Flame-retardant cellulose-based fiber reinforced epoxy resin composite material and preparation method thereof

Abstract

The invention discloses a flame-retardant cellulose-based fiber reinforced epoxy resin composite material and a preparation method thereof.The preparation method comprises the steps that firstly, water is added into a flame retardant for dilution, ammonia water is used for adjusting the pH to be 5-6, flame-retardant liquid is prepared, cellulose-based fibers are soaked in the flame-retardant liquid and taken out after being soaked for a certain time, and the flame-retardant cellulose-based fiber reinforced epoxy resin composite material is obtained through extrusion rolling and drying; the flame-retardant cellulose-based fiber loaded with the flame retardant is obtained; the flame-retardant cellulose-based fiber and epoxy resin are combined layer by layer, and the flame-retardant cellulose-based fiber reinforced epoxy resin composite material is obtained through curing and shaping. The flame-retardant epoxy resin composite material is obtained by firstly forming a flame-retardant protective layer on the surface of the fiber through after-treatment, then compounding the flame-retardant protective layer with the epoxy resin layer by layer and finally curing and molding, the wick effect can be effectively inhibited, the flame-retardant property is greatly improved, and meanwhile, the mechanical property of a resin matrix is improved. In addition, the flame retardant prepared by the invention can be firmly and stably combined with fibers, and meanwhile, the interface bonding performance between the flame-retardant fibers and an epoxy resin matrix is optimized.

Description

Technical Field

[0001] This invention relates to the field of polymer materials technology, specifically to a flame-retardant cellulose-based fiber-reinforced epoxy resin composite material and its preparation method. Background Technology

[0002] Epoxy resin, as a high-performance thermosetting resin, has become an indispensable basic material in aerospace, construction materials, and electronics industries due to its outstanding mechanical strength, bonding properties, chemical corrosion resistance, and dimensional stability. Especially with the development trends of lightweight transportation and high-end equipment manufacturing, fiber-reinforced epoxy resin composites are gradually replacing traditional metal materials and their application range continues to expand because they can achieve an optimized balance between strength and weight. Among these, natural plant fibers have advantages over synthetic fiber reinforcement systems such as glass fiber and carbon fiber in terms of environmental friendliness, cost, lightweight potential, and mechanical adaptability. For example, hemp fiber, derived from plants, is a renewable resource and features high specific strength and high specific modulus. However, the inherent chemical structure of epoxy resin and natural plant fibers results in significant performance shortcomings, severely limiting their application in high-safety-requirement scenarios. The primary problem is their inherently insufficient flame retardant properties; the limiting oxygen index of epoxy resin and natural plant fibers is typically below 23%, classifying them as flammable materials. Building upon this, blending flame-retardant treatments on the resin can affect its viscosity, thus impacting the preparation of fiber-reinforced composites. Furthermore, the fibers within the resin, acting as "wick materials," can accelerate combustion and limit the improvement of flame-retardant effects. Therefore, flame-retardant finishing of the fibers to prepare flame-retardant fibers, followed by combination with epoxy resin, is a reliable method. However, ensuring a strong and stable bond between the flame retardant and the fibers, while simultaneously optimizing the interfacial adhesion between the flame-retardant fibers and the epoxy resin matrix, is the core challenge in achieving high-performance materials. Poor interfacial adhesion leads to low stress transfer efficiency, severely impairing the mechanical properties of the composite material. Conversely, insufficient flame retardant loading or poor compatibility with the matrix can affect the durability and uniformity of flame-retardant efficiency. Summary of the Invention

[0003] To address the aforementioned problems, the present invention aims to provide a flame-retardant cellulose-based fiber-reinforced epoxy resin composite material and its preparation method, thereby solving the problems of poor interfacial compatibility between traditional composite materials and the matrix, as well as the difficulty in synergistically improving flame-retardant performance and mechanical properties.

[0004] To achieve the above objectives, the technical solution of the present invention is as follows:

[0005] A method for preparing a flame-retardant cellulose-based fiber-reinforced epoxy resin composite material specifically includes the following steps:

[0006] (1) Dilute the flame retardant with water and adjust the pH to 5-6 with ammonia water to prepare a flame retardant solution. Immerse the cellulose-based fiber in the flame retardant solution and keep it immersed for a certain time. Then take it out, squeeze and dry it to obtain flame retardant cellulose-based fiber loaded with flame retardant. The fiber refers to continuous uninterrupted fiber, such as fabric.

[0007] (2) Flame-retardant cellulose-based fibers are combined with epoxy resin layer by layer and cured to obtain flame-retardant cellulose-based fiber reinforced epoxy resin composite material.

[0008] The specific preparation method of the flame retardant liquid in step (1) is as follows: A phosphoric acid compound and a polyphenol compound are mixed and reacted at 60-160℃ for 0.5-12 hours to obtain a phosphoric acid-modified polyphenol flame retardant. The mass ratio of the phosphoric acid compound to the polyphenol compound is 7:1 to 1:7.

[0009] Alternatively, the specific preparation method of the flame retardant liquid in step (1) is as follows: Phosphoric acid compound, basic amino acid, and synergist are mixed evenly at room temperature and reacted for 10 min to 3 h to obtain a phosphate amino acid salt flame retardant. The mass ratio of phosphoric acid compound to basic amino acid is 6:1 to 2:1, and the content of synergist in the phosphate amino acid salt flame retardant is 1-5 wt.%. The synergist is one or more of the following: ferric nitrate, nickel nitrate, molybdenum trioxide, zinc borate, aluminum diethylphosphonate, montmorillonite, palygorskite, and hydrotalcite.

[0010] The phosphoric acid compound is one or more of phosphoric acid, phytic acid, phosphorous acid, hypophosphoric acid, phenylphosphonic acid, aminotrimethylene phosphoric acid, diethylenetriaminepentamethylenephosphonic acid, ethylenediaminetetramethylenephosphonic acid, and hexamethylenediaminetetramethylenephosphonic acid; the polyphenolic compound is one or more of tea polyphenols, catechins, tannins, caffeic acid, theaflavins, and anthocyanins; and the amino acid is one or more of lysine, histidine, and arginine.

[0011] It should be noted that in step (1), the cellulose base refers to one of the following: ramie, lyocell, flax, apocynum, jute, etc.

[0012] It should be noted that in step (1), the concentration of the flame retardant liquid is 50 g / L - 400 g / L.

[0013] It should be noted that in step (1), after drying, the loading of flame retardant on the cellulose-based fiber is 10% - 40% of the mass of the cellulose-based fiber.

[0014] It should be noted that step (2) specifically involves: first, laying flame-retardant cellulose-based fibers on the mold; then, applying a mixture of epoxy resin and curing agent to the upper part of the flame-retardant cellulose-based fibers, repeating this process alternately until the required thickness is achieved; then, vacuum defoaming; and finally, transferring the mixture to a flat vulcanizing machine for curing and molding. The curing temperature is 20-170℃.

[0015] It should be noted that in step (2), the flame-retardant cellulose-based fiber accounts for 20% - 80% of the mass of the composite material.

[0016] The cellulose-based fiber-reinforced epoxy resin composites prepared by the above method have flame retardant properties reaching UL-94 V-1 or UL-94 V-0 levels, LOI of 27-45%, tensile strength of 90-140 MPa, and flexural strength of 152-483 MPa.

[0017] The beneficial effects of this invention are: (1) High efficiency and synergistic flame retardancy: By forming a high efficiency flame retardant layer on the surface of cellulose-based fibers through post-treatment, the flame retardant performance of cellulose-based fibers is significantly improved. At the same time, after being compounded with epoxy resin, the flame retardant performance of the resin matrix is ​​simultaneously enhanced, thus exerting a synergistic flame retardant effect. (2) Optimization of mechanical properties: While improving the flame retardant performance, the flame retardant can be well compatible with the epoxy resin matrix, effectively improving the interfacial bonding, thereby significantly enhancing the mechanical properties of the composite material. (3) Outstanding environmental protection and sustainability: The flame retardant raw materials used are derived from natural renewable resources. The preparation process does not require toxic solvents. The overall process is environmentally friendly and meets the requirements of green chemistry and sustainable development. (4) Simple process and wide applicability: The flame retardant finishing process is carried out by padding, which is simple to operate and easy to control, and is suitable for continuous production. This method can be widely applied to various cellulose-based fiber reinforced epoxy resin systems and has good process universality. (5) Broad industrialization prospects: This technology combines performance improvement and environmental protection advantages. The raw material cost is controllable, the process is mature, and it is easy to achieve large-scale production. It has significant application value in the manufacturing of functional composite materials in aerospace, transportation, electronics and electrical fields. Detailed Implementation

[0018] The present invention will be further illustrated below with reference to specific embodiments. It should be understood that the following specific embodiments are only for illustrating the present invention and are not intended to limit the scope of the present invention. If those skilled in the art make some non-essential adjustments and improvements to the present invention based on the content of the present invention, they shall still fall within the protection scope of the present invention.

[0019] A method for preparing a flame-retardant cellulose-based fiber-reinforced epoxy resin composite material, comprising the following steps:

[0020] (1) Dilute the flame retardant with water and adjust the pH to 5-6 with ammonia water to prepare a flame retardant solution. Immerse the cellulose-based fiber in the flame retardant solution and keep it immersed for a certain time. Then take it out, squeeze and dry it to obtain flame retardant cellulose-based fiber loaded with flame retardant. The fiber refers to continuous uninterrupted fiber, such as fabric.

[0021] (2) Flame-retardant cellulose-based fibers and epoxy resin are combined layer by layer and cured to obtain flame-retardant cellulose-based fiber reinforced epoxy resin composite material.

[0022] Compared to directly adding flame retardants to epoxy resin and curing, this invention first forms a flame-retardant protective layer on the fiber surface through post-treatment, then layers it with epoxy resin, and finally cures it to obtain a flame-retardant epoxy resin composite material. This effectively suppresses the wicking effect, greatly improves flame-retardant performance, and simultaneously enhances the mechanical properties of the resin matrix. Furthermore, the flame retardant prepared in this application achieves a strong and stable bond with the fiber, while also optimizing the interfacial adhesion between the flame-retardant fiber and the epoxy resin matrix.

[0023] It should be noted that, as an implementation method, the specific preparation method of the flame retardant liquid in step (1) is as follows: the phosphoric acid compound and the polyphenol compound are mixed and reacted at 60-160℃ for 0.5-12h to obtain a phosphoric acid modified polyphenol flame retardant. The mass ratio of the phosphoric acid compound and the polyphenol compound is 7:1~1:7. The phosphoric acid compound is one or more of phosphoric acid, phytic acid, phosphorous acid, hypophosphite, phenylphosphonic acid, aminotrimethylene phosphoric acid, diethylenetriaminepentamethylenephosphonic acid, ethylenediaminetetramethylenephosphonic acid, and hexamethylenediaminetetramethylenephosphonic acid. The polyphenol compound is one or more of tea polyphenols, catechins, tannins, caffeic acid, theaflavins, and anthocyanins. The polyphenol compound plays a crucial multifunctional role in this system. On the one hand, its abundant phenolic hydroxyl groups can form strong hydrogen bonds with the fiber surface and can react with the phosphoric acid compound to generate modified products with highly efficient phosphoric acid flame retardant effects, significantly improving the flame retardant performance of the system. On the other hand, the polyphenol product modified with phosphoric acid retains both polar groups compatible with fibers and segments compatible with epoxy resins in its molecular structure, thus creating a robust "bridge" interface layer between the fiber and the resin matrix. This interface layer not only strengthens the fixation of the flame retardant on the fiber but also effectively improves stress transfer between the reinforcement and the matrix, achieving a synergistic enhancement of both flame retardant and mechanical properties.

[0024] It should be noted that, as another implementation method, the specific preparation method of the flame retardant liquid in step (1) is as follows: the phosphoric acid compound, basic amino acid and synergist are mixed evenly at room temperature and reacted for 10 min to 3 h to obtain the phosphate amino acid salt flame retardant. The mass ratio of the phosphoric acid compound and the basic amino acid is 6:1 to 2:1. The phosphoric acid compound is one or more of phosphoric acid, phytic acid, phosphorous acid, hypophosphite, phenylphosphonic acid, aminotrimethylene phosphoric acid, diethylenetriaminepentamethylphosphonic acid, ethylenediaminetetramethylphosphonic acid, and hexamethylenediaminetetramethylphosphonic acid. The amino acid is one or more of lysine, histidine, and arginine. The content of the synergist in the phosphate amino acid salt flame retardant is 1-5 wt.%, and the synergist is one or more of ferric nitrate, nickel nitrate, molybdenum trioxide, zinc borate, aluminum diethylphosphite, montmorillonite, palygorskite, and hydrotalcite. Metal salts such as ferric nitrate, nickel nitrate and aluminum diethylphosphite catalyze the decomposition of phosphoric acid compound to generate polyphosphoric acid, which accelerates the dehydration and cross-linking of cellulose and epoxy resin to form a dense carbon layer. Molybdenum trioxide achieves flame retardancy through smoke suppression. Zinc borate releases water of crystallization upon heating, diluting combustible gases and oxygen, while simultaneously decomposing to form a glassy melt that covers the material surface, isolating oxygen and heat, and promoting char formation. Hydrotalcite utilizes its structure to form a physical barrier, improving the quality of the char layer. Phosphate compounds in phosphate amino acid salt flame retardants provide phosphorus (P), and amino acids provide nitrogen (N). Synergistic agents work together through smoke suppression and physical barrier effects to enhance the flame retardant effect. Furthermore, the amino groups in phosphate amino acid salt flame retardants participate in the curing of epoxy resin, thereby improving the interfacial bonding between flame-retardant fibers and resin.

[0025] It should be noted that in step (1), the cellulose base refers to one of the following: ramie, lyocell, flax, apocynum, jute, etc.

[0026] It should be noted that in step (1), the concentration of the flame retardant liquid is 50 g / L - 400 g / L.

[0027] It should be noted that in step (1), after drying, the loading of flame retardant on the cellulose-based fiber is 10% - 40% of the mass of the cellulose-based fiber, such as 10%, 15%, 20%, 25%, 30%, 35%, 40%, or any two of the above values.

[0028] It should be noted that step (2) specifically involves: first, laying flame-retardant cellulose-based fibers on the mold; then, applying a mixture of epoxy resin and curing agent to the upper part of the flame-retardant cellulose-based fibers, repeating this process alternately until the required thickness is achieved; then, vacuum defoaming; and finally, transferring the mixture to a flat vulcanizing machine for curing and molding. The curing temperature is 20-170℃.

[0029] It should be noted that in step (2), the mass percentage of the flame-retardant cellulose-based fiber in the composite material is 20% - 80%, such as 20%, 25%, 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65%, 70%, 75%, 80%, or any two of the above values.

[0030] It should be noted that the curing agent in step (2) is a commonly used curing agent for epoxy resin.

[0031] The cellulose-based fiber-reinforced epoxy resin composites prepared by the above method have flame retardant properties reaching UL-94 V-1 or UL-94 V-0 levels, LOI of 27-45%, tensile strength of 90-140 MPa, and flexural strength of 152-483 MPa.

[0032] Example 1:

[0033] (1) Phytic acid and tea polyphenols in a mass ratio of 3:1 were reacted at 130 °C for 3 h to obtain phytic acid-modified tea polyphenols. Then, the flame retardant was adjusted to pH 5 with ammonia water and diluted to 100 g / L with deionized water to obtain a flame retardant liquid.

[0034] (2) The Lyocell fabric was immersed in flame retardant solution at a liquor ratio of 1:20, finished at 65 °C for 40 min, and dried after extrusion. The flame retardant loading on the fabric was 15%.

[0035] (3) The finished Lyocell fabric is combined with the mixture of epoxy resin and curing agent (m-phenylenediamine) in a mold layer by layer. The proportion of flame retardant fabric in the composite material is 50%. The mold is placed on a flat vulcanizing machine and cured at 80 ℃, 100 ℃ and 120 ℃ for 2 h each under 11 MPa pressure to obtain flame retardant fiber reinforced epoxy resin composite material.

[0036] Example 2:

[0037] (1) Phosphoric acid and tannin in a mass ratio of 7:2 were reacted at 100 °C for 5 h to obtain phosphoric acid modified tannin. Then, the flame retardant was adjusted to pH 5 with ammonia water and diluted to 200 g / L with deionized water to obtain a flame retardant liquid.

[0038] (2) The ramie fabric was soaked in flame retardant solution at a liquor ratio of 1:20, finished at 70 ℃ for 30 min, and dried after extrusion. The loading of flame retardant on the fabric was 30%.

[0039] (3) The treated ramie fabric is combined with the mixture of epoxy resin and curing agent (m-phenylenediamine) in a mold layer by layer. The proportion of flame retardant fabric in the composite material is 50%. The mold is placed on a flat vulcanizing machine and cured at 70 ℃, 90 ℃ and 110 ℃ for 2 h each under 11 MPa pressure to obtain flame retardant fiber reinforced epoxy resin composite material.

[0040] Example 3:

[0041] (1) Phenylophosphonic acid and tea polyphenols in a mass ratio of 4:1 were reacted at 140 °C for 3 h to obtain phenylphosphonic acid modified tea polyphenols. Then, the flame retardant was adjusted to pH 5 with ammonia water and diluted to 100 g / L with deionized water to obtain a flame retardant liquid.

[0042] (2) The jute fabric was soaked in flame retardant solution at a liquor ratio of 1:20, finished at 60 ℃ for 30 min, and dried after extrusion. The loading of flame retardant on the fabric was 20%.

[0043] (3) The treated jute fabric is combined with the mixture of epoxy resin and curing agent (m-phenylenediamine) in a mold layer by layer. The proportion of flame retardant fabric in the composite material is 35%. The mold is placed on a flat vulcanizing machine and cured at 70 ℃, 90 ℃ and 110 ℃ for 2 h each under 11 MPa pressure to obtain flame retardant fiber reinforced epoxy resin composite material.

[0044] Example 4:

[0045] (1) Phosphorous acid and anthocyanin in a mass ratio of 6:1 were reacted at 140 °C for 4 h to obtain phosphorous acid-modified anthocyanin. Then, the flame retardant was adjusted to pH 5 with ammonia water and diluted to 150 g / L with deionized water to obtain a flame retardant liquid.

[0046] (2) The Lyocell fabric was immersed in flame retardant liquid at a liquor ratio of 1:20, finished at 80 ℃ for 20 min, and dried after extrusion. The loading of flame retardant on the fabric was 30%.

[0047] (3) The finished Lyocell fabric is combined with the mixture of epoxy resin and curing agent (m-phenylenediamine) in a mold layer by layer. The flame retardant fabric accounts for 75% of the composite material. The mold is placed on a flat vulcanizing machine and cured at 80 ℃, 90 ℃ and 100 ℃ for 2 h each under 11 MPa pressure to obtain flame retardant fiber reinforced epoxy resin composite material.

[0048] Example 5:

[0049] (1) Phenylphosphonic acid and anthocyanin in a mass ratio of 5:2 were reacted at 160 °C for 12 h to obtain phenylphosphonic acid modified anthocyanin. Then, the flame retardant was adjusted to pH 5 with ammonia water and diluted to 250 g / L with deionized water to obtain a flame retardant liquid.

[0050] (2) The linen fabric was immersed in flame retardant solution at a liquor ratio of 1:20, finished at 80 ℃ for 20 min, and dried after extrusion. The loading of flame retardant on the fabric was 25%.

[0051] (3) The treated flax fabric is combined with the mixture of epoxy resin and curing agent (m-phenylenediamine) in a mold layer by layer. The proportion of flame retardant fabric in the composite material is 75%. The mold is placed on a flat vulcanizing machine and cured at 80 ℃, 90 ℃ and 100 ℃ for 2 h each under 11 MPa pressure to obtain flame retardant fiber reinforced epoxy resin composite material.

[0052] Example 6:

[0053] (1) Ethylenediamine tetramethylphosphonic acid and caffeic acid in a mass ratio of 3:1 were reacted at 140 °C for 4 h to obtain ethylenediamine tetramethylphosphonic acid modified caffeic acid. Subsequently, the flame retardant was adjusted to pH 5 with ammonia water and diluted to 400 g / L with deionized water to obtain a flame retardant liquid.

[0054] (2) The ramie fabric was soaked in flame retardant solution at a liquor ratio of 1:20, finished at 60 ℃ for 20 min, and dried after extrusion. The loading of flame retardant on the fabric was 40%.

[0055] (3) The treated ramie fabric and the mixture of epoxy resin and curing agent (m-phenylenediamine) are layered together in a mold. The proportion of flame-retardant fabric in the composite material is 50%. The mold is placed on a flat vulcanizing machine and cured at 70 ℃, 90 ℃ and 110 ℃ for 2 h each under 11 MPa pressure to obtain flame-retardant fiber-reinforced epoxy resin composite material.

[0056] Example 7:

[0057] (1) Phytic acid and arginine in a mass ratio of 5:1 and 3% organomontmorillonite were reacted at room temperature for 30 min. Then, the flame retardant was adjusted to pH 5 with ammonia water and diluted to 120 g / L with deionized water to obtain the flame retardant liquid.

[0058] (2) The ramie fabric was immersed in flame retardant solution at a liquor ratio of 1:15, finished at 70 ℃ for 30 min, and then dried after extrusion. The flame retardant loading on the fabric was 20%.

[0059] (3) The treated ramie fabric is combined with the mixture of epoxy resin and curing agent (m-phenylenediamine) in a mold layer by layer. The proportion of flame retardant fabric in the composite material is 50%. The mold is placed on a flat vulcanizing machine and cured at 80 ℃, 100 ℃ and 120 ℃ for 2 h each under 11 MPa pressure to obtain flame retardant fiber reinforced epoxy resin composite material.

[0060] Example 8:

[0061] (1) Phosphoric acid and lysine in a mass ratio of 4:1 and 2% ferric nitrate were reacted at room temperature for 40 min. Then, the flame retardant was adjusted to pH 5 with ammonia water and diluted to 200 g / L with deionized water to obtain a flame retardant liquid.

[0062] (2) The cotton fabric was immersed in the flame retardant solution at a liquor ratio of 1:15, finished at 70 ℃ for 30 min, and dried after extrusion. The flame retardant loading on the fabric was 20%.

[0063] (3) The treated fabric is combined with the mixture of epoxy resin and curing agent (4,4-diaminodiphenylmethane) in a mold layer by layer. The proportion of flame retardant fabric in the composite material is 30%. The mold is placed on a flat vulcanizing machine and cured at 11MPa pressure, 120 ℃ and 150 ℃ for 2 h each to obtain flame retardant fiber reinforced epoxy resin composite material.

[0064] Example 9:

[0065] (1) Diethylenetriamine pentamethylphosphoric acid, arginine, and 2% nickel nitrate were reacted at room temperature for 20 min in a mass ratio of 6:1. The flame retardant was then adjusted to pH 5 with ammonia and diluted to 100 g / L with deionized water to obtain the flame retardant liquid.

[0066] (2) The linen fabric was soaked in flame retardant solution at a liquor ratio of 1:15, finished at 70 °C for 30 min, and dried after extrusion. The flame retardant loading on the fabric was 25%.

[0067] (3) The treated fabric and the mixture of epoxy resin and curing agent (4,4-diaminodiphenylmethane) are combined layer by layer in a mold. The proportion of flame-retardant fabric in the composite material is 72%. The mold is placed on a flat vulcanizing machine and the composite is completed at 11MPa pressure, 120 ℃, 150 ℃ and 170 ℃ for 2 h each to obtain flame-retardant fiber reinforced epoxy resin composite material.

[0068] Example 10:

[0069] (1) Phosphorous acid and histidine in a mass ratio of 4:1 and 2% molybdenum trioxide were reacted at room temperature for 30 min. Then, the flame retardant was adjusted to pH 5 with ammonia and diluted to 150 g / L with deionized water to obtain a flame retardant solution.

[0070] (2) The ramie fabric was soaked in flame retardant solution at a liquor ratio of 1:15, finished at 70 ℃ for 30 min, and dried after extrusion. The loading of flame retardant on the fabric was 35%.

[0071] (3) The treated fabric is layered with the mixture of epoxy resin and curing agent (triethylenetetramine) in a mold. The flame-retardant fabric accounts for 45% of the composite material. The mold is placed on a flat vulcanizing machine and cured at 11 MPa pressure for 2 hours at room temperature and 80 ℃ for 2 hours each to obtain flame-retardant fiber-reinforced epoxy resin composite material.

[0072] Example 11:

[0073] (1) Hypophosphoric acid and histidine in a mass ratio of 3:1 and 5% zinc borate were reacted at room temperature for 30 min. Then the flame retardant was adjusted to pH 5 with ammonia water and diluted to 70 g / L with deionized water to obtain a flame retardant liquid.

[0074] (2) The Apocynum venetum fabric was immersed in flame retardant liquid at a liquor ratio of 1:15, finished at 70 ℃ for 30 min, and dried after extrusion. The loading of flame retardant on the fabric was 30%.

[0075] (3) The treated fabric is combined with the mixture of epoxy resin and curing agent (4,4-diaminodiphenylmethane) in a mold layer by layer. The proportion of flame retardant fabric in the composite material is 55%. 4,4-diaminodiphenyl sulfone is used as the curing agent. The mold is placed on a flat vulcanizing machine and cured at 11 MPa pressure, 120 ℃, 150 ℃ and 170 ℃ for 2 h each to obtain flame retardant fiber reinforced epoxy resin composite material.

[0076] Example 12:

[0077] (1) Ethylenediaminetetramethylenephosphonic acid and lysine in a mass ratio of 4:1, along with 5% aluminum diethylphosphonate, were reacted at room temperature for 30 min. Subsequently, the flame retardant was adjusted to pH 5 with ammonia and diluted to 100 g / L with deionized water to obtain the flame retardant liquid.

[0078] (2) The jute fabric was soaked in flame retardant solution at a liquor ratio of 1:15, finished at 70 ℃ for 30 min, and dried after extrusion. The loading of flame retardant on the fabric was 15%.

[0079] (3) The treated fabric is layered with the mixture of epoxy resin and curing agent (triethylenetetramine) in a mold. The flame-retardant fabric accounts for 60% of the composite material. The mold is placed on a flat vulcanizing machine and cured at 11 MPa pressure for 2 hours at room temperature and 80 ℃ for 2 hours each to obtain flame-retardant fiber-reinforced epoxy resin composite material.

[0080] Example 13:

[0081] (1) A mixture of aminotrimethylene phosphate and arginine in a mass ratio of 5:1, along with 5% attapulgite, was reacted at room temperature for 40 min. Subsequently, the flame retardant was adjusted to pH 5 with ammonia and diluted to 120 g / L with deionized water to obtain a flame retardant liquid.

[0082] (2) The sisal fabric was immersed in flame retardant solution at a liquor ratio of 1:15, finished at 70 ℃ for 30 min, and dried after extrusion. The loading of flame retardant on the fabric was 25%.

[0083] (3) The treated fabric is combined with the mixture of epoxy resin and curing agent (4,4-diaminodiphenylmethane) in a mold layer by layer. The proportion of flame retardant fabric in the composite material is 60%. The mold is placed on a flat vulcanizing machine and cured at 11MPa pressure, 120 ℃ and 150 ℃ for 2 h each to obtain flame retardant fiber reinforced epoxy resin composite material.

[0084] Example 14:

[0085] (1) Phosphorous acid and lysine in a mass ratio of 4:1 and 5% hydrotalcite were reacted at room temperature for 25 min. Then, the flame retardant was adjusted to pH 5 with ammonia and diluted to 90 g / L with deionized water to obtain a flame retardant liquid.

[0086] (2) The Lyocell fabric was immersed in flame retardant solution at a liquor ratio of 1:15, finished at 70 °C for 30 min, and dried after extrusion. The flame retardant loading on the fabric was 15%.

[0087] (3) The treated fabric is combined with the mixture of epoxy resin and curing agent (m-phenylenediamine) in a mold layer by layer. The proportion of flame retardant fabric in the composite material is 60%. The mold is placed on a flat vulcanizing machine and cured at 80 ℃, 100 ℃ and 120 ℃ for 2 hours each under 11 MPa pressure to obtain flame retardant fiber reinforced epoxy resin composite material.

[0088] Comparative Example 1

[0089] The epoxy resin and m-phenylenediamine mixture from Example 1 was loaded into a mold and cured under the conditions of Example 1 to obtain pure epoxy resin.

[0090] Comparative Example 2

[0091] Ramie fabric and the epoxy resin and m-phenylenediamine mixture from Example 1 were layered together in a mold. The flame-retardant fabric accounted for 50% of the composite material. The mixture was cured under the conditions of Example 1 to obtain a fiber-reinforced epoxy resin composite material.

[0092] Comparative Example 3

[0093] Lyocell fabric was layered with the epoxy resin and m-phenylenediamine mixture from Example 1 in a mold. The flame-retardant fabric accounted for 50% of the composite material. The mixture was cured under the conditions of Example 1 to obtain a fiber-reinforced epoxy resin composite material.

[0094] Performance testing

[0095] Flame retardant properties: The limiting oxygen index values ​​of the composite materials obtained in Examples 1-14 and Comparative Examples 1-3 were determined according to the relevant provisions of GB / T 2406.2-2009. Vertical burning tests were conducted on the composite materials obtained in Examples 1-6 and Comparative Example 1 according to the relevant provisions of GB / T 2408-2021. The results are shown in Table 1.

[0096] Mechanical properties: In accordance with the relevant provisions of GB / T2567-2021, the bending properties of the composites obtained in Examples 1-14 and Comparative Examples 1-3 were tested. The results are shown in Table 1.

[0097] Those skilled in the art should understand that the above description is merely a specific embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

[0098] Table 1 Vertical combustion test and mechanical property test of composite materials

[0099]

Claims

1. A method for preparing a flame-retardant cellulose-based fiber-reinforced epoxy resin composite material, characterized in that, Includes the following steps: (1) Dilute the flame retardant with water and adjust the pH to 5-6 with ammonia water to prepare the flame retardant solution. Immerse the cellulose-based fiber in the flame retardant solution and keep it immersed for a certain time. Then take it out, squeeze and dry it to obtain flame retardant cellulose-based fiber loaded with flame retardant. (2) Flame-retardant cellulose-based fibers are combined with epoxy resin layer by layer and cured to obtain flame-retardant cellulose-based fiber reinforced epoxy resin composite material. The specific preparation method of the flame retardant liquid in step (1) is as follows: A phosphoric acid compound and a polyphenol compound are mixed and reacted at 60-160℃ for 0.5-12 hours to obtain a phosphoric acid-modified polyphenol flame retardant. The mass ratio of the phosphoric acid compound to the polyphenol compound is 7:1 to 1:

7. Alternatively, the specific preparation method of the flame retardant liquid in step (1) is as follows: Phosphoric acid compound, basic amino acid, and synergist are mixed evenly at room temperature and reacted for 10 min to 3 h to obtain a phosphate amino acid salt flame retardant. The mass ratio of phosphoric acid compound to basic amino acid is 6:1 to 2:1, and the content of synergist in the phosphate amino acid salt flame retardant is 1-5 wt.%. The synergist is one or more of the following: ferric nitrate, nickel nitrate, molybdenum trioxide, zinc borate, aluminum diethylphosphonate, montmorillonite, palygorskite, and hydrotalcite.

2. The method for preparing the flame-retardant cellulose-based fiber-reinforced epoxy resin composite material according to claim 1, characterized in that, The phosphoric acid compound is one or more of phosphoric acid, phytic acid, phosphorous acid, hypophosphoric acid, phenylphosphonic acid, aminotrimethylene phosphoric acid, diethylenetriaminepentamethylenephosphonic acid, ethylenediaminetetramethylenephosphonic acid, and hexamethylenediaminetetramethylenephosphonic acid; the polyphenolic compound is one or more of tea polyphenols, catechins, tannins, caffeic acid, theaflavins, and anthocyanins; and the amino acid is one or more of lysine, histidine, and arginine.

3. The method for preparing the flame-retardant cellulose-based fiber-reinforced epoxy resin composite material according to claim 1, characterized in that, In step (1), the cellulose base refers to one of ramie, lyocell, flax, apocynum, or jute.

4. The method for preparing the flame-retardant cellulose-based fiber-reinforced epoxy resin composite material according to claim 1, characterized in that, In step (1), the concentration of the flame retardant liquid is 50 g / L - 400 g / L.

5. The method for preparing the flame-retardant cellulose-based fiber-reinforced epoxy resin composite material according to claim 1, characterized in that, In step (1), after drying, the loading of flame retardant on cellulose-based fibers is 10%-40% of the mass of cellulose-based fibers.

6. The method for preparing the flame-retardant cellulose-based fiber-reinforced epoxy resin composite material according to claim 1, characterized in that, Step (2) is as follows: First, flame-retardant cellulose-based fibers are laid on the mold. Then, a mixture of epoxy resin and curing agent is applied to the upper part of the flame-retardant cellulose-based fibers. This process is repeated alternately until the required thickness is achieved. Then, the fibers are defoamed under vacuum and finally transferred to a flat vulcanizing machine for curing and molding.

7. The method for preparing the flame-retardant cellulose-based fiber-reinforced epoxy resin composite material according to claim 1, characterized in that, In step (2), the flame-retardant cellulose-based fiber accounts for 20% - 80% of the mass of the composite material.

8. The flame-retardant cellulose-based fiber-reinforced epoxy resin composite material prepared by the method of any one of claims 1-7.

9. The flame-retardant cellulose-based fiber-reinforced epoxy resin composite material according to claim 8 has flame-retardant properties reaching UL-94V-1 or UL-94 V-0 levels, an LOI of 27-45%, a tensile strength of 90-140 MPa, and a flexural strength of 152-483 MPa.

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