Reactive eutecticevaporate solvent flame-retardant modified plant fiber composite material and preparation method thereof

Abstract

The invention discloses a reactive eutecticevaporate solvent flame-retardant modified plant fiber composite material and a preparation method thereof, and belongs to the technical field of natural high polymer materials. The preparation method comprises the following steps: by taking plant fiber as a raw material, modifying the plant fiber with a reaction type eutectic solvent to obtain flame-retardant plant fiber, mixing the flame-retardant plant fiber with water-borne epoxy resin, a curing agent and water, and performing hot press molding and curing to obtain the reaction type eutectic solvent flame-retardant modified plant fiber composite material with the limit oxygen index not lower than 35%. According to the invention, plant fiber surface active hydroxyl is subjected to DES reaction with flame-retardant elements such as phosphorus, nitrogen and sulfur, such that plant fiber surface in-situ grafting flame-retardant modification is realized; flame-retardant groups, namely phosphate groups and amido groups, on the surfaces of DES modified plant fibers are subjected to covalent bond combination with epoxy groups of matrix epoxy resin, so that interface enhancement of a fiber reinforced phase and a resin matrix phase of the composite material is realized; the prepared plant fiber composite material not only has excellent flame retardant property, but also has better mechanical property.

Description

Technical Field

[0001] The present invention belongs to the technical field of natural polymer materials, and more specifically, relates to a reactive deep eutectic solvent flame-retardant modified plant fiber composite material and a preparation method thereof. Background Art

[0002] Compared with traditional composite materials, plant fiber composite materials have the advantages of biodegradability, light weight, good rigidity, etc., and have been applied in the fields of construction, packaging, plates, 3D printing, automobiles, etc., which is the development trend of future composite materials. However, compared with glass fibers, plant fibers and their reinforced composite materials are flammable, which greatly limits the application fields and scope of corresponding products.

[0003] Flame retardancy has always been a difficult problem restricting the development of plant fiber composite materials. The most commonly used flame retardant strategy at present is to directly add flame retardants to plant fiber composite materials to improve the flame retardant performance of the materials. Existing research shows that although adding flame retardants can improve the flame retardant performance of plant fiber composite materials, the amount of flame retardants that need to be added is usually large, which not only reduces the filling amount of plant fibers in the composite materials, but also due to the poor interfacial properties between plant fibers, matrix resins and flame retardants, the mechanical properties of the composite materials are reduced. How to achieve the synergy of flame retardancy and reinforcement of plant fiber composite materials is a scientific problem that needs to be solved urgently in this field.

[0004] Deep eutectic solvents (DESs) are a class of self-associating liquid mixtures, usually composed of a hydrogen bond donor (HBD) and a hydrogen bond acceptor (HBA). A large number of intramolecular hydrogen bonds exist in DESs, which can promote the breaking of strong hydrogen bonds between biomasses. Therefore, DESs have high biomass solubility and good modification effects, and have great development potential in biomass refining, pretreatment and modification. At the same time, DESs have the characteristics of low cost, environmental friendliness, and recyclability, and are currently a green modification method for plant fibers that has received much attention. DESs can be divided into reactive systems and non-reactive systems according to whether they react with the substrate. In recent years, researchers have explored the use of DESs that can react with cellulose hydroxyl groups to treat plant fibers, derivatize cellulose hydroxyl groups, and then endow the materials with more functional characteristics. Introducing flame retardant elements such as sulfur and nitrogen into the cellulose molecular structure by using reactive DESs can endow cellulose materials with flame retardant properties without affecting the mechanical properties of the materials. The greatest advantage of DESs lies in their designability. By flexibly selecting and freely regulating between hydrogen bond donors and hydrogen bond acceptors, multi-component DESs containing flame retardant elements can be prepared, and more flame retardant elements such as phosphorus, nitrogen, sulfur, and silicon can be introduced into the cellulose molecular structure, giving play to the synergistic flame retardant effect between different flame retardant elements and realizing the green and efficient flame retardant modification of plant fibers. Summary of the Invention

[0005] In view of the above problems existing in the prior art, the technical problems to be solved by the present invention are as follows: to provide a preparation method of a reactive deep eutectic solvent flame-retardant modified plant fiber composite material, in which the flame-retardant groups such as phosphate groups and amino groups on the surface of the plant fiber modified by DES react with the epoxy groups of the matrix epoxy resin to form covalent bonds, so as to realize the interface enhancement between the fiber-reinforced phase and the resin matrix phase of the composite material. Another technical problem to be solved by the present invention is to provide a reactive deep eutectic solvent flame-retardant modified plant fiber composite material prepared by the above preparation method, and the prepared plant fiber composite material has both excellent flame-retardant performance and good mechanical properties.

[0006] To solve the above technical problems, the technical solutions adopted by the present invention are as follows:

[0007] A preparation method of a reactive deep eutectic solvent flame-retardant modified plant fiber composite material, using plant fiber as raw material, after being modified by a reactive deep eutectic solvent, the flame-retardant plant fiber is obtained, and the flame-retardant plant fiber is mixed with waterborne epoxy resin, curing agent and water, and then hot-pressed and cured to obtain a reactive deep eutectic solvent flame-retardant modified plant fiber composite material with a limiting oxygen index of not less than 35%.

[0008] Preferably, the reactive deep eutectic solvent is composed of a proton donor and a proton acceptor that can react with cellulose hydroxyl groups.

[0009] Preferably, the proton donor is selected from any one or more of phosphoric acid, phytic acid, aminosulfonic acid, urea, and amino acids.

[0010] Preferably, the proton acceptor is selected from any one or more of betaine, betaine hydrochloride, and choline chloride.

[0011] Preferably, the plant fiber is selected from any one or more of wood fiber, cotton fiber, hemp fiber, and bamboo fiber.

[0012] Preferably, the curing agent is selected from any one or more of polyetheramine, polyamide, aliphatic amine, alicyclic amine, and aromatic amine.

[0013] Preferably, the temperature of the modification treatment is 80~150 °C, and the treatment time is 0.5~5 h.

[0014] Preferably, the temperature of the hot pressing is 160 °C, and the hot pressing time is 50~55 min.

[0015] Preferably, the mass ratio of the flame-retardant plant fiber, waterborne epoxy resin, curing agent and water is 96:40:4:100.

[0016] The reactive deep eutectic solvent flame-retardant modified plant fiber composite material prepared by the preparation method of the reactive deep eutectic solvent flame-retardant modified plant fiber composite material.

[0017] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0018] 1) The present invention uses the hydroxyl groups on the surface of plant fibers to in-situ graft reactive DES containing phosphorus and nitrogen, realizing the uniform dispersion of flame-retardant elements on the fiber surface and solving the problem of the uniform dispersion of flame retardants in the composite material;

[0019] 2) The present invention uses the covalent bond combination of the surface active groups (flame-retardant groups phosphate group and amine group) of DES-modified plant fibers and the epoxy groups of waterborne epoxy resin to realize interfacial chemical coupling, solve the interfacial compatibility problem of flame retardants, plant fibers and matrix resins, and the prepared plant fiber composite material has both excellent flame retardant properties and good mechanical properties, realizing the flame retardant and high strength synergy of plant fiber composite materials. Description of the Drawings

[0020] Figure 1 It is the X-ray photoelectron spectroscopy diagram of wood fibers before and after reactive DES modification in Example 1;

[0021] Figure 2 It is the scanning electron microscopy diagram of wood fibers after reactive DES modification in Example 2;

[0022] Figure 3 It is the P element energy spectrum diagram of wood fibers after reactive DES modification in Example 3. Detailed Embodiments

[0023] To make the objectives, technical solutions and advantages of the present invention clearer, the present invention will be further described below in conjunction with specific embodiments. In the following embodiments, unless otherwise specified, the technical means used are all conventional means well known to those skilled in the art. For those conditions not specified in the embodiments, they are carried out according to conventional conditions or the conditions recommended by the manufacturer. For the reagents or instruments whose manufacturers are not indicated, they are all conventional products that can be obtained through commercial purchase.

[0024] The wood fiber selected in the following examples is Chinese fir fiber, which is produced by the Pulp and Paper R & D Center of the Institute of Chemical Industry of Forest Products, Chinese Academy of Forestry, using a high-yield pulping process, with an average length of 2.3 mm and a width of 45 μm. The hemp fiber is ramie fiber, provided by Chenzhou Xiangnan Hemp Industry Co., Ltd., with an average single fiber length of 11.7 mm and an average fineness of 6.10 dtex. The cotton fiber is long-staple cotton, provided by Qiancengxue Cotton Fluff Factory, Mengcun Hui Autonomous County, with a fiber length of 34.37 mm and a fineness of 7080 m / g. The bamboo fiber is bamboo primary fiber, provided by Sichuan Changsheng New Materials Technology Co., Ltd., with an average fiber length of 14.6 mm and an average fineness of 5.50 dtex.

[0025] The waterborne epoxy resin WER5625 is provided by Jiangsu Ruiyang Antai New Materials Technology Co., Ltd., with a solid content of 50% and an epoxy value of 0.20 mol / 100 g. The polyamide curing agent is 5115x70 polyamide curing agent, with an amine value of 145 - 175 mgKOH / g, provided by Suzhou Hengsite Industry Co., Ltd.

[0026] The aromatic amine curing agent is diaminodiphenylmethane or diethyltoluenediamine; among them, the amine value of diaminodiphenylmethane is 566 mg / g, and the amine value of diethyltoluenediamine is 629 mg / g.

[0027] Example 1

[0028] A preparation method of a reactive deep eutectic solvent flame-retardant modified plant fiber composite material includes the following steps:

[0029] 1) Mix phosphoric acid, urea, and choline chloride in a molar ratio of 1:2:1, heat and stir in an oil bath at 90 °C for 60 min until the solution is clear to obtain a reactive DES;

[0030] 2) Immerse the wood fiber in the reactive DES prepared in step 1) for 10 min, then squeeze the wood fiber dry and bake it in an oven at 100 °C for 4 h. Then wash the baked fiber until it is neutral, and continue to dry it in an 80 °C oven for 4 h to obtain the reactive DES-modified wood fiber;

[0031] 3) Put 96 g of the reactive DES-modified wood fiber prepared in step 2), 40 g of the waterborne epoxy resin WER5625, 4 g of diaminodiphenylmethane, and 100 g of water into a kneader and knead for 30 min to mix thoroughly. Take out the mixture and dry it in a 60 °C oven for 2 h. After drying the moisture, obtain a prepreg;

[0032] 4) Uniformly lay the prepreg prepared in step 3) into a mold, place it in a hot press at 160 °C, pre-press for 5 min first, then hot-press for 50 min to obtain a sample. After demolding, the sample is placed in an oven at 150 °C and cured for 5 h to obtain a reactive DES flame-retardant modified wood fiber / waterborne epoxy resin composite material.

[0033] Example 2

[0034] A preparation method of a reactive deep eutectic solvent flame-retardant modified plant fiber composite material, comprising the following steps:

[0035] 1) Mix phytic acid, urea and betaine in a molar ratio of 1:2:1, heat and stir in an oil bath at 90 °C for 60 min until the solution is clear to obtain a reactive DES;

[0036] 2) Add wood fibers to the reactive DES prepared in step 1) and soak for 10 min. Then squeeze the wood fibers dry and bake in an oven at 100 °C for 4 h. Then wash the baked fibers to neutrality and continue to dry in an oven at 80 °C for 4 h to obtain reactive DES-modified wood fibers;

[0037] 3) Put 96 g of the reactive DES-modified wood fibers prepared in step 2), 40 g of waterborne epoxy resin WER5625, 4 g of diethyltoluenediamine and 100 g of water into a kneader and knead for 30 min to mix thoroughly. Take out the mixture and place it in an oven at 60 °C to dry for 2 h. After drying the moisture, obtain a prepreg;

[0038] 4) Uniformly lay the prepreg prepared in step 3) into a mold, place it in a hot press at 160 °C, pre-press for 5 min first, then hot-press for 50 min to obtain a sample. After demolding, the sample is placed in an oven at 150 °C and cured for 5 h to obtain a reactive DES flame-retardant modified wood fiber / waterborne epoxy resin composite material.

[0039] Example 3

[0040] A preparation method of a reactive deep eutectic solvent flame-retardant modified plant fiber composite material, comprising the following steps:

[0041] 1) Mix phosphoric acid, urea and glycine in a molar ratio of 1:2:1, heat and stir in an oil bath at 90 °C for 60 min until the solution is clear to obtain a reactive DES;

[0042] 2) Add wood fibers to the reactive DES prepared in step 1) and soak for 10 min. Then squeeze the wood fibers dry and bake in an oven at 120 °C for 4 h. Then wash the baked fibers to neutrality and continue to dry in an oven at 80 °C for 4 h to obtain reactive DES-modified wood fibers;

[0043] 3) Put 96 g of the reactive DES-modified wood fibers prepared in step 2), 40 g of waterborne epoxy resin WER5625, 4 g of diethyltoluenediamine, and 100 g of water into a kneader and knead for 30 min to mix thoroughly. Take out the mixture and dry it in an oven at 60 °C for 2 h. After drying the moisture, a prepreg is obtained;

[0044] 4) Uniformly lay the prepreg prepared in step 3) into a mold, put it into a hot press at 160 °C, pre-press for 5 min first, and then hot-press for 50 min to obtain a sample. After demolding, the sample is put into an oven at 150 °C and cured for 5 h to obtain a reactive DES flame-retardant modified wood fiber / waterborne epoxy resin composite.

[0045] Example 4

[0046] A preparation method of a reactive deep eutectic solvent flame-retardant modified plant fiber composite, comprising the following steps:

[0047] 1) Mix phosphoric acid, urea, and glycine in a molar ratio of 1:2:1, heat and stir in an oil bath at 90 °C for 60 min until the solution is clear to obtain a reactive DES;

[0048] 2) Add hemp fibers to the reactive DES prepared in step 1) and soak for 10 min. Then squeeze the hemp fibers dry and dry them in an oven at 120 °C for 4 h. Then wash the dried fibers until neutral and continue to dry them in an oven at 80 °C for 4 h to obtain reactive DES-modified hemp fibers;

[0049] 3) Put 96 g of the reactive DES-modified hemp fibers prepared in step 2), 40 g of waterborne epoxy resin WER5625, 4 g of diethyltoluenediamine, and 100 g of water into a kneader and knead for 30 min to mix thoroughly. Take out the mixture and dry it in an oven at 60 °C for 2 h. After drying the moisture, a prepreg is obtained;

[0050] 4) Uniformly lay the prepreg prepared in step 3) into a mold, put it into a hot press at 160 °C, pre-press for 5 min first, and then hot-press for 50 min to obtain a sample. After demolding, the sample is put into an oven at 150 °C and cured for 5 h to obtain a reactive DES flame-retardant modified hemp fiber / waterborne epoxy resin composite.

[0051] Example 5

[0052] A preparation method of a reactive deep eutectic solvent flame-retardant modified plant fiber composite, comprising the following steps:

[0053] 1) Mix phosphoric acid, urea, and aminosulfonic acid in a molar ratio of 1:2:1, heat and stir in an oil bath at 90 °C for 60 min until the solution is clear to obtain a reactive DES;

[0054] 2) Immerse cotton fibers in the reactive DES prepared in step 1) for 10 min, then squeeze the cotton fibers dry and bake them in an oven at 120 °C for 4 h. After that, wash the baked fibers until neutral, and then continue to dry them in an 80 °C oven for 4 h to obtain reactive DES-modified cotton fibers;

[0055] 3) Put 96 g of the reactive DES-modified cotton fibers prepared in step 2), 40 g of waterborne epoxy resin WER5625, 4 g of polyamide curing agent, and 100 g of water into a kneader and knead for 30 min to mix thoroughly. Take out the mixture and dry it in a 60 °C oven for 2 h to obtain a prepreg after drying the moisture;

[0056] 4) Uniformly lay the prepreg prepared in step 3) into a mold, put it into a 160 °C hot press, pre-press for 5 min first, and then hot-press for 50 min to obtain a sample. After demolding, put the sample into a 150 °C oven and cure for 5 h to obtain a reactive DES flame-retardant modified cotton fiber / waterborne epoxy resin composite material.

[0057] Example 6

[0058] A preparation method of a reactive deep eutectic solvent flame-retardant modified plant fiber composite material, comprising the following steps:

[0059] 1) Mix phytic acid, urea, and betaine hydrochloride in a molar ratio of 1:2:1, heat and stir in an oil bath at 90 °C for 60 min until the solution is clear to obtain a reactive DES;

[0060] 2) Immerse bamboo fibers in the reactive DES prepared in step 1) for 10 min, then squeeze the bamboo fibers dry and bake them in an oven at 100 °C for 4 h. After that, wash the baked fibers until neutral, and then continue to dry them in an 80 °C oven for 4 h to obtain reactive DES-modified bamboo fibers;

[0061] 3) Put 96 g of the reactive DES-modified bamboo fibers prepared in step 2), 40 g of waterborne epoxy resin WER5625, 4 g of diaminodiphenylmethane, and 100 g of water into a kneader and knead for 30 min to mix thoroughly. Take out the mixture and dry it in a 60 °C oven for 2 h to obtain a prepreg after drying the moisture;

[0062] 4) Uniformly lay the prepreg prepared in step 3) into a mold, put it into a 160 °C hot press, pre-press for 5 min first, and then hot-press for 50 min to obtain a sample. After demolding, put the sample into a 150 °C oven and cure for 5 h to obtain a reactive DES flame-retardant modified bamboo fiber / waterborne epoxy resin composite material.

[0063] Example 7

[0064] A preparation method of a reactive deep eutectic solvent flame-retardant modified plant fiber composite material, comprising the following steps:

[0065] 1) Mix phosphoric acid, urea and choline chloride in a molar ratio of 2:2:1, heat and stir in an oil bath at 90 °C for 60 min until the solution is clear to obtain a reactive DES;

[0066] 2) Add wood fibers to the reactive DES prepared in step 1) and soak for 10 min. Then squeeze the wood fibers dry and bake in an oven at 100 °C for 4 h. Then wash the baked fibers until neutral and continue to dry in an oven at 80 °C for 4 h to obtain reactive DES-modified wood fibers;

[0067] 3) Put 96 g of the reactive DES-modified wood fibers prepared in step 2), 40 g of waterborne epoxy resin WER5625, 4 g of diaminodiphenylmethane and 100 g of water into a kneader and knead for 30 min for sufficient mixing. Take out the mixture and dry it in an oven at 60 °C for 2 h to obtain a prepreg after drying the moisture;

[0068] 4) Uniformly lay the prepreg prepared in step 3) into a mold, put it into a hot press at 160 °C, pre-press for 5 min first, and then hot-press for 50 min to obtain a sample. After demolding, the sample is put into an oven at 150 °C for curing for 5 h to obtain a reactive DES flame-retardant modified wood fiber / waterborne epoxy resin composite material.

[0069] Example 8

[0070] A preparation method of a reactive deep eutectic solvent flame-retardant modified plant fiber composite material, comprising the following steps:

[0071] 1) Mix phosphoric acid, urea and choline chloride in a molar ratio of 1:2:1, heat and stir in an oil bath at 90 °C for 60 min until the solution is clear to obtain a reactive DES;

[0072] 2) Add wood fibers to the reactive DES prepared in step 1) and soak for 10 min. Then squeeze the wood fibers dry and bake in an oven at 100 °C for 4 h. Then wash the baked fibers until neutral and continue to dry in an oven at 80 °C for 4 h to obtain reactive DES-modified wood fibers;

[0073] 3) Put 96 g of the reactive DES-modified wood fibers prepared in step 2), 40 g of waterborne epoxy resin WER5625, 4 g of diaminodiphenylmethane and 100 g of water into a kneader and knead for 30 min for sufficient mixing. Take out the mixture and dry it in an oven at 60 °C for 2 h to obtain a prepreg after drying the moisture;

[0074] 4) Uniformly lay the prepreg prepared in step 3) into a mold, place it in a hot press at 160 °C, pre-press for 5 min first, then hot-press for 50 min to obtain a sample. After demolding, the sample is placed in an oven at 150 °C and cured for 5 h to obtain a reactive DES flame-retardant modified wood fiber / waterborne epoxy resin composite material.

[0075] Example 9

[0076] A preparation method of a reactive deep eutectic solvent flame-retardant modified plant fiber composite material, comprising the following steps:

[0077] 1) Mix phosphoric acid, urea and choline chloride according to a molar ratio of 1:2:1, heat and stir in an oil bath at 90 °C for 60 min until the solution is clear to obtain a reactive DES;

[0078] 2) Add wood fibers to the reactive DES prepared in step 1) and soak for 10 min. Then squeeze the wood fibers dry and bake in an oven at 100 °C for 4 h. Then wash the baked fibers until neutral, and continue to dry in an oven at 80 °C for 4 h to obtain reactive DES-modified wood fibers;

[0079] 3) Put 96 g of the reactive DES-modified wood fibers prepared in step 2), 40 g of waterborne epoxy resin WER5625, 4 g of diethyltoluenediamine and 100 g of water into a kneader and knead for 30 min to mix well. Take out the mixture and place it in an oven at 60 °C to dry for 2 h. After drying the moisture, obtain a prepreg;

[0080] 4) Uniformly lay the prepreg prepared in step 3) into a mold, place it in a hot press at 120 °C, pre-press for 5 min first, then hot-press for 50 min to obtain a sample. After demolding, the sample is placed in an oven at 120 °C and cured for 5 h to obtain a reactive DES flame-retardant modified wood fiber / waterborne epoxy resin composite material.

[0081] Comparative Example 1

[0082] A preparation method of an unflame-retardant modified wood fiber / waterborne epoxy resin composite material, comprising the following steps:

[0083] 1) Put 96 g of wood fibers, 40 g of waterborne epoxy resin WER5625, 4 g of diethyltoluenediamine and 100 g of water into a kneader and knead for 30 min to mix well. Take out the mixture and place it in an oven at 60 °C to dry for 2 h. After drying the moisture, obtain a prepreg;

[0084] 2) Uniformly lay the prepreg into a mold, place it in a hot press at 160 °C, pre-press for 5 min, and hot-press for 45 - 50 min to obtain a sample. After demolding, the sample is placed in an oven at 150 °C and cured for 5 h to obtain a wood fiber / waterborne epoxy resin composite material.

[0085] Comparative Example 2

[0086] The preparation method of the conventional wood fiber / waterborne epoxy resin composite material with ammonium polyphosphate flame retardant modification includes the following steps:

[0087] 1) Dissolve 96g of wood fiber, 40g of waterborne epoxy resin WER5625, 4g of diethyltoluenediamine and 20g of water-soluble ammonium polyphosphate in 100g of water, put them in a kneader and knead them for 30min to mix them thoroughly, take out the mixture, put it in a 60℃ oven and dry it for 2h, and dry the water to obtain a prepreg;

[0088] 2) The prepreg was evenly spread in the mold, placed in a 160°C hot press for pre-pressing for 5 minutes, and hot pressed for 45-50 minutes to obtain a sample. After demolding, the sample was placed in a 150°C oven and cured for 5 hours to obtain an ammonium polyphosphate flame-retardant modified wood fiber / waterborne epoxy resin composite material.

[0089] Comparative Example 3

[0090] A method for preparing a hemp fiber / waterborne epoxy resin composite material comprises the following steps:

[0091] 1) 96 g of hemp fiber, 40 g of waterborne epoxy resin WER5625, 4 g of diethyltoluenediamine and 100 g of water were put into a kneader and kneaded for 30 min to fully mix, the mixture was taken out, and dried in a 60°C oven for 2 h to obtain a prepreg after drying the moisture;

[0092] 2) The prepreg was evenly spread in the mold, placed in a 160°C hot press for pre-pressing for 5 minutes, and hot pressed for 45-50 minutes to obtain a sample. After demolding, the sample was placed in a 150°C oven and cured for 5 hours to obtain a wood fiber / waterborne epoxy resin composite material.

[0093] The composite materials prepared in Examples 1-9 and Comparative Examples 1-3 were subjected to performance tests. The bending and tensile performance tests were respectively measured using a universal testing machine equipped with a 30 kN load cell. According to the GT / B1449-2005 standard, the 120×15×3.5 mm2 composite material was tested at a speed of 2 mm / min and a span of 64 mm. 3 According to GT / B1040.2-2022 standard, the tensile sample (80×10×3.5 mm 3 The test was carried out with a narrow section of 5 mm (2 mm wide). According to the national standard GB / T5454-1997, the limiting oxygen index of the sample was measured using a limiting oxygen index instrument (JF-5 oxygen index tester). The results are shown in Table 1.

[0094] Table 1 Performance test results of the composite materials prepared in Examples 1-9 and Comparative Examples 1-3

[0095]

[0096] As can be seen from Table 1, traditional addition of ammonium polyphosphate can improve the limiting oxygen index (flame retardancy) of wood fiber / waterborne epoxy resin composites, but its flexural strength decreases significantly. Flame retardant modification with reactive DES can make the limiting oxygen index of wood fiber / waterborne epoxy resin composites reach 50%, but the flexural strength does not decrease significantly. Excessive dosage of curing agent will reduce the mechanical properties of the composite material. Lowering the hot pressing temperature and making the system cure insufficiently will also reduce the mechanical properties of the composite material.

[0097] From Figure 1 it can be seen that characteristic peaks of flame retardant elements P and N appear in the spectrum after DES modification, and with the increase of reaction temperature, the characteristic peaks of P and N are significantly enhanced, indicating that reactive DES has been successfully grafted onto the surface of the wood fiber structure.

[0098] From Figure 2 it can be seen that the wood fiber still maintains a fibrous rod structure after DES modification.

[0099] From Figure 3 it can be seen that the flame retardant element P is evenly distributed on the surface of the wood fiber, indicating that the uniform distribution of the flame retardant in the fiber structure is achieved, overcoming the disadvantages of ordinary additive flame retardants that are not easy to disperse and prone to agglomeration.

[0100] The above are only the preferred embodiments of the present invention. It should be pointed out that for those of ordinary skill in the art, without departing from the principle of the present invention, several improvements and refinements can be made, and these improvements and refinements should also be regarded as the protection scope of the present invention.

Claims

1. A method for preparing a reactive low eutectic solvent flame retardant modified plant fiber composite material, characterized in that: The flame-retardant plant fiber is prepared by using plant fiber as raw material after modification with a reactive low eutectic solvent. The flame-retardant plant fiber is mixed with a water-based epoxy resin, a curing agent and water, and hot-pressed and cured to obtain a reactive low eutectic solvent flame-retardant modified plant fiber composite material with a limiting oxygen index of not less than 35%.

2. The method for preparing the reactive deep eutectic solvent flame retardant modified plant fiber composite material according to claim 1, characterized in that: The reactive deep eutectic solvent consists of a proton donor and a proton acceptor that can react with cellulose hydroxyl groups.

3. The method for preparing the reactive deep eutectic solvent flame retardant modified plant fiber composite material according to claim 2, characterized in that: The proton donor is selected from any one or more of phosphoric acid, phytic acid, aminosulfonic acid, urea, and amino acids.

4. The method for preparing the reactive deep eutectic solvent flame retardant modified plant fiber composite material according to claim 2, characterized in that: The proton acceptor is selected from any one or more of betaine, betaine hydrochloride, and choline chloride.

5. The method for preparing the reactive deep eutectic solvent flame retardant modified plant fiber composite material according to claim 1, characterized in that: The plant fiber is selected from any one or more of wood fiber, cotton fiber, hemp fiber and bamboo fiber.

6. The method for preparing the reactive deep eutectic solvent flame retardant modified plant fiber composite material according to claim 1, characterized in that: The curing agent is selected from any one or more of polyetheramine, polyamide, aliphatic amine, alicyclic amine and aromatic amine.

7. The method for preparing the reactive deep eutectic solvent flame retardant modified plant fiber composite material according to claim 1, characterized in that: The temperature of the modification treatment is 80-150° C., and the treatment time is 0.5-5 h.

8. The method for preparing the reactive deep eutectic solvent flame retardant modified plant fiber composite material according to claim 1, characterized in that: The temperature of the hot pressing molding is 160° C., and the hot pressing time is 50 to 55 minutes.

9. The method for preparing a reactive deep eutectic solvent flame-retardant modified plant fiber composite material according to claim 1, characterized in that: The mass ratio of the flame retardant plant fiber, the water-based epoxy resin, the curing agent and water is 96:40:4:

100.

10. A reactive deep eutectic solvent flame retardant modified plant fiber composite material prepared by the method for preparing a reactive deep eutectic solvent flame retardant modified plant fiber composite material according to any one of claims 1 to 9.

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