Preparation method of halogen-free flame-retardant basalt fiber-epoxy resin composition composite material

Abstract

The invention relates to a hot-melt halogen-free flame-retardant epoxy resin composition and a preparation method thereof, a prepreg and a fiber reinforced composite material. The composition is composed of an epoxy resin matrix, a halogen-free flame retardant, a curing agent and an auxiliary agent, the organic phosphorus halogen-free flame retardant with a specific molecular structure is adopted to react with the epoxy resin matrix, the flame retardant property and the thermal stability of a system are improved, the mechanical property is considered, and the adding amount of the halogen-free flame retardant is 10-25% of the mass of epoxy resin. The preparation method comprises the following steps: stirring and mixing the epoxy resin and the flame retardant at 50-80 DEG C, adding the curing agent and the auxiliary agent, uniformly dispersing, and cooling to obtain the composition. According to the prepreg, basalt fiber is used as a reinforcing material, a fiber reinforced composite material can be prepared through a hot press molding process, the oxygen index (LOI) of the prepreg is higher than 30%, the vertical combustibility reaches the UL94 V-0 level, and the prepreg is suitable for the fields of new energy automobiles, electronic appliances and the like. Through halogen-free design, the halogen-free flame-retardant halogen-free flame-retardant halogen-free halogen-free flame-retardant halogen-free halogen-free flame-retardant halogen-free halogen

Description

Technical Field

[0001] The present invention relates to the technical field of composite material preparation, and particularly relates to a preparation method of a halogen-free flame-retardant basalt fiber-epoxy resin composition composite material. This method prepares a fiber-reinforced composite material with excellent flame-retardant performance, mechanical properties, and thermal stability by surface modification of basalt fibers and compounding with a halogen-free flame-retardant epoxy resin matrix, which can be widely applied to fields such as aerospace, construction, rail transit, and electronic and electrical industries that require high-performance flame-retardant materials. Background Art

[0002] As a new type of inorganic non-metallic material, basalt fiber has been widely used in the field of high-performance composite materials in recent years due to its excellent mechanical properties, high-temperature resistance, and chemical stability. The high-strength characteristics of basalt fiber enable the composite materials prepared therefrom to exhibit excellent tensile and compressive properties when subjected to external loads. In addition, its good heat resistance enables it to maintain a stable structure in high-temperature environments and is suitable for high-temperature application scenarios such as aerospace, construction, and rail transit. The high resistance of basalt fiber to corrosive substances such as acids and alkalis and its excellent electromagnetic shielding performance further expand its application potential in harsh environments. However, due to the low surface chemical activity of basalt fiber, the interfacial bonding performance with the resin matrix is limited, and the flame-retardant performance of its composite materials needs to be further improved, thus restricting its development and application in the field of flame-retardant composite materials.

[0003] Flame-retardant performance is one of the key requirements for the application of composite materials in many industrial fields. Traditional flame-retardant methods usually achieve this by adding halogen-based flame retardants to the resin matrix. However, halogen flame retardants will release toxic and harmful gases during the combustion process, posing a threat to the environment and human health, and have gradually been replaced by halogen-free flame-retardant systems in recent years. Halogen-free flame retardants (such as organophosphorus flame retardants and phosphazene compounds) have become a research hotspot due to their low toxicity, thermal stability, and environmental friendliness. However, their application in composite materials often affects the mechanical properties of the materials. In addition, the flammable characteristics of the polymer matrix will cause the "wick effect" in composite materials under combustion conditions, that is, the molten polymer penetrates to the fiber surface and spreads rapidly, thereby further increasing the combustion risk of composite materials. Therefore, how to optimize the bonding performance between basalt fiber and halogen-free flame-retardant epoxy resin matrix through interface modification technology, while suppressing the wick effect and improving the flame-retardant performance and mechanical properties of composite materials, has become an important research direction.

[0004] Epoxy resin, as a thermosetting resin, is widely used as the matrix material of composite materials due to its excellent mechanical properties, electrical insulation properties, and chemical corrosion resistance. By adding a halogen-free flame retardant, the epoxy resin matrix can form carbon and a dense carbon layer at high temperatures, thereby effectively blocking the diffusion of heat and oxygen and improving the flame retardancy of the composite material. However, the addition of flame retardants often complicates the curing system of epoxy resin and reduces its mechanical properties. Therefore, how to reasonably select the halogen-free flame retardant and its addition ratio, taking into account the flame retardancy and mechanical properties of the composite material, is one of the key technical challenges in improving the comprehensive performance of epoxy resin-based composite materials. In addition, the existing flame retardant modification methods for basalt fiber-epoxy resin composites are mostly limited to simply adding flame retardants, lacking systematic interface modification design and unable to fully utilize the synergistic performance advantages of basalt fiber and epoxy resin matrix.

[0005] In summary, there are still many deficiencies in the existing technology for the flame retardant modification of basalt fiber-epoxy resin composites. On the one hand, the interfacial bonding performance between basalt fiber and resin matrix is poor, affecting the overall mechanical properties of the composite material; on the other hand, traditional flame retardant methods are difficult to effectively inhibit the "wick effect", limiting the flame retardancy and application scenarios of the material. To solve the above technical problems, the present invention modifies the surface of basalt fiber, constructs an efficient flame retardant system using halogen-free flame retardants, and optimizes the preparation process of the composite material to prepare a basalt fiber-epoxy resin composite material with excellent flame retardancy, outstanding mechanical properties, and high environmental protection, which has important theoretical value and broad practical application prospects. Summary of the Invention

[0006] The present invention provides a preparation method for a halogen-free flame retardant basalt fiber-epoxy resin composite material. By surface-modifying basalt fiber and compounding it with a halogen-free flame retardant epoxy resin matrix, the problems of poor interfacial bonding performance between existing basalt fiber and resin matrix and insufficient flame retardancy are solved, significantly improving the mechanical properties, flame retardancy, and thermal stability of the composite material. The process of the present invention is simple and efficient, and the prepared composite material has high environmental protection and is suitable for fields with high requirements for flame retardancy and mechanical properties such as aerospace, construction, and rail transit.

[0007] 1. Surface Modification of Basalt Fiber

[0008] (1) Preparation of coupling agent solution: Mix 450 mL of absolute ethanol and 50 mL of deionized water to form an ethanol-aqueous solution. Add an amino coupling agent KH-550 (25% of the volume ratio of the ethanol-aqueous solution), and stir evenly to form a homogeneous coupling agent solution.

[0009] (2) Fiber treatment: Immerse 50 g of chopped basalt fiber yarn into the coupling agent solution, maintain a constant temperature of 60 °C, and react for 2 - 4 hours under magnetic stirring conditions. Wash the basalt fiber with deionized water multiple times to remove the excess coupling agent, and then dry it to a constant weight at 80 °C to obtain surface-modified basalt fiber (BF-NH2).

[0010] 2. Preparation of halogen-free flame-retardant epoxy resin mixture

[0011] (1) Epoxy resin matrix: Weigh 100 g of bisphenol A epoxy resin (E-51), place it in a water bath at 50 - 80 °C and heat it until it melts.

[0012] (2) Flame retardant addition: Add 10 - 25 g of organic phosphorus flame retardant (such as pentaerythritol phosphate or phosphazene flame retardant), and stir for 1 hour under constant temperature conditions to uniformly mix the flame retardant with the epoxy resin.

[0013] (3) Additives addition: Add a leveling agent, a defoaming agent, and a dispersant (each 0.5 - 2% of the mass of the epoxy resin) in sequence, and continue stirring for 30 minutes.

[0014] (4) Curing agent addition: Cool down to 50 °C, add methylhexahydrophthalic anhydride (curing agent, 20 - 30% of the mass of the epoxy resin) and stir well to prepare a uniformly dispersed halogen-free flame-retardant epoxy resin composition.

[0015] 3. Impregnation of basalt fiber

[0016] (1) Impregnation process: Add the surface-modified basalt fiber (BF-NH2) to the halogen-free flame-retardant epoxy resin mixture in batches according to a fiber volume fraction of 40 - 60%. Use ultrasonic dispersion equipment to process it at room temperature for 30 minutes to ensure that the basalt fiber is fully wetted by the resin matrix and the basalt fiber is uniformly distributed in the resin matrix.

[0017] (2) Exhaust treatment: Place the impregnated resin-fiber mixture in a vacuum degassing device, maintain a vacuum state for 20 minutes, remove the bubbles in the mixture, and ensure that there are no pores inside the composite material.

[0018] 4. Molding of composite material

[0019] (1) Mold preparation: Coat the surface of the clean mold with a release agent to ensure the integrity of the subsequent composite material molding. Uniformly lay the impregnated fiber-resin mixture into the mold, and control the thickness to be consistent before and after.

[0020] (2) Hot press molding: Place the mold in a hot press, control the pressure at 2 - 5 MPa, carry out pre-curing at 80 - 120 °C for 1 - 2 hours, and then raise the temperature to 150 - 180 °C for post-curing for 2 - 4 hours.

[0021] (3) Demolding and post-treatment: After hot pressing, cool the mold to room temperature; remove the formed composite material from the mold and trim the edges to obtain the final sample.

[0022] 5. Experimental verification and performance testing

[0023] (1) Sample specifications: Prepare composite material samples with different fiber volume fractions (40%, 50%, 60%) and flame retardant additive amounts (10%, 15%, 20%) according to the above process for subsequent performance testing.

[0024] (2) Conduct the following tests on the samples:

[0025] a. Flame retardancy test: Use the limiting oxygen index method (LOI) and UL-94 vertical burning test to evaluate the flame retardancy of the composite material;

[0026] b. Mechanical property test: Use a tensile testing machine and a bending testing machine to test the tensile strength and bending strength of the composite material;

[0027] c. Thermal stability test: Use thermogravimetric analysis (TGA) to test the thermal decomposition temperature and thermal stability of the material.

[0028] The preparation method of the halogen-free flame-retardant basalt fiber-epoxy resin composition composite material provided by the present invention significantly improves the interfacial bonding performance between the fiber and the resin matrix through surface modification of the basalt fiber and optimized design of the flame-retardant resin matrix, effectively inhibits the "wick effect", and improves the flame retardancy (limiting oxygen index ≥ 30%, UL-94 reaches V-0 level) and mechanical properties (tensile strength ≥ 300 MPa, bending strength ≥ 350 MPa) of the composite material. In addition, this method has high environmental protection and simple process, and the obtained composite material is applicable to a variety of high-performance scenarios and has broad application prospects. Specific embodiments

[0029] The following details the preparation method of a halogen-free flame-retardant basalt fiber-epoxy resin composition composite material of the present invention through five embodiments, but the protection scope of the present invention is not limited to these embodiments.

[0030] Example 1

[0031] 1. Modification of basalt fiber

[0032] (1) Prepare an ethanol-aqueous solution (volume ratio of 4:1), add KH-550 coupling agent (50 mL), and stir evenly to form a modification solution;

[0033] (2) Immerse 50 g of chopped basalt fiber into the modification solution and stir at 60 °C for 2 hours;

[0034] (3) Wash with deionized water after filtration, and dry at 80 °C to obtain modified basalt fiber (BF-NH2).

[0035] 2. Preparation of halogen-free flame-retardant epoxy resin

[0036] (1) Heat 100 g of epoxy resin E-51 to melt at 50 °C;

[0037] (2) Add 15 g of organophosphorus flame retardant (pentaerythritol phosphate) and stir for 1 hour;

[0038] (3) Add a leveling agent (1 g) and an antifoaming agent (0.5 g) in sequence and stir for 30 minutes;

[0039] (4) Cool down to 50 °C, add a curing agent (methylhexahydrophthalic anhydride, 30 g), and stir evenly to obtain flame-retardant epoxy resin.

[0040] 3. Molding of composite material

[0041] (1) Immerse 40% by volume of modified basalt fiber in the flame-retardant epoxy resin;

[0042] (2) After vacuum degassing for 20 minutes, evenly lay the mixture in a mold;

[0043] (3) Pre-cure at 80 °C for 1 hour under a pressure of 3 MPa in a hot press, and then post-cure at 150 °C for 3 hours;

[0044] (4) Cool and demold to obtain the composite material.

[0045] 4. Test results

[0046] The oxygen index is 32%; the vertical burning performance is UL-94V-0 grade; the tensile strength is 310 MPa; the flexural strength is 360 MPa (Table 1).

[0047] Example 2

[0048] 1. Modification of basalt fiber: Treat basalt fiber using the same method as in Example 1, except that the modification time in Example 2 is extended to 4 hours to obtain modified fiber (BF-NH2).

[0049] 2. Preparation of halogen-free flame-retardant epoxy resin

[0050] (1) Use 100 g of epoxy resin E-51, add 20 g of phosphazene flame retardant, and mix evenly;

[0051] (2) Add 0.5 g of dispersant and 1 g of antioxidant, and stir for 30 minutes;

[0052] (3) Add a curing agent (4,4'-diaminodiphenyl sulfone, 25 g), and stir evenly to obtain a flame-retardant epoxy resin.

[0053] 3. Composite material forming

[0054] (1) Mix the modified basalt fiber and epoxy resin according to 50% volume fraction;

[0055] (2) After vacuum degassing, place it in a mold. Hot pressing conditions: 3 MPa, pre-cure at 100 °C for 1.5 hours, and post-cure at 160 °C for 2 hours;

[0056] (3) Cool and demold to obtain a composite material.

[0057] 4. Test results

[0058] The oxygen index is 35%; the vertical burning performance is UL-94V-0 level; the tensile strength is 320 MPa; the flexural strength is 370 MPa (Table 1).

[0059] Example 3

[0060] 1. Basalt fiber modification

[0061] (1) Prepare an ethanol-aqueous solution, add KH-550 coupling agent and 3% epoxy silane, and mix evenly;

[0062] (2) Immerse 60 g of basalt fiber in it at 70 °C for 3 hours to obtain modified fiber (BF-NH2).

[0063] 2. Preparation of halogen-free flame-retardant epoxy resin

[0064] (1) Blend epoxy resin E-51 and bisphenol F type epoxy resin (mass ratio 3:1);

[0065] (2) Add 15 g of phosphazene flame retardant and 5 g of nitrogen-phosphorus synergistic flame retardant, and stir evenly;

[0066] (3) Add 1 g of antioxidant 1010 and 1 g of lubricant, and stir evenly;

[0067] (4) Add 30 g of curing agent, and stir evenly to obtain a flame-retardant epoxy resin;

[0068] 3. Composite material forming

[0069] (1) Mix the modified basalt fiber and epoxy resin according to 60% volume fraction;

[0070] (2) Hot pressing conditions: 4 MPa, pre-cure at 120 °C for 2 hours, and post-cure at 180 °C for 3 hours;

[0071] (3) Cool and demold to obtain a composite material.

[0072] 4. Test Results

[0073] The oxygen index is 36%; the vertical burning performance is UL-94V-0 grade; the tensile strength is 340 MPa; the flexural strength is 380 MPa (Table 1).

[0074] Example 4

[0075] 1. Modification of basalt fiber: The chopped basalt fiber is washed with ethanol and directly treated with KH-550 coupling agent solution for 2 hours to obtain modified fiber (BF-NH2).

[0076] 2. Preparation of halogen-free flame-retardant epoxy resin

[0077] (1) Blend 50 g of bisphenol F-type epoxy resin and 50 g of E-51 epoxy resin.

[0078] (2) Add 20 g of phosphazene flame retardant and 2 g of zinc borate as a synergistic flame retardant, and stir evenly.

[0079] (3) Add 2 g of dispersant and 25 g of curing agent, and stir evenly.

[0080] 3. Composite material forming

[0081] (1) Mix basalt fiber and epoxy resin at a volume fraction of 50%.

[0082] (2) Pre-cure at a pressure of 3 MPa and a temperature of 90 °C for 1.5 hours, and then post-cure at a temperature of 160 °C for 2 hours.

[0083] (3) Cool and demold to obtain the composite material.

[0084] Test Results

[0085] The oxygen index is 34%; the vertical burning performance is UL-94V-0 grade; the tensile strength is 315 MPa; the flexural strength is 365 MPa (Table 1).

[0086] Example 5

[0087] 1. Modification of basalt fiber: Prepare a coupling agent solution (KH-550: epoxy silane = 1:1), and treat basalt fiber at 60 °C for 3 hours to obtain modified fiber (BF-NH2).

[0088] 2. Preparation of halogen-free flame-retardant epoxy resin

[0089] (1) Use 100 g of E-51 epoxy resin and add 15 g of pentaerythritol phosphate flame retardant.

[0090] (2) Add 1 g of antioxidant and 0.5 g of leveling agent, and stir evenly.

[0091] (3) Add 25 g of curing agent and stir evenly.

[0092] 3. Composite material forming

[0093] (1) Mix basalt fibers with epoxy resin at a volume fraction of 40%.

[0094] (2) Pre-cure for 1 hour under a pressure of 2 MPa and a temperature of 80 °C, and then post-cure for 3 hours at a temperature of 150 °C.

[0095] (3) Cool and demold to obtain the composite material.

[0096] 4. Test results

[0097] The oxygen index is 31%; the vertical burning performance is UL-94 V-0 level; the tensile strength is 300 MPa; the flexural strength is 355 MPa (Table 1).

[0098] Table 1: Comparison of key parameters and performance of the examples

[0099]

[0100] The various embodiments in this specification are described in a progressive manner. The same or similar parts between the various embodiments can be referred to each other. Each embodiment focuses on the differences from other embodiments (Table 1). The above five examples illustrate the process conditions and performance of the present invention for preparing halogen-free flame-retardant basalt fiber-epoxy resin composites. Each process reflects the excellent flame-retardant performance, mechanical properties and thermal stability of the material, and at the same time verifies the feasibility and wide applicability of the method of the present invention.

[0101] The above examples are only used to illustrate the technical solutions of the present application, rather than limiting the present application; although the present application has been described in detail with reference to the foregoing examples, those of ordinary skill in the art should understand that they can still modify the technical solutions described in the foregoing examples, or perform equivalent replacements on some or all of the technical features; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the scope of the technical solutions of the present application.

Claims

1. A method for preparing a halogen-free flame-retardant basalt fiber-epoxy resin composite material, characterized in that: The following steps are involved: (1) Surface treatment of basalt fiber: Place basalt fiber in an ethanol-water solution (volume ratio of 4:1), add amino coupling agent KH-550, and stir evenly; heat at 60°C for 2-4 hours, then wash and dry to obtain modified basalt fiber; (2) preparing a halogen-free flame-retardant epoxy resin composition: mixing an epoxy resin, an organic phosphorus halogen-free flame retardant with a specific molecular structure (10-25% by mass) and an auxiliary agent, and stirring the mixture at 50-80° C.; adding a curing agent to the mixture, and continuing to stir the mixture to obtain a halogen-free flame-retardant epoxy resin composition; (3) Preparation of composite materials: The modified basalt fiber treated in step (1) is uniformly impregnated in the halogen-free flame-retardant epoxy resin composition obtained in step (2); the impregnated fiber is laid into a mold, and formed by a hot pressing process. After pre-curing at 80-120° C. for 1-2 hours, the temperature is raised to 150-180° C. for post-curing for 2-4 hours to obtain a halogen-free flame-retardant basalt fiber-epoxy resin composite material.

2. The preparation method according to claim 1-2, characterized in that: The halogen-free flame retardant is an organophosphorus flame retardant or a phosphazene flame retardant, or a combination thereof with a synergistic flame retardant, wherein the synergistic agent is selected from nitrogen-phosphorus compounds, zinc borate or a mixture thereof.

3. The preparation method according to claim 1, characterized in that: The epoxy resin is one or more of bisphenol A epoxy resin, bisphenol F epoxy resin or novolac epoxy resin.

4. The preparation method according to claim 1, characterized in that: The curing agent is an alicyclic amine, aromatic amine or anhydride curing agent, preferably methylhexahydrophthalic anhydride or 4,4'-diaminodiphenyl sulfone.

5. The preparation method according to claim 1, characterized in that: The auxiliary agent includes one or more of a leveling agent, a dispersant, an antioxidant or a defoaming agent, and the added amount is 0.5-5% of the mass of the epoxy resin.

6. The preparation method according to claim 1, characterized in that: The pressure during hot pressing is 2-5 MPa, and the volume fraction of basalt fiber in the mold is 40-60%.

7. The preparation method according to claim 1, characterized in that: The obtained composite material has an oxygen index (LOI) of ≥30%, a vertical combustion performance reaching UL94 V-0 level, and mechanical properties including a tensile strength of 300-400MPa and a flexural strength of ≥350MPa.

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