Phenolic resin with low free phenol content and high crosslinking degree and preparation method thereof

Abstract

The invention relates to the technical field of phenolic resin synthesis, and discloses low-free-phenol and high-crosslinking-degree phenolic resin, and particularly relates to phenolic resin taking phenol and a formaldehyde solution as raw materials, barium hydroxide as a catalyst and sulfuric acid as a neutralizer and a preparation method of the phenolic resin. According to the method, the content of free phenol in the resin is smaller than or equal to 05%, the bending strength after curing is larger than or equal to 90 MPa, and the carbon residue rate at 800 DEG C is larger than or equal to 45% by regulating and controlling the dosage of phenol, a formaldehyde solution and a catalyst and accurately controlling the specific reaction process. The method is suitable for the fields of high-temperature-resistant molding compounds and insulating materials. The method solves the problems of high free phenol content and insufficient hinge density of the traditional phenolic resin, and is simple and controllable in process and suitable for industrial production.

Description

Technical Field

[0001] This invention belongs to the field of thermosetting resin synthesis, specifically relating to a low-free-phenol, high-crosslinking phenolic resin prepared from phenol and formaldehyde using a barium hydroxide-sulfuric acid neutralization process, and its applications. Background Technology

[0002] Cyclic phenolic resins are widely used in molding compounds, insulation materials, and adhesives due to their readily available raw materials and stable properties. However, phenolic resins prepared by traditional alkaline catalysis methods (such as sodium hydroxide catalysis) suffer from problems such as high free phenol content and low crosslinking density, resulting in insufficient temperature resistance and mechanical properties. Furthermore, the toxicity of free phenols can cause pollution.

[0003] When used as a catalyst, barium hydroxide exhibits moderate alkalinity, which promotes a more complete condensation reaction between phenol and formaldehyde, reducing the residue of free phenol. Sulfuric acid, as a neutralizing agent, reacts with sodium hydroxide to form barium sulfate precipitate, which is easily separated by filtration and does not introduce other impurity ions, making it an ideal choice for neutralizing agents.

[0004] Therefore, developing a phenolic resin synthesis process based on the barium hydroxide-sulfuric acid system is of practical significance. Summary of the Invention

[0005] Objective of this invention: This invention addresses the shortcomings of existing technologies by providing a phenolic resin with low free phenol content and high cross-linking degree. By optimizing the amount of barium hydroxide, the formaldehyde ratio, and the reaction process, the cross-linking density and environmental performance of the resin are improved. Another objective of this invention is to provide a method for preparing this phenolic resin.

[0006] Technical solution: To achieve the above objectives, the technical solution adopted by this invention is as follows: A phenolic resin with low free phenol content and high crosslinking degree is made from the following raw materials in parts by weight: 80-100 parts phenol, 110-140 parts 37% formaldehyde solution, 1.5-3 parts barium hydroxide, and an appropriate amount of 50% sulfuric acid are used to neutralize to pH 6-7.

[0007] As a preferred embodiment, in the phenolic resin described above, the molar ratio of formaldehyde solution to phenol is 1.2-1.5:1.

[0008] As a preferred embodiment, the phenolic resin described above is made from the following raw materials in parts by weight: 100 parts phenol, 130 parts 37% formaldehyde solution, 2.5 parts barium hydroxide, and an appropriate amount of 50% sulfuric acid are used to neutralize to pH 6-7.

[0009] As a preferred embodiment, the phenolic resin described above is made from the following raw materials in parts by weight: 100 parts phenol, 120 parts 37% formaldehyde solution, 2 parts barium hydroxide, and an appropriate amount of 50% sulfuric acid are used to neutralize to pH 6-7.

[0010] The method for preparing the phenolic resin of the present invention includes the following steps: (1) Add phenol to the reactor according to the weight ratio, heat to 40-50℃, stir until completely melted, slowly add barium hydroxide catalyst, and stir to dissolve; (2) Heat to 70-80℃, add 37% formaldehyde solution dropwise, and control the temperature of the reaction system to not exceed 85℃ during the dropwise addition. After the dropwise addition is completed, keep warm for a period of time to obtain phenolic prepolymer; (3) Slowly add 50% sulfuric acid to the reaction system. After the addition is complete, stir until the pH is 6-7, let it stand, allow it to precipitate, filter the resulting barium sulfate precipitate, and obtain the filtrate. (4) Transfer the filtrate to a distillation apparatus, first heat it to 100-105℃ under normal pressure to dehydrate it, then reduce the pressure to 0.08-0.09MPa, heat it to 110-120℃, continue to dehydrate it until the resin solid content is ≥96%, cool it down, and discharge it to obtain the product.

[0011] As a preferred embodiment, the method for preparing the phenolic resin described above includes the following steps: (1) Add phenol to the reactor according to the weight proportions, heat to 40-50℃, stir until completely melted, slowly add barium hydroxide catalyst, and stir for 20-40 minutes to dissolve; (2) Heat to 70-80℃ and add 37% formaldehyde solution dropwise at a rate of 2-3 mL / min. During the dropwise addition, control the temperature of the reaction system to not exceed 85℃. After the dropwise addition is completed, keep the reaction at the temperature for 2.5 h to obtain phenolic prepolymer. (3) Slowly add 50% sulfuric acid to the reaction system at a rate of 2 mL / min. After the addition is complete, stir until the pH is 6-7, let stand, filter the generated barium sulfate precipitate, and obtain the filtrate. (4) Transfer the filtrate to a distillation apparatus, first heat it to 100-105℃ under normal pressure, dehydrate for 1-1.5h, then reduce the pressure to 0.08-0.09MPa, heat it to 110-120℃, continue dehydration for 2h until the resin solid content is ≥96%, cool it to below 60℃, and the product is obtained.

[0012] Innovation of this invention: Raw material coordination role: Barium hydroxide catalyst: This invention found that, compared with sodium hydroxide, barium hydroxide is more alkaline, which can slow down the rate of ortho- and para-hydroxymethylation of phenol, making the reaction more uniform and reducing the residue of free phenol caused by intense local reactions; at the same time, barium ions can form weak coordination with phenolic hydroxyl groups, promoting cross-linking between molecular chains and increasing the cross-linking density of the resin.

[0013] Formaldehyde ratio: The molar ratio of formaldehyde to phenol should be controlled at 1.2-1.5:1 to ensure that phenol reacts fully and reduce the content of free phenol.

[0014] Sulfuric acid neutralization: 50% sulfuric acid is slowly added dropwise, reacting with barium hydroxide to form barium sulfate precipitate. After filtration, barium ions in the system can be removed to avoid their impact on the resin curing performance.

[0015] Key process control points: Formaldehyde droplet acceleration rate: Controlled at 2-3 mL / min to avoid excessive local formaldehyde concentration leading to the formation of paraformaldehyde and to ensure uniform polycondensation reaction.

[0016] Neutralize the pH value: Adjust it to 6-7 to avoid excessive acidity, which could cause the resin molecular chains to break or alkaline residue to affect subsequent curing.

[0017] Performance advantages: Low free phenol content: ≤0.5%, meeting environmental protection requirements and reducing health hazards to operators.

[0018] High crosslinking density: flexural strength after curing ≥90MPa (GB / T9341-2008), char residue rate at 800℃ ≥45%, and temperature resistance and mechanical properties are superior to traditional alkaline catalytic phenolic resins. Detailed Implementation

[0019] Example 1 1. A phenolic resin with low free phenol content and high cross-linking degree, which is made from the following raw materials in parts by weight: 100 parts phenol, 120 parts 37% formaldehyde solution (molar ratio of formaldehyde to phenol 1.3:1), 2 parts barium hydroxide, and appropriate amount of 50% sulfuric acid.

[0020] 2. A method for preparing a phenolic resin with low free phenol and high cross-linking degree, comprising the following steps: (1) Add 100 parts of phenol to the reactor, heat to 40-50℃, stir until completely melted, slowly add 2 parts of barium hydroxide catalyst, stir for 30 minutes to dissolve the catalyst.

[0021] (2) Heat to 70-80℃ and add 120 parts of 37% formaldehyde solution at a rate of 2-3ML / min. During the addition process, control the temperature of the reaction system to not exceed 85℃. After the addition is completed, keep the reaction at the temperature for 2.5h to form phenolic prepolymer.

[0022] (3) Slowly add 50% sulfuric acid to the reaction system at a rate of 2 mL / min. After the addition is complete, stir until the pH is 6-7, let stand for 20 minutes, and then filter out the generated barium sulfate precipitate.

[0023] (4) Transfer the filtrate to a distillation apparatus, first heat it to 100-105℃ under normal pressure, dehydrate for 1-1.5h, then reduce the pressure to 0.08-0.09MPa, heat it to 110-120℃, continue dehydration for 2h until the resin solid content is ≥96%, cool it to below 60℃, and the product is obtained.

[0024] 3. Performance testing: Free phenol content 0.42% (chromatographic method), flexural strength after curing 92MPa (GB / T9341-2008), char residue rate at 800℃ 46%.

[0025] Example 2 1. A phenolic resin with low free phenol content and high cross-linking degree, which is made from the following raw materials in parts by weight: 100 parts phenol, 130 parts 37% formaldehyde solution (molar ratio of formaldehyde to phenol 1.4:1), 2.5 parts barium hydroxide, and an appropriate amount of 50% sulfuric acid.

[0026] 2. A method for preparing a phenolic resin with low free phenol and high cross-linking degree, comprising the following steps: (1) Add 100 parts of phenol to the reactor, heat to 40-50℃, stir until completely melted, slowly add 2.5 parts of barium hydroxide, stir for 30 minutes to dissolve the catalyst barium hydroxide.

[0027] (2) Heat the temperature to 70-80℃ and add 130 parts of formaldehyde solution at a rate of 2-3 mL / min. During the addition process, control the temperature of the reaction system to not exceed 85℃. After the addition is completed, keep the temperature for 2.5 h to form phenolic prepolymer.

[0028] (3) Slowly add 50% sulfuric acid to the reaction system at a rate of 2 mL / min. After the addition is complete, stir until the pH is 6-7, let stand for 20 minutes, and then filter out the generated barium sulfate precipitate.

[0029] (4) Transfer the filtrate to a distillation apparatus, first heat it to 100-105℃ under normal pressure, dehydrate for 1-1.5h, then reduce the pressure to 0.08-0.09MPa, heat it to 110-120℃, continue dehydration for 2h until the resin solid content is ≥96%, cool it to below 60℃, and the product is obtained.

[0030] 3. Performance testing: Free phenol content 0.38% (chromatographic method), flexural strength after curing 95MPa ((GB / T9341-2008)), char residue rate at 800℃ 48%.

[0031] Example 3 1. A phenolic resin with low free phenol content and high cross-linking degree, which is made from the following raw materials in parts by weight: 100 parts phenol, 110 parts 37% formaldehyde solution (molar ratio of formaldehyde to phenol 1.2:1), 2.5 parts barium hydroxide, and an appropriate amount of 50% sulfuric acid.

[0032] 2. A method for preparing a phenolic resin with low free phenol and high cross-linking degree, comprising the following steps: (1) Add phenol to the reactor, heat to 40-50℃, stir until completely melted, slowly add barium hydroxide, stir for 30 minutes to dissolve the catalyst.

[0033] (2) Heat the temperature to 70-80℃ and add formaldehyde solution dropwise at a rate of 2-3 mL / min. During the dropwise addition, control the temperature of the reaction system to not exceed 85℃. After the dropwise addition is completed, keep the temperature for 2.5 h to form phenolic prepolymer.

[0034] (3) Slowly add 50% sulfuric acid to the reaction system at a rate of 2 mL / min. After the addition is complete, stir until the pH is 6-7, let stand for 20 minutes, and then filter out the generated barium sulfate precipitate.

[0035] (4) Transfer the filtrate to a distillation apparatus, first heat it to 100-105℃ under normal pressure, dehydrate for 1-1.5h, then reduce the pressure to 0.08-0.09MPa, heat it to 110-120℃, continue dehydration for 2h until the resin solid content is ≥96%, cool it to below 60℃, and the product is obtained.

[0036] 3. Performance testing: Free phenol content 0.48% (chromatographic method), flexural strength after curing 89MPa (GB / T9341-2008), char residue rate at 800℃ 45%.

[0037] Example 4 Performance Testing According to Table 1 below, epoxy resin (epoxy resin 607-40, E-06 produced by Jiangsu Sanmu Chemical Co., Ltd.), diluent, filler, additives, and the low-free-phenol, high-crosslinking-degree phenolic resins prepared in Examples 1-3 were mixed in the following proportions to prepare anti-corrosion coatings. The basic properties after curing, compared with phenolic resin DG01 from Sanmu Chemical Co., Ltd., are shown in Table 2 below. The test results of the cured paint film properties are shown in Table 3.

[0038] Table 1 Experimental formulation

[0039] Table 2 Comparative Energy Test Results

[0040] Based on a comprehensive analysis of the three examples and comparative examples, the phenolic resin prepared by this invention is superior to phenolic resin DG01, especially the phenolic resin prepared in Example 2 of this invention, which exhibits the best performance in all aspects. This demonstrates that the molar ratio of phenol to formaldehyde solution significantly affects the overall performance of the resin.

[0041] Table 3 Weather resistance test of paint film

[0042] Based on a comprehensive analysis of the above paint film weathering performance test results, the paint film in Example 2 exhibits the best weathering performance. This also demonstrates that the molar ratio of phenol to formaldehyde solution significantly affects the overall performance of the resin.

[0043] The above performance test results demonstrate that, through extensive experimental screening and using different raw materials, the low-free-phenol, highly cross-linked phenolic resin prepared in this invention exhibits significantly lower free-phenol and free-aldehyde content compared to the comparative example. Its flexural and impact strengths are superior to the comparative example, and the high cross-linking density enhances the resin's structural integrity, resulting in better char residue and heat resistance.

[0044] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A phenolic resin with low free phenol and high crosslinking degree, characterized in that, It is made from the following parts by weight of raw materials: 80-100 parts phenol, 110-140 parts 37% formaldehyde solution, 1.5-3 parts barium hydroxide, and an appropriate amount of 50% sulfuric acid are used to neutralize to pH 6-7.

2. The phenolic resin according to claim 1, characterized in that, The molar ratio of formaldehyde solution to phenol is 1.2-1.5:

1.

3. The phenolic resin according to claim 1, characterized in that, It is made from the following parts by weight of raw materials: 100 parts phenol, 130 parts 37% formaldehyde solution, 2.5 parts barium hydroxide, and an appropriate amount of 50% sulfuric acid are used to neutralize to pH 6-7.

4. The phenolic resin according to claim 1, characterized in that, It is made from the following parts by weight of raw materials: 100 parts phenol, 120 parts 37% formaldehyde solution, 2 parts barium hydroxide, and an appropriate amount of 50% sulfuric acid are used to neutralize to pH 6-7.

5. The method for preparing the phenolic resin according to any one of claims 1 to 4, characterized in that, Includes the following steps: (1) Add phenol to the reactor according to the weight ratio, heat to 40-50℃, stir until completely melted, slowly add barium hydroxide catalyst, and stir to dissolve; (2) Heat to 70-80℃, add 37% formaldehyde solution dropwise, and control the temperature of the reaction system to not exceed 85℃ during the dropwise addition. After the dropwise addition is completed, keep warm for a period of time to obtain phenolic prepolymer; (3) Slowly add 50% sulfuric acid to the reaction system. After the addition is complete, stir until the pH is 6-7, let it stand, allow it to precipitate, filter the resulting barium sulfate precipitate, and obtain the filtrate. (4) Transfer the filtrate to a distillation apparatus, first heat it to 100-105℃ under normal pressure to dehydrate it, then reduce the pressure to 0.08-0.09MPa, heat it to 110-120℃, continue to dehydrate it until the resin solid content is ≥96%, cool it down, and discharge it to obtain the product.

6. The method for preparing phenolic resin according to claim 5, characterized in that, Includes the following steps: (1) Add phenol to the reactor according to the weight proportions, heat to 40-50℃, stir until completely melted, slowly add barium hydroxide catalyst, and stir for 20-40 minutes to dissolve; (2) Heat to 70-80℃ and add 37% formaldehyde solution dropwise at a rate of 2-3 mL / min. During the dropwise addition, control the temperature of the reaction system to not exceed 85℃. After the dropwise addition is completed, keep the reaction at the temperature for 2.5 h to obtain phenolic prepolymer. (3) Slowly add 50% sulfuric acid to the reaction system at a rate of 2 mL / min. After the addition is complete, stir until the pH is 6-7, let stand, filter the generated barium sulfate precipitate, and obtain the filtrate. (4) Transfer the filtrate to a distillation apparatus, first heat it to 100-105℃ under normal pressure, dehydrate for 1-1.5h, then reduce the pressure to 0.08-0.09MPa, heat it to 110-120℃, continue dehydration for 2h until the resin solid content is ≥96%, cool it to below 60℃, and the product is obtained.

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