Inorganic nanoparticle and modified curing agent synergistic flame-retardant epoxy resin and preparation method thereof

Abstract

The invention provides inorganic nanoparticle and modified curing agent synergistic flame-retardant epoxy resin which comprises the following components in parts by mass: 100 parts of epoxy resin, 1-4 parts of inorganic nanoparticles and 2-3 parts of a modified amine curing agent, the modified amine curing agent is obtained by embedding a modifier into an amine curing agent molecular skeleton; the inorganic nano particles are secondary modified nano magnesium hydroxide. The preparation method comprises the following steps: pre-dispersing the inorganic nanoparticles and the modified amine curing agent, uniformly mixing with the epoxy resin at 90-100 DEG C after uniformly dispersing, uniformly stirring, carrying out vacuum defoaming, curing at 75-85 DEG C for 1-5 hours, then curing at 95-125 DEG C for 1-3 hours, and thus obtaining the synergistic flame-retardant epoxy resin. According to the synergistic flame-retardant epoxy resin and the preparation method thereof, phosphorus / nitrogen elements are introduced into the amine curing agent and are subjected to synergistic flame retardance with the secondary modified magnesium hydroxide, and the flame retardance can reach the V-0 level only by a small phosphorus / nitrogen adding amount; in addition, the mechanical strength of the epoxy resin can be further enhanced.

Description

Technical Field

[0001] This invention belongs to the field of flame-retardant epoxy resins, specifically relating to an epoxy resin in which modified magnesium hydroxide inorganic nanoparticles and phosphorus / nitrogen modified curing agents synergistically provide flame retardancy, and its preparation method. Background Technology

[0002] Epoxy resin (EP) refers to linear oligomers containing two or more epoxy groups. Due to the presence of hydroxyl, ether bonds, and epoxy groups, it forms a cross-linked three-dimensional network structure after reacting with a curing agent. This results in excellent corrosion resistance, mechanical properties, good insulation, and a low coefficient of thermal expansion, making it widely used in coatings, adhesives, composite materials, and electronics. However, under very high temperatures and open flame ignition, epoxy resin can burn rapidly in air, releasing heat quickly during combustion. The flame spreads rapidly and is difficult to extinguish, while also producing large amounts of smoke and toxic gases. Therefore, there is a significant flammability hazard when using epoxy resin in finished products. Improving the flame-retardant properties of epoxy resin is therefore of urgent practical significance.

[0003] Magnesium hydroxide (MDH), as a halogen-free flame retardant, can be used for flame retardancy of epoxy resins. Magnesium hydroxide undergoes endothermic decomposition at temperatures around 340–430°C. The decomposition products dilute the oxygen concentration and generate metal oxides, forming an inorganic protective barrier that blocks heat transfer. However, magnesium hydroxide particles have poor compatibility with polymers, negatively impacting interfacial interactions and reducing the flame retardant efficiency and mechanical strength of the product. Therefore, functional modification of magnesium hydroxide particles is necessary to overcome these weaknesses. CN119039736A uses ATC-DOPO / MDH as a flame retardant for epoxy resins, combining the advantages of phosphorus-containing flame retardants and the inorganic flame retardant MDH to improve the flame retardant performance of epoxy resins. However, the formulation includes a large amount of curing agent and flame retardant, which not only increases costs but also hinders the improvement of epoxy resin strength.

[0004] To further improve the flame retardant properties and mechanical strength of epoxy resin, this invention provides an epoxy resin with synergistic flame retardancy by modified magnesium hydroxide inorganic nanoparticles and phosphorus / nitrogen modified amine curing agents, and its preparation method. Summary of the Invention

[0005] This invention provides a flame-retardant epoxy resin synergistically composed of inorganic nanoparticles and a modified curing agent, comprising the following components by mass: 100 parts epoxy resin, 1-4 parts inorganic nanoparticles, and 2-3 parts modified amine curing agent. The modified amine curing agent is obtained by embedding the modifier into the molecular skeleton of the amine curing agent; the modifier is at least one of phosphorus-containing modifier or nitrogen-containing modifier; The phosphorus-containing modifier comprises at least one of phosphate esters, phosphonates, DOPO, or DOPO derivatives; The nitrogen-containing modifier comprises at least one of triazine, imidazole, or piperazine compounds.

[0006] Preferably, the phosphorus-containing modifier comprises at least one of DOPO or a DOPO derivative, the nitrogen-containing modifier is the product of melamine and formaldehyde reacting at a mass ratio of 1:(2~3) at 75~85°C for 0.5~2h, and the amine curing agent comprises at least one of m-phenylenediamine, diethylenetriamine, 3,4'-diaminodiphenylmethane, or 3,3'-diaminodiphenyl sulfone.

[0007] Preferably, when using a phosphorus-containing modifier to modify the curing agent, the modification method is as follows: mix the phosphorus-containing modifier, the amine curing agent and ethanol, react at 70~90℃ under inert gas protection for 5~7h, and remove impurities to obtain a phosphorus-containing curing agent with a phosphorus content of 8~15wt%; the mass ratio of the phosphorus-containing modifier to the amine curing agent is 1:(0.1~0.5). Preferably, when the curing agent is modified with a nitrogen-containing modifier, the modification method is as follows: the nitrogen-containing modifier, the amine curing agent and ethanol are mixed and reacted at 80~100℃ for 3~5h. During the reaction, the pH of the system is controlled at 8~10, preferably pH=9.5. After removing impurities, a nitrogen-containing curing agent with a nitrogen content of 10~30wt% is obtained; the mass ratio of melamine to amine curing agent is 1:(1~3).

[0008] Preferably, the inorganic nanoparticles are secondary modified nano-magnesium hydroxide, and the preparation steps are as follows: (1) Primary modification: The dried magnesium hydroxide nanoparticles are dispersed in an ethanol aqueous solution to obtain a magnesium hydroxide dispersion. Then, a coupling agent is added, and the mixture is reacted at 70~120℃ for 1~3h. After drying and ball milling, the primary modified nano magnesium hydroxide is obtained. (2) Secondary modification: The primary modified nano magnesium hydroxide obtained in step (1) is dispersed in an ethanol aqueous solution, methyl methacrylate and an initiator are added, and the reaction is carried out at 80~100℃ for 5~8h under inert gas protection to obtain secondary modified nano magnesium hydroxide.

[0009] Preferably, the coupling agent in step (1) is at least one of γ-aminopropyltriethoxysilane, γ-methacryloyloxypropyltrimethoxysilane, glyceryl trioleate or isopropyltrioleyloxytitanate.

[0010] Preferably, the mass ratio of magnesium hydroxide nanoparticles to coupling agent in step (1) is 1:(0.01~0.1).

[0011] Preferably, the initiator in step (2) is at least one of azobisisobutyronitrile or azobisisoheptanenitrile.

[0012] Preferably, the mass ratio of methyl methacrylate to initiator in step (2) is 1:(0.01~0.03).

[0013] Preferably, in step (2), the mass ratio of the primary modified nano-magnesium hydroxide to methyl methacrylate is 1:(1.5~3), more preferably 1:2.

[0014] Preferably, the concentration of the ethanol aqueous solution in steps (1) and (2) is 90-95 wt%, more preferably 95 wt%; the concentration of the magnesium hydroxide dispersion in step (1) is 0.4-2 wt%.

[0015] The present invention also provides a method for preparing a flame-retardant epoxy resin synergistically composed of inorganic nanoparticles and modified curing agents. The preparation steps are as follows: inorganic nanoparticles and modified amine curing agents are pre-dispersed, and after being dispersed evenly, they are mixed evenly with epoxy resin at 90~100℃. After stirring evenly, the mixture is degassed under vacuum, cured at 75~85℃ for 1~5h, and then cured at 95~125℃ for 1~3h to obtain a synergistic flame-retardant epoxy resin.

[0016] The beneficial effects of this invention are as follows: 1. Using nano-inorganic particles as fillers, halogen-free flame-retardant epoxy resin materials are prepared, which are more environmentally friendly and sustainable. The magnesium hydroxide nanoparticles used in this invention have better dispersibility after two modifications. At the same time, the modified magnesium hydroxide and the modified curing agent are pre-dispersed, which helps to improve the dispersibility in epoxy resin.

[0017] 2. This design uses amine curing agents and introduces phosphorus / nitrogen elements into the curing agents to synergistically retard with the modified magnesium hydroxide nanofiller. Only a small amount of phosphorus / nitrogen is needed to achieve the flame retardant performance of V-0 level, and the mechanical strength of epoxy resin is also greatly improved, while effectively reducing the cost issues in actual production applications. Detailed Implementation

[0018] The embodiments of the present invention will be described in detail below with reference to the examples. The following examples are only used to illustrate the present invention and should not be regarded as limiting the scope of the present invention.

[0019] Example 1 (1) Modification of inorganic nanoparticles Weigh 25g of untreated magnesium hydroxide nanoparticles and dry them in a vacuum drying oven at 105℃ for 2h. Then, add them to a 5000mL 95wt% ethanol aqueous solution system and sonicate for 1h (power 300W). Then, add 1.25g of γ-methacryloyloxypropyltrimethoxysilane (KH570) and continue sonicating for 30min. Then, react in an oil bath at 120℃ for 2h. After the reaction is complete, filter the solution, wash it three times with deionized water, and dry it in a vacuum oven for 5h. Finally, ball mill it at 300r / min for 5h to obtain the first-modified magnesium hydroxide particles.

[0020] Weigh 10.5g of magnesium hydroxide powder obtained from the first modification and disperse it in 50mL of 95wt% ethanol aqueous solution. Add 21g of methyl methacrylate, purge with nitrogen as a protective gas, and add 0.315g of azobisisobutyronitrile as an initiator. React at 95℃ for 7.5h, then filter, dry, and ball mill at 300r / min for 5h to obtain the second-modified magnesium hydroxide sample.

[0021] (2) Modification with phosphorus-amine curing agents Weigh 50g of DOPO and 10g of 3,3'-diaminodiphenyl sulfone and dissolve them in 200mL of 95wt% ethanol aqueous solution. Stir mechanically for 15min. Place the well-mixed solution into a reaction apparatus, heat to 80℃, and react for 6h under nitrogen protection. Remove the organic solvent by vacuum distillation to obtain a modified curing agent with a phosphorus content of 11.6wt%.

[0022] (3) Preparation of flame-retardant epoxy resin Weigh 11.4g of the magnesium hydroxide powder nanofiller obtained from the secondary modification in step (1) and add it to 100mL of 95wt% ethanol aqueous solution. Sonicate for 30min (300W). Weigh 13.5g of the modified curing agent obtained in step (2) and add it to the well dispersed nanofiller solution. Stir at 500r / min for 20min. Vacuum dry to obtain the pre-dispersed curing agent-filler composite.

[0023] The obtained pre-dispersed composite was mixed with 500g of bisphenol A type epoxy resin (E-44), placed in a 90℃ water bath, and stirred at 500r / min for 20min. At this time, the phosphorus content in the system was 0.3wt%.

[0024] Place the mixture in a vacuum oven for 30 minutes to remove any air bubbles generated during the reaction. Then pour the mixture into a silicone mold (the silicone mold needs to be cleaned with acetone and dried before using methyl silicone oil as a release agent). Cure at 80°C for 2 hours and then at 120°C for 2 hours. After curing, wait for the mold temperature to drop to room temperature before demolding.

[0025] Example 2 (1) Inorganic nanoparticle modification Weigh 25g of untreated magnesium hydroxide nanoparticles and dry them in a vacuum drying oven at 105℃ for 2h. Then add them to a 5000mL 95wt% ethanol aqueous solution system and sonicate for 1h. Then add 0.42g of coupling agent glyceryl trioleate and continue sonicating for 30min. Then react in a water bath at 80℃ for 2h. After the reaction is complete, filter the solution, wash it three times with deionized water, and dry it in a vacuum oven for 5h. Then ball mill it at 300r / min for 5h to obtain the first-modified magnesium hydroxide particles.

[0026] Weigh 10.5g of magnesium hydroxide powder obtained from the first modification and disperse it in 50mL of 95wt% ethanol aqueous solution. Add 21g of methyl methacrylate, purge with nitrogen as a protective gas, and add 0.315g of azobisisobutyronitrile as an initiator. React at 85℃ for 8h, then filter, dry, and ball mill at 300r / min for 5h to obtain the second-modified magnesium hydroxide sample.

[0027] (2) Modification of nitrogen-containing amine curing agents 20g of melamine and 51.4g of formaldehyde were added to a three-necked flask and stirred at 80°C for 1 hour to produce hydroxymethyl melamine (white suspension). 35g of 3,4'-diaminodiphenylmethane (DDM) and 200mL of ethanol were added, and the mixture was heated to 90°C and reacted for 4 hours. The pH was maintained at 9.5 using NaOH solution during the reaction. After the reaction was complete, impurities were removed by vacuum distillation to obtain a pale yellow viscous liquid, yielding a modified curing agent containing 17.18wt% nitrogen.

[0028] (3) Preparation of flame-retardant epoxy resin Weigh 13g of the magnesium hydroxide powder nanofiller obtained from the secondary modification in step (1) and add it to 100mL of 95wt% ethanol aqueous solution. Sonicate for 30min (power 300W). Weigh 11.2g of the modified curing agent obtained in step (2) and add it to the dispersed nanofiller solution. Stir at 500r / min for 20min. Vacuum dry to obtain the pre-dispersed curing agent-filler composite.

[0029] The obtained pre-dispersed composite was mixed with 500g of bisphenol A type epoxy resin (E-44), placed in a 90℃ water bath, and stirred at 500r / min for 20min. At this time, the nitrogen content in the system was 0.37wt%.

[0030] Place in a vacuum oven for 30 minutes to remove the air bubbles generated during the reaction. Then pour the mixture into a silicone mold (the silicone mold needs to be cleaned with acetone and dried before using methyl silicone oil as a release agent). Cure at 80°C for 2 hours and at 100°C for 2 hours. After curing, wait for the mold temperature to drop to room temperature before demolding.

[0031] Example 3 (1) Inorganic nanoparticle modification Weigh 25g of untreated magnesium hydroxide nanoparticles and dry them in a vacuum drying oven at 105℃ for 2h. Then add them to a 5000mL 95wt% ethanol aqueous solution system and sonicate for 1h. Then add 0.42g of coupling agent glyceryl trioleate and continue sonicating for 30min. Then react in a water bath at 80℃ for 2h. After the reaction is complete, filter the solution, wash it three times with deionized water, and dry it in a vacuum oven for 5h. Then ball mill it at 300r / min for 5h to obtain the first-modified magnesium hydroxide particles.

[0032] Weigh 10.5g of magnesium hydroxide powder obtained from the first modification and disperse it in 50mL of 95wt% ethanol aqueous solution. Add 21g of methyl methacrylate, purge with nitrogen as a protective gas, and add 0.315g of azobisisobutyronitrile as an initiator. React at 85℃ for 8h, then filter, dry, and ball mill at 300r / min for 5h to obtain the second-modified magnesium hydroxide sample.

[0033] (2) Modification of nitrogen-containing amine curing agents 20g of melamine and 51.4g of formaldehyde were added to a three-necked flask and stirred at 80°C for 1 hour to produce hydroxymethyl melamine (white suspension). 35g of 3,4'-diaminodiphenylmethane (DDM) and 200mL of ethanol were added, and the mixture was heated to 90°C and reacted for 4 hours. The pH was controlled at 8.5 using NaOH solution during the reaction. After the reaction was complete, impurities were removed by vacuum distillation to obtain a pale yellow viscous liquid, yielding a modified curing agent containing 10.85wt% nitrogen.

[0034] (3) Preparation of flame-retardant epoxy resin Weigh 13g of the magnesium hydroxide powder nanofiller obtained from the secondary modification in step (1) and add it to 100mL of 95wt% ethanol aqueous solution. Sonicate for 30min (power 300W). Weigh 11.2g of the modified curing agent obtained in step (2) and add it to the dispersed nanofiller solution. Stir at 500r / min for 20min. Vacuum dry to obtain the pre-dispersed curing agent-filler composite.

[0035] The obtained pre-dispersed composite was mixed with 500g of bisphenol A type epoxy resin (E-44), placed in a 90℃ water bath, and stirred at 500r / min for 20min. At this time, the nitrogen content in the system was 0.23wt%.

[0036] Place in a vacuum oven for 30 minutes to remove the air bubbles generated during the reaction. Then pour the mixture into a silicone mold (the silicone mold needs to be cleaned with acetone and dried before using methyl silicone oil as a release agent). Cure at 80°C for 2 hours and at 100°C for 2 hours. After curing, wait for the mold temperature to drop to room temperature before demolding.

[0037] Example 4 (1) Inorganic nanoparticle modification Weigh 25g of untreated magnesium hydroxide nanoparticles and dry them in a vacuum drying oven at 105℃ for 2h. Then add them to 5000mL of 95wt% ethanol aqueous solution and sonicate for 1h. Then add 0.42g of coupling agent glyceryl trioleate and continue sonicating for 30min. Then react in a water bath at 80℃ for 2h. After the reaction is complete, filter the solution and wash it with deionized water to obtain modified magnesium hydroxide. Then dry it in a vacuum oven for 5h and ball mill it at 300r / min for 5h to obtain the first-modified magnesium hydroxide particles.

[0038] Weigh 10.5 g of magnesium hydroxide powder obtained from the first modification and disperse it in 50 mL of 5 wt% ethanol aqueous solution. Add 21 g of methyl methacrylate, purge with nitrogen as a protective gas, and add 0.315 g of azobisisobutyronitrile as an initiator. React at 85 °C for 8 h, then filter, dry, and ball mill at 300 r / min for 5 h to obtain the second-modified magnesium hydroxide sample.

[0039] (2) Modification of nitrogen-containing amine curing agents 20g of melamine and 51.4g of formaldehyde were added to a three-necked flask and stirred at 80°C for 1 hour to produce hydroxymethyl melamine (white suspension). 35g of 3,4'-diaminodiphenylmethane (DDM) and 200mL of ethanol were added, and the mixture was heated to 90°C and reacted for 4 hours. The pH was maintained at 9.5 using NaOH solution during the reaction. After the reaction was complete, impurities were removed by vacuum distillation to obtain a pale yellow viscous liquid, yielding a modified curing agent containing 17.18wt% nitrogen.

[0040] (3) Preparation of flame-retardant epoxy resin Weigh 13g of the magnesium hydroxide powder nanofiller obtained from the secondary modification in step (1) and add it to 100mL of 95wt% ethanol aqueous solution. Sonicate for 30min (300W). Weigh 15g of the modified curing agent with a nitrogen content of 17.18wt% obtained in step (2) and add it to the dispersed nanofiller solution. Stir at 500r / min for 20min. Vacuum dry to obtain the pre-dispersed curing agent-filler composite.

[0041] The obtained pre-dispersed product was mixed with 500g of bisphenol A type epoxy resin (E-44), and stirred in a 90℃ water bath at 500r / min for 20min. At this time, the nitrogen content in the system was 0.49wt%.

[0042] Place in a vacuum oven for 30 minutes to remove the air bubbles generated during the reaction. Then pour the mixture into a silicone mold (the silicone mold needs to be cleaned with acetone and dried before using methyl silicone oil as a release agent). Cure at 80°C for 2 hours and at 100°C for 2 hours. After curing, wait for the mold temperature to drop to room temperature before demolding.

[0043] Example 5 The difference from Example 1 is that 3,3'-diaminodiphenyl sulfone is replaced with m-phenylenediamine, otherwise it is the same as Example 1.

[0044] Comparative Example 1 (1) Inorganic nanoparticle modification Weigh 25g of untreated magnesium hydroxide nanoparticles and dry them in a vacuum drying oven at 105℃ for 2h. Then, add them to a 5000mL 95wt% ethanol aqueous solution system and sonicate for 1h. Then, add 0.42g of coupling agent isopropyltrioleoyl oxytitanate and continue sonicating for 30min. Then, react in an oil bath at 150℃ for 2h. After the reaction is complete, filter the solution, wash it three times with deionized water, and dry it in a vacuum oven for 5h. Finally, ball mill it at 300r / min for 5h to obtain the first-modified magnesium hydroxide particles.

[0045] Weigh 10.5g of magnesium hydroxide powder obtained from the first modification and disperse it in 50mL of 95wt% ethanol aqueous solution. Add 21g of methyl methacrylate, purge with nitrogen as a protective gas, and add 0.315g of azobisisobutyronitrile as an initiator. React at 90℃ for 6h, then filter, dry, and ball mill at 300r / min for 5h to obtain the second-modified magnesium hydroxide sample.

[0046] (2) Preparation of flame-retardant epoxy resin a) Add 20g of melamine and 51.4g of formaldehyde to a three-necked flask and stir at 80°C for 1 hour to generate a white suspension of hydroxymethyl melamine; b) Weigh 13g of the magnesium hydroxide powder nanofiller obtained in step (1) and add it to 100mL of 95wt% ethanol aqueous solution. Sonicate for 30min (300W). Weigh 7.25g of the hydroxymethyl melamine white suspension obtained in step a) and 5.4g of 3,4'-diaminodiphenylmethane (DDM) and add them to the well dispersed nanofiller solution. Stir at 500r / min for 20min. Vacuum dry to obtain the pre-dispersed curing agent-filler composite.

[0047] The obtained pre-dispersed composite was mixed with 500g of bisphenol A epoxy resin (E-44), and stirred in a 90℃ water bath at 500r / min for 15min. After removing air bubbles generated during the reaction, the mixture was poured into a silicone mold (the silicone mold needed to be cleaned with acetone and dried, then methyl silicone oil was used as a release agent). The mixture was cured at 80℃ for 2h and then at 120℃ for 2h. After curing, the mold was allowed to cool to room temperature before demolding.

[0048] Comparative Example 2 (1) Inorganic nanoparticle modification Weigh 25g of untreated magnesium hydroxide nanoparticles and dry them in a vacuum drying oven at 105℃ for 2h. Then add them to a 5000mL 95wt% ethanol aqueous solution system and sonicate for 1h. Then add 0.42g of coupling agent glyceryl trioleate and continue sonicating for 30min. Then react in a water bath at 80℃ for 2h. After the reaction is complete, filter the solution, wash it three times with deionized water, and dry it in a vacuum oven for 5h. Then ball mill it at 300r / min for 5h to obtain primary modified magnesium hydroxide particles.

[0049] (2) Modification with phosphorus-amine curing agents Weigh 50g of DOPO and 10g of 3,3'-diaminodiphenyl sulfone and dissolve them in 95wt% ethanol aqueous solution. Stir mechanically for 15min. Place the well-mixed solution into a reaction apparatus, heat to 80℃, and react for 6h under nitrogen protection. Remove the organic solvent by vacuum distillation to obtain a modified curing agent containing 11.6wt% phosphorus.

[0050] (3) Preparation of flame-retardant epoxy resin Weigh 11.4 g of the modified magnesium hydroxide obtained in step (1) and add it to 100 mL of 95 wt% ethanol aqueous solution. Sonicate for 30 min (300 W). Weigh 13.5 g of the modified curing agent 3,3'-diaminodiphenyl sulfone and add it to the well dispersed nanofiller solution. Stir at 500 r / min for 20 min. Vacuum dry to obtain the pre-dispersed curing agent-filler composite.

[0051] The obtained pre-dispersed product was mixed with 500g of bisphenol A type epoxy resin (E-44), and stirred in a 90℃ water bath at 500r / min for 20min. At this time, the phosphorus content in the system was 0.3wt%.

[0052] Place the mixture in a vacuum oven for 30 minutes to remove any air bubbles generated during the reaction. Then pour the mixture into a silicone mold (the silicone mold needs to be cleaned with acetone and dried before using methyl silicone oil as a release agent). Cure at 80°C for 2 hours, then at 120°C for 2 hours. After curing, wait for the mold temperature to drop to room temperature before demolding.

[0053] Comparative Example 3 (1) Modification of inorganic nanoparticles Weigh 25g of untreated magnesium hydroxide nanoparticles and dry them in a vacuum drying oven at 105℃ for 2h. Then, add them to a 5000mL 95wt% ethanol aqueous solution system and sonicate for 1h (power 300W). Then, add 1.25g of γ-methacryloyloxypropyltrimethoxysilane (KH570) and continue sonicating for 30min. Then, react in an oil bath at 120℃ for 2h. After the reaction is complete, filter the solution, wash it three times with deionized water, and dry it in a vacuum oven for 5h. Finally, ball mill it at 300r / min for 5h to obtain the first-modified magnesium hydroxide particles.

[0054] Weigh 10.5g of magnesium hydroxide powder obtained from the first modification and disperse it in 50mL of 95wt% ethanol aqueous solution. Add 21g of methyl methacrylate, purge with nitrogen as a protective gas, and add 0.315g of azobisisobutyronitrile as an initiator. React at 95℃ for 7.5h, then filter, dry, and ball mill at 300r / min for 5h to obtain the second-modified magnesium hydroxide sample.

[0055] (2) Modification with phosphorus-amine curing agents Weigh 50g of DOPO and 10g of 3,3'-diaminodiphenyl sulfone and dissolve them in 200mL of 95wt% ethanol aqueous solution. Stir mechanically for 15min. Place the well-mixed solution into a reaction apparatus, heat to 80℃, and react for 6h under nitrogen protection. Remove the organic solvent by vacuum distillation to obtain a modified curing agent with a phosphorus content of 11.6wt%.

[0056] (2) Preparation of flame-retardant epoxy resin Weigh 11.4 g of the magnesium hydroxide powder nanofiller obtained from the secondary modification in step (1) and add it to 100 mL of 95 wt% ethanol aqueous solution. Sonicate the solution for 30 min (300 W). Weigh 2.3 g of 3,3'-diaminodiphenyl sulfone and 11.3 g of DOPO and add them to the well-dispersed nanofiller solution. Stir at 500 r / min for 20 min. Vacuum dry to obtain the pre-dispersed curing agent-filler composite.

[0057] The obtained pre-dispersed composite was mixed with 500g of bisphenol A type epoxy resin (E-44), placed in a 90℃ water bath, and stirred at 500r / min for 20min. At this time, the phosphorus content in the system was 0.3wt%.

[0058] Place the mixture in a vacuum oven for 30 minutes to remove any air bubbles generated during the reaction. Then pour the mixture into a silicone mold (the silicone mold needs to be cleaned with acetone and dried before using methyl silicone oil as a release agent). Cure at 80°C for 2 hours and then at 120°C for 2 hours. After curing, wait for the mold temperature to drop to room temperature before demolding.

[0059] The epoxy resins obtained in the above examples and comparative examples were tested. The limiting oxygen index was measured by an oxygen indexer according to standard ISO 4589-2. The horizontal and vertical burning tester was used to test the resins according to UL-94 standard. The flexural strength and tensile strength were determined by a universal testing machine according to GB / T2567-2008 standard. The test results are shown in Table 1.

[0060] Table 1. Performance test results of epoxy resins obtained in the examples and comparative examples.

[0061] As can be seen from the above data, this invention introduces phosphorus / nitrogen elements into the amine curing agent, while simultaneously achieving synergistic flame retardancy with modified inorganic nanoparticles. The pre-dispersion of secondary modified magnesium hydroxide in the modified amine curing agent avoids the agglomeration problem associated with direct addition. Both exist together in the epoxy resin system, acting as cross-linking flame retardants. Highly efficient flame retardancy can be achieved with only low addition amounts of the secondary modified magnesium hydroxide and the modified amine curing agent, while simultaneously enhancing the mechanical properties of the epoxy resin.

Claims

1. A flame-retardant epoxy resin synergistically formulated with inorganic nanoparticles and a modified curing agent, characterized in that, By weight, it includes the following components: 100 parts epoxy resin, 1-4 parts inorganic nanoparticles, and 2-3 parts modified amine curing agent; The modified amine curing agent is obtained by embedding the modifier into the molecular skeleton of the amine curing agent; the modifier is at least one of phosphorus-containing modifier or nitrogen-containing modifier; The phosphorus-containing modifier comprises at least one of phosphate esters, phosphonates, DOPO, or DOPO derivatives; The nitrogen-containing modifier comprises at least one of triazine, imidazole, or piperazine compounds.

2. The flame-retardant epoxy resin synergistically formulated with inorganic nanoparticles and a modified curing agent according to claim 1, characterized in that, The phosphorus-containing modifier contains at least one of DOPO or a DOPO derivative, the nitrogen-containing modifier is the product of melamine and formaldehyde reacting at a mass ratio of 1:(2~3) at 75~85°C for 0.5~2h, and the amine curing agent contains at least one of m-phenylenediamine, diethylenetriamine, 3,4'-diaminodiphenylmethane, or 3,3'-diaminodiphenyl sulfone.

3. The flame-retardant epoxy resin synergistically formulated with inorganic nanoparticles and a modified curing agent according to claim 2, characterized in that, When modifying the curing agent with a phosphorus-containing modifier, the modification method is as follows: mix the phosphorus-containing modifier, amine curing agent and ethanol, react at 70~90℃ under inert gas protection for 5~7h, remove impurities to obtain a phosphorus-containing curing agent with a phosphorus content of 8~15wt%; the mass ratio of the phosphorus-containing modifier to the amine curing agent is 1:(0.1~0.5). When modifying the curing agent with a nitrogen-containing modifier, the modification method is as follows: mix the nitrogen-containing modifier, amine curing agent and ethanol, react at 80~100℃ for 3~5h, control the pH of the system at 8~10 during the reaction, remove impurities to obtain a nitrogen-containing curing agent with a nitrogen content of 10~30wt%; the mass ratio of melamine to amine curing agent is 1:(1~3).

4. The flame-retardant epoxy resin synergistically formulated with inorganic nanoparticles and a modified curing agent according to claim 1, characterized in that, The inorganic nanoparticles are secondary modified nano-magnesium hydroxide, and the preparation steps are as follows: (1) Primary modification: The dried magnesium hydroxide nanoparticles are dispersed in an ethanol aqueous solution to obtain a magnesium hydroxide dispersion. Then, a coupling agent is added, and the mixture is reacted at 70~120℃ for 1~3h. After drying and ball milling, the primary modified nano magnesium hydroxide is obtained. (2) Secondary modification: The primary modified nano magnesium hydroxide obtained in step (1) is dispersed in an ethanol aqueous solution, methyl methacrylate and an initiator are added, and the reaction is carried out at 80~100℃ for 5~8h under inert gas protection to obtain secondary modified nano magnesium hydroxide.

5. The flame-retardant epoxy resin synergistically formulated with inorganic nanoparticles and a modified curing agent according to claim 4, characterized in that, The coupling agent in step (1) is at least one of γ-aminopropyltriethoxysilane, γ-methacryloxypropyltrimethoxysilane, glyceryl trioleate or isopropyltrioleyloxytitanate.

6. The flame-retardant epoxy resin synergistically formulated with inorganic nanoparticles and a modified curing agent according to claim 4, characterized in that, The mass ratio of magnesium hydroxide nanoparticles to coupling agent in step (1) is 1: (0.01~0.1).

7. The flame-retardant epoxy resin synergistically formulated with inorganic nanoparticles and a modified curing agent according to claim 4, characterized in that, The initiator in step (2) is at least one of azobisisobutyronitrile or azobisisoheptanenitrile.

8. The flame-retardant epoxy resin synergistically formulated with inorganic nanoparticles and a modified curing agent according to claim 4, characterized in that, The mass ratio of methyl methacrylate to initiator in step (2) is 1:(0.01~0.03).

9. The flame-retardant epoxy resin synergistically formulated with inorganic nanoparticles and a modified curing agent according to claim 4, characterized in that, In step (2), the mass ratio of the primary modified nano magnesium hydroxide to methyl methacrylate is 1:(1.5~3), preferably 1:

2.

10. The method for preparing flame-retardant epoxy resin synergistically composed of inorganic nanoparticles and modified curing agent as described in any one of claims 1 to 9, characterized in that, The preparation steps are as follows: inorganic nanoparticles and modified amine curing agents are pre-dispersed, and after being dispersed evenly, they are mixed evenly with epoxy resin at 90~100℃. After stirring evenly, vacuum degassing is performed, and the mixture is cured at 75~85℃ for 1~5h, and then cured at 95~125℃ for 1~3h to obtain synergistic flame-retardant epoxy resin.

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