber modification and so on. However, these methods result in increased composite manufacturing costs, increased mass, or loss of in-plane properties, among others.

SUMMARY OF THE INVENTION

Aiming at the toughening requirements of carbon fiber epoxy composite materials, the present invention aims to provide a porous nanofiber membrane synergistically toughening carbon fiber epoxy composite materials, so as to solve the problems of delamination, degumming and cracking of composite materials, reduce costs, and prevent in-plane performance loss.

In order to achieve the above object, the technical scheme of the present invention is:

S1. Preparation of electrospinning PA66 nanofiber membrane, the preparation process includes:

S11. Dissolve the PA66 pellets in a mixed solution of formic acid and dichloromethane with a ratio of 3:2w/w, and stir for 3-6h to obtain a PA66 solution with a concentration of 10-15wt%;

S12, electrospin the PA66 nanofibers in the PA66 solution obtained in S11 onto an aluminum foil collector, and collect the PA66 nanofiber membrane from the collector after 15-20 hours;

S2, the preparation of carboxylated CNTs, the preparation process includes:

S21. Put 1 to 3 grams of CNTs into 100 to 140 ml of a mixed acid solution of H ₂ SO ₄ and HNO ₃ with a volume ratio of 3:1, stir evenly, and condense and reflux in a constant temperature water bath at 60 to 90°C for 6 to 9 hours;

S22. When the mixed solution after refluxing is cooled to room temperature, add deionized water to dilute to neutrality, and dry at 50-80° C. for 20-28 hours to obtain carboxylated CNTs;

S3. Preparation of carboxylated PA66/CNTs porous nanofiber membrane, the preparation process includes:

Take 0.3-0.6 g of the carboxylated CNTs prepared in S2, dissolve it in deionized water for 50-70 minutes and ultrasonically treat it for 50-70 minutes to obtain a uniformly dispersed solution, add the PA66 nanofiber film prepared in step S12 and ultrasonically treat it for 10-20 minutes. The PA66 nanofiber membrane loaded with carboxylated CNTs was washed with deionized water for 2-3 times to obtain a carboxylated PA66/CNTs porous nanofiber membrane;

S4, the preparation of carbon fiber epoxy composite laminate, the preparation process includes:

S41. Heat and stir 40-60 g of bisphenol A epoxy resin at 50-70 °C for 25-35 minutes, add 40-50 g of curing agent and mix evenly, remove air bubbles under vacuum at 50-70 °C, apply On 16 layers of carbon fiber cloth;

S42, insert a 20-30 μm thick polytetrafluoroethylene film between the 8th and 9th layers of the 16-layer carbon fiber cloth as an initial crack, and place the carboxylated PA66/CNTs porous nanofiber film obtained in step S3 A PTFE film is inserted between the 8th layer and the 9th layer of the 16-layer carbon fiber cloth to make a composite material;

S43 , sealing and vacuuming the composite material prepared in step S42 as a whole for 20-30 min, and after curing, a carbon fiber epoxy composite material laminate toughened by a PA66/CNTs porous nanofiber membrane is obtained.

Wherein, the electrospinning conditions in step S12 are that the flow rate is 0.5-1 ml/h, and the voltage is 20-25 kV.

Wherein, the radius of the electrospun PA66 nanofibers in step S12 is 100-500 nm.

Wherein, the curing agent described in step S41 is methyl hexahydrophthalic anhydride and N,N-

Dimethylbenzylamine mixture.

Wherein, the curing conditions described in step S43 are at 180-220 kPa, hot pressing at room temperature-90 °C for 30 min, hot pressing at 90 °C-120 °C for 60 min, hot pressing at 120 °C-140 °C for 90 min, hot pressing at 140 °C-160 °C for 90 min Press for 120min.

The results show that the type I fracture energy of the PA66 film toughened carbon fiber epoxy composite laminate is 0.58kJ/m ² increased by 55%, and the type I fracture energy of the PA66/CNTs porous nanofiber toughened carbon fiber epoxy composite laminate is increased by 55%. It is increased by 115% to ^0.82kJ /m2, which effectively realizes the interlayer toughening of the composite material.

The present invention only adds a tough layer in the area where the composite material is prone to stress concentration, that is, in the interlayer part, and this method can more directly and effectively inhibit the delamination of the laminate without changing the original process. The present invention utilizes the excellent properties of PA66 nanofibers such as high porosity and large specific surface area, and the large specific surface area and rigidity of CNTs to synergistically toughen carbon fiber epoxy composite materials, wherein the excellent properties of PA66 nanofibers not only enable carbon nanotubes to be uniformly loaded On the PA66 nanofiber, the permeability of the epoxy resin matrix between the nanofiber membrane layers is also improved, which is a new and effective interlayer toughening method.

Besides, the porous nanofiber membrane prepared by the invention also has the characteristics of low price, excellent chemical stability, high specific surface area, large porosity and the like. The described preparation method is simple, controllable, safe and pollution-free.

Description of drawings

FIG. 1 is an infrared spectrogram of the carboxylated CNTs of Example 1. FIG.

2 is a macrophotograph of the PA66/CNTs porous nanofiber membrane of Example 1.

3 is a scanning electron microscope image of the PA66/CNTs porous nanofiber membrane of Example 1.

4 is a transmission electron microscope image of the PA66/CNTs porous nanofiber membrane of Example 1.

Figure 5 is a scanning electron microscope image of the fracture surface of the untoughened carbon fiber epoxy composite.

FIG. 6 is a scanning electron microscope image of the fracture surface of the PA66/CNTs (12wt%/0.5wt%) porous nanofiber membrane toughened carbon fiber epoxy composite laminate.

Figure 7 is a bar graph of the I-type interlaminar fracture energy (G _Ic ) of the carbon fiber epoxy composite laminate.

Detailed ways

Example 1

1. Preparation of electrospun PA66 nanofiber membrane

3 g of PA66 pellets were dissolved in 25 ml of formic acid and dichloromethane with a ratio of 3:2 w/w, and a PA66 solution with a concentration of 12 wt % was obtained after stirring for 4 h. Subsequently, the PA66 solution was placed in a syringe, and the PA66 nanofibers with a radius of 100 nm were electrospun onto an aluminum foil collector at a flow rate of 1 ml/h and a voltage of 25 kV. After 15 h, the PA66 nanofiber membrane was collected from the collector.

2. Preparation of carboxylated CNTs

Add 3 g of CNTs to 140 ml of a mixed acid solution of H ₂ SO ₄ and HNO ₃ with a volume ratio of 3:1, stir evenly, condense and reflux for 8 h in a constant temperature water bath at 80 °C, and add deionized water to dilute the resulting mixed solution after cooling to room temperature. To neutrality, finally put it into a 60°C oven to dry for 24 hours to obtain carboxylated CNTs, and characterize the product. As shown in Figure 1, the product has a carboxyl peak (1713 cm ^-1 ), so the obtained product is carboxylated CNTs.

3. Preparation of carboxylated PA66/CNTs porous nanofibrous membranes

Take 0.3 g of the carboxylated CNTs prepared in step 2, dissolve it in deionized water for 1 h to obtain a uniformly dispersed solution, then add the PA66 nanofiber film prepared in step 1 and ultrasonically treat it for 15 min. The fiber membrane was washed three times with deionized water to obtain the PA66/CNTs porous nanofiber membrane. The macroscopic photo is shown in Fig. 2, the scanning electron microscope image is shown in Fig. 3, and the transmission electron microscope image is shown in Fig. 4.

4. Preparation of carbon fiber epoxy composite laminates

50g of bisphenol A epoxy resin was heated and stirred for 30min at 60°C, and 45.95g of curing agent was added in a mass ratio of 185:170 and mixed evenly, and the curing agent was methylhexahydrophthalic anhydride with a mass ratio of 100:1 and N,N-Dimethylbenzylamine mixture. After the bisphenol A epoxy resin and the curing agent were removed under vacuum at 60°C, they were uniformly spread on 16 layers of 25cm×30cm carbon fiber cloth by hand lay-up. A 25μm thick PTFE film was inserted into the middle layer of the 16 layers of 25cm×30cm carbon fibers, that is, between the eighth layer and the ninth layer, as an initial crack, the carboxylated PA66/CNTs prepared in step 3 were The porous nanofiber membrane is inserted between the eighth and ninth layers of the laminate next to the PTFE membrane, that is, the stacking sequence is: 8 layers of carbon fiber cloth, PTFE membrane, carboxylated PA66/CNTs porous nanofibers Membrane, 8 layers of carbon fiber cloth. Subsequently, the composite material prepared above was sealed and evacuated for 20 min, and then put into a hot press for curing at 200 kPa to obtain a carbon fiber epoxy composite laminate toughened by PA66/CNTs porous nanofiber membrane. The curing conditions are: room temperature-90°C hot pressing for 30 minutes, 90°C-120°C hot pressing for 60 minutes, 120°C-140°C hot pressing for 90 minutes, and 140°C-160°C hot pressing for 120 minutes.

The WDW-10E microcomputer-controlled electronic universal testing machine was used to test the type I fracture toughness of the samples, and the type I fracture toughness column chart as shown in Figure 7 was obtained, which respectively reflected the untoughened carbon fiber epoxy composite laminate, PA66 nanometer Mode I fracture energy of fiber membrane toughened carbon fiber epoxy composite laminates and PA66/CNTs porous nanofiber membrane toughened carbon fiber epoxy composite laminates. The results show that: the type I fracture energy of the PA66 film toughened carbon fiber epoxy composite laminate is 0.58kJ/m ² , which is increased by 55%, and the I The fracture energy of 0.82kJ/m ² is improved by 115%. The research results show that the use of nylon 66/carbon nanotube porous nanofiber membrane synergistically toughening the carbon fiber epoxy composite material in the present invention can greatly improve its interlaminar fracture toughness. The SEM image of the fracture surface of the untoughened carbon fiber epoxy composite is shown in Figure 5, and the SEM image of the fracture surface of the PA66/CNTs (12wt%/0.5wt%) porous nanofiber membrane toughened carbon fiber epoxy composite laminate is shown in Figure 5. The diagram is shown in Figure 6.

The above is only a specific embodiment of the present invention, but the protection scope of the present invention is not limited to this. The equivalent replacement or modification of its inventive concept shall be included within the protection scope of the present invention.

Claims (5)

1. a method for porous nanofiber membrane synergistic toughening carbon fiber epoxy composite material, is characterized in that, comprises the steps: S1. Preparation of electrospinning PA66 nanofiber membrane, the preparation process includes: S11. Dissolve the PA66 pellets in a mixed solution of formic acid and dichloromethane with a ratio of 3:2w/w, and stir for 3-6h to obtain a PA66 solution with a concentration of 10-15wt%; S12, electrospin the PA66 nanofibers in the PA66 solution obtained in S11 onto an aluminum foil collector, and collect the PA66 nanofiber membrane from the collector after 15-20 hours; S2, the preparation of carboxylated CNTs, the preparation process includes: S21. Put 1 to 3 grams of CNTs into 100 to 140 ml of a mixed acid solution of H ₂ SO ₄ and HNO ₃ with a volume ratio of 3:1, stir evenly, and condense and reflux in a constant temperature water bath at 60 to 90°C for 6 to 9 hours; S22. When the mixed solution after refluxing is cooled to room temperature, add deionized water to dilute to neutrality, and dry at 50-80° C. for 20-28 hours to obtain carboxylated CNTs; S3. Preparation of carboxylated PA66/CNTs porous nanofiber membrane, the preparation process includes: Take 0.3-0.6 g of the carboxylated CNTs prepared in S2, dissolve it in deionized water for 50-70 minutes and ultrasonically treat it for 50-70 minutes to obtain a uniformly dispersed solution, add the PA66 nanofiber film prepared in step S12 and ultrasonically treat it for 10-20 minutes. The PA66 nanofiber membrane loaded with carboxylated CNTs was washed with deionized water for 2-3 times to obtain a carboxylated PA66/CNTs porous nanofiber membrane; S4, the preparation of carbon fiber epoxy composite laminate, the preparation process includes: S41. Heat and stir 40-60 g of bisphenol A epoxy resin at 50-70 °C for 25-35 minutes, add 40-50 g of curing agent and mix evenly, remove air bubbles under vacuum at 50-70 °C, apply On 16 layers of carbon fiber cloth; S42, insert a 20-30 μm thick polytetrafluoroethylene film between the 8th and 9th layers of the 16-layer carbon fiber cloth as an initial crack, and place the carboxylated PA66/CNTs porous nanofiber film obtained in step S3 A PTFE film is inserted between the 8th layer and the 9th layer of the 16-layer carbon fiber cloth to make a composite material; S43 , sealing and vacuuming the composite material prepared in step S42 as a whole for 20-30 min, and after curing, a carbon fiber epoxy composite material laminate toughened by a PA66/CNTs porous nanofiber membrane is obtained. 2 . The method for synergistically toughening carbon fiber epoxy composites with porous nanofiber membranes according to claim 1 , wherein the electrospinning conditions in step S12 are that the flow rate is 0.5-1 ml/h, and the voltage is 20-25 kV. 3 . 3 . The method for synergistically toughening carbon fiber-epoxy composites with porous nanofiber membranes according to claim 1 , wherein the electrospun PA66 nanofibers have a radius of 100-500 nm in step S12 . 4. the method for a kind of porous nanofiber membrane synergistic toughening carbon fiber epoxy composite material according to claim 1, the curing agent described in step S41 is methyl hexahydrophthalic anhydride and N,N- Dimethylbenzylamine mixture. 5. A method for synergistically toughening carbon fiber epoxy composites with porous nanofiber membranes according to claim 1, wherein the curing conditions in step S43 are: ℃-120℃ hot pressing for 60min, 120℃-140℃ hot pressing for 90min, 140℃-160℃ hot pressing for 120min.

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