A modified flame-retardant epoxy resin composite material and a preparation method thereof

Abstract

The application belongs to the technical field of high polymer materials, and relates to a modified flame-retardant epoxy resin composite material and a preparation method thereof.The modified flame-retardant epoxy resin composite material is prepared from 100 parts of bisphenol A type epoxy resin, 15-40 parts of DOPO-MA grafted sodium alginate, 10-30 parts of silicon powder, 5-7 parts of a curing agent and 0.1-1 part of an accelerator, in terms of mass parts.The DOPO-MA grafted sodium alginate is synthesized from DOPO-MA and mercapto sodium alginate, and the molar ratio of the DOPO-MA to the mercapto sodium alginate is 1:1-1.2.The modified flame-retardant epoxy resin composite material provided by the application has greatly improved mechanical properties, flame-retardant properties and transparency relative to general epoxy resin.

Description

Technical Field

[0001] This invention belongs to the field of polymer materials technology and relates to a modified flame-retardant epoxy resin composite material and its preparation method. Background Technology

[0002] Epoxy resins, especially bisphenol A type epoxy resins, are thermosetting resins with excellent comprehensive properties. They possess superior mechanical properties, adhesive properties, electrical insulation properties, chemical corrosion resistance, and molding processability, and are widely used in many fields such as electronic and electrical packaging, composite material matrices, adhesives, aerospace components, and building materials. However, epoxy resins are inherently flammable polymers with a low limiting oxygen index. During combustion, they are prone to melting and dripping, releasing large amounts of toxic and harmful fumes. In the event of a fire, this can easily cause the fire to spread and cause secondary hazards. This inherent defect severely limits the further application of epoxy resins in key areas where high flame retardancy is required. Therefore, efficient and environmentally friendly flame retardant modification of epoxy resins is a core technical problem that urgently needs to be solved in the industry.

[0003] Currently, flame retardant modification methods for epoxy resins are mainly divided into two categories: additive flame retardant modification and reactive flame retardant modification. Among them, additive flame retardant modification has become the mainstream method for epoxy resin flame retardant modification due to its simple process, controllable cost, and wide applicability. Under the industry trend of halogen-free and environmentally friendly development, phosphorus-based flame retardants, with their characteristics of high flame retardant efficiency, low smoke and toxicity release, and excellent char formation, are gradually replacing traditional halogen flame retardants and becoming the preferred flame retardants for epoxy resin flame retardant modification. Among them, 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide (DOPO) and its derivatives are representative varieties of phosphorus-based flame retardants. The phosphorus element in DOPO flame retardants exists in a cyclic structure, has good thermal stability, and can effectively inhibit the combustion process of epoxy resin and significantly improve its flame retardant level through the synergistic effect of gas-phase flame retardancy and condensed-phase flame retardancy during the flame retardant process.

[0004] However, the existing technology of directly adding DOPO-MA as a flame retardant to the epoxy resin matrix still has many technical shortcomings: On the one hand, DOPO-MA is a small molecule organic flame retardant with poor compatibility with epoxy resin. At high addition levels, it is prone to agglomeration and precipitation, which not only leads to a significant decrease in the mechanical properties and molding properties of epoxy resin composites, but also causes uneven dispersion of the flame retardant, failing to fully exert its flame retardant effect; on the other hand, small molecule DOPO-MA has strong migration in the epoxy resin system and is easily lost during long-term use, leading to a decrease in the flame retardant performance of the composite material. At the same time, the addition of DOPO-MA will have a negative impact on the optical properties of epoxy resin, reducing the transparency of epoxy resin composites, making it difficult to meet the requirements of electronic packaging, optical devices and other applications that require high light transmittance. Summary of the Invention

[0005] The present invention aims to provide a modified flame-retardant epoxy resin composite material, which has superior mechanical properties, flame-retardant properties and transparency.

[0006] To address this need, the present invention provides a modified flame-retardant epoxy resin composite material and its preparation method. The present invention uses sodium alginate solid product grafted with a DOPO structure as a flame retardant, which effectively improves the flame-retardant properties and transparency of the modified flame-retardant epoxy resin composite material compared to DOPO-MA.

[0007] On one hand, the present invention relates to a modified flame-retardant epoxy resin composite material, which, by weight, consists of 100 parts of bisphenol A type epoxy resin, 15-40 parts of DOPO-MA grafted sodium alginate, 10-30 parts of silica powder, 5-7 parts of curing agent and 0.1-1 parts of accelerator;

[0008] The DOPO-MA-grafted sodium alginate is synthesized from DOPO-MA and sodium thioglycolate, with a molar ratio of DOPO-MA to sodium thioglycolate of 1:1 to 1.2.

[0009] Furthermore, in the modified flame-retardant epoxy resin composite material provided by the present invention, the fineness of the silicon micropowder is not less than 1250 mesh.

[0010] Furthermore, in the modified flame-retardant epoxy resin composite material provided by the present invention, the curing agent is DMP-30.

[0011] Furthermore, in the modified flame-retardant epoxy resin composite material provided by the present invention, the accelerator is selected from at least one of 2-ethyl-4-methylimidazole, 2,4-dimethylimidazole, and 1-methylimidazole.

[0012] On the other hand, the present invention relates to a method for preparing a modified flame-retardant epoxy resin composite material, comprising: preparing a sodium alginate solution, activating the carboxyl groups in sodium alginate by EDC and NHS, adding cysteine, maintaining the reaction pH at 4.0~5.0, reacting at room temperature for 3~5 h, then adjusting the pH to 6.0, continuing the reaction for 0.5~1 h, and then freeze-drying to obtain mercapto-sodium alginate;

[0013] Sodium thioalginate was dissolved in PBS buffer at pH 8. DOPO-MA was first dissolved in an organic solvent and then slowly added dropwise to the alkaline solution of sodium thioalginate. The DOPO-MA-grafted sodium alginate was obtained by dialysis and lyophilization.

[0014] Bisphenol A type epoxy resin is heated and then mixed with silica powder and DOPO-MA grafted sodium alginate. After cooling, curing agent and accelerator are added and mixed evenly. Finally, pre-curing and curing are performed to obtain the final product.

[0015] Furthermore, in the preparation method of the modified flame-retardant epoxy resin composite material provided by the present invention, the molar ratio of sodium alginate repeating structural unit, EDC and NHS is 1:2:2, and the mass ratio of sodium alginate and cysteine ​​is 1:2.

[0016] Furthermore, in the preparation method of the modified flame-retardant epoxy resin composite material provided by the present invention, the bisphenol A type epoxy resin is heated to 110~140℃.

[0017] Furthermore, in the preparation method of the modified flame-retardant epoxy resin composite material provided by the present invention, the cooling is to cool to 40~50°C.

[0018] Furthermore, in the preparation method of the modified flame-retardant epoxy resin composite material provided by the present invention, the pre-curing temperature is 60~80℃ and the time is 1~3h.

[0019] Furthermore, in the preparation method of the modified flame-retardant epoxy resin composite material provided by the present invention, the curing temperature is 120~160℃ and the time is 1~3h.

[0020] Compared with the prior art, the technical solution provided by the present invention has at least the following beneficial effects or advantages:

[0021] This invention prepares mercapto-sodium alginate by activating the carboxyl groups of sodium alginate with EDC / NHS and reacting it with cysteine. This mercapto-sodium alginate is then covalently grafted with DOPO-MA to form a macromolecular flame retardant, solving the problems of poor compatibility and easy aggregation of small-molecule DOPO-MA with epoxy resin in existing technologies. The cyclic phosphorus structure of DOPO and the char-forming properties of sodium alginate create a synergistic gas-phase-condensed-phase flame retardant effect. Small-molecule DOPO-MA can disrupt the continuity of the epoxy resin matrix, leading to a decrease in mechanical properties at high addition levels. In contrast, the DOPO-MA grafted with sodium alginate in this invention exhibits strong interfacial bonding with epoxy resin, and the synergistic filling of 1250-mesh high-fineness silica powder enhances the matrix density. The matrix constructed in this invention exhibits extremely low light scattering, avoiding the contradiction between transparency and strength in existing technologies. The grafted flame retardant of this invention has good homogeneity with epoxy resin, and the regular molecular chain of sodium alginate reduces light loss caused by phase separation. Detailed Implementation

[0022] The technical solution of the present invention will be described below with reference to embodiments; however, the present invention is not limited to the following embodiments. Unless otherwise specified, the experimental and detection methods described in each embodiment are conventional methods; the reagents and materials described are commercially available unless otherwise specified. Unless otherwise specified, all percentages in the following embodiments refer to mass percentage content. Unless otherwise specified, all ratios in the following embodiments refer to mass ratios.

[0023] In the following examples, the silicon micropowder has a fineness of 1250 mesh;

[0024] The DOPO-MA structure is as follows:

[0025] ;

[0026] The structure of bisphenol A type epoxy resin is as follows:

[0027]

[0028] Where n=1.

[0029] DMP-30 is 2,4,6-tris(dimethylaminomethyl)phenol.

[0030] Example 1

[0031] This embodiment provides a method for preparing modified flame-retardant epoxy resin composite materials.

[0032] S1. Dissolve 1.5g of sodium alginate in 50mL of deionized water, then add a DMSO solution of EDC and NHS. The molar ratio of sodium alginate repeating structural units, EDC and NHS is 1:2:2. Stir for 1h to complete the activation of the carboxyl groups in sodium alginate by EDC and NHS.

[0033] S2. Add 3g of cysteine ​​to the solution obtained in S1, adjust the pH to 4.0 with 1M hydrochloric acid solution, continue stirring for 4h, add 1M sodium hydroxide solution to adjust the pH to 6.0, continue the reaction for 1h, and then freeze-dry under vacuum at -50℃ to obtain sodium thioalginate with a thiol substitution amount of 954.8μmol / g polymer.

[0034] S3. Dissolve 10g of sodium thioalginate in an appropriate amount of pH 8.0 PBS buffer. Dissolve DOPO-MA in a small amount of anhydrous ethanol first, and then slowly add it dropwise to the above sodium thioalginate alkaline solution. The molar ratio of DOPO-MA to sodium thioalginate is 1:1.2. Stir at high speed to ensure uniform mixing. The thiol (-SH) undergoes a nucleophilic ring-opening reaction on the maleic anhydride ring in DOPO-MA to form a covalent graft structure.

[0035] S4. Bubble the reaction mixture with nitrogen or argon for 5 minutes to remove oxygen. Under sealed conditions, stir the reaction mixture at room temperature in the dark for 24 hours. Dialyze the reaction product with deionized water for 2 days, changing the water twice a day, to completely remove unreacted DOPO-MA small molecules, byproducts, and organic solvents. Finally, freeze-dry the dialyzed solution to obtain the solid product of sodium alginate grafted with the DOPO structure (DOPO-MA grafted sodium alginate).

[0036] S5. Slowly heat 100 parts of bisphenol A type epoxy resin in an oil bath to 110°C, add 10-30 parts of silica powder and 15-40 parts of DOPO-MA grafted sodium alginate, stir slowly for 30 minutes, keep stirring and cool naturally to 40-50°C, then add 5-7 parts of curing agent and 0.1-1 parts of accelerator and continue stirring for 1 hour. After mixing evenly, keep warm at 50°C, remove air bubbles under vacuum, pour into a mold and pre-cure at 70°C for 2 hours, then heat to 130°C and cure for 2 hours to finally obtain the modified flame-retardant epoxy resin composite material.

[0037] Example 2

[0038] This embodiment provides transparent flame-retardant epoxy resin composite materials with different formulations.

[0039] Standard formulation #0: 100 parts bisphenol A type epoxy resin, 0 parts DOPO-MA, 20 parts silica powder, 6 parts DMP-30 and 0.5 parts 2-ethyl-4-methylimidazole;

[0040] Standard Formulation 1#: 100 parts bisphenol A type epoxy resin, 15 parts DOPO-MA, 20 parts silica powder, 6 parts DMP-30 and 0.5 parts 2-ethyl-4-methylimidazole;

[0041] Standard Formula 2#: 100 parts bisphenol A type epoxy resin, 30 parts DOPO-MA, 20 parts silica powder, 6 parts DMP-30 and 0.5 parts 2-ethyl-4-methylimidazole;

[0042] Standard Formulation 3#: 100 parts bisphenol A type epoxy resin, 40 parts DOPO-MA, 20 parts silica powder, 6 parts DMP-30 and 0.5 parts 2-ethyl-4-methylimidazole;

[0043] Improved Formula 1#: 100 parts of bisphenol A type epoxy resin, 15 parts of DOPO-MA grafted sodium alginate, 10 parts of silica powder, 5 parts of DMP-30 and 0.1 parts of 2,4-dimethylimidazole;

[0044] Improved Formula 2#: 100 parts bisphenol A type epoxy resin, 30 parts DOPO-MA grafted sodium alginate, 30 parts silica powder, 7 parts DMP-30 and 1 part 1-methylimidazole;

[0045] Improved Formula 3#: 100 parts bisphenol A type epoxy resin, 40 parts DOPO-MA grafted sodium alginate, 20 parts silica powder, 6 parts DMP-30 and 0.5 parts 2-ethyl-4-methylimidazole;

[0046] Comparison Formula 1#: Same as Improved Formula 3#, except that DOPO-MA-grafted sodium alginate is replaced with sodium thioalginate and DOPO-MA, and the molar ratio of sodium thioalginate to DOPO-MA is 1:1.2.

[0047] The flame retardant properties of the above formulation were tested using the UL-94 vertical burning test, and its tensile strength (refer to ASTM D638) and light transmittance (refer to ASTM D1003) were also tested. The test results are shown in Table 1.

[0048] Table 1. Properties of transparent flame-retardant epoxy resin composites with different formulations

[0049]

[0050] The experimental results show that the epoxy resin composite material without DOPO does not have flame retardant properties (second combustion time > 60s). With the increase of DOPO-MA content, its flame retardant properties gradually improve, but the light transmittance gradually decreases, and the tensile strength first increases and then decreases. The modified flame-retardant epoxy resin composite material provided by this invention has significantly improved flame retardant properties, tensile strength, and transparency compared to ordinary epoxy resin. In contrast, the comparative formulation 1#, which uses sodium thioalginate and DOPO-MA without grafting, has lower flame retardant properties, tensile strength, and transparency than the improved formulation.

[0051] As described above, the basic principles, main features, and advantages of the present invention have been well described. The above embodiments and specifications are merely descriptions of preferred embodiments of the present invention, and the present invention is not limited to the above embodiments. Various changes and improvements made to the technical solutions of the present invention by those skilled in the art without departing from the spirit and scope of the present invention should fall within the protection scope defined by the present invention.

Claims

1. A method for improving the transparency of modified flame-retardant epoxy resin composite materials, characterized in that, By weight, the raw materials consist of 100 parts of bisphenol A type epoxy resin, 15-40 parts of DOPO-MA grafted sodium alginate, 10-30 parts of silica powder, 5-7 parts of curing agent and 0.1-1 parts of accelerator; The DOPO-MA-grafted sodium alginate is synthesized from DOPO-MA and sodium thioglycolate, with a molar ratio of DOPO-MA to sodium thioglycolate of 1:1 to 1.

2. The preparation method of DOPO-MA-grafted sodium alginate includes: preparing a sodium alginate solution, activating the carboxyl groups in sodium alginate by EDC and NHS, adding cysteine, maintaining the reaction pH at 4.0-5.0, reacting at room temperature for 3-5 hours, then adjusting the pH to 6.0, continuing the reaction for 0.5-1 hours, and then lyophilizing to obtain mercapto-alginate sodium; dissolving mercapto-alginate sodium in PBS buffer at pH 8, dissolving DOPO-MA in an organic solvent first, then slowly adding it dropwise to the alkaline solution of mercapto-alginate sodium, dialyzing, and lyophilizing to obtain the DOPO-MA-grafted sodium alginate. The additional addition of DOPO-MA-grafted sodium alginate improves the flame retardant properties, tensile strength, and transparency of the modified flame-retardant epoxy resin composite material. Bisphenol A type epoxy resin is heated and then mixed with silica powder and DOPO-MA grafted sodium alginate. After cooling, curing agent and accelerator are added and mixed evenly. Finally, pre-curing and curing are performed to obtain the final product.

2. The method for improving the transparency of modified flame-retardant epoxy resin composite materials according to claim 1, characterized in that, The fineness of the silicon micropowder is not less than 1250 mesh.

3. The method for improving the transparency of modified flame-retardant epoxy resin composite materials according to claim 1, characterized in that, The curing agent is DMP-30.

4. The method for improving the transparency of modified flame-retardant epoxy resin composite materials according to claim 1, characterized in that, The accelerator is selected from at least one of 2-ethyl-4-methylimidazole, 2,4-dimethylimidazole, and 1-methylimidazole.

5. The method for improving the transparency of modified flame-retardant epoxy resin composite materials according to claim 1, characterized in that, The molar ratio of sodium alginate repeating structural units, EDC, and NHS is 1:2:2, and the mass ratio of sodium alginate to cysteine ​​is 1:

2.

6. The method for improving the transparency of modified flame-retardant epoxy resin composite materials according to claim 1, characterized in that, Bisphenol A type epoxy resin is heated to 110~140℃.

7. The method for improving the transparency of modified flame-retardant epoxy resin composite materials according to claim 1, characterized in that, The cooling process involves cooling the temperature to 40-50°C.

8. The method for improving the transparency of modified flame-retardant epoxy resin composite materials according to claim 1, characterized in that, The pre-curing temperature is 60~80℃, and the time is 1~3h.

9. The method for improving the transparency of modified flame-retardant epoxy resin composite materials according to claim 1, characterized in that, The curing temperature is 120~160℃, and the time is 1~3h.

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