Flame retardant phenolic molding compound and preparation method thereof

Abstract

The invention discloses a flame retardant phenolic molding compound and a preparation method thereof, and belongs to the technical field of phenolic molding compounds. It includes the following parts by weight of raw materials: 40-60 parts of modified phenolic resin, 16-22 parts of reinforcing fibers, 20-40 parts of modified chitosan, 3-8 parts of curing agent, 1-3 parts of curing accelerator, and 2-6 parts of lubricant. The molding compound prepared by the present invention, the addition of reinforcing fibers and curing agents can enhance the mechanical strength of the molding compound; the phenolic resin is modified using boric acid to enhance the mechanical strength, heat resistance and ablation resistance of the molding compound; the filler is modified chitosan, which has better compatibility with the matrix than ordinary chitosan, can significantly enhance the flame retardancy and antibacterial properties of the molding compound, and the performance is long-term and stable. Therefore, the molding compound prepared by the present invention has stable and efficient flame retardancy and antibacterial properties, and does not need to be additionally added with flame retardants, has excellent mechanical properties, and has important application value in the technical field of phenolic molding compounds.

Description

Technical Field

[0001] The invention belongs to the technical field of phenolic molding materials, and in particular, relates to a flame retardant phenolic molding material and a preparation method thereof. Background Art

[0002] Molding plastics usually refer to the raw materials used to make plastic products. They are formed in the mold and then solidified into the desired shape. They are widely used in packaging, construction, automobile and other industries. There are many types of molding plastics, including but not limited to the following: thermoplastics, thermosetting plastics, engineering plastics, etc. Among them, thermosetting plastics include phenolic plastics, epoxy resins, unsaturated polyester resins, etc. Among them, phenolic molding plastics have developed rapidly in recent years.

[0003] Phenolic molding compound is a thermosetting plastic material made by mixing thermoplastic phenolic resin and other fillers and modifying, toughening, reinforcing agents, etc. uniformly and through a certain mixing process. It has the characteristics of low price, excellent mechanical properties, good insulation performance, simple and quick molding, and is widely used in military industry, electrical components, instruments, construction and other fields. However, the flame retardancy of phenolic molding compound is insufficient, and the commonly used flame retardant phenolic molding compound on the market has a large amount of flame retardants and fillers added, which greatly reduces the mechanical strength of the phenolic molding compound, seriously limiting the use of the flame retardant phenolic molding compound. Not only that, in some environmental conditions, it is particularly complex. In a dark and humid environment, plastic products are prone to grow various bacteria, which brings great damage to the product itself. Therefore, based on the above problems, it is urgent to invent a phenolic molding compound with flame retardant and antibacterial properties to meet the higher demands in the field of phenolic molding compound technology. Summary of the invention

[0004] The purpose of the present invention is to overcome the defects of the prior art and provide a flame retardant phenolic molding compound and a preparation method thereof.

[0005] The purpose of the present invention can be achieved through the following technical solutions:

[0006] A method for preparing a flame retardant phenolic molding compound comprises the following steps:

[0007] The modified phenolic resin is crushed by a pulverizer, and then added into a mixing barrel with reinforcing fiber, modified chitosan, curing agent, curing accelerator and lubricant for mixing, and then poured into a twin-screw extruder, melt blended, extruded, and then subjected to an injection molding process to obtain a molding molding plastic specimen, which is cured to obtain a flame-retardant phenolic molding plastic.

[0008] Furthermore, the raw materials are calculated in parts by weight as follows: 40-60 parts of modified phenolic resin, 16-22 parts of reinforcing fiber, 20-40 parts of modified chitosan, 3-8 parts of curing agent, 1-3 parts of curing accelerator, and 2-6 parts of lubricant.

[0009] Furthermore, the reinforcing fiber is one of glass fiber, carbon fiber and ceramic fiber.

[0010] Furthermore, the curing agent is one of hexamethylenetetramine and thermosetting phenolic resin.

[0011] Furthermore, the curing accelerator is one of calcium hydroxide, magnesium oxide and calcium oxide.

[0012] Furthermore, the lubricant is one of stearic acid, zinc stearate, calcium stearate, aluminum stearate, magnesium stearate and stearic acid amide.

[0013] The reinforcing fibers can strengthen the molding compound and improve its mechanical strength; the addition of the curing agent can form a cross-linked structure in the molding compound product, further enhancing the mechanical strength of the molding compound.

[0014] Furthermore, the modified phenolic resin is prepared by the following steps:

[0015] Boric acid, phenol, oxalic acid (catalyst) and n-butanol were mixed in a three-necked flask, stirred until the solid was completely dissolved, heated for reaction, and formaldehyde solution was added dropwise. After the addition was completed, the mixture was heated under reflux for reaction, and vacuum dried to obtain a modified phenolic resin.

[0016] Furthermore, the usage ratio of boric acid, phenol, oxalic acid, n-butanol and formaldehyde solution is 5g:50g:1g:200mL:60mL.

[0017] The introduction of boron replaces the hydrogen in the phenolic hydroxyl group with a boron atom. The bond energy of the BO bond is much higher than that of the CC bond, so that the cured product forms a three-dimensional cross-linked network structure containing boron, which effectively improves the heat resistance and ablation resistance of the modified phenolic resin. In addition, the BO bond has good flexibility, which can reduce the brittleness of the modified phenolic resin to a certain extent and improve the mechanical properties.

[0018] Furthermore, the modified chitosan is prepared by the following steps:

[0019] S1. In a three-necked flask equipped with a stirring device, triphenylphosphine (PPh3) was dissolved in toluene, chloroacetaldehyde was slowly added dropwise, and the temperature was raised to 55°C. The mixture was stirred for 3 hours. After the reaction was completed, the solvent was removed by distillation under reduced pressure to obtain intermediate 1. The ratio of triphenylphosphine, toluene and chloroacetaldehyde was 26.2 g:100 mL:7.9 g.

[0020] Triphenylphosphine reacts with the chlorine group of chloroacetaldehyde to obtain the quaternary phosphonium product intermediate 1; the specific reaction process is as follows:

[0021]

[0022] S2. In a three-necked flask equipped with a stirring device, add intermediate 1 and N,N-dimethylformamide (DMF), stir evenly, then add melamine and piperidine (condensing agent), stir and mix evenly, control the reaction temperature to 65°C, keep the reaction warm for 6 hours, and after the reaction is completed, remove part of the solvent by vacuum distillation, and then purify by column chromatography (the eluent is a mixed solvent of ethyl acetate / benzene, the volume ratio of the two is 2:4), and remove the eluent by rotary evaporation to obtain intermediate 2; the ratio of the amount of intermediate 1, N,N-dimethylformamide, melamine, and piperidine is 60.9g:150mL:14.3g:30mL;

[0023] Under the action of the condensing agent, the aldehyde group on the intermediate 1 condenses with the amino group on the melamine to form an imine group (C=N Schiff base structure). By controlling the molar ratio of the two to be close to 2:1 and a slight excess of melamine, only two amino groups on the melamine participate in the reaction to obtain the intermediate 2. The specific reaction process is as follows:

[0024]

[0025] S3. In a three-necked flask equipped with a stirring device, the intermediate 2, glutaraldehyde, piperidine and N,N-dimethylformamide were stirred evenly, and the temperature was raised to 70°C. The mixture was kept warm for 4 hours. After the reaction was completed, part of the solvent was removed by distillation under reduced pressure, and then purified by column chromatography (the eluent was a mixed solvent of ethyl acetate / benzene in a volume ratio of 3:5), and the eluent was removed by rotary evaporation to obtain the intermediate 3; the ratio of the amount of the intermediate 2, glutaraldehyde, piperidine and N,N-dimethylformamide was 69.9 g:12.6 g:15 mL:150 mL;

[0026] Under the action of the condensing agent, the aldehyde group on glutaraldehyde condenses with the amino group on intermediate 2 to form an imine group (C=N Schiff base structure). By controlling the molar ratio of the two to be close to 1:1 and a slight excess of glutaraldehyde, intermediate 3 is obtained; the specific reaction process is as follows:

[0027]

[0028] S4. Add chitosan to a mixed solution of acetic acid and toluene (the mass fraction of acetic acid is 38%), stir until completely dissolved, then add intermediate 3 and piperidine, stir and react at room temperature for 1 hour, add sodium hydroxide solution dropwise to adjust the pH to 7, continue to react for 2 hours, and after the reaction is completed, let stand and precipitate, filter, wash with ethanol and water in turn, and dry in an oven to obtain modified chitosan; the ratio of the mixed solution of acetic acid and toluene, chitosan, intermediate 3, and piperidine is 100mL:1g:24g:10mL;

[0029] Under the action of the condensation agent, the aldehyde group on the intermediate 3 condenses with the amino group on the chitosan to form an imine group (C=N Schiff base structure) to obtain modified chitosan; the specific reaction process is as follows:

[0030]

[0031] Chitosan is a polysaccharide with biodegradability and certain antibacterial properties. In addition, a large number of hydroxyl groups in the molecule can promote the dehydration of the matrix into carbon, converting the matrix into a high-concentration carbon layer, thereby improving the flame retardant properties of the matrix. By modifying chitosan and connecting it to the organic molecular chain through C=N, the hydrogen bonding effect of the chitosan amino group is weakened, the antibacterial properties of chitosan are improved, and the compatibility with the phenolic resin matrix is ​​improved, the dispersibility is improved, and the agglomeration phenomenon is reduced. In addition, the modified chitosan contains multiple C=N Schiff base structures, which can interact with bacterial proteins and enzymes, hindering the synthesis of bacterial nucleotides and amino acids, and further improving the antibacterial properties of the matrix. Moreover, the C=N double bond in the Schiff base structure can generate a carbon-nitrogen six-membered ring at high temperature. This type of six-membered ring structure makes the base The modified chitosan molecules also contain quaternary phosphonium salts and triazine structures, in which the quaternary phosphonium salt functional groups, in which the positively charged phosphonium ions are adsorbed on the surface of the bacteria, can interact with the negatively charged cell membrane of the bacteria, penetrate the cell wall, combine with the cell membrane, destroy the surface structure of the cell, make the intracellular substances flow out, stop the respiratory function of the bacteria and cause cell death, and can play a synergistic role with chitosan and Schiff base, significantly enhance the antibacterial properties of the matrix, and have better antibacterial activity than quaternary ammonium salts; finally, the introduced triazine structure will produce nitrogen-containing gas during combustion, dilute and reduce the smoke density, self-condense at high temperature to form melem to make the carbon layer compact, and can play a synergistic role with chitosan and Schiff base, greatly enhancing the flame retardant and smoke suppression properties of the matrix;

[0032] It should be added that chitosan connects organic molecular chains, which can enhance the resistance of small organic molecules to migration and exudation, making the performance of modified chitosan long-term and stable.

[0033] Beneficial effects of the present invention:

[0034] 1. The molding material prepared by the present invention can enhance the mechanical strength of the molding material by adding reinforcing fibers and curing agents;

[0035] 2. Boric acid is used to modify phenolic resin to enhance the mechanical strength, heat resistance and ablation resistance of the molding compound;

[0036] 3. The filler is modified chitosan, which has better compatibility with the matrix than ordinary chitosan, can significantly enhance the flame retardancy and antibacterial properties of the molding material, and the performance is long-lasting and stable.

[0037] Therefore, the molding material prepared by the present invention has stable and efficient flame retardancy and antibacterial properties, does not require the addition of additional flame retardants, has excellent mechanical properties, and has important application value in the technical field of phenolic molding materials. DETAILED DESCRIPTION

[0038] The following will be combined with the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0039] Example 1

[0040] Preparation of modified chitosan:

[0041] S1. In a three-necked flask equipped with a stirring device, 26.2 g of triphenylphosphine was dissolved in 100 mL of toluene, 7.9 g of chloroacetaldehyde was slowly added dropwise, and the temperature was raised to 55° C. The mixture was stirred for 3 h. After the reaction was completed, the solvent was removed by distillation under reduced pressure to obtain intermediate 1;

[0042] S2. In a three-necked flask equipped with a stirring device, add 60.9 g of intermediate 1 and 150 mL of N,N-dimethylformamide, stir evenly, then add 14.3 g of melamine and 30 mL of piperidine, stir and mix evenly, control the reaction temperature to 65°C, keep the reaction for 6 hours, and after the reaction is completed, remove part of the solvent by vacuum distillation, and then purify by column chromatography (the eluent is a mixed solvent of ethyl acetate / benzene, the volume ratio of the two is 2:4), and remove the eluent by rotary evaporation to obtain intermediate 2;

[0043] S3, in a three-necked flask equipped with a stirring device, 69.9g of intermediate 2, 12.6g of glutaraldehyde, 15mL of piperidine and 150mL of N,N-dimethylformamide were stirred evenly, and the temperature was raised to 70°C, and the reaction was kept warm for 4h. After the reaction was completed, part of the solvent was distilled off under reduced pressure, and then purified by column chromatography (the eluent was a mixed solvent of ethyl acetate / benzene, and the volume ratio of the two was 3:5), and the eluent was removed by rotary evaporation to obtain intermediate 3;

[0044] S4. Add 1 g of chitosan to a mixed solution of 100 mL of acetic acid and toluene (the mass fraction of acetic acid is 38%), stir until completely dissolved, then add 24 g of intermediate 3 and 10 mL of piperidine, stir and react at room temperature for 1 h, add dropwise sodium hydroxide solution to adjust the pH to 7, continue the reaction for 2 h, and after the reaction is completed, let it stand and precipitate, filter, wash with ethanol and water in turn, and dry in an oven to obtain modified chitosan.

[0045] Example 2

[0046] Preparation of modified chitosan:

[0047] S1. In a three-necked flask equipped with a stirring device, 52.4 g of triphenylphosphine was dissolved in 200 mL of toluene, 15.8 g of chloroacetaldehyde was slowly added dropwise, and the temperature was raised to 55° C. The reaction was stirred for 3 h. After the reaction was completed, the solvent was removed by reduced pressure distillation to obtain intermediate 1;

[0048] S2. In a three-necked flask equipped with a stirring device, 121.8 g of intermediate 1 and 300 mL of N,N-dimethylformamide were added, and after stirring, 28.6 g of melamine and 60 mL of piperidine were added, and the mixture was stirred and mixed evenly. The reaction temperature was controlled to 65°C, and the reaction was kept warm for 6 hours. After the reaction was completed, part of the solvent was distilled off under reduced pressure, and then purified by column chromatography (the eluent was a mixed solvent of ethyl acetate / benzene, and the volume ratio of the two was 2:4), and the eluent was removed by rotary evaporation to obtain intermediate 2;

[0049] S3, in a three-necked flask equipped with a stirring device, 139.8g of intermediate 2, 25.2g of glutaraldehyde, 30mL of piperidine and 300mL of N,N-dimethylformamide were stirred evenly, and the temperature was raised to 70°C, and the reaction was kept warm for 4h. After the reaction was completed, part of the solvent was distilled off under reduced pressure, and then purified by column chromatography (the eluent was a mixed solvent of ethyl acetate / benzene, and the volume ratio of the two was 3:5), and the eluent was removed by rotary evaporation to obtain intermediate 3;

[0050] S4. Add 2 g of chitosan to a mixed solution of 200 mL of acetic acid and toluene (the mass fraction of acetic acid is 38%), stir until completely dissolved, then add 48 g of intermediate 3 and 20 mL of piperidine, stir and react at room temperature for 1 h, add dropwise sodium hydroxide solution to adjust the pH to 7, continue the reaction for 2 h, and after the reaction is completed, let it stand and precipitate, filter, wash with ethanol and water in turn, and dry in an oven to obtain modified chitosan.

[0051] Example 3

[0052] Preparation of modified phenolic resin:

[0053] In a three-necked flask, 5 g of boric acid, 50 g of phenol, 1 g of oxalic acid and 200 mL of n-butanol were mixed and stirred until the solid was completely dissolved. The mixture was heated to 90°C and reacted for 1 h. 60 mL of formaldehyde solution (mass fraction 28%) was added dropwise. After the addition was completed, the mixture was refluxed at 90°C for 2 h and dried in vacuo to obtain a modified phenolic resin.

[0054] Example 4

[0055] Preparation of modified phenolic resin:

[0056] In a three-necked flask, 10 g of boric acid, 100 g of phenol, 2 g of oxalic acid and 400 mL of n-butanol were mixed and stirred until the solid was completely dissolved. The mixture was heated to 110°C and reacted for 3 h. 120 mL of formaldehyde solution (mass fraction 28%) was added dropwise. After the addition was completed, the mixture was refluxed at 110°C for 3 h and dried in vacuo to obtain a modified phenolic resin.

[0057] Example 5

[0058] 40 g of the modified phenolic resin prepared in Example 3 was crushed with a pulverizer, and then added into a mixing barrel with 16 g of glass fiber, 20 g of the modified chitosan prepared in Example 1, 3 g of urotropine, 1 g of calcium hydroxide and 2 g of aluminum stearate and mixed for 10 min. After mixing, the mixture was poured into a twin-screw extruder, melt blended, extruded, and then subjected to an injection molding process (mold temperature 150° C., pressure 10 MPa, holding time 5 min) to obtain a molded molding material specimen, which was further cured at 150° C. for 2 h to obtain a flame-retardant phenolic molding material.

[0059] Example 6

[0060] 50 g of the modified phenolic resin prepared in Example 4 was crushed with a pulverizer, and then added into a mixing barrel with 19 g of carbon fiber, 30 g of the modified chitosan prepared in Example 2, 5 g of urotropine, 2 g of magnesium oxide and 4 g of calcium stearate and mixed for 20 min. After mixing, the mixture was poured into a twin-screw extruder, melt blended, extruded, and then subjected to an injection molding process (mold temperature 160° C., pressure 10 MPa, holding time 5 min) to obtain a molded molding material specimen, which was further cured at 160° C. for 3 h to obtain a flame-retardant phenolic molding material.

[0061] Example 7

[0062] 60 g of the modified phenolic resin prepared in Example 4 was crushed with a pulverizer, and then added into a mixing barrel with 22 g of carbon fiber, 40 g of the modified chitosan prepared in Example 2, 8 g of urotropine, 3 g of magnesium oxide and 6 g of zinc stearate and mixed for 10 min. After mixing, the mixture was poured into a twin-screw extruder, melt blended, extruded, and then subjected to an injection molding process (mold temperature 160° C., pressure 10 MPa, holding time 5 min) to obtain a molded molding material specimen, which was further cured at 160° C. for 3 h to obtain a flame-retardant phenolic molding material.

[0063] Comparative Example 1

[0064] Ordinary chitosan of the same mass was used to replace the modified chitosan in Example 7, and the remaining steps were the same as in Example 7 to prepare a molding compound.

[0065] Comparative Example 2

[0066] A commercially available flame retardant phenolic molding compound was used.

[0067] Examples 5-7 and Comparative Examples 1-2 were made into corresponding shapes according to different test standards and the following performance tests were performed:

[0068] The bending strength is measured using the national standard GB / T 9341-2000 "Test method for bending properties of plastics";

[0069] The impact strength is measured using the national standard GB / T 1843-2008 "Determination of Izod Impact Strength of Plastics";

[0070] The national standard GB / T 2408-2008 "Horizontal and vertical methods for the determination of combustion performance of plastics" was used to measure the flame retardant performance of the samples before and after being placed at room temperature for 180 days;

[0071] QB / T 2591-2003A "Test Methods and Antibacterial Effects of Antibacterial Plastics" was used to determine the antibacterial rates of Staphylococcus aureus and Escherichia coli before and after the samples were placed at room temperature for 180 days.

[0072] The measured results are shown in the following table:

[0073]

[0074] It can be seen from the above table that the molding compound prepared in the embodiment of the present invention has stable and efficient flame retardancy and antibacterial properties, does not require the addition of additional flame retardants, has excellent mechanical properties, and has important application value in the field of phenolic molding compound technology.

[0075] In the description of the specification, the description with reference to the terms "one embodiment", "example", "specific example", etc. means that the specific features, structures, materials or characteristics described in conjunction with the embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the schematic representation of the above terms does not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described can be combined in any one or more embodiments or examples in a suitable manner.

[0076] The above contents are merely examples and explanations of the present invention. Those skilled in the art may make various modifications or additions to the specific embodiments described or replace them in a similar manner. As long as they do not deviate from the invention or exceed the scope defined by the claims, they shall all fall within the protection scope of the present invention.

Claims

1. A method for preparing a flame retardant phenolic molding compound, characterized in that: The following steps are involved: The modified phenolic resin is crushed by a pulverizer, and then added into a mixing barrel with reinforcing fiber, modified chitosan, curing agent, curing accelerator and lubricant for mixing, and then poured into a twin-screw extruder for melt blending, extrusion, and injection molding to obtain a molding plastic sample strip, and after curing, a flame-retardant phenolic molding plastic is obtained; Wherein, the modified chitosan is prepared by the following steps: S1. Dissolve triphenylphosphine in toluene, add chloroacetaldehyde dropwise, stir and react at 55°C for 3h, and after the reaction is completed, distill under reduced pressure to obtain intermediate 1; the ratio of triphenylphosphine, toluene and chloroacetaldehyde is 26.2g:100mL:7.9g; S2. After the intermediate 1 and N,N-dimethylformamide are stirred evenly, melamine and piperidine are added, stirred and mixed evenly, reacted at 65° C. for 6 hours, the reaction is completed, vacuum distillation is performed, column chromatography is purified, and rotary evaporation is performed to obtain intermediate 2; the ratio of the amount of intermediate 1, N,N-dimethylformamide, melamine, and piperidine is 60.9 g:150 mL:14.3 g:30 mL; S3, intermediate 2, glutaraldehyde, piperidine and N,N-dimethylformamide were stirred evenly, reacted at 70°C for 4h, and after the reaction was completed, vacuum distillation was performed, column chromatography was purified, and rotary evaporation was performed to obtain intermediate 3; the ratio of intermediate 2, glutaraldehyde, piperidine and N,N-dimethylformamide was 69.9g:12.6g:15mL:150mL; S4, adding chitosan to the mixed solution of acetic acid and toluene, stirring until completely dissolved, then adding intermediate 3 and piperidine, stirring and reacting at room temperature for 1 hour, adjusting the pH to 7, continuing the reaction for 2 hours, and after the reaction is completed, standing and precipitating, filtering, washing, and drying to obtain modified chitosan; the ratio of the mixed solution of acetic acid and toluene, chitosan, intermediate 3, and piperidine is 100mL:1g:24g:10mL; Wherein, the modified phenolic resin is prepared by the following steps: Boric acid, phenol, oxalic acid and n-butanol are mixed in a three-necked flask, stirred until the solid is completely dissolved, heated for reaction, and formaldehyde solution is added dropwise. After the addition is complete, the mixture is heated under reflux for reaction, and vacuum dried to obtain a modified phenolic resin.

2. The method for preparing a flame retardant phenolic molding compound according to claim 1, characterized in that: The raw materials are calculated in parts by weight as follows: 40-60 parts of modified phenolic resin, 16-22 parts of reinforcing fiber, 20-40 parts of modified chitosan, 3-8 parts of curing agent, 1-3 parts of curing accelerator, and 2-6 parts of lubricant.

3. The method for preparing a flame retardant phenolic molding compound according to claim 1, characterized in that: The usage ratio of the boric acid, phenol, oxalic acid, n-butanol and formaldehyde solution is 5g:50g:1g:200mL:60mL.

4. A flame retardant phenolic molding compound, characterized in that: Prepared according to the method according to any one of claims 1 to 3.

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