A method for preparing a nonwoven nylon veil for low temperature toughening of carbon fiber composites

Abstract

The application discloses a preparation method of a non-woven nylon screen gauze for low-temperature toughening of carbon fiber composite materials, and the method comprises the following steps: cutting continuous nylon fibers into nylon short fibers with a certain length, then adding the nylon short fibers into a dispersing agent, uniformly stirring, and sufficiently dispersing the nylon short fibers to obtain nylon short fiber slurry. Then, the nylon short fiber slurry is filtered and settled through a papermaking machine, an adhesive is sprayed on the surface of the nylon short fiber slurry, and the non-woven nylon screen gauze is obtained after drying treatment. The non-woven nylon screen gauze prepared by the method can be intercalated into composite material interlayers, and can effectively improve the interlayer toughness of the composite materials in an ultralow-temperature environment.

Description

TECHNICAL FIELD

[0001] The present application belongs to the field of advanced composite interlaminar toughening at low temperature, and particularly relates to a preparation method of non-woven nylon screen gauze suitable for interlaminar toughening at low temperature. BACKGROUND

[0002] With the rise of interstellar travel and deep space exploration concepts, further improving the structural efficiency of launch vehicles has become a hot topic in the aerospace field. Low-temperature fuels represented by liquid hydrogen and liquid oxygen have the advantages of high specific impulse and green and pollution-free, and have become the ideal space fuel to replace traditional unsymmetrical dimethylhydrazine. However, due to the low density of liquid hydrogen, a larger fuel tank is needed in the design process. The traditional tank with metal as the main material will greatly increase the weight of the rocket propeller, increase the launch cost, and reduce the core carrying efficiency of the rocket. Carbon fiber reinforced epoxy resin matrix composite (CFRP) has the advantages of light weight, high strength, corrosion resistance, and strong designability, and plays an important role in the lightweight process of aerospace, rail transportation, and new energy industries. Research shows that selecting CFRP as the main material of the low-temperature fuel tank can reduce the weight of the tank by 20%-40%, reduce the launch cost of the spacecraft by 30%, and the weight reduction effect is more obvious as the volume of the tank increases.

[0003] In the application of CFRP low-temperature tank, the leakage failure is often more obvious than the structural failure. The leakage failure mainly includes two forms: diffusion leakage and micro-crack leakage. The diffusion rate of fluid through a laminate without micro-cracks or internal defects is very low, so there is no need to worry about diffusion leakage, but micro-crack leakage should be paid attention to. At the same time, due to the lack of fiber connection between the layers of the laminate, only the resin is used for bonding, which leads to delamination damage. For the tank, it will form a leakage channel, which will cause a major safety hazard to the space rocket. At the same time, the difference between the thermal expansion coefficients of the fiber and the resin in the carbon fiber composite material is very large, and stress concentration is more likely to occur between the layers at low temperature, so it is particularly important to toughen the composite material used in low-temperature environment.

[0004] At present, the methods for improving the toughness of carbon fiber composites mainly include matrix toughening, interlaminar toughening, and Z-direction toughening. Among them, interlaminar toughening refers to taking the interlaminar region of the composite material as a separate controllable object, and only the interlaminar region is selectively toughened, which greatly improves the interlaminar toughness of the composite material while maintaining its original in-plane mechanical properties and original process. Common interlaminar toughening techniques for composites mainly include particle interlaminar toughening, film interlaminar toughening, and fiber interlaminar toughening. Among them, fiber interlaminar toughening has a wide range of applications and good toughening effect.

[0005] Chinese patent CN114261110A (published on April 1, 2022) discloses a method for preparing a thermoplastic non-woven fabric interlayer toughened carbon fiber composite material by melt deposition. The method prepares a melt deposition filament from a wire, prints in a continuous manner in four directions on the same plane according to the design, and prints a non-woven fabric. The advantage of this method is that it can ensure the uniformity of the toughening layer and does not affect the flowability of the resin during the molding process. The disadvantage of this method is that the interlayer thickness of the prepared composite material is large, and the size of the prepared thermoplastic non-woven fabric is also limited.

[0006] Chinese patent CN116790092A (published on September 22, 2023) discloses a method for preparing a superfine fiber toughened carbon fiber epoxy resin composite material. The method blends a high-melting-point thermoplastic polymer and a low-melting-point thermoplastic polymer to obtain a uniform spinning solution, and prepares superfine fibers from the uniform spinning solution by electrospinning technology. The advantage of this method is that the toughening material can realize interlayer toughening of the carbon fiber composite material while maintaining the original form of the carbon fiber composite material, which can significantly improve the impact performance, interlayer shear performance, and bending performance of the composite material. However, the preparation process of this method is complex, and the limitation of electrospinning production efficiency makes it impossible to be applied on a large scale. SUMMARY

[0007] The technical problem to be solved by the present application is to provide a non-woven nylon screen for low-temperature toughening of carbon fiber composite materials and a preparation method thereof, which overcomes the shortcomings of poor interlayer toughness and uneven toughening components of existing carbon fiber composite materials.

[0008] The preparation method of the non-woven nylon screen for low-temperature toughening of carbon fiber composite materials of the present application comprises the following steps:

[0009] Step (1) cut the continuous nylon fibers into nylon short fibers of a certain length, then add them to a dispersing agent, and stir at high speed to uniformly disperse the nylon short fibers in the dispersing agent to obtain a nylon short fiber slurry.

[0010] Step (2) filter and settle the nylon short fiber slurry obtained in step (1) through a web forming system to obtain a wet non-woven nylon screen.

[0011] Step (3) spray an adhesive on the surface of the wet non-woven nylon screen obtained in step (2), and then dry the non-woven nylon screen after drying treatment to obtain a non-woven nylon screen.

[0012] The nylon fiber in the step (1) can be a mixture of one or more of poly-caprolactam fiber, poly-hexamethylene adipamide fiber, poly-dodecanolactam fiber, poly-hexamethylene sebacamide, poly-hexamethylene dodecanamide fiber and the like nylon fibers obtained by condensation of different carbon chain length diamines and diacids, the nylon fiber diameter is 10-50 μm, and the length of the chopped nylon fiber is 10-25 mm. The dispersant can be a mixture of one or more of polyethyleneimine, polyvinylpyrrolidone, polyvinyl alcohol, oxidized polyethylene wax, polyethylene glycol 200 and water, and the content of the dispersant is 0.001wt%-1wt% of the content of water.

[0013] The adhesive in the step (3) can be a dispersion of water mixed with one or more of polyurethane, polyacrylate, polysiloxane, ethylene-vinyl acetate copolymer, epoxy resin and the like. The drying temperature is 40℃-100℃, and the time is 3h-12h.

[0014] The technical scheme adopted by the present application has the following effects compared with the prior art:

[0015] 1. The thickness and area density of the low-temperature interlaminar toughening non-woven nylon screen prepared by the present application are controllable, and the melting point, solubility, fiber diameter and fiber density of the non-woven nylon screen can be reasonably adjusted according to the composite material preparation process and preparation conditions.

[0016] 2. The non-woven nylon screen in the present application not only has a toughening effect on the composite material at room temperature, but also has a good interlaminar toughening effect on the carbon fiber composite material at ultra-low temperature (lower than liquid nitrogen temperature-196℃).

[0017] (3) The non-woven nylon screen in the present application is suitable for different composite material forming processes such as prepreg molding process and vacuum resin infusion process, and can ensure that the introduction of the non-woven nylon screen does not significantly reduce the fiber volume content of the composite material. DETAILED DESCRIPTION

[0018] The present application will be further described below in conjunction with specific examples. It should be understood that these examples are only used to illustrate the present application and not to limit the scope of the present application. In addition, it should be understood that those skilled in the art can make various modifications or modifications to the present application after reading the content taught by the present application, and these equivalent forms also fall within the scope defined by the claims attached hereto.

[0019] A preparation method of a non-woven nylon screen for low-temperature toughening of carbon fiber composite material, characterized in that it comprises the following steps:

[0020] Step (1) chop the continuous nylon fiber into nylon short fibers of a certain length, then add them into a dispersant, and stir at high speed to uniformly disperse the nylon short fibers in the dispersant to obtain a nylon short fiber slurry;

[0021] The nylon fiber is a condensate of different carbon chain length diamines and diacids, specifically one or a mixture of poly-caprolactam fiber, poly-hexamethylene adipate fiber, poly-dodecanolactam fiber, poly-hexamethylene sebacate, poly-hexamethylene dodecanedioate fiber, the diameter of the nylon fiber is 10-50 mu m, and the length of the chopped nylon fiber is 10-25 mm.

[0022] The dispersant is a mixture of one or more of polyethyleneimine, polyvinylpyrrolidone, polyvinyl alcohol, oxidized polyethylene wax, and polyethylene glycol 200 and water, and the content of the dispersant is 0.001wt%-1wt% of the content of water.

[0023] Step (2) filters and settles the nylon short fiber slurry obtained in step (1) through a web system to obtain a wet non-woven nylon gauze;

[0024] Step (3) sprays an adhesive on the surface of the wet non-woven nylon gauze obtained in step (2), and then after drying treatment, a non-woven nylon gauze is obtained.

[0025] The adhesive is a water dispersion of one or more mixtures of polyurethane, polyacrylate, polysiloxane, ethylene-vinyl acetate copolymer, and epoxy resin.

[0026] The drying temperature is 40℃-100℃, and the time is 3h-12h. The thickness of the non-woven nylon gauze is less than or equal to 50 mu m, and the area density is 4gsm-20gsm.

[0027] The non-woven nylon gauze prepared by the present application can realize interlaminar toughening of the composite material in a low temperature environment.

[0028] Example 1

[0029] (1) Cut the continuous poly-caprolactam fiber with a diameter of 15 mu m into poly-caprolactam chopped fiber with a length of 10-15 mm, then weigh 30 g of poly-caprolactam chopped fiber and add it to a 0.01% polyvinyl alcohol dispersion, and stir at high speed to uniformly disperse the poly-caprolactam chopped fiber in the polyvinyl alcohol dispersion to obtain a poly-caprolactam chopped fiber slurry.

[0030] (2) Filter and settle the poly-caprolactam chopped fiber slurry obtained in step (1) through a web system to obtain a wet non-woven poly-caprolactam fiber gauze.

[0031] (3) Spray 0.2 g of epoxy resin adhesive on the surface of the wet non-woven poly-caprolactam fiber gauze obtained in step (2), and dry at 60℃ for 12h to obtain a non-woven poly-caprolactam fiber gauze, the area density of the gauze is 8gsm, and the thickness is 30 mu m.

[0032] (4) Cut the carbon fiber / epoxy unidirectional prepreg tape to the desired size, cross-lay the non-woven polycaproamide fiber web yarn obtained in step (3) with the carbon fiber / epoxy prepreg, and place it in a mold after the laying is completed.

[0033] (5) Put the mold in step (4) into a hot press for curing and molding, vacuumize for 30 min, and keep the mold in a vacuum state. The curing and molding system is based on the curing system of the epoxy resin in the prepreg. The resin curing system of the prepreg this time is: 100℃ / 1h+120℃ / 1h+180℃ / 4h. After curing is completed, keep pressure and cool down, and then the toughened carbon fiber composite material can be obtained.

[0034] Example 2

[0035] (1) Cut the continuous polydodecanamide fiber with a diameter of 25μm into polydodecanamide short-cut fiber with a length of 10-20mm, then take 40g of the polydodecanamide short-cut fiber and add it into 0.01% polyethylene glycol 200 dispersion liquid, and stir at high speed to uniformly disperse the polydodecanamide short-cut fiber in the polyethylene glycol 200 dispersion liquid, and obtain polydodecanamide short-cut fiber slurry.

[0036] (2) Filter and settle the polydodecanamide short-cut fiber slurry obtained in step (1) through a webbing system to obtain a wet non-woven polydodecanamide fiber web yarn.

[0037] (3) Spray 0.3g of polyurethane adhesive on the surface of the wet non-woven polydodecanamide web yarn obtained in step (2), and dry at 80℃ for 10h to obtain a non-woven polydodecanamide fiber web yarn, with a web yarn surface density of 12gsm and a thickness of 40μm.

[0038] (4) Cut the carbon fiber / epoxy unidirectional prepreg tape to the desired size, cross-lay the non-woven polydodecanamide fiber web yarn obtained in step (3) with the carbon fiber / epoxy prepreg, and place it in a mold after the laying is completed.

[0039] (5) Put the mold in step (4) into a hot press for curing and molding, vacuumize for 30 min, and keep the mold in a vacuum state. The curing and molding system is based on the curing system of the epoxy resin in the prepreg. The resin curing system of the prepreg this time is: 100℃ / 1h+120℃ / 1h+180℃ / 4h. After curing is completed, keep pressure and cool down, and then the toughened carbon fiber composite material can be obtained.

[0040] Example 3

[0041] (1) Cut continuous polyhexamethylene adipate fibers with a diameter of 30 μm into polyhexamethylene adipate short-cut fibers with a length of 10-15 mm, then take 50 g of the polyhexamethylene adipate short-cut fibers and add them to a 0.02% polyvinyl alcohol dispersion, and stir at high speed to uniformly disperse the polyhexamethylene adipate short-cut fibers in the polyvinyl alcohol dispersion, to obtain a polyhexamethylene adipate short-cut fiber slurry.

[0042] (2) Filter and settle the polyhexamethylene adipate short-cut fiber slurry obtained in step (1) through a web system to obtain a wet non-woven polyhexamethylene adipate fiber web.

[0043] (3) Spray 0.4 g of epoxy resin adhesive on the surface of the wet non-woven polyhexamethylene adipate fiber web obtained in step (2), and dry at 80°C for 12 h to obtain a non-woven polyhexamethylene adipate fiber web with a web surface density of 15 gsm and a thickness of 45 μm.

[0044] (4) Cut the carbon fiber / epoxy unidirectional prepreg tape to the desired size, and cross-lay the non-woven polyhexamethylene adipate fiber web obtained in step (3) with the carbon fiber / epoxy prepreg, and then place it in a mold.

[0045] (5) Place the mold in step (4) in a hot press for curing and molding, and vacuum for 30 min to maintain a vacuum state in the mold. The curing and molding system is based on the curing system of the epoxy resin in the prepreg, and the resin curing system of the prepreg in this case is: 100°C / 1 h + 120°C / 1 h + 180°C / 4 h. After curing, the pressure is maintained and the temperature is lowered, and a toughened carbon fiber composite material is obtained.

[0046] Comparative Example 1

[0047] (1) Cut continuous polyether sulfone fibers with a diameter of 30 μm into polyether sulfone short-cut fibers with a length of 10-12 mm, then take 30 g of the polyether sulfone short-cut fibers and add them to a 0.01% polyethylene glycol 200 dispersion, and stir at high speed to uniformly disperse the polyether sulfone short-cut fibers in the polyethylene glycol 200 dispersion, to obtain a polyether sulfone short-cut fiber slurry.

[0048] (2) Filter and settle the polyether sulfone short-cut fiber slurry obtained in step (1) through a web system to obtain a wet non-woven polyether sulfone fiber web.

[0049] (3) Spray 0.3 g of polyurethane adhesive on the surface of the wet non-woven polyether sulfone fiber web obtained in step (2), and dry at 80°C for 10 h to obtain a non-woven polyether sulfone fiber web with a web surface density of 12 gsm and a thickness of 40 μm.

[0050] (4) Cutting the carbon fiber / epoxy unidirectional prepreg tape into the desired size, and cross-laying the non-woven polyether sulfone fiber web obtained in step (3) with the carbon fiber / epoxy prepreg tape. After the laying is completed, it is placed in a mold.

[0051] (5) Placing the mold in step (4) into a hot press for curing and molding, vacuumizing for 30 min, and keeping the mold in a vacuum state. The curing and molding system is based on the curing system of the epoxy resin in the prepreg, and the resin curing system of the prepreg in this case is: 100℃ / 1h+120℃ / 1h+180℃ / 4h. After the curing is completed, the pressure is maintained and the temperature is lowered, and the toughened carbon fiber composite material is obtained.

[0052]

[0053] The test results of the interlaminar fracture toughness of the toughened carbon fiber composite material I prepared in the implementation examples and comparative examples are shown in the above table. It can be seen from the comparison that the interlaminar fracture toughness of the non-woven nylon web / carbon fiber composite material at room temperature and low temperature is higher than that of the non-woven polyether sulfone web / carbon fiber composite material. It is proved that the non-woven nylon web prepared by the method can effectively improve the toughness of the composite material in a low temperature environment.

Claims

1. A method for preparing nonwoven nylon mesh for low-temperature toughening of carbon fiber composites, characterized in that... Includes the following steps: Step (1) Cut the continuous nylon fiber into short nylon fibers of a certain length, then add them to the dispersant and stir at high speed to make the short nylon fibers evenly dispersed in the dispersant to obtain nylon short fiber slurry; wherein the diameter of the nylon fiber is 10-50μm and the length of the chopped nylon fiber is 10-25mm. Step (2) The nylon short fiber slurry obtained in step (1) is filtered and settled through a web forming system to obtain wet nonwoven nylon mesh; Step (3) The wet nonwoven nylon mesh obtained in step (2) is sprayed with adhesive and then dried to obtain nonwoven nylon mesh; wherein the thickness of the nonwoven nylon mesh is less than or equal to 50 μm and the areal density is 4 gsm-20 gsm.

2. The preparation method according to claim 1, characterized in that... The nylon fiber in step (1) is obtained by condensation of diamines with different carbon chain lengths and diacids, specifically one or more of polycaprolactam fiber, polyhexamethylene adipamide fiber, polydodecanoic acid fiber, polyhexamethylene sebacate fiber, and polydodecanediamide fiber.

3. The preparation method according to claim 1, characterized in that... The dispersant in step (1) is one or more of polyethyleneimine, polyvinylpyrrolidone, polyvinyl alcohol, oxidized polyethylene wax, and polyethylene glycol 200 mixed with water, and the content of the dispersant is 0.001wt%-1wt% of the water content.

4. The preparation method according to claim 1, characterized in that... The adhesive in step (3) is a water dispersion of one or more of the following: polyurethane, polyacrylate, polysiloxane, ethylene-vinyl acetate copolymer, and epoxy resin.

5. The preparation method according to claim 1, characterized in that... In step (3), the drying temperature is 40°C-100°C and the time is 3h-12h.

6. The preparation method according to claim 1, characterized in that... In step (3), the nonwoven nylon mesh can achieve interlayer toughening of the composite material in a low-temperature environment.

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