A bio-based reactive flame retardant and its preparation and application in epoxy resin

Abstract

The present invention relates to a bio-based reactive flame retardant and its preparation and application on epoxy resin. The structural formula of the bio-based reactive flame retardant is and / or its preparation method is: (1) DOPO is completely dissolved to obtain a uniform colorless liquid; (2) resveratrol is added to the completely dissolved DOPO, and the yellow powder R-DOPO is obtained by drying after cooling and stratification; (3) R-DOPO and epichlorohydrin are added to a three-necked flask, and a NaOH solution is added dropwise to the three-necked flask to obtain a bio-based reactive flame retardant; the application is: epoxy resin and the bio-based reactive flame retardant are mixed and reacted to prepare a flame-retardant epoxy resin. The bio-based reactive flame retardant of the present invention is a liquid flame retardant, which has good compatibility with an epoxy resin matrix, and the flame-retardant epoxy resin obtained therefrom has a more durable and efficient flame retardant performance, and can avoid adverse effects on mechanical properties.

Description

Technical Field

[0001] The invention belongs to the technical field of epoxy resins and relates to a bio-based reactive flame retardant and a preparation method thereof and an application thereof on epoxy resins. Background Art

[0002] In recent years, epoxy resin has been widely used in coatings, construction, electronics, aviation and other fields due to its excellent chemical resistance, mechanical properties, relatively low curing shrinkage and many other advantages. The oxygen index of ordinary epoxy resin is only about 19.8%, which is a flammable material, thus limiting its application. Therefore, how to improve the flame retardant properties of epoxy resin has attracted widespread attention from researchers.

[0003] The most commonly used methods to improve the flame retardant properties of epoxy resins are divided into additive flame retardant technology and reactive flame retardant technology. Compared with additive flame retardants, reactive flame retardants can give epoxy resins lasting flame retardancy through chemical combinations and avoid adverse effects on mechanical properties. Therefore, the development and application of reactive flame retardants is the direction of flame retardant development. Traditional halogen flame retardants release toxic gases during combustion, causing environmental pollution and health problems. Therefore, the development of halogen-free flame retardant technology is the main trend of current research. The current halogen-free flame retardant is mainly the synergistic effect of phosphorus, nitrogen, silicon, etc., and the synergistic flame retardant mechanism of gas phase and condensed phase is used to modify epoxy resin.

[0004] Patent CN202210660216.5 uses DOPO, salicylaldehyde, and diamine to synthesize a nitrogen-phosphorus flame retardant for epoxy resin. Its application in epoxy resin not only significantly improves its flame retardant properties, but also greatly improves its mechanical properties.

[0005] Patent CN202210723409.0 uses BTDS, DOPO and vanillin derivatives as raw materials, and prepares a biomass flame retardant containing silicon-oxygen bonds and DOPO structures through a two-step method, giving the modified epoxy resin good thermal stability and flame retardant properties.

[0006] Patent CN202210804446.4 uses a diphenylphosphine oxide derivative generated by the reaction of diphenylphosphine oxide (DPO) and a ketone compound as a flame retardant for epoxy resin, which has a PC-OH structure, and ultimately obtains a modified epoxy resin with high flame retardant properties.

[0007] Patent CN202210743729.2 uses vanillin, hexachlorocyclotriphosphazene and melamine as raw materials to synthesize a bio-based flame retardant and smoke suppressant containing vanillin for use in epoxy resin, which can greatly improve the flame retardant effect of epoxy resin and significantly inhibit the release of smoke and toxic and harmful gases.

[0008] Although the above inventions improve the flame retardancy of epoxy resin to varying degrees, the flame retardant finally obtained is a solid powder. The addition of solid flame retardant increases the viscosity of epoxy resin, making it difficult for the resin to infiltrate fabrics such as carbon fiber.

[0009] Therefore, it is necessary to study a liquid reactive flame retardant applied to epoxy resin, so that the flame retardant has good compatibility with the epoxy resin matrix and improves the problem of difficulty in wetting the resin matrix with other fiber fabrics. Summary of the invention

[0010] The purpose of the present invention is to solve the above problems existing in the prior art and to provide a bio-based reactive flame retardant and its preparation and application in epoxy resin.

[0011] To achieve the above object, the technical solution adopted by the present invention is as follows:

[0012] A bio-based reactive flame retardant for epoxy resin, having a structural formula as shown in formula (I) and / or formula (II):

[0013]

[0014] The present invention also provides a method for preparing the bio-based reactive flame retardant applied to epoxy resin as described above, comprising the following steps:

[0015] (1) DOPO (9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide) was added into a three-necked flask, heated and stirred until it was completely dissolved to obtain a uniform colorless liquid;

[0016] (2) adding resveratrol to the completely dissolved DOPO in step (1), controlling the amount of DOPO to be excessive, reacting at 120-160° C. under nitrogen protection to obtain a uniform light yellow liquid, then adding toluene to wash away the excess DOPO, cooling to 100-105° C., separating the layers, taking out the sample and drying it (drying temperature is 80° C.) to obtain a yellow powder R-DOPO;

[0017] (3) Add the R-DOPO obtained in step (2) and epichlorohydrin into a three-necked flask, and add a NaOH solution dropwise into the three-necked flask at a rate of 0.1 to 0.3 ml / min. During the dropping process, stir and heat to 70 to 110° C. to react, thereby obtaining a bio-based reactive flame retardant for epoxy resin.

[0018] As the preferred technical solution:

[0019] In the method for preparing a bio-based reactive flame retardant for epoxy resin as described above, the heating temperature in step (1) is 120 to 160° C., and the stirring speed is 100 to 500 r / min.

[0020] In the above-mentioned method for preparing a bio-based reactive flame retardant for epoxy resin, the molar ratio of DOPO to resveratrol in step (2) is 1.5 to 3.5:1, and the reaction time is 3 to 6 hours.

[0021] In the method for preparing a bio-based reactive flame retardant for epoxy resin as described above, in step (3), the molar ratio of R-DOPO to epichlorohydrin is 1:8-15, the molar ratio of R-DOPO to NaOH is 1:2-5, and the mass fraction of the NaOH solution is 20-40%.

[0022] In the method for preparing a bio-based reactive flame retardant for epoxy resin as described above, the stirring speed in step (3) is 100 to 500 r / min and the reaction time is 3 to 6 h.

[0023] In the above-mentioned method for preparing a bio-based reactive flame retardant for epoxy resin, after the reaction in step (3) is completed, water washing and standing are performed (adding water for washing, pouring into a separating funnel, standing, and taking out the lower layer after stratification).

[0024] In addition, the present invention also provides an application of the bio-based reactive flame retardant applied to epoxy resin as described above, wherein the epoxy resin is mixed with the bio-based reactive flame retardant and then reacted to prepare a flame-retardant epoxy resin.

[0025] As the preferred technical solution:

[0026] As described above, in the application of a bio-based reactive flame retardant applied to epoxy resin, when the phosphorus content in the flame-retardant epoxy resin is 0.56wt%, the limiting oxygen index of the flame-retardant epoxy resin is 34.7%, the UL-94 vertical burning grade is V-0, and it has excellent flame retardant properties.

[0027] The mechanism of the present invention is as follows:

[0028] The present invention utilizes the functional phenolic hydroxyl group and rigid conjugated structure of resveratrol, introduces phosphorus element through double bonds on the one hand, and then utilizes the phenolic hydroxyl group of resveratrol to react with epichlorohydrin on the other hand, thereby introducing epoxy groups, and preparing a bio-based reactive flame retardant applied to epoxy resin. Since it is necessary to ensure that the double bonds of resveratrol are not oxidized under high temperature reaction, and to react with epichlorohydrin at a lower temperature, a two-step method is adopted to prepare a resveratrol-based flame retardant containing DOPO by introducing nitrogen to protect the reaction system from external oxygen interference, and then react with epichlorohydrin to prepare a bio-based reactive flame retardant applied to epoxy resin. Affected by the molecular structure, the reactive flame retardant applied to epoxy resin synthesized in the prior art is mainly a solid flame retardant, and the present invention introduces epichlorohydrin, which improves the flexibility of the molecular chain and reduces the intermolecular force, so the flame retardant is in a liquid state. The flame retardant can not only be added to epoxy resin as a liquid flame retardant, but also can be used as a flame retardant bio-based epoxy resin. Due to the catalytic carbonization of phosphorus and the carbonization of resveratrol itself, the carbon yield of the cured epoxy resin can be effectively improved, thereby achieving the purpose of low flammability.

[0029] Beneficial effects:

[0030] (1) At present, the flame retardant used for epoxy resin is mainly additive flame retardant, but additive flame retardant reduces the inherent performance of epoxy resin while being flame retardant, and its disadvantages such as poor compatibility with the matrix and easy precipitation hinder its further development. The flame retardant prepared by the present invention is a reactive flame retardant. Compared with the additive type, the reactive flame retardant prepared by the present invention does not have precipitation phenomenon, has good compatibility with the resin, has better dispersibility in epoxy resin, can give epoxy resin more durable and efficient flame retardant performance through chemical combination, and avoids adverse effects on mechanical properties.

[0031] (2) At present, the reactive flame retardant used for epoxy resin mainly adopts petroleum-based materials, but the disadvantage of traditional petroleum-based materials being non-renewable has caused problems such as excessive carbon emissions and resource shortages. The bio-based reactive flame retardant prepared by the present invention adopts the bio-based raw material resveratrol. Compared with petroleum-based raw materials, bio-based materials have the advantages of green environmental protection, energy saving and emission reduction, and renewable raw materials. Its sustainability, natural abundance and environmental friendliness have good development prospects.

[0032] (3) At present, the preparation of bio-based reactive flame retardants is still subject to the extraction and refining process of bio-based compounds. Compared with other bio-based raw materials, the bio-based raw material used in the present invention, namely resveratrol, is abundant in nature and can be easily produced from plant species such as grapevines, pine trees and beans. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] Figure 1 is the reaction equation of DOPO and resveratrol;

[0034] Figure 2 is the reaction equation of R-DOPO and epichlorohydrin. DETAILED DESCRIPTION

[0035] The present invention will be further described below in conjunction with specific embodiments. It should be understood that these embodiments are only used to illustrate the present invention and are not intended to limit the scope of the present invention. In addition, it should be understood that after reading the content taught by the present invention, those skilled in the art can make various changes or modifications to the present invention, and these equivalent forms fall within the scope limited by the appended claims of the application equally.

[0036] The testing method adopted by the present invention is as follows:

[0037] (1) Limiting oxygen index: tested according to ASTM D2863 using HC-2 oxygen index instrument (Nanjing Jiangning Instrument Factory, China);

[0038] (2) UL-94 vertical burning rating: tested according to ASTM D3801 using a JT-HVR5455 burning tester (Jinju Testing Instrument Co., Ltd., Taiwan, China).

[0039] Example 1

[0040] A method for preparing a bio-based reactive flame retardant comprises the following steps:

[0041] (1) DOPO was added into a three-necked flask and heated (heating temperature was 120°C) and stirred (stirring speed was 500 r / min) until it was completely dissolved to obtain a uniform colorless liquid;

[0042] (2) adding resveratrol to the completely dissolved DOPO in step (1), controlling the molar ratio of DOPO to resveratrol to be 3.5:1, and reacting at 120° C. for 6 h under nitrogen protection to obtain a uniform light yellow liquid, the reaction equation of which is as follows: Figure 1 As shown, toluene was then added to wash away the excess DOPO, the temperature was lowered to 105°C, the sample was taken out and dried (drying temperature was 80°C), and yellow powder R-DOPO was obtained;

[0043] (3) Add the R-DOPO and epichlorohydrin obtained in step (2) into a three-necked flask, and drop a 40% NaOH solution into the three-necked flask at a rate of 0.1 ml / min. During the dropwise addition, stir (stirring speed is 500 r / min), raise the temperature to 70° C., and react for 6 hours. Finally, add water for washing, pour into a separating funnel, let stand, and take out the lower layer after stratification to obtain a bio-based reactive flame retardant.

[0044] Among them, the reaction equation of R-DOPO and epichlorohydrin is as follows Figure 2 As shown, the molar ratio of R-DOPO to epichlorohydrin is 1:15, and the molar ratio of R-DOPO to NaOH is 1:2.

[0045] The prepared bio-based reactive flame retardant has the structural formulas shown in formula (I) and formula (II):

[0046]

[0047] The bio-based reactive flame retardant prepared above is used to prepare a flame-retardant epoxy resin, specifically: first, the prepared bio-based reactive flame retardant and DDM (4,4'-diaminodiphenylmethane) are added to DGEBA (bisphenol A diglycidyl ether) (the mass of DGEBA and DDM is 100:25), and uniformly dispersed at 80°C by mechanical stirring to obtain a uniform mixture; then the mixture is transferred to a mold, cured at 80°C for 2 hours, and then cured at 150°C for 2 hours; finally, the sample is cooled to room temperature and taken out from the mold to obtain a flame-retardant epoxy resin. The phosphorus content in the prepared flame-retardant epoxy resin is 0.56wt%, the limiting oxygen index of the flame-retardant epoxy resin is 35.1%, and the UL-94 vertical combustion rating is V-0.

[0048] Example 2

[0049] A method for preparing a bio-based reactive flame retardant comprises the following steps:

[0050] (1) DOPO was added into a three-necked flask and heated (heating temperature was 130°C) and stirred (stirring speed was 330 r / min) until it was completely dissolved to obtain a uniform colorless liquid;

[0051] (2) adding resveratrol to the completely dissolved DOPO in step (1), controlling the molar ratio of DOPO to resveratrol to be 2.3:1, reacting at 135° C. for 4 h under nitrogen protection to obtain a uniform light yellow liquid, then adding toluene to wash away excess DOPO, cooling to 100° C., separating layers, taking out the sample and drying it (drying temperature is 80° C.), to obtain a yellow powder R-DOPO;

[0052] (3) Add the R-DOPO and epichlorohydrin obtained in step (2) into a three-necked flask, and drop a 20% NaOH solution into the three-necked flask at a rate of 0.26 ml / min. During the dropwise addition, stir (stirring speed is 330 r / min), raise the temperature to 85° C., and react for 4 h. Finally, add water for washing, pour into a separating funnel, let stand, and take out the lower layer after stratification to obtain a bio-based reactive flame retardant.

[0053] The molar ratio of R-DOPO to epichlorohydrin is 1:12, and the molar ratio of R-DOPO to NaOH is 1:3.

[0054] The prepared bio-based reactive flame retardant has the structural formulas shown in formula (I) and formula (II):

[0055]

[0056] The bio-based reactive flame retardant prepared above is used to prepare a flame-retardant epoxy resin, specifically: first, the prepared bio-based reactive flame retardant and DDM are added to DGEBA (the mass of DGEBA and DDM is 100:25), and uniformly dispersed at 80°C by mechanical stirring to obtain a uniform mixture; then the mixture is transferred to a mold, cured at 80°C for 2 hours, and then cured at 150°C for 2 hours; finally, the sample is cooled to room temperature and taken out of the mold to obtain a flame-retardant epoxy resin. The prepared flame-retardant epoxy resin has a phosphorus content of 0.56wt%, a limiting oxygen index of 34.9%, and a UL-94 vertical combustion rating of V-0, and has excellent flame retardant properties.

[0057] Example 3

[0058] A method for preparing a bio-based reactive flame retardant comprises the following steps:

[0059] (1) DOPO was added into a three-necked flask and heated (heating temperature was 150°C) and stirred (stirring speed was 400 r / min) until it was completely dissolved to obtain a uniform colorless liquid;

[0060] (2) adding resveratrol to the completely dissolved DOPO in step (1), controlling the molar ratio of DOPO to resveratrol to be 1.8:1, reacting at 150° C. for 3.5 h under nitrogen protection to obtain a uniform light yellow liquid, then adding toluene to wash away excess DOPO, cooling to 102° C., separating the layers, taking out the sample and drying it (drying temperature is 80° C.), to obtain a yellow powder R-DOPO;

[0061] (3) Add the R-DOPO and epichlorohydrin obtained in step (2) into a three-necked flask, and dropwise add a 30% NaOH solution into the three-necked flask at a rate of 0.24 ml / min. During the dropwise addition, stir (stirring speed is 100 r / min), raise the temperature to 100° C., and react for 5 h. Finally, add water for washing, pour into a separating funnel, let stand, and take out the lower layer after stratification to obtain a bio-based reactive flame retardant.

[0062] The molar ratio of R-DOPO to epichlorohydrin is 1:13, and the molar ratio of R-DOPO to NaOH is 1:3.5.

[0063] The prepared bio-based reactive flame retardant has the structural formulas shown in formula (I) and formula (II):

[0064]

[0065] The bio-based reactive flame retardant prepared above is used to prepare a flame-retardant epoxy resin, specifically: first, the prepared bio-based reactive flame retardant and DDM are added to DGEBA (the mass of DGEBA and DDM is 100:25), and uniformly dispersed at 80°C by mechanical stirring to obtain a uniform mixture; then the mixture is transferred to a mold, cured at 80°C for 2 hours, and then cured at 150°C for 2 hours; finally, the sample is cooled to room temperature and taken out of the mold to obtain a flame-retardant epoxy resin. The prepared flame-retardant epoxy resin has a phosphorus content of 0.56wt%, a limiting oxygen index of 34.7%, and a UL-94 vertical combustion rating of V-0, and has excellent flame retardant properties.

[0066] Example 4

[0067] A method for preparing a bio-based reactive flame retardant comprises the following steps:

[0068] (1) DOPO was added into a three-necked flask and heated (heating temperature was 160°C) and stirred (stirring speed was 100 r / min) until it was completely dissolved to obtain a uniform colorless liquid;

[0069] (2) adding resveratrol to the completely dissolved DOPO in step (1), controlling the molar ratio of DOPO to resveratrol to be 1.5:1, reacting at 160° C. for 3 h under nitrogen protection to obtain a uniform light yellow liquid, then adding toluene to wash away excess DOPO, cooling to 100° C., separating layers, taking out the sample and drying it (drying temperature is 80° C.), to obtain a yellow powder R-DOPO;

[0070] (3) Add the R-DOPO and epichlorohydrin obtained in step (2) into a three-necked flask, and drop a NaOH solution (mass fraction of 25%) into the three-necked flask at a rate of 0.3 ml / min. During the dropwise addition, stir (stirring speed of 450 r / min), raise the temperature to 110° C. and react for 3 h. Finally, add water for washing, pour into a separatory funnel, let stand, and take out the lower layer after stratification to obtain a bio-based reactive flame retardant;

[0071] The molar ratio of R-DOPO to epichlorohydrin is 1:8, and the molar ratio of R-DOPO to NaOH is 1:5.

[0072] The prepared bio-based reactive flame retardant has the structural formulas shown in formula (I) and formula (II):

[0073]

[0074] The bio-based reactive flame retardant prepared above is used to prepare a flame-retardant epoxy resin, specifically: first, the prepared bio-based reactive flame retardant and DDM are added to DGEBA (the mass of DGEBA and DDM is 100:25), and uniformly dispersed at 80°C by mechanical stirring to obtain a uniform mixture; then the mixture is transferred to a mold, cured at 80°C for 2 hours, and then cured at 150°C for 2 hours; finally, the sample is cooled to room temperature and taken out of the mold to obtain a flame-retardant epoxy resin. When the phosphorus content in the prepared flame-retardant epoxy resin is 0.56wt%, the limiting oxygen index of the flame-retardant epoxy resin is 34.5%, and the UL-94 vertical combustion grade is V-0, which has excellent flame retardant properties.

Claims

1. A bio-based reactive flame retardant for epoxy resin, characterized in that Having the structural formula shown in formula (I) and / or formula (II):

2. The method for preparing a bio-based reactive flame retardant for epoxy resin according to claim 1, characterized in that The steps include: (1) Add DOPO into a three-necked flask, heat and stir until it is completely dissolved to obtain a uniform colorless liquid; (2) adding resveratrol to the completely dissolved DOPO in step (1), controlling the amount of DOPO to be excessive, reacting at 120-160° C. under nitrogen protection to obtain a uniform light yellow liquid, then adding toluene to wash away the excess DOPO, cooling to 100-105° C., separating the layers, taking out the sample, and drying it to obtain a yellow powder R-DOPO; wherein the structure of the yellow powder R-DOPO is: (3) Add the R-DOPO obtained in step (2) and epichlorohydrin into a three-necked flask, and add a NaOH solution dropwise into the three-necked flask at a rate of 0.1 to 0.3 ml / min. During the dropping process, stir and heat to 70 to 110° C. to react, thereby obtaining a bio-based reactive flame retardant for epoxy resin.

3. The method for preparing a bio-based reactive flame retardant for epoxy resin according to claim 2, characterized in that: In step (1), the heating temperature is 120-160° C., and the stirring speed is 100-500 r / min.

4. The method for preparing a bio-based reactive flame retardant for epoxy resin according to claim 2, characterized in that: In step (2), the molar ratio of DOPO to resveratrol is 1.5 to 3.5:1, and the reaction time is 3 to 6 hours.

5. The method for preparing a bio-based reactive flame retardant for epoxy resin according to claim 2, characterized in that: In step (3), the molar ratio of R-DOPO to epichlorohydrin is 1:8-15, the molar ratio of R-DOPO to NaOH is 1:2-5, and the mass fraction of the NaOH solution is 20-40%.

6. The method for preparing a bio-based reactive flame retardant for epoxy resin according to claim 2, characterized in that: The stirring speed in step (3) is 100 to 500 r / min, and the reaction time is 3 to 6 h.

7. The method for preparing a bio-based reactive flame retardant for epoxy resin according to claim 2, characterized in that: After the reaction in step (3) is completed, the mixture is washed with water and allowed to stand.

8. The use of a bio-based reactive flame retardant for epoxy resin according to claim 1, characterized in that: The epoxy resin and the bio-based reactive flame retardant are mixed and reacted to prepare the flame-retardant epoxy resin.

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