An in-situ interlaminar modification method for composite materials based on short fibers and polyurethane

Abstract

This invention discloses an in-situ interlaminar modification method for composite materials based on short fibers and polyurethane, belonging to the field of resin material modification technology. This invention utilizes discrete short carbon fibers and microphase-separated polyurethane to synergistically modify epoxy resin, thereby enhancing the interlaminar properties of toughened continuous carbon fiber reinforced epoxy composite laminates. Toughening the epoxy resin by adding microphase-separated polyurethane improves the interlaminar fracture toughness of the composite material. Furthermore, adding an appropriate amount of discrete short carbon fibers to the epoxy resin utilizes the high strength of the short carbon fibers to improve the interlaminar shear strength of the composite material. This method not only has advantages such as easy thickness control, simple operation, and low cost, but also comprehensively improves the interlaminar properties of continuous carbon fiber reinforced epoxy composites, meeting the requirements of aerospace engineering applications for laminate interlaminar performance.

Description

Technical Field

[0001] This invention relates to the field of resin material modification technology, specifically to an in-situ interlayer modification method for composite materials based on short fibers and polyurethane. Background Technology

[0002] Epoxy resin is a thermosetting material with potential applications in multiple disciplines. Due to its excellent dimensional stability, good mechanical properties and high chemical resistance, it is widely used in construction, electronic instruments, adhesives and composite matrix.

[0003] Continuous carbon fiber reinforced epoxy composite laminates exhibit satisfactory weight reduction efficiency and economic advantages in heavy-duty aerospace launch vehicles, especially in cryogenic storage tank applications, due to their excellent specific stiffness and strength.

[0004] However, the extreme thermo-coupling effect of the cold and hot cycling conditions of cryogenic storage tanks (room temperature when unloaded and low temperature when storing cryogenic propellants) can lead to the initiation of early microcracks. Subsequently, the cracks cross multiple layers and eventually form a complete path for propellant leakage, posing a huge risk to the interlayer region of the laminate.

[0005] Furthermore, in laminates, the interlaminar regions between the layers are rich in epoxy resin matrix, and interlaminar damage, such as delamination, has always been one of the main failure modes of laminate structures. Therefore, in the past decade, how to improve the interlaminar fracture toughness and shear strength of laminates has been a key focus of attention for many scholars and engineering designers.

[0006] Therefore, a new solution is needed to address the above problems. Summary of the Invention

[0007] The purpose of this invention is to provide an in-situ interlayer modification method for composite materials based on short fibers and polyurethane, so as to solve the technical problems mentioned in the background art.

[0008] To achieve the above objectives, the present invention provides the following technical solution: a method for in-situ interlaminar modification of composite materials based on short fibers and polyurethane, comprising at least the following steps:

[0009] S1: Prepare a sufficient quantity of carbon fiber cloth for the preparation of continuous fiber reinforced epoxy composite laminate;

[0010] S2: After preheating the epoxy resin in the heating jacket, add polyurethane according to the required mass ratio and stir thoroughly until uniform. Then add the required amount of short carbon fiber and continue stirring until uniform. Finally, add the curing agent according to the required mass ratio and stir until uniform.

[0011] S3: After removing air bubbles by placing the mixture in a vacuum oven, coat the mixture evenly onto the surface of the fiber cloth;

[0012] S4: After laying up the layers to the required thickness, place them in a hot press and hot press to form the desired shape.

[0013] Furthermore, the carbon fiber type of both the carbon fiber cloth and the short carbon fiber in S1 is T300.

[0014] Furthermore, the epoxy resin in S2 is a bisphenol A type epoxy resin (E51) with an epoxy equivalent of 186 g / mol.

[0015] Furthermore, the temperature of the heating jacket in S2 is 110°C.

[0016] Furthermore, the polyurethane active group content in S2 is 0.08±0.02, and the mass ratio of polyurethane to epoxy resin is 1:20 (5 phr).

[0017] Furthermore, the mass fraction of short carbon fiber added in S2 is 0% to 0.075%, and the stirring time is 30 minutes.

[0018] Furthermore, the curing agent in S2 is 4,4'-diaminodiphenyl sulfone (DDS), and the mass ratio of the curing agent to the epoxy resin is 34:100 (34 phr).

[0019] Furthermore, the temperature of the vacuum oven in S3 is 110°C.

[0020] Furthermore, the heating program of the hot press in S4 is as follows: heat up to 100°C and hold for 0.5 hours, heat up to 130°C and hold for 1 hour, heat up to 160°C and hold for 1.5 hours, heat up to 180°C and hold for 1 hour, with a heating rate of 2°C / min for all of them.

[0021] Compared with the prior art, the beneficial effects of the present invention are:

[0022] 1. This invention improves the interlaminar properties of continuous carbon fiber reinforced epoxy composite laminates by simultaneously introducing short carbon fibers and polyurethane into epoxy resin for synergistic modification. For short carbon fibers, due to their excellent mechanical properties, the mechanical properties of epoxy resin can be improved, thereby increasing the interlaminar fracture strength. At the same time, the fiber bridging effect inhibits interlaminar delamination propagation and increases energy dissipation, thereby improving the interlaminar fracture toughness. On the other hand, polyurethane can act as a plasticizer to toughen epoxy resin and also improve the interlaminar fracture toughness. Since the toughening mechanisms of the two are different, their simultaneous addition has a synergistic effect, which can significantly enhance the interlaminar properties of the laminate. Its interlaminar fracture strength and fracture toughness are significantly better than those of the unmodified laminate.

[0023] 2. The method proposed in this invention directly introduces short carbon fibers and polyurethane into epoxy resin, which can easily control the thickness of the laminate. The preparation process is simple and the cost is low. At the same time, it comprehensively improves the interlaminar properties of continuous carbon fiber reinforced epoxy composite materials, meeting the requirements of cryogenic storage tanks for the interlaminar properties of laminates. Attached Figure Description

[0024] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the following briefly introduces the drawings required for describing the embodiments. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without creative work.

[0025] Figure 1 This is a diagram showing the interlaminar fracture strength of the laminate prepared according to the present invention.

[0026] Figure 2 This is a diagram showing the interlaminar fracture toughness of the laminate prepared in this invention.

[0027] Figure 3 This is a schematic diagram of the laminate layer prepared according to the present invention. Detailed Implementation

[0028] The technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings of the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments.

[0029] The design process of this invention is as follows:

[0030] Given the highly cross-linked spatial network structure of epoxy resin, its inherent brittleness severely limits its application in engineering. Therefore, improving its toughness and enhancing its overall mechanical properties is crucial. Polyurethane, formed by the addition polymerization of polyisocyanates and polyhydroxy polymers, is a polymer compound containing numerous repeating urethane segments (-NHCOO-) in its main chain. Polyurethane can be considered a type of thermoplastic resin, possessing advantages such as high plasticity, high elasticity, resistance to low-temperature environments, and good chemical compatibility. It is a highly attractive toughening agent, and its numerous polar groups can connect with epoxy resin through covalent and hydrogen bonds, forming interpenetrating or semi-interpenetrating polymer networks. Its synthesis, reaction mechanism, morphology, and mechanical properties have received extensive attention and research. The polyurethane molecular backbone consists of flexible long-chain polyols and rigid isocyanate blocks, which can effectively disperse stress. Furthermore, the widespread hydrogen bonding within the polyurethane further enhances the material's mechanical properties. In addition, polyurethane-toughened epoxy resin exhibits a unique phase separation phenomenon. Numerous studies have shown that epoxy resin toughness only increases significantly when phase separation occurs in the thermoplastic resin within the matrix. Furthermore, the phase separation process between polyurethane and epoxy resin, as well as its reinforcing and toughening mechanism on epoxy resin, has been thoroughly investigated. Therefore, the introduction of polyurethane as a toughening agent into epoxy resin is considered.

[0031] Because epoxy resin itself has relatively low mechanical properties, this invention considers directly introducing high-strength discrete short carbon fibers into the epoxy resin to achieve in-situ reinforcement, without needing to add an additional intermediate layer to the laminate to improve its interlaminar fracture strength. The incorporated short carbon fibers are expected to be discretely distributed in the resin-rich regions of the interlaminar layer, which theoretically will improve the inherent mechanical properties of the epoxy resin, while inducing more interlaminar bridging fibers, thereby effectively inhibiting subsequent interlaminar delamination propagation and increasing energy dissipation, thus also playing a toughening role.

[0032] See Figure 3 Furthermore, an in-situ interlaminar modification method based on short fibers and polyurethane is proposed:

[0033] Prepare a sufficient quantity of carbon fiber cloth for the preparation of continuous fiber reinforced epoxy composite laminates;

[0034] After preheating the epoxy resin in the heating jacket, add polyurethane according to the required mass ratio and stir thoroughly until uniform. Then add the required amount of short carbon fiber and continue stirring until uniform. Finally, add the curing agent according to the required mass ratio and stir until uniform.

[0035] After removing air bubbles by placing the mixture in a vacuum oven, the mixture is then evenly coated onto the surface of the fiber cloth.

[0036] After laying up the layers to the required thickness, the layers are placed in a hot press and hot-pressed into shape.

[0037] Please refer to the following examples for details:

[0038] Example 1

[0039] Prepare a sufficient quantity of T300 carbon fiber cloth (10 layers of carbon fiber cloth for interlaminar fracture strength test and 18 layers of carbon fiber cloth for interlaminar fracture toughness test) to prepare continuous fiber reinforced epoxy composite laminate.

[0040] After preheating the E-51 epoxy resin in a heating mantle at 110°C, add the curing agent to the epoxy resin at a mass ratio of 34:100 (34 phr) and stir until homogeneous.

[0041] After removing air bubbles by placing the mixture in a vacuum oven at 110°C, the mixture is then evenly coated onto the surface of the fiber cloth.

[0042] After laying up the layers to the required thickness (2 mm for interlaminar fracture strength test and 3 mm for interlaminar fracture toughness test), the layers are placed in a hot press for hot pressing and forming. The heating program of the hot press is set to 100℃ for 0.5 h, 130℃ for 1 h, 160℃ for 1.5 h, and 180℃ for 1 h.

[0043] The interlaminar properties of the prepared laminate were tested according to the ASTM D2344 test standard, such as... Figure 1 As shown, the interlaminar tensile strength of the laminate is 51.7 MPa. According to the ASTM D5528 test standard, as... Figure 2 As shown, the initial and stable values ​​of the interlaminar fracture toughness of the laminate are 269.0 J / m. 2 and 363.5J / m 2 .

[0044] Example 2

[0045] Prepare a sufficient quantity of T300 carbon fiber cloth (10 layers of carbon fiber cloth for interlaminar fracture strength test and 18 layers of carbon fiber cloth for interlaminar fracture toughness test) to prepare continuous fiber reinforced epoxy composite laminate.

[0046] After preheating E-51 epoxy resin in a heating mantle at 110°C, add 0.075% short carbon fibers by mass and continue stirring for 30 minutes until uniform. Add curing agent to epoxy resin at a mass ratio of 34:100 (34 phr) and stir until uniform.

[0047] After removing air bubbles by placing the mixture in a vacuum oven at 110°C, the mixture is then evenly coated onto the surface of the fiber cloth.

[0048] After laying up the layers to the required thickness (2 mm for interlaminar fracture strength test and 3 mm for interlaminar fracture toughness test), the layers are placed in a hot press for hot pressing and forming. The heating program of the hot press is set to 100℃ for 0.5 h, 130℃ for 1 h, 160℃ for 1.5 h, and 180℃ for 1 h.

[0049] The interlaminar properties of the prepared laminate were tested according to the ASTM D2344 test standard, such as... Figure 1 As shown, the interlaminar tensile strength of the laminate is 60.7 MPa. According to the ASTM D5528 test standard, as... Figure 2 As shown, the initial and stable values ​​of the interlaminar fracture toughness of the laminate are 313.5 J / m. 2 and 467.1 J / m 2 .

[0050] Example 3

[0051] Prepare a sufficient quantity of T300 carbon fiber cloth (10 layers of carbon fiber cloth for interlaminar fracture strength test and 18 layers of carbon fiber cloth for interlaminar fracture toughness test) to prepare continuous fiber reinforced epoxy composite laminate.

[0052] After preheating E-51 epoxy resin in a heating mantle at 110℃, add polyurethane to the epoxy resin at a mass ratio of 1:20 (5 phr) and stir evenly. Then add curing agent to the epoxy resin at a mass ratio of 34:100 (34 phr) and stir evenly.

[0053] After removing air bubbles by placing the mixture in a vacuum oven at 110°C, the mixture is then evenly coated onto the surface of the fiber cloth.

[0054] After laying up the layers to the required thickness (2 mm for interlaminar fracture strength test and 3 mm for interlaminar fracture toughness test), the layers are placed in a hot press for hot pressing and forming. The heating program of the hot press is set to 100℃ for 0.5 h, 130℃ for 1 h, 160℃ for 1.5 h, and 180℃ for 1 h.

[0055] The interlaminar properties of the prepared laminate were tested according to the ASTM D2344 test standard, such as... Figure 1 As shown, the interlaminar tensile strength of the laminate is 60.7 MPa. According to the ASTM D5528 test standard, as... Figure 2 As shown, the initial and stable values ​​of the interlaminar fracture toughness of the laminate are 322.7 J / m. 2 and 423.6J / m 2 .

[0056] Example 4

[0057] Prepare a sufficient quantity of T300 carbon fiber cloth (10 layers of carbon fiber cloth for interlaminar fracture strength test and 18 layers of carbon fiber cloth for interlaminar fracture toughness test) to prepare continuous fiber reinforced epoxy composite laminate.

[0058] After preheating E-51 epoxy resin in a heating mantle at 110℃, polyurethane is added to the epoxy resin at a mass ratio of 1:20 (5 phr) and stirred evenly. Then, 0.075% of short carbon fibers are added and stirred for another 30 minutes until evenly mixed. Finally, curing agent is added to the epoxy resin at a mass ratio of 34:100 (34 phr) and stirred evenly.

[0059] After removing air bubbles by placing the mixture in a vacuum oven at 110°C, the mixture is then evenly coated onto the surface of the fiber cloth.

[0060] After laying up the layers to the required thickness (2 mm for interlaminar fracture strength test and 3 mm for interlaminar fracture toughness test), the layers are placed in a hot press for hot pressing and forming. The heating program of the hot press is set to 100℃ for 0.5 h, 130℃ for 1 h, 160℃ for 1.5 h, and 180℃ for 1 h.

[0061] The interlaminar properties of the prepared laminate were tested according to the ASTM D2344 test standard, such as... Figure 1 As shown, the interlaminar tensile strength of the laminate is 66.6 MPa. According to the ASTM D5528 test standard, as... Figure 2 As shown, the initial and stable values ​​of the interlaminar fracture toughness of the laminate are 384.7 J / m. 2 and 551.3J / m 2 .

[0062] In summary, this invention utilizes discrete short carbon fibers and microphase-separated polyurethane to synergistically modify epoxy resin, thereby enhancing the interlaminar properties of toughened continuous carbon fiber reinforced epoxy composite laminates. The addition of microphase-separated polyurethane toughens the epoxy resin, improving the interlaminar fracture toughness of the composite. Furthermore, the addition of an appropriate amount of discrete short carbon fibers to the epoxy resin leverages the high strength of the short carbon fibers to enhance the interlaminar shear strength of the composite. This method not only offers advantages such as easy thickness control, simple operation, and low cost, but also comprehensively improves the interlaminar properties of continuous carbon fiber reinforced epoxy composites, meeting the requirements for interlaminar performance in aerospace engineering applications.

[0063] It will be apparent to those skilled in the art that the present invention is not limited to the details of the exemplary embodiments described above, and that the invention can be implemented in other specific forms without departing from its spirit or essential characteristics. Therefore, the embodiments should be considered in all respects as exemplary and non-limiting, and the scope of the invention is defined by the appended claims rather than the foregoing description. Thus, all variations falling within the meaning and scope of equivalents of the claims are intended to be included within the present invention. No reference numerals in the claims should be construed as limiting the scope of the claims.

Claims

1. A method for in-situ interlaminar modification of composite materials based on short fibers and polyurethane, characterized in that: At least the following steps are included: S1: Prepare a sufficient quantity of carbon fiber cloth for the preparation of continuous fiber reinforced epoxy composite laminate; S2: After preheating the epoxy resin in the heating jacket, add polyurethane according to the required mass ratio and stir thoroughly until uniform. Then add the required amount of short carbon fiber and continue stirring until uniform. Finally, add the curing agent according to the required mass ratio and stir until uniform. S3: After removing air bubbles by placing the mixture in a vacuum oven, coat the mixture evenly onto the surface of the fiber cloth; S4: After laying up the layers to the required thickness, place them in a hot press and hot press them into shape; The carbon fiber type of both the carbon fiber cloth and the short carbon fiber in S1 is T300. The epoxy resin in S2 is a bisphenol A type epoxy resin with an epoxy equivalent of 186 g / mol; The temperature of the heating jacket in S2 is 110 ℃; The polyurethane active group content in S2 is 0.08±0.02, and the mass ratio of polyurethane to epoxy resin is 1:

20. The short carbon fiber added in S2 has a mass fraction of 0%~0.075%, and the stirring time is 30 min; The curing agent in S2 is 4,4'-diaminodiphenyl sulfone, and the mass ratio of the curing agent to the epoxy resin is 34:

100. The temperature of the vacuum oven in S3 is 110 ℃; The heating program of the hot press in S4 is as follows: heat up to 100 ℃ and hold for 0.5 h, heat up to 130 ℃ and hold for 1 h, heat up to 160 ℃ and hold for 1.5 h, heat up to 180 ℃ and hold for 1 h, with a heating rate of 2 ℃ / min.

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