Toughening flame-retardant epoxy resin and preparation method thereof

Abstract

The invention provides toughened flame-retardant epoxy resin and a preparation method thereof. The toughened flame-retardant epoxy resin comprises the following components in parts by mass: 100 parts of epoxy resin, 5-20 parts of a curing agent and 0.5-1 part of an accelerant. The curing agent is prepared from phytic acid and organic diamine through a neutralization reaction, and the organic diamine is one of 1, 7-diaminoheptane, 1, 8-diaminooctane, 1, 9-diaminooctane, 1, 10-diaminodecane, 1, 11-diaminoundecane and 1, 12-diaminododecane. The phytic acid-based toughening flame-retardant epoxy resin curing agent is a latent curing agent, has a long curing storage life, can improve the mechanical properties and flame retardancy of epoxy resin, is simple in preparation process and low in energy consumption, and has good economic benefits and market application potential.

Description

Technical Field

[0001] The invention relates to the technical field of epoxy resins, in particular to a toughened flame-retardant epoxy resin and a preparation method thereof. Background Art

[0002] As an important thermosetting resin, epoxy resin has the advantages of excellent mechanical properties, high chemical stability, good electrical properties and processing performance. It has been widely used in adhesives, coatings, electronic components, aerospace and other fields. However, due to its high cross-linking density, epoxy resin is brittle, resulting in poor tensile and impact properties. In addition, as an organic polymer material, epoxy resin has the inherent defect of being flammable. Therefore, toughening and flame retardant modification of epoxy resin has always been a hot research issue.

[0003] At present, people have developed a variety of methods to improve the toughness and flame retardancy of epoxy resins. Adding toughening agents and flame retardants is currently the most common and the lowest cost effective method. However, while adding toughening agents improves the toughness of epoxy resins, it often leads to a decrease in strength, while adding flame retardants has the problem of poor compatibility with the matrix, affecting the mechanical properties.

[0004] Therefore, developing an epoxy resin with both toughening and flame retardant functions, which can achieve both the toughness and flame retardancy of epoxy resin without adding any second phase components, has important practical application value. Summary of the invention

[0005] In view of the above existing problems, the present invention proposes a toughened flame-retardant epoxy resin and a preparation method thereof. The present invention synthesizes a phytic acid-based epoxy resin by a one-step neutralization reaction of phytic acid and an organic diamine. The preparation process is simple, the cost is low, the raw material source is wide, and the industrial application prospect is high. The epoxy resin prepared by the present invention has good toughening and flame retardant effects.

[0006] Studies have found that the introduction of ionic bonds in polymer systems can greatly improve the toughness of materials. This is because when subjected to external forces, the ionic bonds in the system can act as sacrificial bonds, break and dissipate energy to achieve the purpose of toughening. Therefore, it is expected that the toughness and strength of materials can be greatly improved by constructing ionic sacrificial bonds in epoxy resin systems. Phytic acid-based epoxy resin curing agents were synthesized by simple neutralization reactions with phytic acid and linear organic diamines. Phytic acid and organic diamines aggregated into ionic complexes through electrostatic interactions. During the curing process, the complex can dissociate to release phytic acid and organic diamines with active amine groups. Organic diamines and epoxy resins form a three-dimensional cross-linked network structure through ring-opening polymerization, and phytic acid interacts with tertiary amines in the cross-linked network to form ionic sacrificial bonds.

[0007] Phytic acid (PA), also known as inositol hexaphosphate, is a natural organic phosphate compound extracted from plant seeds. Its phosphorus content is as high as 28%, which can be used as an acid source and carbon source for intumescent flame retardants. When it is compounded with a substrate, the high concentration of phosphorus content can effectively inhibit the generation of volatile products and promote the carbonization of the substrate, thereby improving the flame retardant ability of the material. By combining ionic sacrificial bonds with phytic acid, a phytic acid-based toughened flame retardant epoxy resin was developed to solve the mechanical brittleness and flammability defects of epoxy resin.

[0008] To achieve the above object, the present invention provides a toughened flame-retardant epoxy resin, comprising the following components in parts by mass: 100 parts of epoxy resin, 5 to 20 parts of curing agent, and 0.5 to 1 part of accelerator; The curing agent is prepared by neutralization reaction of phytic acid and organic diamine.

[0009] Furthermore, the preparation method of the curing agent is: dissolving an organic diamine in a solvent, dropping a phytic acid solution into the organic diamine solution under stirring at 50-70°C, reacting for 6-12 hours, then filtering to remove the solvent, and vacuum drying the obtained solid at 50-70°C for 8 hours.

[0010] Furthermore, the organic diamine is a linear organic diamine.

[0011] Furthermore, the linear organic diamine is one of 1,7-diaminoheptane, 1,8-diaminooctane, 1,9-diaminodecane, 1,10-diaminodecane, 1,11-diaminoundecane and 1,12-diaminododecane.

[0012] Furthermore, the solvent is one of ethanol, toluene, acetonitrile and N,N-dimethylformamide.

[0013] Furthermore, the reaction molar ratio of the phytic acid to the organic diamine is 1:6-12.

[0014] Furthermore, the accelerator is one of imidazole, 2-methylimidazole, 2-ethylimidazole, 2-phenylimidazole and 2-ethyl-4-methylimidazole.

[0015] The present invention also provides a method for preparing the toughened flame-retardant epoxy resin mentioned above, comprising adding epoxy resin, curing agent and accelerator into a container in a weight ratio, heating to 110-130° C. and stirring for 20-40 minutes to obtain a uniform solution; then pouring the epoxy resin into a tetrafluoroethylene mold, placing the mold in a vacuum box for degassing for 8-12 minutes, placing the mold in a blast oven, curing at 150-160° C. for 1-3 hours, and post-curing at 180-190° C. for 1-2 hours.

[0016] The present invention has the following beneficial effects: 1. The present invention provides a toughened flame-retardant epoxy resin having excellent toughening and flame-retardant effects. The curing agent in the present invention is prepared by neutralization reaction of phytic acid and organic diamine. The toughness of the epoxy resin is improved by the curing agent, and the concept of ionic sacrificial bonds is proposed. The toughening mechanism is as follows: the ionic bonds in the curing agent are introduced into the epoxy resin matrix with the cross-linking reaction of the amino group and the epoxy group. Since the bond energy of the ionic bond is lower than that of the covalent bond, when the epoxy resin is subjected to stress, the ionic bond will break as a sacrificial bond, dissipating energy and thus improving the toughness and strength of the material. Because phytic acid contains phosphoric acid, it has flame retardant ability.

[0017] 2. The present invention provides a toughened flame-retardant epoxy resin, which uses phytic acid and linear organic diamine to react to form a complex, and has a good toughening effect. Because linear amine molecules have better flexibility, compared with amines containing aromatic rings, the synthesized curing agent can give the epoxy resin cross-linked network better mobility and lower rigidity, and the toughening effect is better.

[0018] 3. In addition to the synthetic phytic acid-based curing agent, the toughened flame-retardant epoxy resin provided by the present invention also contains imidazole substances. The imidazole substances can undergo addition reaction with the epoxy resin through the secondary amine and tertiary amine groups in their structures, and at the same time act as a catalyst for anionic polymerization, thereby promoting the curing of the epoxy resin and greatly reducing the curing temperature of the epoxy resin.

[0019] 4. The toughened flame-retardant epoxy resin provided by the present invention is environmentally friendly, low-cost, and has a wide range of raw material sources. The present invention uses a simple one-step neutralization reaction, and the preparation method is simple and easy, with low equipment requirements, and is easier to be applied in industrial large-scale production.

[0020] In addition to the above-described purposes, features and advantages, the present invention has other purposes, features and advantages. The present invention will be further described in detail with reference to the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] The drawings constituting a part of this application are used to provide a further understanding of the present invention. The exemplary embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute an improper limitation of the present invention. In the drawings: Figure 1 This is an infrared spectrum of the phytic acid-based toughened flame-retardant epoxy resin curing agent prepared in Example 1; Figure 2 This is the thermogravimetric diagram of the phytic acid-based toughened flame-retardant epoxy resin curing agent prepared in Example 1; Figure 3 The tensile stress-strain comparison curves of the epoxy resins prepared in Example 1 and Comparative Example 1 are shown; Figure 4The bending stress-strain comparison curve of the epoxy resin prepared in Example 1 and Comparative Example 1 is shown. DETAILED DESCRIPTION

[0022] The embodiments of the present invention are described in detail below with reference to the accompanying drawings, but the present invention can be implemented in many different ways as defined and covered by the claims.

[0023] The present application relates to the technical field of epoxy resin curing agents, and specifically discloses a toughened flame-retardant epoxy resin, comprising the following components in parts by mass: 100 parts of epoxy resin, 5 to 20 parts of curing agent, and 0.5 to 1 part of accelerator.

[0024] The curing agent is prepared by neutralization reaction of phytic acid and an organic diamine, and the synthesis process is shown in Formula 1, wherein the organic diamine is one of 1,7-diaminoheptane, 1,8-diaminooctane, 1,9-diaminoarbane, 1,10-diaminodecane, 1,11-diaminoundecane and 1,12-diaminododecane.

[0025] The reaction equation is as follows: .

[0026] Embodiment 1: A method for preparing a toughened flame-retardant epoxy resin comprises the following steps: Step 1: Dissolve 1,10-diaminodecane (21.32 g, 0.12 mol) in 400 ml of ethanol, then slowly add phytic acid solution (9.43 g, 0.01 mol) under stirring at 60 °C, react for 6 h, then filter to remove the solvent, and vacuum dry the obtained solid at 60 °C for 8 h to obtain a phytic acid-based toughened flame-retardant epoxy resin curing agent.

[0027] Step 2: Weigh 100 parts of epoxy resin into a beaker, add 5 parts of the phytic acid-based toughened flame-retardant epoxy resin curing agent prepared in step 1 and 0.5 parts of 2-methylimidazole, heat to 120 °C and stir for 30 min to obtain a uniform solution. Then pour the epoxy resin into a tetrafluoroethylene mold, place it in a vacuum box for degassing for 10 min, put it in a blast oven, cure it at 160 °C for 2 h, and post-cure it at 180 °C for 2 h.

[0028] Embodiment 2: A method for preparing a toughened flame-retardant epoxy resin comprises the following steps:

[0029] Step 1: Dissolve 1,10-diaminodecane (15.51 g, 0.09 mol) in 300 ml of acetonitrile, then slowly add phytic acid solution (9.43 g, 0.01 mol) under stirring at 60 °C, react for 12 h, then filter to remove the solvent, and vacuum dry the obtained solid at 60 °C for 8 h to obtain a phytic acid-based toughened flame-retardant epoxy resin curing agent.

[0030] Step 2: Weigh 100 parts of epoxy resin into a beaker, add 10 parts of the phytic acid-based toughened flame-retardant epoxy resin curing agent prepared in step 1 and 0.5 parts of 2-phenylimidazole, heat to 120 °C and stir for 30 min to obtain a uniform solution. Then pour the epoxy resin into a tetrafluoroethylene mold, place it in a vacuum box for degassing for 10 min, put it in a blast oven, cure it at 160 °C for 2 h, and post-cure it at 180 °C for 2 h.

[0031] Embodiment 3: A method for preparing a toughened flame-retardant epoxy resin comprises the following steps: Step 1: Dissolve 1,10-diaminodecane (10.66 g, 0.06 mol) in 200 ml toluene, then slowly add phytic acid solution (9.43 g, 0.01 mol) under stirring at 60 °C, react for 6 h, then filter to remove the solvent, and vacuum dry the obtained solid at 60 °C for 8 h to obtain a phytic acid-based toughened flame-retardant epoxy resin curing agent.

[0032] Step 2: Weigh 100 parts of epoxy resin into a beaker, add 15 parts of the phytic acid-based toughened flame-retardant epoxy resin curing agent prepared in step 1 and 1 part of 2-methylimidazole, heat to 120 °C and stir for 30 min to obtain a uniform solution. Then pour the epoxy resin into a tetrafluoroethylene mold, place it in a vacuum box for degassing for 10 min, put it in a forced air oven, cure it at 160 °C for 2 h, and post-cure it at 180 °C for 2 h.

[0033] Comparative Example 1 (curing agent directly uses organic diamine) Weigh 100 parts of epoxy resin into a beaker, add 5 parts of 1,10-diaminodecane and 0.5 parts of 2-methylimidazole, heat to 120 °C and stir for 30 min to obtain a uniform solution. Then pour the epoxy resin into a tetrafluoroethylene mold, place it in a vacuum box for degassing for 10 min, put it in a forced air oven, cure it at 160 °C for 2 h, and post-cure it at 180 °C for 2 h.

[0034] Comparative Example 2 (too little amount of organic diamine) The difference between Comparative Example 2 and Example 1 is that in step 1, the amount of 1,10-diaminodecane used is 10.66 g, and the remaining steps are the same as Example 1.

[0035] Comparative Example 3 (the organic diamine is an amine containing an aromatic ring) The difference between Comparative Example 3 and Example 1 is that in step 1, an equal mass of p-phenylenediamine is used instead of 1,10-diaminodecane, and the remaining steps are the same as in Example 1.

[0036] Comparative Example 4 (containing no imidazole substances) The difference between Comparative Example 4 and Example 1 is that in step 2, no 2-phenylimidazole is added, that is, the added amount is 0, and the remaining steps are the same as Example 1.

[0037] Figure 1 This is the infrared spectrum of the phytic acid-based toughened flame-retardant epoxy resin curing agent prepared in Example 1. Figure 1 It can be seen that 2400 cm -1 The characteristic peak of (P=O)-OH at 3329 cm -1 The peaks at 1554 and 1075 cm-1 were assigned to the stretching vibration of NH in 1,10-diaminodecane. In the synthetic product, the characteristic peaks of (P=O)-OH and NH disappeared, and the new peaks at 1554 and 1075 cm-1 were -1 NH 3+ and PO3 2- , which indicates that a neutralization reaction occurred between phytic acid and 1,10-diaminodecane, and the phytic acid-based toughened flame-retardant epoxy resin curing agent was successfully synthesized.

[0038] Figure 2 The thermogravimetric diagram of the phytic acid-based toughened flame-retardant epoxy resin curing agent prepared in Example 1. Figure 2 It can be seen that the phytic acid-based toughened flame-retardant epoxy resin curing agent has two maximum degradation rates at 227 ℃ and 399 ℃ respectively; the first degradation is caused by the cleavage of the ionic bond between phytic acid and 1,10-diaminodecane and the dehydration reaction, and the second degradation is caused by the catalytic carbonization of phytic acid, which releases substances such as pyrophosphoric acid and polyphosphoric acid, leading to further degradation of the product.

[0039] Figure 3 This is a tensile stress-strain comparison curve of the epoxy resin obtained by comparative example 1 and example 1. It can be found that the curing agent obtained by complexing 1,10-diaminodecane with phytic acid has excellent toughening and strengthening effects on epoxy resin. Compared with the epoxy resin cured by 1,10-diaminodecane, the epoxy resin cured by the phytic acid-based curing agent has been significantly improved in tensile strength and elongation at break. Figure 4 It is a bending stress-strain comparison curve of the epoxy resin prepared in comparative example 1 and example 1, which also shows similar performance, and the bending strength and elongation at break are greatly improved.

[0040] The mechanical properties and limiting oxygen index of Example 1 and Comparative Examples 1-4 were tested, and the experimental results are shown in Table 1.

[0041] Table 1: Performance comparison between comparative example and embodiment 4 , It can be seen from Table 1 that compared with the epoxy resin in which 1,10-diaminodecane is directly used as a curing agent (i.e., Comparative Example 1), the performance of the epoxy resin cured by the phytic acid-based toughened flame-retardant epoxy resin curing agent (i.e., Example 1) in terms of tensile toughness, bending toughness and oxygen index has been comprehensively improved. This shows that the synthesized phytic acid-based curing agent can effectively improve the mechanical and flame retardant properties of the epoxy resin. When the amount of organic diamine used is too low, such as in Comparative Example 2, this will result in a low content of amine groups in the synthesized curing agent, poor curing performance for the epoxy resin, and a decrease in mechanical strength compared to Example 1. The oxygen index in Comparative Example 2 has increased because the content of phytic acid components in the synthesized curing agent has increased, so the flame retardant ability has also increased. If a rigid aromatic amine is used instead of aliphatic amine to prepare a curing agent, due to the greater rigidity of the aromatic ring and the weaker molecular mobility, this will cause the cured epoxy resin to become more brittle and the mechanics to deteriorate. As shown in Comparative Example 3, the epoxy resin is cured with a phytic acid-based curing agent prepared with p-phenylenediamine, which results in a significant decrease in the tensile toughness and bending toughness of the epoxy resin, and does not have a toughening effect. If imidazole accelerators are not added to the curing system, the curing temperature of the epoxy resin will increase, which will lead to incomplete curing and affect the mechanical properties. For example, no imidazole substances are added in Comparative Example 4, which results in the mechanical properties of the prepared epoxy resin being reduced compared to Example 1. The all-biobased greases prepared in Examples 2 and 3 have similar properties to those prepared in Example 1, and will not be repeated here.

[0042] In summary, a toughened flame-retardant epoxy resin is provided, which has excellent toughening and flame retardant effects. The curing agent in the present invention is prepared by neutralization reaction of phytic acid and organic diamine, and the toughness of epoxy resin is improved by the curing agent, and the concept of ionic sacrificial bond is proposed. Its toughening mechanism is as follows: the ionic bond in the curing agent is introduced into the epoxy resin matrix along with the cross-linking reaction of the amino group and the epoxy group. Since the bond energy of the ionic bond is lower than that of the covalent bond, when the epoxy resin is subjected to stress, the ionic bond will break as a sacrificial bond, dissipate energy and thus improve the toughness and strength of the material. Because phytic acid contains phosphoric acid, it has flame retardant ability. The present invention uses phytic acid to react with linear organic diamine to form a complex, which has a good toughening effect. Because linear amine molecules have better flexibility, compared with amines containing aromatic rings, the synthesized curing agent can give the epoxy resin cross-linked network better mobility and lower rigidity, and the toughening effect is better. At the same time, in addition to the synthetic phytic acid-based curing agent, the toughened flame-retardant epoxy resin provided by the present invention also contains imidazole substances. The imidazole substances can undergo addition reactions with the epoxy resin through the secondary amine and tertiary amine groups in their structures, and at the same time act as a catalyst for anionic polymerization, thereby promoting the curing of the epoxy resin and greatly reducing the curing temperature of the epoxy resin.

[0043] In addition, the toughened flame-retardant epoxy resin provided by the present invention is environmentally friendly, low-cost, and has a wide range of raw material sources. The present invention uses a simple one-step neutralization reaction, and the preparation method is simple and easy, with low equipment requirements, and is easier to be industrially mass-produced and applied.

[0044] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. For those skilled in the art, the present invention may have various modifications and variations. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A toughened flame retardant epoxy resin, characterized in that: The composition comprises the following components in parts by weight: 100 parts of epoxy resin, 5 to 20 parts of curing agent, and 0.5 to 1 part of accelerator; The curing agent is prepared by neutralization reaction of phytic acid and organic diamine.

2. A toughened flame retardant epoxy resin according to claim 1, characterized in that: The preparation method of the curing agent is as follows: dissolving an organic diamine in a solvent, dropping a phytic acid solution into the organic diamine solution under stirring at 50-70° C., reacting for 6-12 hours, then filtering to remove the solvent, and vacuum drying the obtained solid at 50-70° C. for 8 hours.

3. A toughened flame retardant epoxy resin according to claim 2, characterized in that: The organic diamine is a linear organic diamine.

4. A toughened flame retardant epoxy resin according to claim 3, characterized in that: The linear organic diamine is one of 1,7-diaminoheptane, 1,8-diaminooctane, 1,9-diaminodecane, 1,10-diaminodecane, 1,11-diaminoundecane and 1,12-diaminododecane.

5. A toughened flame retardant epoxy resin according to claim 2, characterized in that: The solvent is one of ethanol, toluene, acetonitrile and N,N-dimethylformamide.

6. A toughened flame retardant epoxy resin according to claim 2, characterized in that: The reaction molar ratio of the phytic acid to the organic diamine is 1:6-12.

7. A toughened flame retardant epoxy resin according to claim 1, characterized in that: The accelerator is one of imidazole, 2-methylimidazole, 2-ethylimidazole, 2-phenylimidazole and 2-ethyl-4-methylimidazole.

8. A method for preparing a toughened flame-retardant epoxy resin according to any one of claims 1 to 7, characterized in that: Add epoxy resin, curing agent and accelerator into a container in proportion by weight, heat to 110-130°C and stir for 20-40 minutes to obtain a uniform solution; then pour the epoxy resin into a tetrafluoroethylene mold, place it in a vacuum box for degassing for 8-12 minutes, put it in a forced air oven, cure it at 150-160°C for 1-3 hours, and post-cure it at 180-190°C for 1-2 hours.

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