Preparation method of flame-retardant modified basalt fiber-polyamide (PA) composite material

Abstract

The invention relates to the technical field of composite materials, and discloses a preparation method of a flame-retardant modified basalt fiber-polyamide composite material. According to the method, basalt fibers are taken as a reinforcing phase, polyamide is taken as a matrix, and synergistic optimization of flame retardance and mechanical properties is realized through surface modification, a phosphorus-nitrogen synergistic flame-retardant system and a hot-pressing molding process. The preparation method comprises the following specific steps: (1) carrying out surface activation treatment on basalt fibers, and improving the interface bonding force between the fibers and a matrix by adopting a silane or titanate coupling agent; (2) carrying out melt blending on the polyamide matrix and phosphorus and nitrogen flame retardants to prepare a flame-retardant polyamide premix; and (3) mixing the modified fiber and the flame-retardant polyamide in proportion, and molding through a hot-pressing molding process. The obtained composite material has high flame retardance, mechanical strength and thermal stability, and is suitable for the fields of new energy automobiles, rail transit and the like. The preparation method is simple in process, solves the problems of weak interface bonding and difficulty in considering flame retardance and mechanical properties, and has industrial application potential.

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 flame-retardant modified basalt fiber-polyamide (PA) composite material. This method prepares a composite material with excellent flame retardancy, mechanical properties and heat resistance by performing surface modification on basalt fibers and combining them with a polyamide matrix and a flame retardant, and is widely applicable to the fields of new energy vehicles, rail transit and electronic and electrical appliances. Background Art

[0002] Basalt fiber is a new type of inorganic fiber material made by high-temperature melting and drawing of natural basalt ore. It has received extensive attention in the field of composite materials due to its rich raw materials, low cost and excellent performance. Basalt fiber has high specific strength, high specific modulus, good high-temperature resistance, corrosion resistance and chemical stability. It is a reinforcing material with performance close to carbon fiber but cost comparable to glass fiber, and has broad application prospects in the fields of aerospace, rail transit, construction engineering and the automotive industry. However, the surface of basalt fiber is smooth and its chemical activity is relatively low. When directly compounded with a polymer matrix, the interfacial bonding is weak, and it is difficult to fully exert the reinforcing effect, resulting in the mechanical properties of the composite material not reaching the ideal level. Therefore, it is often necessary to perform surface modification on basalt fibers to improve the interfacial bonding performance between the fibers and the matrix by introducing chemical bonds or using coupling agents, thereby enhancing the comprehensive performance of the composite material.

[0003] Polyamide (PA) is an engineering plastic with excellent performance. Due to its high mechanical strength, good wear resistance and heat resistance, it is widely used in the fields of industrial manufacturing, electronic and electrical appliances and building materials. However, the polyamide material itself has the problem of insufficient flame retardancy. Its oxygen index is generally lower than 22%, belonging to a flammable material, and it is easy to burn and spread rapidly in a high-temperature or open-fire environment, which limits its application in fields with high requirements for flame retardancy such as aerospace, rail transit and construction engineering. To solve this problem, it is usually necessary to add a flame retardant to the polyamide matrix. Currently, commonly used flame retardants include halogen-based flame retardants, phosphorus-based flame retardants, nitrogen-based flame retardants and silicon-based flame retardants. Among them, halogen-based flame retardants were widely used due to their significant flame retardant effect, but they release toxic gases and corrosive products during combustion, posing a serious threat to the environment and human health, so their use has been gradually restricted. In contrast, phosphorus-based flame retardants and nitrogen-based flame retardants have gradually become research hotspots due to their environmental friendliness and high efficiency. In particular, the phosphorus-nitrogen synergistic flame retardant system has become one of the important choices for polyamide flame retardant modification due to its significant flame retardant effect and small impact on the mechanical properties of materials.

[0004] Although basalt fiber-reinforced polyamide composites have excellent comprehensive properties, the following technical problems still exist in practical applications: First, the interfacial bonding force is insufficient. Due to the low surface chemical activity of basalt fibers, the interfacial bonding with the polyamide matrix is weak, resulting in limited enhancement effect of the composite material and difficulty in fully exerting its mechanical properties. Second, the dispersibility of the flame retardant is poor. The flame retardant is unevenly dispersed in the polyamide matrix, easily causing stress concentration, reducing the mechanical properties of the material, and at the same time resulting in unstable flame retardant effect. Third, it is difficult to balance the flame retardant performance and mechanical properties. Although the addition of the flame retardant can significantly improve the flame retardant performance of the composite material, it often has an adverse effect on the mechanical properties, especially in the case of high flame retardant addition amount, this problem is particularly obvious. Fourth, the preparation process is complex. The existing preparation methods of basalt fiber-reinforced polyamide composites usually require multiple steps, with complex process and high cost, which is not conducive to large-scale industrial production.

[0005] Therefore, how to optimize the surface modification method of basalt fibers, improve their interfacial bonding force with the polyamide matrix, adopt an efficient and environmentally friendly flame retardant system to achieve the balance of the flame retardant performance and mechanical properties of the composite material, and simplify the preparation process at the same time, is the focus and difficulty of current research. In view of the deficiencies in the prior art, the present invention proposes a preparation method for flame retardant modified basalt fiber-polyamide composites. By performing surface modification treatment on basalt fibers, and adopting a phosphorus-nitrogen synergistic flame retardant system and an optimized dispersion process, the interfacial bonding performance and flame retardant performance of the composite material are significantly improved, while maintaining high mechanical properties. The preparation method of the present invention has a simple process and balanced performance, and has good industrial application prospects, providing an innovative technical solution for the development and application of basalt fiber-reinforced polyamide composites. Summary of the Invention

[0006] The present invention provides a preparation method for flame retardant modified basalt fiber-polyamide (PA) composites. Through surface modification treatment of basalt fibers, optimized dispersion of the flame retardant, and molding process of the composite material, a composite material with excellent mechanical properties, flame retardant performance and heat resistance is prepared. This method has a clear process and standardized steps, and is suitable for industrial production.

[0007] To achieve the above object, the present invention adopts the following technical solutions:

[0008] 1. Surface modification treatment of basalt fibers

[0009] (1) Cleaning of basalt fibers: Weigh the basalt fibers and place them in deionized water. Use an ultrasonic cleaning device to clean the fibers for 10 - 15 minutes to remove dust, impurities, and attachments on the fiber surface, ensuring the fiber surface is clean. After cleaning, dry the basalt fibers in an 80°C oven until constant weight to avoid residual moisture affecting subsequent processing.

[0010] (2) Modification with coupling agent: Select the silane coupling agent KH - 550 and prepare it in a solvent at a mass concentration of 2% - 5% (the solvent is a mixture of ethanol and deionized water with a volume ratio of 7:3). Use a stirrer to fully mix until the coupling agent is completely dissolved. Immerse the dried basalt fibers in the coupling agent solution, stir evenly, and place the immersion system in a 70°C constant temperature water bath and stir for 30 minutes to ensure the coupling agent is evenly attached to the fiber surface. After immersion, take out the basalt fibers, gently wipe off the excess liquid on the surface with a clean filter cloth, and then dry in a 120°C oven for 2 hours to ensure the coupling agent is firmly attached and the basalt fibers are completely dry. After processing, the modified fibers are set aside for use.

[0011] 2. Premixing treatment of flame retardant and polyamide

[0012] (1) Preparation of flame retardant: According to the flame retardant requirements, select a phosphorus - based flame retardant (such as ammonium polyphosphate) and a nitrogen - based flame retardant (such as melamine cyanurate), and weigh and mix them according to a phosphorus - nitrogen mass ratio of 7:3. The total addition amount of the flame retardant is 10% - 20% of the mass of the polyamide matrix, and the specific ratio can be adjusted according to the material performance requirements.

[0013] (2) Melting and blending of flame retardant and polyamide: Place the polyamide particles (such as PA6 or PA66) in a high - temperature melting and blending device, heat to 200°C - 230°C (determine the specific temperature according to the melting point of the used polyamide), and wait until it is completely melted. Gradually add the mixed flame retardant to the molten polyamide matrix, and at the same time, carry out blending treatment through a twin - screw extruder, with the screw speed controlled at 50 - 80 revolutions per minute to ensure the flame retardant is evenly dispersed in the polyamide matrix. After blending, extrude the melt through an extrusion device, cool and pelletize to prepare flame - retardant modified polyamide particles.

[0014] 3. Mixing and melting blending of composite materials

[0015] (1) Raw material ratio: Calculated based on the total mass of the composite material, the addition amount of basalt fibers is 20% - 40%, and the flame - retardant polyamide particles are 60% - 80%. A certain amount of additives (such as toughening agents or antioxidants, with an addition amount generally 1% - 3% of the total mass of the composite material) can be added according to requirements.

[0016] (2) Mixing: Mix the surface-modified basalt fibers, flame-retardant polyamide particles and additives in proportion, and use a high-speed stirring device or mixer to pre-treat the mixture to ensure the preliminary uniform distribution of the raw materials.

[0017] (3) Melt blending: Place the pre-mixed materials in a twin-screw extruder for melt blending, control the temperature at 210°C - 240°C, and adjust the screw speed to 50 - 100 revolutions per minute; during the melt blending process, optimize the screw configuration and shear force to ensure the uniform dispersion of basalt fibers and flame-retardant polyamide matrix, and avoid fiber agglomeration and stress concentration; after the blending is completed, extrude the melt and cool and pelletize to obtain flame-retardant modified basalt fiber-polyamide composite particles.

[0018] 4. Molding of the composite material

[0019] (1) Preparation of molding equipment: Put the prepared composite particles into a hot pressing and molding equipment, select a suitable mold according to the size of the product, and clean the surface of the mold to prevent impurities from affecting the quality of the product.

[0020] (2) Hot pressing molding process: Uniformly fill the composite particles into the mold, adjust the equipment temperature to 230°C - 260°C, the molding pressure is 10 - 15 MPa, and the holding pressure time is 10 - 20 minutes; during the hot pressing process, ensure the precise control of temperature, pressure and time parameters to achieve the dense molding and performance optimization of the material.

[0021] (3) Cooling and demolding: After the hot pressing is completed, take out the mold from the equipment and place it in a room temperature environment for natural cooling or quickly cool it through a cooling device; demold after cooling to obtain the finally prepared flame-retardant modified basalt fiber-polyamide composite product.

[0022] The beneficial effects of the present invention are that by optimizing the surface modification process of basalt fibers, the dispersion method of flame retardants and the composite material molding process, the flame retardant performance of the prepared composite material is significantly improved, the oxygen index (LOI) reaches more than 30%, and it passes the UL-94V-0 level test; the mechanical properties are significantly enhanced, and the tensile strength and bending strength are increased by 15% - 30% compared with the un-reinforced materials; the material also has good thermal stability and durability, and can be widely used in fields such as aerospace, rail transit and construction engineering. The method of the present invention is simple and efficient, suitable for industrial production, and has important market promotion value. Specific embodiments

[0023] In order to make the content of the invention easier to understand, the following lists 5 specific implementation examples of the present invention to illustrate the preparation method and performance of the flame-retardant modified basalt fiber-polyamide composite material, but the present invention is not limited thereto.

[0024] Example 1

[0025] Preparation of composite material with 20% basalt fiber addition and 10% flame retardant addition

[0026] (1) Surface modification of basalt fiber: Place 100 g of basalt fiber in deionized water, ultrasonically clean for 10 minutes, and dry at 80 °C to constant weight; Prepare a 3% concentration silane coupling agent solution (the solvent is ethanol and deionized water, volume ratio 7:3), soak the basalt fiber in the solution, and stir at 70 °C for 30 minutes; Take out the basalt fiber and dry it at 120 °C for 2 hours for standby use.

[0027] (2) Premixing treatment of flame retardant and polyamide: Take 1000 g of polyamide (PA6) particles, heat to 210 °C to melt; Add 100 g of flame retardant (phosphorus-based flame retardant ammonium polyphosphate and nitrogen-based flame retardant melamine cyanurate, mass ratio 7:3), and use a twin-screw extruder for blending, then cool and pelletize.

[0028] (3) Preparation of composite material: Mix 200 g of modified basalt fiber with 900 g of flame-retardant polyamide, and perform melt blending with a twin-screw extruder (temperature 220 °C, screw speed 70 revolutions per minute), then cool and pelletize for standby use.

[0029] (4) Molding: Place the above composite material particles in a hot press molding machine, the molding temperature is 240 °C, the pressure is 12 MPa, and the pressure is maintained for 15 minutes; Cool and demold to obtain a composite material plate (size 150×150×3 mm).

[0030] (5) Secondary heat treatment: Place the molded plate in an oven at 120 °C for 2 hours to eliminate internal stress.

[0031] Performance test results:

[0032] The oxygen index (LOI) is 30%, passing the UL-94 V-0 level test; The tensile strength is 110 MPa, and the flexural strength is 140 MPa (the tensile strength test is based on ASTM D638, and the flexural strength test is based on ISO 178) (Table 1).

[0033] Example 2

[0034] Preparation of composite material with 30% basalt fiber addition and 15% flame retardant addition

[0035] (1) Surface modification of basalt fiber: Take 300 g of basalt fiber and perform surface cleaning and coupling agent modification treatment in the same method as in Example 1.

[0036] (2) Premixing treatment of flame retardant and polyamide: After melting 850 g of PA6 particles, add 150 g of flame retardant (mass ratio of phosphorus-based flame retardant to nitrogen-based flame retardant 7:3), and perform twin-screw blending, then cool and pelletize for standby use.

[0037] (3) Preparation of composite material: Mix 300 g of modified basalt fiber with 850 g of flame-retardant polyamide particles, and conduct melt blending (temperature 230 °C, screw speed 80 revolutions per minute), then cool and pelletize.

[0038] (4) Molding: Use hot press molding equipment, with a molding temperature of 250 °C, a pressure of 15 MPa, and a holding pressure of 20 minutes; then cool and demold to obtain the composite material board.

[0039] (5) Secondary heat treatment: Place the molded board in an oven at 120 °C for 2 hours to eliminate internal stress.

[0040] Performance test results:

[0041] The limiting oxygen index (LOI) is 33%, passing the UL-94 V-0 level test; the tensile strength is 105 MPa, and the flexural strength is 135 MPa (the tensile strength test is based on ASTM D638, and the flexural strength test is based on ISO 178) (Table 1).

[0042] Example 3

[0043] Appropriately increase the coupling agent concentration to 5% to improve the interfacial bonding and alleviate the decline in mechanical properties. Preparation of a composite material with a basalt fiber addition amount of 40% and a flame retardant addition amount of 20%

[0044] (1) Surface modification of basalt fiber: Take 400 g of basalt fiber and conduct surface cleaning and modification treatment in the same method as in Example 1.

[0045] (2) Premixing treatment of flame retardant and polyamide: After melting 800 g of PA6 particles, add 200 g of flame retardant (mass ratio of phosphorus-based flame retardant to nitrogen-based flame retardant is 7:3), and conduct twin-screw blending, then cool and pelletize for standby.

[0046] (3) Preparation of composite material: Mix 400 g of modified basalt fiber with 800 g of flame-retardant polyamide particles, and conduct melt blending (temperature 240 °C, screw speed 60 revolutions per minute), then cool and pelletize.

[0047] (4) Molding: In the molding equipment, with a molding temperature of 260 °C, a pressure of 13 MPa, and a holding pressure of 18 minutes; then cool and demold to obtain the composite material board.

[0048] (5) Secondary heat treatment: Place the molded board in an oven at 120 °C for 2 hours to eliminate internal stress.

[0049] Performance test results:

[0050] The limiting oxygen index (LOI) is 35%, passing the UL-94 V-0 level test; the tensile strength is 100 MPa, and the flexural strength is 130 MPa (the tensile strength test is based on ASTM D638, and the flexural strength test is based on ISO 178) (Table 1).

[0051] Example 4

[0052] Composite material prepared with PA66 matrix material

[0053] (1) Surface modification of basalt fibers. Take 250 g of basalt fibers and perform surface cleaning and modification treatment in the same manner as in Example 1.

[0054] (2) Premixing treatment of flame retardant and polyamide. After melting 900 g of PA66 particles, add 150 g of flame retardant (the mass ratio of phosphorus-based flame retardant to nitrogen-based flame retardant is 8:2), and perform twin-screw blending. Cool and pelletize for standby.

[0055] (3) Preparation of composite material. Mix 250 g of modified basalt fibers with 900 g of flame-retarded PA66 particles, and perform melt blending (temperature 240 °C, screw speed 70 revolutions per minute). Cool and pelletize.

[0056] (4) Molding. In a molding press, the molding temperature is 260 °C, the pressure is 14 MPa, and the pressure holding time is 15 minutes; cool and demold to obtain a composite material plate.

[0057] (5) Secondary heat treatment: Place the molded plate in an oven at 120 °C for 2 hours to eliminate internal stress.

[0058] Performance test results:

[0059] The limiting oxygen index (LOI) is 32%, passing the UL-94 V-0 level test; the tensile strength is 120 MPa, and the flexural strength is 145 MPa (the tensile strength test is based on ASTM D638, and the flexural strength test is based on ISO 178) (Table 1).

[0060] Example 5

[0061] Preparation of composite material with the addition of silicon-based flame retardant

[0062] (1) Surface modification of basalt fibers. Take 200 g of basalt fibers and perform surface cleaning and modification treatment in the same manner as in Example 1.

[0063] (2) Premixing treatment of flame retardant and polyamide. After melting 850 g of PA6 particles, add flame retardant (70% phosphorus-based flame retardant, 20% nitrogen-based flame retardant, 10% silicon-based flame retardant), and the total addition amount is 150 g. Perform twin-screw blending. Cool and pelletize for standby.

[0064] (3) Preparation of composite material: 200 g of modified basalt fibers and 850 g of flame-retardant polyamide particles are mixed and melt-blended (temperature 220 °C, screw speed 65 revolutions per minute), and then cooled and pelletized.

[0065] (4) Molding: Molding parameters for compression molding: temperature 240 °C, pressure 12 MPa, holding pressure for 15 minutes; cooling and demolding to obtain a composite material plate.

[0066] (5) Secondary heat treatment: The molded plate is placed in an oven at 120 °C for 2 hours to eliminate internal stress.

[0067] Performance test results:

[0068] The limiting oxygen index (LOI) is 34%, passing the UL-94 V-0 level test; the tensile strength is 108 MPa, and the flexural strength is 138 MPa (the tensile strength test is based on ASTM D638, and the flexural strength test is based on ISO 178) (Table 1).

[0069] Table 1 Comparison of key parameters and performance of the examples

[0070]

[0071] Each embodiment in this specification is described in a progressive manner. The same or similar parts between each embodiment can be referred to each other. The key points of each embodiment are the differences from other embodiments (Table 1). The above five examples show that by adjusting the addition amounts of basalt fibers and flame retardants, and selecting appropriate matrix materials and process parameters, a composite material with excellent flame retardant performance and mechanical properties can be prepared to meet the requirements of different fields.

[0072] 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 for 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 flame retardant modified basalt fiber-polyamide (PA) composite material, comprising the following steps: (1) Surface modification of basalt fiber: including cleaning, coupling agent treatment and drying; After cleaning the surface of the basalt fiber, a coupling agent is used to treat the surface of the basalt fiber to improve the interface bonding performance between the fiber and the polyamide matrix. (2) Premixing of flame retardant with polyamide matrix: premixing flame retardant with polyamide (PA) matrix material, wherein the flame retardant is selected from phosphorus flame retardant, nitrogen flame retardant or a combination thereof, and uniformly dispersed in the polyamide matrix by melt blending or mechanical mixing; (3) Mixing of surface modified fiber and flame retardant polyamide and hot pressing molding process: The surface modified basalt fiber and the pretreated flame retardant polyamide material are mixed in proportion, and processed by hot pressing molding process to obtain a flame retardant modified basalt fiber-polyamide composite material; (4) Secondary heat treatment is performed after the composite material is formed.

2. The preparation method according to claim 1, characterized in that: The coupling agent used in the surface modification treatment of the basalt fiber is a silane coupling agent or a titanate coupling agent.

3. The preparation method according to claim 1, characterized in that: The added amount of the flame retardant is 10-20% of the mass of the polyamide matrix.

4. The preparation method according to claim 1, characterized in that: The added amount of the basalt fiber is 20-50% of the total mass of the composite material.

5. The preparation method according to claim 1, characterized in that: The temperature range of the hot pressing molding process is 240° C.-260° C., the pressure range is 5-15 MPa, and the holding time is 5-30 minutes.

6. The preparation method according to claim 1, characterized in that: The flame retardant is phosphate ester, ammonium polyphosphate, melamine, silicon-based flame retardant or a composite thereof.

7. The preparation method according to claim 1, characterized in that: The cleaning is carried out by ultrasonic cleaning with deionized water for 10-15 minutes, and the drying temperature is 80°C.

8. The preparation method according to claim 1, characterized in that: After the composite material is formed, a secondary heat treatment is performed at a temperature of 100° C.-150° C. for 1-3 hours.

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