A polyvinyl alcohol fiber composite material and a preparation method thereof

Abstract

The present invention relates to the technical field of chemical products, and specifically to a polyvinyl alcohol fiber composite material and a preparation method thereof. The present invention overcomes the problem that the interfacial bonding force between the polyvinyl alcohol fiber and the epoxy resin in the composite material is weak, resulting in poor corrosion resistance and mechanical properties of the composite material. The present invention modifies the epoxy resin by using an unsaturated compound, methacrylic acid; activates the polyvinyl alcohol fiber and then modifies it; modifies the aluminate coupling agent to introduce active functional groups such as epoxy groups; and improves the fiber-resin interfacial bonding state and gives full play to the synergistic effect of each component through the processes of primary mixing, in-situ growth, hot pressing and in-situ polymerization, and pulsed magnetic field-assisted forming, so that the corrosion resistance and mechanical properties of the composite material are improved.

Description

Technical Field

[0001] The present invention relates to the technical field of chemical products, and particularly to a polyvinyl alcohol fiber composite material and a preparation method thereof. Background Art

[0002] In the field of building construction, the performance of materials plays a decisive role in the quality, safety and durability of buildings. With the continuous improvement of people's requirements for building quality and the continuous development of building technology, the demand for high-performance building materials is becoming increasingly urgent. As a commonly used building material, epoxy resin has a wide range of applications in building construction due to its excellent adhesion, chemical corrosion resistance and good mechanical properties. For example, it can be used for the reinforcement and repair of building structures to improve the bearing capacity of damaged structures; it can also be used as a floor coating to enhance the wear resistance and corrosion resistance of the floor. However, epoxy resin itself still has some obvious shortcomings: its toughness is insufficient, and when facing dynamic loads such as earthquakes and wind loads, it is prone to brittle failure and cannot effectively disperse and absorb energy, resulting in cracks or even collapse of building structures; in addition, although epoxy resin has a certain ability to resist chemical corrosion, its corrosion resistance is still insufficient when facing some harsh environments such as acid rain and industrial wastewater, and problems such as coating peeling and structural damage may occur after long-term contact.

[0003] In order to improve the performance of epoxy resin, fiber reinforcement technology has become a research hotspot. Polyvinyl alcohol fiber has high strength, high modulus, good flexibility and certain chemical stability. Using polyvinyl alcohol fiber to reinforce epoxy resin composite material in building construction can enhance the seismic performance, anti-deformation ability and corrosion resistance of building structures. However, there are still some problems in the actual application of this composite material at present. The interfacial bonding force between polyvinyl alcohol fiber and epoxy resin is weak, and the stress cannot be effectively transmitted between the fiber and the matrix, resulting in limited improvement in the mechanical properties and corrosion resistance of the composite material.

[0004] Therefore, a polyvinyl alcohol fiber composite material and a preparation method thereof are proposed. Summary of the Invention

[0005] The purpose of the present invention is to provide a polyvinyl alcohol fiber composite material and a preparation method thereof. By using an unsaturated compound, methacrylic acid, to modify epoxy resin; activating polyvinyl alcohol fiber and then modifying it; modifying an aluminate coupling agent to introduce active functional groups such as epoxy groups; and through the processes of primary mixing, in-situ growth, hot pressing and in-situ polymerization, and pulsed magnetic field assisted forming, the interfacial bonding state between the fiber and the resin is improved, and the synergistic effect of each component is fully exerted, so that the corrosion resistance and mechanical properties of the composite material are improved.

[0006] To achieve the above purpose, the present invention provides the following technical solutions:

[0007] It should be noted that all parts in the present invention are parts by mass.

[0008] On the one hand, the present invention provides a method for preparing a polyvinyl alcohol fiber composite material, and the preparation method is as follows:

[0009] S1 Primary mixing: Add modified epoxy resin, modified polyvinyl alcohol fiber, nano-silica, toughening agent and modified coupling agent into a planetary ball mill and ball mill and mix at a speed of 400 rpm for 1.5 h to obtain mixture one;

[0010] S2 In-situ growth: Add 15-20 parts of tetraethyl orthosilicate and 0.9 part of hydrochloric acid to mixture one, and carry out hydrolysis and polycondensation reaction at 55 °C for 5 h to obtain mixture two;

[0011] S3 Hot pressing and in-situ polymerization: Transfer mixture two to a hot pressing mold, add 15-20 parts of methyl methacrylate and 0.3 part of benzoyl peroxide, and then carry out hot pressing to form, and use the hot pressing conditions to initiate in-situ polymerization of the monomer, so that the polymer is synchronously generated in the network structure of the modified polyvinyl alcohol fiber and nano-silica to obtain a hot-pressed material;

[0012] S4 Pulse electric field assisted forming: Transfer the hot-pressed material to a mold, and under the conditions of a temperature of 130 °C and a pressure of 10 MPa, apply a pulse electric field at the same time, the electric field strength is 5-10 kV / cm, the pulse frequency is 15 Hz, and process for 15 min to obtain a polyvinyl alcohol fiber composite material;

[0013] The modified epoxy resin is obtained by reacting epoxy resin E51, methacrylic acid, azobisisobutyronitrile, triphenylphosphine and N,N-dimethylbenzylamine;

[0014] The modified coupling agent is obtained by carrying out a surface grafting reaction of glycidyl methacrylate on an aluminate coupling agent;

[0015] The modified polyvinyl alcohol fiber is obtained by reacting activated polyvinyl alcohol fiber with an initiator solution.

[0016] Preferably, the preparation method of the activated polyvinyl alcohol fiber is as follows: Place 50 parts of polyvinyl alcohol fiber in a mixed solution containing dopamine and ferric ions, oscillate and process at 30-40 °C for 3-4 h. After the reaction is completed, rinse with deionized water until neutral to obtain activated polyvinyl alcohol fiber; the dopamine concentration is 2.5 g / L; the ferric ion concentration is 0.2 g / L; the total amount of the mixed solution is 100 parts.

[0017] Preferably, the preparation method of the modified polyvinyl alcohol fiber is as follows: Dissolve 3 parts of sodium p-styrenesulfonate in 80 parts of deionized water, and add 0.3 part of potassium persulfate thereto to obtain an initiator solution; Add 25 parts of activated polyvinyl alcohol fiber to a reaction kettle containing the initiator solution, seal it, heat it to 55 °C, start stirring, and react at a rotation speed of 200 rpm for 3-6 h. After rinsing with deionized water, place it in a vacuum drying oven at 60 °C and dry it to constant weight to obtain the modified polyvinyl alcohol fiber.

[0018] Preferably, the preparation method of the modified epoxy resin is as follows: Add 100 parts of epoxy resin E51 to a three-necked flask, add 160 parts of acetone thereto, and stir at a rotation speed of 400 rpm at a temperature of 45 °C for 15 min to obtain an epoxy resin solution; After mixing 15-30 parts of methacrylic acid and 0.5-1 part of azobisisobutyronitrile evenly, add it dropwise to the epoxy resin solution at a speed of 2 drops / s. While adding, raise the temperature to 75 °C, then add 0.8-1.8 parts of triphenylphosphine and 0.5 part of N,N-dimethylbenzylamine and continue to react for 4.5 h, and then carry out vacuum distillation to obtain the modified epoxy resin.

[0019] Preferably, in S3, the hot pressing temperature is 110 °C, the pressure is 10 MPa, and the time is 21-31 min.

[0020] Preferably, the preparation method of the modified coupling agent is as follows: Add 50 parts of aluminate coupling agent and 10-20 parts of glycidyl methacrylate to a three-necked flask containing 100 parts of toluene, start stirring, the stirring speed is 350 rpm, heat it to 80 °C, add benzoyl peroxide thereto, react for 3.5-5.5 h, cool it to room temperature, and remove toluene by vacuum distillation to obtain the modified coupling agent.

[0021] On the other hand, the present invention provides a polyvinyl alcohol fiber composite material, which is prepared by any one of the above preparation methods; The raw materials used for the production of the polyvinyl alcohol fiber composite material include 50-70 parts of modified epoxy resin, 20-30 parts of modified polyvinyl alcohol fiber, 10 parts of nano-silica, 5 parts of toughening agent carboxyl-terminated liquid nitrile rubber, and 1-3 parts of modified coupling agent.

[0022] Compared with the prior art, the beneficial effects of the present invention are:

[0023] 1. The present invention uses unsaturated compound methacrylic acid to modify epoxy resin, thereby introducing active groups such as carboxyl and unsaturated double bonds into the epoxy resin. The carboxyl can undergo esterification reaction with the hydroxyl group on the surface of the polyvinyl alcohol fiber to form hydrogen bonds or ester bonds, thereby enhancing the interfacial bonding force between the fiber and the resin. The unsaturated double bonds can participate in subsequent polymerization reactions, thereby further increasing the crosslinking density of the resin and improving the mechanical properties of the composite material. In addition, the introduction of methacrylic acid destroys the originally relatively rigid molecular structure of the epoxy resin to a certain extent, increases the flexibility of the molecular chain, and reduces the possibility of brittle fracture of the composite material when subjected to stress.

[0024] 2. The present invention activates polyvinyl alcohol fiber, and dopamine undergoes self-polymerization reaction on the fiber surface under the catalysis of alkaline environment and trivalent iron ions to form a polydopamine coating, which not only enhances the surface activity of the fiber, but also has a certain anti-corrosion ability; then the active groups on the polydopamine coating on the fiber surface are used to react with sodium p-styrene sulfonate, and the sulfonic acid group has strong acidic environment tolerance. After being grafted to the fiber surface, the stability of the fiber in an acidic corrosive environment can be effectively improved, and the compatibility with epoxy resin can be better; at the same time, the silica network structure formed by in-situ growth is wrapped on the fiber surface, and the nano-silica, fiber and epoxy resin matrix are tightly connected, the fiber-resin interface bonding state is improved, the density of the internal structure of the material is increased, the pores and defects are reduced, and the intrusion channel of the corrosive medium is reduced.

[0025] 3. The present invention prepares a modified coupling agent, grafts glycidyl methacrylate onto an aluminate coupling agent, and introduces active functional groups such as epoxy groups into the coupling agent. The epoxy groups can react with the hydroxyl groups on the fiber surface to establish a strong chemical bridge between the fiber and the resin, thereby significantly enhancing the interfacial bonding force, enabling the composite material to more effectively transfer stress when subjected to force and improving the mechanical properties. By controlling the amount of modified epoxy resin, modified polyvinyl alcohol fiber and modified coupling agent, the synergistic effect of each component can be further enhanced.

[0026] 4. The present invention adopts a process of simultaneous hot pressing and in-situ polymerization. During the hot pressing process, the monomer methyl methacrylate is in-situ polymerized under the action of an initiator, and the polymer is simultaneously generated in the network structure composed of polyvinyl alcohol fibers, nano-silicon dioxide and epoxy resin, so that the synergistic effect between the components can be fully exerted, and the polymer chains are entangled with the fibers, resins, etc., further enhancing the interfacial adhesion. The pulsed electric field is used to promote the orientation of the molecular chains, further improve the fiber-resin interface state, and improve the crystallinity of the composite material, thereby enhancing the mechanical properties and corrosion resistance. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1This is the process flow diagram for preparing the polyvinyl alcohol fiber composite material of the present invention. Detailed implementation mode

[0028] Next, the technical solutions in the embodiments of the present invention will be clearly and completely described in conjunction with the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the protection scope of the present invention.

[0029] Please refer to Figure 1 , the present invention provides a polyvinyl alcohol fiber composite material and a preparation method thereof, and the technical solutions are as follows:

[0030] It can be seen from Figure 1 that the polyvinyl alcohol fiber composite material in the present invention is obtained by initially mixing a modified epoxy resin, modified polyvinyl alcohol fibers, nano-silica, a toughening agent, and a modified coupling agent, and then through in-situ growth, hot pressing and in-situ polymerization, and pulsed electric field-assisted forming.

[0031] The substance information involved in the present invention is as follows:

[0032] Tetraethyl orthosilicate CAS: 78-10-4; Hydrochloric acid CAS: 7647-01-0; Methyl methacrylate CAS: 80-62-6; Benzoyl peroxide CAS: 94-36-0; Polyvinyl alcohol fiber CAS: 9002-89-5; Dopamine CAS: 51-61-6; Sodium p-styrenesulfonate CAS: 2695-37-6; Potassium persulfate CAS: 7727-21-1; Epoxy resin E51 CAS: 61788-97-4; Acetone CAS: 67-64-1; Methacrylic acid CAS: 79-41-4; 2,2'-Azobis(2-methylpropionitrile) CAS: 78-67-1; Triphenylphosphine CAS: 603-35-0; N,N-Dimethylbenzylamine CAS: 103-83-3; Glycidyl methacrylate CAS: 106-91-2; Toluene CAS: 108-88-3; Nano-silica was purchased from Xuancheng Jingrui New Materials Co., Ltd.; Aluminum aluminate coupling agent was purchased from Guangdong Wengjiang Chemical Reagent Co., Ltd.; Carboxyl-terminated liquid nitrile rubber was purchased from Guangdong Wengjiang Chemical Reagent Co., Ltd.

[0033] Example 1

[0034] S1 Initial mixing: Add 50 parts of modified epoxy resin, 20 parts of modified polyvinyl alcohol fibers, 10 parts of nano-silica, 5 parts of toughening agent carboxyl-terminated liquid nitrile rubber, and 1 part of modified coupling agent to a planetary ball mill and ball mill and mix at a speed of 400 rpm for 1.5 h to obtain mixture one;

[0035] In-situ growth of S2: Add 15 parts of tetraethyl orthosilicate and 0.9 parts of hydrochloric acid to the first mixture, and carry out hydrolysis and polycondensation reaction at 55 °C for 5 h to obtain the second mixture.

[0036] Hot pressing and in-situ polymerization of S3: Transfer the second mixture to a hot pressing mold, add 15 parts of methyl methacrylate and 0.3 parts of benzoyl peroxide, and then carry out hot pressing. Use the hot pressing conditions to initiate in-situ polymerization of the monomer, so that the polymer is synchronously generated in the network structure of modified polyvinyl alcohol fibers and nano-silica to obtain a hot-pressed material; the hot pressing temperature is 110 °C, the pressure is 10 MPa, and the time is 21 min.

[0037] Pulse electric field-assisted forming of S4: Transfer the hot-pressed material to a mold, and under the conditions of a temperature of 130 °C and a pressure of 10 MPa, apply a pulse electric field at the same time. The electric field strength is 5 kV / cm, the pulse frequency is 15 Hz, and after treatment for 15 min, a polyvinyl alcohol fiber composite material is obtained.

[0038] The preparation method of the modified epoxy resin is as follows: Add 100 parts of epoxy resin E51 to a three-necked flask, add 160 parts of acetone to it, and stir at a speed of 400 rpm at a temperature of 45 °C for 15 min to obtain an epoxy resin solution; after mixing 15 parts of methacrylic acid and 0.5 parts of azobisisobutyronitrile evenly, add them dropwise to the epoxy resin solution at a speed of 2 drops / s. While dropping, raise the temperature to 75 °C, then add 0.8 parts of triphenylphosphine and 0.5 parts of N,N-dimethylbenzylamine and continue to react for 4.5 h, and then carry out vacuum distillation to obtain the modified epoxy resin.

[0039] The preparation method of the modified polyvinyl alcohol fiber is as follows: Place 50 parts of polyvinyl alcohol fiber in a mixed solution containing dopamine and ferric ions, oscillate and treat at 30 °C for 3 h. After the reaction is completed, rinse with deionized water until neutral to obtain activated polyvinyl alcohol fiber; the dopamine concentration is 2.5 g / L, and the ferric ion concentration is 0.2 g / L; dissolve 3 parts of sodium p-styrenesulfonate in 80 parts of deionized water, add 0.3 parts of potassium persulfate to it to obtain an initiator solution; add 25 parts of activated polyvinyl alcohol fiber to the reaction kettle containing the initiator solution and seal it, heat up to 55 °C, start stirring, and react at a speed of 200 rpm for 3 h. After rinsing with deionized water, put it into a vacuum drying oven at 60 °C and dry to constant weight to obtain the modified polyvinyl alcohol fiber; the total amount of the mixed solution is 100 parts; the ferric ions are from ferric chloride.

[0040] The preparation method of the modified coupling agent is as follows: Add 50 parts of aluminate coupling agent and 10 parts of glycidyl methacrylate into a three-necked flask containing 100 parts of toluene. Start stirring at a stirring speed of 350 rpm, heat up to 80 °C, add benzoyl peroxide to it, react for 3.5 h, cool to room temperature, and remove toluene by vacuum distillation to obtain the modified coupling agent.

[0041] Examples 2 - 5

[0042] Refer to the preparation method and parameter conditions of Example 1. The specific differences are shown in Table 1.

[0043] Comparative Example 1

[0044] Refer to the preparation method and parameter conditions of Example 4. The difference is that the epoxy resin was not modified.

[0045] Comparative Example 2

[0046] Refer to the preparation method and parameter conditions of Example 4. The difference is that epoxy resin E51 was replaced with epoxy resin E44.

[0047] Comparative Example 3

[0048] Refer to the preparation method and parameter conditions of Example 4. The difference is that N, N-dimethylbenzylamine was not added during the preparation of the modified epoxy resin.

[0049] Comparative Example 4

[0050] Refer to the preparation method and parameter conditions of Example 4. The difference is that triphenylphosphine was not added during the preparation of the modified epoxy resin.

[0051] Experimental Example 1 Mechanical Property Test

[0052] Refer to the standard of GB / T 1449 - 2005 to test the mechanical properties of the composite material; the obtained results are shown in Table 1.

[0053] Table 1 Mechanical Properties of Examples 1 - 5 and Comparative Examples 1 - 4

[0054]

[0055] As can be seen from Table 1, in Examples 1-5, unsaturated compound methacrylic acid was selected to modify epoxy resin, introducing active groups such as carboxyl groups and unsaturated double bonds into the epoxy resin. The carboxyl groups can undergo esterification reactions with the hydroxyl groups on the surface of polyvinyl alcohol fibers to form hydrogen bonds or ester bonds, enhancing the interfacial bonding force between the fibers and the resin. The unsaturated double bonds can participate in subsequent polymerization reactions to further increase the crosslinking density of the resin and improve the mechanical properties of the composite material. Moreover, the introduction of methacrylic acid destroys the originally relatively rigid molecular structure of the epoxy resin to a certain extent, increases the flexibility of the molecular chain, and reduces the possibility of brittle fracture of the composite material when stressed. In Example 4, when the dosage of methacrylic acid was 20 parts, the dosage of azobisisobutyronitrile was 0.7 parts, and the dosage of triphenylphosphine was 1.3 parts, the composite material prepared had the best mechanical properties, and the flexural strength was 220 MPa. In Comparative Example 1, the epoxy resin was not modified, and its reactivity with the fibers and coupling agent was low, and the interfacial bonding strength was insufficient. When stressed, debonding easily occurred between the fibers and the resin, and the stress could not be effectively transmitted, resulting in a decrease in the mechanical properties of the composite material. In Comparative Example 2, epoxy resin E51 was replaced with epoxy resin E44, and the crosslinked structure was relatively loose, affecting the interfacial bonding and overall performance, resulting in a decrease in the mechanical properties of the composite material. In Comparative Examples 3-4, when preparing the modified epoxy resin, N, N-dimethylbenzylamine or triphenylphosphine was not added, and the two could not have a synergistic effect, and the reaction was not sufficient. The content of active groups in the modified epoxy resin was relatively low, resulting in a decrease in its reactivity with the fibers and coupling agent, which hindered the internal stress transfer and energy dissipation of the composite material when stressed, thus leading to a decrease in mechanical properties.

[0056] Examples 6-10

[0057] Referring to the preparation method and parameter conditions of Example 4, the specific differences are shown in Table 2; in Table 2, Temperature 1 and Time 1 are the temperature and time for activating the polyvinyl alcohol fibers, and Time 2 is the time for modifying the activated polyvinyl alcohol fibers.

[0058] Comparative Example 5

[0059] Referring to the preparation method and parameter conditions of Example 7, the difference is that the polyvinyl alcohol fibers were not activated.

[0060] Comparative Example 6

[0061] Referring to the preparation method and parameter conditions of Example 7, the difference is that the activated polyvinyl alcohol fibers were not modified.

[0062] Comparative Example 7

[0063] Referring to the preparation method and parameter conditions of Example 7, the difference is that in-situ growth in Preparation Step S2 is not carried out, but the mixture 1 obtained in S1 is directly subjected to hot pressing and in-situ polymerization in S3.

[0064] Experimental Example 2 Corrosion Resistance Test

[0065] The composite material was immersed in a hydrochloric acid solution with a concentration of 10% until cracking, collapse and other damage phenomena were found in the composite material, then the experiment was terminated and the erosion time was recorded; the results are shown in Table 2.

[0066] Table 2 Corrosion Resistance Test of Examples 4, 6 - 10 and Comparative Examples 5 - 7

[0067]

[0068] As can be seen from Table 2, in Examples 4 and 6 - 10, by activating polyvinyl alcohol fibers, dopamine undergoes a self - polymerization reaction on the fiber surface under alkaline conditions and catalysis by ferric ions, forming a polydopamine coating. This coating not only enhances the surface activity of the fibers but also has a certain anti - corrosion ability. Then, using the active groups on the polydopamine coating on the fiber surface to react with sodium p - styrene sulfonate, the sulfonic acid group has strong acid - resistant environmental tolerance. After grafting onto the fiber surface, it can effectively improve the stability of the fibers in an acidic corrosion environment and has better compatibility with epoxy resin. At the same time, the in - situ formed silica network structure wraps around the fiber surface, tightly connecting nano - silica, fibers, and the epoxy resin matrix, improving the fiber - resin interface bonding state, increasing the compactness of the internal structure of the material, reducing pores and defects, and reducing the intrusion channels of corrosive media. In Example 7, when the temperature for activating polyvinyl alcohol fibers is 36 °C, the time is 3.6 h, the time for modifying the activated polyvinyl alcohol fibers is 5.0 h, and the dosage of tetraethyl orthosilicate during in - situ growth is 18 parts, the fiber - resin interface bonding state is the best, and the corrosion - resistant performance of the prepared composite material is the best, with an acid - resistant time of 120 days. In Comparative Example 5, the polyvinyl alcohol fibers were not activated, resulting in insufficient surface activity of the fibers, loose bonding with the resin and coupling agent, and easy formation of pores and micro - cracks at the interface. Corrosive media can penetrate into the interior of the composite material through the interface defects, react chemically with the fibers and the resin, leading to a decrease in fiber strength, swelling or degradation of the resin matrix, thus reducing the corrosion - resistant performance of the composite material. In Comparative Example 6, the activated polyvinyl alcohol fibers were not modified, lacking functional groups such as sulfonic acid groups on the fiber surface, making the interface bonding between the fibers and the resin not firm enough, and corrosive media more likely to diffuse between the fibers and the resin, accelerating the corrosion of the material. The silica network structure has a certain chemical stability and can act as a barrier to prevent further intrusion of corrosive media. In Comparative Example 7, the in - situ growth in Preparation Step S2 was not carried out, and the silica network structure was not formed. The composite material lost this effective protective layer, allowing corrosive media to reach the fibers and the resin matrix more easily, thereby reducing the corrosion - resistant performance of the composite material.

[0069] Examples 11 - 15

[0070] Referring to the preparation method and parameter conditions of Example 7, the specific differences are shown in Table 3; the reaction time in Table 3 is the reaction time for preparing the modified coupling agent.

[0071] Comparative Example 8

[0072] Referring to the preparation method and parameter conditions of Example 12, the difference is that the coupling agent was not modified.

[0073] Comparative Example 9

[0074] Referring to the preparation method and parameter conditions of Example 12, except that the modified polyvinyl alcohol fiber was not added.

[0075] Comparative Example 10

[0076] Referring to the preparation method and parameter conditions of Example 12, except that the modified coupling agent was not added.

[0077] Experimental Example 3 Mechanical Property Test

[0078] The mechanical properties of the composite material were tested according to the standard of GB / T 1449-2005; the obtained results are shown in Table 3.

[0079] Table 3 Mechanical Property Test of Examples 7, 11-15 and Comparative Examples 8-10

[0080]

[0081] As can be seen from Table 3, in Examples 7, 11-15, by preparing the modified coupling agent, glycidyl methacrylate was grafted onto the aluminate coupling agent, introducing active functional groups such as epoxy groups into the coupling agent. The epoxy groups can react with the hydroxyl groups on the fiber surface, establishing a strong chemical bridge between the fiber and the resin, thus significantly enhancing the interfacial bonding force, enabling the composite material to transfer stress more effectively when stressed, and improving the mechanical properties; by controlling the dosages of the modified epoxy resin, modified polyvinyl alcohol fiber and modified coupling agent, the synergistic effect of each component can be further improved. In Example 12, when the dosage of glycidyl methacrylate was 16 parts and the reaction time was 4.5 h during the preparation of the modified coupling agent, and the dosages of the modified epoxy resin, modified polyvinyl alcohol fiber and modified coupling agent were 60 parts, 26 parts and 2.0 parts respectively, the composite material prepared had the best mechanical properties, and the flexural strength was 226 MPa. In Comparative Example 8, the coupling agent was not modified, and the coupling agent could not form effective chemical bonding or physical adsorption with the modified epoxy resin, modified polyvinyl alcohol fiber and nano-silica well, which would lead to stress concentration at the interface easily when stressed, and when the composite material was subjected to external force, relative sliding or separation would easily occur between the components, reducing the overall mechanical properties of the composite material. In Comparative Example 9, the modified polyvinyl alcohol fiber was not added, and the composite material lacked this important reinforcing phase and could not improve the overall mechanical properties through the load-bearing capacity of the fiber, resulting in a significant decrease in the flexural strength of the composite material. In Comparative Example 10, the modified coupling agent was not added, and it was difficult to form good interaction and cooperative working mechanism among the phases. The composite material could not give full play to the advantages of each phase when stressed, and the mechanical properties would be limited.

[0082] Examples 16-20

[0083] Referring to the preparation method and parameter conditions of Example 12, the specific differences are shown in Table 4.

[0084] Comparative Example 11

[0085] Referring to the preparation method and parameter conditions of Example 16, the difference is that in the preparation step S3, hot pressing is carried out first, and then in-situ polymerization is carried out. The specific steps are as follows: Transfer the mixture two to a hot pressing mold for hot pressing. The hot pressing temperature is 110 °C, the pressure is 10 MPa, and the hot pressing time is 25 min to obtain a hot pressing intermediate product; then add the hot pressing intermediate product to a reaction kettle, add 18 parts of methyl methacrylate and 0.3 parts of benzoyl peroxide, and carry out in-situ polymerization reaction at 80 °C. The in-situ polymerization pressure is 0.5 MPa and the time is 60 min to obtain a hot pressing material.

[0086] Comparative Example 12

[0087] Referring to the preparation method and parameter conditions of Example 16, the difference is that in the preparation step S3, in-situ polymerization is carried out first, and then hot pressing is carried out. The specific steps are as follows: Add 18 parts of methyl methacrylate and 0.3 parts of benzoyl peroxide to the mixture two, and carry out in-situ polymerization reaction at 80 °C. The in-situ polymerization pressure is 0.5 MPa and the time is 60 min to obtain an in-situ polymerization product; then transfer the in-situ polymerization product to a hot pressing mold for hot pressing. The hot pressing temperature is 110 °C, the pressure is 10 MPa, and the hot pressing time is 25 min to obtain a hot pressing material.

[0088] Comparative Example 13

[0089] Referring to the preparation method and parameter conditions of Example 16, the difference is that pulsed electric field-assisted forming is not used.

[0090] Comparative Example 14

[0091] Referring to the preparation method and parameter conditions of Example 16, the difference is that the pulse frequency is 30 Hz.

[0092] Comparative Example 15

[0093] Referring to the preparation method and parameter conditions of Example 16, the difference is that the pulse frequency is 5 Hz.

[0094] Experimental Example 4

[0095] Corrosion resistance test: Immerse the composite material in a hydrochloric acid solution with a concentration of 10% until cracking, collapse and other damage phenomena are found in the composite material, then terminate the experiment and record the erosion time;

[0096] Mechanical property test: Refer to the standard of GB / T 1449-2005 to test the mechanical properties of the composite material; the obtained results are shown in Table 4.

[0097] Table 4 Corrosion Resistance Tests of Example 12, Examples 16 - 20, and Comparative Examples 11 - 15

[0098]

[0099] As can be seen from Table 4, in Example 12 and Examples 16 - 20, by adopting the process of synchronous hot - pressing forming and in - situ polymerization, during the hot - pressing process, the monomer methyl methacrylate undergoes in - situ polymerization under the action of an initiator, and the polymer is synchronously generated in the network structure composed of polyvinyl alcohol fibers, nano - silica, and epoxy resin, enabling the full play of the synergistic effect among the components. The polymer chains are intertwined with fibers, resins, etc., further enhancing the interfacial adhesion force; by promoting the orientation arrangement of molecular chains through pulsed electric fields, the fiber - resin interface state is further improved, and the crystallinity of the composite material is increased, enhancing the mechanical properties and corrosion resistance. In Comparative Examples 11 - 12, separating the hot - pressing forming and in - situ polymerization will result in insufficiently tight and uniform bonding between the polymer and fibers and nanoparticles, weakening the interfacial bonding force, making the composite material prone to problems such as interfacial debonding when subjected to external forces, reducing the mechanical properties; and there are more defects and pores inside the material, becoming channels for the penetration of corrosive media, accelerating the corrosion of the material, and reducing the corrosion resistance. In Comparative Example 13, without using pulsed - electric - field - assisted forming, the regularity and orderliness of the internal structure of the material may be poor, and it is difficult to achieve the optimal mechanical properties; the density of the material is relatively low, and corrosive media are more likely to enter the interior of the material and react with the material, resulting in a decrease in the corrosion resistance of the material. In Comparative Example 14, the pulse frequency is 30 Hz. An excessively high pulse frequency will cause the molecular chain movement inside the material to be too intense, which is instead unfavorable for the orderly arrangement and stable bonding of molecular chains, and the internal structure of the material becomes unstable or generates more defects, leading to a decrease in the mechanical properties and corrosion resistance of the composite material. In Comparative Example 15, the pulse frequency is 5 Hz. The action of the electric field on the molecular chains inside the material is not sufficient, and it is unable to effectively promote the orientation and arrangement of molecular chains. It is difficult to effectively improve the structural regularity and density of the material, which will also cause a decrease in the mechanical properties and corrosion resistance of the composite material.

[0100] Although the embodiments of the present invention have been shown and described, for those of ordinary skill in the art, it can be understood that various changes, modifications, substitutions, and variations can be made to these embodiments without departing from the principles and spirit of the present invention. The scope of the present invention is defined by the appended claims and their equivalents.

Claims

1. A method for preparing a polyvinyl alcohol fiber composite material, characterized in that: The preparation method is as follows: S1: initial mixing: adding modified epoxy resin, modified polyvinyl alcohol fiber, nano-silica, toughening agent and modified coupling agent into a ball mill and mixing them at a speed of 400 rpm for 1.5 h to obtain a mixture 1; S2 in-situ growth: 15-20 parts of tetraethyl orthosilicate and 0.9 parts of hydrochloric acid were added to the mixture one, and a hydrolysis and polycondensation reaction was carried out at 55° C. for 5 hours to obtain a mixture two; S3 hot pressing and in-situ polymerization: the mixture is transferred to a hot pressing mold, 15-20 parts of methyl methacrylate and 0.3 parts of benzoyl peroxide are added, and hot pressing is performed, and the monomer is initiated to polymerize in situ under hot pressing conditions to obtain a hot pressing material; S4 pulse electric field assisted molding: the hot pressed material is transferred to a mold, and a pulse electric field is applied at a temperature of 130° C. and a pressure of 10 MPa at the same time, with an electric field strength of 5-10 kV / cm, for 15 minutes to obtain the polyvinyl alcohol fiber composite material; The modified epoxy resin is obtained by reacting epoxy resin E51, methacrylic acid, azobisisobutyronitrile, triphenylphosphine and N,N-dimethylbenzylamine; The modified coupling agent is obtained by surface grafting reaction of glycidyl methacrylate on an aluminate coupling agent; The preparation method of the modified polyvinyl alcohol fiber is as follows: 50 parts of polyvinyl alcohol fiber are placed in a mixed solution containing dopamine and trivalent iron ions, and oscillated at 30-40°C for 3-4 hours. After the reaction is completed, the fiber is rinsed with deionized water until it is neutral to obtain activated polyvinyl alcohol fiber; the dopamine concentration in the mixed solution is 2.5 g / L, and the trivalent iron ion concentration is 0.2 g / L; 3 parts of sodium p-styrene sulfonate are added to 80 parts of the deionized water, stirred and dissolved, and 0.3 parts of potassium persulfate are added thereto to obtain an initiator solution; 25 parts of the activated polyvinyl alcohol fiber are added to a reactor containing the initiator solution and sealed, heated to 55°C, reacted at a speed of 200 rpm for 3-6 hours, rinsed with the deionized water, and placed in a vacuum drying oven at 60°C to dry to constant weight to obtain the modified polyvinyl alcohol fiber.

2. The method for preparing a polyvinyl alcohol fiber composite material according to claim 1, characterized in that: The preparation method of the modified epoxy resin is as follows: 100 parts of the epoxy resin E51 are added into a three-necked flask, acetone is added thereto, and the mixture is stirred at a temperature of 45° C. and a rotation speed of 400 rpm for 15 minutes to obtain an epoxy resin solution; 15-30 parts of methacrylic acid and 0.5-1 part of azobisisobutyronitrile are uniformly mixed, and then dripped into the epoxy resin solution at a speed of 2 drops / s, and the temperature is raised to 75° C. while dripping, and then 0.8-1.8 parts of triphenylphosphine and 0.5 parts of N, N-dimethylbenzylamine are added, and the reaction is continued for 4.5 hours, and then reduced pressure distillation is performed to obtain the modified epoxy resin.

3. The method for preparing a polyvinyl alcohol fiber composite material according to claim 1, characterized in that: The hot pressing molding temperature in S3 is 110° C., the pressure is 10 MPa, and the time is 21-31 min.

4. The method for preparing a polyvinyl alcohol fiber composite material according to claim 1, characterized in that: The preparation method of the modified coupling agent is as follows: 50 parts of the aluminate coupling agent and 10-20 parts of the glycidyl methacrylate are added to a three-necked flask filled with 100 parts of toluene, stirring is started at a stirring speed of 350 rpm, the temperature is raised to 80° C., the benzoyl peroxide is added thereto, the reaction is carried out for 3.5-5.5 hours, the mixture is cooled to room temperature, and the toluene is removed by reduced pressure distillation to obtain the modified coupling agent.

5. A polyvinyl alcohol fiber composite material, characterized in that: The polyvinyl alcohol fiber composite material is prepared by the preparation method described in any one of claims 1 to 4; the raw materials used in the production of the polyvinyl alcohol fiber composite material include 50-70 parts of modified epoxy resin, 20-30 parts of modified polyvinyl alcohol fiber, 10 parts of nano-silicon dioxide, 5 parts of toughening agent terminal carboxyl liquid nitrile rubber and 1-3 parts of modified coupling agent.

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