Flame-retardant plant fiber composite material and preparation method thereof

Abstract

The invention provides a flame-retardant plant fiber composite material and a preparation method thereof, and the preparation method comprises the following steps: modifying a phosphorus-containing flame retardant by using a biomass phenolic group-containing compound, and compounding with low-temperature molten glass powder and a two-dimensional lamellar nanosheet to construct a flame-retardant system; the composite material fiber reinforced phase is pretreated; and distribution optimization of a flame-retardant system is realized through layering hot press molding. According to the flame-retardant plant fiber composite material designed by the invention, the combustion characteristic of the plant fiber composite material is considered, and the consumption of a flame retardant can be greatly reduced by the distribution optimization design; no toxic solvent is used in the technological process, so that the method has relatively good safety and environmental friendliness; meanwhile, the excellent flame retardant property is realized.

Description

Technical Field

[0001] The invention relates to the technical field of flame retardant treatment, and in particular to a flame retardant plant fiber composite material and a preparation method thereof. Background Art

[0002] Plant fiber reinforced resin-based composite materials prepared with plant fiber as reinforcing phase and resin as matrix have the advantages of green environmental protection, light weight and high specific modulus. They can partially replace traditional fiber reinforced composite materials in the fields of gardening, construction, automotive parts and sporting goods. Due to the increasing demand for lightweight green products in daily life and the new energy vehicle industry, the annual growth rate of plant fiber reinforced composite materials will remain at around 11.8% in the next few years. However, plant fiber and resin matrix are highly flammable, and there are certain fire hazards in engineering applications. Once a fire occurs, it will cause serious casualties and property losses. Improving the flame retardancy of composite materials is a key issue facing the further promotion of their application.

[0003] In the prior art, the work on flame retardant modification of plant fiber reinforced composite materials is still mainly based on adding traditional flame retardants.

[0004] The Chinese invention patent with application number CN201610194141.0 discloses a flame-retardant natural fiber composite board and a preparation method thereof. The raw natural fiber and thermoplastic resin fiber are flame-retarded by phosphorus-containing flame retardant and inorganic boron flame retardant, ensuring the excellent flame retardant effect of the natural fiber composite board.

[0005] The Chinese invention patent with application number: CN202310192414.8 discloses a flame-retardant natural fiber reinforced thermoplastic composite material and a method for manufacturing the same. The fiber surface is treated with a siloxane-containing ionic liquid, and the ionic liquid is grafted onto the surface of the natural fiber. The ionic liquid has very excellent flame retardancy and improves the flame retardant properties of the natural fiber composite material.

[0006] The Chinese invention patent with application number: CN201210223106.9 discloses a flame-retardant natural fiber composite material and a preparation method thereof. Nano-additives and functionalized DOPO are used to treat the polylactic acid matrix and natural fibers respectively to obtain a flame-retardant natural fiber reinforced polylactic acid composite material with good flame retardancy and mechanical properties.

[0007] However, most of the flame retardancy of plant fiber reinforced composite materials is still achieved by adding traditional flame retardants and randomly distributing them inside the composite materials through blending. This does not take into account the combustion characteristics of plant fiber reinforced composite materials that are different from pure polymers, nor does it take into account the actual fire scenarios of plant fiber reinforced composite materials in engineering applications. According to flame retardant theory, once a fire occurs in a composite material, the flame retardant in the pyrolysis area will quickly take effect, forming a physical barrier to prevent the composite material in the non-pyrolysis area from being decomposed by heat, but at the same time it will also cause the internal flame retardant to remain in the condensed phase and be unable to exert a flame retardant effect, reducing the flame retardant efficiency. Summary of the invention

[0008] The present invention is made to solve the above problems, and aims to provide a flame retardant plant fiber composite material and a preparation method thereof, which has good flame retardant efficiency.

[0009] The invention provides a method for preparing a flame retardant plant fiber composite material, which has the following characteristics and comprises the following steps: S1, dispersing a phosphorus-containing flame retardant in deionized water, continuously stirring and dispersing the mixture evenly, adding a phenolic compound, adjusting the pH value according to the type of the phenolic compound, fully stirring and filtering, washing with deionized water, placing the mixture in an oven for drying, and fully grinding to obtain a powder A; S2, dispersing the powder A in deionized water, adjusting the pH value, adding the phenolic compound for stirring, adding NiCl2·6H2O, centrifuging, washing, drying, grinding and sieving to obtain a powder B; S3, placing an epoxy resin and a curing agent in a container, and stirring to obtain a pure epoxy resin; S4, mixing a two-dimensional sheet-like nanosheet, a low-temperature molten glass powder and the powder B, and then mixing and stirring the mixture with an epoxy resin matrix, adding a curing agent and stirring to obtain a powder with added flame retardant. Flame retardant epoxy resin; S5, select the required type of plant fiber, cut, wash and dry, and evenly apply pure epoxy resin on the surface of the plant fiber to obtain plant fiber prepreg A; S6, select the required type of plant fiber, cut, wash and dry, and evenly apply epoxy resin added with flame retardant system on the surface of the plant fiber to obtain plant fiber prepreg B; S7, take several layers of plant fiber prepreg A as required, place them in a mold and lay them flat layer by layer, pre-cure them for 0.2-0.8h, and obtain plant fiber pre-cured layer A, lay several layers of plant fiber prepreg B on the plant fiber pre-cured layer A, pre-cure them for 0.2-0.8h, and obtain plant fiber pre-cured layer B, then cure them at 100-140℃ for 1-3h, cool them to room temperature, and obtain a 3-9mm plant fiber reinforced resin-based composite material with a flame retardant distribution structure.

[0010] In the preparation method of the flame-retardant plant fiber composite material provided by the present invention, it can also have the following characteristics: wherein the plant fiber is one or more of flax fiber, ramie fiber, kenaf fiber, sisal fiber, cotton fiber, jute fiber, bamboo fiber and seaweed fiber, the phosphorus-containing flame retardant in step S1 is one or more of high-polymerization ammonium polyphosphate, ammonium pyrophosphate, ammonium tripolyphosphate and ammonium tetrapolyphosphate, and the phenolic group-containing compound in step S1 is one or more of polydopamine, tannic acid, tea polyphenols and proanthocyanidins.

[0011] The method for preparing the flame-retardant plant fiber composite material provided by the present invention may also have the following characteristics: wherein, in step S1, 1-7 wt % of sodium hydroxide or 1-5 wt % of hydrochloric acid is used to adjust the pH to the desired target value.

[0012] The method for preparing the flame-retardant plant fiber composite material provided by the present invention may also have the following characteristics: wherein, after dispersing the phosphorus-containing flame retardant in deionized water in step S1, the stirring time is 0.5-10 hours and the temperature is 20-80°C; the drying is vacuum drying at a temperature of 40-90°C; the number of deionized water washings is 3-6 times, so that the residual sodium hydroxide or hydrochloric acid is fully washed away.

[0013] The method for preparing the flame-retardant plant fiber composite material provided by the present invention may also have the following characteristics: wherein the nanosheets of the two-dimensional sheet structure in step S3 are one or more of graphene, graphene oxide, boron nitride and molybdenum disulfide.

[0014] The method for preparing the flame-retardant plant fiber composite material provided by the present invention may also have the following characteristics: wherein, in step S3, the mass ratio of the epoxy resin to the curing agent is 50:(10-16).

[0015] In the preparation method of the flame retardant plant fiber composite material provided by the present invention, it can also have the following characteristics: wherein in step S4, the ratio of the epoxy resin matrix, powder B, low-temperature melting glass powder, two-dimensional sheet-structured nanosheets and curing agent is 30:6: (2-4): (1-2): (2-4).

[0016] In the preparation method of the flame-retardant plant fiber composite material provided by the present invention, it can also have the following characteristics: wherein, in step S5, the flame retardant distribution structure of the plant fiber reinforced resin-based composite material is one or more of a bionic gradient structure and a sandwich structure, and when the distribution structure is a bionic gradient structure, several layers of plant fiber prepreg B are laid on top of the plant fiber prepreg A.

[0017] In the preparation method of the flame-retardant plant fiber composite material provided by the present invention, it can also have the following characteristics: wherein, the flame retardant distribution structure of the plant fiber reinforced resin-based composite material in step S5 is one or more of a bionic gradient structure and a sandwich structure, and when the distribution structure is a sandwich structure, several layers of plant fiber prepreg B are respectively laid above and below the plant fiber prepreg A.

[0018] The present invention also provides a flame retardant plant fiber composite material having the following characteristics, which is prepared according to any of the above-mentioned methods for preparing the flame retardant plant fiber composite material.

[0019] Functions and Effects of the Invention

[0020] According to a flame-retardant plant fiber composite material and a preparation method thereof involved in the present invention, the plant fiber reinforced composite material is mainly used in aviation and automotive interiors. According to the different positions of the structural parts, the fire mode can be divided into single-sided thermal radiation ignition and double-sided thermal radiation ignition. Based on the ignition mode, the present invention directionally distributes the flame retardant in the heat radiation area in the real fire scene through structural regulation, which can achieve efficient utilization of the flame retardant, avoid thermal decomposition of the composite material in the non-pyrolysis area, and prevent the flame retardant from remaining in the condensed phase.

[0021] The invention regulates the distribution of the flame retardant system, while maintaining the flame retardant performance, and also greatly reduces the amount of flame retardant used. After the structure is regulated and the distribution is optimized, the required amount of addition can be reduced by 30%-50%. The flame retardant system only needs about 7%, and the limiting oxygen index of the composite material can reach more than 30%, and the UL-94 test achieves the V-0 level, and the peak value of the heat release rate and the peak value of the toxic gas release rate are reduced by 50%, which has very excellent flame retardant performance, good flame retardant efficiency and good promotion value. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 The surface morphology of the ammonium polyphosphate of Example 1 of the present invention and Comparative Example 1 is compared;

[0023] Figure 2 The content of surface elements when the ammonium polyphosphate in Comparative Example 1 of the present invention and the ammonium polyphosphate in Example 1 are processed into powder A and powder B;

[0024] Figure 3 is the limiting oxygen index of the flame retardant composite material in Example 1, Example 2 and Comparative Example 1 of the present invention; and

[0025] Figure 4 The CO release rate of the flame retardant composite materials in Example 1, Example 2 and Comparative Example 1 of the present invention was tested using a cone calorimeter. DETAILED DESCRIPTION

[0026] In order to make the technical means, creative features, objectives and effects of the present invention easy to understand, the following examples and drawings specifically describe the method for preparing the flame-retardant plant fiber composite material of the present invention.

[0027] Example 1

[0028] The preparation method of the flame retardant plant fiber composite material in this embodiment is as follows:

[0029] S1, take 20g of ammonium polyphosphate and put it into 1000ml of deionized water, stir it magnetically at 30℃ for 0.5 hour, wait for it to be evenly dispersed, and obtain an ammonium polyphosphate dispersion; then add 0.6g of trishydroxymethylaminomethane and 0.5g of dopamine hydrochloride, and adjust the pH to 8.5 with NaOH solution, stir continuously at room temperature for 12 hours, centrifuge at 1000rpm for 5min, then wash it with deionized water 3 times, dry it in an oven at 80℃, and grind it into powder A with a ball mill.

[0030] S2, 5 g of powder A was dispersed in 150 mL of deionized water, and the pH was adjusted to 3 with hydrochloric acid under continuous stirring, and then 0.8 g of tannic acid was added and stirred continuously at 50 ° C for 2 hours, and 2.0 g of NiCl2·6H2O was slowly added to the solution. Finally, the centrifuge was centrifuged at 800 rpm for 3 min, and the powder was washed with deionized water for 3 times, and then dried, ground and sieved to obtain powder B.

[0031] S3, taking appropriate amounts of epoxy resin and diethylenetriamine in a ratio of 50:13, placing them in a container, and continuously stirring for 0.5 hours to obtain pure epoxy resin.

[0032] S4, taking appropriate amounts of epoxy resin, powder B, low melting point glass powder, graphene oxide nanosheets and diethylenetriamine in a ratio of 30:6:2:1:2, mixing and stirring evenly to obtain epoxy resin with added flame retardant system.

[0033] S5, soaking the unidirectional flax fiber in a 2wt% sodium hydroxide solution for 3 hours, taking it out and washing it with deionized water for 3 times, then immersing the linen fabric in deionized water at a temperature of 30°C for 30 minutes, taking it out and placing it in a vacuum oven at 60°C, taking it out after placing it for 5 hours, and coating the surface of the unidirectional flax fiber with pure epoxy resin evenly layer by layer to obtain a plant fiber prepreg A.

[0034] S6, coating the epoxy resin with flame retardant added uniformly on the surface of the unidirectional flax fiber layer by layer to obtain the plant fiber prepreg B.

[0035] S7, lay four layers of plant fiber prepreg A layer by layer, place them in a mold under hot pressing, the gasket thickness is 2 mm, pre-cured at 0.5 MPa and 80°C for 0.5 hour, take them out, lay four layers of plant fiber prepreg B on the upper and lower sides respectively, pre-cured at 0.5 MPa and 80°C for 0.5 hour, then cured at 120°C for 2 hours, cooled to room temperature, and obtained a composite material G-PFRP with a flame retardant sandwich structure with a thickness of 6 mm.

[0036] Example 2

[0037] Based on the preparation method of the flame retardant plant fiber composite material of Example 1, in this embodiment,

[0038] Replace step S4 with "S4, mix appropriate amounts of epoxy resin, powder B, low-melting point glass powder, graphene oxide nanosheets and diethylenetriamine in a ratio of 30:6:2:1:2, stir evenly, and obtain epoxy resin A with added flame retardant system; mix appropriate amounts of epoxy resin and powder B, low-melting point glass powder, graphene oxide nanosheets and diethylenetriamine in a ratio of 30:6:1:0.5:1, stir evenly, and obtain epoxy resin B with added flame retardant system."

[0039] Replace step S6 with “S6, uniformly coating epoxy resin A with added flame retardant on the surface of unidirectional flax fiber layer by layer to obtain plant fiber prepreg B, uniformly coating epoxy resin B with added flame retardant on the surface of unidirectional flax fiber layer by layer to obtain plant fiber prepreg C.”

[0040] Replace step S7 with "S7, lay four layers of plant fiber prepreg A layer by layer, place them in a mold under hot pressing, the gasket thickness is 2 mm, pre-cured at 0.5 MPa and 80°C for 0.5 hour, take them out, and then lay two layers of plant fiber prepreg C and two layers of plant fiber prepreg B on top of them, pre-cured at 0.5 MPa and 80°C for 0.5 hour, then cured at 120°C for 2 hours, and cooled to room temperature to obtain a composite material S-PFRP with a flame retardant gradient structure and a thickness of 6 mm."

[0041] Example 3

[0042] The preparation method of the flame retardant plant fiber composite material in this embodiment is as follows:

[0043] S1, take 40g of ammonium polyphosphate and put it into 2000ml of deionized water, stir it magnetically at 40℃ for 1 hour, wait for it to be evenly dispersed, and obtain an ammonium polyphosphate dispersion; then add 1.2g of trishydroxymethylaminomethane and 1.0g of dopamine hydrochloride, and adjust the pH to 8.5 with NaOH solution, stir continuously at room temperature for 12 hours, centrifuge at 1000rpm for 5min, then wash it with deionized water 3 times, dry it in an oven at 80℃, and grind it into powder A with a ball mill.

[0044] S2, 5 g of powder A was dispersed in 150 mL of deionized water, and the pH was adjusted to 3 with hydrochloric acid under continuous stirring, and then 0.8 g of tannic acid was added and stirred continuously at 50 ° C for 2 hours, and 2.0 g of NiCl2·6H2O was slowly added to the solution. Finally, the centrifuge was centrifuged at 800 rpm for 3 min, and the powder was washed with deionized water for 3 times, and then dried, ground and sieved to obtain powder B.

[0045] S3, taking appropriate amounts of epoxy resin and diethylenetriamine in a ratio of 50:13, placing them in a container, and continuously stirring for 1 hour to obtain pure epoxy resin.

[0046] S4, taking appropriate amounts of epoxy resin, powder B, low melting point glass powder, graphene and diethylenetriamine in a ratio of 30:6:2:1:2, mixing and stirring evenly to obtain epoxy resin with added flame retardant system.

[0047] S5, soaking the unidirectional flax fiber in a 2wt% sodium hydroxide solution for 3 hours, taking it out and washing it with deionized water for 3 times, then immersing the linen fabric in deionized water at a temperature of 30°C for 30 minutes, taking it out and placing it in a vacuum oven at 60°C, taking it out after placing it for 5 hours, and coating the surface of the unidirectional flax fiber with pure epoxy resin evenly layer by layer to obtain a plant fiber prepreg A.

[0048] S6, coating the epoxy resin with flame retardant added uniformly on the surface of the unidirectional flax fiber layer by layer to obtain the plant fiber prepreg B.

[0049] S7, lay two layers of plant fiber prepreg A layer by layer, place them in a mold under hot pressing, the gasket thickness is 1 mm, pre-cured at 0.5 MPa and 80°C for 0.5 hour, take them out, lay four layers of plant fiber prepreg B on the upper and lower sides respectively, pre-cured at 0.5 MPa and 80°C for 0.5 hour, then cured at 120°C for 2 hours, cooled to room temperature, and obtained a composite material with a flame-retardant sandwich structure with a thickness of 3 mm.

[0050] Example 4

[0051] Based on the preparation method of the flame retardant plant fiber composite material of Example 3, in this embodiment,

[0052] Replace step S4 with "S4, mix appropriate amounts of epoxy resin, powder B, low-melting glass powder, graphene and diethylenetriamine in a ratio of 30:6:2:1:2, stir evenly, and obtain epoxy resin A with added flame retardant system; mix appropriate amounts of epoxy resin and powder B, low-melting glass powder, graphene and diethylenetriamine in a ratio of 30:6:1:0.5:1, stir evenly, and obtain epoxy resin B with added flame retardant system."

[0053] Replace step S6 with “S6, uniformly coating epoxy resin A with added flame retardant on the surface of unidirectional flax fiber layer by layer to obtain plant fiber prepreg B, uniformly coating epoxy resin B with added flame retardant on the surface of unidirectional flax fiber layer by layer to obtain plant fiber prepreg C.”

[0054] Replace step S7 with “S7, lay two layers of plant fiber prepreg A layer by layer, place them in a mold under hot pressing, the gasket thickness is 1 mm, pre-cured at 0.5 MPa and 80°C for 0.5 hour, take them out, lay a layer of plant fiber prepreg C and a layer of plant fiber prepreg B on top of them, pre-cured at 0.5 MPa and 80°C for 0.5 hour, then cured at 120°C for 2 hours, and cooled to room temperature to obtain a composite material with a flame retardant gradient structure with a thickness of 3 mm.”

[0055] Example 5

[0056] The preparation method of the flame retardant plant fiber composite material in this embodiment is as follows:

[0057] S1, take 80g of ammonium polyphosphate and place it in 4000ml of deionized water, stir it magnetically at 30℃ for 1 hour, wait for it to be evenly dispersed, and obtain an ammonium polyphosphate dispersion; then add 1.6g of trishydroxymethylaminomethane and 1.5g of dopamine hydrochloride, and adjust the pH to 8.5 with NaOH solution, stir continuously at room temperature for 21 hours, centrifuge at 1200rpm for 3min, then wash it with deionized water 5 times, dry it in an oven at 80℃, and grind it into powder A with a ball mill.

[0058] S2, 10 g of powder A was dispersed in 300 mL of deionized water, and the pH was adjusted to 3 with hydrochloric acid under continuous stirring, and then 1.6 g of tannic acid was added and stirred continuously at 60 ° C for 1 hour, and 3.0 g of NiCl2·6H2O was slowly added to the solution. Finally, the centrifuge was centrifuged at 1200 rpm for 5 min, and the powder was washed with deionized water for 3 times, dried, ground and sieved to obtain powder B.

[0059] S3, taking appropriate amounts of epoxy resin and diethylenetriamine in a ratio of 50:13, placing them in a container, and continuously stirring for 1 hour to obtain pure epoxy resin.

[0060] S4, taking appropriate amounts of epoxy resin, powder B, low melting point glass powder, hexagonal boron nitride and diethylenetriamine in a ratio of 30:6:2:1:2, mixing and stirring evenly to obtain epoxy resin with added flame retardant system.

[0061] S5, soaking the unidirectional flax fiber in a 3wt% sodium hydroxide solution for 1 hour, taking it out and washing it twice with deionized water, then immersing the linen fabric in deionized water at a temperature of 50°C for 30 minutes, taking it out and placing it in a vacuum oven at 70°C, taking it out after 5 hours, and coating the surface of the unidirectional flax fiber with pure epoxy resin evenly layer by layer to obtain a plant fiber prepreg A.

[0062] S6, coating the epoxy resin with flame retardant added uniformly on the surface of the unidirectional flax fiber layer by layer to obtain the plant fiber prepreg B.

[0063] S7, lay six layers of plant fiber prepreg A layer by layer, place them in a mold under hot pressing, the gasket thickness is 3 mm, pre-cured at 0.5 MPa and 80°C for 0.5 hour, take it out, lay six layers of plant fiber prepreg B on the upper and lower sides respectively, pre-cured at 0.5 MPa and 80°C for 0.5 hour, then cured at 120°C for 2 hours, cooled to room temperature, and obtained a composite material with a flame-retardant sandwich structure with a thickness of 9 mm.

[0064] Example 6

[0065] Based on the preparation method of the flame retardant plant fiber composite material of Example 5, in this embodiment,

[0066] Replace step S4 with "S4, mix appropriate amounts of epoxy resin, powder B, low melting point glass powder, hexagonal boron nitride and diethylenetriamine in a ratio of 30:6:2:1:2, stir evenly, and obtain epoxy resin A with added flame retardant system; mix appropriate amounts of epoxy resin and powder B, low melting point glass powder, hexagonal boron nitride and diethylenetriamine in a ratio of 30:6:1:0.5:1, stir evenly, and obtain epoxy resin B with added flame retardant system."

[0067] Replace step S6 with “S6, uniformly coating epoxy resin A with added flame retardant on the surface of unidirectional flax fiber layer by layer to obtain plant fiber prepreg B, uniformly coating epoxy resin B with added flame retardant on the surface of unidirectional flax fiber layer by layer to obtain plant fiber prepreg C.”

[0068] Replace step S7 with "S7, lay six layers of plant fiber prepreg A layer by layer, place them in a mold under hot pressing, the gasket thickness is 3 mm, pre-cured at 0.5 MPa and 80°C for 0.5 hour, take them out, and then lay six layers of plant fiber prepreg B on top of them, pre-cured at 0.5 MPa and 80°C for 0.5 hour, then cured at 120°C for 2 hours, and cooled to room temperature to obtain a composite material with a flame retardant gradient structure with a thickness of 9 mm."

[0069] Example 7

[0070] Based on the preparation method of the flame-retardant plant fiber composite material in Example 1, in this embodiment, the step S4 of "taking appropriate amounts of epoxy resin, powder B, low-melting point glass powder, graphene oxide nanosheets and diethylenetriamine and mixing them in a ratio of 30:6:2:1:2" is replaced by "taking appropriate amounts of epoxy resin and powder B, low-melting point glass powder, graphene oxide nanosheets and diethylenetriamine and mixing them in a ratio of 30:6:4:2:4"

[0071] Example 8

[0072] Based on the preparation method of the flame retardant plant fiber composite material of Example 7, in this embodiment,

[0073] Replace step S4 with "S4, mix appropriate amounts of epoxy resin, powder B, low-melting glass powder, graphene oxide nanosheets and diethylenetriamine in a ratio of 30:6:4:2:4, stir evenly to obtain epoxy resin A with added flame retardant system; mix appropriate amounts of epoxy resin and powder B, low-melting glass powder, graphene oxide nanosheets and diethylenetriamine in a ratio of 30:6:2:1:2, stir evenly to obtain epoxy resin B with added flame retardant system."

[0074] Replace step S6 with “S6, uniformly coating epoxy resin A with added flame retardant on the surface of unidirectional flax fiber layer by layer to obtain plant fiber prepreg B, uniformly coating epoxy resin B with added flame retardant on the surface of unidirectional flax fiber layer by layer to obtain plant fiber prepreg C.”

[0075] Replace step S7 with "S7, lay four layers of plant fiber prepreg A layer by layer, place them in a mold under hot pressing, the gasket thickness is 2 mm, pre-cured at 0.5 MPa and 80°C for 0.5 hour, take them out, lay two layers of plant fiber prepreg C and two layers of plant fiber prepreg B on top of them, pre-cured at 0.5 MPa and 80°C for 0.5 hour, then cured at 120°C for 2 hours, and cooled to room temperature to obtain a composite material with a flame retardant gradient structure with a thickness of 6 mm."

[0076] Comparative Example 1

[0077] S1, take appropriate amount of epoxy resin and diethylenetriamine, place them in a container in a ratio of 50:13, and continue stirring for 0.5 hour to obtain pure epoxy resin.

[0078] S2, soaking the unidirectional flax fiber in a sodium hydroxide solution with a mass fraction of 2% for 3 hours, taking it out and washing it with deionized water for 3 times, then immersing the linen fabric in a deionized water solvent at a temperature of 30°C for 30 minutes, taking it out and placing it in a vacuum oven at 60°C, and evenly coating the pure epoxy resin on the surface of the unidirectional flax fiber layer by layer to obtain a plant fiber prepreg A.

[0079] S3, four layers of plant fiber prepreg A are laid flat layer by layer and placed in a mold under hot pressing, with a gasket thickness of 2 mm. They are pre-cured at 0.5 MPa and 80°C for 0.5 hour, then cured at 120°C for 2 hours, and cooled to room temperature to obtain a composite material PFRP.

[0080] Figure 1 The figure is a comparison of the surface morphologies of the ammonium polyphosphate of Example 1 of the present invention and Comparative Example 1. Figure 2 It is the change in the content of surface elements when the ammonium polyphosphate in Comparative Example 1 of the present invention and the ammonium polyphosphate in Example 1 are processed into powder A and powder B. Figure 3 It is the limiting oxygen index of the flame retardant composite material in Example 1, Example 2 and Comparative Example 1 of the present invention. Figure 4 The CO release rate of the flame retardant composite materials in Example 1, Example 2 and Comparative Example 1 of the present invention was tested using a cone calorimeter.

[0081] like Figure 1-4 As shown, the bending strength of comparative example 1 is 154 MPa, and the peak heat release rate is 416.7 kW / m 2 .

[0082] like Figure 1 As shown, the microscopic morphology of the ammonium polyphosphate in Example 1 and Comparative Example 1 was analyzed using a scanning electron microscope and an X-ray spectrometer. The ammonium polyphosphate in Comparative Example 1 showed a block structure and a smooth surface, while the surface of the ammonium polyphosphate in Example 1 became rough.

[0083] like Figure 2 As shown, the element content on the surface of powder B changed significantly, indicating that the modification was successful.

[0084] like Figure 3 As shown, the limiting oxygen index of Example 1 was increased from 20.5% to 30.7%. After distribution optimization, the amount of flame retardant added was reduced by 50% compared with the random distribution blending addition method. The limiting oxygen index of Example 2 was increased from 20.5% to 32.8%. After distribution optimization, the amount of flame retardant added was reduced by 33.3% compared with the random distribution blending addition method.

[0085] like Figure 4 As shown, the CO release peak value of Comparative Example 1 is 0.26 g / s, the CO release peak value of Example 1 is 0.12 g / s, and the CO release peak value of Example 2 is 0.16 g / s, which is of great significance for reducing casualties in fires.

[0086] It can be seen that in Examples 1-2, flame-retardant composite materials with sandwich structures and gradient structures were constructed by regulating the distribution of the flame retardant system in the composite material, which proves that distribution regulation can effectively improve the flame retardant properties of the composite material while reducing the amount of flame retardant added, without deteriorating the original mechanical properties, thereby achieving high-efficiency flame retardancy.

[0087] The limiting oxygen index of Example 3 reaches 29.8%, and the bending strength is 165 MPa.

[0088] The limiting oxygen index of Example 4 reaches 31.7%, and the bending strength is 170 MPa.

[0089] It can be seen that in Examples 3-4, by regulating the distribution of the flame retardant system in the composite material, the amount of flame retardant added was greatly reduced. While maintaining the flame retardant properties, the addition of graphene (GO) improved the mechanical properties of the composite material.

[0090] The limiting oxygen index of Example 5 reaches 30.3%. After distribution optimization, the amount of flame retardant added is reduced by 50% compared with the randomly distributed blending addition method. The peak heat release rate is 163.4 kW / m 2 .

[0091] The limiting oxygen index of Example 6 reaches 31.6%. After distribution optimization, the amount of flame retardant added is reduced by 33.3% compared with the randomly distributed blending addition method. The peak heat release rate is 220.9 kW / m 2 .

[0092] It can be seen that in Examples 5-6, by regulating the distribution of the flame retardant system in the composite material and reducing the amount of flame retardant added, the flame retardant properties of the composite material are effectively improved while maintaining the original mechanical properties of the composite material, thereby achieving a balance between flame retardancy and mechanical properties.

[0093] The limiting oxygen index of Example 7 is 33.2%, and the bending strength is reduced by 11.4% compared with Comparative Example 1.

[0094] The limiting oxygen index of Example 8 is 35.7%, and the bending strength is reduced by 10.7% compared with Comparative Example 1.

[0095] It can be seen that in Examples 7-8, too much flame retardant addition will still affect the mechanical properties of the composite material, and too large an addition amount will lead to agglomeration, affecting the mechanical properties of the composite material.

[0096] Functions and Effects of the Embodiments

[0097] According to a flame-retardant plant fiber composite material and a preparation method thereof involved in the present invention, the plant fiber reinforced composite material is mainly used in aviation and automotive interiors. According to the different positions of the structural parts, the fire mode can be divided into single-sided thermal radiation ignition and double-sided thermal radiation ignition. Based on the ignition mode, the present invention directionally distributes the flame retardant in the heat radiation area in the real fire scene through structural regulation, which can achieve efficient utilization of the flame retardant, avoid thermal decomposition of the composite material in the non-pyrolysis area, and prevent the flame retardant from remaining in the condensed phase.

[0098] The invention regulates the distribution of the flame retardant system, while maintaining the flame retardant performance, and also greatly reduces the amount of flame retardant used. After the structure is regulated and the distribution is optimized, the required amount of addition can be reduced by 30%-50%. The flame retardant system only needs about 7%, and the limiting oxygen index of the composite material can reach more than 30%, and the UL-94 test achieves the V-0 level, and the peak value of the heat release rate and the peak value of the toxic gas release rate are reduced by 50%, which has very excellent flame retardant performance, good flame retardant efficiency and good promotion value.

[0099] The flame retardant system and distribution optimization method of the present invention have excellent flame retardant effect, low cost and simple preparation process. In addition, the experimental process of the present invention does not involve toxic solvents, has high safety and is environmentally friendly, and therefore has broad application prospects.

[0100] The present invention can reduce the amount of flame retardant added and save costs by regulating the distribution of the flame retardant system in the composite material, and can also prevent agglomeration caused by excessive addition of the flame retardant, thereby avoiding affecting the mechanical properties of the composite material.

[0101] Those skilled in the art should understand that the present invention is not limited to the above embodiments, and the above embodiments and descriptions are only for explaining the principles of the present invention. Without departing from the spirit and scope of the present invention, the present invention may have various changes and improvements, and these changes and improvements fall within the scope of the present invention to be protected. The scope of protection of the present invention is defined by the attached claims and their equivalents.

Claims

1. A method for preparing a flame retardant plant fiber composite material, characterized in that: The specific steps include: S1, dispersing the phosphorus-containing flame retardant in deionized water, continuously stirring and dispersing evenly, adding a phenolic compound, adjusting the pH value according to the type of the phenolic compound, fully stirring and filtering, washing with deionized water, drying in an oven, and fully grinding to obtain powder A; S2, dispersing the powder A in deionized water, adjusting the pH value, adding a phenolic compound and stirring, adding NiCl2·6H2O, centrifuging, washing, drying, grinding and sieving to obtain powder B; S3, placing epoxy resin and curing agent in a container, and stirring to obtain pure epoxy resin; S4, taking a two-dimensional sheet-like nanosheet, a low-temperature melting glass powder and the powder B, mixing them with an epoxy resin matrix, adding a curing agent and stirring, and obtaining an epoxy resin with a flame retardant system added; S5, selecting a desired type of plant fiber, cutting, washing and drying, and evenly coating the pure epoxy resin on the surface of the plant fiber to obtain a plant fiber prepreg A; S6, selecting the desired type of plant fiber, cutting, washing and drying, and evenly coating the epoxy resin with the flame retardant system added on the surface of the plant fiber to obtain a plant fiber prepreg B; S7, take several layers of the plant fiber prepreg A as required, place them in a mold and lay them flat layer by layer, pre-cure them for 0.2-0.8h to obtain the plant fiber pre-cured layer A, lay several layers of the plant fiber prepreg B on the plant fiber pre-cured layer A, pre-cure them for 0.2-0.8h to obtain the plant fiber pre-cured layer B, then cure them at 100-140°C for 1-3h, cool them to room temperature, and obtain a 3-9mm plant fiber reinforced resin-based composite material with a flame retardant distribution structure.

2. The method for preparing a flame retardant plant fiber composite material according to claim 1, characterized in that: in, The plant fiber is one or more of flax fiber, ramie fiber, kenaf fiber, sisal fiber, cotton fiber, jute fiber, bamboo fiber and seaweed fiber; the phosphorus-containing flame retardant in step S1 is one or more of high-polymerization ammonium polyphosphate, ammonium pyrophosphate, ammonium tripolyphosphate and ammonium tetrapolyphosphate; the phenolic group-containing compound in step S1 is one or more of polydopamine, tannic acid, tea polyphenols and proanthocyanidins.

3. The method for preparing a flame retardant plant fiber composite material according to claim 1, characterized in that: in, In the step S1, 1-7 wt % sodium hydroxide or 1-5 wt % hydrochloric acid is used to adjust the pH to the desired target value.

4. The method for preparing a flame retardant plant fiber composite material according to claim 1, characterized in that: in, In the step S1, after dispersing the phosphorus-containing flame retardant in deionized water, the stirring time is 0.5-10 hours at a temperature of 20-80° C.; the drying is vacuum drying at a temperature of 40-90° C.; the deionized water washing times are 3-6 times, so that the residual sodium hydroxide or hydrochloric acid is fully washed away.

5. The method for preparing a flame retardant plant fiber composite material according to claim 1, characterized in that: in, The nanosheets of the two-dimensional sheet structure in step S3 are one or more of graphene, graphene oxide, boron nitride and molybdenum disulfide.

6. The method for preparing a flame retardant plant fiber composite material according to claim 1, characterized in that: in, The mass ratio of the epoxy resin to the curing agent in step S3 is 50:(10-16).

7. The method for preparing a flame retardant plant fiber composite material according to claim 1, characterized in that: in, In the step S4, the ratio of the epoxy resin matrix, the powder B, the low-temperature melting glass powder, the nanosheets with two-dimensional sheet structure and the curing agent is 30:6:(2-4):(1-2):(2-4).

8. The method for preparing a flame retardant plant fiber composite material according to claim 1, characterized in that: in, In step S5, the flame retardant distribution structure of the plant fiber reinforced resin-based composite material is one or more of a bionic gradient structure and a sandwich structure. When the distribution structure is a bionic gradient structure, the several layers of plant fiber prepreg B are laid on top of the plant fiber prepreg A.

9. The method for preparing a flame retardant plant fiber composite material according to claim 1, characterized in that: in, In step S5, the flame retardant distribution structure of the plant fiber reinforced resin-based composite material is one or more of a bionic gradient structure and a sandwich structure. When the distribution structure is a sandwich structure, the several layers of plant fiber prepreg B are laid above and below the plant fiber prepreg A, respectively.

10. The flame retardant plant fiber composite material according to claim 1, characterized in that: The flame retardant plant fiber composite material is prepared by the preparation method of any one of claims 1 to 9.

Images