High-strength flame-retardant phenolic molding compound and method for preparing the same

Abstract

The application discloses high-strength flame-retardant phenolic molding compound and a preparation method thereof, and belongs to the technical field of phenolic molding compound. The high-strength flame-retardant phenolic molding compound comprises the following raw materials in parts by weight: 70-90 parts of phenolic resin, 5-8 parts of hexamethylenetetramine, 10-20 parts of pretreated glass fiber, 8-16 parts of flame retardant and 1-3 parts of lubricant. The pretreated glass fiber reinforced molding compound solves the interface compatibility problem of the fiber and the resin matrix, reduces stress concentration and improves the strength of the molding compound. The flame retardant has phosphorus-boron-nitrogen synergistic flame-retardant effect, can significantly improve the flame-retardant performance of the phenolic molding compound, overcomes the problem of insufficient flame retardance of the traditional phenolic molding compound, and is halogen-free and environment-friendly. Therefore, the prepared phenolic molding compound has both flame retardance and high strength, and has important application value in the technical field of phenolic molding compound.

Description

Technical Field

[0001] This invention belongs to the field of phenolic molding compound technology, specifically, it relates to a high-strength flame-retardant phenolic molding compound and its preparation method. Background Technology

[0002] Phenolic molding compounds, as a type of thermosetting plastic with a long history, have been widely used in electrical and electronic, automotive, and aerospace fields due to their excellent mechanical properties, heat resistance, electrical insulation, and dimensional stability. However, with the increasing demands of modern industry on material performance, traditional phenolic molding compounds have gradually revealed some shortcomings. For example, in the field of electrical insulation, the material not only needs to withstand long-term current loads but also needs to prevent the spread of flames under short-circuit or overload conditions. While ordinary phenolic molding compounds possess certain flame-retardant properties, their flame retardancy still needs to be improved to meet high standards. Currently, the flame retardants used in phenolic molding compounds, such as decabromodiphenyl ethane, are halogenated flame retardants. These flame retardants cause serious environmental pollution during their preparation, use, and post-processing, which is inconsistent with the current green and environmentally friendly development concept.

[0003] In terms of strength, the industry typically uses fiber filling or inorganic filler blending to improve mechanical properties. For example, while glass fiber reinforced phenolic plastics can significantly improve tensile strength and impact toughness, interfacial compatibility issues between the fiber and the matrix often lead to stress concentration, and uneven fiber orientation is prone to occur during the molding of complex shapes. While commonly used fillers such as wood flour and mineral powder are inexpensive, adding more than 30% can increase material brittleness, reduce fluidity, and affect molding processability.

[0004] In summary, there is an urgent need to invent a phenolic molding compound that combines high strength and flame retardant properties to meet the higher technical requirements of the phenolic molding compound field. Summary of the Invention

[0005] The purpose of this invention is to overcome the shortcomings of the prior art and provide a high-strength flame-retardant phenolic molding compound and its preparation method.

[0006] The objective of this invention can be achieved through the following technical solutions:

[0007] A high-strength flame-retardant phenolic molding compound comprises the following raw materials in parts by weight: 70-90 parts phenolic resin, 5-8 parts hexamethylenetetramine, 10-20 parts pretreated glass fiber, 8-16 parts flame retardant, and 1-3 parts lubricant.

[0008] As a further technical solution, the lubricant is one of polyethylene wax, zinc stearate, and stearic acid.

[0009] As a further technical solution, the pretreated glass fiber is obtained through the following steps:

[0010] Short glass fibers, silane coupling agent and anhydrous ethanol are mixed, acetic acid solution is added dropwise, the pH is adjusted to 4-5, ultrasonic treatment is performed for 10-15 minutes, the fibers are separated with a filter screen, excess liquid is drained, and dried in an oven at 80-100℃ for 2-3 hours to obtain pretreated glass fibers.

[0011] As a further technical solution, the weight parts of each raw material are as follows: 20-30 parts chopped glass fiber, 1-2 parts silane coupling agent and 80-100 parts anhydrous ethanol.

[0012] As a further technical solution, the silane coupling agent is KH-550.

[0013] As a further technical solution, the flame retardant is prepared through the following steps:

[0014] A1. Add pentaerythritol, boric acid, toluene, and p-toluenesulfonic acid to a three-necked flask, purge with nitrogen for 10 minutes to remove air, start stirring, and slowly heat to 80°C. Hold at this temperature for 30 minutes to partially dissolve the boric acid. Then heat to 130-140°C and stir under reflux. Remove the generated water through an oil-water separator. Once no water droplets are generated in the separator, continue the reaction for 1-2 hours to ensure complete esterification. After the reaction is complete, cool to 80°C and recover toluene by vacuum distillation. Dissolve the product in hot ethanol, filter while hot to remove unreacted boric acid, cool the filtrate, and precipitate a white solid. Filter and wash with cold ethanol, then dry under vacuum to obtain the borate ester product.

[0015] A2. Add 2-chloro-4,6-diamino-1,3,5-triazine, 4-dimethylaminopyridine, and tetrahydrofuran to a three-necked flask, purge with nitrogen for 10 min to remove air, start stirring, and slowly raise the temperature to 40°C. Stir until the solid is completely dissolved. Then dissolve diethylphosphoacetic acid and dicyclohexylcarbodiimide in tetrahydrofuran and slowly add them dropwise through a constant pressure dropping funnel under ice bath conditions of 0-5°C. After the addition is complete, remove the ice bath, raise the temperature to 25-30°C, and continue stirring for 10-12 h. After the reaction is complete, filter, wash the filter cake with cold tetrahydrofuran, combine the filtrates, concentrate under reduced pressure, add ice water to precipitate the solid, filter, wash with cold water and cold ethanol, and dry to obtain the amidated product.

[0016] A3. The borate ester product, amidation product, tetrahydrofuran, and triethylamine were added sequentially to a three-necked flask. Nitrogen gas was purged for 10 min to remove air, and the mixture was stirred for 10-20 min in an ice bath at 0-5°C. The reaction was then promoted by heating to 40-60°C and the reaction time was controlled at 6-8 h. After the reaction was completed, water was added to quench the reaction, and the mixture was extracted with ethyl acetate. The organic phases were combined, dried over anhydrous sodium sulfate, filtered, and the solvent was removed by rotary evaporation. The flame retardant was obtained by column chromatography.

[0017] As a further technical solution, the ratio of pentaerythritol, boric acid, toluene, and p-toluenesulfonic acid in step A1 is 13.6g:14.1-15.7g:75mL:0.1-0.2g.

[0018] As a further technical solution, in step A2, the ratio of the amounts of 2-chloro-4,6-diamino-1,3,5-triazine, 4-dimethylaminopyridine, tetrahydrofuran, diethylphosphoacetic acid, and dicyclohexylcarbodiimide is 14.5g:2.4g:150mL:39.0-40.6g:42.2-47.4g.

[0019] As a further technical solution, the ratio of the amount of borate ester product, amidation product, tetrahydrofuran, and triethylamine in step A3 is 18.6g:105.7-110.9g:200mL:20.2g.

[0020] The reaction formulas for steps A1 and A2 of this invention are as follows:

[0021]

[0022]

[0023] In the preparation of flame retardants, it is important to note that in step A1, the molar ratio of pentaerythritol to boric acid must be strictly controlled to be close to 1:2, and boric acid must be in excess to ensure complete reaction. Similarly, in step A2, the molar ratio of 2-chloro-4,6-diamino-1,3,5-triazine to diethylphosphoacetic acid must be strictly controlled to be close to 1:2, and diethylphosphoacetic acid must be in excess to ensure complete reaction. Likewise, in step A3, the molar ratio of borate ester product to amidation product must be strictly controlled to be close to 1:2, and amidation product must be in excess to ensure complete reaction.

[0024] It is easy to deduce from the above reaction formula that the flame retardant prepared by the present invention constructs a phosphorus-boron-nitrogen synergistic flame retardant structure with molecular symmetry and contains multiple phosphoric acid structures, which further enhances the flame retardant performance. The introduced pentaerythritol skeleton can not only inhibit the hydrolysis of borate esters and improve the stability of the flame retardant, but also promote the formation of a dense carbon layer in the matrix, further improving the flame retardancy.

[0025] This invention also provides a method for preparing high-strength flame-retardant phenolic molding compound, comprising the following steps:

[0026] Phenolic resin is heated to 80-90℃ to soften it, then hexamethylenetetramine (curing agent) is added and stirred for 5-10 minutes to achieve initial mixing. Flame retardant and lubricant are then added sequentially, and high-speed stirring is used to ensure uniform dispersion. Pretreated glass fiber is then added and stirred at low speed to prevent fiber breakage, resulting in a mixture. The mixture is fed into a twin-screw extruder, extruded, and then pelletized to obtain molding compound granules. The molding compound granules are placed in a mold and compressed to obtain high-strength flame-retardant phenolic molding compound.

[0027] As a further technical solution, the high-speed stirring speed is 1000-1200 rpm, and the time is 10-20 min.

[0028] As a further technical solution, the low-speed stirring speed is 300-500 rpm, and the time is 5-10 min.

[0029] As a further technical solution, the temperature of the mold in the compression molding is 170-180℃, the molding time is 5-10min, and the pressure is 15-20MPa.

[0030] The beneficial effects of this invention are:

[0031] 1. This invention solves the interfacial compatibility problem between the fiber and the resin matrix by pre-treating the glass fiber reinforced molding compound, reducing stress concentration and improving the strength of the molding compound;

[0032] 2. This invention constructs a phosphorus-boron-nitrogen synergistic flame retardant that significantly improves the flame retardant properties of phenolic molding compounds, overcoming the problem of insufficient flame retardancy in traditional phenolic molding compounds. Furthermore, the flame retardant is halogen-free and environmentally friendly.

[0033] In summary, the phenolic molding compound prepared by this invention has both flame retardancy and high strength, and has important application value in the field of phenolic molding compound technology. Detailed Implementation

[0034] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0035] Example 1

[0036] Preparation of pretreated glass fibers:

[0037] Mix 20 parts of chopped glass fiber, 1 part of KH-550 and 80 parts of anhydrous ethanol, add acetic acid solution, adjust the pH to 4, sonicate for 10 min, separate the fiber with a filter, drain the excess liquid, and dry in an oven at 80℃ for 2 h to obtain pretreated glass fiber.

[0038] Example 2

[0039] Preparation of pretreated glass fibers:

[0040] Mix 30 parts of chopped glass fiber, 2 parts of KH-550 and 100 parts of anhydrous ethanol, add acetic acid solution, adjust the pH to 5, sonicate for 15 min, separate the fiber with a filter, drain excess liquid, and dry in an oven at 100℃ for 3 h to obtain pretreated glass fiber.

[0041] Example 3

[0042] Preparation of flame retardants:

[0043] A1. Add 13.6g pentaerythritol, 14.1g boric acid, 75mL toluene, and 0.1g p-toluenesulfonic acid to a three-necked flask. Purge with nitrogen for 10 minutes to remove air, start stirring, and slowly heat to 80°C. Maintain this temperature for 30 minutes to partially dissolve the boric acid. Then heat to 130°C and stir under reflux. Remove the generated water using an oil-water separator. Once no water droplets are generated in the separator, continue the reaction for 1 hour to ensure complete esterification. After the reaction is complete, cool to 80°C and recover the toluene by vacuum distillation. Dissolve the product in hot ethanol, filter while hot to remove unreacted boric acid, cool the filtrate, and precipitate a white solid. Filter and wash with cold ethanol, then dry under vacuum to obtain the borate ester product.

[0044] A2. Add 29.0 g of 2-chloro-4,6-diamino-1,3,5-triazine, 4.8 g of 4-dimethylaminopyridine, and 60 mL of tetrahydrofuran to a three-necked flask, purge with nitrogen for 10 min to remove air, start stirring, and slowly raise the temperature to 40 °C. Stir until the solid is completely dissolved. Then dissolve 78.0 g of diethylphosphoacetic acid and 84.4 g of dicyclohexylcarbodiimide in 240 mL of tetrahydrofuran. Add the solution dropwise through a constant pressure dropping funnel under ice bath conditions at 0 °C. After the addition is complete, remove the ice bath, raise the temperature to 30 °C, and continue stirring for 10 h. After the reaction is complete, filter, wash the filter cake with cold tetrahydrofuran, combine the filtrates, concentrate under reduced pressure, add ice water to precipitate the solid, filter, wash with cold water and cold ethanol, and dry to obtain the amidated product.

[0045] A3. 18.6 g of borate ester product, 105.7 g of amidation product, 200 mL of tetrahydrofuran and 20.2 g of triethylamine were added sequentially to a three-necked flask. Nitrogen gas was purged for 10 min to remove air, and the mixture was stirred for 10 min under ice bath conditions at 0 °C. The reaction was then heated to 40 °C to promote the reaction. The reaction time was controlled at 8 h. After the reaction was completed, water was added to quench the reaction, and the mixture was extracted with ethyl acetate. The organic phases were combined, dried over anhydrous sodium sulfate, filtered, and the solvent was removed by rotary evaporation. The flame retardant was obtained by column chromatography (the volume ratio of petroleum ether to ethyl acetate was 9:1).

[0046] A method for preparing a high-strength flame-retardant phenolic molding compound includes the following steps:

[0047] 70 parts of phenolic resin were heated to 80°C to soften it, and then 5 parts of hexamethylenetetramine were added and stirred for 5 minutes to achieve initial mixing. Next, 8 parts of flame retardant and 1 part of polyethylene wax were added sequentially, and the mixture was stirred at 1000 rpm for 10 minutes to ensure uniform dispersion. Then, 10 parts of pretreated glass fiber prepared in Example 1 were added and stirred at 300 rpm for 5 minutes to prevent fiber breakage, resulting in a mixture. The mixture was fed into a twin-screw extruder, extruded, and then pelletized to obtain molding compound granules. The molding compound granules were placed in a mold at 170°C and molded at 15 MPa for 5 minutes to obtain high-strength flame-retardant phenolic molding compound.

[0048] Example 3

[0049] Preparation of flame retardants:

[0050] A1. Add 13.6g pentaerythritol, 15.7g boric acid, 75mL toluene, and 0.2g p-toluenesulfonic acid to a three-necked flask. Purge with nitrogen for 10 minutes to remove air, start stirring, and slowly heat to 80℃. Hold at this temperature for 30 minutes to partially dissolve the boric acid. Then heat to 130-140℃ and stir under reflux. Remove the generated water using an oil-water separator. Once no water droplets are generated in the separator, continue the reaction for 1-2 hours to ensure complete esterification. After the reaction is complete, cool to 80℃ and recover the toluene by vacuum distillation. Dissolve the product in hot ethanol, filter while hot to remove unreacted boric acid, cool the filtrate, and precipitate a white solid. Filter and wash with cold ethanol, then dry under vacuum to obtain the borate ester product.

[0051] A2. Add 29.0 g of 2-chloro-4,6-diamino-1,3,5-triazine, 4.8 g of 4-dimethylaminopyridine, and 60 mL of tetrahydrofuran to a three-necked flask, purge with nitrogen for 10 min to remove air, start stirring, and slowly heat to 40 °C until the solid is completely dissolved. Then dissolve 81.2 g of diethylphosphoacetic acid and 94.8 g of dicyclohexylcarbodiimide in 240 mL of tetrahydrofuran, and slowly add them dropwise through a constant pressure dropping funnel under ice bath conditions at 5 °C. After the addition is complete, remove the ice bath, heat to 25 °C, and continue stirring for 12 h. After the reaction is complete, filter, wash the filter cake with cold tetrahydrofuran, combine the filtrates, concentrate under reduced pressure, add ice water to precipitate the solid, filter, wash with cold water and cold ethanol, and dry to obtain the amidated product.

[0052] A3. 18.6 g of borate ester product, 110.9 g of amidation product, 200 mL of tetrahydrofuran and 20.2 g of triethylamine were added sequentially to a three-necked flask. Nitrogen gas was purged for 10 min to remove air, and the mixture was stirred for 20 min under ice bath conditions at 0-5℃. The reaction was then heated to 60℃ to promote the reaction, and the reaction time was controlled at 6 h. After the reaction was completed, water was added to quench the reaction, and the mixture was extracted with ethyl acetate. The organic phases were combined, dried over anhydrous sodium sulfate, filtered, and the solvent was removed by rotary evaporation. The flame retardant was obtained by column chromatography (the volume ratio of petroleum ether to ethyl acetate was 9:1).

[0053] A method for preparing a high-strength flame-retardant phenolic molding compound includes the following steps:

[0054] 80 parts of phenolic resin were heated to 90°C to soften it, and then 6.5 parts of hexamethylenetetramine were added and stirred for 10 minutes to achieve initial mixing. Then, 12 parts of flame retardant and 2 parts of zinc stearate were added sequentially, and the mixture was stirred at 1100 rpm for 15 minutes to ensure uniform dispersion. Then, 15 parts of pretreated glass fiber prepared in Example 2 were added and stirred at 400 rpm for 7.5 minutes to prevent fiber breakage, resulting in a mixture. The mixture was fed into a twin-screw extruder, extruded, and then pelletized to obtain molding compound granules. The molding compound granules were placed in a mold at 170°C and molded at 20 MPa for 10 minutes to obtain high-strength flame-retardant phenolic molding compound.

[0055] Example 5

[0056] The only difference between this embodiment and Embodiment 4 is that, in this embodiment, a method for preparing a high-strength flame-retardant phenolic molding compound includes the following steps:

[0057] 90 parts of phenolic resin were heated to 90°C to soften it, and then 8 parts of hexamethylenetetramine were added and stirred for 0 min to achieve initial mixing. Then, 16 parts of flame retardant and 3 parts of stearic acid were added sequentially, and the mixture was stirred at 1200 rpm for 20 min to ensure uniform dispersion. Then, 20 parts of pretreated glass fiber prepared in Example 2 were added and stirred at 500 rpm for 10 min to prevent fiber breakage, resulting in a mixture. The mixture was fed into a twin-screw extruder, extruded, and then pelletized to obtain molding compound granules. The molding compound granules were placed in a mold at 180°C and molded at 20 MPa for 10 min to obtain high-strength flame-retardant phenolic molding compound.

[0058] Comparative Example 1

[0059] The only difference between this comparative example and Example 5 is that in this comparative example, an equal amount of DOPO was used to replace the flame retardant to prepare the molding compound.

[0060] Comparative Example 2

[0061] The only difference between this comparative example and Example 5 is that, in this comparative example, an equal amount of untreated chopped glass fibers were used to replace the pretreated glass fibers to obtain the molding compound.

[0062] The following performance tests were conducted on Examples 3, 4, and 5, and Comparative Examples 1 and 2:

[0063] The oxygen index was determined according to GB / T 2406.2-2009 standard;

[0064] Tensile strength was determined according to GB / T 1040.2-2006 standard;

[0065] The performance test results are shown in Table 1:

[0066] Table 1

[0067] Test Project Example 3 Example 4 Example 5 Comparative Example 1 Comparative Example 2 Limiting oxygen index / % 42.4 43.8 45.2 29.6 44.5 Tensile strength (MPa) 59.7 62.5 65.1 64.8 51.9

[0068] As can be seen from the table above, the phenolic molding compound prepared in the embodiments of the present invention has higher flame retardancy and strength than the comparative example. Therefore, the present invention has important application value in the field of phenolic molding compound technology.

[0069] It will be apparent to those skilled in the art that the present invention is not limited to the details of the exemplary embodiments described above, and that the invention can be implemented in other specific forms without departing from the spirit or essential characteristics of the invention. Therefore, the embodiments should be considered in all respects as exemplary and non-limiting, and the scope of the invention is defined by the appended claims rather than the foregoing description. Thus, it is intended that all variations falling within the meaning and scope of equivalents of the claims be included within the present invention.

Claims

1. A high-strength flame-retardant phenolic molding compound characterized by, The raw materials include the following weight parts: 70-90 parts of phenolic resin, 5-8 parts of hexamethylenetetramine, 10-20 parts of pretreated glass fiber, 8-16 parts of flame retardant, 1-3 parts of lubricant; The flame retardant is prepared by the following steps: A1, pentaerythritol, boric acid, toluene and p-toluenesulfonic acid are added to a flask, nitrogen is passed, stirring is started, the temperature is raised to 80 DEG C, and the temperature is kept for 30 min, then the temperature is raised to 130-140 DEG C, and reflux reaction is carried out, when no water is generated in the water separator, the reaction is continued for 1-2 h, the reaction is completed, and a borate ester product is obtained; A2, 2-chloro-4, 6-diamino-1, 3, 5-triazine, 4-dimethylamino pyridine and tetrahydrofuran are added to a flask, nitrogen is passed, stirring is started, the temperature is raised to 40 DEG C, and stirring is carried out until dissolution, then diethyl phosphoacetic acid and dicyclohexyl carbodiimide are dissolved in tetrahydrofuran, and dropwise addition is carried out at 0-5 DEG C, after dropwise addition is completed, reaction is carried out at 25-30 DEG C for 10-12 h, the reaction is completed, and an amidation product is obtained; A3, the borate ester product, the amidation product, tetrahydrofuran and triethylamine are added to a flask, nitrogen is passed, stirring is carried out at 0-5 DEG C for 10-20 min, heating is carried out to 40-60 DEG C, reaction is carried out for 6-8 h, the reaction is completed, and a flame retardant is obtained; The pretreated glass fiber is prepared by the following steps: The chopped glass fiber, silane coupling agent and anhydrous ethanol are mixed, acetic acid solution is added dropwise, the pH is adjusted to 4-5, ultrasonic treatment is carried out for 10-15 min, the fiber is separated, the excess liquid is drained, and drying is carried out, and the pretreated glass fiber is obtained.

2. A high-strength flame-retardant phenolic molding compound according to claim 1, characterized in that, The ratio of the amounts of pentaerythritol, boric acid, toluene and p-toluenesulfonic acid in step A1 is 13.6 g: 14.1-15.7 g: 75 mL: 0.1-0.2 g.

3. A high-strength flame-retardant phenolic molding compound according to claim 1, wherein The ratio of the amounts of 2-chloro-4, 6-diamino-1, 3, 5-triazine, 4-dimethylamino pyridine, tetrahydrofuran, diethyl phosphoacetic acid and dicyclohexyl carbodiimide in step A2 is 14.5 g: 2.4 g: 150 mL: 39.0-40.6 g: 42.2-47.4 g.

4. A high-strength flame-retardant phenolic molding compound according to claim 1, wherein The ratio of the amounts of the borate ester product, the amidation product, tetrahydrofuran and triethylamine in step A3 is 18.6 g: 105.7-110.9 g: 200 mL: 20.2 g.

5. A high-strength flame-retardant phenolic molding compound according to claim 1, wherein The lubricant is one of polyethylene wax, zinc stearate and stearic acid.

6. A high-strength flame-retardant phenolic molding compound according to claim 1, wherein The weight parts of each raw material are as follows: 20-30 parts of chopped glass fiber, 1-2 parts of silane coupling agent and 80-100 parts of anhydrous ethanol.

7. A process for the preparation of a high-strength flame-retardant phenolic molding compound for the preparation of a high-strength flame-retardant phenolic molding compound according to any one of claims 1 to 6, characterized in that The method comprises the following steps: The phenolic resin is heated to soften, hexamethylenetetramine is added, and stirring is carried out to preliminarily mix; the flame retardant and the lubricant are added in sequence, high-speed stirring is carried out until uniform, the pretreated glass fiber is added with low-speed stirring, a mixed material is obtained; the mixed material is fed into a double screw extruder, and after extrusion, pelletization is carried out, and molding material particles are obtained; the molding material particles are placed in a mold, and compression molding is carried out, and a high-strength flame-retardant phenolic molding material is obtained.

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